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 solutio ns. The single crystals of highly isotactic synthetic PHB were spear o r lath shaped, like those of bacterial PHB; those from essentially ata ctic polymer were wrinkled but displayed the same electron diffractogr am as isotactic PHB. Syndiotactic PHB gave a nondiffracting precipitat e of two different morphologies; further examination suggests that the se morphologies differ in tacticity. The average overall tacticities o f the precipitated and soluble material were determined by C-13 NMR an d found to be unchanged by the precipitation. This provides evidence t hat some cocrystallization of the R and S repeat units can occur and t hat the single crystals obtained can be correlated with original sampl e tacticities.