Photochemical evolution of poly(ether ether ketone)

Abstract

The photochemical evolution of poly(ether ether ketone) (PEEK) has been investigated under polychromatic irradiation ( λ>300 nm) in the absence and in the presence of oxygen. The modifications of the structure of the films resulting from irradiation was monitored by Fourier transform infrared (FTIR) and UV-visible spectroscopy. The various photoproducts formed were identified by HPLC analysis of the low molecular weight fragments after methanolic extraction. Confirmation of the photoproducts nature was obtained by derivatisation reactions, chemical titration and physical treatments. Under vacuum exposure, as a result of direct absorption of the incident radiation by the basic backbone structure of PEEK, the photolytical processes that occur involve pinacolisation reaction, photo-Claisen type rearrangement and direct chain scissions; subsequent H-abstraction leads to the formation of numerous molecular compounds. Photoproducts resulting from inter- and intra-molecular phenylation reactions and the formation of light absorbing transients account for the photodiscoloration of the irradiated films. Under exposure in aerated media, the oxidation of the photoproducts issue from direct phototransformations accounts for the photodegradation of PEEK; the oxidative attack of the phenyl moieties via ring opening reactions is also involved.