Dendrimers side-chain liquid-crystalline

Fig. 35 Relationship between dendritic core deformation and mesogen type and the conformation of the side-chain liquid crystalline dendrimers...

The mesogenic behavior of 43 emphasizes the role played by the oc-tasilsesquioxane core when comparing with the related side-chain liquid-crystalline polysiloxanes [95,96]. It is remarkable that the thermal stability of the chiral nematic phase is similar in both the polymer and the dendrimer, suggesting that the cubic core does not perturb significantly the associations between the mesogens necessary to support the chiral nematic phase. 

More recently, a systematic study of the properties of side-chain LC dendrimers has been undertaken on these PPI dendrimers and also on PAMAM systems by Serrano et al. [211]. In these dendrimers, the mesogenic group is connected to the dendritic scaffold by an imine linkage. In all cases, it was found that the enthalpic gain of the mesogenic units arranged as in a classical liquid crystalline mesophase dominates over the entropic tendency of the dendrimer core to adopt a globular isotropic conformation. The flexibility of the dendritic PAMAM and PPI cores allows the macromolecule to adopt... 

Side-chain LC dendrimers exhibiting the nematic mesophase, which is the most disordered liquid crystalline phase, can also be achieved by the appropriate choice of the mesogenic unit(s) attached to the dendrimer central core. For example, side-chain PPI-derived dendrimers containing mesogenic units of type Li (Fig. 28) but with short terminal alkoxy chains (ethoxy, butoxy... 

Figure 1. Structures of liquid crystalline polymers (LCPs) (A) rigid rod LCP [25, 65] (B) main chain LCP with flexible spacer [26] (C) side group LCP with flexible spacer [27] (D) combined main/side group LCP [28] (E) side group LCP without flexible spacer or mesogen jacketed LCP [29], (F) well-defined three-arm star [30] (G) LC dendrimer [33].

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