Аннотация:In terms of the random phase approximation, a global analysis of the thermodynamic stability of solutions of di- and triblock copolymers was performed. It was shown that competition between trends towards micro- and macrophase separation in diblock copolymer solutions has only one outcome. In contrast, this competition in triblock copolymer solutions may lead, under certain values of the parameters, to the situation when the degradation of the homogeneous state of a solution will proceed via the simultaneous growth of fluctuations with substantially different wavelengths and possible subsequent formation of superstructures. Phase diagrams in the composition–polymer concentration–solvent selectivity coordinates were constructed, which indicated the feasibility of one or another separation process. The light scattering indicatrixes in the solutions of interest were calculated. The possibility of observation of superstructures in actual systems was discussed.