A series of polybenzimidazoles containing sulfonyl groups were synthesized in Eaton's reagent for high temperature H-2/CO2 separation membranes. The key monomer, 3,3',4,4'-tetraaminodiphenylsulfone, was prepared via a novel and economical synthetic route starting from 4,4'-dichlorodiphenylsulfone. These polybenzimidazoles with sulfonyl moieties had enhanced solubilities in dipolar aprotic solvents relative to the commercial Celazole(R) that is prepared from diaminobenzidine. Thermal gravimetric analysis showed that the materials were stable at elevated temperatures with 5% weight loss values of at least 485 degrees C in either air or N-2. Glass transition temperatures of three polybenzimidazoles in this series were ascertained by dynamic mechanical analysis to be 438-480 degrees C. These sulfonyl-containing polybenzimidazoles exhibited excellent gas separation properties for H-2/CO2. Polymers from tetraaminodi-phenylsulfone and either terephthalic or isophthalic acid crossed Robeson's upper bound for H-2/CO2. (C) 2015 Elsevier Ltd. All rights reserved.