Synthesis of polymer brush by nanoporous surface-initiated polymerization

Abstract

Chemically grafted tris(trimethylsiloxy)silyl (tris(TMS)) monolayer on the silicon oxide substrate was used as a nanometer-scale template for controlling the graft density of polymer brushes. Polymer brushes were synthesized by surface- initiated polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and tert-butyl methacrylate (Pt-BMA) from ∝-bromoester groups tethered to the residual silanol groups on the surface after creating a range of tris(TMS) coverage via atom transfer radical polymerization (ATRP). CuBr/bpy or CuBr/PMDETA was used as a catalytic system for PMPC and Pt-BMA synthesis, respectively. The percentage of tris(TMS) coverage significantly influenced the thickness and morphology of polymer brushes. Protrusions representing self-aggregation of PMPC brushes in nanopores as visualized by AFM analysis evidently suggested that PMPC brushes distributed nanoscopically on the surface. The size of protrusion and surface roughness corresponded quite well with the graft density of PMPC brushes. The fact that Pt-BMA brushes grown from nanopores were almost featureless implies that self-aggregation of PMPC brushes is truly a consequence of phase incompatibility between hydrophilic PMPC brushes and hydrophobic tris(TMS).