Dendrimers, polymeric

Figure 3.18 Polymeric dendrimer coatings on glass. (From Renters, R. et al.. Nucleic Acid Res., 30(2), 1-7, 2002. With permission.)...

A small, non-polymeric dendrimer with a. solid core and 27 alcohol end groups was obtained from l,3,5-tris(bromomethyl)benzene, the sodium enolate of triethyl methanetricar-boxylate, and 2-amino-2-(hydroxymethyl)-l, 3-propanediol ( TRIS"). This highly water-soluble compound, a so-called arborol , forms globular micelles containing about 40 molecules (G.R. Newkome, 1986). 

Table 1.A Characterization of arborescent polystyrene [88]a (polymeric dendrimer)...

The physical properties of these polymeric dendrimers have been studied to some extent. Intrinsic viscosity measurements combined with MW afford values of according to Eq. (5). Alternatively, the translational diffusion coefficient leads to Rh according to Eq. (6). These equations may well be applicable, since it is observed that Rn and Rh scale with the 1/3 power of MW in support of the equal density hard-sphere assumption [88]. 

Multiple weak interactions allow small pharmaceutically active molecules to be trapped in polymeric dendrimers. Over time the molecules slowly break free and are released in a controlled manner to the sites where they are required. The formation of dendrimer prodrugs allows for covalent attachment of many copies of a drug to a single dendrimer. Under predetermined conditions, such as pH or oxygen content, the bonds break and the drug is released in a concentrated burst. Weak interactions can also be harmful. The entanglement of small amyloid proteins appears to be responsible for the formation of plaques associated with Alzheimer s disease. The presence of transition metals poses an added complication as they have been implicated in protein crosslinking. A multifunctional molecule that can both disrupt... 

The macromolecules treated here may be considered as either dendrimers with polymeric cores or alternatively dendronized polsrmers (or polymers with ap-pendent dendrons) depending on whether one sees them from the vantage point of an organic or macromolecular chemist (Fig. 1). The first view is somewhat puzzling, because dendrimers are normally considered monodisperse, which they certainly are not (16), whereas polymeric dendrimers are intrinsically polydisperse. At best the pol5mieric core may have a narrow molecular weight distribution. Not considered here are polymers which do not carry dendrons at every repeat unit (r.u.) but at a few ones only, eg, at both termini (17-22), as well as works on... 

The materials chemistry we discussed in Chapter 13 was in some ways "classical", in that we were making polymers from monomers that have fairly conventional functional groups. Nylon has been around a long time, and while new advances such as group transfer polymerization, dendrimers, and metallocene catalysts continue to vitalize the field, the production of polymers is a relatively mature industry. 

Keywords metathesis, polymerization, dendrimer, arene, iron, olefin... 

One of the most important applications of the dendronized supports is the preparation of support-bound dendritic catalysts. Such systems, based on outward branching dendrons, were prepared and explored by the groups of Alper and Arya, Reymond, Portnoy, Kawi, Rhee, and Sreekumar. A number of heterogeneous dendritic catalysts based on a different design (e.g., polymerized dendrimers bearing catalytic units) are also known, but are beyond the scope of this book. ° ... 

Recently, there has been much interest in the use of structurally perfect polymeric dendrimers (see Chapter 5) as stabilizing templates for nanocluster growth. By varying the peripheral groups and number of repeat branching units (known as... 

In (he first example, the perfluorocyclopoitene bridge was bound to positions 3 and 3 of the thienyl groups, whereas in (he product 72 (he fluorinated fragment was linked with positions 2,2 and 3,3 of dithienothiophene and thiophenes, respectively. The photochromic polymeric dendrimers 73 in which (he multiple bond of the bridge was also connected with positions 2,2 of the benzothienyl rings were described in [78]. 

---