Four new aromatic diisocyanates containing pendent flexible alkoxy chains, namely, 5-butyloxy-l,3-phenylenediisocyanate, 5-octyloxy-l,3-phenylenediisocya- nate, 5-dodecyloxy-l,3-phenylenediisocyanate, and 5-hexa-decyloxy-l,3- phenylenediisocyanate, were synthesized by Curtius rearrangement of the corresponding 5-alkoxy-l,3-phenylene diacylazides. These diisocyanates were each polycondensed with three commercially available aromatic dianhydrides: 4,4'-oxydiphthalic anhydride, 3,3',4,4'-(hexa-fluoroisopropylidene) diphthalic anhydride, and 3,3',4,4'-benzophenonetetracarboxylic dianhydride - in benzonitrile in the presence of l,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, l-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 159-246C as measured by differential scanning calorimetry. The temperature for the 10% weight loss of the polyimides was in the range 410-160C in a nitrogen atmosphere, which indicated good thermal stability. A pretilt angle of 2.97 was observed for the polyimide derived from 5-octyloxy-l, 3- phenylenediisocyanate and 4,4'-oxydiphfhalic anhydride. © 2008 Wiley Periodicals, Inc;