A high-temperature-triggered crosslinking reaction to achieve excellent intrinsic flame retardancy of organic phase change composites

The host-guest composite that integrates a porous scaffold and organic phase change materials (PCMs) features high energy density and customizable function, promising for advanced thermal storage/utilization. However, highly flammable organic PCMs are prone to severe combustion in porous structures, making it challenging for traditional flame-retardant methods to balance fire safety and latent heat. Herein, a high-temperature-triggered crosslinking reaction between the host and guest is designed using a polybenzoxazine-based aerogel (PB-1) and benzoxazine-based PCMs (C-dad). At high temperatures, the ring-opening polymerization (ROP) of C-dad can be initiated by and reacted with the phenolic groups of PB-1 to form a polybenzoxazine copolymer monolith with an improved char yield and intrinsic low flammability and without using the typical flame-retardant components. This enables the obtained composite (PB-1/C-dad) to well balance latent heat (145.3 J g^-1), char yield (a char residue of 13.1% at 600 °C), and flame retardancy (a peak heat release rate of 231 W g^-1), outperforming the representative flame-retardant modified polymer/organic PCM complexes reported in the literature. This thermal-triggered mechanism allows PB-1/C-dad to be repeatedly and stably used within the working temperature and activates its flame retardancy when exposed to open flames. The proposed host-guest crosslinking strategy is believed to inspire the development of inherently nonflammable phase change composites for safer thermal management.