Hydrophobic Chain Conjugation at Hydroxyl Group onto γ-Ray Irradiated Chitosan

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Abstract
Gamma-Ray irradiation of chitosan flakes and introduction of hydrophobic chains onto hydroxyl groups are discussed. At 25 kGy, chain degradation without cross-linking reduces the molecular weight to one-fourth; however, structural characterization by FT-IR, 1H NMR, and 13C CP/MAS NMR indicates that the saccharide units are maintained. Introduction of hydrophobic chains is accomplished by introduction of alkylamine groups onto the chitosan carbonyl imidazole precursor. The chitosan coupling reaction is improved and can be done homogeneously as a result of gamma-ray irradiation. The optimum conditions for phthalimido group deprotection are studied to generate a unique product with a hydrophobic chain attached mainly at the hydroxyl group (C-6 and/or C-3) while the amino group (C-2) is retained as characterized by FT-IR and 1H NMR. The final product shows fair solubility in organic solvents, such as DMSO, DMAc, DMF, and pyridine.