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 been studied for styrene-acrylonitrile, styrene-methacrylic acid, styrene-acrylamide, styrene-acrylic acid, styrene-butyl methacrylate, vinyl acetate-2-methyl-5-vinyl-pyridine and vinyl acetate-2-vinyl pyridine. In the simplest cases, the copolymer composition and microstructure can be described by the May-Lewis model with the apparent or effective monomer reactivity ratios: r(2) = r(2)(0) gamma, r(1) = r(1)(0)/gamma, where r(1)(0), r(2)(0) are ideal reactivity ratios defined by the monomer structure, gamma is the monomer distribution coefficient. The most fundamental effect of preferential solvation is the relation between the copolymer composition and molecular weight caused by the dependence of preferential solvation coefficient lambda upon the length of a growing chain. This dependence leads to two previously unknown types of chemical heterogeneity of low-conversion copolymers, viz. intra- and intermolecular gradient chemical heterogeneity. Copyright (C) 1996 Elsevier Science Ltd