Prog. Polym. Sci., Vol. 17, 917-951, 1992 0079-6700•92 $15.00 Printed in Great Britain. All rights reserved. © 1992 Pergamon Press Ltd THERMODYNAMICS OF COPOLYMERIZATION RYSZARD SZYMANSKI Polish Academy of Sciences, Center of Molecular and Macromolecular Studies, Sienkiewicza 112, 90-361 Lodz, Poland CONTENTS 1. Introduction 2. Equilibrium in copolymerization. General outlook 3. Analysis of copolymerization thermodynamics. Previous results 4. Dyad model copolymerization 4.1. Application of equations to real systems 4.2. Recent analogous treatments of other authors 5. Triad model copolymerization 5.1. Application of equations to real systems 6. Chain-ring equilibria in equilibrium copolymerization systems 7. Copolymerization equilibrium in systems with physical interactions 8. Homopolymerizations which can be regarded as copolymerizations References 917 919 921 926 929 929 933 937 938 940 944 950 1. INTRODUCTION Studies of thermodynamics of copolymerization processes provide data on equilibrium concentrations of comonomers and microstructure of the resulting copolymer. This allows one to determine the enthalpy (AH) and entropy (AS) of homo- and cross-propagations (other thermodynamic functions can be deter- mined as well). This information, in turn, enables one to predict the values of propagation equilibrium constants for the copolymerization systems con- sidered. Consequently, one can predict whether copolymer can be formed from the given mixture of comonomers at the chosen conditions (provided the appro- priate mechanism of copolymerization is available) and also the composition and microstructure of the resultant copolymer. Besides, one can estimate the maximum (equilibrium) degree of comonomer conversion. Polymerization thermodynamics has been reviewed several times ~-6 but ther- modynamics of copolymerization was treated in such reviews marginally. The only exception is the review by Sawada z covering papers appearing before 1974. The present review, after introducing general concepts, is mostly based on the papers published during the last decade. Generally, in copolymerization reactions, as in homopolymerization, the molar Gibbs free energy can be defined as the difference between the Gibbs free 917