Often a nonohydric alcohol or a monocarboxlyic acid is included in the reactants. From this, reactive end groups eliminated and the molecular weight can be controlled. In a typical process, the mixture of reactants is heated at 200 to 250 deg C in an inert atmosphere for several hours with continuous removal of H2O. Polyesters of molecular weight up to 1000 may be prepared to serve as plasticizers. Applications of saturated polyesters - plasticizers which are less volatile, and more resistant to solvent extraction than conventional monomeric plasticizers. The preparation of saturated polyesters involves continuously heating, up to 200 deg C, the mixture of reactants in the presence of a catalyst.
Water is removed from the reaction by azeotropic distillation.
Note that these molecular weights are considered high. The notes are unclear as to intent on page 112. The reactions show a stoichiometric imbalance of 2 moles diol to 1 mole diacid. I believe excess diol is used because the diol is more volatile than the diacid, and some is expected to be lost by evaporation during the reaction. Perhaps this is a good time to discuss the need for stoichiometric balance .