From organic chemistry to macromolecules : A scientific autobiography based on my original papers 9780471820864, 0471820865

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Hermann Staudinger

From Organic Chemistry to Macromolecules A scientific autobiography based on my original papers

TRANSLATED FROM THE GERMAN With a Foreword by

HERMAN F. MARK

109917 Wiley-Interscience a Division of John Wiley & Sons, Inc. New York London

Sydney

Toronto

Translated from Hermann Staudinger, Arbeitserinnerungen, © 1961, Dr. Alfred Hiithig Verlag GmbH, Heidelberg, by Jerome Fock and Michael Fried Copyright © 1970, by John Wiley & Sons, Inc. All rights reserved. No part of this book may be reproduced by any means, nor transmitted, nor translated into a machine language without the written permission of the publisher. Library of Congress Catalogue Card Number: 67-21664 SBN 471

82086 5

Printed in the United States of America 10 9

8 7

6

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To my dear wife Magda THE INSPIRING AND UNTIRING COLLABORATOR IN THE FIELD OF MACROMOLECULES

in gratitude

Foreword

Thirty years ago, there appeared a volume containing the papers published by W. H. Carothers, the great American pioneer in polymer science, as a result of ten years of intense research together with some ten able co-workers in the Experimental Station of the Du Pont Company in Wilmington, Delaware. A similar book should have appeared at the same time containing the collected papers of the great European pioneer of this field, Hermann Staudinger, covering his work over twenty years with some fifty students and associates. It did not appear. War emergencies, postwar needs, and urgent pressure to rebuild the Institute prevented Staudinger's pausing to take stock of his life's work. Finally, in 1961 the German edition of Arbeitserinnerungen was published. Now, another ten years later, we have in our hands an English version of the account of his work. It is fifty years after the first paper was printed and ten years after the last was published; this is a long span. But monuments do not lose their appeal with time; in fact, as they grow older, they become even more venerable. We can savor opening this book and reading, in the master's own words, about how the concept slowly emerged from the haze of conflicting opinions, how interest and intensity gradually increased, and how by the tortuous path of trial and error clarification was finally reached in a stepby-step approximation. Every page breathes the air of firsthand authenticity; we have entered the laboratory with its odor of styrene and formaldehyde, its glittering glassware, and its slowly agitated thermostats. We can see the Professor surrounded by his students as he explains to them how they should conduct their experiments, register their data, draw their conclusions, appraise their significance, and assist him in weaving the complex fabric of macromolecular chemistry. Vll

viii

FOREWORD

Carothers in ten tense years of his short life enriched the world with an impressive list of extremely useful polymers, which not only established his and his associates' reputation in the forefront of the art but also produced, in the hands of congenial engineers, an enormous dividend for his company and convenience, pleasure, and safety for millions of people. Staudinger in fifty years of his long life created a galaxy of distinguished polymer chemists, many of whom reached leading positions in universities and in industrial organizations and ultimately had a very similar impact on the science and technology of the art. In the clarified atmosphere of hindsight it becomes evident that Staudinger's impact on his time was caused by a triple role which he kept on playing with never-failing enthusiasm for more than forty years-as explorer, teacher, and preacher. Guided by true scientific curiosity for the unknown, Staudinger selected as the work of his life in the early 1920's a field which, at that time, was hardly considered to be a worthy goal for an organic chemist of his reputation-the study of the natural organic substances of high molecular weight. Until then, Staudinger had cultivated typical problems of classical organic chemistry with its well-defined substances which could be characterized by such methods as melting and boiling point, freezing point depression, and boiling point elevation. A stimulating monograph, The Chemistry of the Ketenes, was the fruit of these efforts, a book that seemed to foreshadow Staudinger's career as that of a synthetic organic chemist worthy of such great predecessors as Baeyer, Fischer, and Gattermann and of such distinguished contemporaries as Schlenk and WillsHitter. However, he chose the more romantic, though less comfortable, life of an invader of unknown areas, where every step would have to be a fight for new concepts, new methods, and new interpretations. In this area of the natural and synthetic substances of high molecular weight he performed first of all the miraculous task of carrying out, with the help of his numerous collaborators, many thousands of individual experiments on materials varying from natural substances, like starch, cellulose, and rubber, to synthetic materials, such as polystyrene and polyamides, and applying purely organic methods, such as hydrogenation, nitration, and end group determination, with the same systematic persistence as he applied such physical measurements as osmotic pressure and viscosity determinations. Through this work Staudinger ranks first in having introduced the new branch of macromolecular chemistry with the largest number of facts and figures, both by observation and by measurement. The second great achievement of the author of our book was his success

FOREWORD

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IX

in transmitting the spirit of adventurous thinking, combined with sober experimental reliability, to a large number of students, who sat at the master's feet and could not fail to become thoroughly persuaded that his macromolecular chemistry was a strong and big branch on the tree of science, destined to grow just as fast and irresistibly as macromolecules themselves. Together with this idea, however, they carried into their positions in academic and industrial life also the deep conviction that the growth of polymer chemistry would depend entirely on meticulous and careful experimentation with m thods newly designed and developed for this field. A generation of leaders in high schools, universities, and industrial laboratories emerged from Zurich and Freiburg, the "Highboroughs of High Polymers." The third and, indeed, not the least important role that Staudinger had to assume as his work progressed was that of an apostle. Many of his colleagues in high academic positions remained for a long time skeptical and overcautious. They did not approve of the strong terms with which Staudinger elevated his own working field to a "new branch of organic chemistry," and they displayed mistrust in a number of his methods and results. It was this atmosphere of negative incredulity that Staudinger combated throughout the years without fatigue and impatience. Again and again-in conferences, symposia, and conventions-he stood up as chairman, lecturer, or discussion speaker. He developed his ideas, explained the coherent pattern of the new concepts, and defended his position against all attacks with his native ingenuity and enthusiasm. There exist numerous, unforgettable occasions, in the 1920's and 1930's, when history of chemistry was made in the eloquent clashes between Staudinger and the representatives of the "aggregation theory of the small units." Holding firm to his main ideas and introducing modifications wherever the facts demanded them, Staudinger emerged from these battles as the grand old man of macromolecular chemistry, the Nobel Prize winner, the honorary doctor of many institutions of higher learning, the fatherly friend to his pupils, and the benevolent counce! of his colleagues. High ideals, creative imagination, and hard work were never more splendidly and more deservedly rewarded than in the case of the man whose life's work is now finally in our hands. All readers of this volume will be grateful to him for giving it to us and to his wife for patiently and faithfully insisting on the publication of this English version. HERMAN

Polytechnic Institute of Brooklyn Apri/1970

F.

MARK

Preface to the English Edition

Shortly after my husband's Arbeitserinnerungen appeared in 1961, the translation of this book into English was suggested, and my husband was very pleased when John Wiley & Sons, Inc.-Interscience Publishers took on the task in 1962. Unfortunately, my husband passed away before the completion of the translation, which is presented now. It is a literal rendition of the original, because it is a "biography of work" and thus a kind of historical review of the exciting beginnings of macromolecular chemistry, which has now attained an enormous volume both in research and in industry. My best thanks are due to Professor Dr. Heinrich Hopfffor his assistance in the translation, and to Professor Dr. Hermann F. Mark for his offer to write a foreword. I also owe many thanks to the publishers for their interest and the help given in producing the book. In looking through the proofs of this last book of my husband's I feel deep gratitude for having been able to share in the development of his macromolecular science. MAGDA STAUDINGER

Freiburg i.Br. May 1970

X

Preface to the German Edition

Several years ago it was suggested that I publish a complete collection of my scientific papers. This plan was soon discarded because the book would have become much too large. Instead, we compiled a catalog of all my scientific papers, grouping them according to subject areas, to achieve a better overview of the more than 800 publications within the different branches of chemistry. This task was accomplished a few years ago by two of my collaborators, Dr. Walter Hahn and Dr. Helmut Ringsdorf, to whom I wish to express my appreciation. Subsequently, we added to this listing, during recent years, introductory notes to explain the historical development which led to the publication of these papers. Since I have been asked repeatedly about the considerations which led me to the development of the concept of macromolecules, I described these in greater detail. In doing so, I surveyed the development of macromolecular chemistry during the past decades. The resulting manuscript has been carefully examined by Dr. Gunther Welzel, for which I extend my warmest thanks to him. The several drafts necessary for the completion of the present book were prepared with great care by Mrs. H. Rossmy. As my secretary for many years, she helped me also in the transcribing of all other papers and books in the last decade, for which I express my deepest appreciation. This book is published by Dr. Alfred Hiithig Verlag, the publisher of the journal, Die Makromolekulare Chemie, which I founded and was the editor for more than ten years. I express my gratitude to Dr. Alfred Hiithig for the care he took in publishing this book. Only through the joint effort of many collaborators was it possible to accomplish the scientific work of which the papers treated in this book are XI

xii

PREFACE TO THE GERMAN EDITION

the result. To these many collaborators I would like again, on this occasion, to express my gratitude. At the same time, I gratefully acknowledge the assistance which I received for the execution of this research from financial grants and for counsel and advice. I am presenting these Arbeitserinnerungen in the hope that they will be useful to the chemist of today and that the present-day investigators of macromolecules will receive stimulation from them by becoming acquainted again with the historical development of this field. H. STAUDINGER Freiburg i.Br. March 1961

Contents

..

Foreword by Herman F. Mark .

Vll

Preface to the English Edition

X

Preface to the German Edition

XI

Introduction

1

PART A. RESEARCH ON LOW MOLECULAR COMPOUNDS AND PUBLICATIONS ON GENERAL SUBJECTS

1. The Ketenes.

2.

Aliphatic Diazo Compounds

I1

.

18

3. New Organic Phosphorus Compounds

24

4. Reactions of Methylene .

28

5. Autoxidation of Organic Compounds

31

6.

Oxalyl Chloride

36

7. Explosions .

39

8. Synthesis of Isoprene

43

9. Insecticides . 10. Synthetic Pepper

46

49 Xlll

CONTENTS

XIV

11. The Aroma of Roasted Coffee.

51

12. Synthesis of Pharmaceuticals .

53

13. Asymmetric Synthesis

.

14. MisceJianeous Investigations 1. Organic Problems 2. Inorganic Problems

55

.

57

.

57 59

15. Contributions to Educational Problems

61

Part A References

64

PART B. RESEARCH ON MACROMOLECULAR COMPOUNDS

1. The Development of Macromolecular Chemistry during the Period from 1920 to 1930

77

1. The Old Micelle Theory . 2. The First Evidence for the Existence of Macromolecules 3. The New Micelle Theory.

78 83 87

2.

Macromolecular Chemistry, a New Field of Organic Chemistry

91

3.

The Nature of Colloidal Solutions

.

4. Evidence for the Existence of Macromolecules

98 .

5. The Characterization of Macromolecular Compounds

1. Elemental Analysis 2. Investigations with the Ultra Microscope of Siedentopf and Zsigmondy, and with Raman Spectroscopy. 3. The Fractionation of Polymolecular Mixtures

6. Determination of Molecular Weight 1. Determination of a Characteristic Group 2. Ultramicroscopy and Electron Microscopy . 3. Cryoscopic Method 4. Osmotic Method

104 109 109 114 115 117 117 118 119 120

CONTENTS

5. 6.

Precipitation-Titration Viscometric Method

7. Viscometry . 1. Viscosity Measurements on Solutions of Low Molecular Compounds . 2. Viscometric Investigations on Solutions of Linear Macromolecular Colloids and on Flow Birefringence . 3. The Viscosity of Heteropolar Linear Macromolecular Colloids (Polyelectrolytes) 4. Viscometric Investigations on Spherical Colloids

8. Macromolecular Substances in the Solid State . 1. X-Ray Diffraction Measurements 2. Microscopic Investigation 3. Swelling and Inclusion

9. Polymerization

xv 121 121 123 125

128 133 135 137 137 141 145 148

1. Early Concepts 2. Polymerizable Compounds 3. The Constitution of Polymers . 4. Macropolymeric Compounds 5. Catalysts (Initiators) 6. Chain Reactions

148 149 151 152 153 154

10. Synthetic Macromolecular Products.

157

1. Polymerizations of Cyclopentadiene . 2. Polystyrene 3. Polyindenes, Polyanetholes, Polypropenylbenzenes, Polyvinyl Carbazols 4. Polyiso butylene 5. Polyvinyl Acetates, Polyvinyl Alcohols, Polyacrylic Esters, etc. 167 6. 7. 8. 9.

Halogen-Containing Polymers . Copolymers . Heteropolar Macromolecular Substances (Polyelectrolytes) Polyoxymethylenes

157 158 163 165

171 173 175 177

XVI

10. Polyoxyethylenes CONTENTS 11. Polysiloxanes . 12. Polyesters

183 188

189 13. Polyamides 193 14. Aminoplasts 195 15. High Molecular and Polycyclic Schiff's Bases 200

11.

Macromolecular Natural Products 202

.

Rubber and Balata . Cellulose (a) Cellulose Acetates and Cellulose Ethers (b) Cellulose Nitrates (c) Celluloses with Defects {d) Cellulose Xanthates . (e) Structure of the Fibers (f) Inclusion Phenomena and Acetylation (g) The Formula of Cellulose. (h) Further Works (i) Summarizing Publications on Cellulose 3. Starch, Glycogen, and Other Polysaccharides 4. Wood . 5. On Tannins and Leather

.

202 211 211 217 220 222 223 226 229 230 230 231 233 236

Macromolecular Chemistry and Biology .

.

237

.

243

PART C. MACROMOLECULAR CHEMISTRY: HERMANN STAUDINGER'S NOBEL LECTURE, DECEMBER 11, 1953

280

1. 2.

12.

Part B References

. . . .

Introduction

When now, at the age of eighty, reviewing my scientific work, I would like to begin describing the path which finally led me to the study of macromolecules. At the beginning, there was no question of macromolecules at all, and my point of departure was a completely unrelated one. After I had taken my examination (Abitur) at the age of 18 at the Gym­ nasium of Worms in 1899, I did not intend to study chemistry. I preferred botany, because from an early age I had been interested in floristics and, to a modest extent, dealt with microscopic work in the field of scientia amabilis. First, I went to the University of Halle to the well-known botanist Klebs. At the same time I started there to work on analytical chemistry in the Institute of Volhard because my father-having consulted the botanist Professor Dittmer in Jena-advised me to study chemistry intensively in order to enter more readily into the problems of botany. I have not concluded these "preliminary" studies even now, and the following summary of my work gives a report of the extensive chemical investigations preceding my study of botany! Some of my findings in the field of macromolecular chemistry should be useful to the biologist as well as the botanist since they might lead to some new points of view in this field. When my father-Professor Dr. Franz Staudinger, who was well known as a philosopher (" Neukantianer," i.e., a philosophical movement i Germany following I. Kant) and as a leader in the movement for cooperative societies, was promoted from his position at the Gymnasium in Worms to the Gymnasium in Darmstadt in the fall of 1899, I continued studying chemistry for two semesters at the Techniche Hochschule in Darmstadt and completed my studies in analytical chemistry there under the direction of Professor Kolb. In 1900 I passed my first examination (Verbands­Examen) with Professor Stadel. Afterwards I worked for two semesters in the laboratory of A. von Baeyer with Professor Piloty in Munich. In 1901 I returned to Halle in order to do my doctoral thesis under the supervision of Professor 1

2

INTRODUCTION

D. VorHinder. The title of my dissertation at the University of Halle in 1903 was "Anlagerung des Malonesters an ungesiittigte Verbindungen" (1). D. VorHinder was then interested in as to whether and to what extent the Thiele theory of 1,4 addition was correct. During that time my thesis supervisor gave me much inspiration in the field of theoretical organic chemistry, a field which interested him deeply and in which he had published several papers. With my friend E. Weitz (later a professor in Giessen), who had worked for a longer time with VorHinder than I did, I later had many discussions about these" Vorlander thoughts," pursued and extended by Weitz. As a contribution to the partial valence theory, three papers were published (2-4). Upon finishing my dissertation I worked as an assistant (Privatassistent) for one semester with 0. Dobner in Halle. In the fall of 1903 I obtained a position as an instructor ( Unterrichtsassistent) in the institute of J. Thiele in Strassburg, where I first worked in the Inorganic Department under the direction of V. Kohlschtitter (later a professor in Bern) and then in the Organic Department. Those colleagues who worked with J. Thiele at the same time remember with great admiration his direction of the Institute. Not only did he care about the instruction of each student and the scientific work of the assistants, but he also maintained excellent order in the Institute. For instance, he expected the punctual arrival of all assistants at 8: 15 A.M. and controlled this by going through the laboratories. Once, when I was 15 minutes late, I found Thiele waiting at my place of work with his watch in his hand. Later, when I was already in Karlsruhe as an Extraordinarius, Thiele told me at a meeting how important he considered this regulation and that he felt it was negligent to ·be 10 minutes late. However, he had no objections if an assistant stayed away for some hours or even for the entire morning, provided the assistant had informed him in advance. At that time, in Thiele's laboratories the conversion of carboxylic acids into aldehydes was discussed often. This gave rise to my first independent research which was published considerably later (5). Inspired by the investigations of M. Gomberg on triphenylmethyl I hoped to get new and more stable methyl derivatives out of derivatives of fluorene, and also from diphenyl- and diphenylenechloroacetic esters. Here, I supposed that the unsaturated carbonyl group as well as the phenyl group would favor the formation of methyl derivatives, an assumption which, later on, turned out to be wrong (6). In the course of these experiments diphenyl chloroacetylchloride was treated with zinc, and so, in 1905, the first ketene,

INTRODUCTION

3

diphenylketene, was discovered, which is interesting because of its high reactivity. After my "Habilitation"* in the spring of 1907 for my work on ketenes in the institute of J. Thiele in Strassburg, I gave a lecture on that subject at the meeting of the Deutsche Naturforscher und .ilrzte in Dresden [cf. Angew. Chern., 20, 1673 (1907)]. In the same year, in October, I was offered the position of associate professor at the Technische Hochschule in Karlsruhe as the successor of Roland Scholl. There I had the opportunity to observe for almost five years the manner in which Carl Engler, an· outstanding personality, directed this large institute. He considered it his main task to support the research being done and he gave much valuable advice to everyone. My experiences in the Engler laboratory impressed me so much that in later years-when I myself had the direction of an institute-before making an important decision, I used to ask myself how Engler would have decided in this particular case. In Karlsruhe I continued my research on ketenes and started numerous other projects, e.g., work on oxalylchloride, the preparation of isoprene and butadiene, and some work on aliphatic diazo compounds. Furthermore, I started to work with L. Ruzicka on the active component of the "Dalmatian" insecticide (Pyrethrum). In the summer of 1912, I received a call to the Eidgenossische Technische Hochschule in Zurich as the successor of R. WillsHitter, who had moved to the Kaiser­ JYilhelm­Institute in Berlin. I received congratulations from many colleagues on my appointment to this distinguished professorship. Only Fritz Haber, whose physical chemistry laboratory in Karlsruhe was in the same building as the organic chemistry department, came to me to express his condolences because the lucky days of undisturbed research were now over. He was completely right because the institute of C. Engler was so organized at that time that the associate professor and section head had to supervise only the research being done in his own department and to give his special lectures. He was not burdened with participation in faculty meetings and administrative work, so that he could concentrate on scientific research problems. Moving to ZUrich was made much easier for me because several of my co-workers-E. Anthes, R. Endle, E. Ott, and L. Ruzicka-accompanied me from Karlsruhe. However, it also brought a lot of work because in addition to the six hours of lectures on inorganic and organic chemistry,

*

After preparation of a special dissertation (Habilitationsschrift) "Privat Dozent" (corresponding to Assistant Professor) is conferred.

the title of

Prof. DANIEL VoRLANDER Halle/Saale (1867-1941)

Prof. JoHANNES THIELE Strassburg (1865-1918)

Geheimrat Prof. CARL ENGLER Karlsruhe (1842-1925)

INTRODUCTION

5

I had to give two hours of lectures each semester on special topics in organic chemistry. Besides that, there were study hours (Repetitorien) for the students according to the instructional organization used there. Furthermore, preliminary and final examinations (Diplomexamen) were very numerous. Thus, I sometimes had occasion to think about Fritz Haber's prophetic words as many research projects started in the Karlsruhe institute proceeded only slowly or had to be postponed altogether. I worked for 14 years in Zurich. I did not accept either of two calls during that time, one to Graz, the other to Hamburg. In those years in Zurich (1912 to 1926), the research on ketenes and aliphatic diazo compounds continued and the work on the active components of the "Dalmatian" insecticide, the pyrethrines, was finished in collaboration with L. Ruzicka. Caused by the situation during World War I, the synthesis of a pepper substitute was worked out successfully in collaboration with H. Schneider and numerous other investigations, for example, on the aroma of coffee, were started with Th. Reichstein. After a number of preliminary investigations on polymerizationespecially on the polymerization of isoprene-which already had been begun in Karlsruhe, I started in Zurich, in 1920 to work on the structure of macromolecular compounds, in particular on polyoxymethylene, natural rubber, and polystyrene. In 1926, I accepted the call to Freiburg as successor to H. Wieland, who had gone to Munich. I remained in this position as Director of the chemical laboratories of Freiburg University for 25 years, until my retirement at the age of 70 in the spring of 1951. A. Liittringhaus was nominated as my successor. Moving from the well-equipped institute of the Eidgenossische Technische Hochschule in Zurich to Freiburg involved considerable difficulties, because at that time the Freiburg laboratories were so obsolete that numerous repairs had to be undertaken, even within the first year. The erection of a new building, planned at the time of my nomination in 1926, and then again in 1932 when I refused a call to Berlin-Charlottenburg as successor to R. Pschorr, was postponed again and again. The Institute was only slightly enlarged in 1933 and 1937 in order to create additional work space for research in the field of macromolecular chemistry, an area which had expanded in the meantime. In Freiburg I continued to work almost exclusively on macromolecular compounds and put aside nearly all other research because it took all my energy to develop this new field besides fulfilling my obligations in teaching

6

INTRODUCTION

and my extensive administrative duties. During this time, the following persons participated in teaching in the Inorganic Department of the Institute: Robert Schwarz, Eduard Zintl, who unfortunately died very young, thereafter Werner Fischer, and finally Georg Brauer. In the Organic Department there were Hans Lecher, Walter Hiickel, Gottwalt Fischer, Georg Wittig, and Gerhard Hesse. This writing gives me an opportunity to thank all of these persons again for their collaboration. I also remember gratefully Oberinspektor K. Hall who, for three decades, conscientiously carried out his administrative functions in the Institute. During World War II it became increasingly difficult to continue our research in the field of macromolecular chemistry. Finally it was interrupted completely because the chemistry laboratories were almost destroyed during an air raid on Freiburg on November 27, 1944. Thanks to the immediate action and help of assistants and students, the few remaining parts of the Institute were sheltered and then partly rebuilt after the end of the war. It was mainly thanks to the initiative of my assistant, H. Batzer, that we could resume teaching in the chemical laboratories and, to a small extent, begin research in the Department of Macromolecular Chemistry as early as 1947. After my retirement in the spring of 1951, my research department became the State Research Institute for Macromolecular Chemistry, the honorary direction of which I took over from then on. When I gave up this position in 1956, at the age of 75, the Baden-Wiirttemberg Government Department of Cultural Affairs established a permanent associate professorship in macromolecular chemistry, under the jurisdiction of the natural sciences and mathematics faculty of Freiburg University. Upon my retirement from the directorship of the laboratories, I continued with my literary work, especially as Editor of the journal Die M akromolekulare Chemie, which had increased in volume with the growth in this field. And now finally I can devote my time again to my earliest field of interest, botany! The research carried out in the chemical laboratories of Freiburg University, and later at the Staat fiches Forschungsinstitut fiir makromolekulare Chemie is described in Part B of this book. All our publications in the field of macromolecular chemistry are included in it, as are those which were published independently by different co-workers, within the series Mitteil­ ungen iiber makromolekulare Verbindungen. Furthermore, dissertations are mentioned as well as a great number of my lectures, bringing the number of

INTRODUCTION

7

references in Part B to 644. However, it should be taken into consideration that as a result of the destruction of the Institute in 1944, manuscripts and other notes, which were kept there in safes, were lost. This means that some papers might not have been sufficiently mentioned in this book. On the other hand, the library in my home and the reprints of the publications kept there were saved and remained available. This made it possible to consider most of the papers. Papers which were published in Strassburg, Karlsruhe, and Zurich in various fields of low molecular organic chemistry are collected in Part A of this book. My motivation for including this work was the following: In 1950, I was invited to Helsinki in order to speak there about macromolecular chemistry and especially about cellulose. On that occasion, my friend N.J. Toivonen asked me to give an account of my earlier investigations in the field of low molecular organic chemistry to the chemists of his institute in Helsinki. This lecture was published (7), and when I sent reprints of this lecture to my former co-workers, some of them suggested the publication of a summary of these investigations. This has been done now in the present book. Looking back to past decades, I feel deeply satisfied and pleased to see that my original ideas on macromolecular structure have been confirmed and were appreciated. This found its expression in a series of honors: the Technische Hochschulen of Karlsruhe, Zurich, and the University of Strassburg, to which I belonged in former times, and, further, the Universities of Mainz, Turin, and Salamanca, awarded me honorary doctorates, and several chemical societies nominated me to honorary membership. But, above all, the Nobel Prize in chemistry, which was presented to me in 1953, was not only a great honor and pleasure for me, but also meant recognition of the field o macromolecular chemistry. In his address to me for the award of the l'Tobel Prize, Professor A. Fredga, a member of the Nobel Committee for chemistry, said at the Nobel celebration on December 10, 1953 in Stockholm*:

"Professor Staudinger. Thirty years ago, you adopted the view that a chemical molecule is able to reach almost any size and that these macromolecules play a great role in our world. You also gave logical reasons for your opinion. You indicated that so-called high polymers are formed, if for some reason an expected ring closure does not occur. You thus submitted an argument which an organic chemist could not ignore. Moreover, in an extensive and painstaking series of studies you have provided experimental *From the book, Les Prix Nobel en 1953, Stockholm, 1954, p. 27.

8

INTRODUCTION

proofs. It is no secret that for a long time many colleagues rejected your views which some of them even regarded as abderitic. Perhaps this was understandable. In the world of high polymers, almost everything was new and untested. Long standing, established concepts had to be revised or new ones created. The development of macromolecular science does not present a picture of peaceful idylls. As time passed, the conflicts vanished and the controversies were stilled. Unity has been achieved on the major issues, and the importance of your pioneer work became more and more evident. In appreciation of your services to natural science and the material culture ma e possible by your discoveries in the field of macromolecular compounds, the Royal Academy of Sciences has resolved to aw rd you the Nobel Prize of this year. Expressing to you the best congratulations of the Academy, I ask you to accept the Nobel Prize from the hands of His Majesty, The King."

Let me conclude these "Arbeitserinnerungen" with my lecture given on December 11, 1953, in Stockholm on the occasion of the Nobel celebration and which until now has been published only in the Yearbook of the Nobel Foundation, Les Prix Nobel en 1953, Stockholm, 1954.

References 1. Anlagerung des Malonesters an ungesiittigte Verbindungen, Dissertation

University of Halle, 1903. 2. D. VorHinder and H. Staudinger, Naturwissenschaften (Halle), 75, 385432 (1903). Uber Zwischenprodukte bei Additions­ und Kondensa­ tionsreaktionen des Malonesters; and pp. 433-454, Uber die Anlagerung des Malonesters an das System CH=CH-CH=CH-C=O. 3. H. Staudinger, Liebigs Ann. Chem., 341, 99-117 (1905). Einwirkung von Natriummalonester auf A.'thoxybernsteinsiiureester und A.'thoxybenzyl­ malonester. 4. H. Staudinger, Liebigs Ann. Chem., 345, 217-226 (1906). Cinnamyli­ denacetophenon und Natrium1nalonester (erschienen als Unterabschnitt der Arbeit von D. Vorliinder, Zur Kenntnis der Additionsvorgiinge). 5. H. Staudinger, Ber. Deutsch. Chem. Ges., 41, 2217-2219 (1908). Um­ wandlung der Carbonsiiuren in ihre Aldehyde. 6. H. Staudinger, Ber. Deutsch. Chem. Ges., 39, 3060-3062 (1906). Uber die Chlor­Entziehung aus einigen a­chlorierten Fluorenderivaten. 7. H. Staudinger, Suomen Kemistilehti A, 24, 79-87 (1951). Uber Arbeiten auf dem Gebiet der niedermolekularen Chemie.

Part

A

Research on Low Molecular Compounds and Publications on General Subjects

1 The Ketenes

In 1905 the first ketene was discovered by treatment of diphenylchloroacetyl chloride with zinc (16).

In the beginning I had difficulties with the preparation of the pure, beautifully colored orange diphenylketene (I), since its sensitivity to oxygen and moisture was not sufficiently known. During vacuum distillation moisture from the water aspirator pump got into the apparatus, so that the diphenylketene obtained was permanently contaminated with diphenylacetic acid or with the anhydride of the latter. Finally J. Thiele called my .attention to the point that there should be a drying tube with sulfuric acid between the aspirator pump and the distillation apparatus. This or similar methods are common nowadays. H. W. Klever, my first co-worker, prepared dimethylketene [(CH 3)2C=C=O] from a-bromodimethylacetyl bromide in Strassburg in 1906 (17,66). In contact with air this compound instantaneously forms an explosive peroxide (130) and undergoes fast dimerization. L. Ruzicka (12,70) in Karlsruhe worked with phenylmethylketene, which takes an interesting midposition between the two above-mentioned ketenes. Meanwhile N. T. M. Wilsmore [cf. J. Chern. Soc. (London), 91, 1938 (1907)] was able to obtain the simple ketene CH 2=C=O by decomposing acetoanhydride on an electrically heated platinum wire. However, this method, which is, in an improved form, of great technical importance nowadays, initially did not yield a completely pure product. Furthermore, the authors questioned whether the product could not eventually be 11

12

LOW MOLECULAR COMPOUNDS

oxyacetylene. H. W. Klever prepared the pure ketene from bro1noacetyl bromide (21) and it has been proved that it was not oxyacetylene, but the simple ketene [cf. the following discussions with N. T. M. Wilsmore and A. W. Stewart: Keten: Bemerkungen zu den Abhandlungen der HHrn. Staudinger und Klever, Ber., 41, 1025 (1908) and H. Staudinger and H. W. Klever: Keten: Bemerkung zur Abhandlung der HHrn. N. T. M. Wilsmore und A. W. Stewart, Ber., 41, 1516 (1908)]. Soon afterwards E. Ott found a new method for the preparation of ketenes: the thermal decomposition of disubstituted malonic anhydrides (25,36,68). This method was frequently used for the synthesis of unstable

ketenes. In this case it is advantageous to use the mixed anhydrides of malonic acid and diphenylacetic acid (II), which are easily obtained from malonic acid and diphenylketene (39,57). Since the diphenylketene was easily obtainable from azibenzil (see p. 18) according to the work of G. Schroeter [Ber., 42, 2336 (1909)] work on diphenylketenes was facilitated. After we had developed a procedure for the preparation of new carbonyl-substituted diazo derivatives (see p. 20), we were able to apply G. Schroeter's method in synthesizing new ketenes, like ketenedicarboxylic ester (III) (42).

One of the most interesting ketenes, ·carbon suboxide (IV), was obtained by 0. Diels soon after the discovery of ketenes [Ber., 39, 689 (1906)], when he treated malonic acid with phosphorous pentoxide. Later we were able

THE KETENES

13

to prepare the same product from dibromomalonyl bromide (26):

At that time no more diketenes could be prepared (61), neither the simple diketene, the dimolecular carbon monoxide (O=C=C=O) (141), nor the alleneketene (R 2 C=C=C=O) (60). During further research - on ketenes and phosphorus compounds we succeeded in getting ketene imine derivatives (V) from phosphine imine derivatives by a new procedure (45,52).

Thioketenes (VI), on the contrary, could be obtained from phosphine sulfides only in their polymeric state (49).

The ketene acetals, R 2 C=C (OR') 2 are comparatively stable (55). Of special interest are the yellow, autoxidizable salts of methylenecarbonic acid (VII), which can be described as salts of the ketene hydrates (56). This work has been done in collaboration with P. Meyer.

These salts were prepared by reacting potassium amide with the potassium salts of the diphenyl- or diphenylene acetic acid in liquid ammonia. The high reactivity of the ketenes was·of special interest. They all are easily converted to acids and acid derivatives by reacting them with water, alcohols, and amines.

On the other hand they differ very much in their tendency to polymerize and in the structure of their polymerization products, to autoxidize, and to add to unsaturated compounds. Substituents do not influence the reactivity of the ketenes in the same manner during these different reactions. For example, the colored diphenylketene polymerizes slowly but it is autoxidizable and very reactive toward unsaturated compounds. The colorless,

14

LOW MOLECULAR COMPOUNDS

simple ketene, on the other hand, polymerizes very quickly but reacts much more slowly with oxygen and unsaturated compounds than diphenylketene, Among the reactions of ketenes with unsaturated compounds (63,64) those of diphenylketene with aldehydes, ketones, quinones, thioketones, Schiff's bases, nitrosobenzene (30), and azobenzene (8), should be mentioned here.

Others are the addition reactions of diphenylketene to pyridine and quinoline (VIII) (9).

Compound VIII is easily split into its original components when heated to 100℃ and can therefore be used as "masked" diphenylketene. The derivatives of dimethylketene are more stable than those of diphenylketene (10,67). Studies on the influence of substituents on the reactivity of the carbonyl group were carried out by a determination of the velocity of carbon dioxide evolution on heating the diphenylketene with aldehydes and ketones (13,71). As a result of these experiments it was found that auxochromic groups in the ortho and para positions of aromatic aldehydes and ketones

THE KETENES

15

increased the addition reactivity of the carbonyl group toward diphenylketene. As a result of the reactions of ketenes a whole group of new compounds -mainly four-membered rings-like, β -lactones, β -lactams, etc. became available. The β -lactone from 2 molecules of diphenylketene and of quinone splits off carbon dioxide very easily to yield the quinoid hydrocarbon, tetraphenylquinodimethane (IX) (I 1,23) which J. Thiele and H. Balhorn had obtained by a different method a short time before [Ber., 37, 1463 (1904)].

(IX)

Furthermore, a great number of unsaturated compounds became accessible as fragments of the intermediate, unstable ,8-lactones (24), for example,

During the polymerization of the ketenes and during their addition to unsaturated compounds, cyclobutane derivatives are formed (13,46,47) and many heterocyclic four-membered rings were obtained. Due to this

16

LOW MOLECULAR COMPOUNDS

experience we were able to study in many cases the stability of four membered rings and their thermal cleavage (31). The autoxidation of the ketenes which we studied extensively (130) will be described in Chapter 5, page 33. The influence of the substituents on the tendency of the ketenes to polymerize is very different from the influence of the same substituents on carbonyl groups. While carbonyl compounds with inorganic substituents (carbonic acid esters and phosgene) do not tend to polymerize, the ketenes with analogous inorganic substituents are very unstable or cannot be prepared at all [cf. E. Ott, Ann., 401, 159 (1913)]. Furthermore, the "aldoketenes" (RCH=C=O) are much less stable than the "ketoketenes" (R 2 C=C=0). Therefore, usually we could obtain only the polymerization products of the aldoketenes (32). The polymerization of ketenes can proceed in different ways. According to recent investigations, the simple ketene yields by polymerization, vinylaceto-f3-lactone (X) which can easily be split to acetylketene and therefore is used in the preparation of acetic acid derivatives. From dimethylketene tetramethyldiketocyclobutane (XI) (17) is formed, as well as other liquid isomers and polymers whose structures were not yet proved. The structure of the polymer that forms a colloidal solution is not known either.

During 1920-1925 the structure of colloidally soluble polymers was approached by P. Karrer from a different point of view than is done today; in Part B, page 78, this will be discussed more thoroughly. At that time the polymerization of dimethylketene with t imethylamine as the catalyst to colloidally soluble compounds seemed striking, since the addition of carbon dioxide on dimethylketene yielded crystalline products of the following composition: 3 moles of dimethylketene and 2 moles of carbon dioxide. With isocyanates and carbon disulfide, on the contrary, products with colloidal properties were formed which actually were the first known copolymers [(65,81) cf. p. 82]. These results initiated an interest in elucidating the structure of the polymerization products. Unfortunately, these investigations, as well as investigations on the polymerization prod. ucts of diphenylketene, have not been continued. In the last 40 years many chemists have worked in the field of ketenes. I would like to cite only the following review articles: W. E. Hanford

THE KETENES

11

and J. C. Sauer, "Preparation of Ketenes and Ketene Dimers" [(Organic Reactions, Vol. III, R. Adams, ed., Wiley, New York, 1949, pp. 108-140); G. Quad beck, "Ketene in der priiparativen organischen Chemie" (Angew. Chern., 68, 361-370 (1956)]. In 1912 I published a book on earlier work with ketenes (8). The publications on ketenes were divided into two groups. Seven papers have the title Zur Kenntnis der Ketene (9-15). The other group is entitled Uber Ketene and contains 50 more papers (16-65). Furthermore, the dissertations in the field of the ketenes are quoted here as, in some cases, their findings have been published only partially or not at all (66-82).

2 Aliphatic Diazo Compounds

In 1910 in Karlsruhe research was done on aliphatic diazo compounds mainly in the hope of obtaining methylene derivatives by decomposition of these compounds (see Chapter 4). Furthermore, the aliphatic diazo compounds were of int rest since G. Schroeter had prepared diphenylketene from phenylbenzoyldiazomethane in 1909 [Ber., 42, 2336 (1909)]. At that time the structure of these compounds was not yet well known. Diphenyldiazomethane, which was obtained by Curtius and co-workers by oxydizing benzophenone hydrazone with mercury oxide [J.Prakt. Chern., 44, 192, 544 (1891)], was thought to be a dimolecular compound, namely, the tetrazo derivative (I), because it decomposed easily to benzophenone ketazine (II).

On the other hand the structure of a monomolecular cyclic azo compound was assigned to phenylbenzoyldiazomethane (III)

The structure of the hydrazones was also under discussion at this time, and it was still undecided whether they had the structure of either cyclic hydrazi compounds or open-chain hydrazones. 18

ALIPHATIC DIAZO COMPOUNDS

19

The question of the structure of aliphatic diazo compounds became still more complicated by the discovery of diazo anhydrides (IV) by L. Wolff in 1902 [Ann., 325, 169 (1902)].

Since these were easily transformed into thiodiazole derivatives, he postulated a five-membered ring structure. In our first publication (83) with 0. Kupfer we proved that all aliphatic diazo compounds are to be considered as derivatives of diazomethane in spite of their different behavior. We initially assigned a cyclic structure to them, while we formulated the hydrazones as open-chain systems. In a publication which followed ours J. Thiele [Ber., 44, 2522 (1911)] argued that an open-chain structure be assigned to the aliphatic diazo compounds, hydrazones, hydrazoic acid, and the azides (104). Our following work was devoted to the structure of diazo compounds (85) and hydrazones. Mainly, we investigated the possibility that hydrazi compounds could be formed, as well as hydrazones (92). For this purpose we reduced diazo compounds under different conditions (101-103). Depending on how easily nitrogen is split off during the reduction, either CH 2 derivatives or hydrazones were obtained. With L. Hammet and J. Siegwart diazoacetic ester was reduced and two isomeric reaction products obtained (103), namely, the two stereoisomeric hydrazones:

The final proof for the open-chain structure of diazo compounds and the hydrazoic acid, which was postulated by Thiele, was their reaction with tertiary phosphines (53, 98,105). This will be discussed in the following chapter. Substituents have a strong influence on the properties of diazomethane derivatives. The monosubstituted ones like ethyldiazomethane and the phenyldiazomethane are rather unstable. The disubstituted aromatic diazomethanes, like diphenyldiazomethane and especially the diazofluorene, are more stable. A neighboring carbonyl group gives rise to great stability in diazo compounds: e.g., the slightly colored diazomalonic

20

LOW MOLECULAR COMPOUNDS

ester is much more stable than the strongly colored diphenyldiazomethane. The influence of substituents on the reactivity and color are similar for the aliphatic diazo compounds, also called "azene derivatives," and the ketenes or "carbonylene derivatives." This is shown in the following table.* Diazo compounds (azene derivatives)

Ketenes (carbonylene derivatives)

The aliphatic diazo compounds were prepared partly according to Curtius by oxidation of the hydrazones with mercury oxide. We found a ne'v simple method for the preparation of diazomethane by reacting hydrazine with chloroform and alkali (84) (see also p. 30):

With this simple preparation of diazomethane-this compound was already known from the work of Pechmann and Thiele-we were able to prepare a good yield of high purity and to determine its melting point (145°C) and boiling point (-24 to -23°C). This was very unpleasant work because liquid diazomethane often explodes spontaneously and an explosion of even small amounts might cause heavy damage. We found a new method to prepare carbonyl-substituted diazo compounds, which later became important for the synthesis of other ketenes, by reacting acid chlorides with diazoacetic esters and other diazo compounds (94,95). Diazoacetic ester reacts with phosgene to give as an intermediate diazomalonic ester acid chloride which was reacted with alcohol. In this way we easily obtained diazomalonic ester (V) which already had been prepared by a different method:

From oxalic ester acid chloride and diazoacetic ester we obtained

*

H. Staudinger, Helv. Chim. Acta, 5, 88 (1922).

ALIPHATIC DIAZO COMPOUNDS

21

diazoketosuccinic ester (VI) which we transformed to ketenedicarboxylic ester (VII) by a rearrangement according to G. Schroeter (96).

At that time hydrazine became easily available through the Raschig synthesis and thus work on diazo and hydrazo compounds was facilitated. Therefore, hydrazine was considered as a reagent to transform carbonyl compounds to hydrocarbons according to the following reaction:

Curtius [J. Prakt. Chern., 44, 538 (1891)] already had noticed that benzil hydrazone easily splits off nitrogen to form desoxybenzoin. We observed the same reaction on many other hydrazones (83) and we have pointed out the importance of this reaction for the transformation of carbonyl compounds into hydrocarbons as follows*: "... The main importance of the above-mentioned reaction is the possibility of transforming the carbonyl group of aldehydes and ketones into methylene groups. It is not necessary to isolate the hydrazones or ketazines. The compounds containing carbonyl groups are heated with an excess of hydrazine to elevated temperatures and yield the corresponding methane derivatives. Experiments are under way to find out whether this reaction is more generally applicable if, for instance, the low-boiling hydrocarbons can be prepared with this reaction from aliphatic aldehydes and ketones (diethylketone and dipropyl ketone have already been transformed into their corresponding hydrocarbons). Until now they hardly could have been obtained in a pure state. They are of special interest because of their presence in the first runnings of petroleum. Furthermore, we would like to know if corresponding hydrocarbons can be obtained from the terpene ketones."

Shortly after the publication of these results L. Wolff [Ann., 394, 86 (1912)] published a detailed investigation on this subject. He showed that the reaction proceeds very easily in the presence of traces of alkali. We therefore did not proceed with the investigations we had planned in this field. Meanwhile the conversion of aldehydes and ketones into hydrocar-

* H. Staudinger

and 0. Kupfer, Ber., 44, 2206 (1911).

22

LOW MOLECULAR COMPOUNDS

bons according to this method became known in the literature as the Kishner-Wolff reduction (cf. R. Adams, Organic Reactions, Vol. IV, Wiley, New York, 1949; V. Franzen, Reaktionsmechanismen, Dr. A. Hiithig Verlag, Heidelberg, 1958). Because of the high reactivity of the aliphatic diazo compounds we decided to investigate them more thoroughly, e.g., the reaction of diazoacetic ester with diphenylketene (51) and that of diphenyldiazomethane with sulfur dioxide (90) and thiobenzophenone (99):

Furthermore, new nitrones were easily accessible from diazo compounds and nitroso compounds: e.g., diphenyl-N-phenylnitrone (VIII) was prepared from diphenyldiazomethane and nitrosobenzene (97):

By reacting these nitrones with diphenylketene we prepared nitrene {IX) with K. Mischer (97):

(IX)

By reducing tetraphenyl- N-phenylnitrene (IX) to dibenzhydrylaniline (X) the structure of this remarkable nitrogen derivative (IX) was proved.

ALIPHATIC DIAZO COMPOUNDS

23

Dibenzhydrylaniline was independently synthesized from benzhydrylaniline and diphenylbromomethane:

The structure of nitrenes had been discussed in several publications since the proposed structure was not in agreement with the valence theory [cf. L. J. Smith, Chem. Rev., 23, 193 (1938); T. W. J. Taylor, J. S. Owen, and D. Whittaker, J. Chem. Soc., 1938, 206; C. H. Hassal and A. E. Lippman, J. Chem. Soc., 1953, 1059]. Unfortunately there is no discussion in the above works as to how the structure of the reduction product, dibenzhydrylaniline (X), confirmed by synthesis, could be explained on the basis of the new concepts about their structure. Still further clarification of this question is expected with great interest. Work on diazo compounds was published in 26 papers (51,53,83-106). It was also treated in 10 dissertations (78,80, 107-114).

3 New Organic Phosphorus Compounds

In connection with our work on nitrenes with K. Miescher we made some other attempts, together with J. Meyer, to synthesize compounds carrying five substituents on the nitrogen. Therefore, we reacted phenyldimethylamine oxide with diphenylketene, hoping to get an aminomethylene derivative according to the following reaction (115):

The reaction did not proceed as expected, because the diphenylketene was oxidized by amine oxide. Phenylisocyanate did not yield the desired product either and the expected amine-imine compound therefore could not be synthesized ·(115). Synthesis of pentamethyl nitrogen from tetramethylammonium iodide and dimethylzinc was not successful either (115) [cf. later investigations of G. Wittig and M. H. Wetterling, Ann., 557, 193 (1947) who reacted tetramethylammonium chloride with phenyllithium and, instead of phenyltetramethyl nitrogen, got the first known ylide: trimethylammonium methylide]. In 1919 we tried together with J. Meyer to obtain organic phosphorus compounds containing pentavalent phosphorus, but we could not get pentaethyl phosphorus from tetraethylphosphonium iodide and diethylzinc (116). G. Wittig and M. Rieber [Ann., 562, 187 (1949)] succeeded later in 24

NEW ORGANIC PHOSPHORUS COMPOUNDS

25

getting the interesting pentaphenyl phosphorus, a homopolar compound, from tetraphenylphosphonium iodide and phenyllithium. In another attempt to synthesize new organic compounds with five substituents on the phosphorus we reacted triethylphosphine with diphenylketene and carbon disulfide. The unstable addition products were not investigated further (116). The interaption of tertiary phosphines and aliphatic diazo compounds led us to the discovery of a new group of substances, the phosphazines (I) (98). On heating these compounds carefully, we obtained phosphinemethylene (II), another riew and interesting class of organic phosphorus compounds (117):

This conversion does not proceed quantitatively, because the phosphazine (I) dissociates primarily on heating into its components. The diphenyldiazomethane decomposes further to diphenylmethylene, which can react with triphenylphosphine to phosphinemethylene derivatives (II) or with undecomposed diphenyldiazomethane to ketazines (III). "In some cases it could be proved that the phosphazines primarily dissociate into their components when heated, e.g., if triphenylphosphine ethyl glyoxylate azine is carefully heated under reduced pressure, the diazoacetic ester can be distilled off and separated from the less volatile triphenylphosphine.

In the same way phosphazine could be split from diazomalonic ester and acetyldiazoacetic ester. Whenever the diazo compound is sufficiently stable and volatile, the components can be separated. Furthermore, the dissociation of the phosphazines into their components is another proof for the structure of the diazo compounds; according to the formulation of Curtius a ring would have to be opened during the formadon of the phosphazines and closed again during the dissociation."*

We also succeeded in reacting phenylazide or other azides with tertiary phosphines. The primarily formed phosphazides (III) are frequently unstable and yield phosphinimines (IV) under evolution of nitrogen (118): *H. Staudinger and G. LUscher, Helv. Chim. Acta, 5, 77,78 (1922).

26

LOW MOLECULAR COMPOUNDS

It is of some interest that hydrazoic acid reacts easily with phosphines too. In this case we did not obtain the free phosphinimine (V) but its hydrazoic acid salt (VI) (118):

It is surprising that phosphorus hydride does not react with azides (118). As we found out later, phosphinemethylenes can be obtained more easily than described above by splitting off hydrogen halides from phosphonium salts with potassium (122):

By using this and two similar reactions, H. Isler (122) prepared a number of relatively stable phosphinemethylene derivatives. Triphenylphosphinediphenylenemethylene (VII) is a representative example. Most of these compounds are colored. The following table shows the colors of equally substituted phosphinemethylenes and ketenes.

NEW ORGANIC PHOSPHORUS

COMPOUNDS

27

The dark blue addition products of bromine with phosphinemethylene derivatives were of interest as well. They are described in the dissertations of G. Luscher and especially of H. Isler (122). The reaction of phosphinemethylene with phenylisocyanate was of special interest since it yielded diphenylketene phenylimine (VIII) (52, 119):

The same product was obtained by reacting triphenylphosphine phenylimine with diphenylketene (52):

The phosphine imines also react very easily with carbon dioxide to give isocyanates, with carbon disulfide to give ·mustard oils, and further with isocyanates to give carbodiimides (118):

Some other results in the field of phosphorus compounds are not published but can be found only in various dissertations (114, 120-122) because at that time I had decided to stop my work on low molecular compounds and to concentrate only on macromolecules. Other scientists have recently continued to work on phosphine alkylenes and phosphine imines. G. Wittig and his co-workers were especially successful in this field; by means - of lithium organic compounds even unsubstituted phosphinemethylenes became easily accessible. When they reacted triphenylphosphinemethylene with carbonyl compounds, the methylene group was substituted for the carbon ! oxygen. This procedure, known as the "Wittig reaction," made it possible to convert carbonyl derivatives into olefins and is of importance in preparative organic chemistry, particularly in the synthesis of vitamins [cf. G. Wittig and coworkers, "Uber Triphenyl­phosphin­methylene a/s olefinbildende Reagen­ zien," Ber., 87, 1318 (1954); 88, 1654 (1955); G. Wittig, "Ursprung und Entwicklung in der Chemie der Phosphinalky/ene," Angew. Chern., 68, 505 (1956); and the contribution of G. Wittig to the Stoll­Festschrift, Zi.irich, 1957, pp. 48-58]. References 98, 105, 114-122 are relevant.

4 Reactions of Methylene

The investigations on the derivatives of methyl (6) led to the question as to whether suitably substituted methylene derivatives are more stable than the derivatives of methyl (seep. 1886 in ref. 85). J. U. Nef [Ann., 270, 267 (1892)] has published several p pers on the reactions of methylene; he investigated phenylisonitrile, which had been prepared by A. W. Hofmann. In a later paper [Ann., 298, 332 (1897)] he discussed the possibility of dibromoacetylene being an acetylidene derivative [cf. H., Biltz, Ber., 46, 143 (1913)]. In our original work with O. Kupfer (123) we studied the pyrolysis of ethylene derivatives, e.g., tetrachloroethylene, and we hoped that when heated, they would decompose to methylene derivatives. This work was initiated by the discovery that dimeric carbon monoxide cannot exist (141). These investigations were unsuccessful. G. Schroeter [(Ber., 42, 2336 (1909)] has proved that diphenylketene is formed from phenylbenzoyldiazomethane under loss of nitrogen. From this result it had to be assumed that the intermediate methylene derivative (I) is very unstable and immediately rearranges to diphenylketene:

Therefore, it was of interest to investigate the splitting off of nitrogen from diphenyldiazomethane and from diphenylenediazomethane in order to study the behavior of both diphenylmethylene and diphenylenemethylene. 28

REACTIONS OF METHYLENE

29

These methylene derivatives are extraordinarily unstable as already has been shown by Curtius. During the decomposition of diazo compounds, either ketazines are formed by addition of a methylene derivative on a diazo compound (117) (see also p. 1887 in ref. 85):

which is analogous to the- reaction

or, especially at higher temperatures, ethylene derivatives are formed by the combination of two methylenes (83):

During the pyrolysis of diazomethane vapor in the presence of carbon monoxide small amounts of ketene were obtained. Hence, in this way the intermediate formation of methylene, which combines with carbon monoxide to form a ketene, was proved (p. 508 in ref. 84):

The second reaction is reversible because at higher temperatures ketene decomposes to carbon monoxide and methylene. The pyrolysis of ketene was studied in another investigation (124) and

30

LOW MOLECULAR COMPOUNDS

it was found that fluorene is formed from diphenylketene, propylene, and tetramethylethylene from dimethylketene:

An unknown methylene derivative is diisonitrile:

This should form from hydrazine with chloroform and alkali. This reaction, however, did not yield the desired result but led us to the synthesis of diazomethane (84), which has already been described on page 20. Lately more articles have been published on the synthesis and reactions of methylene derivatives. Herein these compounds frequently are called carbenes [cf. W. Kirmse, "Reaktionen mit Carbenen und Iminen als Zwi­ schenstufen," Angew. Chern., 71, 537 (1959)]. Several authors pointed out that the above-mentioned carbonylation of methylene proceeds already at low temperatures. Ch. Riichardt and G. N. Schrauzer [Ber., 93, 1840 (1960)] succeeded in preparing the carbonylation product of diphenylmethylene, namely, diphenylketene, by decomposition of diphenyldiazomethane with an excess of nickel tetracarbonyl. Several papers deal with the reactions of methylene (83-85,123,124).

5 Autoxidation of Organic Compounds

During my work in Karlsruhe, autoxidation processes were of special interest. Because of C. Engler's work they could be looked upon from a new point of view (cf. C. Engler and J. Weissberg, Kritische Studien iiber die Vorgiinge der Autoxydation, Verlag Vieweg, Braunschweig, 1904). A number of remarkable observations have been made, especially in the field of ketenes. Thus the aldoketenes, which polymerize very easily, only undergo autoxidation very slowly. The same holds for the ketenedicarbonic esters. Diphenylketene and diphenyleneketene polymerize very slowly but readily undergo autoxidation and form nonexplosive monoxides. On the contrary, the easily polymerized dimethylketene forms a very explosive peroxide according to H. W. Klever (17,66). L. Ruzicka found that slowly polymerizing phenylmethylketene yields either monoxide or peroxides, depending on reaction conditions (12,70). In order to explain these different oxidation and polymerization processes it was assumed that the primary reaction products of molecular oxygen with unsaturated compounds have an asymmetric structure. (C. Engler called these products "moloxides.") In this case the oxygen molecule does not react with the double bond, but reacts in the following way:

(I)

31

32

LOW MOLECULAR COMPOUNDS

The primary "moloxide" (I) never has been observed as such; only its decomposition or rearrangement products have been found. The autoxidation processes with ketenes are easily understood by assuming the initial formation of energy-rich moloxides. Further proof for this structure may be seen in the fact that reaction of oxygen with unsaturated compounds under pressure may lead to spontaneous explosions. Thus, when 10 g of asymmetric diphenylethylene were reacted with oxygen in a steel autoclave under a pressure of 100 atm at room temperature, an explosion occurred which tore apart the manometer with the copper capillaries attached to the steel autoclave (129). This experiment was performed because we wanted to obtain the polymeric peroxide of asymmetric diphenylethylene in higher yield, as this reaction proceeds at atmospheric pressure only very slowly. Since this polymeric peroxide explodes only on strong heating, it is possible that the explosion at room temperature was initiated by the spontaneous decomposition of an energy-rich "moloxide" (I) (129), which is formed in large amounts under elevated oxygen pressure. The well-known autoxidation of trichloroethylene can thus be formulated in the following manner (125,126):

Assuming the initial formation of a "moloxide" the autoxidation of ketenes can be described as follows: the "moloxide" of diphenylketene deco1nposes to a monoxide (II), which polymerizes as an a-lactone (130):

These diphenylketene oxide polymers are not uniform and can be separated into fractions of different solubilities and melting points. During the autoxidation of diphenylketene at elevated temperatures benzilide (III) is formed, which can be regarded as the dimeric monoxide.

AUTOXIDATION

OF ORGANIC COMPOUNDS

33

It can also be obtained by heating benzilic acid (33,130):

(III)

This work on the ketene oxides led to the investigation of the structure of such polymeric products. · Explosive dimethylketene peroxide is insoluble in any solvent and is a highly polymeric copolymer of molecular oxygen and dimethylketene which has the following structure (IV):

During explosion it decomposes to acetone and carbon dioxide (130). At -80°C a very unstable peroxide from phenylmethylketene 1s obtained which decomposes to carbon dioxide and acetophenone (12):

However, if oxygen is bubbled through a solution of phenylmethylketene at room temperature, an amorphous white powder, polymeric phenylmethylketene monoxide, is obtained as well as acetophenone and carbon dioxide. This polymer is a mixture of polymeric a-lactones of phenylmethylglycolic acid (cf. ref. 15). An insoluble polymeric peroxide was obtained from the autoxidation of the asymmetric diphenylethylene (129); it is to be interpreted as a high molecular weight copolymer of diphenylethylene and oxygen. The autoxidation of the potassium salt of diphenylmethylene carbonic acid also was investigated. Besides the polymeric peroxides, monoxides are formed (see p. 675 in ref. 56; cf. also ref. 202). This work on autoxidation and the results of H. A. Bruson's work on the elucidation of the structure of dicyclopentadiene (B 251) led in 1925 to the

34

LOW MOLECULAR COMPOUNDS

change in C. Harries' formula (V) for ozonides, which predicted the formation of glycols. The compounds were formulated as isoozonides instead (VI) (131) and this was proved through the formation of aldehydes and ketones during reduction of the ozonides. The formula of the isoozonide

(VI) is generally accepted today and was experimentally proved by A. Rieche [Ber., 65, 1274 (1932)] and R. Criegee [Ber., 86, 1 (1953)] by ozonide synthesis. A polymeric structure was assigned to the insoluble ozonides similar to that of the insoluble peroxides (131):

During the autoxidation of aldehydes oxygen is not added to the unsaturated carbonyl group as assumed by Engler and Weissberg:

but the oxygen molecule adds to the aldehyde with the migration of a hydrogen atom, e.g., during the formation of perbenzoic acid from

AUTOXIDATION

OF ORGANIC COMPOUNDS

35

benzaldehyde

The latter can be identified by its conversion to benzoylacetyl peroxide (127). Aldehydes with very reactive carbonyl groups like p-dimethylaminoor p-hydroxybenzaldehyde are therefore less able to be autoxidized than benzaldehyde itself, since the hydrogen atom on the strongly unsaturated carbonyl group is less mobile. The results of these experiments shed new light on the influence of substituents on benzoin formation (128). Furthermore, the autoxidation of the thiobenzophenone was investigated with the hope of finding sulfur monoxide (132):

This reaction proceeds in a much more complicated way than expected. These new works were reported the first time on the Naturforscher­ kongress in Karlsruhe in 1911 (125). This was followed by a discussion with E. Erdmann (126). A series of articles (127-132) and dissertations (133-135) was published on the autoxidation of organic compounds.

6 Oxalyl Chloride

In connection with our investigations on ketenes we prepared oxalyl chloride in order to obtain the simplest ketene, the bimolecular carbon monoxide (O=C=C=O) (141). This compound could not be prepared by reacting mercury with oxalyl bromide since it instantaneously decomposes into two molecules of carbon monoxide. In the next chapter the very explosive system, oxalyl chloride/alkali metals, will be discussed. In 1908, when the work on oxalyl chloride was started, pure oxalyl chloride was not yet available. Fauconnier [Compt. Rend., 114, 122 (1892)] reacted phosphorus pentachloride and oxalic ester and obtained a mixture of oxalyl chloride and phosphorus trichloride which he then was not able to separate. Oxalyl chloride was frequently overlooked because it decomposes in contact with water to carbon dioxide, carbon monoxide, and hydrogen chloride, usually without formation of oxalic acid:

This peculiar hydrolysis is due to the instability of the oxalic acid halfchloride. The formation of oxalyl chloride during the reaction of oxalic acid with phosphorus pentachloride can be followed by its conversion to the oxalic acid anilide. The yield of oxalyl chloride can be estimated in this manner: it usually is 50-55% of the theoretical value. However, yields frequently were much higher and it was not possible to discover the optimum conditions required. The first preparation of oxalyl chloride yielded a slightly red-colored liquid. It then was assumed that this was the appropriate color of the dicarbonyl compound. Even the Kahlbaum Company in Berlin at 36

OXALYL CHLORIDE

37

that time sold oxalyl chloride with a slightly reddish-yellow color. In later experiments the oxalyl chloride obtained was colorless. The red color originated from an impurity which was volatile and very sensitive to moisture; possibly, this red compound contained phosphorus. In spite of many attempts, it could not be identified. We interrupted the investigations in this direction because of the unpleasant properties of oxalyl chloride which, like phosgene, affects the respiratory organs (132). On the preparation of oxalyl chloride a German patent was granted (136). Several reactions were carried out with this very reactive compound. By the addition of oxalyl chloride to diphenylketene the thus far unknown diphenylmalonyl chloride was prepared (40):

With oxalyl chloride the CO group of reactive carbonyl compounds also can be converted into the CC12 group, for instance, in dibenzalacetone (I). In this way keto chlorides are easily available (139):

Furthermore, oxalyl chloride serves for the preparation of o-diketones; these are formed, for instance, during reaction with dimethylaniline (138):

The Friedel-Crafts reaction which meanwhile was also studied by C. Liebermann [Ber., 44, 202 (1911)] yields ketones or o-diketones, depending on the reactivity of the aromatic compound (137,140,142). The formation of a ketone or an o-diketone depends on the relative rates of the reaction of oxalyl chloride with the aromatic compound and of its decomposition into phosgene and carbon monoxide by the action of aluminum chloride. Oxalyl bromide, because of its greater reactivity, yields o-diketones more easily during the Friedel-Crafts reaction, even though it is more sensitive toward aluminum chloride. Oxalyl bromide is obtained by bubbling dry hydrogen bromide into oxalyl chloride (141).

38

LOW MOLECULAR COMPOUNDS

Since some of the cyclic o-diketones were of technical interest as starting materials for indigoid dyes, they were also the subject of two patent applications (145a,145b). Because oxalyl chloride had proved to be a stable, easily available compound, we tried together with J. Meyer (120) in Zurich to prepare formyl chloride or formyl fluoride. These experiments were not successful. Since it was possible that formyl chloride existed only at low temperatures, liquid formaldehyde and liquid chlorine were reacted in equimolar amounts at -80°C. Under the influence of light, ho ever, a heavy explosion occurred. Formyl fluoride (bp -29°C) was prepared later by A. N. Nesmejanow and E. J. Kahn [Ber., 67, 370 (1934)]. They reacted dry formic acid with benzoyl chloride and potassium fluoride. Several investigations on oxalyl chloride in Karlsruhe and Zurich have been published (137-143) and dissertations written (73,144).

7 Explosions Interesting observations were made when oxalyl chloride was treated with potassium-sodium alloy. In the cold and on warming no reaction occurs, provided that even the slightest concussion is avoided. At that time I distilled some oxalyl chloride over liquid sodium-potassium alloy. From later experience we know that even a small touch with the burner or the ring on my hand could have caused a terrible explosion. Such an explosion occurred when my assistant in the Karlsruhe laboratories Dr. E. Anthes tried to react oxalyl bromide with potassium-sodium alloy in a sealed glass tube, in order to obtain the his-carbon monoxide (O=C=C=O) (141).0n shaking, a strong explosion occurred and the glass tube shattered. Fortunately Dr. Anthes was not hurt seriously. By chance, the reaction was carried out near an open window and the pressure wave could expand in that direction. Later I heard about an accident my colleague Hieber had in Munich: a heavy explosion occurred when a bottle containing bromoform and potassium was hit. Other similar explosions have been reported to me from industry. These accidents initiated an investigation on explosions that occur on shock. I found that many inorganic and organic halide compounds form shock-sensitive systems with alkali metals or barium. Of these metals the potassium-sodium alloy turned out to be the most reactive, followed by potassium, sodium, and barium. Lithium and magnesium do not form very shock-sensitive systems. Among the inorganic compounds the liquid halides like silicon tetrachloride, tin tetrachloride, titanium tetrachloride, phosphorus tribromide, phosphorus trichloride, phosphorus oxychloride, and disulfur dichloride explode in contact with potassium-sodium on the slightest touch of the vessel. During experiments with these systems it is particularly necessary to 39

40

LOW MOLECULAR COMPOUNDS

pay strict attention, since explosions can even occur spontaneously. The violence of such explosions can be explained by the fact that all of the systems are extremely energy rich. It is surprising that in all these cases the reactions were induced by the slightest shock. In some cases an explosion occurred at the point when the alkali metal was introduced into the liquid, as in the well-known lecture demonstration where a vigorous explosion occurs on the combination of liquid bromine and metallic potassium. In contrast to this case, liquid chlorine and potassium explode only on shock. In the group of organic halides the iodine compounds are more sensitive to shock in contact with potassium-sodium than the bromine compounds and the latter are more sensitive than chlorine compounds. Halogen-rich materials like carbon tetrachloride and chloroform are more shock sensitive than halogen-poorer materials. The reactivity of the different systems was tested by the following arrangement: Test tubes of 6-7 em length and about 1 em in diameter were filled with approximately 0.5 ml of liquid potassium-sodium alloy under nitrogen. Then 0.5 ml of the liquid halogen compound was added. Hands and eyes have to be protected during this preparation since an explosion may occur even at that point. From a brass tube 0.5 em in diameter small lead balls were dropped into the test tube from various heights. The height was changed in intervals of 5 em by small slots in the brass tube. The shock sensitivity was then determined by the height that a lead ball of defined weight has to fall to initiate an explosion. With this method it could be proved that systems like carbon tetrachloride and potassium-sodium are 200 times more shock sensitive than mercury fulminate. The records of these experiments unfortunately were lost in the destruction of the Chemical Institute in Freiburg in November, 1944, and only preliminary data on this subject have been published (149, 150). The explosions of halide compounds with alkali metals are well suited for demonstrations in lectures. The following procedure is advisable. In a test tube approximately 10 em in height and 1 em in diameter 0.2 g of metallic potassium and sodium are fused together. After cooling, about 0.5 ml of carbon tetrachloride is added to the liquid alloy. The test tube is then dropped from a height of 1-1.5 m onto a stone plate or, even more impressive, into a metal bucket. The detonation occurs immediately. It is advisable to remove rings from the fingers since even a slight shock can initiate the explosion. I did not take the precaution of using test-tube holders or clamps because one can work more steadily without them.

EXPLOSIONS

41

The safest method of operation is carefully using the fingertips as long as the test tube is not held too tightly. In this case even an unexpected explosion will not cause serious damage to the hand. It is surprising that detonation of these explosive systems usually is not initiated by simple heating but by the slightest shock. In the earlier literature it was even recommended that carbon tetrachloride be dried over sodium. A number of accidents happened in industry, because the shock sensitivity of such systems was not known. - The fact that no reaction occurs on standing or warming could be compared with the phenomenon of passivity. The surface of the metal may be coated with a deactivating intermediate compound. When this layer is destroyed by shock, the reaction is initiated. The following observations support this assumption. A mixture of pentachloroethane and potassium is not very sensitive against shock; a test tube with approximately 0.2 g of solid potassium and 0.5 ml of pentachloroethane can be dropped onto an iron plate without exploding. After only a few minutes a reaction is observed and a grey substance is formed. If the test tube is then dropped, a violent explosion occurs. Sometimes the system even detonates spontaneously. If the reaction mixture sits for 1530 minutes, the system is no longer shock sensitive and potassium chloride and carbon can be found. It was not possible to determine the nature of the explosive intermediate. A number of inorganic and organic halide compounds do not seem to react under formation of reactive intermediates (cf. oxalyl bromide + K, Na: ref. 141). A number of nitrates and nitro compounds also give shock-sensitive systems with alkali metals. Ammonium nitrate or a mixture of ammonium nitrate and ammonium sulfate (" Oppau Mixture") can easily be brought to detonation on an anvil by adding small amounts of alkali metal-either sodium or potassium. In this way it can be demonstrated in a lecture that even safety explosives can be exploded. It was originally assumed that the shock-sensitive systems, like that of carbon tetrachloride and potassium-sodium alloy, could be used as primers for blasting with dynamite instead of the usual detonators. This system would have the advantage that the primer would be produced by combination of the components at the place of blasting. In case of failure the primer could be removed without hazard. For this reason several patents were applied for (146-148). These patents never found an application in practice because the \

42

LOW MOLECULAR COMPOUNDS

explosion wave of such systems-in contrast to mercury fulminate-is not sufficiently strong to induce the detonation of picric acid or dynamite. This was found from experiments on a large scale. Therefore, the strong explosion that occurs with ammonium nitrate and potassium on an anvil by a stroke with a hammer is not caused by the detonation of ammonium nitrate but by the reaction of the energy-rich system of ammonium nitrate and potassium. Finally we tried to react carbon tetrachloride and potassium-sodium in a bomb in order to precipitate carbon under high pressure in the melt of potassium and sodium chloride. These conditions might have been favorable for diamond formation. In a quarry near Zurich we made an experiment in this direction, taking every precaution, but the bomb exploded. As a result, I lost my pleasure in these high spirited experiments. To date we have been unable to initiate repetition of these experiments by some commercial organization. [cf. the essay of H. J. Rodewald:" Neues uber die Diamantsynthese der General Electric Co.," Chimia (Zurich), 14,162 (1960)]. During my stay at the ETH in Zurich, I had to give several expert opinions on industrial explosions. One of them concerned firecrackers, which were so sensitive to shock that the entire box exploded during unpacking. Some results of these cases were published (149) as well as some of our experiences with explosions in the laboratory (151). In this connection it should be noted that it is dangerous to mix potassium chlorate and red phosphorus in large quantities. A student in Freiburg lost his life during an attempt to prepare fireworks from such a mixture on a New Year's Eve. Such unexpected explosions may occur on handling endothermic compounds or energy-rich mixtures even when they seem to be relatively stable because such compounds frequently decompose under explosion; however, they do so only under certain conditions, for instance, within a small temperature range. At the ETH in Zurich I found a number of sealed via containing 50-100 g of phenyl azide. A disastrous accident could have happened if a drop of the phenyl azide had detonated on the hot glass surface, as phenyl azide, like glycerol trinitrate, explodes within specific temperature ranges. Many other endothermic compounds as, for instance, glycerol trinitrate, behave in the same way-they explode in a certain temperature range, whereas at a higher or lower temperature they only decompose by fulmination. This is shown in the well-known lecture experiment where a drop of glycerol trinitrate is dropped from a pipet onto a heated iron plate. I took over this experiment from R. WillsHitter in Zurich.

