Synthesis and Self-Assembly of Silicon-Containing Azobenzene Liquid Crystalline Block Copolymers

The synthesis and self-assembly of a high interaction parameter silicon-containing liquid crystalline block copolymer (SiLCBCP) are reported, containing thermally and photo-responsive azobenzene mesogens in the side chains which undergo molecular structural transitions, influencing phase transitions and orientation in the block copolymer. A series of the azobenzene-containing SiLCBCPs, poly{dimethylsiloxane-b-11-[4-(4-cyanophenylazo)-phenoxy]undecane methacrylate}, were synthesized through atom transfer radical polymerization, and the bulk self-assembly as well as the influence of the liquid-crystalline (LC) phase transition of the LC block on the microphase-separated nanostructure of the BCPs is described. As the volume fraction of the PMAAzo block (fPMAAzo) changes from 41 to 71%, lamellar, double gyroid (GYR), orthorhombic Fddd network, hexagonally packed cylindrical (HEX), and body centered cubic nanostructures were obtained. When f PMAAzo = 55-57%, a thermally reversible HEX-GYR-Fddd phase transition induced by the temperature change and LC phase transition was observed. Bulk morphologies are compared with thin-film self-assembly, and pattern transfer into silica nanostructures is demonstrated.