Synthesis of a novel DOPO-based ionic liquid flame retardant and its application in epoxy resin†

The low mechanical properties of flame-retardant epoxy resins restrict their applicability; therefore, the development of flame retardants designed to enhance the mechanical properties while maintaining the flame retardancy of epoxy resins presents significant potential for various applications. The present study introduces a novel fused-type ionic-liquid flame retardant, [DAmim]Ps, which is developed and applied to enhance the flame retardancy of EP. Unlike conventional additive flame retardants, [DAmim]Ps exhibits unique characteristics such as a melting point at 101 °C and active participation in the curing reaction of EP, thereby significantly facilitating the improvement of flame retardancy. Upon the incorporation of [DAmim]Ps, the EP composite system exhibited a [DAmim]Ps content of 6.8%, demonstrating exceptional performance with a remarkable limiting oxygen index (LOI) value of 32.9% and achieving a V-0 rating in a UL-94 vertical combustion test; meanwhile, the combustions of THR and HRR in EP-5 are 39.3% and 36.3% lower than those in EP-0, respectively, reflecting the excellent flame-retardant performance. Furthermore, the addition of [DAmim]Ps ionic liquid also promotes the mechanical properties of the EP system. The tensile strength, bending modulus, and impact strength increase by 51.14%, 57.7%, and 146.0%, respectively.