New aspects of the photo‐oxidation and photo‐stabilization of polymers

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Abstract
The mechanism of the photo‐oxidation of an ethylene‐propylene random copolymer (EPM) has been compared with that of a styrene‐butadiene‐styrene block copolymer (SBS). The former is considered as a model for polyolefins that undergo chain scission on irradiation and the latter as a model for unsaturated rubbers that become cross‐linked. A hindered amine light stabilizer (HALS) that is a better inhibitor of the absorption of oxygen in SBS than in EPM is, however, less efficient to prevent formation of carbonyl groups and change of the mechanical properties. These results are discussed and an explanation is proposed.