Study on Methyl Substitued Diarylphosphine Oxide Flame Retardant Modified Epoxy Resin

Two new compounds, (4-methylphenyl) phenylphosphine oxide (4-MPO) and (2, 4-dimethylphenyl) phenylphosphine oxide (2, 4-DMPO) were synthesized by the reaction of phenylphosphorus dichloride (DCPP) with toluene and meta-xylene, respectively. The target compounds were introduced as reactive flame retardants into bisphenol A epoxy resin to prepare phosphorus-containing epoxy and flame retardant epoxy resin cured by 4, 4'-diaminodiphenylsulfone was further prepared. Thermal stability, flame retardancy, water absorptivity and dielectric property of the flame retardant epoxy resin were tested, and the flame retardant mechanism was studied. It was found that the two flame retardants can effectively improve the flame retardancy of epoxy resin, the 2, 4-DMPO exhibits higher flame retardant efficiency. The resulting flame retardant EP achieved a LOI of 31.5% and a UL-94 V-0 rating when the 4-MPO modified epoxy resin phosphorus content was 0.9% (mass fraction, the same below), while the flame retardant EP demonstrated a LOI of 30. 3% and received a UL-94 V-0 rating when the phosphorus content of the 2, 4-DMPO modified epoxy resin was 0.6%. Compared with unmodified epoxy, the thermal stability, Tg and water absorptivity were slightly decreased, but the dielectric property was significantly improved. 2, 4-DMPO modified epoxy resin showed higher flame retardancy and better dielectric property. The two flame retardants both act through gas phase and solid phase flame retardant mechanism, and the gas phase mechanism plays an important role. © 2024 Cailiao Daobaoshe/ Materials Review. All rights reserved.