Preparation and NMR characterization of highly substituted N-trimethyl chitosan chloride

N,N,N-Trimethyl chitosan chloride (TMC) is a chemically modified chitosan with improved aqueous solubility, compared with the native chitosan. It is essential to follow a synthesis procedure in which the degree of substitution of the final product can be controlled by means of the number of reaction steps, the duration of each reaction step and the amount of methyl iodide as reagent. A two-step reaction yields products with high degrees of substitution (40-80%). Comparison of the NMR spectra of the product TMC, after a two-step reaction, indicates that there is a peak assigned to the substituted amino group that shifts from 2.5 to 3.1 ppm upon acidification. This peak must be assigned to N(CH3)(2) and not to N(CH3)(3)(+). A three-step reaction procedure yields products with a degree of substitution > 80%, but with substantially decreased water-solubility. (C) 1998 Elsevier Science Ltd. All rights reserved.