Molecular level chain scission mechanisms of epoxy and urethane polymeric films exposed to UV/H2O. Multidimensional spectroscopic studies

Step-scan photoacoustic Fourier transformed infrared (FT-IR) spectroscopy, FT-IR microscopy, and Raman chemical imaging were utilized to examine molec ular level degradation processes in epoxy (EP) and polyurethane (PUR) films . A combination of these techniques allowed us to determine a three-dimensi onal representation of degradation processes and showed that the extent of cross-linking in EP films varies as a function of depth from the surface. W hen exposed to 340 nm ultraviolet (UV) radiation and water vapor condensati on, EP films degrade to form cracks on the surface, which are composed of p rimary amines and result from a chain scission of the C-N bonds in cross-li nked bisphenol A EP films. PUR films exhibit the presence of two surface do mains, which are composed of PUR- and polyurea (PUA)-rich regions. When exp osed to 340 nm UV radiation and water vapor condensation, PUA is converted to PUR entities. Mechanisms leading to these processes are proposed and ind icate that isocyanate and polyol reactions occur in the presence of H2O and UV light.