Emulsion polymerization of an epoxy-acrylate emulsion stabilized with polyacrylate. II. Using the results of statistically designed experiments to deduce a possible polymerization mechanism

7Epoxy-acrylate composite emulsions such as the one in this study can be us ed as metal coatings, etc. Many factors can influence the final quality of the product, and it is the aim of this study to highlight some of these fac tors. Statistically designed experiments were performed to investigate the influence of monomer level, the polymeric dispersant level, epoxy level, an d the initiator level on particle size (light scattering), particle size di stribution, and fractional conversion. It was found that the monomer level significantly influenced particle size and particle size distribution. The epoxy level and the monomer level influenced fractional conversion signific antly. A qualitative model based on these observations is put forward to de scribe the mechanism of particle formation and polymerization. This model s tates that the high internal viscosity of the initial dispersed epoxy phase inhibits the formation of smaller particles and accelerates the polymeriza tion rate during the first few minutes of polymerization by inducing a gel effect that inhibits termination and chain transfers of radical species. Th e addition of a monomer lowers the internal viscosity of the particles and causes them to break up into droplets containing dissolved epoxy, polyacryl ate, and monomer. At the same time, radical species inside the smaller drop lets can now undergo termination and chain transfer reactions. To confirm t his model, polyacrylates of varying molecular masses were synthesized. Vari ation of the molecular masses of these polyacrylates resulted in variation in the viscosity of the dispersed phase. Polymerizations conducted with the polyacrylates confirmed the model observations. A dispersed phase with a h igh viscosity results in an increased polymerization rate, larger overall p article size, and a higher mass average molecular mass copolymer compared t o lower molecular mass polyacrylates. (C) 2000 John Wiley & Sons, Inc.