Morphological Control of Helical Structures of an ABC-Type Triblock Terpolymer by Distribution Control of a Blending Homopolymer in a Block Copolymer Microdomain

The control of microphase-separated structures in a poly(styrene-block-butadiene-block-methyl methacrylate) (SBM) was investigated in three dimensions by transmission electron microtomography. Neat SBM self-assembled into a double-helical structure of polybutadiene (PB) domains around hexagonally packed core polystyrene (PS) cylinders in a poly(methyl methacrylate) matrix. When PS homopolymer with a lower molecular weight than that of the PS block in SBM was added to the SBM, the PB domains transformed from double-helical structures to spherical domains, while maintaining the helical trajectories. In contrast, adding a higher molecular weight PS to the SBM changed the helical structures from double- to triple-stranded structures and even to four. stranded. structures. The helical structures of the PB domains were strongly affected by the distribution of the blended polystyrenes in the core cylindrical PS domains.