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 lignins. 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 copolymer 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 wt % 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.