Preparation and flame retardancy of DOPO–based epoxy resin containing bismaleimide

Epoxy resins were modified with 10-(2,5-dihydroxyl phenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 1,1′-(methylenedi-4,1-phenylene) bismaleimide (BDM). The resulting blends were then cured with 4, 4′-diaminodiphenyl sulfone. Thermal properties of the cured epoxy resins were investigated by differential scanning calorimetry and thermogravimetric analysis. Flame retardancy of the cured epoxy resins was checked by limiting oxygen index test, UL-94 vertical burning test, and cone calorimeter test. The char residue after cone calorimeter test was investigated by scanning electron microscopy/energy-dispersive X-ray analyses. The results indicated that the cured resins exhibited high glass transition temperature and excellent flame-retardant properties. BDM promoted the carbonization property of phosphorus-containing epoxy resin and facilitated the formation of cross-linked char layer with compact and continuous structure, thus enhancing the flame-retardant properties.