Enhanced droplet nucleation in styrene miniemulsion polymerization. 2. Polymerization kinetics of homogenized emulsions containing predissolved polystyrene

The effect on the subsequent polymerization of predissolving polystyrene into the styrene monomer prior to its homogenization via a Microfluidizer was studied. It was noted that particle nucleation shifted from either the micelles or the aqueous phase to the monomer droplets when polymer is predissolved. This shift to the droplets was a result of the droplets being preserved by the presence of the polymer in the initial droplet distribution. When homogenized emulsions do not; contain predissolved polymer, the majority of the droplets disappear by Ostwald ripening. Homogenized emulsions that contain predissolved polymer exhibit higher rates of polymerization and numbers of particles nucleated compared to similar systems not containing predissolved polymer. This enhancement in the kinetics was similar (although to a slightly lesser extent) to what was noted for miniemulsions containing cetyl alcohol as cosurfactant. Since both homogenized emulsion and miniemulsion systems (using cetyl alcohol as the cosurfactant) initially possess unstable droplet size distributions, the enhancement in both of these systems was taken as evidence that "enhanced droplet nucleation" caused by predissolving polymer is primarily a result of preserving the droplet number due to the presence of the polymer.