Amphiphilic polymer brushes grown from the silicon surface by atom transfer radical polymerization

Homopolymer and block amphiphilic polymer brushes on silicon wafers have be en successfully prepared by combining the self-assembled monolayer of initi ator and atom transfer radical polymerization (ATRP). Two methods for self- assembly of initiator monolayer were compared: One was to treat the silicon surface with 6-((2-bromo-2-methyl)propionyloxy)hexyltrichlorosilane soluti on (solution method), and the other was to treat it with the vapor of 3-ami nopropyl)triethoxysilane, followed by amidization with 2-bromoisobutyric ac id (vapor method). While the solution method produced particles due to cros s-linked products of the chlorosilane on silicon surface, the vapor method gave a uniform surface. The homopolymer brushes of poly(methyl methacrylate ) (PMMA) and poly(acrylamide) (PAAM) were prepared by ATRP on the modified silicon wafer by the initiator. The amphiphilic block copolymer brushes con sisting of PAAM and PMMA blocks mere obtained by using the homopolymer brus h as the macroinitiator for the second ATRP polymerization of another monom er. XPS revealed that the first polymer layer of the surface was partly cov ered with the second polymer layer after block copolymerized with the secon d monomer. AFM measurement of the amphiphilic block polymer brush imaged di fferent morphology when they were treated with water and toluene. The amphi philic polymer brush was stretched out from the surface and the individual polymer chains have sufficient free volume to permit the conformational cha nge in different solvents.