Structure and mechanism of dehydrochlorination of polyvinyl chloride

Abstract

Abstract Polyvinyl chloride when heated loses HCl, presumably by a “zipper” mechanism. The loss of each molecule of HCl from the polymer results in the formation of a double bond, which activates adjacent chlorine and causes the decomposition reaction to propagate along the resin chain. Virgin and degraded resins were subjected to ozonization in order to ascertain the type and location of the labile structures responsible for initiating the “zipper” HCl loss. The molecular weight decrease and formation of carbonyl structures (detected by infrared) produced by ozone indicate that unsaturated chain ends are primarily responsible for HCl loss. Tertiary chloride chain branches contribute to a lesser degree in the initial stages but become more important as dehydrochlorination proceeds. Stability measurements on simple prototypes of structures presumed to be present in polyvinyl chloride provide additional information which is in essential agreement with this mechanism.