Surface-initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate: Effect of solvent on graft density

Oligo(ethylene glycol) methacrylate (OEGMA) was grafted from silicon wafer surfaces by surface-initiated atom transfer radical polymerization (ATRP) with (CuBr)-Br-1/2.2'-bipyridine (bpy) as a catalyst and various water/alcohol mixtures as solvents. The ellipsometric thickness of the poly-(OEGMA) layer on the surface increased linearly with monomer conversion in solution. High graft densities were achieved in alcohols. The graft density of poly(OEGMA) in methanol was found to be 0.26 chains . nm(-2), which is 50% higher than that in water/methanol (30.70, v/v). The differences in graft density were correlated to the conformation of tethered poly(OEGMA) chains. Large poly(OEGMA) coils on the surface in the presence of water limited the access of initiation sites to the catalyst complex and monomer molecules.