Facile synthesis of thermo-responsive episulfide group-containing diblock copolymers as robust protecting ligands of gold nanoparticles for catalytic applications

We herein report the synthesis of well-defined novel thermo-responsive diblock copolymers, poly(N-isopropylacrylamide-co-2,3-epithiopropyl methacrylate)-block-poly(poly(ethylene glycol) methyl ether methacrylate) P(NIPAM-co-ETMA)-b-P(PEGMA), bearing an episulfide moiety as a ligand via reversible addition fragmentation chain transfer (RAFT) polymerization, followed by assembly into micelles in aqueous solution. The diblock copolymer-stabilized gold nanoparticles (Au NPs@P) could be further obtained by a Au³⁺-induced episulfide opening reaction and in situ reduction of HAuCl₄. The block copolymer played a great role in the stabilization of Au NPs. These Au NPs@P were employed as an efficient catalyst and presented excellent catalytic activity to reduce 4-nitrophenol to 4-aminophenol. The content of PETMA segments, different ratios of Au atoms to sulfur atoms (MRs) of Au NPs@P1 and the dosage of catalytic carriers and reductants had varying degrees of influence on the catalytic activity. It was found that the catalytic activity of Au NPs@P increased with the decreasing content of PETMA segments. The size of the diblock copolymer-stabilized Au NPs also increased and the catalytic activity became higher with the increase of the MRs. The Au NPs@block copolymer with PNIPAM blocks also exhibited excellent temperature-responsive behavior for the catalytic reduction of 4-nitrophenol.