Reaction parameters in the RAFT mediated dispersion polymerization of styrene

Monodisperse polystyrene (PS) particles were prepared by a living radical dispersion polymerization with a reversible addition-fragmentation chain transfer (RAFT) agent in an ethanol medium. In the presence of RAFT agent, the effects of various reaction parameters on the characteristics of PS particles were systematically investigated. When no RAFT agent was involved, the number-average molecular weight (M-n) of the PS particles increased from 17,800 to 30,000 g/mol, but the weight-average diameter (D-w) decreased from 2.54 to 2.06 mu m with the increase of poly(N-vinylpyrrolidone) content from 4.0 to 16.0 wt %. No correlation between the Mn and the coefficient of variation (CV) was observed. However, when the RAFT concentration varied from 0 to 2.0 wt %, all of the conversion, M-n, D-w CV, and polydispersity index (M-w/M-n) decreased. This indicates that the RAFT agent alters the inverse behavior between the molecular weight (MW) and particle size shown in the conventional dispersion polymerization. (C) 2007 Wiley Periodicals, Inc.