High char yields of DOPO/organosilicon-modified epoxy resins and phosphorus-silicon synergism of thermal stability

The phosphorus/silicon-modified epoxy resin (ED231) was prepared via a two-step reaction process. Firstly, the 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)-modified epoxy was synthesized by ring-opening reaction between DOPO and epoxy resin of diglycidyl ether of bisphenol A (E51). Afterward, the organic silicone intermediate (SY231) was grafted onto the DOPO-modified epoxy to obtain the ED231 product. The thermal stability and thermal-mechanical properties of ED231 systems were characterized by thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis, respectively. TGA results indicated that the phosphorus/silicon-modified epoxy resin (ED231) exhibited high char yields. For example, the solid residue for ED231-40 (5 phr DOPO and 40 phr SY231) at 800 degrees C increased from 16.77% for the pure epoxy resin to 36.25% under nitrogen atmosphere and from 0% to 14.29% under air atmosphere, respectively. Scanning electron microscopy observations suggested that the ED231 systems could form an intact and continuous char layer which could significantly improve the thermal properties.