SOME ASPECTS OF A NEW CLASS OF SULFUR-CONTAINING PHENOLIC ANTIOXIDANTS

The commercial sulfur containing antioxidant AO2 (Irganox 1520) is com pared with other classical phenolic antioxidants, and its special auto synergistic profile, particularly under dynamic test conditions (Brabe nder, 160 degrees C), in commercial polybutadiene rubber is investigat ed. 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 insta nce the role of the phenoxy radical 8 or its C,O-recombination product s with oxygen centered radicals (such as macroalkylperoxy radicals) an d of the recently synthesized stable quinone methide 10 are discussed. CIDNP experiments, generating the radical 8 from AO2, demonstrate tha t the main reaction between phenoxy radicals 8 is regioselective C,O-r ecombination, giving rise to the dimers 9a and 9b and no direct format ion of quinone methide 10 and C,C-coupling products is observed.