THERMAL-OXIDATION OF EXTRUDED POLY(2,6-DIMETHYL-1,4-PHENYLENE OXIDE)

The oxidation of extruded polyphenylene ether resin at moderate temperatures has been shown to obey Arrhenius kinetics with first-order dependence on the hydroxyl endgroups and half-order dependence on oxygen. In blends, the oxidation is overall second order in uncapped resin. The phenolic endgroup catalyzes the oxidation of the benzylic methyl groups, so capping the resin leads to a much reduced oxidation rate. The rate of oxidation of the capped commercial resin is approximately the same as that of pure capped model compounds, showing that other factors such as residual catalyst or structural irregularities play only a minor role in promoting the oxidation. A mechanism involving attack of the endgroup phenoxyl radical on the benzylic methyl group is suggested as the first step in the oxidation of the uncapped polymer.