AbstractAromatic hydrogen atoms in thermostable polymers can be surprisingly labile at relatively low temperatures and may participate extensively in degradative reactions. If hydrogen were eliminated from the polymer chain, a number of degradative pathways would be excluded. Replacement of hydrogen with other pendent groups such as fluoride or trifluoromethyl still leaves a potential “handle” to enter into unwanted reactions, therefore, all bonds not required to create the chain were eliminated. The polyimide devoid of hydrogen from pyrazinetetracarboxylic dianhydride and 2,5‐diamino‐1,3,4‐thiadiazole was synthesized. This polymer exhibits extraordinary high temperatureoxidation stability. Films of this composition support weight in air up to 592°C, and rupture at this temperature is accompanied by no charring whatever. By comparison, the corresponding polymer from pyromellitic dianhydride, with two hydrogen atoms per repeating unit begins to cha