Dr. Wang Jingsheng from Wuhan University of Technology, Principal Investigator of NEXCEL 2024 Ph.D. project titled 'Synthesis of Phosphorus-Metal-Imidazole Complexes as Latent Flame-retardant Curing Agents and Their Impact on the Curing and Flame-retardant Properties of Epoxy Resin', has published a paper entitled "Liquid phosphorus-based bis-imidazole compounds as latent curing agents for enhancing thermal, mechanical, and flame-retardant performances of single-component epoxy resins" in "Polymer Degradation and Stability" (SCI) recently.

The escalating need for advanced, fire-resistant, single-component epoxy resin (EP) is fueled by its practicality and economic benefits, highlighting the necessity for the development of multifunctional flame-retardant latent curing agents. Herein, two liquid phosphorus-containing bis-imidazole compounds, PPDM and DPCMI, were synthesized as latent curing agents for EP, demonstrating multiple effects in improving latency, thermal stability, mechanical properties, and fire safety. EP/PPDM and EP/DPCMI showcased superior storage stability and rapid curing at moderate temperatures, with EP/PPDM standing out for its long shelf life of 7 d and being gelled within 18 min at 100 ◦C. The resulting thermosets presented increased glass transition temperatures (189.5 and 178.9 ◦C), due to the enhanced crosslinking densities. The presence of bis-imidazole groups in PPDM and DPCMI enabled EPs to form denser crosslinked networks, leading to improved mechanical strength and toughness. The limiting oxygen index (LOI) values of EP/PPDM and EP/DPCMI reached 29.5% and 29.0%, respectively. Compared to the control EP, EP/PPDM and EP/DPCMI showed 23.1% and 18.8% reductions in total heat release and 22.0% and 23.11% decreases in total smoke production. These results confirm the enhanced flame retardancy and smoke suppression of EP/PPDM and EP/DPCMI because of introducing phosphorus-containing groups. Even though the curing time was halved to 2.5 hours, EP/PPDM systems maintained satisfactory overall performances. Therefore, this work offers a scalable strategy for the fabrication of single-component EP systems combining rapid curing, satisfactory flame retardancy, and enhanced thermal stability and mechanical properties, aligning with the needs of industrial applications.

PolymerDegradationandStability230(2024)111066

https://doi.org/10.1016/j.polymdegradstab.2024.111066