Synthesis of alkyne functional cyclic polymers by one-pot thiol-ene cyclization

We demonstrate the versatility of polymers made by reversible addition-fragmentation chain transfer (RAFT) to be cyclized in one-pot using the thiol-ene reaction. Hexylamine was used to convert the RAFT end-group to a free thiol which rapidly reacted with the acrylate on the other chain-end of the polymer to form a cyclic polymer. This procedure allowed a wide range of polymers (polystyrene, poly(tert-butyl acrylate), poly(N-isopropylacrylamide) and poly(N,N-dimethylacrylamide)) to be cyclized with close to 80% cyclic formation. These cyclic polymers all contained a reactive alkyne functional group. Attempts to use the thio-bromo reaction to cyclize polystyrene were not as successful as the thiol-ene cyclization reaction, producing less than 25% cyclic.