Molecularly engineered bio-based benzoxazine for organic phase change materials with latent flame retardancy and 80–100 °C thermal storage applications†

The inherent flammability of hydrocarbon-based phase change materials (PCMs) unavoidably poses safety risks. Herein, amide-containing benzoxazine-based PCMs (AMBZ-PCMs) were engineered using bio-based materials and benzoxazine chemistry, 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, an enthalpy of 160.5 J g⁻¹, and excellent flame resistance (peak heat release rate: 274.1 W g⁻¹, lower than tetracosanoic acid with 951.8 W g⁻¹), 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 molecules, provides a feasible solution to fill the gap in high-performance PCMs (80–100 °C). Also, it pioneers a chemical approach to design flame-retardant organic PCMs.