Mechanisms of antioxidant action: Mechanochemical transformation products of 2,2,6,6–tetramethyl‐4–hydroxypiperidinoxyl in polypropylene

摘要

AbstractThe effect of the processing operation on the nature and quantity of transformation products of 2,2,6,6‐tetramethyl‐4‐hydroxypiperidinoxyl (〉NO.) and its corresponding hydroxylamine (〉NOH) was investigated in polypropylene. It was found that both 〉NO.and 〉NOH are actively involved in a regenerative cycle and that this redox couple is responsible for the stability of the polymer whether the initial additive is 〉NO.or 〉NOH. The alkyl hydroxylamine (〉NOR), on the other hand, does not appear to play a significant role in the melt stabilization of the polymer. Quantitative measurements of 〉NOH and 〉NO.concentrations show that, under conditions of both restricted oxygen (CM) and oxygen excess (OM), the concentrations of both species change reciprocally throughout the processing operation. In a closed mixer (CM), the total overall concentration of 〉NO.and 〉NOH remains at a high constant level, whereas in an open mixer (OM), their total concentration decreases continuously to a low level, indicating the irreversible destruction of the redox couple (〉NO.and 〉NOH). The photo‐oxidative stability of the polymer was found to depend on the total concentration of the redox couple left in the system af