Phase behavior and thermal properties for binary blends of bacterial poly (3-hydroxybutyrate-co-3-hydroxyhexanoate)s with narrow-comonomer-unit compositional distribution

The miscibility and effect of compositional distribution physical properties were investigated for binary blends of biosynthesized poly(3-hydroxybutyrate)-[P(3HB)] and comonomer compositionally fractionated poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)s. [P(3HB-co-3HH)] with narrow compositional distribution. Biosynthesized P-(3HB-co-3HH) samples were compositionally fractionated using solvent (chloroform)/nonsolvent (n-heptane) mixtures. The binary blends of fractionated P(3HB-co-3HH)s with different 3HH unit content were prepared by casting from solution in chloroform. The miscibility and the thermal properties of these blends were analyzed by differential scanning calorimetry (DSC). It was found that the two components are miscible in the amorphous phase when the difference in 3HH unit content between the two component polymers of these blends is less than 20 mol-%, subsequently they are immiscible when the difference is larger than 30 mol-%. By comparing the thermal properties of the binary blends of fractions, with those for the fractions themselves, and with those for the bacterially as produced unfractionated copolyester, the effects of compositional distribution on the properties of copolyesters were discussed.