Metal salts of 2-[(1-hydroxy-4-methyl-2-benzoyl)carbonyl] and 2-[(1-hydroxy-4,5-dimethyl-2-benzoyl)carbonyl]benzoic acids as photo-stabilizers for cis-1,4-polybutadiene

Abstract

The effects of metal salts (Ni 2+, Co 2+, Mn 2+) of 2-[(1-hydroxy-4-methyl-2-benzoyl)carbonyl] and 2-[(1-hydroxy-4,5-dimethyl-2-benzoyl)carbonyl] benzoic acids on the photo-oxidation of cis-1,4-polybutadiene (PB) in solution, and on its photo-sensitized degradation in the presence of methylene blue in solution have been studied. Since all of the salts showed very strong absorptions in the long wave UV region, they can act as UV screening agents for polymers. The salts also significantly reduced rates of chain scission and formation of oxidation products, such as carbonyls and hydroperoxides, during the photo-oxidation of PB. It was concluded that they were functioning as retarders of free radical processes, and this was confirmed by the observation of qualitatively similar retardation of the polymerization of styrene. The rates of sensitized degradations of PB were similarly depressed when the salts were present, indicating that they were interacting with singlet oxygen. Similar inhibition of the sensitized oxidation of diphenylbenzofuran confirmed their role not only as singlet oxygen quenchers, but also as multifunctional photo-stabilizers of PB.