Benzimidazolyl-substituted cyclotriphosphazene derivative as latent flame-retardant curing agent for one-component epoxy resin system with excellent comprehensive performance

Epoxy resin (EP) is inherently inflammable and most flame retardants used now unavoidably deteriorate other properties of EP. Moreover, the components of EP system tend to be formulated as one-component system for large-scale industrial production instead of being blended just before use. In order to overcome these issues, benzimidazolyl-substituted cyclotriphosphazene (BICP) was synthesized and utilized as latent flame-retardant curing agent for EP. According to the curing and rheological behavior studies, BICP maintained chemically inert towards EP at room temperature and could rapidly cure EP when heated. The combustion test results indicated the outstanding flame retardancy of EP/BICP thermosets. With 10.7 wt% addition of BICP, the limited oxygen index (LOI) of EP/BICP-12 thermoset was as high as 33.5% and UL94 V-0 rating was achieved; the peak of heat release rate (pk-HRR), average of heat release rate (av-HRR), total heat release (THR) and fire growth rate (FIGRA) of EP/BICP-12 thermoset were decreased by 69.8%, 33.2%, 34.7% and 71.8%, respectively, compared with those of the neat EP thermoset. Most attractively, other properties of the EP/BICP thermosets were not impaired despite of the enhancement of flame retardancy. Compared with the neat EP thermoset, the EP/BICP thermosets showed comparable mechanical properties and improved dielectric properties. Especially, the Tg values of EP/BICP thermosets (except for EP/BICP-8 sample) were around 190 °C, 34 °C higher than that of the neat EP thermoset. All these results demonstrated that EP/BICP system with remarkable comprehensive performance has the potential to achieve wider application in key fields.