Synthesis of gold nanoparticles coated with well-defined, high-density polymer brushes by surface-initiated living radical polymerization

The synthesis of a gold nanoparticle (AuNP) coated with a well-defined polymer is reported. The AuNP coated with an initiator group for living radical polymerization was prepared by the simple one-pot reduction of tetrachloroaurate with sodium borohydrate in the presence of an initiator group-holding disulfide. The surface-initiated living radical polymerization of methyl methacrylate (MDAA) mediated by a copper complex was carried out with the initiator-coated AuNP in the presence of a "sacrificial" free initiator. Living polymerization proceeded exhibiting a first-order kinetics of monomer consumption and an evolution of molecular weight of the graft polymer proportional to monomer conversion, thus providing well-defined, low-polydispersity graft polymers with an approximate graft density of 0.3 chains/nm(2). Transmission electron microscopic observations of as-cast films of the AuNPs coated with PMMAs (PMMA-AuNPs) revealed that the particles were well dispersed in the polymer matrix without forming aggregates and that the interparticle distance increased with increasing graft chain length. Absorption spectra of the PMMA-AuNPs dissolved in an organic solvent exhibited an intense surface plasmon absorption band peaked at 525-535 nm with a weak blue shift becoming more significant with increasing PMMA chain length.