Silicone modified epoxy resins is prepared via polycondensation of polymethylphenylsilicone DC-3074(PMPS) and epoxy resin from acrylic acid rosin(AR-EGDE).The chemical structure of the produced resins was determined by FTIR

13C NMR and epoxy content testing.At the same time，physical modified resin is obtained by mixture of PMPS and AR-EGDE.Mechanical properties and limiting oxygen index(LOI) value of the cured epoxy resins were studied.The results indicated that the method of modification played an important role in the properties of cured resins.The cured system of chemically modified resin had better properties.The tensile strength of the system was slightly lower than the unmodified resin AR-EGDE

at the same time its breaking elongations increased rapidly.The LOI value of the system increased from 21.6%(unmodified) and 25.3%(physically modified) to 30.2%.The thermogravimetric analysis(TGA) result showed that the thermal stabilities of the modified resins were better than those of unmodified resin.Because PMPS segment could absorb more thermal energy and dissipate thermal energy through its flexible siloxane structure

the onset decomposition temperatures(T-5%) for modified resins were higher than that of unmodified resin.The solid residue at 700℃ of the modified resins were 14.9% for chemically modified and 16.2% for physically modified

more than that of the unmodified resin.The chemical structure of char for the resin at the end of LOI test was analyzed by Fourier transform infrared spectroscopy.Based on the above results

the flame retardant mechanism was discussed.At an elevated temperature or upon burning

the silicone-containing group immigrated to the surface of material rapidly and formed a stable carbon-silicon residue.The carbon-silicon residue could act as thermal insulation which inhibited the degradation of the underlying material and improved the flame retardancy of the material.The physically modified resin could not form efficient carbon-silicon residue during burning

so its LOI value was lower than that of the chemically modified resin.