Ring-opening polymerization of racemic β-butyrolactone promoted by salan- and salen-type yttrium amido complexes

摘要

A series of yttrium amido complexes bearing quadridentate binaphthyl-bridged Schiff-base salen-like and diamine bisphenolate salan-like ligands are synthesized and characterized. The complexes act as active initiators in the polymerization of rac-β-butyrolactone (rac-BBL) under mild conditions. The obtained poly(3-hydroxybutyrate) (PHBs) are syndiotactic enriched. ~13C NMR spectroscopy microstructure analysis shows the probability of racemic linkages P_r to be up to 0.81. Statistical Bernoullian analysis evidences that a chain-end mechanism of steric control operates for the salan-like compound bearing cumyl substituents in the ortho position of the phenolate rings. The melting temperatures of the syndiotactic enriched PHBs are in the range 120-157 °C, depending on the degree of stereoregularity of the polymers.