Grafting of technical lignins through regioselective triazole formation on β-O-4 linkages

Abstract

A new method has been developed to enable the modification of the organosolv technical lignin. Using a walnut shell butanol alkoxasolv lignin as a source of high β-O-4 content material, the β-O-4 γ-position has been selectively modified via tosylation, azidation and copper-catalyzed azide-alkyne triazole formation . In addition, extensive model studies were used to aid the detailed characterization of the modified lignin structure. The copper catalyzed click reaction was used to attach modified PEG chains and the resulting lignin-based co-polymer displayed improved thermal stability. This protocol was also used to incorporate a novel BODIPY-type fluorophore, generating a fluorescent lignin. Copper catalytic loadings were effective as low as 0.3 weight% and were found to catalyze the cycloaddition efficiently. This efficient and generic approach to preparing lignin-derived polymers is relevant to the core societal challenge of improving biorefinery efficiency.