Liquid-crystal oligomer

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

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. 

Main-chain ferroelectric liquid crystal oligomers (MW 6000) have been made by the ADMET polymerization of H2C—CH(CH2)70C6H4C6H4C00C6H3(N02) OCHMe(CH2) CH=CH2(M = 2-4) using 18 at 80°C as a catalyst (Walba 1996). 

S. Furutni, N. Tamaoki, Glass-forming cholesteric liquid crystal oligomers for new tunable solid-state laser. Adv. Mater. 22, 886-891 (2010)... 

Sato, M. Yoshizawa, A. Electro-optical switching in a blue phase III exhibited by a chiral liquid crystal oligomer. Adv. Mater. 2007, 19, 4145-4148. 

Walba DM, Keller P, Shao RF, Clark NA, Hillmyer M, Grubbs RH (1996) Main-chain ferroelectric liquid crystal oligomers by acyclic diene metathesis polymerization. J Am Chem Soc 118(11) 2740-2741. doi 10.1021/ja953779z... 

Side chain crystallisation or side chain interactions ( with partial and/or full intercalation) occur and play a dominant role in the determination of the structure of many organic polymethylenic systems such as liquid crystal oligomers and polymers etc. X ray structure determinations on polyalkylthiophenes are presently being performed by various groups [164-165]. 

Certain diglyceryl alkyl ethers (vide supra) that form, by self-assembly, liquid crystals have a future in nanochemistry [46, 47]. Evidently, therefore, selective catalytic synthesis of specific oligomers of glycerol in a shape selective environment (vide supra) will contribute significantly to the generation of new classes of bio-and nano-materials. 

Keith C, Dantlgraber G, Reddy RA, Baumeister U, Prehm M, Hahn H, Lang H, Tschierske C (2007) The influence of shape and size of silyl units on the properties of bent-core liquid crystals - from dimmers via oligomers and dendrimers to polymers. J Mater Chem 17 3796-3805... 

The filtrate from the nutsch filter enters receptacle 9, and from there into vapour-heted tank 10 for distilling chlorobenzene in vacuum (chlorobenzene is sent back to synthesis). The cooled oily residue from the tank is sent into nutsch filter 13 to be separated into crystals (raw phosphonitrilechloride trimer) and oily liquid (phosphonitrilechloride oligomers). Trimer crystals are sent into collector 14 (it is also filled with light petroleum, which does not dissolve oily oligomers). The emulsion formed in the collector is sent into extractor 16. A temperature equal to the boiling point of light petroleum is maintained in this apparatus. 

B) Ion-exchange of silicate oligomers with Br and OH" to form inorganic-organic aggregates. (C) Self-assembly of SLC meso-phases. D4R = double four ring SLC = silicatropic liquid crystal. 

Materials 27 and 28 decomposed above ca. 200 °C. Regarding the high thermal stability of the model compounds, this result was unexpected and was attributed to the presence of unreacted end-groups. None of the l,l -isomeric structures 28 exhibited liquid crystal properties before decomposition. Interestingly, oligomers 27 clearly showed nematic phases between ca. 180—200 °C. 

Liquid polymers (at ambient temperature) are in general macromolecules with a relatively low molecular weight, many of them being in fact oligomers. Some liquid polymers are utilized as synthetic oils. Certain polymers can form liquid crystals in other words they can have an ordered structure while being in liquid state (either melted or in a solution). The orientation of certain polymeric molecules in liquid state such that the properties of the material are anisotropic is possible. Polymer liquid crystals have practical applications, and solution of liquid crystal polymers can be used for extruding fibers that have a highly crystalline structure after solvent elimination. 

When surface active agents are considered, a further complication may be encountered. Because of their surface active nature, the surfactants not only emich at the surfaces, but also form extended structures themselves. At low concentrations, the surfactants remain as dissolved monomers or asssociate to oligomers. However, when the critical micellization concentration (cmc) is surpassed, a cooperative association is activated to micelles (1 to 10 nm) consisting typically of some 50 to 100 monomers. At stiU higher concentrations, or in the presence of cosurfactants (alcohols, amines, fatty acids, etc.), liquid crystalline phases may separate. These phases have an infinite order on the x-ray scale, but may remain as powders on the NMR (nuclear magnetic resonance) scale. When the lamellar liquid crystalline phase is in equilibrium with the liquid micellar phase the conditions are optimal for emulsions to form. The interface of the emulsion droplets (1 to 100 pm) are stabilized by the lamellar liquid crystal. Both the micelles and the emulsions may be of the oil in water (o/w) or water in oil (w/o) type. Obviously, substances that otherwise are insoluble in the dispersion medium may be solubilized in the micelles or emulsified in the emulsions. For a more thorough analysis, the reader is directed to pertinent references in the literature. ... 

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