Ionic dendrimers

In addition to alkyl-substituted derivatives, soluble PPPs 6 are also known today containing alkoxy groups as well as ionic side groups (carboxy and sulfonic acid functions) [18]. Schliiter et al. recently described the generation of soluble PPPs decorated with densely packed stcrically demanding dendrons on the formation of cylindrically shaped dendrimers, so-called cylinder dendrimers ] 19]. 

Dendrimers can be constructed from chemical species other than purely organic monomers. For example, they can be built up from metal branching centres such as ruthenium or osmium with multidentate ligands. The resulting molecules are known as metallodendrimers. Such molecules can retain their structure by a variety of mechanisms, including complexation, hydrogen bonding and ionic interactions. 

Ionic interactions have been used to prepare lanthanide-core dendrimers. This has been achieved using a convergent synthesis, in which polyether den-drons with a carboxylic acid group at the focal point were assembled around a lanathanide cation. This involved a metathetical reaction with compounds such as Er(OAc)3, Tb(OAc)3 or Eu(OAc)3 to introduce the appropriate lanthanide ion. 

Engel, R., Ionic dendrimers and related materials, Adv. Dendritic Macromol., 2, 73, 1995. 

As described below, ionic catalyst complexes can be supported to both inorganic and polymer (dendrimer) carriers. The efficiency of the support is determined by the general rules of ion exchange and, for this reason, in order to achieve a successful approach it is important to exclude the formation or presence of other ionic compounds, which might compete for (liberate) the catalyst ion from the support. 

Structure controlled dendritic polymers that have been studied using gel electrophoresis generally behave as mimics of either proteins or nucleic acids, and possess similar ionic groups such as -NH3 , -COO , or P04 functionality. Dendrimer structures may be widely modified as a function of their interior composition and as well as the nature of their surface groups. Depending on their structure, the influence of pH may vary dramatically for different dendrimers. 

PAMAM dendrimer in methanol[19], and larger also than the 60 A maximum physical radius of a completely stretched structure, but has been employed consistently. In terms of the model, some of the scatter in Figure 4 can be explained by considering that the radius of gyration of this polyelectrolyte is likely to depend on the ionic strength, pH, and even the concentration of borate diesters (internal cycles) none of these factors were systematically controlled in this study. 

Recently fluorinated chains were also attached to amine based dendrimers, like PPI and poly(amido amine) (PAMAM), by means of ionic self assembly with semiperfluorinated alkanoic acids (Fig. 71, 216, 217). All dendrimer complexes 216 with perfluorinated alkanoic acids show SmA phases except the fifth generation dendrimer which shows a Colrec phase [378]. Also semiperfluorinated 4-alkoxybenzoic acids 217 [379] and mixed systems combining fluorinated and nonfluorinated alkanoic or benzoic acids (216, 217) have been reported [379-381]. In most cases layer structures (SmA) and for higher generation dendrimers also modulated SmA phases (Colrec phases) were observed. The layer thickness of the SmA phases of the mixed complexes 216 depends on the ratio of fluorinated and non-fluorinated acids, where smaller d values were observed for dendrimers with low Rp-content for Rp-rich dendrimers the more rigid Rp-chains provide... 

Ionic dendrimers [57] can bear positive or negative electric charges in the interior of the molecule (core, branching units) or on terminal (functional) groups. 

Van Koten et al. successfully prepared silicon-based dendrimers with a polyca-tionic branching shell. The dendrimer type shown in Fig. 4.37 consists of a non-polar core (tetraarylsilane) bearing an ionic layer which, in turn, is surrounded by a less polar polyether shell [67]. Such dendrimers are predestined for potential inclusion of anionic guests - with anion exchange - in the positively charged host scaffold. 

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