Abstract
A novel type of polybenzimidazole that is soluble in polar organic solvents and in concentrated sulfuric acid has been functionalized for use as a fuel cell membrane via electrophilic substitution of hydrogen by sulfonic acid groups by direct sulfonation using sulfuric acid. The novel polybenzimidazole has three different types of site available for substitution, and the extent of their modification depends, for a given concentration of sulfuric acid, on the temperature of the reaction medium, and the duration of the reaction. The progress of the sulfonation reaction with reaction time and temperature has been monitored using 1H NMR. Polymers with ion exchange capacities up to ca. 4.2 meq/g are obtained, the properties of which depend upon the degree of sulfonation, but in all cases membranes show much more moderate water uptake and dimensional change than polyaromatic polymers of equivalent degrees of sulfonation.
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