Functionalization of Hydrogen-Terminated Silicon with Polybetaine Brushes via Surface-Initiated Reversible Addition−Fragmentation Chain-Transfer (RAFT) Polymerization

Abstract

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 three-step 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 LiAlH4, 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 si...