Synthesis and Self-Assembly of Rod–Rod Block Copolymers with Different Rod Diameters

We synthesized a series of rod–rod block copolymers, poly(octyl-4′-(octyloxy)-2-vinylbiphenyl-4-carboxylate)- b -poly(γ-benzyl- l -glutamate) (PVBP- b -PBLG) with different rod diameters, and we focused on the effect of size disparity on their self-assembling behaviors in bulk. By using differential scanning calorimetry, wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering, and transmission electron microscopy techniques, we found that the columnar nematic (Φ N ) liquid crystalline phase of PVBP and the hexagonal columnar (Φ H ) phase of PBLG were disrupted to different extents depending on the volume fractions of PVBP ( f PVBP ’s). When f PVBP is about 60%, the Φ H phase of PBLG is retained with the appearance of the two second-order diffractions in WAXD patterns. When f PVBP is increased to above 73%, the ordered structure of PBLG is destroyed, and when f PVBP is 91% even the first-order diffraction peak disappears. At the same time, the Φ N phase of PVBP changes from poorly ordered to well ordered with increasing f PVBP . Accordingly, with f PVBP increasing from 60% to 91%, the microphase-separated structure goes through a poorly ordered structure to an interdigitated lamellar morphology and to a bilayer lamellar structure.