Studies on photodegradation of poly(vinylchloride) (part 2)

The electron spin resonance of poly(vinyl chloride) was measured under irradiation by ultraviolet rays. At 0°C, a broad singlet spectrum was observed in case of PVC powder, but a four‐line spectrum having a splitting constant of 11.5 gauss was observed in case of a cast film of PVC. It was found that the radical causing this spectrum is converted to a different radical when irradiation is continued. The mechanism of photodegradation of low‐molecular‐weight model compounds, i. e., 2,3‐dichlorobutane and 2,4‐dichloropentane, was examined. From results of these experiments, it is believed that the mechanism of photodegradation of PVC is such that a radical generated on the terminal methyl group is converted to an alkoxy radical through a peroxide and this alkoxy radical pulls off the hydrogen atom from the methylene group to form a carbonyl compound, and finally the Norrish type cleavage takes place, resulting in reduction of the molecular weight.