Dendrimer convergent synthetic approach

Figure 5.2 Schematization of the convergent synthetic approach to buildup dendrimers.

FIGURE 15.3 Two most common synthetic strategies for dendrimers. (a) Divergent synthetic approach, (b) Convergent synthetic approach. 

An interesting variant on metal polypyridyl-type metallodendrimers is the material 8.34, which was prepared by a convergent synthetic approach (Scheme 8.2) [70]. A further example is the dendrimer 8.35, which possesses 18 ruthenium centers [71]. 

Fig. 3 The convergent synthetic approach for second-generation dendrimers the initial modification of a branched oligomer with (c) prospective surface groups, and (b) after a series of activation and (a) branching steps, a last branching reaction with a suitable core yields the final product (bottom).

In 1990, Hawker and Frechet described the convergent (ontside-in) approach, where dendritic polyethereal macromolecnles, based on 3,5-dihydroxybenzyl alcohol as the building block, were synthesized. That same year, Neenan reported the convergent synthetic approach of dendrimers based on 1,3,5-trisubstituted benzenes. " Since then, research on dendrimers has grown to such an extent... 

Different synthetic routes to dendrimers have been reported in literature however, the most widely known methods include the classical divergent and convergent synthetic approaches. The development of other synthetic methods for preparation of dendrimer is aimed at decreasing the disadvantages of the classical methods. Most of the newly developed methods have their own merits and drawbacks. Therefore, the S3mthesis method chosen for a particular dendrimer depends on the properties required of the dendrimer. 

Dendrimers produced by divergent or convergent methods are nearly perfectly branched with great structural precision. However, the multistep synthesis of dendrimers can be expensive and time consuming. The treelike structure of dendrimers can be approached through a one-step synthetic methodology.31 The step-growth polymerization of ABx-type monomers, particularly AB2, results in a randomly branched macromolecule referred to as hyperbranch polymers. 

Dendrimers are structurally defined branched polymeric molecules and can form good X-ray quality crystals. This is particularly useful in the correlation of structure and properties. Two main synthetic approaches have been used divergent, which is appropriate for smaller dendrimers, and convergent, which is better for larger dendrimers. Branched polysilanes with a structurally defined branched core were described in 1994, but the growth from the core was not controlled and non-uniform structures were obtained.357... 

In another study, nucleic acid dendrimers were synthesized via both convergent and divergent approaches, and their purity assessed using PAGE [23, 24], In Figure 10.6 is shown convergent synthetic route, which involves ... 

The convergent growth approach to dendrimers [1] first introduced [2] in 1989 at the IUPAC meeting on macromolecules in Seoul, Korea, has provided a useful alternative to the divergent methods exemplified by the work of Tomalia et al. on PAMAM dendrimers [3] and Meijer et al. on polypropylene imine) dendrimers [4], Today several hundred papers have exploited the convergent approach to dendrimers to prepare a variety of synthetic functional macromolecules of unparalleled structural precision. 

Figure 7. Divergent synthetic strategy to obtain polynuclear metal complexes of dendrimer shape. - ° Each deprotected compound of the dive ent synthetic approach can be used as a core in convergent synthetic processes. Some of these routes starting from a tetranuclear core are illustrated in Figure 8.

Fig. 3.7-6 Synthetic approaches for dendrimers (a) divergent method (b) convergent method (c) self-assembly.

The first example of a dendrimer-like polymer (in fact, a dendrimer-like PEO of the third generation) was described in 1995 by Gnanou et al. [10]. Iterative synthetic approaches, using either a divergent or a convergent strategy, can be followed... 

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