Interaction of a hindered piperidine stabilizer with hydroxy‐substituted aromatic carbonyl compounds in the photostabilization of polypropylene

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Abstract
The effect of a hindered piperidine compound, Bis[2,2,6,6‐tetramethyl‐4‐piperidinyl] sebacate on the photostability and light‐stabilizing performance of hydroxy‐substituted benzophenone and anthraquinone compounds in polypropylene film has been examined using three different light exposure units. The stabilizing effects observed were found to be highly dependent on the utraviolet content (300–340 nm) of the light source. In the absence of this utraviolet component the hindered piperidine compound inhibited the photolysis of all the hydroxy‐substituted compounds, whereas in its presence no protective effect was observed. In fact, direct absorption of ultraviolet light was found to be totally ineffective in photostabilizing the polymer. The protective effects were associated with the ability of the hindered piperidine compound to destroy the hydroperoxides formed during processing. This was confirmed by the observation of no protective action with unsubstituted benzophenone and anthraquinone through both steady‐state and laser flash‐photolysis experiments. A further novel protective effect was observed when the hindered piperidine molecule was linked to the anthraquinone chromophore in the 2‐position to the carbonyl group. In this case photoprotection is associated with an intramolecular excited‐state quenching process.

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