An infrared spectrophotometric examination of the oxidative degradation of acid‐ and base‐catalyzed phenol‐formaldehyde polycondensates, novolaks and resoles, respectively, has been carried out in the temperature range form 100–200°C. The existence of structural moieties such as quinone methides and dibenzyl ethers in the cured phenolic resins systems could not be substantiated. The oxidation of phenolic resins was shown to be a stepwise degradation. Attack of oxygen, a surface reaction, was shown to be at the doubly activated methylene bridge linkage to form a substituted dihydroxybenzophenone system. This species was substantiated by the synthesis of polymers containing the ketonic linkage and their spectral identity to the degrading resin. The initial oxidation was shown to continue through the formation of quinone structures and secondary oxidation was shown to continue through the formation of quinone structures and secondary oxidation at these functional linkages to produce carboxylic acids as one of the fragments during chain scission. This degradation mechanism is in good agreement with other supporting experimental data concerning phenolic resin degradation.

The 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 species.

No abstract

No abstract