Highly branched macromolecules

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. 

Simon, P.F.W., Muller, A.H.E., and Pakula, T. Characterization of highly branched poly(methyl methacrylate) by solution viscosity and viscoelastic spectroscopy. Macromolecules, 34, 1677, 2001. 

Gauthier, M. and Mdller, M. Uniform highly branched polymers hy anionic grafting Arborescent graft polymers. Macromolecules, 24, 4548, 1991. 

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. 

In nature, polycondensations of trifunctional monomers having two different functional groups occur under enzymatic control, resulting in tree-shaped, highly branched, but still soluble, macromolecules. 

Two new developments are the dendrimers (highly branched, globular, synthetic macromolecules) and modified buckyballs. Together with hydrogels, they are tailored to provide targeted delivery. 

Polymer composed of highly branched macromolecules containing mesogenic groups of which any linear subchain generally may lead in either direction, to at least two other subchains. 

These polymers have high intrinsic viscosities [e.g., about 22 (ml/g), for polyvinylpyrrolidone], which indicates that the macromolecules are swollen and extended in water. In contrast, serum albumin, with an intrinsic viscosity near 4 (ml/g), must be relatively compact. Promising approaches might be, therefore, to obtain a relatively compact conformation with a water-soluble polymer by introducing cross-linkages or by using a highly branched matrix. The latter has proved to be particularly fruitful. 

An interesting polymer constrained to a relatively compact conformation is polyethylenimine (PEI), which can be prepared by suitable polymerization of ethylenimine (Fig. 2) to give a highly branched rather than a linear macromolecule.19 The structure of a segment of this polymer is shown in Fig. 2. Approximately 25% of its nitrogens are primary amines, 50% secondary, and 25% tertiary.19 The branching of the polymer may be represented schematically as shown in Fig. 3. 

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