ABSTRACT

Suspension polymerization is widely used for the preparation of microsphere and microcapsules for many applications. However, the formation of secondary particle byproducts decreases drastically the obtained microsphere yield and microcapsule shell strength. It is surprisingly finding that the secondary particles were not observed in the preparation of polymethyl methacrylate particles by suspension polymerization using particulate surfactant called Pickering emulsion. Therefore, in this work, the mechanism of secondary particle formation during suspension polymerization was investigated using various surfactants (zinc oxide, titanium dioxide, and silica nanoparticles compared to polyvinyl alcohol) and monomers (styrene, methyl methacrylate, and methyl acrylate) with different water solubilities. Results showed that submicrometer-sized secondary particles were still formed by homogeneous nucleation mainly due to radical exit from the monomer droplets. However, the formed secondary particles were unstable and then adsorbed on the main microsphere surface. The number of secondary particles increased when monomers with higher water solubility were used.

摘要

悬浮聚合被广泛用于制备微球和微胶囊，用于许多应用。然而，次级颗粒副产物的形成大大降低了获得的微球产率和微胶囊壳强度。令人惊讶地发现，在使用称为Pickering乳液的颗粒表面活性剂通过悬浮聚合制备聚甲基丙烯酸甲酯颗粒中未观察到次级颗粒。因此，在这项工作中，研究了使用各种表面活性剂（与聚乙烯醇相比，氧化锌，二氧化钛和二氧化硅纳米粒子，与聚乙烯醇相比）和单体（苯乙烯，甲基丙烯酸甲酯和丙烯酸甲酯）在悬浮聚合过程中形成次级颗粒的机理。溶解度。结果表明，亚微米级的次级颗粒仍然是通过均匀成核形成的，这主要是由于自由基从单体液滴中逸出所致。然而，形成的次级颗粒是不稳定的，然后被吸附在主微球表面上。当使用具有较高水溶性的单体时，二次粒子的数量增加。