Synthesis and hierarchical self-assembly of rod-rod block copolymers via click chemistry between mesogen-jacketed liquid crystalline polymers and helical polypeptides

A series of novel rod-rod diblock copolymers containing poly{2,5-bis[(4-methoxyphenyl)-oxycarbonyl]styrene} (PMPCS) and poly(γ-benzyl-L-glutamate) (PBLG) were synthesized by click chemistry from alkyne-and azide-functionalized homopolymers. The α-alkyne PMPCS homopolymers were synthesized by copper-mediated atom transfer radical polymerization with a bromine-containing α-alkyne bifunctional initiator, and α-azido PBLG homopolymers were synthesized by ring-opening polymerization of γ-benzyl-L-glutamate N-carboxyanhydride with an amino-containing α-azide initiator. The molecular structures of the rod-rod block copolymers were confirmed by ¹H NMR spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography analysis. The self-assembling behavior of the rod-rod block copolymers in bulk was investigated using differential scanning calorimetry, polarized light microscopy, wide-angle X-ray diffraction, and transmission electron microscopy techniques. A lamellar structure was observed with f_PBLG of ∼0.50, in which PMPCS was in a columnar nematic phase and PBLG assignedto a hexagonally packed-cylinder structure (Φ_H). Accordingto the TEM micrographs and simulated lengths of the copolymers, a stacked bilayer structure in a hexagon in lamella morphology for the selfassembly of the rod-rod block copolymers was proposed. Finally, by increasing f_PBLG to ∼0.69, a microphase-separated hexagon in cylinder morphology was found, in which PMPCS formed the core of the cylinders surrounded by PBLG in Φ_H phase and both rods were in an interdigitated packing.