Preparation of hyperstar polymers with encapsulated Au25(SR)18 clusters as recyclable catalysts for nitrophenol reduction

Abstract

A robust approach is developed to prepare hyperstar polymer–Au₂₅(SR)₁₈ nanocomposites for catalysis. The synthesis started with atom transfer radical copolymerization of an inimer with a cyclic disulfide-containing methacrylate monomer in a microemulsion to produce hyperbranched copolymers with high molar mass, low polydispersity, and a vital fraction of dangling disulfide groups. The core–shell structured hyperstar polymers were then prepared using hyperbranched copolymers as macroinitiators to polymerize oligo(ethylene glycol) methyl ether methacrylate (M_n = 500) and grow the radiating arms. The hyperstar polymers with disulfide groups were proved to efficiently encapsulate Au₂₅(SR)₁₈ nanoclusters through ligand exchange without destroying the fine structure of the Au₂₅(SR)₁₈ clusters. The obtained hyperstar-Au₂₅(SR)₁₈ nanocomposites showed great stability with no size change after a three-month shelf storage. They were used as efficient catalysts for the catalytic reduction of 4-nitrophenol by NaBH₄, showing convenient recovery and reuse without losing catalytic efficiency.