C-13 NUCLEAR MAGNETIC-RELAXATION MEASUREMENTS OF POLY(4-HYDROXYBUTYRATE) AND POLY(3-HYDROXYBUTYRATE-CO-4-HYDROXYBUTYRATE) IN THE BULK

C-13 NMR spectroscopy is used to study the local segmental dynamics in the bulk of biodegradable poly(4-hydroxybutyrate) and a random copoly mer of 3-hydroxybutyrate and I-hydroxybutyrate that contained 18% 4-hy droxybutyrate units. The crystalline phase of the copolymer is shown b y solid-state C-13 NMR to be comprised of 3HB units, in accord with re ports based on X-ray diffraction. C-13 relaxation measurements indicat e that the local dynamics in the amorphous phase are of different time scale for the two different types of monomer units in the copolymer. Furthermore, the segmental motions of the 4-hydroxybutyrate units are found to be slower in the copolymer than in the homopolymer.