AbstractAn attempt is made to treat the formation of supercrystalline lattices in solution of melts of block copolymers on the macromolecular level using the effective flexibility parameters appearing in the equivalence principle of thermokinetics. All known data are in accord with the assumption which proposes an extremal dependence of the interaction of χ and χAB parameters on composition (χAB attaining its maximal value at A/B molar ratios close to unity). Therefore, the effective flexibility parameters fA and fB characterizing the corresponding blocks should pass through a minimum close to the χ maxima, the lines for fA and fB being, however, somewhat shifted along the composition axis. At first sight this type of behavior fits the experimental data, but closer consideration shows that the assumption of chain extension due to segreation inherently appearing in the whole concept does not hold.Therefore the situation is reconsidered, and it is shown that if the units (i.e., spheres, cylinders, and lamellae) occupying the sites of the superlattice are treated as “supermacromolecules” (or structons, following a somewhat improved definition of Huggins) the earlier theory holds.Moreover, it is shown that the supercrystals can be treated in terms of the kinetic theory of liquids and real crystals which leads to a understandable explanation of their unusual properties, especially their high thermal stability. Probably a general theory starting from ideal supercrystals may be developed by means of a stepwise introduction of paracrystalline defects (in the manner of Hosemann) in the lattice. The most disordered paracrystalline lattices will then correspond to polymer blends.Special attention is given to the formation of ordered structures from extended (or extruded) binary melts, the segregation parameter ϕAB being high, but where no junctions between A and B components occurs. This corresponds to the so‐called Yudin effect, and a catastrophic deliberation of the excess enthalpy of mixing on elimination of the noncrystallizable component (matrix) leads to an annihilation of the nematic units on annealing, thus showing the influence of the ϕAB parameter on the thermodynamic and morphologic properties of the structon forming component.Finally, something of the nature of ϕAB in phase equilibria during polymerization and its influence on the molecular‐weight distribution of branches during the course of graft copolymerization are considered.