New data referring to the mechanism and quantum efficiency of electronically excited macroradicals and radical anion reactions in various carbon- and heterochain polymers at temperatures below their glass transition or melting points are presented and discussed. Basic mechanisms of the photochemical reactions, including new data on the mechanism of the photochemical reactions of peroxide radicals, the effect of various factors (photon energy, free volume, molecular organization of the medium) on the direction and efficiency of reactions of electronically excited macroradicals are considered. The important role of photochemical chain reactions in photoageing, including photooxidation of polymers, is demonstrated. It was found that by varying photon energy, temperature, photolysis time and by taking advantage of the competition between thermal and photochemical reactions, it is possible to change the functional composition and molecular mass distribution of polymers in some desired direction.
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