Ema Žagar* and Andrej Kržan
National Institute of Chemistry, Laboratory for Polymer Chemistry and Technology,
Hajdrihova 19, 100 Ljubljana, Slovenia
* Corresponding author: E-mail: ema.zagar@ki.si;
Phone +386-1-4760203; Fax +386-1-4760420
Abstract
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