AbstractFour new aromatic diisocyanates containing pendent flexible alkoxy chains, namely, 5‐butyloxy‐1,3‐phenylenediisocyanate, 5‐octyloxy‐1,3‐phenylenediisocyanate, 5‐dodecyloxy‐1,3‐phenylenediisocyanate, and 5‐hexadecyloxy‐1,3‐phenylenediisocyanate, were synthesized by Curtius rearrangement of the corresponding 5‐alkoxy‐1,3‐phenylene diacylazides. These diisocyanates were each polycondensed with three commercially available aromatic dianhydrides: 4,4′‐oxydiphthalic anhydride, 3,3′,4,4′‐(hexafluoroisopropylidene) diphthalic anhydride, and 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride—in benzonitrile in the presence of 1,4‐diazabicyclo[2.2.2]octane as a catalyst to obtain a series of polyimides with inherent viscosities in the range 0.16–0.43 dL/g. Except for 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride based polyimides, all of the polyimides were found to be soluble in dichloromethane, m‐cresol, 1‐methyl‐2‐pyrrolidinone, tetrachloroethane, and pyridine either at room temperature or on heating and could be cast into tough, flexible, transparent films from a solution in m‐cresol or tetrachloroethane. X‐ray diffractograms revealed that the polyimides with longer alkoxy chains had layered structures. The glass‐transition temperature of the polyimides containing pendent flexible alkoxy chains were in the range 159–246°C as measured by differential scanning calorimetry. The temperature for the 10% weight loss of the polyimides was in the range 410–460°C in a nitrogen atmosphere, which indicated good thermal stability. A pretilt angle of 2.97° was observed for the polyimide derived from 5‐octyloxy‐1,3‐phenylenediisocyanate and 4,4′‐oxydiphthalic anhydride. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009