8 Synthesis of Isoprene

Numerous observations on cleavages of four-membered rings, e.g., on cyclobutane derivatives as well as on four-membered heterocyclic compounds, easily accessible from ketenes (31,63,64), induced us to study the pyrolytic cleavages of other ring systems, particularly those of six-membered rings. The pyrolytic decomposition of terpenes was investigated because here ring systems of different structures with variable arrangements of the double bounds were available. The studies showed that limonene especially and, respectively, dipentene decompose with exceptionally good yields into isoprene, but other terpenes with different arrangements of double bonds do not (152).

Particularly good yields of isoprene have been obtained by decomposition of dilute limonene vapor on a platinum coil, which was electrically heated to red heat. This procedure was described in a preliminary paper (152). I. Prodrom investigated the decomposition of different terpenes in his thesis (135). A summary of these results was published much later (153). In this last paper data were given on the yields of isoprene obtained from different terpenes, such as limonene, dipentene, pinene, terpinolene, myrcene, etc.; also, a sketch of the pyrolysis apparatus used is shown. 43

44

LOW MOLECULAR COMPOUNDS

Since isoprene was obtainable by this procedure for the first time on a large scale, a patent on this method was applied for on September 4, 1910 (154, 155). This procedure was taken over by the Badische Anilin & Soda Fabrik with the mediation of Geheirnrat C. Engler. At that time it gave the possibility of producing isoprene to the industry on a technical scale and hence made it possible to study polymerization of isoprene into rubber, as A. Holt has pointed out in his lecture "Neuere Arbeiten auf dern Kautschukgebiet" [Angew. Chern., 27, 153 (1914)]. Later the chemists of the Badische Anilin & Soda Fabrik, particularly 0. Schmidt, investigated the pyrolytic decomposition of similarly built hydrocarbons, e.g., cyclo- hexene, which is split into ethylene and butadiene as predicted. A patent was applied for on this procedure by the Badische Ani/in & Soda Fabrik on May 23, 1911, and the patent was granted relatively quickly on September 23, 1912, under the number 252,499. For this reason it appeared earlier in Friedlander, 10, p. I035 (1913) than the patent on the preparation of isoprene. Results of the pyrolysis of terpenoid hydrocarbons led to a further conclusion, namely that carbon bonds in the ,$-position to an unsaturated group can be considered weakened (156),

These conclusions were also drawn from investigations of the pyrolytic decay of dicyclopentadiene and its hydrogenation products, since the hydrogenated hydrocarbon is much more stable than the unsaturated one. The latter is known to decompose very easily (156). In numerous other works on the pyrolytic decomposition of rubber and hydrorubber, as well on the decomposition of polystyrene and hexahydropolystrene (see p. 160), the above-mentioned rule was repeatedly pointed out and later I proposed for it the name "Allylgruppierungsregel" (cf. ref. B411). About ten years later 0. Schmidt [Z. Physik. Chem., A159, 337 (1932)] took over this idea in his paper "Uber den Ort der Sprengung von C-C Bindungen in Kettenrnolekulen." Later I pointed out (153) that the essential results had already been described in the above-mentioned paper which was published in 1924 (156). This "Allylgruppierungsregel" was then cited several times as "Schmidt's 'Doppelbindungsregel"' (double-bond rule). However, this designation is inconsistent with the facts described above.

SYNTHESIS

OF ISOPRENE

45

The easy accessibility of isoprene also led to an investigation on the addition of ?romine and hydrogen bromide on isoprene. The goal of this investigation was to prove whether these additions occur in the 1,4 position according to Thiele's rule (157, 158). Later A. Kirrmann worked in this field. He was able to prove the occurrence of very complicated rearrangements. During the pyrolysis of isoprene- and other butadiene-type hydrocarbons in a red-hot tube, an isoprene tar is formed. With respect to its features and composition it -resembles coal tar to a great degree; it consists essentially of a mixture of different hydrocarbons (159). Through the research of E. L. Kennaway this isoprene tar later gained some interest because of the discovery of carcenogenic hydrocarbons found in it (cf. Chem. Zentr. II, 1373. (1925). Together with several co-workers, Dr. Klever and Dr. Herold, the synthesis of butadiene was tried during my stay in the laboratories in Karlsruhe. We hoped to obtain butadiene by addition of ethylene on acetylene. However, this and similar pyrolytic reactions yielded only very low amounts of butadiene. The yields of butadiene were determined by transforming the butadiene into the crystallized tetrabromide. Geheimrat C. Engler induced us also to study the pyrolytic decomposition in vacuum of different fractions of mineral oil. A patent was granted on this process which, however, never found a technical application (160). Since isoprene was now easily available, I and my co-workers studied its polymerization to rubber. This field had gained much importance through the discussions between C. Harries and Farbenfabriken Bayer. We also applied for a patent on Polymerisation des Isoprens mit Benzoylperoxyd. However, this patent was not granted to us because it already had been granted to another party for the same process. References 135, I 52-160 are relevant.

9 Insecticides During 1910 and 1911 Professor Fritz Haber arranged a meeting between Dr. P. Immerwahr, director of the Auer Company, Berlin, and myself. Dr. Immerwahr suggested that the active component of pyrethrum, the socalled" Dalmatian insect powder," be investigated. After his graduation L. Ruzicka took charge of this research. Pyrethrum, a powder made by grinding blossoms of Chrysanthemum cinerariifolium Bocc. was extracted with large amounts of petroleum ether. The extracts were fractionated according to the methods of organic analysis, by treatment with precipitating agents. The different fractions were then tested for their insecticide activity on cockroaches (Blatta germanica). Finally two active components were isolated and were called pyrethrine I and pyrethrine II. Their concentrations in the blossoms of Chrysanthemum cinerariifolium Bocc. were found to be 0.3-0.5%. Both pyrethrines are esters of the pyrethrolone (I), which is esterified in the case of pyrethrine I with chrysanthemum monocarboxylic acid (II) and in the case of the pyrethrine II with the monomethylester of chrysanthemum dicarboxylic acid (III):

46

INSECTICIDES

47

The structure of the chrysanthemum carboxylic acids was investigated and proved to be correct (162), while for the pyrethrolone structure some doubts still existed with respect to the position of the OH group and the double bond in the side chain (163). The correct structure was finally established in later investigations by American authors. The pyrethrines are extremely effective insecticides. After their structure had been established, the instability of alcoholic extracts of this insect powder [which was also used for combating boll weevils ("Heu­und Sauer­ wilrmer ")] was understood, since the esters are easily hydrolized or transesterified and then become ineffective. Later on, in the well-known fly repellent Flit, relatively stable extracts of pyrethrum in inert organic solvents were put on the market. The goal of our investigations was to find a synthesis for the active components. In the course of these investigations chrysanthemum monocarboxylic acid (II) was synthesized (Ill,167). However, it was not possible to synthesize the pyrethrolone or other effective carbinols of similar structure (168, 169). On the basis of information available at that time it had to be assumed that it was not possible to change the structure of the pyrethrines to a larger extent without destroying their effectiveness. Even esters of the chrysanthemum carboxylic acids with reduced pyrethrolone are inefficient. Since the synthesis of the pyrethrines did not seem too protnising, investigations were made on the efficiency of other esters of chrysanthemum monocarboxylic acid, particularly on the esters of the terpene alcohols. Attempts were also made to obtain active materials by combining different acids with pyrethrolone as an ester component. These experiments, however, led to no result (170). Later on the works on structures of pyrethrines were continued mainly by American chemists, e.g., by LaForge and Haller [J. Org. Chern., 2, 546 (1938)] [cf. M. Matsui, F. B. LaForge, N. Green, and M. S. Schechter, J. Am. Chern. Soc., 74, 2181 (1952)]. Finally, a synthesis of the pyrethrines was described by S. H. Harper [Sci. Progr., 155, 449 (1951)]. Since pyrethrine is one of the most efficient insecticides and attempts to find a synthesis for it were unsuccessful, I made some efforts to solve the pyrethrineproblem in a different way. As the content ofpyrethrine in pyreth­ rum is low and ranges in examined samples between 0.3 and 0.5%, it seemed possible to grow species of chrysanthemum which possibly would contain much larger amounts of pyrethrines. If, for instance, the content of pyrethrines in the blossoms could have been increased to 3-5 times the previous

48

LOW MOLECULAR COMPOUNDS

value, the cultivation of such pyrethrine-rich species would have had some importance. As a basis for such efforts we developed a method to determine the pyrethrine content (172, 173). As far as I know, however, such cultivations (which seemed promising on the basis of other experiments) were not undertaken in Germany [cf. T. F. West, "The History of the African Pyrethrum Industry," J. Roy. Soc. Arts, 17, 423-441 (1959)]. During World War I, when the problem of an effective insecticide became of pressing importance because of the lice which carry typhus germs, L. Ruzicka tested the effectiveness of almost all materials stored in the compound collection of the ETH in Zurich. These works never were published, being of no scientific value. Besides the poisonous nicotine, which has been well known for a long time, it was found that anisole shows rather good insecticidal features and hence found frequent application. Other relatively efficient insecticides are halide compounds, e.g., hexachloroethane and the dichlorobenzenes. Later p-dichlorobenzene was put on the market under the name Global and replaced the not very effective naphthalene, which was often used before. In the last three decades many scientists searched for other insecticides, so that industry today produces a great variety of products for combating insects. The importance of such investigations was shown by award of the Nobel Prize for medicine in 1948 to Paul H. Miiller, of Basel, for his discovery of DDT. We have written a series of papers (161-172) and dissertations (173,174) on insecticides.

10 Synthetic Pepper

During World War I, when there was a shortage of pepper in Germany, Dr. P. Immerwahr in Berlin asked me whether it could be possible to synthesize the effective component of the pepper, piperine (1), from the raw materials available in Germany. Pepper contains about 7-10% 0 piperine:

With the wartime situation in Germany at that time such a synthesis did not seem promising. Therefore, attempts were made to find out whether the piperidides of simple carboxylic acids would have the taste of pepper. These experiments were carried out by Dr. H. Schneider and led relatively quickly to success. It was found that the dioxymethylene group of piperic acid does not contribute to the taste of pepper. The piperidide of the ,8-cinnamenylacrylic acid (II) tastes even stronger than piperine. Furthermore, the hydrogenation products, e.g., the piperidide of ,8-dihydrocinnamenylacrylic acid (III), exhibits a pronounced pepper flavor:

49

50

LOW MOLECULAR COMPOUNDS

According to investigations by M. Cloetta at the Pharmacological Institute in Zurich these synthetic products are also superior to piperine in another respect: tests on dogs have shown that the synthetic products cause a lower excretion of proteins than piperine itself. Technical synthesis by industry during 1916 and 1917 was rather difficult. In this connection a more simple synthesis was also developed for malonic acid (175). Since 1917 considerable amounts of {3-dihydrocinnamenylacrylic acid piperidide (III) mixed with inert fillers and with flavorings, like phellandrene, were put on the market as "synthetic pepper." Other experiments showed that, especially under malnutrition conditions, i.e., diets consisting mainly of potatoes and beets, the latter are digested much more easily on addition of this spice. Because of its technical importance the production of pepper substitute was patented (176,177). Meanwhile, my former co-worker E. Ott in Stuttgart also was occupied with experiments on the flavor of pepper [Ann., 425, 314 (1921)]. After the war, the production of synthetic pepper was discontinued until World War II. Then Farbwerke Hochst, for instance, again manufactured cinnamenylacrylic acid piperidide (II). During peacetime the industrial production of synthetic pepper, in spite of its favorable features, is uneconomical because of the low price of natural pepper. Apart from this, it is difficult to exactly imitate the flavor of the natural product (178-181).

11 The Aroma of Roasted Coffee

With our quick success in synthesizing pepper arose the question as to whether it would also be possible to synthesize the fragrance of coffee. This question seemed interesting due to the shortage of coffee in Germany during World War I. It was comparatively easy to distil an aroma in high vacuum fron1 well-roasted coffee which was collected in a cold trap. On the basis of this success the Internationale Nahrungs und Genu.fJmittel­ Gesellschaft (INGA) in Schaffhausen-Zurich sponsored later research generously. In Berlin Richard Frank in particular supported this endeavor. We encountered many more difficulties than we had initially expected so that the research could not be carried out intensively until the end of the war. Th. Reichstein studied the coffee aroma for several years. From the fragrant material-an unstable yellow oil-which had been collected during distillation, it was possible to isolate by laborious separations and identify more than 70 different compounds. It is noteworthy that furfuryl mercaptan (I) is the 1nost effective and most substantial component, although in high concentrations it has a very unpleasant odor:

(I)

Also methyl mercaptan, the odor of which is even more unpleasant, was discovered in traces in the coffee aroma. However, the mercaptans mentioned are not found in a free state, but bound as hemiacetals to aldehydes and ortho-diketones present in excess, such as diacetyl- and acetylpropionyl. These compounds change very rapidly during storage. 51

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LOW MOLECULAR COMPOUNDS

By a well-balanced combination of large numbers of compounds (more than 40), it was possible to obtain a mixture which, on appropriate dilution, exhibited the typical smell of coffee. The technical development of this problem was undertaken by the Haarmann and Reimer Company in Holzminden. A couple of years before World War II this company put the synthetic coffee aroma "Coffarom" on the market. During the war this product was produced on a larger scale. In the meantime different companies in Switzerland and the United States manufactured coffee aromas, taking advantage of our former knowledge. Several patents were granted on the results of our work. The Interna­ tionale Nahrungs und Genuβmittel AG., in Schaffhausen, applied for some of them. Extensive investigations in this field remain unpublished thus far. Th. Reichstein and I still hope to see publication of the results, a major part of which already have been written. Some important patents and papers have been published (182-189). [See also the investigations of Th. Reichstein and H. Beitter on the composition of the aroma of roasted chicory [Ber., 63, 816 (1930)].]

12 Synthesis of Pharmaceuticals

During World War I attention was drawn to the lack of atropine. This was the reason for our interest in its synthesis with K. Miescher. This synthesis was effected simultaneously in a different way by Sir R. Robinson [J. Chern. Soc., 111, 762 (1917)]. We tried to replace tropine with its complicated double-ring system by simpler compounds without losing tropine's physiological effect. Therefore, together with Th. Reichstein we prepared "open-chain tropine," 1,2,6-dimethyl-4-oxypiperidine (II), and several derivatives. The mydriatic effect of the different stereoisomers was tested (192,195,196).

All bases we synthesized gave, as far as tested, benzoic esters with a local anaesthetic effect. It was possible to increase this effect by replacing the N-methyl group in these compounds by the N-phenylethyl group. These results were protected by several patents, which were sold to Gesellschaft fur Chernische Industrie in Basel (190). Also patents in Switzerland, England and the United States were granted on this procedure (191) [cf. Chem. Zentr., I, 811 (1927)]. Besides the patents only a short communication was published (192). Furthermore, attempts were made to prepare new pharmaceuticals from 53

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LOW MOLECULAR COMPOUNDS

allylic derivatives (196) as, for example, diallylcyanamid (III), whose synthesis was patented (193):

An attempt was also made to obtain new pharmaceuticals by conversion of diallylbarbituric acid, Dial of the CIBA Company. In doing so, bicyclic products with the following structure were prepared (180, 194):

Furthermore, water-soluble barbituric acid derivatives were synthesized which could be used as pharmaceuticals (194). No attempts led to any technically suitable product. This research is covered in a series of dissertations (180,194-196).

13 Asymmetric Synthesis

During my assistantship in the laboratory at Strassburg my friends Fr. Henle, H. Haakh, and I repeatedly discussed the problem of asymmetric synthesis. At that time, when Emil Fischer had great success with the synthesis of natural products, one group of scientists was of the opinion that living organic material originated from an abiogenesis. Another group denied this idea for ideological reasons and postulated that chemists could indeed produce organic materials but that it was not possible for them to bring about an asymmetric synthesis. For this reason Franz Henle and Hermann Haakh [Ber., 41, 4261 (1908)] tried to carry out an asymmetric synthesis by means of photochemical reactions, using circularly polarized light. These experiments had no positive result, whereas W. Kuhn in Basel later succeeded in enriching the respective antipode during the photochemical decomposition of a-azidopropionic acid dimethylamide with right and left circularly polarized light, respectively [cf. W. Kuhn and E. Knopf, Z. Physik. Chern., B7, 292 (1930); W. Kuhn, Experientia (Basel), 11, 429 (1955)]. Since it seemed probable that photochemical reactions might occur with the colored ketenes and aliphatic diazo compounds, such compounds were synthesized whose carbon atom carried two different substituents. By reacting these compounds with optically active materials such as acids or carbinols an asymmetric synthesis was attempted.

55

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LOW MOLECULAR COMPOUNDS

Since it was not possible to accomplish a reproducible enrichment either of the d or of the I enantiomer, the results of this investigation were of minor value. No paper was presented on this work; the results were only recorded in two dissertations (197, 198). In this connection H. Pracejus recently [Ann. Chem., 634, 9 (1960)] was abJe to obtain partially optically active 2-phenylpropionic acid ester by reacting phenylmethylketene with alcohols in the presence of optically active alkaloids.

14 Miscellaneous Investigations

1. ORGANIC PROBLEMS Our experiments with colored ketenes and aliphatic diazo compounds led to an investigation on thiocarbonyl compounds in order to study the influence of substituents on the color and the reactivity of this class of compounds. Indeed, some analogous properties between the different groups have been observed. For instance, diphenylketene and thiobenzophenone are deeply colored and very reactive, but have only a slight t.endency to polymerize. On the contrary, the nonsubstituted compounds such as phenylketene, methylketene, or the thioaldehydes cannot be obtained in their monomeric state since they polymerize immediately. Thiobenzophenone, prepared by L. Gattermann's method [Ber., 29,2944 (1896)] according to our experiences, was not obtainable in a pure state, always being contaminated with benzophenone. This deep violet compound (mp 51-52°C) was prepared in the pure state by the method of H. Freudenberger. According to h;s method dried hydrogen chloride and hydrogen sulfide are bubbled into tn alcoholic solution of benzophenone (199,200). The thus far unkno'Nn thiobenzoyl chloride was synthesized in good yields with a method by J. Siegwart from dithiobenzoic acid and thionyl chloride. It is a deep orange-colored substance (110,201). Both compounds, thiobenzoyl chloride and thiobenzophenone, react readily with diphenyldiazomethane (99,100). The thiobenzophenone reacts also with diphenylketene (50). It undergoes autoxidation easily; this reaction was studied in more detail (50,99, 100,110,132,199,200,201). The interesting behavior of the salts of diphenylmethylene carbonic acid (I) (56) led us to a study of their asymmetrically substituted ethylene derivative as well as their symmetrically substituted derivative (II): this is the potassium salt of stilbendiol and can be synthesized from benzil by 57

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LOW MOLECULAR COMPOUNDS

reaction with metallic potassium (202,203). It is a colored, highly reactive compound:

Whereas malonic ester readily forms the enolate (III), it was not possible to prepare the corresponding salt of methylencarbonic acid (IV) from potassium malonate in liquid ammonia (56}:

Nor was it possible to synthesize the following salts by treating acetic acid and oxalic acid with metallic potassium in liquid ammonia (56,82,202,203):

Since at that time acyl bromides and acyl iodides were comparatively difficult to obtain, an easy method for the preparation of these compounds was worked out. This method consisted of treating the acyl chlorides with gaseous hydrogen bromide or hydrogen iodide, whereupon the acyl bromides and acyl iodides were formed in excellent yields by a simple exchange reaction (204):

As a result of the experiments of E. Bauer on the assimilation, I and my co-workers performed a series of experiments to detect formaldehyde in intensively assimilating leaves by using not only color tests but also its transformation into crystallized derivatives. These attempts were unsuccessful. On the other hand, we were able to isolate and to characterize by melting point and mixed melting point the osazone of the glycolaldehyde,

MISCELLANEOUS INVESTIGATIONS

59

which was obtained by treating the leaf extracts with dinitrophenylhydrazine. Therefore, we assumed that eventually glycolaldehyde rather than formaldehyde has to be regarded as the primary assimilation product.

2. INORGANIC PROBLEMS Yellow arsenic, As 4 , is known to be obtainable as very unstable material by fast and intense cooling of arsenic vapor to low temperatures. In analogy to this, attempts were made to get S2 by quenching sulfur vapor that had been heated earlier to high temperatures, where it consisted of S2 molecules. By comparing F2 , Cl2 , and 02 with S2 one can conclude that at the temperature of liquid air the latter should be a blue substance with a boiling point around -30°C; it should polymerize rapidly to S8 units. Many different experiments were not successful (205,206). However, B. Meyer and E. Schumacher recently [Helv. Chim. Acta, 43, 1333 (1960)] were able to detect the existence of green S2 by means of IR, UV, and ESR spectra and other methods. These molecules are formed by quenching a molecular beam of sulfur vapor to temperatures below -100°C. In connection with the research on preparation of S2 molecules an attempt was also made to obtain sulfur monoxide (SO) by quenching the decomposition products of thionyl bromide. It should be formed according to the reaction

However, only a mixture of bromine, sulfur, and sulfur dioxide has been isolated. Another series of experiments for the preparation of SO was also unsuccessful. During the reaction of thionyl chloride with diphenyldiazomethane diphenyldichloromethane, sulfur, and sulfur dioxide were formed, not the expected diphenylchloromethylsulfinyl chloride:

A similar reaction also occurs on treating diphenylketene with thionyl chloride (205):

60

LOW MOLECULAR COMPOUNDS

Also, during the autoxidation of thiobenzophenone sulfur dioxide and sulfur, rather than sulfur monoxide, are formed (132). Later sulfur monoxide, an extremely unstable compound, was prepared; P. W. Schenk, in particular, worked on this problem [cf. Chemiker­Ztg., 67, 251 (1943)] (205,206). When we studied the behavior of carbon monoxide toward different catalysts in order to get formaldehyde from carbon monoxide and hydrogen, the observation was made that in the presence of palladium(II) chloride, copper(Il) chloride is reduced by carbon monoxide to copper(!) chloride. Since copper(!) chloride can be reoxidized by oxygen to copper(!I) chloride, it was obvious that an experiment could be performed on this basis with a carbon monoxide system. However, the electromotive force turned out to be less than 0.2 V, which corresponds approximately to the Cu + /Cu 2 + system whose emf is 0.17 V. This emf is also much smaller than that expected for the transformation of carbon monoxide into carbon dioxide. The experiments in this field were discontinued later because of more intensified research on problems in macromolecular chemistry. Nothing has been published on this subject. In 1944 the records of these results as well as many others were destroyed during the fire at the chemical laboratories in Freiburg.

15 Contributions to Educational Problems

At the turn of the century education in organic chemistry consisted of making organic compounds; also, a long time was required for carrying out elemental analysis, frequently up to one semester. On the other hand, as far as I know, no organic analyses were performed in any laboratories which correspond to inorganic qualitative analysis. However, in practice and in scientific research such analytical methods are of great importance because chemists frequently face the problem of separating mixtures of compounds into their components, which then have to be identified. This led me to establish a course in qualitative organic analysis at the chemical laboratories of the Eidgeniissische Technische Hochschule in Zurich. During this course the student had to separate out the components in a mixture of several different compounds and he then had to identify them. Elaboration of analytical methods was facilitated by the fact that the Diplomkandi­ daten had to solve one problem within four weeks. Whereas formerly in their courses students had to synthesize an organic compound, I now had them analyze mixtures and was therefore able to control the success of analytical methods in the analysis of complicated mixtures. My experiences in this field were recounted in a small volume in 1923, whose first edition was dedicated to Geheimrat Engler in Karlsruhe (207). Meanwhile, English, French, Japanese, and Spanish translations of this booklet have appeared. An excerpt from these analytical methods has appeared in Chemisch­tech­ nische Untersuchungsmethoden (208). During my activity in Zurich I initially also had to give a six- and later a five-hour lecture on inorganic chemistry for chemists, other scientists, and pharmacists who had acquired previous knowledge in this field at the 61

62

LOW MOLECULAR COMPOUNDS

gymnasium because admission to the Eidgenossische Technische H ochschule depended on their knowledge in basic chemistry. Since at that time no special lectures were given in inorganic chemistry and therefore an extensive amount of material had to be covered, I had a series of tables made up. Later these tables were compiled and mimeographed by the students. In Freiburg these same tables were then used in my five-hour lecture for the students of chemistry, medicine, natural science, pharmacy, and forestry; since special lectures in inorganic chemistry were given here these tables were omitted; later these tables were published to make them accessible to students. I was helped in preparing the first edition by my lecture assistant, A. Hensle. On the following editions I enjoyed the help of my assistant G. Rienacker with whom I also collaborated after his appointment as Professor in Gottingen and later in Rostock. During revision of the fourth edition my former assistant H. Batzer gave me valuable help by checking all of the data material (209). In my principal lectures on inorganic and organic chemistry I always have tried to emphasize the general importance of chemistry in our time and the changes in our lives due to technical developments. Control of coal and petroleum combustion have changed the way of life in industrialized countries since 1900 in so far as technical power has greatly exceeded man power. While 100 years ago men depended mainly on the work of their hands and older cultures even needed slave work for their existence and development, the civilized nations of today have new and entirely different sources of power as a result of the use of technical energy. In order to find a simple measure of this technical energy, it was converted into horse power-years. Since one horse power is equivalent to 6-7 man powers, one horse power-year is equivalent to the work done by 6-7 men during one year. This technical energy was called "technical slaves." By this conversion it becomes clear how much technical energy exceeds man power in industrialized societies. The big technical achievements of this century, automobile traffic, and finally all kinds of reconstructions during the last years can only be understood in terms of the availability of legions of "technical slaves." Political changes have to be seen from this new point of view. For instance, Victorian England possessed four "technical slaves" for each man (the United States, 1:1; Germany, 1:1). For this reason England was then a world power. In 1914, Germany had reached the same technical possibilities as England and America. Since 1930 the United States had developed the fastest with respect to technical energy while Europe fell behind.

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63

I stressed the importance of technical energy not only in my lectures (cf. 209) but also in a series of publications (210-215). Today atomic energy adds completely new possibilities for peaceful application as well as for warfare. Perhaps, therefore, technical energy coming from the use of coal and mineral oil is neglected but it is still of outstanding importance, and only the sum of " technical slaves" is increased enormously by the addition of atomic energy. For this reason I find it necessary that a professor of chemistry demonstrate technical power to his students. Some of them will later take leading roles in economy and politics. Therefore, they should have a good knowledge of the possibilities and dangers of technology and especially of the dimensions of technical power.

Part A References [References 1-7 are listed on page 8.] 8. H. Staudinger, Die Ketene, Verlag Enke, Stuttgart, 1912. 9. (1) H. Staudinger, Ann., 356, 51-123 (1907). Diphenylketen. 10. (2) H. Staudinger, H. W. Klever, and P. Kober, Ann., 374, 1-39 (1910). Vber Dimethylketen­Basen. 11. (3) H. Staudinger and St. Bereza, Ann., 380, 243-277 (1911). Einwir­ kung von Diphenylketen auf Chinone. 12. (4) H. Staudinger and L. Ruzicka, Ann., 380, 278-303 (1911). Phenyl­ methylketen. 13. (5) H. Staudinger and N. Kon, Ann., 384, 38-135 (1911). Vber die Reaktionsfiihigkeit des Carbonyls. 14. (6) H. Staudinger and R. Endle, Ann., 401, 263-292 (1913). Vber die Bildung von '8­Lactonen aus Diphenylketen. 15. (7) H. Staudinger and J. Maier, Ann., 401, 292-303 (1913). Versuche mit Diiithylketen. 16. (1) H. Staudinger, Ber., 38, 1735-1739 (1905). Ketene, eine neue Korperklasse. 17. (2) H. Staudinger and H. W. Klever, Ber., 39, 968-971 (1906). Di­ methylketen. 18. (3) H. Staudinger, Ber., 39, 3062-3067 (1906). Diphenylenketen. 19. (4) H. Staudinger, Ber., 40, 1145-1148 (1907). Reaktionen des Di­ phenylketens. 20. (5) H. Staudinger and H. W. Klever, Ber., 40, 1149-1153 (1907). Re­ aktionen des Dimethylketens. 21. (6) H. Staudinger and H. W. Klever, Ber., 41, 594-600 (1908). Keten. 22. (7) H. Staudinger and H. W. Klever, Ber., 41,906-909 (1908). Einteilung der Ketene. 23. (8) H. Staudinger, Ber., 41, 1355-1363 (1908). Darstellung chinoider Kohlenwasserstoffe aus Diphenylketen. 24. (9) H. Staudinger, Ber., 41, 1493-1500 (1908). Gefiirbte Kohlenwasser­ stoffe aus Diphenylketen. 25. (10) H. Staudinger and E. Ott, Ber., 41, 2208-2217 (1908). Malon­ siiure­halbchloride, Malonsiiure­anhydride und ihre Vberfuhrung in Ketene. 26. (11) H. Staudinger and St. Bereza, Ber., 41, 4461-4465 (1908). Neue Bildungsweisen des Kohlensuboxyds. 27. (12) H. Staudinger and J. Kubinsky, Ber., 42, 4213-4215 (1909). Zur Darstellung des Ketens.

64

PART A REFERENCES

65

28. (13) H. Staudinger, Ber., 42, 4249-4262 (1909). Vber die Einwirkung von Diphenylketen auf carbonylhaltige Verbindungen. 29. (14) H. Staudinger and St. Bereza, Ber., 42, 4908-4918 (1909). A."thyl­ keten­carbonsiiureester. 30. (15) H. Staudinger and S. Jelagin, Ber., 44, 365-374 (1911). Einwirkung von Diphenylketen auf Nitrosoverbindungen. 31. (16) H. Staudinger, Ber., 44, 521-533 (1911). Vber Bildung und Spa/tung von Vierringen. 32. (17) H. Staudinger, Ber., 44, 533-543 (1911). Phenylketen und Methyl­ keten. 33. (18) H. Staudinger, Ber., 44, 543-547 (1911). Vber die Zersetzung der Benzilsiiure. 34. (19) H. Staudinger, Ber., 44, 1619-1623 (1911). Vber Bildung und Darstellung des Diphenylketens. 35. (20) H. Staudinger and K. Clar, Ber., 44, 1623-1633 (1911). Versuche zur Darstellung von Chinoketenen. 36. (21) H. Staudinger and E. Ott, Ber., 44, 1633-1637 (1911). Versuche zur Darstellung von Allenketenen. 37. (22) H. Staudinger and 0. Kupfer, Ber., 44, 1638-1640 (1911). Ver­ suche zur Darstellung von Phenyl­methoxy­keten. 38. (23) H. Staudinger, K. Clar, and E. Czako, Ber., 44, 1640-1647 (1911). Vber die Reaktionsfiihigkeit des Halogenatoms gegen Metal/e. 39. (24) H. Staudinger, E. Anthes, and H. Schneider, Ber., 46, 3539-3551 (1913). Vber gemischte Diphenyl­essigsiiure­anhydride und ihre Zer­ setzung. 40. (25) H. Staudinger, 0. Gohring, and M. Scholler, Ber., 47, 40-48 (1914). Vber die Einwirkung von Siiurechloriden auf Diphenylketen. 41. (26) H. Staudinger and H. Becker, Ber., 50, 1016-1024 (1917). Vber Keten­monocarbonester. 42. (27) H. Staudinger and H. Hirzel, Ber., 50, 1024-1035 (1917). Keten­ dicarbonester und Phenyl­keten­carbonester. 43. (28) H. Staudinger, Ber., 50, 1035-1041 (1917). Keten­carbonester und Schiffsche Basen. 44. (29) H. Staudinger and R. Endle, Ber., 50, 1042-1046 (1917). Vergleich der Isocyanate mit den Ketenen. 45. (30) H. Staudinger and J. Meyer, Ber., 53, 72-76 (1920). Darstellung eines Keten­imid­ Derivates aus dem Diphenyl­keten. 46. (31) H. Staudinger, Ber., 53, 1085-1092 (1920). Vber Cyclobutandion­ Derivate und die polymeren Ketene. 47. (32) H. Staudinger and E. Suter, Ber., 53, 1092-1105 (1920). Cyclobutan­ Derivate aus Diphenylketen und A."thylen­ Verbindungen. 48. (33) H. Staudinger and S. Schotz, Ber., 53, 1105-1124 (1920). Ver­ suche zur Herstellung von optisch­aktiven Ketenen. 49. (34) H. Staudinger, G. Rathsam, and F. Kjelsberg, Helv. Chim. Acta, 3, 853-861 (1920). Vber das Diphenyl­thioketen. 50. (35) H. Staudinger, Helv. Chim. Acta, 3, 862-865 (1920). Einwirkung von Diphenylketen auf Thioketone.

66

LOW MOLECULAR COMPOUNDS 51. (36) H. Staudinger and Th. Reber, Helv. Chim. Acta, 4, 3-23 (1921). Ketene und aliphatische Diazoverbindungen. 52. (37) H. Staudinger and E. Hauser, Helv. Chim. Acta, 4, 887-896 (1921). Keteniminderivate. 53. (38) H. Staudinger, Helv. Chim. Acta, 5, 87-103 (1922). Uber alipha­ tische Diazoverbindungen und Ketene. 54. (39) H. Staudinger, Helv. Chim. Acta, 5, 103-108 (1922). Uber das Verhalten von Ringsystemen. 55. (40) H. Staudinger and G. Rathsam, Helv. Chim. Acta, 5, 645-655 (1922). Uber Ketenacetale. 56. (41) H. Staudinger and P. J. Meyer, Helv. Chim. Acta, 5, 656-678 (1922). Uber die Methylenkohlensiiurederivate. 57. (42) H. Staudinger, H. Schlubach, and H. Schneider, Helv. Chim. Acta, 6, 287-290 (1923). Uber die Darstellung von Ketenen aus Malonsiiure­ anhydriden. 58. (43) H. Staudinger, H. Schneider, P. Schotz, and P.M. Strong, Helv. Chim. Acta, 6, 291-303 (1923). Uber alkyl­ und arylsubstituierte Ketoketene. 59. (44) H. Staudinger and H. Schneider, Helv. Chim. Acta, 6, 304-315 (1923). Uber anorganisch substituierte Ketene. 60. (45) H. Staudinger and H. Schneider, Helv. Chim. Acta, 6, 316-321 (1923). Versuche zur Darstellung von Allenketen. 61. (46) H. Staudinger and W. Kreis, Helv. Chim. Acta, 6, 321-326 (1923). Versuche zur Darstellung von Diketenen. 62. (47) H. Staudinger, Helv. Chim. Acta, 7, 3-8 (1924). Uber die Konsti­ tution der dimeren Ketene, ein Beitrag zum Valenzproblem der organ­ ischen Chemie. 63. (48) H. Staudinger and A. Rheiner, Helv. Chim. Acta, 7, 8-18 (1924). Cyclobutanderivate aus Diphenylketen und }lthylenverbindungen. 64. (49) H. Staudinger and P. J. Meyer, Helv. Chim. Acta, 7, 19-22 (1924). Cyclobutanderivate aus Dimethylketen und }i'thylenverbin­ dungen. 65. (50) H. Staudinger, Helv. Chim. Acta, 8, 306-332 (1925). Uber Ad­ ditions­ und Polymerisationsreaktionen des Dimethylketens. 66. Helmut Klever, dissertation, University of Strassburg, 1907. Uber.. Dimethylketen. 67. Paul Kober, dissertation, University of Strassburg, 1909. Uber die Anlagerung von Dimethylketen an C=N- Doppelbindung. 68. Erwin Ott, dissertation, University of Strassburg, 1909. Uber Versuche zur Darstellung von Allenketenen. Uber Malonsiiurehalbchloride, Malonsiiureanhydride und deren Uberfiihrung in Ketene. 69. Stanislaus Bereza, dissertation, TH Karlsruhe, 1910. Uber Darstellung neuer Ketene und iiber Anlagerung von Diphenylketen an substituierte Chinone. 70. Leopold Ruzicka, dissertation, TH Karlsruhe, 1911. Uber Phenyl­ methylketen.

PART A REFERENCES

67

71. Norbert Kon, dissertation, TH Karlsruhe, 1911. Uber Einwirkung von Diphenylketen auf carbonylhaltige Verbindungen. 72. Max Reinhold Scholler, dissertation, University of Freiburg (Schweiz), 1913. Uber Versuche zur Darstellung von Dimethoxydiphenylketen und Reaktionen des Oxalylchlorids. 73. Eugen Anthes, dissertation, ETH Zurich, 1913. Uber Oxalylbromid und andere Siiurehaloide. Reaktionen des Diphenylenketens. 74. Rudolf Endle, dissertation, ETH Zurich, 1913. Einwirkung von Diphenylketen auf ungesiittigte Ketone. Vergleich von Isocyanaten mit Ketenen und iiber pyrogene Zersetzungen. 75. Schachno Peisach Schotz, dissertation, ETH Zurich, 1914. Versuche zur Darstellung von Ketenen der Campherreihe. 76. Hermann Becker, dissertation, ETH Zurich, 1915. Uber Ketenmono­ carbonsiiureester und Ketendicarbonsiiureester. 77. Hermann Schneider, dissertation, ETH Zurich, 1916. Uber den Einflufi von Substituenten auf die Ketengruppe. 78. Hermann Hirzel, dissertation, ETH Zurich, 1916. Uber Ketencarbon­ ester. Beitriige zur Kenntnis der aliphatischen Diazoverbindungen. 79. Ludwig Hauck, dissertation, TH Karlsruhe, 1919. Beitriige zur Kenntnis der Ketenbildung. Uber Formaldehydsalze. 80. Theodor Reber, dissertation, ETH Zurich, 1921. Ketene und ali­ phatische Diazoverbindungen. 81. Friedrich Felix, dissertation, ETH Zurich, 1923. I. Darstellung von Ketenen. II. Polymerisation und neue Anlagerungsreaktionen des Dimethylketens. 82. Paul Jos. Meyer, dissertation, ETH Zurich, 1922. I. Uber den Einflufi der Substituenten auf die Bestiindigkeit des Cyclobutanonringes. II. Uber Methylenkohlensiiurederivate. Cf. also the dissertation, carried out in the institute for physical chemistry of the ETH Zurich, with Prof. Dr. V. Henri: Guillaume C. Lardy, ETH Zurich, 1924. Spectres d'Absorption Ultra­violets de quelques Cetenes et de leurs Dimeres. 83. (1) H. Staudinger and 0. Kupfer, Ber., 44, 2197-2212 (1911); (zugl. 2. Mitt. iiber Reaktionen des Methylens). Vberdie Einwirkung von Hydrazin auf carbonylhaltige Verbindungen. 84. (2) H. Staudinger and 0. Kupfer, Ber., 45, 501-509 (1912); (zugl. 3. Mitt. iiber Reaktionen des Methylens). Diazomethan. 85. (3) H. Staudinger, Ber., 49, 1884-1897 (1916). Uber aliphatische Diazoverbindungen. 86. (4) H. Staudinger and A. Gaule, Ber., 49, 1897-1918 (1916). Vergleich der Stickstoff­Abspaltung bei verschiedenen aliphatischen Diazover­ bindungen. 87. (5) H. Staudinger and J. Siegwart, Ber., 49, 1918-1923 (1916). Ein­ wirkung von Schwefelwasserstoff auf Diazoverbindungen. 88. (6) H. Staudinger and J. Goldstein, Ber., 49, 1923-1928 (1916). Diphenyl­diazomethan­ Derivate.

68

LOW MOLECULAR COMPOUNDS 89. (7) H. Staudinger, E. Anthes, and F. Pfenninger, Ber., 49, 1928-1941 (1916). Diphenyl­diazomethan. 90. (8) H. Staudinger and F. Pfenninger, Ber., 49, 1941-1951 (1916). Uber die Einwirkung von Schwefeldioxyd auf Diphenyldiazomethan. Cf. the publication: H. Staudinger, Chemiker­Ztg., 38, 758-759 (1914). Uber aliphatische Diazoverbindungen. 91. (9) H. Staudinger and A. Gaule, Ber., 49, 1951-1960 (1916). Di­ phenylen­diazomethan. 92. (10) H. Staudinger and A. Gaule, Ber., 49, 1961-1968 (1916). Versuche zur Herstellung isomerer Diazoverbindungen bzw. Hydra­ zone. 93. (11) H. Staudinger, Ber., 49, 1969-1973 (1916). Reaktionen des Phenyl­benzoyl­diazomethans. 94. (12) H. Staudinger and Ch. Machling, Ber., 49, 1973-1977 (1916). Einwirkung von Siiurechloriden auf Phenyl­diazomethan­carbonester. 95. (13) H. Staudinger, J. Becker, and H. Hirzel, Ber., 49, 1978-1994 (1916). Einwirkung von Siiurechloriden auf Diazoessigester. 96. (14) H. Staudinger and H. Hirzel, Ber., 49, 2522-2529 (1916). Uber die Zersetzung von Diazoessigester­Derivaten in der Wiirme. 97. (15) H. Staudinger and K. Miescher, Helv. Chim. Acta, 2, 554-582 (1919). Uber Nitrone und Nitrene. 98. (16) H. Staudinger and J. Meyer, Helv. Chim. Acta, 2, 619-635 (1919). Uber neue organische Phosphorverbindungen. II. Phosphazine. 99. (17) H. Staudinger and J. Siegwart, Helv. Chim. Acta, 3, 833-840 (1920). Einwirkungen von aliphatischen Diazoverbindungen auf Thioketone. 100. (18) H. Staudinger and J. Siegwart, Helv. Chim. Acta, 3, 840-852 (1920). Uber die Einwirkung von Thiosiiurechloriden auf aliphatische Diazoverbindungen. 101. (20) H. Staudinger, A. Gaule, and J. Siegwart, Helv. Chim. Acta, 4, 212-217 (1921). Reduktion 1nit Wasserstoff bei Gegenwart von Pal­ ladium. 102. (21) H. Staudinger and L. Hammet, Helv. Chin1. Acta, 4, 217-228 (1921). Uber die Konstitution der Hydrazone, insbes. des Mesoxalester­ hydrazons. 103. (22) H. Staudinger, L. Hammet, and J. Siegwart, Helv. Chim. Acta, 4, 228-238 (1921). Uber die Reduktion des Diazo­essigesters. 104. (23) H. Staudinger, Helv. Chim. Acta, 4, 239-241 (1921). Zur For­ mulierung des Diazo­essigesters und der Diazo­anhydride. 105. (24) H. Staudinger and G. Luscher, Helv. Chim. Acta, 5, 75-86 (1922). Uber Darstellung und Reaktionen von Phosphazinen. 106. (26) J. Meyer, Helv. Chim. Acta, 8, 38-41 (1925). Uber eine Reaktion zwischen Diazo­desoxybenzoin (Phenyl­benzoyl­diazomethan) und Schwefelkohlenstoff. 107. Fritz Pfenninger, dissertation, ETH Zurich, 1915. Diphenyldiazo­ methan.

PART A REFERENCES

69

108. Alice Gaule, dissertation, ETH Zurich, 1916. Beitriige zur Kenntnis aliphatischer Diqzoverbindungen. 109. Charles Maechling, dissertation, ETH Zurich, 1916. I. Zur Konstitu­ tion der Diazoanhydride. II. Einwirkung von organischen Siiure­ chloriden auf Phenyldiazomethan­o­karbonester. III. Einwirkung von anorganischen Siiurechloriden auf Diazoessigester. 110. Josef Siegwart, dissertation, ETH Zurich, 1917. Uber Thiobenzoyl­ chlorid und Einwirkung von schwefelhaltigen Verbindungen auf Diazokorper. 111. Otto Muntwyler, dissertation, ETH Zurich, 1917. Uber die Einwirk­ ung von Diazoessigester auf ungesiittigte Verbindungen. 112. Karl Miescher, dissertation, ETH Zurich, 1918. Nitrone und Nitrene. 113. Eugen Wulkan, dissertation, ETH Zurich, 1919. Uber die Einwirkung aliphatischer Diazoverbindungen auf Azoverbindungen. Die Konstitu­ tion der aliphatischen Diazoverbindungen. 114. Gottlieb Luscher, dissertation, ETH Zurich, 1922. Beitrag zur Kon­ stitution der aliphatischenDiazokorper und Hydrazone. Neue organische Phosphorverbindungen. 115. H. Staudinger and J. Meyer, Helv. Chim. Acta, 2, 608-611 (1919). Versuche zur Herstellung neuer Stickstoffverbindungen. 116. (1) H. Staudinger and J. Meyer, Helv. Chim. Acta, 2, 612-618 (1919). Uber neue organische Phosphorverbindungen. 117. (3) H. Staudinger and J. Meyer, Helv. Chim. Acta, 2, 635-646 (1919). Phosphinmethylenderivate und Phosphinimine. 118. (4) H. Staudinger and E. Hauser, Helv. Chim. Acta, 4, 861-886 (1921). Phosphinimine. 119. (5) H. Staudinger and W. Braunholtz, Helv. Chim. Acta, 4, 897-900 (1921). Uber die Einwirkung von Carbonylenderivaten auf Phos­ phazine. 120. Jules Meyer, dissertation, ETH Zurich, 1919. Versuche zur Herstel­ lung von Formylchlorid und iiber neue organische Stickstoff­ und Phosphorderivate. 121. Ernst Hauser, dissertation, ETH ZUrich, 1922. Uber Phosphinimine und iiber Ketenimine. 122. Hans Isler, dissertation, ETH Zurich, 1924. I. Uber Phosphin­ methylene. II. Uber eine neue Gruppe von farbigen Halogenverbin­ dungen aus Phosphin­methylenen. 123. H. Staudinger and 0. Kupfer, Ber., 44, 2194-2197 (1911). Versuche zur Darstellung von Methylenderivaten. 124. H. Staudinger and R. Endle, Ber., 46, 1437-1442 (1913). Uber die Zersetzung der Ketene bei hoher Temperatur. 125. H. Staudinger, Chemiker­Ztg., 35, 1097-1098 (1911). Uber die Autoxy­ dation organischer Verbindungen; also Angew. Chern., 24, 1915-16 (1911). 126. H. Staudinger, J. Prakt. Chern., 85, 330 (1912). Bemerkung zu der Arbeit von E. Erdmann: Uber die Autoxydation von Trichloriithylen.

70

LOW MOLECULAR COMPOUNDS 127. (1) H. Staudinger, Ber., 46, 3530-3535 (1913). Uber die Autoxydation aromatischer Aldehyde. 128. (2) H. Staudinger, Ber., 46, 3535-3538 (1931). Beziehungen zwischen Autoxydation und Benzoin­Bildung. 129. (3) H. Staudinger, Ber., 58, 1075-1079 (1925). Uber Autoxydation des asymmetrischen Diphenyl­athylens. 130. (4) H. Staudinger, K. Dyckerhoff, H. W. Klever, and L. Ruzicka, Ber., 58, 1079-1087 (1925). Uber Autoxydation der Ketene. 131. (5) H. Staudinger, Ber., 58, 1088-1096 (1925). Uber die Konstitution der Ozonide. 132. (6) H. Staudinger and H. Freudenberger, Ber., 61, 1836-1839 (1928). Uber die Autoxydation des Thiobenzophenons. 133. Kurt Dyckerhoff, dissertation, TH Karlsruhe, 1910. Beitrage zur Autoxydation organischer Stoffe. 134. Ludwig Lautenschlager, dissertation, TH Karlsruhe, 1913. Aut­ oxydation und Polymerisation ungesattigter Kohlenwasserstoffe. 135. loan Prodrom, dissertation, ETH Zurich, 1913. Untersuchungen iiber Autoxydation und iiber Umwandlung verschiedener Terpene in Isopren. 136. H. Staudinger, DRP 216918 KL. 12o (July 10, 1908); Friedlander, 10, 80 (1913). Verfahren zur Darstellung von Oxalylchlorid aus Oxal­ saure und Phosphorpentachlorid. H. Staudinger, DRP 216919 Kl. 12o (Nov. 10, 1908); Friedlander, 10, 81 (1913). Verfahren zur Darstel­ lung von Oxalylchlorid aus Oxalsaure und Phosphorpentachlorid (Zusatzpatent). 137. (1) H. Staudinger, Ber., 41, 3558-3566 (1908). Oxalylchlorid. 138. (2) H. Staudinger and H. Stockmann, Ber., 42, 3485-3496 (1909). Uber die Einwirkung von Oxalylchlorid auf Dimethylanilin. 139. (3) H. Staudinger, Ber., 42,3966-3985 (1909). Einwirkung von Oxalyl­ chlorid auf carbonylhaltige Verbindungen. 140. (4) H. Staudinger, Ber., 45, 1594-1596 (1912). Uber die Friedel­ Crafts' sche Reaktion mit Oxalylchlorid und Oxalylbromid. 141. (5) H. Staudinger and E. Anthes, Ber., 46, 1426-1437 (1913). Uber Oxalylbromid und Versuche zur Darstellung von Di­Kohlenoxyd. 142. (6) H. Staudinger, E. Schlenker, and H. Goldstein, Helv. Chim. Acta, 4, 334-342 (1921). Uber die Friedel­Crafts'sche­Reaktion mit Oxalyl­ chlorid. 143. (7) H. Staudinger, H. Goldstein, and E. Schlenker, Helv. Chim. Acta, 4, 342-364 (1921). Uber die Friedel­Crafts'sche­Reaktion mit Oxal­ saure­imidchlorid­derivaten. 144. Ernst Schlenker, dissertation, ETH Zurich, 1920. Versuche zur Dar­ stellung von Acenaphthen­chinonderivaten. 145a. H. Staudinger, Schw. P. 92688 (Dec. 11, 1920); Chern. Zentr., II, 573 (1923). Verfahren zur Darstellung von heterocyclischen Verbin­ dungen der Naphthalinreihe. 145b. H. Staudinger, H. Veraguth, and R. Tobler, A.P. 1461435 (Nov. 11,

PART A REFERENCES

71

1922); Chern. Zentr., I, 251 (1924). Transferred to the" Gesellschaft fiir Che1nische Industrie in Basel. lndigoide Farbstoffe. 146. H. Staudinger, EP 199 734 (June 21, 1923); Che1n. Zentr., IV, 970 (1923). Sprengsto./f. 147a. H. Staudinger, Schw. P. 100 199 (June 21, 1922); Chen1. Zentr., I, 528 (1924). Darstellung von Sprengmitteln. 147b. H. Staudinger, Schw. P. 100 628 (Oct. 9, 1922); Chern. Zentr., I, 1611 (1924). Herstellung von Sprengmitteln. 148a. H. Staudinger, Schw. P. 100 200 (June 21, 1922); Chern. Zentr., I, 528 (1924). Initialziindung von Sprengstoffen. 148b. H. Staudinger, Schw. P. 100 629 (Oct. 10, 1922); Schw. P. 100 874 (Oct. 9, 1922); Chern. Zentr., I, 1611 (1924). lnitialziindung von Sprengstoffen. 149. H. Staudinger, Angew. Chern., 35, 657-659 (1922). Erfahrungen iiber einige Explosionen. 150. H. Staudinger, Z. Elektrochern., 31, 549-552 (1925). Vber Explosionen mit Alkalimetallen. 151. H. Staudinger, Angew. Chern., 39, 98 (1926). Warnung vor dem ublichen Verfahren zur Herstellung von Kiihlbadern aus brennbaren Verbindungen mit fliissiger Luft. 152. H. Staudinger and H. W. Klever, Ber., 44, 2212-2215 (1911). Vber die Darstellung von Isopren aus Terpenkohlenwasserstoffen. 153. H. Staudinger and H. W. Klever, Ber., 75, 2059-2064 (1942). Vber die Darstellung von Isopren aus Terpenkohlenwasserstoffen. 154. H. Staudinger, DRP 257 640 Kl. 12o (Sept. 4, 1910); Friedlander, 11, 814 (1915). Verfahren zur Darstellung von Isopren aus Terpenkoh­ lenwasserstoffen. 155. H. Staudinger, DRP 264 923 Kl. 12o (Aug. 15, 1911); Friedlander, 11, 812 (1915). Verfahren zur Darstellung von Isoprenen. 156. H. Staudinger and A. Rheiner, Helv. Chim. Acta, 1, 23-31 (1924). Vber die Konstitution des Dicyclopentadiens. 157. H. Staudinger, W. Kreis, and W. Schilt, Helv. Chim. Acta, 5, 743-756 (1922). Uber die Addition von Halogenwasserstoff an Isopren. 158. H. Staudinger, 0. Muntwyler, and 0. Kupfer, Helv. Chim. Acta, 5, 756-767 (1922). Uber das Isopren­dibromid. 159. H. Staudinger, R. Endle, and J. Herold, Ber., 46, 2466-2477 (1913). Vber die pyrogene Zersetzung von Butadien­Kohlenwasserstoffen. 160. C. Engler and H. Staudinger, DRP 265 172 Kl. 12o (Apr. 28, 1912), Friedlander, 11, 827 (1915). Verfahren zur Darstellung von Butadien und Butadienhomologen. 161. (1) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 1, 177-201 (1922). Vber /solierung und Konstitution des wirksamen Teiles des dalmatininischen Insektenpulvers. 162. (2) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 1, 201-211 (1922). Zur Konstitution der Chrysanthemum­monocarbonsaure u. ­dicarbonsaure.

72

LOW MOLECULAR COMPOUNDS 163. (3) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 7, 212-235 (1922). Konstitution des Pyrethrolons. 164. (4) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 7, 236-244 (1922). Konstitution des Tetrahydro­pyrethrons. 165. (5) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 7, 245-259 (1922). Synthese des Tetrahydro­pyrethrons, des Reduktionsproduktes des Pyrethrolons. 166. (6) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 7, 377-390 (1922). Untersuchungen fiber Cyclopentanolonderivate und ihr Ver­ gleich mit dem Pyrethrolon. 167. (7) H. Staudinger, 0. Muntwyler,' L. Ruzicka, and S. Seibt, Helv. Chim. Acta, 7, 390-406 (1922). Synthese der Chrysanthemum­ siiure und anderer Trimethylencarbonsiiuren mit ungesiittigter Seiten­ kette. 168. (8) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 7, 406-441 (1922). Versuche zur Herstellung von pyrethroloniihnlichen Alkoholen. 169. (9) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 7, 442-448 (1922). Weitere Versuche zur Herstellung von Cyclopentanolonderi­ vaten mit ungesiittigter Seitenkette. 170. (10) H. Staudinger and L. Ruzicka, Helv. Chim. Acta, 7, 448-458 (1922). Vber die Synthese von Pyrethrinen. 171. (11) H. Staudinger, L. Ruzicka, and E. Reuss, Annales Academiae Scientiarum Fennicae, Serie A, 29, No. 17, 3-8 (1927). Die Konstitu­ tion und die Synthese der Pyrethrine. 172. (12) H. Staudinger and H. Harder, Annales Academiae Scientiarum Fennicae, Serie A, 29, No. 18, 3-14 (1927). Vber die Gehaltsbestim­ mung des Insektenpulvers. 173. Hugo Harder, dissertation, ETH Zurich, 1927. I. Ober Additions­ und Polymerisationsreaktionen des Dimethylketens. II. Ober die Bestiln­ mung des wirksamen Bestandteiles des Insektenpulvers und fiber die Herstellung technisch haltbarer Pyrethrinlosungen. 174. Eric W. Reuss, ETH Zurich, 1926. I. Synthetische Versuche auf dem Gebiet des dalmatinischen Insektenpulvers (Pyrethrum). II. Eine neue Klasse organischer Kolloide: eukolloide Salze aus Kautschuk und Guttapercha. 175. H. Staudinger, DRP 362538, Kl. 12o (June 28, 1916); Friedlander, 14, 295 (1926). Verfahren zur Darstellung von Malonsiiure. 176. H. Staudinger, Schw. P. 94436 (Feb. 13, 1919); D. Prior. (March. 30, 1916); Chern. Zentr., II, 486 (1923). Verfahren zur Herstellung eines Ersatzmittels fur scharf schmeckende Stoffe. 177. H. Staudinger, DRP 384295, Kl. 53k (Feb. 22, 1920); Ungar. Prior. (Oct. 10, 1916); Chem.Zentr., I, 1289 (1924). Herstellung von Pfefferer­ satz. 178. (1) H. Staudinger and H. Schneider, Ber., 56, 699-711 (1923). Vber den Zusammenhang zwischen Konstitution und Pfeffergeschmack. 179. (2) H. Staudinger and F. Muller, Ber., 56,711-715 (1923). Uber den

PART A REFERENCES

73

Zusammenhang zwischen Konstitution und Pfeffergeschmack: Vber fett­aromatische Saure­piperidide. 180. Fritz Muller, dissertation, ETH Zurich, 1922. Synthetische Versuche in der heterocyclischen Reihe. 181. Josef Peter, dissertation, ETH Zurich, 1926. Vber den Zusammenhang zwischen Pfeffergeschmack und chemischer Konstitution. 182. Internationale Nahrungs­ und Genuftmittel AG and H. Staudinger, EP 246454 (Jan. 4, 1926); Chem. Zentr., I, 3189 (1926). Entaromati­ sieren von Kaffee. 183. Internationale Nahrungs­ und Genuflmittel AG and H. Staudinger, EP 286152 (July 25; 1927); Chem. Zentr., II, 2405 (1928). Herstellung von M ercaptanen der Furfuryl­ Reihe. 184. Internationale Nahrungs­ und Genuftmittel AG, and H. Staudinger, DRP 457266 Kl. 53d (Jan. 24, 1925); Chenz. Zentr., I, 2024 (1928). Gewinnung der Aromastoffe aus gerostetem Kaffee. 185. Internationale Nahrungs­ und Genuflmittel AG, H. Staudinger, and Th. Reichstein, Aust. P. 4448/1926 (Oct. 28, 1926); Chem. Zentr., II, 117 (1928). Gewinnung von kunstlichem Kaffeearoma. 186. Internationale Nahrungs­ und Genuftmittel AG, H. Staudinger, and Th. Reichstein, AP 1715795 (July 22, 1927) Chem. Zentr., II, 2502 (1929). Herstellung von Furfurylmercaptan. 187. Th. Reichstein and H. Staudinger, Angew. Chem., 62, 292 (1950). Vber das Kaffeearoma. 188. Th. Reichstein and H. Staudinger, Experientia (Basel), 6, 280 (1950). Das Aroma des gerosteten Kaffees. 189. Th. Reichstein and H. Staudinger, CIBA-Zeitschrift Nr. 127, 46924694 (Nov. 1951). Das Kaffeearoma. 190. H. Staudinger, DRP 436442, Kl. 12p (Apr. 11, 1924); Friedlander, 15, 1448 (1928). Verfahren zur Darstellung von Derivaten des 4­ 0xypiperidins. 191. H. Staudinger, DRP451731, Kl. 12p (Apr.11. 1924); Friedlander, 15, 1449 (1928). Verfahren zur Darstellung aromatischer Ester N­sub­ stituierter 4­0xypiperidine. 192. H. Staudinger, Schweiz. med. Wschr., 57, 465 (1927). Vber ein neues Lokal­Anasthetikum. 193. H. Staudinger, DRP 404174, Kl. 12o (Apr. 16, 1922); Friedlander, 14, 1443 (1926). Verfahren zur Darstellung von ungesattigten Derivaten des Cyanamids. 194. Paul Graf., dissertation, ETH Zurich, 1923. I. Versuche mit Diallyl­ derivaten. II. Darstellung wasserloslicher Arzneimittel. 195. Thadeus Reichstein, dissertation, ETH Zurich, 1924. Vber das offenkettige Tropin und einige seiner Homologen. 196. Werner Obrist, dissertation, ETH Zurich, 1926. Untersuchungen uber Homologe des Novocains und offenkettigen Tropins. 197. Werner Schilt, dissertation, ETH Zurich, 1920. Beitrage zur asym­ metrischen Synthese.

74

LOW MOLECULAR COMPOUNDS 198. Werner Enz, dissertation, ETH Ziirich, 1922. Uber die Reaktions­ fiihigkeit einiger Siiurechloride gegen Wasser und Beitriige zur asym­ metrischen Synthese. 199. H. Staudinger and H. Freudenberger, Ber., 61, 1576-1583 (1928). Uber Thio­benzophenon. 200. Heinrich Freudenberger, dissertation, University of Freiburg i. Br., 1928. I. Zur Konstitution der Jodalkylate von Thio­amiden. II. Uber das Thio­benzophenon. 201. H. Staudinger and J. Siegwart, Helv. Chim. Acta, 3, 824-833 (1920). Uber Thiobenzoylchlorid. 202. H. Staudinger and A. Binkert, Helv. Chim. Acta, 5, 703-710 (1922). Uber Alkalisalze des Benzils und ilber die Benzilsiiure­Umlagerung. 203. August Binkert, dissertation, ETH Ziirich, 1923. Uber die Alkalisalze von o­Diketonen und die Benzilsiiure­Umlagerung. 204. H. Staudinger and E. Anthes, Ber., 1417-1426 (1913). Uber die Darstellung und die Reaktion der Siiurehaloide. Cf. H. Staudinger and R. Endle, Ber., 50, 1046-1047 (1917). Notiz uber das Dimethylamino­ benzoylchlorid. 205. H. Staudinger and W. Kreis, Helv. Chim. Acta, 8, 71-74 (1924). Versuche mit einem heijJ­kalten Quarzrohr. 206. Walter Kreis, dissertation, ETH Ziirich, 1918. I. Versuche zur Darstellung von Diketenen. II. Die Konstitution des Isopren­hydro­ bromids. III. Versuche mit einem hei.fJ­kalten Quarzohr. 207. H. Staudinger, Anleitung zur organischen qualitativen Analyse, Springer Verlag, Berlin, 168 pp.; 1. Auflage 1923. 2. Auf/age 1929, with collaboration of W. Frost. 3. Auflage 1939 bis 6. Auf/age 1955, with collaboration of W. Kern. 208. Berl-Lunge, Chemisch­technische Untersuchungsmethoden, Bd. I, 8. Au/f., Springer Verlag, Berlin, 1931, pp. 168-228. H. Staudinger and W. Frost, Qualitative Analyse organischer Verbindungen. 209. H. Staudinger, Tabellen zu den Vorlesungen uber allgemeine und anorganische Chemie, Verlag G. Braun, Karlsruhe, 192 pp.; 1.Auflage 1927, herausgegeben mit A. Hensle. 2. Auflage 1935 bis 5. Auflage 1947, herausgegeben mit G. Rienacker. 210. H. Staudinger, Schweiz. Bau­Ztg., 71, No. 18 (1918). Aufgaben des Chemikers in der Gegenwart. 211. H. Staudinger, Naturwissenschaften, 7, 608-611 (1919). Leistungen der Chemie in der Gegenwart. 212. H. Staudinger, Revue Internationale de Ia Croix­Rouge Geneve, 1, 508-515 (1919). La technique moderne et Ia guerre. 213. H. Staudinger, Universitas, 1, 339-348 (1946). Das Zeitalter der Technik. 214. H. Staudinger, Vo1n. Au/stand der technischen Sklaven, Verlag Chamier, Essen-Freiburg, 1947, 103 pp. 215. H. Staudinger, IKIA, Internationaler Kongrej3 fur lngenieur­Ausbil­ dung, Darmstadt, Juli, 1947, Verlag Ed. Roether, Darmstadt 1949. Uber das Zeitalter der Technik.

Part

B Research on

Macromolecular Compounds

1 The Development of Macromolecular Chemistry during the Period from 1920 to 1930

During the last years of my stay in Zurich the research described in Part A was more and more set aside. When I took over the directorship of the chemical laboratories at the University of Freiburg in 1926 I discontinued further work in this field. My colleagues were very sceptical about this change, and those who knew my publications in the field of low molecular chemistry asked me why I was neglecting this interesting field and instead was working on very unpleasant and poorly defined compounds, like rubber and synthetic polymers. At that time the chemistry of these compounds often was designated, in view of their properties, as Schmierenchemie ("grease chemistry"). However, my interest in the elucidation of their structures had been aroused by different observations I had made before. For example, in the laboratories in Karlsruhe a new and simple synthesis of isoprene from limonene (1910 with H. W. Klever, see Part A, p. 43) had been worked out and the polymerization product of isoprene, that is, synthetic rubber, had been obtained. However, differences were observed between this synthetic rubber and natural rubber. These differences in a number of properties, in particular, stimulated my research in this field, especially investigations on the colloidal solutions of these materials. Furthermore, the first experiments on the polyoxymethylenes were under way. As early as 1913 in the laboratories at Karlsruhe other polymerization products had already been worked on with L. Lautenschlager (cf. ref. A 134, p. 70). All these experiences on polymerization were published in an essay in

77

78

RESEARCH ON MACROMOLECULAR COMPOUNDS

the Berichte der deutschen chemischen Gesellschaft in 1920. For high molecular polymerization products like polyoxymethylenes, polystyrenes, polyvinyl chlorides, 'malonic acid anhydrides, polyglycolides, and also rubber and similar compounds, a structure of long-chain 1nolecules was postulated in which hundreds of molecular units (Grundmolekiile) were linked together through main valence bonds: "And therefore I believe that with the available experimental data it is not necessary to make such an assumption (of molecular compounds which are held together by secondary valences) in order to explain the nature of the different polymerization products, and that normal valence formulas are an adequate representation; in organic chemistry, especially, one will try as far as possible to describe the properties of such compounds by formulas with normal valence bonds." (Ref. 1, p. 1073.)

The concepts developed in this first work were basic for our later investigations.

1. THE OLD MICELLE THEORY Some of my colleagues thought it was too early to work on polymeric materials. They were of the opinion that the structure of an organic compound could be worked out successfully only if it was pure and homogeneous, which is true in low molecular chemistry. Furthermore, it was believed at that time according to Emil Fischer that very high molecular compounds could not exist. In 1913, in a lecture at the Naturforscher­ versamJnlung in Vienna, Emil Fischer supported the opinion that a sugar derivative with a molecular weight of 4021-a synthetic compound of the highest molecular weight then known, which he had synthesized in collaboration with K. Freudenberg-had a higher molecular weight than most natural proteins. He said: "... and I believe that it (the molecular weight of 4021) is higher than the molecular weight of most of the natural proteins. Of course for oxyhemoglobin, which is known to crystallize nicely, a molecular weight of 16,000, based on its iron content, has been determined. However, against this kind of evaluation the objection can be made that the existence of crystals alone does not prove the chemical individuality of the compound. It still could be an isomorphous mixture, as is known for the silicates. Doubts of this kind are not necessary with synthetic products, whose formation can be controlled by analogous reactions" [E. Fischer, Ber., 46, 3288 (1913)].

MACROMOLECULAR

CHEMISTRY 1920­1930

79

I often was asked to consider this opinion. At the end of the 1920s my colleague H. Wieland gave me the following friendly advice: "Dear colleague, drop the idea of large molecules; organic molecules with a molecular weight higher than 5000 do not exist. Purify your products, for example, your rubber, then it will crystallize and prove to be a low molecular compound!" He probably was influenced by R. Pummerer's work on rubber and that of K. Hess on cellulose. They came to the conclusion that these compounds have a low molecular structure. However, this interpretation of their results later proved not to be tenable. It was a strange coincidence that at the same time, that I obtained the first experimental evidence for the existence of macromolecules, P. Karrer, K. Hess, M. Bergmann, and other scientists published results on the structure of cellulose and starch, as did R. Pummerer on rubber, which seemed to have established a low molecular structure. Their opinions were supported by several very important arguments. At the same time it became known by X-ray studies, especially at P. Scherrer's physics laboratories in Zurich, that cellulose was crystalline. The same result was reported by I. R. Katz for stretched natural rubber. These X-ray studies showed that the unit cell of these crystalline compounds was small [cf. H. Mark, "Ober die rontgenographische Ermittlung der Struktur organischer, besonders hochmolekularer Substanzen," Ber., 59, 2982 (1926)]. This led to the conclusion that the molecules of these compounds were small as well, under the assumption that a molecule could not be larger than the unit cell determined by the X-ray technique. This is an assumption that holds for low molecular compounds. This opinion was also supported by molecular weight determinations of cellulose acetate and starch acetate in phenol. The following table from the careful research of M. Bergmann shows a surprising agreement between the molecular weight found for starch acetate and the calculated value for its basic molecular weight, 288 [cf. also Angew. Chern., 38, 1141 (1925); Naturwissenschaften, 14, 1224 (1926); Ber., 59, 2973 (1926)]. The results of those investigations seemed then to be a certain proof that the starch.molecule was a glucose anhydride. It was assumed that the colloidal particles of a starch solution were formed by association of these small molecules. In this connection it is of interest to remember what P. Karrer said in

80

RESEARCH ON MACROMOLECULAR COMPOUNDS

Table 1 Cryoscopic Determination of the Particle Size ofTriacetylamylose in Phenol (basic molecular weight calculated for C 12H1608: 288) according to M. Bergmann and E. Knehe, Ann. 452, 149 (1927) Amylosetriacetate, g

Phenol,

0.0213 0.0430 0.0620 0.0695 0.0228 0.0525 0.0745 0.0929

13.95 13.95 13.95 13.95 13.60 13.60 13.60 13.60

Mol. Weight, from Δt

g

0.038 0.068 0.109 0.121 0.040 0.075 0.124 0.151

289 326 294 296 301 371 318 325

his first work on starch. He published the following [Helv. Chim. Acta, 3, 622 (1920)]: "I understand the starch particle and the cellulose fiber as 'crystalloids,' which are insoluble in water due to their chemical nature. A starch 'crystalloid' can be dissolved in a solvent as a colloid if it was well dispersed in the solvent by grinding, swelling, etc. However, the particles still contain many molecules, as the silver crystal contains 125 atoms, and therefore molecular weight determination must fail."

