Morphology and growth of a hydroxybutyrate oligomer with 24 repeat units

The crystallization behaviour of an oligomer of hydroxybutyrate containing 24 repeat units has been studied over a wide range of temperature using optical microscopy to measure growth rates and observe morphologies and small angle X-ray scattering to measure crystal thicknesses. Crystals grew with a wide range of thicknesses between E/2 and E, where E is the extended chain length. Preferred crystal thicknesses corresponded to simple fractions of E, which result in a relatively higher proportion of chain folds in the surface. Growth rates peaked at 75 °C and were unusually scattered at temperatures corresponding to a change in preferred chain conformation. Spherulites grown at the lower temperatures were banded: as the crystallization temperature was increased the banding disappeared, the shapes of the spherulites became less regular, and a coarser texture associated with reduced branching developed.