Side dendronized linear polymers

The concept of making brush-type polymers in which a linear polymer is funtionalized with dendritic side-chains was first suggested by Tomalia in a 1987 patent, though actual experimental work on his approach was only reported recently recently [15]. Hawker and Frechet were first to document the preparation of a vinyl copolymer containing a few pendant Frechet-type dendrons (Figure 7.9). 

Dendronized polymers are a class of polymers produced by the combination of linear polymers and dendritic molecules as side chain pendant moieties [67-69],... 

Dendrons attached as side chains on linear polymer chains behave different from free dendrimers and dendrons. Block copolymers, poly(3,5-bis(3,5-bis (benzyloxy)benzyloxy)-benzyl methacrylate-random-methacrylic acid)-block-poly(2-perfluorooctylethyl acrylate), possess poly(benzylether) dendrons and perfluorinated alkyl chains in their side chains (Fig. 4) [85], While an LB film of a copolymer with a medium substitution fraction of poly(benzylether) dendron side chain in poly(methacrylic acid) displays flat surface, a copolymer with high fraction of poly(benzylether) dendron side chains produces the zone texture. Dendron rich blocks are hydrophobic and oleophilic but perfluorinated blocks are solvophobic. Therefore, in this case, the solvophobicity-to-solvophilicity balance must be considered. As a result, copolymers with medium fraction of dendron are laid on solid substrate, but dendron blocks of copolymers with high fraction prefer to arrange at air side of air/ water interface and the fluorocarbon blocks are enforced to exist close to water subphase, resulting in the zone texture [86]. These situations of molecular arrangements at air/water interface are kept even after transfer on solid substrate. By contrast, when perfluorooctadecanoic acids are mixed with block copolymers with high dendron fraction, the flat monolayers are visualized as terrace [87], The monolayers are hierarchized into carboxyl, per-fluoroalkyl, and dendron layers, that is, hydrophilic, solvophobic, and oleophilic layers. In this case, perfluorooctadecanoic acids play a role for ordering of block copolymers. 

Dendrimers usually exhibit spherical (isotropic) shape. However, wedge-like dendrimer fragments ( dendrons ) that have been attached to linear polymers as side groups can be used to create anisotropic nanocylinders , leading to uncoiling and extension of the polymer chains. Synthetic macromolecules of this type can be visualized directly on surfaces and their contour length determined from the images. Unexpected acceleration effects in the self-encapsulated polymerization of dendron monomers used to prepare such polymers as well as the structural consequences of dendritic pieces of cake on linear polymer chains are discussed. 

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. 

Following the first papers of Tomalia et al. (1985) and Newkome et al. (1985) dealing with dendrimers, a large number of dendrimers have been presented in the literature ranging from polyamidoamine (Tomalia et al., 1991), polyethers (Hawker and Frechet, 1990 Padias et al., 1987), and polyesters (Miller et al., 1992 Ihre et al., 1996) to polysilane (van der Made and van Leeuwen, 1992). Copolymers of linear blocks with dendrimer segments (dendrons), block copolymers of different dendrons, and polymers with dendritic side chains (Frauenrath, 2005) have been described. 

Some polymers are linear—a long chain of connected monomers. PE, PVC, Nylon 66, and polymethyl methacrylate (PMMA) are some linear commercial examples found in this book. Branched polymers can be visualized as a linear polymer with side chains of the same polymer attached to the main chain. While the branches may in turn be branched, they do not connect to another polymer chain. The ends of the branches are not connected to anything. Special types of branched polymers include star polymers, comb polymers, brush polymers, dendronized polymers [1], ladders, and dendrimers. A cross-linked polymer, sometimes called a network polymer, is one in which different chains are connected. Essentially the branches are connected to different polymer chains on the ends. These three polymer structures are shown in Figure 1.3. 

Macromolecules that contain two or more topologically distinct components are complex architectures that can lead to emergent properties or behaviors that are different to those of either of the individual molecular architectures. Dendronized polymers [16-19] are examples of such complex molecular architectures and are composed of a linear polymer backbone and perfectly branched dendritic side chains on each repeat unit (Scheme 1). The molar masses of such polymers emphasize the shift in thinking brought about by Staudinger s concept of macromolecules [1,2]. Individual dendronized polymers are nanoscopic objects [20-25] whose organization in bulk is determined by hierarchical processes that occur on a different set of length scales compared to conventional polymers [16,26]. By virtue of the size and shape of dendronized polymers, interest in this complex macromolecular architecture has moved toward how to extract functionality from these nanoscale molecular objects. 

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. 

Dendronized polymers, originally termed rod-shaped polymers , are polymers having a linear backbone with dendritic side chains (Frauenrath, 2005 Tonga et al, in press Schluter and Rabe, 2000 Malkoch et al, 2004). This structure may be synthesized via three conceptually... 

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