The thermal‐oxidative degradation of PAN/OPAN in the primary stage in a pentaerythritol ester at 200°C was characterised by the recombination of aminyl radicals giving the corresponding dimers. Primary transformation products such as quinone imines, anils and benzophenoxazone derivatives were also found in small concentrations. A major contribution by the nitroxyl radical is not evident, and the supposed combination of an aminyl radical with the fatty acid chain of the ester was not detected.