A simple preparation of half N-acetylated chitosan highly soluble in water and aqueous organic solvents
Section snippets
1. Introduction
Chitin, poly-β-(1→4)-N-acetyl-d-glucosamine, is the second most abundant natural polysaccharide and exists largely in the shells of crustacea and insects. Chitosan, poly-β-(1→4)-d-glucosamine, can be readily obtained from chitin by deacetylation with alkali. The use of chitin and chitosan in various functional materials, including biomedical materials, have recently been developed [1], [2]. We have also reported on the membrane applications of chitosan and its derivatives [3], [4], [5].
Materials
Commercially available chitosan from Tokyo Kasei Kogyo, Tokyo, Japan, was purified thrice by reprecipitation using aq AcOH (5%) and aq KOH in advance. It was finally washed with deionized water and acetone, and then dried in vacuo. Standard pullulans for size-exclusion chromatography (SEC) were purchased from Showa Denko, Tokyo, Japan. Acetic anhydride, acetone, N,N-dimethylacetamide (DMA), and Me2SO from Wako Pure Chemical Industries, Osaka, Japan, were distilled just before use. All other
3. Results and discussion
Although various methods are available for depolymerization of chitosan, we employed an oxidative degradation with NaBO3 to save time. Also aqueous acetic acid was used as the solvent to achieve the reaction under homogeneous conditions. Consequently, the main chain of chitosan seems to be randomly cut up. Table 1 lists the degradation conditions along with the weight-average molecular weight and the number-average degree of polymerization for the chitosan samples obtained. The weight-average
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