Recently, sulfur-containing copolyimides have attracted increasing attention as membrane materials for the separation of gaseous, vaporous, or liquid mixtures because of their superior separation properties. Therefore, a novel sulfur-containing copolyimide based on 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 4,4'-diaminodiphenylsulfide, and 3,5-diaminobenzoic acid was synthesized, characterized, and extensively investigated in toluene/n-decane pervaporation experiments. To characterize the separation properties of the copolyimide, the flux and selectivity were determined with separation mixtures between 60 and 80 wt % toluene. The separation temperature was varied between 70 and 110 degrees C. Thereby, we observed that when the temperature was increased from 70 to 90 degrees C, the flux and selectivity did not change significantly. In contrast, a temperature change from 90 to 110 degrees C caused an extensive increase in the flux. The most significant change was found for an 80 wt % toluene mixture, where an increase from 1.9 to 7 kg.mu m.m-2.h-1 was observed. Simultaneously, the selectivity which is a measure of the quality of the separation (a) decreased from a = 11.8 to a = 9.3. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013