Phase equilibria in random multiblock copolymers

(Received 13 July 2001)

Abstract
A mean-field theory for domain structures in random multiblock copolymer melts is developed. We focus on the finite molecular weight effects resulting in a competition between macroscopic phase separation and microdomain formation in the system. We identify an essential parameter controlling the phase behavior of the system, where N is the number of blocks per chain and is the composition asymmetry parameter (= the difference between the mean copolymer composition and its critical value). The phase diagram involving and the reduced temperature as variables is obtained. The regions of coexistence of two or more phases are identified. We show that a superstructure formation on cooling is always pre-empted by a macroscopic phase separation of the macroscopically homogeneous (disordered) system yielding two homogeneous phases: . The third (lamellar) phase separates on further cooling. Then hexagonal and body-centred-cubic phases take over if . As the Flory interaction parameter increases further, the standard transitions take place.