The Solid-State Structure, Thermal and Crystalline Properties of Bacterial Copolyesters of (R)-3-Hydroxybutyric Acid with (R)-3-Hydroxyhexanoic Acid

摘要

Both WAXD and solid-state ~(13)C NMR results confirm that the randomly distributed 3HH units in P(3HB-co-3HB) copolyesters are excluded from the P(3HB) crystalline phase, thus reducing the crystallinity and the crystallization rate of copolyesters. The presence of 3HH units also results in the distribution of 3HB sequences with different length that is responsible of the complicated melting behaviour with multiple peaks. The existence of two types of crystals in P(3HB-co-3HH) has been suggested on the basis of the melting behaviour. The crystals with melting peak T_(m1) are composed of 3HB sequences with a length longer than the critical length ζ,(T_c); the growth of these crystals is affected by both temperature and chemical composition. On the other hand, the crystals with melting temperature T_(s1) are thought to be composed of shorter 3HB sequences and their crystallization is not affected by the composition. The results of the annealing treatment seem to indicate that T_(s1) crystals are located outside the T_(m1) crystals.