EMULSION POLYMERIZATION AND ITS APPLICATIONS IN INDUSTRY

EMULSION POLYMERIZATION AND ITS APPLICATIONS IN INDUSTRY

V. I. Eliseeva S. S. Ivanchev S. I. Kuchanov A. V. Lebedev

Translated from Russian by

Sylvia J. Teague

® CONSULTANTS BUREAU • NEW YORK AND LONDON

Library of Congress Cataloging in Publication Data

Emul'sionnaia polimerizatsiia i ee primenenie v promyshlennosti. English. Emulsion polymerization and its applications in industry.

Translation of: Emul'sionnaia polimerizatsiia i ee primenenie v promyshlennosti. Includes index. 1. Emulsion polymerization. I. Eliseeva, V. I. (Valentina I vanovna) II. Title.

QD382.E48E4913 668.9 81-17477 ISBN-13: 978-1-4684-1643-5 e-ISBN-13: 978-1-4684-1641-1 AACR2 DOl: 10.1007/978-1-4684-1641-1

The original Russian text was published by Khimiya in Moscow in 1976. This transla­tion is published under an agreement with the Copyright Agency of the USSR (V AAP).

EMUL'SIONNA Y A POLIMERIZA TSIY A I EE PRIMENENIE

V PROMYSHLENNOSTI

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© 1981 Consultants Bureau, New York Softcover reprint of the hardcover 1st edition 1981

A Division of Plenum Publishing Corporation 233 Spring Street, New York, N. Y. 10013

All rights reserved

No part of this book may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the publisher

Foreword

There is a large body of Soviet work on emulsion polymerization, spanning a period of over three decades, that has been published primarily in the Russian language. Most of this has remained untranslated into English and hence un­available to most other scientists. The value of this book lies primarily in the fact that it brings together the most important of these Soviet contributions, along with comment and analysis by the authors, who may be considered among the foremost authorities in this field in the Soviet Union. But the hundreds of literature citations go far beyond the borders of the Soviet Union and serve as an excellent bibliography of the world literature on emulsion polymerization up to the time this book was written.

The book covers both fundamental and applied aspects. In the former are included discussions of particle formation mechanisms, a comprehensive theory of emulsion polymerization, copolymerization of polar monomers, and particle morphology and its implications with regard to derived film properties. Among the applied aspects are discussions of continuous emulsion polymerization, both tubular reactors and continuous stirred tank cascades, and various aspects con­cerning the manufacture of some of the most important monomers, such as styrene, butadiene, vinyl acetate, methyl methacrylate, acrylonitrile, and chloroprene.

This book will be an indispensable reference source for scientists who are entering the field as well as those who are experienced and who have wanted a ready access to this large body of literature.

v

Robert M. Fitch Storrs, Connecticut

Preface to the English Edition

In view of the growing interest in recent years on the part of production engineers and scientists in the problem of preparing polymers and latexes by emulsion poly­merization, it seemed desirable to the authors to prepare this monograph to pre­sent experimental data in this area that they and other specialists have collected.

The authors are specialists in various areas of emulsion polymerization, and they have written different sections of the book, according to their field of specialization. The authors, systematizing the material available to them, have developed their own concepts of the process of emulsion polymerization. In so doing, it seemed to them that the use of modern methods of investigation, the accumulation of new facts in this area, and the increase in the variety of mono­mers and other components of the polymerization systems have impeded under­standing of the complex process of emulsion polymerization. This process, apparently, cannot be fitted into a single general scheme, so that each class of polymerization system requires the creation of a corresponding model taking into consideration the main physicochemical properties of the class.

A first attempt is made in this book to systematically present data on the influence of the nature of the interface (which is related to the polarity of the monomer), the kinetics of the process, the mechanism of particle formation, and the physical structure of the polymer and copolymer. Research in this area was first conducted in the Soviet Union.

In describing the emulsion polymerization of hydrophobic monomers, Soviet work little known abroad is included in the book. This includes research on poly­merization in the presence of nonionic emulsifiers and weakly soluble initiators, which lead to microdroplets of monomer emulsion; research on the features of peroxide-initiated polymerization in the presence of cationic emulsifiers; and research on the activating influence of the interface on the decomposition of peroxide and the rate of initiation. The book also contains a critical review, in condensed form, ofthe classical theory of emulsion polymerization and its refine­ment and extension, in particular in works by Soviet investigators.

vii

viii PREFACE TO THE ENGLISH EDITION

In describing industrial methods of emulsion polymerization, the authors used data from Soviet industrial practice.

