Inhibition of the photo-oxidation of three different polymers by the same HALS has been studied: an ethylene-propylene random copolymer (EPM), a styrene-butadiene-styrene block copolymer (SBS) and the same block copolymer previously hydroperoxidized by reaction with singlet oxygen. Two techniques have been used and compared: oxygen absorption measurements and infra-red spectroscopy in the carbonyl region. The results indicate that HALS inhibits more efficiently the propagation of the photo-oxidation in the unsaturated polymers studied. However, it also catalyses a new type of termination that in EPM delays and in SBS promotes the production of ketones. It is suggested that the practical efficiency of HALS could be mainly dependent of that last effect.
展开▼
