Synthesis and Characterization of Film-Forming Colloidal Nanocomposite Particles Prepared via Surfactant-Free Aqueous Emulsion Copolymerization

The efficient synthesis of film-forming colloidal nanocomposite particles is described. A 50:50 mass ratio of styrene and n-butyl acrylate is statistically copolymerized using a cationic azo initiator at 60 °C under aqueous emulsion polymerization conditions in the presence of a commercially available glycerol-functionalized ultrafine silica sol. This new formulation leads to the production of copolymer/silica particles with relatively narrow size distributions and a well-defined “core−shell” morphology. These nanocomposite particles contain up to 43% silica by mass, and the silica aggregation efficiency can exceed 95%, so very few nonaggregated silica nanoparticles remain in solution after the in situ copolymerization is conducted. Upon drying these dispersions, highly transparent free-standing nanocomposite films are obtained. Control experiments confirm the importance of using the cationic azo initiator in combination with the glycerol-functionalized silica sol. Moreover, it is also shown that simple a...