(409d) The Impact of ATRP Initiator Spacer Length On Grafting Poly(Methyl Methacrylate) From Silica Nanoparticles

Huang, C. - Presenter, Merck and Company

The focus of this work is to quantify the impact of the carbon spacer length (CSL) of immobilized alkoxysilanes initiators on grafting poly(methyl methacrylate) (PMMA) from the surfaces of monodisperse silica nanoparticles. PMMA was grafted using surface-initiated atom transfer radical polymerization (SIATRP), a facile technique to produce well-controlled polymer brushes of high graft densities; the polymerizations were carried out in environmentally friendly 4:1 (v/v) methanol-water solutions at room temperature. Monoethoxysilane initiators of 3, 11, and 15 carbon spacer lengths were synthesized and characterized with 1H NMR and 13C NMR. The initiators were then used to modify the surfaces of monodisperse silica nanoparticles in methyl isobutyl ketone, producing dense initiator monolayers with site densities between 1.80 ? 3.64 initiators/nm2. PMMA was subsequently grafted from the functionalized nanoparticles using both CuCl and CuBr catalysts. It was found that polymerizations performed with CuBr were uncontrolled, whereas those with CuCl were controlled. PMMA graft densities ranged between 0.10 ? 0.43 polymers/nm2, which increased with the initiator carbon spacer length (CSL). Interestingly, longer CSLs make nanoparticle surfaces hydrophobic, causing nanoparticle aggregation in methanol-water solutions. Our results indicate that surface hydrophobicity is correlated to increases in PMMA graft density through the adsorption of hydrophobic MMA monomers on initiators with longer CSLs. Thus, to augment PMMA graft densities, a subtle balance must be struck between enabling particle stability and increasing MMA adsorption in methanol-water solutions.