Polymers bottle-brush

Poor solvent conditions for the side chains grafted to, e.g., a linear polymer (bottle brushes) will lead to intermolecular aggregation however, interestingly, they can also lead to intramolecular microphase separation within a homopolymer chain. Consider a bottle brush polymer with a very stiff backbone (in the simulations [92] it was modeled as a rigid rod) placed into poor solvent conditions. The resulting structures then depend on solvent quality and grafting density of the side chains, as exhibited in Fig. 34. 

Graft poiymer Comb polymer Bottle brush... 

The field of densely grafted copolymers has received considerable attention in recent years. The materials (also called bottle-brush copolymers) contain a grafted chain at each repeat unit of the polymer backbone. As a result, the macromolecules adopt a more elongated conformation. Examples of brush copolymers have been provided within the context of ATRP [307-309]. Synthesis of the macroinitiator was achieved through one of two approaches. One method used conventional radical polymerization of 2-(2-bromopropionyloxy)ethyl acrylate in the presence of CBr4 to produce a macroinitiator with Mn=27,300, and a high polydispersity of Mw/Mn=2.3 (Scheme 46A) The alternative involved the ATRP of 2-trimethylsilyloxyethyl methacrylate followed by esterification of the protected alcohol with 2-bromopropionyl bromide. While synthetically more challenging, the latter method provided a macroinitiator of well-defined structure... 

By this way, polymers with Janus-type, sphere-type bottle brush-type shapes, or dumbbell-like, palm-tree-like contours were derived with excellent control and precise topological features. 

The problem of understanding the persistence length and its consequences is also taken up by Butt et al. [26] for bottle-brush polymers, there is the challenging problem of understanding how their stifliiess depends oti the grafting density and degree of polymerization of the grafted side chains. 

As a second example cylindrical brush polymers, often called bottle brushes, are described (Sect. 3). Cylindrical brush polymers usually consist of a flexible main chain, densely grafted by flexible, stiff or dendritically branched side chains. The latter are known as dendronized polymers and have been fi equently investigated by both theory and experiment. In the present review, we focus on brush polymers with linear side chains. 

Fig. 34 Schematic phase diagram of a bottle brush polymer with a rigid backbone under poor-solvent conditions, in the plane of variables scaled grafting density and scaled distance to the Theta temperature [92], The lines separating the different regions have been proposed by mean field arguments [74], They are not to be understood as quantitative estimates of phase transition lines, but rather as rough estimates of smooth crossovers. Representative simulation snapshots visualize the different microphases...

For the adsorption of macromolecules with complex architecture, such as bottle brush polymers, it is an intriguing question how the above picture of polymer adsorption changes after all, most manipulations of macromolecules with external devices (e.g., AFM tips) presuppose that the macromolecule is situated at a suitable surface [156], rather than freely diffusing in the 3D space of a more or less dilute polymer solution. 

Fig. 2. Schematic illustration of side-chain polymer crystals where (1) represents the polymer backbone, (2) represents the alkylene spacer and (3) represents the different side-group moieties. In a real polymer the backbone would not generally be in the rigid configuration shown. For example, with an SiO backbone the alkylene chains are attached to each Si atom (for a fully substituted system) and rotational isomerism due to free rotation about the linking oxygen would ensure a random backbone configuration. Typical spacer groups consist of between 4 and 12 methylene units and the side-group moieties contain several bulky phenylene units. Therefore, in three-dimensional space the molecules would look more like a bottle brush with random bristles attached to a flexible backbone stem.

Figure21 Generalized phase diagram including morphologies found in polystyrene-block-poly(Z-L-lysine), linear block copolymers, O bottle-brush shaped block copolymers, and schematic presentation of the undulated lamellar morphology. (Reprinted from H. Schlaad, H. Kukula, B. Smarsly, M. Antonietti, and T. Pakula. Polymer 43 5321,2002. Copyright [2002], with permission from Elsevier Science.)...

Haddleton and Ohno reported on maltodextrin modified polymers via copper(I)-mediated living radical polymerization [125]. Comblike structures based on polystyrene with amylose entities were synthesized by Kobayashi et al. [126] and bottle-brush-like structures by Kakuchi and coworkers [127]. 

Figure 19 (a) Dependence of storage (S ) and loss (S") modulus of a bottle brush with polymethacrylate backbone with DP = 3500 and poly(nBA) SC with DP = 30. (b) Dynamic mechanical spectra of a cross-linked sample of polymer shown in spectrum (a). 

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