New thermally and chemically stable sulfonic acid-containing polymers are synthesized via post-sulfonation of aromatic polymers. These new polymers provide unique benefits to proton exchange membrane fuel cell technology ("PEMFC"). As a sulfonic acid moiety can be easily installed into an aromatic ring via electrophilic sulfonation, even in the presence of an electron-withdrawing substituent such as --F, rigid polymers consisting of aromatic rings at either the side chain or main chain can be prepared with a wide range of substituents and flexibility in properties. Novel synthetic procedures are provided for synthesis of the polymers.