Hydrocarbon side-chain liquid-crystalline

Hydrocarbon Side-Chain Liquid Crystalline Polymers... 

Chang-Chien, G., Terminally carboxyl oligo(ethylene oxide) monomethyl ether-substituted side chain liquid crystalline polysiloxane polymer as stationary phase in capillary gas chromatography for the separation of polynuclear aromatic hydrocarbons, J. Chromatogr. A, 808, 201-209, 1998. 

Arehart SV, Pugh C (1997) Induction of smectic layering in nematic liquid crystals using immiscible components. 1. laterally attached side-chain liquid crystalline poly(norbomene)s and their low molar mass analogs with hydrocarbon/fluorocarbon substituents. J Am Chem Soc 119 3027-3037... 

Polymer A showed a crystalline X-ray diffraction pattern and an endothermic peak at 31-42 C in differential scanning thermograms. The polymer had birefringence below 90 C under a polarizing microscope. It is of interest to speculate as follows. Both of the hydrocarbon side chains and the polysaccharide main chains are crystalline and the polymer A exhibits a unique two-stage melting process of both crystalline regions. The polymer possibly forms a liquid-crystalline mesophase between these two transition temperatures. 

Cho et al. described the synthesis and polymerization of 4,8-cyclododeca-dien-l-yl-(4 -methoxy-4-biphenyl) terephthalate VIII [54,55]. Polymerization was carried out with WCl4(OAr)2/PbEt4. The double bonds in the polymer backbone were subsequently hydrogenated with H2/Pd(C), leading to a SCLCP with a fully saturated hydrocarbon backbone. This polymer system had a very flexible polymer backbone but a stiff connection between the main chain and the mesogenic unit. The distance between two adjacent side chains was about 12 methylene units. This very flexible main chain allowed the polymer to organize into a LC mesophase. Both polymers - the unsaturated and the saturated -showed smectic liquid crystalline mesophases with almost the same transition temperatures (see Table 5). 

The introduction of perfluorinated groups generally favors microphase separation due to the immiscibility of fluorocarbons with hydrocarbons [66]. Norbornene derivatives with perfluorinated endgroups in the side chain were prepared by Wewerka et al. [67]. Monomer XII contained a relatively long (CF2)8-chain, separated via a long spacer (11 methylene-groups) from the norbornene, whereas monomer XIII has two relatively short (CH2)2(CF2)4-side chains (Fig. 11). Homopolymers and block copolymers were synthesized with one fluorinated monomer (XII or XIII) and one non-fluorinated non-liquid crystalline monomer (NBDE or COEN) with the Schrock-type initiators 4 and 5, respectively, leading to microphase-separated block copolymers. Table 9 and Table 10 summarize the physico-chemical properties of the homopolymers and block copolymers. 

To summarize our results on side-chain all-hydrocarbon LC polymers [I], we found that they displayed Smectic E phases at lower temperatures and Smectic B phases at higher temperatures. The corresponding LC monomers exhibited only Smectic B phases. The presence of tails seems to enhance and stabilize liquid crystallinity. The monomers and polymers that do not have tails are not liquid crystalline. All of the substituted biphenyl hydrocarbon liquid crystals found in the literature are disubstituted. Examples of monosubstituted biphenyl hydrocarbon liquid crystals have not been found. The results obtained from this work support the idea that disubstitution of the biphenyl moiety is necessary to obtain a liquid crystalline phase. 

The stracture of the cell plasma membrane is illustrated in Figure 7.7. The phosphohpid molecules aggregate into a bilayer which serves to remove the hydrophobic chains from the aqueous environment and place a polar, hydrophilic head group at eaeh side of the bilayer which is exposed to water. The bilayer aggregate is liquid crystalline in nature, in that the head groups do not have any periodic ordering and the hydrocarbon chains are not rigid. The liquidity of the stracture aUows the movement of phospholipid molecules about the cell membrane. Of course, the associated proteins can also move within the cell membrane but they do so more slowly. This liquid crystalline stractrrre of the cell membrane provides form and allows the selective movement of materials in and out of the cells. 

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