The thermal degradation behavior of poly (vinyl chloride), PVC, in presence of poly(N-acryloyl-Mcyanoacetohydrazide), PACAH, has been studied using continuous potentiometric determination of the evolved HCl gas from the degradation process from one hand and by measuring the extent of discoloration of the degraded samples from the other. The efficiency of blending PACAH with dibasic lead carbonate, DBLC, conventional thermal stabilizer has also been investigated. A probable radical mechanism for the effect of PACAH on the thermal stabilization of PVC has been proposed. (c) 2008 Wiley Periodicals, Inc.