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

Previous work has established a correlation between photooxidation rate and hydroperoxide concentration in crosslinked polymer coatings. The experimental relationship was in qualitative agreement with a photooxidation model based on photolysis of hydroperoxides to free radicals followed by standard free radical oxidation chemistry. In this paper, the kinetic scheme is extended to include the effects of chromophores other than hydroperoxides and to account properly for the addition of hindered amine light stabilizer (HALS). It is shown that the abstraction of hydrogen atoms by excited state nitroxide limits HALS effectiveness in agreement with experimental results. This agreement lends further credence to the use of hydroperoxide measurements for the rapid assessment of coating photooxidative stability.