Controlled grafting of polybetaine brushes onto hydrogen-terminated Si(100) substrates (Si-H substrates) was carried out via surface-initiated reversible addition-fragmentation chain-transfer (RAFT) polymerization. The azo initiator was immobilized on the Si-H surface through a threestep process: (i) coupling of an ω-unsaturated alkyl ester to the Si-H surface under UV irradiation, (ii) reduction of the alkyl ester into a hydroxyl group by LiAlH 4 , and (iii) esterification of the hydroxyl group with the initiator 4,4′-azo-bis(4-cyanopentanoic acid) after acid chlorination. In the presence of the chain-transfer agent, RAFT-mediated polymerization of the sulfobetaine monomer N,N′-dimethyl(methylmethacryloyl ethyl) ammonium propane sulfonate (DMAPS) was initiated from the surface-immobilized azo initiator to produce DMAPS polymer (PDMAPS) brushes on the silicon substrate (Si-g-PDMAPS). X-ray photoelectron spectroscopy (XPS) analysis indicated that the PDMAPS brushes had been successfully grafted onto the silicon surface. Atomic force microscopy (AFM) images revealed changes in the surface topography of the silicon substrates and the presence of polymer overlayers. Ellipsometry results indicated that the thickness of the polybetaine film increased linearly with the polymerization time. The "living" characteristics of the end functionality of the polybetaine brushes from the RAFT-mediated process was ascertained by block copolymerization with the anionic monomer sodium 4-styrene sulfonate (SS) to form the diblock polymer brushes (a Si-g-PDMAPS-b-PSS surface).

We quantified 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 (SI-ATRP), a facile technique to produce well-controlled polymer brushes. 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 (1)H NMR and (13)C 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 1.8-3.6 initiators/nm(2). PMMA was subsequently grafted from the functionalized nanoparticles using both CuCl and CuBr catalysts. We found that polymerizations performed with CuBr were uncontrolled, whereas those with CuCl were controlled. PMMA graft densities ranged between 0.10-0.43 polymers/nm(2), 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 correlates 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.