Structural defects in polyvinylchloride—I. Internal unsaturation as initiation sites for dehydrochlorination

To obtain double bonds in PVC, copolymerizations of vinyl chloride (VC) with phenylacetylene (PA) and dimethylester of 2-butyne dioic acid (ADCE) were carried out. Copolymer compositions, as measured by i.r., were compared with ozonolytically evaluated chain scission numbers. Only the PA-units seemed to be incorporated at random in the PVC-chain. Phenyl groups conjugated to the double bonds led to a striking increase in thermal dehydrochlorination. Ozonolysis on degraded PVC samples provides insight into the mechanism of the dehydrochlorination, revealing the formation of additional unsaturated sites after degradation and permitting the estimation of average polyene sequence lengths.