Hierarchical superstructures of norbornene-based polymers depending on dendronized side-chains

For understanding the self-assembly behaviors of norbornene-based main-chain polymers depending on dendronized side-chains, a series of polynorbornenes containing the programmed dendrons (AT3P and BP3P) is newly designed and successfully synthesized via ring-opening metathesis polymerization (ROMP) with high molecular weights and narrow polydispersity indices. The phase transitions and molecular packing structures of AT3P and BP3P are investigated by the combination of thermal, scattering and microscopic analyses. AT3P with flexible and hydrophobic alkyl chain dendrons forms the columnar nematic (ColN) liquid crystal (LC) phase. By introducing a rigid biphenyl mesogen and a hydrophilic triethylene oxide linker between the hydrophobic alkyl chain and the polynorbornene main-chain, a smectic A (SmA) LC phase is formed, mainly due to the nanophase separations and the strong intermolecular interactions between the biphenyl mesogens. This study reveals that the hierarchical superstructures of norbornene-based polymers can be precisely controlled by tuning the chemical structures and the physical interactions of side-chain pendants.