Reactive phosphaphenanthrene aromatic ether diamine endowing epoxy resin with excellent fire resistance, liquid oxygen compatibility and cryogenic mechanical properties

Endowing conventional epoxy resin (EP) with great liquid oxygen compatibility (LOC) and desirable ultra-low-temperature mechanical property is essential to the applications in fields of cryogenic engineering. A reactive phosphaphenanthrene aromatic ether diamine (PBAH) flame retardant including phosphorus and nitrogen elements was synthesized by a simple one-pot reaction between HB (salicylaldehyde), DOPO (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide) and BAPP (2,2-bis[4-(4-aminophenoxy)phenyl]propane), then utilized to modify EP/BCI (biscitraconimide resin) system as a multifunctional component in this study. The resultant EP represented improved heat stability; outstanding fire resistance with an improvement of limiting oxygen index (LOI) value of 31.7% and V-0 rating in UL-94 test, as well as the desirable LOC and enhanced mechanical properties. The tensile strength (130.49 MPa) and fracture toughness (2.93 MPa·m^1/2) increased by 51.3% and 78.7%, respectively, and the bending strength (255.30 MPa) increased by 116.8% than that of pure EP at cryogenic (77 K). All these results demonstrated the reactive PBAH showed a broaden potential in ultra-low-temperature engineering fields.