Cyclo dehydration reaction of polyhydrazides. I. Kinetic parameters obtained with nonisothermal thermogravimetry

The thermal conversion reaction of poly‐(1,3‐phenyl‐1,4‐phenyl)‐hydrazide into poly‐(1,3‐phenyl‐1,4‐phenyl)‐1,3,4‐oxadiazole has been studied using thermogravimetry (TG). For the evaluation of the energie of activation and other kinetic parameters of this cyclo dehydration reaction a method developed by Ozawa was used, where polymer samples are heated with different constant heating rates. With this method the energy of activation can be determined accurately as a function of the degree of conversion. In this way a parallel reaction could be observed starting at the end of the nonisothermal conversion process. The polymer was used in two different morphological states, a powder and a film. A slightly higher energy of activation and a considerably higher pre‐exponential factor were observed for the film indicating a dependency of the kinetics on the morphological state or on the history of the polymer sample.