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The phase structure of the stereocomplex (DILIP) prepared from poly(D-lactic acid) (PDLA) and poly(L-lactic acid) (PLLA) in a dilute acetonitrile solution has been examined by high-resolution solidstate 13C NMR spectroscopy. Three resonance lines I-III appear at 173.3,172.0, and 169.7 ppm respectively, for the carbonyl carbons of DILIP. Line I is further resolved into two components with 13C spin-lattice relaxation times (Tic) of 128 and 17 s at 113 °C, whereas lines II and III are composed of single components with Tic = 40 and 5.4 s, respectively. The components with Tic = 128 and 17 s for line I can be assigned to the rigid and disordered racemic crystalline components, respectively. Line III is the contribution from the noncrystalline region, where the segments of PDLA and PLLA may be almost randomly mixed. Moreover, line II may be ascribed to the crystalline component of homopolymers incidentally produced. The total spectrum reflecting quantitatively all the components has been resolved into those four components by a line shape analysis. The degree of crystallinity estimated as a sum of mass fractions of the rigid and disordered racemic crystalline components is in agreement with that determined by differential scanning calorimetry or X-ray diffractometry. On the basis of the long period (12.0 nm) evaluated by small-angle X-ray scattering and mass fractions for the respective components, the thicknesses of the racemic crystalline and noncrystalline regions have also been determined to be 8.2 and 3.8 nm, respectively, by assuming the lamellar structure. is o-c -co-I CH, Thermal analyses, SEM observations, ED analyses, and polarimetry have already been performed on the PLA

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Cross-polarization/magic-angle-spinning (CP/MAS) 13C NMR spectra of the crystalline components of different native celluloses have been measured in the hydrated state by using the difference in 13C spin-lattice relaxation times T,c of the crystalline and noncrystalline components. As a result, it has been found that the crystalline spectra of native cellulose can be classified into two groups, cotton-ramie type and bacterial-valonia type, which are referred to as celluloses I, and Ib, respectively. The validities of the structural models previously proposed have been also discussed on the basis of the line-shape analyses of the C1 and C4 triplets of the crystalline spectra.

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