An increase in the operation temperature of polymeric materials that also possess high mechanical strength at that temperature is undoubtedly one of the most important problems of modern polymer science. This prob-lem can be solved only on the basis of a thorough investigation of the heat resistance of these polymers. Meanwhile, one must answer with clarity the question “What is the best criterion of heat resistance in polymers?” Also, the polymeric structure that leads to the ultimate in heat resistance has notbeen determined. For instance, the loss of weight (ΔM) of the diglycidyl ether of bis-phenol A (DGEBA) cured with iso-methyltetrahydrophthalic anhydride (iso-MTHPA) after thermal oxidative destruction in air at 533°K for 100 hours has been determined experimentally to equal 2.8% w. However, DGEBA cured with the complex of copper salicylate with triethylenetetramine [Cu(trien)(HOC6H4COO)2] has AM = 3.5% w after thermal oxidative destruction under the same conditions [1]. Comparison of these data seems to lead to the conclusion that the epoxy-anhydride polymer is more heat resistant than the epoxy-chelate polymer. However, a similar investigation of these polymers at 573°K showed that after thermal oxidative destruction for 10 hours, DGEBA cured with iso-MTHPA has ΔM = 5.0% w while the copper-containing polymer has AM one-half of this value [1]. Thus it is obvious that an answer to the question about the more heat-resistant polymer is dependent on the temperature of the poly-mer treatment.