Thermal and photo-sensitised oxidation of polypropylene: Influence of hindered piperidine compounds |
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Authors: | NS Allen KO Fatinikun J-L Gardette J Lemaire |
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Institution: | Department of Chemistry, John Dalton Faculty of Technology, Manchester Polytechnic, Chester Street, Manchester M1 5GD, Great Britain;Laboratoire de Photochimie, Université de Clermont II, 63170: Aubière, France |
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Abstract: | The effect of two hindered piperidine compounds on the photo-sensitised oxidation of polypropylene by anthracene, anthraquinone, benzhydrol and benzophenone has been examined using infra-red, ultraviolet absorption luminescence and flash photolysis techniques. The compounds—a stable N-oxy radical and a hindered amine—are found to inhibit, to different extents, the photo-sensitised oxidation of the polymer. Neither of the compounds, however, inhibits photo-decomposition of the sensitisers, indicating that mechanisms involving excited state quenching and/or sensitiser regeneration are not operative in stabilisation. On flash photolysis of benzophenone, anthraquinone and benzhydrol, the presence of the N-oxy radical inhibits transient absorption due to the ketyl, semi-quinone and triphenyl methyl radicals. The N-oxy radical also inhibits the thermal reduction of anthraquinone in polypropylene, again indicating that excited state quenching in photo-stabilisation is unimportant. The results are discussed on the basis of a radical trapping mechanism. |
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