Functionalized mesogens

Beside the synthesis of linear polysiloxanes, hydrosilylation was also nsed to obtain liquid crystalline elastomers. This can be performed in two ways, either a one pot reaction involving a diolefln together with the functionalized mesogen or a two step process involving first the synthesis of a linear polysiloxane, bearing adequate functions for a further crossfinking. For example, a photosensitive group such as benzophenone could be introduced (Fig. 5, x and y are theoretical values). In order to ensure a full conversion in silane, the time of reaction was increased here to 65 h [17]. 

Another type of supramolecular side-chain polymers (shown in Fig. lOB) is obtained by the complexation of functionalized mesogenic molecules with polymer backbones. The hydrogen-bonded complex of 37 is obtained by mixing poly(4-vinylpyridine) or poly(4-vinylpyridine-co-styrene) with mesogenic compounds terminated by a carboxylic acid moiety through a flexible spacer [84-88]. The hydrogen bonding between imidazole and carboxylic acid is also useful for the formation of supramolecular complexes. Polymeric complex 38 exhibits a smectic A phase from 10 to 65 °C [89]. 

Figure 3.19 Molecular components for ionic complexes of simple functional polymers and functionalized mesogens.

Figure 3.25 Representation of ionic complexes prepared from poly(ethylene imine) and carboxylic acid-functionalized mesogens.

Figure 3.27 Schematic representation comparing (a) an ionic complex of a cationic polymer and an anionically functionalized mesogen, (b) an ionic complex of a cationic polymer and an anionic surfactant, and (c) a polymer to which a mesogen is covalently attached at a cationic site neutralized by a counterion.

End-functionalized mesogenic molecules are used to form the second type of supramolecular side-chain polymers (Figure 2(a) [ii], Figure 23) [97-108], Polymeric complex 28 has been prepared based on poly(4-vinylpyridine) [97], The hydrogen-bonding formation between imidazole and carboxylic acid moieties yields supramolecular side-chain polymers of 29 [103], which exhibit smectic A phases. The interactions of carboxylic acid/dialkylamine [104-106], phenol/amine [107], and hydroxyl/pyridine [108] were used for the preparation of the side-chain mesogenic complexes. 

As indicated in Figure 8, the crosslinking of discotic monomers might lead to insulated wires. The crosslinking of diacetylene-functionalized mesogens via a topochemical polymerization in a columnar phase was reported, but no electronical charartetization was performed. ... 

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