Tunable Thermotropic Liquid Crystals Using Amphiphilic Sequence-Defined Macromolecules

Abstract

Liquid crystals (LCs) are a class of materials that combine molecular order and fluidity, making them crucial for technologies from displays to sensors. However, polymeric LC materials typically lack molecular precision, limiting systematic control over their phase behavior. Here, we report a modular synthetic strategy to prepare amphiphilic columnar liquid crystals based on hydrophobic di- and trialkylated galloyl cores attached to a sequence-defined polar oligomer grown by a thiolactone-based iterative protocol. This approach enables independent variation of (i) polar monomer type (e.g., hydroxyethyl acrylate and N,N-dimethylacrylamide), (ii) oligomer length (from 1-mer to tetramer), and (iii) core topology (two or three C18 chains). Differential scanning calorimetry, polarized optical microscopy, and X-ray scattering show that the number of hydrophobic C18 chains on the aromatic core is the dominant parameter governing mesophase stability. Derivatives with three C18 chains exhibit higher melting and isotropization temperatures and more pronounced transitions from lamellar crystals to hexagonally packed columnar mesophases than their two C18 analogues. The chemistry and length of the sequence-defined polar block further tune crystallization and mesophase behavior, i.e. hydrogen-bonding heads increase thermal stability, whereas bulkier PEG-like heads reduce crystallinity and can destabilize mesophases. Increasing oligomer length reduces crystallization enthalpies and can introduce competing liquid-crystalline states. These results demonstrate that the liquid crystalline behavior can be encoded at the molecular level, providing a basis for designing responsive and sequence-programmed LC materials.