Using nitroxide decay to study the photooxidation kinetics of automotive topcoat enamels.

Free radical scavenging by nitroxide dopant is used to quantify the photoinitiation rate of free radicals in acrylic/melamine and polyester/urethane coatings during photolysis under "near ambient" exposure conditions. Photoinitiation rate measurements on weathered coatings reveal that acrylic/melamine coatings photooxidize non-autocatalytically, while polyester/urethane coatings photooxidize autocatalytically. The decomposition of hydroperoxide photolysis products by melamine crosslinker is claimed to account for this difference in photooxidation kinetics.