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 °C to 65 °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 °C to 78 °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 °C. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 1159–1166 Varying the temperature during the growth phase of crosslinking precipitation polymerizations near the theta‐condition can lead to different types of core‐shell structures. This is attributed to temperature‐dependent crosslink densities of the growing surface gel layer being deposited, resulting in differential swellabilities of core versus shell domains. This article illustrates the process, and introduces model experiments that may help screen for suitable solvents.