Formation of Monodisperse Polymer@SiO₂ Core–Shell Nanoparticles via Polymerization in Emulsions Stabilized by Amphiphilic Silica Precursor Polymers: HLB Dictates the Reaction Mechanism and Particle Size

Heterophase polymerization is the main tool to prepare polymer dispersions. In this work, we report on a new type of heterophase polymerization that allows synthesizing in one step monodisperse polymer@SiO₂ core–shell particles in a wide size range from tens to hundreds of nanometers. The strategy utilizes amphiphilic silica precursor polymers, namely, PEGylated polyethoxysiloxanes, which can reduce the interfacial tension between oil and water close to zero. An oil phase containing such a kind of surfactants can be emulsified in water spontaneously or just under low-energy stirring. Polymerization of styrene in the resulting emulsions using an oil-soluble initiator leads to the formation of monodisperse polystyrene@SiO₂ particles, whose size can be precisely adjusted by the PEGylation degree of precursor molecules and can reach as small as 30 nm. It is demonstrated that the PEGylation degree, that is, the HLB, also dictates the reaction mechanism that varies from suspension polymerization with breakup of monomer droplets and miniemulsion polymerization to microemulsion polymerization leading to exact “copying” of initial emulsion droplets. This technique paves a new avenue for simple, controllable, and environmentally friendly production of dispersions of composite polymer particles.