During this time (1924-1928) R. Pummerer also published a number of molecular weight determinations, showing that rubber had a low molecular weight according to the ideas of C. Harries. This will be discussed in Chapter 11 of this part. The fact that cellulose and its derivatives, as well as starch, rubber, etc., form colloids in many solvents was not inconsistent with the interpretation of a low molecular structure. It was known from the work of F. Krafft, H. Freundlich, and others that typical low molecular compounds, for example, soaps, form colloids in water, while they give normal solutions in other solvents, like alcohol. The similarity seemed to be that the natural compounds were soluble only in some special solvents, e.g., natural rubber in menthol and starch triacetate in phenol, while for unknown reasons they form colloids in most of the other solvents. In addition to this, the solution properties of these natural compounds-which later were found to havelinearmacromolecules-weresimilar to those of the soaps. However,

MACROMOLECULAR

CHEMISTRY 1920­1930

81

they differ very much from those of low molecular compounds as 1s shown in the following table. Table 2

Comparison between Low Molecular Compounds, Linear Macro­ molecular Compounds, and Micellar Colloids (cf ref 55, p. 2)

Properties Dissolve Dissolved particles are The solution is 1% solution has The viscosity of the solution on standing Dissolved particles If the colloidal properties of the solution are changed

Low Molecular ComP.ounds

Linear Macromolecular Compounds, e.g., Rubber, Cellulose

Micellar Colloids, e.g., Soaps

Without swelling

With swelling

With swelling

Monodisperse Newtonian Low viscosity

Polydisperse Not Newtonian High viscosity

Polydisperse Not Newtonian High viscosity

Does not change

Ages

Ages

Dialyze

Do not dialyze

Do not dialyze

Molecules are unchanged

Molecules = Molecules are unmacromolecules changed, but the are decomposed size of the micelle is

Because of these similarities it was assumed that, in solution, many macromolecular compounds, e.g., cellulose nitrate [J. W. McBain, Ind. Eng. Chem., 28, 470 (1936)], form micelles like soaps. In 1925 R. 0. Herzog [Ber., 58, 1254 (1925)] seemed to have another proof in favor of the micellar structure of high molecular co1npounds, a structure which had been developed by the botanist C. Nageli in Zurich for starch and cellulose in the 1870s (cf. C. Nageli, Die Micellartheorie, Ostwalds Klassiker No. 227, Akad. Verlags-Ges., Leipzig, 1928). R. 0. Herzog made diffusion measurements on cellulose nitrate solutions and found that the size of the micelles of the cellulose in solution was similar to the size of the crystallites of solid cellulose determined by X-ray investigations. He came to the following conclusion:

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"A comparison of the above mentioned crystallite dimensions with the diameter of the micelle, which has been calculated from the diffusion coefficient, shows in a first approximation that the size of the micelle and the size of the crystallite are of the same order of magnitude ... One can make the statement: what is combined in cellulose as a crystal stays together as a micelle, unless external forces are acting" [R. 0. Herzog, Ber., 58, 1257 (1925)].

All these experimental data and their interpretation in favor of micelles were very impressive at that time. Even my own observations in the laboratory in Zurich in 1924 and 1925 could very well have been interpreted in this way (A65) as from dimethylketene and carbon dioxide crystalline low molecular, soluble addition products were obtained, while dimethylketene and isocyanates or carbon disulfide gave amorphous colloidally soluble products:

For this reason I discussed with my co-workers whether the colloidal solubility of the amorphous products could not be explained by association of small molecules. It was impossible, however, to find a solvent in which these colloidally soluble compounds would form regular solutions. They already had been assigned a chain structure in a 1925 publication (A65 and pp. 16, 17); they were therefore the first copolymers. On consideration of experimental experience with starch, cellulose, and natural rubber during 1920-1926, it is understandable that it seemed certain that these materials were built up by small molecules. The elucidation of their structures seemed to be accomplished-from the standpoint of organic chemistry-since the structure of the low molecular structural units, which later formed colloids, was proved. Research on these colloidal solutions and their remarkable behavior became the field of research in colloid theory, mainly through the efforts of W. Ostwald. Therefore, it is understandable that my opinion on macromolecular structure, published in my first papers, was not accepted initially. Authors

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·who are surprised today that it took so long for macromolecular chemistry to be accepted in Germany should bear this situation in mind.

2. THE FIRST EVIDENCE FOR THE EXISTENCE OF MACROMOLECULES At that time my viewpoint on the existance of macromolecules was based on investigations on the hydrogenation of rubber. With C. Harries it was generally believed that rubber was of low molecular weight and that the colloidal particles in the rubber solution are formed by the association of its small molecules. Therefore, R. Pummerer believed that hydrogenated rubber would be a volatile hydrocarbon (seep. 204). However, the hydrogenation of rubber, done in collaboration with J. Fritschi (2), yielded colloidally soluble hydrorubber. We concluded from this that the molecules of hydrorubber, as well as the molecules of rubber, had the size of colloidal particles, a size which exceeds by far the size of low molecular material. It was very improbable that this saturated reaction product could display secondary valences \Vhich were then considered to be responsible for the formation of colloidal particles in rubber. Therefore, in 1922 we suggested the name "macromolecules" for these molecules (ref. 2, p. 788). In a later paper macromolecules were defined in the following way (ref. 3, p. 1206):

"We propose the name 'macromolecules' for those colloidal particles in which the molecule is identical with the primary particle, in other words, where the single atoms of the colloidal molecule are bound together by normal valence forces. Such colloidal particles form true colloidal materials, which, in correspondence with the valence forces characteristic for the carbon atom, will occur, particularly in organic chemistry and in organic natural materials. Here the colloidal properties are determined by the structure and size of the molecule and it cannot be expected that a low molecular dispersion can be accomplished in any other solvent." The above interpretation of the macromolecular structure of rubber and hydrorubber was supported by investigations on polystyrene during 1923-1926. It was found that polymer homologous series exist analogous to the homologs of the paraffin hydrocarbons in that their representatives differ in physical properties. Investigations on polystyrene solutions, mainly viscosity measurements at different temperatures, after shaking, etc., were performed in order to prove that the colloidal particles of polystyrene in solvents were not micelles but macromolecules. It was found that

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polystyrene solutions were very stable and, in contrast to micellar colloids, they did not age. From this behavior of polystyrene solutions it was concluded that the colloidal particles were macromolecules. These and other investigations were performed with A. A. Ashdown (220), later professor at the Massachusetts Institute of Technology, Cambridge, and with K. Frey (252), later director of the Ciba AG., Basel. Later on, relatively low molecular polystyrene with a molecular weight of 2000-3000 was reduced to hexahydropolystyrene with approximately the same molecular weight as the unhydrogenated product (83). This transformation of a polymer into a derivative of equivalent molecular weight was proof that the dissolved particles were molecules and did not result from association. This type of reaction later was called "polymer analogous reaction." Investigations on polyoxymethylene were further support for the existence of long-chain molecules. They were started in 1920 with M. Luthy (313) and continued with other co-workers, particularly H. Johner, R. Signer, and later W. Kern (see p. 177). The fact that the molecular weights of polyoxymethylene obtained from end-group determinations corresponded to those molecular weights obtained by physical methods was proof for the long-chain structure of polyoxymethylene. This research was reported in the Versammlung Deutscher Naturforscher und A rzte in Innsbruck in 1924 (4). At the end of this lecture the following was said: "In these and similar experiments the lecturer sees a confirmation of his concept that in high polymers many single molecules are held together by normal valence bonds. The tendency to form such compounds is observed in particular in organic chemistry, due to the special nature of carbon."

This experimental evidence was convincing to my co-workers and for me, but we were alone in this opinion. When Professor James B. Conant, later American ambassador to the Federal Rebublic of Germany, visited my laboratories in Zurich in 1925, my co-workers and I told him our arguments in favor of the macromolecular structure of these compounds. On his visit to Germany which immediately followed he was told not to believe a word of Staudinger's views! Professor Conant described this to me in his letter congratulating me on n1y receiving the Nobel Prize in 1953. Even my colleagues in Zurich did not accept my arguments on the macromolecular structure of these compounds after P. Karrer was awarded the Marcel-Benoist Prize for his work in this field in 1923. During a lecture given in 1925 I thought I had given good evidence for the

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existence of macromolecular structures, using as examples rubber, polystyrene, and polyoxymethylene; then, however, the well-known mineralogist Paul Niggli rose and his only discussion remark was, "Such a thing does not exist!" This statement was based at that time on the concept that a molecule could not be bigger than the unit cell of the material determined by X-ray diffraction. Those X-ray experiments on crystalline polyoxymethylene which disproved this opinion were first published in 1927. Soon after that my colleague Niggli changed his mind and in later discussions we remembered his initial rejection of macromolecules with great pleasure. In this situation it was very important that the Gesellschaft Deutscher Naturforscher und Arzte called for a discussion on the structure of these materials during August, 1926, in Dusseldorf. Cellulose, starch, and proteins in particular were discussed. The lecturers, M. Bergmann, H. Mark, E. Waldschmidt-Leitz, and H. Pringsheim, presented arguments in favor of the view that these natural products were built by small molecules. The arguments of M. Bergmann were given particular attention [cf. Ber., 59, 2973 (1926)]. In my lecture I discussed evidence, already quite numerous, for the macromolecular constitution and the chain structure of many high polymers (5). In this lecture I pointed out that polymer compounds were inseparable mixtures: "There is an essential difference between a simple and uniform material and a high molecular substance, the neglect of which prevented application of the molecule concept. All molecules have the same size in simple uniform compounds. On the contrary, high molecular compounds are mixtures of molecules of similar structure but different size. A separation into uniform products is not possible due to the small differences in their physical and chemical properties. If a molecular weight for high polymers is given, it can only be an average value" (ref. 5, p. 3021).

In 1928 my wife proposed the name "polymer homologs" for such mixtures. In this lecture in Dusseldorf I proposed a new classification for colloids based on my latest results. I pointed out the differences between "eucolloids" (molecular colloids) and association colloids (micellar colloids). In 1926 these statements were rejected at the discussion. Only R. WillsHitter who presided over this meeting realized the evidence of my argument and said at the end that by the reduction of polystyrene to hexahydropolystyrene the existence of long-chain molecules was proved. Today these statements form the basis of macromolecular chemistry.

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I am pleased with the fact that in 1959 the BASF in Ludwigshafen affixed the following sentences from my 1926 lecture in Dusseldorf in "macromolecular" letters in the entrance hall of their new plastics department:

"Since high polymers are typical organic compounds, these homopolar materials must form molecules; however, when compared with simple compounds, they are very large. Therefore it was proposed that they be called 'macromolecules.' "The world of organic compounds lies between the simplest carbon compounds like methane, carbon monoxide, cyanogen and the largest molecules, the high polymeric carbon compounds. In spite of our knowledge of a large number of organic substances we are standing today at the beginning of the chemistry of organic compounds rather than at the end." The experimental work on which this lecture in Dusseldorf was based was published in a number of dissertations at the Eidgenossische Tech­ nische Hochschule Zurich (5a-p). In 1955 my colleague A. Stoll asked me to contribute to the Festschrift of the Gesellschaft ehemaliger Polytechniker (GEP) celebrating the hundredth anniversary of the Eidgenossische Technische Hochschule Zurich. The results of the research on macromolecular compounds upon which I worked in Zurich between 1920 and 1926 were summarized in this contribution (6). In the period following at Freiburg an essential argument for the existence of small molecules in this field was devaluated, namely, the conclusions drawn from the size of unit cells, determined by the X-ray technique. In an investigation on polyoxymethylene it was shown that this compound forms long-chain molecules, while the unit cell contains only four CH 2 0- groups. This can correspond to only a small fraction of the entire molecule. The following conclusions were drawn (cf. ref. 7, p. 448): "The size of high molecular compounds cannot be determined by X-ray measurements. Furthermore, it can be concluded from the many parallels between polyoxymethylene and cellulose that cellulose also is a high molecular weight compound" (7). It was more difficult to contradict the results of the many cryoscopic molecular weight determinations, which seemed to point to a small size for these molecules. Many of them, e.g., the molecular weight determinations of rubber, hydrorubber, and rubber-isonitrone published by R. Pummerer, were only disproved later (see Chapter 11, p. 202). However,

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some of the molecular weight determinations, e.g., that of polyoxymethylene dimethyl ether, gave a molecular weight which agreed with the molecular weights obtained from end-group determination (cf. ref. 15, p. 234). It is not yet understood why M. Bergmann's cryoscopic molecular weight determinations on triacetylamylose gave such closely corresponding values, as shown in Table 1, page 80. By means of polymer analogous transformations, which proved the existence of macromolecules (587), it was shown that the cryoscopic method did not give correct values in these cases. These discussions during 1920 to 1930 are still of some interest, since today all the arguments for a low molecular structure of those materials are usually disregarded. More important, the experimental evidence which disproved opinions held at that time did not sufficiently penetrate the literature since at that time it was considered misleading.

3. THE NEW MICELLE THEORY The investigations described above provided the foundation of macromolecular chemistry. Nevertheless, this field did not develop from then on in an uncontroversial way. From 1928 to 1930 K. H. Meyer and H. Mark published a number of works supporting the opinion that colloidal particles in solutions of macromolecular compounds were micelles [cf. K. H. Meyer, Angew Chem., 41, 935 (1928); 42, 76 (1929); Naturwissenschaften, 16, 781 (1928); 17, 255 (1929); Biochern. Z., 208, 1 (1929); Kolloid­Z., 53, 8 (1930); H. Mark, Naturwissensch., 16, 892 (1928); K. H. Meyer and H. Mark, Ber., 61, 593, 1939 (1928); H. Mark and K. H. Meyer, Z. physik. Chern., (B)2, 115 (1928) and others]. These authors, like P. Karrer, followed the micelle theory of C. Nageli, but developed modified concepts on the structure of the micelles based on the experimental evidence for long-chain molecules. The micelle theory of K. H. Meyer and H. Mark can be called the second micelle theory. They assumed that long, primary valence chains are held together by special micellar forces. According to this theory the particles in a colloidal solution are not the macromolecules themselves but micelles; the weights of these particles, determined by physical methods, were called micellar weights. K. H. Meyer thought that the molecular concept in chemistry could not be applied to this micelle chemistry. Changes in colloidal solutions of natural products seemed to he explained by the

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micelle theory because the size of the micelle-comparable to that of soap micelles-could change with concentration and temperature (cf. Table 2, p. 81). The new micelle theory also was based on the results of R. 0. Herzog, described on page 82, showing the similar size of the micelles in a colloidal solution of cellulose nitrate and those of crystalline cellulose. Furthermore, K. H. Meyer and H. Mark made use of the previously mentioned results of X-ray investigations of polyoxymethylene (7), which proved that the size of the unit cell determined by X-ray diffraction does not give any information on the size of the chain molecules, and finally of the results of 0. L. Sponsler and W. H. Dore, published in 1926, on the structure of ramie cellulose derived from X-ray investigations. At the beginning this work was not well known in Germany since it was published in a journal with a small circulation [Colloid Symposiunz Mono­ graph, 174 (1926)]. Later, however, his research became generally accessible in the form of its German translation [cf. Cellulosechemie, 11, 186 (1930)]. As R. 0. Herzog did previously, K. H. Meyer and H. Mark believed they could determine the size of the micelles with X-ray investigations on crystalline material and by determining the particle size in a colloidal solution by osmotic pressure measurements. They made the following statements in their first publication on cellulose: "All the experiences can best be summed up by assuming that 40-60 chains form one particle, each chain being built up from 30 to 50 glucose units" [Ber., 61, 609 (1928)].

Furthermore, they assumed that the stability of the micelles depended on the strength of the micellar forces between the primary valence chains. They stated: "From this viewpoint rubber takes a mid position between soap solutions, where the micelles are in a continuous equilibrium with free fatty acids and cellulose or starch where the micelles cannot be split reversibly by any solvent" [Ber., 61, 1945 (1928)].

The representatives of the colloid theory especially took special note of this second micelle theory. Although these concepts have become outdated, they can still be found in some textbooks. The basic mistake lies in the assumption that micelles would be very stable in solution because of the considerable molar cohesion forces, which were calculated for long, primary valence chains by M. Dunkel [Z. Physik. Chern., A138, 42 (1928)].

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These molar cohesion forces only verify the known fact that macromolecular materials cannot be distilled, even under high vacuum, since the boiling point of such compounds, like that of rubber, must be extremely high [cf. H. Staudinger, Kautschuk, 3, 64 (1927)]. Consequently, it cannot be concluded that long, primary valence chains cannot dissolve as individual macromolecules because of the high molar cohesion forces. Considerable molar cohesion forces between the chain molecules can be overcome by the liberated heat of solution. Furthermore, the solubility of chain molecules depends not only on their length but also on their shape. Substituents can increase considerably the solubility of atactic chain molecules in various materials, as is known today. These and similar considerations were presented by me against the opinions of K. H. Meyer and H. Mark. A number of important ideas on macromolecular chemistry were proposed in a review paper (8). This paper prompted a discussion [cf. K. H. Meyer, Angew. Chern., 42, 76-77 (1929)] from which I quote an interesting description of the main difference between micelle theory and the macromolecular concept: "We do not agree with Staudinger's assumptions on the structure of particles in solution which are responsible for the osmotic pressure. While Staudinger assumes that these particles are identical in every case with the long-chain molecule (that is, with the primary valence chain, 'eucolloids '), we are of the opinion that these particles consist of groups or bundles of such chains. There are many indications for the fact that these bundles are not of uniform size, but that an aggregation equilibrium exists and that micelles of different sizes, down to the isolated primary valence chain, can be present. Osmotic pressure measurements do not necessarily determine the primary valence chain, but a more or less complicated mixture of aggregated chains. With this assumption one of Staudinger's main proofs on the structure of his synthetic high molecular compounds becomes questionable; the molecular weights he determines on polymer products may be several times too high." In my summary (9) I again pointed out the results of my investigations, which proved the macromolecular structure. This discussion continued over a number of years (10,11). After 1935, K. H. Meyer and H. Mark accepted the macromolecular concept (cf. K. H. Meyer and H. Mark, Makromolekulare Chemie, Akad. Verlagsges., Leipzig, 1950, 2nd edition completely revised by K. H. Meyer). M. Bergmann did the same and also K. Hess no longer referred to his previous views on micellar structure in his newer work on cellulose, but

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formulated his results on the basis of the macromolecular structure of cellulose. In the following the proof for the existence of macromolecules by exact chemical methods shall be described. Today one is used to hearing of macromolecules in which thousands or millions of atoms are held together by primary valence forces. Nevertheless, the existence of such large structures is remarkable. The definitive proof for a macromolecular structure was by analogous polymer conversions and also by investigating the colloidal solutions of these compounds as will be described in the following chapter. At the beginning of these investigations it was necessary to separate the chemistry of macromolecular compounds from that of the colloids, irrespective of the fact that the behavior of a typical representative, glue, initially gave the name to this field and has led to the treatment of colloid chemistry as a separate area. However, the problems of general colloid theory are classified according to physical principles and progress in the field of macromolecular compounds came only when the macromolecular materials were characterized as organic compounds (cf. "Molekulkolloide und organische Chemie," in H. Staudinger, Organische Kolloidchemie, Verlag Vieweg, Braunschweig, 1950, p. 287), and when their colloidal phenomena found a chemically based interpretation as molecular colloids. In this way I became more and more convinced that macromolecular chemistry was a new field within organic chemistry.

2 Macromolecular Chemistry, a New Field of Organic Chemistry

On viewing the development of natural sciences during the last decades, it is striking that the knowledge gained in different fields exceeds prior knowledge a thousand or a million times in its dimension [cf. article by H. Staudinger in the magazine Germany (English edition), No. 7, 18-21 (German text pages 22-23) (1958): "Germany's Share in the Crucial Advances of Natural Science," published for the 1958 World Fair in Brussels]. This is the case in physics where, by nuclear fission or nuclear fusion, energy a million times greater than that of chemical processes is available. Crucial knowledge was gained in the "submicroscopic" field with the electron microscope. Thanks to its high resolving power, the smallest cell structures, viruses, and supermolecular structures of macromolecules, even single macromolecules, could be seen directly. Macromolecular chemistry has opened a field of chemistry where molecules are 1000-100,000 times the size of those of the well-known low molecular compounds. If new dimensions are opened in a field, new methods have to be found to work with the new phenomena. For this reason, macromolecular chemistry must be partially treated from a different point of view than low molecular chemistry because of the size of macromolecules. A number of new methods had to be worked out in order to answer the questions which arose. The knowledge gained in working with low molecular compounds is not sufficient and cannot always be applied to macromolecular products. This holds even though the macromolecular field is continuously connected with that of small molecules and even though these macromolecules are structured on the same principle as low molecular compounds, i.e., according to the Kekule structure theory. 91

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In a number of publications and especially in lectures I tried to point out the novelty of macromolecular chemistry by comparisons with buildings. Molecules as well as ,macromolecules can be compared with buildings which are built essentially from a few types of building stones: carbon, hydrogen, oxygen, and nitrogen atoms. If only 12 or 100 building units are available, then only small molecules or relatively primitive buildings can be constructed. With 10,000 or 100,000 building units an infinite variety of buildings can be made: apartment houses, factories, skyscrapers, palaces, and so on. Constructions, the possibilities of which cannot even be imagined, can be realized. The same holds for macromolecules. It is understandable that new properties will therefore be found which are not possible in low molecular materials. The number of possible macromolecular compounds is infinitely large (57). A consequence of macromolecular size is a great variation in their shapes, again analogous to buildings: as one can build different types of buildings with the same amount of structural units, so can the macromolecules differ in their shape. This shape of the molecule is essential for the properties of macromolecular natural products, as well as plastics. These new properties include the following: ability to form fibers, elasticity, tensile strength, swelling phenomena, such as finite and infinite swelling, which are so important in biological phenomena. These and other essential features of macromolecules, unknown in low molecular chemistry, were pointed out with many experiments. It is important to realize that one is dealing with a new field of organic chemistry and not only with a part of it like terpenes, alkaloids, and dyes, which can be treated with the methods of low molecular chemistry. In low molecular chemistry, for example, only pure and uniform compounds are treated, and structures of even the smallest amounts of natural products can now be elucidated with the final proof of structure being a stepwise synthesis. The molecular weight as the sum of the atomic weights can be given as accurately as permitted by knowledge of the atomic weights. Here, the determination of molecular weights by physical methods is only a control, not its exact determination. If the structure of a low molecular compound is known, this compound can be classified according to the system of M. M. Richter. Due to the work of this scientist, it was possible to survey more than half a million organic compounds [cf. M. M. Richter, "Ein Beitrag zur Nomenclatur," Ber., 29, 586-608 (1896); Ber., 31, 3378 (1898); "Festschrift" on the occasion of the 50th anniversary of the Deutsche Chemische Gesellschaft and the 100th birthday of its founder A. W. von

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Hofmann, Sonderheft Ber., 51, 125 (1918)]. I enjoy remembering some of the conversations I had with Professor Richter in Karlsruhe between 1907 and 1912. He was director of the dyer's firm Printz in Karlsruhe and I admired him because he did this important documentation work along with his main work. A completely different situation to that for low molecular compounds exists for the macromolecular ones. Most of them are polymolecular and their separation into uniform compounds is not possible with today's tools. For this reason the molecular weight of macromolecular compounds is an" average" value. A -special difficulty arises from the fact that this average average value depends on the method of determination: either the number average or weight average molecular weight is obtained [cf. W. D. Lansing and E. 0. Kraemer, J. Am. Chem. Soc., 57, 1369 (1935); G. V. Schulz (9195)]. Therefore, the molecular weights of macromolecules, which are important values for their characterization, cannot be given as the sum of their atomic weights with the same accuracy as that for low molecular compounds. The molecular weight is known exactly for only some relatively low molecular proteins, like insulin, C254 H 377 075 N65 S6 , the molecular weight of which is 5733,43. This could be determined exactly because the structure had been completely elucidated by F. Sanger. No such case is yet known for actual macromolecular compounds. Since macromolecular compounds are, almost without exception, polymolecular mixtures, one does not deal with uniform materials as is the case for low molecular compounds. In the most favorable case, such a material is polymer uniform, that is, a mixture of macromolecules of the same structure, but different chain lengths. In an essay on low molecular and macromolecular chemistry it was stated that "working with macromolecular compounds, one finds it practically impossible to identify one macromolecular material with another one" (13). In low molecular chemistry only a limited number of compounds exists, which are distinguished from each other by their properties; the possibilities of combining a small number of atoms to small molecules are limited. Therefore, in order to identify a low molecular organic compound, only a few properties have to be determined, e.g., the melting point of an organic compound, combined with a mixed melting point. This procedure in analytical chemistry was characterized by Wilhelm Ostwald in his Wissenschaftliche Grundlagen der Analytischen Chemie (see ref. 13, pp. 911): "The number of different properties of a certain compound seems at the

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beginning to be indeterminably large; therefore, from the beginning it is not possible to ascertain that two objects coincide in all their properties. Following an inductive reasoning of general value, we think that such a proof is not really necessary since we know that if two compounds coincide in some properties completely, they will do so in all other properties as well. "This empirical statement expresses the fact that the number of existing different materials is finite. The differences among materials lies in the differences in their properties. The different properties and their values obviously cannot be combined infinitely, or else an infinite number of materials would exist ... "This methodical proceeding is useful for low · molecular compounds, but cannot be applied to macromolecular materials since they exist in infinite numbers . . . Furthermore, technically produced macromolecular materials are polymolecular; that means mixtures of polymer homologs of continually changing composition ... If some physical properties of such a polymolecular material are determined, it is by no means identical with another one possessing the same physical properties; both materials can differ widely in other characteristics ... This variability in the composition of such mixtures makes it impossible to obtain, for example, two celluloses with completely identical properties, while cellobiose will always have constant properties."

The differences between low molecular and macromolecular compounds were summarized several times in the following table (cf. p. 221, ref. 57). Table 3

Differences Between Low Molecular and Macromolecular Natural Products Low molecular

Macromolecular

> 10,000 > 1500

Molecular weight Number of atoms per molecule Pure compounds are

< 10,000 < 1500 Uniform

Solutions

Normal, dializable

Volatility Influence of the molecular shape on physical properties Stepwise synthesis Molecular weight determination

Partly volatile

Rarely uniform, mostly polymolecular Colloidal, not dializable Not volatile

Minor Possible

Large Until now not possible

Sum of atomic weights

Accuracy depends on physical method applied

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Experimental evidence for the existence of macromolecules is of great importance, especially as concerns biology (see pp. 237 and 238). In particular, the technology involving macromolecular compounds has greatly increased in importance during the last few decades. The value of macromolecular products in industry, i.e., plastics, rubber, and fibers, already exceeds the value of low molecular products. The technical importance of macromolecular compounds is another justification for giving this branch of organic chemistry the new name of macromolecular chemistry. Macromolecular co:p1pounds also exist in inorganic chemistry, mainly in silicon compounds which are of great technical importance. My coworkers and I did little research on these materials (see Part B, Chapter 10, part 11, p. 188). Therefore, inorganic macromolecular compounds will only be touched upon here. Several people quickly realized the importance of macromolecular chemistry. The general secretary of the International Union for Pure and Applied Chemistry, Professor Raymond Delaby, of Paris, who unfortunately died young, planned to form a special committee on macromolecules within the International Union for Pure and Applied Chemistry on the basis of a lecture I gave on June 12, 1931, before the French Chemical Society in Paris about the structure of molecular colloids [cf. Bull. Soc. Chim. France (4), 49, 1267 (1931)]. My lecture gave him the impression that a new field of chemistry was evolving. His plan only became reality in 1946. This committee did valuable services, especially in bringing together the scientists who worked in this field. Until July, 1957, Professor H. Mark, of Brooklyn, and from July, 1957, Professor Sir H. Melville, of London, led the committee. Working on this committee for macromolecules, M. L. Huggins made a proposal for the nomenclature for chemistry and physics of macromolecular compounds which was published in the Journal of Polymer Science, 8, 257 (1952). The German translation by 0. Kratky appeared in Die makromolekulare Chemie, 9, 195 (1953). I commented on the proposed nomenclature which had been formulated mainly from a physical-chemical viewpoint (12). These nomenclature proposals were examined further and, not too long ago, a new formulation for the nomenclature of macromolecular compounds was published [Makromol. Chem., 38, 1 (1960)]. I was a member of this committee only for a short time; the German representative now is my colleague, Werner Kern, of Mainz.

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Colleague F. A. Henglein, of Karlsruhe, proposed very early that a special journal be founded for this new field. At that time the publishers Barth, of Leipzig, conveniently offered me the editor's position of the Journal fiir praktische Chemie. This old journal was then continued from Volume 155 (1940) as Neue Folge with the subtitle Unter Beriicksichtigung der makromolekularen Chemie. As an introduction I published an essay entitled: Vber niedermolekulare und makromolekulare Chemie (13). In 1943, after Volume 162, the title was changed; starting in 1944, the journal was published as Journal fiir makromolekulare Chemie. Only two volumes appeared due to the war. The second volume of this journal, published in December, 1944, was as a result of wartime conditions onlyincompletelydistributed at the beginning of 1945. Therefore, its material is not well known. After the war I tried again to start a journal for this new field since it was not possible to continue the Journal fiir makromolekulare Chemie at Barth in Leipzig. After 1947, with the collaboration of many well-known colleagues, I started a new journal with the title Die makromolekulare Chemie. It was published by Karl Alber, a subsidiary company of the well-known publishing firm Herder in Freiburg, and by Wepf & Co. in Basel. My first editorial was an essay: M akromolekulare Naturstoffe und makronzolekulare synthetische Produkte (14). Forty-two volumes of Die makromolekulare Chemie appeared until 1960. Dr. A. Hiithig, in Heidelberg, who also publishes Chemiker­Zeitung, took over the journal starting with Volume 8. The collaboration with Wepf & Co., of Basel continues. I also published a number of books and booklets on the subject of macromolecular chemistry (15, see also ref. 73). Unfortunately, my first book in this field (15) appeared in a limited edition and was sold out very quickly. It was printed again in the U.S.S.R. in a Russian translation. During the war it appeared as a photolithoprint reproduction in the United States (15). This edition is also out of print. Since the book contained basic experimental investigations which are of interest even today, Springer decided to publish a new edition which appeared at the end of 1960. Besides a general part it contains a number of original papers (15 a-1). Furthermore, in 1939, Verlag Lehmann in Munich published reports on the progress in different fields of macromolecular chemistry which I edited together with W. Rohrs and R. Vieweg. Due to circumstances caused by the war only two volumes appeared (16). The papers in the chemistry section, which I edited, are cited in references 16 a-j.

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A lecture on macromolecular chemistry which I held at the Freiburger Wissenschaftliche Gese!lschaft on December 10, 1938, was published as a pamphlet by Verlag Schulz, in Freiburg (17). I want to mention also the book of H. Batzer, Einfilhrung in die mak­ romo!ekulare Chen1ie, published by Dr. A. Hiithig Verlag, Heidelberg, 1958 (223 pages). I have written a preface commemorating our long collaboration. In 1943 and 1944, Professor Dr. Oskar Vogt, director of the Brain Research Institute in Neustadt (Schwarzwald), invited me to give a number of lectures on macromolecular chemistry and biology. These lectures were repeated at other places and published as a book (18). This book is dedicated to Dr. 0. Vogt on his 75th birthday. Further publications of a general nature are partly based on lectures in Germany and other countries (13,14, 19-67).

3 The Nature of Colloidal Solutions

As was pointed out in Part A, macromolecular materials originally were thought to have a micellar structure. It took a long time for the true concept to be accepted. I observed often that people working in this field in industry accepted new ideas much faster than scientists at the universities. The latter could take the time to discuss such new concepts, compare them with others and wait for further developments; industry, on the other hand, had to accept those theories which would solve their problems best. For this purpose the macromolecular view-point was more useful than others and turned out to be very fruitful. In 1950, when I gave a lecture to cellulose chemists, many participants who had published works on the micellar structure of cellulose before assured me now that they believed my theory. I said that it was not a matter of belief and asked them what arguments had convinced them. The answers were often unsatisfactory. Because of this, I started my lecture in the following way: "If a student is asked about the formula of indigo during an examination and replies that he believes that A. von Baeyer's formula is the right one, this would not be enough to pass the examination. He surely would be asked how the formula was proved. Similarly, it is necessary to know exactly the proofs for the macromolecular structure of cellulose and many other natural products, as well as those of synthetic products, if one intends to work with them on the basis of this macromolecular concept."

I explained the evidence in the lecture which followed. This shall be presented here, starting with colloidal solutions. In macromolecular chemistry, as well as in low molecular chemistry, the elucidation of a structure is started by dissolving the material and by determining the size and composition of the dissolved particles. In a 98

THE NATURE OF COLLOIDAL SOLUTIONS

99

solution of low molecular weight materials, the small particles, which consist of a few atoms, will be either molecules or double molecules (e.g., fatty acids), or they may be aggregations (e.g., soap micelles) the structures of which are easily recognized. The situation is different with materials which form only colloidal solutions as do soluble macromolecular compounds where the particles contain thousands of atoms. It is not appropriate to distinguish colloids from low molecular materials and disperse systems by the diameter of the particles in the manner that W. Ostwald had proposed. They should rather be distinguished according to the number of atoms in one colloidal particle. Of course, there are no sharp boundaries. Particles which contain 103-l09 atoms can be called colloidal particles. The structure of a particle with this number of atoms can be much more easily differentiated than that of small particles formed by dissolving· low molecular materials. The different possibilities are given in Table 4. In the 1920s when I started to work in this field, colloid theory was of great importance because of the work of Ostwald. He had pointed out that under appropriate conditions any compound can form a colloidal solution. The colloidal particles which could not be seen under a normal microscope became visible under the ultramicroscope of Siedentopf and Zsigmondy. These are the dispersed colloids. It is also possible to disperse macromolecular compounds in the same way. But then very often the diameter of these more or less isodiametrical colloidal particles is much smaller than the length of a linear macromolecule of the macromolecular compound; therefore, these molecules must be strongly degraded when ground in a ball mill. W. Heuer and I were able to prove this with polystyrene (68). This was demonstrated again with E. Dreher while investigating polystyrene, cellulose, and cellulose nitrate (69). These experiments show how important it is to find out what a colloidal particle really contains. Such experiments were later continued by K. Hess and co-workers [cf. Z. Physik. Chern. (B) 49, 64 (1941)]. It is well known that one has to distinguish between lyophobic and lyophilic colloids. This distinction is very easy to make in the case of dispersed colloids. At that time only the structure of colloidal particles of the lyophilic colloids was still uncertain. As can be seen in Table 2, page 81, one group of macromolecular compounds shows surprisingly similar properties with the micellar colloids. Therefore, it is quite understandable that an analogy was drawn and the colloidal particles of macromolecular compounds in solution were also assigned a micellar structure. The

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COMPOUNDS

Table 4 Types of Structures possible with Colloidal Particles of Organic Compounds (cfref 73,p. 20) Behavior-in Dispersing medium

Electrical Charge

/

Viscosity of the solution

Examples

I. Dispersed Colloids (a) Suspensoids Lyophobic

Charged

Lyophobic

Charged

II. Micellar colloids (particles are formed by aggregation of small molecules) III. Molecular colloids (solutions of macromolecules)

Lyophilic

Mostly charged

Lyophilic

IV. Macromolecular aggregates

Lyophilic

Glycogens, Low viscosity: proteins spherocolloids High visCellulose, cosity: proteins linear colloids Charged or Low visProteins, uncharged cosity or symplexes, high visbiocolcosity loids

(b) Emulsoids

Low viscosity Low viscosity High viscosity

Sugar in benzene Oil in water Soaps in water

Charged or uncharged

experimental investigations mentioned in Part B, Chapter 1, however, especially the reduction of rubber to hydrorubber and further investigations on polystyrene, have demonstrated the existence of organic molecules which have the size of colloidal particles. Therefore, I called this group of colloids the "true colloids," eucolloids, in an article "Zur Chemie des Kautschuks und der Guttapercha," published in Kautschuk, August, 1925 (428). In this publication I stated: "One has to assume that those products contain very large molecules; the colloidal nature is determined by the special structure of the material. Graham, the founder of colloid chemistry, had already suspected this. One can assume that the primary colloidal particles represent the molecules. Such big molecules should be called macromolecules. This group of colloids, in which the

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101

colloidal nature is destroyed only by changes in the material itself, is the group of the true colloids, the 'eucolloids.'"

I proposed the name "pseudocolloids" for soaps where the colloidal particles are formed by the aggregation of fatty acid ions. Today, this term is no longer necessary since this group of colloids according to C. Nageli's concept, is known as micellar colloids. In the polymer homologous series, e.g., in polystyrene, only the highest molecular fractions show typical colloidal properties like swelling and high viscosity solutions. Therefore, the expression "eucolloids" was restricted to them. The low molecular representatives of the polymer homologous series, like polystyrene with a molecular weight of 2000-10,000, are called hemicolloids. In a later article, published in 1929, I suggested that all those colloids whose colloidal particles are macromolecules be called molecular colloids (70). (After the publication of this work H. Mark pointed out to me that A. Lumiere had suggested that a certain group of colloids be called molecular colloids as early as 1925 (compare the quotation from ref. 3, p. 83). After the influence of the shape of macromolecules on the properties of colloidal solutions had been proven, a classification of the molecular colloids into spherical and linear colloids was made (71). Spheromacromolecular materials and their colloidal solutions differ very little in their properties fr,om low molecular materials, as is shown in Table 5. However their behavior differs greatly from that of linear macromolecular materials which, as shown in Table 2, page 81, have some colloidal properties similar to the micellar colloids. This behavior is due to the fact that linear macromolecular materials and micellar colloids have particles of a similar long shape, even though their structures are completely different. The special properties of linear colloids, for example, swelling and the high viscosity of their solutions, were explained by a special state of solution which does not exist for low molecular and spheromacromolecular materials: the gel state (see p. 130). In this state the dissolved molecules are completely solvated, but cannot move freely because of their length. Such chain molecules hinder each other in solution since the sum of their spheres of activity is larger than the volume of the solvent. In 1925 when I proposed in my essay in Kautschuk the name" eucolloids" for the real colloids, I had overlooked that in September 1922 W. Ostwald had pointed out the difference between colloidal materials and colloidal systems in his lecture at the Versammlung Deutscher Naturforscher und Arzte [cf. Kolloid­Z., 32, 1 (1923)]. He had called the former "eucolloids."

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Table 5

COMPOUNDS

Comparison between Low Molecular Weight Materials, Sphero­ Macromolecular Materials, and Micellar Colloids (cf ref 55, p. 2)

Properties

Low molecular weight materials

Spheromacromolecular materials, e.g., Spheroproteins, Glycogen

Micellar Colloids, e.g., Soaps with swelling poly dispersed

Newtonian low viscosity

without swelling monodispersed and pf.;ydispersed Newtonian low viscosity

not Newtonian high viscosity

does not change

does not change

aging phenomena

dialyzable

not dialyzable

not dialyzable

Dissolve Dissolved particles are

without swelling monodispersed

Solution is 1lo solution has Viscosity of the solution on standing Dissolved particles are

This term, however, did not appear in the seventh and eighth editions of W. Ostwald's book Die Welt der Vernachliissigten Dimensionen, printed in 1922, which, being interested in colloid science, I was then studying. Also, in the general index for Volumes 1-50 of Kolloid­Zeitschrift (1931), one cannot find the expression "eucolloids," which, I hope, excuses my overlooking the term. The name" Eukolloidik" originated with H. Schade, Miinch. Med. Wschr., 68, 144 (1921). I emphasize this because during the 1940s, when macromolecular chemistry had finally been accepted, I was frequently asked by W. Ostwald, to "return" to him the word "eucolloids." Since he could have supported my theory on the existence of macromolecules in previous years, his later actions were so much the less understandable. Instead of supporting me, he favorably reviewed the books ofP. Karrer [cf. Kolloid­Z., 44, 182 (1928)] and K. Hess [Kolloid­Z., 47, 288 (1929)] without acknowledging the fact that the concepts of micellar structure, e.g., of cellulose, described in these books contradicted his own ideas on eucolloids, which were mentioned in 1922. For this reason I expressed my opinion of Ostwald's comments [cf. Kolloid­Z., 90, 370-75 (1940)] in an essay, Kolloidik und Makromolekulare Chemie, in 1942 (72).

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103

These controversies with W. Ostwald and other representatives of the micellar theory were useful at least from one point of view: they led to the result that colloidal solutions were examined on the basis of organic chemistry considerations rather than from the colloid theory. Colloid theory can be applied fruitfully to the large field of dispersion colloids and true micellar colloids. Nevertheless, it seems advantageous even today to describe that special group of linear macromolecular compounds as "eucolloids." These compounds exhibit properties which are very characteristic and very different from the behavior of low molecular compounds, provided they have a sufficient chain length (length determined by X-ray technique > 2000 A) (see Table 2, p. 81). Numerous discussions, especially those on the structures of organic colloids, induced me to write a book on organic colloid chemistry: Organische Kolloidchemie (73). This book provides a modern understanding of organic, colloidally soluble materials, their new classification, and the methods of their investigation with special attention to viscosity measurements. The book also shows that macromolecular compounds and their colloidal solutions represent a new field within organic chemistry. A number of other papers on organic colloids have been published (31,66,74-82).

4 Evidence for the Existence of Macromolecules

"Professor Staudinger, are macromolecules merely ideas to help explain many phenomena, or is there strict scientific evidence for their existence, and if so, by which methods?" Seldom has a question impressed me more than this one. It was thoughtful and carefully considered, and pointed to deep interest and understanding. The question was asked by His Majesty the Emperor of Japan during an audience on April 17, 1957, in Tokyo, to which my wife and I had been invited by the Japanese Imperial Family. It is just this experimental demonstration of the existence of macromolecules which forms the essential part of my work in the field of macromolecular science. I tried to give evidence for this in my lectures in Japan and I was honored on that day to have an opportunity to comment on these basic questions about macromolecules to the Japanese Emperor, who has a great interest in natural science. What decisive evidence can be given for the existence of macromolecules, i.e., molecules which surpass in dimension those of the earlier known low molecular compounds by a factor of a thousand or even more? The essential proof for the existence of macromolecules was adduced by classical organic chemical methods via polymer analogous reactions; thus, polymers were converted into their derivatives without their degree of polymerization being changed. This is proved further when such polymer analogous reactions are carried out on the high and low molecular parts of a polymer homologous series, as in many cases was done. The argument for the existence of macromolecules is based on the same consideration as that for the existence of small molecules in organic chemistry one century earlier. Thus Wohler and Liebig in their research on the radicals ethyl and 104

EVIDENCE FOR THE EXISTENCE OF MACROMOLECULES

105

benzoyl in 1832 [Liebigs Ann. Pharmazie, 3, 249 (1832)] were able to convert organic compounds into derivatives with other properties, whereas a large part of the molecule-the radical-remained unchanged in size. This discovery was very surprising at that time. In the same manner it can be demonstrated that under suitable conditions macromolecules leave their "macroradicals" unchanged with respect to size when they are converted into their derivatives. However, it is necessary to note the addition" under suitable conditions" because polymer analogous reactions sometimes involve great difficulties. Between 1924 and 1926 polystyrenes with a molecular weight of 2000-5000 were converted by catalytic reduction into polymer analogous hexahydropolystyrenes (83,84). [In these first papers the term "polymer analogous" had not been used. It appeared first in a later publication with my co-worker H. Scholz on the conversion of cellulose into polymer analogous compounds (476).] We also tried to convert polystyrenes with a high molecular weight through hydrogenation into polymer analogous products. This turned out to be impossible because this hydrogenation resulted in strong degradation. This is understandable because of the great "cracking" tendency of polystyrenes (see allyl group). In the case of polysaccharides such polymer analogous reactions can be carried out more easily with the hydroxyl group which reacts easily without the "macroradical" being changed. The first experiments along these lines were done in 1929 with 0. Schweitzer, who succeeded in converting a series of polymer homologous celluloses into polymer analogous acetates (85). From similar further investigations on cellulose, evidence for the macromolecular structure of colloidal particles of cellulose in Schweitzer's agent could be obtained. This was also possible for several derivatives of cellulose (see p. 217), amylopectin (see p. 231), and glycogen (see p. 232). Besides measures to avoid the degradation of polymers, another essential difference between work with low and high molecular substances has to be kept in mind. Reaction products of low molecular substances can be purified from by-products by recrystallization. Such a procedure cannot be used for polymers due to possible changes which might occur during the process of reprecipitation. Consequently, only reactions which proceed clearly without side reactions and in as quantitative a manner as possible can be used for polymer homologous conversions. Earlier investigations of polymer homologous series were regarded as

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further criteria in favor of a macromolecular structure. The physical properties of each single element of such a polymer homologous series, e.g., of polystyrenes, change regularly with an increase in molecular weight, a behavior similar to that of the paraffin homologous series. After having shown that hemicolloidal polystyrenes with a molecular weight of 5000 are chain molecules, it was possible to assume the same structure also for polystyrenes with a very high molecular weight. I mentioned this hypothesis as early as 1926 during a lecture at a meeting of the Deutsche Gesell­ schaft der Naturforscher und Arzte (German Society of Natural Scientists and Physicians) in Dusseldorf (ref. 5, see p.. 83). However, it could be argued that the parts of a polymer homologous series with very high molecular weight having different eucolloidal properties (e.g., swelling and high viscosity in dilute solutions) have a different structure than the lower molecular-weight parts of the series which do not exhibit such properties. Further evidence for the existence of macromolecules results from the determination of molecular weight in several solvents. If identical molecular weights are obtained from solutions in different solvents, then there should be a great probability for the existence of macromolecules. A. Dobry [Kolloid­z., 81, 190 (1937)] came to this conclusion, but due to the fact that polymer homologous species, i.e., substances with the same type of structure were investigated, the existence of aggregates having the same size in different solvents was therefore possible. This would be in accord with the behavior of palmitic acid which dissolves in several homopolar solvents as a double molecule. From polymer analogous reactions one obtains, in turn, derivatives with a different chemical constitution that are usually not soluble in the same solvents as the starting material. Thus, determination of the size of "macroradicals" was undertaken for differently constituted materials in several solvents, e.g., that of starch and glycogen in formamide, and that of their acetates in other organic solvents (see p. 231). After all the experience in organic chemistry, it cannot be expected that aggregates of the same size are formed for these different derivatives in very different solvents. If, on the other hand, after having changed the solvent one finds different particle weights, such as is the case with proteins, then particles with a high weight must represent aggregates, whereas particles with low weight possibly give the correct molecularweight. [Polyvinyl chlorides show different particle weights in several solvents (P. Doty, H. Wagner, and S. Singer, J. Phys. Colloid Chem., 51, 32 (1947): The Association of

EVIDENCE FOR THE EXISTENCE OF MACROMOLECULES

107

Polymer Molecules in Dilute Solution). The authors demonstrated that aggregates have to be assumed to account for the higher particle weights]. One can see, for example with insulin, how the particle weight of proteins can change in dependence on the determination procedure. Initially a particle v,reight of 39,000 was assumed; now, after the investigations of F. Sanger [cf. F. Sanger and H. Tuppy, Biochem. J., 49, 463, 481 (1951); Nobel Prize lecture, Stockholm, December 1958] the molecular weight of insulin is known to be exactly 5733,43. Other evidence for the existence of macromolecules is given by the correspondence of the molecular weight determined by a physical method to that evaluated from the determination of characteristic end groups. However, this procedure is only applicable to chain molecules with a welldefined structure and a characteristic end group, e.g., polyoxymethy- lenedimethyl ethers or -diacetates (cf. ref. 15, Table 123, p. 234). It was also used successfully in the case of polyoxyethylenes (see p. 184), and further by Carothers for polyesters and polyamides. As a prerequisite, these polyesters have to be prepared cautiously, as in later experiments by H. Batzer (seep. 191) to avoid the splitting off of end groups. Completely insoluble materials cannot be assumed forthwith to be polymers. Surprisingly, some amorphous and insoluble low molecular substances look like high molecular substances, e.g., the condensation product of two molecules of formaldehyde with three molecules of ethylenethiourea (compare with the formula on page 198). Polymeric products might be considered insoluble simply because no suitable solvent had been found for them yet. This was true for a long time for aminoplasts (seep. 1 95) and is still true for Teflon. On the other hand, the macromolecules are crosslinked in other materials, and, thus, only chemical degradation can make them soluble. Into this class belong materials with limited swellability (earlier termed colloids with limited swellability), e.g., the copolymeric product from styrene and divinylbenzene, the structure of which was elucidated with W. Heuer in 1934 (213). Such products, which existed only in the solid state, were termed onephase materials (see ref. 86, p. 168). A fundamental prerequisite for investigations in the field of macromolecular science is proof that the colloidal particles in polymeric solutions are really macromolecules. If it turns out that this proof is positive, ordered relations between the length of dissolved chain molecules and such properties as the viscosity of the solution, swelling, and so forth, may be found; however, if there exist aggregates in the colloidal solutions of

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polymers, such as can be found in certain solutions of low molecular compounds, then there is no clear relationship between the particle size of these aggregates and the properties mentioned above. Soluble macromolecular substances can go into solution only as colloids due to the size of the molecules; this is their normal manner of dissolving. In comparison, solutions of soaps in water represent a special state because the micelles formed are unstable. After a change of external conditions, for example, increase in temperature, the micelles disintegrate, and thus the viscosity of such a solution decreases considerably. On the other hand, colloidal solutions of polymers, e.g., polystyrene or cellulose acetates with a very high degree of polymerization, are stable with changes in temperature. This is a valuable indication as to the macromolecular nature of the colloids but not definite proof, since it can be assumed that particles with micellar structure, e.g., cellulose or its derivatives, are particularly stable. Thus, the polymer analogous chemical reaction with preservation of the "macroradical" represents the main conclusive reaction for establishing a macromolecular structure. In this respect, the chemistry of macromolecules is connected with classical organic chemistry, which is concerned with low molecular materials.

5 The Characterization of Macromolecular Compounds

1. ELEMENTAL ANALYSIS As the editor of the journal Die M akromolekulare Chemie I correspond with authors who submit articles on new derivatives of polysaccharides, on copolymers, and on many other polymeric products. Although much physical and chemical investigation has been done, such as on the nature of their colloidal solutions or on reaction kinetics, these substances have not been characterized by elemental analysis. One author replied that elemental analysis can only be used successfully for low molecular crystallized sugars and is not useful in the case of complicated polysaccharide derivatives. I wrote back that it is relatively easy to prepare low molecular crystallized sugars with such high purity that the values found by elemental analysis correspond well within a certain tolerance to the calculated values. By comparison, with high molecular polysaccharide derivatives, one often obtains different results due to difficulties in purification. For this reason, however, it is necessary to characterize these materials also by elemental analysis to get some information about the degree of their purity. Therefore only compounds the composition of which was known by elemental analysis were investigated in our studies in Zurich and Freiburg. The application of organic and colloid-chemical methods seems to me to be of essential importance in research on macromolecular compounds. One can find by reading the older volumes of Kolloid­Zeitschrift descriptions of valuable observations on macromolecular compounds, the viscosity of colloidal solutions, deviations from the Hagen-Poiseuille law, etc. However, the composition of the materials being investigated was never controlled. 109

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RESEARCH ON MACROMOLECULAR COMPOUNDS

This was due to the fact that colloids were regarded as a special physical state of matter into which all materials could be converted by means of a suitable procedure (seep. 99). Therefore, special care was taken of the equipment in a microanalytical laboratory. Moreover, I have pointed out in many lectures that microanalysis is an essential part of a macromolecular laboratory. I was fortunate in this respect to have always been supported in these investigations by excellent co-workers, such as Dr. S. Kautz, a student of Professor Pregl, and later by Otto Windisch. Thus, from the beginning of research in this field, many well-known synthetic polymers, such as polystyrenes, polyvinyl acetates, polyvinyl chlorides, and also natural products such as natural rubber, cellulose, and starch, were subjected repeatedly to elemental analysis before they were characterized by other means such as determination of the molecular weight and of the viscosity. As a result, it was discovered that some compounds do not always have the expected composition, e.g., technical polyvinyl chlorides actually contain less chloride than predicted. In the summer of 1959, I met one of my earlier co-workers, Dr. F. Felix, now director of the Ciba AG, Basel, in the Engadin. We talked about the beginnings of this field, now more than 30 years ago, and he mentioned how much I emphasized at the time the importance of correct elemental analysis. At that time, I had given him the problem of evaluating the constitution of soluble polymeric product of dimethylketene. This compound was prepared from an ether solution of dimethylketene by polymerization with trimethylamine under an atmosphere of carbon dioxide, which protected the extremely autoxidizable dimethylketene from oxygen. The product obtained had too high an oxygen content to be explained. When the polymerization at last was carried out in an atmosphere of nitrogen, the polymerization products of dimethylketene showed the correct results with respect to oxygen content. Subsequent studies on the influence of carbon dioxide on dimethylketene led to the discovery of crystallized complexes of three molecules of dimethylketene and two molecules of carbon dioxide. This has already been reported on page 82. The narration of my earlier co-worker was a further example of the significance of elemental analysis in this field. Furthermore, the often repeated elemental analysis of cellulose and its derivatives brought the surprising discovery of the inclusion phenomenon. In order to prepare a particularly pure cotton cellulose, mercerized cotton cleaned by common methods was carefully washed with acetone and

CHARACTERIZATION OF MACROMOLECULAR COMPOUNDS

Ill

cyclohexane. These solvents should have been removed easily [experiments of R. Mohr (ref. 478), seep. 218] due to the fact that they would not be bound by the glucose residues, as water is bound by secondary valences. However, the elemental analysis of these celluloses by S. Kautz brought an unexpected result-the carbon content of cellulose cleaned in the above manner was much higher than calculated. It was first assumed that the results were incorrect, but repeated analysis always gave the same values. After later investigations on this phenomenon, mainly by W. Dahle (ref. 506 and p. 227), it is now believed that these "inert" liquids are included (includiert) between the molecules of cellulose. This inclusion is of a mechanical nature since the solvent molecules are not able to break the secondary valences between the hydroxy groups of two neighboring cellulose chains. Thus, a few per cent of "inert" solvents can be included between the chains, but only solvents that are hydrophobic and therefore form no secondary bonds with the hydroxy groups of the cellulose. However, one obtains a pure cellulose where theoretically and experimentally obtained values correspond well if the well-cleaned material is washed with water and is finally dried under high vacuum at 50-100°C. Water included between the chains-in contrast to opinions advanced earlier-can be removed under high vacuum when heated because the water molecules are able to break the secondary valences between the chains. As a demonstration, results of the elemental analysis of cellulose and "cyclohexane" cellulose are given in Table 6. An essential difference in the preparation of low and high molecular samples for analysis is a result of the inclusion phenomenon. Solid low molecular compounds are first recrystallized and washed, then are dried under vacuum, if necessary, until their weight is constant, and finally are subjected to elemental analysis. This type of procedure is also sufficient for powdery spheromacromolecular compounds, e.g., glycogen, but not for linear macromolecular ones. As in cellulose, these substances include small molecules between the long-chain molecules, and the small molecules cannot be removed at all or only very slowly, even under high vacuum at elevated temperatures. Therefore, the constant weight proof is by no means an indication that there is a pure macromolecular substance free of any traces of solvent. Technical polymers such as Plexiglas or polystyrene often contain unreacted monomers in a concentration of ca. 0.5/0 , which cannot easily be removed. The percentage of unreacted monomers can be determined by titration with solutions of bromine. These investigations, which were carried out by G. Lorentz in 1943, have not been

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COMPOUNDS

Table 6 Elemental Analysis of Cellulose and "Cyclohexane Cellulose" after Drying for 2 Days under high vacuum (0.1 mm) at 100°C (cf ref 506,p. 221) Degree of polymerization of cellulose

Analysis of Pure cellulose "Cyclohexane cellulose"

%C

%H

%C

%H

44.44 44.29 44.38

6.33 6.30 6.22

46.06 47.58 47.19 46.95

6.62 6.97 6.97 7.00

44.51 44.22 44.32

6.23 6.29 6.32

47.81 47.63 47.33 48.03

7.02 6.99 6.90 6.97

44.43

6.21 47.68

6.85

Cotton

2250 1570 950 580 Ramie

1150 800 600 330 Calc. C6H10O5 Calc. 6(C6H10O5) + C6H12

published yet, nor has there been further research on the purification of these materials. If linear macromolecular compounds are purified by reprecipitation and subsequently dried, it is difficult to decide if solvent is still included between the chain molecules, and, if so, how much. If one dries such linear macromolecular substances which were dissolved in benzene or carbon tetrachloride after evaporation of the solvent in high vacuum, one finds out that there are two groups of products which behave in different manners. The solvent can be completely removed after two days in the first group whereas the chain molecules of the polymers of the second have side groups which hold back the solvent much more effectively. This is shown in Table 7 which reports the results of experiments carried out in 1943-1944 by G. Lorentz. Of course it is also possible to remove the solvent completely from polymers of the last group too when they are washed with other solvents; e.g., methanol. The removal of methanol can be proved by the determination of the methoxy group. If one intends to determine the degree of inclusion of solvents with macromolecular carbon hydrides or oxygencontaining compounds, then the use of volatile compounds with halogen

CHARACTERIZATION OF MACROMOLECULAR COMPOUNDS

113

Table 7 Inclusion of Benzene and Carbon tetrachloride in Plastics after Two Days of Drying at 20°C under High Vacuum (0.1 mm) (cf ref 5l,p. 152)

7o Product Not including materials: Polyethylene Polyoxyethylene Polyoxyundecylic acid Rubber Oppanol B 100 Including materials: Polystyrene Neoprene PCU PC Plexiglas Mowilith H

Mn

35,000 200,000 40,000 200,000 100,000 130,000 300,000 60,000 60,000 180,000 120,000

inc1uded

Benzene

CCl4

0.5 0.0 0.1

0.3 0.0 0.0 0.6 2.0

3.2 13 11 15 23 28 42

11 16 20 30 32 30

atoms, such as CC14 or chloroform, also is possible. On the basis of an analysis of halogens, one knows whether molecules of the solvent are still held by the macromolecules. Thus, the preparation of macromolecular substances for analysis is much more difficult than that of low molecular compounds. Although it is necessary to control the composition of a macromolecular substance before further investigation by means of elemental analysis, one cannot determine important differences in the chemical and physical properties of macromolecular materials by elemental analysis only. Owing to the size of macromolecules, small amounts of additives are sufficient to make essential chan,ges in their chemical aod physical behavior. Thus, polyoxymethylene dihydrate and polyoxymethylene dimethyl ether with a degree of polymerization of 100, for example, cannot be distinguished by elemental analysis although their chemical differences are remarkable. The first product is soluble in aqueous sodium hydroxide solution; the latter is not. On the other hand, a distinction of the two is easily made by determining the methoxy content since the dimethyl ether polymer (degree of polymerization of 100) contains 2% methoxy groups. Similarly, the elemental analysis of two polystyrenes showing limited and unlimited swelling results in the same values, although

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their physical behavior is very different. However, the small divinylbenzene content in the latter cannot be shown by elemental analysis. It is necessary to use other procedures to explain the differences in the constitution of both products, to recognize that the insoluble polystyrene is a copolymer of styrene, and to detect very small amounts-below 0.01 /o -of divinylbenzene (213,214). Finally, another reason may be mentioned for the significance of microanalysis in macromolecular science: although most artificial polymers and natural products such as cellulose are available in large amounts, so that one need not be thrifty with them, microanalysis is advantageous because small amounts of material, e.g., 0.1 g and less which are sufficient for many microanalyses are much easier to purify, and solvents can be removed from them more readily than from the larger amounts necessary for the usual elemental analysis. 2. INVESTIGATIONS WITH THE ULTRA MICROSCOPE OF SIEDENTOPF AND ZSIGMONDY, AND WITH RAMAN SPECTROSCOPY

At the beginning of my research on macromolecular substances, I hoped to obtain valuable results by determining the number of colloidal particles with the aid of the ultramicroscope, as was possible with inorganic colloids. However, this expectation was not fulfilled. It is not possible to recognize and to count single chain molecules, but on the other hand, it is very convenient to determine the degree of purity in solutions of macromolecules. In 1923 after low molecular (hemicolloidal) polystyrenes were obtained by the polymerization of dilute solutions of styrene containing tin tetrachloride, the solutions of these polymers were investigated with an ultramicroscope after purification and reprecipitation. As a result, a large number of particles with a bright shine could be seen. It turned out that these particles did not consist of polystyrene, but were particles of colloidal stannic acid, which could only be removed from solution with difficulty. Only after multiple fractionated reprecipitation was it possible to produce solutions of polystyrene almost free from colloidal stannic acid. Thereafter, the purity of colloidal solutions of macromolecular substances was always controlled in this manner. In other experiments, polystyrene and synthetic rubber was prepared by thermal polymerization of "optically empty" styrene and isoprene in a

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bomb. The polymers obtained were dissolved in an "optically empty" solvent and turned out to have no shining particles which proved that in these linear polymers the macromolecules cannot be recognized by the method of Siedentopf and Zsigmondy (cf. ref. 258, p. 95, the dissertation of Max Brunner, ETH Zurich, 1926), which was so successful in the case of inorganic colloids. Although macromolecules are not visible, these investigations of their solutions by means of an ultramicroscope were very valuable, since it is possible to determine impurities such as dust particles or catalyst residues easily. Such a catalyst content, for example, can strongly influence the resistance of polyethylene foils to light and air. Planned research in this field was discontinued. In 1932 R. Signer investigated the Raman spectra of polystyrenes prepared in different manners: one polystyrene was obtained thermally; the other was obtained with tin tetrachloride. as a catalyst. As a result, the Raman spectra were similar to those of ethylbenzene. One observation was remarkable: thermally polymerized polystyrene contained fluorescent admixtures, which appeared stronger the higher the temperature of polymerization. However, the nature of these fluorescent impurities could not be explained, and the question still remains as to the possibility of chain molecules containing fluorescent end groups (87,88).

3. THE FRACTIONATION OF POLYMOLECULAR MIXTURES One of the first and most important realizations in the field of polymer synthetic as well as natural materials was that these materials are not uniform, but inseparable mixtures of polymerhomologs (see p. 85). The determination of molecular weight, and therefore the degree of polymerization, results in average values which differ and depend on the method of determination, for almost all cases. In 1938 G. V. Schulz termed such mixtures "polymolecular" (89). In a paper published in 1923 [220] I pointed out the following on p. 942: "The average molecular weight of a fraction is decreased relatively strongly by the presence of small molecules, while the viscosity is not influenced very much by this. The viscosity depends primarily on the number of large molecules. Therefore, products with the same average molecular weight can show a different relative viscosity if the mixture of large and small molecules is different in these products."

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The purpose of further research was to obtain fractions which were as uniform as possible out of the mixtures. Since the majority of the macropolymeric materials was available in large amounts, 10 g were fractionated into three parts. The middle fraction was again fractionated and thus a further middle fraction of about 1 g was obtained which was relatively free of disturbing low and very high molecular shares. Determinations of the molecular weight were carried out with these final fractions. In the beginning these determinations were made by cryoscopy, and later by means of osmometry and viscometry. This manner of investigation was successful, since for a polymer homologous series of cellulose acetates and cellulose nitrates approximately the same Km constants for several members of the series were obtained (see pp. 216 and 289). However, the fractions prepared by the above procedure are still not completely uniform: Km values of products which were subjected to further fractionation are about 10-20% lower than those of the fractions mentioned above. In order to characterize a polymolecular macromolecular material with accuracy, it is necessary to know its distribution and to determine how many low and high molecular parts it contains. R. Signer and G. V. Schulz worked on this problem. G. V. Schulz fractionated polymers, degraded cellulose and its derivatives, and determined the amount and the molecular weight of single fractions. On the basis of this knowledge, it is possible to determine the weight average and number average distribution, and these are measures for the non-uniformity of the polymer concerned (90-95).

6 Determination of Molecular Weight

The important difference between the average molecular weight, i.e., the average degree of polymerization of a macromolecular material and the average particle weight of polydisperse colloids, has already been discussed in many publications, e.g., in a discussion with K. H. Meyer in 1929 (see p. 89). Accordingly, the terms molecular weight and degree of polymerization should be used in macromolecular chemistry in the same way as in the field of low molecular substances (96,43). The following paragraphs will give a short description of several methods used for the determination of the molecular weight in the laboratories in Zurich and later in Freiburg. Unfortunately, in Freiburg we did not have an ultracentrifuge at our disposal. When my co-worker, R. Signer received a grant from the Rockefeller Foundation in 1932, he was able to investigate polystyrene with the aid of the ultra-centrifuge in the laboratory of The Svedberg in Uppsala. His results were reported in two papers (97,98).

1. DETERMINATION OF A CHARACTERISTIC GROUP It is possible to obtain the molecular weight of a macromolecular substance by the determination of the content of a characteristic atom or functional group in the molecule. This procedure was applied in the protein field, where the molecular weight of 16,000 for oxyhemoglobin was determined on the basis of its iron content. However, Emil Fischer had raised doubts about this method, because the existence of crystals, as in the case of oxyhemoglobin, does not guarantee a chemical individuality (homogeneity) owing to the fact that one may be concerned with isomorphous mixtures (see quotation on p. 78). This particular method for 117

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the molecular weight gives correct information only when the constitution of the substance is exactly known. It was frequently used in the case of linear macromolecules with characteristic end groups, e.g., for polyoxymethylene and polyoxyethylene diacetates, polyesters, and polyamides. The evaluation of molecular weight by the determination of end groups is restricted to a relatively small molecular weight range. This is due to the relatively low content of end groups in substances with a molecular weight higher than 50,000. In the case of macropolymers with a molecular weight over 100,000, like rubber or cellulose, this procedure fails completely. When the constitution of a polymer is not exactly known, end-group determination may be misleading in establishing the molecular weight. This happened in the early works of W. N. Haworth [cf. J. Chern. Soc. (London), 1932, 2277, 2375; 1935, 1201; J. Soc. Chern. Ind., Chern. Ind., 54, 865 (1935)] who calculated molecular weights for glycogen and starch that were too low. They were obtained on the basis of end-group determinations which neglected the effects of branching. This procedure is applicable for cellulose which consists of unbranched macromolecules [cf. W. N. Haworth and H. Machemer, J. Chern. Soc. (London), 1932, 2270].

2. ULTRAMICROSCOPY AND ELECTRON MICROSCOPY Owing to the great success of ultramicroscopy in the field of colloids, where number and size of inorganic colloidal particles could be evaluated, I hoped at the beginning to apply this method to macromolecules. According to the discussion on p. 114, however, this method is not applicable to linear polymer molecules. Because of their small diameter, they cannot be detected with an ultramicroscope. However, it is possible to recognize spherical macromolecules of high molecular glycogen (DP 9000) by means of electron microscopy. This was first stated in a joint investigation of my wife and G. A. Kausche in 1939. Later on, E. Husemann and H. Ruska were able to photograph molecules of p-iodobenzoyl glycogen with an average molecular weight of 6,000,000 (99, 100). The determination of the molecular weight of high molecular glycogens by osmosis or other physical methods could not be supplemented by electron microscopy. Nevertheless, this method contributed much valuable information about the shape of macromolecules (see p. 141).

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3. CRYOSCOPIC l\1ETHOD In order to determine the molecular weight of polyoxymethylene derivatives, which have been under investigation since 1922, and of low molecular weight polystyrenes, the cryoscopic method, common in organic chemistry, was employed using very accurate thermometers. At the beginning objections were raised by colleagues with respect to this method owing to the fact that there are no depressions in temperature in colloidal solutions except those caused by impurities. Therefore, the results obtained from cryoscopic measurements were assumed to have no significance. However, in the case of polyoxymethy lene diacetates, as well as for polyoxymethylene dimethyl ethers, these objections were not justified because research carried out in the 1920s resulted in an agreement of the molecular weights obtained by both the cryoscopic method and the easily applicable method of end-group determination (see p. 178). Molecular weights of polystyrene in a range of 2000-5000 were re-examined by several coworkers e.g. S. Wehrli and M. Brunner in Zurich, and always yielded identical results. These samples did not contain any impurities, as shown by ultramicroscopic investigations (seep. 114). Furthermore, in 1924 A. A. Ashdown carried out a number of reprecipitations of hemicolloidal polyphenylbutadiene without fractionating the polymer; he found that all cryoscopic depressions remained constant (101). Through these investigations we obtained additional evidence that the cryoscopic depressions were caused by dissolved polymeric molecules rather than by impurities. The cryoscopic determination of the molecular weight of polystyrene, as well as the determination of the specific viscosity of its solution, was repeated in Freiburg (1928-1930), where W. Heuer obtained the same results. Accordingly, in 1930 the relation between the degree of polymerization and viscosity was found (122 and p. 125). There have been some doubts as to the usefulness of cryoscopy due to the anomalous molecular weights of starch acetates reported in Chapter 1 (compare Table 1, p. 80). However, these anomalies must be caused by special phenomena, because the results of the experiments described above have been reliable. As a consequence, the cryoscopic method in the field of polysaccharides was assumed at that time to fail because of unknown reasons, whereas this method was found to be applicable to polymeric systems with a simple structure [cf. K. Freudenberg, E. Bruch, and H. Rau, Ber. 62, 3078 (1929)].

