Functionalization of hydrogen-terminated Si(100) substrate by surface-initiated RAFT polymerization of 4-vinylbenzyl chloride and subsequent derivatization for photoinduced metallization

Well-defined and covalently bonded poly(4-vinylbenzyl chloride) (PVBC) brushes on single-crystal silicon were prepared by surface-initiated reversible addition-fragmentation chain transfer (RAFT)-mediated graft polymerization of 4-vinylbenzyl chloride (VBC) on hydrogen-terminated Si(100) (Si-H) surface. Surface initiators were immobilized on the Si-H substrates in three ;consecutive steps: W coupling of an omega-unsaturated alkyl ester to the Si-H surface under U-V irradiation, (ii) reduction of the ester groups by LiAlH4, and (iii) esterification of the surface-tethered hydroxyl groups with 4,4'-azobis(4-cyanopentanoic acid). Kinetic studies revealed a linear increase in VBC polymer (PVBC) film thickness with polymerization time, indicating that the chain growth from the surface was a controlled process. Subsequent growth of a poly(pentafluorostyrene) (PFS) block from the PVBC-grafted silicon (Si-g-PVBC) surface, using the PVBC brushes as the macro chain transfer agents, provides further evidence of the existence of "living" chain ends. The benzyl chloride groups of the grafted PVBC were derivatized by reaction with an equimolar mixture of 1,4-di-(chloromethyl)benzene and 4,4-bipyridine to give rise to the Si-g-viologen surface. The redox-responsive property of the Si-g-viologen surface was demonstrated by photoreduction of the surface-adsorbed Pd(II) and Au(III) ions to their respective metallic form.