The photo-oxidation of polymers. A comparison with low molecular weight compounds

The photo-oxidation of polymers involves different steps in which their reactivity is different frorn that of low rnolecular weight cornpounds. This is rnainly due to the close vicinity of reactive groups in polymers and to the rigidity of the rnatrix. As a consequence, transfer of energy has a rnajor role in the initiation of the photo-oxidation of rnost polymers on exposure to sunlight. It results in the sensitized decornposition of neighbouring hydroperoxide groups which, however, produce free radicals and thus initiate the oxidation less efficiently than rnodel cornpounds in fluid solution. Scission of the polymer backbone, responsible for the alteration of the physical and rnechanical properties, involves the decornposition of isolated hydroperoxide groups by two different rnechanisms the relative importance of which changes with temperature.