Mechanisms of antioxidant action: Evidence for a regenerative cycle during the melt stabilisation of polypropylene by galvinoxyl

Evidence is presented to show that galvinoxyl (G·), a ‘stable’ aryloxyl radical, is converted to the corresponding phenol(GH) in polypropylene during processing. The redox couple (G·/GH) is a catalytic CB-A/CB-D antioxidant and is capable of deactivating 50 kinetic chains, thus effectively protecting polypropylene against oxidative chain scission for up to 20 min at 200°C in a closed mixer. A reciprocal alternation of the concentration of G· and GH is accounted for by changing conditions in the mixer and G· is slowly and irreversibly destroyed by alkylperoxyl radicals.