<正> Phenolic hydroxyl-terminated polysiloxanes were incorporated into epoxy resins to reducethe internal stress owing to the mismatch in coefficient of thermal expansion （CTE）.Polysiloxane-epoxy resin block copolymers were made by a pre-reaction step prior to thecuring. In the cured resin

the domain size of the polysiloxane phase depended on thestructure of the phenolic hydroxyl-terminated polysiloxane. It was found that the modulus ofthe cured resin depended largely on the level of the modifier

while the CTE was affectedgreatly by the structure of the polysiloxane. By means of incorporating a few percent ofmethylphenylsiloxane unit into the polydimethylsiloxane chain

or by introducing morecompatible end-capping groups

the compounds of more effective low stress modifiers weresynthesized.