THE EFFECT OF MONOMER PREFERENTIAL SOLVATION IN RADICAL COPOLYMERIZATION - REACTIVITY RATIOS AND COMPOSITIONAL DISTRIBUTION

The effects of preferential solvation of monomers by polymer coils in homogeneous radical copolymerization at low conversion (5-7%) have bee n studied for styrene-acrylonitrile, styrene-methacrylic acid, styrene -acrylamide, styrene-acrylic acid, styrene-butyl methacrylate, vinyl a cetate-2-methyl-5-vinyl-pyridine and vinyl acetate-2-vinyl pyridine. I n the simplest cases, the copolymer composition and microstructure can be described by the May-Lewis model with the apparent or effective mo nomer reactivity ratios: r(2) = r(2)(0) gamma, r(1) = r(1)(0)/gamma, w here r(1)(0), r(2)(0) are ideal reactivity ratios defined by the monom er structure, gamma is the monomer distribution coefficient. The most fundamental effect of preferential solvation is the relation between t he copolymer composition and molecular weight caused by the dependence of preferential solvation coefficient lambda upon the length of a gro wing chain. This dependence leads to two previously unknown types of c hemical heterogeneity of low-conversion copolymers, viz. intra- and in termolecular gradient chemical heterogeneity. Copyright (C) 1996 Elsev ier Science Ltd