BLOCK COPOLYMER, METHOD FOR PRODUCING SAME, EPOXY RESIN COMPOSITION, CURED PRODUCT, AND SEMICONDUCTOR ENCAPSULATING MATERIAL

A polysiloxane-polyalkylene glycol block copolymer obtained by reacting a polysiloxane (A) having any functional group selected from a carboxylic anhydride group, a hydroxyl group, an epoxy group, a carboxyl group, and an amino group with a polyalkylene glycol (B) having any functional group selected from a carboxylic anhydride group, a hydroxyl group, a carboxyl group, an amino group, an epoxy group, a thiol group, and an isocyanate group, in which the content of a structure derived from the polysiloxane (A) is 20% by mass or more and 90% by mass or less with respect to 100% by mass of the block copolymer. The polysiloxane-polyalkylene glycol block copolymer of the present invention is homogeneously and finely dispersed in an epoxy resin in the case of being blended with the epoxy resin, bleed-out of the block copolymer from the cured epoxy resin to be obtained can be suppressed, and decreased stress and improved toughness of the cured epoxy resin can be achieved. Moreover, a decrease in fluidity caused by the addition of the block copolymer to an epoxy resin is also suppressed. From these facts, this block copolymer is also useful as various additives such as a surfactant and a resin modifier and is particularly suitable as a stress relief agent for semiconductor encapsulating materials.