Dual Catalytic System for Combination of Chain and Step Polymerizations: Ring-Opening Polymerization of ϵ-Caprolactone and Successive Dehydration Polycondensation with Dicarboxylic Acid Using the Same Catalyst

Abstract

We demonstrate a new system for the combination of chain and step polymerizations in which scandium trifluoromethanesulfonate [Sc(OTf)3] catalyzes both polymerization modes. Ring-opening polymerization of ϵ-caprolactone initiated from a diol was carried out in acetonitrile at 45 °C (Mn =1.2 × 103−3.6 × 103, Mw/Mn = 1.3). After removing acetonitrile under reduced pressure, bulk polycondensation with methylsuccinic acid was performed at 100 °C for 15 h to give the polyester in an excellent yield (92−94%): Mn and Mw/Mn were respectively 1.4 × 104 and 1.9. To check whether transesterification occurred or not during the two polymerizations, 13C NMR measurement was carried out in CDCl3. Suppressed transesterification was also supported from reductive cleavage of polyester containing disulfide linkage synthesized using ring-opening copolymerization of ϵ-caprolactone and successive polycondensation with 3,3′-dithiopropionic acid. Reversibly, chemoselective polycondensation of dicarboxylic acid containing a hydroxyl group and a diol and subsequent ring-opening copolymerization initiated from the pendent hydroxyl groups were also demonstrated using Sc(OTf)3 as the dual catalyst.