Frechet dendrimer

Commercially available POPAM and PAMAM dendrimers (see Chapter 4) bearing terminal primary amino groups are currently the most commonly used divergently grown dendrimer structures, followed by poly(benzyl ether) den-drons or poly(benzyl ether) dendrimers (Frechet type) as representatives of con-vergently synthesised dendritic molecules. 

However, dendrimeric and hyperbranched polyesters are more soluble than the linear ones (respectively 1.05, 0.70, and 0.02 g/mL in acetone). The solution behavior has been investigated, and in the case of aromatic hyperbranched polyesters,84 a very low a-value of the Mark-Houvink-Sakurada equation 0/ = KMa) and low intrinsic viscosity were observed. Frechet presented a description of the intrinsic viscosity as a function of the molar mass85 for different architectures The hyperbranched macromolecules show a nonlinear variation for low molecular weight and a bell-shaped curve is observed in the case of dendrimers (Fig. 5.18). 

J.M.J. Frechet and D. TomaUa, Dendrimers and Other Dendritic Polymers, Wiley, Chichester, 2001. 

Fig.1. Rotaxane dendrimers from crown ether type macrocycle ring, bipyridinimn derivatives rod component and Frechet-type dendron stoppers...

Fig. 2. Rotaxane dendrimers from isophthalamide [2]rotaxane-core and Frechet-type den-dron stoppers...

JMJ Frechet, DA Tomalia (2001) Dendrimers and other Dendritic Polymers. Wiley, Chichester, UK. GR Newkome, CN Moorefield, F VBgtle (2001) Dendrimers and Dendrons. Wiley-VCH,Weinheim, Germany. 

In 2008, these authors reported a new strategy to attach chiral trans-l-arenesulfonylamino-2-isoborneolsulfonylaminocyclohexane to an achiral Frechet dendron (polyether having a repeated 3,5-dioxybenzyl structure) by a radical approach.The dendrimers obtained were successfully used in the enantioselective nucleophilic alkylation and arylation of ketones, providing... 

Chiral //A(oxazolinc) ligands disubstituted at the carbon atom linking the two oxazolines by Frechet-type polyether dendrimers coordinated with copper(II) triflate were found to provide good yields and moderate enantioselectivities for Mukaiyama aldol reactions in water that are comparable with those resulting from the corresponding smaller catalysts.291 AgPF6-BINAP is very active in this reaction and the addition of a small amount of water enhanced the reactivity.292... 

A large family of new dendrimers has been synthesized following this divergent method. Hawker and Frechet developed polyaryl(-benzyl)ether dendrimers [27], Miller andNeenan [28], and also Moore and Xu [29] prepared hydrocarbon dendrimers. The latter have reported the largest monodisperse organic hydrocarbon dendrimer with a molecular mass of 18 kDa and a diameter of 12.5 nm [30]. 

Fig. 3i-iii. Dendrimer synthesis using branched building blocks i Denkewalter s polylysine dendrimers ii Newkome s polyamide dendrimers iii Frechet s aryl ether dendrimers... 

Fig. 6. Frechet s water-soluble poly aryl ethereal dendrimer...

Delivery of physically encapsulated small molecules at targeted sites by dendrimers has been superbly envisioned in a recent report by McGrath and Junge [95]. Second generation Frechet type dendrons linked to a central azo-benzene-derivative (32, Fig. 15) underwent reversible cis/trans isomerization of... 

Solvatochromic probes have been used for a variety of applications like the study polarity of pure and mixed solvents [99], and the retention behavior in reverse-phase liquid chromatography [100] among other applications. Frechet et al. used 4-(N-methylamino)-l-nitrobenzene (p-MANB), as the chromophore, to probe the microenvironment of polyaromatic ether based dendrimers [101]. 

Moss and Liao [182,183] reported a metallo-dendrimer built by a convergent strategy. An approach similar to that of Frechet was used to synthesize a fourth generation dendrimer containing 48 peripheral ruthenium atoms. 

Following the convergent procedure, dendrimers of type 58,59 and 60 have been prepared from the chiral core triol 54 and achiral Frechet-type [62] ben-zylic branch bromides. In the series of dendrimers with aromatic spacers (60) and without spacers (58), the optical activity [a]D decreased on going from the 1st (not shown in Fig. 21) to the 2nd generation, whereas with aliphatic spacers... 

J. M. J. Frechet and D. Tomalia, Dendrimers and other dendritic polymers, Wiley, New York, 2001. 

Unlike linear or ordinary branched polymers, dendrimers display intrinsically low viscosity, even at high mass. As standard polymeric molecules increase in mass and size, their viscosity normally increases continually. With dendrimers, viscosity increases only up to about the fourth generation, after which it actually begins to decline (Mourey, 1992 Frechet, 1994). In addition, with control over the type of pendent groups that adorn the surface, dendrimers can maintain high solubility regardless of size. 

Eichman, J.D., Bielinska, A.U., Kukowska-Latallo, J.F., Donovan, B.W., and Baker Jr., J.R. (2001) Bioapplications of PAMAM dendrimers in dendrimers and other dendritic polymers. In Wiley Series in Polymer Science (M.J. Frechet, and D.A. Tomalia, eds.), pp. 441M61. John Wiley Sons, Ltd, West Sussex, UK. 

Frechet, J.M.J. (1994) Functional polymers and dendrimers Reactivity, molecular architecture, and interfacial energy. Science 263, 1710-1715. 

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