Synthesis of a DOPO Derivative to Improve the Fire Safety and Mechanical Performance of Epoxy Resin

A 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative is prepared. At first, an intermediate 4,4'-((triazole)bis(azaneylylidene)bis(2,6-dimethoxyphenol)) (SGA) is obtained from the Schiff-base reaction between syringaldehyde (S) and 3,5-diamino-1,2,4-triazole (GA). The further product DOPO-SGA is then introduced into epoxy by blending to improve flame retardancy and mechanical properties. The flammability evaluation is implemented by limited oxygen index (LOI), UL-94, and cone calorimeter tests. The presence of 3wt.% DOPO-SGA increases the LOI to 33.2%, upgrades the UL-94 rating to V-0, and reduces the release of smoke and heat of epoxy. The tensile strength and impact strength are also enhanced after the introduction of DOPO-SGA. The addition of 5% DOPO-SGA increases the tensile strength and impact strength by 47% and 42%, respectively, compared with that of the control EP sample. It is suggested that the mechanical strengthening is ascribed to the ternary cross-linked network among epoxy monomer, curing agent, and DOPO-SGA. This work provides a feasible solution to obtain flame-retardant epoxy resin with enhanced mechanical performance.