It is the hope of the authors that the present monograph will interest foreign specialists working in the area of emulsion polymerization.

V. I. Eliseeva

Preface

Emulsion polymerization continues to attract the attention of scientists and industrial workers since the possibilities for this interesting, convenient, and economical method of preparation of polymers and latexes with various prop­erties are far from exhausted. Ever since the publication in 1955 of a monograph on emulsion polymerization by American scientists, the scale of research in this area has increased significantly.

New directions have emerged in the study of emulsion polymerization (ionic and radiation-initiated polymerization as well as polymerization in nonaqueous media). Copolymerization with functionally substituted monomers has undergone broad practical development and the assortment of such monomers grows from year to year. Interest has also arisen in the study and preparation of monodisperse latexes with regulated particle size. The range of monomers, emulsifying agents, and initiating systems being studied has expanded and new methods have appeared for using latex polymers in technology (particularly for increasing the impact strength of polymeric glasses) and in agriculture, biology, and medicine.

The increased use of latex polymers has provoked interest in industry in creating technological schemes for the continuous polymerization of various monomers. This, in turn, led to the necessity for mathematically describing the processes.

The development of new phYSicochemical methods of investigation permitted a new interpretation of the processes of emulsion polymerization taking into consideration the nature of the interface and intermolecular interactions at the boundary phase using thermodynamics and conformational statistics. This pro­vided a key to understanding "anomalies" in the polymerization and copolymer­ization of polar monomers. This same approach was used to explain specifics of the morphology of latex polymers formed at an interface.

The expansion of the variety of necessary components of reactive emulsion systems (monomers, emulsifiers, initiators, dispersion media) and of production methods (semicontinuous, continuous) along with increased demands of industry regarding the properties of the products obtained, have led to new technical and practical problems in emulsion polymerization. These problems include the ki-

ix

x PREFACE

netics of polymerization of monomers differing in solubility in water, polarity, and reactivity; copolymerization with multifunctional monomers; the principles of selecting an emulsifying agent for different polymerization systems; the formation of polymeric colloids in nonaqueous media; the morphology and structure of latex polymers; the mechanism of film formation and cross-linking oflatex poly­mers; the automation of production processes of emulsion polymerization; pro­cess optimization; the creation of continuous reactors.

The present monograph covers as completely as possible the aqueous-phase radical latex polymerization of "classical" monomers such as styrene and the polymerization and copolymerization of polar monomers, which is assuming ever greater practical and scientific interest. Whereas the former presently serves as the basis for large-scale production of rubbers and has been studied more exten­sively, the emulsion polymerization of polar monomers has begun to be system­atically studied only in recent years. Polymers and, especially, copolymers from polar monomers are widely used in construction and in the film, paint, leather, textile, paper, etc., industries. Prospects for using such latexes for medical pur­poses have also appeared. In this monograph a systematic review of the latest research in this area is given first. Also presented is the mathematical theory of the emulsion polymerization of styrene, an acquaintance with which is necessary in constructing mathematical models and for optimization of industrial processes. In addition, this theory suggests an approach to the quantitative description of the polymerization of other monomers in complex colloidal systems.

The questions of radiation-induced and stereospecific polymerizations, since they are still in the laboratory and pilot-plant stage, are not included in this book, and because of space limitations the problems of latex polymerization in non­aqueous media also are not discussed.

It seemed expedient to the authors to deal separately with the emulsion poly­merization of nonpolar monomers such as styrene and of polar monomers such as vinyl acetate, acrylates, and vinyl chloride as well as the copolymerization of vinyl monomers with functionally substituted monomers. The expediency of such a separation arises from the theory advanced that a polymer in the form of a latex (colloidal dispersion) has new properties that are not characteristic of a polymer in bulk or in solution and that are caused by the presence of a strongly developed interface of the polymer and the aqueous phase. The properties of this interface change in a specific manner with the nature of the polymer and depend on such processes (important in the synthesis and properties of the products formed) as adsorption of the surfactant, flocculation of particles, particle inter­action, and conformational behavior of the macromolecules formed. In addition, this interface can be used as a carrier of chemically, biologically, and catalytically active groups. This phenomenon should not be overlook.;J during copolymeriza­tion with functionally substituted monomers and it opens up new possible uses of polymeric materials. Although these factors have been disregarded in the in-

