Flame-Retarding Epoxy Resin Films by Curing with Organophosphorus Containing Diamine

An organophosphorus-based diamine has been synthesized and used as a curing and flame retarding bifunctional agent for epoxy resins.This phosphorodiamidate functions not only as a crosslinking materials in the Epon 828 epoxy resin curing process but also as a fire retarding compound to produce thin films or composites upon curing.This phosphorus-containing reactive amine was synthesized via condensation of phenyphosphonic dichloride with ethylenediamine in the presence of sodium methoxide.The product was then purified and later characterized by NMR and FTIR spectroscopy as well as MALDI-TOF mass spectrometry.Kinetics studies of the curing reaction of the phosphorodiamidate were carried out in comparison with the non-phosphorus containing ethylenediamine reference crosslinking agent.Thermal stability of the cured epoxy ware investigated by thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC).Moreover,flame retardant properties of the obtained materials was investigated by limiting oxygen index(LOI)measurements as well as the UL-40 method.The obtained results show that epoxy resin cured with phosphorodiamidate possesses higher thermostability compared to the epoxy cured with the regular ethylenediamine counterpart.This is evident by higher amount of char formed upon burning.More importantly,the LOI value of 27 was observed in the phosphorodiamidate-cured epoxy resin compared with LOI of 20 of the epoxy resin cured with ethylenediamine where no phosphorus was present.The UL-94 highest rating of V-0 materials was obtained with only about 2-3 wt%of the phosphorus element.The chemistry,curing kinetics,and thermal properties of these new epoxy formulations are discussed.