A Liquid Phosphaphenanthrene-Derived Imidazole for Improved Flame Retardancy and Smoke Suppression of Epoxy Resin
Siqi Huo, Shuang Yang, Jun Wang, Jianwen Cheng, Qianqian Zhang, Yefa Hu, Guoping Ding, Qiaoxin Zhang, Pingan Song, Hao Wang
Abstract
The fabrication of high-performance thermosetting polymers with intrinsic flame retardancy and smoke suppression is necessary but challenging. Herein, we have successfully synthesized a liquid phosphaphenanthrene/imidazole-containing curing agent (DOPO-AI) for epoxy resin (EP) by the Atherton–Todd reaction of 1-(3-aminopropyl)imidazole (AI) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). The as-prepared EP/DOPO-AI samples exhibit comparable mechanical properties to the reference EP/AI-6 sample, with slightly decreased glass transition temperatures. Impressively, the EP/DOPO-AI sample can pass the UL-94 V-0 rating and achieve a limited oxygen index (LOI) value of 37.0%. Additionally, the EP/DOPO-AI sample shows 26.3%, 36.6%, and 24.4% reductions in the total heat release (THR), peak of heat release rate (pHRR), and total smoke production (TSP) relative to the EP/AI-6 sample, indicating a significantly reduced fire hazard. The significant enhancements in flame retardancy and smoke suppression are attributed to the condensed- and gaseous-phase effects of DOPO-AI. This work demonstrates a feasible methodology for creating high-performance EPs with inherent flame retardancy and smoke suppression, holding great promise in the future.