Rate constants for the quenching of singlet oxygen (1O2, 1δg) for a series of piperidines, piperidine-N-oxyl free radicals and some commercially used hindered amine light stabilisers (HALS) have been measured by a laser flash photolysis method. Quenching rate constants are in the order: piperidine-N-oxyl free radicals ≤ secondary piperidines < tertiary piperidines. For some commercial HALS, 1O2 quenching rate constants and the light protective effect towards polypropylene photo-oxidation have been compared. No correlation has been found between the stabilizing action and the quenching efficiency towards 1O2. The data obtained point to little contribution of singlet oxygen to the key steps of polyolefin photo-oxidation.
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