Characteristics and properties of carboxymethylchitosan

Four samples of N,O-carboxymethylchitosan ( 0.5 < DS ¯ < 1.5 ) were prepared by reacting chitosan ( DA ¯ = 24 % ) with monochloroacetic acid in the presence of excess sodium hydroxide. The carboxymethylchitosan samples were soluble in a wider range of pH as compared to the parent chitosan and the X-ray diffraction showed that they adopt a less ordered arrangement. The carboxymethylation of chitosan decreased the thermal stability of the polymer as evaluated by thermogravimetry but no clear dependence of the activation energy on the average degree of substitution of carboxymethylchitosan was identified. However, the values of activation energy of carboxymethylchitosan issued from the isothermal study depended on the degree of conversion, suggesting the occurrence of a complex set of simultaneous reactions.