Particle nucleation and growth mechanisms in styrene microemulsion polymerization

A water-insoluble dye was used to study nucleation and growth of particle nuclei in styrene microemulsion polymerizations, stabilized by sodium dodecyl sulfate/1-pentanol and initiated by sodium persulfate (SPS). Both the rate of polymerization and concentration of latex particles increase with an increase in the initial SPS concentration ([SPS](0)). Least-squares best fitting experimental data with a modified Morgan-Nomura model leads to the conclusion that the limited flocculation of latex particles plays an important role in the reaction system. The weight percentage of dye incorporated into latex particles (P-dye) increases with the progress of polymerization. This implies that particle nucleation takes place continuously throughout the reaction. At constant monomer conversion, Pdye decreases with increasing [SPS](0), which is attributed to the increased probability of particle formation in the aqueous phase with [SPS](0). Measurements of zeta potential of latex particles and polymer molecular weight were also conducted to gain a better understanding of polymerization mechanisms and kinetics.