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The results obtained later on by E. Dreher [269] from an investigation of polymer homologous polyanetholes in naphthalene spoke against this application: molecular weights determined by cryoscopy decrease the higher they are according to viscosity measurements, so that finally with the high molecular polyanetholes one gets molecular weights which are smaller than the molecular weight of the monomer unit. When these experiments were repeated by W. Kern and J. J. Herrera [102], the same results were obtained. At this time the molecular weights of four polyisobutylenes with an average degree of polymerization of 28-59 were determined by cryoscopy in cyclohexane. It was assumed that the values obtained in this manner were correct because the constants Kaqu from the relationship between molecular weight and viscosity in three different solvents had identical values compared with those obtained with homogeneous low molecular weight samples (cf. Table 9, p. 165). How far molecular weights of polystyrenes determined by means of cryoscopy were valid became doubtful according to further investigations, e.g. of J. W. Breitenbach and A. W. Renner [Monatsh. Chern., 81, 454 (1950)]. These authors demonstrated that the osmotic method yields higher values for the molecular weights than does the cryoscopic one. This result was obtained earlier by E. Husemann, who did not publish it. Consequently, the common cryoscopic method is only suitable for application to molecular weight determination of relatively low molecular polymers if it is checked with another method, e.g., the method of end-group determination (cf. Table 10, p. 185).

4. OSMOTIC METHOD The osmotic method was used by many authors, such as J. Duclaux, A. Dobry, and W. Biltz, for the determination of the particle size of colloids. In the laboratory in Freiburg experiments in this direction were undertaken by W. Frost, while R. Signer tried to apply the isothermal distillation method suggested by G. Barger (103). The investigation on this field in Freiburg were intensified in 1933 when G. V. Schulz with his extensive experience in osmometry moved from H. Freundlich's laboratory in Berlin to Freiburg [cf. G. V. Schulz, Z. Physik. Chern., 158, 237 (1932), Das Solvatationsgleichgewicht in kolloiden Losungen; Z. Physik. Chern. 161, 441 (1932), Die Bestirnrnung der GrojJe, Gestalt und Solvatation von Makrornolekiilen]. In 1935 G. V. Schulz constructed an appropriate osmometer which

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was used to carry out measurements in Freiburg during the following decades. Numerous determinations of the average degree of polymerization were made and compared with values for cellulose derivatives, natural rubber, and plastics evaluated by the viscosity number. Further research of G. V. Schulz was devoted to the explanation of the osmotic behavior of linear molecular substances in solution. It was found that in such solutions an increase in the osmotic pressure is not proportional to the concentration but increases to a much higher extent. In good solvents this increase is faster than in bad solvents, and it is higher in the case of high-molecular materials than with low-molecular products. This research was covered in a series of publications (91, 103-116).

5. PRECIPITATION-TITRATION In 1934 a paper was published with W. Heuer (I17) in which the following result was reported: "For the determination of the solubility of polystyrenes in a solvent, a procedure was applied, which is based on precipitation by a nonsolvent. "The solubility of polymer homologous polystyrenes decreases as the molecular weight increases, that is, hemicolloidal materials dissolve rapidly, and mesocolloidal and eucolloidal polymers dissolve slowly." These investigations were contined by G. V. Schulz, and later on with the collaboration of B. Jirgensons. As a result, the relationship between solubility and molecular weight could be evaluated. Thus, it was possible to determine the molecular weight of a macromolecular product by precipitation-titration after a calibration curve has been obtained (118, 119).

6. VISCOMETRIC METHOD The simplest method for the determination of the average degree of polymerization of linear macromolecular substances is viscometry, and it is largely used today in industries dealing with cellulose and its derivatives. This method is used also for many fiber materials and plastics. To carry out this work, the idea had been postulated that solvated macromolecules do not have an extraordinary high degree of solvatization, (solvation husks) as it has been assumed, e.g., by H. Fikentscher and H. Mark (Kolloid­Z., 19, 135 (1929)], but that macromolecular substances are solvated in the same manner as low molecular substances (see ref. 70, p. 2903).

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In the determination of the degree of polymerization by viscometry, one has to be aware that the molecular weight of polymolecular mixtures obtained by means of viscometry is higher than the average molecular weight obtained by cryoscopy or osmometry. This is due to the fact that the length of the molecules is effective in the viscosity phenomena. In accordance with W. D. Lansing and E. 0. Kraemer [J. Am. Chern. Soc., 57, 1369 (1935)] and, furthermore, G. V. Schulz [91], the value obtained by viscometry is termed the weight average molecular weight, whereas the molecular weight obtained by osmometry is termed the number average molecular weight. On that point, W. Kern made a series of calculations, which were published simultaneously with those mentioned above by W. D. Lansing and E. 0. Kraemer (120). For this reason in all viscometric investigations on polymolecular mixtures, products were used which were prepared by the method of fractionation mentioned above (seep. 115).

7 Viscometry

When polystyrenes were investigated in the early 1920s, it was found that polymers obtained under different conditions showed large differences in the viscosity of their solutions. Therefore, it was reasonable to characterize these polymers by their viscosity in solutions having the same concentration. For this purpose, solutions with low viscosity were used as their viscosity increases approximately proportionally to their concentration. All measurements were consistent with the statement that solutions of polystyrene with a high molecular weight have a higher viscosity than those with a low molecular weight. When I presented some of the results on several hemicolloidal polystyrenes, which were obtained in Zurich by my collaborators M. Brunner and S. Wehrli (258,259), they were not received with much notice at the meeting of the Tagung Deutscher Naturforscher und A.'rzte in Dusseldorf in 1926. At that time it was generally believed that the colloidal particles of such solutions consisted of micelles formed by small mol.ecules. The adherents of the colloid theory pointed out that the viscosity of colloids is very complicated and depends on many different conditions. Therefore, one cannot expect to find a simple relationship between the viscosity of solutions and the molecular size of a dissolved substance. In 1913, W. Ostwald [cf. Kolloid­Z., 12,213 (1913)] had pointed out in a lecture before the Faraday Society, that the viscosity of colloids differs widely from that of solutions containing low molecular weight substances. The viscosity of the latter depends only on concentration and temperature, whereas the viscosity of colloidal solutions is additionally influenced by the solvation of the colloidal particles, their mechanical pretreatment, aging and additives. Furthermore, from 1910 to 1913 W. Biltz and his coworkers [cf. Z. Physik. Chern., 73, 507 (1910); 83, 703 (1913)] had done 123

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research on the viscosity of colloidal solutions of dyes, gelatin, and starch which resulted in the conclusion that there is a relationship between the degree of dispersity and the optimum viscosity. With respect to this work in particular, it seemed to be questionable whether further research in this field was warranted due to the fact that W. Biltz had found correlations between the viscosity and the particle size of colloids with an entirely different structure, for example, dyes, which are micellar colloids, and on the other hand, starch, a macromolecular substance. However, a series of our experiments had demonstrated that colloidal particles of macromolecular compounds in solutions contained molecules with a structure similar to those of molecules of low molecular compounds. In this case the viscosity of their solutions, at least in the case of homopolar products, has to be dependent on the same conditions as is the viscosity of low molecular substances. There should be no fundamental difference between them. Investigations on the viscosity of low molecular compounds with a known structure by R. Nodzu (123) and E. Ochiai (124) in 1929-1930 resulted in the conclusion that Einstein's law is not valid for solutions of low molecular compounds with linear molecules, since for this case the viscos­ ity number changes proportionally with the number of chain elements in the compounds. On the other hand, the Einstein's law is valid for solutions of spherical molecules [71]. Consequently, the shape of the molecules must be responsible for the viscosity of their solutions, and this was the basis for further successful research in this field. This resulted finally in the possibility of evaluating the degree of polymerization of linear macromolecular substances, e.g., cellulose and its derivatives by means of viscometry. Thus, the prediction made in 1930 which was based on the experiences gained at that time was fulfilled (see ref. 121, p. 2334): "The simplest method of determining the molecular weight of cellulose is by means of viscometry. Differences in the size of long molecules can be observed by easily recognizeable differences in the viscosity of solutions. Therefore, viscometry will be of great significance in the ascertainment of the constitution of high molecular substances." (121).

The establishment of relationships between viscosity and molecular weight resp. the degree of polymerization in solutions of linear molecules, was eased by the introduction of a new term: Previously the relative viscosity YJr of the different solutions had been compared. Now we used the specific viscosity YJsp which was introduced in 1930: it is defined

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as the increase in viscosity caused by the dissolved material in a solvent (ref. 122, p. 226). Therefore the specific viscosity YJsp is YJr- 1. In early papers YJsp/c values of solutions containing 1 mol/1 (basic molar, grundmolare Losung) were compared, later on the YJsp values of solutions with 1 g of polymer dissolved in 1 liter of solvent were used. The limes value (limes-Wert) of this term was denoted as the viscosity number ZYJ (173,174). In American literature the term [YJ ], "intrinsic viscosity," was used instead of "viscosity number."

1. VISCOSITY MEASUREMENTS ON SOLUTIONS OF LOW

MOLECULAR COMPOUNDS In 1930 higher paraffins were fractionated in collaboration with R. Nodzu (123). The average molecular weight of the fractions was determined by cryoscopy, and then viscometric measurements in diluted solutions were made. It turned out that in this case too YJsp/c values proportionally increased with the molecular weight. The same result had been reported earlier with W. Heuer on a series of polymer-homologous polystyrenes (122). Then a larger number of uniform paraffins and paraffin derivatives with well-known compositions were investigated. At the beginning results were obtained which were quite surprising since E. Ochiai (124) had found out that cetylpalmitate, palmitic anhydride, and palmitic acid in solutions of carbon tetrachloride, have approximate-ly the same viscosity number. The proportionality factor was nearly the same for these oxygen-containing compounds as for paraffinic carbon hydrides. The same relation for viscosity was obtained in the case of aliphatic, nitrogencontaining compounds. Thus, oxygen and nitrogen atoms in the chains do not influence the viscosity to a large extent. According to experiments carried out with W. Kern, the same holds for short side chains (125). For derivatives of polyoxyethylene the same relationship between chain length and viscosity was found (see Table 10, p. 185) as that for esters. Therefore, the fact that a chain contains more or fewer oxygen atoms seemed insignificant. As a result, the viscosity number of solutions of threadlike molecules is based mainly on the length of their chains. However, the nature of the solvent as such has a certain influence, e.g., the viscosity number is higher in the case of the above-mentioned compounds in solutions of carbon tetrachloride than in solutions of benzene. These differences are connected with the different solvation of the linear

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macromolecules. In 1934, W. Heuer found out (117) that the viscosity number of a dissolved substance is higher the better the solvation of the substance in the solvent is. Thus, for solutions of low molecular substances with linear molecules, the nonvalidity of Einstein's law was demonstrated. On the other hand, this law holds for solutions with more or less spherical molecules. For example, aqueous solutions of several saccharides have approximately the same viscosity number, a result already obtained in 1920 by 0. Pulvermacher. In accordance with further investigations with A. E. Werner (ref. 471, p. 266), the viscosity number of pentabenzoylglucose is also approximately the same as that of pentaacetylglucose in the same solvent. Therefore, differences in the solvation are not very influential, although the numbers of the dissolved molecules of both compounds in solutions of identical concentrations show the relation 1 : 1.8. Nevertheless, the factor K = 0.0025 calculated by Einstein is valid only for suspensoids and such emulsoids as natural rubber latex (71), whereas it is higher than calculated for dissolved spherical molecules, e.g., sugars, due to solvation. Further investigation on derivatives of malonic esters showed that the substitution of longer side chains influences the size of the viscosity number, i.e., with growing length of these side chains the viscosity number is first lowered and then increased (140,141,143). Investigations on the viscometry of unsaturated compounds lead to surprising results. For example, G. Bier demonstrated that fumaric esters with long chains show a higher viscosity number than the corresponding derivatives of maleic esters. Research on polyenes* showed that every additional double bond in a long chain causes a certain increase in viscosity (129, 144). A similar increase in viscosity is also caused by phenyl groups being linked in the chain, or at the end of it. The increase in viscosity due to the presence of a phenyl group approximately corresponds to that caused by the presence of two double bonds (130,131,144). Similar results were obtained in the case of naphthalene derivatives with long paraffinic chains. These and other results were unfortunately destroyed in the fire during the war in the Freiburg Institute in 1944. By viscometric investigations on low molecular compounds, it becomes evident that a higher chain length results in a higher viscosity number.

*

These investigations were supported by the aid of colleagues Paul Karrer (Zurich) and Richard Kuhn (Heidelberg), who provided valuable polyenes for us (129).

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Therefore, it can be understood that compounds with double bonds in linear macromolecules are more stretched in solution than those with only saturated atoms in the chain. It seems obvious that the viscometric length* of linear molecules in solution is not identical with their length calculated by X-ray diffraction* in a crystal, but is smaller (144). Therefore, it was assumed that chain molecules of saturated paraffin derivatives in solution are more or less folded. On the other hand, chain molecules containing double bonds are stiff and resist deformation. We spoke of the folding rather than coiling (as assumed by W. Kuhn), of the linear chain molecules. These chain molecules in solution were compared with elastic, vibrating, thin-glass filaments instead of randomly coiling wool filaments, which are able to take any shape. The basis for this assumption is .that there is not sufficient freedom of rotation available for simple bonds in stretched-out molecules, but that a linear molecule has a definite shape in solution too. Thus, the molecules of acid anhydrides in solution, according to the results of viscometry, have approximately the same shape as paraffinic carbonhydrides with the identical number of chain elements. Isomorphy is very frequent in organic compounds and the shape of the molecules in several isomorphic forms varies a little bit. Experiments with W. Kern investigated saturated organic compounds with long chains which had well-defined isomorphic shapes. The problem was to discover whether differences in the viscosity possibly appear in the solution of these isomorphic compounds which would indicate different shapes in solution. These experiments were inconclusive however. The folding of molecules depends on two factors: first, parts of a chain molecule attract each other by van der Waals forces, which results in folding and shortening of these molecules in solution. As a result one should expect chain molecules to contract to a nearly spherical shape when they are in the gaseous state. Therefore, we tried to evaporate higher molecular paraffins, e.g., triacontane and hexacontane, in vacuum and cool them rapidly to - 180°C, hoping to get solid paraffins in the amorphous state. However, these experiments, which were carried out in quartz containers, yielded a microcrystalline and not an amorphous powder. Secondly, this coiling (Verknauelung), which is assumed for chain molecules in the gaseous state, is opposed in solution by solvation through solvent molecules. As a consequence, the molecule attempts to assume a form as stretched out as possible. R. Signer [Trans. Faraday Soc., 32, 305 (1936)] pointed out that single monomer units of a chain molecule

* These terms were suggested by R. Signer.

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would withdraw from each other by diffusion as far as possible if they were not held together by primary valence forces. This tendency to stretch also exists in chain-molecules. Therefore, the viscosity in a good solvent is higher than in a poor one (117). I intended to extend these viscometric investigations to compounds with cumulated double-bonds,* but due to the low solubility of these compounds viscometric measurements were only possible in highly dilute solutions. These experiments, undertaken by H. Batzer, have not led to a welldefined result. Therefore, one can evaluate many problems .concerning the shape of the molecule by undertaking viscometry measurements in solutions of uniform low molecular compounds with a well-defined structure. Such investigations are presently being carried out in many laboratories. References 123-151 are relevant.

2. VISCOMETRIC INVESTIGATIONS ON SOLUTIONS OF LINEAR MACROMOLECULAR COLLOIDS AND ON FLOW BIREFRINGENCE As mentioned above, investigations in the laboratory in Zurich and later in the Freiburg Institute resulted in the statement that there are definite relationships between the molecular weight of linear macromolecular substances and the viscosity of their solutions. This was also shown with natural rubber, the constitution of which at that time was not yet known. A paper with H. F. Bondy in 1929 pointed out that "It is interesting that here (in the case of natural rubber and its derivatives)

relationships between molecular weight and viscosity appear."

Investigations with W. Heuer in 1930 (122) on hemicolloidal polystyrenes of molecular weight 2000-5000 showed that the viscosity of equally concentrated solutions changes proportionally with the molecular weight in the following manner:

For the concentration c the proportion of 1 mol/1 was used (grundmolare Losung). Later on this relation was formulated as:

where the concentration c is 1 g per liter and n is the number of chain

* These were generously

provided by my colleague Richard Kuhn (Heidelberg).

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elements in the main chain. The proportionality factor Kaqu of hemicolloidal polystyrenes at 1 x 10-4 had nearly the same value as that of lowmolecular normal paraffins, which, in accordance with experiments simultaneously done by R. Nodzu (123) averaged 0.9 x 10-4 • At that time, it was surprising that the relationships between the viscosity of low molecular compounds with well-defined constitution and their molecular weight were approximately identical with those of polystyrenes, the structure of which was still questionable at that time, as discussed in Chapter 1. This gave new evidence for the assumption that colloidal particles in the solutions of these polystyrenes are molecules with the same linear structure as those of normal paraffins. The relationships obtained between chain length and viscosity were therefore designated as the law of viscosity. In further investigations on cellulose and its derivatives from 1930 to 1940, it was found that viscosity also increases proportionally with the degree of polymerization. The same relationship was also assumed for synthetic high polymers based on the investigations with G. V. Schulz on polystyrenes in 1935 (105). However, according to these investigations, polystyrenes polymerized at different temperatures have different Kmvalues. It was concluded that the constitution of these polystyrenes differs if conditions of preparation change. But during the fractionation of these various polystyrenes it became evident that for the fractions obtained from the same product the same relation as for hemicolloids holds, i.e., a proportionality between the viscosity number and the molecular weight. This result obtained with polystyrene first gave the impression that deviations from the simple viscosity law, which were also found in other synthetic polymers, e.g., polyvinyl acetates, polymethyl acrylates [investigated by H. Warth in 1938 (279)], or in polyvinyl chlorides [elaborated with J. Schneiders (293)], are based on the branching of the macromolecules. Then, in a paper published in 1941, R. Houwink [J. Prakt. Chem. N.F., 157, 15 (1941)] pointed out that the results obtained in the latter investigations are in good correspondence with the viscosity relation, which was evaluated by W. Kuhn [Kolloid­Z., 68, 9 (1934); Angew. Chem., 49, 860 (1936); Helv. Chirn. Acta, 26, 1394 (1943)] for coiled macromolecules: The validity of this equation was verified by H. Batzer between 1946 and 1950 for solutions of polyesters with polymer uniform threadlike molecules of well-known constitution (ref. 347, and seep. 192). Later on in 1956, W. Hahn demonstrated by the reinvestigation of the

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work done in 1935 on polystyrene (105) that the results obtained for polystyrenes, which were prepared at different temperatures, were not correct: actually, the relation between the degree of polymerization and the molecular weight for polystyrenes prepared at different temperatures is always the same (152). The statement that solutions of chain molecules, low molecular as well as linear macromolecular substances, do not obey Einstein's law, had farreaching consequences, as it was now possible to understand the somewhat strange highly viscous nature of polymer solutions, which was earlier explained, for example, by K. H. Meye and H. Mark, in terms of a strong solvation of dissolved micelles. According to Einstein's law, the viscosity of equally concentrated solutions of spherical particles is dependent on the total volume of the dissolved particles, regardless of whether these consist of smaller or bigger particles, i.e., molecules. But with substances with linear chain molecules, the viscosity of equally concentrated solutions increases with the length of the chain molecules. If one tries to relate this to Einstein's law, one must assume that the volume of the dissolved particles effective for the viscosity in a solution is not identical with their original volume, but increases proportionally with the length of the chain. In other words, linear chain molecules require a bigger volume in solution than would correspond to their original volume, whereas in the case of spherical particles the effective volume for the viscosity is identical with their original volume. With this large sphere of action required by the dissolved linear chain molecules, which increases proportionally with their growing length, a new state of solution results which is characteristic for linear macromolecular substances: the state of the gel solution. This is an intermediate state between the solid body and its solution, which is character­ ized by the fact that dissolved chain molecules of a linear macromolecular substance are solvated, but are not able to move unhindered in their solution due to their length. These ideas were published in several papers, first with F. Freudenberger (see ref. 121, p. 2339) and in further publications (73,82,117,158, 162). It is remarkable that this essential result of my work is not much considered in later literature. This may be due to the fact that no exact statement could be made on the viscometric length of linear molecules at that time, contrary to their calculated length in the solid state by means of X-ray diffraction measurements. This viscometric length is dependent on the internal mobility of linear molecules and changes from solvent to solvent according to their solvation.

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With linear macromolecular substances with chain molecules, for which the simple viscosity law formulated by the author is valid, one can approximately estimate the point at which a sol solution with free mobile molecules turns into a gel solution with molecules hindered in their free mobility. This critical limit concentration (Grenzkonzentration) decreases proportionally with the length of the linear macromolecules. In solutions with very long molecules, this concentration is far below 1%. Therefore, highly viscous solutions, 1% or more, e.g., of high polymeric cellulose nitrates, polystyrenes, and natural rubber, are not anomalous states but are gel solutions. The nonproportional increase of the viscosity with concentration in this range is caused by the mutual hindrance of chain molecules in solution. This phenomenon is also responsible for the fact that the osmotic pressure does not increase proportionally with the concentration, whereas this proportionality is observed in solutions with spherical molecules (106). The transition from gel solutions to the real gels occurs continuously. In this gel state, molecules are solvated too, and therefore the material is swollen. A gel is relatively resistant to deformation. By the addition of a solvent, gels can be transferred into gel solutions and finally after further dilution into sol solutions. But if in such an unlimited swellable gel (like polystyrene) some of its chain molecules get connected by crosslinks, the product becomes a gel, the swelling of which is limited. Thus, although the chain molecules are still solvated, they cannot be dissolved any more. Such a gel with crosslinked macromolecules is very resistant to deformation (see Fig. 1, p. 296), as was demonstrated with W. Heuer in 1934 (213,215). At the beginning of the investigation on colloidal solutions of linear macromolecular substances, a further serious difficulty had to be overcome. Several scientists (e.g., W. R. Hess and W. Ostwald) found out that it seems impossible to measure exactly the viscosity of such colloidaL solutions, because it changes with the measurement conditions. Thus, a solution containing chain molecules and subjected to a high flow rate is less viscous than a solution with a low flow rate. Consequently, these solutions do not obey the Hagen-Poiseuille law. In 1929 an investigation with H. Machemer resulted in the statement that these anomalous phenomena are connected with the orientation of the linear chain molecules in the flowing solution (I57). This orientation appears more and more, as the chain molecules increase in size. In this field very extensive work was done by W. Heuer from 1930 to 1932 (cf. ref. 15, p. 193). His investigations,

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as well as those of M. Sorkin (169), on solutions of cellulose nitrates showed that the orientation of linear macromolecules for a very lowvelocity gradient is so small that one can compare such solutions with respect to their viscosity with those of low molecular substances consisting of chain molecules. In the latter, there is either no orientation of the chain molecules at all, or a negligible small one due to their free mobility. Furthermore, it was demonstrated that these deviations from the HagenPoiseuille law are less pronounced in very dilute solutions than in concentrated ones. Eventually, in cases of diluted solutions with chain molecules of a length below 2000 A as determined by X-ray diffraction measurements, one can neglect these deviations if the measurements are carried out on solutions with a low viscosity, i.e., where

and with a small velocity gradient q. But in solutions with long chain molecules, one has to extrapolate to a limit value at the velocity gradient q = 0. Thus, the following equation holds for such solutions:

The insight into this apparently difficult field of non-Newtonian solutions was simultaneously deepened by investigations of R. Signer in Freiburg on flow birefringence of linear macromolecular substances. Here is could be shown that the orientation of molecules in a flowing liquid becomes stronger with increasing length of the chain molecules, e.g., polystyrenes (153-155). Later on, a number of investigators, e.g., B. W. Philippoff ( viskositat der Kolloide, Verlag Steinkopff, Dresden, 1942), were engaged in the problem of the particular behavior of solutions of linear molecules with respect to their viscosity. The fact was overlooked that basic statements already had been n1ade as a result of the work, mentioned above, which was carried out between 1929 and 1932. This may be due to the fact that one of the most important investigations, carried out at that time by W. Heuer, appeared in a rather small-edition book published in 1932 by Springer (15).

These phenomena were termed "macromolecular viscosity phenomena," because they are not accidental properties of the colloidal state, but are related to the macromolecular constitution of the material (see refs. 29,70,76,80,82, 105,112,117,120,122, 156-179).

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3. THE VISCOSITY OF HETEROPOLAR LINEAR MACRO­ MOLECULAR COLLOIDS (POLYELECTROLYTES) As ·mentioned on p. 123, W. Ostwald pointed out in 1919 the essential differences in the viscosity of low molecular and colloidal solutions, e.g., the fact that additives influence the viscosity of colloidal solution. These statements were based on experimental observations of protein solutions which are colloidal solutions of heteropolar molecular colloids (cf. W. Pauli and E. Valko, Kolloidchemie der Eiweisskorper, Steinkopff, Dresden, 1933, Chap. 15). The behavior of these colloidal solutions is far more complicated than that of solutions of homopolar molecular colloids. At the beginning of the 1930s, polyacrylic acids were investigated as a model together with E. Trommsdorff (cf. ref. 15, p. 333). In this investigation on low-polymeric and higher-polymeric polyacrylic acids by means of viscometry, it was shown that abnormal viscosity phenomena are more pronounced in the case of the higher polymers. The viscosity of sodium polyacrylate is particularly high compared with those of equally concentrated solutions of homopolar molecular colloids with the same chain length (Zn = 0.07 for solutions of polyvinyl alcohol with average degree of polymerization ≈ 1000, Zn ≈ 40 for solutions of sodium polyacrylate with the same average degree of polymerization). Solutions of polyacrylic acids and their salts show further fundamental differences compared with those of homopolar linear colloids: the nsp/c values of polyacrylic acid in water are very high in very dilute solutions; with increasing concentration they first strongly decrease, then increase again at higher concentrations. Moreover, nsp/c values of polyacrylic acid strongly increase when sodium hydroxide is added up to pH 7, and decrease finally. After a sufficient addition of sodium hydroxide, the nsp/c values remain constant for the same concentration. An essential result of these earlier investigations is that solutions of sodium ,Polyacrylate after the addition of sufficient sodium hydroxide show the identical behavior with respect to viscosity as solutions of homopolar chain molecules do. Therefore, in 1932 a statement in the paper on cellulose was made with 0. Schweitzer (see ref. 15, p. 477): "Actually, on the basis of our measurements the circumstances are simpler: if one uses an excess of Schweizer's reagent, the formation of Clusters between the threadlike ions will be avoided; solutions of the heteropolar molecular colloid behave under these conditions like those of homopolar ones. Therefore, one obtains the same simple relation between viscosity and chain length as

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with cellulose acetates if one compares the viscosity of solutions of different celluloses with a large excess of Schweizer's reagent."

This result is important for the determination of the degree of polymerization of cellulose in Schweizer's reagent. The deviations of solutions of sodium polyacrylate from the HagenPoiseuille law were remarkable. They are considerably higher than those of equally concentrated solutions of homopolar linear molecular colloids with the same degree of polymerization. Again, one can see that these considerable differences disappear after sufficient addition of a base. Therefore, these anomalous phenomena in solutions of polyelectrolytes were termed "polyionic viscosity phenomena." To explain these phenomena it was assumed in the work mentioned above (15) that the formation of clusters occurs in the same manner between long threadlike ions of the polyacrylic acid and the low-molecular cations as it occurs in solutions of low-molecular salts. This formation of clusters causes something like a structural formation between long threadlike ions and the low-molecular cations. This process is disturbed more or less through the flow of the liquid, so that these striking phenomena of viscosity are reduced. Further investigation on the viscosity of heteropolar molecular colloids was carried out by W. Kern and resulted in the possibility of distinguishing between two factors being responsible for the specific viscosity of solutions of these substances: the ionic factor, determined in its extent by the H + activity, and the macromolecular factor, determined by the length of the linear macromolecules of the dissolved material (180). Later on, W. Kuhn and also A. Katchalsky worked thoroughly on polyacrylic acid and other heteropolar molecular colloids. It could be demonstrated that threadlike ions fully extended in the neutral state fold up when acids or bases are added, and that this was the reason for strong changes in viscosity. In these investigations on the viscosity of heteropolar molecular colloids, the formation of clusters is not taken into account, although probably both factors, formation of clusters and the folding or unfolding of longer molecules, influence the phenomena of viscosity. Finally, F. Zapf demonstrated in an investigation on glycogen xanthogenates (183) that anomalous phenomena with respect to viscosity appear only in the case of linear macromolecular substances. The viscosity of solutions of these spherical macromolecular products does not show abnormal properties but behaves with respect to their swelling like other spherical macromolecular substances.

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4. VISCOMETRIC INVESTIGATIONS ON SPHERICAL COLLOIDS The suspensoids and emulsoids belong to the class of spherical colloids. In 1935 it was demonstrated (76) by viscometric measurements on organic spherical and linear colloids that not only gummigutt suspensions [M. Bancelin, Compt. Rend., hebd. Acad. Sci., 152, 1382 (1911)] but also suspensions of natural and synthetic latexes behave in accordance to Einstein's law of viscosity. This means, in other words, that in all cases Zŋ = K. Accordingly, K has the approximate value 0.0025 as calculated by Einstein, since the solvation of these spherical compact colloid particles can be neglected. For the globular protein ovalbumen the same value for K by viscometry was obtained by conversion of the viscosity measurements of F. Loeb. Consequently, it has to be assumed that this protein exists in the form of compact spherical particles (cf. ref. 73, p. 218). Until that time spherical colloids with particles which are macromolecules were not frequently observed. Investigations in 1937 with Husemann (182) demonstrated through polymer analogous reactions that colloidal particles in solutions of glycogens are macromolecules. By degradation of these glycogen molecules, a polymer-homologous series of glycogens was obtained. The highest member of this series had a molecular weight of 1,530,000, and the lowest had one of 20,300. The viscosity numbers of these polymer-homologous products were the same although the number of the molecules in solutions of glycogen with the highest molecular weight was 75 times smaller than that of the lowest molecular weight. This is an excellent example of Einstein's statement that the viscosity of solutions with spherical molecules is only dependent on their total volume, and not on their number, except that in this case the constant of Einstein's law is approximately 5 times higher than the value calculated by Einstein for unsolvated, spherical particles. This is due to the fact that large amounts of solvents are bound by solvation in the interior of the strongly branched macromolecules of glycogen. It was also interesting that hydrophobic glycogen acetates behave in a completely identical manner, as do hydrophilic glycogens. Further investigations with F. Zapf on aqueous solutions of polymerhomologous glycogen xanthogenates proved that these products obey Einstein's law and show no deviation from the Hagen-Poiseuille law even though they are electrically charged. This is contrary to the behavior of heteropolar linear macromolecular colloids, e.g., cellulose xanthogenate. It is remarkable that the K-values for solutions of glycogen xanthogenate

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are lower than those of the glycogen acetates; the spherical molecules of the xanthogenates must be more compact than those of glycogen or the glycogen acetates. Investigation on spheromacromolecular substances was particularly instructive in respect to the influence of the shape of macromolecules on the viscosity of their solutions. These results were published in a series of papers (76,181-183).

8 Macromolecular Substances in the Solid State

1. X-RAY DIFFRACTION MEASUREMENTS

Through the work of M. Brunner (258) and S. Wehrli (259) in the laboratory in Zurich it was demonstrated that the great differences in the physical properties of several polystyrenes in the solid state is caused by differences in the degree of polymerization rather than those of a micellar structure: the lower molecular polystyrenes, with molecular weights of 2000-10,000 and termed hemicolloids at that time, are powdery and can be dissolved without swelling, whereas high molecular polystyrenes, with molecular weights of 100,000 or more, represent eucolloids; they are tenacious glasses which form elastic properties when heated above 120°C. The following ideas on X-ray diffraction investigations of polystyrenes were pointed out in a book published in 1932 by Springer (ref. 15, 164165): "When we started the research, the crystalline structure of high molecular substances was not known yet. We assumed at the beginning that polystyrenes would not be crystalline, since they consist of a mixture of polymer homologs, and it is well known through experience in organic chemistry that mixtures of compounds crystallize much less readily than the pure compounds. Therefore, we tried to obtain products as uniform as possible, hoping to get them crystallized by frequent fractionation of mixtures of polymer homologs. In this manner we hoped to be able to crystallize them. But, according to the result of X-ray diffraction, we never succeeded in obtaining crystals. Then the crystalline structure of polyoxymethylenes and polyoxyethylenes was determined, and, with these examples, it could be demonstrated that even material consisting of a mixture of polymerhomologs can be crystallized. The crystallizing ability of high molecular organic compounds, which consist of chain molecules, does not so much depend on the uniform length of the chain molecules, as on

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the uniform structure of the single chains. In this case, the chain molecules can be packed to a crystallite-like a bunch of wooden rods, unequal with respect to their length, but equal with respect to their structure. This holds for the examples mentioned above, and also for gutta-percha. On the other hand, the chain molecules of polystyrene are built up irregularly, since their single monomer units when linked together can form a large number of diastereoisomers as shown in the following formula. Such asymmetric molecules are not able to crystallize."

Common polymerization products of styrene are therefore atactic compounds. This very suitable term was given by G. Natta. On the contrary, the isotactic polymers discovered by Natta are crystalline (see p. 152). In contrast to atactic polystyrenes, polyoxymethylenes crystallize readily. As pointed out in Chapter 1, p. 84, at the beginning of the 1920s it was stated in the laboratory in Zurich that polyoxymethylenes are built up of long chain molecules. Then, in 1926-1927, this polymer was investigated by J. Hengstenberg in the Physical Institute of the University of Freiburg under Geheimrat G. Mie by X-ray diffraction. They showed that all polyoxymethylenes, even the seemingly amorphous powder, are well crystallized. Since their unit cell is small, it could be concluded that one chain molecule stretches out through a series of unit cells: "The crystalline structure built up out of small unit cells is realized in these crystalline high polymers because the single molecules exhibit, so to speak, the principle of a crystal by showing a periodically recurring arrangement of small groups of atoms" (see ref. 184, p. 201).

This result, as mentioned above, refuted an important argument for the assumption of a low molecular structure of cellulose and other macromolecular substances (7,184). Degraded crystallized polyoxymethylene diacetates were then split up by R. Signer during a long fractionation into uniform polyoxymethylene diacetates containing 4-17 molecules of formaldehyde per chain (86). Xray diffraction investigation of these products by J. Hengstenberg showed that they crystallize like other low molecular, uniform substances with chain molecules, e.g., fatty acids with long chains in a molecular lattice [cf. S. Hengstenberg, Ann. Physik, 84, (4) 245, (1927)].

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Higher molecular polyoxymethylene diacetates also crystallize, although they consist of an inseparable mixture of polymer homologs, i.e., macromolecules with different chain lengths. For this kind of crystallization the term "macromolecular lattice" was suggested (in a paper with R. Signer) to characterize the peculiarity of this crystallization, since in this case, "no plane boundary can be formed as is possible for crystals of molecules with equal lengths; but with macromolecules some will be somewhat longer, and others will be shorter" (ref. 184, p. 205).

Another polyoxymethy!ene prepared by R. Signer had a fiber structure (see :figures, p. 145): "These fibers show a fiber diagram in X-ray measurements as do cellulose fibers. This is the first synthetic fiber built up from small structural elements" (ref. 184, p. 209).

A discussion arose with E. Ott, who also had worked with these products, on the structure of the polyoxymethylenes determined by means of X-ray diffraction, [cf. Helv. Chim. Acta, 11, 300 (1928)]. He interpreted his results on the assumption that these substances were built up by small molecules, which was in accord with the conceptions of P. Karrer at that time. We summarized our results in ref. 185. The term "macromolecular lattice" was taken over by 0. Gerngross, K. Hermann, and W. Abitz [Biochem. Z., 228 409, (1930)] under the name "fringe micelle" (Fransenmicelle). The difference was that in such a micelle macromolecules were supposed to be only partially ordered in a crystalline lattice, whereas the overhanging ends were not stiff, but behaved like "amorphous" fringes. X-ray diffraction investigations by P. H. Hermans [compare, e.g., Makromol. Chem., 6, 25 (1951)] indicate that cotton fibers consist of 70% crystalline and 30% amorphous cellulose, whereas in regenerated cellulose fibers the amorphous part is much higher. Today it is generally believed that in these amorphous parts of the cellulose fiber the molecules are not crystallized. Therefore, these amorphous parts of the cellulose fiber should be more reactive than the crystallized parts in which the cellulose molecules are closely packed. But this is in contradiction with results obtained in experiments on inclusion celluloses, which are dis- cussed on page 146. Therefore, in a paper on the micellar or macromolecu- lar structure of cellulose the following opinion was assumed (ref. 208, p. 182): "According to X-ray diffraction observations, one part of the chains in the cellulose fiber is crystallized and the other part is amorphous. Since no

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difference in the reactivity of crystalline and amorphous parts can be stated, both must show the same principle of structure. This leads to the assumption that crystallites in the crystalline areas of the cellulose fiber have such dimensions that they can be identified by means of X-ray diffraction, whereas their diameter in the amorphous areas is too small to permit their detection. From the idea of the macromolecular lattice arises the possibility of describing such macro- and micro-crystalline, i.e., 'X-ray crystalline' and 'X-ray amorphous,' areas of cellulose in the solid state as well as explaining the phenomena of inclusion and the manner of acetylation already mentioned in this investigation. This assumption of an analogous nature, but with different dimensions of crystalline parts in solid cellulose also explains that the crystalline portion in regenerated celluloses is much smaller than in native ones: during the precipitation of cellulose out of solution, numerous crystalline nuclei are formed due to the great tendency of the long chain molecules to cohere. Therefore, the cellulose in solution is consumed before bigger crystallites can be formed. The theories of F. Haber [cf. Ber., 55, 1717 (1922)] give further explanation for this. He pointed out that the tendency for the formation of crystallized colloidal particles is dependent on the velocity with which a gel, separated from a sol solution, turns into the order of a lattice, which means that this formation is dependent on the rate of orientation (Ordnungsgeschwindigkeit). On the other hand, the rate of formation of nuclei (Haufungsgeschwindigkeit) prevents the growth to bigger crystallites thus, a precipitate may appear amorphous" (cf also ref. 73, p. 198).

The question as to whether in these amorphous parts of the solid cellulose fibers the macromolecules are loosely folded and therefore do not crystallize, or whether they are parallel in order as is assumed for crystalline parts, has not been answered to date. In 1955 and 1956, H. Krassig carried out experiments in Freiburg to clarify whether hydroxy groups in amorphous parts of cellulose will be substituted faster than in crystalline areas. However, no final decision in this field was possible after this investigation. The X-ray diffraction investigation started in 1926 was continued by E. Sauter between 1932 and 1937. He worked on fiber diagrams of cellulose, thus continuing the investigation of O. L. Sponsler and W. H. Dore [Colloid Symposium Monograph, 1926, 174; Cellulosechemie, 11, 186 (1930)]. Furthermore, he determined the lattice of crystalline natural rubber. The successful studies of E. Sauter described in a series of papers (I86-196) were interrupted in 1937 when he accepted a position in industry. Further research was done by E. Plotze and H. Person in the Physics Institute of the University of Freiburg i. Br. They demonstrated that it is

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impossible to determine the length of cellulose molecules by X-ray diffraction measurements (197-199).

2. MICROSCOPIC INVESTIGATION Microscopic investigation on macromolecules was carried out by M. Staudinger beginning in 1937. Common, polarized and ultraviolet light (the ultraviolet microscope was developed by A. Kohler) were first used; later on the phase-contrast method by F. Zernike and especially the electron microscope also were used. The electron microscope, obtained by support of his Excellency Schmidt-Ott, the president of the Notgemeinschaft der Deutschen Wissenschaft, was installed in the Freiburg Institute in the spring of 1942. It was one of the first electron microscopes of the Siemens-Schuckert Company of Berlin. Unfortunately, it was completely destroyed as was the Chemical Institute itself during an air raid on Freiburg on November 27, 1944. Thus, these investigations, valuable for the completion of pure chemical research on macromolecular substances, were interrupted for a long time. First, M. Staudinger investigated the polymer homologous series of polyoxyethylenes by means of microscopy. Before that, E. Sauter had done X-ray diffraction research on this series (331). As in many linear macromolecular substances crystallization in the form of spherulites is characteristic for polyoxyethylenes. This investigation on the polymer homologous series of polyoxyethylene showed that the size of the spherulites was dependent on the degree of polymerization: if the degree of polymerization increases, the number of spherulites formed becomes larger, whereas their size declines [cf. also Ordnungsgeschwindig­ keit und Hiiufungsgeschwindigkeit, F. Haber, Ber., 55, 1717 (1922)]. It was possible to draw a fiber at room temperature from a high molecular polyoxyethylene with a degree of polymerization of about 2000 (compare ref. 331 and p. 187). Microscopic investigation of this fiber showed that it has a typical fibrillar structure, which up to that time was only known for native cellulose fibers and was therefore looked upon as a bio structure grown in nature. The same fibrillar structure was also observed in polyoxymethylene dihydrate. Thus, it was demonstrated for the first time that a fibrillar structure is connected with a structure of linear macromolecules and does not represent a specific biostructure. For the same polyoxyethylene polymer homologous series, it could be stated that the capability to form fibrillar structures is dependent on the

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degree of polymerization: medium degrees of polymerization yield only short fibrils during deformation, whereas the lowest members of the series disintegrate to a crystalline powder (200,201). The processes of rearrangement of macromolecules going on here, in other words, the transition from the spherulite crystal structure to a fibrillar fiber structure, was the subject of further investigations. This phenomenon was studied using polyoxyethylenes, polyoxyundecanoic acids of high molecular weight (353), and polyamides. As set forth in the following quotation, it turned out that the needles of spherulites and the fibrils of fibers have completely different structures·(cf. ref. 18, pp. 122-123): "Spherulites are optically negative with respect to their radius (na in the longitudinal axis of the "rays"). On the other hand, fibers and their structural elements, the fibrils, are optically positive (nr in their longitudinal direction). Since, according to X-ray diffraction investigations, macromolecules are ordered parallel to the longitudinal direction in the fibrils, they must be oriented in the transverse direction in the radii of the spherulites. This results from the opposite optical character of the rays of the spherulites and, on the other hand, the fibrils of the fibers. The "transition" from one crystalline structure to the other is possible if the melted substance is not allowed to crystallize without disturbance, but is moved, as is common during the production of synthetic fibers, e.g., polyamide fibers. Accordingly, not spherulites, but crystallized structures of very different forms arise: their longitudinal axis (in which na has its course) is perpendicular to the direction of the movement. But according to their optical character, macromolecules in them must be oriented parallel to the direction of the movement. Thus, the transition of the original rays of the spherulites to fibrils occurs by the former gliding apart completely along the axis of the linear macromolecules. This process is also dependent on the molecular weight; products with a low degree of polymerization disintegrate to a fine crystalline powder, whereas high molecular members of the polymer homologous series show clearly the phenomenon of "reconstruction" by the gliding apart of the crystals. In products with a very high molecular weight, the melted substance is extremely sticky: it spontaneously draws fibers, so to speak, by itself, with the macromolecules ordered parallel to the longitudinal direction in the fibres." (cf. also refs. 202 and 203). If one tries to find the conditions for the formation of a fibrillar structure starting from the opposite direction, i.e., the formation of a polymer homologous series by degradation of a linear macromolecular substance

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instead of a stepwise polymerization, then another picture is obtained. This is shown in the following quotation (see also ref. 204a, pp. 206-207): "In contrast to the polymer homologous series of polyoxyethylenes a constant picture is always observed under the microscope for native fibers, although their degrees of polymerization are very different. Thus, there was no difference between a ramie fiber with a degree of polymerization of 3000 and another one of 300, and the same holds for cotton fibers. Compared with the results for the polymer homologous series of polyoxyethylene this seemed to be surprising at first. Thus, it is of significance whether a polymer homologous series is obtained by synthesis or degradation. If such a series of products is obtained synthetically, then the specific macromolecular properties appear more strongly the higher the degree of polymerization of the synthesized material. If, on the other hand, a native fiber is degraded in a topochemical reaction, which results in a polymer homologous series of fiber celluloses, then this is not apparent at the beginning: all fibers investigated exhibit the characteristic fibrillar structure. This means that a naturally formed macromolecular structure is very stable. This structure is retained, even if the macromolecules of the natural product are degraded" (204a,204b). Investigation of polyoxymethylene dihydrate gave information about the possibility of building a structure which is based on the presence of a macromolecular lattice. This polymer is obtained by the slow polymerization of formaldehyde in aqueous solution with sulfuric acid as a catalyst. It has the shape of large hexagonal prisms of extremely high birefringence (,8-polyoxymethylenes according to Auerbach and Barschall, see p. 178). Like fibers, these crystals split up into fibrils. Macromolecules and crystals are formed simultaneously and grow together. We explained this in the following manner: "Macromolecules of insoluble polyoxymethylenes are formed in the solid state when single formaldehyde molecules become linked to the lattice of the crystalline nuclei and simultaneously are linked by covalent bonds, i.e., the process of polymerization occurs together with the growth of the crystals. Thus, synthesis and degradation of these insoluble polyoxymethylenes are topochemical reactions. The existence of macromolecules forming these polyoxymethylenes is connected to the crystalline state, since such large single molecules cannot appear either in the melted state or in solution: their stability is due to the strong forces of the crystalline lattice being effective between the single chain molecules" (see ref. 86, p. 166). "While the formaldehyde molecules in the crystal are linked by normal covalences in one direction to form long chain molecules, the long chain

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COMPOUNDS

molecules are connected with each other in the two vertical directions by the molecular forces of the crystal lattice" (ref. 184, p. 206). The same assumption was also made for cellulose (ref. 202, p. 50):

"The formation of polymeric molecules occurs simultaneously with crystal growth. This process can be called a polymerizing crystallization. Such a mechanism can also be assumed for native cellulose as the separation of the already formed linear macromolecules from a solution always yields products with a much smaller crystalline portion. On the other hand, an operation with long linear macromolecules is .difficult for the cell due to the increased viscosity produced by them. It is definitely simpler to synthesize the cellulose from small molecules directly in the wall of the cell simultaneously as a macromolecule and as a wall." Information was obtained on the regular structure of the slowly grown crystals of polyoxymethylene dihydrate by degradation with caustic soda solution or sulfuric acid (ref. 201, p. 413) as well as electron-microscope investigations by M. Ardenne and D. Beischer [Z. Physik. Chern. (B), 45, 465 (1940)]. Sulfuric acid dissolves the crystal, whereas caustic soda, which can only attack the end-groups of polyoxymethylene dihydrate, splits the crystals into slices. This indicates that the end groups of these macromolecules are located preferably in one and the same plane of the crystal (205). Further microscopic investigations involved the acetylation and nitration of cellulose (206-208). E. Husemann carried out electron-microscope investigations on fibers: in the case of fibers degraded by means of hydrolysis, considerable differences in the structure were shown between native and regenerated cellulose fibers. In 1943, beautiful pictures of fibrils, the first one of this kind, obtained with the aid of an electron microscope from cellulose which was wet-ground in a ball mill (209-211). The formation of fissures in fibers investigated by microscopy is reported in the chapter on cellulose (seep. 226 and figure, p. 145). A peculiar destruction of cellulose in fibers of decayed fish nets was investigated by means of microscopy after no considerable amount of degradation could be detected by chemical means This investigation showed that the fibers were attacked by microorganisms in a way that cellulose was degraded completely in some areas, whereas in other parts the original degree of polymerization remained intact and was sustained (212). For the microscopic investigation of wood, seep. 235.

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145

The first synthetic fiber. Polypxymethylene dihydrate crystals and their splitting into fibrils (magn. 200 x)

Cotton fiber degraded by acid, DP 350. Swelling in Schweizer's Reagent (magn. 400 x)

3. SWELLING AND INCLUSION Swelling, and especially unlimited swelling, is a transitional state between the solid and the dissolved state of a linear macromolecular material. In this respect the following was stated in a paper published in 1929 on polystyrene (ref. 252, p. 251): "A characteristic property of high polymers is swelling. In his monographs on swelling J. R. Katz [Kolloidchem. Beihefte, 9, 1 (1917)] thoroughly discussed the question of whether swelling could be attributed to the existence of large molecules. However, it had not been possible to demonstrate a relationship between swelling and molecular weight in the case of natural high molecular products, where swelling was thoroughly investigated, as neither the constitution nor size of the molecules were clearly elucidated. In the case of polystyrene, however, a demonstration succeeded for the first time in showing that swelling occurs only when a substance consists of large molecules. For several polystyrenes swelling is greater, the higher the average molecular weight. Since several members of the polymer homologous series are available here, one can also quantitatively evaluate the relation between swelling and molecular weight.

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Since, with increasing molecular weight the dissolution gradually changes over to swelling, it seems probable that swelling is not different from dissolution in principle. During the process of dissolution, small molecules are solvated and separated. With increasing molecular size, intermolecular forces also increase. Thus, the solvent cannot immediately dissolve single molecules, but first penetrates between the molecules, solvates them, and only after complete solvation do the molecules go into solution. This means, as already pointed out by J. R. Katz, that swelling is an intermolecular rather than an intermicellar phenomenon. Since swellable modifications require polystyrenes with an average molecular weight of about 100,000, one can assume that other high molecular substances which also swell, like natural rubber, proteins, cellulose derivatives, and starch, consist of very large molecules. On the other hand, swelling was never observed for average molecular weights of 3000-15,000, either in this or in other cases" (compare also ref. 70, p. 2903 and ref. 117, p. 143).

In the case of unlimited swelling, the solid material loses its original form, whereas a linear macromolecular product with limited swellability keeps its shape and enlarges only its volume by absorption of solvent. Limited swellability is based on crosslinkages between the linear chain molecules of macromolecular material, which therefore can still be solvated but no longer be removed by dissolution. This was first demonstrated for the copolymer of styrene and divinyl benzene: this polystyrene is an example of a polymer with limited swellability. The degree of swelling is dependent on the number of crosslinkages in the linear macromolecular substance. Swelling only occurs with lyophilic solvents (213-216). A peculiar type of swelling is inclusion, since in this case linear macromolecular substances are "swollen" by lyophobic and not by lyophilic liquids. The phenomena of inclusion in particular were studied with fiber materials, e.g., cellulose fibers, wool, and silk. Inclusion is obtained, so to speak, by a trick, for the fibers are first preswollen by a hydrophilic solvent like water. The cellulose fibers swell because the hydroxy groups bind the water by coordinative covalences, without dissolving the cellulose. Thus, this swelling of cellulose in water is also limited although there is no crosslinkage between the cellulose molecules by principal valences. Water imbedded in this manner with relatively loose bonds can be displaced by water-soluble organic liquids like alcohol, acetone, or pyridine. These liquids are then imbedded between the cellulose chains and sustain the swollen state, although they are not capable themselves of swelling cellulose. These water-soluble solvents can, in turn, be replaced by waterinsoluble, hydrophobic liquids like benzene, cyclohexane, petrol ether,

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carbon tetrachloride, or chloroform. Thus, it is possible to embed even hydrophobic liquids between cellulose chains, although they are not bound to them by secondary valences, but are only included. It is impossible to distinguish these indirectly swollen fibers from dry fibers, be they cotton or wool, simply by their outward appearance. Whether one can recognize qualitative and also quantitative differences bet\veen dry fibers and fibers including solvents by X-ray diffraction investigation could not yet be decided after the first measurements were carried out by W. Kast. It is also peculiar that the included liquids cannot be completely removed from the fibers, in spite of their high volatility, not even through remaining in vacuum at 60-80°C for a few days. In any event, 6-8% of the liquids remain included (see Table 6, p. 112). This observation has to be taken into account when linear macromolec_ular substances are purified, as is necessary for the preparation of analytical samples (see Chapter 5, Section 1). One of the most remarkable properties of fibers including liquids compared with dry fibers is their higher reactivity: dry fibers, for example, will be only incompletely acetylated by a mixture of acetic anhydride and pyridine, even after having been treated for many days at elevated temperatures, while included fibers can be acetylated relatively quickly with this mixture. The latter can penetrate the indirectly swollen fibers, whereas this is not possible in the dry fibers, since the coordinative covalences of the hydroxy groups between the single fibers cannot be broken. When indirect swelling was observed for the first time, it was reasonable to assume that the molecules of the liquid are imbedded mainly in the amorphous areas of cellulose and less in the crystalline ones. If this is true, differences in acetylation should be expected in such a way that amorphous areas are acetylated faster than crystalline areas. Actually, acetylation occurs completely homogeneously, as it had been shown in microscopy investigations with polarized light. It also was not possible to extract cellulose triacetate with a solvent from incompletely acetylated fibers. These results were not consistent with the general concept with respect to the structure of the cellulose, which assumes crystalline and amorphous areas. Therefore, the question was raised whether the crystalline and "X-ray amorphous" parts of the fiber have the same structure, and are only distinguished by different dimensions of their crystallites (208,217,506 and p. 140).

9 Polymerization

1. EARLY CONCEPTS For a long time it was known that some unsaturated compounds react after long storage or through the influence of heat or light, yielding products with the same composition but with differing physical properties. Such products generally were called polymer products. Early interpretations of the structure of these products were for the most part erroneous. J. Thiele [Liebigs Ann. Chem., 306, 92 (1899)], on the basis of his theory of partial valences, believed that polystyrene-called metastyrene at that time-is formed by the monomer by an assembling of the monomer molecules to larger particles due to the effect of partial valences. Such a concept could easily explain the thermal degradation of polystyrene and also the fact that the physical properties of the polymer are dependent on the experimental conditions during their formation. At that time, there was discussion as to what the process of polymerization was, as well as the question of whether polymeric products are formed by primary or secondary valences. Thus, G. Schroeter, using the example of low polymer ketenes, wrote [cf. Ber., 49, 2698 (1916)]: "The concept of molecular aggregates cannot be abandoned, which means that single molecules do not lose their autonomy in a complex. Molecules emit lines of forces as a result of all chemically active forces in their atomic groups. These forces of molecular valences have an independence from the atomic valences. Molecular valences enable single molecules to form a polymer molecule, i.e., a polymolecule."

When I started my first experiments in 1910 in Karlsruhe on the polymerization of isoprene to rubber, I met A. Kronstein who worked on the polymerization of chinese wood oil and its conversion into lacs. Kronstein 148

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pointed out [Ber., 35, 4150 (1902)] that two processes of polymerization have to be distinguished according to their outward appearance. In one case, e.g., the polymerization of styrene, a highly viscous material gradually is formed, a so-called isocolloid (see W. Ostwald: Welt der vernachliissigten Dimensionen, Steinkopff, Dresden, 1927, p. 138), which finally becomes the glassy polystyrene. In the other polymerization processes, e.g., that of liquid vinyl bromide, insoluble precipitates are formed during exposure to light, but no thickening of the monomer occurs, i.e., no isocolloid is formed. In my first publication on polymerization (1) I adopted the view that the formation and the properties of these products can be explained in terms of normal primary valences (see p. 78), and that polymers are true chemical compounds. Accordingly, I distinguished (ref. I, p. 1075) between real polymerization processes, which yield polymeric products with the same kind of atomic binding as that in the monomolecular compound, and condensation polymerization processes which occur with more or less pronounced shifting of the atoms. As concerns the differences in the course of a polymerization reaction, it turned out in the investigation of the polymeric products that in spite of a different outward appearance during the formation there is no fundamental difference in the constitution of the polymers. In both cases monomers are bound by primary valences, yielding polymeric chain molecules. The only difference is that polystyrene is soluble in its monomer, whereas polyvinyl bromide is not. An answer to that question was given by investigations carried out with E. Urech in 1925-1926 in Zurich on the polymerization of acrylic acid and acrylic ester. The latter behaves similarly to styrene-during the polymerization the liquid thickens and finally forms a glass. But during the polymerization of the acid, the macropolymer product separates from the monomer and no transitional low molecular weight polymers can be detected in the monomer (see p. 176). However, in both examples of polymerization processes mixtures of polymer homologs, not uniform materials, are formed. I have already pointed this out in my lecture in the Gesellschaft Deutscher Naturforscher und Arzte in 1926 (see ref. 5 and p. 86).

2. POLYMERIZABLE COMPOUNDS The difference in the capacity of unsaturated compounds to polymerize is considerable. This was investigated in the dissertation of E. Suter, published in 1920 (218). In this dissertation the addition of diphenylketene to ethylene derivatives, which had been investigated at that time

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(A 47), was compared with the ability of ethylene derivatives to polymerize. The result was that substituents can either increase the ability to polymerize, like the benzene group in styrene, or can also decrease it, as in the case of stilbene. The influence of substituents on the ability of a double bond to polymerize was thoroughly investigated later on by several scientists. In the following it is discussed why certain unsaturated compounds yield polymeric products consisting of a mixture of polymer homologs, whereas others form low molecular products such as dimers, trimers, and tetramers, which are generally uniform products. Table 8 gives some examples with respect to this problem.* Table 8 Polymerization of Several Double Bonds

*This table was taken from the manuscript for a textbook on macromolecular chemistry, which was supposed to be published in 1956 by Springer Verlag, BerlinGottingen-Heidelberg. My contribution was written in 1955.

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Great differences are observed when ketenes are polymerized. Dimethyland dibenzylketene yield derivatives of cyclobutane in a spontaneous polymerization, whereas dimethylketene in the presence of small amounts of tertiary bases such as trimethylamine yields polymers soluble as colloids with a higher molecular weight, the constitution of which is not known yet (seep. 16).

3. THE CONSTITUTION OF POLYMERS The polymerization of 'monosubstituted ethylene derivatives results in products in which the substituents in the chain are either in the 1,3position: (I)

or in the 1,2-position: (II)

This problem was already discussed in a paper published in 1927 (219) on polyvinyl acetate and polyvinyl alcohol. It was possible to demonstrate that for these polymers the monomers are linked with each other in the 1,3-position (formula I) (219). The constitution of polystyrene also corresponds to formula I (see p. 158) and it was believed that polymers generally have this structure. Later on this problem was discussed by C. S. Marvel in his books The Chemistry of Large Molecules (Interscience, New York, 1943, Chapter VII) and An Introduction to the Organic Chemistry of High Polymers (Wiley, New York, 1959). In the American literature, the term for the linkage corresponding to formula I is a "head-to-tail" polymerization, and that corresponding to formula II is a "head-to-head" or "tail-to-tail" polymerization. These terms now are often used in the German literature also. However, it seems to be more appropriate to maintain the clear chemical terms 1,2- and 1,3-substitution, as, for example, it turned out that the substituents in the chain of polypropenylbenzene are in the 1,4position (269,270). In the polymerization of monosubstituted ethylene derivatives, paraffinic chains with asymmetrical carbon atoms are formed in all cases. As a result the formation of stereoisomers can be expected, which was already pointed out in my book (see ref. 15, p. 114) published in 1932 (see alsop. 138).

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Therefore, these polystyrenes are amorphous and even their polymers with lower molecular weights cannot be crystallized. Recently, G. Natta succeeded in obtaining so-called isotactic and syndiotactic polymers by the use of Ziegler catalysts. In these polymers the substituents are regularly ordered. Their physical properties are often surprisingly different from the atactic polymers, in which the substituents are ordered irregularly. This work represents one of the most important steps in the progess of macromolecular chemistry. As to the further knowledge of the constitution of high polymers, it was first believed that they consisted of rings of very high molecular weight (23,220). This assumption was based on the result that no end groups could be detected in low polymeric products. It was later abandoned when it turned out that there is no difference in the relationship between molecular weight and viscosity for polystyrenes with low molecular weight which were obtained either with the aid of tin tetrachloride or by the heat degradation of a high polymeric product. A decision on the end groups of polymeric products should be obtained by an exact elucidation of the constitution of low polymeric products. Therefore, in 1928 N. J. Toivonen carefully fractionated hemicolloidal polystyrenes prepared with the aid of tin tetrachloride. In this manner he hoped to obtain uniform polymers of low molecular weight, the constitution of which could be elucidated. They could have subsequently been registered into the system of M. M. Richter, like other low molecular products. From such an investigation of low polymeric products, we also hoped to obtain more knowledge on the structure of higher polymers. These experiments were suggested by the successful fractionation carried out by R. Signer on polyoxymethylene diacetates which resulted in relatively high molecular uniform products with a degree of polymerization of 17 (86). There is a note on this work with N.J. Toivonen in the publication celebrating his 70th birthday (221).

4. MACROPOLYMERIC COMPOUNDS According to the definition given in 1920 in reference 1, real polymerization products are those in which a larger number of monomer units (base molecules, Grundmolektile) are connected with each other by principal (primary) valences without a shift in the atoms. According to this definition, such polymeric products can only be polycyclic compounds. However, a polycyclic structure could not be positively detected. On

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the contrary, end groups of chain molecules are differently constituted than the main part of the chain. Furthermore, it is also possible that there is branching and there are other "deviating" groups in such molecules. Nevertheless, we are still concerned with high polymers, even in the case of polyprenes and polysaccharides, such as cellulose, since they are mainly built out of identical monomer units (base molecules). Accordingly, the end groups of these macromolecules are still partially unknown. Furthermore, it is conceivable that foreign molecules are imbedded in cellulose, for example (seep. 229). Eventually, polycondensation products could also be termed polymeric compounds, e.g., the polyesters and polyamides elaborated by W. H. Carothers, since one and the same grouping is repeated in their chain molecules, although in this case also the end groups have a structure other than the chain elements. At the beginning I accepted the terminology common at that time. Thus, I called the first 200 publications on macromolecular compounds "Communications on High Polymeric Compounds." However, starting with the 200th publication up to the 446th, I published my papers with the title" Communications on Macromolecular Compounds." The latter is a more general term for these materials, since many macromolecular compounds, e.g., proteins, are not high polymers owing to their composition from various monomer units (base molecules). Nevertheless, high polymers are an important subunit of the macromolecular compounds. For a better characterization I suggested in 1947 that such polymeric products which have the size of macromolecules be termed macropolymers. These are compounds with a molecular weight of more than 10,000. In the case of macropolymer products with chain molecules the physical properties appear to be different from those of low molecular ones (cf. Table 3, p. 94). Furthermore, it is essential that the end groups in the chain molecules of macropolymeric compounds have no influence on physical properties due to the high degree of polymerization. Consequently, with respect to physical but not with chemical properties, end groups may be neglected in macropolymeric products (14). Nevertheless, macropolymers are connected with low polymers by gradual transitions. Today the appropriate term "oligomers" has become common for low polymeric products. 5. CATALYSTS (INITIATORS)

Owing to the influence of C. Engler's book Critical Studies on the Process of Autooxidation (Vieweg, Braunschweig, 1904), experiments were

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carried out with L. Lautenschlager from 1910 to 1912 in the Karlsruhe Laboratory on the relationship between the processes of autooxidation and polymerization. Thus, L. Lautenschlager demonstrated in his dissertation, which was submitted in 1913 in Karlsruhe, that unsaturated compounds polymerize faster in the presence of oxygen than in an atmosphere of nitrogen. Furthermore, peroxides like benzoyl peroxide, phellandrene peroxide, and diphenylethylene peroxide accelerate the polymerization, but not as much as pure oxygen. Therefore, it was believed that the primary products of autooxidation, not isolated peroxides, are responsible for the catalytic effect in which oxygen is asymmetrically bound (compare p. 34 of L. Lautenschlager's dissertation and p. 31, Part A). Stobbe's observation that aged polystyrene polymerizes faster than one just distilled was also explained in terms of the formation of primary peroxides as a catalyst (A134,222). In polymers prepared with peroxides as a catalyst (initiators), fragments of the initiators appear as end groups. Thus, W. Kern and coworkers studied, for example, the polymerization of styrene induced by bromo benzoyl peroxide as a labelled catalyst. They demonstrated that these catalysts inserted as end groups into the polymeric molecules (223) [cf. also W. Kern and H. Kammerer, Makromol. Chern., 2, 127, (1948). Uber den Einbau peroxydischer Katalysatoren in die Makromolekule von Poly­ merisaten bei der Polymerisation von Methacrylsauremethylester, Vinyl­ acetal und M ethacrylnitril].

6. CHAIN REACTIONS Macropolymers of a high molecular weight, e.g., polystyrene, are formed quickly by heating the monomers. Therefore, polystyrenes cannot arise by condensation polymerization, i.e., by the addition of one unsaturated molecule to another via hydrogen transfer as was first believed by G. S. Whitby and M. Katz [J. Am. Chern. Soc., 50, 1160 (1928)]. The reason is that the reactivity of the dimer or trimer is very low compared with that of the monomer. The formation of the polymer actually occurs in an entirely different manner, i.e. by a chain reaction. With reference to this, the following was stated in 1929 in a paper with E. Urech on polyacrylic acid (cf. ref. 224, p. 1111): "Furthermore, it can be concluded that the polymerization reaction does not start with the formation of the di- and subsequently the triacrylic acid

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from the monomer, but there is an activated single molecule to which numerous other molecules are added. The polymeric molecule can grow until it becomes insoluble in the monomer and therefore is precipitated" (224).

(Compare also the statement on p. 182 and the quotation in ref. 302 with H. W. Kohlschiitter, on page 176.) In the book on high molecular organic compounds (15), published in 1932, I made the following statements on page 150:

"The formation of synthetic high polymers of eucolloidal character, i.e., polymers with 1000 or more monomer units in a chain, occurs in a manner comparable with the chain reaction governing the chemical interaction of gases. For example, in the reactions of chloro-oxyhydrogen gas an activated molecule induces the reaction of about 105 other molecules by transferring the "activation" from one molecule to another. A similar reaction occurs here: an activated molecule induces the polymerization of numerous other molecules. These chain reactions differ in the fact that the result in the case of polymerization is a chain molecule." Further papers on this matter were published in 1935-36 (32a,32b,32c, 225). Chain polymerization was elaborated by several scientists, since by this time polymers such as polystyrene, polyvinylchloride, polyvinylacetate, and polymethacrylates had reached great industrial significance. In the laboratory in Freiburg, G. V. Schulz investigated extensively the kinetics of polymerization processes. He published, partially with several co-workers, primarily E. Husemann, many papers on this subject. He distinguished between the primary reaction (starting reaction), propagation (growing) and termination (break off) (226-241) (see also in ref. 16, Vol. 1, pp. 28-53, the contribution by G. V. Schulz, Die Entstehung makromolekularer Stoffe durch Polymerisation und Polykondensation. Thus, it was confirmed that polymerization is a chain reaction. However, as a result of further research, it turned out that the mechanism of polymerization is generally much more complicated than originally believed. Activated an9 therefore unstable radicals can be built into the growing chain, thus forming branched macromolecules. Therefore, polymer isomer

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products are often generated by the chain reaction, in which macromolecules are not only distinguished from each other by their length, but also by the manner of branching. Later on, W. Hahn and his co-workers did research in this field. He introduced new peroxides as initiators, namely, bifunctional initiators for the preparation of polymers with branched chains (242-246).

10 Synthetic Macromolecular Products

1. POLYMERIZATION OF CYCLOPENTADIENE As described on p. 148, G. Schroeter and others raised the question whether polymeric products are aggregates in which monomers are loosely connected with each other. This assumption was supported by the easily occurring disintegration of some polymers into monomers. Therefore, in 1922 an evaluation of the constitution of dicyclopentadiene was repeated in collaboration with A. Rheiner, since this compound yields cyclopentadiene easily when heated. H. Wieland [Ber., 39, 1492 (1906)] and H. Wieland and F. Bergel [Liebigs Ann. Chem., 446, 13 (1926)] reported, that the monomer is bound by primary valences in the dimer due to reactions with the dimer. This was also demonstrated by obtaining a saturated dimeric product through hydrogenation of dicyclopentadiene. The saturated dimer has a much higher thermal stability than the unsaturated compound. In 1924 in a publication with A. Rheiner it was pointed out that double bonds loosen neighboring carbon bonds. The disintegration of natural rubber to isoprene and that of hexaphenylethane to triphenylmethyl was cited as an example of this rule. The double bonds rule was later termed the rule of the allyl grouping (ref. 411, see p. 206). A. Rheiner (A156) and H. A. Bruson (247) obtained various higher polymeric products through the heating of cyclopentadiene: trimers, tetramers, pentamers, and an insoluble polymer, which, according to its melting point, has a relatively low degree of polymerization of about 67. All these polymers, as already emphasized by Kramer and Spilker, were considered to be cyclobutane derivatives. This opinion was based on a number of observations on ketene derivatives, for which an easy formation and the cleavage of four-membered rings was stated (ref. A63, see 157

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p. 66). Furthermore, X-ray investigations carried out by J. Hengstenberg [cf. Liebigs Ann. Chem., 467, 91 (1928)], and also chemical experiments by F. Bergel and E. Widmann [cf. Liebigs Ann. Chern., 467, 76 (1928)], supported this viewpoint. Later on, K. Alder and G. Stein demonstrated [Liebigs Ann. Chem., 485, 223 (1931); 496, 204 (1932)] that polymeric cyclopentadienes are formed via a Diels-Alder reaction. The considerations mentioned above on the cleavability of unsaturated polymers and on the stability of the products of hydrogenation are still valid with such a constitution. In an investigation with H. A. Bruson (248) it was found that the polymerization of cyclopentadiene with tin tetrachloride and similar catalysts yields different soluble, high molecular products. These polymers, having a degree of polymerization of 20-100, were supposed to have a constitution similar to that of natural rubber. Therefore, it was assumed that cyclopentadiene molecules are connected with each other in the 1,4-position, thus yielding long chain molecules. However, evidence for this constitution of rubberlike polycyclopentadienes is not complete, since oxidative degradation and that by ozone allows no conclusions in this respect. At that time the statement was important that polymers of different constitution can be formed from a monomer. This meant that an evaluation of the constitution of a polymer was necessary. H. A. Bruson investigated the efficiency of several metal halogenides as catalysts for the polymerization of cyclopentadiene (248; see also refs. A156,247,249-251).

