Photodegradation of organic photochromes in polymers - naphthopyrans and naphthoxazines series

The natural solar and artificial induced photodegradation of naphthopyran and naphthoxazine series was investigated in PMMA and in a polyurethane network. The degradation profiles through the depth of the coatings were monitored by Raman spectroscopy in function of the cumulated UV-A doses. The analyses of the formed photoproducts in each series were carried out by different off-line hyphenated chromatographic techniques. The detected products are clearly oxidized species and are similar to those found in apolar solvents. Moreover, the mechanisms of degradation seem to be of the same order between natural solar exposure and artificial solar simulation (suntests) that allows to use Xenon arc sources for accelerated degradation tests. The use of an oxygen barrier layer above the photochromic coating allows to demonstrate the formation of the naphtho[1,2]furan, which is the precursor of the 2-hydroxy-1-naphthaldehyde formation, in the naphthopyran series.