Thin-Film Self-Assembly of Block Copolymers Containing an Azobenzene-Based Liquid Crystalline Polymer and a Poly(ionic liquid)

By combining reversible addition–fragmentation chain transfer (RAFT) with postfunctionalization and ion exchange, we synthesized a series of block copolymers (BCPs) containing an azobenzene-based liquid crystalline (LC) polymer (PAzo) and an imidazolium-containing poly­(ionic liquid) (PIL, PVB­(TFSI)) with the volume fraction of PIL (f PIL) values ranging from 15.9% to 69.9%. The samples obtained self-assemble into hexagonally packed cylinders (HEX), lamellae (LAM), and the mixed phase with coexisting HEX and LAM. The thin-film self-assembly of the samples PAzo101-b-PVB­(TFSI)22 and PAzo101-b-PVB­(TFSI)67 was studied systematically. We investigated the assembled structures of the thin films with various initial thicknesses after thermal annealing (145 °C for 12 h) or mixed solvent vapor annealing with tetrahydrofuran and n-hexane. Thin films with large-scale uniaxial PIL nanocylinders were obtained, which will greatly broaden the application of IL-based BCPs. Inverse phases were also observed for the thin films with thicknesses less than ∼120 nm. The different mechanisms of the formation of inverse nanostructures formed in the thinner films under the thermal annealing and mixed solvent vapor annealing conditions were also elucidated.