A mathematical model for prediction of monomer conversion, of particle number and of the evolution of the particle size distribution (PSD) in dispersion polymerization is developed. Despite being completed very early during the polymerization process (monomer conversion <1%), nucleation of new particles is the most important factor affecting the PSD. In order to describe the particle nucleation phenomena, the mechanism of homogeneous coagulative nucleation is considered. According to this mechanism, polymer chain aggregates can either coagulate and grow, to give birth to new polymer particles (particle nucleation), or be captured by existing polymer particles. Two sets of population balance equations are used: one for the aggregates, and a second one for the stable polymer particles. It is shown that the model is able to describe the dispersion polymerization of styrene in ethanol and the formation of micron-size monodisperse polymer particles.

Particle size distribution (PSD) of polystyrene particles produced by suspension polymerization is of fundamental importance in determining suspension stability and product quality attributes. Within a population balance framework, a model is proposed for suspension polymerization reactors to describe the evolution of the PSD. The model includes description of breakage and coalescence rates in terms of reaction kinetics and rheology of the dispersed phase. The model is validated with experimental data of styrene suspension polymerization.