Synthesis of a Novel Phosphorus- and Nitrogen-Containing Acrylate and Its Performance as an Intumescent Flame Retardant for Epoxy Acrylate

A novel acrylate monomer containing phosphorus and nitrogen— N,N-bis(2-hydroxyethyl acrylate) aminomethyl phosphonic acid diethylester (BHAAPE)—was first synthesized by the combination of the Kabachnik–Fields reaction and esterification, and then incorporated into epoxy acrylate (EA) resins through an ultraviolet (UV) curing process. The structure of BHAAPE was confirmed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). The functionalized epoxy acrylate (FEA) resins exhibit significantly enhanced flame retardancy, which were evidenced by LOI, microscale combustion calorimetry (MCC) and cone calorimetry testing (CCT). Thermogravimetric analysis (TGA) results show that the introduction of BHAAPE promotes degradation of the EA matrix and catalyzes its char formation. The thermal degradation mechanism of FEA was further investigated by RTIR and direct pyrolysis/mass spectroscopy (DP-MS). The char structure of FEA, as characterized by scanning electron microscopy (SEM), reveals that the BHAAPE acts as a good intumescent fire retardant in the enhanced flame retardancy. Based on the analysis for thermal degradation and char structure, a detailed flame-retardant mechanism was proposed.