Synthesis of Aliphatic Polyesters via Ring‐Opening Polymerization of Macrocyclic Oligoesters

Abstract

SummaryTo synthesize high molecular weight aliphatic polyesters, ring‐opening polymerization (ROP) of macrocyclic oligoesters made from several dicarboxylic acids and diols was investigated. Macrocyclic oligoesters used for the ROP were synthesized in ca. 50% yield via polycondensation of dicarboxylic acids (small excess) and diols under dilute condition in toluene, followed by washing with aq. NaHCO3 to remove linear oligomers. The obtained products were the mixtures of macrocyclic oligoesters with various ring size (dimer to heptamer). The polymerization of the macrocyclic oligoesters made from succinic acid and 1,4‐butanediol using rare earth catalysts such as Nd(BH3)(thf)3 and Nd(OiPr)3 was found to give high molecular weight polymers in good yields. Cyclic dimer of butylene succinate ((BS)2) was isolated from the mixture of the cyclic oligomers by column chromatography, and was similarly polymerized by the rare earth catalysts. Bulk polymerization of (BS)2 by Nd(BH3)(thf)3 yielded poly(butylene succinate) with Mn up to 38 000. Cyclic oligomers of trimethylene oxalate were not polymerized under the similar conditions applied in this study.