New fluorine free, thermally stable polymer electrolytes are desirable for fuel cells intended for operation over 100 °C. Sulfonated polyarylenes, prepared by Diels-Alder polymerizations, have recently been demonstrated to be excellent fuel cell membranes at temperatures as high as 120 °C. This effort is focused on less costly diene monomers for Diels-Alder polymerizations with diethynylbenzene co-monomers. A particular emphasis has been placed on monomers with new configurations of substituents that permit the properties of the polymer electrolyte membranes to be tailored to meet applications.