Abstract
The photodegradation of aromatic polymers involves several distinctive reactions including both direct photolytic pathways and photo-oxidative processes. To account for such a complexity, the photoreactivity of four aromatic polymers is detailed. The mechanisms of photochemical evolution were probed using various techniques such as FTIR and UV spectroscopies, chemical derivatization reactions, physical treatments of irradiated films and mass spectrometric analysis of the low molecular weight fragments. A dual photochemistry, largely dependent upon the spectral distribution of the excitation light source, is well evidenced with bisphenol-A polycarbonate (PC). Excitation of PC at short wavelengths involves two consecutive photo-Fries rearrangements of the aromatic carbonate units; on irradiation at long wavelengths, photoproducts are shown to result from the photo-induced oxidation on the side chain and from the phenyl rings oxidation. The photo-oxidation of poly(butylene terephthalate) (PBT) largely involves pure photolytic pathways; on the opposite, the dominant photo-oxidative pathway of phenoxy resins (PR) is attributed to the high oxidizability of methylene groups in α-position to the oxygen atom of the ether groups. It is shown at last that the photo-oxidation of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) largely involves the oxidation of phenyl rings.
Published Version
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