Synthesis of N, N-Bis-(diphenylphosphinyl)-p-toluenesulfonamide for endowing epoxy resin simultaneously with better flame retardancy and transparency

It is still a great challenge to achieve flame retardant epoxy resin (EP) without sacrificing its transparency and mechanical properties. In the present work, A P/N/S containing sulfonamide compound (DPPBSA) was synthesized and adopted to improve the fire safety of transparent epoxy resin. With the incorporation of 5 wt% DPPBSA, the EP composite presented UL-94 V-0 rating and 35.4% of LOI value, its peak of heat release rate and total heat release were also reduced by 51.0% and 40.8% as compared with the pure EP, respectively. The improved flame retardancy was attributed to the comprehensive flame retardant effect of the P, N, and S elements. In the condensed phase, much continuous and denser char layers with greater graphitization degree were formed during the combustion. In the gas phase, the pyrolysis of the DPPBSA released dilution gases and P-containing free radical scavengers. Moreover, the EP composite containing 5 wt% DPPBSA displayed almost comparable tensile strength and transparency with the pure EP.