Bottlebrush polymers

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. 

Bottlebrush polymers contain a long flexible macromolecule as a backbone to which side chains, which may also be flexible, are grafted [59, 60]. The idea then is that via suitable choices of parameters such as the grafting density, solvent quality, and side chain molecular weight the local stiffness of this cylindrical molecular brush can be controlled. The qualitative pictine one draws is that of a wormlike... 

However, for bottlebrush polymers where the backbone chain and the arms are flexible, the chain stiffness is a consequence of chain thickness. The simulations give rather clear evidence [61, 66, 70] that the chains do get stiffer with increasing chain lengths of the side chains (Fig. 13a). However, there is a monotonic increase of the mean square end-to-end distance of the backbone with backbone chain length Ab, from the rod-like behavior at small Np, where we find oc ... 

For the simulations we consider cylindrical bottlebrush polymers, where two types (A, B) of flexible side chains of length Na, A b are densely grafted to a backbone. The degree of (in)compatibility between these constituents can be characterized by a Flory-Huggins parameter and the solvent quality is described by... 

Several other research works on the synthesis of bottlebrush polymers and copolymers have also been reported [127-134], including dendronized... 

Cyclic bottlebrush polymers are uniquely accessible in high yields through ring-expansion metathesis polymerization (REMP) (Figure 8.14). For example, the alkyne-containing macrocycle 27 was modified with PEG substituents to generate cyclic bottlebrush copolymer 28, which exists as a toroid [141]. To date, REMP has yielded bottlebrushes that serve as proof of concept, and it will be interesting to see whether this toroidal shape makes a difference in their function. 

AAC to produce a doxorubicin-loaded, water-soluble, bivalent bottlebrush polymer 26... 

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. 

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. 

Poly(macromonomers) with moderately long side chains attached to every few (second) atom along the backbone are very densely branched polymers. When the degree of polymerization of the backbone is low then the poly(macromon-mers) tend to resemble star polymers [39, 40]. When the degree of polymerization is very high the poly(macromonomer) acquires a cylindrical conformation (bottlebrush), due to the stretching and linearization of the backbone [40]. 

When a linear polymer is grafted with a large number of much shorter side chains, cylindrical polymer brushes are formed [33, 108-111]. They are also denoted as bottlebrushes or molecular brushes. Although most cylindrical polymer brushes contain linear side chains, dendritic or even hyperbranched space demanding grafts can also render cylindrical shapes, which leads to the so-called dendronized [112-116] andhypergrafted[117, 118] polymers, respectively. In this review, we will focus on cylindrical brushes with linear side chains. Due to their anisotropic nature in topology, they have attracted more and more research interest in their synthesis, bulk, or solution properties, as well as applications. 

Figure 4.8 Schematically presented synthesis of hybrid bottlebrushes with a PLL backbone and synthetic polymer side-chains via a combination of ZLL-NCA ROP and ATRP.

I. Mitra, X. Li, S.L. Pesek, B. Makerenko, B.S. Lokitz, D. Uhrig, J.R Anker, R. Verduzco, G.E. Stein, Thin film phase behavior of bottlebrush/linear polymer blends. Macromolecules 47 (15) (2014) 5269-5276. 

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-... 

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]. 

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