Efficient Synthesis of Snowman- and Dumbbell-like Silica/Polymer Anisotropic Heterodimers through Emulsion Polymerization Using a Surface-Anchored Cationic Initiator

We report a novel original synthetic route to hybrid dissymmetrical snowman- and dumbbell-like silica/polymer colloidal particles through emulsion polymerization of methyl methacrylate (MMA) or styrene using a bicationic initiator previously anchored on the silica surface. Anistropic particles with a polymer nodule attached to a single silica sphere were successfully obtained in high yield in the presence of a mixture of nonionic and anionic surfactants under optimized initiator concentration conditions. Both nonionic surfactant and cationic initiator were key ingredients in controlling particle morphology as evidenced by transmission electron microscopy. By optimizing the silica content and the surfactant composition, latexes with a latex-to-silica seed number ratio (N-Latex/N-silica) close to 1 were produced using either MMA or styrene as monomers. Their shapes evolved from snowman-like and reverse snowman-like at low and high conversions to dumbbell-like for intermediate conversions. The evolution of particle morphology with time provided insights into the mechanism of composite particles formation.