An Introduction to Basic Silicone Chemistry By

[ 01 ft< 58449 > OU_1 [g ^ CD ^ C/) LI ' Call No. - ~L> Accession No. Author fidCJi*lO. Tak CL^v betew. This book should be re/Urned on or before the date last marked An Introduction to the CHEMISTRY of the SILICONES An Introduction to the CHEMISTRY of the SILICONES By EUGENE G. ROCHOW Research Laboratory, General Electric Company NEW YORK: JOHN WILEY & SONS, INC. LONDON: CHAPMAN & HALL, LIMITED COPYRIGHT, 1946 BY EUGENE G. ROCHOW AU Rights Reserved This book or any part thereof must not be reproduced in any form without the written permission of the publisher. SECOND PRINTING, MARCH, 1947 PRINTED IN THE UNITED STATES OF AMERICA To P. G. F. PREFACE The organic compounds of silicon, which have been the subject of many scholarly researches during the past 80 years, at last show promise of emerging from the laboratory and finding a place in industry. An understanding of the behavior of organosilicon materials is necessary to their intelligent use and, inasmuch as the chemistry of these substances ordinarily is not treated in our textbooks, it is possible that a compact yet comprehensive survey of our present knowledge in this field would be of service to chemists, engineers, and industrial designers. This volume has just such a purpose. The first few chapters review the silanes and their derivatives in some detail, in order to provide an understanding of the fundamental chemistry of the nonsilicate compounds of silicon. The later chapters emphasize the silicone polymers which have achieved commercial importance and deal with the methods for their preparation, their chemical and physical properties, and their possible usas. The processes available for large-scale production are treated separately, and a review of methods of analysis is included. In order not to burden the text with definitions and explanations of nomenclature which might already be familiar to some readers, an extensive glossary of terms is appended. An exhaustive review of the literature on organic compounds of silicon cannot very well be included in a volume intended for the non- specialist. However, many references are provided, and tables of most of the known compounds and their properties are included in the appropriate chapters. The reader will find comprehensive reviews of publications in Friend's Textbook of Inorganic Chemistry, Volume 11, Part 2; Krause and von Grossed Chemie der Metallorgamschen Ver- bindungen, Dolgow's Chemistry of the Silica-Organic Compounds, and Bygden's Silizium als Vertreter des Kohlenstoffs organischen Verbindun- gen. A more recent and more complete compilation of the literature on organic compounds of silicon would be welcomed by every investigator in the field. Since this work presents a point of view rather than an uncritical compilation of published fact, the author must assume entire responsi- bility for the opinions expressed. However, he is greatly indebted to his coworkers iu the research laboratory of the General Electriq Com- vii viii PREFACE pany for helpful advice and criticisms. In a larger sense this work is the result of many years of common endeavor in a most interesting field of research. CONTENTS CHAPTER PAGE 1. THE SIMPLE COVALENT COMPOUNDS OF SILICON 1 Introduction 1 Chemical Behavior of the Element 3 The Hydrides 4 The Halides 9 The Esters or Ethers 12 Index of Representative Compounds 16 2. THE ORGANOSILICON MONOMERS 18 Methods for Carbon-Silicon Bonds 19 The Alkyls 30 The Alkylsilanes 32 The Alkylhalosilanes 33 The Alkylalkoxysilanes 37 Index of Representative Compounds 39 3. TYPES OF ORGANOSI LICON POLYMERS 45 Silicon Chains 45 Silicon-Carbon Chains 46 Siloxane Chains 49 Siloxane Networks 53 Index of Representative Compounds 58 4. PROPERTIES OF THE SPECIFIC SILICONS POLYMERS 60 Alkyl Silicones 62 Methyl Silicone Oil 64 Methyl Silicone Resins 70 Silicone Rubber 72 Ethyl Silicone Resins 73 Other Alkyl Silicone Resins 74 Aryl Silicones 77 Alkyl-Aryl Silicones 80 5. WATER-REPELLENT FILMS FROM ORGANOSILICON MATERIALS 83 Reaction of Methylchlorosilanes 83 Uses 85 6. TECHNICAL ASPECTS OF SILICONES 89 The Intermediates 90 The Grignard Method 91 The Direct Method 96 Processing 101 Toxicity 103 Future Expansion 104 ix CONTENTS CHAPTER 7. ANALYTICAL METHODS ............................................ 106 GLOSSARY .......................................................... Ill INDEX ............................................................. 