Abstract: This paper concerns with lowering the internal stress of epoxy molding com-pounds by incorporation of epoxy-terminated polydimethylsiloxanes.When the modifier wasblended with epoxy resin and novolac resin curing agent directly,surface bleeding of thepolysiloxane occurred.When the polysiloxane was first prereacted with the novolac resin toform a block copolymer and then blended with the epoxy resin,the polysiloxane bleedingwas prevented,the polysiloxane phase was smaller in size and the domain distribution in theresin matrix was more even.The main factors influencing the internal stress were investigated.It was found that the domain size of the polysiloxane phase depended on the syntheticconditions of the copolymers,the length of polysiloxane chain and the content of polysilox-ane in the cured resin.The flexural modulus of the epoxy molding compounds dependedmainly on the interface area between the polysiloxane phase and the resin matrix, while thethermal expansion coefficient below T_g was dependent not only on the interface area betweenthe two phases, but also on the interaction between the resin/filler matrix and polysiloxanephase to a great extent.

Key words: polysiloxane, epoxy resin, internal stress, mechanical property, morphology