Preparation and rheological behaviors of 6-carboxy-chitosan

The hydroxymethyl groups of 2‐amino‐2‐deoxy‐D‐glucose units in chitosan were selectively oxidized to carboxyl groups with NO2 gas to form 6‐carboxy‐chitosan in aqueous 0.5 mol/L acetic acid. In optimal conditions, the 52.5% hydroxymethyl groups in chitosan could be converted into carboxyl groups. When the pH value of the solution is lower than 4.0 or more than 5.4, 6‐carboxy‐chitosan has common characteristics of a polycation or polyanion electrolyte, respectively, and when the pH value of the solution is 4.0—5.4, 6‐carboxy‐chitosan has common characteristics of an amphoteric polyelectrolyte. 6‐Carboxy‐chitosan has same macromolecular backbones as chitosan, and its isoelectric point (pI) value is 4.9. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1126–1130, 2004