Study of thermal melting behavior of microbial polyhydroxyalkanoate using two-dimensional Fourier transform infrared correlation spectroscopy

The molecular level premelting process of purified biosynthesized polyester poly(hydroxybutyrate-co-hydroxyvalerate) or P(HB-co-HV) (20.4% HV) was inv estigated by two-dimensional Fourier transform infrared (2D FT-IR) correlat ion spectroscopy. Intensity variations and band shifts in the characteristi c spectral regions for C=O groups (1710-1770 cm(-1)), C-H groups (2910-3010 cm(-1)), and C-O-C groups (1220-1310 cm(-1)) were selected for a detailed study of the thermally induced phase transition of the copolymer. The 2D co rrelation approach successfully demonstrated that a fully amorphous liquid- like structure was formed following the disappearance of the crystals in th e sample, by going through an intermediate state related to the lost confor mation of the highly ordered and helical polyester main chain.