Hawker and Frechet

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]. 

The concept of making brush-type polymers in which a linear polymer is funtionalized with dendritic side-chains was first suggested by Tomalia in a 1987 patent, though actual experimental work on his approach was only reported recently recently [15]. Hawker and Frechet were first to document the preparation of a vinyl copolymer containing a few pendant Frechet-type dendrons (Figure 7.9). 

Frechet and coworkers have popularized poly(aryl ether) dendrimers and polyester dendrimers (Fig. 13.7), which have been widely used (Hawker and Frechet 1990 Dire et al. 1998). Addition of the aromatic rings adds rigidity to the dendiimer framework that is lacking in the PPI and PAMAM dendrimers. The polyester dendrimers may be more like the PPIs and PAMAMs in terms of rigidity, but the ester linkages enable degradation of the polyester dendrimers by esterases in vivo. Thus, the biological stability of the PAMAMs and the polyester frameworks is quite different. 

Path B in Fig. 2 is the convergent method. It is the outside-inward method, proposed independently by Miller and Neenan [9] and by Hawker and Frechet [10]. This method is well suited when the branch point is an aromatic ring. As an example of the convergent process we show in Scheme 3 the preparation of poly(benzyl ether) dendrimers. The phenol functionality of 2,5-dihydroxyben-zyl alcohol is first protected by Williamson reaction with benzyl bromide to provide the first generation dendron [G-l]-OH. The benzyl alcohol in [G-l]-OH is then converted to the benzyl bromide form [G-1]-Br. This in turn reacts with... 

At about the same time as Hawker and Frechet s publication1 1 of the convergent methodology, Miller and Neenan reported131 the synthesis of monodisperse molecular... 

Hawker and Frechet in 1992 [18]. However, only in the last 4 years has the maturing of dendrimer synthesis and related characterization methods made it possible to study dendron (macro) monomers and to exploit their potential for the synthesis of dendron-bearing polymers. 

Developed by Hawker and Frechet in 1989—1990, the poly(benzyl ether) synthesis10 65 75 makes use of 3,5-dihydroxybenzyl alcohol (Scheme 1) as the mono-... 

The macromonomer approach refers to the polymerization of a monomer that is functionalized with a dendron. The first attempts to make these compounds via the convergent approach were reported by Hawker and Frechet and utilized a fourth genera-... 

The second option is the convergent approach, as introduced in 1990 by Hawker and Frechet [67], In this approach, dendritic wedges, so-called dendrons, are produced first and assembled on the core molecule in the last step, e.g. [68, 69]. A benefit of this route is that it is possible to mix wedges with different terminal groups with the opportunity to synthesize designed dendrimer surfaces and multifunctional dendrimers. 

Following the first papers of Tomalia et al. (1985) and Newkome et al. (1985) dealing with dendrimers, a large number of dendrimers have been presented in the literature ranging from polyamidoamine (Tomalia et al., 1991), polyethers (Hawker and Frechet, 1990 Padias et al., 1987), and polyesters (Miller et al., 1992 Ihre et al., 1996) to polysilane (van der Made and van Leeuwen, 1992). Copolymers of linear blocks with dendrimer segments (dendrons), block copolymers of different dendrons, and polymers with dendritic side chains (Frauenrath, 2005) have been described. 

Many methods have been reported to synthesize hyperbranched polymers. These materials were first reported in the late 1980s and early 1990s by Odian and Tomalia [9], Kim and Webster [10], and Hawker and Frechet [11]. As early as 1952, Hory actually developed a model for the polymerization of AB -type monomers and the branched structures that would result, identified as random AB polycondensates [46], Condensation step-growth polymerization is likely the most commonly used approach however, it is not the only method reported for the synthesis of statistically branched dendritic polymers chain growth and ringopening polymerization methods have also been applied. 

Dendrimer-d-polyethyleneoxide-/> Polyether dendrimers from Hawker and Frechet [132] used [2, 49, 250]... 

In 1990, Hawker and Frechet described the convergent (ontside-in) approach, where dendritic polyethereal macromolecnles, based on 3,5-dihydroxybenzyl alcohol as the building block, were synthesized. That same year, Neenan reported the convergent synthetic approach of dendrimers based on 1,3,5-trisubstituted benzenes. " Since then, research on dendrimers has grown to such an extent... 

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