THERMAL OXIDATION OF POLYACETYLENE.

Abstract

In the reported experiments, the thermal oxidation of undoped trans-polyacetylene powder in dry air has been studied and the principal features of the mechanism have been developed. Thermogravimetric and differential thermal analysis reveal an exothermic process that first leads to a weight increase, followed by precipitous weight loss above 240 degree C due to formation of volatile oxidation products. Isothermal weight gain studies between 25 and 142 degree C show first-order kinetics below 90 degree C with a rate constant of 3. 10** minus **7s** minus **1 at 25 degree C and an apparent activation energy of 16 kcal/mol. A weight gain of more than 40% has been observed at 25 degree C after 2000 h of exposure to air. A change in first-order kinetics occurs at temperatures above 90 degree C. At elevated temperatures or for long-term oxygen exposure, the concentration of dopant oxygen decreases, probably by intramolecular regrouping of hydrogen atoms, resulting in the formation of hydroxyl groups and enhanced polymer degradation. This mechanism is consistent with the finding of others that the conductivity of polyacetylene upon oxygen exposure increases initially before decreasing significantly with continued exposure, especially at elevated temperatures.