Using the copper-catalyzed 1,3-dipolar "click" cycloaddition reaction, poly(sulfone)s containing pendant azide moieties were functionalized with various quantities of sodium 3-(prop-2-ynyloxy)propane-1-sulfonate and crosslinked with 1,7-octadiyne. The degrees of sulfonation and crosslinking were systematically varied by changing the ratios of the aforementioned reagents. The polymers were cast into membranes, acidified, and then tested for proton conductivity, methanol permeability, and membrane-electrode assembly (MEA) performance. The membranes showed a reduction in methanol permeability with increasing concentration of crosslinker and exhibited performance on par with direct methanol fuel cells containing Nation-based membranes. (C) 2010 Elsevier Ltd. All rights reserved.