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Synthesis of an α,β-alkyl branched polyester, i.e., poly(2-methyl-3-hydroxyoctanoate), has been accomplished via anionic polymerization of α-methyl-β-pentyl-β-propiolactone mediated by supramolecular complexes of potassium methoxide or potassium hydroxide, respectively. The structure of resulting polymers has been established by electrospray ionization multistage mass spectrometry (ESI−MSⁿ), FT-IR, NMR, and GPC analyses. Previously proposed addition−elimination mechanism of the polymerization of β-lactones containing α-hydrogen by alkoxide anion has been confirmed to operate also in the case of β-lactone having alkyl substituents in both α and β positions.

Sequence distribution and chemical structure of mass-selected macromolecules of poly(3-hydroxybutyrate-co-3-hydroxyvalerate), PHBV, biopolyester macroinitiator obtained by partial alkaline depolymerization of natural PHBV containing 5 mol % of HV units was determined by electrospray ionization multistage mass spectrometry (ESI-MSⁿ). On the basis of the ESI-MSⁿ studies of PHBV individual oligomers, the microstructure of this bacterial copolyester was assessed, starting from dimer up to the oligomer containing 22 repeat units, and the results obtained were compared with those described previously for other “soft” ionization MS techniques.

Water-soluble a-PHB oligomers (from dimer to dodecamer) were synthesized by anionic oligomerization of (R,S)-β-butyrolactone and characterized by electrospray ionization tandem mass spectrometry (ESI-MSⁿ). The oligomers were analogous to the degradation products remaining after enzymatic hydrolysis of synthetic high molecular weight atactic poly[(R,S)-3-hydroxybutyrate] by extracellular PHB depolymerases. Selected bacterial strains were used to test bioassimilability of a-PHB oligomers. It was found that not only two PHB-degrading bacteria (Alcaligenes faecalis T1 and Comamonas sp.) but also a non-PHB-degrading bacterium (Ralstonia eutropha H16) could grow on a-PHB oligomers as sole source of carbon and energy. Utilization of a-PHB oligomers by the three bacterial strains (total oligomer consumption and molecular weight distribution changes) was investigated by ESI-MS. Total oligomer consumption (tested after 30 h of bacterial growth) followed the same trend as the observed bacterial growth (A. faecalis > Comamonas sp. > R. eutropha). Mineralization of a-PHB oligomers demonstrates total biodegradability of synthetic high molecular weight atactic poly[(R,S)-3-hydroxybutyrate].

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 Tg = 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.

Blends of synthetic atactic poly(3-hydroxybutyrate) (a-PHB) with a natural bacterial isotactic copolymer of 3-hydroxybutyrate with 3-hydroxyvalerate (PHBV) containing 10 mol % of 3HV units were prepared using a simple casting procedure. In the range of compositions explored (10−50% a-PHB), blends of bacterial PHBV and synthetic atactic a-PHB were miscible in the melt and solidified with spherulitic morphology. The influence of a-PHB content on the thermal and mechanical properties of the blends was evaluated. The degree of crystallinity decreased with increasing content of a-PHB in the film samples, and the elongation at break for a sample containing 50% of a-PHB was 30-fold that of pure PHBV. Degradation experiments, both hydrolytic (pH = 7.4, T = 70 °C) and enzymatic (PHB-depolymerase A from Pseudomonas lemoignei, Tris-HCl buffer (pH = 8), T = 37 °C), were performed for both polymers and polymer blends. The rate of enzymatic degradation of the blends was higher than that of PHBV and increased with a-PHB content in the blends studied, whereas pure a-PHB did not biodegrade under these conditions. 3-Hydroxybutyric acid and its dimer were identified by HPLC as biodegradation products of both pure PHBV and its blends with a-PHB. Higher oligomers up to heptamer were detected as degradation products of the blends by APCI-MS and ESI-MS.

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.