Sphere Forming SISO Tetrablock Terpolymers

A series of poly(styrene-$b$-isoprene-$b$-styrene-$b$-ethylene oxide) (SISO) tetrablock terpolymers was synthesized using anionic polymerization methods and investigated for melt morphology by synchrotron small-angle x-ray scattering (SAXS), electron microscopy and dynamic mechanical spectroscopy. Thermodynamic incompatibility between the I and O blocks, relative to that characterizing S and I and S and O leads to the formation of spherical domains containing an O core surrounded by a S rich shell embedded in a matrix of mixed S and I. Varying the composition and relative length of the internal and terminal S blocks resulted in five distinct states of ordering, including two cubic (Im3m and Pm3n symmetry), a hexagonal (p6/mm), a tetragonal (P4$_{\mathrm{2}}$/mnm) and a quasicrystalline (dodecagonal) phase. These results demonstrate the concept of decoupling domain geometry from domain packing in multiblock polymers.