Initiation mechanism of the photo-degradation of poly(vinyl chloride)

Abstract

To elucidate the initiation mechanism of the photodegradation of PVC, luminescence and ultra-violet spectra of PVC film and model compounds (3-chloro-2-butanone(I), 1-chloro-2-butene(II) and 2-butanone(III)) assumed to present in PVC were measured. Neat PVC film showed a fluorescence spectrum with a peak at 360 nm (a maximum excitation peak at 296 nm). The intensity of the peak decayed rapidly and new additional peaks appeared in the longer wavelength region. The new peaks which were ascribed to conjugated double bonds increased in intensity and shifted during the photo-irradiation. None of the model compounds showed fluorescence and II showed no phosphorescence. The phosphorescence of PVC was very similar to that of I, and its intensity decreased rapidly during the photo-irradiation. The phosphorescence spectrum of III was very weak and similar to that of photo-irradiated I. Among the products of the photolysed 3-chloro-2-butanone, III was detected by GC-mass spectrometry. The number of chlorine atoms evolved from I was much higher than that from II. The results obtained suggest that for the initiation of the photodegradation of PVC, allylic C-Cl does not necessarily play so important a role as α-chloroketone structures.