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 in to the styrene monomer prior to its homogenization via a Microfluidizer was studied. It was noted that particle nucleation shifted from either the mic elles or the aqueous phase to the monomer droplets when polymer is predisso lved. This shift to the droplets was a result of the droplets being preserv ed by the presence of the polymer in the initial droplet distribution. When homogenized emulsions do not; contain predissolved polymer, the majority o f the droplets disappear by Ostwald ripening. Homogenized emulsions that co ntain predissolved polymer exhibit higher rates of polymerization and numbe rs of particles nucleated compared to similar systems not containing predis solved polymer. This enhancement in the kinetics was similar (although to a slightly lesser extent) to what was noted for miniemulsions containing cet yl alcohol as cosurfactant. Since both homogenized emulsion and miniemulsio n systems (using cetyl alcohol as the cosurfactant) initially possess unsta ble droplet size distributions, the enhancement in both of these systems wa s taken as evidence that "enhanced droplet nucleation" caused by predissolv ing polymer is primarily a result of preserving the droplet number due to t he presence of the polymer.