Preparation of raspberry-like polymer/silica nanocomposite microspheres via emulsifier-free polymerization in...

Raspberry-like polymer/silica nanocomposite microspheres were prepared by emulsifier-free copolymerization of styrene (St) with butyl acrylate (BA) in the presence of 20 nm silica nanoparticles in water/acetone media. A cationic monomer, 2-(methacryloyl)ethyltrimethylammonium chloride (MTC), was used as comonomer and nanosilica particles were adsorbed onto the growing latex core via the electrostatic interaction between negatively charged silica particles and positively charged polymer particles. The average particle sizes and the final silica contents of the nanocomposite microspheres ranged from 200 to 500 nm and 20 to 40 wt%, respectively, depending on the reaction conditions. The solid content of the obtained dispersions could be adjusted between 10 and 25 wt%. The influence of some synthetic parameters, for instance, the ratio of acetone/water, initial silica amount, the mass ratio of the St/BA, MTC, and the APS concentration on the polymerization stability, the average particle size, silica content, and morphology of the composite microspheres, were studied here in detail. It was found that the addition of acetone to the continuous phase resulted in smaller particle sizes and for the lower dielectric medium electrostatic repulsion becomes larger; hence coagulative nucleation is reduced compared to that in aqueous media.