Abstract: A process for preparing a polyester which includes the step of heating a reaction mixture comprising (i) diesters of dihydric phenols and C.sub.1-10 aliphatic monoacids, (ii) aromatic dicarboxylic acids, and (iii) a catalytic amount of an organic cation-containing salt at a temperature above the melt temperature of the diesters, under reaction conditions sufficient to form the corresponding polyester. Use of this process subjects the polymers prepared thereby to a thermal history which causes relatively little deterioration of the polymer's properties.