Dendrimers skeleton

Attaching the functionality to already constructed dendrimer skeletons by suitably refunctionalizing the end groups or other moieties in the dendrimers 14 141... 

Divergent or convergent synthesis of dendrimers which already carry the desired functionality in the branching unit, i.e within the dendrimer skeleton.11 10 11 19 21 221... 

Way (3) (Figure 12) also leads to polyfunctional-ized molecules. In most cases, it involves a considerable synthetic effort, since it is necessary to synthesize the whole dendrimer skeleton de novo. Moreover, the functionalities which are introduced have to tolerate the often quite drastic reaction conditions of the dendrimer synthesis. The advantage of... 

Dendrimers are ideal scaffolds to construct these devices since (i) a large number of proper redox units can be placed in the periphery and/or branching points of their structure with the possibility of tuning their distance, (ii) the dendrimer skeleton can be designed to minimize electronic interaction between the redox centers, and (iii) the dendrimer periphery can be optimized to get the desired solubility properties and processability to eventually deposit the dendrimers on a surface. Other possible scaffolds are constituted by polymers11 and nanoparticles,12 which are easier to synthesize, but they do not enable control and tuning of the number, position, and distance of the active units. 

Sharpless et al. noted an increase of the specific rotation with increasing generation number in the case of dendrimers having trimesic acid as achiral core unit and a completely chiral polyether dendrimer skeleton based on 1,2-diol branching units (Fig. 4.72) [27]. The observed molar optical rotations corresponded to... 

Recently, Soai et al. reported the synthesis of series of chiral dendrimer amino alcohol ligands based on PAMAM, hydrocarbon and carbosilane dendritic backbones (Figure 4.31) [99-102]. These chiral dendrimers were used as catalysts for the enantioselective addition of dialkylzincs to aldehydes and N-diphenylphosphi-nylimines (Scheme 4.25). The molecular structures of the dendrimer supports were shown to have a significant influence on the catalytic properties. The negative dendrimer effect for the PAMAM-bound catalysts was considered due to the fact that the nitrogen and oxygen atoms on the dendrimer skeleton could coordinate to zinc. 

This work demonstrates that functionalization of the internal cavities of various dendrimers can be done via a post modification of the skeleton. Various functional groups can be selectively introduced aminophosphite, aldehyde, hydrazone, dichlorophosphane sulfide. Therefore all the chemistry reported on the surface of dendrimers can be now envisaged to be done into the cavities and it is demonstrated for the first time that a macromolecular chemistry can be performed into the internal voids of a dendrimer. 

Figure 12. Way (3) Synthesis of dendrimers functionalized in the core, in the skeleton, and on the periphery.

A closer investigation of the hyperbranched base polyester reveals that the repeating unit can be incorporated in three different ways in the polymer skeleton, assuming that no side reactions occur. The terminal units all have both their hydroxyl groups left unreacted (C), while bis-MPA in interior layers are either fully branched or linearly incorporated (B) (Figure 8). These linearly incorporated building blocks do not exist in a dendrimer. In order to mimic these differently incorporated building blocks, low molar mass model compounds were synthesized and characterized with C-NMR (Table 5). The base polyesters were subsequently... 

The dendritic core adopts an extended conformation which is possible due to the great flexibility (conformational freedom) of the PAMAM and PPI skeletons. In this way, the molecular model of thick disks proposed for the LC dendrimers with two-terminal chain mesogenic units is transformed into a model consisting of a long cylinder, which is the result of the axial elonga-... 

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