Performance comparison of epoxy resins modified with diphenylphosphine oxide and DOPO

By curing the reaction mixture of diphenylphosphine oxide (DPO) and diglycidyl ether of bisphenol A with 4,4 '-diaminodiphenylsulfone, flame-retardant epoxy resins (EP/DPO) were prepared. Flame-retardant epoxy resins modified with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) were similarly prepared (denoted as EP/DOPO). The limiting oxygen index value of pure epoxy resin, EP/DPO-P-0.9 (with a phosphorus content of 0.9 wt%), and EP/DOPO-P-0.9 are 23.0, 30.5, and 29.4%, respectively. EP/DPO-P-0.9 reached a UL-94 vertical burning test V-0 rating, while EP/DOPO-P-0.9 failed. The results of the cone calorimetry test, thermo-oxidative degradation behavior study, and pyrolysis-gas chromatography/mass spectrometry analysis indicated that both flame retardants mainly act through the gas-phase activity mechanism. Together, the results of this study suggest that EP/DPO are high performance resins with good thermal stability, high glass transition temperature, and low water absorptivity for practical applications.