H. Kim et Mw. Urban, Molecular level chain scission mechanisms of epoxy and urethane polymeric films exposed to UV/H2O. Multidimensional spectroscopic studies, LANGMUIR, 16(12), 2000, pp. 5382-5390
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.