Arborol dendrimers

Arborol Dendrimers. The spherical topology of dendrimers resembles the size and shape of the Hartley model (1936) of a micellar aggregate formed by surfactant molecules (Fig. 11.2 Tomalia et al. 1990). Micellar stmctuies have a dynamic, spherical structure possessing a close-packed, solvent-incompatible core surrounded by an open, solvent-compatible layer. 

Figure 11.3 Chemical structures of the (a) arborol dendrimer and (b) water-soluble, allhydrocarbon dendrimer.

In contrast, neutral hydroxy-terminated dendrimers generally exhibit hydrodynamic volumes that are invariant with pH (Young et al. 1994). The stmcture of carboxyl-terminated arborol dendrimers has been extensively characterized by... 

Figure 17 Classical divergent growth of PAMAM dendrimers. 6.04.2.4.3 Arborol dendrimers...

The synthesis and study of dendrimers is a relatively new branch of macro-molecular chemistry. It began in 1985 with the publication of two landmark papers (D.A. Tomalia, H. Baker, J. Dewald, J.M. Hall, G. Kallos, R. Martin and J. Ryder, Polym. J., 1985,17,117-132 and G.R. Newkome, Z. Yao, G.R. Baker and V.K. Gupta, J. Org. Chem., 1985, 50, 2003-2004), and has grown to become a very vibrant research field. The word dendrimer comes from the Greek word dendra, meaning tree, and was applied to these compounds by Tomalia et al. in their very first paper. Newkome s team, by contrast, called their molecules arborols from the Latin word arbor, which also means a tree. The term cascade molecule has also been used, but the word dendrimer is the one that is used most widely throughout the literature, and is also used in the present chapter. 

Dendrimers, or arborols, or cascade, or cauliflower, or starburst polymers, were first synthesized in the early 1980s [3,4]. In 1985 Tomalia et al. [5] and Newkome et al. [6] presented the first papers dealing with dendrimers. A multitude of dendrimers have been presented in the literature ranging from polyami-doamine [7,8],poly(propylene imine) [9,10], aromatic polyethers [11-13] and polyesters [14, 15], aUphatic polyethers [16] and polyesters [17], polyalkane [18-19], polyphenylene [20], polysilane [21] to phosphorus [22] dendrimers. Combinations of different monomers as well as architectural modifications have also been presented. For example, chirality has been incorporated in dendrimers [23,24]. Copolymers of linear blocks with dendrimer segments (dendrons) [25-27] and block-copolymers of different dendrons have been described [28]. 

In this context, much attention is currently devoted to the preparation of highly branched tree-like species, variously called cascade molecules, arborols, or dendrimers. The reasons why such compounds are interesting from a fundamental viewpoint and promising for a variety of applications have been reviewed and highlighted by several authors. Many of the dendrimers obtained so far are organic in nature. This review describes a novel family of dendrimers containing metal ions, prepared in our laboratories over the last few years. 

Polymers have provided an alternative approach to self assembly. Particularly exciting are the recently developed hyperbranched dendrimers [383] and arborols [384] (32), both of which can be synthesized in a relatively simple step-wise manner. Pairs of arborols, connected with proper-length spacers, have been found to self assemble to form gels and long fibrous rods similar to those formed from chiral aldonamides [384],... 

Another approach to controlled molecular morphogenesis is provided by the generation of globular molecules such as the starburst dendrimers and the arborols , based on highly branched structures formed via cascade processes and growing from a central core [7.55-7.60]. Most such molecular scaffolding hase been produced by repetitive processes the use of sequences of different reactions is expected to give access to an even richer variety of non-repetitive branched architectures. 

Linear Polymeric Supermolecules Supramolecular CROSS-LINKING Self-assembled Dendrimers, ARBOROLS... 

A small, non-polymeric dendrimer with a. solid core and 27 alcohol end groups was obtained from l,3,5-tris(bromomethyl)benzene, the sodium enolate of triethyl methanetricar-boxylate, and 2-amino-2-(hydroxymethyl)-l, 3-propanediol ( TRIS"). This highly water-soluble compound, a so-called arborol , forms globular micelles containing about 40 molecules (G.R. Newkome, 1986). 

Dendrimers are molecules with regularly placed branched repeat units. They are also known as Starburst, Cascade or Arborols. These names describe aspects of their molecular architecture. Dendrimers consist of different parts (see Fig. 1). Each dendrimer has a core or focal point. The core is the central unit of the den-drimer and can formally be regarded as the center of symmetry for the entire molecule. The core has its characteristic branching functionality, i.e. the number of chemical bond by which it is connected to the rest of the molecule (Fig. la). The focal point plays the same role as the core. Moreover,it has a chemical functional group not found elsewhere in the dendrimer. 

Figure 5.5. Reduction of the carbonyl moieties of the crowned arborols (Scheme 2.24) afforded these more lipophilic crowned dendrimers.

As early as 1986 dumb-bell-shaped dendrimers were reported to form linear networks.[87,881 These surfactant-like dendrimers possessed external, branched, ball-shaped architecture connected to either sides of a linear alkyl chain interior (Figure 9.10) these dendrimers were termed arborols and were discussed earlier in detail (Section 4.12.1.1). 

Incorporation of an alkyne moiety within the lipophilic core (e.g., 23) imparts helical and scissors-like morphology to the stacked array (e.g., 24 and 25, respectively). Disclike, benzene-based arborols have also been reported1891 to form //-bonded aggregates, or networks, comprised of approximately 50-60 dendrimers. The approximation is based on network diameters determined from electron microscopy. 

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