A new aromatic asymmetrical ether diamine, 5-(4-aminophenoxy)-1-naphthylamine, was synthesized through the nucleophilic displacement of 4-chloronitrobenzene with the potassium phenolate of 5-amino-1-naphthol in dimethylformamide, followed by hydrazine palladium-catalyzed reduction. A series of novel aromatic polyimides containing asymmetrical diaryl ether segments were prepared from the diamine with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The poly(amic acid) precursors had inherent viscosities of 1.21-1.99 dL/g, and all of them could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides derived from less stiff dianhydrides generally displayed higher solubility. The glass-transition temperatures of these polyimides were recorded between 307 and 336degreesC by differential scanning calorimetry, and the softening temperatures of the polymer films were 299-344degreesC according to thermomechanical analysis. The polyimides showed insignificant decomposition before 520degrees C in air or nitrogen. For a comparative study, two series of analogous polyimides based on symmetrical diamines such as 1,5-diaminonaphthalene and 1,5-bis(4-aminophenoxy)naphthalene were also prepared and characterized. (C) 2004 Wiley Periodicals, Inc.