Fabrication of high-density polymer brush on polymer substrate by surface-initiated living radical polymerization

A well-defined, high-density poly(2-hydroxyethyl methacrylate) (PHEMA) brush was fabricated on the surface of a poly(tetrafluoroethylene-co- hexafluoropropylene) (FEP) film by surface-initiated living radical polymerization (LRP). First, a sufficient amount of peroxides as initiating moieties were successfully introduced on the film surface without causing etching by the O₂-plasma treatment. Subsequently, the polymerization mediated by reversible addition-fragmentation chain transfer (RAFT) was carried out at a mild temperature in a nonsolvent for FEP to minimize the swelling of the FEP film surface and avoid the growth of chains from deep inside of the film. The contact angle and ESCA measurements indicated that the boundary intermixing layer between FEP and PHEMA layers was reasonably thin (≤10 nm), meaning that the PHEMA brush was grown nearly regioselectively from the surface of the FEP film. The graft density was estimated to be about 0.3 chains/nm2, which is almost the same as the one achievable by the RAFT technique on inorganic substrates with a hard surface. This graft density is much higher than the ones obtainable by conventional techniques.