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 degrees from the lamellar normal. The peak melting temperature (T-m) of the PE crystals was at 93.8 degrees 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 degrees C. Intriguingly, the N-D to isotropic (or vice versa) transition was observed to coincide with the melting (or crystallization) of the PE block.