Photo‐oxidation of the 2,4‐dichloropentanes and PVC

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Abstract
The photo‐oxidation of PVC and its model compounds, the dl‐ and meso‐2,4‐dichloropentanes, were studied by high‐resolution NMR spectroscopy. The structure, CHClCH2COCH2 was found to be present in PVC after photo‐oxidation. Two peaks, which corresponded to the CHCl and CH2 groups next to the carbonyl group, were observed in carbon disulfide–acetone‐d5 mixture, at 6.15 and 7.25τ, respectively. From the NMR spectra, the ratio of the CH2 to CHCl protons in PVC and the model compounds were found to increase linearly with the time of photo‐oxidation after induction periods. The initial rates of the model compounds were comparable with that of PVC; i.e., 1.6 × 10−2 hr−1, at 30°C. Since similar gaseous products were also detected by mass spectrometry in the initial stage, their photo‐oxidation probably assumed the same rate‐determining step. According to the results that the dl‐2,4‐dichloropentane was photo‐oxidized 1.5 times faster than the meso‐compound, it would be likely that the syndiotactic sequences in PVC might be more easily photo‐oxidized than the isotactic sequences.