Composition fractionation and thermal characterization of poly(3-hydroxybutyrate-co-3-hydroxypropionate)

The compositional distribution has been investigated for poly(3-hydroxybutyrate-co-3-hydroxypropionate) [P(3HB-co-3HP)]s, which were microbially synthesized by Alcaligenes latus with 3-hydroxypropionic acid, sucrose or 3-hydroxybutyric acid as the sole carbon source. With a chloroform/n-heptane mixed solvent, they were found to be fractionated into several fractions with different comonomer composition. It was concluded that the as-produced bacterial P(3HB-co-3HP) samples have a broad distribution of comonomer composition. Using the fractions with a narrower comonomer composition distribution, the composition dependence of thermal properties and isothermal spherulite growth behavior were investigated. One of as-produced unfractionated P(3HB-co-3HP) showed the DSC melting behavior reflecting that of only minor fractions with 3HP content differed remarkedly from average 3HP content of original unfractionated P(3HB-co-3HP). It was concluded that each of the fractions affects thermal properties of the original P(3HB-co-3HP).