The oxidation of hindered amine light stabilisers to nitroxy radicals in solution and in polymers. Part II

Abstract

Different types of hindered amine light stabilisers (HALS) have been oxidised by peroxy radicals generated by gamma irradiation of air saturated cyclohexane solutions. In all cases the concentration of nitroxy radicals, measured by EPR spectroscopy, increases linearly with absorbed dose. The sequence of reactivity observed is: amino ether > sec. amine > tert. amine The same HALS have been oxidised in a hydroperoxidised styrenebutadiene-styrene block copolymer by peroxy radicals resulting from the decomposition of clustered hydroperoxides. At room temperature the nitroxy radical concentration slowly increases with time and tends to a limit corresponding to the fraction of HALS molecules that are in a suitable environment to be oxidised. The sequence of reactivity observed is the reverse of that mentioned above. In this case, it reflects the ability of the different HALS to catalyse the decomposition of clustered hydroperoxides.