Resonance Raman spectroscopic investigation of the mechanism and kinetics of the degradation of N,N-hexamethylene bishexamide, a Nylon 6,6 model compound

We report a mechanistic study of the photo-oxidative degradation of N,N-hexamethylene bishexamide, a Nylon 6,6 model compound. Resonant Raman intensities of the amide and its previously identified enal degradation product are recorded as a function of the duration of the irradiation of the amide with 266 nm laser pulses. The time dependences of the Raman intensities are consistent with those predicted by a kinetic mechanism for photo-oxidation. In particular, the rate of formation of the enal, probed by monitoring the Raman intensity of its CO stretch peak at 1680 cm−1, agrees well with the rate of cleavage of the C–N bond in the amide, revealed by the time dependence of the intensity of the Am II (C–N stretch) vibration at 1537 cm−1. Rate constants for important steps in the degradation mechanism are obtained from the analysis.