Dendrimer flexible

The data presented in Figure 8 graphically illustrate the tremendous and rapid growth in interest in FOSS chemistry, especially for patented applications. This looks set to continue with current applications in areas as diverse as dendrimers, composite materials, polymers, optical materials, liquid crystal materials, atom scavengers, and cosmetics, and, no doubt, many new areas to come. These many applications derive from the symmetrical nature of the FOSS cores which comprise relatively rigid, near-tetrahedral vertices connected by more flexible siloxane bonds. The compounds are usually thermally and chemically stable and can be modified by conventional synthetic methods and are amenable to the usual characterization techniques. The recent commercial availability of a wide range of simple monomers on a multigram scale will help to advance research in the area more rapidly. 

The reason for the low intrinsic viscosities in solution is that dendrimers exist as tightly packed balls. This is by contrast with linear polymers, which tend to form flexible coils. The effect of this difference is that, whereas polymer solutions tend to be of high viscosity, dendrimer solutions are of very low viscosity. In fact, as dendrimers are prepared, their intrinsic viscosity increases as far as the addition of the fourth monomer unit to growing branches (the so-called fourth generation), but this is the maximum value that the viscosity reaches, and as the side chains grow beyond that, the viscosity decreases. 

The cavities in dendrimers are not permanent, but can be redistrubuted as the branches, which can possess considerable degrees of flexibility, move about. The inclusion of guest molecules within a dendrimer may occur as a result of movements in the branches, which allow temporary inclusion of the guest molecule within the dendrimer structure. In solution, it is assumed that molecules of solvent are able to move with ease through the branches of dendrimers, hopping between such temporary cavities with little or no hindrance. When the solvent is removed, the dendrimer may collapse to a distinctly reduced volume. 

The use of ordered supramolecular assemblies, such as micelles, monolayers, vesicles, inverted micelles, and lyotropic liquid crystalline systems, allows for the controlled nucleation of inorganic materials on molecular templates with well-defined structure and surface chemistry. Poly(propyleneimine) dendrimers modified with long aliphatic chains are a new class of amphiphiles which display a variety of aggregation states due to their conformational flexibility [38]. In the presence of octadecylamine, poly(propyleneimine) dendrimers modified with long alkyl chains self-assemble to form remarkably rigid and well-defined aggregates. When the aggregate dispersion was injected into a supersaturated... 

This increase was ascribed to diminished molecular flexibility on increasing dendrimer size. 

The conformational flexibility and the lack of difference of the electronic properties of the polyether branches in 32 have been forwarded to explain this zero rotation. Therefore a similar dendrimer 34 has been prepared which carries a more sterically demanding branch, leading to a more rigid structure [66] interestingly, this dendrimer indeed exhibited a very small but measurable optical activity, which underlines the thesis that nanoscopic chirality depends on the rigidity of the investigated structure. 

To increase efficiency and ease of product separation from reaction mixtures, we also prepared styryl-substituted TADDOL-dendrimers that can act as crosslinkers in styrene suspension polymerizations, and thus lead to beads with intimately incorporated TADDOL sites [106,107]. Due to the presence of the con-formationally flexible dendritic spacers between the chiral ligand and the poly-... 

D. A. Tomalia, A. M. Naylor, and W. A. Goddard, Starburst dendrimers-molecular level control of size, shape, surface chemistry, topology, and flexibility from atoms to macroscopic matter, Angew. Chem. Int. Ed. Engl., 29 (1990) 138-175. 

In general, dendrimers of size G-0 through G-3 have open, asymmetric, and flexible structures with effectively no protected internal areas, due to a large freedom of motion in their branches, and they can readily accommodate additional covalent attachments to their surfaces. See Figures 73-7.5 for illustrations of the two-dimension and three-dimension structure of a... 

The above examples of the dendrimeric Gdm complexes clearly illustrate how flexibility of the macromolecule is important in limiting proton relaxivity. This flexibility can originate from the intrinsic flexibility of the macromolecule itself, or/and from the non-rigid coupling of the chelate to the dendrimer surface. In both cases, the surface chelate benefits only partially from the slow motion of the dendrimer (or other macromolecule). In order... 

Figure 1.21 Periodic properties for poly(amidoamine) (PAMAM) dendrimers as a function of generation G = 0-10 (I) flexible scaffolding (G = 0-3) (II) container properties (G = 4-6) and (III) rigid surface scaffolding (G = 7-10) various chemo/ physical dendrimer surfaces amplified according to Z = NCN where Nc = core multiplicity, Nb = branch cell multiplicity, G = generation...

Dendrimers within a generational series, can be expected to present their terminal groups in at least three different modes, namely flexible, semi-flexible or... 

These dendritic boxes (Figure 13.7) were synthesized by the conjugation of a chiral shell of protected amino acids onto a flexible polypropylene imine) dendrimer with 64 amino end groups. In solution, the shell was highly hydrogen-bonded and dense-packed, displaying a solid-phase behavior, which was indicated by the low NMR relaxation time of the surface groups [11]. 

B., 37, 362 (1995). The authors claimed that acetone solutions (5, 10 and 20%, specifically) of a sample that had gel permeation chromatography retention time close to that of a linear polystyrene of 1.1 x 106 molecular mass, had four decades lower viscosity than the corresponding solutions of flexible-chain linear poly(butyl methacrylate). However, in our opinion, neither the examined sample was characterized satisfactorily enough to be referred to as a dendrimer, nor the rheology was described sufficiently enough to draw any conclusions about the solution s flow behavior. Therefore, we refer to this paper here only for reasons of curiosity. 

The preparation of thin films and layers from dendrimers by self-assembly is a topic of great current interest since it allows the construction of functional interfaces that use specific dendritic properties such as size, shape, porosity, end-group density and multifunctionality. It is also an area of research that benefits substantially from the flexible character intrinsic to most dendrimers. 

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