Glyoxal-Based Bi-Oxazine Benzoxazines: Formaldehyde-Free Biothermosets

Natural abundant resources and safe chemicals are attractive feedstocks for achieving circular sustainability. A wide variety of biophenols and greener amines offered interesting avenues in the evolution of the upcoming class of phenolic thermosets, polybenzoxazines (PBZ). High dependence on formalin as a starting material for monomer synthesis has prompted exploration of alternative safe chemicals. In this study, we designed a family of glyoxal-based benzoxazine (BZ) monomers to synthesize formaldehyde-free biothermosets, leveraging a proximity and promiscuity oxazine–oxazine dependent polymerization. The bi-oxazine functionality at the reactive C₂ center in the monomers demanded significantly low temperature for ring-opening polymerization with high polymerization enthalpy favoring an ease in polymer growth, overcoming challenges posed by earlier generation BZ monomers. Current work demonstrates the proof-of-concept for a highly efficient methodology for formaldehyde replacement in benzoxazine chemistry and holds promise for the exploration of a new platform chemical, glyoxal, toward the next generation of benzoxazine with unique reactivities.