Three homologous sulfonated diamines bearing a bis(aminophenoxyphenyl)sulfone structure, namely, bis[4-(4-aminophenoxy)phenyl]sulfone-3,3-disulfonic acid (pBAPPS-3DS), bis[4-(4-aminophenoxy)phenyl]sulfone-2,2'-disulfonic acid (pBAPPS-2DS), and bis[4-(4-aminophenoxy)-2-(3-sulfobenzoyl)phenyl]sulfone (pBAPPS-2DSB), were synthesized. A series of sulfonated polyimides (SPIs) were synthesized from 1,4,5,8-naphthalene tetracarboxylic dianhydride, these sulfonated diamines, and nonsulfonated diamines, and their properties were investigated in comparison with those reported for the SPIs from another homologous diamine or bis[4-(3-aminophenoxy)phenyl]sulfone-3,3'-disulfonic acid (mBAPPS-3DS). These SPIs were soluble in common aprotic solvents and showed reasonably high proton conductivity, except for pBAPPS-2DS-based SPls, the conductivity of which was slightly lower because of the lower water uptake. The water stability of these SPIs considerably depended on the structure of the sulfonated diamines and was in the order of pBAPPS-2DSB approximate to pBAPPS-2DS > pBAPPS-3DS > mBAPPS-3DS. Their water stability was much lower than that of the SPIs from 4,4-bis(4-aminophenoxy)biphenyl-3,3'-disulfonic acid. The reason was discussed on the basis of the basicity of the sulfonated diamine and the solubility property of the SPIs. (c) 2007 Wiley Periodicals, Inc.