Polymer electrolytes, or more specifically, proton exchange membranes (PEM)s for fuel cell applications have been a growing area of research and development worldwide in the last decade. DuPont's Nafion® perfluorinated membranes have played an integral role in the success of recent PEM fuel cell technology. However, its high cost, poor performance at temperatures above 100 °C, and relatively high permeability to fuels and oxidizers material has driven researchers to look for alternative materials, including sulfonated polysulfones and polyether-ether-ketones (PEEK). We have looked at sulfonating polyarylenes prepared by Diels-Alder polymerizations as possible PEM fuel cell candidates; high proton conductivity, chemical and thermal stability, and film toughness demonstrated that these materials are promising candidates. However, sulfonation reactions using sulfuric acid, sulfur trioxide, or chlorosulfonic acid can also cause cross-linking through the formation of sulfone links between polymer chains and lead to lower yields of usable ionomers. In this work we have adapted the Friedel-Crafts reactions that cause cross-linking to prepare sulfonated polymers by reacting polyarylenes with 1,3,5-benzenetrisulfonyl chloride.