Surface aspects of the natural and artificial aging of some aromatic polymers as studied by means of ESCA

Abstract

X-ray photoelectron spectroscopy, (ESCA), has been used to investigate the changes in surface chemistry of some aromatic polymers during natural and artificial weathering. Particular emphasis has been placed on the photodegradation (λ>290nm) of Bisphenol A polycarbonate. Model studies to investigate the changes in surface chemistry as functions of irradiation time, photon flux, temperature and the partial pressure: of oxygen and water at the solid/gas interface have been carried out in conjunction with natural exposures. The results show that photooxidation (involving the gem dimethyl and phenyl groups) and not a photo-Fries type rearrangement is the predominant process in the surface regions. Calculations at the non- and semi-empirical levels on model polycarbonate systems suggest that the first excited singlet state of polycarbonate arises from a II→II⃰ transition. The changes in surface chemistry of polycarbonate exposed to reactive oxygen species have been studied and indicate that singlet oxygen does not react with this polymer. The photoaging studies for polycarbonate have been extended to polystyrene, Bisphenol A polysulphone, polyethersulphone, polyphenylene oxide phenoxy resin and polyetherketone and similar trends to those observed for polycarbonate are shown to occur in these systems, i.e. extensive oxygen uptake in the surface regions with the mechanism involving the aromatic groups of the various systems.