Molecularly engineered bio-based benzoxazine for organic phase change material with latent flame retardancy and 80-100 °C thermal storage application

The inherent flammability of hydrocarbon-based phase change materials (PCMs) unavoidably breeds safety risks. Herein, an amide-containing benzoxazine-based PCMs (AMBZ-PCMs) was engineered through benzoxazine chemistry and bio-based materials, achieving tunable phase-change properties while balancing energy density and fire safety. AMBZ-PCMs integrate long alkyl chains with improved phase-change performance, amide-derived reversible hydrogen bonds, and oxazine rings with latent flame retardancy. Upon heating or flame exposure, these materials undergo ring-opening polymerization, forming cross-linked, easily-carbonized networks that suppress combustion without compromising phase-change performance. Representatively, 18-am-18 exhibits a melting temperature of 95.9 °C, enthalpy of 160.5 J/g, and excellent flame resistance (peak heat release rate: 274.1 J/g), outperforming conventional methods through chemically grafting or physically blending flame-retardant components. In addition, the phase transition behavior remained almost unchanged after 50 cycles, confirming the excellent hydrogen-bond reversibility. Practical applications in photothermal drying and automotive thermal management demonstrate the viability of 18-am-18. This strategy based on engineering bio-based benzoxazine molecular provides a feasible solution to fills the gap for high-performance PCMs (80-100 °C). Also, it pioneers a chemical approach to design flame-retardant organic PCMs.