Dendrimer synthesis divergent

Meijer and co-workers also used a divergent dendrimer synthesis to prepare AB diblock structures (Figure 7.13B) in which the polystyrene linear block is used to initiate growth of the polypropylene imine) dendritic block [45], An amino end group had to be introduced in the polystyrene as a core for subsequent growth of the dendritic fragment via an iterative protocol of sequential... 

To obtain polystyrene-poly(propylene imine) block copolymers, the divergent dendrimer synthesis as described in 2.1 was performed onto the PS-CH2-O-CH2-CH2-CH2-NH2 core molecule, with M = 3.2kgmor (based on GPC of PS-CH2-OH). 

Gossage, R. A., Munoz-Martinez, E., Frey, H., Burgath, A., Lutz, M., Spek, A. L., Van Koten, G. A novel phenol for use In convergent and divergent dendrimer synthesis access to core functlonallzable trifurcate carbosllane dendrimers-the X-ray crystal structure of [1,3,5-trls 4-(triallylsllyl)phenyl ester benzene]. Chem.- Eur. J. 1999, 5, 2191-2197. 

Figure 18 Schematic representation of divergent dendrimer synthesis (top) and convergent synthesis (bottom). Reproduced from http //en.wikipedia.org/wiki/Dendrimer.

D. Supramolecular Aspects of the Classical Divergent Dendrimer Synthesis... 

Further evidence to support the role of self-assembly in divergent dendrimer synthesis can be found in the construction of poly(amidoamine) PAMAM dendrimers. First, ideality and fidelity of structure is usually a signature of a self-assembly event. This is a universal observation throughout biological systems. In all cases, nearly ideal PAMAM structures are obtained only under mild conditions favoring such organizational events as a prerequisite to bond formation [88]. Attempts to impose more severe reaction conditions (i.e., reaction temperature >40 C) dramatically reduces the ideality of dendrimer structures even in the early generations. Under mild, kinetically favorable reaction conditions however, nearly ideal dendrimer structures are obtained up to the onset... 

Each step in dendrimer synthesis occurs independent of the other steps therefore, a dendrimer can take on the characteristics defined by the chemical properties of the monomers used to construct it. Dendrimers thus can have almost limitless properties depending on the methods and materials used for their synthesis. Characteristics can include hydrophilic or hydrophobic regions, the presence of functional groups or reactive groups, metal chelating properties, core/shell dissimilarity, electrical conductivity, hemispherical divergence, biospecific affinity, photoactivity, or the dendrimers can be selectively cleavable at particular points within their structure. 

Figure 8. Doubly exponential dendrimer synthesis involving simultaneous growth in divergent and convergent directions.

The concept of repetitive growth with branching was first reported in 1978 by Vogtle [4] (University of Bonn, Germany) who applied it to the construction of low molecular weight amines. This was followed closely by the parallel and independent development of the divergent, macromolecular synthesis of true dendrimers in the Tomalia Group [5,6] (Dow Chemical Company). The first... 

In order to investigate dendrimers of a different nature [230], Bradley described the synthesis and transfection efficiency of polyamidourea dendrimers synthesised from isocyanate-containing AB3 monomers [231-234]. The use of this kind of tris-branched building block was addressed to enhance dendrimer synthesis by replacement of the 1,4-addition step typical of PAMAM synthesis and to a rapid increase in terminal functionality. The dendritic structures were synthesised using a divergent, microwave-assisted, solid-phase approach with the dendrimers assembled on polystyrene resin via an acid labile linker (see Fig. 26). In particular, a G3.0 polyamidourea bis-dendron with the peripheral amino groups conjugated to L-lysine residues demonstrated remarkable transfection abilities [234],... 

Scheme 1 Schematic representation of divergent and convergent approaches to dendrimer synthesis...

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