Electrostatic assembly of functional polymer combs onto gold nanoparticle surfaces: combining RAFT, click and LbL to generate new hybrid nanomaterials

Comb polymers have been synthesized using a "grafting-onto" method via a combination of Reversible Addition Fragmentation Chain Transfer (RAFT) polymerization and hetero-Diels-Alder (HDA) cycloaddition. A random copolymer comprised of tert-butyl acrylate (tBA) and hydroxyethyl acrylate (HEA) was post-modified via a two step process to introduce diene functionality. Polymers synthesized using benzyl pyridin-2-yldithioformate as a RAFT agent were used as the dienophile in a click reaction with polymer bearing diene pendant groups thus forming comb polymers. Polystyrene (PS), poly(n-butyl acrylate) (PnBA), poly(tert-butyl acrylate) (PtBA) and poly(oligoethyleneglycol methyl ether acrylate) (POEGMEA) were then grafted onto P(tBA-r-HEAdiene) backbones using a reaction time of 24 h. The grafting densities of the comb polymers ranged from 100% to 50%, depending on the chemical structure and the molecular weight of the linear side chain, as well as the initial molar ratio of dienophile to diene groups. Hydrolysis of the poly(tert-butyl acrylate) (PtBA) yielded hydrophilic or amphiphilic polymers with a poly(acrylic acid) (PAA) backbone. Finally a layer-by-layer approach was utilized to build up an initial layer of poly(ethylene amine) followed by a layer of PAA-g-POEGMEA onto gold nanoparticles (GNPs) yielding hybrid organic/inorganic nanoparticles. UV-vis spectroscopy, zeta-potential measurement and X-ray photoelectron spectroscopy (XPS) were used to characterize the hybrid nanoparticles showing that the POEGMA surface layer can shield the charges of the outer layer effectively.