Thermal Dehydrochlorination of Poly(vinyl chloride) in Syndiotactic Systems

The thermal dehydrochlorination of syndiotactic poly(vinyl chloride) sequences has been studied theoretically on low-molecular weight models ranging from vinyl chloride dimer to pentamer using the semiempirical quantum chemical MNDO method. Parameters obtained with saturated systems and their change caused by the proceeding elimination of hydrogen chloride accompanied by the formation of the corresponding unsaturated structures are discussed with respect to the repeated chloroallyl or α-chloropolyene activation of the dehydrochlorination process. The study of the assumed radical and ionic intermediates is used in discussing the reaction mechanism of dehydrochlorination, and the radical or ionic mechanism is supposed to be operative depending on the reaction conditions.