Grafting of poly(ethylene glycol) to chitosan at C(6) position of glucosamine units via "click chemistry" reactions

N-Phthaloyl chitosan derivatives containing azide or propargyl moieties at C(6) positionof glucosamine units were synthesized for the first time. The products obtained are useful as precursors for modification of chitosan via "click chemistry" reactions. New chitosan-MPEG derivatives containing intermediate triazolyl moieties at C(6) position of glucosamine units were prepared by coupling via 1,3-dipolar cycloaddition between azide and propargyl groups of chitosan and poly(ethylene glycol) monomethyl ether (MPEG). Comb copolymers were characterized by FT-IR and H-1 NMR spectroscopy, intrinsic viscosity, elemental and functional group analysis. The degree of chitosan substitution in new copolymers depended on the ratio of azide and propargyl groups and was in the range 20 to 65%, proving an efficient control of the graft density. The intrinsic viscosity of the chitosan derivatives was low, evidencing a significant degradation of the chitosan backbone during modification.