Molecular mobility and crystalline phase structure of biodegradable poly[(R)-3-hydroxybutylic acid-co-(R)-3-hydroxyhexanoic acid]

Solid-state C-13 NMR analyses have been carried out on the temperature dependence of the molecular mobility and phase structure of biodegradable poly[(R)-3-hydroxybutyric acid-co-(R)-3-hydroxyhexanoic acid] [P(3HB-co-3HH)] copolyesters. C-13 spin-lattice relaxation time (T-1C) experiments for the main chain CH and CH2 carbons have shown the existence of two components with different T-1C values for each carbon. This T-1C result is in accord with the previous T-1C results for poly[(R)-3-hydroxybutyric acid] [P(3HB)] homopolymer and other P(3HB)-type random copolyesters. In previous papers, however, the assignment of the two components with different T-1C values have been remained unsolved. In this study, by performing variable-temperature experiments and by comparing with the results of other partially crystalline polymers, we have investigated the assignment of the two components in detail. As the results, it has been concluded that both the two components are crystalline components. The crystalline component with longer T-1C value is assignable to the internal region of crystalline lamellae and the shorter T-1C component is ascribed to the interfacial crystalline region near amorphous phase. T-1C analyses have also detected the gradual increase in molecular mobility with an increase of temperature. When compared with the previous T-1C results for poly(butylene adipate) (PBA), poly(ethylene succinate) (PES), and poly(butylene succinate) (PBS), the tendency of the temperature change observed for P(3HB-co-3HH) has been close to that for PES. (C) 2004 Elsevier Ltd. All rights reserved.