Hydrophilic modification of a polyimide film surface

The surface of a polyimide [poly(biphenyl 3,3′,4,4′-dianhydride-p-phenylene diamine)] film was modified with an O2 glow plasma and subsequent treatment with polyethyleneimine (PEI) and poly(maleic anhydride-co-vinyl methyl ether) (PMAVM). The density of peroxide groups formed on the surface after O2 plasma exposure was determined with 1,1-diphenyl-2-picrylhydrazyl and was found to level off to 1.2 nmol/cm2 within the plasma exposure time of 20-60 s. The peroxide groups formed were utilized to immobilize PEI covalently onto the plasma-treated polymer film. After that, PMAVM was immobilized on the surface through the formation of amide bonds between the amino groups of PEI and the anhydride groups of PMAVM. The water contact angle on the modified films showed that the hydrophilic durability of the PMAVM-PEI-modified polyimide film was superior to that of the polyimide film treated by O2 plasma alone.