Infrared spectra (1800-1450 cm-1) were studied for CPVC stabilized with Pb stearate(Ⅰ)

dibutyltin dilaurate (Ⅱ) and di-sodium hydrophosphate (Ⅲ) as a secondary stabilizer along with(Ⅰ) or (Ⅱ)

and previously subjected to different degree of thermal degradation. Infrared spectroscopy made it possible to follow the consumption of the effective ingredient of the primary stabilizer during thermal

decomposition by means of a band assigned to the stretching vibration of RCOO- (1510 or 1590 cm-1). The secondary stabilizers slow down the consump-tion. Conductometric measurments and Brabender torque rheometer tests confirmed the above results.