PREFACE

vestigation and theoretical examination of the emulsion polymerization of hy­drophobic monomers, in the polymerization and copolymerization of polar monomers (where molecular interactions at the interface are intensified) the properties of the interface of polymer colloids are of primary importance both with respect to the colloidal behavior of the system and the kinetics of the process.

xi

The chapter devoted to the polymerization of monomers such as styrene covers problems which began to be studied at the turn of the century and which are the subject of a large number of works. In this chapter the authors generalize recent (and mainly) Soviet research in which special attention is given to the specific action of the emulsifier on the mechanism of initiation and on the kinetics of the process.

In the chapter devoted to the polymerization and copolymerization of polar monomers, a systematic report is given of research begun relatively recently. Considerable attention is given to the nature of the interfacial region and its in­fluence on the kinetics of the process, the behavior of a polymerization system, and the conformational behavior of the macromolecules formed. For the first time, an experimental and a quantitative approach is given for evaluating the be­havior of a statistically heterogeneous copolymer macromolecule at its interface; this approach offers a new means of studying emulsion copolymerization.

In the second part, which is devoted to practical problems, the physico­mechanical principles of the polymerization technology of important monomers are described. The properties and variety of latexes and polymers derived from them are also discussed. In writing this book, the authors have striven to present the latest data and to avoid repetition of previously published material.

Chapter 1 of the book was written by S. S. Ivanchev, Chapter 2 by S. I. Kuchanov, Chapter 3 by V. I. Eliseeva, Chapters 4 and 8 by A. V. Lebedev, Chapter 5 by S. S. Ivanchev and E. V. Gromov, Chapter 6 by S. S. Ivanchev and S. S. Mnatsakanov, and Chapter 7 by V. I. Eliseeva and A. S. Gerasimova.

The authors express deep gratitude to P. M. Khomikovskii for reading the manuscript and for valuable advice and comments. This book is not without short­comings. All critical comments will be appreciated by the authors.

V. I. Eliseeva

Contents

PART 1

1. EMULSION POLYMERIZATION OF NONPOLAR MONOMERS. . . . 3

Classification of Emulsion Polymerization Systems. . . . . . . . . . . . . . 4 Classification of Systems according to Monomer . . . . . . . . . . . . . 5 Classification of Systems according to the Emulsifier . . . . . . . . . . 6 Classification of Systems according to Initiator. . . . . . . . . . . . . . 7

Role of Emulsifier in Emulsion Polymerization ................ 9 Properties of Emulsifier Solutions ...................... 9 Formation and Structure of Micelles. . . . . . . . . . . . . . . . . . . . . 10 Solubilization of Surfactant Solutions. . . . . . . . . . . . . . . . . . . . 11 Influence of Emulsifier Type on Properties of Monomer Emulsions 12 Role of Ionic Emulsifier . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 13 Role of Nonionic Emulsifier . . . . . . . . . . . . . . . . . . . . . . . . .. 23 Emulsifiers Containing Reactive Functional Groups. . . . . . . . . .. 28

Influence of Initiator on the Kinetics of Polymerization .......... 33 Water-Soluble Initiators . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 38 Initiators Soluble in Monomer. . . . . . . . . . . . . . . . . . . . . . . .. 40

References .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 41

2. QUANTITATIVE DESCRIPTION OF EMULSION POLYMERIZATION ........ - . . . . . . . . . . . . . . . . . . . . . . .. 47

Smith-Ewart Theory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 47 Refinement and Extension of the Smith-Ewart Theory. . . . . . . . . .. 56 Average Molecular Weight and Molecular Weight Distribution of

Polymerization Products. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 67 Size Distribution of Latex Particles . . . . . . . . . . . . . . . . . . . . . . .. 69 References ........................ . . . . . . . . . . . . . . .. 77

3. CHARACTERISTICS OF EMULSION POLYMERIZATION AND COPOLYMERIZATION OF POLAR MONOMERS. . . . . . . . . . . . .. 79

Deviations from Kinetic Dependences Established for Styrene ...... 80 Mechanism of Particle Nucleation . . . . . . . . . . . . . . . . . . . . . . . .. 86

xiii

xiv CONTENTS

Role of Interfacial Surface Nature. . . . . . . . . . . . . . . . . . . . . . . .. 91 Characteristics of Emulsifier Adsorption . . . . . . . . . . . . . . . . .. 91 Equilibrium Concentration of Monomer in Latex Particles ...... 94

