Sequence Distribution Dependence on Molar Mass in Microbial Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolyesters

Ema Žagar* and Andrej Kržan

National Institute of Chemistry, Laboratory for Polymer Chemistry and Technology, Hajdrihova 19, 100 Ljubljana, Slovenia
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The comonomer composition distribution (CCD) of natural aliphatic polyhydroxyalkanoate copolyesters has a strong influence on their morphology and thus on their properties. Using 13C NMR spectroscopy, based on dyad and triad analysis, we examined the composition and CCD dependence on molar mass in two non-random poly(3-hydroxybutyrate- co-3-hydroxyvalerate)s (PHBV) with different comonomer ratios. For this purpose the copolyesters were fractionated using preparative size exclusion chromatography and their fractions were analyzed according to composition, CCD and thermal properties. The PHBV copolyester with a higher content of hydroxyvalerate comonomer units (HV, 27.1%) showed a more pronounced dependence of composition and CCD on molar mass than the PHBV with a lower content of HV units (12.9%), which showed very little variation. Both PHBV copolyesters and their fractions showed multiple melting peaks in their DSC curves.

Keywords: Polyhydroxyalkanoate; poly(3-hydroxybutyrate-co-3-hydroxyvalerate) copolyesters; microstructure; comonomer composition distribution; NMR; molar mass