NMR characterization of methylcellulose: Chemical shift assignment and mole fraction of monomers in the polymer chains

Hiroyuki Kono; Sayaka Fujita; Kenji Tajima

doi:10.1016/j.carbpol.2016.10.056

NMR characterization of methylcellulose: Chemical shift assignment and mole fraction of monomers in the polymer chains

Carbohydr Polym. 2017 Feb 10:157:728-738. doi: 10.1016/j.carbpol.2016.10.056. Epub 2016 Oct 20.

Authors

Hiroyuki Kono¹, Sayaka Fujita², Kenji Tajima³

Affiliations

¹ Division of Applied Chemistry and Biochemistry, National Institute of Technology, Tomakomai College, Nishikioka 443, Tomakomai, Hokkaido 059 1275, Japan. Electronic address: kono@tomakomai-ct.ac.jp.
² Division of Applied Chemistry and Biochemistry, National Institute of Technology, Tomakomai College, Nishikioka 443, Tomakomai, Hokkaido 059 1275, Japan.
³ Faculty of Engineering, Hokkaido University, N13W8, Kita-ku, Sapporo 060 8628, Japan.

PMID: 27987985
DOI: 10.1016/j.carbpol.2016.10.056

Abstract

Methylcellulose samples with different degrees of substitution were prepared by a heterogeneous reaction of cellulose. Two-dimensional NMR spectroscopy provided complete assignment of the ¹H and ¹³C chemical shifts of the un-, 2-mono-, 3-mono-, 6-mono-, 2,3-di-, 2,6-di-, 3,6-di-, and 2,3,6-tri-substituted anhydroglucose units (AGUs). Comparative analysis of the chemical shift data revealed the relationship between the methyl substituents at the 2-, 3-, and 6-positions and the ¹H and ¹³C chemical shifts of the AGUs; additivity could be applied to the ¹H and ¹³C chemical shifts of methylcellulose. Quantitative ¹³C NMR spectra of the samples determined the composition of the eight AGUs and the substituent distribution at the 2-, 3-, and 6-positions of cellulose. This provided estimations of the hydroxyl group reactivity toward methylation and the interactions between the substituent groups within the same AGU.

Keywords: Methylcellulose; Monomer composition; Nuclear magnetic resonance; Steric hindrance; Substituent distribution.