Cross-linkable phosphorus/nitrogen-containing aromatic ethylenediamine endowing epoxy resin with excellent flame retardancy and mechanical properties

Endowing epoxy resins (EPs) with enhanced flame retardancy without losing its mechanical properties is a considerable challenge for applications in wide areas. Herein, a phosphorus/nitrogen-containing aromatic ethylenediamine (BSEA) was synthesised by a simple addition reaction between N, N’-bis(salicylidene)ethylenediamine (NEA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and utilised as a reactive flame retardant for EP/biscitraconimide resin (BCI) system. With only 0.35 wt% of phosphorus, EP/BCI/BSEA-4 showed excellent flame retardancy with an increased LOI of 32.1 %; a UL-94V-0 rating; and lower peak of heat release rate, total heat release, fire growth rate index and average effective heat combustion than pure EP. The flame-retardant mechanism of BSEA was revealed to be in gas and condensed phase. Additionally, modified EP possessed increased storage modulus and good mechanical properties in room and cryogenic temperatures. All these results verified that the BSEA was a high-efficiency flame retardant for EP matrix and have a broad application prospect.