Controlled Grafting of Well-Defined Polymers on Hydrogen-Terminated Silicon Substrates by Surface-Initiated Atom Transfer Radical Polymerization

Abstract

Controlled grafting of well-defined polymer brushes on the hydrogen-terminated Si(100) substrates (the Si−H substrate) was carried out via the surface-initiated atom transfer radical polymerization (ATRP). Surface initiators were immobilized on the Si−H substrates in three consecutive steps: (i) coupling of an ω-unsaturated alkyl ester to the Si−H surface under UV irradiation, (ii) reduction of the ester groups by LiAlH4, and (iii) esterification of the surface-tethered hydroxyl groups with 2-bromoisobutyrate bromide. Homopolymer brushes of methyl methacrylate (MMA), (2-dimethylamino)ethyl methacrylate (DMAEMA), and poly(ethylene glycol) monomethacrylate (PEGMA) were prepared by ATRP from the α-bromoester functionalized silicon surface. The chemical composition and topography of the graft-functionalized silicon surfaces were characterized by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), respectively. Kinetic studies revealed a linear increase in polymer film thickness with reaction time, indicating that chain growth from the surface was a controlled process with a "living" characteristic. Diblock copolymer brushes consisting of PMMA and PDMAEMA blocks were obtained by using the homopolymer brushes as the macroinitiators for the ATRP of the second monomer, providing further evidence to the existence of "living" chain ends. ATRP from the Si−H surfaces allowed the preparation of polymeric-inorganic hybrid materials with well-structured surface and interface.