Abstract: The rate constants for the quenching of singlet oxygen by a series of nitroxyl radicals and some hindered amines were determined. It wa found that the abilities of nitroxyl radicals with different structures for quenching singlet oxygen are very similar but their photostabilizing efficiencies are remarkably different. The quenching efficiencies of tetramethyl piperidinol and its derivatives are much more lower than that of pentamethyl piperidinol and the corresponding derivatives, but the photostabilizing efficiencies of the former are better than that of the latter. It shows that the quenching action towards ¹O₂ is not important during photostabiliza-tion of PP film by nitroxyl radicals and hindered amines. It would also imply the little contribution of singlet oxygen to photooxidation of PP film.

Key words: photodegradation, quenching of ¹O₂, nitroxyl radical, hindered amine, polypropylene