Novel aromatic polyesters have been synthesized by solution condensation reactions between hydroquinone and 3,4-disubstituted 2,5-thiophenedicarbonyl chlorides. The introduction of phenyl substituents in these poly(p-phenylene 3,4-disubstituted 2,5-thiophendicarboxylate)s did not enhance the fusibility nor the solubility of the resulting material when compared to the unsubstituted parent polyester. The presence of ethyl groups led to the formation of an insoluble semicrystalline aromatic polyester with a melting transition at 304 degrees C. Poly(p-phenylene 3-methyl-4-propyl-2,5-thiophenedicarboxylate) was found to be soluble in chloroform and exhibited a melting transition at 242 degrees C. All these polyesters are stable up to 350-400 degrees C. However, in contrast to the unsubstituted parent polymer, all these aromatic polyesters did not show any evidence of liquid crystallinity in the melt. On the basis of theoretical calculations, this behaviour can be related to the ca. 143 degrees core angle of 3,4-disubstituted thiophenes.