Modelization of the photocatalyzed oxidation of polyolefins, 3. Oxidation of model hydrocarbons with ZnO

The present paper reports on analytical aspects of the ZnO photocatalyzed oxidation of linear and cyclic alkanes. Normal and branched hydrocarbons were examined as models in the photoageing of both polyethylene and polypropylene, respectively. IR, GC‐MS and chemical analyses confirm the formation of hydroxyl and carbonyl groups and ascertain the presence of γ‐lactones in the photooxidation of polyolefins. In the presence of ZnO as pigment, ketone groups accumulate and no acidic groups are observed. The formation of γ‐lactones is favoured in substituted aliphatic alkanes like 2,4‐dimethylpentane and 2,2,4‐trimethylpentane, i.e. in molecules where methyl groups are in β‐position of a tertiary carbon atom. A mechanism of the formation of γ‐lactones in photooxidation of both model alkanes and polyolefines is proposed.