Composition dependence of nanophase-separated structures formed by star-shaped terpolymers of the A_1.0B_1.0C_X type

Several hierarchical nanophase-separated structures have been observed for a series of ABC star-shaped terpolymers by transmission electron microscopy (TEM) and electron computerized tomography (3D-TEM). The seven terpolymers synthesized are composed of polyisoprene (I), polystyrene (S), and poly(2-vinylpyridine) (P), their volume fraction ratios of I:S:P are 1:1:X, where X equals 0.2, 0.4, 0.7, 1.2, 1.9, 3.0, and 4.9, respectively, and additional four samples were prepared by blending each two parent terpolymers. From morphological observation by TEM and tomography, a terpolymer with X of 0.2 shows lamellar structure with spheres at the interface, those with X ranging from 0.4 to 1.9 show cylindrical structures with twodimensional tiling, while those with X of 3.0 and 4.9 show hierarchical cylinders-inlamella structure. Two the other terpolymer samples with X of 7.9 and 10 were produced by blending a P homopolymer with the terpolymer I_1.0S_1.0P_4.9, and they both exhibited columnar piled disk cylinders in P matrix. From the comparison of the present results with the predictions by the Monte-Carlo simulation, it was confirmed that the observed nanophase-separated structures of the ISP star-shaped terpolymers are mostly in good agreement with the prediction.