Comonomer Compositional Distribution and Thermal Characteristics of Bacterially Synthesized Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)s

Abstract

The comonomer composition and its distribution have been investigated for poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) [P(3HB-co-3HH)], which was bacterially synthesized by Ralstonia eutropha from coconut oil as a carbon source. Using a chloroform/heptane mixed solvent, they were fractionated into several fractions with different comonomer composition. Bacterially synthesized P(3HB-co-3HH)s were found to have a wide compositional distribution. Using the fractions with a narrower comonomer composition distribution, the compositional dependence of thermal properties was investigated. The differential scanning calorimetry (DSC) melting behavior of a sample of unfractionated P(3HB-co-3HH) did not reflect that of fractions with similar average 3HH content. It was concluded that each of the fractions affects the thermal properties of the original unfractionated P(3HB-co-3HH), which should therefore be considered as polymer blends.