2. POLYSTYRENE At the beginning of the 1920s in Zurich, when I started to investigate polystyrene in collaboration with M. Brunner and S. Wehrli, there was only a small amount of literature on this field. Of primary significance was the beautiful work of H. Stobbe and G. Posnjak [Liebigs Ann. Chern., 371, 259-286 (1909)] and H. Stobbe [Liebigs Ann. Chern., 409, 1-13 (1915)]. The polymerization of monomeric styrene induced by light and heat, in both the presence and absence of air was investigated with the following aim (p. 264 of the first paper): The first task was to clarify the true nature of the products of the polymerization and, if possible, to prepare a uniform and pure metastyrene." H

(As is well known, polystyrene had previously been called "metastyrene.")

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Since no double bonds could be detected in these polymeric products, the authors assumed a ring formula for metastyrene wi h the general formula (C8H 8)x, in which x was supposed to be larger than 5. Today, polystyrene is one of the most important plastics, and there is now very extensive literature on this field. I only mention two books: H. Ohlinger, Polystyrol, 1. Vol.: Herstellungsverfahren und Eigenschaften der Produkte, Springer, Berlin-Gottingen-Heidelberg 1955, 155 pages; R. H. Boundy and R. F. Boyer, Styrene, Its Polymers, Copolymers and Derivatives, Reinhold, New York 1952, 1304 pages. Hundreds of patents are mentioned in the latter. Since that time a lot has changed with respect to the scientific situation. Between 1924 and 1926 the polymerization of styrene was carried out under varying conditions, e.g., by the addition of catalysts like tin tetrachloride and by heating to elevated temperatures. Through investigation of these polymers it was shown that powdery, relatively low molecular products-at that time called hemicolloids-areobtained when polymerization is fast. These products dissolve without swelling, yielding a low-viscosity solution. On the other hand, slow polymerization yields hard, glassy products which swell and yield a highly viscous solution. Polymers from the slow reaction were called "eucolloids." Thus, polymeric products showed significant differences in physical properties when prepared under different reaction conditions. This early investigation on styrene turned out to be very successful for us since a complete polymer homologous series was obtained. Thus, the relation between chain length and physical properties, e.g., the viscosity of their solutions, could be studied. In 1929 the following was reported about this (ref. 252, p. 243): "Consequently, these are mixtures of members of a polymer homologous series, just as paraffin is a mixture of members of a homologous series. In a homologous series the physical properties change with the molecular size. The same holds for a polymer homologous series. Since all polystyrenes have the same principle of construction, the only question we have to answer is how big are the molecules on the average in order to explain the differences in the physical properties of the polystyrenes. There are no chemical differences between the several products, since they all have the identical principle of structure" (252).

Since a block of polystyrene gets soft and somewhat elastic after long heating at 120°C, polystyrene was regarded as the · model for natural

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rubber; but solutions of polystyrene are distinguished from those of natural rubber by their high stability. Therefore, investigations on the properties of colloidal solutions could be carried out best with polystyrene (156, 157). The relatively late publication (1929) of the results described in 1926 in the dissertation of M. Brunner and S. Wehrli is due to the fact that I had been very busy with the edition of the Tabellen der anorganischen Chemie [A209] during the first years of my residence in Freiburg. The students attending my lecture on inorganic chemistry needed this book. The postponement of the publications on polystyrene was disadvantageous since the work of K. H. Meyer and H. Mark who established a new theory on micelles according to C. Nageli, was published in 1928. This theory seemed to fit into the conceptions of the structure of macromolecules at that time much more easily than our interpretation on this matter. This gave rise to animated discussions (seep. 87). It had already been demonstrated during my work in Zurich that monomeric molecules with molecular weights of about 5000 in low molecular polystyrenes are connected to each other by primary valences. This was shown by the reduction of these polystyrenes with hydrogen under pressure in the presence of catalysts, yielding hexahydropolystyrenes. Thus, in this case, the same procedure was applied, and this permitted the evaluation of the structure of natural rubber by conversion of the material into hydrorubber (see p. 203). Unfortunately, it was not possible to convert high polymeric polystyrenes with a molecular weight of from 10,000 to 100,000 into polymer analogous hexahydropolystyrenes. Although hexahydropolystyrenes were obtained, the reaction products were considerably degraded. As easy degradation of polystyrene was known previously, the question arose as to whether monomer units in polystyrenes are connected with each other by primary valences. In 1924, a relatively simple answer, based on the rule for allyl grouping was found; this was published with A. Rheiner (A156, see p. 44). The rule states that a simple carbon bond is weakened if the adjacent bond is a double bond. Thus, an explanation was given for the easily occurring thermal degradation of polystyrene into monomeric styrene. The influence of the phenyl group on the cleavage of the bonds in the paraffinic chain can be easily understood if the phenyl groups in the chain are in the 1,3-position. This was demonstrated in 1935 by A. Steinhofer, now a member of the directory board of the Badische Anilin- und Soda-Fabrik, who was able to isolate substituted di- and trimeric degradation products after having cautiously decomposed polystyrene by heat (256).

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As expected, hexahydropolystyrenes (83,84) are much harder to crack, just as hydrogenated rubber possesses much higher thermal stability than natural rubber. The reduction of polystyrene was not investigated further, but this would be a worthwhile project. A reinvestigation could be interesting, as hexahydropolystyrenes could show valuable technical properties because of their stability. [See (253) H. Staudinger, Zurich, DRP 504,215 (St. 40,793), Kl. 12o, G. 25, of March 30, 1926 [Friedlander, 17,434 (1932)]: Verfahren zur Darstellung von hydrierten Polystyrolen und Polyindenen]. Initially, at the start of research on the constitution of polystyrenes, it was assumed according·to H. Stobbe that these are high-membered rings. This assumption was abandoned on the basis of experiments on the thermal degradation of eucolloidal to hemicolloidal polystyrenes and on the degradation of polystyrene by the rupture of its long chain molecules in a ball mill (68,69). Polystyrenes degraded by heat or by grinding yield products with properties similar to those obtained by polymerization with tin tetrachloride as a catalyst. At that time, I supposed that ring polymers must be different from chain polymers by their viscosity in solution. With the assumption that polystyrenes are chain molecules, questions on the nature of the end groups became especially interesting. Double bonds could not be detected, even in low molecular products. To obtain the characteristic end groups in the chain molecules of polystyrenes, W. Heuer treated higher molecular polystyrenes with bromine. Thus, we hoped to be able to characterize the chain molecules by determining the bromine atoms attached at their ends. However, it turned out that degradation had taken place (15). Recently, the nature of the degradation of polystyrenes by halogens was evaluated in an investigation by W. Hahn (152,296). Furthermore, W. Heuer treated polystyrene with potassium permanganate (15), in order to obtain carboxylic groups at the ends by cautious degradation. Since polystyrenes are remarkably stable against potassium permanganate in acetone, their degradation occurs only slowly. If the monoor dicarboxylic acids of polystyrenes were formed, they could have been characterized by the reaction of their acyl chlorides with phenylhydrazine. Unfortunately, these experiments were not successful either, since one obtains insoluble products from the reaction of polystyrene with thionyl chloride when it is pretreated with permanganate. The insolubility of these products was explained in terms of crosslinking by intermolecular ester groups (15). Later on, W. Kern and H. Kammerer succeeded in obtaining

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characteristic end groups in the macromolecules by the use of halogensubstituted benzoyl peroxides. Thus, determination of the molecular weight by chemical means was made possible (223,257). In the polymerization of a-methylstyrene, already studied by F. Breusch, the compound exhibits a different behavior in many respects from that of styrene. It is not converted into macropolymer products merely by standing or heating, but yields small amounts of unsaturated dimers after long heating. On the other hand, it polymerizes easily and vigorously with tin tetrachloride, yielding relatively low molecular products with a degree of polymerization of 2-8. These oligomers are saturated, i.e., rings are present (254). According to E. Bergmann et al. [Ber., 64, 1493 (1931)] the saturated dimer is a derivative ofhydrindene. Experience with the polymerization of a-methylstyrene does not exclude the possibility that in the course of the polymerization of styrene ring molecules may also be formed besides chain molecules. This problem has not definitely been solven to date, which actually means that the constitution of polystyrene, one of the most important plastics, is not exactly known yet. I have to refer to the papers already mentioned on page 155 concerning the formation of polystyrene by a chain reaction. Refurences15,68,74,83,84,87,97, 117,122,152, 156,157,223,and254264 deal with polystyrene. The idea that there is a polymer homologous series of polystyrenes in which the very high molecular weight members show eucolloidal properties, such as slow dissolution with strong swelling, seemed to contradict the fact that polystyrenes were found in industry at that time which seeme'd quite identical to soluble polystyrenes, but were, in contrast, insoluble and only swellable to a limited degree. Nevertheless, the composition of both products was identical according to elemental analysis. It was already known that soluble natural rubber, from which anticatalysts were removed by reprecipitation, is converted into an insoluble product when exposed to air, in other words, to a material with a limited swellabi1ity. The conversion from natural rubber with limitless swellability into one which only swells to a certain extent was explained in 1931 in a publication with H. F. Bondy (424) in terms of a linkage of unsaturated chain molecules through single oxygen atoms. Such an explanation was not possible for the formation of insoluble polystyrene since soluble polystyrene does not form an insoluble one under the influence of air, even when exposed to it for a long time. It

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also was not probable that saturated paraffinic chains of polystyrene could be subsequently linked with each other by secondary reactions. Therefore, the formation of an insoluble polystyrene should be caused by the presence of another compound in monomeric styrene, which forms linkages between the chains during the polymerization of styrene. This problem was investigated in 1933 with my co-worker W. Heuer, who unfortunately died young. He checked the effect of several additives, mainly phenylacetylene, on the polymerization of styrene, but without success. During a conversation with director G. Kranzlein in Hoechst I heard that polystyrene-is prepared from ethylbenzene, which was obtained from benzene and ethylene in the presence of aluminum chloride. Now, I supposed that, besides ethylbenzene, small amounts of diethylbenzene also are formed in this condensation, which yields divinyl benzene through the process of dehydrogenation. Consequently, W. Heuer prepared p-divinyl-benzene and used it as an additive-and thus the material was found which causes the formation of a network in styrene through crosslinking. Since an extremely small amount (0.01% or less) is sufficient to cause crosslinking, these traces could not be detected in styrene at that time. A patent was granted for this method of preparing an insoluble polystyrene, which was taken over by IG Farben-industrie Hoechst. However, I was informed it did not find technical application (265). Later on, however, I heard that this procedure attained some significance because of the possibility for increasing the viscosity of relatively low molecular polystyrene by the addition of very small amounts of divinylbenzene (213-215).

3. POLYINDENES, POLYANETHOLES, POLYPROPENYLBENZENES, POLYVINYL CARBAZOLS At the beginning of the 1920s, a series of experiments was undertaken in order to polymerize indene and anethole. These compounds were commercially available, whereas at that time monomeric styrene had to be prepared in the laboratory and therefore was not available in large quantities. In comparison to styrene, indene and anethole polymerize in a different manner, i.e., at low temperatures or after heating without a catalyst, and do not yield eucolloidal products. On the other hand, pmethoxystyrene behaves like styrene according to experiments carried out by H. Stobbe and K. Toepfer [Ber., 57, 484 (1924)], and it is possible to prepare a polymer homologous series from the lowest to the highest degree of polymerization.

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Relatively low molecular products with molecular weights of from 1000 to 20,000, which are amorphous and powdery, were obtained with the aid of tin tetrachloride, from indene and anethole. These products were fractionated in the common manner. Polyindenes were reduced, but, as in the case of polystyrene, only relatively low molecular products could be reduced without degradation in a polymer analogous reaction (267). Since no double bonds could be detected in these polymers, they were considered to be high molecular rings (220). In the polymerization of anethole and propenylbenzene, it was observed that the linking of monomers does not occur in the 1,2-position, as is common for vinyl derivatives, but at least partially in the 1,3-position. The methyl group located at the end of the propenyl benzene and anethole molecules is mobile due to the influence of the neighboring double bonds. Therefore, an addition of the monomers can occur by the migration of hydrogen in the following manner (269):

The cracking of polypropenylbenzene yields 1,4-diphenylbutadiene as well as the monomer. Similar results were obtained in the case of polyanethole (269). Values from cryoscopic determinations were obtained for low polymeric, polymer homologous polystyrenes and polyindenes, as well as for poly- a-phenylbutadienes, which agreed with the other properties of the products, especially with the results of viscometry. As already mentioned, cryoscopic measurements on polypropenylbenzene and polyanetholes in naphthalene resulted, on the contrary, in very remarkable phenomena: the depression of the freezing point for high polymeric products was lower that that of low polymeric ones, and with increasing dilution relative depressions for these products increased. Unfortunately, these anomalous phenomena could not be explained (102).

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In 1940, W. Keller investigated polyvinyl carbazol (271), which was supplied as Luvican by the I. G. Farbenindustrie Ludwigshafen. We supposed that substituted carbazol residues could stiffen the paraffinic chain. Subsequently, we expected to find an increase in the degree of polymerization of polymer homologous members proportional to the viscosity number, as was observed in the case of cellulose. This assumption turned out to be erroneous, but the relationship between viscosity number and degree of polymerization, obeys the viscosity law of W. Kuhn (see p. 129), as it does for polystyrene. References 101, 102,220,258, and 266-271 are relevant.

4. POLYISOBUTYLENE Isobutylene, which is easy to obtain, was polymerized in 1924--25 in Zurich with M. Brunner (258,272) according to the procedure described by S. W. Lebedew with the aid of Florida Erde. Trimers to pentamers were obtained that could be isolated by distillation, as were some higher polymeric hemicolloidal products, which were not investigated further. In 1936, this polymer was prepared by G. Berger in larger quantities and divided by fractionation into four fractions with average degrees of polymerization of 26, 39, 40, and 59. The molecular weight was determined in cyclohexane by cryoscopy. Measurements of the viscosity in several solvents showed that the viscosity number increases proportionally with the number of chain elements for these polymers. The same Kaq constants were obtained as those for low molecular uniform materials in several solvents (compare Table 7 in ref. 273) (see Table 9).

Table 9 Comparison of Kaq Constants of Fractionated Hemicolloidal Polyisobutylenes with Those Found for Low Molecular Uniform Substances Kaq constants in Cyclohexane

For low molecular uniform substances For hemicolloidal polyiso butylenes

carbon tetrachloride

Benzene

1.2 x 10-4

1.05 x 10-4

0.95

1.2 x 10-4

1.08 x 10-4

0.9 x 10-4

X

10-4

This result was very valuable at that time because it showed that determinations of the molecular weight of these hemicolloidal polyisobutylenes

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by means of cryoscopy gave the correct values, otherwise, one could not have understood the conformity of their Kaq values with those of low molecular uniform products. At approximately the same time, W. Kern ap.d J. Herrera obtained the surprising result, already mentioned above, that remarkably anomalous values for hemicolloidal polyanetholes were obtained in naphthalene. During 1939-1940, Kl. Fischer investigated high molecular polyisobutylenes with a degree of polymerization of 600-9000. These were obtained by fractionation of technical products, which were supplied by Badische Anilin- und Soda-Fabrik, Ludwigshafen. They were prepared by polymerization of the monomer with boron trifluoride at low temperatures. For macropolymeric polyisobutylenes viscosity numbers do not increase proportionally with molecular weight but, as for other vinyl polymers, there is a relationship between both values according to Kuhn's formula. This result was obtained by R. M. Thomas, W. J. Sparks, K. Frolich, M. Otto, and M. Mueller-Cunradi [J. Am. Chem. Soc., 62, 276 (1940)] and was later confirmed by a number of experiments, e.g., by those of P. J. Flory. The viscosity of solutions ofmacropolymeric polyisobutylenes is strongly dependent on the nature of the solvent. These changes are much more considerable here than, for example, with polystyrenes. This was stated by Kl. Fischer as a result of the precipitation titration already mentioned on p. 121 (compare Table 3 in ref. 273). If macropolymeric polyisobutylenes are dissolved in a good solvent, e.g., cyclohexane, highly viscous solutions are obtained, the viscosity of which strongly increases with the concentraction and decreases a little when heated from 20 to 60°C. Thus, these solutions behave like those of a linear macromolecular substance. In a poor solvent, e.g., such as benzene, the viscosity, on the contrary, is low and increases proportionally with concentration. These solutions behave like those of a spherical colloid. It may be assumed that the chain molecules are strongly folded in the latter case, since intermolecular forces between the single molecular parts of the chain molecules are more efficient here than in solutions of good solvents, which is due to insufficient solvation with the poor solvent. According to experiments carried out in 1951 with H. Hellfritz (81), these polyisobutylenes show a behavior already predicted by W. Kuhn [cf. Helv. Chim. Acta, 32, 735 (1949)]. If a solution of very high molecular (eucolloidal) polyisobutylene is heated in benzene, then the viscosity of these solutions strongly increases. This means that the chain molecules are stretch d due to the strong

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solvation. In solutions with toluene or xylene as a solvent, these anomalous phenomena are not as pronounced as in a benzene solution, because the methyl groups of the solvent contribute to a better solvation of the polyisobutylene molecules. A study was intended on the viscosity of polyisobutylenes in several derivatives of benzene with aliphatic substituents in order to evaluate the influence of aliphatic side chains of the solvent on the solvation. This would answer the question of whether stretching of polyisobutylene molecules happens. However these experiments have not been carried out yet. If these high polymeric 'polyisobutylenes had been available to us at the beginning of the investigations in 1926, then the relationship between viscosity number and degree of polymerization would hardly have been found at that time. Solutions of polyisobutylene give an impressive example of changes in the physical shape of macromolecules, depending on the nature of the solvent. (See ref. 81, 272-275.) Polyethylenes, which today are of high technical importance, were not known when we began our investigations. In 1943, I received a plastic that was taken from an English airplane. It was investigated by Fr. Berndt. This was a polyethylene of a very high molecular weight mixed with polyisobutylene , which ·could be easily removed by a solvent. Then, H. Hopff in Ludwigschafen sent us samples of high pressure polyethylenes. We found out that their solubility was somewhat higher and that they had a somewhat lower melting point than the high molecular normal paraffins which were obtained from carbon monoxide with the FischerTropsch method, and which were sent to us for investigations at the same time. Therefore, it was assumed that high-pressure polyethylenes contain methylene groups as side chains. We assumed firstly that some propylene had been added to the ethylene, but this was not true according to a communication from H. Hopff. Thus, we supposed that ethylene reacts asymmetrically during polymerization, so that branching occurs and methylene side chains are formed. This assumption, which was published in 1952 (ref. 51, p. 150) was not correct either. It was soon pointed out in papers by American scientists that branches can be formed in a very different manner in high-pressure polyethylene.

5. POLYVINYL ACETATES, POLYVINYL ALCOHOLS, POLYACRYLIC ESTERS, ETC. In order to support the idea that long chain molecules are formed during polymerization, investigations on polyvinyl acetates and poly-

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vinyl alcohols turned out to be very valuable. After my move to Freiburg in 1926, monomeric and polymeric vinyl acetate was placed at my disposal by Director Kranzlein of IG-Farben Fabrik Hoechst and by the syndicate for the electrochemical industry. At that time, G. Kranzlein investigated the technical preparation of polyvinyl acetate by polymerization of the monomer in bulk. I still remember the difficulty of processing such a big block at that time. Polyvinyl acetate is a hydrophobic colloid which is only soluble in organic solvents. It can be converted into a water-soluble, i.e., hydrophilic, polyvinyl alcohol by saponification. In .turn, it can be acetylated to yield the polyvinyl acetate again. The colloidal properties of these materials are sustained in the course of the chemical reaction. In my lecture at the Gesellschaft Deutscher Naturforscher und ;lrzte in 1926 (5), I also mentioned these results as a proof for the macromolecular structure of these polymeric products. W. 0. Herrmann, who was member of the electrochemical industry syndicate drew my attention to his own observations which were rather similar. As a consequence, we agreed to publish our results simultaneously. Thus, in 1927 a paper, "Uber den Polyvinylakohol," by W. 0. Herrmann and W. Haehnel, in Ber., 60, 1658 (1927), and my paper with K. Frey and W. Starck as co-authors, " Uber Polyvinylacetat und Polyvinylalkohol," in the same journal, 60, 1782 (1927) came out simultaneously (219). In this work, polyvinyl alcohol was used as a model for starch, and its macromolecular structure was checked on the basis of its preparation from polyvinylacetate, as mentioned above. By varying the conditions for polymerization and by fractionating the polymeric products, it was possible to obtain a polymer homologous series of polyvinyl acetates and also polyvinyl alcohols similar to that of polystyrenes. However, experiments for converting both materials into each other in a polymer analogous reaction were not successful at that time. Furthermore, it was demonstrated in this research that the substituents are in the 1,3-position in the paraffinic chain of polyvinyl acetate, and not, or very seldom, in the 1,2-position. Polyvinyl alcohol yields oxalic acid when oxidized with nitric acid with only traces of succinic acid, which should be formed if the hydroxy groups were in the 1,2-position. Later on, other scientists, e.g., C. S. Marvel [J. Am. Chem. Soc., 60, 1045 (1938)], also demonstrated that the substituents in polyvinyl acetate are in the 1,3position (see also p. 151). Beginning in 1927, this field was elaborated together with A. Schwal-

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bach. To obtain low molecular (hemicolloidal) polymers, the polymerization of vinyl acetate was carried out in solution. As a result, it was found that products with a high chlorine content are obtained when chloroform is used as a solvent. This product was called a telomer, and later was studied extensively by other authors [cf. review of Eugene Muller, Angew. Chern., 64, 246 (1952)]. At that time it was assumed that decomposition of chloroform occurs with cleavage of hydrogen chloride during lightinduced polymerization and that there are two chlorine atoms at the end of the chain (276). The average degree of polymerization for the single fractions of these chlorine-containing polyvinyl acetates was determined through an analysis of the chlorine content. The results were in fair agreement with those determined by means of cryoscopy. The viscosity of the same products in solution was measured, and a relationship between the viscosity of basic molar solutions and a molecular weight was established. It could be shown that the viscosity of basic molar solutions of hemicolloidal polyvinyl acetates polymerized in chloroform changes proportionally with the molecular weight in a manner similar to hemicolloidal polystyrenes, which were simultaneously investigated with W. Heuer (ref. 122, see p. 125). It was surprising that the Km constants of polyvinyl acetates (2.6 x 10-4) was about the same as that of polystyrene (2.5 x 10-4 ), although both compounds have entirely different structures. In 1931 it was concluded from this result that the viscosity of chain molecules is mainly dependent on the length of the whole chain and not on the side chains. A monomer unit (basic molecule) of polyvinyl acetate contains two chain elements, as does that of polystyrene, so that the agreement of the Km constants of the hemicolloidal members could be understood. The agreement in the viscous properties ·of polystyrenes and polyvinyl acetates thus led to the conclusion that both polymers have chains with a similar structure, and their monomers are connected to each other by primary valences in their respective chain molecules. Research with A. Schwalbach gave further evidence for this assumption. We succeeded in reducing the polyvinyl alcohols with the aid of hydrogen iodide to yield high molecular paraffins (276). The product with the highest molecular weight of that series had a molecular weight of about 930, which corresponds to an average molecular weight of 33. Thus, it was demonstrated at that time that at least 33 monomers were linked with each other by primary valences during polymerization. A. Schwalbach also did experiments on the polymerization of the monomer by heating and light with the exclusion of oxygen. These experiments showed that,

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unlike styrene, vinyl acetate does not polymerize when oxygen is absent. A few years later (1938) the degree of polymerization of higher molecular polymer homologous polyvinyl acetates and polyvinyl alcohols was determined by osmometry with H. Warth. In addition, viscosity measurements were made. It was shown that the viscosity numbers do not increase proportionally with the degree of polymerization. The same results were obtained for polyacrylic esters, and it was postulated that those irregularities are due to branching. It was also demonstrated that these irregularities exist in the case of polyvinyl acetate by showing that technical polyvinyl acetates do not yield polymer analogous polyvinyl alcohols when saponified, but always have a much smaller degree of polymerization than the starting materials. On the other hand, polyvinyl alcohols can be reacetylated to polyvinyl acetate in a polymer analogous reaction, i.e., without being degraded. Thus, it was demonstrated that the colloidal particles and macromolecules are identical for these macropolymer products (279). It was assumed at that time that in technical polyvinyl acetates there are other groups in the chain which are cleaved when saponified. It was also believed that such groups originate from impurities of the technical monomeric vinyl acetate. H. Warth fractionated a large quantity of vinyl acetate and prepared polymers from the middle fraction. It was found out that these polyvinyl acetates, which were prepared in the laboratory with a degree of polymerization of 1400-1700, can be saponified to polyvinyl alcohols in a polymer analogous reaction. This result seemed to show that pure polyvinyl acetates may be saponified, yielding polyvinyl alcohols or, in other words, that the divergent behavior of the technical products is caused by impurities (279). However, this result had to be checked. The investigation of 0. L. Wheeler, E. Lavin, and R. N. Crozier, "Branching Mechanisms in the Polymerization of Vinyl Acetate" [J. Polymer Sci., 9 157 (1952) ], demonstrated that branching occurs via the formation of side chains at the acetyl groups in the polymerization of vinyl acetate. When saponified, these branches are cleaved, so that there are polyvinyl alcohols formed with a lower degree of polymerization than that in acetates. After a diketene from Lonza AG in Basel was supplied through Dr. E. Stirnemann, M. Haberle prepared polyvinyl acetyl acetates by reacting diketene with polyvinyl alcohol (284). These products were interesting due to the reactivity of their branches. Derivatives also were obtained, but these pass easily by crosslinking into insoluble products.

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The polymerization of isopropenyl methyl ketone was investigated with B. Ritzenthaler in 1934, with the idea that interesting reactions could be easily carried out with the polymer on the basis of the reactive carbonyl groups, but this work did not yield the results we originally hoped to obtain (278). At that time the polymerization of acrylic ester was also investigated. G. V. Schulz and F. Blaschke (239,280) studied the kinetics of the polymerization using methacrylic ester. The polymerization of acrylonitrile and methacrylonitrile was investigated by W. Kern and E. Fernow (281,282). It was demonstrated through elemental analysis (see also p. 109) that the polymeric products have a somewhat lower content of nitrogen than calculated; for polyacrylonitrile, a separation of hydrocyanic acid was detected during polymerization. Polyacrylonitriles could be saponified, yielding polyacrylic acids, but this could not be done with polymethylacrylonitriles. References 219, 239, 276-289 are relevant. 6. HALOGEN­CONTAINING POLYMERS Starting in 1927, an investigation on polyvinyl bromide, which is easily obtainable, was carried out with W. Feisst (291) in Freiburg. This work

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had already been started with M. Brunner in Zurich. Polyvinyl chloride and polyvinylidene chloride, supplied by industry, were also studied at that time.The plan was to determine whether these polymeric products, which are barely soluble or even insoluble, consist of chain molecules as does polyvinyl acetate, which was being investigated simultaneously. At that time we tried in vain to convert polyvinyl bromide into polyvinyl alcohol and polyvinyl acetate. As a result of this reaction the constitution of these products could have been easily elucidated. Later on, H. E. PierzDavid and Hch. Zollinger [Helv. Chim. Acta, 28, 455 (1945)] succeeded in carrying out this conversion by reacting polyvinyl chloride with silver acetate. It was surprising that bromine and chlorine atoms, respectively, do not exhibit the same reactivity as do halogen atoms in corresponding compounds of low molecular weight. Thus, these halogen derivatives could not be converted into the amines with a corresponding structure by treatment with ammonia or primary organic bases. It was proved that monomeric molecules in these polymers are linked with each other by primary valences by the reduction of these halogen derivatives with iodine and phosphorus to normal paraffinic hydrocarbons, 850 being the molecular weight of the highest fraction. Therefore, this carbon hydride contained about 60 carbon atoms, i.e., at least 30 monomeric molecules were linked to each other by primary valences. Through reaction with dimethyl zinc, a high molecular carbon hydride was obtained which had the composition of natural rubber, i.e., about 60 monomeric molecules linked by primary valences. Through reduction with zinc in these experiments, a distillable carbon hydride was obtained with eight monomeric molecules per chain molecule. This reaction could have given evidence for the assumption that polyvinyl bromide is not a very high molecular compound, but has the formula (C2H 3Br) 8 • However, this assumption was refuted by other experiments. Since these halogen derivatives easily split off halogen hydrides, preparation of polymeric polyene carbon hydrides from polyvinyl bromide and polyvinyl chloride, respectively, was attempted. This approach was not successful, however, since dark, insoluble products were formed which still contained halogens. A high polymeric carbon chain from the asymmetric polyvinylidene chloride could not be prepared by separation of the hydrogen halide, either. These failures can be explained in terms of the great tendency of unsaturated chain molecules to crosslink. Later on it was demonstrated with J. Schneiders on the basis of osmometry that polyvinyl chlorides-technical products as well as those prepared in the

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laboratory-are high molecular compounds and have a degree of polymerization of 1000 and even more (293). For these products, the viscosity number does not proportionally increase with the number of chain elements as for cellulose and its derivatives. R. Houwink demonstrated later on [J. Prakt. Chem. N.F., 157, 15 (1941)] that in this case the viscosity changes with the degree of polymerization according to the Kuhn relation (seep. 129). M. Haberle tried to convert polyvinyl chloride (PVC products) into polymer analogous PC pr.oducts by chlorination. In spite of little degradation during this reaction, this work proved that colloidal particles are identical with macromolecules (294). (See reference 296 for the degradation of chains by chlorine.) W. Hahn and W. Muller demonstrated that polyvinyl chlorides have a macromolecular structure by converting this polymer with lithium aluminium hydride into polyethylene in a polymer analogous reaction (295). Since these polyethylenes have a high melting point, the starting products, the polyvinyl chlorides, cannot be branched at all or only very little (294). At the end of the 1920s, the polymerization of allyl chloride was investigated with Th. Fleitmann, but very high molecular products could not be obtained. These products did not show the reactivity of the low molecular aliphatic chlorine derivatives. References 51, 263, 289, 290-298 are relevant.

7. COPOLYMERS In the early work of Th. Wagner-Jauregg [Ber., 63, 3213 (1930)], copolymers were termed heteropolyn1ers. Th. Wagner-Jauregg had prepared some copolymers of special interest. Later on, copolymers were called mixture polymers, while today it is useful to employ the new nomenclature (seep. 95 and ref. 12). The first copolymers were the already mentioned addition products of dimethylketene to isocyanates and carbon disulfide, respectively, which are soluble as colloids (see alsop. 82) (A65). It was known through a number of earlier observations that insoluble addition products are formed when sulfur dioxide is reacted with ethylene, butadiene, isoprene, etc. The addition occurs in the ratio 1 :1, and the products disintegrate easily when heated. It was believed that these were high molecular materials, but an exact evaluation of the molecular

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weight could not be done at that time. Under certain conditions soluble monomeric addition compounds were formed which had the same composition. During 1934.:._ 1935, B. Ritzenthaler investigated these products and found that the fast formation of macromolecular addition products is favored when peroxides, especially autoxidated ether, are present as catalysts. On the other hand, anticatalysts like polyvalent phenols yield monomeric addition products, which are readily available in this way (299). Since the macropolymeric addition products of propylene and S02 and butadiene and S02 are soluble in concentrated sulfuric acid without being decomposed, viscosimetric measurements could be carried out on these products. They were evaluated as very high molecular chain polymers, with more than I 000 monomeric carbon hydride molecules linked with S02 • This conclusion resulted from a comparison of the viscosity of these polysulfones in solution with that of macropolymeric polystyrenes (300,301). Macromolecular peroxides and ozonides are also copolymers. In 1925 it was assumed that polymeric asymmetric diphenylethylene peroxide (AI29) consists of very long chain molecules with the following structure:

Owing to their insolubility, the molecular weight of these macromolecular peroxides and ozonides could not be determined. The assumption that they contained long chains was based on the analogy to the constitution of sulfones (Al29-Al31). Furthermore, copolymers like those made from divinyl benzene and styrene and other unsaturated compounds yield polymers with a limited swellability. These copolymers were discussed in Chapter 10, Section 2, p. 158. Copolymers, which are very important in industry, are therefore subject to extensive scientific investigation. They recently were used to prepare graft polymers. For example, W. Hahn and A. Fischer prepared copolymers from methyl methacrylate and p-N-acetylaminostyrene. Nitroso groups were introduced into these copolymers and side branches were grafted onto the main chain with the initiating N-nitroso-N-acetylamino group. Similar experiments were also carried out with copolymers of methyl methacrylate and isopropenyl acetate. Here, the acetate groups

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were saponified and converted into initiating hydrogen peroxide groups (242,244,245).

8. HETEROPOLAR MACROMOLECULAR SUBSTANCES (POLYELECTROLYTES) If my assumption that the single monomer units (basic molecules) in the polymerization of unsaturated compounds yielding long chain molecules are linked with each other by primary valences (demonstrated, for example, in the polymerization of homopolar compounds) was correct, then it could be expected that the polymerization of unsaturated acids or bases yields polyacids and polybases. Corresponding to their degree of polymerization, hundreds or thousands of heteropolar groups are substituted in these polymers and their salts should be soluble in water. Thus, when the constitution of natural rubber was studied, W. Reuss converted natural rubber via a rubber dibromide into a rubber phosphonium salt. This was soluble in water, as expected, and yielded highly viscous solutions. These results are discussed mainly in E. W. Reuss's dissertation (ref. A174, see alsop. 205). In 1924, polyacrylic acid and its esters and salts were investigated by W. Urech as simple models for such compounds. The polymerization of acrylic acid was studied by Otto Rohm at the turn of the century in the laboratory of H. v. Pechmann. A dimeric and trimeric product was obtained [cf. H. v. Pechmann and 0 Rohm, Ber., 34, 427 (1901)]. In his dissertation (University of Tiibingen, 1901), "Uber die Polymerisations­ produkte der Acrylsaure," 0. Rohm terms polyacrylic acids as "pseudopolymers" and compares them with allotropic modifications of the elements and modifications of inorganic compounds, e.g., stannic acid. He supposed that natural polymers are based on a similar structural principle. As is known, 0. Rohm later did very successful studies on polyacrylic acid and its esters in industry. E. Urech stated that polyacrylic esters which are soluble in organic solvents can be saponified, yielding water-soluble polyacrylic acids (224). Since both products give colloidal solutions, we assumed that the colloidal particles are macromolecules, i.e., the polymeric products are formed from the monomer via linkage by primary valences. Furthermore, polyacrylic esters were converted into a tertiary alcohol by treatment with grignard reagents. In turn, a higher molecular carbonhydride was obtained from the alcohol with hydrogen iodide (224).

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S. Wehrli (ref. 224, p. 1124) succeeded in obtaining an acid by the ozonization of polystyrene, which dissolves in water as a colloid, and represents a polyacrylic acid which is not completely pure.

It was not proved then that tl).e degree of polymerization of the poly acrylic acid obtained is identical with that of polystyrene, but by the conversion of a colloidal carbon hydride into a colloidal acid evidence was given in 1929 for the macromolecular structure of these materials. A definite proof for the macromolecular structure of polyacrylic acids was given in 1933 with E. Trommsdorff, using classical methods of organic chemistry, i.e., by conversion of a polymer homologous series of polyacrylic esters into polymer analogous polyacrylic salts (277). The essential result of these investigations was proof for the existence of acids with 1000 and even more basic groups. The polymerization of acrylic acid was investigated with H. W. Kohlschi.itter in 1930 and the following was stated (compare ref. 302, pp. 20932094): "There are two possibilities for the formation of long chains from the monomeric acrylic acid molecule: 1. Molecule can be added to molecule by a slow process under hydrogen migration until a long chain has been formed. Subsequently, every polymer thus formed is a completed stable molecule. During this kind of polymerization trimers, etc., should be formed from dimers, and higher polymers only should be obtained at a later stage of the reaction.

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2. Polymerization occurs first by the activation of a molecule and subse-

quently by the fast addition of more molecules in a chain reaction. If this process is described by a formula, then one must be aware that the chain has free valences at the end that are unstable and continue to grow until finally the end groups are inactivated in a manner which is not known yet. The formation of polyacrylic acid is in accordance with reaction process 2. This is supported by the phenomena observed in spontaneous polymerization: it is possible to separate monomeric acid from the high polymeric acid by distillation in a n1ixture of polyacrylic acid and acrylic acid. Accordingly, no intermediate products, which should be easily detectable, are obtained. The case of polyacrylic esters is not as clear, because the polymeric products seem to be soluble in the monomer, as is the case with polystyrenes."

These statements gave essential proof for the formation of polymers by chain reaction (see p. 154). Studies on the viscosity of heteropolar molecular colloids were reported on p. 133. Peculiar phenomena in the viscosity of these materials were termed polyionic viscosity phenomena. They have not been observed with homopolar molecular colloids. W. Kern (cf. Habilitatioschrift, 1937, ref. 304) made extensive studies on the osmotic behavior of aqueous solutions of polyacrylic acids and their salts, as well as the viscosity of their solutions (180,305-307). His further investigation concerned polyvalent amines (308,309). All these heteropolar molecular colloids have attained a high significance as models for proteins and were recently elaborated extensively (compare the work of W. Kuhn and A. Katchalsky; see also the contribution on polyelectrolytes by U. P. Strauss and R. M. Fuoss in Das Makromolekiil in Losungen, Vol. 2, Die Physik der Hochpolymeren, H. A. Stuart, ed. Springer, Berlin-Gottingen-Heidelberg, 1953, pp. 680-701). Research with F. Zapf (183) finally demonstrated that anomalous viscosity of polyelectrolytes in solution is only observed in linear macromolecular materials by investigating the glycogenxanthogenates. The viscosity of the solutions of these spheromacromolecular products does not exhibit anomalous properties, but behave according to their swellability as do other such materials (seep. 135). References 15, 180, 183,216,224,277,302-312 are relevant.

9.

POLYOXYMETHYLENES

In 1920 when I published the paper on the chain structure of macromolecular substances, mentioned in reference 1, p. 78, it seemed reasonable to do research on paraformaldehyde and polyoxymethylenes, respectively,

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due to their simple, clear structure. At that time, a number of papers were published, which in part were not clear. Especially interesting were the excellent investigations of F. Auerbach and H. Barschall [compare papers from the Kaiser fiches Gesundheitsam! Berlin, 22, 607 (1905); 27, 183 (1907); 47, 116 (1914)]. In these publications, four new modifications of polymeric formaldehyde were described, besides paraformaldehyde which had often been regarded as amorphous at that time. The more or less crystallized modifications were not only distinct with respect to their physical properties, e.g., in their solubility in water and their vapor pressure at several temperatures, but also in their chemical properties. Thus, α-and β -polyoxymethylenes are very reactive, disintegrate easily when heated, and then yield quantitatively gaseous formaldehyde or trioxymethylene, respectively. They dissolve by decomposition in boiling water, and also in solutions of sodium hydroxide and sodium sulfite. yPolyoxymethylene has less tendency to split off formaldehyde or polymeric molecules, when heated, than the two compounds mentioned before. It is not soluble in hot water, or in solutions of sodium hydroxide and sodium sulfite. Therefore, γ -polyoxymethylene can easily be separated from α­ and β -polyoxymethylene. δ -Polyoxymethylene does not decompose very readily. When heated, it yields formaldehyde or polymeric molecules, leaving a residue, and is not soluble in water, or sodium hydroxide, or a solution of sodium sulfite. I assumed that these remarkable differences between the polyoxymethylenes are based on their chemical constitution and not on differences in an unknown degree of aggregation. In 1920, M. Luthy (313) started work on evaluating the constitution of polyoxymethylenes. Long chains of α­ and β -polyoxymethylene were degraded with acetic anhydride, and, as a result, a polymer homologous series ofpolyoxymethylene diacetates was obtained. Furthermore, the reaction of benzoyl chloride with paraformaldehyde and polyoxymethylene, elaborated earlier, e.g., by Descude [compare Ann. Chim., 29, (7) 502 (1903)] was again studied with the following surprising result: after long shaking in cold or after short heating of the components, a dibenzoate of dioxymethylene is formed, even when 1 mole of benzoylchloride and 1 mole of formaldehyde are reacted with each other. On the other hand, the monooxymethylene (formaldehyde) dibenzoate is obtained in the presence of zinc chloride, because then the derivative of dioxymethylene is converted into the derivative of monooxymethylene with the splitting of formaldehyde. However, benzoates with longer polyoxymethylene chains could not be obtained.

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If we had restricted our interest to evaluating the cleavage of polyoxymethylene with benzoyl chloride we would apparently have found a good example for P. Karrer's interpretation of the low molecular structure of high polymers. A. Hantzsch and J. Oechslin already had assumed [compare Ber., 40, 4341 (1907)] that metaldehyde and also paraformaldehyde are dimolecular compounds capable of aggregating further. But the degradation of polyoxymethylenes with acetic anhydride demonstrated that this concept is incorrect. At that time we emphasized these results more than the degradation of paraformaldehyde with benzoylchloride because the concept of a chain structure in polyoxymethylene agreed with these and many other results. However, a consideration of the observations at that time is still valuable, since it is not known yet why only dimolecular decomposition products are formed when polyoxymethylenes are degraded with benzoylchloride, whereas acetates with longer chains are formed when acetic anhydride is used. The reaction of cx-polyoxymethylenes with several other acid anhydrides or acylchlorides, ought to be studied in order to elucidate this problem. When the interpretation of polyoxymethylenes as chain molecules was confirmed through the investigations of M. Luthy, differences in the several polyoxymethylenes could be explained in terms of differences in the chemical structure. The following formulas were established: Formulas of polyoxymethylenes (n Polyoxymethylene dihydrates, hydroxide and sodium sulfite:

=

degree of polymerization)

decomposed

by solutions of sodium

Polyoxymethylene dimethyl ether, not decomposable by solutions of sodium hydroxide and sodium sulfite:

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Therefore, α­and β -polyoxymethylene are polyoxymethylene dihydrates, which are degraded by solutions of sodium hydroxide or sodium sulfite, starting from the ends of the chains. a-Polyoxymethylene is microcrystalline and is more easily soluble than β -polyoxymethylene, which is obtained in hexagonal crystals of various sizes. Whereas the degree of polymerization of α­polyoxymethylene may reach 200, β -polyoxymethylene can consist of very long chains due to the slow growth of its crystals, which have an estimated degree of polymerization of 1800-2000. The chain ends of β -polyoxymethylene are generally arranged in layers in the crystal. This is shown by microscopy, as already mentioned on p. 144: if treated with caustic soda solution, these crystals are attacked only in more or less regular layers, whereas acids attack the chains of polyoxymethylene everywhere and thus finally dissolve the crystal (20 1,205). It can be assumed that the chain ends of β -polyoxymethylene are occupied by residues of sulfuric acid, so that it represents a high molecular ester of sulfuric acid. Sulfuric acid can also be imbedded between the layers of the crystal. At any rate, β -polyoxymethylene contains very small amounts of sulfuric acid which easily induce degradation to formaldehyde when heated. In the colder areas of the test tube formaldehyde is being polymerized in turn by traces of sulfuric acid. Thus, it seems that β -polyoxymethylene can be sublimated in a test tube. The α­polyoxymethylene that is free from sulfuric acid forms formaldehyde gas when heated, and only slowly polymerizes again. However, α­and β -polyoxymethylene cannot be clearly separated, but both modifications are distinguished from γ- and δ -polyoxymethylene, since the latter are polyoxymethylene dimethyl ethers. Their end groups are methoxy groups and are therefore stable in solutions of caustic soda and sodium sulfite. δ -Polyoxymethylene is obtained from γ-polyoxymethylene by boiling in water for a long time. Accordingly, a Cannizzaro rearrangement occurs which is due to the content of alkali in glass. As a result, δ -polyoxymethylene does not contain methylene ether groups exclusively, but also C-C- bound carbon atoms with hydroxy side groups. Therefore, δ -polyoxymethylene can only be split incompletely into formaldehyde gas, as already observed by Auerbach and Barschall, leaving a residue due to a new arrangement of δ -polyoxymethylene. The content of hydroxy groups in δ -polyoxymethylene dependent on the length of time in which y-polyoxymethylene is treated with boiling water, was determined after degradation of δ -polyoxymethylene by boiling dilute acids and subsequent conversion of the glycol aldehyde formed into p-nitrophenyl osazone.

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The investigation of polyoxymethylenes by means of X-rays, mentioned on p. 138, showed the important result that even mixtures of polyoxymethylenes can crystallize, forming a macromolecular lattice. In 1927, the preparation of a fibrous polyoxymethylene with R. Signer marked another significant step in this field. This was the first completely synthetic fiber (7, 184 and fig. p. 145). H. W. Kohlschi.itter (318,319), who investigated the morphology of the polyoxymethylenes made further interesting observations. He found that trioxymethylene is converted into a fibrous polyoxymethylene, i.e., by cleavage of the low polymeric ring and polymerization, a high polymeric chain molecule can be formed which, in turn, disintegrates by heating, at least partially, into trioxymethylene. Such reversible conversions from low molecular rings into long chains were also observed in 1955 by H. Krassig and G. Greber with many-membered Schiff's bases (395399). Polyoxymethylenes raised some problems which have not yet been answered. Thus, M. Luthy (314) stated that trioxymethylene is formed from α -polyoxymethylene only if small amounts of water are present. Completely dried α-polyoxymethylene yields only formaldehyde gas. It was surprising to find another low-molecular polymeric product in tetraoxymethylene, which corresponds to metaldehyde in composition. It is formed only when dried polyoxymethylene diacetate is evaporated, but cannot be obtained from α-polyoxymethylene, even if this is moistened with acetic acid or its anhydride (314). Therefore there must be fine structures in polyoxymethylenes which favor the formation of trioxymethylene and tetraoxymethylene. The polyoxymethylenes mentioned above are not formed by a real polymerization process, but by polycondensation, which occurs by reacting molecules of formaldehyde hydrate with each other and splitting off water or by the addition of formaldehyde molecules to formaldehyde hydrate. Due to the conditions of the reaction, polycondensation products with different degrees of polymerization can be formed, the molecules of which are all stable. Formaldehyde, however, can be polymerized by a chain reaction, like ethylene derivatives (see p. 154). This process occurs in an etheric solution, with water excluded, in the presence of catalysts like trimethylamine at low temperatures. The conditions of the polymerization are described in my book (15) published in 1932 on pp. 280-287. Since the polymerization is strongly exothermic, it can occur as an explosion. Therefore, great care has to be taken when the polymerization of liquid

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formaldehyde is carried out in a bomb tube. The following may be quoted from the above-mentioned book, p. 256 on "eupolyoxymethylene," which was elaborated in collaboration with W. Kern: "This kind of polymerization can be fundamentally distinguished from polycondensation and condensating polymerization. We call this reaction a chain reaction, just as the formation of hydrogen chloride from hydrogen and chlorine is a chain reaction. These chain polymerizations are processes which can yield high polymeric products. Such a chain polymerization can be formulated in the following manner:

Finally, the chain reaction is terminated by a different chemical reaction, otherwise the chain molecule would grow infinitely. Through this termination of the reaction, a foreign group is inserted in the molecule."

Polyoxymethylenes obtained in this way are called eupolyoxymethylenes because of the assumption that they have a very high degree of polymerization. If a solvent were known for them, they should yield highly viscous solutions like eupolystyrenes. The following was said on the physical properties of these eupolyoxymethylenes on pp. 260-261 of the book cited above (15): "The eupolyoxymethylenes have especially remarkable physical properties. Besides their tendency to form a glass, their slight elastic properties at room temperature and viscoelastic properties at elevated temperatures are remarkable. Elastic properties are exhibited by films of polyoxymethylenes and also by the fibers which are mentioned later on. All polyformaldehydes polymerized at low temperature become viscoelastic when heated to 160-200°C. They do not show a melting point. They sinter with separation of formaldehyde and can be mould and cast. This property distinguishes polyoxymethylenes obtained from liquid formaldehyde from all others known. Paraformaldehyde and α-, β γ-, orδ -polyoxymethylenes do not exhibit plastic or elastic properties. Eupolyoxymethylenes prepared at -80°C, e.g., glasses, are very tough in the plastic state. On the other hand, the polymers obtained at -20°C are relatively soft and easy to stretch, so that long fibers (1 m length and more) can be obtained. This is a procedure which reminds one of melt-spinning viscous solutions of cellulose or molten glass or quartz. Polymeric products in the viscoelastic state can be pressed into films which have the same properties as films from the vacuum distillation of monomeric formaldehyde. The fibers obtained are extendably elastic. They can be reversibly stretched, when sufficiently thin to up to 10% of their length. A stress experiment on a

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thin filament showed a partially irreversible stretching of more than 20/0 of the original length after three days. From physical constants, the specific weight determined by pycno-metry for a glassy, clear block was 1.407 at 20°C. The density of the glass is lower than that of y-polyoxymethylene. A very remarkable property of polyoxymethylene made from liquid formaldehyde, as already mentioned, is its elasticity and plasticity."

[See also W. Kern's lecture on polyoxymethylene films and fibers, Kolloid­ Z., 61, 308-310 (1932).] Within a few years, after E. I. du Pont de Nemours Company started the technical synthesis these eupolyoxymethylenes became of high significance in industry. Plastics from eupolyoxymethylene are sold on the market under the trade name Delrin. A number of patents were published on that subject; I only mention U.S. Patent No. 2,768,994, October 30, 1956. Several German companies also are involved in the manufacture of this product. For industrial synthesis, it is important to stabilize eupolyoxymethylenes by preventing degradation of the chain molecules at the positions of the few hydroxy groups. These hydroxy groups can be located at the ends, and they also can be imbedded in the chain by a Cannizzaro rearrangement, similar to δ -polyoxymethylene, since such a rearrangement is conceivable with weak alkaline catalysts (trimethylamine). References 4, 7, 15, 86, 187, 188, 201, 203, 205, 313-329 are relevant.

10. POLYOXYETHYLENES Today, polyoxyethylenes, due to their interesting physical properties, are of high importance in industry. In 1863, A. Wurtz, who discovered ethylene oxide, found polymeric products of these compounds but was not able to characterize them. The initial research was made in 1929 with 0. Schweitzer subsequent to work on polyoxymethylenes (330). Through polymerization of the monomer with tin tetrachloride, polyoxyethylenes with a molecular weight of up to 4000 (DP about 100) were prepared. These experiments were carried out in bomb tubes. In a few cases-mostly after hours of standing-explosions occurred which were induced by the large quantities of heat, released during the exothermic polymerization, which in turn caused a fast evaporation of the still unreacted monomer. According to the unpublished results of Prof. P. SchHipfer at the Institut fur Material­ prufung of the ETH Zurich, the combustion heat of monomeric ethylenoxide is 308 cal/mole, but only 280 cal/mole for polyoxyethylenc with a molecular

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weight of about 5000, so that 28 caljmole of monomer are released during the polymerization. After publishing my experience with explosions (330), I was told that these explosive polymerizations also had been observed in industry. Between 1930 and 1932, further work in this field was done in collaboration with- H. Lohmann,* and these results were published in 1932 in (15), chapter Polyiithylenoxyde, ein Modell der Starke on pp. 287-332. H. Lohmann synthesized polyoxyethylenes with a molecular weight of up to about 14,000 (DP about 350) mainly with the aid of tin tetrachloride as a catalyst. These polymeric products are · polyoxyethylene dihydrates (I), with OH-groups at the ends of each chain. It was possible to prepare a polymer homologous series by fractionation. Its members were converted into the corresponding diacetyl derivatives (II) by boiling in acetic anhydride:

The molecular weight of both products (hydrates and acetates) was determined by cryoscopy. The molecular weight of the diacetates was also evaluated by determining the acetyl group content. The values obtained through this end-group determination were in fair correspondence with those obtained through cryoscopy. It turned out that dihydrates can be converted into diacetates in a polymer homologous reaction, i.e., without cleavage of the chain. Both series were also characterized by viscometry. The results are plotted in Table 10 (p. 298 in ref. 15). The mechanism of the polymerization has not been evaluated yet. When the reaction is carried out in a solution of potassium hydroxidesometimes this reaction occurs very vigorously-it is assumed that this is a polycondensation where ethylene glycol, which is formed first, adds more ethylene oxide molecules. This mechanism may be probable, since chlorine-containing polymers are obtained with ethylene chlorohydrin, and nitrogen-containing polymers are obtained with primary and secondary amines. However, there is no correspondence between the molecular weight for the latter products obtained by end-group method and by cryoscopy; the former value 'vas lower (p. 327 in ref. 15). It is conceivable

*

H. Lohmann, my co-worker for many years, later worked in the Deutschen Rhodiaceta AG in Freiburg i. Br. He was an experienced mountaineer, and succeeded in climbing many of the highest mountains of the Alps. He was killed in an easy climbing tour in the Black Forest in 1936.

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Table 10 Polymer Analogous Conversion of Polymer Homologous Polyoxyethylene Dihydrates into Their Diacetates

Degree of polym erization 5 9 18 20 27 37 39 59 70 140 145 210 290

Acetyl Content %

Mol. wt. from Acetyl Content

26.7 17.6 9.5 8.4 6.5 4.6 4.4 2.8 2.6 1.3 1.25 0.92 0.62

236 405 820 940 1,240 1,890 1,750 3,000 3,200 6,500 6,800 9,300 13,800

Cryoscopic Mol. Wt. Dihydrates 220 415 790 900 1,170 1,230 1,610 2,200 3,040 5,900 5,900 12,000

Diacetates

860 1,550 3,000

5,500 9,200

Zn in Benzene at 20°C Dihydrates 0.10 0.15 0.20 0.23 0.33 0.29 0.40 0.48 0.54 1.01 1.05 1.8 2.2

Diacetates 0.08 0.12 0.17 0.21 0.25 0.29 0.37 0.56 0.48 0.94 1.01 1.92

that polyoxyethylene dihydrates are also formed besides the polymeric products with chlorine and nitrogen-containing end groups. Therefore, the preparation of a polymer homologous series of polyoxyethylenes with nitrogen-containing end groups originally planned was discontinued. The polymerization of ethylene oxide with trimethylamine or alkali metals, where the latter often occurs as an explosion, is probably a real polymerization in which che opened ethylene oxide ring reacts with other ethylene oxide molecuks. Therefore, this is a chain reaction similar to that of the monomeric pure formaldehyde or to that of styrene (p. 290 in ref. 15). As already assumed by Roithner [Mh. Chem., 15, 679 (1894)] high molecular rings can be formed in this reaction. In the chain polymerization of ethylene oxide it is also conceivable that radicals react with a growing chain by splitting off hydrogen atoms. Thus, branched polymeric products are formed in a side reaction, which is not possible in the case of polycondensation. However, these problems have to be further investigated. A few years later (1933), I reported together with H. Lohmann on the formation of macromolecular polyoxyethylenes. These polymers were

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obtained by the polymerization of liquid ethylene oxide with solid calcium or strontium oxide. A molecular weight of 100,000-120,000, i.e., an average degree of polymerization of 2000-2500, was obtained by viscometry (332). The formation of such macropolymeric products by solid catalysts can be understood today much better on the basis of observing the polymerization of ethylene and ethylene derivatives with Ziegler catalysts. The formation of these polymers probably is similar to a stereospecific polymerization. This is also supported by the fact that R. A. Miller and C. C. Price recently were able to convert ethylene oxides into macropolymeric products with an aluminum organic catalyst [cf. J. Polymer Sci., 34, 161 (1959)]. Macropolymeric polyoxyethylenes, which were termed eupolyoxyethylenes, exhibit remarkable properties. Like low molecular polymers, not only are they soluble in organic solvents such as benzene or carbon tetrachloride, but also in water; this solution is preceded by swelling. These solutions are highly viscous and show deviations from the HagenPoiseuille law similar to those of macropolymeric polystyrenes (332). Consequently, polyoxyethylenes have both a lyophilic and a hydrophilic character, which is not found with other macropolymeric materials. The solubility in organic solvents is understandable, since polyoxyethylenes represent high molecular ethers. However, the good solubility of the polyoxyethylenes in water is remarkable. This may be explained by the fact that dimethyl ether groups are linked to each other in a long chain within the chain molecules. Monomeric dimethyl ether and glycerin trimethyl ether are also soluble in water. On the other hand, it is remarkable that polyoxymethylenes are soluble neither in water nor in organic solvents. The high solubility of polyoxyethylenes, unlike polyoxymethylenes, is caused by the different shape of the polyoxyethylene chains. Whereas the carbon and oxygen atoms of polyoxymethylenes are arranged in a zigzag chain, the chains of polyoxyethylenes have a meandrous shape as shown in the following scheme:

paraffinic chain

polyoxymethylene chain

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187

In a paper published with H. Lohmann in 1932, (p. 293 in ref. 15), as a result of viscometric measurements on solutions of polyoxyethylenes it was concluded that the chain molecules must have a meandrous shape, since the viscosity numbers of these polymers are much smaller than those calculated for a stretched zigzag chain. It was also demonstrated that the chain molecules of glycol derivatives also have meandrous shapes, since esters of ethylene glycols with long-chain fatty acids have a lower viscosity number than esters of fatty acids with monovalent alcohols of the same chain length (ref. 133, seep. 252). At the same time, E. Sauter demonstrated by means of X-ray measurements that chains in solid polyoxyethylene also have a meandrous shape (331). For this purpose, high molecular polyoxyethylene was melted and then drawn to fibers. These were the first experiments for the preparation of fibers in the melt­spinning process, which later gained great significance in the manufacture of Nylon and Perlon. Seep. 141 and references 18, 200, 201, and 205 for the formation and structure of such fibers, which depends on the degree of polymerization. The conclusion that the polyoxyethylene molecules had a meandrous shape was first drawn from viscometric measurements. Later, it was detected in crystalline products. Thus, I assumed that chain molecules in solution have approximately the same shape as in the crystal. This conclusion had to be modified by the assumption that the viscometric length of chain molecules in solution may be much lower, due to folding, than the length determined by means of X-ray measurements. Therefore, the behavior of polyoxymethylenes and polyoxyethylenes in solution should be investigated further, since the former are less folded in solution than the latter (compare Table 123 on p. 234 in ref. 15 and Table 10, p. 185). In this respect, the investigation of R. Fordyce, E. L. Lovell, and H. Hibbert [J. Am. Chern. Soc., 61, 1916 (1939)] was remarkable. They succeeded in preparing uniform high molecular polyoxyethylenes with a degree of polymerization of 90 up to 186 by stepwise synthesis in order to study the relationship between viscosity number and chain length. However, this kind of synthesis is very laborious, and the following procedures seem

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to be more useful for these studies: from an easily obtained polycondensation product with a molecular weight of 20,000-30,000, a polymer homologous series of nearly uniform polyoxyethylenes should be prepared by careful fractionation, and the relationship between molecular weight or chain length and viscosity number should be evaluated again. This investigation is advantageous, since the molecular weight for polyoxyethylene hydrates can be evaluated by end-group determination after conversion into the diacetates. Macropolymeric polyoxyethylenes have found technical application and therefore were carefully studied. For example, F. N. Hill, F. E. Bailey, and J. T. Fitzpatrick [Ind. Eng. Chern., 50, 5 (1958)] describe the polymerization of ethylene oxide with alkaline earth carbonates. They improve the catalytic efficiency of the carbonates by pretreatment, then prepare macropolymeric products with a molecular weight of up to 1 million after an induction period of only a few hours-which is important in technical preparation. In the following paper of the same periodical, the solubility is described and that in water especially is emphasized. Furthermore, the deviations of these solutions from the Hagen-Poiseuille law are discussed. In 1933, these observations were already described in a publication with H. Lohmann (332). Relationships between the molecular weight and viscosity of these macromolecular products were also reported by F. E. Bailey, J. L. Kucera, and L. G. Imhof [J. Polymer Sc., 32, 517 (1958)]. See page 142 for the results of investigations on several modifications of the crystalline structure of polyoxethylene. References 15, 18, 104, 201, 202, 328, 330-333 are relevant.

11. POLYSILOXANES After it was demonstrated by M. Luthy, R. Signer, and others that polyoxymethylenes consist of long chain molecules (see p. 178), polysiloxanes, which, up to that time, had not been thoroughly elaborated, also were investigated in order to find long chain molecules. This work was carried out between 1928 and 1930 by E. Konrad, later director of the Farbenfabriken Bayer in Leverkusen, and by R. Signer (now in Bern) with their collaborators. This work was not very successful because the structure of polysiloxanes is more complicated than that of polyoxymethylenes and only condensation products with relatively low molecular weights could be obtained.

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These investigations were not continued for long. However, after World War II, when the successful American work in the silicon field became known, the Oberbaden Company for Chemical Industry (Verband der Chemischen Industrie Oberbadens) gave us a grant in 1947 (before the German monetary reform) in order to enable us to carry out similar work in Freiburg. However, I did not consider it rewarding to work in the field of silicones, which already had been elaborated extensively in the U.S.A. Moreover, I was not very familiar with the American literature immediately after the war. Therefore, it seemed more promising to start once more with polysiloxanes, in order to prepare long chain molecules. For this purpose, diphenoxydichlorosilane was reacted with dibasic alcohols, and chain molecules were obtained which, however, did not have a high molecular weight and could be easily saponified by water. Products from the reaction of dicyclohexoxydichlorosilane with dibasic alcohols are more stable, but in this case also, monocyclic condensation products are obtained along with chain molecules. However, the reaction products of hydroaromatic siloxanes with terpine hydrate (337) have a remarkable stability. W. Hahn, who investigated siloxanes, prepared relatively stable low molecular rings from pinaconene and dichlorosubstituted siloxanes. Furthermore, he investigated the reaction products of cyanohydrin with silicon tetrachloride. Accordingly, siloxanes containing different numbers of nitrile groups were obtained. References 86, 88, 334-342 are relevant.

12. POLYESTERS In a lecture at the E. I. du Pont de Nemours Company in Wilmington in September 1958 I mentioned that the new ideas on the structure of macromolecular compounds were introduced in the United States by W. H. Carothers. During 1929 and after, this scientist published with a considerable number of collaborators many interesting papers on the formation of macromolecules through polycondensation [cf. H. Mark and G. Stafford Whitby, Collected Papers of Wallace Hume Carothers (High Polymers, Vol. I), Interscience, New York, 1940; W. Carothers, J. Am. Chern. Soc., 51, 2548 (1929)]. Chain molecules were obtained through the polycondensation of oxyacids or of dibasic alcohols with dicarboxylic acid, i.e., by a reaction well known in low molecular organic chemistry. However, through this polycondensation, W. H. Carothers and co-workers obtained only products having a molecular weight not higher than 30,000.

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These are materials with chain molecules that do not exhibit the typical "eucolloidal" properties of macromolecular natural products like rubber, cellulose, or starch. Originally, the constitution of these polycondensation products was not quite as clear as it appears to be today. I remember with interest several conversations with W. H. Carothers at a meeting of the Faraday Society in 1935 in Cambridge. After his lecture, we discussed the proofs for the existence of chain molecules and methods of molecular weight determination. W. H. Carothers emphasized end group determinations, which could easily be carried out in the case of his chain molecules if these had the expected constitution. For a number of examples, however, especially for superpolyesters, the values obtained by end-group determination were different from those obtained by a physical method. In our conversations as well as in his first publication [J. Am. Chern. Soc., 51, 2548 (1929)], Carothers pointed out that the proof for the existence of macromolecules was clearly shown with the polyoxymethylenes, since, for polyoxymethylene dimethyl ethers, for example, molecular weights obtained by end group determination agreed with those obtained by physical methods (compare p. 234 in ref. 15). Deviations in the case of polyesters could be explained according to the concept at that time by the formation of very high-molecular rings. The same concept mentioned on page 152 was also discussed for products of a polymerization. Furthermore, it was conceivable that decomposition of the superpolyester, e.g., splitting off of end groups, had taken place due to thermal degradation. Unfortunately, this great scientist died soon afterwards. After 1938, research in this field was carried out in the Freiburg laboratory the purpose of which was to decide if the simple viscosity law, which is valid especially for cellulose and its derivatives as well as for other polysaccharides, is also valid for polyesters. Deviations from the law, in other words, the fact that the viscosity number does not increase proportionally with the molecular weight, as stated by H. Warth in 1938 for several polymers, could be explained in terms of branching at that time. However, E. 0. Kramer and F. J. Van Natta [J. Phys. Chem., 36, 3186 (1932)] and W. H. Carothers and F. J. Van Natta [J. Am. Chem. Soc., 55, 4714 (1933)] had published their results on the relationship between viscosity and molecular weight for polyoxyundecanoic acids with molecular weights from 780 to 25,000. It was found that there is no proportionality between viscosity and molecular weight for these condensation products either: low molecular products are relatively more viscous than high

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molecular ones. When these results were checked, it turned out surprisingly that for the products with the highest molecular weight, i.e., 25,000, which was determined with an ultracentrifuge, the relationship between the viscosity number and molecular weight or the number of chain elements, respectively, was identical with that for low-molecular, uniform long-chain esters (cf. ref. 165, p. 97). The relatively high viscosity numbers of low molecular products were explained in terms of stretched out double molecules in this case as well as in the case of fatty acids with long chains (ref. 133, p. 729). At that time, I regarded this result as essential, since the viscosity seemed to be applicable not only to cellulose derivatives, but also to simple chain molecules. However, six years later in the Freiburg Institute, H. Batzer was able to show that the agreement of the Kaq constants for a high molecular polyoxyundecanoic acid with those of uniform low-molecular polyesters was merely coincidental. This was probably due to the fact that the authors had no carefully fractionated products at their disposal at that time. Further investigation on the viscosity of polymers, published by several authors, induced a series of investigations which were carried out after 1938 with H. Schmidt (343,363), 0. Nuss (344,364), and Fr. Berndt (345,346,365). It was necessary to determine more exactly whether a proportionality exists between the viscosity number and the number of chain elements for polyesters. We only had relatively small quantities of monomers at our disposal for this research, most of which was carried out during the war. The results of this work on relatively low molecular polyesters with a molecular weight of a few thousand only seemed to support the validity of the simple viscosity law. However, deviations were found with higher molecular polyesters. Since there was no agreement between the molecular weight found by end-group determination and by the cryoscopic or osmotic method in the latter compounds, branching was again discussed as an explanation, [e.g., in the paper with Fr. Berndt (345)]. Consequently, it was important that this problem was reinvestigated by H. Batzer after the war. His work was made easier by a larger supply of polyoxyundecanoic acid and more starting material which could be obtained in purer form. The experiments of H. Batzer resulted in the statement that polycondensates made from starting n1aterials with poor purity have a lower molecular weight than those from carefully purified starting materials. This fact was of great significance in the technical preparation of polycondensates (p. 65 in ref. 347). Moreover, H. Batzer

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succeeded in improving the conditions of condensation by adding catalysts like p-toluenesulfonic acid, which yields high molecular products at relatively low temperatures (about 120°C). As a result, F. Lombard (353) could obtain polycondensates with a molecular weight of more than 200,000 mainly from polyoxyundecanoic acid. Thus, chain molecules could be prepared which have a chain length similar, for example, to that of macropolymeric polystyrenes, natural rubber, and cellulose. This was progress in the field of polyesters because H. Batzer and his co-workers were able to demonstrate that condensates prepared under cautious conditions contain chain molecules without branches. Polyesters from fumaric, maleic, and acetylene dicarboxylic acids and hexanediol could be converted into succinic acid hexanediol polyesters, which were identical to polyesters prepared directly from succinic acid and hexanediol (359).

An accurate identification of these polymolecular products of course is not possible, as can be done in the case of uniform low molecular materials, e.g., by the melting point and by the melting point depression. However, the same relationship between molecular weight and viscosity number is found with all succinic acid hexanediol polyesters obtained in various ways, which shows that these polyester molecules have the same shape. Therefore, if the hexanediol polyesters prepared with the four different dicarboxylic acids were more or less branched, it would be improbable that the branching would be identical in all cases with that of the succinic acid hexanediol polyesters differently prepared. Thus, these polyesters are polymer-uniform products. Since today it is possible to fractionate such a mixture by new methods, e.g., that developed by R. Signer [Dechema Monograph, 27, 32-44 (1956)], fractions having a relatively high degree of uniformity can be prepared from these polyesters. This is a great advantage with respect to such polymeric

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products with varying degrees of branching, since within the fractionation of polymer isomeric compounds the fractions may be different, not only with respect to their chain length, but also with respect to their degree of branching. Therefore it is useful to make more accurate evaluations of the relationships between molecular weight or chain length, respectively, and other physical properties, especially the viscosity number, for polymeruniform compounds. Furthermore, H. Batzer demonstrated that the viscosity number of polyesters does not increase proportionally, but functionally, with the chain length (347), and that single polyesters show different relationships between viscosity and molecular weight, which permits conclusions about the shape of the chain molecules. Thus, polyesters of fumaric acid are stiffer than those of maleic acid, the ZYJ values of the former being much higher (354). On the other hand, polyesters from acetylene carboxylic acid are strongly folded. Therefore, they do not form fibers and the solutions have a relatively low viscosity (358). Relationships between the ability of the polyesters to form fibers and the structure of the molecule were investigated particularly in the case of hydroaromatic polyesters (361). References 343-372 are relevant.

13. POLYAMIDES As is known, W. H. Carothers' research was very successful because nylon, which later attained tremendous technical significance, was obtained in the condensation of adipic acid with hexamethylenediamine. Very resistant fibers with a high melting point were obtained by melt-spinning. Because of his tragic death in 1937, Carothers was unable to see the technical success of his work. Later P. Schlack in Wolfen demonstrated that e-caprolactam can also be condensed to long chains or polymerized. IG Farben produced Perlon with this method. At that time, no reference to the molecular weights of either of these important synthetic fibers could be found. The very high chain length of the condensates could be assumed because of the high viscosity of the melt and the high tensile strength of the fibers. In order to obtain this information a series of acid amides, diamides, and tetraamides was investigated with H. Jorder (373,378), in 1940 in respect to their viscosity in chloroform and m-cresol so that a basis

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could be established for evaluating the chain length of technical polyamides by viscosity measurements. The subsequent viscometric measurement of polyamides in m-cresol showed surprisingly that technical polyamides only have a molecular weight of I 0,000-20,000 at most. This is much lower than the molecular weight of macropolymers, like polystyrene, polymethyl methacrylate, or cellulose. In a dissertation, published in 1941 (378), H. Jorder explained the peculiar properties of the polyamides in terms of links by secondary valences between the NH group and the carbonyl group. Therefore, acid amides, for example, have a remarkably high melting point. The following was said on p. 90 in reference 373: "Since polyamide fibers have much better mechanical properties than cellulose fibers of the same chain length, we concluded, as published by R. Brill [cf. Naturwissenschaften, 29, 220, 337 (1941)], that the excellent physical properties of the polyamide fibers are based on the strong dipolar forces between CO and NH groups."

