Phosphorus-containing liquid imide derivatives for enhancing fire safety, smoke suppression, UV shielding and mechanical properties of epoxy resins

Designing and preparing highly transparent EP thermosetting materials with excellent flame retardancy and mechanical properties has always been a challenge. This work prepared liquid flame retardant (PCM) derived from imides through a simple one-step esterification reaction, and applied it to prepare high-performance EP composites. Due to the π−π interaction between phosphorus containing aromatic PCM and EP, the rigidity of EP composites was enhanced. At the same time, the larger internal free volume of PCM provided space for the movement of EP chain segments. As a result, the impact, tensile and bending strengths of EP-5 % increased by 96.5 %, 14.3 % and 28.4 %, respectively. Surprisingly, EP composites exhibited transparency no less than EP, while also achieving excellent UV shielding properties. The combustion behavior showed that the UL-94 and LOI classifications of EP-7 % were V-0 and 31.6 %, with a decrease of 36.3 % in HRR and a decrease of 57.8 % in TSP. This phenomenon was attributed to the combination effect of the barrier of high-quality char layer, the free radical quenching of phosphorus groups, and the dilution effect of non-combustible gases.