Disclosed are polybenzimidazoles containing sulfonyl groups. The polymers can be synthesized in Eaton's reagent from 3,3′,4,4′-tetraaminodiphenylsulfone, which itself can be synthesized from 4,4′-dichlorodiphenylsulfone. Methods of synthesizing the polymers are disclosed. The disclosed polymers can be used for high temperature H2/CO2 separation membranes and other uses.