Synthesis and characterization of a DOPO-substitued organophosphorus oligomer and its application in flame retardant epoxy resins

摘要

Advanced flame retardant epoxy resins with different contents of poly(DOPO substituted phenyl dimethanol pentaerythritol diphosphonate) (PFR) were prepared. PFR was synthesized from the polycondensation of DOPO-disubstituted benzenedimethanol (TDCA-DOPO) with pentaerythritol diphosphonate dichloride (SPDPC). The flame retardancy and thermal stability of the EP/PFR hybrids were investigated by limiting oxygen index (LOI), UL-94 test and thermogravimetric analysis (TGA) in air. LOI values increased from 21.5 for pure EP to 36.0 for phosphorus-containing resins, and UL-94 V-0 materials were obtained with the 15 wt% PFR. The TGA results indicated that incorporation of PFR significantly enhanced the char yield and the thermal stability of char layer at higher temperature. Differential scanning calorimetry revealed that the EP/PFR composites possessed higher glass transition temperatures than phosphorus-free EP, which was consistent with dynamic mechanical analysis results. The thermal degradation behaviors of the EP/PFR composites were investigated by real time Fourier transform infrared spectra (RTFTIR), thermogravimetric analysis/infrared spectrometry (TG-IR) and direct pyrolysis/mass (DP-MS) analysis. The results suggested that the addition of PFR can reduce the release of combustible gas, trap the H and OH radicals by releasing the PO radical and induce the formation of char layer, thus retard the polymer degradation and combustion process.