Paul Dubs

Some aspects of a new class of sulfur containing phenolic antioxidants

Abstract The commercial sulfur containing antioxidant AO2 (Irganox 1520) is compared with other classical phenolic antioxidants, and its special autosynergistic profile, particularly under dynamic test conditions (Brabender, 160 °C), in commercial polybutadiene rubber is investigated. AO2 outperforms all other tested phenolic stabilizers. A tentative mechanistic explanation for the action of AO2 is given, consisting of either a concerted reaction or a ‘tandem reaction’ of the antioxidant with macroalkylperoxy radicals. Other mechanistic pathways, for instance the role of the phenoxy radical 8 or its C,Orecombination products with oxygen centered radicals (such as macroalkylperoxy radicals) and of the recently synthesized stable quinone methide 10 are discussed. CIDNP experiments, generating the radical 8 from AO2 , demonstrate that the main reaction between phenoxy radicals 8 is regioselective C,O-recombination, giving rise to the dimers 9a and 9b and no direct formation of quinone methide 10 and C,C-coupling products is observed.

ESR- and CIDNP-investigation of industrial additives

ESR and CIDNP are applied to the investigation of the reaction mechanisms of several phenolic antioxidants and initiators of polymerization. It is shown how the ESR- and CIDNP-techniques complement each other.