Dendrimers monodisperse

Figure 2 Schematic representation of the difference in the morphology of dendrimer (monodisperse) and Hyperbranched polymer (polydisperse). 

This modular concept allows for the synthesis of monodisperse dendritic phen-ylene dendrimers of the first (43a, 22 benzene rings) and second (43b, 62 benzene rings) generation [65]. Due to the dense packing of the phenylene rings, shape-persistent nanostructures result. Several of these large phcnylene-type dendrimers (e.g. 43a) can be further cyclized to giant polycyclic PAHs. 

Dendrimers have structures similar to that of hyperbranched polymer and can be taken as the perfectly branched polymer with monodispersity. However, they need to be prepared by a multistep procedure. Therefore, very little work has been done on dendritic polyfarylcnc ether)s. Morikawa et al. prepared a series of monomers with a various number of phenylene units.164,165 These monomer were used to prepare poly(ether ketone) dendrons with graded structures (Scheme 6.24). 

The sequential growth and branching involved in the preparation of dendrimers had been considered by Flory many years before they were actually prepared. Flory developed a sound understanding of the kind of processes that would occur in the self-polymerization of a molecule of the type ABj most of which have been shown to be correct by the relatively recent experimental studies. In particular, the existence of a limit to growth was predicted. This limit has become known as the starburst limit, and is the reason for the highly monodisperse nature of fully developed dendrimers. 

All the fullerene-containing dendrimers reported to date have been prepared with a Cgo core but never with fullerene units at their surface or with Cgg spheres in the dendritic branches. We have recently started a research program on the synthesis of dendrons substituted with fullerene moieties. These fulleroden-drons are interesting building blocks for the preparation of monodisperse fullerene-rich macromolecules. In addition, they are also amphiphilic compounds capable of forming stable Langmuir films at the air-water interface. 

This Topics volume also shows that in the development of dendrimer chemistry there is still a need for efficient synthetic methods ensuring multiple high-yield conversion and leading to more or less pure (monodisperse, structurally perfect) dendritic molecules. Large libraries of imperfect substances are often formed at higher generations, only differing in small structural details. 

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]. 

H. Baigude, K. Katsuraya, K. Okuyama, S. Tokunaga, and T. Uryu, Synthesis of sphere-type monodispersed oligosaccharide-polypeptide dendrimers, Macromolecules, 36 (2003) 7100-7106. 

The monodispersed nature of dendrimers has been verified extensively by mass spectroscopy, size exclusion chromatography, gel electrophoresis and electron microscopy (TEM). As is always the case, the level of monodispersity is determined by the skill of the synthetic chemist, as well as the isolation/purification methods utilized. 

As discussed earlier, mass spectroscopy has shown that PAMAM dendrimers (Figure 1.17) produced by the divergent method4 are very monodisperse and... 

Dendrimers with terminal functional groups represent mode compact precursors that are spherical and almost monodisperse, with reactive groups placed on their periphery. Their synthesis, structure and properties have been reviewed in monographs and review articles often together with hyperbranched polymers (cf., e.g. [15-20]), as well as in this book. Application of dendrimers as precursors for conventional materials is limited at this time by their relatively high cost. 

In summary, dendrimers are a unique class of monodispersed synthetic molecules reminiscent of proteins or nucleic acids. If they can be functionalized to be soluble in water with appropriately charged terminal groups, they are generally ideal candidates for gel electrophoretic analyses. 

It is widely recognized that dendrimers are the first synthetic structure controlled polymers that rival the control and monodispersity observed for proteins. Their precise masses and behavior as analytes on electrophoretic gels demonstrate the contention that dendrimers (i.e. specifically poly(amidoamines)) may be viewed as artificial proteins . 

In the AFM images of Figure 12.15, one can see many separated and randomly deposited globular particles on the mica surface. In each image, the particles appear to be substantially uniform in size, i.e. they are essentially monodisperse. This is not surprising if each bright spot represents a single dendrimer molecule. 

As outlined in other chapters in this volume, Tomalia et al. first reported the successful well-characterized synthesis of dendrimers in the early 1980s [1], These molecules range in size from 10 A to 130 A in diameter for generation 0 (GO) through generation 10 (G10). In the ideal situation, PAMAM dendrimers are monodispersed spherical conformation with a highly branched three-dimensional structure (Figure 18.1) that provides a scaffold for the attachment of... 

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