Degradation of chlorinated polyethylene. I. Effect of antimony oxide on the rate of dehydrochlorination

The degradation of two chlorinated polyethylene compounds CPE 25 (45% chlorine) and CPE 16 (36% chlorine) was studied by following their rates of dehydrochlorination at two temperatures, 150°C and 180°C in pure nitrogen and pure oxygen atmospheres. Studies on the powdered polymers showed that the dehydrochlorination rate of CPE 25 is about fourteen times faster than that of CPE 16 in nitrogen atmospheres and only three to four times faster in oxygen. The molded polymers gave a lower rate of dehydrochlorination than when in the powdered form. This effect is attributed to diffusion factors. The antimony oxide brought about an induction period in the dehydrochlorination reaction during which only a small amount of HCl is evolved, followed by a very fast rate of dehydrochlorination both in oxygen and nitrogen atmospheres. The duration of the induction period increases with increase in the Sb₂O₃ concentration, but is followed by an accelerated HCl loss which is faster when Sb₂O₃ concentration is higher. This work provides supporting evidence that SbCl₃ was formed and lost during degradation. Mechanisms of dehydrochlorination are suggested for the reaction in the case of pure chlorinated polyethylene and for the polymer containing antimony oxide.