Macro-and microphase separation in nonaqueous solutions of binary multiblock copolymers

In terms of the random phase approximation, a global analysis of the thermodynamic stability of solutions of multiblock copolymers (A_nB_m)_k and (A_nB_m)_kA_n was performed. Phase diagrams for various parameters of the copolymer structure including the macrophase and microphase separation regions were obtained. Critical lines near which this approximation still holds and the microphase separation corresponds to the weak segregation mode were also constructed. The formation of ordered structures with a period of the order of a wavelength of visible light becomes possible under certain conditions. It was shown that the homogeneous state of solutions of multiblock copolymers in certain narrow ranges of values of the parameters breaks down through a simultaneous growth of fluctuations with substantially different wavelengths, a phenomenon which must lead to the appearance of structures ordered at two length scales. The width of such regions increases with an increase in the number of blocks k and a decrease in the degree of polymerization n + m of a block. The potential use of these multiblock-copolymer solutions as photonic crystals is discussed.