Integrating Intrinsic Solid-Solid Phase Change and Flame Retardancy Into Closed-Loop Recyclable Polyimine Aerogels via Dynamic Covalent Networks

Organic aerogels are promising scaffolds for phase change materials (PCMs) in thermal management, but their inherent flammability and PCM leakage limit practical applications. In this work, we report a molecular design strategy for fully recyclable, bio-based polyimine aerogels (DPI-P_x-OA_y) that synergistically integrate intrinsic phase-change functionality, flame retardancy, and closed-loop recyclability within a single dynamic covalent network. A vanillin-derived organophosphate node (TFMP) was incorporated as a flame-retardant cross-linker, while octadecylamine (OA) served as a phase-change unit, achieving leakage-free thermal regulation with a melting enthalpy up to ~17.81 J/g. The resulting aerogels exhibited excellent processability, high load-bearing capacity, and self-extinguishing behavior with reduced heat release. Moreover, the OA side chains further improved thermal insulation through increased phonon scattering and latent heat absorption, collectively contributing to excellent infrared stealth and thermal protection. In addition, the aerogels also acted as high-capacity scaffolds for solid-liquid PCMs. Upon encapsulation of polyethylene glycol (PEG10K), the melting enthalpy further increased to ~147.4 J/g. Furthermore, the dynamic imine bonds enabled closed-loop monomer recycling under mild acidic conditions, further enhancing the material's sustainability. This work offers a unified platform for sustainable multifunctional aerogels that reconciles thermal storage, fire safety, and closed-loop recyclability.