Defined Chitosan-based networks by C-6-Azide-alkyne "click" reaction

Chitosan was converted to its –NH2-protected derivative by reacting with phthalic anhydride and then selectively functionalized with an azido group in C-6 position. Two different procedures were employed. The first was a ‘‘one-pot” procedure and the second was a two steps reaction through the tosylated intermediate. Both methods resulted in an effective functionalization of chitosan with azido groups. For the two before mentioned procedures, the functionalization degree was estimated by elemental analysis as number of azido groups per pyranoside ring and was 0.28 mol/mol and 0.26 mol/mol, respectively. The azido-functionalized derivatives underwent further modification by Cu(I) catalyzed dipolar cycloaddition with mono- or di-alkynes. The reaction with phenylacetylene produced soluble derivatives that were fully characterized at molecular level by FT-IR and NMR spectroscopies, elemental analysis and size exclusion chromatography (SEC). Crosslinked derivatives were obtained by reactions with 1,7-octadiyne or 1,4-diethynylbenzene and subsequently deprotected to restore the free amino groups. These last systems showed selective swellability in acid medium.