Reactive xylan derivatives for azid-/alkyne-click-chemistry approaches — From modular synthesis to gel-formation

A modular synthesis was developed to obtain reactive xylan derivatives that are accessible for further functionalization and chemical crosslinking by click-chemistry approaches. Xylan phenylcarbonates (XPCs) with degrees of substitution (DS) from 0.62 to 1.94 were converted with propargyl amine (PA) or 6-azidohexan-1-amine (AA) to introduce either alkynyl- or azido moieties into the polymer backbone. Quantitative conversion of the XPC derivatives into functional xylan carbamates (XCs) with well-defined DS values was achieved. The molecular structure of the compounds was confirmed by FTIR- and NMR spectroscopy. Covalent crosslinking of alkynyl-functionalized XCs with bisazide linkers was achieved by copper-catalyzed 1,3-dipolar cycloaddition in an organic medium and the gelation process was studied by rheological experiments. Finally, it was demonstrated that mixed XCs with a reactive moiety and another functional group, which induce water solubility, are accessible. The corresponding products are suitable for the preparation of xylan-based hydrogels.