Preparation of new membranes based on sulfonated aromatic copolyimides

Abstract New sulfonated aromatic copolyimides with controlled degree of sulfonation were prepared via polycondensation reactions of a sulfonated diamine and two unsulfonated diamines with 1,4,5,8‐naphthalene tetracarboxylic dianhydride (NDA). The sulfonated diamine 3,3′‐disulfonic acid‐ bis[4‐(5‐amino‐1‐naphthoxy)phenyl]sulfone (DANPS) was synthesized through nucleophilic substitution reaction of 5‐amino‐1‐naphthol with disodium‐3,3′‐disulfonate‐4,4′‐dichlorodiphenysulfone (SDCDPS) and subsequent acidification. Two unsulfonated diamines 4,4′‐(5‐amino‐1‐naphthoxy)diphenylsulfone (ANDS) and 4,4′‐(4‐aminophenoxy)diphenylsulfone (APDS) were prepared by nucleophilic reaction of 5‐amino‐1‐naphthol and 4‐aminophenol with 4,4′‐dichlorodiphenylsulfone in the presence of potassium carbonate, respectively. After characterization of the monomers and polymers with common methods, the physical properties of the polymers including thermal behavior and stability, viscosity, molecular weight, and ion exchange capacity (IEC) were studied. The polymers showed high thermal stability and ion exchange capacity which were the basic requirements for application as fuel cell membranes. Copyright © 2008 John Wiley & Sons, Ltd.