A Facile One-Step Approach toward Polymer@SiO2 Core–Shell Nanoparticles via a Surfactant-Free Miniemulsion Polymerization Technique

We present a surfactant-free miniemulsion process for the preparation of monodisperse polystyrene@SiO2 nanoparticles with a well-defined core shell structure. The strategy utilizes a silica precursor polymer, hyperbranched polyethoxysiloxane (PEOS), as a sole miniemulsion stabilizer due to its water insolubility and at the same time pronounced amphiphilicity induced by hydrolysis at the oil/water interface. The core shell particles are obtained by emulsifying a PEOS/styrene mixture in water and subsequent heating to initiate polymerization. As the polymerization proceeds, driven by osmotic pressure and incompatibility with polystyrene, PEOS macromolecules migrate continuously toward the oil/water interface where sol gel reaction takes place. As soon as the polymerization is completed, PEOS is fully expelled from the polymer phase and is converted to silica on the polystyrene surface. This method allows an easy control of silica shell thickness by varying the PEOS concentration. The particle size, on the other hand, can be regulated not only by the shearing force but also by the pH of the aqueous medium. This process offers a new type of miniemulsion polymerization technique for the preparation of composite polymer particles that is facile, low cost, highly scalable, and environmentally friendly.