Yielding Behavior of Bottlebrush and Linear Block Copolymers

Opportunities in Bottlebrush Block Copolymers for Advanced Materials

Bottlebrush block copolymers (BBCPs) are a unique class of materials that contain a backbone with densely grafted and chemically distinct polymeric side chains. The nonlinear architecture of BBCPs provides numerous degrees of freedom in their preparation, including control over key parameters such as grafting density, side chain length, block arrangement, and overall molecular weight. This uniquely branched structure provides BBCPs with several important distinctions from their linear counterparts, including sterically induced side chain and backbone conformations, rapid and large self-assembled nanostructures, and reduced or eliminated entanglement effects (assuming sufficient grafting density and that the molecular weight of the side chains is below their respective entanglement molecular weight). These distinctions allow access to large domain sizes, very rapid assembly, and the ability to preferentially add additives and/or precursors to one domain, thereby enabling the efficient fabrication of a wide range of advanced materials and devices. BBCPs have been utilized to create finely controlled and well-ordered nanostructures for use in applications, such as photonic crystals, drug delivery systems, energy conversion, energy storage devices, and key components in surface coatings. To further deploy BBCPs as templates for the formation of precise nanostructures, having a thorough understanding of their synthesis, self-assembly, and templating is necessary. To explore and understand the self-assembly and subsequent applications of BBCPs, this review emphasizes the physics of self-assembly for BBCPs (including architectural, rheological, and thermodynamic considerations) and structure-property relationships between BBCPs and their resulting nanostructures. Lastly, we provide an overview of current research trends using BBCPs in energy storage, energy conversion, photonic, 3D printing, and drug delivery applications. We aim to provide researchers with the fundamentals of BBCP self-assembly in their use as nanostructured materials to continue their development of advanced materials.

Liquid Crystal Promoted Self-Assembly of Statistical Copolymers into Diverse Nanostructures with Precise Dimensions

In both natural and synthetic systems, the segregation of multicomponent entities is vital for regulating functions and the ultimate usage of materials. To accomplish the desired properties via nanosegregation or microphase separation, great effort is usually demanded in the synthesis. For example, microphase-separated block copolymers rely on the delicate controlled/living polymerization of different monomers in sequence. Here, we demonstrate that a facile one-pot copolymerization can generate statistical side-chain copolymers exhibiting well-defined and diverse nanostructures. Two hemiphasmidic (or wedge-shaped) cyclooctene monomers were designed, differing in the peripheral tails of the wedges (dodecyl vs. tetraethylene glycol), with lengths of ca. 1 nm. When combining the two monomers together, the statistical copolymers can show columnar liquid crystal (LC) phase and microphase-separated structures of the two monomers, including sphere, cylinder, double gyroid, and lamella. To the best of our knowledge, this is the first time the gyroid phase has been achieved in statistical copolymers. We further demonstrate that changing the side chains to calamitic (or rod-like) mesogens or the backbone to less flexible polynorbornene, the statistical copolymers can also undergo microphase separation of the side chains. The intrinsic self-assembly scheme of statistical copolymers with mesogenic side chains, which are chemically accurate, affords the resultant nanostructures with precise periodicities at the 10- or sub-10-nm scale. Given the small chemical difference between the side-chain tails, microphase separation is promoted by the anisotropic packing of mesogens. It is validated that the statistical side-chain LC copolymers can be a versatile platform for creating nanostructured materials with tailored functionalities.

Bottlebrush Networks: A Primer for Advanced Architectures

Bottlebrush networks (BBNs) are an exciting new class of materials with interesting physical properties derived from their unique architecture. While great strides have been made in our fundamental understanding of bottlebrush polymers and networks, an interdisciplinary approach is necessary for the field to accelerate advancements. This review aims to act as a primer to BBN chemistry and physics for both new and current members of the community. In addition to providing an overview of contemporary BBN synthetic methods, we developed a workflow and desktop application (LengthScale), enabling bottlebrush physics to be more approachable. We conclude by addressing several topical issues and asking a series of pointed questions to stimulate conversation within the community.

Biodegradable reactive compatibilizers for efficient in-situ compatibilization of poly (lactic acid)/poly (butylene adipate-terephthalate) blends

The wide application of fully biodegradable polylactic acid/polybutylene terephthalate (PLA/PBAT) blends in environmentally friendly packaging were limited because of poor compatibility. Normal compatibilizers suffer from poor thermal stability and non-biodegradability. In this work, epoxy copolymer (MDOG) with different molecular structures were made of 2-methylene-1, 3-dioxoheptane, and glycidyl methacrylate as raw materials by free radical copolymerization. MDOG copolymers have good biodegradability and a high thermal decomposition temperature of 361 °C. The chemical reaction of the epoxy groups in MDOG with PLA and PBAT during the melting reaction improved the interfacial bonding by decreasing the particle size of PBAT. Compared to the PLA/PBAT blends, the tensile strength and fracture toughness of PLA/PBAT/MDOG blends were enhanced to 34.6 MPa and 115.8 MJ/m3, which are 25 % and 81 % higher, respectively. As a result, this work offers new methods for developing thermally stable and biodegradable compatibilizers, which will hopefully promote the development of packaging industry.

3D printable soft and solvent-free thermoplastic elastomer containing dangling bottlebrush chains

Polymer networks containing bottlebrush chains are emerging materials with exceptionally soft and highly tunable mechanical properties. However, such materials have not been extensively implemented in functional processing techniques such as three-dimensional (3D) printing. Here, we introduce a new design of soft and solvent-free polydimethylsiloxane (PDMS)-based thermoplastic elastomer which contains dangling and space-filling bottlebrush chains, featuring a yield stress and a rapid recovery after stress removal; both required for high spatial fidelity 3D printing. The developed material is composed of two copolymers; the main building block is a diblock copolymer with linear polystyrene (PS) block and bottlebrush PDMS block (PS-b-bbPDMS) while the second component is PS-b-PDMS-b-PS triblock, self-assembling to a physical network. This design provides independent tunability of each structural parameter on the molecular level, hence, macroscopic control of the materials' mechanical properties. Multiple self-supportive 3D structures with spanning elements are 3D printed at elevated temperatures using a developed material with a low shear modulus of G' = 3.3 kPa containing 3 : 1 molar ratio of diblock to triblock copolymers without the need for volatile solvent, or post-treatment. This 3D printing compatible design opens new opportunities to utilize the distinctive mechanical properties of bottlebrush materials for applications such as soft tissue scaffolds, sensors, actuators, and soft robots.

From macromonomers to bottlebrush copolymers with sequence control: synthesis, properties, and applications

Bottlebrush polymers (BBPs) are a type of comb-like macromolecules with densely grafted polymeric sidechains attached to the polymer backbones, and many intriguing properties and applications have been demonstrated due to...