Dendrimer macromolecules preparation

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 field of synthetic enzyme models encompasses attempts to prepare enzymelike functional macromolecules by chemical synthesis [30]. One particularly relevant approach to such enzyme mimics concerns dendrimers, which are treelike synthetic macromolecules with a globular shape similar to a folded protein, and useful in a range of applications including catalysis [31]. Peptide dendrimers, which, like proteins, are composed of amino acids, are particularly well suited as mimics for proteins and enzymes [32]. These dendrimers can be prepared using combinatorial chemistry methods on solid support [33], similar to those used in the context of catalyst and ligand discovery programs in chemistry [34]. Peptide dendrimers used multivalency effects at the dendrimer surface to trigger cooperativity between amino acids, as has been observed in various esterase enzyme models [35]. 

Nonetheless, it was a fairly short step from octopus compounds to dendrimers, and the step was taken by Vogtle in the late 1970s when he attempted to use a cascade reaction to prepare a molecule of the dendrimer type that would now be considered a dendron rather than a fully developed dendrimer. It began with the addition of acrylonitrile to an anfine, followed by reduction of the nitrile to amine. This was followed by a further reaction with acrylonitrile, and the process was repeated several times to yield highly branched macromolecules. There were initially problems with the reduction step but these were overcome, and the preparation of these poly(propylene imine) dendrimers was later commercialized. 

All the fullerene-containing dendrimers reported to date have been prepared with a Cgo core but never with fullerene units at their surface or with Cgg spheres in the dendritic branches. We have recently started a research program on the synthesis of dendrons substituted with fullerene moieties. These fulleroden-drons are interesting building blocks for the preparation of monodisperse fullerene-rich macromolecules. In addition, they are also amphiphilic compounds capable of forming stable Langmuir films at the air-water interface. 

Recently, highly branched macromolecular polyamidoamine dendrimers have been prepared with Co11 bound where the metal ions have additional exchangeable coordination sites.450 These macromolecules show a capacity for catalyzing the hydrolysis of phosphate esters, presumably via intermediate bound phosphoester species. 

Application of the Horner-Wadsworth-Emmons reaction to the functionalization of dendrimers allows one to prepare amino acid terminated macromolecules. Such a reaction conducted with dendrimers 10-[G ], 10-[G 3], lO-fG ] and phosphonates unsubstituted at the carbon a to the phosphoryl group affords in moderate yield dendrimers bearing various a, / unsaturated functional groups on the surface [18]. (Schemes 17 and 18). 

Nitroxide attached to macromolecules also induces the living radical polymerization of St. Yoshida and Sugita [252] prepared a polymeric stable radical by the reaction of the living end of the polytetrahydrofuran prepared by cationic polymerization with 4-hydroxy-TEMPO and studied the living radical polymerization of St with the nitroxide-bearing polytetrahydrofuran chain. The nitroxides attached to the dendrimer have been synthesized (Eq. 69) to yield block copolymers consisting of a dendrimer and a linear polymer [250,253]. 

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