Gelation and hollow particle formation in nitroxide-mediated radical copolymerization of styrene and divinylbenzene in miniemulsion

Abstract

Network formation in the nitroxide-mediated cross-linking copolymerization of styrene and divinylbenzene (3 or 8.2 mol-% relative to total monomer) using the nitroxide 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) at 125 °C can proceed markedly differently in aqueous miniemulsion compared to the corresponding solution polymerization depending on the organic-phase composition. When the organic phase comprises 54 vol-% of the hydrophobe tetradecane, gelation occurs at much lower conversion in miniemulsion than in solution, and at significantly lower conversion than predicted by Flory-Stockmayer gelation theory. This is proposed to be a result of an effect of the oil-water interface, whereby the concentration of polymer with pendant unsaturations is higher near the interface than in the particle interior. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA.