Confined discotic liquid crystalline self-assembly in a novel coil - Coil - Disk triblock oligomer

An asymmetric ABC coil - coil - disk triblock oligomer, based on polyethylene-block-poly-(ethylene oxide)-block-pentakis(pentyloxy)triphenylene (PE-b-PEO-b-P5T or EEO - P5T), was successfully synthesized by coupling a hydroxyl-terminated PE-b-PEO diblock oligomer and 2-hydroxy-3,6,7,10,11-pentakis(pentyloxy)triphenylene using oxalyl chloride. The structure and morphology of the supramolecular self-assembly in bulk EEO - P5T were studied by differential scanning calorimetry, small- and wide-angle X-ray scatterings, polarized light microscopy, and transmission electron microscopy. The PE block crystallized into interdigitated, extended chain crystals with a chain-tilting angle of 23° from the lamellar normal. The peak melting temperature (T _m of the PE crystals was at 93.8°C. The PEO block remained in the amorphous state because of its both ends being tethered to other two blocks and the mismatch of the cross-section areas at the PE - PEO and PEO - P5T interfaces. Bilayer P5Ts, sandwiched between amorphous PEO layers, exhibited a nematic columnar (N _col) to nematic discotic (N _D) transition at ca. 23°C. Intriguingly, the N _D to Isotropic (or vice versa) transition was observed to coincide with the melting (or crystallization) of the PE block.