Polyelectrolyte membranes suitable for use in a fuel cell are provided as a solid state sulfonation product of particular fluorinated polymers, or alternatively as a fluorination product of particular sulfonated polymers. A sulfonated polymer is provided that contains repeating units represented by structure, ##STR00001## wherein the groups Ar3 and Ar4 are independently selected from the group consisting of aryl rings, aryl ring systems, and thiophene rings, and where at least one of Ar3 and Ar4 is substituted with a sulfonate group. Films suitable for use as a polyelectrolyte membrane are prepared from the sulfonated polymers.