Mechanisms of antioxidant action. The role of nitroxyl radicals as chain-breaking acceptor antioxidants in the mechanodegradation of rubber

It is shown that 4-hydroxy-2,2,6,6-tetramethylpiperidinoxyl (HTMPO) becomes partially attached to natural rubber during mechano-oxidation in a shearing mixer at ambient temperatures. It is concluded that the main mechanism responsible for the antidegradant activity of HTMPO under shearing conditions is direct oxidation of mechanochemically produced macroalkyl radicals to species containing conjugated unsaturation.