Bio-based phthalonitrile resin derived from quercetin as a sustainable molecular scaffold: Synthesis, curing reaction and comparison with petroleum-based counterparts

Quercetin (Q), one of the most abundant molecules in nature, remains relatively unexplored in the realm of bio-based thermosets. In line with the pursuit of sustainability, we report the successful synthesis of a novel bio-based phthalonitrile (PN) monomer (Q-Ph) using Q. The synthesis involved a nitro displacement reaction with 4-nitrophthalonitrile (4-NPN). Confirmation of the monomer’s structure utilized hydrogen and carbon nuclear magnetic resonances (1H and 13C NMR), Fourier transform infrared spectra (FTIR), and elemental analysis. Curing characteristics were examined by differential scanning calorimetry (DSC), and polymerization was analyzed using FTIR. The resulting monomers showed a wide processing window and low melt viscosity via rheological analysis. Thermal and thermomechanical properties were assessed using dynamic mechanical analyzer (DMA) and thermogravimetric analysis (TGA), revealing lower curing and polymerization temperatures compared to petroleum-based counterparts. The synthesized resin achieved a high Tg exceeding 400°C, a char yield of 79% at 1000°C, and T5% and T10% values of 564 and 660°C, respectively. The Q-Ph polymer demonstrated superior performance, with evidence of an autocatalytic curing mechanism. These results highlight quercetin as a promising petrochemical replacement for the preparation of self-curable PN thermosets, especially for high-performance applications.