Preparation of nano-sized silica/poly(methyl methacrylate) composite latexes by heterocoagulation: comparison of three synthetic routes

Continuing earlier work, 2,2'-azobis(isobutyramidine) dihydrochloride (AIBA) was used as a cationic initiator to generate positively charged polymers, and promote interaction of these polymers with the negatively charged surface of colloidal silica particles in aqueous solution. Three different synthetic routes have been investigated. In a first route, emulsion polymerization of MMA, initiated by AIBA, was performed directly in an aqueous suspension of the silica beads using a non-ionic polyoxyethylenic surfactant (NP30). In a second route, AIBA was first adsorbed on the silica surface, and the free amount of initiator was discarded from the suspension. The silica-adsorbed AIBA adduct was suspended in water with the help of surfactant, and used to initiate the emulsion polymerization of MMA. In a third route, cationic PMMA particles were synthesized separately and subsequently adsorbed on the silica surface. Whatever the approach used for their elaboration, the colloidal nanocomposites were shown to exhibit a raspberry-like morphology. Quantitative determination of the amount of surface polymer enabled us to evaluate the efficiency of the heterocoagulation process and establish a comparison among the three synthetic routes. (C) 2004 Society of Chemical Industry.