Sustainable synthesis of a novel bio-based low temperature curable benzoxazine monomer from quercetin: Synthesis, curing reaction and thermal properties

In an attempt to make polybenzoxazines more sustainable, a novel bio-based benzoxazine monomer namely Q-Bz was synthetized via the Mannich condensation reaction utilizing Quercetin, paraformaldehyde and aniline. The chemical structure of the monomer was confirmed by 1 H nuclear magnetic resonance ( 1 H NMR) and Fourier transform infrared spectroscopies (FTIR). The curing behaviour was studied by differential scanning calorimetry (DSC) and the polymerization process was investigated by FTIR. The obtained results showed very low melting and polymerization temperatures (73 and 183°C, respectively) and the disappearance of the oxazine ring absorption bands due to the ring opening polymerization of the monomers. Afterwards, the cured bio-based thermoset, referred to as PQ-Bz, was obtained and its thermal stability and thermo-mechanical properties were also assessed by DSC and thermogravimetric analysis (TGA). As expected the newly developed thermoset exhibited high thermal stability along with excellent processability. Indeed, the results showed that PQ-Bz had a relatively high T g of approximately 280°C, with a 53% char yield at 800°C, 5% and 10% weight reduction temperature (T 5% and T 10% ) values of 349 and 373°C, respectively. These findings demonstrate the potential of the novel bio-based benzoxazine monomer as a sustainable alternative to traditional petroleum-based thermosets in high performance applications.