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Determination of mole fractions of ethyl-cellulose-containing monomers by NMR
1Division of Applied Chemistry and Biochemistry, National Institute of Technology, Tomakomai College, Nishikioka 443, Tomakomai, Hokkaido, 059 1275, Japan.
Abstract:
Three samples of ethyl cellulose (EC) with different degrees of substitution (DS)-0.51, 1.41, and 2.28-were prepared by a slurry method using ethyl bromide as the etherification reagent. 1H-13C HSQC and HSQC-TOCSY NMR spectral analysis allowed for complete assignment of the 1H and 13C chemical shifts, respectively, of eight anhydroglucose units (AGUs) comprising EC chains-un-, 2-mono-, 3-mono-, 6-mono-, 2,3-di-, 2,6-di-, 3,6-di-, and 2,3,6-tri-substituted AGUs. In addition, the lineshape of the quantitative 13C NMR spectra of the three EC samples provided change in the mole fractions of these AGUs against DS, making it possible to estimate the reaction mechanism for the production of EC, elucidating reactivities of the hydroxyl groups at the 2, 3, and 6 positions of cellulose and interactions between the substituent groups within the same AGU and vicinal AGUs.