The role of oxygen in the photoaging of bisphenol A polycarbonate. 2. GC/GC/high-resolution MS analysis of Florida-weathered polycarbonate

Photo-oxidation of aromatic polymers

“…A noticeable difference between short-and long-wavelength photo-oxidation is that the thermal elimination of the acidic band at 1713 cm -1 parallels also the increase in intensity of the cyclic anhydride band at 1840 cm -1 in the long-wavelength photo-oxidized film. As the opening of phenyl rings of PC has been assessed by several authors 4,6,7) , it is suggested that cyclic anhydrides (1840 cm -1 ) are formed in the thermal transformation of dicarboxylic acidic products (1713 cm -1 ) which appear in ring scissions at long-wavelength. A probable mechanism of formation is reported in Scheme 3; the initiation steps by OH9 and 1 O 2 have been proposed by Clark and Munro 6) .…”

“…The concentration of these secondary species is observed to go on increasing while L 1 and L 2 have reached a plateau. SF 4 and thermolysis treatments of photo-oxidized films associated with mass spectroscopic analysis of the gas phase allowed the band at 1713 cm -1 to be assigned to the dimer form of acetic and formic acids that are trapped in the polymer matrix and that may be lost by evaporation from the polymer sample. Treatments reveal also the presence of aromatic acids (benzoic acid at 1696 cm -1 and salicylic acid at 1670 cm -1 ) and aliphatic ketones (1723 cm -1 ).…”

“…Initiation of the photo-oxidation of polymers at long wavelengths is usually described in the literature as resulting from light absorption by chromophoric impurities or by charge-transfer complex. It has been suggested 4) that the photo-oxidation of PC at long wavelengths could be initiated by a photo-Fries process. UV and FTIR spectroscopies, when used to detect changes upon exposure for very short periods of time, unambiguously show the formation of the photo-Fries product L 1 (320 nm, 1689 cm -1 ) under vacuum exposure at k A 300 nm and in photo-oxidative conditions.…”

“…6) spectra of irradiated films. The absorption band of L 1 at 320 nm is overlapped by unstructured absorption at wavelengths longer than 300 nm, which has been attributed 4) to a mixture of highly colored ring oxidation species formed in ultimate oxidation steps of products created in side-chain photo-oxidation.…”

“…15B) The characterization of photoproducts on the basis of in-situ chemical treatments carried out with gases such as NH 3 and SF 4 , gives essential informations on the photooxidation products. The carbonyl absorption appears complex as it results from the convolution of various carbonylated species.…”