Structured Poly(divinylbenzene-co-chloromethylstyrene) Microspheres by Thermal Imprinting Precipitation Polymerization

The formation of monodisperse, crosslinked, thermally inscribed core-shell microspheres by free radical precipitation copolymerization of chloromethylstyrene and divinylbenzene in acetonitrile is reported. The radial density profiles of these microspheres match the thermal profiles used during copolymerization: stepping down the polymerization temperature from 75 degrees C to 65 degrees C several hours into the copolymerization led to core-shell microspheres with porous cores and denser shells, while stepping up the polymerization temperature from 68 degrees C to 78 degrees C during the polymerization led to formation of microspheres with denser cores and more swellable shells. Microsphere size distributions and internal morphologies were studied using optical and transmission electron microscopy. The change in network swellability with temperature was compared with model studies of aggregation of corresponding nanogels, both in acetonitrile and in related solvent systems, as a function of temperature, indicating the theta-temperature for this copolymer/solvent system to be around 30 degrees C. (C) 2015 Wiley Periodicals, Inc.