Pushing the Limit: Synthesis of SiO2-g-PMMA/PS Particle Brushes via ATRP with Very Low Concentration of Functionalized SiO2-Br Nanoparticles

The kinetics and mechanism of the synthesis of SiO2-g-poly(methyl methacrylate) (SiO2-g-PMMA) and SiO2-g-polystyrene (SiO2-g-PS) nanoparticles were investigated through studies conducted at very low concentrations of the ATRP initiator functionalized silica particles (SiO2-Br) in the presence of reducing agent (tin(II) 2-ethylhexanoate) and low ppm loadings of the Cu-II catalyst (25 ppm) complex. In the SiOrg-PMMA system, the grafting density decreased under very low concentrations (<100 ppm) of SiO2-Br. However, in the SiO2-g-PS system, the initiation efficiency, defined through the grafting density of polymer chains on the particle surface, decreased significantly for lower concentrations of the initiator SiO2-Br. In addition, model systems with linear polymer chains (untethered) were studied to investigate the difference in initiation efficiency between polymers attached to nanoparticle surfaces and untethered chains. Because of the localization of initiating sites on the surface of nanoparticles and lower probabilities of collisions between nanoparticles, as compared to small initiator molecules, particle brush systems exhibited less interparticle termination. This observation was employed to synthesize very high molecular weight (M-n> 500K) particle brushes with relatively narrow molecular weight distribution (M-w/M-n < 1.3).