Polymer electrolyte membranes (PEMs) provide electrical insulation between the electrodes in fuel cells while allowing protons to pass freely. Mechanically tough PEMs that can operate at higher temperatures and resist oxidation without fluoride substituents are needed for fuel cells to be economical. To meet these goals we are developing new polyarylene PEMs that are prepared by Diels-Alder polymerizations. In this research we are synthesizing novel bis(styryl)benzene dienophile monomers. These monomers will be co-polymerized with bis(tetracyclopentadienone) monomers will provide a new route to oxidatively stable PEMs with site-specific sulfonic acid groups for better ionic conductivity even at low humidification.