Dendrimer convergent growth

In general, convergent methods produce the most nearly isomolecular dendrimers. This is because the convergent growth process allows purification at each step of the synthesis and therefore no cumulative effects of failed couplings are found [85, 89]. Appropriately purified convergent dendrimers are probably the most precise synthetic macromolecules that exist today. 

Preparation of Frechet-type Polyether Dendrons and Aliphatic Polyester Dendrimers by Convergent Growth An Experimental Primer... 

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. 

The near monodispersity typically associated with dendrimers prepared by both the divergent or convergent growth approaches presents a number of interesting characterization traits when compared to traditional narrow polydisper-sity linear polymers. These features are further enhanced by the high degree of symmetry normally associated with dendritic macromolecules and permit an unprecedented amount of structural information to be obtained using standard characterization techniques. 

As the name impHes, the core unit, or focal point group, is located at the center of the dendritic macromolecule and, as such, constitutes only a small proportion of the overall dendrimer structure. However the role of functional groups at the central core can have a profound effect on a number of physical properties and be extremely useful in investigating the structure of dendrimers. The central role played by the focal point group in the success of the convergent growth approach has also been well documented in the above discussions. 

The first part of this review deals with the synthesis and characterization of dendritic aliphatic polyesters based on 2,2-bis(dimethylol)propionic acid (bis-MPA) and 1,1,1 -tris(hydroxyphenyl)ethane (THPE), as core molecule. The convergent growth approach described earlier was applied. We also present H NMR self-diffusion studies of dendrimers of first, second, and third generation. 

The chosen ABj monomer for the synthesis of die dendritic aliphatic polyesters Dl, D2, and D3 was bis-MPA. In the convergent growth approach, dendrons of certain generations were initially synthesized. In a final step these dendrons were coupled to the polyfunctional core molecule (see Scheme 2). To get an acceptable overall yield it is important that all reactions such as coupling, protection, and deprotection are selective and proceed in high yields since a laige number of steps are involved in the synthesis of the final dendrimers. 

The convergent growth approach showed to be a useful method in the synthesis of monodisperse dendrimers. The use of bis-MPA, as a building block, resulted in dendrimers with simple H NMR and NMR spectra where different generations... 

Figure 4. Schematic of dendrimer synthetic strategies A. Divergent growth B. Convergent growth ...

The other accelerated approach for dendrimer synthesis, the orthogonal approach, involves convergent growth with two different monomers. The monomers, an AB2 and a CD2 must be carefully selected such that the focal functionalities of each individual monomer will only react with the periphery of the other monomer (B couples only with C and D only with A) thus removing the need for activation reactions. As... 

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