Synthesis of α,ω-dimercapto poly(N-isopropylacrylamides) by RAFT polymerization with a hydrophilic difunctional chain transfer agent

A new hydrophilic difunctional reversible addition-fragmentation chain transfer (RAFT) agent, diethylene glycol di(2-(1-isobutyl)sulfanylthiocarbonylsulfanyl-2-methylpropionate) (DEGDIM) was synthesized and shown to be effective in imparting living characteristics to the radical polymerization of N-isopropylacrylamide (NIPAM), providing a route to telechelic poly(N-isopropylacrylamides) (PNIPAM) of predictable molecular weights and narrow molecular weight distributions. The thiocarbonylthio end groups were transformed into thiol groups via aminolysis with near quantitative yields, as determined by a thiol-specific quantitative UV absorbance assay. By using a pyrene-substituted initiator, bis(N-(1-pyrenylbutyl))-4,4'-azobis-(4-cyanopentanamide) (BPAC), it was found that the amount of initiator-derived polymer chains in the DEGDIM mediated polymerization of NIPAM was negligible (similar to 1%) compared to the amount of polymer chains derived from DEGDIM, the difunctional chain transfer agent. These results support the theoretical calculations and confirm the high purity of alpha,omega-dithiol telechelic hydrosoluble polymers prepared by the RAFT polymerization process.