Novel semi-rigid rod-like homo- and copoly(ester-imide)s, composed of 3,3,3＇,4＇-diphenyl ether dicarboximide rings having no N-phenyl groups next to the imide ring, were synthesized by transesterification of a dihexanol derivative of 3,4,3＇,4＇-diphenyl ether dicarboximide and/or a dioxydihexanol of biphenyl with aliphatic dimethyl esters. The thermal and mesogenic properties of these polymers were evaluated. The expected structures of the polymers were confirmed by FTIR, C-13-NMR spectroscopy and elemental analyses. From DSC measurements, optical texture observations by means of a polarizing microscope equipped with a hot stage, and temperature-dependent X-ray analyses, it was determined that the biphenyl-unit-rich polymers form nematic phases, but the diphenyl ether dicarboximide containing homopolymers have no liquid crystalline phases in the melt, It was suggested that the mesogenic character of the 3,4,3＇,4＇-diphenyl ether dicarboximide ring is low. TG-DTA measurements showed that the polymers are thermally stable up to 300 degrees C in air.