New Vistas in Polymer Degradation. Thermal Oxidation Processes in Poly(ether imide)

Poly{2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride-1,3-phenylendiamine} copolymer (ULTEM) was subjected to thermoaging in an attempt to det. the structure of the species formed during oxidative degrdn. The oxidative process was followed as a function of exposure time by using MALDI-TOF MS. Thermal oxidn. produces charring after only 15 min and the formation of insol. residue amts. to 50% after 180 min at 350°C. Highly valuable structural information (including the end groups) was extd. from the MALDI spectra of the thermally oxidized ULTEM sol. samples. Oxidized specimens contained acetophenone, phenylacetic acid, phenols, benzoic acid, bisphenol A, phthalimide, and phthalic anhydride end groups. The mechanisms accounting for their formation involve several reactions: (i) cleavage of the di-Ph ether units; (ii) oxidative degrdn. of the isopropylidene bridge of BPA units; (iii) thermal cleavage of phenylphthalimide units.