Hydrogen Bond Induces Hierarchical Self‐Assembly in Liquid‐Crystalline Block Copolymers

Microphase‐separated structures of block copolymers (BCs) with a size of sub‐10 nm are usually obtained by hydrogen‐bond‐induced self‐assembly of BCs through doping with small molecules as functional additives. Here, fabrication of hierarchically self‐assembled sub‐10 nm structures upon microphase separation of amphiphilic liquid‐crystalline BCs (LCBCs) at the existence of hydrogen bonds but without any dopants is reported. The newly introduced urethane groups in the side chain of the hydrophobic block of LCBCs interact with the ether groups of the hydrophilic poly(ethylene oxide) (PEO) block, leading to imperfect crystallization of the PEO blocks. Both crystalline and amorphous domains coexist in the separated PEO phase, enabling a lamellar structure to appear inside the PEO nanocylinders. This provides an elegant method to fabricate controllable sub‐10 nm microstructures in well‐defined polymer systems without the introduction of any dopants. In amphiphilic liquid‐crystalline block copolymers without any dopants, the hydrogen bonds introduced by urethanes interfere with poly(ethylene oxide) (PEO) crystallization, leading to coexistence of crystalline and amorphous domains in the PEO phase, showing lamellar sub‐10 nm structures upon hierarchical self‐assembly.