N-15 CP/MAS solid-state NMR spectroscopy of a N-15-enriched hindered aminelight stabilizer photolyzed in acrylic/melamine and acrylic/urethane coatings

Solid-state cross-polarization magic angle spinning N-15 nuclear magnetic r esonance spectroscopy has been used to follow the chemistry of a N-15-enric hed hindered amine light stabilizer and its corresponding nitroxide in an a crylic/melamine and an acrylic/ urethane coating system, as a function of u ltraviolet light exposure. The two coating systems are based on the same ac rylate copolymer, Samples were photolyzed in a QUV accelerated weathering t ester equipped with FS-340 UV-A fluorescent bulbs. The tester was operated in the "light only" exposure mode at an air temperature of 40 degrees C and a dew point of 25 degrees C. Spectra reveal the formation of HALS based am ino ether derivatives and hydroxylamine. No evidence for the accumulation o f HALS decomposition products or non-reactive HALS products was found. Dire ct evidence that, the amino ether derivatives formed in the two coatings sy stem are distinctly different, was found. One amino ether derivative was un ambiguously identified as a methyl adduct. The formation of methyl radicals during the photolysis of both coatings was demonstrated. (C) 2000 Publishe d by Elsevier Science Ltd. All rights reserved.