Bacterial copolymers from Alcaligenes eutrophus containing ß-hydroxybutyrate and ß-hydroxyvalerate monomer units were characterized by X-ray diffraction, differential scanning calorimetry, solution NMR, and solid-state 13C NMR. The copolyesters were shown to be statistically random and of high crystallinity (>60%) throughout a range of compositions varying from 0 to 47 mol % ß-hydroxyvalerate units. A minimum in the melting point vs. composition curve was found at approximately 30 mol % ß-hydroxyvalerate. Only two crystal forms were detected: the ß-hydroxybutyrate crystalline phase on one side of the melting point minimum and the ß-hydroxyvalerate crystalline phase on the other. Solid-state 13C NMR spectra support the conclusion that the poly(d-hydroxybutyrate-co-d-hydroxyvalerate) system is isodimorphic with each crystalline phase accommodating the repeating unit of the other monomer as part of its organized structure.

Samples of bacterial poly(d-hydroxybutyrate-co-fl-hydroxyvalerate) (P(HB-co-HV)) were analyzed by 250-MHz 1H nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. The compositions of 40 copolyester samples, as determined by NMR, ranged from 0 to 47 mol % ß-hydroxyvalerate (HV). The shapes and intensities of numerous IR bands, particularly those at 1279,1228, and 1185 cm"1, were found to be sensitive to the degree of crystallinity. FTIR bands sensitive to composition include the C-H bands around 2900 cm'1 and the C-C band at 977 cm"1. By use of the 2900-cm"1 bands, methods were developed for composition analysis of as-received samples of equal degree of crystallinity in the solid state and in solution. Relative areas, in which the C-H area was normalized to the compositioninsensitive C=0 area, were calibrated to the copolymer compositions determined by 250-MHz 1H NMR. The experimental uncertainties of composition analysis of P(HB-co-HV) by NMR and FTIR were estimated to be ±1 and ±2-3 mol % HV, respectively. FTIR and wide-angle X-ray diffraction (WAXS) studies on solution-cast and melt-quenched samples showed a dramatic trend in that the rate of crystallization of these copolyesters decreases with increasing HV content. A two-stage crystallization process was identified for P(HB-co-HV) cast from solution and was attributed to changes in both nucleation rate and rate of crystal growth, whereas crystallization from the melt is largely nucleation rate limited. The crystallinity index (Cl) determined by FTIR for as-received samples of P(HB-co-HV) was nearly independent of HV content, indicating that the copolyesters are as highly crystalline as PHB homopolymer. The degree of crystallinity (Xc) derived from X-ray diffraction was used to follow crystallization from the melt. The final value of Xc ranged from 62 to 69% for equilibrated copolyesters quenched from the melt. Crystallization of these copolyesters from the melt is faster than for solution-cast samples. However, both processes are slow when compared to the rate of crystallization of solution-precipitated samples.

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