Divergent-growth synthesis

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... 

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... 

Scheme 30.18 Accelerated synthesis of a fourth-generation bis-MPA dendrimer using CuAAC click coupling reactions in combination with esterification chemistry by the divergent growth approach. Reproduced with permission from Ref [132] 2007, The Royal Society of Chemistry.

Scheme 30.19 The rapid synthesis of a sixth-generation dendrimer using an orthogonal AB2 — CD2 divergent growth approach employing both thiol-ene and CuAAC click coupling reactions, (i) Thiol-ene coupling (ii) CuAAC (iii) Thiol-ene coupling (iv) CuAAC (v) Thiol-ene coupling (vi) CuAAC. Reproduced with permission from Ref [133] 2010, American Chemical Society.

Figure 18 Schematic representation of the synthesis of Arborols using the classical divergent growth.

In 1989, Fr chet and co-workers first reported the convergent growth approach [8,9]. In contrast to the divergent growth approach, dendrimer construction is initiated at what will eventually become the outer surface shell of the ideally branched macromolecule and proceeds inward, by a stepwise addition of branching monomers, followed by the final attachment of each branched dendritic sub-unit (or dendron ) to a poly-functional core. This synthesis generated a poly(aromatic ether) dendrimer and a repetitive sequence of Williamson ether coupling and bromination reactions were employed as shown in Scheme 8.1. 

The synthesis of radially layered poly(amidoamine-organosilicon) (PAMAMOS) copolymeric dendrimers starts from amine terminated PAMAM dendrimers, which, in turn, are obtained by a well-known excess-reagent divergent growth method that involves a reiterative sequence of (a) Michael addition reactions of methyl acrylate (MA) to primary amines, and (b) amidation of the resulting methyl ester intermediates with ethylenediamine (EDA), as shown in Reaction Scheme 1 (39-41). These PAMAM dendrimers are commercially obtained from Dendritech Inc., (Midland, MI) and they can be used for PAMAMOS preparation without any further purification. The synthesis then involves another Michael addition reaction, this time of a silylated acryl ester, such as (3-acryloxypropyl)dimethoxymethylsilane, as shown in Reaction Scheme 2 (4). 

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