Silicone modified epoxy resins were prepared by polycondensation of polyphenylmethoxysilicone (PPMS) and polymethylphenylsilicone (PMPS) with E-20 epoxy resin.Oxirane ring and epoxy values were determined by Fourier transform infrared (FTIR) spectroscopy and HCl/acetone method.The data indicated that silicone oligomers were incorporated into epoxy resin with a random polycondensation and without involving the opening of the oxirane ring in the silicone modified epoxy structure.The influences of silicone contents on the heat-resistant properties of cured silicone modified epoxy resin systems were investigated by differential scanning calorimetry (DSC) and thermogravimetic analysis (TGA).The DSC data showed with increasing siloxane content in copolymers the glass transition temperature (Tg) lowered gradually.But when the mass ratio of epoxy resin to PPMS

PMPS was 7∶3

the Tg was 958℃ and 883℃

higher than those of unmodified epoxy resins systems by 9.0℃ and 1.5℃ respectively.The TGA data indicated that siloxane moiety exerts its thermal stability on the copolymer through dissipation of the heat

thus delaying thermal degradation of the copolymers.when the mass ratio of epoxy resin to PPMS

PMPS was 7∶3

the 50% weight loss temperature of degradation (Td) was 476.5℃ and 487.8℃

higher than those of unmodified epoxy resins systems by 58.3℃ and 69.5℃ respectively.In contrast to ED-30 cured system

the heat-resistance and toughness of EPMS-30 cured systems improved more obvious

and its film coatings also showed more excellent filming properties.