Convergent approach to dendrimer

The convergent approach to dendrimer synthesis has evolved considerably over the past dozen years. With the benefit of hindsight, it is clear that the key criteria for a successful convergent synthesis include ... 

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. 

Scheme 1 Schematic representation of divergent and convergent approaches to dendrimer synthesis...

This review will focus on the development of the convergent approach to dendrimers since its conception over a decade ago. In addition to discussing a number of noteworthy convergent syntheses, it will also cover their chemical modification for incorporation of function. The divergent approach, which has provided numerous valuable contributions to the field of functional macromolecules, is beyond the scope of this review and has been covered elsewhere.20-22-24-26-28... 

Multidimensional NMR techniques with pulse field gradient (PFG) enhancement have been applied to study l , 2" and 3" generation polyurethane dendritic wedges, which are a novel type of linking element in the convergent approach to dendrimer synthesis. By using PFG- HMQC and HMBC 2D NMR experiments, H and C resonance assignments have been obtained for these compounds, and structure proofs have been accomplished. 

As a matter of fact, the two approaches used to build dendritic structures can be viewed as a means to generate species with n X/terminal functions from a precursor exhibiting/similar groups by condensation techniques. This feature has thus been used to construct branched polymers with perfectly defined structure. After a brief historical account, this paper will focus on the convergent approach to dendrimer synthesis and review the different dendritic structures that have been obtained via this method. 

Seebach and coworkers[341 successfully utilized a convergent approach to the preparation of chiral dendrimers. They wished to address three basic questions (1) Will the incorporation of chiral cores impact asymmetry to dendritic structures (2) Can enantio-selective host-guest interactions occur near the core (3) Can chiral recognition be translated to the dendritic surface ... 

Star poly(methylmethacrylates) were synthesized via atom transfer polymerization using a small carbosilane dendrimer functionalized with a tertiary bromide moiety as an initiator core (Figure 12)100,101. a convergent approach to star polymers with a carbosilane dendrimer core was described in a report by Allgaier and coworkers102, in which living poly(butadienyl-lithium) arms were coupled with various SiCl-terminated carbosilane den-drimers. Utilizing smaller dendrimers with lower functionality was found to yield nearly ideal results in terms of substitution and polydispersity. 

Very recently, Shinkai et al. (see Ref. 200) synthesized tri-dendron type dendrimers (generation = 1 and 2). The branch cell reagent shown below was utilized in a convergent approach to synthesize the dendrons. These dendrons were then anchored in each case around a 1,3,5-benzene tricarbonyl chloride core. This... 

Co-ordination chemistry is not the only possible approach to the successful preparation of supramolecular dendrimers. Other examples include hydrogen-bonded dendrimers, which have been prepared using tetracar-boxylic acid moieties as the linking species, and others have been prepared where the hydrogen bonds were developed using melamine and cyanuric acid at the focal point (i.e. the point towards which convergent synthesis is directed). 

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