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A new six‐membered tetracarboxylic dianhydride, 2,5‐di(carboxymethyl)terephthalic dianhydride, was synthesized in six steps, starting with pyromellitic dianhydride. The polyimides were prepared from dianhydride and diamines in a two‐step procedure. The polyamic acids, which were formed in the first step by the ring‐opening polyaddition in DMAc, had inherent viscosities of 0.1–0.7 and were converted to the polyimides by thermal cyclodehydration. These polyimides were insoluble in organic solvents. Thermogravimetric analysis (TGA) in air and nitrogen atmospheres revealed that rapid decomposition began above 400°C for aromatic polyimides.