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Photooxidation of benzil groups in the presence of hindered amine stabilizers in the polystyrene film

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Abstract

The photoperoxidation at λ > 400 nm of benzil (BZ) groups with the air oxygen to benzoyl peroxide (BP) groups in the polystyrene matrices was investigated in the presence of hindered amine stabilizer (HAS). HAS was used as a free molecule or was bound in combined molecule with BZ. HAS was in the form of parent amine as 2,2,6,6-tetramethyl-4-hydroxypiperidine (TMP) and in the form of stable nitroxyl radical 1-oxo-2,2,6,6-tetramethyl-4-hydroxypiperidine (NO). Both HAS forms effected the photooxidation of BZ structures. The main product of the photooxidation in the presence of parent amine TMP as well as in its absence is benzoyl peroxide (BP). The rate of BZ consumption increases in the presence of TMP. Irradiation of BZ in the presence of sufficient concentration of freely added NO results only in the formation of benzoic acid esters and benzoic acid, which are the main decomposition products of BP. The benzoic acid esters/benzoic acid ratio increases with the increasing concentration of NO. Bounding of BZ and TMP into one molecule (BZNH) results in slower dicarbonyl depletion, as compared with the case when mixture of BZ and TMP was used. Very slow depletion of BZ carbonyl absorption was observed in the case of bounded BZ and NO in one molecule (BZNO), in comparison with the mixture of free NO and BZ. In the case of BZNO, an effective intramolecular quenching of BZ excited triplet states with NO structures proceeds. Steady stay and dynamic emission (phosphorescence) measurements also show an effective quenching of BZ excited states by unbounded or bounded NO. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4420–4428, 2006

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