New aromatic diamines were prepared in two steps from 4,5-dichlorophthalic anhydride and primary amines. The resulting 4,5-dichlorophthalimide was reacted with 4-mercaptoaniline, so that the chloroatoms were substituted by the mercapto groups (via the sulfide anions). The new diamines were polycondensed either with the diphenyl ether 3,3',4,4'-tetracarboxylic anhydride or with bicyclooctane tetracarboxylic anhydride. These polycondensations were conducted in boiling m-cresol with azeotropic removal of water. The isolated polyimides were characterized by viscosity measurement, IR-spectroscopy, elemental analyses, and MALDI-TOF mass spectrometry. The mass spectra evidenced a high content of cyclic polyimides, indicating nearly perfect reaction conditions. The mass spectra also proved the formation of copolymers containing one diamine with a trialkylamine group in the side chain. High glass transition temperatures but a low crystallization tendency were found by DSC measurements. (c) 2005 Wiley Periodicals, Inc.