Nanoparticle modifications with surface initiated polymerization via organometallic catalysts

Well-defined organometallic catalysts are used for synthesizing organic-inorganic hybrid materials utilizing a “from the ground up” approach to modify nanometer scale inorganic cores. The transition metal catalyst is ligated to the nanometer-size fumed silica, the inorganic core, after “seeding” the silica surface with a coupling agent, and, consequently, a polymeric coating is formed through the surface bound catalyst. Due to the nature of the polymerization reaction, the monomer inserts between the surface to be modified and the active site of the organometallic catalyst which in turn directs the polymerization to take place only at the surface and not in the bulk.

Living poly(hexyl isocyanate) semiflexible polymer brushes are covalently attached to the silica surface through synthesis that uses a Ti(IV) catalyst. The living chains are end-capped by acetyl chloride to seal off the chain ends. Bis(tricyclohexylphosphine)benzylidine ruthenium(IV) dichloride (Grubbs's catalyst) is used as a Ring Opening Metathesis Polymerization (ROMP) catalyst to prepare covalently attached surface layers from strained cyclic olefins. The living chain ends are end-capped by reaction with vinyl acetate.

The modified surfaces are characterized using FT-IR, NMR, TGA, GC-MS, SEM. Polymers grown on the surface are cleaved off using tetrabutyl ammonium fluoride as a “soft” mediator without disturbing the polymer structure. Brushes separated in this way are dissolved in THF, and GPC analysis is done to determine the molecular weight distribution and polydispersity.