SURFACE MODIFICATION OF POLYIMIDE FILMS BY GRAFT-COPOLYMERIZATION

Surface modifications of polyimide (PI) films by Ar-plasma, O-2-plasma, and O-3 pretreatment and by near-UV light-induced graft copolymerization with water-soluable monomers, such as acrylamide (AAm), acrylic acid (AAc), and sodium salt of 4-styrenesulfonic acid (NaSS), have been carried out. The angle-resolved x-ray photoelectron spectroscopy (XPS) results show that surface pretreatment results in the formation of peroxide species on the polymer film surfaces and leads to a substantial enhancement of the density of surface graft. The XPS results further suggest that in the case where substantial grafting has taken place, the grafted polymer either forms a surface layer uniformly intermixed with the substrate chains, or a graft-rich surface layer in the case of sterically hindered migration of the graft. The resulting surface structures are further supported by dynamic water contact angle measurements. These surface structures are probably associated with the thermoset character of PI, as they differ from the stratified microstructures observed on most thermoplastic films after surface modification by graft copolymerization with hydrophilic monomers. (C) 1995 John Wiley & Sons, Inc.