Heterophases in block‐copolymer/solvent systems in the liquid and in the solid state

A general review of the observed isothermal phase diagram (structure as a function of the concentration) of a number of (A–B)/S systems is given where A–B is a linear blockcopolymer containing the long sequences A and B and S is a preferential solvent for one of the sequences. Special attention is devoted to the third region of the diagram (large concentration of A–B) where periodic and regular (mesomorphic) structures are observed. The effect of the concentration on the structure (cubic, hexagonal and lamellar) and on the values of the structural parameters as they are observed by X‐ray diffraction or electron micrography is discussed. It is shown that the type of structure of a given A–B copolymer in a given solvent S is determined mainly by the ratio of the volumes of the phase containing the insoluble sequence and the volume of the phase formed by the solution, a fact which can be considered as a generalization of a law given by G. E. MOLAU.