Direct modification of polyolefin films by surface-initiated polymerization of a phosphobetaine monomer

The surfaces of polyethylene and polypropylene sheets were modified by grafting with polymeric brushes formed from a phosphobetaine monomer. Pressed sheets of bromo-functionalized polyethylene or polypropylene macroinitiators (PE-MIs and PP-MIs, respectively) were used to initiate the atom-transfer radical polymerization of 2-(methacryloyloxy)ethyl phosphorylcholine (MPC) under mild conditions to form a superhydrophilic grafted surface layer. The grafted polyolefin sheets showed excellent wettability and oil-detachment behaviour in water. Even three years after surface grafting had been performed, the PMPC-g-PP sheet retained a water contact angle of less than 10°. Furthermore, the water contact angle of the PMPC-g-PP sheet remained as low as 12° after it had been annealed at 373 K for 60 min under reduced pressure. Dynamic friction tests performed on the PMPC-g-PE sheet by sliding it against a glass ball revealed a marked reduction in the friction coefficient in water at sliding velocities in the range of 10^-5 to 10^-1 m s^-1, possibly as a result of lubrication by water.