Due to the low solubility of technical polyamides, no determination of the molecular weight could be carried out on the basis of osmometry at that time. Therefore, H. Jorder prepared condensates soluble in chloroform from substituted diamines, e.g., diisobutylhexamethylenediamine and sebacic acid. The molecular weight of these compounds could be determined by osmometry and viscometry, giving a further basis for the determination of the chain length of technical polyamides (374). In a work carried out in the laboratories of the IG-Farben Wolfen, A. Matthes [J. Prakt. Chem. N.F., 162, 245 (1943)] tried to demonstrate that the viscosity number in polymerhomologous polyaminocaproic acids, which were prepared from e-caprolactam, does not proportionally increase with the molecular weight. According to H. Schnell (376), however, this is not correct, since :t;elatively low-molecular condensates were used. H. Schnell, who is now director of the Farbenfabriken Bayer in Uerdingen, worked on this problem in Freiburg in 1943 and 1944. We prepared polymer homologous polyaminocaproic acids in the presence of halogenbenzoic acid as a catalyst and, in this way, polyaminocaproic acids which contained an analytically detectable end group were obtained. In a polymer homologous series of such products, having a molecular weight of up to 15,000, the molecular weight evaluated by the end-group determination agreed with that obtained from viscometric measurements within a certain limit of error. Intact chain molecules were taken for these measurements, whereas in technical products chain

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molecules are often somewhat affected by a change in the end groups due to the high temperature of the condensation. The synthesis was carried out by H. Schnell at as low a temperature as possible (150-200°C). Accordingly, a polycaprolactam with low solubility slowly separated from the melt. The precipitate is a high molecular product and relatively uniform, since the low molecular condensates remain dissolved in the melt. Therefore, polyamides thus obtained are not as polymolecular as the technical products, which still contain considerable amounts of low molecular condensates. The fractions with the highest molecular weight have an average molecular weight of, at most, 20,000 according to endgroup determination (377). H. Schnell showed that the viscosity number proportionally increases with the chain length, i.e., the molecular weight, in a polymer homologous series. It was also demonstrated that the conclusions of A. Matthes did not hold, since double molecules were present in solutions of low molecular polyaminocaproic acids which he investigated. A series of further investigation on viscosity and molecular weight relationships in technical polyamides was published later, mainly by American scientists, who found out that the Kuhn law is valid for the relationship between viscosity and chain length. The results of H. Schnell should be checked once more for this reason, since th polyamides he used were prepared under very favorable conditions. References 373-379 are relevant. 14. AMINOPLASTS

At the beginning of the 1920s, F. Pollack [cf. Chemiker Ztg., 48, 569 (1924)] prepared unbreakable glasses from condensation products of urea and thiourea, respectively, with formaldehyde. At first, his efforts were not very successful, since fissures were formed in these glasses and they cracked. Today, the preparation has been modified, and aminoplasts play a very important role in the plastics field. When I received the first artificial glasses from urea and formaldehyde in 1928, I often showed an "unbreakable dish" in my lectures and threw it on the floor to demonstrate these new properties. In 1930, I had to give a lecture on the development of plastics and fibers in an advanced course to chemistry teachers. On this occasion, I also demostrated the "unbreakable dish." When, after some explanation, I threw it to the floor, it broke, surprisingly, into many small pieces, to the amusement of the

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audience. Seldom did I receive such applause-even after a successful demonstration! When the stable Plexiglas became known at this time, I found the difference in the behavior of both glasses quite remarkable. After further investigation, I realized that these organic glasses have fundamental differences in their structure. Aminoplasts are products of a polycondensation in which the enlargement of the molecules occurs through loss of water. Since the condensation process continues in the interior of these glasses, tensions are unavoidable. On the other hand, Plexiglas is a product of polymerization. Although in this case too the· included monomer (about 0.5%) can polymerize further with decrease in volume, the resulting tensions are much lower than those in aminoplasts. White, insoluble condensation products result from the acidic condensation of urea and formaldehyde, which I previously thought were high molecular products. At that time, i.e., the beginning of the 1920s, unsaturated compounds, for example, styrene, were very difficult to obtain. Therefore, it seemed reasonable to study the condensation products of urea and formaldehyde, mainly in connection with the work on polyoxymethylenes started in 1920, in order to get information on structure and, especially, on the relationship between their physical properties and the size of the molecules. Looking back, I would say that we were lucky not to have started an investigation of this compound, which was easily available. Otherwise, I too would have accepted the idea in Zurich, that there really are no high molecular products. This assumption would have agreed with P. Karrer's theory on the micellar structure of the "socalled" high molecular materials and, furthermore, the concept of colloid science represented in Zurich, for example, that of G. Wiegner who was a student of W. Ostwald. Condensation products of urea and formaldehyde are actually compounds with relatively short chains, which on)y seem to be of a macromolecular nature. At that time, research on this field was not being carried out because the condensation products of formaldehyde and urea did not have the expected composition according to elemental analysis: analytical values did not agree with the theoretical values for a polymeric methylene urea, which should be formed like polystyrene in the following manner:

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At that time, as always, I endeavored to investigate only those macromolecular products that had a composition known exactly by elemental analysis (see p. 109). Therefore, work on aminoplasts was postponed for a long time, until at the end of the 1930s Dr. R. E. Vogel, who had done work in the technical production of aminoplasts, carried out a few experiments of more or less technical interest. He wanted to use modified aminoplasts for the production of wood fiber plates which would prevent too fast a hardening within the manufacturing process. This work was interrupted by the events of the war, but it attracted attention again to the research on aminoplasts, about which many contradictory statements had been made in the extensive literature. Then, from 1951 on, K. Wagner did work in this field. The results of his investigation are published (besides his diploma and doctoral thesis) in refs. 381 and 383. Progress in the evaluation of their constitution was made by investigating thiourea and formaldehyde condensation products , since an oxygen content can only be due to the presence of ether bridges or hydroxy groups. Furthermore, new solvents for thiourea condensates, i.e., dimethylformamide and caprolactam, were found. Their application was protected by the German patent DBP 910,336, September 26, 1951. As a result, a determination of the molecular weight of the condensates could be carried out by cryoscopy in caprolactam. These results agreed with the molecular weight, which was evaluated by endgroup determination of the methoxy content of the etherified methylol group at the end of the chain and the chloral derivative of the amide end group.

A special difficulty in the investigation of the condensates is the fact that these powders, which are very fine and amorphous, are extremely hygroscopic. As a result so much water vapor is absorbed from the air during the process of weighing that the analytical values are invalidated.

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Therefore, elemental analysis had to be carried out under special conditions, e.g., the weighing in had to be done with the exclusion of humidity as far as possible. As a result of this investigation it was shown that relatively low molecular weight products which contain 4-6 thiourea groups are formed in the condensation of thiourea with formaldehyde. Primary products, formed through polycondensation, contain a hydroxy group at the end of the chain. With heating, these methylol compounds lose one molecule of water and are transformed into products having the composition of polymeric methylenethiourea (383,389). If the primary methylol derivatives are dried in vacuum for a long time (eventually at elevated temperatures), partial splitting off of water is possible. Mixtures of changing com position result, an analysis of which yields the confusing results mentioned formerly. Products of analogous composition were also obtained from urea and formaldehyde. Due to the higher solubility of the urea component in water, somewhat higher molecular condensates with up to 10 urea groups were obtained. Since these products are only soluble in a concentrated solution of lithium iodide, their molecular weights were evaluated only on the basis of etherified end groups or with chloral-reacted end groups. This work, in which H. Kdissig and G. Welzel (389) participated later, was abandoned in 1956 after my retirement. Therefore, the investigations proposed for condensation products prepared in the presence of alkali unfortunately were not carried out. Very peculiar results were obtained with G. Niessen in the condensation of thiourea derivatives with formaldehyde (384). A completely insoluble, amorphous product results from the condensation of ethylenethiourea and formaldehyde, in which three ethylene thiourea rings are linked by two methylene bridges:

Surprisingly, no solvent could be found for this condensate, in spite of its low molecular weight. However, it could be transferred into a soluble di-p-chlorobenzoyl derivative, by reacting NH groups at the chain end with p-chlorobenzoylchloride, the molecular weight of which was determined by cryoscopy.

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In the condensation of ethyleneurea and formaldehyde, amorphous, water-soluble condensates are formed, in which 5-6 ethylene urea rings are condensed. In 1950, H. Krassig started an elaboration of the condensation products of aliphatic diamines with formaldehyde, continuing the investigation of C. A. Bischoff and F. Reinfeld [cf. Ber., 36 35 (1903)]. These scientists had obtained low molecular products of well-defined constitution from lowmembered diamines with formaldehyde, whereas amorphous and completely insoluble condensates were obtained from higher-membered diamines, e.g., pentameihylenediamine and formaldehyde. An investigation on the condensation of ethylenediamine with 1 or 2 moles of formaldehyde carried out with G. Greber (p. 83 in ref. 387, and ref. 400) resulted in the detection of two low molecular isomeric products. Hexamethylenediamine yields completely insoluble products, in the condensation with 2 moles of formaldehyde as does pentamethylenediamine. An evaluation of the constitution showed that these products were formed through the crosslinking of primary derivatives, whereby a hexahydrotriazene ring was formed as a structural element. The formation of such a hexahydrotriazene ring was detected in the condensation of hexamethylenediamine with 1 mole of formaldehyde (387). The monomeric azomethine derivatives resulting from the condensation of formaldehyde with primary amines are not stable, but polymerize immediately, yielding six-membered rings, i.e., hexahydrotriazene derivatives. There is no chain reaction as in the case of ethylene and ethylene derivatives. The azomethine derivatives do not have the ability to polymerize in the case of Schiff's bases from higher aldehydes or ketones and . . pnmary am1nes. Furthermore, H. Krassig and H. Ringsdorf (390) investigated the condensates of formaldehydes and primary aromatic amines, which had been also of technical interest for some time. As C. A. Bischoff and F. Reinfeld already had discovered, two isomeric products were formed in this process. The rearrangement of both isomers was investigated and it was found that the triazene ring is split and forms methyleneaniline during thermal treatment. The formation of this unstable monomer was demonstrated by addition of diphenylketene with the formation of ,8-lactam. This investigation showed that only six-membered rings, i.e., hexahydrotriazene derivatives, not chain molecules, are formed in the polymerization of methyleneaniline and similar products.

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References 380-394 are relevant.

15. HIGH MOLECULAR AND POLYCYCLIC SCHIFF'S BASES H. Krassig and G. Greber (395) tried to obtain high molecular Schiff's bases from terephthal aldehyde and aliphatic diamines. The condensation products were not very high molecular. This is remarkable because due to the high reactivity of the aldehyde group with the amine group, macromolecular poly-Schiff's bases were expected from polycondensation. Interesting results were obtained when ether diamines instead of aliphatic diamines were condensed with terephthal aldehyde. In this reaction, crystalline dimeric high-membered ring compounds, not chain molecules, are formed. Particularly remarkable is the easily achieved transfer of these ring compounds into the desired high molecular Schiff's bases. Thus, according to H. Krassig and G. Greber (396), a strong increase in the viscosity takes place when a 4% solution of the 30-membered terephthal aldehyde- γ , γ'-diamino dipropyl ether condensate in benzene is boiled. When the thus formed viscous solution is precipitated in petrol ether, a fibrous product is obtained, which has a degree of polycondensation of at least 40 according to viscometric measurements. However, this product with a fiber structure is very unstable in solution and again forms the starting material, i.e., the dimeric ring, with cleavage of the macromolecule, particularly in dilute solutions. In order to vary the dialdehyde component, G. Greber (397) prepared dialdehyde by condensation of p-oxybenzaldehyde with w,w' -dihalogen compounds; by reaction with diamines it also yielded poly-Schiff's bases. In further work (399) by G. Greber, 54-, 58-, and 66-membered dimeric rings were prepared and their rearrangement into high molecular polySchiff's bases was thoroughly investigated.

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An osmometric molecular weight determination of the poly-Schiff's bases was not possible due to their instability in solution. It turned out, however, that stabilization of the ring compounds and the high molecular poly-Schiff's bases could be achieved by hydrogenation as well as by addition of diphenylketene to the azomethine compounds. The minimum values for the molecular weight could be determined with these stable derivatives. If these results had been obtained earlier, e.g., in the middle of the 1920s, they would have been interpreted in a different manner: it would have been assumed that the crystalline rings are actually single molecules, the solutions of which would be highly viscous under certain conditions through the association of the rings to colloidal particles.

Accordingly, the high molecular poly-Schiff's bases, would actually be aggregates. Thus, the easily reversible reaction to the crystalline dimeric products from the only apparently high molecular ones could be well understood. Since multiple dialdehyde components and all kinds of diamines can be used for condensation, a large field of investigation for the formation of ring species and their rearrangement to high molecular poly-Schiff's bases is open. Such investigations should give more information on the problem of ring chain polymerization. References 395-400 are relevant.

11 Macromolecular Natural Products

1. RUBBER AND BALATA The first 48 communications were published under the title "Uber lsopren und Kautschuk," separated from the other communications on high polymers, i.e., macromolecular compounds. The first 4 communications of this series deal with the syntheses of isoprene and its low molecular derivatives. They are mentioned in part A under the numbers 152, 157, 158, and 159 (see p. 43). Only the last publications (49th through 53rd communications) can be found under the title "Mitteilungen uber makromolekulare Verbindungen."

After our work with H. W. Klever in Karlsruhe in 1911, isoprene was easily accessible through the pyrolysis of dipentene (see page 43). Experiments to polymerize isoprene to rubber were made and isoprene was polymerized with dibenzoyl peroxide and other peroxides. In 1912 it was proved with L. Lautenschlager that peroxides accelerate the polymerization of styrene and other unsaturated compounds (A134, B222). The work on the polymerization of isoprene with peroxide was not published but a patent was applied for. The patent was not granted because patents employing similar procedures were applied for at the same time. During these experiments we became familiar with synthetic rubber in our Karlsruhe laboratory. It showed some similarities with natural rubber but differed in some properties, e.g., the viscosity of colloidal solutions. The explanations for the differences between natural and synthetic rubber, given by G. Steimmig [Ber., 47, 350 (1914)] did not seem satisfactory to us. In connection with the work on high polymer materials, mainly polyoxymethylene, the elucidation of the structure of rubber was started. Because of the changeability of rubber, this was quite difficult. 202

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In 1920, two structures of rubber were thought to be possible: either it was a low molecular, unsaturated hydrocarbon, associated to colloidal particles-this opinion was held at that time by C. Harries [cf. Ber., 37, 3988 (1905)] as mentioned on page 83 and later by R. Pummerer [Ber., 60, 2167 (1927)]-or the molecules of rubber were long chains with many isoprene molecules connected by primary valences. In the latter case, rubber would have a structure similar to polyoxymethylene just investigated then. According to C. Harries, the distinction between the two possibilities should have been easily established by hydrogenation: "It would be necessary to hydrogenate rubber. Hydrorubber could probably

be distilled in vacuo without decomposition. Thus, its structure could easily be proved." (Compare C. D. Harries, Untersuchungen uber die naturlichen und kunstlichen Kautschukarten," Springer, Berlin, 1919, p. 48.) This reduction was made together with J. Fritschi in an autoclave with an agitator at 270°C and 100 atm with platinum as catalyst. The saturated hydrorubber obtained had the composition C5H 10 ; it could not be distilled, but it had properties similar to those of rubber and gave a colloidal solution. This result confirmed the opinion which has been published in a short paper (ref. 1, seep. 78) in 1920, that rubber molecules are long chain molecules. With this interpretation many properties of rubber and hydrorubber could be explained: hydrorubber, a paraffin hydrocarbon, is cracked at much higher temperatures than rubber, whichas already mentioned (see page 44)-decomposes easily on heating because of the allyl substitution effect of the double bond (Allylgruppierungsregel). In this work, the designation "macromolecules" was proposed for the first time for molecules of the size of colloidal particles (seep. 83). Shortly after this first publication, R. Pummerer and P. A. Burkard [Ber., 55,3458 (1922)] published on the same topic. They reduced rubber in a hexahydrotoluene solution with platinum black as catalyst. The analysis of this hydrorubber gave the expected composition (C5H 10) but, according to the authors, it was autoxidable and transformed to an isorubber (C5 H 8)x. Therefore, the question arose as to whether the hydrogene in this hydrorubber was bound by primary valences. This hydrorubber definitely was not a paraffin derivative, since these are not autoxidizable. The reason for these erroneous statements is not clear even today.*

*

It is strange that even today the production of hydrorubber is assigned to R.

Pummerer (cf., e.g., L. F. Fieser and M. Fieser, Lehrbuch der organischen Chemie, translated by Hans R. Hensel, Verlag Chemie, Weinheim, 1955, p. 350).

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Shortly after this, C. Harries published two works [Kolloid­Z., 33, 183 (1923); Ber., 56, 1050 (1923)] in which he mentions that R. Pummerer succeeded in hydrogenating rubber in dilute solutions; he says that he too obtained strongly degraded rubber under the conditions of R. Pummerer and P. A. Burkard. He does not mention the transition of hydrorubber to isorubber. The work of H. Staudinger and J. Fritschi, which led to hydrorubber, is mentioned only briefly by C. Harries: "The method of reducing rubber without solvent at 250°C and 100 atm of Staudinger [Helv. Chim. Acta, 5, 785 (1922)] is a different case. It leads to the reduction of pyrolytic scission products of rubber. Therefore, I think that Staudinger's theoretical conclusions are premature [cf. Ber., 56, 1050 (1923)].

In a further communication (3) I pointed out that C. Harries' arguments did not hold but that the transformation of rubber to a macromolecular hydrorubber was proof for the chain structure of rubber. In this work we also proved that the hydrorubber obtained by reduction of rubber in hexahydrotoluene solution was identical with the hydrorubber described in our communication with Fritschi (2). Today, this has to be corrected insofar as the hydrorubber obtained by high temperature reduction is a degraded product. The hydrorubber obtained from solutions has longer chains and therefore gives solutions of higher viscosity. It was also pointed out that by reacting rubber hydrohalids with dimethyl zinc and diethyl zinc, homologous hydrorubbers are obtained which also give colloidal solutions (402).

In the same year, R. Pummerer and A. Koch [Ann., 483, 294 (1924)] published a surprising work saying that well-purified rubber could be crystallized. This was in accord with R. Pummerer's view that rubber was relatively low molecular. Harries' opinion was furthermore supported by the communication that one-third of the hydrorubber was distillable under high vacuum. The distilled product had the composition C45 H 92. Two-thirds of the undistillable product was reported to be saturated as well; its cryoscopically determined molecular weight in camphor was

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approximately 1500. I proved later that both statements were wrong (413-416), but at that time, Harries' conception that hydrorubber was at least partly distillable seemed to be proved. This concept was backed in a number of papers by R. Pummerer and co-workers by different experiments such as molecular weight determination [R. Pummerer, H. Nielsen, and W. Gundel, Ber., 60, 2167 (1927)], and by investigations on isorubber nitron which, according to R. Pummerer and W. Gundel [Ber., 61, 1591 {1928)] has a molecular weight corresponding to a rubber molecule with the composition (C5H 8)8 . At this time, R. Pummerer's opinion that rubber was relatively low molecular was widely accepted. E. Ott tried to support this opinion by Xray investigations on crystallized rubber as well [Physik­Z., 27, 174 (1926); Helv. Chim. Acta, 9, 31 (1926)]. Two years after my call to the chemistry chair at the University of Freiburg, one of my older colleagues from the Freiburg faculty told me that he had heard from Erlangen that through Pummerer's work the question of the structure of rubber was solved, and that my concept therefore was untenable. I asked him if he and the faculty were now of the opinion that they had made a mistake by offering me the chair! However, it took quite a bit of work to show that Pummerer's opinion was incorrect. For example, it was proved (in references 403 and 404) that the molecular weight determinations of Pummerer were wrong. In a work with H. Joseph proof was given that isorubber nitron was a mixture of degraded products of different molecular weight which could be separated by fractionation (405). Further evidence for the macromolecular structure of rubber was its transformation to rubber triethylphosphonium bromide, a salt which formed colloidal high viscous solutions in water. This work showed that the homopolar macromolecular hydrocarbon could be transformed into a heteropolar macromolecular salt (see page 175). We reported on this transformation in a short essay (406):

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Experimental details can be found in the dissertation* of Reuss (A174). In Zurich and later in Freiburg my co-workers and I continued to work on the reduction of rubber. C. Harries and F. Evers (Chern. Zentr., 1921, III, 1358) stated that the reduction of rubber hydrogen halides with zinc powder gave a partially reduced rubber of the composition C35 H 6 2 or C40 H 70 , the a-hydrorubber. We could not confirm these results byrepeating this experiment because an isomeric rubber, a cyclorubber, (C5H 8)x, is formed:

The transformation of rubber hydrogen chloride into a cyclized rubber is comparable to the transformation of open-chain terpenes to cyclic terpenes. This cyclorubber still contains double bonds and can be transformed into cyclic hydrorubber by hydrogenation. By repeated treatment with hydrogen chloride and zinc a polycyclorubber is obtained which is a powdery, strongly degraded product (407,408). Cyclization of unsaturated rubber molecules can be also obtained by heating to more than 250°C. This cyclorubber is identical with the one mentioned above, as far as it was possible to identify macromolecules as identical at all; it is a mixture of degraded cyclic products. Besides the cyclization, cracking of the rubber molecules occurs, and this finally leads to isoprene. The volatile products contain a relatively large amount of dipentene. At an earlier time this experiment could have led to the opinion that dipentene was the basic molecule of rubber. In references 409 and 410 it was pointed out that the cracking of rubber proceeds much easier than the cracking of hydrorubber and cyclorubber because of the already mentioned allyl substitution effect(Allylgruppierungsregel, see page 44). This effect was often cited in the literature as Schmidt's double-bond rule. In a special publication (411) I explained the historical background of this rule.

*

Shortly after I came to Freiburg in 1926, I talked to Professor Opitz, who was director of the women's hospital, on pharmaceuticals against cancer which was his special field of work. I proposed to him the idea of trying the water-soluble rubber phosphonium salts which I had prepared. After injecting the aqueous salt solution in rats their tumors disappeared very quickly, but the salts were very toxic and the rats died shortly after treatment. In the same year Professor Opitz died in a car accident. For a short time these experiments were continued by Dr. Heinrich Jung. I don't know anything about his later work on this field at the IG Company in Elberfeld.

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In 1930, the investigations made with W. Heuer on polystyrene showed the relationship between the viscosity number and molecular weight (ref. 122, see p. 125). This was proved as well for paraffin hydrocarbons by R. Nodzu (123). Thus, it was possible to get more information on the degree of polymerization from viscosity measurements of hydrorubber and rubber. By careful reduction in the cold, a high molecular rubber with a molecular weight of 31,000 was obtained from a rubber having a molecular weight of 45,000. This experiment showed that the colloidal particles in a rubber solution Wt:re not aggregates or micelles, but the macromolecules themselves (161,412-417). This question had to be discussed in relation to the micellar theory of K. H. Meyer and H. Mark. These scientists had published (see p. 87) an essay on rubber based on this theory [Ber., 61, 1939 (1928)]. They assumed that the primary valence chain of rubber contained 75 to 150 isoprene units and that these chains formed the micelles. The osmometrically determined particle size of the micelles therefore did not give any information on the length of the primary valence chain, since the chain aggregates and not the chains are osmotically effective: "The osmometrically determined value can therefore be a multitude of the value attributed to a single main valence chain" [Ber., 61, 1943 (1928)].

For this reason it was important for us to prove by polymer analogous transformation with the methods of classical organic chemistry that the colloidal particles in rubber solutions are real macromolecules and not aggregates or micelles. For this reason, a polymer homologous series of polyprenes, that is, of rubber and balata, were transformed into the corresponding polymer analogous polypranes. Carrying through this investigation, which finally proved the structure of rubber, asked for a good supply of patience from E. 0. Leupold who started this work in 1931, because rubber solutions-unlike hydrorubber solutions-are extremely autoxidizable. This is revealed in the decrease of the viscosity of their solutions. Based on our experience with solutions of polystyrene and hydrorubber, we were sure that the decrease in viscosity of rubber solutions was due to degradation of the macromolecules by autoxidation and not to a change in the unstable colloidal micelles. We therefore tried to work in the absence of oxygen. The solvents, e.g., tetraline, were distilled once or twice under nitrogen in order to free them of oxygen as our experiments had shown that bubbling pure nitrogen through a rubber solution was not sufficient. Only by taking these precautions were rubber

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solutions finally prepared which did not change their viscosity on standing or on slight warming, i.e., where no degradation of molecules took place. In order to make the solutions, the rubber was cut and weighed in vacuo in a box with a glass cover and with openings on the side in order to introduce the hands through corresponding cuffs. The rubber was purified and dried under high vacuum, then cut under pure nitrogen, and small pieces were put into vials. The weighing as well as the preparation of the solution for reduction was done in vacuo. It is necessary to work in this way since when pure rubber is cut and weighed in air, peroxides are formed on the surface by autoxidation which will cause degradation of the rubber in solution. It was planned to expand these experiments and publish them in a book on rubber, but this plan was never realized. Therefore I was surprised when I visited the B. F. Goodrich Company in Brecksville, U.S.A., iri 1958 and Dr. Semon showed me a similar device for working with rubber. Rubber and balata were hydrogenated in solutions prepared with these precautions. The viscosity number of the unhydrogenated polyprenes and the hydrogenated polypranes were compared. The viscosity numbers of polyprenes and polypranes turned out to be approximately the same (418). Viscosity measurements on squalene and its hydrogenation products, made at the same time, proved that both hydrocarbons had the same viscosity number (419). In today's literature it is often taken for granted that the colloidal particles of rubber are macromolecules. In Table 11 data of our experiments are given which prove this statement.

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The question could arise: Why is the polymer analogous transformation of polyprenes into polypranes not supported by osmotic molecular weight determination. Now, osmotic measurements are easily made on solutions of polypranes but not on polyprenes, since they decompose readily. Later on, molecular weight determinations by osmotic measurements were done with Kl. Fischer (420). Special osmometers made of V4A steel were used since, according to our experience, the rubber solutions were quite stable in them. The degree of polymerization (DP) of natural rubber determined in this work was approximately 2000. Newer measurements, e.g., those by G. V. Schulz, K. Altgelt, and H. J. Cantow [Makrornol. Chern., 21, 13 (1956)] and K. Altgelt and G. V. Schulz [Makrornol. Chern., 32, 66 (1959)] gave much higher values. The viscometrically determined degrees of polymerization of these polyprenes were much lower than the values obtained by osmometric methods. Therefore, in references 420 and 421 the question was raised if perhaps the rubber molecules were branched like the molecules of buna. As shown by fractionation, rubber is a mixture of polymer homologues. In order to examine if macromolecules of uniform length are build in nature, an evonymus gutta-percha was investigated which was prepared carefully in vacuo. The main part of these gutta-percha molecules had an average degree of polymerization (determined by osmosis) of 1600. It may be that it is a natural product with uniform macromolecules (422). Chlororubber was investigated as well. Its solutions are of relatively low viscosity, which is of importance for its industrial use. In the beginning we assumed that rubber is degraded during chlorination. Determinations of the degree of polymerization of chlororubber which were made by my son Hansji.irgen Staudinger (now in Giessen) gave the surprising result that chlororubber was a high polymer and had approximately the same degree of polymerization as the original rubber (see Table 13, p. 296) (423). The reason for the low viscosity of chlororubber solutions is in the cyclization of the rubber molecules and not in the degradation of rubber. In the beginning, the work on natural rubber and balata, as well as on synthetic buna, was made quite difficult by the fact that for unforeseen reasons the purified materials all of a sudden became insoluble and could not be worked with. I remember that in Zurich one of my co-workers purified a large amount of balata by extraction and reprecipitation. This beautifully pure white product became insoluble after standing in a desiccator for several days. At this time-about 1925-we thought that

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it was perhaps premature to work with such a peculiar product. In further works, mainly through the experiments of Ch. Moureu and Ch. Dufraisse [Ch. Moureu and Ch. Dufraisse, Institut International de Chimie Solvay, 2me Conseil de Chimie, Avril 1925, Gauthier- Villars et Cie, Editeurs, Paris, 1926, p. 524; Ch. Dufraisse, Rev. Gen. Caoutchouc, 8, 9 (1931) ], it was shown that specially purified rubber was much more autoxidable than raw rubber which contains anticatalysts. Two reactions are possible during interaction of oxygen and rubber: in solution rubber usually is degraded, as can be easily seen by the depression of the viscosity. In the solid state, on the other hand, small amounts of oxygen crosslink the chain molecules and make rubber, i.e., balata, insoluble. Therefore, the pure polyprenes have to be kept with the rigorous exclusion of air. (See references 15 and 424.) The question concerning the structure of rubber and balata is not answered completely even today; e.g., the end groups of these hydrocarbons are not yet known. The works of C. Harries and later the investigations of R. Pummerer and co-workers [Ber., 64, 809 (1931)] have shown that more than 90%of the isoprene units in rubber were bound in the 1,4 position. However, it is still possible that some different groupings were present. I considered the possibility that rubber had a few long chain branchings since rubber has the same Km values as buna, where branching definitely has been demonstrated (420,421). Perhaps the elastic properties of rubber were due to this branching. At that time, the assumption was discussed that the branchings could cause the elasticity in such a way that the valence bonds on the branching points were bent during the stretching and therefore a strain is created in stretched rubber corresponding to the Baeyer strain theory (cf. footnote 564 on p. 197 of ref. 73). In order to prove such branching in rubber, we degraded it with ozone and then oxidized it with permanganate. Also, the rubber solution was treated directly with permanganate in pyridine solution in the hope of obtaining small amounts of tricarbonic acid as a degradation product which would have been evidence of branching. These experiments, which were not finished, did not yield such results, but it is possible that there are other, not yet known, groupings present in the rubber molecule. An essential result of this work on rubber, its degradation products, and its cyclization products was the knowledge that long chain molecules are necessary for a product to show elasticity, since strongly degraded products do not show it. This holds as well for several other macromolecular materials, e.g., polystyrene (18,425).

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In order - to obtain evidence for the macromolecular structure of rubber many other investigations, e.g., viscosity measurements of its solution, were performed, and a number of summarizing communications were published as well (I5, 19,27,28,40 160,168,181, 195,426-460). 2. CELLULOSE

(a) Cellulose Acetates and Cellulose Ethers 120 of the 446 publications on high polymer, i.e., macromolecular compounds, have the heading "On Cellulose." These are summarized here.

In the autumn of 1923, when K. Frey started to prepare his dissertation (461), I proposed that he work on the elucidation of the structure of cellulose. I hoped that we could proceed here in the same way as in the case of polyoxymethylenes, i.e., by acetolytic degradation and end-group determination. This degradation should have been done on trim . ethylcellulose; if this turned out to be a chain molecule it could be compared with the chain molecules of polyoxymethylenes. Instead of the CH2groups of polyoxymethylene chains, trimethylglucose groups are present in the trimethylcellulose chain. By acetolytic degradation of such a trimethylcellulose, a mixture of polymer homologous trimethylcellulosediacetates should be obtained. From the acetyl content of the single representatives, the chain length could be determined. From this a conclusion about the minimum chain length of undegraded trimethylcellulose should be possible.

Therefore, it was necessary to prepare a trimethylcellulose where all hydroxy groups should be transformed to methoxy groups. Such a trimethylcellulose could not be obtained with the methods of preparation known at that time. Together with K. Frey we tried to prepare the tripotassium salt of cellulose by reacting potassium amide with cellulose in

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liquid ammonia,* with the hope that this could be permethylated. The dry potassium salts are very unstable and often explode spontaneously. With methyl bromide or methyl iodide we could not obtain permethylated products [cf. the works of L. Schmid and B. Becker, Ber., 58, 1966 (1925), published at the same time]. Since it is often easier to obtain the allyl derivatives than the methyl derivatives, we tried this in order to get a completely substituted triallylcellulose, but again without success. The acetolytic degradation of cellulose ethers was not investigated further. Afterwards we tried another way to disprove the opinion of P. Karrer, K. Hess, and others on a micellar structure of cellulose. At the beginning of the 1920s P. Karrer's concept of a low molecular structure for cellulose was accepted in Switzerland (see p. 84), but the elucidation of the structure of polyoxymethylenes (p. 179), mainly by X-ray investigation, (p. 138), but also by other experiments with different polymeric materials, seemed to refute P. Karrer's assumption. Therefore, in a work published in 1929 on polyoxymethylenes (86), arguments in favor of the chain structure of cellulose were summarized in a special chapter. Experiments done with W. Starck in 1928 (462) showed that the assumption of cellulose being a low molecular glucose or cellobiose anhydride could not be valid. At that time one could assume that the bonds between the single glucose residues in cellulose acetate were so loose that they would break up in glacial acetic acid. The mono- and dimolecular acetates in this solution would cause a strong freezing point depression (cf. Table 1, p. 80). But a number of acetates with different physical properties, mainly with big differences in the viscosity of solutions of equal concentration, were known. If these acetates in glacial acetic acid solution really were dissolved as low molecular substances, equal cellulose acetates should be obtained on evaporating the glacial acetic acid from solutions of different acetates, but experi1nents published in 1930 with W. Starck have showed that from the glacial acetic acid solutions different cellulose acetates are obtained with the same properties they had before being dissolved. They had, for instance, the same viscosity properties (cf. ref. 462, p. 2313). The surprisingly large freezing-point depressions could not be explained in this way. In order to explain these striking observations, K. Hess and M. Ulmann [Ann., 504, 87 (1933)] published a communication where the dissolved cellulose acetates were assigned "a memory of their foregoing experiences." This led me to publish a paper (463) on "The

* Such a procedure

has been successfully applied for the preparation of the potassium salt of diphenylmethylene carbonic acid (A56).

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213

Memory of Cellulose Acetates," wherein I said that according to the experiments described this memory had to be a phenomenal one indeed! Later it was proved that the osmotic behavior of celites in glacial acetic acid was not different from other macromolecular compounds (109,110). In 1927-1928 it was not possible any more to hold to the opinion that cellulose was low molecular: as mentioned on p. 86, it was no longer possible to claim that X-ray investigations proved a low molecular structure of cellulose because of the. investigations on polyoxymethylene. In 1921 K. Freudenberg [Ber., 54, 767 (1921)] supported the chain structure against the comb structure of K. Hess. Together with E. Braun [Ann., 460, 288 (1928)] he described the low molecular trimethylglucose anhydride which could be distilled separately from trimethylcellulose. Therefore, it was proved that trimethylcellulose could not be an aggregation of low molecular glucose anhydrides. M. Bergmann in collaboration with H. Machemer [Ber., 63, 316 (1930)] gave up his former opinion [Ber., 59, 2973 (1926)] in favor of the chain structure of cellulose. They published results on minimum chain length of cellulose, i.e., cellulose acetate, using a method for the determination of aldehydes with iodine which had been introduced by R. WillsHitter. Highly noteworthy were the works of K. H. Meyer and H. Mark, starting at 1928, on the micellar structure of cellulose and cellulose derivatives. They showed, in connection with the work of O. L. Sponsler and W. H. Dore (Colloid Symposium Monograph 1926, p. 174) that the results of X-ray investigations could be explained by assuming a chain structure of cellulose, but nevertheless they assumed a micellar structure of cellulose and its derivatives. As explained on p. 88, one cellulose micelle [Ber., 61, 609 (1928)] should contain about 50 primary valence chains; each of these primary valence chains should contain up to 50 glucose residues. This new micellar theory of cellulose received a great deal of attention, since it seemed to explain many observations. It is surprising that even today the term "cellulose micelle" can be found in literature on cellulose, even though the macromolecular nature of cellulose is established and it is proved that the colloidal particles in cellulose solutions are macromolecules. It would be desirable in the interest of the chemistry of cellulose that the expression "micelle" should disappear. It is misleading when the crystallized parts of natural and regenerated cellulose fibers are called micelles and micellar filaments. Instead of micelles, one should talk about crystallites, where macromolecules of different length are arranged in a macromolecular lattice. I

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don't even dare to hope that some day nomenclature in this field will be clear! But it is not only a question of nomenclature whether one talks about micelles or macromolecules, there are basic differences involved. In several lectures I have tried to explain these differences as follows: Let us take a box of matches containing about 50 matches 5 em in length. Such a bunch of matches would be a micelle of primary valence chains according to K. H. Meyer (the box itself could be called the skin substance according to K. Hess, [Naturwissenschaften, 22, 469 (1934)]. If each chain contains 50 glucose residues, then the micelle holds 2500 such residues and its weight would be 162 ·x 2500 = approx. 400,000. According to the macromolecular conception, these 50 primary valence chains are not held together loosely by micellar forces to form a micelle, but the 2,500 glucose residues are connected through primary valences to form a long chain molecule, the cellulose. These macromolecules have a degree of polymerization of 2500. The length of such a chain would be approx. 21/2 m in the above mentioned model. The length of such a cellulose molecule, if determinable by X-ray investigation, would be 1.28μ. Thus, a single cellulose molecule should be visible under the microscope, but because of its extremely small diameter, approx. 5 Å, it is not. In the 1930s these were strange and striking concepts which often were ironically discarded since the micellar theory of K. H. Meyer seemed to be more plausible. Our arguments proceeded step by step. For a long time different celluloses and cellulose derivatives were known which differed in their physical properties, especially in their viscosities of solutions of equal concentration. If they had a micellar structure, then this different behavior could be caused by differences in the size of the micelles or the length of the primary valence chain. But if these products were macromolecules, then these differences were caused by the different lengths of the macromolecules. Polymerhomologous series of celluloses and cellulose derivatives like acetates and nitrates exist; all products were mixtures of polymer homologs. It was possible that the native celluloses like cotton cellulose and ramie cellulose were uniform. According to newer investigations, e.g., G. V. Schulz and M. Marx [Makromol. Chem., 14, 52 (1954)] it is possible that they have a very high degree of polymerization, but that cannot yet be decided with certainty. From the beginning, viscosity measurements supported the macromolecular concept and showed that cellulose and its derivatives do not dissolve as micelles but are dispersed macromolecules (159). See also references 164, 169, and 464.

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215

Furthermore, cellulose and cellulose derivatives behave like normal organic compounds. They can be dissolved and recovered from solution without change. This was shown with W. Starck for cellulose acetates (462). As formerly some people, like K. Hess, assigned cellulose a special biostructure with skin substance, reprecipitated cellulose was used during the first investigations. It was proved that on careful reprecipitation of polymer homologous celluloses from Schweizer's reagents under exclusion of air, they can be recovered almost unchanged (465). In order to slow down the degradation in Schweizer's reagent, cuprous (I)-chloride was added to the solution (466). Later H. Krassig and E. Siefert found out that solutions of celluloses in tetraethylammonium hydroxide are quite stable and therefore well suited for viscosity measurements (467, see also 472). In 1930, when it was proved that the viscosity number of solutions increases in proportion to the chain length of dissolved chain moleculeswith W. Heuer on polystyrene (122) and with R. Nodzu and E. Ochiai (123, 124) on long chain paraffins and paraffin derivatives-this experience was used to determine the minimum size of the macromolecules of cellulose and cellulose derivaties. The basis for these investigations were viscosity measurements on oligosaccharides and oligosaccharide derivatives which we obtained from L. Zechmeister. Furthermore, polymer homologous cellulose acetates were used, the molecular weights of which had been determined by the cryoscopic method. Km-constants for cellulose acetates were calculated (121,464). In this way we arrived at the conclusion (1930) that native cellulose must have a high degree of polymerization, at least one of 1200 (85). References 15 (p. 446, 483), 85, 121, 464, 468, 469 are relevant. In 1935 osmotic measurements of cellulose derivatives were made with G. V. Schulz (105). In 1937 it was shown in an extensive work (470) with G. Daumiller, now director of the BASF, that fiber celluloses can be transformed by careful acetylation with acetic anhydride and pyridine into their polymer-analogous acetates. These cellulose acetates were saponified and the initial celluloses were recovered (Table 12). With this work definitive proof was given through the methods of classical organic chemistry that the colloidal particles in the solutions of cellulose and cellulose acetates are macromolecules with degrees of polymerization up to 1600. In order to obtain these results, the average degree of polymerization was determined by osmosis on a number of polymer homologous cellulose

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Table 12 Conversion of Reprecipitated Celluloses into the Polymer­ Analogous Triacetates and Saponification of these Triacetates into the Initial Celluloses (cf ref. 470, p. 263) (Degree of Poly­ merization DP Determined by Viscosity Measurements)

Celluloses in Schweizers Reagent DP

Triacetates in m-Cresol DP

Celluloses from Acetates in Schweizers Reagent DP

500 495 790 955 1220 1600

505 510 795 955 1180 1650

490 470 780 935 1165 1630

triacetates. From the ZYJ values of these products the Km-constant was calculated (see Table 6, p. 289). Using this constant, the DP-value of the triacetates could be easily obtained from viscosity measurements. The DPvalue of the polymer homologous celluloses was also determined by viscosity measurements in Schweizer's reagent. This is possible since there is a constant proportion between the viscosity numbers of cellulose triacetate in m-cresol and of its polymer analogous celluloses. The Km-constant in Schweizer's reagent could be calculated as 5 x 10-4 (see Table 7, p. 290). The transformation of cellulose into the polymer-analogous cellulose acetates was difficult in the beginning. A strong degradation of the cellulose occurred when the normal acetylating mixture of acetic anhydride with acid as catalyst was used. The acetylation had to be done with acetic anhydride in pyridine, a method which has been proposed by K. Hess and N. Ljubitsch [Ber., 61, 1460 (1928)]. With this method one obtains soluble acetates from strongly degraded celluloses (up to DP 500), while higher polymer celluloses, which can be obtained by hydrolytic degradation from fiber cellulose, yield insoluble acetates. During work with G. Daumiller it was found that soluble acetates* are obtained from reprecipi-

*

Celluloses of different origins behave differently. The following was found (ref. 504, p. 69): "Flax shows a different behavior. If flax cellulose is transformed into its xanthates, and if these are dissolved in 1% solutions and then the cellulose is

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217

tated high molecular cotton, or ramie cellulose or from cellulose recovered from xanthate solutions; thus, their molecular weight could be determined by osmometric measurements (470-475). The same investigations were made on cellulose ethers. The polymeranalogous transformation of cellulose acetates into methylcelluloses was shown with H. Scholz (476). During this work H. Scholz proposed this type of reaction be called "polymer-analogous" reactions. With F. Reinecke it was shown that differently substituted cellulose ethers, that is, the methyl, ethyl, butyl, or benzyl ethers of cellulose have approximately the same Km-constants (171,477). This means that the size of the substituent has no or only a minor influence on the viscosity of the solutions. It was also planned to investigate cellulose ethers with longer side chains, e.g., cetyl side chains, as well as acetyl celluloses, and cellulose esters of higher fatty acids. These investigations have npt been accomplished. (b) Cellulose Nitrates In the first works the generally applied but incorrect term "nitrocellulose" was used. It is hoped that this will be replaced in literature by the correct term "cellulose nitrate."

At the beginning of the work on cellulose, the field of cellulose nitrates especially seemed to be quite unclear. Since cellulose is easily degraded by acids, one would expect that strongly degraded products would be obtained on treatment with technical nitration mixture. On the contrary, cellulose nitrates from cotton yield solutions of high viscosity. Therefore, it seemed possible that here relatively small molecules form the micelles. J. W. McBain and D. A. Scott [Ind. Eng. Chern., 28, 470 (1936)] stated: "... it is concluded that cellulose derivatives (nitrocotton) are association colloids like soaps and that association and formation of micelles or more complicated structures appear to be an essential feature of cellulose and its derivatives." recovered and acetylated, insoluble acetates are obtained. This behavior is opposite to ramie and cotton acetates obtained in the same way. According to these experiments, there is a difference between the flax fibre on one side and cotton and ramie fibres on the other, which has to be elucidated. Such observations lead to the assumption that cellulose is a collective name for a polysaccharide which is mainly built up from glucose residues with ,8-glucoside links. Between these celluloses of different plants, there must exist small differences which appear only on more thorough investigations. There is the possibility that each type of plant builds up its own characteristic cellulose."

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During our investigations it turned out that the work with cellulose nitrates had special difficulties. On treatment with technical nitration mixture, celluloses are more or less degraded, depending on their prior treatment. In 1932 in one of the first works with H. Haas (15) a number of experiments could not be explained: the cellulose nitrates often had a higher degree of polymerization than the initial celluloses. This average degree of polymerization was determined from the viscosity numbers with the Km-constants. An interpretation became possible when A. Af Ekenstam [Ber., 69, 549 (1936)] showed that cellulose is not or· is only slowly degraded in concentrated phosphoric acid. Based on this experience, more nitrations with the known mixture of phosphoric acid and nitric acid were done with R. Mohr (478). It was found that a polymer-homologous series of celluloses, obtained by hydrolytic degradation, yielded polymer-analogous nitrates. The degree of polymerization of the celluloses was determined in Schweizer's reagent, using the Km-constant 5 x 10-4 which was obtained by transforming celluloses into their polymer-analogous acetates (see Table 7, p. 290). Some of the results are given in Table 8, p. 290; they prove the macromolecular structure of cellulose nitrates up to a DP of3500. Despite many attempts, it unfortunately was not possible to transform the cellulose nitrates into the polymer-analogous cellulose; as is known, degradation occurs even on the most careful splitting off of the nitro group. Even the addition of strongly reducing agents does not prevent this degradation (unpublished experiments of H. Krassig and coworkers). Polymer-homologous native celluloses, obtained by hydrolytic degradation, as well as mercerized celluloses and reprecipitated celluloses can be transformed into polymer-analogous nitrates with the phosphoric acidnitric acid mixture. If the esterification is done with the usual nitrating mixture of nitric acid and sulfuric acid, the native celluloses and their degradation products are transformed into polymer-analogous or almost polymer-analogous compounds; on the other hand, mercerized celluloses and reprecipitated celluloses are strongly degraded; therefore, the average DP of these "sulfuric acid nitrates" is only half of the one of the "phosphoric acid nitrates." This degradation is explained by the fact that reprecipitated celluloses are easier to split hydrolytically than native celluloses. This was shown by 0. Eisenhut and E. Schwartz [Angew. Chem., 55, 380 (1942)].

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PRODUCTS

Native and reprecipitated celluloses therefore differ largely in their behavior toward the two nitrating mixtures. In order to characterize this difference, the nitrating number was introduced. It gives the ratio between the average degree of polymerization of sulfuric acid nitrates and phosphoric acid nitrates. The results on differently treated cotton celluloses are shown in Table 13, taken from reference 479. This nitration number makes it possible to characterize wood pulps too, and shows how much of the native character of the cellulose is lost during the pulping process (479). Another difficulty in -working with cellulose nitrates is the fact that their viscosity numbers are highly dependent on the degree of esterification. Thus, each cellulose nitrate has to be characterized by a nitrogen determination. This dependence of the viscosity numbers was pointed out first by H. A. Wannow [Kolloid­Z., 102, 33 (1943)]; at the same time F. Zapf made the same observations at our institute in Freiburg. These and other results in the field of cellulose nitrates were published in a special booklet which is out of print (480). Further work on cellulose nitrate is reported in references 169, 179, 206, and 481. Table 13

Differences between Native, Mercerized, and Reprecipitated Celluloses

PolymerHomologous Series Native fiber cellulose, DP =

200-3000 Mercerized cellulose, DP =

200-3000 Reprecipitated cellulose, DP =

50-2000

Spherical Swelling

X-Ray Diagram

Solubility in 10% NaOH

Only when Native Soluble degree of cellulose until polymeriDP = 400 zation is high Only when Hydrated Soluble degree of cellulose until polymeriDP = 400 zation is high Hydrated Soluble None cellulose until DP =

1200

Solubility of the Triacetates in m-Cresol Soluble until DP =

Nitration Number 1

500 Soluble until DP =

0.5

500 Soluble until DP =

2000

0.5

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COMPOUNDS

(c) Celluloses with Defects

At the beginning it was an inexplicable surprise that-as already mentioned-nitrates of bleached celluloses had a higher degree of polymerization than their starting materials, according to viscosity measurements. The degree of polymerization of these cellulose nitrates could be determined by osmotic pressure measurements; the relation between this degree of polymerization and the viscosity number was the same as that of the nitrates from hydrolytically degraded celluloses (Km = 11 x 10-4) obtained from fractionated products (478). Therefore, this striking result had to have its origin in some unknown changes in the cellulose molecule. During the interaction with the acidic oxidation medium, some groups had to be formed in these molecules which were destroyed under chain degradation on dissolving in Schweizer's reagent, while the whole chain with its defects was transformed into the palmer-analogous nitrate during nitration. Such defects can occur by formation of ester-type groupings in some glucose molecules during the oxidation in acidic media. They are split again by saponification:

This type of cellulose was called esteroxycellulose (484). The number of defects in the cellulose chain can be determined from the relation of the degree of polymerization of the phosphoric acid nitrates to the degree of polymerization of the celluloses in Schweizer's reagent. I must say that we were very lucky because we used cotton cellulose for our first investigations. It was reprecipitated from Schweizer's reagent

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Table 14 Nitration of Esteroxy Celluloses (cf. ref. 487) Esteroxy Celluloses Before and After Treatment A. Esteroxy Celluloses B. After reprecipitation of A from Schweizer's reagent c. After treating A with 2n-NaOH on heating (10 min)

DP of Cellulose in Schweizer's Reagent No.

DP of the Nitrate in Acetone

Chain Length Difference* in /o

1 2 3 1 2 3

460 360 260 400 290 240

1550 1700 1400 430 310 250

+240 +370 +440 + 7 + 7 + 4

1

420 320 270

480 390 300

+ 14 + 22 + 11

2 3

*chain length difference =

DP of nitrates - DP of cellulose DP of cellulose

X

100.

and therefore no oxycellulose was present (465). Such celluloses do not have defects because they are split by alkali when dissolved in Schweizer's reagent. Therefore, bleached cellulose fibers cannot be characterized without restriction by the degree of polymerization of their phosphoric acid nitrates as this gives a measure of the chain length of the cellulose molect:le with its defects. The degree of polymerization obtained in Schweizer's reagent on the other hand gives the chain length of the stable, defectless cellulose. This is of importance for the textile industry, since bleached cotton materials very often are celluloses with defects. They contain relatively long chains and they therefore have good tensile strength, but on washing such textiles splitting occurs at the defect positions and the tensile strength is lowered (487). A number of works have been published in this field with A. W. Sohn (482-486,489); later E. Roos-who had to join the army after his graduation and unfortunately did not come back from Russiainvestigated chlorine bleaching under different conditions in order to determine how much defected cellulose is formed during this process (487, 490). H. Krassig studied the influence of oxidizing detergents on cotton material (488).

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(d) Cellulose Xanthates The technically important VIscose solution, the cellulose xanthate solution, shows a very complicated viscosity behavior. Many authors, e.g., Th. Lieser, assigned a micellar structure to their colloidal particles. The viscosity behavior of the xanthate solutions was explained through investigations of heteropolar linear molecular colloids, e.g., the polyacrylic acids (see pp. 133 and 175). It is very complicated because the viscosity of the viscose solutions depends on its xanthate content which is changed by the saponification of the xanthate groups in alkaline solution. In this case-as with all high molecular polyacids-the viscosity determinations were made in an excess of sodium hydroxide. Proof for the macromolecular structure of the cellulose xanthates was given by their transformation into polymer-analogous celluloses with G. Daumiller (491) and later with F. Zapf (493). It was not possible to transform cotton cellulose into the polymer-analogous xanthates because degradation occurred. In later experiments, done with P. Herrbach (494), we found ramie celluloses could be xanthated to their polymer analogoues since ramie contains anticatalysts which prevent degradation. The degradation of cotton and wood pulp fibers can also be prevented by adding antioxidizing agents such as polyvalent phenols. Some unpublished results from Herrbach's dissertation can be found in Tables 15 and 16. It can be seen from Table 16 that well purified wood cellulose, like alpha lint, is degraded more strongly than raw wood cellulose. It was intended to expand these investigations on xanthation for characterizaTable 15

Degradation of Celluloses on Xanthation during 9 Days at 20°C

Type of Cellulose Cotton

Ramie

DP of the Starting Cellulose

2300 1500 640 390 1390 630 390 230

DP of Dissolved Xanthate

460 440 330 300 1380 600 370 240

Degradation in %

80 70 50 23 1 5 5 0

MACROMOLECULAR

Table 16

NATURAL

223

PRODUCTS

Determination of the Degradation of Different Celluloses during Xanthation DP of Celluloses Regenerated from Xanthates

Degradation in%

1550 1600 2000

1450 450 600

7 72 70

2000 640 630 520

2150 630 310 280

0 2 51 46

780

730

6

820

760

7

DP of Mercerized CelluDesignation of Celluloses loses Ramie Cotton I Cotton II Cotton II, pretreated with hydroquinone Spruce wood pulp Alpha lint I Aliph a lint II Alipha lint, pretreated with hydroquinone Alpha lint, pretreated with pyrogallol

tions of wood celluloses, but the experiments could not be continued because the institute was destroyed in 1944. References 491-494 are relevant. (e) Structure of the Fibers During our work with 0. Schweitzer (85) in 1930, it turned out that synthetic fibers like Bemberg silk had a much lower degree of polymerization than cotton celluloses. This seemed to explain the fact that the synthetic fibers had a lower tensile strength than natural fibers, since it has been assumed that here as in the case of the polymer-homologous series of polyprenes, the physical properties of the fibers depended on the average length of the chains. This statement-to a certain degree-is true today also, and industry in the last decade has produced viscose and cellulose acetate fibers with a much higher degree of polymerization than before. The connection between chain length and tensile strength is not that simple, since the tensile strength of a fiber depends on its inner structure which in turn depends on the conditions under which it was made.

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Table 17 Tensile Strength of Cotton, Native Fiber Nitrates, and Repre­ cipitated Fiber Nitrates (504)

DP

Titer den

Tensile Strength in g/den Dry

Buckle Strength

Cotton Native nitrate Reprecipitated nitrate

1900 2200

1.3 2.4

3.0 1.6

7,500 > 150,000

1700

1.4

0.6

5

Cotton Native nitrate Reprecipitated nitrate

380 380

2.1 3.0

0.9 0.7

30 50

420

2.9

1.4

5

Material

Viscose fibers were made in 1941 with H. Stock (504), the cellulose of which had a degree of polymerization of > 1000. The fibers obtained did not have very high tensile strengths for they tore and broke much easier than cotton fibers of the same degree of polymerization. The tensile strength of cotton, or ramie-fibers, were then compared to nitrate fibers which were prepared by polymer-analogous reactions from natural fibers. These native nitrate fibers were dissolved in acetone and spun again into fibers. The tensile strength of this reprecipitated fiber was much lower than that of the native cellulose nitrate fibers, as can be seen in Table 17. If the same procedure is followed with a degraded cotton fiber, it has a lower tensile strength as does the native nitrate fiber obtained from it. This is due to the cross cracks (see below). Fibers from reprecipitated nitrate have rather a better tensile strength than do native fibers because cross cracks are not present. In judging these experiments, it must be kept in mind that fibers with a high degree of polymerization must be spun under different conditions than fibers with a low degree of polymerization because it is not possible to make a 20% spinning solution from viscose or cellulose nitrate with a DP of 1000 to 2000. The tensile strength of a fiber depends greatly on the

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concentration of the spinning solution, as can be seen from Table 18 (504). One could conclude from the results in Table 18 that fibers with better properties should be obtained from still higher concentrated spinning solutions. However, the concentration of the spinning solution can be increased only to a certain degree because at high viscosity the swollen material can no longer be worked into fibers. Therefore, fibers with especially good properties should be obtained by the melt spinning procedure. Cellulose acetates cannot be spun by this procedure because they start to decompose below the melting point. Fibers from ethyl celluloses were obtained by the melt spinning procedure with H. Stock (503). They were strongly degraded but had a relatively good tensile strength. Numerous investigations on the oxidative and hydrolytic degradation of natural fibers had led to the knowledge that the tensile strength of fibers is lowered by degradation (495); this seemed to be a proof for a relationship between tensile strength and the chain length of the cellulose molecules. Natural fibers have a low tensile strength and buckling strength after degradation to a DP of 400-500; cotton breaks and tears easily when it is degraded to this degree of polymerization by bleaching. Synthetic fibers with DP 300-350, prepared according to the viscose and cuprammonium silk process, on the contrary, have good usage values. The brittleness of degraded natural fibers therefore must be due to another cause which was determined by the microscopic investigation of M. Staudinger: the degradation of the long cellulose molecules does not

Table 18

Dependence of the Tensile Strength of Viscose Fibers of DP 420 on the Concentration of the Spinning Solution

Amount of Cellulose in Spinning Solution, %

1.5 3 6

9

Titer den

Tensile Strength in g/den Dry

Buckle Strength

5.9 4.0 5.7 5.2

0.4 0.8 0.9 1.0

10 150 550 1350

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proceed regularly in the whole fiber, but starts on the surface through the formation of cracks at different places. These can be easily observed after swelling with 20% sodium hydroxide or Schweizer's reagent (see figure, p. 145). Such cross cracks are formed during the hydrolytic as well as the oxidative degradation of natural fibers. The fibers become brittle because of the formation of these cracks (204a,204b,206). The oxidative and hydrolytic degradation of synthetic fibers proceeds without crack formation. Natural and synthetic fibers differ in this respect. M. Staudinger stated the following in a work published in 1951: "There is a basic difference in the behavior of fibres either degraded to a certain degree of polymerization topochemically or build up from an already degraded material of the same degree of polymerization. These different pictures arise from the fact that those fibers with the same degree of polymerization are formed in different ways." (Ref. 206, p. 80; see also ref. 501, p. 695.)

The observations of G. W. Schulz and E. Husemann (517,518), which will be discussed on p. 229, seemed to give a good explanation for the formation of the cracks. They found that the cellulose molecules contained different groups which could easily be split after approximately 500 glucose units. They concluded that these special groups appear regularly in natural fibers and in this way form periodic irregularities, i.e., a long period lattice of cellulose. This picture was a simple explanation for the formation of cross cracks, since it could be assumed that the degradation would start at those places in natural fibers but could not occur in synthetic fibers. This interpretation of G. V. Schulz and E. Husemann has to be modified in the light of newer investigations. The differences in the degradation of cellulose fibers can, according to experiments of H. Krassig on tunicin fibers (505), be a consequence of their morphological structure and do not have to originate from "defects" in the cellulose molecule. See ref. 212 and p. 144 for a special type of degradation with microorganisms. References 204a, 204b, 206, 495-505 are relevant.

(f) Inclusion Phenomena and Acetylation In 1940 I suggested to O. Heick* that he investigate the acetylation of celluloses with aceti anhydride and pyridine after different pretreatments.

* O. Heick

had to finish his thesis quickly since he had to join the army; unfortunately, this very gifted chemist did not return from Stalingrad.

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221

These investigations revealed different behaviors. Mercerized fibers, especially reprecipitated celluloses and wood pulp, are hardly acetylated in the dry state with an acetylating mixture made from acetic anhydride and pyridine after 24 hours at 60°C. It can therefore be assumed that only those hydroxy groups react which are at the surface. If the water from the moist fibers is replaced by pyridine and then acetylated, acetylation occurs very quickly, mainly with reprecipitated celluloses. The first celluloses were therefore called inactive celluloses, the second ones active or highly active celluloses. The beh'!-vior was independent of the DP. Native cotton and ramie fibers show a strikingly different behavior. They are much faster acetylated in the dry state than the dry mercerized or reprecipitated celluloses. The acetylation increases very little on treatment with water and pyridine. The native fibers therefore were called semi-active. Here also the behavior is independent of the DP. The experiments were continued by W. Doble. We gained more insight into this different behavior of celluloses by analyzing them. In order to obtain especially pure and dry celluloses, we washed them with water, ether, and finally with cyclohexane. After drying these celluloses under high vacuum at 60°C, they still contained 6 to 7% cyclohexane which could not be removed with longer drying under high vacuum (see Table 6, p. 112). The cyclohexane is slowly removed on heating to more than 100 to 120°C, but the cellulose is slightly degraded. It turned out that many indifferent organic solvents, not only hydrocarbons · but also halide derivatives, are included between the cellulose molecules (see Table 14, p. 298). As described on p. 147, such inclusion fibers show a higher reactivity, i.e., their acetylation with acetic anhydride and pyridine proceeds much faster. Fibers with high or low degrees of polymerization behave alike, as can be seen from Table 19 (208). Similar results are obtained when cellulose fibers are acetylated heterogeneously with acetic anhydride in the presence of benzene and small amounts of sulfuric acid as catalyst. In this case the fibers with included benzene or glacial acetic acid are quickly and uniformly acetylated to the triacetate. On the other hand, the acetylation of dry and unincluded fibers proceeds very slowly. After one day of acetylation, only the hydroxy groups on the surface react, as can be seen from Table 20 (208). In the acidic acetylation mixture the fibers are more or less degraded, unlike the acetylations with acetic anhydride and pyridine. During this procedure, the above mentioned cross cracks occur in native fibers. The

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Table 19 Acetylation of Mercerized Fibers with Pyridine­Acetic An­ hydride Time of Acetylation (hours) Cotton

Ramie

Flax

Included Fibers

Dry Fibers DP 2200 acetyl 0.7

24 408

%

24 408

lo acetyl "

24 408

"

290 0.7 2.3 3.3 1800 160 0.9 1.6 3.0 5.4 1500 150 0.4 0.5 3.9 5.4

" DP DP %acetyl

DP 2200 %acetyl 14.2

37.9 1800 lo acetyl 15.6 36.0 " DP 1500 % acetyl 15.7 39.0 " " DP

290 14.5 37.2 160 14.9 34.4 150 14.4 38.2

cetylating mixture can penetrate into these cracks faster than into the intact parts of the fibers: After long acetylation, cellulose triacetate is formed close to the cracks. This can be extracted, and the unchanged fiber parts remain as spindle-shaped particles. Those were described by K. Hess and G. Schultze [Ann., 456, 55 (1927)] and by K. Kanamaru [Helv. Chim. Acta, 17, 1436 (1934)]. This phenomenon is therefore a consequence of the crack formation during the degradation of cellulose and Table 20 Acetylation of Mercerized Fibers with Benzene­Acetic An­ hydride­Sulfuric Acid after 24 Hours* Dry fibers Cotton Ramie Flax

DP 2200 % acetyl 0.9 DP 1800 % acetyl 1.5 DP 1500 % acetyl 1.2

*Acetyl content of a triacetate = 44.8%

Included fibers

290 1.3 160 2.2 150 2.4

% % %

DP acetyl DP acetyl DP acetyl

2200 44.9 1800 43.6 1500 41.4

290 44.3 160 42.8 150 40.7

MACROMOLECULAR

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229

is not due to the presence of crystallized and amorphous parts in the fiber (see also ref. 208 and p. 140). It would be interesting to make X-ray investigations of such particles in order to find out if they also contain 70% crystallized and 30% amorphous cellulose as described by B. G. Ranby and E. Ribi [Experientia (Basel), 6, 12, 27 (1950); see also P. H. Hermans, Makromol. Chern., 6, 29 (1950)] for similar cellulose particles which they obtained on hydrolytic degradation of cellulose. References 208, 217 and 506-514 are relevant.

(g) The Formula of Cellulose K. Freudenberg and co-workers [Ber., 63, 1510 (1930)] and W. Kuhn [Ber., 63, 1503 (1930)] have investigated the rate of hydrolysis of cellulose and have proved that at least 95% of the linkages between the glucose units were β -glucoside links. The same results were obtained in later investigations by A. Af Ekenstam [Ber., 69, 549 (1936)] who studied the kinetics of degradation of cellulose in phosphoric acid solutions by measuring the DP. Still later this question was investigated by G. V. Schulz and H. J. Lohmann in 1941 who obtained the same result (515). Therefore, it was surprising when in 1942 G. V. Schulz and E. Husemann published the following conclusions based on new methods of determining degradation (ref. 517, p. 23): "Fractionation experiments as well as determinations of the non-uniformity by comparing osmotic and viscometric measurements with native and hydrolytically degraded celluloses led to the result that native cellulose has a regular structure with long periods. The cellulose from cotton has a uniform degree of polymerization of 3100±100. In regular distances they contain five linkages with a 103 times higher velocity of hydrolysis than the other -glucoside links. Because of these easily split links the cellulose molecule is divided into six equal parts with a degree of polymerization of 510 ± 20. Kinetic measurements have shown that there are no easily split special links within those periods .... Many phenomena led to the conclusion that native cellulose has a long period lattice which is destroyed on dissolving and reprecipitating."

This finding was supported by E. Husemann and co-workers in a number of works by electronmicroscopic investigations of hydrolytically

230

RESEARCH ON MACROMOLECULAR COMPOUNDS

degraded fibers (519). These loose links were not obvious on enzymatic degradation (524). Since these results are of great importance for the cellulose industry, these experiments were often repeated but could not be verified in all cases. In 1953 H. Kdissig showed that animal cellulose, the tunicin, has the same structure as plant cellulose (527). The heterogeneous, homogeneous, hydrolytic, and oxidative degradation of cellulose chains in this material was studied. H. Kdissig arrived at the following conclusion (see ref. 505, p. 17): "We conclude that the preferential splitting of links during heterogeneous degradation have their origin in the morphologic structure of the tunicin fibers, which makes some parts of the fiber more easily accessible. They do not originate from structurally determined differences towards chemical influences of hydrolysis or oxidation in the native tunicine molecule."

Cellulose chemists will look forward to the explanation of this question which is of great importance for cellulose industry. E. Husemann defined her position in two short communications on this subject [E. Husemann and E. Spingler, Makromol. Chem., 24, 79 (1957); 26, 178 (1958)]. References 209-211, 505, 515-527, are relevant. (h) Further Works (212, 528-541)

From the different works on cellulose cited here especia1ly those on the oxidative degradation have to be mentioned. It was shown that very small amounts of oxygen degrade the chains of native cellulose to approximately one-half (531). This result is important in understanding the sensitivity of cellulose chains towards oxidative degradation agents. Eo Husemann and 0. H. Weber found a method for molecular weight determinations of cellulose via end-group determination (534,539,540). References 212, 528-541 are relevant. Finally, the X-ray investigations of cellulose by E. Sauter and E. Plotze (191-194,197-199), which were discussed on p. 140, shall be mentioned again. (i) Summarizing Publications on Cellulose

A number of summarizing works including reports of lectures, were published on the structure of cellulose in order to make known the new knowledge on the macromolecular structure of cellulose (27,35,40, 173,203,

MACROMOLECULAR

NATURAL PRODUCTS

231

207,461,489,490,494,511,513,542, 543a, 543b, 544-546, 547a, 547b, 548-585). Further, these publications pointed out the importance of viscosity measurements for the fast determinations of the average DP. Today I see with satisfaction that these basic results on cellulose chemistry have been taken over by the industries of cellulose and of synthetic fibers containing cellulose.

