The phase transitions in two liquid crystalline polyesters have been studied by diffraction techniques employing synchrotron radiation. The two polyesters, derived from p,p'-bibenzoic acid and 3-methyl-1,6-hexanediol, only differ on the optical activity of the chiral spacer: both the active and racemic polymers have been investigated. Time-resolved experiments at variable temperature were performed, analyzing the cooling from the isotropic melt and the subsequent melting. The analysis of the different diffraction profiles (covering WAXS, MAXS, and SAXS regions) shows important differences in the phase behavior of the two polyesters, more important than those anticipated from the analysis of the DSC curves. Nevertheless, a common feature is the obtention of Sc mesophases in both polymers, characterized by a continuous increase of the tilting angle as the temperature is decreased (before the appearance of high-order mesophases).