Rigid aromatic polyesters containing alkoxy or phenyl-substituted oligophenyls were prepared. Soluble polymers were obtained also in cases where phenyl-substituted quinquephenyl diols were combined with asymmetric phenyl-substituted terephthalic acid. The synthesized polyesters were characterized by viscosimetry, gel permeation chromatography, thermal analysis, and dynamic mechanical analysis. The temperature dependence of the intrinsic viscosity was sensitive to the type of side groups. Thermogravimetry has shown that polyesters with aromatic substituents were stable up to 380-400 degrees C. The glass transition temperatures of the polyesters with aromatic side groups were in the 220-260 degrees C range as determined by DSC. Polyesters with hexyloxy side chains show crystallinity. Dynamic mechanical analysis showed that in the cases where aromatic substituents were used to increase solubility, the obtained polymers have very useful mechanical properties at high temperatures. The polymer having the quinquephenyl unit in the main chain has an almost constant modulus up to 340 degrees C.