Mesogenic oligomer

MONTE CARLO SIMULATIONS OF LIQUIDS OF MESOGENIC OLIGOMERS... 

Liquid crystalline main chain polymers with siloxane spacer groups were obtained by the hydrosilation of (Si—H) terminated polydimethylsiloxane oligomers and mesogenic groups with terminal double bonds as shown in Reaction Scheme XVII-(a). Reactions were usually carried out in THF with the Wacker Oil catalyst 255). Completion of the reactions was followed by the disappearance of the strong (Si—H) absorption band at 2140 cm-1 using IR spectroscopy. 

Note 2 The term is also used for the group linking two or more mesogenic units in liquid-crystal oligomers. 

Highly branched oligomer or polymer of dendritic structure containing mesogenic groups that can display mesophase behaviour. 

Figure 23 Synthesis of twin discotic dimer and branched oligomers from CTTV-7 mesogens connected with a hexadecane spacer. (From Ref. 76.)...

Polymers of this type have been prepared with various mesogenic units connected by oligomers of poly(ethylene oxide), PEO, and it is possible in some cases to use spacers having a broad distribution of molecular weights instead of a monodisperse molecular species. It shoxxld be noted that each oxyethylene unit adds three bond lengths to the spacer, so the comparison of polymers with different types of spacers should be between spacers having the same numbers of atoms in the spacer chain. 

Cyclic main-chain liquid crystal oligomers have been shown to display a number of crystalline polymorphs in addition to smectic and nematic phases.133 These collapsed rings have rigid mesogens in their stems while folds form selectively in the flexible spacer. Significant difference between even and odd-membered rings are seen, particularly where the flexible spacer is short. 

Various mesogenic groups were connected through oligomers of polyfethylene oxide), even with a polydisperse distribution of chain lengths. However, to understand the individual effect exerted by the polyfethy-lene oxide) spacers it is necessary to employ monodisperse molecular species. It is im-... 

Scheme 10a in Fig. 5 represents the formation of low-MW closed assemblies such as host-guest complexes, supermolecules, and cyclic oligomers. Examples include the supermolecules 11 and 12 and the cyclic folic acid tetramer (3 in Fig. 3). These compounds aroused interest due to their pronounced thermotropic behaviors compared to the unbound components. The enhancement of liquid crystallinity for Complex 11 is explainable by general consideration of soft interactions in low-MW mesogens. " More complex is the case of Complexes 12 and 3 that, due to discotic shape, can form columnar stacks. A close relationship between liquid crystallinity and columnar growth was anticipated.However, recent analysis showed that columnar growth of the folate tetramer receives only a minor contribution from contact forces. The large excluded volume effect of thin disks is the main driving force for liquid crystallinity and self-assembly.

This paper describes novel approaches to the exploitation of both furan monomers and a specific facet of furan reactivity in order to synthesize either conjugated oligomers incorporating the heterocycle in their backbone, or polymeric structures which can be crosslinked and returned to linear structures through the reversible chemistry of the Diels-Alder reaction. The first family of compounds showed interesting features in terms of conductivity, luminescence, mesogenic character and photoactivity. The second class of materials owes its interest to the possibility of recycling otherwise intractable polymers, e.g. tires, thanks to a simple thermal process. 

These conjugated oligomers are likely to form organized molecular assemblies if coupled with suitable complementary structures. The dimers la and Ila-IId were made to react with various aromatic mono- and diamines in order to build mesogenic molecular structures capable of giving rise to thermotropic liquid ciystals ( ). When the dimer moiety was entirely furanic, no mesophase appeared, whereas the thiophenic and mixed moieties produced clear-cut nematic phases. 

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