Bottlebrush structure

The combination of brushes with soft surfaces is clearly a key aspect of biological lubrication. However, it is less clear whether carbohydrates possess any specific or unique properties that are absent in other, synthetic brush-forming hydrophilic polymer chains. Moreover, natural lubricant additives appear to form hierarchical bottlebrush structures, such as that shown in the figure, more readily than the synthetic water-soluble brushes that have been investigated to date (9, 12, 14). The role of both the composition and struc-... 

Fig. 5-24 Portion of a proteoglycan aggregate showing the bottlebrush-like structure.

Leptospermone (72) is an allelochemical produced by the bottlebrush plant (Calispermon spp.).46 This compound is herbicidal, causing bleaching symptoms, and is a potent inhibitor of HPPD. The triketone-type HPPD-inhibiting herbicides such as sulcotrione (73) were developed based on the structure of... 

Third, molecular branched architecture can be tuned to ensure maximum concentration of mechanical tension at a specific chemical bond. For example, star-like [134] and pom-pom structures [125] as well as short bottlebrushes [135] may be used to introduce site-specific activation at the branching center. Figure 10b displays the concentration of tension in the middle of the backbone resulting in its mid-chain scission. In a similar fashion (Fig. 10c), molecular stars with a spoke wheel core and bottlebrush arms exhibit preferential dissociation of the arms followed by the scission of covalent bonds in the bottlebrush backbones... 

Li Y, Nese A, Hu X, Lebedeva NV, LaJoie TW, Burdyhska J, Stefan MC, You W, Yang W, Matyjaszewski K, Sheiko SS (2014) Shifting electronic structure by inherent tension in molecular bottlebrushes with polythiophene backbones. ACS Marco Lett 3 738... 

Graft Copolymers In which the main chain, the macromolecular backbone supports side-chains that exhibit distinct chemical structure. If the side-chains possess the same chemical stracture as the main chain, we deal with a comb-like polymer. A block copolymer, one part of which is formed by a linear chain and another part is a grafted chain is denoted bottlebrush polymer. 

Figure 19 Representative scheme for the preparation of hollow nanotubes with one open end from a bottlebrush block copolymer, (a) Chemical structure of a bottlebrush copolymer, (b) AFM height image of the corresponding shell-cross-linked copolymer adsorbed on mica, (c) TEM characterization of organic nanotubes obtained after core degradation. Reproduced with permission from Huang, K. Rzayev, J. J. Am. Chem. Soc. 2009, 131 (19), 6880-6885. ...

In contrast, the AFM pictures as well as cryo-TEM of sample CB-PLL55 prepared from 5 mM NaBr aqueous solution (Fig. 20) show extended cylinders. The cylinders exhibit undulations of the cross-section that are reminiscent of the pinned clusters [74, 91] postulated by scaling arguments. The occurrence of pearl-necklace-type structures, where pinned clusters of side chains alternate with regimes that are almost free of side chains, has also been seen in simulations of bottlebrushes, provided one has poor solvent conditions. These clusters are formed by collective collapse of several neighboring side chains [92]. We return to this problem in Sect. 3.5. 

Biodegradable comb-like polymer prepared by free radical copolymerization of PLA macromonomer with vinyl (A-vinylpyrrolidone) and acrylic monomers (MMA, methacrylic acid (MA)) has been reported [86]. The hydroxyl group of poly(2-hydroxyethyl methacrylate) (HEMA) anchored to a gold surface-initiated ROP of lactide using Sn (Oct)2 as a catalyst. The final structure of the polymer is a surface-anchored poly(hydroxyethyl methacrylate)-g-poly-lactide, to yield an overall structure of a bottlebrush [87]. 

A number of opportunities still remain to be developed for both fundamental and applied work regarding bottlebrush polymers. One specific area is a more quantitative understanding of bottlebrush block copolymer self-assembly in bulk and thin films. Also, deeper understanding leading to a predictive model of bottlebrush copolymer self-assembly would enable the design of bottlebrush copolymers to target specific self-assembled structures with desired phase behavior. 

Verduzco Rafael, Li Xianyu, Pesek L. Stacy, and Stein E. Gila. Structure, function, self-assembly, and applications of bottlebrush copolymers. Chem. Soc. Rev. 44 no. 8 (2015) 2405-2420. 

Polymers attached to a linear backbone form another class of tethered chains, which are intermediate between the stars and brushes. Long-chain comb polymers are branched polymers in which branches of length A are attached to a flexible polymer chain. The branches can either be equally spaced or random. When the branches are long and closely spaced, excluded volume interactions among the tethered side chains can significantly stiffen the central contour. Though such bottlebrush polymers have been synthesized, so far the backbone has been substantially shorter than the side branches. In this case, the structure will not be very different than for a star polymer in which the branches (arms) are attached to a central point. Diblock copolymers in a selective solvent can also form cyhndrical micelles that have similar structures. 

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