KINETICS OF PHOTOOXIDATION AND PHOTOSTABILIZATION IN CROSS-LINKED POLYMER-COATINGS

Previous work has established a correlation between photooxidation rat e and hydroperoxide concentration in crosslinked polymer coatings. The experimental relationship was in qualitative agreement with a photoox idation model based on photolysis of hydroperoxides to free radicals f ollowed by standard free radical oxidation chemistry. In this paper, t he kinetic scheme is extended to include the effects of chromophores o ther than hydroperoxides and to account properly for the addition of h indered amine light stabilizer (HALS). It is shown that the abstractio n of hydrogen atoms by excited state nitroxide limits HALS effectivene ss in agreement with experimental results. This agreement lends furthe r credence to the use of hydroperoxide measurements for the rapid asse ssment of coating photooxidative stability.