SURFACE MODIFICATION AND ADHESION CHARACTERISTICS OF POLYCARBONATE FILMS AFTER GRAFT-COPOLYMERIZATION

The surfaces of ozone-pretreated polycarbonate films were subjected to further modification by thermally induced graft copolymerization with acrylic acid (AAc), sodium salt of styrene sulfonic acid (NaSS), N,N- dimethylacrylamide (DMAA), N,N(dimethylamino)ethyl methacrylate (DMAEM A) and 3-dimethyl(methacryloyl ethyl)ammonium propanesulfonate (DMAPS) monomers. The structure and composition at the copolymer interface we re studied by angle-resolved X-ray photoelectron spectroscopy (XPS). F or polycarbonate films with a substantial amount of grafted polymer, t he hydrophilic graft penetrates or becomes partially submerged beneath a thin surface layer of dense substrate chains. This microstructure w as further supported by the water contact angle measurements. Adhesive -free adhesion studies revealed that the AAc, DMAA or DMAPS graft copo lymerized polycarbonate film surface adhered strongly to another simil arly modified surface (home-interface) when brought into direct contac t in the presence of water and subsequently dried. The development of the lap shear strength is dependent on the concentration of the surfac e graft, the microstructure of the grafted surface, the adhesion (dryi ng) time, and the nature of the interfacial interaction. The simultane ous presence of chain entanglement and electrostatic interaction readi ly results in substantially enhanced adhesion strengths between two DM APS graft copolymerized surfaces or between an AAc and a DMAA graft co polymerized surface (hetero-interface). XPS analyses of the delaminate d surfaces suggest that failure occurred cohesively below the graft-su bstrate interface. (C) 1998 John Wiley & Sons, Inc.