Hierarchically ordered nanostructures of a supramolecular rod-coil block copolymer with a hydrogen-bonded discotic mesogen

Abstract

Using a triphenylene derivative 4-{6-[3,6,7,10,11-pentakis(hexyloxy)triphenylen-2-yloxy]hexyloxy}pyridine (PHTC6) as the hydrogen-bonding acceptor and four samples of a rod-coil block copolymer (BCP) poly(dimethylsiloxane)-b-poly[2,5-bis(4-carboxy phenyl)styrene] (PDMS-b-PM3H) bearing different lengths of the PM3H block as the hydrogen-bonding donors, we constructed a series of hydrogen-bonded supramolecular liquid crystalline (LC) BCPs (SLCBCPs). Different microphase-separated nanostructures at a larger length scale (30–50 nm) and LC phases of the supramolecular block at a smaller length scale (<10 nm) were realized by changing the PHTC6 : PM3H molar ratio. The self-assembled structures of the SLCBCPs range from hexagonally packed cylinders (HEX) with a continuous PDMS phase, lamellae, to inverted HEX having PDMS cylinders with increasing molar ratios and degrees of polymerization of the PM3H block. When the molar ratio is high enough, the supramolecular block PM3H(PHTC6) can develop into a smectic A (SmA) phase, and the PHTC6 moiety can develop into a discotic nematic (N_D) phase, which have a smaller length scale compared with that of the microphase-separated nanostructures. In addition, the SmA and N_D phases are synergistic and promotional. As a result, these hydrogen-bonded SLCBCPs can self-assemble into hierarchically ordered nanostructures, including HEX with PDMS as cylinders on the whole and the N_D-within-SmA phase of the supramolecular block.