AbstractThe oxidative thermal degradation of polyacrylonitrile has been examined using infrared spectroscopy. It was found that the generally accepted mechanism for the thermal degradation of polyacrylonitrile in air, which involves direct interaction of neighboring nitrile groups, and alternate proposals, involving azomethine crosslinks through reaction of the nitrile group and a neighboring tertiary hydrogen atom, do not satisfactorily represent an initial degradation scheme accounting for the observed infrared spectral changes. Rather, it must be concluded that these reactions take place after the initial degradation, to produce highly complex pyridinoid systems, and are not observable under the experimental conditions employed here. By detailed interpretation of the spectral changes using, in part, a difference spectral examination technique, an alternate route for the oxidative degradation involving the introduction of double bonds in the polymer chain could be formulated. This reaction can best be visualized as occurring via the attack of molecular oxygen at the activated tertiary carbon–hydrogen bond adjacent to the electron‐withdrawing nitrile group. The nitrile group was shown to remain unreacted during the course of the initial oxidation. After the introduction of the double bond, a number of secondary degradative reactions, of which the previously proposed routes of degradation are representative, take place; these include degradation reactions of the nitrile groups to form acid and amide groups. It was observed that the accumulation of oxygenated intermediates on the surface of the polymer film is a rapid reaction and that the initial degradation process is controlled by the concentration of these spec
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