Regioselective grafting of poly(ethylene glycol) onto chitosan through C-6 position of glucosamine units

Regioselective modification of chitosan through C-6 position of glucosamine units by poly(ethylene glycol) was studied for the first time. Three different schemes of the synthesis of chitosan-PEG derivatives of well-defined structure using 6-oxo-2-N-phthaloylchitosan, 6-O-dichlorotriazine-2-N-phthaloylchitosan and 3-O-acetyl-2-N-phthaloylchitosan intermediates were examined. High degree of substitution of chitosan (≈ 90%) was obtained and brush copolymers with high density of PEG attachments were synthesised. Chitosan-PEG derivatives were characterised by analysis of functional groups, 1H-NMR and FT-IR spectroscopy, GPC measurements and viscometry. Despite the fact that high-molecular-weight chitosan was used as a starting material graft oligomers with molecular weight ≈ 3000–4000 were synthesised. The breakdown of chitosan backbone is thought to depend on amine group protection–deprotection procedure as well as on catalytic system used. Novel chitosan derivatives were soluble in most organic solvents and aqueous solutions of wide pH range.