SYNOPSISThe kinetics for dehydrochlorination and benzene formation has been studied during the degradation of two samples of poly(viny1 chloride) (PVC) at 180-200°C under vacuum with and without the removal of hydrogen chloride. The effects of various additives, such as organic phosphites, mercury, silver, gold, and glass upon the thermal degradation of PVC were investigated. Mercury, silver, and glass decrease the rate of autocatalytic dehydrochlorination of the polymer in the presence of hydrogen chloride but silver and glass do not affect PVC degradation rate in the absence of HCI. PVC thermal decomposition under vacuum with removal of HCI mostly proceeds by a molecular mechanism. At the same time, radical reactions take place. But there are some very endothermic stages of chain propagation, this is why in this case, the radical mechanism of PVC dehydrochlorination does not compete with the molecular one. In the presence of HCI, the rate of radical reactions increases and predominates over rate of molecular reactions.