Cross-linking photodegradation process

Since many polymers are to a certain degree photo-cross-linkable and photodegradable, the result of the overall reaction depends on the prevailing process, because cross-linking and degradation are competing processes. 

Photodegradation of polymers (photoageing), involving chain scission and/or cross-linking, occurs by exposure to solar or artificial radiation and causes structural modifications, usually accompanied by a dramatic deterioration of the physical and mechanical properties of the polymer.954 Typically, radical intermediates are formed upon excitation, which initiate subsequent (dark) degradation. The presence of other species, such as oxygen, water, organic solvents or additives, and also mechanical stress and heat, may enhance the efficiency of these processes. 

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