PHOTOOXIDATION MECHANISMS OF POLY(2,6-DIMETHYL-1,4-PHENYLENE OXIDE)

A re-examination of the photo-oxidation mechanism of poly(2,6-dimethyl -1,4-phenylene oxide) (PPO) at both long and short irradiation wavelen gths under accelerated conditions is reported. The formation rate of p oly-2,6-dimethylphenoxy (PDMP) radicals, have been observed by esr spe ctroscopy, while benzylic-type radicals have been detected by spin tra pping experiments using nitrosodurene under UV irradiation conditions. The changes of FTIR spectra obtained under accelerated photo-oxidativ e conditions show the formation of primary oxidation products such as aromatic aldehydes and quinones. The direct formation of radical catio ns and superoxide anions by a photo-induced electron-transfer reaction is suggested under our conditions. In addition, some results on the o f photo-oxidation PPO/PS blends as a function of polystyrene tacticity are also reported. In the case of syndiotactic polystyrene the blend photostability shows some differences in comparison with the blend con taining atactic polystyrene. This effect has been ascribed to the abse nce of excimers in syndiotactic polystyrene which are not revealed by fluorescence measurements. Finally, the chemical modification of PPO w ith bromine gave a bromomethylated PPO with different amounts of CH2Br groups, which has been used for further substitution reactions with a lkoxy sodium salts of 4-hydroxy-2,2,6,6-tetramethyl-1-piperidinyloxy ( TEMPO) and 4-hydroxy-1,2,2,6,6-pentamethylpiperidine (PMPP). The accel erated photo-oxidation of a modified copolymer PPO-PMPP containing a 6 0% PMPP moieties as side groups and its blends with pure PPO has been followed by FTIR and esr spectroscopies. Some comparisons with a comme rcially available hindered amine light stabilizers (HALS) and a modifi ed copolymer PPO-PMPP are also reported under the same photo-oxidative conditions.