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Thermogravimetry of polyimides based on dianhydrides of pyromellitic, diphenyland diphenyloxidetetracarboxylic acids and a series of diamines has been used to determine their temperature characteristics and calculate their activation energies. The dependence of the thermal stability of the polyimides on the structure of their diamine component was established. It was shown that the effect of the thermal stability of the polyimides progressively weakens with the increase in the rigidity of their chemical structure.Investigations of the thermal stability of polymers by thermogravimetric analysis are very widely used for rapid determination of their relative chemical resistance to high temperature. A method for establishing weight losses with progressively and linearly increasing temperature used in TG permits a relatively rapid determination of the effect of the chemical structure on thermal stability for polymers of the same class synthesized under similar conditions. In this respect a widely-used method of isothermal analysis yielding more information on the polymer behaviour in the course of prolonged heating at a fixed temperature has an important disadvantage: when a polymer sample is maintained for a long time at a high temperature, cross-linking occurs. Thermogravimetry enables us to avoid this disadvantage to a considerable extent and to determine the contributions of different chemical structures to the thermal stability of the polymer on the basis of several comparative criteria obtained under identical conditions of analysis. One of these criteria used in recent literature [1 ] is the temperature characterizing a definite point on the TG curve, such as the temperature of the onset of weight loss (To), determined in most cases as the point in which the TG curve deviates from the initial horizontal portion. These criteria also include temperatures of 5, 10, 50 and 100% weight loss, and the values of the weight loss at fixed temperatures (200, 300, 400 ~ etc.).Much work is in progress on the synthesis and investigation of high-temperatureresistant polymers of the polyimide class, which, owing to their thermal stability and many valuable physico-mechanical properties, occupy a very important place in the manufacture of polymer materials. A comparison of the thermal stabilities of different aromatic polyimides and establishment of their temperature characteristics make it possible to determine the effect of the chemical structure

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