Effective interaction between monolayers of block copolymer compatiblizer in a polymer blend

The stability of ternary blends of two immiscible homopolymers and a block copolymer compatiblizer depends crucially on the effective interaction betw een the copolymer monolayers that form between the unlike homopolymer domai ns. Here, the interaction is calculated for blends involving A and B homopo lymers of equal size with AB diblock copolymers of symmetric composition us ing both self-consistent field theory (SCFT) and strong-segregation theory (SST). If the homopolymers are larger than the copolymer molecules, an attr active interaction is predicted which would destroy the blend. This conclus ion coupled with considerations regarding the elastic properties of the mon olayer suggests that the optimum size of the homopolymer molecules is about 80% that of the copolymer molecule. A detailed examination of the theory d emonstrates that the attraction results from the configurational entropy lo ss of the homopolymer molecules trapped between the copolymer monolayers. W e conclude by suggesting how the monolayers can be altered in order to supp ress this attraction and thus improve compatiblization. (C) 2000 American I nstitute of Physics. [S0021-9606(00)50615-1].