(628b) Impact of SI-ATRP Initiator Carbon Spacer Length On Grafting Poly(Styrene) From Silica Nanoparticles

Living polymerization methods, such as surface-initiated atom transfer radical polymerization (SI-ATRP), represent new ways to formulate well controlled polymer brushes from the surface of silica nanoparticles. These nanoparticles are increasingly used in a variety of high tech applications including mechanical reinforcement and protein separations. Grafting polymers from nanoparticle surfaces first requires the immobilization of covalently attached initiator monolayers. Interestingly, while a wide variety of initiators have been developed, no systematic study has been performed to elucidate how controlled changes in monolayer properties impacts the polymer grafting. Moreover, our previous studies have shown that during grafting reactions, immobilized monolayers keep nanoparticles suspended by preventing particle aggregation and the bridging of polymers between nanoparticle surfaces, both of which can erode the performance of high tech materials. Thus, our goal is to quantify the impact of grafting polystyrene from three different immobilized initiator monolayers attached to monodisperse silica nanoparticles. The initiators consist of a monoethoxysilane anchoring group, a bromine-terminated initiator group, and a carbon spacer connecting the two; the initiators are differentiated by their carbon spacer length of 3-, 11-, or 15 repeat units. PS brushes were grown from nanoparticle surfaces using SI-ATRP in anisole where a large drop in the PS graft density was observed with the 11-carbon spacer initiator, indicating that the conformation of the initiator monolayer changes with carbon spacer length. Ultimately, our results show that the carbon spacer length of the initiator impacts the graft density and molecular weight of PS from silica nanoparticle surfaces with SI-ATRP.