Racemic lactide was polymerized with various initiators containing Zn and Al, and the structures of the obtained polymers were determined by means of 13C N M R spectroscopy. The extent of transesterifiition reactions was calculated on the basis of the analysis of the methine carbon signal in the polymer 13C NMR spectra. Three groups of initiators can be distinguished in view of their influence on tmnsesterification: ZnCl, exhibits the strongest transesterification activity, ZnEt, and ZnEt,/Al(oiPr), are among those of medium activity, and Al(acac), does not show transesterification activity at all.

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.

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The anionic polymerization of L-lactide in the presence of the sodium poly(ethy1ene g1ycol)ate in tetrahydrofuran at 25 "C yields "tailored" ABA triblock copolymers having the expected compositions and molecular weights. During the polymerization, a slight racemization of L-lactide was observed. The water absorption experiments indicate that the introduction of the poly(ethy1ene glycol) block into the L-lactide polymer chain markedly increases its hydrophilicity. It was revealed that the morphology and mechanical properties of block copolymers depend strongly on their composition and thermal treatment.

The anionic ring‐opening polymerizations of (R,S)‐β‐butyrolactone and (S)‐β‐butyrolactone initiated with tetrabutylammonium salts of carboxylic acids as initiators were investigated. Poly[(R,S)‐3‐hydroxybutyrate] and poly[(R)‐3‐hydroxybutyrate], with relatively high molecular weights (170,000 and 35,000, respectively) and low molecular weight distributions, were synthesized. Moreover, biomimetic poly(3‐hydroxybutyrate)s with well‐defined microstructures and predictable iso‐dyad contents were obtained. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2184–2189, 2002

The electrospray ionization tandem mass spectrometry technique applied for the first time to aliphatic polyester analysis, allowed fast and reliable identification of the various macromolecules of poly(3-hydroxybutanoic acid) (PHB), synthesized via ring-opening polymerization of b-butyrolactone. It was demonstrated that the biomimetic polymers studied contain various end groups, depending on the anionic initiator employed, and show close similarity to the natural PHB produced by enzymes in living cells of prokaryotic and eukaryotic organisms. #

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.