Synthesis of Silica Particles Grafted with Well-Defined Living Polymeric Chains by Combination of RAFT Polymerization and Coupling Reaction

A combinatorial approach based on reversible addition-fragmentation chain transfer (RAFT) polymerization and coupling reaction was used to prepare well-defined silica-polymer hybrids. Chain-end-functionalized homopolymers were synthesized by RAFT polymerization of vinyl monomers such as methyl acrylate, butyl acrylate, N,N-dimethylacrylamide, N-isopropylacrylamide, N-acrylomorpholine, methyl methacrylate, and styrene mediated by S-methoxycarbonylphenylmethyl S-trimethoxysilylpropyltrithiocarbonate in toluene or dioxane at 60 degrees C, and di-, tri-, and tetrablock copolymers were further synthesized by successive chain extension polymerization. These polymers comprising a trimethoxysilane functionality in the chain end were then grafted to the surface of flash silica by coupling reaction between trimethoxysilane and hydroxyl groups. IR and thermogravimetric analyses results indicated the grafting ratios of polymeric chains on the surface of silica were relatively high. The grafted polymeric chains were cleaved from the surface of silica by aminolysis, and gel permeation chromatography results revealed all the grafted polymers possessed low polydispersity (typically less than 1.2)and molecular weight similar to that of the "as-prepared" polymers. Furthermore, the solid-supported polymeric chains were almost 100% living, evident from highly efficient chain extension polymerization to prepare well-defined block copolymers grafted onto silica particles.