Chain and Photochain Mechanisms of Photooxidation of Polymers

The mechanisms of photooxidation of the popular commercial polymers polystyrene (PS), poly-ethylene (PE), and an ethylene-carbon monoxide copolymer (polyketone, PK) differing in the polymer chain structure and the nature and concentration of chromophore groups are considered. In the case of the formation of photosensitive intermediates in polystyrene, taken as an example, the photochain oxidation mechanism was revealed and thoroughly studied, according to which the polymer "burns" into complete oxidation products (CO(2), H(2)O) with a degree of conversion of >= 50% and a kinetic-chain length of l = 10(3)-10(4) units. The hydroperoxide mechanism plays a minor role in the photooxidation of PS, it is a short-chain pro-cess (as in the case of thermal oxidation, l similar to 10) and does not exceed 1.5% of the total amount of absorbed oxygen. Carbonyl groups, as weak photoinitiators, induce in PE and PK the conventional radical chain mechanism of photooxidation with degenerate branching of kinetic chains on hydroperoxide groups and other oxidations products.