Solid poly[(R)-3-hydroxybutyric] acid was examined by high-resolution C-13 MAS NMR, differential scanning calorimetry and infrared spectroscopy. The C-13 methyl group resonance consists of three components: the rigid amorphous phase, the crystalline phase and the mobile amorphous phase. Spectral deconvolution, using the Lorentz function, reveals the relative amounts as 62% crystalline and 38% amorphous at 333 K, and 42% crystalline, 40% pure amorphous and 18% beta-orthorhombic at 413 K. NMR indicates a large difference in molecular mobility between the crystalline and amorphous regions of the sample. Infrared spectroscopy shows that the stretching at 1725 cm(-1) (characteristic of the a-form) comes from the crystalline region, and the bands at 1744 cm(-1) (characteristic of the beta-form) and 1800 cm(-1) come from the amorphous region.
(C) 2002 Elsevier Science (USA).