Thermoresponsive Amphiphilic Block Copolymer-Stablilized Gold Nanoparticles: Synthesis and High Catalytic Properties

A series of novel well-defined 8-hydroxyquinoline (HQ)-containing thermoresponsive amphiphilic diblock copolymers {poly(styrene- co-5-(2-methacryloylethyloxy-methyl)-8-quinolinol)- b-poly( N-isopropylacrylamide) P(St- co-MQ)- b-PNIPAm (P1,2), P(NIPAm- co-MQ)- b-PSt (P3,4)} and triblock copolymer poly( N-isopropylacrylamide)- b-poly(methyl-methacrylate- co-5-(2-methacryloylethyloxymethyl)-8-quinolinol)- b-polystyrene PNIPAm- b-P(MMA- co-MQ)- b-PSt (P5) were prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization, and their self-assembly behaviors were studied. Block copolymer P1-P5-stabilized gold nanoparticles (Au@P1-Au@P5) with a small size and a narrow distribution were obtained through the in situ reduction of gold precursors in an aqueous solution of polymer micelles with HQ as the coordination groups. The resulting Au@P nanohybrids possessed excellent catalytic activity for the reduction of nitrophenols using NaBH₄. The size, morphology, and surface chemistry of Au NPs could be controlled by adjusting the structure of block polymers with HQ in different block positions, which plays an important role in the catalytic properties. It was found that longer chain lengths of hydrophilic or hydrophobic segments of block copolymers were beneficial to elevating the catalytic activity of Au NPs for the reduction of nitrophenols, and the spherical nanoparticles (Au@P5) stabilized with triblock copolymers exhibit higher catalytic performance. Surprisingly, the gold nanowires (Au@P4) produced with P4 have the highest catalytic activity due to a large abundance of grain boundaries. Excellent thermoresponsive behavior for catalytic reaction makes the as-prepared Au@P hybrids an environmentally responsive nanocatalytic material.