3. STARCH, GLYCOGEN, AND OTHER POLYSACCHARIDES According to its properties, such as swelling and its partly abnormal viscosity behavior, starch seemed to be a typical colloid, the colloidal particles being formed by the aggregation of small molecules. In the years 1920-1927 several authors i.e., P. Karrer, M. Bergmann, and others, assumed that low molecular units formed the aggregates partly because of the abnormal molecular weights obtained from starch acetates in glacial acetic acid (see Table 1, p. 80) K. H. Meyer, H. Hopff, and H. Mark [Ber., 62, 1103. (1929)] assumed starch contained zig-z g maltose chains which should be shorter than the cellobiose chains of cellulose. With the works of W. N. Haworth who tried to determine the molecular weight of starch and of glycogen by end-group determination, it seemed to be proved that polysaccharides contained relatively short chain molecules. W. N. Haworth and co-workers [J. Chern. Soc. (London), 1932, 2277, 2375; 1935, 1201] found an average chain length of approximately 25 to 30 units for starch and I0 to 15 units for glycogen. Haworth and his co-workers then assumed that these relatively small molecules were aggregated by secondary valence forces to unstable large colloid particles. In our first work on starch (586) we found that viscosity measurements indicated a macromolecular structure of the colloid particles. The shape of these macromolecules had to be different from the shape of those in cellulose since their K n-constant was much smaller. Therefore we concluded (ref. 586, p. 828) that it was "not impossible that the macromolecules of starch are branched." This question was clarified by an investigation done with E. Husemann (587). A number of polymerhomologous amylopectins were transformed into their acetates. The unchanged starting materials could be recovered from the acetates by careful saponification. The molecular weights of the amylopectins (starch) in formamide and of their triacetates in acetone were determined by osmotic measurements. The values obtained for the DP indicated that the reaction had proceeded polymer analogously and therefore the colloidal particles were macromolecules with a partly high degree

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RESEARCH ON MACROMOLECULAR COMPOUNDS

of polymerization. The opinion of Haworth and other authors, that the colloidal molecules in starch solutions are formed by the aggregation of small molecules, was therefore disproved. This finding, together with the results of viscosity measurements, provided evidence that the molecule of amylopectin is branched. The long starch molecule contains a large number of end groups which can be explained only by branching of the macromolecule (see formula in ref. 587, p. 234). Amylose, a starch component, described by Pringsheim, was more thoroughly investigated by E. Husemann (593,594). The situation of glycogen is quite similar. The former opinion of Haworth, that it was a relatively low molecular polysaccharide aggregated to colloidal particles, seemed quite reasonable according to its physical properties: glycogen is a powdery substance which dissolves without swelling to solutions of low viscosity, which means that it behaves like a relatively low molecular compound. Our investigations led to the striking result that it was a very big macromolecule with spherical shape (see formula in ref. 182, p. 16). A number of polymer-analogous glycogens obtained by hydrolytic degradation were transformed into the polymeranalogous acetates which could be saponified to the starting glycogen. These polymer-homologous glycogens are the first proof for the validity of Einstein's law on spheromacromolecular compounds, since their viscosity number is the same, independent of the DP, as was pointed out earlier (p. 135). From this we concluded that the glycogens had spherical macromolecules and, furthermore, that they must be branched with relatively short side chains. The spherical shape was then proved by electron microscopic investigations of a glycogen derivative (99, 100). Later Hj. Staudinger (588), at the Pathology Institute of the University of Freiburg i. Br. with Professor F. Buchner, isolated glycogens from liver with a very high molecular weight (2.2 million). The molecular weight was determined by osmotic and light-scattering measurements. The validity of Rayleigh's law was proved for a number of very high molecular glycogens. These precious samples were lost during the destruction of the Institute in November, 1944. Therefore, the macromolecular structure could not be proved by polymer-analogous transformation, e.g., into their acetates. But it is very probable that in this case the colloidal particles are the macromolecules themselves. On the other hand, in the case of proteins, the particle size of which is similar to that of the glycogens, it is not yet certain that the weight of

MACROMOLECULAR NATURAL PRODUCTS

233

the particles is identical with the molecular weight in the chemical sense. Further chemical investigations of these products with new methods are necessary. Investigations of the three polysaccharides, cellulose with unbranched chain molecules, the amylopectins with branched, long chain molecules, and the glycogens with spherically-shaped macromolecules were the results of long efforts for the structure elucidation of macromolecular compounds; they led to a clear knowledge on the relation between viscosity properties of solutions and the sha:p_e of dissolved macromolecules, and finally to the classification of macromolecules depending on their shape (35). During the past ten years these concepts of the structure of macromolecules of starch and glycogen have been developed further in different places. Some altered proposals about the type of branching have been made, but very often it has been overlooked that the basic results on the macromolecular nature of colloidal particles were possible only through the above-mentioned polymer analogous reactions. Important progress concerning starch and glycogen was made through elucidation of their enzymatic degradation. Of great importance as well is the enzymatic synthesis of polysaccharides (e.g., the works of C. and G. Cori). A good summary of these works can be found at K. Heyns, Die neueren Ergebnisse der Starkeforschung, Verlag Vieweg, Braunschweig, 1949. References 35, 99, 100, 183, 589-596 are relevant. Some work on other polysaccharides with relatively short chains like the lichenins and the macromolecular salepmannan is reported in references 525 and 597-606. All polysaccharides follow the simple viscosity rule. E. Husemann and her co-workers have worked further on the sulfuric acid esters of xylan as anticoagulating compounds.

4. WOOD The main components of wood are, according to former statements, cellulose, hemicellulose, and lignin. The cellulose is bound in the wood, since it can be extracted with Schweizer's reagent only to a small degree. Only after decomposition of wood a cellulose soluble in Schweizer's reagent is obtained as wood pulp. The following works deal with the type of binding of cellulose molecules with other wood components. According to experiments done with E. Dreher, the long chain molecules of cellulose fibers are degraded by grinding in an agate ball mill from a

234

RESEARCH ON MACROMOLECULAR COMPOUNDS

DP of 1500 to approximately 380 (69). In the same way the long chain molecules of polystyrene are degraded (68). The investigation of degradation of linear macromolecules by grinding, especially of cellulose, was later continued at several places, especially by K. Hess. If wood is grpund in the same way, a large part of the cellulose becomes soluble (608); based on these results our conception was that in wood the cellulose with a high degree of polymerization was bound to lignin by cross links and, therefore, was insoluble. On grinding, the cellulose macromolecules as well as their bonds to other wood components are destroyed and the shorter fragments of the cellulose molecules can be extracted. In a similar way a slightly crosslinked, insoluble copolymer of polystyrene and divinylbenzene is degraded and becomes soluble after being ground in the ball mill (ref. 608, p. 1100). Lignin, which K. Freudenberg has investigated extensively in the last years, was studied very little in the Freiburg Institute. In a work done together with E. Dreher (609) it has been shown that the soluble hignin gives solutions of low viscosity which means that it cannot contain very long chain molecules. This soluble lignin is not a linear macromolecular compound and probably the insoluble lignin is not either, since it is a powder. The expression hemicellulose for the other wood components is incorrect. It originates from the time when not much was known about the structure of cellulose and the other wood polysaccharides. It should be replaced by the expression "wood polyoses." E. Husemann worked on the structure elucidation of the wood polyoses in the years 1938/39 (615,616). These wood polyoses, the xylans, mannans, and arabo-galactans, are quite low molecular unlike wood cellulose. The molecular weights of the wood celluloses and pulp were determined by viscosity measurements in several investigations; the DP of the cellulose in different wood species was also investigated (610). The finding of E. Husemann that the Km-values of wood pulp nitrates from unreprecipitated wood pulp were extremely high was surprising. If the wood pulp is reprecipitated from Schweizer's reagent, then its nitrates have approximately the same Km-values as the cotton nitrates (618). Later, F. Zapf showed that the abnormally high Km-values of wood pulp nitrates obtained from unreprecipitated wood pulp are based upon the fact that unlike the cotton cellulose nitrates two components are present: besides the cellulose nitrate they also contain the lower molecular nitrates of the ·wood polyoses. The osmometrically-detennined molecular weights

MACROMOLECULAR

NATURAL PRODUCTS

235

of these mixtures are relatively low while the viscosity numbers are relatively high (619,620). F. Zapf also investigated the lignin-rich kapok cellulose (621). Unfortunately these successful works, which were performed under very difficult conditions after the destruction and during the reconstruction of the Institute, were interrupted when F. Zapf started to work in industry in 1952. It is economically important to know if the cellulose content of wood is constant or if it is possible to find wood species with specially high cellulose content. Therefore, the cellulose content of different wood species was determined (617), and we learned that the most important cellulose sources, i.e., spruce, pine, and beech, have approximately the same cellulose content, even if they come from different regions. Differing cellulose content was found in the different poplar species, mainly in the bastards. One of the poplar species contained more than 50% cellulose, another only about 30%. It would be of great importance, especially for the paper industry, to cultivate fast-growing and cellulose-rich poplars. This question was extensively discussed with Professor Fr. W. Bauer, the head of the Institute for Wood Cultivation at the University of Freiburg i. Br. He started the cultivation of poplars-mainly those with high cellulose content -in order to find out if the cellulose content was dependent on the place of growth, or-more likely-if it was a hereditary property. It is known, however, that by cultivation the content of important components in plants can be raised, as for instance sugar in sugar beets. During these investigations on wood cellulose the separation of lignin and cellulose in different woods was investigated microscopically. Such investigations have already been made by a number of scientists, e.g., K. Freudenberg (Tannin, Cellulose, Lignin, Springer, Berlin, 1933). In our experiments we wanted to determine the distribution of the two main components, cellulose and lignin, in wood under the most careful conditions. We proceeded by making a thin wood cut from which the cellulose was removed, first by slow degradation with dilute acids (in order to prevent swelling and destruction of the cut) and then by extraction with Schweizer's reagent, leaving only the lignin. Another time the lignin was extracted with chlorodioxide and pyridine, according to a procedure of E. Schmidt [Cellulosechemie, 12, 201 (1931)] which leaves only the cellulose. It was found that the distribution of lignin in conifers and in deciduous trees differs: in the first the lignin penetrates the whole cell wall, in the latter it is almost exclusively in the middle lamella. References 69, 607-621 are relevant.

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COMPOUNDS

5. ON TANNINS AND LEATHER

H. Batzer (now director at the CIBA, Basel) worked on these products with the aim of elucidating tanning processes on well-defined model compounds like polyamides, instead of animal skin. The original intention was to elucidate the structure of collagen. This could not be done because the investigations were made under very difficult working conditions after the destruction of the Institute on November 27, 1944, and its partly reconstruction during the years of 1945-1947 (see page 6). Batzer's publications (622-630) are based on work performed in the Institute in Freiburg and appeared in the series "Mitteilungen ilber makromolekulare Verbindungen."

12 Macromolecular Chemistry and Biology

The problems discussed in this Chapter where mostly investigated with my wife. She was especially interested in this scientific border region, and she had been stimulated by her father, Excellency Dr. med. Oskar Woit, Ambassador of Latvia to Germany from 1920 to 1932. During her studies in Berlin with the plant physiologist Geheimrat Gottlieb Haberlandt, her father again and again pointed out the importance of this area. As a consequence she has been deeply engaged in the macromolecular science and she has drawn my attention to the great importance of the shape of the macromolecules for biological questions. In her microscopic work she studied especially the supermolecular structures of macromolecules. She introduced the idea of the "atoms of the living matter" (see page 300) which overcame the hypotheses of such "life units" as plasomes, bioblasts, probionts, etc., and she introduced some new points of view relating macromolecular chemistry to biological and philosophical questions (635,202,641). In earlier years, the living processes were treated from the point of view of colloid science developing at that time, because colloidal phenomena occur so often in the living cell. It should be remembered here that H. Schade [cf. Miinchener med. Wschr., 68, 144 (1921)] termed the colloidal state in the living cell "eucolloidal ". Since evidence for the existence of macromolecules was given in which 105 and more atoms are connected by primary valences, which means real molecules and not just aggregates, new possibilities for the treatment of the processes in the living cell were open because important parts of the cell proved to be built up of macromolecules. They approach the same order of magnitude as the smallest living cells, like bacterial spores which contain 107 to 108 atoms (see Table 16, page 300). 237

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The dimensions of the macromolecules are to be found just in the ·range between the dimensions of the molecules known until now in low molecular chemistry and the dimensions of the components of the living cell. In this field well-ordered units have been missing and have always been searched for. The micelles of Nageli are probably the best-known hypothetical units of this sort. With the knowledge of macromolecules available, it was found that many properties of living matter, like the colloidal nature, i.e., a character between liquid and solid state, changing viscosity, swelling, elasticity, and especially the strange combination of high stability combined with manyfold reactivity, are typical macromolecular properties. Because of the size of macromolecules, there exists an unimaginable large number of structural possibilities (see page 299) of the components essential for life, like the proteins and the nucleic acids. Thus, the demand can be filled for every living creature to have its own special macromolecular compounds. Such a demand exists because every living being develops from a germ in a specific way, and no living creature resembles another one completely. This particularity of development has to be preformed in the germs which consist of approximately 108 atoms. The development of the living cell is, from the point of view of macromolecular chemistry, no longer left to the interactions of small molecules alone: the living matter in its structure and functions is bound to the existence of macromolecules of certain structures. Only they are in the position to form the stable and nevertheless reactive substrates on which the processes of life with its countless reactions can develop. We are far from elucidating the structure of such individual macromolecules, but new aspects for the understanding of life processes are obtained by investigating the special features of macromolecular chemistry with new methods. As was pointed out before, macromolecular compounds composed of thousands and millions of atoms can show completely new and unexpected properties which are not possible with low molecular compounds. Because of the macromolecules, I returned at the end of my scientific career to the studies which I had begun in 1899 in Halle with the intention of studying botany. I directed my interest especially to chemistry in order to gain a deeper insight into the life processes and the chemical reactions in plants. The proof of the existence of macromolecules had shown how complicated these areas are, and in a way which could not have been thought of before; at the same time, a vast new field was opened. References 18, 37, 73, 202, and 631-644 are relevant.

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My wife and I often discussed with interested friends the results of macromolecular chemistry and their role in the understanding of life processes and their general consequences. On April 1, 1956, when I resigned my honorary office as Director of the State Research Institute (see p. 6), the University of Freiburg arranged a farewell celebration in honor of my 75th birthday, March 23, 1956, where, among others, the rector Professor Welte addressed me. During our discussions he had shown a great interest in the consequences of macromolecular chemistry, described above and on p. 299. In his speech he mentioned some of the important implications of it. With his kind permission I present his speech. "Mister Minister, Members of the Bundestag and Landtag, Honorary Senators, Lord Mayor, Spektabilities and Colleagues, Members of the Council of the university, Ladies and Gentlemen! I have the extraordinary pleasure and honor as acting rector of this university to pre ent the joyful and proud wishes of our university on today's occasion to you, dear colleague Staudinger, in the midst of a large and radiant circle of friends and guests. Dear colleague Staudinger! About 30 years ago you opened a door in the dark wallofnaturewhichscienceisalwaystrying to light up and open. You halted and concentrated your thoughts at a part of this dark wall where from nobody thought a path could lead further. You were firm enough to remain with all the force of your mind and your enlightenment at this strange, unnoticed point. You succeeded in opening a big door. Today a whole world has stepped through this door and continues to do so. It is the whole technological world of fibers and plastic materials, which is spread all over the earth, and without which our life would be unthinkable; further, it is the whole world of those who use the fibers and plastics in the most diverse ways. We all make use of these materials. We dress in them, we use them in the tires of our cars, and we depend on their abundant variety, externally and internally. A vast, new country of science, economy, and life has been found behind this door which you opened with your scientific work 30 years ago! Let me honor and praise your achievement in my function as rector of the university as well as theologian and philosopher, but only as a dilettante in chemistry. Amidst the quantitative methods of modern chemistry, your attention was attracted by a zone in the chemical structure of our material world-and this seems very notable to me-in which the quantum, the number of building units and elements of the material substances, are not anymore only a quantum but go over to quality, to cite a thought from Hegel's logic. You became aware of configurations and formations in which law, order, and shape-e.g.,

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the shape of chains and rings of various types-are more important than the mere number of building units or the elementary active forces. Perhaps I may illustrate the point, where the quantum changes to quality by an allegory. Let us go with you and your science in the way you first went, thinking and exploring the way from classical quantitative chemistry to macromolecuJar chemistry. On this way it seems that we first walked over a big construction area, filled with a lot of valuable raw material, stones, iron bars, woods, and more things of this sort, and then we stepped in front of a building, a big house, perhaps a cathedral. A cathedral which certainly is more than the sum of the many single working units and building materials from which it is build up. It is more because the multitude of single building units are combined in it to a formed unity of higher level and of higher range. The quantum became a quality. This metaphor does not come from me, it is yours, dear colleague Staudinger. I cherish the memory of a wonderful conversation with you and your wife during which you expressed these thoughts and ideas, and I am pleased to present them like a blossom to you today on the occasion of your birthday. Let me, following up this dear memory, remind you that at that time you connected the force and importance of the quality, the shape, the idea with St. John's word of the logos, and that you said to me that you would like to know what really is meant in the gospel in the word of the creative logos, in which it is said that everything was created in it. In any case, you have shown us the path on which inanimate material, following a mysterious law, converges in a wonderful way to the highest level of nature, to life, in which shape and structure start to rule and build themselves. With your magnificent empirical research, you have made a contribution to the old idea of the occidental thinkers on nature. Much has been thought about "logos" and "forma" since the days of the Greek philosophers and the great thinkers of the middle ages, Thomas and Bonaventura, since the days of Hegel and the natural philosophy of Schelling. You gave new fulfillment to the old thought of logos in nature from the empirical side. You made it possible to participate in mind in one of the greatest feasts of creation. In a new way you let us have a presentiment of a deeper coherence of all appearances of dead and living nature and of the congruity of all nature with mind and therefore with philosophy and theology. Amidst a specialized field of research, proceeding in the modern way of specialization of knowledge, you have opened a view on things which overcame this specialization and which makes visible the continuous, the connecting, and the combining, which unites the inorganic, the living, and the mind, and in this way can be called a universe. Therefore, the feast of creation-which you have taught us

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to join-became also a feast of the university and her essential idea as universitas. This, dear colleague Staudinger, has to be expressed thankfully as congratulation and I am happy to express it as rector of this university. May all this which you have given to the world, and especially to the university, be a special feast for you, both today and for many more years!"

PART B REFERENCES 1. H. Staudinger, Ber., 53, 1073-1085 (1920). Uber Polymerisation.

2. H. Staudinger and J. Fritschi, Helv. Chim. Acta, 5, 785-806 (1922). Uber die Hydrierung des Kautschuks und iiber seine Konstitution. 3. H. Staudinger, Ber., 57, 1203-1208 (1924). Uber die Konstitution des Kautschuks. 4. H. Staudinger, Angew. Chem., 37, 892-893 (1924). Uber die Konstitu­ tion des Paraformaldehydes und anderer hochpolymerer Verbindung­ en. 5. H. Staudinger, Ber., 59, 3019-3043 (1926). Die Chemie der hochmole­ kularen organischen Stoffe im Sinne der Kekuleschen Strukturlehre. 5a. J. Fritschi (1923): Uber die Konstitution des Kautschuks. 5b. A. Rheiner(1923): Uber die AuffassungderdimerenPolymerisations­ produkte als Cyclobutanderivate. 5c. M. Liithy (1923): Uber die Konstitution der polymeren Formalde­ hyde. 5d. F. Felix (1923): Uber die Polymerisation und neue Anlagerungsreak­ tionen des Dimethylketens. 5e. H. A. Bruson (1925): Die Polymerisation von Cyclopentadien und Inden. 5f. W. Widmer (1925): Untersuchungen iiber neue Kautschukderivate. 5g. M. Brunner (1926): Uber hochpolymere organische Stoffe. 5h. K. Frey (1926): Uber die Konstitution der Polysaccharide. 5i. E. Geiger (1926): Uber die Konstitution der Hochpolymeren. 5j. E. Huber (1926): Uber die Hydrierung und die pyrogene Zersetzung hochmolekularer Kohlenwasserstoffe. 5k. S. Wehrli (1926): Uber die Polymerisation des Styrols. 51. E. W. Reuss (1926): /. Synthetische Versuche auf dem Gebiet des dalmatinischen Insektenpulvers (Pyrethrum). II. Eine neue Klasse org. Kolloide: Eukolloide Salze aus Kautschuk u. Guttapercha. 5m. H. Harder (1927): Uber Additions­ und Polymerisationsreaktionen des Dimethylketens. 5n. H. W. Johner (1927): Uber die Konstitution der verschiedenen Polymerisationsprodukte des Formaldehyds. 5o. R. Signer (1927): Uber die Konstitution der Polyoxymethylene. 5p. E. Urech (1927): Sur Ia Polymerisation de!' Acide acrylique et de ses ethers. 6. H. Staudinger, Festgabe der GEP zur Hundertjahrfeier der Eidgenos­ sischen Technischen Hochschule Zurich, Zurich, 1955, pp. 399-409. Uber die Entwicklung der makromolekularen Chemie in den Jahren 1920 bis 1926. 7. H. Staudinger, H. Johner, R. Signer, G. Mie, and J. Hengstenberg, Z. Physik. Chern., 126, 425-448 (1927). Der polymere Formaldehyd, ein Modell der Cellulose.

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RESEARCH ON MACROMOLECULAR COMPOUNDS 8. H. Staudinger, Angew. Chem., 42, 37-30, 67-73 (1929). Die Chemie der hochmolekularen Stoffe im Sinne der Kekuleschen Strukturlehre. 9. H. Staudinger, Angew. Chem., 42, 77 (1929). Schluj3wort (zu den Bemerkungen von K. H. Meyer). 10. H. Staudinger, Ber., 64, 2721-2724 (1931). Uber die Wandlungen der Micellartheorie von K. H. Meyer. 11. H. Staudinger, Ber., 69, 1168-1185 (1936). Zur Entwicklung der makromolekularen Chemie. Zugleich Antwort auf die Eutgegnung von K. H. Meyer and A. van der Wyk [Ber., 69, 545 (1936)]. 12. H. Staudinger, Makromol. Chem., 9, 221-240 (1953). Zur Nomenkla­ tur auf dem Gebiet der Makromolekiile. 13. H. Staudinger, J. Prakt. Chem., N.F. 155, 1-12 (1940). Uber nieder­ molekulare und makromolekulare Chemie. 14. H. Staudinger, Makromol. Chem., 1, 7-21 (1947). Makromolekulare Naturstoffe und makromolekulare synthetische Produkte. 15. H. Staudinger, Die hochmolekularen organischen Verbindungen­ Kizutschuk und Cellulose, Spril}ger Verlag, Berlin, 1932, 540 pp. new print 1960; Photo Lithoprint Reproduction, Edwards Brothers, Inc., Ann Arbor, Michigan. 15a. Das Polystyrol, ein Modell des Kautschuks. By W. Heuer. 15b. Das Polyoxymethylen, ein Modell der Cellulose. By W. Kern. 15c. Das Polyiithylenoxyd, ein Modell der Starke. By H. Lohmann. 15d. Die Polyacrylsiiure, ein Modell des Eiweisses. By E. Trommsdorff. 15e. Zur Chemie des Kautschuks und der Guttapercha. 15f. Das Molekulargewicht des Kautschuks. By H. F. Bondy. 15g. Die Konstitution der Balata. By E. 0. Leupold. 15h. Die Umwandlung von loslichem in unloslichen Kautschuk. By E. 0. Leupold. 15i. Die Konstitution der Acetylcellulose. By H. Freudenberger 15j. Viskositiitsuntersuchungen anLosungen von Cellulose in Schweizers Reagens. By 0. Schweitzer. 15k. Das Molekulargewicht der Cellulose. By H. Scholz. 151. Die Konstitution der Nitrocellulose. By H. Haas. 16. W. Rohrs, H. Staudinger, and R. Vieweg, Fortschritte der Chemie, Physik und Technik der makromolekularen Stoffe. Verlag J. F. Lehmann, Miinchen-Berlin vol. I, 1939, 331 pp.; vol. II, 1942, 412 pp. References in their chemical parts: vol. I: 16a. Die makromolekulare Chemie. By H. Staudinger. 16b. Die Enstehung makromolekularer Stoffe durch Polymerisation und Polykondensation. By G. V. Schulz. 16c. Uber makromolekulare Siiuren und Basen. By W. Kern. 16d. Zur Chemie der Phenoplaste. By E. Dreher. References in their chemical parts: vol. II: 16e. Chemie und Technik der Pektine. By F. A. Henglein. 16f. Molekularer Bau und Deformationsmechanismus der regenerierten Zellulose im Vergleich mit anderen Linearpolymeren. By P. H. Hermans.

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16g. Uber die Wirkung von organischen Inhibitoren auf die Polymer­ isation des Styrols. By W. Kern. 16h. Osmotische Molkulargewichtsbestimmungen. By G. V. Schulz. 16i. Uber Holzpolyosen. By E. Husemann. 16j. Uber den Aufbau der Starke. By H. Staudinger and E. Husemann. 17. H. Staudinger, Uber die makromolekulare Chemie, Verlag Hans Ferd. Schulz, Freiburg i. Br., 1939, 32 p. Second revised edition, 1954. 18. H. Staudinger, Makromolekulare Chemie und Biologie, Verlag Wepf & Co., Basel, 1947, 160 pp. 19. H. Staudinger, "Uber die Konstitution des Kautschuks und anderer hochpolymerer Stoffe," in Verhandlungen der Schweizerischen Natur­ forschenden Gesellschaft, Luzern, 1924, pp. 125-126. (Information on a lecture given at the Schweizerische Naturforschende Gesellschaft.) 20. H. Staudinger, Ber., 61, 2427-2431 (1928). Uber die Konstitution der Hochpolymeren. 21. H. Staudinger, Naturwissenschaften, 17, 141-144 (1929). Uber die Konstitution der hochmolekularen Stoffe. 22. H. Staudinger. Helv. Chim. Acta, 12, 1183-1197 (1929). Der Bau der hochmolekularen organischen Stoffe im Sinne der Kekuleschen Struk­ turlehre (lecture given in Hochst October 17, 1929). 23. H. Staudinger, "Sur Ia Structure des Composes a poids moleculaire eleve," in IV. Internal. Solvay­Kongrej3, Briissel April 1931, Gauthier­ Villars, Paris, 1931, pp. 101-176 (see also the discussion on pp. 177190). 24. H. Staudinger, Bull. Soc., Chim. France, 49 (4), 1267-1279 (1931). Sur Ia Constitution des Colloi'des moleculaires (lecture to the Societe Chimique de France, June 12, 1931). 25. H. Staudinger, Z. Physik. Chem. (A), 153, 391-424 (1931). Uber die Konstitutionsaufkliirung hochmolekularer Verbindungen (lecture at Harnack-Haus, Berlin, November 1930). 26a. H. Staudinger, Bericht zum IX. Internat. Chemiker-Kongre,B, Madrid 1932, C. Bermejo, Impressor, Madrid, pp. 3-62 im Sonderdruck, Die Chemie der hochmolekularen organischen Stoffe im Sinne der Kekuleschen Strukturlehre. 26b. H. Staudinger, An. Soc. espaii. Fislca Quim., 30, 183-205, 225-246 (1932). La Quimica de los Polimeros Organicos Elevados segun Ia Teoria Estructural de Kekule. 27. H. Staudinger, Scientia, 1933, 73-92 (August). Die hochmolekularen organischen Verbindungen, Kautschuk und Cellulose. 28. H. Staudinger, Forsch. u. Fortschr., 9, 219-221 (1933). Uber den Aufbau der hochmolekularen organischen Verbindungen Kautschuk und Cellulose. 29. H. Staudinger, Trans. Faraday Soc., 29, 18-32 (1933). Viscosity Investigations for the Examination of the Constitution of Natural Products of High Molecular Weight and of Rubber and Cellulose.

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30. H. Staudinger, Naturwissenschaften, 22, 65-71, 84-89 (1934). Der Aufbau der hochmolekularen organischen Verbindungen (lecture at the UniversiHit Madrid on March 22, 1933). 31. H. Staudinger, KongrejJbericht Madrid Bd. IV, Reine und angewandte organische Chemie (pp. 3-41 in reprint). Die neuere Entwicklung der organischen Ko/loidchemie (lecture given April 10, 1934, at the IX. Internat. KongrejS fiir reine und angewandte Chemie, Madrid, April511, 1934). 32a. H. Staudinger, Trans. Faraday Soc., 32,97-115 (1936). The Formation of High Polymers of Unsaturated Substances. 32b. H. Staudinger, Forsch. u. Fortschr., 11, 452-453 (1935). Ober die Polymerisation von ungesiittigen Verbindungen (abstract of a lecture given to the Faraday Society, Cambridge, September 26-28, 1935). 32c. H. Staudinger, Res. and Progr., 2, 97-101 (1936). The Formation of High Polymers of Unsaturated Substances (abstract of a lecture given to the Faraday Society, Cambridge, September, 1935). 33. H. Staudinger, Rdsch. Techn. Arb., 16, Nr. 28, 2 (1936). Die Chemie der grofJen Molekule. 34. H. Staudinger, Angew. Chern., 49, 801-813 (1936). Ober die makro­ molekulare Chemie (summary of lecture given to Reichstreffen der Deutschen Chemiker, Mi.inchen on July 10, 1936). 35. H. Staudinger, Naturwissenschaften, 25, 673-681 (1937). Ober Cellu­ lose, Starke und Glykogen (lecture to the Bezirksverein Oberhessen des VDCh, Giessen, April1937). 36. H. Staudinger, Chemiker­Ztg., 61, 14-15 (1937). Ober die Entwicklung der makromolekularen Chemie. 37. H. Staudinger, Unterrichtsbliitter fur Mathern. und Naturwissensch., 43, 33-45 (1937). Ober die Bedeutung der Hochmolekularen fur Biologie und Technik. 38. H. Staudinger, Chemiker­Ztg., 62, 749-754 (1938). Ober die Kon­ stitutionsaufkliirung der makromolekularen Verbindungen. 39. H. Staudinger," Ober die Entwicklung der makromolekularen Chen1ie," in Der feste Korper (collection of lectures on the 50th year of the Physikal. GesellschaftZi.irich), Verlag Hirzel, Leipzig, 1938,pp.105-123. 40. H. Staudinger, Chemiker­Ztg., 62, 117-119 (1938). Der Aufbau der makromolekularen Stoffe Kautschuk und Cellulose (lecture to the Gautagung der Technik, Stuttgart, 1937). 41. H. Studinger, Kunststoffe, 29 (1939) (pp. 1-3 in reprint). Vom Aufbau des Kunststoff­Molekuls. 42. H. Staudinger, Kunststoffe, 30, 157-163 (1940). Uber die makromoleku­ lare Chemie der Kunststoffe. 43. H. Staudinger, J. Prakt. Chern. N.F., 156, 11-26 (1940). Ober den Molekulbegriffin der niedermolekularen und makromolekularen Chemie. 44. H. Staudinger, Techn. Mitt., 33, No. 17/18, 71-76 (1940). Ober die Bedeutung der makromolekularen Chemie fur die Technik (lecture to the Haus der Technik, Essen, May 17, 1940).

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45. H. Staudinger, Res. and Progr. 7, 133-141 (1941). The Chemistry of Macro­Molecular Compounds. 46. H. Staudinger, Kunststoffe, 33, 197-203 (1943). Uber die Form­ bestiindigkeit der Makromolekiile. 47. H. Staudinger, Physik. Bl., 4, 315-323 (1948). Makromolekiile und ihre Gestalt. 48. H. Staudinger, Ber. Ges. Kohlentechn., 5, 347-374 (1950). Makro­ molekulare Chemie (extended lecture given to the Gesellschaft fi.ir Kohlentechnik im Haus der Technik, Essen, October 28, 1942). 49. H. Staudinger, "Methoden der Konstitutionsaufkliirung makromole­ kularer Kunststoffe," in Atti del 2. Congresso Internazionale delle Materie Plastiche;Torino, October 1950, pp. 10-18. 50. H. Staudinger, Chern. Industrie, 3, 595-597 (1951). Uber die Entwick­ lung der Kunststoffchemie. 51. H. Staudinger, Angew. Chern., 64, 149-158 (1952). Zur Konstitutions­ aufkliirung makromolekularer Kunststoffe (lecture to the GDChFachgruppe 'Kunststoffe und Kautschuk,' Koln, September 25, 1951). 52. H. Staudinger, Chemiker­Ztg., 76, 337-339 (1952). Probleme der makromolekularen Chemie (opening address to the Erweitertes Makromolekulares Kolloquium in Freiburg i. Br., April, 1952). 53. H. Staudinger, Chemiker­Ztg., 77,401-403 (1953). Zur Entwicklung der makromolekularen Chemie (opening address to the Erweitertes Makromolekulares Kolloquium in Freiburg i. Br., April, 1953). 54. H. Staudinger, Chemiker­Ztg., 77, 679-687 (1953). Uber die Entwick­ lung der makromolekularen Chemie zu einem neuen Zweig der organis­ chen Chemie (introductory lecture to the Macromolecular Section of the IUPAC, Stockholm, July 29, 1953). 55. H. Staudinger, Makromol. Chern., 13, 1-4 (1954). Zur Entwicklung der makromolekularen Chemie (opening address to the Erweitertes Makromolekulares Kolloquium, Freiburg i. Br., April17, 1954). 56. H. Staudinger, Reyon, Zellwolle, andere Chemiefasern, 32, No. 6, X-XII (1954). Makromolekulare Chemie und Chemiefasern (opening address to the Internationaler Chemiefaser-Kongress, Paris, June 1954). ' In French: Rayonne et Fibres Synthetiques, No. 10, October 15, 1954. 57. H. Staudinger, Naturwissenschaften, 42, 221-230 (1955). Uber die Grundlagen der makromolekularen Chemie (lecture at the meeting of the Deutsche Naturforscher und Arzte in Freiburg i. Br., September 13, 1954. 58. H. Staudinger, Chim. e Ind. (Milano), 37, 27-36 (1955). I fondamenti della chimica macromolecolare (lecture in Turin on October 2, 1954, (at receipt of Dr chem. h.c.). 59. H. Staudinger, "L'Evolution de Ia Chimie Macromoleculaire, branche nouvelle de Ia Chimie Organique," in Quelques aspects generaux de Ia Science des Macromolecules, Editions du Centre National de la Recherche Scientifique, Paris, 1955, pp. 10-21. Lecture to the inauguration

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RESEARCH ON MACROMOLECULAR COMPOUNDS of the Centre de Recherches sur les Macromolecules, Strasbourg, October, 1954. 60. H. Stauding r, Chimia (Zurich), 9, 225-232 (1955). Die makromole­ kulare Chemie (lecture to the Chemische Gesellschaft Zurich, November 3, 1954). 61. H. Staudinger, Acta Salmanticensia, Serie de Ciencias N.S., Torno II, num. 1, Universidad de Salamanca, 1956. La Quimica macromolecular, un nuevo dominio de trabajo de Ia Quimica organica (lecture at the UniversiHit Salamanca on March 15, 195, at receipt of Dr. [C] h.c. 62. H. Staudinger, XXVIII Congresso International de Quimica Industrial, Madrid, October, 1955. Die makromolekulare Chemie, ein neues Gebiet der organischen Chemie in Wissenschaft und Technik (lecture given October 26, 1955). 63. H. Staudinger, Chim. et Ind., 73, 519-530 (1955). La stabilite des matieres plastiques en fonction de leur composition et de leur structure (lecture at the Symposium tiber plastische Stoffe, Paris, December 11, 1954). 64. H. Staudinger, Naturwiss. Rdsch., 9, 8-13, 43-49 (1956). Niedermole­ kulare und makromolekulare Chemie (lecture at the meeting of the Nobel Prize winners, Lindau, 1955). 65. H. Staudinger, Sonderheft der Society of Polymer Science Japan, Tokyo, April 1957, pp. 6-37. Die makromolekulare Chemie, ein neues Gebiet der organischen Chemie (lecture given in Tokyo, April 5, 1957). 66. H. Staudinger, "Organische Kolloide als Makromolekiile," in Kolloid­ chemisches Taschenbuch, A. Kuhn, Ed., Akadem. Verlagsges., Leipzig, 1st ed., 1935; 5th ed., 1960, pp. 432-449. 67. H. Staudinger, Nobel lecture in Les Prix Nobel en 1953, Kungl. Boktryckeriet P. A. Norstedt & Soner, Stockholm, 1954, pp. 115138. (Part C in this volume.) 68. H. Staudinger and W. Heuer, Ber., 67, 1159-1164 (1934). Vber das Zerreij]en der Fadenmolekiile des Polystyrols. 69. H. Staudinger and E. Dreher, Ber., 69, 1091-1098 (1936). Vber das Zerreij]en von Fadenmolekiilen der Cellulose beim Vermahlen. 70. H. Staudinger, Ber., 62, 2893-2909 (1929). Vber die organischen Kolloide. 71. H. Staudinger, Ber., 68, 1682-1691 (1935). Vber die Einteilung der Kolloide. 72. H. Staudinger, J. Prakt. Chern. N.F., 160, 245-280 (1942). Kolloidik und makromolekulare Chemie. 73. H. Staudinger, Organische Kolloidchemie, Verlag Vieweg & Sohn, Braunschweig, 308 Seiten, 1. Auflage 1940, 2. Auflage 1941, 3. Auflage 1950. French translation: Chimie des collofdes organiques. translated by Henri Gibello, revised by M. Staudinger, Verlag Dunod, Paris, 1953. Italian translation: Chimica organica colloidale. translated by Valerio Broglia, Verlag Hoepli, Milano, 1957.

PART B REFERENCES

249

74. H. Staudinger and W. Heuer, Ber., 62, 2933-2943 (1929). Uber die Assoziation und Solvatation von Polystyro!en. 75. H. Staudinger, Kolloid­Z., 53, 19-32 (1930). Organische Chemie und Kol!oidchemie. 76. H. Staudinger and E. Husemann, Ber., 68, 1691-1697 (1935). Vis­ kositiitsuntersuchungen an organischen Sphiiro­ und Linearkolloiden. 77. H. Staudinger, Chemiker­Ztg., 59, 733-736, 756-757 (1935). Fort­ schritte der organischen Kolloidchemie. 78. H. Staudinger, C. R. Lab. Carlsberg, Ser. chim., 22, 494-503 (1937). S0rensen-Festschrift. Uber die Bedeutung der Gestalt der Makromole­ kiile in der Kolloidchemie. . 79. H. Staudinger, Scientia, 1938, 53-65 (August). Neue Gesichtspunkte zur Einteilung der Kolloide. 80. H. Staudinger, Chemiker­Ztg., 66, 380-385 (1942). Uber die Visko­ sitiit der Molekiilkolloide. 81. H. Staudinger and H. Hellfritz, Makromol. Chem., 7, 274-293 (1951). Linearkol!oide und Sphiirokolloide in Polyisobutylenlosungen. 82. H. Staudinger, Chemiker­Ztg., 76, 661-666 (1952). Uber Gellosungen und ihre Bedeutung fur die lndustrien der Kunststoffe, der Faserstoffe und des Kautschuks. 83. H. Staudinger, E. Geiger, and E. Huber, Ber., 62, 263-267 (1929). Uber die Reduktion des Polystyrols. 84. H. Staudinger and y. Wiedersheim, Ber., 62, 2406-2411 (1929). Uber die Reduktion des Polystyrols. 85. H. Staudinger and 0. Schweitzer, Ber., 63, 3132-3154 (1930). Uber die Molekiilgroj3e der Cellulose. 86. H. Staudinger, R. Signer, H. Johner, M. Luthy, W. Kern, D. Russidis, and 0. Schweitzer, Leibigs Ann. Chem.; 474, 145-275 (1929). Uber die Konstitution der Polyoxymethylene. 87. R. Signer and J. Weiler, Helv. Chim. Acta, 15, 649-657 (1932). Raman­Spectrum und Konstitution hochmolekularer Stoffe. 88. R. Signer and J. Weiler, Helv. Chim. Acta, 16, 115-121 (1933). Der Raman­Effekt von Kieselsiiure­methylestern. 89. G. V. Schulz, Z. Elektrochem. Angew. Physik. Chem., 44, 102-104 (1938). Uber Polydispersitiit und Polymolekularitiit. 90. R. Signer and H. Gross, Helv. Chim. Acta, 17, 726-735 (1934). Ultrazentrzfugale Polydispersitiitsbestimmungen an hochpolymeren Stoffen. 91. G. V. Schulz, Z. Physik. Chem. (B), 32, 27-45 (1936). Uber die Vertei­ lung der Molekulargewichte in hochpolymeren Gemischen und die Bestimmung des mittleren Molekulargewichtes. 92. G. V. Schulz and E. Nordt, J. Prakt. Chem. N.F., 155, 115-128 (1940). Fraktionierung polymolekularer Stoffe durch Verteilung zwischen zwei fliissigen Phasen. 93. G. V. Schulz, Z. Physik. Chem. (B), 46, 137-156 (1940). Die Trennung polymolekularer Gemische durchfraktionierte Fiillung.

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COMPOUNDS

94. G. V. Schulz, Z. Physik. Chern. (B),47, 155-193(1940). Die Verteilungs­ funktionen polymolekularer Stoffe und ihre Ermittelung durch Zer­ legung in Fraktionen. 95. G. V. Schulz, Z. Physik. Chern. (B), 51, 127-143 (1942). Uber die Molekulargewichtsverteilungen, die beim Abbau von Stoffen mit Kettenmolekiilen auftreten. 96. H. Staudinger, Ber., 68, 2357-2362 (1935). Uber den Begriff des Molekulargewichtes bei nieder­ und hochmolekularen Verbindung­ en. 97. R. Signer and H. Gross, Helv. Chim. Acta, 17, 59-77 (1934). Uber das Verhalten von Polystyrolen in der Svedberg'schen Sedimentations­ geschwindigkeits­Zentrifuge. 98. R. Signer and H. Gross, Helv. Chim. Acta, 17, 335-351 (1934). Ultrazentrifugale Molekulargewichtsbestimmungen an synthetischen hochpolymeren Stoffen. 99. E. Husemann and H. Ruska, J. Prakt. Chern. N.F., 156, 1-10 (1940). Versuche zur Sichtbarmachung von Glykogenmolekiilen. 100. E. Husemann and H. Ruska, Naturwissenschaften, 28, 534 (1940). Die Sichtbarmachung von Molekiilen des p­Jodbenzoylglykogens. 101. H. Staudinger and A. A. Ashdown, Ber., 63, 717-721 (1930). Uber Poly­a­phenyl­butadien. 102. H. Staudinger, W. Kern and J. Jimenez Herrera, Ber., 68, 2346-2350 (1935). Uber anomale Molekulargewichte bei hochmolekularen Ver­ bindungen. 103. R. Signer, Liebigs Ann. Chern., 478,246-266 (1930). Uber eine Abander­ ung der Molekulargewichtsbestimmungsmethode nach Barger. 104. H. Staudinger and H. Lohmann, Ber., 68,2313-2319 (1935). Molekular­ gewichstbestimmungen an hochmolekularen Polyathylenoxyden. 105. H. Staudinger and G. V. Schulz, Ber., 68, 2320-2335 (1935). Ver­ gleich der osmotischen und viskosimetrischen Molekulargewichtsbe­ stimmungen an polymerhomologen Reihen. 106. H. Staudinger and G. V. Schulz, Ber., 68, 2336-2346 (1935). Uber osmotische Bestimmungen an Losungen mit stab­ und kugelformigen Teilchen. 107. G. V. Schulz, Z. Physik. Chern. (A), 176, 317-337 (1936). Osmotische Molekulargewichtsbestimmungen in polymerhomologen Reihen hoch­ molekularer Stoffe. 108. G. V. Schulz, Angew. Chern., 49, 863-865 (1936). Uber osmotische Molekulargewichtsbestimmungen an Hochmolekularen. 109. G. V. Schulz, Z. Physik. Che1n. (A), 177, 453-459 (1936). Uber den osmotischen Druck von Methylcellulosen. 110. H. Staudinger and G. V. Schulz, Ber., 70, 1577-1582 (1937). Osmotische Messungen an Celliten in Eisessig. 111. G. V. Schulz, Z. Physik. Chen1. (A), 180, 1-24 (1937). Uber die Tempe­ raturabhangigkeit des osmotischen Druckes und den Molekularzustand in hochmolekularen Losungen.

PART B REFERENCES

251

112. H. Staudinger, Kolloid­Z., 82, 129-131 (1938). Uber das Molekularge­ wicht und die Viskositiit von Hochpolymeren. Bemerkungen zu der Arbeit von A. Dobry. 113. G. V. Schulz, Z. Physik. Chern. (B), 40, 319-325 (1938). Temperatur­ abhiingigkeit des osmotischen Druckes, Verdunnungswiirme und Ver­ dunnungsentropie hochmolekularer Losungen. 114. G. V. Schulz, Z. Elektrochem. Angew. Physik. Chern., 45, 652-658 (1939). Experimentelle Beitriige zur Thermodynamik hochmolekularer Losungen. 115. G. V. Schulz and A. Dinglinger, J. Prokt. Chern. N.F., 158, 136-162 (1941). Molekulargewichtsbestimmungen an einer Reihe von Poly­ methacrylsiiuremethylestern nach verschiedenen Methoden (osmotisch, viskosimetrisch und durch Fiillungstitration). 116. G. V. Schulz, J. Prakt. Chern. N.F., 159, 130-138 (1941). Bemerkungen zu einer Arbeit uber osmotische Molekulargewichtsbestimmungen an Acetylcellulosen von Lachs und Grossmann. 117. H. Staudinger and W. Heuer, Z. physik. Chern. (A), 171, 129-180 (1934). Zusammenhiinge zwischen Solvatation, Loslichkeit und Visko­ sitiit von Polystyrolen. 118. G. V. Schulz, Z. Physik. Chern. (A), 179, 321-355 (1937). Uber die Loslichkeit und Fiillbarkeit hochmolekular Stoffe. 119. G. V. Schulz and B. Jirgensons, Z. Physik. Chern. (B), 46, 105-136 (1940). Die Abhiingigkeit der Loslichkeit vom Molekulargewicht. Uber die Loslichkeit makromolkularer Stoffe. 120. W. Kern, Ber., 68, 1439-1443 (1935). Vergleich der osmotisch und viskosimetrisch bestimmten Molekulargewichte von Gemischen von Polymerhomologen. 121. H. Staudinger and H. Freudenberger, Ber., 63,2331-2343 (1930). Mole­ kulargewichtsbestimmungen an Acetyl­Cellulosen. 122. H. Staudinger and W. Heuer, Ber., 63, 222-234 (1930). Beziehungen zwischen Viskositiit und Molekulargewicht bei Polystyrolen. 123. H. Staudinger and R. Nodzu, Ber., 63, 721-724 (1930). Viskositiitsun­ tersuchungen an Paraffin­Losungen. 124. H. Staudinger and E. Ochiai, Z. Physik. Chern. (A), 158, 35-55 (1932). Viskositiitsmessungen an Losungen von Fadenmolekulen. 125. H. Staudinger and W. Kern, Ber., 66, 373-378 (1933). Viskositiits­ messungen an Losungen von Fadenmolekulen mit verzweigten Ketten. 126. H. Staudinger and R. C. Bauer, Helv. Chim. Acta, 16, 418-426 (1933). Viskositiitsmessungen an Losungen von hohermolekularen Paraffinderi­ vaten mit verzweigter Kette. 127. H. Staudinger and R. C. Bauer, Helv. Chim. Acta, 17, 863-865 (1934). Uber Viskositiitsuntersuchungen an hochgliedrigen Ringsystemen. 128. H. Staudinger, Helv. Chim. Acta, 17, 866-868 (1934). Bemerkungen zu den Viskositiitsuntersuchungen von P. Karrer und Cesare Ferri. 129. H. Staudinger and A. Steinhofer, Ber., 68, 471-473 (1935). Viskosi­ tiitsmessungen an Carotinoiden.

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COMPOUNDS

130. H. Staudinger and A. Steinhofer, Liebigs Ann. Chern., 517, 54-66 (1935). Viskositiitsmessungen an Losungen von cyclischen Verbindungen. 131. H. Studinger and F. Staiger, Liebigs Ann. Chern., 517, 67-72 (1935). Viskositiitsuntersuchungen an Polyphenyliithern. 132. H. Staudinger and F. Staiger, Ber., 68, 707-726 (1935). Viskositiits­ messungen an Paraffinen. 133. H. Staudingen and H. Schwalenstocker, Ber., 68, 727-749 (1935). Bestimmung der Molekulgestalt durch Viskositiitsmessungen. 134. H. Staudinger and K. Rossler, Ber., 69, 49-60 (1936). Viskositiitsunter­ suchungen an langkettigen aliphatischen Aminen. 135. H. Staudinger and K. Rossler, Ber.,. 69, 61-73 (1936). Viskositiits­ messungen an Fettsiiureamiden und ­aniliden. 136. H. Staudinger, Ber., 69, 203-208 (1936). Bemerkungen zu der Arbeit von K. H. Meyer und A. van der Wyk: Die Viskositiit von Losungen aliphatischer Kohlenwasserstoffe. 137. H. Staudinger and H. Moser, Ber., 69, 208-213 (1936). Viskositiits­ untersuchungen an Losungen von Glycolestern und Dicarbonsiiureestern. 138. H. Staudinger, Helv. Chim. Acta, 19, 204-218 (1936). Bemerkungen zu der Arbeit von K. H. Meyer und A. van der Wyk: La viscosite des solutions d' hydrocarbures aliphatiques. 139. H. Staudinger and H. v. Becker, Ber., 70, 889-900 (1937). Viskositiits­ messungen an Aminosiiuren. 140. H. Staudinger and H. Jorder, J. Prakt. Chern. N.F., 160, 166-175 (1942). Viskositiitsmessungen an Estern mit unverzweigten und verz­ weigten Ketten. 141. H. Staudinger, G. Bier, and G. Lorentz, Makromol. Chern., 3, 251-280 (1949). Viskositiitsuntersuchungen an niedermolekularen Estern mit verzweigten Molekulen. 142. G. Bier, Makromol. Chern., 4, 41-49 (1949). Vber den Ein.flu./3 der Doppelbindung auf die Viskositiitszahl von Kettenmolekulen. 143. G. Bier, Makromol. Chern., 4, 124-133 (1949). Vber die Viskositiit von verzweigten Verbindungen. 144. H. Staudinger, Makromol. Chern., 4, 289-307 (1950). Uber die ront­ genographische und viskosimetrische Kettenliinge von Fadenmole­ kulen. 145. Heinz Schwalenstocker, dissertation, UniversiHit Freiburg i. Br., 1934. Bestimmung der Molekulgestalt durch Viskositiitsmessungen. 146. Hans von Becker, dissertation, UniversiHit Freiburg i. Br. 1935. I. Viskositiitsmessungen an Aminosiiuren. II. Untersuchungen an hochmolekularen Poly­ammonium­ Verbindungen. 147. Hubert Frey, dissertation, Universitat Freiburg i. Br., 1935. Viskosi­ tiitsuntersuchungen an Siiuren, Alkoholen und Phenolen. 148. Fritz Staiger, dissertation, Universitat Freiburg i. Br., 1935. Viskosi­ tiitsuntersuchungen an niedermolekularen Verbindungen. 149. Karl Rossler, dissertation, Universitat Freiburg i. Br., 1935. Viskositiits­ untersuchungen an Aminen und Siiureamiden.

PART B REFERENCES

253

150. Alfred Emil Werner, dissertation, UniversiHit Freiburg i. Br., 1936. Uber Viskositiitsrnessungen an cyclischen Verbindungen. 151. Guido Lorentz, dissertation, UniversiHit Freiburg i. Br., 1943. Visko­ sitiitsuntersuchungen an Malonestern. 152. W. Hahn, W. Miiller and R. V. Webber, Makrornol. Chern., 21, 131168 (1956). Untersuchungen an Polystyrolen verschiedener Herstel­ lung. 153. R. Signer, Z. Physik. Chern. (A), 150, 257-284 (1930). Uber die Strornungsdoppelbrechung der Molekiilkolloide. 154. R. Signer and G. Boehm, Helv. Chirn. Acta, 14, 1370-1403 (1931). Uber die Strornungsdoppelbrechung von Eiweifllosungen. 155. R. Signer and H. Gross,Z. Physik. Chern. (A), 165,161-187 (1933). Uber die Strornungsdoppelbrechung verdiinnter Losungen der Molekiilkolloide. 156. H. Staudinger and K. Frey, Ber., 62, 2909-2912 (1929). Viskositiits­ untersuchungen an Polystyrollosungen. I. 157. H. Staudinger and H. Machemer, Ber., 62, 2921-2932 (1929). Vis­ kositiitsuntersuchungen an Polystyrollosungen. II. 158. H. Staudinger, Kolloid­Z., 51, 71-89 (1930). Viskositiitsuntersuchungen an Molekiilkolloiden. 159. H. Staudinger and 0. Schweitzer, Ber., 63, 2317-2330 (1930). Visko­ sitiitsrnessungen an Polysacchariden und Polysaccharidderivaten. 160. H. Staudinger and E. 0. Leupold, Ber., 63, 730-733 (1930). Viskosi­ tiitsuntersuchungen an Balata. 161. H. Staudinger and R. Nodzu, Helv. Chirn. Acta, 13, 1350-1354 (1930). Uber Beziehungen zwischen Viskositiit und Molekulargewicht bei Hydro­ kautschuken. 162. H. Staudinger, Helv. Chirn. Acta, 15, 213-221 (1932). Viskositiitsgesetze bei hochpolyrneren Verbindungen. 163. H. Staudinger, Ber., 65, 267-279 (1932). Uber Beziehungen zwischen der Kettenliinge von Fadenmolekiilen und der spezifischen Viskositiit ihrer Losungen. 164. H. Staudinger, Ber., 65, 1754-1756 (1932). Zur Ternperaturabhiingig­ keit der Viskositiit von Cellulose­Losungen. 165. H. Staudinger, Ber., 67, 92-101 (1934). Uber die Giiltigkeit des Viskositiitsgese tzes. 166. H. Staudinger, Z. Elektrochern. Angew. Physik. Chern., 40, 434-446 (1934). Uber das Viskositiitsgesetz. 167. H. Staudinger, Ber., 67, 1242-1256 (1934). Uber den Aufbau der Hochrnolekularen und iiber das Viskositiitsgesetz. 168. H. St., !.R.I. Trans., 10, 263-279 (1935). The Constitution of Rubber and the Nature of Its Viscous Solutions. 169. H. Staudinger and M. Sorkin, Ber., 70, 1993-2017 (1937). Uber Viskositiitsuntersuchungen an Cellulosenitraten. 170. G. V. Schulz, Z. Elekrochern. Angew. Physik. Chern., 43, 479-485 (1937). Uber die Verwendbarkeit des Ostwald­ Viskosirneters fur die Bestirnrnung hoher Molekulargewichte.

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RESEARCH ON MACROMOLECULAR COMPOUNDS

171. H. Staudinger and F. Reinecke, Ber., 71, 2521-2535 (1938). Uber das Viskositiitsgesetz in der Cellulosereihe. 172. G. V. Schulz, Z. Physik. Chern. (A), 184, 1-41 (1939). Der Zustand des Losungsmittels im System Aceton­Nitrocellulose bei niedrigen und hohen Konzentrationen (0,1-75/0 ). 173. H. Staudinger, Papier­Fabr., 38, 285-292 (1940). Vber die Bedeutung von Viskositiitsmessungen fiir die Cellulosechemie. 174. G. V. Schulz and F. Blaschke, J. Prakt. Chern. N. F., 158, 130-135 (1941). Eine Gleichung zur Berechnung der Viskositiitszahl fiir sehr kleine Konzentrationen. 175. H. Staudinger and K. Eder, Naturwissenschaften, 29, 221 (1941). Uber das Viskositiitsgesetz fiir Fadenmolekiile. 176. H. Staudinger, Kolloid­Z., 98, 330-332 (1942). Bemerkung zu dem Aufastz von K. H. Meyer: "Vber die Viskositiit und das Molekularge­ wicht von Hochpolymeren." 177. H. Staudinger, Z. Elektrochem. Angew. Physik. Chern., 49, 7-16 (1943). Charakterisierung von Losungen organischer Stoffe durch ihre Viskositiit. 178. E. Husemann and G. V. Schulz, J. Makromol. Chern., 1, 197-202 (1944). Die Bestimmung der Viskositiitszahl von Cellulosen in Schweizers Reagens durch Messungen bei hoheren Konzentrationen. 179. H. Krassig and H. Muller, Chemiker­Ztg., 78, 209-212 (1954). Vber die Beziehung zwischen Viskositiitszahl und Polymerizationsgrad bei Cellulosenitraten. 180. W. Kern, Z. Physik. Chern. (A), 181, 283-300 (1938). Die Viskositiit von Losungen der Polyacrylsiiure und ihrer Salze. 181. H. Staudinger, J. Joseph, and E. 0. Leupold, Liebigs Ann. Chern., 488, 150-153 (1931). Latex, ein Emulsoid. [In the paper of H. Staudinger and H. F. Bondy, Liebigs Ann. Chern., 488, 127-153 (1931).] 182. H. Staudinger and E. Husemann, Liebigs Ann. Chern., 530, 1-20 (1937). Vber die Konstitution des Glykogens. 183. H. Staudinger and F. Zapf, J. Prakt. Chern. N.F., 157, 1-14 (1940). Vber das Glykogenxanthogenat. 184. H. Staudinger and R. Signer, Z. Krist., 70, 193-210 (1929). Vber den Kristallbau hochmolekularer Verbindungen. 185. H. Staudinger and R. Signer, Helv. Chim. Acta, 11, 1047-1051 (1928). Bemerkungen zu der Arbeit von E. Ott, "Rontgenometrische Unter­ suchungen an hochpolymeren organischen Substanzen." G. Mie and J. Hengstenberg, Helv. Chim. Acta, 11, 1052 (1928). Notiz zur Arbeit: E. Ott, "Rontgenometrische Untersuchungen an hochpolymeren, organischen Substanzen." 186. E. Sauter, Z. Krist. (A), 83, 340-353 (1932). Rontgenuntersuchungen an polymeren und monomeren Butadiensulfonen. 187. E. Sauter, Z. Physik. Chern. (B), 18, 417-435 (1932). Rontgenomet­ rische Untersuchungen an hochmolekularen Polyoxymethylenen.

PART B REFERENCES

255

188. E. Sauter, Z. Physik. Chem. (B), 21, 186-197 (1933). Ein Modell der Hauptvalenzkette im Makromolekiilgitter der Polyoxymethylene. 189. E. Sauter, Z. Krist. (A), 93, 93-106 (1936). Uber die Herstellung von vollstiindigen Faserdiagrammen. 190. E. Sauter, Z. Physik. Chem. (B), 36, 405-426 (1937). Elementar­ zellendiagramme und Mikrostruktur von Kautschuk­ 'Einkristallen.' Ermittlung des Kautschuk­ Makromolgitters nach neuen Rontgen­ methoden. 191. E. Sauter, Z. Physik. Chem. (B), 35, 83-116 (1937). Beitriige zur Rontgenographie und Morphologie der Cellulose. I. Ermittlung des Makromolgitters der nativen Cellulose nach neuen Rontgen­Struktur­ bestimmungsmethbden. 192. E. Sauter, Z. Physik. Chem. (B), 35, 117-128 (1937). Beitriige zur Rontgenographie und Morphologie der Cellulose. II. Die kristalline und ultrakristalline Fibrilliirstruktur der Cellulose. 193. E. Sauter, Z. Physik. Chem. (B), 36, 427-434 (1937). Uber die Kris­ tallstruktur der Cellulose. 194. E. Sauter, Z. Physik. Chem. (B), 37, 161-167 (1937). Uber eine neue Art von Faserdiagramm: Das Drehgoniometer­Faserdiagramm. Uber die Polymorphie zwischen nativer Cellulose und Hydratcellulose. I. 195. E. Sauter, Z. Physik. Chem. (B), 43, 292-293 (1939). Zur Gitterbestim­ mung des Kautschuks. 196. E. Sauter, Z. Physik. Chem. (B), 43, 294-308 (1939). Uber Beziehungen zwischen den Gittern der nativen und der Hydratcellulose (answer to K. H. Meyer and H. Mark). 197. E. Plotze and H. Person, Naturwissenschaften, 27, 693 (1939). Ront­ genographische Untersuchungen polymerhomologer Cellulosefasern. 198. E. Plotze and H. Person, Z. Physik. Chem. (B), 45, 193-200 (1940). Die Kristallitorientierung in Fasercellulosen. 199. E. Plotze, Naturwissenschaften, 29, 707 (1941). Systematische rontgeno­ graphische Untersuchungen an polymerhomologen Reihen von Cellulose­ fasern. 200. H. Staudinger, M. Staudinger, and E. Sauter, Melliand Textilber, 18, 849-853 (1937). Modellversuche zum Faserstoffproblem an synthetischen hochmolekularen Stoffen. 201. H. Staudinger, M. Staudinger, and E. Sauter, Z. Physik. Chem. (B), 37, 403-420 (1937). Mikroskopische Untersuchungen an synthetischen hochmolekularen Stoffen. 202. H. Staudinger and M. Staudinger, Die makromolekulare Chemie und ihre Bedeutung fiir die Protoplasmaforschung, in Protoplasmatologia, Handbuch der Protoplasmaforschung, Vol. I, 1, Verlag Springer, Vienna, 1954, p. 1-73. 203. H. Staudinger and M. Staudinger, Z. Ges. Textil­lnd., 56, No. 13, 807 (1954). Das Makromolekiil als Baustein der Faserstoffe. 204a. M. Staudinger, J. Prakt. Chem. N.F., 160, 203-216 (1942). Der fibril/are Bau natiirlicher und kiinstlicher Cellulosefasern.

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204b. M. Staudinger, J. Makromol. Chem., 2, 67-77 (1944). Vber den Faserabbau im mikroskopischen Bild. 205. M. Staudinger, Chemiker­Ztg., 67, 316-320 (1943). Mikroskopische und elektronenmikroskopische Untersuchungen an makromolekularen Stoffen. (Lecture given in June 1943 in the Karlsruhe-section of the VDCh and in October 1943 in the Hessen-Nassau section of the VDCh in Frankfurt, Main.) 206. M. Staudinger, Makromol. Chem., 7, 70-81 (1951). Zur Morphologie natiirlicher und kiinstlicher Cellulosefasern und ihrer Nitrate. 207. M. Staudinger, Assoc. Tech. Industrie Papetiere Bull., 6, 103-119 (1952). Sur Ia structure macromoleculaire ou micellaire des celluloses so/ides (lecture given by invitation of the Commission des Etudes Generales de L'Association Technique de l'Industrie Papetiere, Paris, March 1952). 208. H. Staudinger, K.-H. In den Birken, and M. Staudinger, Makromol. Chem., 9, 148-187 (1953). Vber den micellaren oder makromolekularen Bauder Cellulosen. 209. E. Husemann, J. Makromol. Chem., 1, 16-27 (1944). Vbermikrosko­ pische Untersuchungen an hydrolytisch abgebauten Fasern. 210. E. Husemann, J. Makromol. Chem., 1, 158-167 (1944). Vbermikro­ skopische Untersuchungen an gemahlen(m Cellulosefasern. 211. E. Husemann, Makromol. Chem., 1, 158-163 (1947). Elektronen­ mikroskopische Untersuchungen iiber submikroskoskopische Fibrillen aus Kunstfasern. 212. H. Staudinger, M. Staudinger and H. Schmidt, Zellwolle, Kunstseide, Seide, 45, 2-4 (1940). Vber die Zerstorung der Cellulose durch Mikro­ organismen. 213. H. Staudinger and W. Heuer, Ber., 67, 1164-1172 (1934). Vber ein unlosliches Polystyrol. 214. H. Staudinger and E. Husemann, Ber., 68, 1618-1634 (1935). Vber das begrenzt quellbare Polys tyro!. 215. H. Staudinger, W. Heuer, and E. Husemann, Trans. Faraday Soc., 32, 323-332 (1936). The Insoluble Polystyrene. 216. W. Kern, Kunststoffe, 28, 257-260 (1938). Vber die Polymerisation der monomeren Acrylsiiure zu loslichen und unloslichen Polymeren. 217. H. Staudinger, W. Doble, and 0. Heick, J. prakt. Chem. N.F., 161, 191-218 (1943). Vber topochemische Reaktionen der Cellulose. 218. E. Suter, dissertation, ETH Zurich, 1920. Vber den Einfluj3 von Substituenten auf die Kohlenstoffdoppelbindung. 219. H. Staudinger, K. Frey, and W. Starck, Ber., 60, 1782-1792 (1927). Vber Polyvinylacetat und Polyvinylalkohol. 220. H. Staudinger, A. A. Ashdown, M. Brunner, H. A. Bruson and S. Wehrli, Helv. Chim. Acta, 12, 934-957 (1929) especially pp. 944945). Vber die Konstitution des Polyindens. 221. H. Staudinger, Suomen Kemistilehti A, 31, 4-7 (1958). Vber die Registrierung makromolekularer Verbindungen nach dem System von M. M. Richter.

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257

222. H. Staudinger and L. Lautenschlager, Liebigs Ann. Chern., 488, 1-8 (1931). Vber Polymerisation und Autoxydation. 223. W. Kern and H. Kammerer, J. Prakt. Chern. N.F., 161, 81-112 (1943). Die chemische Molekulargewichtsbestimmung von Polystyrolen. 224. H. Staudinger and E. Urech, Helv. Chim. Acta, 12, 1107-1133 (1929). Vber die Polyacrylsiiure und Polyacrylsiiureester. 225. H. Staudinger and W. Frost, Ber., 68, 2351-2356 (1935). Vber die Polymerization als Kettenreaktion. 226. G. V. Schulz, Z. Physik. Chern. (B), 30, 379-398 (1935). Vber die Beziehung zwischen Reaktionsgeschwindigkeit und Zusammensetzung des Reaktionsproduktes bei Makropolymerisationsvorgiingen. 227. G. V. Schulz ana E. Husemann, Z. Physik. Chern. (B), 34 187-213 (1936). Vber die Kinetik der Kettenpolymerisationen: Die Polymerisa­ tion von reinem Styrol durch Wiirme. 228. G. V. Schulz and E. Husemann, Z. Physik. Chern. (B), 36, 184-194 (1937). Vber die Kinetik der Kettenpolymerisationen: Die Wiirme­ polymerisation des Styrols unter Ausschluj] von Sauerstoff, sowie einige Bemerkungen iiber den Kettenabbruch. 229. G. V. Schulz and E. Husemann, Angew. Chern., 50, 767-773 (1937). Dber die Kinetik der Kettenpolymerisationen: Dberblick iiber die Methoden und bisherigen Ergebnisse. 230. G. V. Schulz and E. Husemann, Z. Physik. Chern. (B), 39, 246-274 (1938). Vber die Kinetik der Kettenpolymerisationen: Die Be­ schleunigung der Polymerisation des Styrols durch Benzoylperoxyd. 231. G. V. Schulz, Z. Physik. Chern. (A), 182, 127-144 (1938). Die Bildung polymerer Stoffe durch Kondensationsgleichgewichte. 232. G. V. Schulz, Ergebn. Exakt. Naturwiss., 17, 367-413 (1938). Kinetik der Polymerisationsprozesse. 233. G. V. Schulz, Z. Physik. Chern. (B), 43, 25-46 (1939). Vber die Kinetik der Kettenpolymerisationen: Der Einfluj] verschiedener Reaktionsarten auf die Polymolekularitiit. 234. G. V. Schulz and A. Dinglinger, Z. Physik. Chern. (B), 43,47-57 (1939). Vber die Kinetik der Kettenpolymerisationen: Die Verteilung der Molekulargewichte in Polymerisaten von Polystyrol. 235. G. V. Schulz, A. Dinglinger, and E. Husemann, Z. Physik. Chern. (B), 43, 385-408 (1939). Vber die Kinetik der Kettenpolymerisationen: Die thermische Polymerisation von Styrol in verschiedenen Losungsmitteln. 236. G. V. Schulz, Naturwissenschaften 27, 659-660 (1939). Anregung von Kettenpolymerisationen durch freie Radikale. 237. G. V. Schulz, Z. Physik. Chern. (B), 44, 227-247 (1939). Dber die Kinetik der Kettenpolymerisationen: Verzweigungsreaktionen. 238. G. V. Schulz, Z. Elektrochem. Angew. Physik. Chern., 47, 265-274 (1941). Vber die Kinetik der Kettenpolymerisationen: Die Anregung von Polymerisationsreaktionen durchfreie Radikale. 239. G. V. Schulz and F. Blaschke, Z. Physik. Chern. (B), 50, 305-322 (1941). Vber die Kinetik der Kettenpolymerisationen: Orientierende Versuche zur Polymerisation des Methacrylsiiuremethylesters.

258

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240. G. V. Schulz and F. Blaschke, Z. Elektrochem. Angew. Physik. Chern., 47, 749-761 (1941). Polymerisationsreaktionen mit explosivem Verlauf 241. G. V. Schulz, Ber., 74, 1766-1768 (1941). Uber die Aktivierungsenergien der 1,4­ und der 1,2­Polymerisation des Butadiens. 242. W. Hahn and A. Fischer, Makromol. Chern., 16, 36-49 (1955). Mehrfunktionelle Peroxyde als Initiatoren der Vinylpolymerisation. 243. W. Hahn and H. Lechtenbohmer, Makromol. Chern., 16, 50-64 (1955). Die Peroxydation von Polystyrol und Poly­p­isopropylstyrol. 244. W. Hahn and A. Fischer, Makromol. Chern., 21, 77-105 (1956). Die Initiierung der Polymerisation durch polyfunktionelle makromole­ kulare N­ Nitroso­ N­acetylarylamine und Diazoaminoverbindungen. 245. W. Hahn and A. Fischer, Makromol. Chern., 21, 106-112 (1956). Vber die Initiierung der Polymerisation mit cyclischen Peroxyden. Arnold Fischer, dissertation, UniversiHit Freiburg i. Br., 1956 (under supervision of W. Hahn): Die Initiierung der Vinylpolymerisation mit bifunktionellen, cyclischen und polyfunktionellen /nitiatoren. 246. W. Hahn and L. Metzinger, Makromol. Chern., 21, 113-120 (1956). Organosiliciumperoxyde als Initiatoren. 247. H. Staudinger and H. A. Bruson, Liebigs Ann. Chern., 447, 97-110 (1926). Ober das Dicyclopentadien und weitere polymere Cyclopenta­ diene. 248. H. Staudinger and H. A. Bruson, Liebigs Ann. Chern., 447, 110-122 (1926). Vber die Polymerisation des Cyclopentadiens. 249. H. Staudinger, Liebigs Ann. Chern., 467, 73-75 (1928). Uber die Konstitution des Dicyclopentadiens. 250. Alfred Rheiner, dissertation, ETH Zurich, 1923. Uber die Auffassung der dimeren Polymerisationsprodukte als Cyclobutanderivate, ein Beitrag zu den Valenzproblemen der organischen Chemie. 251. Hermann Alexander Bruson, dissertation, ETH Zurich, 1925. Uber lzochpolymerisierte Kohlenwasserstoffe. Die Polymerisation von Cyclo­ pentadien und lnden. 252. H. Staudinger, M. Brunner, K. Frey, P. Garbsch, R. Signer, and S. Wehrli, Ber., 62, 241-263 (1929). Uber das Polystyrol, ein Modell des Kautschuks. 253. H. Staudinger, Zurich, DRP 504,215 (St. 40,793), Kl. 12o, Gr. 25, of March 30, 1926 [Friedlander, 17, 434 (1932)]: Verfahren zur Darstellung von hydrierten Polystyrolen und Polyindenen. 254. H. Staudinger and F. Breusch, Ber., 62, 442-456 (1929). Uber die Polymerisation des a­Methylstyrols. 255. H. Staudinger, K. Frey, P. Garbsch, and S. Wehrli, Ber., 62, 29122920 (1929). Vber den Abbau des makromolekularenPolystyrols. 256. H. Staudinger and A. Steinhofer, Liebigs Ann. Chern., 517, 35-53 (1935). Beitriige zur Kenntnis der Polystyrole. 257. W. Kern and H. Kammerer, J. Prakt. Chern. N.F., 161, 289-292 (1943). Die chemische Molekulargewichtsbestimmung von Polystyrolen/1.

