Dendritic cylindrical shape

In one of several important studies on dendronized polymers [4c, 4d]. Schluter and coworkers explored the stiffening of polystyrene chains through the incorporation of Frechet-type dendrons as side chains [28, 29]. While the G-l and G-2 dendrons were not sufficiently bulky to effectively stiffen the polystyrene chain, the G-3 dendron provides enough steric bulk to force the hybrid polymer into adopting a cylindrical shape in solution [28b], In a complementary study, Neubert and Schluter demonstrated that adding charges to the dendritic wedges leads to an expansion of the chains of the hybrid copolymer in aqueous solution [29],... 

SHAPE CONTROL WITH QUASI-EQUIVALENT DENDRITIC SURFACES - DENDRITIC CYLINDRICAL AND SPHERICAL SHAPES... 

Recent seminal work reported by Percec et al. [45-47] has shown that either spheroidal or cylindrically shaped dendronized polymers may be obtained by the polymerization of a dendronized macromonomer . The degree of polymerization of these monomers determines the ultimate shape which appears to demonstrate the quasi-equivalence of dendritic coats . 

The self-assembly mechanism proposed for these spherical and cylindrical polymer backbones surrounded with quasi-equivalent dendritic coats is outlined in Figure 12.9. This knowledge allows the rational design of polymers with well defined spherical and cylindrical shapes. Quasi-equivalent character of these... 

When dendritic fragments are attached to polymer chains, the conformation of the polymer chain is strongly affected by the size and chemical structure of the dendritic wedges attached. Dense attachment of dendritic side chain converts a linear polymer into a cylindrically shaped, rigid and nanoscopic dimension. Frechet and Flawker [70] were one of the first to recognize these hybrid architectures . 

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. 

The supramolecular transformation from sphere to cylinder is supported by X-ray data indicating that the spherical polymers adopt a cubic phase, whereas the cylindrical polymers adopt a hexagonal phase [23b]. Further studies involving a library of dendritic macromonomers led to the conclusion that the effect of DP on polymer shape is a general phenomenon [24], More recently, scanning... 

Schliiter et alJ65,66 have recently used rod-shaped polymers1673 such as poly(p-phe-nylene)s and poly([l.l.l]propellane)s as cores for the attachment of convergently generated dendrons. These new branched macromolecules possess a rigid backbone wrapped with structural wedges, which become increasingly more dense toward the outer cylindrical surface. The Pd-catalyzed copolymerization of dibromobiphenyl derivatives with the Frechet-type ethereal dendrons with a substituted aryl diboronic acid afforded the dendritic coated poly(p-phenylene) rod. 

Self-organization of tapered and dendritic, i.e., fan- and cone-shaped dendron molecules in the solid was reported by Percec et al. in a series of papers [15J. Detailed diffraction experiments evidenced that spherical or cylindrical, (i.e. co-... 

Scheme 16 Schematic representation of novel hyperbranched glycostructures illustrating regularly interspaced ligands onto poly(ethyleneimine) backbone (75), comb-branch (GO) structure (76), interspaced spheroidal dendrimer (77), rod-shaped, cylindrical polymer with dendritic branch (78), and dendrigraft (79).

Fig. 8.9 Typical powder agglomerates detected in the powder electrodeposited at the Ni /Co = 0.67. (a) Narrow (cylindrical) cavities with fem-like dendrites on their bottom, (b) Cone-shaped cavities without fem-like dendrites on their bottom (Reprinted from Ref [1] with kind permission from Springer)...

With further decrease of Ni /Co + ions ratio to 0.67 (65 at.% Co in the powder), no cauMower-Iike agglomerates are detected. All agglomerates are spongy-like, again with two types of cavities narrow (cylindrical) ones with fem-like dendrites on their bottom (Fig. 8.9a) and cone-shaped ones (Fig. 8.9b) without fem-like dendrites oti their bottom. The top surface of all agglomerates obtained from these three solutions is practically identical, being characterized by cauliflower nature, as shown in Fig. 8.7c. 

Apropos tree trunks and cylindrical surface This may also be a starting point to think about dendritic rods as supports with defined curvatures to which cat-alytically active components could be attached (Fig. 3b). In a way, cylinders of the size discussed here bridge the gap between homogeneous and heterogeneous catalysis. They may combine the respective advantages of both. Attachment of cat-alytically active groups to the surface at more or less constant distances may well provide candidates, eg, for applications in flow reactors. Spherically shaped den-drimers equipped with transition-metal complexes have already been successfully employed for such purposes (47-50). 

Figure 4 DNA-synthetic polymer conjugates, (a) Incorporating extended aromatic molecules into DNA creates folded stmctures through jT-stacking. (b) Block copolymers consisting of DNA and synthetic polymers can be assembled into micelles via microphase separation of incompatible blocks, (c) A PEG-DNA-brush block copolymer can shape shift between spherical and cylindrical micelles depending on the specific DNA input, (d) Dendritic DNA, created by covalently modifying short DNA strands with dendritic oligoethylene moieties, self-assembles into long-range fibers without the need for sticky-end cohesion.

Cylindrical, rod-shaped dendrimer assemblies were first synthesized by TomaUa et al. as early as 1987 [35,37,177]. These structures represent some of the first examples of hybridized dendritic architecture. Since they possess a linear polymeric core and dendritic arms, they are called architectural copolymers or dendronized, linear polymers. This work was recently reported in detail [160]. The method involved the divergent dendronization of //near poly(ethyleneimine) (PEI) cores... 

Poly(propylene imine) dendrimers functionalized with hydrophobic alkyl chains (palmitoyl chains or alkyloxyazobenzene chains) assembled into stable monolayers at the air-water interface [122,180]. In the assemblies, the dendrimers adopted a cylindrical amphoteric shape in which the ellipsoidal dendritic moiety acted as a polar head-group and the alkyl chains arranged in a parallel fashion to form an apolar tail (Fig. 33b). This representation is based on the observation that the molecular area of a dendritic molecule increases linearly with the number of end-groups in this molecule. 

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