Synthesis of DOPO‐based pyrazine derivative and its effect on flame retardancy and thermal stability of epoxy resin

A novel DOPO‐based pyrazine derivative 6‐((2‐hydroxyphenyl)(pyrazin‐2‐ylamino)methyl)dibenzo[c,e][1,2]oxaphosphinine 6‐oxide (DHBAP) was triumphantly synthesized by a two‐step addition reaction using 2‐aminopyrazine, 2‐hydroxybenzaldehyde and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) as reactants, and characterized by Fourier‐transform infrared (FTIR), 31 P nuclear magnetic resonance (NMR) and 1 H NMR. Afterwards, the addition type flame retardant (DHBAP) was utilized to modify epoxy resin (EP) by blending method. When the content of DHBAP in neat EP was 8 wt%, it reached to the V‐0 rating and the limited oxygen index (LOI) value up to 34.0%. Furthermore, according to the cone calorimeter (CC) test results, the heat release rate (HRR), total heat release (THR), smoke produce rate (SPR) and total smoke production (TSP) of EP/8% DHBAP decreased by 26.3%, 21.3%, 37.0% and 60.9% when compared with neat EP, respectively, indicating that DHBAP had good inhibition on heat and smoke releases. Eventually, the flame‐retardant mechanism of DHBAP was further explored by X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, and pyrolysis‐gas chromatography/mass spectrometry (Py‐GC/MS). The results showed that DHBAP had good flame‐retardant activity in the gasous‐condensed two phases.