High molar mass epoxy prepolymers containing rubber dispersions based on carboxyl-terminated butadiene-acrylonitrile random copolymer (CTBN) were prepared from initially miscible solution of low molar mass epoxy prepolymers, bisphenol A and CTBN-based rubber. During chain extension inside a twin-screw extruder due to epoxy-phenoxy and epoxy-carboxy reactions, a phase separation process occurs. Epoxy-phenoxy and epoxy-carboxy reactions were catalyzed by the triphenyl phosphine. The effect of reaction parameters (temperature, catalyst, reactant stoechiometry) on the reactive extrusion process were analyzed. The structure of the prepolymers showed low branching reactions (2-5%). Low molar mass prepolymers have a Newtonian rheological behavior. Cloud-point temperature of different reactive liquid butadiene acrylonitrile random copolymer (RLP)/epoxy resin blends were measured for different RLP concentrations. It was shown that rubber particles remain insoluble in a range of temperature from room temperature to 180°C, typical of temperatures used for epoxy curing reactions. Prepolymers containing different rubber concentrations were cured using dicyandiamide as the hardener. The practical adhesion of the issued networks to an aluminium alloy increased with rubber concentration.