Recently, we reported that scandium trifluoromethanesulfonate [Sc(OTf)(3)] and scandium trifluoromethanesulfonimide could catalyze polycondensations of dicarboxylic acids and diols. Although these polycondensations were one-step and Occurred at the moderate temperature of 35 degrees C, they required large amounts of the catalysts (ca. 1 mol%) and long reaction times (> 100 h). Therefore, scandium catalysts having stronger electron-withdrawing ligands (scandium perfluorooctanesulfonate, scandium nonafluoro-butanesulfonate, and scandium, bis(nonafluorobutanesulfonyl)imide [Sc(NNf(2))(3)]) were synthesized, and their catalytic efficiencies were tested. We have now demonstrated and report herein that scandium Catalysts with the stronger electron-withdrawing ligands could catalyze the polycondensation of adipic acid and 3-methyl-1,5-pentanediol under conditions of a moderate temperature, a short time period, and a lesser amount of catalyst. Other rare-earth-metal catalysts containing ligands with strong electron-withdrawing abilities were also synthesized, and their catalytic efficiencies were tested using the aforementioned polycondensation. As a result, thulium bis(nonafluorobutanesulfonyl)imide [Tm(NNf(2))(3)] was a more effective catalyst than was Sc(OTf)(3), Sc(NNf(2))(3), thulium trifluoromethanesulfonate [Tm(OTf)(3)], or thulium trifluoromethanesulfonimide [Tm(NTf2)(3)]. Our work now makes it possible to synthesize aliphatic polyesters of M-n > 1.0 x 10(4) at a moderate temperature (60 degrees C), within I short period of time (6h). and using it small amount of catalyst (0.05-0.1 mol %).