A nitrogen‐rich DOPO‐based phosphoramide for improving the fire resistance of polycarbonate with comparable mechanical property

Abstract

A nitrogen‐rich DOPO‐based phosphoramide (DPAPZ) was synthesized using aminopyrazine and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide (DOPO) as raw materials, and blended with polycarbonate (PC) through melting method. The chemical structure of DPAPZ was validated by FTIR, 1H NMR and 31P NMR. The presence of DPAPZ endowed PC/DPAPZ composites with better fire safety and smoke suppression. With the incorporation of 6 wt% DPAPZ, PC/DPAPZ‐6 composite reached UL‐94 V‐0 rating and 30.2% of limiting oxygen index value. Simultaneously, the peak of heat release rate and total heat release of PC/DPAPZ‐6 were reduced by 44.8% and 47.0% as compared with the pure PC, respectively. The DPAPZ displayed bi‐phase flame retardant roles. In the gas phase, the decomposition of DPAPZ released phosphorus‐containing free radicals acting as the quencher of reactive H·/OH· and nonflammable NH3 diluting O2/combustible volatiles. In the condensed phase, the phosphorus‐containing components were dehydrated into metaphosphoric acid or polymetaphosphate covering the surface to protect the PC matrix from further combustion, and to promote the formation of a dense carbon layer to interrupt the transmission of O2 and volatiles between the combustion zone and the inner. The tensile strength of the composites displayed almost no change but the elongation at break decreased slightly with the addition of DPAPZ.