We present phase diagrams of binary blends (or mixtures) of a homopoly
mer H, with a block copolymer, A-B, in which there is an exothermic in
teraction between two types of segments, H and A. In trying to constru
ct phase diagrams, we extend the approach of predicting phase separati
on behaviour in such binary blends where H is chemically identical wit
h one of the blocks of the copolymer, e.g. A. A binary blend of a homo
polymer with a block copolymer is divided into two distinct states, i.
e, an ordered state and a disordered state. On the assumption that the
block copolymer in the disordered state acts as a random copolymer, t
he free-energy change in the disordered state can be estimated by a mo
del including the localized solubilization of added homopolymers, whic
h is a modification of the confined-chain model originated by Meier. T
o determine coexisting phases under a given temperature, we examine th
e relative stabilities (i.e. the chemical potential of each component
in the blend) of the two states. As a result, the concentration-temper
ature phase diagrams of blends of H and A-B can be obtained. From the
predicted phase diagrams, it is found that the exothermic interaction
of this system greatly increases the solubility of H into the A domain
s and affects the shape of the phase diagram.