127 Chapter 1 THE SIMPLE COVALENT COMPOUNDS OF SILICON INTRODUCTION Silicon is the most plentiful electropositive element on the earth's crust, being three times as abundant as aluminum and six times as abundant as iron. Yet the only compounds of silicon which have been important to human history are those natural forms of silica and the silicate minerals which are used in the building arts and in ceramic technology. Only within the past 90 years have hydrides and organic derivatives of silicon been synthesized, and the chlorides 30' years before; up to a few years ago it could be said that all these substances were still relatively unknown products of the laboratory, unimportant save for their scientific interest. The chemistry and technology of silicon continued to be dominated entirely by consideration of the inorganic silicates. It has seemed quite natural to think of silicon only in terms of the oxide, for practically all of the earth's silicon is bound up with oxygen. Together these two elements constitute some 76 per cent of the solid crust of the earth, and there is more than enough oxygen to combine with all the silicon. Free silicon therefore does not occur in nature, nor do its organic compounds.* The only natural substance which has been demonstrated to have carbon-silicon bonds is the rare mineral moissanite, which is silicon carbide, and this ordinarily is not thought of as an organosilicon compound. The lack of natural products undoubtedly hindered the early studies of organic compounds of silicon, for synthetic methods had to be de- veloped from the very beginning. Fortunately the problem received the attention of some of the ablest investigators of the nineteenth century, such men as Friedel, Crafts, and Ladenburg, who were able to make the first organic compounds of silicon by what now seem to be laborious methods. Then in 1901 Kipping began his monumental re- * It is true that straw and feathers contain silicon, for its oxide is found in the ash when these materials are burned, but the mechanism by which this silicon entered into the plant or animal is not understood, and it has not been demonstrated that silicate esters or organosilicon compounds are involved. 1 2 THE SIMPLE COVALENT COMPOUNDS OP SILICON searches which were to extend over 43 years, and which stand as the basis of most of our present knowledge of organosilicon compounds. l Much as these men and many others have contributed, the science of organosilicon chemistry is still rather meager in content and limited in scope, considering the abundance of silicon and the versatility of its chemical behavior. Possibly the lack of simple inexpensive methods of synthesis has hindered more widespread laboratory study and has deterred commercial exploitation of the known materials; possibly chemical science has been concerned with many other interesting things and has been slow to consider the possibilities of silicon. The demonstrated utility of organosilicon materials has wrought a great change, however. The period since 1940 has seen rapid develop- ment of the organosiloxanes or silicone polymers, and some of the organosilicon intermediates are coming into further importance of their own. To serve this newly awakened interest, this book seeks to review the reactions and properties of all the nonmineral compounds of silicon in terms of their potential usefulness, and to consider organosilicon compounds in particular as promising new synthetic substances which may fill a need heretofore unsatisfied by the natural and by the con- ventional synthetic materials. In later chapters it will be necessary to limit the term "organo- " silicon to those compounds in which carbon is linked directly to silicon. The esters or ethers of silicic acid, in which organic groups are linked to the silicon atom through oxygen, have structures and properties which warrant setting them aside in a separate class, here treated less thoroughly than the class of organosilicon compounds. 2 Such esters are described more completely elsewhere, and long since have acquired a commercial importance and a literature of their own. In this chapter we shall consider briefly the chemical behavior of silicon and its simple compounds with hydrogen, the halogens, and alkoxy or aroxy groups These covalent compounds in themselves do not contain carbon-silicon bonds, but a preliminary study of their behavior serves two important purposes: it provides an introduction to the chemistry of the more complex substances to follow, and it provides the background necessary to an understanding of those organosilicon compounds which also have halogen, hydrogen, or alkoxy groups at- tached to the silicon atoms. 1 See bibliography in Krause and von Grosse, Die Chemie der metallorganischen Verbindungen, pp. 290-5 (Borntraeger, Berlin, 1937; photolithographed by J. W. Edwards, Ann Arbor, Mich., 1943). 2 Post, The Chemistry of the Aliphatic Orthoesters, Am. Chem. Soc. Mono- graph 92 (Remhold Publishing Company, New York, 1943); King, /. OH Colour Chem. Aasoc. 13, 28 (1930); Frydlender, Rev. prod. chim. 33, 720 (1930). CHEMICAL BEHAVIOR OF SILICON 3

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