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 2 66 nm pulsed UV laser irradiation of these amides. The product is identifie d by UV resonance Raman spectroscopy, which shows characteristic band frequ encies and intensities of the C=C and C=O stretches of the enal. The vibrat ional assignment and product identification are supported by experiments wi th N-15-labeled nylon-6,6. Degradation and spectroscopic characterization u nder O-16(2), O-18(2), and N-2 show that the degradation channel leading to the enal requires molecular oxygen and thereby indicate an oxidative mecha nism. The product resonance Raman intensities are directly proportional to the number of photons incident on the sample, consistent with a direct phot ooxidative process, rather than a thermal-oxidative one with the laser serv ing 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, exce pt when the heating produces melting.