Characterization of polychloroprenes and cationically modified polychloroprenes by thermal dehydrochlorination

Thermal dehydrochlorination of polychloroprenes and modified polychloroprenes was studied and was found to be rapid, readily reproducible, and reliable for the characterization of these rubbers. The rates of thermal dehydrochlorination of polychloroprenes and modified polychloroprenes are first order at 190°C under nitrogen. Significantly, the plot of dehydrochlorination rate (VHCl) versus dehydrochlorination extent (ζHCl) for polychloroprenes shows three regions. These data may be attributed to three dehydrochlorination regimes associated with four contributing repeat structures that have been identified by 13C‐NMR spectroscopy: magnified image In contrast to polychloroprene, VHCl vs. ζHCl plots for modified (cyclopentadienylated and grafted) polychloroprenes, i.e., polychloroprenes that do not contain allylic chlorines, exhibit only one region suggesting only one dehydrochlorination mechanism in these materials. The slopes of the VHCl vs. ζHCl plots of the modified polychloroprenes are virtually identical. Moreover, the slopes of the VHCl vs. ζHCl plots for modified polychloroprenes and that of the latest of the three regions for unmodified polychloroprene are indistinguishable. This similarity in the VHCl vs. ζHCl curves suggests dehydrochlorination by a fundamentally similar mechanism in these materials, most likely one involving the CH2C(Cl)CHCH2 structure common to all of them. Concentration of labile chlorines in polychloroprene may be estimated by the differences in the dehydrochlorination kinetics of polychloroprene and modified polychloroprenes.