Studies of the series of cellooligosaccharide peracetates as a model for cellulose triacetate by 13C CP/MAS NMR spectroscopy and X-ray analyses

The series of crystalline oligomers from α-cellobiose octaacetate through α-cellohexaose eicosaacetate, listed as below, was prepared from homogeneous acetylation of the corresponding cellooligosaccharides and characterized by 13C CP/MAS NMR spectroscopy and X-ray analysis in order to obtain the structural models of cellulose triacetate (CTA) in solid state. Progressing toward the hexamer, the NMR spectral feature of the oligomers, in comparison with two allomorphs of CTA I and CTA II, gradually approached that of CTA I. Specifically, chemical shifts of both the hexamer and the pentamer were in considerable respective agreement with those of CTA I. In addition, X-ray diffraction patterns of the oligomers established that the crystalline pentamer and hexamer have a CTA I lattice in spite of recrystallization from ethylacetate–hexane. We therefore concluded that the pentamer and hexamer would be useful models for the CTA I structure.