Segregation in a solution of rigid copolymeric molecules with two different sequences leading to co‐existence of two smectic mesophases has been studied. Thermodynamic characteristics of these mesophases and their equilibrium compositions were found in the frame of two discrete models. It was shown that the degree of ordering in the mesophase depends on the sequence of units in the identical molecules forming this mesophase. The concentration of “mismatched” molecules in the mesophase (the purity of mesophase) is determined both by the composition and the sequence of such molecules. It was shown, that a difference in the sequences can be sufficient to cause phase separation.
