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 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).

Living Radical Polymerization by the RAFT Process

“…[228] Most work has used ATRP or NMP, though papers on the use of RAFT polymerization have begun to appear. [229][230][231][232][233][234][235] The first to apply RAFT in this context were Tsujii et al [229] and Brittain and coworkers. [230,231] Recent papers describe RAFT polymerization from plasma-treated Teflon surfaces [232] and ozonolyzed polyimide films.…”

“…[230,231] Recent papers describe RAFT polymerization from plasma-treated Teflon surfaces [232] and ozonolyzed polyimide films. [235] The approach used in these and most other studies [230][231][232][233][234][235] has been to immobilize initiator functionality on the surface by chemical or plasma modification and use this to initiate polymerization in the presence of a dithioester RAFT agent. Tsujii et al [229] have indicated that some difficulties arise in using RAFT for grafting from particles because of an abnormally high rate of radical-radical termination caused by a locally high concentration of RAFT functionality.…”

Surface treatment and characterization: Perspectives to electrophoresis and lab‐on‐chips

“…The living character of this polymerization was demonstrated by the reinitiation of the polymer chains. The same strategy was used by Zhai et al [208] to grow polyelectrolyte brushes (polybetaine) from the surface-immobilized azoinitiator (silicon wafer).…”

New designed nerve conduits with a porous ionic cross-linked alginate/chitisan structure for nerve regeneration

“…The design, synthesis and development of new functional materials were studied to provide suitable materials for biomedical applications such as polyacrylate, polyester, polyurethane, polyamide, polyimide, polyester, polynorborene, polytetrafluoroethylene, polydiphenylacetylenes and polymeric resins . Also, surface modification technology was considered to change the surface microenvironment of the materials [22][23][24][25][26]. Therefore, a suitable material and fabrication process can be selected, designed and established.…”