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.

Novel model block copolymers of (R,S)-β-butyrolactone with pivalolactone (PVL) are prepared in order to define the effect of crystalline domains provided by poly(pivalolactone) on the biodegradability of atactic poly(β-butyrolactone), a-PHB. The “living” a-PHB is synthesized from racemic β-butyrolactone, in the presence of potassium alkoxide/18-crown-6 complex, and such a living polymer is applied for polymerization of PVL, yielding block copolymers, a-PHB-b-PPVL, of tailored molecular weight and composition. The copolymers contain an amorphous phase with T g = 5 °C, associated with the a-PHB block, and a high melting crystalline phase, whose amount increases with PPVL content. Films of copolymers containing 9 (PVL9), 17 (PVL17), and 23 mol % of PPVL (PVL23) are exposed to PHB-depolymerase A from Pseudomonas lemoignei (37 °C, Tris−HCl buffer pH = 8). While plain a-PHB does not biodegrade, the biodegradation rate of a-PHB-b-PPVL copolymers increases (PVL9 ≪ PVL17 < PVL23) along with the increase of crystalline PPVL domains. The biodegradation rate of PVL23 is similar to that of natural (crystalline) PHB. On the basis of a comparison of a-PHB-b-PPVL composition changes (by 1H NMR) with weight loss during biodegradation experiments, it is concluded that in the copolymers studied only the a-PHB block is attacked by the enzyme and that the crystalline block of nonbiodegradable PPVL efficiently promotes enzymatic attack to a-PHB, by providing a binding support to the enzyme.

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The anionic polymerization of 2-oxetanone and 4-methyl-2-oxetanone initiated with the potassium hydride/l8-crown-6 complex was investigated. The a-proton abstraction of the monomer was found to proceed at the initiation step of this polymerization. The salt of the unsaturated carboxylic acid formed initiates further propagation, leading to functionalized polyesters with unsaturated, dead end-groups.