Kinetics of isothermal degradation of poly vinyl bromide (PVBr). A typical case of “autocatalytic” thermal degradation

The kinetics of thermal degradation of a sample of 46.0% isotactic polyvinyl bromide (PVBr) was studied in a static procedure. An integrated analytical method is presented for the estimation of rate constants. Reaction curves for the formation of hydrogen bromide (HBr) can be interpreted in terms of two concurrent first‐order reactions; namely, magnified image with activation energies of 29.7 and 40.6 kcal/mol, respectively. The mathematical derivation does not involve an approximation; thus the accuracy of the procedure depends only on the experimentation. Good agreement between calculated and experimentally determined values of a series of characteristic kinetical parameters was obtained. The formation of HBr from PVBr was studied kinetically by a thermogravimetric programmed procedure at room temperature to 700°C. By this method it is possible to determine the activation energy of the stripping process of the main chain without knowing the form of the kinetic equation. The activation energy of 40.1 kcal/mol for the overall process was evaluated by the MacCallum and Tanner method. This dynamic heating developed two distinct temperature regions in which maximum rate loss occurred at characteristic temperatures. The first temperature region was associated with the quantitative evolution of 100% HBr molecules.