Sulfonated Poly(meta-phenylene isophthalamide)s as Proton Exchange Membranes

Random and block sulfonated poly(meta-phenylene isopthalamide) s as proton exchange membranes were synthesized through the Higashi-Yamazaki phosphorylation method. Polymers with different degrees of sulfonation from 40 to 100 mol percent were prepared by adjusting the molar feed ratio of 5-sulfoisophthalic acid sodium salt (SIPA) and isophthalic acid (IPA) in the reaction with meta-phenylene diamine. Creasable polymer films were obtained by casting DMSO polymer solutions and the membrane films could be exchanged to the proton form in strong acid. H-1 NMR spectroscopy and titration confirmed the degree of sulfonation. Thermogravimetric analysis demonstrated good thermal stabilities with 5% weight loss greater than 380 degrees C. The copolymers with low degrees of sulfonation (DS=40 mol %) exhibited low water uptake (water uptake <17 wt %) at room temperature. A segmented multiblock copolymer prepared by preforming a sulfonated block showed lower water uptake at high temperatures than the random polymer with the same DS of 40 mol % and displayed stability in water up to 80 degrees C. Both random and block copolymers showed higher proton conductivities at high temperature than that of Nafion-117 under 95% relative humidity. (C) 2016 Wiley Periodicals, Inc.