Synthesis of positively charged silica-coated polystyrene microspheres via dispersion polymerization initiated with amphoteric initiator

The positively charged silica-coated polystyrene microspheres are synthesized by dispersion polymerization using an amphoteric initiator, 2,2′-azobis [N-(2-carboxyethyl)-2-2-methylpropionamidine] (HOOC(CH₂)₂HN(HN=)C(CH₃)₂CN=NC(CH₃)₂C(=NH)NH(CH₂)₂COOH. The effects of silica addition time and the amount of silica on the polymerization behavior and the properties of the ultimate particles are investigated in terms of the rate of polymerization, morphology, size distribution, and dispersion stability. It is found that the fastest polymerization is achieved when the silica is present at the beginning of the polymerization and the optimum silica content is 12-15 wt% to monomer. Herein, amphoteric polystyrene microspheres stabilized by positively charged silica can be prepared since the silica serves as an inorganic stabilizer providing electrostatic repulsion. Also, the silica promotes the nucleation, that is, generation of growing particles and also accelerates the rate of polymerization.