Single crystals and crystalline morphology of synthetic racemic poly(beta-hydroxybutyrate)

Single crystals of synthetic racemic poly(beta-hydroxybutyrate), PHB, of varying tacticities were grown in dilute chloroform/ethanol solutions. The single crystals of highly isotactic synthetic PHB were spear or lath shaped, like those of bacterial PHB; those from essentially atactic polymer were wrinkled but displayed the same electron diffractogram as isotactic PHB. Syndiotactic PHB gave a nondiffracting precipitate of two different morphologies; further examination suggests that these morphologies differ in tacticity. The average overall tacticities of the precipitated and soluble material were determined by C-13 NMR and found to be unchanged by the precipitation. This provides evidence that some cocrystallization of the R and S repeat units can occur and that the single crystals obtained can be correlated with original sample tacticities.