Reverse Atom Transfer Radical Graft Polymerization of 4-Vinylpyridine onto Inorganic Oxide Surfaces

Thin poly(4-vinylpyridine) films terminally anchored onto nonporous inorganic oxide substrates were synthesized by aqueous phase reverse atom transfer radical graft polymerization (ATRGP). Surface initiators were immobilized on the inorganic substrate surface by chemically attaching glycidoxytrimethoxy silane onto the substrates followed by conversion of the glycidoxy silane into azobis silane by a reaction with 4,4'-azobis(4-cyanovaleric acid). Reverse ATRGP of 4-vinylpyridine onto the active surface azo sites was carried out in a 1-methyl-2-pyrrolidone/water solvent mixture using CuCl2/2,2'-bipyridine as the catalyst-ligand complex with initial monomer concentration [M](0) = 2.32M at 90 degrees C. Controlled radical polymerization was achieved at catalyst to initiator molar ratios of 2 : 1 and 3 : 1, with a catalyst to ligand molar ratio of 1 : 2. Controlled polymerization was indicated by a first-order rate of polymerization kinetics, with respect to monomer conversion at the surface and in solution, the linear increase of the P4VP graft yield with time, and a low polydispersity index (PDI < 1.40). The highest graft yield of 8 mg/m(2) was achieved at a 3 : 1 catalyst to initiator molar ratio which corresponded to a number-average molecular weight of 11,500 g/mol, surface density of 0.69 mol/m(2), and a polydispersity index of 1.28. AFM surface analysis of the grafted polymer films, prepared by reverse ATRGP of 4VP, revealed a decrease in the RMS surface roughness (R-RMS) = 1.04 nm) and feature size (feature diameter = 20-45 nm), relative to uncontrolled free radical graft polymerization (R-RMS) = 1.42 nm; feature diameter - 60-145 nm), thereby providing an additional indication that a denser and controlled reaction was achieved via reverse ATRGP. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 437-449, 2009