Morphological study of bacterial poly(3-hydroxybutyrate-co-3-hydroxypropionate)

The solid-state structure of a bacterially synthesized copolyester, poly(3-hydroxybutyrate-co-3-hydroxypropionate), P(3HB-co-3HP), with the '3HP content ranging from 0 to 37 mol-%, was analyzed by C-13 solid-state high-resolution NMR, X-ray diffraction, differential scanning calorimetry and optical microscopy. For the copolymers containing up to about 40 mol-% 3HP, it was confirmed from the X-ray diffraction measurement that the crystallographic parameters are similar to those of P(3HB) homopolymer and the degree of crystallinity decreases as the 3HP content increases. From the measurement of C-13 spin-lattice relaxtion time (T-1(c)) using solid-state high-resolution C-13 NMR, it was concluded that the crystalline region is composed only of 3HB units, suggesting that the cocrystallization of 3HB and 3HP units in the same crystal lattice does not occur in P(3HB-co-3HP). This conclusion is supported by the thermal properties and the rate of spherulite growth.