Flocculation Mechanism of Particle Formation ................ 96 Kinetics of Polymerization. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 100 Polymerization in the Absence of Emulsifier. . . . . . . . . . . . . . . . .. 104 Role of Emulsifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 111 Colloidal Stability of Latexes from Polar Monomers . . . . . . . . . . . .. 114

Electrostatic Stabilization. . . . . . . . . . . . . . . . . . . . . . . . . . .. 115 Steric Stabilization ..... . . . . . . . . . . . . . . . . . . . . . . . . . .. 117

Selection of Emulsifier .................. . . . . . . . . . . . . .. 119 Emulsion Copolymerization of Polar Monomers. . . . . . . . . . . . . . .. 122

Copolymerization with Acids and Other Ionizable Monomers .... 125 Copolymerization with Amide Derivatives of Unsaturated Acids .. 129

Morphology of Latex Particles and Polymer Properties Related to It .. 136 References ............ . . . . . . . . . . . . . . . . . . . . . . . . . . .. 143

PART 2

4. BUTADIENE POLYMERS AND COPOLYMERS. . . . . . . . . . . . . .. 153

Characteristics of Butadiene as a Component of a Polymerization System ......................................... 153

Characteristics of the Technological Process for Preparing Rubbers and Latexes from Butadiene ........................... 156

Continuous and Batch Polymerization. . . . . . . . . . . . . . . . . . .. 157 Agglomeration of Particles ........................... 160 Subsequent Stages in the Production of Rubbers and Latexes ... , 162

Main Types and Trade Names of Butadiene-Based Rubbers and Latexes and Their Uses .................................... 164

Polybutadiene Rubbers and Latexes ................... " 165 Butadiene-Styrene Rubbers and Latexes (SBR) ............. 167 Nitrile Rubbers and Latexes ....... . . . . . . . . . . . . . . . . . .. 168 Functional-Group-Containing Butadiene Rubbers and Latexes. . .. 170 Other Butadiene Copolymers and Their Latexes . . . . . . . . . . . .. 174

References .... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 175

5. POLYMERS BASED ON POLYSTYRENE LATEXES . .......... 179

Main Types of Styrene Emulsion Polymers and Latexes and Their Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 179

Preparation of Styrene-Based Polymers and Latexes . . . . . . . . . . . .. 181 References ........................................ 184

6. POLYMERS AND LATEXES BASED ON VINYL ACETATE . ..... 185

Characteristics of Vinyl Acetate Polymerization. . . . . . . . . . . . . . .. 185 Molecular Structure of Poly (vinyl acetate) ................ 186

CONTENTS xv

Types of Poly (vinyl acetate) Dispersions .................... 188 Classification according to Degree of Dispersity . . . . . . . . . . . .. 188 Homo- and Copolymer Dispersions. . . . . . . . . . . . . . . . . . . . .. 189

Preparation of Dispersions Based on Vinyl Acetate . . . . . . . . . . . . .. 192 Use of Dispersions of Poly(vinyl acetate) and Its Copolymers . . . . . .. 192 References ..................... . . . . . . . . . . . . . . . . . .. 193

7. LATEXES BASED ON ACRYLIC MONOMERS ............... 195

Methods of Emulsion Polymerization of Acrylic Monomers . . . . . . .. 196 One-Stage and Semicontinuous Methods . . . . . . . . . . . . . . . . .. 196 Continuous Method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 203 Industrial Methods of Preparing Acrylic Latexes . . . . . . . . . . . .. 205

Emulsifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 208 Types of Soviet Acrylic Latexes and Their Production Technology ... 210 Use of Acrylic Latexes ................................ 213 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 213

8. CHLOROPRENE POLYMERS AND LATEXES. . . . . . . . . . . . . .. 215

Features of the Homo- and Copolymerization of Chloroprene. . . . . .. 215 Features of the Production Technology for Rubbers and Latexes from

Chloroprene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 217 Principal Types of Rubbers and Latexes Based on Chloroprene . . . . .. 219 Aging of Chloroprene Latexes. . . . . . . . . . . . . . . . . . . . . . . . . . .. 220 References ........................................ 224