Amphiphilic Polymer Brushes Grown from the Silicon Surface by Atom Transfer Radical Polymerization

Homopolymer and block amphiphilic polymer brushes on silicon wafers have been successfully prepared by combining the self-assembled monolayer of initiator 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 solution (solution method), and the other was to treat it with the vapor of 3-aminopropyl)triethoxysilane, followed by amidization with 2-bromoisobutyric acid (vapor method). While the solution method produced particles due to cross-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 consisting of PAAM and PMMA blocks were obtained by using the homopolymer brush as the macroinitiator for the second ATRP polymerization of another monomer. XPS revealed that the first polymer layer of the surface was partly covered with the second polymer layer after block copolymerized with the second monomer. AFM measurement of the amphiphilic block polymer brush imaged different morphology when they were treated with water and toluene. The amphiphilic polymer brush was stretched out from the surface and the individual polymer chains have sufficient free volume to permit the conformational change in different solvents.