Synthesis and properties of chitosan-N-dextran graft copolymers

Novel chitosan-N-dextran graft copolymers with a degree of substitution (DS) of chitosan varying from 16 to 60% and carrying 9 or 36 glucopyranose units in the grafted dextran chains were synthesized via reductive amination. The chemical structure of the chitosan derivatives was confirmed by FTIR, 1H NMR and XPS spectroscopy, the DS of chitosan was determined from the content of primary amino groups in the products. Degree of deacetylation of chitosan was ascertained from XPS spectra and was shown to remain unchanged during derivatization of chitosan. N-Modified chitosans were soluble in aqueous solutions in a wide pH range. Intrinsic viscosities of these chitosan derivatives were moderate to high and had a tendency to decrease at high DS of chitosan and longer grafted chains. Despite high density of dextran grafts, chitosan derivatives possessed polyelectrolyte effect, indicating that these copolymers retained the cationic properties of chitosan and could be used as surface conditioners.