31 the precursor reactants are generally combined in proportions corresponding to the molar proportions of the units desired in the copolyester products except that it is preferred to use a molar excess indicated in the examples as of the more volatile diacetate of hydroquinone or substituted hydroquinone conventional polymerization techniques may be employed such as described in the aforementioned u s pat no 4 118 372 and more particularly in the examples described below in general a mixture of monomers is heated with stirring under nitrogen in a 250 ml 3 necked flask or polymerization tube in a wood 39 s metal bath or other suitable heating medium from approximately 250 u00b0 c to 330 u00b0 380 u00b0 c polymerization is continued for up to a total of 0 5 to one hour or longer if necessary until a polymer of fiber forming molecular weight is obtained usually a vacuum is applied to obtain a final product with high molecular weight the copolyesters of the invention exhibit optical anisotropy in the melt as described in u s pat no 4 118 372 the copolyesters of the invention are spun into filaments by conventional melt spinning techniques without substantial degradation in the examples below filaments were prepared by melt spinning into a quenching atmosphere of air or nitrogen and collected at a windup speed specified.