Pickering emulsion polymerization kinetics of styrene: Comparison of bare and surface modified SiO2 nanoparticles

Abstract

ABSTRACTA step towards the understanding of some mechanistic events occurring in the styrene Pickering emulsions, using a SiO2 dispersion, is presented. Polymerizations at 80°C with different levels of a water soluble initiator were performed. The emulsion polymer content was ca. 15% with conversions close to 90%. With conversion and particle size measurements, the particle density was estimated for bare and surface modified SiO2 particles. Then, the average number of radicals per particle was inferred, yielding a pseudo-bulk type polymerization. It was found that bare SiO2 nanoparticles do not participate in the nucleation mechanism; however, they, along with the initiator, promote an enhanced oligomer coagulation. On the other hand, the hexadecyltrimethylammonium bromide modified SiO2 nanoparticles do participate in the nucleation and coagulation mechanisms, yielding more stable and smaller poorly-covered polymer particles. This approach allowed untangling some events such as: particle nucleation, radical entry to particles, particle density, coagulation and vitreous and Trommsdorff effects.