Bottlebrush polymers are a type of branched or graft polymer with polymeric side-chains attached to a linear backbone, and the unusual architecture of bottlebrushes provides a number of unique and potentially useful properties. These include a high entanglement molecular weight, enabling rapid self-assembly of bottlebrush block copolymers into large domain structures, the self-assembly of bottlebrush block copolymer micelles in a selective solvent even at very low dilutions, and the functionalization of bottlebrush side-chains for recognition, imaging, or drug 2 delivery in aqueous environments. This review article focuses on recent developments in the field of bottlebrush polymers with an emphasis on applications of bottlebrush copolymers.Bottlebrush copolymers contain two (or more) different types of polymeric side-chains. Recent work has explored the diverse properties and functions of bottlebrush polymers and copolymers in solutions, films, and melts, and applications explored include photonic materials, bottlebrush films for lithographic patterning, drug delivery, and tumor detection and imaging. We provide a brief introduction to bottlebrush synthesis and physical properties and then discuss work related to: i) bottlebrush self-assembly in melts and bulk thin films, ii) bottlebrushes for photonics and lithography, iii) bottlebrushes for small molecule encapsulation and delivery in solution, and iv) bottlebrush micelles and assemblies in solution. We briefly discuss three potential areas for future research, including developing a more quantitative model of bottlebrush self-assembly in the bulk, studying the properties of bottlebrushes at interfaces, and investigating the solution assembly of bottlebrush copolymers.

Bottlebrush polymers are highly branched macromolecules with potential applications in antifouling coatings, rheological modifiers, and drug delivery systems. However, the solution conformation of bottlebrush polymers has been studied in only a limited set of materials made primarily by grafting-from polymerization. Here we present small-angle neutron scattering (SANS) measurements on a series of polystyrene bottlebrush polymers with varying side-chain and backbone lengths in d 8-toluene to analyze their size, shape, and conformation. Bottlebrush polymers with 2–7 kg mol–1 polystyrene side chains (degree of polymerization DP = 14–54) and poly(oxanorbornene) backbones (DP = 10–264) were synthesized using reversible addition–fragmentation chain transfer (RAFT) followed by a ring-opening metathesis polymerization (ROMP) grafting-through synthesis scheme. Analysis by Guinier–Porod, rigid cylinder, and flexible cylinder models provided estimates of the bottlebrush polymer length, radius, and stiffness. The bottlebrush polymer cross-sectional area depends primarily on side-chain DP, and the radius of gyration R g exhibits a power-law dependence with side-chain DP. We also observe a sphere-to-cylinder transition with increasing backbone DP, with the transition occurring at a backbone DP of approximately 120 for the polystyrene bottlebrush polymers studied. The maximum molecular dimension for the series studied varies from 25 to 350 nm.

Monodomain liquid crystal elastomers (LCEs) are shape-responsive materials, but shape changes are typically limited to simple uniaxial extensions or contractions. Here, we demonstrate that complex surface patterns and shape changes, including patterned wrinkles, helical twisting, and reversible folding, can be achieved in LCE-polystyrene (PS) bilayers. LCE-PS bilayer shape changes are achieved in response to simple temperature changes and can be controlled through various material parameters including overall aspect ratio and LCE and polystyrene film thicknesses. Deposition of a patterned PS film on top of an LCE enables the preparation of an elastomer that reversibly twists and a folding leaf-like elastomer, which opens and closes in response to temperature changes. The phenomena are captured through finite element simulations, in quantitative agreement with experiments.

We explore the phase behaviour, solution conformation, and interfacial properties of bottlebrush polymers with side-chains comprised of poly(N-isopropylacrylamide) (PNIPAAM), a thermally responsive polymer that exhibits a lower critical solution temperature (LCST) in water. PNIPAAM bottlebrush polymers with controlled side-chain length and side-chain end-group structure are prepared using a "grafting-through" technique. Due to reduced flexibility of bottlebrush polymer side-chains, side-chain end-groups have a disproportionate effect on bottlebrush polymer solubility and phase behaviour. Bottlebrush polymers with a hydrophobic end-group have poor water solubilities and depressed LCSTs, whereas bottlebrush polymers with thiol-terminated side-chains are fully water-soluble and exhibit an LCST greater than that of PNIPAAM homopolymers. The temperature-dependent solution conformation of PNIPAAM bottlebrush polymers in D2O is analyzed by small-angle neutron scattering (SANS), and data analysis using the Guinier-Porod model shows that the bottlebrush polymer radius decreases as the temperature increases towards the LCST for PNIPAAM bottlebrush polymers with relatively long 9 kg mol(-1) side-chains. Above the LCST, PNIPAAM bottlebrush polymers can form a lyotropic liquid crystal phase in water. Interfacial tension measurements show that bottlebrush polymers reduce the interfacial tension between chloroform and water to levels comparable to PNIPAAM homopolymers without the formation of microemulsions, suggesting that bottlebrush polymers are unable to stabilize highly curved interfaces. These results demonstrate that bottlebrush polymer side-chain length and flexibility impact phase behavior, solubility, and interfacial properties.