DYNAMIC BEHAVIOR IN POLY(VINYL ACETATE) GELS AND SOLUTIONS

Relaxation time distributions from dynamic light scattering measurements on poly(vinyl acetate) solutions and gels prepared by acetylation of PVA polymer and gels are reported. The solvents are acetone and methanol (THETA-solvent at 6-degrees-C). In all cases, the gels display sharply unimodal autocorrelation curves. It is significant that the slow (probably viscoelastic) modes observed in semidilute THETA-solutions of high molecular weight chains are not observed in the gels. All gels contain significant proportions of static scatterers. Behavior in acetone solutions is more complex: with lower solvent quality at 6-degrees-C, the correlation curves for the solutions become bimodal due to the presence of clusters. However, at THETA-conditions in methanol solutions the distributions are essentially unimodal. At a given concentration, the dynamic correlation length (xi-H) in the solution exceeds that for the corresponding gel. The xi-H-concentration exponents for solutions and gels are closely similar. Below the THETA-temperature in methanol, interchain association leads to large aggregates in the solution that is inhibited by cross-linking in the corresponding gel.