A novel phosphorus-nitrogen-containing hardener toward antiflammable, smoke-suppressed and low-dielectric epoxy thermosets

Abstract

The application of epoxy resins (EPs) in the new generation of electronic and electrical applications has been significantly hindered by their poor dielectric properties and flammability. To develop high-performance epoxy thermosets, a multifunctional phosphorus-nitrogen-containing curing agent (TFDP) was synthesized in this work via the reactions of 1formylpiperazine (FPA), tris(2-aminoethyl)amine (TAEA), and dimethyl phosphonate (DMP). The epoxy thermosets prepared from the co-curing system composed of TFDP and diethyltoluenediamine (DETDA) presented remarkable advantages in terms of flame retardancy, mechanical properties, and dielectric properties. Specifically, EP-TFDP-2 presented a limiting oxygen index (LOI) value of 28 and achieved a UL-94 V-0 rating. Relative to those of neat EP, the peak heat release rate (pHRR), total heat release (THR), and total smoke production (TSP) of EP-TFDP-2 decreased by 73.1%, 48.4%, and 80.8%, respectively, indicating superior flame-retardant and smoke-suppressing capabilities. In addition, the EP-TFDP thermosets exhibit marked improvements in tensile and impact strengths, with maximum increases of 51.5% and 67.4%, respectively.Importantly, the introduction of the TFDP effectively reduced the signal transmission loss of the epoxy thermosets. EP-TFDP thermosets exhibit lower dielectric constants and dielectric losses than unmodified EP thermosets. This strategy is highly significant for applications that require the simultaneous integration of lightweight, high-strength, low-dielectric, and highly flame-retardant EPs.