Generalized dendrimers

Recent developments in the design of dendritic molecules has provided both new methodology and molecular architecture which are structure controlled macromolecules, globular-shaped, dendritic-branched tree-like structures with nanoscscale dimensions [1], Dendrimers generally consist of a focal core, many building blocks (monomer units) and a mathematically defined number of ex-... 

In contrast, neutral hydroxy-terminated dendrimers generally exhibit hydrodynamic volumes that are invariant with pH (Young et al. 1994). The stmcture of carboxyl-terminated arborol dendrimers has been extensively characterized by... 

Ru(ll) AND Os(ll) POLYPYRIDINE DENDRIMERS GENERAL REDOX PROPERTIES AND SELECTED EXAMPLES... 

T. M. Miller, T. X. Neenan, Chem Mater. 1990, 2, 346-349. T. M. Miller, T. X. Neenan, R. Zayas, H. E. Bair, /. Am. Chem. Soc. 1992, 334, 1018-1025. We use the family name polybenzene dendrimers (generally polyarene dendrimers) instead of polyphenylene dendrimers because the rules of nomenclature restrict pheny-lene to -QHg-. 

Hyperbranched polymers are more simple to produce on a large scale than dendrimers. Generally, a one-pot synthesis is used, yielding fewer regular structures and very broad molecular weight distributions (45). 

Polysilazanes represent another important class of ceramic materials that contain N-Si-N and C-Si-N units, sometimes wifli or without oxygen. The structural forms of polysilazanes may be chains, rings, crosslinked networks, or, more recently, dendrimers. Generally, the prepolymers contain sihcon bonded to nitrogen in the backbone and organic groups or hydrogen as substituents on Si and N (65). 

The synthesis of dendrimers generally involves numerous protection/deprotec-tion and purification steps, but the general architectural growth patterns for the divergent and convergent routes are shown schematically in Schemes 8 and 9,... 

Dendrimers have been characterized by a variety of general techniques of analytical chemistry, and also by some specialized techniques that are particularly suitable for dendrimers. The following sections describe these techniques as they have been applied to dendrimers. For more details, the reader is referred to the books fisted in Further Reading section. 

In general, dendrimers show sharp M+ signals at the expected values. This confirms the overall dendrimer structure. Mass spectra may be complicated by the presence of small peaks corresponding to two- or three-molecule aggregates bearing a single charge and this phenomenon is... 

Wiesler U-M, Weil T, Mullen K (2001) Nanosized Polyphenylene Dendrimers. 212 1-40 Williams RM, Stocking EM, Sanz-Cervera JF (2000) Biosynthesis of Prenylated Alkaloids Derived from Tryptophan. 209 97-173 Wirth T (2000) Introduction and General Aspects. 208 1-5 Wirth T (2003) Introduction and General Aspects. 224 1-4... 

Since mild activation conditions appear to be important, a number of solution activation conditions were tested. PAMAM dendrimers are comprised of amide bonds, so the favorable conditions for refro-Michael addition reactions, (low pH, high temperature and the presence of water) may be able to cleave these bonds. Table 1 shows a series of reaction tests using various acid/solvent combinations to activate the dendrimer amide bonds. Characterization of the solution-activated catalysts with Atomic Absorption spectroscopy, FTIR spectroscopy and FTIR spectroscopy of adsorbed CO indicated that the solution activation generally resulted in Pt loss. Appropriate choice of solvent and acid, particularly EtOH/HOAc, minimized the leaching. FTIR spectra of these samples indicate that a substantial portion of the dendrimer amide bonds was removed by solution activation (note the small y-axis value in Figure 4 relative... 

The present volume gives a general and at the same time rather detailed review on main research developments in the field of dendrimers (oligomer and polymer) during the past several years, but also offers views and visions of the future - of what could soon be achieved in this area at the interface between small organic molecules and macromolecules (polymers). We are sure that the rapid development of fractal-shaped molecules will continue in academic institutes as well as in industry - there is still more to come. 

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