Investigation of the cellulose/LiCl/dimethylacetamide and cellulose/LiCl/N‐methyl‐2‐pyrrolidinone solutions by 13C NMR spectroscopy

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Abstract
The cellulose/lithium chloride/dimethylacetamide (DMAc) and cellulose/lithium chloride/N‐methyl‐2‐pyrroilidinone (NMP) solutions were investigated by 13C NMR spectroscopy. Well‐resolved spectra were obtained for both solutions and indicated that cellulose was present in these systems in the form of underivatized cellulose. The change in 13C chemical shifts of DMAc and NMP in the presence of LiCl and LiBr was compared with that of several salt/aprotic solvents, and the results point to the existence of a cellulose–LiCl–DMAc (or NMP) complex in which the lithium cation is strongly bound to the amide carbonyl oxygen and the chloride anion involved in the dissociation of the cellulose hydrogen bonds. Spin–lattice relaxation times (T1 of the 13C carbons of the solvent molecules, DMAc and NMP, show a large decrease in T1 for all solvent carbons upon addition of LiCl. Further decrease in T1 is observed when cellulose is introduced to the LiCl/NMP but not to the LiCl/DMAc systems. These observations are attributed to slower molecular motions of DMAc and NMP in the presence of LiCl, and, in the case of NMP, in the presence of cellulose.

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