Synthesis of poly(ethylene oxide)-based thermoresponsive block copolymers by RAFT radical polymerization and their uses for preparation of gold nanoparticles

The amphiphilic block copolymers were synthesized by reversible addition fragmentation chain transfer (RAFT) radical polymerization of N-isopropylacrylamide (NiPAM) using poly(ethylene oxide) (PEO)-based xanthate-type of RAFT agent and 2,2′-azobisisobutyronitrile (AIBN) in aqueous media at 85 °C for 12 h. The PEO-based RAFT agent could be easily synthesized by the reaction of terminally brominated PEO with o-ethylxantic acid potassium salt. The yield was over 95 mol% on the basis of incipient amount of polymeric alkoxide obtained from a ring opening polymerization of ethylene oxide. The different molecular weights of the poly(N-isopropylacrylamide) (PNiPAM) fragments of poly(ethylene oxide-b-N-isopropylacrylamide) played an important role to exhibit different thermoresponsive behaviors. The resulting block copolymers were successfully used as polymeric stabilizers to prepare water-soluble nano-sized gold particles. All the materials were characterized by the combination of 1H NMR, SEC, TEM, and XRD analyses.