Ladder‐like cross‐linked network of epoxy resin through multi‐site interaction: Flame retardancy and mechanical properties

Abstract Most epoxy resins (EP) suffer from sacrificial mechanical properties in flame retardancy applications. Through a facile reaction between N‐aminoethylpiperazine (N‐AEP) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO), a novel multi‐site interaction flame retardant, DOPO‐based aminoethylpiperazine (abbreviate as AEPO), was successfully synthesized, which could form a ladder‐like cross‐linked network with EP. EP modified by AEPO (EP‐AEPO) was tested for flame retardancy using the limiting oxygen index (LOI), the vertical burning test (UL‐94), and the cone calorimeter test (CCT). According to the results, EP‐10 (EP with 10 phr of AEPO) could pass UL‐94 V‐0 rating and get a LOI value of 35.5%, the peak heat release rate (PHRR) and total heat release (THR) of EP‐10 were also decreased by 25.2% and 29.8%, respectively, which caused by the synergistic charring effect of phosphorus and nitrogen elements contained in the structure of AEPO. Due to the ladder‐like cross‐linked network formed through multi‐site interaction, the mechanical properties demonstrated a significant improved. This work opened up a new strategy for achieving a comprehensive improvement on multifunctional EP through the design of a novel ladder‐like cross‐linked network with multi‐site interaction.