Polymer particle formation in styrene polymerization in aqueous media at low surfactant concentrations.

Emulsion polymerizations of styrene were carried out in the absence and presence of a surfactant and the number of polymer particles was measured mainly in a range of surfactant concentrations up to the critical micelle concentration with a change in initiator concentration. Experimental results for the number of polymer particles in the absence of the surfactant were compared with predictions from a homogeneous nucleation model which includes the assumption that the rate of radical entrance into the polymer particles is proportional to particle surface area uncovered by ionic end-groups of polymers contained in the polymer particles. The model also takes into account electrostatic effects on radical entrance into the polymer particles and coagulation between polymer particles. The experimental results in the absence of the surfactant compared well with the predictions. The model was extended to the reaction system in the presence of the surfactant, taking into consideration surfactant adsorption to the polymer particles and the adhesion of surfactant molecules to growing radicals. The model predicted well the tendency of the experimental results of the number of particles.