Engineering flame retardant epoxy resins with strengthened mechanical property by using reactive catechol functionalized DOPO compounds

In this work, we synthesized a 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) derivative flame retardant dopamine modified DOPO (DOPO-DA) for flame retardant thermosetting epoxy resins (EP). The effects of different amounts of flame retardants on the flame retardancy, thermal properties, and mechanical properties of EP composites were studied. Compared with the control EP, the peak heat release rate (PHRR) of EP/5 wt% DOPO-DA decreased by 26.1%. In addition, EP/5 wt% DOPO-DA reached V-0 level. It can be attributed to the quenching effect of P element and catechol groups in DOPO-DA, reducing the active free radicals. N element can release non-combustible gases to dilute the concentration of oxygen. Meanwhile, P element can promote the formation of a dense carbon protective layer and slow down the heat and oxygen transfer on the surface. In addition, DOPO-DA can also participate in the crosslinking reaction of EP as a curing promoter, reducing crosslinking density and improving tensile properties.