New sulfonated copolyimides containing ether, carbonyl, and bulky naphthyl group in backbone were synthesized in two reaction media: organic solvent and ionic liquid media. For this purpose a new sulfonated diamine (BANBPDS) and an unsulfonated diamine (BANBP) was prepared through reactions of 4,4'-dichlorobenzophenone-3,3'-disulfonic acid, and also 4,4'-dichlorobenzophenone with 5-amino-1-sodium naphthoxide, respectively. Three series of sulfonated copolyimide with different sulfonation contents (40-80%) were prepared by reaction of the sulfonated diamine (BANBPDS) in companion with three unsulfonated diamines including BANBP, 4,4'-oxydianiline (ODA), and 1,8-diamino-3,6-dioxaoctane (DADO) with 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA). Two media were selected for preparation of copolyimides. Copolyimides synthesized in ionic liquid had higher inherent viscosity and higher molecular weight in comparison with similar copolyimides that were synthesized via common organic solvent method. Incorporation of flexible groups in polyimide structures increased solubility and processability of the copolyimides. After characterization of polymers with common methods, their water uptake, water stability, ion exchange capacity (IEC), thermal behavior and stability, crystallinity, and morphology were studied. The polymers showed suitable properties including high thermal stability and ion exchange capacity, which were the basic requirements for application as fuel cell membranes. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012