Monomers branch cells

Cores Monomers Branch Cells Dendrons Dendrimers... 

FIGURE 42.20. Approximate nanoscale dimensions as a function of atoms, monomers, branch cells, dendrimers, and megamers. (Reproduced from [129] with permission of Aldrichimica Acta.)... 

A comparison of the covalent connectivity associated with each of these architecture classes (Figure 1.7) reveals that the number of covalent bonds formed per step for linear and branched topology is a multiple (n = degree of polymerization) related to the monomer/initiator ratios. In contrast, ideal dendritic (Class IV) propagation involves the formation of an exponential number of covalent bonds per reaction step (also termed G = generation), as well as amplification of both mass (i.e. number of branch cells/G) and terminal groups, (Z) per generation (G). 

III.) BRANCHED Thermoplastic Divalent Branch Cell Monomers V 0 "AiQrr 0 Z J n... 

IV.) DENDRITIC Thermoplastic Polyvalent Branch Cell Monomers ( l) Z /vZ ( L)... 

New advances beyond the traditional AB2 Flory-type branch cell monomers have been reported by Frechet et al [65, 66]. They have introduced the concept... 

It is apparent that both the core multiplicity (Nc) and branch cell multiplicity (Nh) determine the precise number of terminal groups (Z) and mass amplification as a function of generation (G). One may view those generation sequences as quantized polymerization events. The assembly of reactive monomers [48, 78], branch cells [48, 83, 89] or dendrons [85, 90] around atomic or molecular cores... 

The precise structure subset, dendrimers are prepared using iterative protection-condensation-deprotection reaction cycles. These reiterative cycles incorporate ABn monomers (i.e. branch cell units) into structural domains referred to as dendrons. Assembly of these dendrons can proceed in a divergent [1] (core... 

Figure 27.1 Hierarchy of empirical construction components (A) monomers, (B) branch cells, (C) dendrons and (D) dendrimers leading to (E) core-shell tecto(dendrimers)...

Using more simple reagents and protocols, the GDS strategy has been used to successfully produce over twenty different families of dendrons/dendrimers based on classical repeat (monomer) units and branch cell reagents. Interestingly, these GDS strategies have been used recently by Damha (see Refs. 121-123) to produce dendritic DNA and RNA type structures. 

These three cases are classical examples of fractal curves and dimensions as pioneered by Mandelbrot [96, 97] for macroscopic objects. They suggested to us possible extensions for the creation and analysis of unique spatial organizations of atoms within monomer repeat units, within branch cells, within dendrons, within a dendrimer, to give molecular-level surfaces in three dimensions of nanoscopic properties. 

Alternatively, dendrimers may be synthesized directly by our original II Divergent Core Proliferation method. This method may involve the exponential covalent assembly of monomer units around a multi-valent core to produce branch cells in situ or it may involve the direct use of pre-formed branch cell reagents. In either case the resulting covalent structure consists of precise numbers of dendrons organized around the initiator core. 

Using the convergent strategy described earlier, Frechet et al. [102] completed the synthesis of a series of polyether monodendrons based on the use of 3,5-dihydroxybenzyl alcohol 29 as the branch cell reagent unit. The synthesis is illustrated in Scheme 12 and involves first reaction of benzylic bromide, [G-1]-Br, 28, with monomer, 29, to produce [G-2]-OH, 30. 

Dendritic macromolecules constructed from small-molecule monomers incorporate three major components a core, repeating branch cell units, and a corona or outer shell. The branch cells (BC), also known as repeating units (RU), are defined in terms of a branching angle. 

III.) Branched Thermoplastic Divalent branch cell monomers m z n... 

IV.) Dendritic Thermoplastic Polyvalent branch cell monomers z... 

Z = monomer-shell-saturation level, = core (cystamine) multiplicity, A/t, = branch-cell (BC) multiplicity, G = generation. 

In the case of dendron/dendrimer syntheses, one may view those processes leading to those structures as simply sequentially staged (generations), quantized polymerization events. Of course, these events involve the polymerization of AB2 monomer units around a core to produce arrays of covalently bonded branch cells that may amplify up to the shell saturation limit as a function of generation. 

In summary, it is readily apparent that these abiotic, amplified genealogically directed polymerizations of AB2 monomers have many things in common with biological systems. For example, certain biological processes, such as PCR [92] or cell mitosis [8-10] may be thought of as analogous examples of amplification, but at much larger dimensional scales than are found in dendrimers. Most importantly, branch-cell amplification and DNA amplification may be viewed as special... 

IV.) DENDRITIC Thermoplastic Polyvalent Branch Cell Monomers ... 

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