Efficient synthesis of poly(2-hydroxypropyl methacrylate)-silica colloidal nanocomposite particles via aqueous dispersion polymerization

Colloidally stable poly(2-hydroxypropyl methacrylate)-silica nanocomposite particles can be efficiently prepared by aqueous dispersion polymerization at 60 °C using a binary mixture of an ultrafine aqueous silica sol and poly(N-vinylpyrrolidone) [PVP] as the stabilizer system. Optimization of the initial silica sol concentration allows relatively high silica incorporation efficiencies (close to 100%) to be achieved. The key to the formation of colloidally stable nanocomposite particles is the judicious choice of a suitable anionic initiator, PVP and a commercial 20 nm aqueous silica sol. In contrast, other formulations typically lead to either coagulation or flocculation. Such purified poly(2-hydroxypropyl methacrylate)-silica nanocomposite particles can have relatively narrow particle size distributions, with mean diameters typically varying from 480 to 900 nm as judged by dynamic light scattering (DLS), and with mean silica contents ranging from 10 to 22% by mass. The nanocomposite particles have a well-defined ‘core-shell’ morphology with a silica-rich surface, but a significant fraction of silica appears to be located within the interior of the nanocomposite particles.