Determination of substituent distribution in cellulose ethers by means of a C nuclear magnetic resonance study on their acetylated derivatives: 3. Hydroxyethylcellulose

The distribution of substituent, i.e. oligo(ethylene oxide) groups, in hydroxyethylcelluloses having various values of molar substitution was determined by means of ¹³C nuclear magnetic resonance after the acetylation of hydroxyl groups both at the unsubstituted position in the anhydroglucose unit and at the substituent end position of the parent hydroxyethylcellulose. The acetyl carbonyl signal of the acetylated hydroxyethylcellulose samples was found to split into a triplet in DMSO-d₆ at 100°C corresponding to the positions of acetyl groups (2, 3 or 6 overlapped with the substituent end) on the anhydroglucose unit. While in CDCl₃ at 40°C, the acetyl carbonyl signal for the substituent end position was observed to be separated from those on the anhydroglucose unit. By combining these results, the distribution of the substituent groups was determined for a series of hydroxyethylcellulose samples of a wide range of molar substitution values.