Dendrimer fragments

H. Frey, From Random Coil to Extended Nanocylinder, Dendrimer Fragments Shape Polymer Chains , Angew. Chem. 1998,110,2313-2318 Angew. Chem Int. Ed 1998,37, 2193-2197. 

The persistence of the dendrimer decomposition products is the likely cause of the catalyst deactivation over time. The presence of dendrimer and dendrimer byproducts indicates that even the more active catalysts are not particularly clean. It is difficult to distinguish between species adsorbed on the NPs from those primarily on the support however, it is likely that the location of the dendrimer decomposition varies widely along the surface of the catalyst. The dendrimer fragments present on the support could migrate over time and poison the metal active sites, resulting in the lower catalytic activity over time. It is also possible that the residual dendrimer undergoes some slower oxidation processes that result in a stronger, unobservable poison. 

From Random Coil to Extended Nanocylinder Dendrimer Fragments Shape Polymer Chains... 

Dendrimers usually exhibit spherical (isotropic) shape. However, wedge-like dendrimer fragments ( dendrons ) that have been attached to linear polymers as side groups can be used to create anisotropic nanocylinders , leading to uncoiling and extension of the polymer chains. Synthetic macromolecules of this type can be visualized directly on surfaces and their contour length determined from the images. Unexpected acceleration effects in the self-encapsulated polymerization of dendron monomers used to prepare such polymers as well as the structural consequences of dendritic pieces of cake on linear polymer chains are discussed. 

Dendrimers including heterocyclic fragments 97CRV1681, 98CSR233, 98T8543. 

Structure, physical properties, and applications of dendrimers including heterocyclic fragments 99CRV1665. 

Mass spectroscopy is a useful technique for the characterization of dendrimers because it can be used to determine relative molar mass. Also, from the fragmentation pattern, the details of the monomer assembly in the branches can be confirmed. A variety of mass spectroscopic techniques have been used for this, including electron impact, fast atom bombardment and matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. 

Scheme 4. Antibody dendrimers prepared by the combination of IgM with IgG attached hapten to the carbohydrate moiety in the Fc fragment... 

For instance, some time ago Newkome et al. reported the synthesis of ruthenium based dendrimers [170]. A dendrimer (80) with twelve peripheral terpyridine ligands was built around a central quaternary carbon-based core. In the final step complexation between the terminal ligand of the dendrimer and a terpyridinyl ruthenium chloride building block afforded the dodecaruthenium cascade molecule 80 (Fig. 35). Thus, preconstructed cores and dendritic fragments were linked by Ru2+ as the connecting unit and this mode of connectivity could be denoted by [—(Ru)—]. 

Remarkably, alkylation of the core of a dendrimer of generation 6 (two P = N-P(S) fragments on the core, 64 for the fifth generation, and an upper generation incorporating 256 terminal aldehyde groups) can be performed. This clearly demonstrates that the core of this sixth generation dendrimer is available for certain reactions. 

Meijer and co-workers also used a divergent dendrimer synthesis to prepare AB diblock structures (Figure 7.13B) in which the polystyrene linear block is used to initiate growth of the polypropylene imine) dendritic block [45], An amino end group had to be introduced in the polystyrene as a core for subsequent growth of the dendritic fragment via an iterative protocol of sequential... 

The incorporation or complexation of transition metal fragments by dendrimers has led to a broad spectrum of metallodendrimers. Dendrimers are well-defined branched structures (Fig. 13.2). The dimensions of a dendrimer can easily be adjusted by changing its generation, which can be very practical for their application... 

---