Multiple endothermic peaks resulted from different crystal structures in an isomorphous copolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

The multiple endothermic peaks of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(HB-co-HV)) in differential scanning calorimetry (DSC) results, as one representative phenomenon of polymer with unique cocrystallization behavior, were generally considered as the results of melting/recrystallization. In this study, wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS) experiments were conducted to analyze the phenomena of multiple endothermic peaks in DSC results. The results of these analyses indicated that the multiple endotherms were mainly caused by different lamellae structures. For P(HB-co-HV) with lower HV content, it was comprised of two structures of HV total exclusion and HV partial inclusion in the crystal lamellae. For P(HB-co-HV) with higher HV content, it was also comprised of two structures of HV total inclusion and HV partial inclusion in the crystal lamellae. However, only structure with HV partial inclusion in the crystal lamellae remained existing after first melting peak for all samples.