Stereochemical Control in the Anionic Polymerization of β-Butyrolactone Initiated with Alkali-Metal Alkoxides

The anionic polymerization of ( R )-β-butyrolactone initiated with either 18-crown-6 complexes of a potassium alkoxide or a simple carboxylate (reference initiator) proceeded with inversion of configuration. As a result ( R )-β-butyrolactone formed an isotactic poly(( S )-β-hydroxybutyrate) with these initiators at room temperature. Polymerization of ( R, S )-β-butyrolactone under the same conditions gave an atactic polymer, but at lower temperatures the predominantly syndiotactic form of poly(( R, S )-β-hydroxybutyrate) was produced from the racemic monomer.