Synthesis of a novel DPPA-containing benzoxazine to flame-retard epoxy resin with maintained thermal properties

The flame-retarded epoxy resin with improved thermal properties based on environmentally friendly flame retardants is vital for industrial application. Hereby, a novel reactive-type halogen-free flame retardant, 10-(3-(4-hydroxy phenyl)-3,4-dihydro-2H-benzo[e] [1,3] oxazin-4-yl)-5H-phenophosphazinine 10-oxide (DHA-B) was synthesized via a two-step reaction route. Its structure was characterized using 1 H, 13 C, and 31 P NMR and HRMS spectra. For 4,4′-diaminodipheny ethane (DDM) and diglycidyl ether of bisphenol A (DGEBA)-cured systems, the epoxy resin with only 2 wt% loading of DHA-B passed V-0 rating of UL-94 test. Significantly, its glass transition temperature ( T g ) and initial decomposition temperature ( T 5% ) were as high as 169.6°C and 359.6°C, respectively, which were even higher than those of the corresponding original epoxy resin. Besides, DHA-B decreased the combustion intensity during combustion. The analysis of residues after combustion suggested that DHA-B played an important role in the condensed phase.