Of the entire variety of polyaryletherketones, the most promising representatives of this class of polymers with high thermal and mechanical properties (polyether ether ketone, polyether ketone ketone) were studied in this work. The dependence of the rate of thermal decomposition on the structure was revealed, and the temperature-time ranges for the onset of gas evolution were shown. The order of destruction of the main polymer chain depending on temperature has been established. Due to the complexity of processing this class of polymers into products, the possibilities of changing the temperatures of phase transitions were shown in order to improve the technological conditions of processing without loss of performance characteristics. Comparative studies of the kinetics of the release of the main gaseous degradation products for polyether ether ketones from various manufacturers were carried out. The influence of hydrogen formed during the destruction process on the rate of decomposition of polymers is shown, and the dependences of the formation of carbon oxide and carbon dioxide on the structure and manufacturer of polymer materials are revealed. It has been established that polyether ether ketone has slightly higher mechanical properties compared to polyether ketone ketone, which is associated with the lower crystallinity of the latter due to the content of a comonomer with an irregular structure - isophthaloyl chloride