MECHANISMS OF ANTIOXIDANT ACTION - THE ROLE OF O-MACROALKYL HYDROXYLAMINES IN THE PHOTOANTIOXIDANT MECHANISM OF HALS

O-Macroalkyl hydroxylamines (> NOP) have been synthesised by reaction of 2,2,6,6-tetramethpl-4-hydroxy piperidinoxyl (> NO .) with ethylene- propylene rubber (EPR) and polypropylene (PP) by reactive processing i n the presence of a dialkyl peroxides. Under optimal conditions, 70% o f >NOP was formed based on > NO . added to the polymer, the remainder being free hydroxylamine ( > NOH). >NOEPR and >NOPP are effective phot oantioxidants for EPR and PP respectively. After exhaustive extraction of the films to remove >NOH, a proportion of the activity remained pr o-rata to the [>NO-] covalently bound to the polymer. It is concluded that > NOPs are converted to > NO . from the commencement of photooxid ation without a significant induction period. possibly through the int ermediate >NOH. However, most of the >NO- is present in the polymers a s macromolecular >NOP during UV since it is resistant to repeated cycl es of solvent extraction/photooxidation. Some possible mechanisms for the regeneration of > NO . from > NOP are considered. (C) 1996 Elsevie r Science Limited