Synthesis - Divergent and Convergent Methods

There are two defined methods of synthesis, divergent and convergent. 

Combination of divergent and convergent methods can be exploited to improve the synthesis and purity of dendrimers [4]. 

Two main strategies for the synthesis of dendrimers can be differentiated divergent and convergent methods [123]. The divergent method is particularly suited for the large-scale preparation of dendrimers. However, products often suffer from purification problems and imperfection. In contrast, the convergent... 

Dendrimers produced by divergent or convergent methods are nearly perfectly branched with great structural precision. However, the multistep synthesis of dendrimers can be expensive and time consuming. The treelike structure of dendrimers can be approached through a one-step synthetic methodology.31 The step-growth polymerization of ABx-type monomers, particularly AB2, results in a randomly branched macromolecule referred to as hyperbranch polymers. 

Figure 7.6 The divergent and convergent synthesis methods of dendrimer formation.

The fundamental requirements for the synthesis of dendrimers and hyperbranched macromolecules is examined. Examples of the divergent and convergent approaches are presented and a comparison of both methods with respect to each other and also the one-step procedure for hyperbranched macromolecules is made. The structural similarities and differences between dendrimers and hyperbranched macromolecules are described and the effect of this on the physical properties of these novel three-dimensional materials is discussed. Finally, a comparison of these materials with linear polymers is examined. 

Star and hyperbranched (dendritic) polymers have attracted increasing attention in organic, supermolecular, and polymer chemistry as well as coordination chemistry because of their specific structures and characteristics [1-5]. For the preparation of these highly branched polymers, two kinds of synthetic methods have been developed a one-step pol)nnerization and a stepwise method. By the one-step method, various star and hyperbranched polymers with many structural and functional group variations have been prepared [6-10]. On the other hand, the stepwise method is quite useful, especially for the synthesis of dendritic polymers. Both divergent and convergent s)mthetic approaches have been employed [2,11]. 

In the divergent method (Fig. 4), the molecule is assembled from the core to the periphery, while in the convergent method, the molecule is synthesized from the periphery to the core. In either method, the synthesis requires a stepwise process, attaching each layer to the previous one, purifying and then changing functional groups for the next stage of reaction. 

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