Studies on the Sequence Distributions of Microbial Polyester by NMR and Determination of Melting Temperature

The composition and dyad sequence distributions of bacterially synthesized copolymers of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) P(3HB-co-4HB) have been studied by means of high-resolution 1H-, 13C-NMR spectroscopy and differential scanning calorimetry. These biodegradable copolyesters are mixtures of copolymers having different 4HB contents. The fractionation was carried out to obtain fractionated copolymers having narrower compositional distribution. The dyad sequence distributions of P(3HB-co-4HB) measured by NMR shows close to block copolymer in lower 4HB content side, whereas in higher 4HB content side, the that of P(3HB-co-4HB) indicates statistically random copolymer. The heat of fusion of P(3HB) and P(4HB) was estimated using Flory's equation. The values of heat of fusion of P(3HB) and P(4HB) measured were 1490 cal/mol and 2484 cal/mol. The values of number-average sequence lengths calculated from NMR and DSC show the P(3HB-co-4HB) copolymer including long continuous sequence in lower and higher 4HB content side.