Oxydation photocatalytique des polypropylènes isotactique et atactique

By photooxidation of isotactic and atactic polypropylene (PP), irradiated at wavelengths >300 nm in air, alcoholic, acidic, ester, lactonic, and unsaturated functions are formed as shown by IR spectrophotometry. The primarily formed hydroperoxy and ketone groups are rapidly photolyzed and their concentrations are kept low. In presence of UV absorbing pigments like TiO2 or ZnO, the same photoproducts are formed with lower rates than in the transparent polymers. In atactic PP, ZnO and TiO2 (rutile or anatase) show different photoactivities. When the light is absorbed in ZnO, accumulation of ketone and lactonic groups is observed. When TiO2 is the absorbing species, oxidation is going further and acidic, ester, and lactonic functions may be observed; TiO2 appears to be able to photocatalyze the disappearance of ketone groups. In isotactic PP of high cristallinity, direct photooxidation and photocatalyzed oxidation are superimposed and differences between ZnO and TiO2 cannot be observed.