Double in Situ Preparation of Raspberry-like Polymer Particles.

Well-defined raspberry-like poly(styrene- co-4-vinylpyridine)-SiO2 nanocomposite particles with a diameter of around 200 nm were easily prepared by a double in situ process in nanoemulsion with the water-soluble dye Eosin Y as the stabilizer. During radical polymerization of the nanodroplets comprising styrene, 4-vinylpyridine (4-VP), and tetraethoxysilane (TEOS), the silane phase is expelled from the polymer phase to the oil/water (o/w) interface. In the later polymerization stage, SiO2 nanoparticles with a size of around 25 nm were produced via the in situ sol-gel reaction of TEOS at the o/w interface promoted by the negatively charged dye. The pyridine moieties in the copolymer fix the SiO2 nanoparticles on the surface of the polymer particles by electrostatic interactions without any sign of free unbound silica particles as proven by transmission electron microscopy.