An attempt is made to extend the model of Leibler for the emulsifying activity and Interfacial properties of A-b-B diblock copolymers in incompatible blends of the homopolymers A and B - which are identical with the respective copolymer components - to enthalpically interacting C-b-D diblock copolymers, the block C being thermodynamically compatible with A and D with B. Due to the attractive enthalpic interaction the A/C-b-D/B compatibilized blends are promising for optimum phase adhesion (bold types for thermodynamically compatible partners). Thus, the extended model for a plane interfacial layer includes the enthalpic interaction of the compatible polymer pairs beside the entropic effects. The approach starts with the equilibrium supposition, not taking into consideration enthalpy driven migration effects of the block copolymer from the bulk to the Interface. The model confirms a dominant role of the enthalpic interaction between blocks of the diblock copolymer and the respective homopolymers to the compatibilization of incompatible blend components. It is applicable also for blends compatibilized with block copolymers of unfavourable repulsive type interaction, A/C-b-D/B, and for blend systems with mixed type interactions, e.g. A/C-b-B/B or A/C-b-D/B.