Effects of metal chelates on the oxidation of polyolefins at high temperatures

The oxidation of carboxy-terminated polybutadiene (CTPB) and polypropylene (PP) has been investigated at temperatures above 150°C. Studies have also been made of the effects on the oxidation of these polymers of a number of transition metal chelates, namely, the bis(3,5-diisopropyl salicylato) (DIPS) derivatives of Co(II), Ni(II) and Cu(II), bis(3,5-diisopropyl salicylato) hydroxyaquo Cr(III), the bis(N-n-butyl salicylaldimino) (NBS) compounds of Cu(II) and Ni(II), and bis(stilbene dithiolato)nickel (II) (NiSDT). At the temperatures concerned, the antioxidant activity of some of the chelates, in particular the DIPS compounds, was limited by their thermal stability. NiSDT was found to be a uniquely effective antioxidant at temperatures up to ～290°C. Mechanisms have been proposed to account for the dual role, as both catalysts and inhibitors of thermal oxidation, of the DIPS and NBS chelates.