Reversible addition-fragmentation chain transfer graft polymerization mediated by fumed silica supported chain transfer agents

In this study, the Z supported reversible addition-fragmentation chain transfer (RAFT) graft polymerization to prepare silica-polymer hybrids was investigated. Two chain transfer agents (CTAs), S-benzyl S'-trimethoxysilylpropyltrithiocarbonate and S-methoxycarbonylphenylmethyl S'-trimethoxysilylpropyltrithiocarbonate, were synthesized and covalently attached to the surface of fumed silica. The resultant silica supported CTAs were used to mediate RAFT polymerization of vinyl monomers such as methyl acrylate, butyl acrylate, N,N-dimethylacrylamide, N-isopropylacrylamide, methyl methacrylate, and styrene in the presence of a free CTA to synthesize polymer grafted silica particles. Effects of CTA loadings on solid supports, types of free CTAs, and reaction media on graft polymerization were investigated in detail. Under optimal conditions such as using 2-(2-cyanopropyl)dithiobenzoate as a free CTA and controlling the polymerization at a low conversion (typically less than 40%), well-defined polymeric chains with polydispersity indices less than 1.2 and chain lengths similar to those of free polymers could be successfully grafted onto the surface of fumed silica, and relatively high grafting ratios could be achieved, as is evident from GPC, FT-IR, and TGA analyses. As compared with polymerization in toluene, RAFT graft polymerization of methyl acrylate in methanol could afford longer grafted chain lengths and significantly increased grafting efficiency at identical conditions, suggesting the potential effects of reaction media on graft polymerization.