The synthesis and characterization of a novel series of soluble polyimides, which are based on alkyloxydiaminobenzene (AODB) and have long-chain linear alkyl groups with 10—14 carbon atoms, are described. Polyimides obtained from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and AODB-10—14 were soluble in polar solvents such as N-methyl-2-pyrrolidone (NMP) and the effect of long-chain linear alkyl groups for the enhancement of solubility was confirmed. Soluble copolyimides based on AODB and the conventional aromatic diamine diaminodiphenylether (DDE) may also be obtained. The incorporation of DDE resulted in an increase of the molecular weight and improved the thermal stability. These polyimides and copolyimides based on AODB were soluble in various polar solvents and exhibited high thermal stability in air and nitrogen. The copolymerization experiments and the solubility tests demonstrated that the most effective alkyl chain length for improving the solubility is twelve.