Hydrogen Bonding-Guided Strategies for Thermal Performance Modulation in Biobased Oxazine Ring-Substituted Benzoxazine Thermosets

Diverse applications of polybenzoxazines (PBZs) accounted for a surge in advanced synthetic regimes of benzoxazine monomers to witness excellent performances. However, the requirement of a high polymerization temperature remains a matter of concern. Herein, eco-friendly synthon-derived latest oxazine ring-substituted benzoxazine monomers are designed to reduce the polymerization temperature without compromising the shelf life by leveraging the strategy of in-built latent catalysis. A regiomeric variation in functionalities (phenolic–OH, anisolic–OMe, and both) demonstrates the effect of the varying nature (intra-/intermolecular) and strength (weak/strong) of hydrogen bonding on the shelf life, thermal performance, and curing accelerators in the current series of monomers. Detailed structural analyses of the monomers reveal that geometry-guided interactions improved the stability and alleviated the mass-loss issue during polymerization, which is often encountered in earlier generations of benzoxazines. Interestingly, the polybenzoxazines also possessed a high thermal stability, thanks to the polar and nonbonding interactions within the cross-linked network. Furthermore, the self-catalyzing feature of the phenolic–OH empowered us to apply these monomers as curing accelerators and effectively upgrade the thermal performance of another underperforming monomer and the corresponding copolymer. The present work advocates a sustainable strategy of structural engineering in developing next-generation thermosets for cutting-edge applications seeking low energy-intensive processing and brilliant performance.