Aminobenzothiazole-substituted cyclotriphosphazene derivative as reactive flame retardant for epoxy resin

Aminobenzothiazole-substituted cyclotriphosphazene derivative (ABCP) was successfully synthesized and used as reactive flame retardant to improve the fire safety of epoxy resin (EP). The chemical structure of ABCP was confirmed by Fourier transform infrared spectroscopy (FTIR), H-1 and P-31 nuclear magnetic resonance (NMR), high-resolution mass spectroscopy (HR-MS) and elemental analysis (EA). The curing behavior, thermal stability, thermo-mechanical property and flame retardancy of the prepared EP systems were studied. The differential scanning calorimeter (DSC) results indicated that ABCP induced the anionic polymerization of EP and facilitated the addition reaction between EP and 4,4'-diamino-diphenyl sulfone (DDS). The thermogravimetric analysis (TGA) results indicated that ABCP accelerated the thermal degradation of EP matrix and contributed to the formation of more residual chars with better thermo-oxidative stability. The dynamic mechanical analysis (DMA) results indicated that EP/DDS/ABCP thermosets exhibited higher storage modulus at 50 degrees C and their glass transition temperature (T-g) values were slightly reduced by 6-10 degrees C, in comparison with EP/DDS thermoset. The combustion test results revealed the fire hazards of EP/DDS/ABCP thermosets were effectively reduced. Compared with EP/DDS thermoset, the limiting oxygen index (LOI) value of EP/DDS/ABCP-1.2 thermoset was increased to 31.2% and the sample passed UL94 V-0 rating; the average of heat release rate (av-HRR), peak of heat release rate (pk-HRR) and total heat release (THR) values of EP/DDS/ABCP-1.2 thermoset were reduced by 36.5%, 53.7% and 34.5%, respectively; particularly, the fire growth rate (FIGRA) of EP/DDS/ABCP-0.6 thermoset was reduced by half. The research on flame retardant mechanism disclosed that ABCP played dominated flame retardant effect in condensed phase.