Recent advances in flame retardant epoxy systems from reactive DOPO–based phosphorus additives

Epoxy resins are widely applied in industry for producing fire safe materials. Unfortunately, epoxy resins have the disadvantage of being highly flammable and thus require suitable modifications with reactive or non-reactive flame retardant additives. Recent literature have shown that the derivatives 9,10–dihydro–9–oxa–10–phosphaphenanthrene–10–oxide (DOPO) are the most researched flame retardants for epoxy resins. Both classes of DOPO derivatives generally endow epoxy resins with high thermal stability, non–oxidative character, water resistance and excellent flame retardancy through the generation of phosphorus based flame-inhibiting species in the gas phase. The non–reactive derivatives may lead to leaching from the epoxy resin during use. Thus reactive DOPO derivatives have gained importance, where they are either directly coupled to the epoxy resin in form of monomers via a pre-reaction, as a reactive curing agent or as a hybrid structure. This review focuses mainly on noteworthy technological advances in this area which have been published in the past ten years.