Ordering of Sphere Forming SISO Tetrablock Terpolymers on a Simple Hexagonal Lattice

Hexagonally ordered spherical and cylindrical morphologies (P6/mmm and P6/mm space group symmetries) have been identified in bulk poly(styrene-b-isoprene-b-styreneb-ethylene oxide) (SISO) tetrablock terpolymers. These materials were synthesized by adding up to 32% by volume O blocks to a parent hydroxy-terminated SIS triblock copolymer containing 40% S by volume, and the resulting morphologies were characterized by small-angle X-ray scattering, transmission electron microscopy, differential scanning calorimetry and dynamic mechanical spectroscopy. Disordered, spherical and cylindrical phases were documented with increasing O content, where both ordered states exhibit hexagonal symmetry. Theoretical calculations based on a numerical self-consistent field theory for polymers provide crucial insights into the molecular configurations associated with these morphologies. These results offer a new approach to independently control domain shape and packing in block copolymer melts through manipulation of the magnitude and sequencing of the binary segment−segment interactions (χSI ≤ χSO ≪ χIO), which dictate core segregation and the effective interdomain interactions.