ИСТИНА

Chitin or poly(β(1-4)-N-acetyl-D-glucosamine) is one of the most abundant polysaccharides found in nature. It is well known that chitin cannot be dissolved in common solvents. This obviously limits practical utilization of this material. Additionally, the N-deacetylated derivative of chitin – chitosan, can be dissolved in aqueous solutions only with a pH<6.5. Carboxymethyl derivative of chitin is water-soluble in a wide pH interval and exhibits low toxicity, biodegradability and biocompatibility. Due to such unique combination of properties carboxymethyl chitin (CMC) found wide application in various areas of biology and medicine: controlled drug delivery systems, biosensors, bone repairing, wound healing and etc. For chemical CMC modification, in particular, polymer-similar transformations it is necessary to realize CMC polyelectrolyte macromolecules behavior at different pH media during such modification. Considering it, various forms of 6-O-carboxymethyl chitin (degree of substitution 1.0) have been obtained: acidic form (CMC-H), salt form (CMC-Na) and mixed form with equal (50%) share of CMC-H and CMC-Na links in CMC chain. Structure and properties of these CMC forms and films on their basis were investigated. The absorption bands with the maximum at 1733 and 1567 cm-1 in FTIR spectra of CMC-H confirmed the presence of C=O bond in the carboxylic groups and carboxylate-ions, correspondingly. In contrast to that, intensity of characteristic absorption peak at 1563 cm-1 (C=O in the carboxylate-ion) of mixed form is significantly reduced; at the same time in CMC-Na FTIR data the spectral sings of such band are absent. Comparative study using TGA showed that CMC hygroscopicity is significantly depend on CMC form. So, the most hygroscopic CMC-Na is able to absorb 20% mass. of water at room temperature, at the same time this index for CMC-H was 9% mass. and for mixed form – 13% mass. Beginning decomposition temperature of CMC for acid form CMC-H was 197ºС, for mixed form – 221ºС and for CMC-Na – 262ºС. Apparently, the presence of free carboxylic groups in acid form CMC-H promotes such reactions as decarboxylation, formation of anhydride bonds and etc., accompanying the thermal transformations of the polymer. Analysis of data on the mechanical strength investigation of CMC films showed that index of elastic modulus for CMC-H film was higher than for CMC-Na film. Such difference is possibly due to additional intermacromolecular hydrogen bonds formation in CMC-H as compared to CMC-Na form.