High molecular weight polyimide was successfully prepared from thianthrene-2,3,7,8-tetracarboxylic acid-5,5,10,10-tetraoxide (TADATO-4A) and 3,7-diamino-2,8(6)-dimethyldibenzothiophene sulfone (DDBT) via the Yamazaki-Higashi phosphorylation method in the presence of triphenyl phosphite (TPP) and pyridine (Py). The obtained polyimide showed about 3-4 times larger inherent viscosity than that prepared by the conventional two-step method in which the anhydride form (TADATO) of TADATO-4A was used. The combination of the conventional two-step method and Yamazaki-Higashi phosphorylation method, in which a dianhydride monomer [3,3',4,4'-diphenylsulfonetetracarboxyli dianhydride (DSDA)] was allowed to react with excessive DDBT to form an amine end-capped polyamic acid oligomer and subsequently the oligomer was further polymerized with TADATO-4A in the presence of TPP and Py, succeeded in giving the high molecular weight copolyimide, TADATO/DSDA(1/ 1)-DDBT. However, both TADATO-DDBT and TADATO/DSDA(1/1)-DDBT showed fairly poor thermal stability due to the highly rigid structures. The pervaporation (PV) properties of the prepared polyimide membranes for benzene/cyclohexane (Bz/Cx) and benzene/n-hexane (Bz/n-Hx) mixtures were investigated. TADATO-DDBT showed similar PV performance to DSDA-DDBT at 60 degrees C. The sorption measurement revealed that these two kinds of polyimide membranes had a similar sorption amount, solubility selectivity, and diffusivity selectivity. The PV performance of TADATO/DSDA(1/1)DDBT was also found similar to DSDA-DDBT for Bz/Cx mixture.