Gel Formation and Structure of Junctions in Poly(vinyl alcohol)–Water Systems

Abstract

The main purpose of this investigation was to elucidate the mechanism of gelation of poly(vinyl alcohol)-water systems and the structure of junctions in gel networks. Changes of gel rigidities were measured as a function of gelling time at the temperatures of 30-80°C for four samples of different tacticities, and the numbers of junctions in the gel were calculated using the theory of rubber elasticity. The formation of junctions can be treated as the binary association of free cross-linking sequences with the activation energy of 13 kcal/mol. The study of the correlation between gelling temperatures and melting temperatures of gels shows that the junctions formed at a given temperature should be treated as multitudinous in structure and the copolymeric character of atactic poly(vinyl alcohol) chains should be considered. The structures of junctions for various gelling temperatures are discussed, assuming that cross-linking loci in poly(vinyl alcohol) chains are syndiotactic sequences of different sequence lengths.