Ring gradient copolymers as amphiphiles in their ternary blends with two linear homopolymers

•Gaussian i,j-correlation functions are deduced for ring gradient copolymers of different composition gradient lengths.•Copolymers of ring topology or augmented gradient sequence in ternary blends narrow the feasible region for Lifshitz points.•Such ternary blends tend more to macrophase separate along with shrunken lamellae stability than the other way around.

Phase equilibria in a ternary blend of linear A/B homopolymers of equal sizes and a symmetric A-co-B ring gradient copolymer as an amphiphile with α as the ratio of their chain sizes are investigated in the mean-field picture. The monomer sequence on the copolymer chain is taken in between a step gradient and a fully linear gradient, to which a gradient number λ = 0 and 1 are assigned, respectively. Along the isopleths of equal homopolymer amounts, the resultant phase diagrams for the blends are to be built from multicritical points such as Lifshitz or bulk tricritical point depending on α and λ. It is shown that the copolymer of doubling-back ring topology or augmented gradient sequence in the ternary blend narrows the feasible region for the Lifshitz point. The ternary blend accordingly becomes more prone to macrophase separation starting from the tricritical point and the stabilization of its lamellar mesophase is more shrunken than that containing the copolymer of linear topology or diminished gradient sequence.

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