Ion transport within random-sulfonated and block-sulfonated copolyimides

A series of sulfonated copolyimides was prepared from 4,4-oxydianiline, sulfonated 4,4′-oxydianiline, and 4,4′-(4,4′-isopropylidenediphenoxy) bis(phthalic anhydride). Both random- and block structures were prepared by varying the timing of monomer addition to the polymerization reaction. The polymers were converted to their acid forms and then cast into films. ¹H NMR, FTIR, and non-aqueous titration verified the degree of polymer sulfonation. The block copolymers showed higher water uptake and proton conductivities than random copolymers with similar ion exchange capacity (IEC) values. These differences became pronounced as the IEC value was increased.