Carboxylic acid-functionalized mesogen

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

The polymeric complexes derived from 4-nitro- and cyanostilbazoles also show a smectic A phase up to about 200 °C [78a]. Polysiloxane complexes 32 also exhibit thermally stable smectic A or C mesophases [79-81]. These carboxyl-functionalized polymers and stilbazoles are miscible in a whole range of composition and show stable mesomorphic behavior [26, 79]. The introduction of the chiral stilbazole for the formation of a mesogenic complex leads to the induction of ferroelectricity [80]. Polymeric complex 33 exhibits a chiral smectic C phase, while no ferroelectricity is observed for each of single components. The value of spontaneous polarization for 33 x — 0.43, n = 5) is 21.0 nC/cm at 112 °C. The hydrogen bonding between the carboxylic acid and... 

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]. 

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. 

The use of hydrogen bonding for mesogenic network formation has been expected for the formation of dynamic mesomorphic states due to the induction of dynamic properties, e.g. reversibility and fast exchange of the H-bonding [108-111]. Supramolecular liquid-crystalline networks have been prepared by the self-assembly of a polyacrylate with a benzoic acid moiety and 4,4 -bipyridine [108]. Complexes 46 form dynamically cross-linked structures obtained by the complexation of a carboxyl-functionalized polyacrylate and a mixture of a stilbazole, which has the single H-bond acceptor, and a bipyridine, which has the two acceptors. 

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