Reactions and intermediates at the metal-polymer interface as observed by XPS and NEXAFS spectroscopy

Potassium or chromium were evaporated by means of a Knudsen effusion cell u nder ultra-high vacuum conditions onto a number of common polymers, prepare d as stretched foils and spin-coated films. The metal-polymer interface was studied by X-ray Absorption and X-ray Photoelectron Spectroscopy. Evaporat ed samples were analyzed without exposure to the atmosphere. Different gene ral types of reactions of the metal atoms with the polymers were observed. With deposited K and Cr a redox process including the transfer of substrate oxygen atoms across the interface was found. The formation of pi-electron complexes and covalent metal-carbon bonds were obtained exclusively with ch romium. Aromatic rings, carbonyl groups and, to a lesser extent, ether link ages are scissioned by metal-polymer interactions. The fourfold substitutio n of aromatic rings and the exclusive existence of C-O-C structures within polyphenylene ether (PPE) make this polymer most stable toward reactions wi th chromium. In contrast, bisphenol-A polycarbonate is susceptible to redox reactions with the carbonate group and to forming Cr complexes with aromat ic rings using the chromium 3d orbitals. The result is a succession of comp lex formation, followed by Cr substitution onto aromatic rings and destruct ion of rings with the formation of chromium carbides.