Fate of amine antioxidants during thermal oxidative ageing of neopentylpolyl ester oils

Abstract

The main products of the thermal-oxidative degradation of p, p'-di-tert- octyldiphenylamine, phenothiazine and 3,7-di-tert-octylphenothiazine (DODPA/PTZ/DOPTZ) in pentaerythritol ester at 200°C were isolated and identified. Recombination o f aminyl radicals giving various dehydrodimers and dehydro-trimers is obviously the dominating reaction in the primary stage of antioxidant depletion during ageing of inhibited ester oils. Minor degradation products include quinone imines, quinones, sulphoxides, phenoxazine and phenoxazone derivatives. Because of the complexity of the reactions product analyses are inevitably incomplete.