Comparative Study of Amphiphilic Hyperbranched and Linear Polymer Stabilized Organo-Soluble Gold Nanoparticles as Efficient Recyclable Catalysts in the Biphasic Reduction of 4-Nitrophenol

A series of organo-soluble spherical gold nanoparticles (AuNPs) were prepared through the reduction of HAuCl4 by NaBH4 in the presence of amphiphilic hyperbranched polymers that had a hydrophilic hyperbranched polyethylenimine core and a hydrophobic shell formed by many palmitamide (C16) chains. For comparison, the corresponding linear polymeric analog derived from linear polyethylenimine was also used to prepare the organo-soluble AuNPs. The obtained AuNPs were characterized by transmission electron microscopy. It was found that higher feed ratio of polymer to HAuCl4 and utilization of polymers with higher C16 density usually resulted in smaller AuNPs with relatively lower polydispersity. Except of the polymer having the pronounced low molecular weight, the molecular weight and the morphology of the amphiphilic polymers had almost no obvious effect on the size of the formed AuNPs. These organo-soluble AuNPs could be used as efficient catalysts for the biphasic catalytic reduction of 4-nitrophenol by NaBH4. Their apparent rate coefficients had correlation with the molecular weight of the used amphiphilic polymers, but were less relevant to the morphology of these polymers. These organo-soluble AuNPs could be conveniently recovered and reused many times. The morphology of the capping polymers had obvious effect on the lifetime of the AuNPs catalysts in the catalytic reduction of 4-nitrophenol. Except of the pronounced low molecular weight hyperbranched polymer, the other hyperbranched ones with relatively high molecular weight rendered the AuNPs to have bigger turnover number values than their linear analog. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 3826-3834, 2011