SINGLET OXYGEN AND PHOTO-OXIDATION OF POLYMERS

In the reported experiments, the rates of accumulation of oxygen-containing species in photooxidation have been determined for a series of polymers such as polystyrene, polyisoprene, and polybutadiene in a wide range of singlet oxygen stationary concentrations in the polymers. An increase in singlet oxygen (**1O//2) concentration was achieved by introducing a polymer which is a **1O//2 donor into a polymer and by irradiating a sample with an additional source of light absorbed by the dye only. To decrease **1O//2 concentration, 1,2,5-trimethyl-4-hydroxyphenylpiperdine, which is a quencher of **1O//2, was introduced into a sample. The **1O//2 stationary concentration in an oxidized polymer was measured via singlet oxygen oxidation of 2,2,6,6-tetramethyl-4-oxypiperdiene which leads to the formation of the corresponding nitroxyl radical. The photooxidation rate has been found to vary only slightly with **1O//2 concentration, even when the concentration changes 10-25-fold. Thus, **1O//2 does not participate appreciably in the process of polymer photooxidation. It may be due to the lowering of **1O//2 reactivity toward unsaturated groups in the polymer matrix as compared with that in solution.