Synthesis of thermo-shear-responsive dynamic covalent networks based on humins and the Diels–Alder reaction

Abstract

Humins are abundant yet largely underutilised by-products of sugar-based biorefineries, commonly regarded as low-value waste streams despite their intrinsically furan-rich structure. By leveraging their furan-rich architecture, we demonstrate that humins can serve as a versatile and sustainable source of dienes in Diels–Alder (DA) chemistry when employed directly as reagents. We show that they readily form dynamic covalent networks upon reaction with conventional dienophiles, such as bismaleimides, under mild conditions. Notably, the cycloaddition proceeds predominantly via an endo-selective pathway. Moreover, the DA equilibrium exhibits an unconventional, inverted thermo-mechanical response under oscillatory shear, with the forward reaction favored at elevated temperatures and the retro-DA reaction promoted at lower temperatures. The resulting materials exhibit tunable thermal and mechanical properties, self-healing behaviour, and chemically controllable electrical conductivity. Taken together, our findings establish a practical pathway for converting biorefinery side streams into value-added functional materials.