Novel multi‐element DOPO derivative toward low‐flammability epoxy resin

In order to obtain cured epoxy resin (EP) with satisfactory thermal stability and flame retardancy, a multi‐element P/N/Si‐containing flame retardant (DPAK) was synthesized by a facile way and was used as a reactive flame retardant to prepare flame‐retardant EP. The flame‐retardant efficiency of DPAK was subsequently evaluated by limiting oxygen index (LOI), UL‐94, and cone calorimeter (CC) test. With a low incorporation amount of DPAK (4 wt%), the resultant EP achieve to UL‐94 V‐0 rating, and the corresponding LOI value reached to 30%, which was higher than that of EP containing DOPO (2.9 wt%). More importantly, the thermogravimetric analysis (TGA) revealed their higher thermal stability than those of EP containing DOPO. Furthermore, dynamic mechanical analysis (DMA) shown the maintained glass transition temperature of DPAK‐EP. The increase of CO/CO2 ratio in the CC test for the DPAK‐EP samples proved the gas‐phase activity of DPAK. Additionally, DPAK showed evidence of condensed phase activity by increasing char residue in TGA and CC test. The scanning electronic microscope together with the energy dispersive X‐ray spectrometer (SEM–EDX) and X‐ray photoelectron spectroscopy (XPS) exhibited that DPAK promoted the formation of compacted phosphorus‐silicon char layer. Subsequently, TG‐FTIR results indicated that DPAK‐EP produced lesser combustible gases than neat sample did, improving flame‐retardant properties of epoxy resin.