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259

258. Max Brunner, dissertation, ETH Zurich, 1926. Uber hochpolymere organische Stoffe. 259. Siegfried Wehrli, dissertation, ETH Zurich, 1926. Uber die Polymeri­ sation des Styrols. 260. Werner Heuer, dissertation, UniversiHit Freiburg i. Br., 1929. Uber Polystyrol. Ein Beitrag zur Kenntnis hochmolekularer Stoffe. 261. Adolf Steinhofer, dissertation, Universitat Freiburg i. Br., 1933. Beitriige zur Kenntnis des Polystyrols und Viskositiitsmessungen an Losungen von Fadenmolekiilen. 262. Hermann Kammerer, dissertation, Universitat Freiburg i. Br., 1941 (under supervision of W. Kern). Peroxydische Katalysatoren bei der Polymerisation des Styrols und anderer Vinylverbindungen. 263. Wilhelm Muller, dissertation, Universitat Freiburg i. Br., 1956 (under supervision of W. Hahn). Konstitutionelle Fragen bei Vinylpoly­ nzeren (Polystyrol, seine Chlorierungsprodukte und Polyvinylchlorid). 264. Hans Lechtenbohmer, dissertation, Universitat Freiburg i. Br., 1956 (under supervision of W. Hahn). Die Auslosung der Vinylpolymerisation mit verschiedenen lnitiatorsystemen. 265. H. Staudinger, DRP 610,478 (St. 51,427), Kl. 39b, 402, of November 2, 1933 [Friedlander, 21, 1662 (1937)]: Verfahren zur Darstellung von unloslichem Polystyrol. 266. H. Staudinger, H. Johner, and V. Wiedersheim, Helv. Chim. Acta, 12, 958-961 (1929). Verhalten der Polyindene beim Erhitzen. 267. H. Staudinger, H. Johner, G. Schiemann, and V. Wiedersheim, Helv. Chim. Acta, 12, 962-972 (1929). Uber die Hydropolyindene. 268. H. Staudinger and M. Brunner, Helv. Chim. Acta, 12, 972-984 (1929). Uber das Polyanethol. 269. H. Staudinger and E. Dreher, Liebigs Ann. Chem., 517, 73-104 (1935). Uber die Konstitution von Polypropenylbenzol und Derivaten. 270. Emil Dreher, dissertation, Universitat Freiburg i. Br., 1934. Uber die Konstitution von Poly­propenyl­benzol und iihnlicher Verbindungen. Ein Beitrag zur Kenntnis hohermolekularer Stoffe. 271. Walter Keller, dissertation, Universitat Freiburg i. Br., 1942. Uber den Zusammenhang von Polymerisationsgrad und Viskositiitszahl bei Polystyrol und Polyvinylcarbazol. 272. H. Staudinger and M. Brunner, Helv. Chim. Acta, 13, 1375-1379 (1930). Uber die Polymerisation des lsobutylens. 273. H. Staudinger, G. Berger, and Kl. Fischer, J. Prakt. Chem. N.F., 160, · 95-119 (1942). Uber die Polyisobutylene. 274. H. Staudinger, Atti del 2. Congresso Internaz. delle Materie Plastiche, Torino, October 1950, pp. 60-63. Uber Polyisobutylene (Oppanole). 275. Heinrich Hellfritz, dissertation, Universitat Freiburg i. Br., 1944. Untersuchung der kolloiden Losungen von Polyisobutylenen. 276. H. Staudinger and A. Schwalbach, Liebigs Ann. Chem., 488, 8-56 ( 1931). Uber die Polyvinylacetate und Polyvinylalkohole.

260

RESEARCH ON MACROMOLECULAR COMPOUNDS

277. H. Staudinger and E. Trommsdorff, Liebigs Ann. Chern., 502, 201-223 (1933). Uber das Molekulargewicht von Polyacrylsiiure und Poly­ acrylsiiureester. 278. H. Staudinger and B. Ritzenthaler, Ber., 61, 1773-1783 (1934). Uber Polyisopropenyl­methylketon. 279. H. Staudinger and H. Warth, J. Prakt. Chern. N.F., 155, 261-298 (1940). Uber die Konstitution von hochpolymeren Kunststoffen. 280. G. V. Schulz and F. Blaschke, Z. Physik. Chern. (B), 51, 75-102 (1942). Die Polymerisation von Methacrylsiiuremethylester unter Einwirkung von Benzoylperoxyd. 281. W. Kern and H. Fernow, J. Prakt. Chern. N.F., 160, 281-295 (1942). Uber die Polymerisation des Acrylnitrils und Polyacrylnitril. 282. W. Kern and H. Fernow, J. Prakt. Chern. N.F., 160, 296-312 (1942). Uber die Polymerisation des Methacrylnitrils und Polymethacrylnitril. 283. H. Staudinger and M. Haberle, Angew. Chern., 64, 532-533 (1952). Uber Polyvinyl­acetylacetate. 284. H. Staudinger and M. Haberle, Makromol. Chern., 9, 52-75 (1953). Uber Polyvinylacetylacetate. 285. Werner Starck, dissertation, Universitat Freiburg i. Br., 1928. Uber Polyvinylalkohol und Polyvinylacetat. 286. August Schwalbach, dissertation, Universitat Freiburg i. Br., 1930. Uber die Polymerisation des Vinylacetates. 287. Hans Warth, dissertation, Universitat Freiburg i. Br., 1938. Uber die Konstitution von hochpolymeren Kunststoffen. 288. Helmut Fernow, dissertation, Universitat Freiburg i. Br., 1940 (under supervision of W. Kern). Uber Polyacrylnitril und Polymethacrylnitril. 289. Manfred Haberle, dissertation, Universitat Freiburg i. Br., 1952. Polymeranaloge Umsetzungen an Polymerisaten. 290. H. Staudinger and Th. Fleitmann, Lie bigs Ann. Chern., 480, 92-108 (1930). Uber Polyallylchlorid. 291. H. Staudinger, M. Brunner and W. Feisst, Helv. Chim. Acta, 13, 805-832 (1930). Uber das Polyvinylbromid. 292. H. Staudinger and W. Feisst, Helv. Chim. Acta, 13, 832-842 (1930). Uber das asymmetrische Polydichloriithylen. 293. H. Staudinger and J. Schneiders, Liebigs Ann. Chern., 541, 151-195 (1939). Uber die Polyvinyl chloride. 294. H. Staudinger and M. Haberle, Makromol. Chern., 9, 35-51 (1953). Uber Polyvinylchloride. 295. W. Hahn and W. Muller, Makromol. Chern., 16, 71-73 (1955). Uber die Reduktion von Polyvinylchlorid mit Lithiumaluminium­ hydrid. 296. W. Hahn and F. Grafmiiller, Makromol Chern., 21 121-130 (1956). Uber die Chlorierung von Polyvinylacetat und von Polymethacrylsiiure­ methylester. 297. Walter Feisst, dissertation, Universitat Freiburg i. Br., 1930. Uber Poly­ vinylbromid und Polydichloriithylen.

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261

298. Joseph Schneiders, dissertation, UniversiHit Freiburg i. Br., 1938. Dber Polyvinylchlorid. 299. H. Staudinger, DRP 506,839 (St. 46,126) Kl. 12o, Gr. 23 of July 13, 1929 [Friedlander, 17, 137 (1932)]: Verfahren zur Darstellung von monomelekularen Reaktionsprodukten von ungesiittigten Kohlenwasser­ stoffen der Butadienreihe mit Schwefeldioxyd. 300. H. Staudinger and B. Ritzenthaler, Ber., 68, 455-471 (1935). Vber die Anlagerung von Schwefeldioxyd an Jlthylenderivate. 301. Bernhard Ritzenthaler, dissertation, UniversiHit Freiburg i. Br., 1935. I. Uber Isopropenyl­methyl­keton. II. Vber die Anlagerung von Schwefeldioxyd al} A."thylenderivate. 302. H. Staudinger and H. W. Kohlschutter, Ber., 64, 2091-2098 (1931). Dber Polyacrylsiiure. 303. H. Staudinger and H. v. Becker, Ber., 70, 879-888 (1937). Unter­ suchungen an hochmolekularen Polyammonium­ Verbindungen. 304. W. Kern, Z. Physik. Chern. (A), 181, 249-282 (1938). Die Poly­ acrylsiiure, ein Modell des EiweifJes (Habilitationsschrzft). 305. W. Kern, Z. Physik. Chern. (A), 184, 197-210 (1939). Der osmotische Druck wiisseriger Losungen polyvalenter Siiuren und ihrer Salze. 306. W. Kern, Z. Physik. Chern. (A), 184, 302-308 (1939). Der osmotische Druck wiisseriger Losungen polyvalenter Siiuren und ihrer Salze mit ein­ und zweiwertigen Basen. 307. W. Kern, Biochem.­Z., 301, 338-356 (1939). Die Dissoziation poly­ valenter, makromolekularer Siiuren. 308. W. Kern and E. Brenneisen, J. Prakt. Chern. N.F., 159, 193-218 (1941). Polymere Amine als Modelle des EiweifJes. 309. W. Kern and E. Brenneisen, J. Prakt. Chern. N.F., 159, 219-240 (1941). Untersuchungen an Sa/zen polymerer Amine und an Polyiithylen­ zmmen. 310. Ernest Urech, dissertation, ETH Zurich, 1927. Sur Ia Polymerisation de I' Acide acrylique et de ses ethers. 311. Ernst Trommsdorff, dissertation, UniversiHit Freiburg i. Br., 1932. Dber Polyacrylsiiure. 312. Erich Brenneisen, dissertation, UniversiHit Freiburg i. Br., 1939 (under supervision of W. Kern). Dber heteropolare Molekiilkolloide. 313. H. Staudinger and M. Luthy, Helv. Chim. Acta, 8, 41-64 (1925). Dber die Konstitution der Polyoxymethylene. 314. H. Staudinger and M. Luthy, Helv. Chim. Acta, 8, 65-67 (1925). Dber Tri­ und Tetra­oxymethylen. 315. H. Staudinger, Helv. Chim. Acta, 8, 67-70 (1925). Dber die Konstitu­ tion der Polyoxymethylene und anderer hochpolymerer Verbindungen. 316. H. Staudinger, H. Johner, R. Signer, G. Mie, and J. Hengstenberg, Naturwissenschaften, 15, 379-380 (1927). Der polymere Formaldehyd, ein Modell der Cellulose. 317. H. Staudinger, Osterr. Chemiker­Ztg., 32, Nr. 12, 98-99 (1929). Polyoxymethylene, ein Modell der Cellulose.

262

RESEARCH ON MACROMOLECULAR

COMPOUNDS

318. H. W. Kohlschutter, Liebigs Ann. Chem., 482, 75-104 (1930). Zur Morphologie hochmolekularer Stoffe. /. Faserbildung mit Polyoxy­ methylen. 319. H. W. Kohlschutter, Liebigs Ann. Chem., 484, 155-178 (1930). Zur Morphologie hochmolekularer Stoffe. II. Polyoxymethylennieder­ schlage aus Losung. 320. H. Staudinger, R. Signer, and 0. Schweitzer, Ber., 64, 398-405 (1931). Ober die Einwirkung von Basen auf Formaldehyd­Losungen. 321. H. W. Kohlschutter and L. Sprenger, Z. Physik. Chem. (B), 16, 284302 (1932). Ober die Umwandlung kristallisierten Trioxymethylens zu hochmolekularem Polyoxymethylen. 322. H. Staudinger and W. Kern, Ber., 66·, 1863-1866 (1933). Ober die Konstitution der Polyoxymethylene. 323. H. Staudinger, Ber., 67, 475-479 (1934). Die Polyoxymethylene als Modell der Cellulose. 324. Max Luthy, dissertation, ETH Zurich, 1923. Ober die Konstitution der polymeren Formaldehyde. 325. Hans Wolfgang Johner, dissertation, ETH Zurich, 1927. Ober die Konstitution der verschiedenen Polymerisationsprodukte des Formalde­ hyds. 326. Rudolf Signer, dissertation, ETH Zurich, 1927. Ober die Konstitution der Polyoxymethylene. 327. Diomidis Russidis, dissertation, UniversiHit Freiburg i. Br., 1928. Ober Polyoxymethylene. 328. Otto Schweitzer, dissertation, UniversiHit Freiburg i. Br., 1930. Ober Polyoxymethylene und Polyathylenoxyde. 329. Werner Kern, dissertation, UniversiHit Freiburg i. Br., 1932. Das Polyoxymethylen, ein Modell der Cellulose. Ober Polyoxymethylen­ dimethyliither, Polyoxymethylen­dihydrate und die Polymerisation von monomeremfliissigem Formaldehyd. 330. H. Staudinger and 0. Schweitzer, Ber ., 62, 2395-2405 (1929). Ober die Polyiithylenoxyde. 331. E. Sauter, Z. Physik. Chem. (B), 21, 161-185 (1933). Ober das Makro­ molekiilgitter des Polyiithylenoxyds. 332. H. Staudinger and H. Lohmann, Liebigs Ann. Chem., 505, 41-51 (1933). Ober eukolloides Polyathylenoxyd. 333. Heinrich Lohmann, dissertation, UniversiHit Freiburg i. Br., 1932. Ober Polyiithylenoxyd. Ein Beitrag zur Kenntnis hochmolekularer Stoffe. 334. E. Konrad, 0. Bachle, and R. Signer, Liebigs Ann. Chem., 474, 276-295 (1929). Ober polymere Kieselsiiureester. 335. R. Signer and H. Gross, Liebigs Ann. Chem., 488, 56-73 (1931). Ober polymere Kieselsaureester und Kieselsauren. 336. R. Signer and H. Gross, Liebigs Ann. Chem., 499, 158-168 (1932). Viskositiitsmessungen an Kieselsiiurelosungen. 337. H. Staudinger and W. Hahn, Makromol. Chem., 11, 24-50 (1953). Versuche zur Darstellung von polymeren Kzeselsiiureestern.

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263

338. W. Hahn, Makromol. Chem., 11, 51-63 (1953). Dber die Bildung von spirocyclischen Kieselsiiureestern aus Siliciumtetrachlorid und zwei­ wertigen Alkoholen. 339. W. Hahn, Makromol. Chem., 11, 64-69 (1953). Ober die Bildung von Kieselsiiureestern aus Siliciumtetrachlorid und Cyanhydrinen. 340. Otto Bachle, dissertation, Universitat Freiburg i. Br., 1928 (under supervision of E. Konrad). I. Zur Kenntnis der Hydrazin­ und Azo­ Disulfosiiure. II. Ober polymere Kieselsiiureester. 341. Hans Gross, dissertation, Universitat Freiburg i. Br., 1931 (under supervision of R. Signer). Ober polymere Kieselsiiureester und Kiesel­ sauren. . 342. Walter Hahn, dissertation, Universitat Freiburg i. Br., 1952. Ober monomere und poly mere Kieselsiiureester. 343. H. Staudinger and H. Schmidt, J. Prakt. Chem. N.F., 155, 129-162 (1940). Ober Polyester. 344. H. Staudinger and 0. Nuss, J. Prakt. Chem. N.F., 157, 283-337 (1941). Zur Giiltigkeit des Viskositiitsgesetzes: Untersuchungen an Poly­w­oxyundecansiiuren. 345. H. Staudinger and Fr. Berndt, Makromol. Chem., 1, 22-35 (1947). Ober die Giiltigkeit des Viskositiitsgesetzes bei Polyoxydecansiiuren. 346. H. Staudinger and Fr. Berndt, Makromol. Chem., 1, 36-43 (1947). Ober Polyoxyundecansiiuren. 347. H. Batzer, Makromol. Chem., 5, 5-82 (1950). Ober lineare Polyester (Habilitationsschrift). 348. H. Batzer and F. Wiloth, Makromol. Chem., 6, 60-70 (1951). Bestim­ mung des partiellen Molvolumens von Polyestern in Benzol. 349. H. Batzer, H. Holtschmidt, F. Wiloth, and B. Mohr, Makromol. Chem., 7, 82-103 (1951). Ober ein Verfahren zur Darstellung von Polykondensaten in Fliissigkeiten. 350. H. Batzer, Chemiker­Ztg., 75, 164-167 (1951). Ein experimenteller Beitrag zu einer Theorie der Faserbildung. 351. H. Batzer and F. Wiloth, Makromol. Chem., 8, 41-71 (1952). Ober substituierte Polyester. 352. F. Wiloth, Makromol. Chem., 8, 111-123 (1952). Ober den Einfluj3 der chemischen Konstitution auf die Molekiilgestalt bei'Polyestern. 353. F. Lombard, Makromol. Chem., 8, 187-207 (1952). Contribution a I' etude des produits de polycondensation de I' acide hydroxy­11­ undecylique. 354. H. Batzer and B. Mohr, Makromol. Chem., 8, 217-251 (1952). Ober Polyester mit sterisch einheitlichen Doppelbindungen. 355. H. Batzer, Makromol. Chem., 10, 13-29 (1953). Ober physikalische Eigenschaften linearer Polyester. 356. H. Batzer and G. Weif3enberger, Makromol. Chem., 11, 83-84 (1953). Eigenschaften der Polyester der Acetylendicarbonsiiure. 357. H. Batzer and G. Fritz, Makromol. Chem., 11, 85-86 (1953). Polyester aus cycloaliphatischen Verbindungen.

264

RESEARCH ON MACROMOLECULAR COMPOUNDS

358. H. Batzer and G- . WeitBenberger, Makromol. Chern., 12, 1-19 (1954). Vber Polyester der Acetylendicarbonsiiure. 359. H. Batzer, Angew. Chern., 66, 513-519 (1954). Vber den Nachweis des polymereinheitlichen Aufbaues linearer Polyester. 360. H. Holtschmidt, Makromol. Chern., 13, 141-170 (1954). Vber Ester­ kondensationen an Polyestern und die Herstellung reaktionsfiihiger Polyester. 361. H. Batzer and G. Fritz, Makromol. Chern., 14, 179-232 (1954). Vber hydroaromatische Polyester, ein experimenteller Beitrag zur Theorie der Faserbildung. 362. H. Batzer and H. Lang, Makromol. Chern., 15, 211-242 (1955). Vber lineare aliphatische Polyester, insbesondere Polyester der Oxal siiure. 363. Heinrich Schmidt, dissertation, UniversiHit Freiburg i. Br. 1938 Vber Polyester. 364. Otto Nuss, dissertation, UniversiHit Freiburg i. Br. 1939. Zur Gi.iltigkeit des ViskosiHitsgesetzes. 365. Fritz Berndt, dissertation, UniversiHit Freiburg i. Br. 1942. Vber die Giiltigkeir des Viskositiitsgesetzes an Polyestern. 366. Fritz Wiloth, dissertation, UniversiHit Freiburg i. Br., 1951 (under supervision of H. Batzer). Dber den Einfluj3 der chemischen Konstitu­ tion auf Molekiilgestalt und physikalische Eigenschaften bei Polyestern. 367. Francis Lombard, dissertation, UniversiHit Lyon, 1951 (under supervision of H. Batzer). Contribution a 1' etude des produits de poly con­ densation de l'acide hydroxy­l] undecylique et de l'acide amino­11 undecylique. 368. Hans Holtschmidt, dissertation, UniversiHit Freiburg i. Br., 1952 (under supervision of H. Batzer). Vber die Darstellung linearer, substituierbarer Polyester. Beitrag zum Einfluj3 der chemischen Kon­ stitution auf die physikalischen Eigenschaften von Polyestern. 369. Bernhard Mohr, dissertation, UniversiUit Freiburg i. Br., 1952 (under supervision of H. Batzer). Dber den Einfluj3 sterisch einheitlicher Doppelbindungen auf die Eigenschaften linearer Polyester. 370. G. WeitBenberger, dissertation, UniversiHit Basel, 1953 (under supervision of H. Batzer). Dber die Polyester der Acetylendicarbonsiiure. 371. Heinz Lang, dissertation, UniversiHit Freiburg i. Br., 1954 (under supervision of H. Batzer). Vber lineare aliphatische Polyester unter besonderer Beriicksichtigung der Polyester der Oxalsiiure, Glutarsiiure und Pimelinsiiure. 372. Gerhard Fritz, dissertation, UniversiHit Freiburg i. Br., 1954 (under supervision of H. Batzer). Vber hydroaromatische Polyester. 373. H. Staudinger and H. Jorder, Jentgens Kunstseide und Zellwolle, 24, 88-91 (1942). Vber die Kettenliinge der Polyamidfasern. 374. H. Staudinger and H. Jorder, J. Prakt. Chern. N.F., 160, 176-194 (1942). Vber die Bestimnzung der Kettenliinge von Polyamiden. 375. H. Staudinger, H. Schnell, and H. Stock, Addendum No. 47 to Zeitschrift des Vereins Deutscher Chemiker, 1943, 1-6. Vber den

PART B REFERENCES

265

Zusammenhang zwischen Kettenliinge und Festigkeitseigenschaften von Polyamidfasern. 376. H. Staudinger and H. Schnell, Makromol. Chem., 1, 44-60 (1947). Uber die Giiltigkeit des Viskositiitsgestzes bei Polyaminocapron· sauren. 377. H. Schnell, Makromol. Chem., 2, 172-175 (1948). Uber die titri· metrische Bestimmung der Carboxylendgruppe bei Polyaminocapron· siiuren. 378. Helmut Jorder, dissertation, UniversiHit Freiburg i. Br., 1941. Viskositiitsuntersuchungen an Siiureamiden und Polyamidfasern. 379. Hermann Schnell, dissertation, UniversiHit Freiburg i. Br., 1944. Untersuchungen uber die Konstitution der Polyamide und iiber die Zusammenhiinge zwischen der Kellenliinge und der Festigkeit ihrer Fasern. 380. H. Kdissig, Makromol. Chem., 8, 208-216 (1952). Uber die Umsetzung von Hexamethylendiamin mit Formaldehyd. 381. H. Staudinger and K. Wagner, Makromol. Chem., 11, 79-80 (1953). Zur Konstitution der Harnstoff­Formaldehyd·Kondensate. 382. H. Staudinger and G. Niessen, _ Makromol. Chem., 11, 81-82 (1953). Uber die Kondensationsprodukte von A"thylenthioharnstoff mit Formal· dehyd. 383. H. Staudinger and K. Wagner, Makromol. Chem., 12, 168-235 (1954). Uber die Konstitution der Harnstoff· resp. Thioharnstoff·Formaldehyd· kondensate. 384. H. Staudinger and G. Niessen, Makromol. Chem., 15, 75-90 (1955). Uber die Kondensation von Formaldehyd mit disubstituierten Thioharn· stoffen. 385. H. Staudinger and G. Niessen, Makromol. Chem., 15, 91-94 (1955). Uber die Einwirkung von Formaldehyd auf Hexamethylendithioharns­ toff. 386. H. Staudinger and G. Niessen, Makromol. Chem., 15, 95-97 (1955). Umsetzung von Hexamethylendiamin mit Schwefelkohlenstoff. 387. H. Kdissig, Makromol. Chem., 17, 77-130 (1956). Uber die Umse· tzungsprodukte v. a!iphatischen Diaminen mit Formaldehyd. 388. H. Krassig and G. Egar, Makromol. Chem., 18/19, 195-200 (1956). Uber Reaktionsprodukte von Harnstoff bzw. Thioharnstoff mit Benz­ aldehyd. 389. H. Staudinger, H. Krassig, and G. Welzel, Makromol. Chem., 20, 1-18 (1956). Uber die Konstitution von Harnstoff­ resp. Thioharnstoff­ Formaldehyd· Kondensaten. 390. H. Krassig and H. Ringsdorf, Makromol. Chem., 22, 163-182 (1957). Untersuchungen iiber cyclische Azomethinderivate. 391. Kuno Wagner, dissertation, Universitat Freiburg i. Br., 1954. Zur Konstitution der Harnstoff­ und Thioharnstoff­Formaldehyd­Konden­ sate. 392. Gunter Niessen, dissertation, Universitat Freiburg i. Br., 1954. Uber Kondensationen von Thioharnstoffderivaten mit Formaldehyd.

266

RESEARCH ON MACROMOLECULAR COMPOUNDS

393. Helmut Ringsdorf, diploma thesis, Universitat Freiburg i. Br., 1956 (under supervision of H. Krassig). Untersuchungen iiber cyclische Azomethinderivate. 394. Gunther Welzel, diploma thesis, Universitat Freiburg i. Br., 1955. Zur Struktur der Aminoplaste. 395. H. Krassig and G. Greber, Makronwl. Chern., 11,231-232 (1953). Vber vielgliedrige, cyclische Kondensationsprodukte aus Terephthalaldehyd und Diaminen. 396. H. Krassig and G. Greber, Makromol. Chern., 17, 131-153 (1956). Vber die Umsetzungen von Terephthalaldehyd mit aliphatischen Diaminen. 397. G. Greber, Makromol. Chern., 17, 154-157 (1956). Vber die Darstel­ lung aromatischer A.'therdialdehyde. 398. H. Krassig and G. Greber, Makromol. Chern., 17, 158-180 (1956). Vber die Umsetzungen aromatischer A.'therdialdehyde mit aliphatischen Diaminen. 399. G. Greber, Makromol. Chern., 22, 183-194 (1957). Vber Umsetzungen aromatischer A.'therdialdehyde mit y, y'­ Diaminodipropylather. [Com­ pare also G. Greber, Kunststoffe/Plastics, 4, 127-134 (1959). Vber cyclische und polymere Schiffsche Basen.] 400. Gerd Greber, dissertation, Universitat Freiburg i. Br., 1955 (under supervision of H. Krassig). Vber Schiffsche Basen aus aromatischen Dialdehyden und aliphatischen Diaminen. [Compare also Gerd Greber, diploma thesis, Universitat Freiburg i. Br., 1952. Vber die Reaktion von A.'thylendiamin mit Formaldehyd.] 401. H. Staudinger, DRP 415,871 (St. 35,650) Kl. 39b. of April 16, 1922 [Friedlander, 15, 1062, (1928): Verfahren zur Herstellung von hydriertem Kautschuk. 402. H. Staudinger and W. Widmer, Helv. Chim. Acta, 1, 842-848 (1924). Vber Homologe des Hydrokautschuks. 403. H. Staudinger, M. Asano, H. F. Bondy, and R. Signer, Ber., 61, 2575-2595 (1928). Vber die Konstitution des Kautschuks. 404. H. Staudinger and H. F. Bondy, Ber., 63, 2900-2905 (1930). Vber kryoskopische Messungen an Kautschuk­Losungen. 405. H. Staudinger and H. Joseph, Ber., 63, 2888-2899 (1930). Vber das lsokautschuknitron. 406. H. Staudinger, Kautschuk, 1927, 63-67. Vber die Chemie des Kaut­ schuks. 407. H. Staudinger and W. Widmer, Helv. Chim. Acta, 9, 529-549 (1926). Vber die Bildung von Cyclokautschuk aus Kautschukhydrohalogeniden. 408. H. Staudinger, DRP462748 (St. 41942) Kl. 39b, Gr. 3, of December 14, 1926 [Friedlander, 16, 1836, (1931)]: Verfahren zur Darstellung von Hydrocyclokautschuk. 409. H. Staudinger and E. Geiger, Helv. Chim. Acta, 9, 549-557 (1926). Verhalten des Kautschuks beim Erhitzen. 410. H. Staudinger and H. F. Bondy, Liebigs Ann. Chern., 468, 1-57 (1929). Vber den Abbau von Kautschuk und Guttapercha.

PART B REFERENCES

261

411. H. Staudinger Kautschuk, 11, 101-102 (1941). Die Doppelbindungs­ regel beim Kautschuk. 412. H. Staudinger and J. R. Senior, Helv. Chim. Acta, 13, 1321-1324 (1930). Ober die Reduktion des Kautschuks mit Jodwasserstoffsiiure. 413. H. Staudinger, Helv. Chim. Acta., 13, 1324-1334 (1930). Ober die polymerhomologen Hydrokautschuke. 414. H. Staudinger, E. Geiger, E. Huber, W. Schaal, and A. Schwalbach, Helv. Chim. Acta., 13, 1334-1349 (1930). Ober hemikolloide Hydro­ kautschuke. 415. H. Staudinger and W. Schaal, Helv. Chim. Acta., 13, 1355-1360 (1930). Ober die Fraktionierung und Verkrackung von Hydrokautschuk. 416. H. Staudinger and W. Feisst, Helv. Chim. Acta., 13, 1361-1367 (1930). Uber hochmolekulare Hydrokautschuke. 417. H. Staudinger, M. Brunner, and E. Geiger, Helv. Chim. Acta., 13, 1368-1374 (1930). Ober Hydro­methyl­kautschuk. 418. H. Staudinger and E. 0. Leupold, Ber., 61, 304-311 (1934). Uber die Hydrierung von Kautschuk und Balata. 419. H. Staudinger and H.-P. Mojen, Kautschuk, 12, 121-123 (1936). Viskositiitsmessungen an Squalen­ und Hydrosqualenlosungen. 420. H. Staudinger and Kl. Fischer, J. prakt. Chem. N.F., 157, 19-88 (1940). Ober die Bestimmung des Molekulargewichtes und den Aufbau von Kautschuk, Guttapercha und Balata. 421. H. Staudinger and Kl. Fischer, J. prakt. Chem. N.F., 157, 158-176 (1941). Ober die Konstitution der Butadienpolymerisate. 422. H. Staudinger and Kl. Fischer, J. prakt. Chem. N.F., 158, 303-314 (1941). Ober die Konstitution der Evonymus­Gutterpercha. 423. H. Staudinger and Hj. Staudinger, J. prakt. Chem. N.F., 162, 148-180 (1943). Ober Halogenderivate der Kautschukkohlenwasserstoffe. 424. H. Staudinger and H. F. Bondy, Liebigs Ann. Chem., 488, 153-175 (1931). Ober loslichen und unloslichen Kautschuk und iiber die Fraktion­ ierung des Kautschuks. 425. H. Staudinger, Kolloid­Z., 60, 296-298 (1932). Ober die Elastizitiit des Kautschuks. 426. H. Staudinger, Schweiz. Chemiker­Ztg., 1919, 1-5, 28-33, 6D-64. Kautschuk­Synthese. 427. H. Staudinger, Vortrag auf der XXXVI. ord. Generalvers. der Schwei­ zerischen Gesellschaft fur Chemische Industrie, Ber., pp. 1-20. Kauts­ chuk­Synthese. 428. H. Staudinger, Kautschuk, 1925, August, pp. 5-9; September, 8-10. Zur Chemie des Kautschuks und der Guttapercha. 429. H. Staudinger, Angew Chem., 38, 226-228 (1925). Uber die Konstitu­ tion des Kautschuks und einen neuen Kautschuk. 430. H. Staudinger, Kautschuk, 5, 94-97, 126-129 (1929). Ober die Konstitu­ tion des Kautschuks. 431. H. Staudinger and H. F. Bondy, Ber., 62, 2411-2416 (1929). Uber die Konstitution des Kautschuks.

268

RESEARCH ON MACROMOLECULAR COMPOUNDS

432. H. Staudinger and H. F. Bondy, Ber., 63, 724-730 (1930). Uber die Fraktionierung der Balata. 433. H. Staudinger and H. F. Bondy, Ber., 63, 734-736 (1930). Uber die Molekiilgroj3e des Kautschuks und der Balata. 434. H. Staudinger, Ber., 63, 921-934 (1930). Uber die Kolloidnatur von Kautschuk, Guttapercha und Balata. 435. H. Staudinger, Kautschuk, 6, 153-158 (1930). Uber die Molekiilgroj3e des Kautschuks und die Natur seiner kolloiden Losungen (lecture at the Hauptvers. der Deutschen Kautschuk.­Ges., Frankfurt/M., June 1930). 436. H. Staudinger, lecture, Kongre./3 der Kautschuk­Chemiker Paris, June 10-13, 1931,9 pp. La Constitution du Caoutchouc. 437. H. Staudinger, Kolloid­Z., 54, 129-140 (1931). Zur Konstitution des Kautschuks. 438. H. Staudinger, Ber., 64, 1407-1408 (1931). Uber Endgruppen im Kautschuk. 439. H. Staudinger, Angew. Chern., 45, 276-280, 292-295 (1932). Uber die Konstitution des Kautschuks. 440. H. Staudinger and E. 0. Leupold, Helv. Chim. Acta, 15, 221-230 (1932). Uber homologe Polyprane. 441. H. Staudinger, An. Soc. espafi. Fisica Quim., 32, 426-435 (1934). Sabre Ia Constitucion del Caucho (Vortrag UniversiHit Madrid 23.3. 1933). 442. H. Staudinger, Chemiker­Ztg., 58, 225-228 (1934). Uber die Kon­ stitution des Kautschuks. 443. H. Staudinger, Kautschuk, 10, 157-158, 170-173, 192-195 (1934). Die wissenschaftliche Erforschung des Kautschuks (lecture given at the meeting of the Deutschen Kautschuk-Gesellschaft, Koln, May, 1934). 444. H. Staudinger, Res. and Progr., 2, 238 (1936). The Structure of the Organic Compounds of High Molecular Weight, Rubber and Cellulose. 445. H. Staudinger and H.-P. Mojen, Kautschuk, 12, 159-162 (1936). Viskositiitsvermessungen an Losungen von Kautschuk und Hydro­ kautschuk in verschiedenen Losungsmitteln. 446. H. Staudinger and H.-P. Mojen, Kautschuk, 13, 17-23 (1937). Viskositiitsmessungen an Gellosungen von Kautschuk und Hydro­ kautschuk. 447. H.-P. Mojen, Kautschuk, 13, 39-41 (1937). Uber den Abbau des Kautschuks durch Siiuren. 448. H. Staudinger, communication to the Rubber Technology Conference, London, May, 1938, Paper No. 98. Uber loslichen und unloslichen Kautschuk. 449. F. Wiloth, Gummi u. Asbest, 5, 392-396, 445-447 (1952). Viskositiit und Polymerisationsgrad bei Kautschuken. 450. Jakob Fritschi, dissertation, ETH Zurich, 1923. Uber die Konstitution des Kautschuks. 451. Willy Widmer, dissertation, ETH Zurich, 1925. Untersuchungen iiber neue Kautschukderivate.

PART B REfERENCES

269

452. Ernst Geiger, dissertation, ETH Zurich, 1926. Vber die Konstitution der Hochpolyrneren. 453. Ernst Huber, dissertation, ETH Zurich, 1926. Vber die Hydrierung und die pyrogene Zersetzung hochrnolekularer Kohlenwasserstoffe. 454. Heinrich Thron, dissertation UniversiHit Freiburg i. Br., 1928. Uber Kautschuk und Guttapercha. 455. Herbert Fritz Bondy, dissertation, UniversiHit Freiburg i. Br., 1929. Vber Kautschuk und Guttapercha. 456. Willi Schaal, dissertation, UniversiHit Freiburg i. Br., 1931. Vber Kautschuk, Guttapercha, Balata. 457. E. 0. Leupold, pissertation, UniversiHit Freiburg i. Br., 1932. Die Konstitution der Balata. 458. Hans-Peter Mojen, dissertation, UniversiHit Freiburg i. Br., 1935. Vber Viskositatsuntersuchungen und chernische Untersuchungen an Kautschuk und Balata. 459. Kletus Fischer, dissertation, UniversiHit Freiburg i. Br., 1938. Vber die Bestirnrnung des Molekulargewichts und den Aufbau von Kautschuk, Guttapercha und Balata. 460. Hansjurgen Staudinger, dissertation, UniversiHit Freiburg i. Br., 1940. Vber Halogenderivate der Kautschuk­Kohlenwasserstoffe. 461. K. Frey, dissertation, ETH Zurich, 1926. Vber die Konstitution der Polysaccharide. 462. H. Staudinger, K. Frey, R. Signer, W. Starck, and G. Widmer, Ber., 63, 2308-2316 (1930). Vber Cellulose. 463. H. Staudinger Ber., 68, 474-478 (1935). Vber das Erinnerungsver­ rnogen der Celluloseacetate. 464. H. Staudinger and H. Freudenberger, Liebigs Ann. Chern., 501, 162 174 (1933). Vber Viskositiitsrnessungen an Zechrneisters 0/igo­ saccharidderivaten und iiber die Konstitution der Cellulose. 465. H. Staudinger, and B. Ritzenthaler, Ber., 68, 1225-1233 (1935). Cellulose in Schweizers Reagens. 466. H. Staudinger, and K. Feuerstein, Liebigs Ann. Chern., 526, 72-102 (1936). Vber den Polyrnerisationsgrad natiirlicher und technischer Cellulosen. 467. H. Krassig, and E. Siefert, Makrornol. Chern., 14, 1-14 (1954). Vber Losungen von Cellulose in Tetraathylarnrnoniurnhydroxyd. 468. H. Staudinger and E. 0. Leupold, Ber., 67, 479-486 (1934). Vber das Cellopentaoseacetat und die Konstitution der Cellulose. 469.H. Staudinger and H. Eilers, Ber., 69,1611-1618 (1935). Vber die Urnwandlung von Cellulose in polyrneranaloge Cellulosetriacetate. 470. H. Staudinger and G. Daumiller, Liebigs Ann. Chern., 529, 219-265 (1937). Untersuchungen an Celluloseacetaten und Cellulosen. 471. H. Staudinger and A. E. Werner, Ber., 70, 2140-2148 (1937). Vber die Km­Konstante der Celluloseacetate. 472. H. Staudinger and G. Daumiller, Ber., 70, 2508-2513 (1937). Vber Celluloselosungen.

270

RESEARCH ON MACROMOLECULAR

COMPOUNDS

473. H. Staudinger and K. Eder, J. Prakt. Chern. N.F., 159, 36-69 (1941). Molekulargewichtsbestirnrnungen und Viskositiitsuntersuchungen an abgebauten Cellulosetriacetaten. 474. H. Staudinger and Th. Eicher, Makrornol. Chem., 10, 235-253 (1953). Uber Celluloseacetate. 475. H. Staudinger and Th. Eicher, Makrornol. Chern., 10, 261-279 (1953). Uber Cellulosetriacetylacetate und Celluloseacetat­acetylacetate. 476. H. Staudinger and H. Scholz, Ber., 67, 84-91 (1934). Uber das Mo/e­ kulargewicht der Methylcellulose. 477. H. Staudinger and F. Reinecke, Liebigs Ann. Chern., 535, 47-100 (1938). Uber Mo/ekulargewichtsbestirnn:ungen an Celluloseiithern. 478. H. Staudinger and R. Mohr, Ber., 70, 2296-2309 (1937). Uber die Konstitution der Cellulosenitrate. 479. H. Staudinger and R. Mohr, J. prakt. Chern. N.F., 158, 233-244 (1941). Uber den Unterschied zwischen urngefiillten und rnercerisierten Cellulosen von den nativen Fasercellulosen. 480. H. Staudinger, Uber die rnakrorno/ekulare Chernie der Cellulosenitrate, Herder-Druckerei, Freiburg i. Br., 1945, 52 pp. 481. H. Kdissig, Makrornol. Chern., 26, 1-16 (1958). Uber den EinflufJ des Substitutionsgrades und Geschwindigkeitsgefiil/es auf die Viskositiit von Tunicinnitraten und die Beziehung zwischen Viskositiitszahl und MolekiilgrofJe. 482. H. Staudinger and A. W. Sohn, Naturwissenschaften, 27, 548-549 (1939). Uber Fehlerstellen in Cellulosernolekiilen. 483. H. Staudinger and A. W. Sohn, Ber., 72, 1709-1717 (1939). Uber norrnale undfehlerhafte Cellulosen. 484. H. Staudinger and A. W. Sohn, J. Prakt. Chern. N.F., 155, 177-215 (1940). Uber native und urngefiillte Cellulosen und deren Nitrate. 485. H. Staudinger and A. W. Sohn, Melliand Textilber., 21, 205-208 (1940). Uber die Kettenliingendifferenz zwischen Cellulosenitraten und Cellulosen bei Kunstfasern. 486. H. Staudinger and A. W. Sohn, Cellulosechernie, 18, 25-29 (1940). Uber die Kettenliingendifferenz zwischen Cellulosen und Cellulosenitraten bei Zellstoffen. 487. H. Staudinger and E. Roos, Melliand Textilber., 22, 369-372 (1941). Uber das Bleichen von Cellulosefasern. 488. H. Kdissig, Melliand Textilber., 36, 55-58, 163-166, 265-267 (1955). Einwirkung oxydativer Waschrnittel auf Baurnwollgewebe. 489. August W. Sohn, dissertation, UniversiHit Freiburg i. Br., 1938. Uber native und urngefiillte Cellulose und deren Nitrate. 490. Eugen Roos, dissertation, UniversiHit Freiburg i. Br., 1941. Uber Oxycellulosen. 491. H. Staudinger and G. Daumiller, Ber., 71, 1995-2002 (1938). Uber Cellulose­Xanthogenatlosungen. 492. H. Staudinger and F. Reinecke, Papierfabrikant, 36, 557-559 (1938). Uber den Polyrnerisationsgrad der Cellulose in Folien und den Abbau der Cellulose beirn Viskoseprozess.

PART B REFERENCES

271

493. H. Staudinger and F. Zapf, J. Prakt. Chem. N.F., 156, 261-284 (1940). Vber Cellulosexanthogenat. 494. Paul Herrbach, dissertation, UniversiHit Freiburg i. Br., 1944. Vber den Abbau von Cellulosen wiihrend der Xanthogenierung und iiber die Loslichkeit von Celluloseacetaten in m­Kresol. 495. H. Staudinger and M. Sorkin, Ber., 70, 1565-1577 (1937). Vber Hydrocellulosen (Abbau der Fasern mit Siiuren, A.'nderung der Festig­ keit der Fasern beim Abbau und Viskositiitsuntersuchungen). 496. H. Staudinger, M. Sorkin, and E. Franz, Melliand Textilber., 18, 681684 (1937). Vber den Zusammenhang zwischen Festigkeitseigen­ schaften und Poly'}'lerisationsgrad bei Cellulosefasern. 497. H. Staudinger and F. Reinecke, Kunstseide und Zellwolle, 21, 280-284 (1939). Vber den Aufbau der Natur­ und Kunstfasern. 498. H. Staudinger, Melliand Textilber., 20, 631-635 (1939). Vber natiirliche und synthetische Fasern. 499. H. Staudinger and I. Jurisch, Zellwolle, Kunstseide, Seide, 44, 375-377 (1939). Vber die Festigkeit von Fasercellulosen verschiedenen Poly­ merisationsgrades. -500. H. Staudinger and I. Jurisch, Zellwolle, Kunstseide, Seide, 44, 377-378 (1939). Vber die Festigkeit von Cellulose­Nitratfasern verschiedenen Poly merisationsgrades. 501. H. Staudinger and I. Jurisch, Melliand Textilber., 20, 693-696 (1939). Vergleich der Festigkeit von abgebauten Naturfasern und Kunstfasern aus Cellulose. 502. H. Staudinger and F. Reinecke, Melliand Textilber., 20, 109-110. (1939). Vber den Polymerisationsgrad von Cellulosen in a/ten Geweben. 503. H. Staudinger, H. Stock, and K. F. Damisch, Melliand Textilber., 22, 620-621 (1941). Vber das Verspinnen von A.'thylcellulosen. 504. H. Staudinger, P. Herrbach, and H. Stock, Makromol. Chem., 1, 6069 (1947). Vber den Aufbau von natiirlichen und synthetischen Cellulosefasern. 505. H. Kdissig. Makromol. Chem., 26, 17-46 (1958). Morphologie und Reaktionsfiihigkeit von Cellulose. I. Der heterogene und homogene Abbau von Tunicin. 506. H. Staudinger and W. Doble, J. Prakt. Chem. N.F., 161, 219-240 (1943). Vber Inclusions­Cellulosen. 507. H. Staudinger and W. Doble, Makromol. Chem., 9, 188-189 (1953). Vber die Acetylierung von Jnclusionscellulosen. 508. H. Staudinger and W. Doble, Makromol. Chem., 9, 190-192 (1953). Der Vbergang von nativen in mercerisierte Cellulosen. 509. H. Krassig, Makromol. Chem., 10, 1-12 (1953). Vber die Einwirkung von H examethylendiisocyanat auf benzolincludierte Zellwolle. 510. H. Staudinger and Th. Eicher, Makromol. Chem., 10, 254-260 (1953). Vber die Que/lung resp. Inclusion der Cellulose mit niederen Fettsiiuren. 511. H. Krassig and E. Schrott, Makromol. Chem., 13, 179-193 (1954). Der EinflujJ der Inclusion auf die Reaktivitiit unvernetzter und ernetzter Zellwolle.

272

RESEARCH ON MACROMOLECULAR COMPOUNDS

512. H. Kdissig and E. Schrott, Makromol. Chern., 28, 114-139 (1958). Morphologie und Reaktionsfiihigkeit von Cellulose. II. Die Reaktions­ fiihigkeit primiirer und sekundiirer Hydroxylgruppen im Verlaufe heterogener und homogener Acetylierung. 513. Otto Heick, dissertation, UniversiHit Freiburg i. Br., 1941. Uber die Acetylierung von Cellulosen. 514. Wolfgang Dohle, dissertation, UniversiUit Freiburg i. Br., 1942. Vber topochemische Reaktionen an Cellulosen. 515. G. V. Schulz and H. J. Lohmann, J. Prakt. Chern. N.F., 157, 238282 (1941). Uber die Kinetik des hydrolytischen Abbaus der Cellulose. 516. E. Husemann and G. V. Schulz, Z. Physik. Chern. (B), 52, 1-22 (1942). Vergleichende osmotische und viskosimetrische Molekulargewichts­ bestimmungen an fraktionierten und unfraktionierten Nitrocellulosen. 517. G. V. Schulz and E. Husemann, Z. Physik. Chern. (B), 52,23-49 (1942). Uber die Verteilung der Molekulargewichte in abgebauten Cellulosen und ein periodisches Aufbauprinzip im Cellulosemolekiil. 518. G. V. Schulz, Z. Physik. Chern. (B), 52, 50-60 (1942). Vber die Mole­ kulargewichtsverteilung beim Abbau von Kettenmolekiilen mit un­ regelmii]Jig einebauten Lockerstellen. 519. E. Husemann and A. Carnap, Naturwissenschaften, 32, 79-80 (1944). Uber die Lagerung der Lockerstellen von Cellulosemolekiilen in der Faser. 520. E. Husemann, Cellulosechemie, 22, 132-135 (1944). Uber submikro­ skopische Strukturelemente in Cellulosefasern. 521. E. Husemann, Makromol. Chern., 1, 140-157 (1947). Vber Locker­ stellen und ihre Spaltungsgeschwindigkeit in hydrolytisch abgebauten Ramiecellulosen. 522. E. Husemann and M. Goecke, Makromol. Chern., 2, 298-314 (1948). Uber Lockerstellen und ihre Spaltungsgeschwindigkeit in oxydativ abgebauten Baumwoll­ und Ramiecellulosen. 523. E. Husemann and M. Goecke, Makromol. Chern., 4, 194-208 (1949). Vber Lockerstellen in oxydativ und hydrolytisch abgebauten Holzcellu­ losen. 524. E. Husemann and R. Lotterle, Makromol. Chern., 4, 278-288 (1950). Uber den fermentativen Abbau von Polysacchariden. I. Der heterogene Abbau der Cellulose. 525. E. l-Iusemann, E. Loes, and R. Lotterle, Makromol. Chern., 6, 163-173 (1951). Uber den fermentativen Abbau von Polysacchariden. II. Die Bestimmung der Aktivitiit von Cellulase, Xylanase und Mannanase. 526. E. Husemann, Papier, 8, 157-162 (1954). Uber den sauren, fermentati­ ven und oxydativen Abbau von Cellulose und Cellulosederivaten. 527. H. Krassig, Makromol. Chern., 13, 21-29 (1954). Untersuchungen zur Konstitution des Tunicins. 528. H. Staudinger and H. Freudenberger, Ber., 66, 76-79 (1933). Uber das Biosan­acetat von K. Hess und H. Friese.

PART B REFERENCES

273

529. G. V. Schulz, Naturwissenschaften, 25, 346-347 (1937). Quellungs­ messungen an polymerhomologen Nitrocellulosen. 53.0. H. Staudinger and I. Jurisch, Zellstoff und Papier, 1938, 690-691. Vber den autoxydativen Abbau der Alkalicellulose. 531. H. Staudinger and I. Jurisch, Ber., 71, 2283-2289 (1938). Ober den oxydativen Abbau von Cellulosen in Phosphorsiiure. 532. E. Husemann, Papierfabrikant, 36, 559-563 (1938). Die Bedeutung der Endgruppenbestimmungen in der Polysaccharidchenzie. 533. H. Staudinger and I. Jurisch, Kunstseide u. Zellwolle, 21, 6-9 (1939). Vber die Loslichkeit von Cellulosen in Alkali/augen. 534. 0. H. Weber, J. Prakt. Chern. N.F., 158, 33-60 (1941). Eine neue Methode zur Besttmmung von Carboxylgruppen in Cellulose, Cellu­ losederivaten und anderen Polyosen. 535. H. Staudinger and K. W. Eder, Cellulosechemie, 19, 125-131 (1941). Vber die Charakterisierung von Cellulose durch die Kupferzahl. 536. H. Staudinger, Zellwolle, Kunstseide, Seide, 46 495 (1941). Bemerkung zu der Arbeit von W. Weltzien, G. Stollmann und Schotte iiber "Reak­ tionen nativer Cellulosen mit Natronlauge unter Sauerstoffausschluj3." 537. E. Husemann and 0. H. Weber, J. Prakt. Chern. N.F., 159, 334-342 (1942). Der Carboxylgehalt von Faser­ und Holzcellulosen. 538. E. Husemann and 0. H. Weber, Naturwissenschaften, 30, 28Q-281 (1942). Bestimmung des Molekulargewichtes von Cellulosen nach einer Endgruppenmethode. 539. E. Husemann and 0. H. Weber, J. Prakt. Chern. N.F., 161, 1-19 (1942). Die Bestimmung des Molekulargewichtes von Cellulosen nach einer Endgruppenmethode. 540. 0. H. Weber and E. Husemann, J. Prakt. Chern. N.F., 161 2Q-29 (1942). Ober Zusammenhiinge zwischen Carboxylgehalt und Poly­ merisationsgrad von Cellulosen bei der Vorreife der Viskose und der Chlorbleiche. 541. E. Husemann and U. Consbruch, Makromol. Chern., 5, 179-183 (1950). Vber die Celluloseformel von Pacsu. 542. H. Staudinger, Chemiker­Ztg., 58, 145-147 (1934). Vber die Konstitu­ tion der Cellulose. 543a. H. Staudinger, Cellulosechemie, 15, 53-59, 65-67 (1934). Vber die Konstitution der Cellulose (lecture at IG Ludwigshafen, October 23, 1933). 543b. H. Staudinger, An. Soc. espaii. Fisica Quim., 33, 74-90 (1935). Sobre Ia constitution de Ia celulosa (lecture at the University of Madrid, March 23, 1933). 544. H. Staudinger, Naturwissenschaften, 22, 797-819 (1934). Die Chemie der Cellulose. 545. H. Staudinger, Zellstoff­Faser, 33, 153-165 (1936). Vber die Bedeutung der Konstitutionsaufkliirung der Cellulose fiir die Zellstoffindustrie (lecture at the Versammlung Zellstoff- u. Papier-Chemiker, Darmstadt, January 30, 1936).

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546. H. Staudinger, Melliand Textilber., 18, 53-57 (1937). Die Bedeutung der Konstitutionsaufkliirung der Cellulose fur die Kunstfaserindustrie (lecture in Mi.inchen, July 1936). 547a. H. Staudinger, Svensk Kemisk Tidskrzft, 49, 3-23 (1937). Uber die Konstitution der Cellulose (lecture at the Chemischen Gesellschaft Stockholm and Uppsala on October 22, 1936). 547b. H. Staudinger, Papierfabrikant, 35, 233-242 (1937). Uber die Kon­ stitution der Cellulose. 548. H. Staudinger and I. Jurisch, Papierfabrikant, 35, 459-462 (1937). Uber Oxycellulosen. 549. H. Staudinger and I. Jurisch, Papierfabrikant, 35, 462-468 (1937). Uber den Abbau von Cellulose durch Oxydationsmittel. 550. H. Staudinger and I. Jurisch, Papierfabrikant, 35, 469-471 (1937). Uber den autoxydativen Abbau von Cellulose in Schweizers Reagens. 551. H. Staudinger, Ber., 70, 2514-2517 (1937). Bemerkungen zur Micellar­ theorie der Cellulose von Th. Lieser. 552. H. Staudinger, Zellwolle, 4, 3-5 (1938). Uber den makromolekularen Bauder Cellulose. 553. H. Staudinger, Holz als Roh­ und Werkstoff, 1, 259-265 (1938). Uber die Konstitution der Cellulose. 554. H. Staudinger, Papierfabrikant, 36, I: 373-380; II: 381-388; III: 473-485 (1938). Uber die Zusammenhiinge zwischen der Konstitution der Cellulose und ihren physikalischen Eigenschaften (lecture at the Versammlung Zellstoff- u. Papier-Chemiker, Berlin, December 3, 1937). 555. H. Staudinger, Zellstoff u. Papier, 8, 449-454 (1938). Uber Cellulose, Hemicellulosen und Lignin. 556. H. Staudinger, Melliand Textilber., 20, 781-783 (1939). Uber Poly­ mereinheitlichkeit, Polydispersitiit und Polymolekularitiit der Cellulose. 557. H. Staudinger, Cellulosechemie, 20, 1-14 (1942). Uber den micellaren, makromolekularen und ubermolekularen Bauder Cellulose. 558. H. Staudinger, Melliand Textilber., 29, 302-305 (1948). Uber den Aufbau von naturlichen und synthetischen Fasern und seine Bedeutung fur die Seifen, Wasch­ und Reinigungsmittelindustrie (lecture at the Treffen der Chen1iker dieser Industrie, Rothenburg o. d. Tauber, September, 1947). 559. H. Staudinger, "Uber Cellulose," in Fiat Review, Preparative Organic Chemistry, Part III, K. Ziegler, Ed., Dieterich, Wiesbaden 1948, pp. 2-48. 560. H. Staudinger, Textil­Rundschau, 4, 3-17 (1949). Uber den Aufbau von naturlichen und synthetischen Fasern (lecture at the Versammlung Chemiker-Coloristen, Zurich, April, 1948). 561. H. Staudinger, Papier, 5, 438-444 (1951). Uber den micellaren oder makromolekularen Bau der Cellulose (lecture at the Treffen der Zellstoff- und Papier-Chemiker, Detmold, June 6, 1951).

PART B REFERENCES

275

562. H. Staudinger, Association Techn. Ind. Papetiere, 6, 89-102 (1952). Les solutions colloi'dales des eel/uloses et de leurs derives (lecture given by the invitation of the Commission des Etudes Generales de L'Association Technique de l'Industrie Papetiere, Paris, March 1952). 563. H. Staudinger, Holz als Roh­ und Werkstoff, 11, 260-262 (1953). Riickblicke und Ausblicke auf die Konstitutionsaufkliirung der Cellulose. 564. H. Staudinger, Suomen Kemistilehti (A), 24, 111-123 (1951). Uber den Bau von natiirlichen und halbsynthetischen Cellulosefasern. 565. H. Staudinger, Sonderheft der Society of Polymer Science Japan (1957), pp. 38-63. Uber die Konstitution der Cellulose (lecutre in Tokyo, April1957). 566. Friedrich Reinecke, dissertation, UniversiHit Freiburg i. Br., 1937. Uber M olekulargewichstbestimmungen an Celluloseiithern. 567. Max Sorkin, dissertation, Universitat Freiburg i. Br., 1936. Visko­ sitiitsuntersuchungen an Hydrocellulosen und Cellulosenitraten. 568. Gunther Daumiller, dissertation, Universitat Freiburg i. Br., 1937. Untersuchungen an Celluloseacetaten und Cellulosen. 569. lngo Jurisch, dissertation, Universitat Freiburg i. Br., 1937. Uber den oxydativen Abbau von Cellulose. 570. Franz Zapf, dissertation, U niversitat Freiburg i. Br., 1939. I. Uber das Cellulosexanthogenat. II. Uber das Glykogenxanthogenat. 571. Karl Ferdinand Daemisch, dissertation, Universitat Freiburg i. Br., 1939. Viskositiitsuntersuchungen an Celluloseestern und Celluloseiithern. 572. Kurt Eder, dissertation, Universitat Freiburg i. Br., 1940. Molekularge­ wichtsbestimmungen und Viskositiitsuntersuchungen an abgebauten Cellulosetriacetaten. 573. Hans Joachim Lohmann, dissertation, Universitat Freiburg i. Br., 1940 (under supersivion of G. V. Schulz). Uber die Kinetik des hydro­ lytischen Abbaus der Cellulose. 574. Friedrich Finck, dissertation, U niversitat Freiburg i. Br., 1940. Uber den Zusammenhang zwischen Polymerisationsgrad, technischen Viskositiitszahlen und Festigkeit bei Hydrocellulosen. 575. Hermann Sattel, dissertation, Universitat Freiburg i. Br., 1945. Uber die Erhohung des Gebrauchswertes von Zellwollen durch heterogene Versterung und Versuche zur Charakterisierung von Zellstoffen. 576. Karl-Heinz In den Birken, dissertation, Universitat Freiburg i. Br., 1949. Zur Kenntnis des Aufbaues der Cellulosefasern aufgrund der topochemischen Acetylierung. 577. Theo Eicher, dissertation, Universitat Freiburg i. Br., 1953. Uber Celluloseacetate und Celluloseacetylacetate. 578. Marianne Goecke, dissertation, Universitat Freiburg i. Br., 1945 (under supervision of E. Husemann). Uber den oxydativen Abbau von Baumwoll­, Ramie­ und Holzcellulosen. 579. Irmgard Kohn, dissertation, Universitat Freiburg i. Br., 1948 (under supervision of E. Husemann). Beitriige zur Kenntnis der oxydativen Cellulosebleiche.

276

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COMPOUNDS

580. Ruth Lotterle, dissertation, UniversiHit Freiburg i. Br., 1950 (under supervision of E. Husemann). Uber den Abbau von Cellulose und Cellulosederipaten durch Ferment, Saure und Oxydationsmittel. 581. Elisabeth Loes, dissertation, UniversiHit Freiburg i. Br., 1951 (under supervision of E. Husemann). Uber den fermentativen Abbau von Cellulose, Xylan und Mannan. 582. Helmut Miiller, dissertation, UniversiHit Freiburg i. Br., 1956 (under supervision of H. Kdissig). Uber die Denitrierung von Cellulosenit­ raten. 583. Erwin Schrott, dissertation, UniversiHit Freiburg i. Br., 1956 (under supervision of H. Krassig). Uber den Verlauf der Acetylierung von Cellulose. 584. Egon Siefert, (diploma thesis, Universitat Freiburg i. Br., 1955 (under supervision of H. Krassig). Uber Losungen von Cellulose in Tetra­ athylammoniumhydroxyd. 585. Freidrich Exner, dissertation, Universitat Freiburg i. Br. 1956 (under supervision of H. Englemann). Vber Cellulosecrotonate. 586. H. Staudinger and H. Eilers, Ber., 69, 819-848 (1936). Uber den Bauder Starke. 587. H. Staudinger and E. Husemann, Liebigs Ann. Chern., 527 195-236 (1937). Uber die Konstitution der Starke. 588. Hj. Staudinger and J. Haenel-Immendorfer, J. Makromol. Chern., , 1, 185-196 (1944). Molekulargewichtsbestimmungen an Glykogen durch Anwendung des Rayleighschen Gesetzes. 589. H. Staudinger and E. Husemann, Ber., 70, 1451-1457 (1937). Vber die Bestimmung des Molekulargewichts von Polysacchariden nach der Engruppenmethode. 590. H. Staudinger and E. Husemann, Ber., 11, 1057-1066 (1938). Uber die Konstitution der Weizenstarke. 591. E. Husemann,J. Prakt. Chem. N.F., 158, 163-175 (1941). Molekularge­ wichtsbestimmungen an hydrolytisch abgebauten Glykogenen durch Fallungstitration. 592. H. Staudinger and E. Husemann, Naturwissenschaften, 29, 364 (1941). Bemerkungen zu der Arbeit von K. H. Meyer: "Die Anordnung der Glucosereste im Glykogen" [Naturwissenschaften, 29, 287 (1941)]. 593. E. Husemann and H. Bartl, Makromol. Chern., 10, 183-184 (1953). Uber die Grofle und Gestalt der Amylosemolekiile. 594. E. Husemann, Starke, 6, 2-5 (1954). Vber natiirliche und synthetische Amylose. 595. E. Husemann, B. Fritz, and B. Pfannemiiller, Z. Naturforsch., 9b 800 (1954). Uber die Unterschiede zwischen natiirlicher und synthetischer Amylose. 596. Herbert Bartl, dissertation, Universitat Freiburg i. Br., 1952 (under supervision of E. Husemann). Vber Amylose aus Kartoffelstarke. 597. H. Staudinger and H. Eilers, Ber., 69, 848-851 (1936). Vber den makromolekularen Aufbau des Lichenins.

PART B REFERENCES

277

598. H. Staudinger and B. Lantzsch, J. Prakt. Chern. N.F., 156, 65-94 (1940). Uber den makromolekularen Bau des Lichenins. 599. E. Husemann, J. Prakt. Chern. N.F., 155, 241-260 (1940). Uber die Konstitution von Salepmannan. 600. E. Husemann, K. N. von Kaulla, and R. Kappesser, Z. Naturforsch., 1, 584-591 (1946). Uber blutgerinnungshemmende Substanzen. 601. E. G. Hoffmann, E. Husemann, R. Lotterle, M. Wiedersheim, and W. Hertlein, Makromol. Chern., 10, 107-121 (1953). Vber die Aus­ scheidung und Speicherung von radioaktiv indizierten Xylanschwefel­ siiureestern. 602. E. Husemann and G. Soder, Z. Naturforsch., 9b, 237-238 (1954). Untersuchung der Ausscheidung und Speicherung von Dextran durch lndizierung mit 35 S. See also Gunter Soder, dissertation, UniversiHit Freiburg i. Br., 1953 (under supervision of (E. Husemann): Zur Konstitution und physiologischen Chemie des Bakterienpolysaccharids "Dextran." 603. E. Husemann, R. Lotterle, M. Wiedersheim, and W. Hertlein, Makromol. Chern., 12, 79-93 (1954). Uber die Pharmakologie wasser­ loslicher Polysaccharide und ihrer Derivate in Abhiingigkeit von MolekiilgrofJe, Molkiilgestalt und Art der Substituenten. 604. E. Husemann, B. Pfannemiiller, w Hertlein, and E. G. Hoffmann, Z. Naturforsch., 9b 704-712 (1954). Uber die Ausscheidung und Speicherung von radioaktiv indizierten Xylan­Schwefelsiiureestern. 605. Hajo Eilers, dissertation, UniversiUit Freiburg i. Br., 1934. Beitrag zur Konstitutionsaufkliirung der Starke und des Lichenins. 606. Bernhard Lantzsch, dissertation, Universitat Freiburg i. Br., 1939. Uber den makromolekularen Bau des Lichenins. 607. M. Staudinger, Holz als Roh­ und Wekstoff 5, 193-201 (1942). Chem­ ische Anatomie des Holzes. (See also ref. 18, p. 126, and ref. 202, p. 58.) 608. H. Staudinger, E. Dreher and A. af Ekenstam, Ber., 69, 1099-1100 (1936). Uber Vermahlen von Holz. 609. H. Staudinger and E. Dreher, Ber., 69, 1729-1737. (1936). Uber das Lignin. 610. H. Staudinger, E. Dreher, and I. Jurisch, Ber., 70, 2502-2507 (1937). Uber den Polymerisationsgrad der Cellulose in verschiedenen Holzsorten. 611. H. Staudinger and F. Reinecke, Papierfabrikant, 36, 489-495 (1938). Vber die Charakterisierung von Zellstoffen durch Viskositiitsmessungen. 612. H. Staudinger, Forst!. Hochschulwoche Freiburg i. Br., 1938, 53-55. Holz und Cellulose. 613. H. Staudinger and I. Jurisch, Papierfabrikant, 37, 181-184 (1939). Vber den Polymerisationsgrad der Cellulose in Ligniten. 614. H. Staudinger and F. Reinecke, Holz als Roh­ und Werkstoff 2, 321-323 (1939). Uber den Polymerisationsgrad verschiedener Zellstoffe. 615. E. Husemann, Naturwissenschaften, 27, 595 (1939). Uber die Kon­ stitution von Holzpolyosen.

278

RESEARCH ON MACROMOLECULAR COMPOUNDS

616. E. Husemann, J. Prakt. Chern. N.F., 155, 13-64 (1940). (Habilitationsschrift) Uber die Konstitution der Holzpolyosen. 617. H. Staudinger and E. Husemann, Holz als Roh­ und Werkstoff, 4, 343347 (1941). Bestimmung des Cellulosegehaltes an verschiedenen Holzsorten. 618. H. Staudinger and E. Husemann, Naturwissenschaften, 29, 534-535 (1941). Uber anormale Viskositiitszahlen von Nitrocellulosen aus Holz. 619. F. Zapf, Makromol. Chem., 3, 164-175 (1949). Uber die Km­Werte von Zellstoffnitraten und Zellstoffen. 620. F. Zapf, Makromol. Chem., 10, 35-70 (1953). Uber das Viskositiitsver­ halten von Holzcellulosenitraten. 621. F. Zapf, Makromol. Chem., 10, 71-77 (1953). Uber Kapok­Cellulose. 622. H. Batzer and H. Fischer, Makromol. Chern., 7, 168-176 (1951). Uber die Verwendung wasserloslicher Stoffe in der histologischen Technik. 623. H. Batzer and G. Weii3enberger, Makromol. Chern., 7, 320-327 (1951). Gerbversuche mit Polyamiden. 624. H. Batzer and G. Petry, Makromol. Chern., 7, 328-334 (1951). Uber Gerbung und Entgerbung von elastischen und kollagenen Fasern. 625. H. Batzer, Chemiker­Ztg., 76, 397-402 (1952). Experimenteller Beitrag zu einer makromolekularen Theorie der Gerbung. 626. H. Batzer, Makromol. Chern., 8, 183-185 (1952). Ultramid 6 A als Adsorbens bei der Gerbstoffanalyse nach dem Filterverfahren. 627. H. Batzer and H. J Grunewald, Makromol. Chern., 9, 116-147 (1953). Uber Gerbung mit polymerisationsfiihigen Substanzen. 628. H. Batzer, Makromol. Chern., 10, 185-193 (1953). Uber die Gestalt von Gerbstoffteilchen in wiisseriger Losung. 629. Hans Batzer, dissertation, UniversiHit Freiburg i. Br., 1946. Uber die Einordnung der Gerbstoffe in die makromolekulare Chemie und iiber ihre Analysenverfahren. 630. Hans Joachim Grunewald, dissertation, UniversiHit Freiburg i. Br., 1952 (under supervision of H. Batzer). Uber Gerbung mit polymerisa­ tionsfiihigen Substanzen. 631. H. Staudinger, "Die Bedeutung der Erforschung der Konstitution hoch­ polymerer Stoffe fiir die Biologie," in Zangger-Festschrift, Verlag Rascher, Zurich 1934, pp. 939-953. 632. H. Staudinger, Chemiker­Ztg., 61, 549 (1937). Uber die Bedeutung der makromolekularen Chemie fiir die Biologie. 633. H. Staudinger, Universitas, 1, 853-864 (1946). Makromolekulare Chemie und Biologie. 634. G. Rozsa and M. Staudinger, Makromol. Chern., 2, 66-76 (1948). Elektronenmikroskopische Untersuchungen an Muskelproteinen. 635. M. Staudinger, Naturwiss. Rdsch., 1950, 200-204. Was ist Leben? 636. H. Staudinger, "Die Bedeutung der makromolekularen Chemie fiir das Lebensproblem," in Die Natur das Wunder Gottes, 6th ed., Dennert, Bonn, 1957, pp. 104-119.

PART B REFERENCES

279

637. H. Staudinger, Scientia [Milano], 44, 57-61, 139-143 (1950). Makro­ molekulare Chemie und Biologie. 638. H. Staudinger, "Bedeutung der makromolekularen Chemie fiir die Biologie," in Festschrift zur Feier des 200jiihrigen Beste hens der Akademie der Wissenschaften, Gottingen, 1951, pp. 65-70. 639. H. Staudinger, Chemiker­Ztg., 75, 25-28 (1951). Die Bedeutung der Makron1olekiile fiir biologische Vorgiinge. 640. M. Staudinger, Zeitschrift 'Die Miidchenbildung,' 1, 25-31 (1951). Makromolekiile und biologische Vorgiinge. 641. M. Staudinger, Scientia [Asso], 48, 1-7 (1954). Les colloides mole­ culaires et Ia matjere vivante (Molekiilkolloide und lebende Materie) (lecture at Centro Romano di Studi, Roma, November 9, 1950). 642. H. Staudinger and M. Staudinger, Deutsche Zeitung und Wirtschafts­ Zeitung, Sept. 11, 1954, p. 4. Wo das Spiel des Lebens einsetzt. 643. H. Staudinger and M. Staudinger, "Gedanken iiber die Bedeutung der makromolekularen Chemie fiir die Biologie," in Ann. Acad. Scient. Fennicae Ser. A II. Chemica, Biochemistry of Nitrogen, Virtanen­ Festschrift, Helsinki, 1955, pp. 251-256. 644. M. Staudinger, "Das Lebensproblem im Licht makromolekularer Forschung," in Festschrift zur Jahresvers. des Verbandes Deutscher Biologen, Hamburg, 1956, pp. 24-33 (Wiss. Verlags, G. m. b. H., Stuttgar).