Preparation, mechanical properties, and thermal degradation of flame retarded epoxy resins with an organophosphorus oligomer

An organophosphorus oligomer, poly(DOPO-substituted hydroxyphenyl methanol pentaerythritol diphosphonate) (PFR), was synthesized from the dehydrohalogenation polycondensation of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide substituted hydroxyphenyl methanol (DOPO-HBA) with 3,9-bis(chloro)-2,4,8,10-tetraoxa-3,9-diphosphaspiro [5.5]undecane-3,9-dioxide (SPDPC). The structure of PFR was confirmed by FTIR, ¹H NMR, and ³¹P NMR. Advanced flame retardant epoxy resins (FREP) were obtained by incorporating PFR into EP, cured by 4,4′-diaminodiphenylmethane (DDM). Effects of PFR on thermal, dynamic mechanical properties, and flame retardant properties of the epoxy resins were investigated. The dynamic mechanical analysis (DMA) results showed that EP/PFR exhibited higher glass transition temperature than that of neat EP. Moreover, incorporation of PFR significantly enhanced the char yield at higher temperatures. The addition of PFR into epoxy resins significantly improved their flame retardancy, due to the reduction of peak heat release rate, total heat release as well as the mass loss rate.