Catalytic thermal oxidation of phenolic antioxidants by hindered piperidine compounds

The interactions of two hindered piperidine compounds, bis(2,2,6,6,-tetramethyl-4-piperidinyl) sebacate and 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxy, with various phenolic antioxidants, during the thermal processing of polypropylene have been examined using ultraviolet-visible absorption, infra-red and ESR techniques. Evidence is presented to show that the stable N-oxy radical generated during thermal processing catalytically oxidises phenolic antioxidants to their corresponding quinone forms. The implications of this interaction, particularly with regard to its effect on light stability, are discussed.