Characterization of photo-degradation of a polyurethane coating system by electron spin resonance

Photo-degradation studied by electron spin resonance (ESR) is described. Se lected polyurethane film samples were exposed to different accelerated agin g environments. These included narrow-band irradiation from 340 and 313 nm UV sources, broadband irradiation from a xenon are lamp, and elevated tempe rature without irradiation. The effect of oxygen was investigated. In addit ion, the influence of titania on free radical formation was examined. Early stage radicals were detected by generating them in the ESR cavity at -196 degreesC. A correlation between ESR and positron annihilation spectroscopy (PAS) data is shown, which indicates that free-radical-type chemical defect s may be the cause of sub-nanometer physical defects. (C) 2001 Elsevier Sci ence B.V. All rights reserved.