Brush block copolymers are a class of comb polymers that feature polymeric side chains densely grafted to a linear backbone. These polymers display interesting properties due to their dense functionality, low entanglement, and ability to rapidly self‐assemble to highly ordered nanostructures. The ability to prepare brush polymers with precise structures has been enabled by advancements in controlled polymerization techniques. This Feature Article highlights the development of brush block copolymers as photonic crystals that can reflect visible to near‐infrared wavelengths of light. Fabrication of these materials relies on polymer self‐assembly processes to achieve nanoscale ordering, which allows for the rapid preparation of photonic crystals from common organic chemical feedstocks. The characteristic physical properties of brush block copolymers are discussed, along with methods for their preparation. Strategies to induce self‐assembly at ambient temperatures and the use of blending techniques to tune photonic properties are emphasized.

Controlling solid-state order of π-conjugated polymers through macromolecular design is essential for achieving high electronic device performance; yet, it remains a challenge, especially with respect to polymer-packing orientation. Our work investigates the influence of backbone coplanarity on a polymer’s preference to pack face-on or edge-on relative to the substrate. Isoindigo-based polymers were synthesized with increasing planarity by systematically substituting thiophenes for phenyl rings in the acceptor comonomer. This increasing backbone coplanarity, supported by density functional theory (DFT) calculations of representative trimers, leads to the narrowing of polymer band gaps as characterized by ultraviolet-visible-near infrared (UV-vis-NIR) spectroscopy and cyclic voltammetry. Among the polymers studied, regiosymmetric II and TII polymers exhibited the highest hole mobilities in organic field-effect transistors (OFETs), while in organic photovoltaics (OPVs), TBII polymers that display intermediate levels of planarity provided the highest power conversion efficiencies. Upon thin-film analysis by atomic force microscropy (AFM) and grazing-incidence X-ray diffraction (GIXD), we discovered that polymer-packing orientation could be controlled by tuning polymer planarity and solubility. Highly soluble, planar polymers favor face-on orientation in thin films while the less soluble, nonplanar polymers favor an edge-on orientation. This study advances our fundamental understanding of how polymer structure influences nanostructural order and reveals a new synthetic strategy for the design of semiconducting materials with rationally engineered solid-state properties.

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We characterize shear-induced states of order and disorder in a symmetric lamellae forming poly(cyclohexylethylene) (C)−polyethylene (E) CECEC pentablock copolymer. When subjected to a large amplitude reciprocating shear strain (γ = ±600%) in the ordered lamellae state, the sample rapidly aligns in a perpendicular orientation with long-range order. The order−disorder transition temperature T ODT(γ̇) decreases with increasing shear rate γ̇, such that a shear rate of γ̇ = 7 ± 1 s-1 is sufficient to disorder the material nearly 30 °C below the quiescent T ODT. Small-angle neutron scattering (SANS) from the sheared disordered state displays a symmetry that suggests a fundamentally different influence of shear compared to earlier observations of shear-induced anisotropy in the disordered states of lamellae forming diblock and triblock copolymers. Abrupt cessation of shear leads to spontaneous lamellar ordering into a macroscopically well-aligned transverse orientationan arrangement that previously has been inaccessible via processing. In contrast to this behavior, the perpendicular alignment forms when cooling the sample from above the T ODT while applying low shear rates, similar to the response of di- and triblock copolymers. These findings shed fresh insight into the complex phenomena that govern flow- and deformation-induced alignment of block copolymer melts.

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