Nucleation of particles in seeded emulsion polymerization of vinyl acetate with poly(vinyl alcohol) as emulsifier

Abstract

Seeded emulsion polymerizations of vinyl acetate with and without poly(vinyl alcohol) were carried out in a batch reactor. Two types of poly(vinyl alcohol) (different molecular weights but the same degree of hydrolysis) have been investigated. In the absence of poly(vinyl alcohol) no new nucleation was observed, while in its presence new particles were formed, giving a bimodal particle size distribution. The number of new particles was greater with the higher-molecular-weight poly(vinyl alcohol). Compared with emulsifier-free seeded emulsion polymerization, the reaction rate increased when the higher-molecular-weight poly(vinyl alcohol) was used. However, the polymerization rate decreased when the lower-molecular-weight poly(vinyl alcohol) was applied. It was also shown that for seeded emulsion polymerization of vinyl acetate in the absence of poly(vinyl alcohol), the kinetics follows Smith-Ewart case III theory. These observations are discussed and a theory is proposed to explain the effect of macromolecular emulsifier on the nucleation of particles in seeded emulsion polymerization. This theory involves nucleation of new particles via precipitation of “copolymer” poly(vinyl alcohol)-poly(vinyl acetate) radicals in the water phase.