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 under ultra-high vacuum conditions onto a number of common polymers, prepared as stretched foils and spin-coated films. The metal-polymer interface was studied by X-ray Absorption and X-ray Photoelectron Spectroscopy. Evaporated samples were analyzed without exposure to the atmosphere. Different general 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 π-electron complexes and covalent metal-carbon bonds were obtained exclusively with chromium. Aromatic rings, carbonyl groups and, to a lesser extent, ether linkages are scissioned by metal-polymer interactions. The fourfold substitution of aromatic rings and the exclusive existence of C ─ O ─ C structures within polyphenylene ether (PPE) make this polymer most stable toward reactions with chromium. In contrast, bisphenol-A polycarbonate is susceptible to redox reactions with the carbonate group and to forming Cr complexes with aromatic rings using the chromium 3d orbitals. The result is a succession of complex formation, followed by Cr substitution onto aromatic rings and destruction of rings with the formation of chromium carbides.