Evidence for the reduction of quinones added during thermal processing of polypropylene and the resultant effect on polymer light stability

The thermal and photochemical oxidation of anthraquinone‐ and p ‐benzoquinone‐doped polypropylene has been studied by absorption, luminescence, and infrared spectroscopy. Prior to irradiation, fluorescence and phosphorescence measurements showed that some of the anthraquinone and most of the p ‐benzoquinone had been converted into their corresponding hydroquinones during processing. The p ‐benzoquinone, unlike anthraquinone, also imparted a blue coloration to the polymer before irradiation, which is associated with the formation of a quinhydrone complex (or complexes). These results indicate that the quinones are thermally reduced to their corresponding hydroquinones during processing by a mechanism of hydrogen atom abstraction from the polymer substrate. On photo‐oxidation, whereas anthraquinone acted as a photosensitizer, p ‐benzoquinone acted as a photostabilizer.