PHOTOOXIDATION KINETICS IN CROSS-LINKED POLYMER-COATINGS

Quantitative relationships have been developed between photooxidation rates and hydroperoxide concentrations in acrylic urethane and acrylic melamine coatings. The rate of photooxidation in both urethane and melamine crosslinked coatings is found to be linear in hydroperoxide concentration. In urethane coatings, the photooxidation rate goes to zero as the hydroperoxide concentration goes to zero, while in melamine coatings there is a residual photooxidation rate at zero hydroperoxide concentration. This residual photooxidation appears to be related to melamine photochemistry. The simple relationships derived suggest that hydroperoxide measurements can be used to screen coatings for photostability using outdoor-like exposure conditions.