Highly efficient flame‐retardant and transparent epoxy resin

Abstract In this study, a high effective phosphorus‐containing flame retardant (DOP‐DDM) was synthesized using phenylphosphonic dichloride, p ‐hydroxybenzaldehyde, 9,10‐dihydro‐9‐oxa‐10‐phosphaphenan‐ threne‐10‐oxide (DOPO) and 4,4′‐diaminodiphenyl methane (DDM) as raw materials. The chemical structure of DOP‐DDM was confirmed by Fourier transform infrared spectroscopy (FT‐IR), 1 H nuclear magnetic resonance ( 1 H NMR) and 31 P nuclear magnetic resonance ( 31 P NMR). The epoxy resin (EP) material with 4.7 wt% DOP‐DDM (EP‐4.7) can reach V‐0 degree in UL 94 test and has LOI value as high as 33.5%. If neat EP (EP‐0) material is used as a control, even if the loading of DOP‐DDM in the flame‐retarded EP material reached 7.6 wt%, the transmittance can reach 96.8% of EP‐0. From cone combustion (CC) test, the peak of heat release rate (pHRR), total heat release (THR) and total smoke release (TSR) values of EP‐4.7 material were decreased in comparison to those of EP‐0. Compared with EP‐0 material, differential scanning calorimetry (DSC) and dynamic thermo mechanical (DMA) results showed that the glass transition temperature of EP‐4.7 material slightly increased, and the storage modulus (E′) and loss modulus (E′′) increased 65.7% and 47.3%, respectively. The morphology and graphitization degree of residual char after CC test were measured by SEM and Raman spectroscopy, respectively. Concurrently, the gas components of EP‐4.7 material were well analyzed by thermogravimetric analysis FTIR. All these results demonstrated that the DOP‐DDM played a role in gas‐phase and condensed‐phase.