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), P-31 nuclear magnetic resonance (NMR) and H-1 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.