ZUSAMMENFASSUNGTechnische Polyvinylchloride verschiedener Herkunft unterscheiden sich teilweise stark in der Geschwindigkeit der thermischen Chlorwasserstoffabspaltung und in der Verteilung der dabei entstehenden Polyensequenzlangen. I n Gegenwart von Diphenylbleidichlorid wird die DehydrochIorierung von Polyvinylchlorid beschleunigt, wobei jedoch infolge Verschiebung der Polyensequenzliingenverteilung eine weniger starke Verfiirbung als bei reinem Polyvinylchlorid auftritt. Dagegen bewirken echte Stabilisatoren sowohl eine Verzogerung der Chlorwasserstoffabspaltung als auch eine Verschiebung der Sequenzliingenverteilung nach kurzeren Polyensequenzen. Die Ursachen hierfur werden am Beispiel von Blei-und Cadmiumoctoat als zugemischten Stabilisatoren und fur innerlich stabilisiertes Polyvinylchlorid diskutiert . SUMMARY :The rates of dehydrochlorination of commercial poly (vinyl chlorides) and the distribution of the lengths of the resulting polyene sequences may vary widely depending on the origin of the polymer. -In the presence of diphenyllead dichloride the rate of dehydrochlorination is increased, while the resulting discoloration is less intense compared to that of pure poly (vinyl chloride) because of a shift of the polyene sequence lengths distribution. Genuine stabilizers, on the other hand, effect retardation in dehydrochlorination as well as a shift of the sequence lengths distribution towards shorter polyene sequences. The causes for this behavior of admixed stabilizers using lead and cadmium octoate as examples as well as of internally stabilized PVC are discussed.

Investigation of the thermal behavior of copolymers of vinyl chloride (VC) and diethylfumaric ester (FDE), isobutene (IBu), vinyl bromide (VBr), and 2‐chloropropene (2CP) gives an insight into the mechanism of thermal dehydrochlorination in an inert atmosphere. The rate of decomposition at 180°C. increases in the following order: VC‐homopolymer < VC–FDE‐copol. < VC‐IBu‐copol. < VC‐VBr‐copol. < VC‐2CP‐eopol. The thermal elimination of hydrogen chloride from the copolymers in a nitrogen atmosphere starts from the comonomer unit. The first step of the decomposition of the VC‐VBr and the VC‐2CP‐copolymers requires a sequence of at least two neighboring comonomer units. The behavior of the 2CP‐copolymers indicates that the thermal decomposition of PVC can start from branches. The growth of the forming polyene sequences is stopped at the FDE‐ or IBu‐units Thus shorter sequences result, in reference to the VC‐homopolymer. However, the length of the polyene sequences increases from PVC to VC‐VBr‐copolymers to VBr‐homopolymer. The activation energies of hydrogen halide elimination from VC–VBr‐ and VC–2CP‐copolymers are lower than that of PVC.