Resonance Raman Studies of Photoinduced Decomposition of Nylon-6,6: Product Identification and Mechanistic Determination

We report observation of an enal product of the decomposition of both nylon-6,6 and a nylon-6,6 model compound, N,N -hexamethylenebis(hexamide), upon 266 nm pulsed UV laser irradiation of these amides. The product is identified by UV resonance Raman spectroscopy, which shows characteristic band frequencies and intensities of the C C and C O stretches of the enal. The vibrational assignment and product identification are supported by experiments with 15 N-labeled nylon-6,6. Degradation and spectroscopic characterization under 16 O 2, 18 O 2, and N 2 show that the degradation channel leading to the enal requires molecular oxygen and thereby indicate an oxidative mechanism. The product resonance Raman intensities are directly proportional to the number of photons incident on the sample, consistent with a direct photooxidative process, rather than a thermal−oxidative one with the laser serving as a heat source. We do not observe the enal product when the nylon-6,6 or model compound are simply heated in oxygen-containing atmospheres, except when the heating produces melting.