Isoprene polymerization via reversible addition fragmentation chain transfer polymerization

Until recently, the primary living radical polymerization method available for preparing polyisoprene was nitroxide-mediated radical polymerization, with reversible addition-fragmentation chain transfer polymerization being applied only in a few cases within the last couple of years. We report here the preparation of polyisoprene by RAFT in the presence of the trithiocarbonate transfer agent S-1-dodecyl-S '-(r,r '-dimethyl-r ''-acetic acid)trithiocarbonate and t-butyl peroxide as the radical initiator. The kinetics of this polymerization at an optimized temperature of 125 degrees C and radical initiator concentration of 0.2 equiv relative to transfer agent have been studied in triplicate and demonstrate the living nature of the polymerization. These conditions resulted in polymers with narrow polydispersity indices, on the order of 1.2, with monomer conversions up to 30%. Retention of chain-end functionality was demonstrated by polymerizing styrene as a second block from a polyisoprene macrotransfer agent, resulting in a block copolymer presenting a unimodal gel permeation chromatogram, and narrow molecular weight distribution.