We report the synthesis of Janus bottlebrush block copolymers by graft-through polymerization of branched diblock macromonomers. Self-assembly of the bottlebrushes was characterized by small-angle X-ray scattering, atomic force microscopy, and scanning electron microscopy. Phase separation and packing models of the bottlebrushes were computed, and their self-assembly behavior was corroborated experimentally in bulk and in thin films. Lamellar, hexagonal cylinder, and gyroid phases were observed and modeled. The A-branch-B Janus bottlebrush structure provides several unique advantages in the context of bottlebrush polymer assembly, including access to the first examples of gyroid phases.

The self-assembly of block copolymers (BCPs) with novel architectures offers tremendous opportunities in nanoscale patterning and fabrication. Here, the thin film morphology, annealing kinetics, and topographical templating of an unconventional Janus-type "PS- branch-PDMS" bottlebrush copolymer (BBCP) are described. In the Janus-type BBCP, each segment of the bottlebrush backbone connects two immiscible side chain blocks. Thin films of a Janus-type BBCP with M = 609 kg/mol exhibited 22 nm period cylindrical microdomains with long-range order under solvent vapor annealing, and the effects of as-cast film thickness, solvent vapor pressure, and composition of the binary mixture of solvent vapors are described. The dynamic self-assembly process was characterized using in situ grazing-incidence X-ray scattering. Templated self-assembly of the BBCP within lithographically patterned substrates was demonstrated, showing distinct pattern orientation and dimensions that differ from conventional BCPs. Self-consistent field theory is used to elucidate details of the templated self-assembly behavior within confinement.

The long-range ordering and directed self-assembly of thin films of a high interaction parameter rod–coil liquid crystalline block copolymer (LC BCP), poly­(dimethylsiloxane)-b-poly­{2,5-bis­[(4-methoxyphenyl)-oxycarbonyl]­styrene} (PDMS-b-PMPCS, or DM), is described. The LC BCP was spin-coated on a polystyrene brush functionalized substrate and then thermally annealed at different temperatures with respect to the LC ordering temperature. The effects of the wetting behavior, commensurability between the film thickness and the periodicity, and the LC orientation on the ordering and orientation of the microdomains are described. A monolayer of in-plane cylinders with excellent long-range ordering was produced, and was transferred into SiO x patterns with tunable sub-10 nm feature sizes. Well-ordered multilayer in-plane cylinders were produced in thicker films, and the correlation between microstructure evolution and the LC ordering process was studied by grazing-incidence small-angle X-ray scattering (GISAXS) and wide-angle X-ray scattering (GIWAXS). Finally, the cylindrical rod–coil BCP was directed into a novel ladder morphology within lithographically patterned substrate trenches, as well as into patterns of parallel or transverse cylinders. The ordering of cylinders, the ladder morphology, and the etch selectivity and thermal stability of this high-interaction parameter silicon-containing LC rod–coil BCP demonstrate its applicability to nanoscale lithography.

The self-assembly of multiblock copolymers generates diverse hierarchical nanostructures and greatly extends the range of microdomain geometries beyond those produced by diblock copolymers. We report the synthesis of a conformationally asymmetric ABC triblock terpolymer in which the end blocks are a mesogen-jacketed liquid crystalline polymer and poly(dimethylsiloxane), respectively, and its selfassembly under mixed solvent vapor annealing forms a range of sphere, cylinder, and perforated lamellar core−shell morphologies, as well as stacked multilevel structures. Sub-7 nm diameter SiO x nanopatterns were generated by selective plasma etching of the small volume fraction Si-containing core block giving a line/space ratio of ∼1:4. Moreover, the conformational asymmetry of this terpolymer leads to zigzag cylinders on a flat substrate and stable cylinder alignment transverse to template sidewalls within lithographically patterned trenches.

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