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Highly crystalline cellulose samples, which also have a high purity of crystal form, were used or prepared as models of cellulose polymorphs, cellulose I, III,, IV,, II, IIIn, and IVn, for solid-state 13C NMR and X-ray diffraction analyses. Differences between cellulose I, II, and III in the 13C NMR spectra appear at the chemical shifts of C6 in the anhydroglucose units; they have signals at 65.5-66.2, 63.5-64.1, and 62.1-62.8 ppm, respectively. Cellulose IV has a doublet signal for C4 at 83.6-84.6 ppm and a signal for C6 at 63.3-63.8 ppm, which is identical with that of cellulose II. Thus the mechanisms for the formation of cellulose polymorphs are primarily ascribed to some conformational and/or environmental transformations of C4 and C6. So-called cellulose IV, is likely to be a mixture of cellulose I and real cellulose IV,. The differences between cellulose III, and III,, were not detected clearly at the chemical shifts of C4 and C6 but at the chemical shift of Cl and the signal pattern of C2, C3, and C5.

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