The preparation of flame-retardant materials with complex shapes based on a dual-modulus network strategy†

Flame-retardant thermosetting polymers are extensively used in construction materials and aerospace applications due to their inherent stability and performance characteristics. Traditional processing methods, however, are limited to producing simple geometries such as strips, blocks, and plates. Additionally, small molecule flame retardants exist in the resin matrix in a free form, and as the resin is used over time, these small molecule flame retardants tend to migrate, which deteriorates the flame-retardant performance of the material. Herein, we synthesized a flame retardant containing P and N elements with a double bond, which also serves as a curing agent, through molecular design and applied it in an acrylate–epoxy resin dual-modulus network system. Initial photopolymerization facilitated the creation of a low-modulus acrylate network, endowing the material with significant flexibility and allowing for arbitrary shaping. The double bonds present in the designed flame retardant ensure its integration into the acrylate network during photopolymerization, thereby mitigating migration issues. Subsequently, this flexible material undergoes thermal curing to form a high-modulus epoxy resin network, increasing the material's tensile modulus by up to 2500 times, tensile strength by up to 300 times, and glass transition temperature by up to 180 °C, resulting in a rigid material. Therefore, this work introduces an innovative approach to fabricating flame-retardant thermosetting materials with complex shapes while effectively reducing the migration of flame retardant molecules within the resin matrix.