SEGMENTAL DYNAMICS IN POLY(3-HYDROXYBUTYRATE-CO-4-HYDROXYBUTYRATE)S ABOVE THE GLASS-TRANSITION TEMPERATURE - C-13 NUCLEAR MAGNETIC-RELAXATION IN THE AMORPHOUS PHASE

Variable-temperature C-13 NMR spin-lattice relaxation times, T-1, and nuclear Overhauser enhancements (NOE) at two magnetic fields have been recorded for the amorphous phase of semicrystalline poly(4-hydroxybut yrate), P4HB, and two random copolymers: poly(3-hydroxybutyrate-co-4-h ydroxybutyrate) with 18% (P3/4HB-18) and 69% (P3/4HB-69) 4hb units. Th e T-1 and NOE data were successfully interpreted by the DLM model in t erms of conformational transitions and librational motions of the back bone C-H vectors. The mobility of both the 3hb and 4hb units was found to increase with increasing 4hb content of the copolymer. In both cop olymers, the segmental motion of the 4hb unit was found to be 2-4 time s faster than that of the 3hb unit, thus reflecting the local characte r of the segmental motions that affect C-13 relaxation in bulk polymer s. In addition, the segmental dynamics followed the Williams-Landel-Fe rry equation, indicating that they are involved in the glass transitio n phenomena. Literature P3HB dynamic modeling data adhere to the Willi ams-Landel-Ferry data presented here, indicating that P3HB in bacteria l inclusions has a T-g similar to that of the extracted material.