A re-examination of the photo-oxidation mechanism of poly(2,6-dimethyl-l,4phenylene oxide) (PPO) at both long and short irradiation wavelengths under accelerated conditions is reported. The formation rate of poly-2,6-dimethylphenoxy (PDMP) radicals, have been observed by esr spectroscopy, while benzylic-type radicals have been detected by spin trapping experiments using nitrosodurene under W irradiation conditions. The changes ofFTIR spectra obtained under accelerated photo-oxidative conditions show the formation of primary oxidation products such as aromatic aldehydes and quinones. The direct formation of radical cations and superoxide anions by a photo-induced electron-transfer reaction is suggested under our conditions. In addition, some results on the of photo-oxidation PPOPS blends as a fkction of polystyrene tacticity are also reported. In the case of syndiotactic polystyrene the blend photostability shows some differences in comparison with the blend containing atactic polystyrene. This effect has been ascribed to the absence of excimers in syndiotactic polystyrene which are not revealed by fluorescence measurements. Finally, the chemical modification of PPO with bromine gave a bromomethylated PPO with different amounts of CHar groups, which has been used for krther substitution reactions with alkoxy sodium salts of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 4-hydroxy-1,2,2,6,6-pentamethylpiperidine (PMPP). The accelerated photo-oxidation of a modified copolymer PPO-PMPP containing a 60% PMPP moieties as side groups and its blends with pure PPO has been followed by FTIR and esr spectroscopies. Some comparisons with a commercially available hindered amine light stabilizers (HALS) and a modified copolymer PPO-PMPP are also reported under the same photo-oxidative conditions.
In this paper the mechanism of the thermo‐and photo‐oxidation of catena‐ poly[bis(4‐benzylphenoxy)‐λ5‐phosphazene] films at short and long wavelengths has been followed under accelerated conditions using FTIR and UV‐visible spectroscopic techniques. The decrease of the band at 1453 cm−1 and the simultaneous appearance of new bands at 3400 and 3481 cm−1, due to free and bonded hydroperoxides, show that the primary hydroperoxidation in this polymer occurs at CH2 groups belonging to benzylic moietics. According to our previous paper, the bands observed in the carbonyl region at 1657, 1704 and 1725 cm−1 during photo‐oxidation have been assigned to the formation of benzophenone, benzaldehyde and benzoic acids (dimmers), respectively. The formation rate of benzophenone groups increases during irradiation at long wavelengths (λ > 400 nm). Under thermo‐oxidative condition (90°C), the benzophenone groups are the main oxidation products derived from hydroperoxide decomposition. In addition, the photooxidation of a film pre‐thermo‐oxidized for 500 h shows clearly that the benzophenone groups can generate aldehydes, benzoic acids and peracids. Crosslinking takes place in high yields by hydrogen abstraction occurring at both benzylic and secondary alcohol units. The regeneration of benzophenone groups has been evidenced during the photo‐oxidation.
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