Design, Synthesis, and Self‐Assembly of Janus Bottlebrush Polymers

Abstract

in solution, [28-30] and at the interfaces [31,32] features the unique microstructures and varied applications (Figure 1C). Janus bottlebrush polymers are a class of special molecular brushes, which have two incompatible side chains on the same repeating unit of the backbone. [33] "Janus" is the god in ancient Roman religion and myth with two faces looking to the past and the future. [34] In scientific community, the phrases containing Janus, such as "Janus nanoparticles," [35-38] "Janus beads," [39,40] and "Janus polymerization," [41-43] indicate something consisting of counterparts. [44-46] The design of Janus bottlebrush polymers was inspired by Janus particles. [35,47-49] The characteristic of Janus bottlebrush polymers is that the repeating unit of the backbone possesses two immiscible side chains. [50-52] Core-shell bottlebrush polymers with block copolymers as the side chains are usually not Janus-type unless the block side chains are unsymmetrical. [6] An emerging Janus core-shell bottlebrush polymer has been developed by transferring the side chains from homo polymers to two different block copolymers. [53] Design, synthesis, and self-assembly of Janus bottlebrush polymers have arouse much interest in polymer chemistry and material science. [54,55] In general, Janus bottlebrush polymers could be prepared via backbone-first [50] (grafting-to and graftingfrom) or side-chain-first [56] (grafting-through) strategy. Most of Janus bottlebrush polymers were reported via grafting-through approach. Macromonomers are first designed and subsequently polymerizations occur to form the backbone. [23] Backbonefirst route also allows for the synthesis of Janus bottlebrush polymers by using combined grafting-to and grafting-from approach. [57] The special unsymmetrical architectures enable Janus bottlebrush polymers to achieve ideal phase separation in bulk, [58,59] in solution, [52] and at the interface. [32] The preorganized interface can promote self-assembly process and avoid the distorted phase separation. [32,33] The self-assembly of Janus bottlebrush polymers achieves small domain size and tunable bulk property, [58,59] which is challenging for the traditional linear or bottlebrush polymers. [60,61] Therefore, Janus bottlebrush polymers have great potential applications in nanolithography, [58] photonic crystals, [62] biomedicine, [53] surfactants, [63] etc. The big families of bottlebrush polymers have been nicely reviewed by Grubbs and co-workers, [64] Müllner and coworkers, [65-67] Rzayev and co-workers, [7] Verduzco and coworkers, [6] and Matyjaszewski and co-workers [2]. As a young but significant class, Janus bottlebrush polymers have achieved remarkable advances in recent years. Therefore, this review attempts to focus on Janus bottlebrush polymers, covering Janus bottlebrush polymers are a class of special molecular brushes, which have two immiscible side chains on the repeating unit of the backbone. The characteristic architectures of Janus bottlebrush polymers enable unique selfassembly properties and br...

Simultaneous Synthesis and Self‐Assembly of Bottlebrush Block Copolymers at Room Temperature via Photoinitiated RAFT Dispersion Polymerization

“…This phenomenon can be attributed to three possible reasons: i) the bottlebrush core-forming block can avoid the interchain entanglement, reducing the energy for the formation of higher-order morphologies; ii) the mobility of bottlebrush core-forming block is higher due to the shorter PHPMA side chain, facilitating the morphological transition from spheres to higher-order morphologies; iii) geometrical constraints in the chain conformation limits the bottlebrush structure to remain with a rather spherical volume, while the linear counterpart can stretch and thus enable the formation of even large spherical micelles (Figure 2m,n). [3,11,54] Several further series of bottlebrush block copolymer nanoobjects (using PPEGMA 24.5 -P(HEMA 4.8 -g-CEPA 4.5 )-CEPA as the macro-RAFT agent) were prepared by systematically changing the total DP of PHPMA and the HPMA concentration. In each case the morphology was checked by TEM and the total DP of PHPMA was determined by 1 H NMR spectroscopy to construct a morphological phase diagram.…”

“…[4][5][6][7][8][9][10] Moreover, the unique molecular architectures of bottlebrush polymers can lead to different self-assembly behaviors in solution, allowing the preparation of novel polymer nanoparticles. [11] In general, bottlebrush polymers can be synthesized by three different strategies including: i) polymerization of macromonomers ("grafting-through"); ii) coupling of side chains to a polymeric backbone ("grafting-to"); and iii) polymerization of monomers from a polymeric backbone ("grafting-from"). Particularly, the "graftingfrom" strategy combined with reversible deactivation radical polymerization (RDRP) techniques has become one of the most commonly employed methods for precise synthesis of bottlebrush polymers.…”

Research progress in multi-modal combined anti-tumorJanusnano-platform based on chemotherapy

“…自组装是由简单小单元形成有序复合结构过程的 一种方法 [45] , 主要包括嵌段共聚物的自组装和不相容 配体在均质颗粒表面的竞争性吸附 [46] . 嵌段共聚物自 组装通过自由基聚合制备具有明确的结构、组成和分 子量的小单元嵌段共聚物 [47,48] , 并可以应用到许多不 同的聚合物类型. Ge等 , 对球形Janus树状大分子进行了模拟 [51,52] , .…”

Dumbbell‐Shaped, Graft and Bottlebrush Polymers with All‐Siloxane Nature: Synthetic Methodology, Thermal, and Rheological Behavior

“…to high porosity and specific surface area. Various branched (co)polymers with graft (in particular, bottlebrush [8][9][10] ), (macro) cyclic, dumbbell- [1][2][3] and star-shaped (in particular, dendrimers [11][12][13] ) macrostructures are used to make soft materials, artificial muscles and tissues, self-healing and smart materials, etc. [14][15][16][17][18][19][20][21][22][23][24] Undoubtedly, the key role in the development and application of such macromolecules in science, technology, and medicine belongs to the well-studied, proven, and robust organic approaches of their synthesis, namely, cross-coupling [25] and CH activation reactions, [26,27] metathesis polymerization, [28,29] atom transfer radical polymerization, [30][31][32] etc., where the main skeleton of macromolecules and their building blocks are usually (fully or partially) organic in nature.…”