Effect of acrylic acid and hydroxyethyl methacrylate modified nano-SiO₂ particles on poly(methyl methacrylate-hydroxyethyl methacrylate) soap-free emulsion polymerization

Nano-SiO₂ powder was modified with acrylic acid (AA) and hydroxyethyl methacrylate (HEMA), respectively. The kinetics of the soap-free emulsion polymerization of methyl methacrylate (MMA) and HEMA in the presence of unmodified or modified nano-SiO₂ particles was investigated. The structure of the nano-SiO₂ particles and the Poly(MMA-HEMA) composite emulsion was characterized by Fourier transform infrared spectroscope (FT-IR). The particle size and size distribution of the emulsion, the morphology of emulsion particle, the surface tension, and ionic conductivity of these systems before and after polymerization were determined. The IR spectra showed that the organic modifiers were incorporated onto the surface of the nano-particles. In addition, the solid content and monomer conversion of the Poly(MMA-HEMA) composite emulsion with modified nano-SiO₂ are higher than that with original inorganic particles. The particle size became smaller and the particle distribution narrowed after applying the modified nano-SiO₂ particles. The SEM observation demonstrated that the shapes of these emulsion particles were uniform sphere. The surface tension and ionic conductivity increased significantly after polymerization.