Preparation of poly(methyl methacrylate)–TiO2 nanoparticle composites by pseudo-dispersion polymerization of methyl methacrylate in supercritical CO2

Poly(methyl methacrylate) (PMMA)–TiO2 nanoparticle composites and poly(styrene) (PS)–TiO2 nanoparticle composites are synthesized by pseudo-dispersion polymerization in supercritical carbon dioxide (CO2) in the presence of 3-(trimethoxysilyl)propylmethacrylate (MPS)-modified TiO2 nanoparticles. These composites are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, and laser diffraction particle size analysis. On the polymerization of PMMA, the product composites were microparticles, and were PMMA shell on TiO2 core particles. The formation mechanism of these composite particles in supercritical CO2 is analyzed by the FT-IR analysis and turbidity measurement of MPS-modified TiO2. It is found that MPS-modified TiO2 serves as not only an inorganic filler but also an effective stabilizer for the polymerization of PMMA in supercritical CO2. On the other hand, the polymerization of PS yields a bulk solid. The morphologies of the PMMA and PS composites are found to be quite different from each other, presumably due to the difference in the interaction mechanisms between the carbonyl group of the monomers and the hydroxyl group on the TiO2 surface. The degree of aggregation of PMMA–TiO2 composite particles increases with the MPS-modified TiO2/MMA monomer ratio.