Liquid crystals main-chain

Muller K, Kothe G (1985) NMR dudies of liquid crystal main chain polymers. Ber. Bunsen Ges. Phys. Chem. 89 1214... 

Fig. la-d. Molecular structures of rod-like (calamitic) and disc-like (discotic) liquid crystals a) Low molecular weight liquid crystals, b) liquid crystal main chain polymers, c) liquid crystal side chain polymers, d) combined main-chain/side-chain polymers... 

Fig. 13. Molecular structures of the liquid crystal systems studied Liquid crystal side chain polynKrs (1,2), liquid crystal main chain polymers (3,4) and low molecular wdght analogues (5-8). The Greek letters, a, P, 8, ip and ip, refer to five different derivatives of the same liquid crystal, deuteriated at different sites of the mesogen or alkyl chain, as indicated in the formula of liquid crystal polymer 4...

Table 3. Constant parameters used in the analysis of NMR experiments of liquid crystal main chain polymers and corresponding model compounds...

TaUe 7. Conformational order of liquid crystal main chain polymers and low molecular weight analogues, characterizing the order gradient in the nematic phase (T 0.85)... 

Beyer P, Terentjev EM, Zentel R (2007) Monodomain liquid crystal main chain elastomers by photocrosslinking. Macromol Rapid Commun 28(14) 1485-1490. doi 10.1002/ marc.200700210... 

Krause S, Dersch R, Wendorfif IH, Finkelmann H (2007) Photocrosslinkable liquid crystal main-chain polymers thin films and electrospinning. Macromol Rapid Commun 28(21) 2062-2068. doi 10.1002Anarc.200700460... 

RIGID MA -IHHHHh IN CHAIN -o-o-o-o- -(KHKF LIQUID CRYSTAL MAIN CHAIN POLYMERS iia NEUATIC SUCCTIC... 

J. Hirschinger, W. Kranig, and H. W. Spiess, A deuteron NMR study of axial motion and side chain conformation in the mesophase of discotic liquid crystal main-chain polymers. Colloid Polym. Sci. 269 993-1002 (1991). 

Gao et al. have recently prepared a number of thermotropic liquid crystalline main-chain fer-rocenes exhibiting fluorescent properties.182 The reaction of 1,1 -bisf functionalized)ferrocenes, 95, with 1,4-dibromobutane, 97a, or a,a -dibromo-p-xylene 97b generated polyelectrolytes 97a,b with Mn ranging from 5400-14,700 (Scheme 2.29). These polymers were highly thermally stable with the first weight loss occurring between 172 and 330°C. The liquid crystalline properties showed these materials formed smectic liquid-crystal phases and displayed batonnet textures. 

Some studies dealing with the solid state properties of graft copolymers with liquid-crystal side chains have appeared in the literature [353-355]. The main attention is focused on the influence of molecular parameters (nature of the backbone and the side chains, molecular weight, etc.) on the mesomorphic properties of the liquid-crystal side chain. Salt complexes of PEO grafted onto various backbones were also considered [356] and the influence of the nature of thebackbone and salts on the conductivity of the resulting materials was studied. 

The thermal behavior of liquid crystalline main chain polymers is more complicated. Depending on thermal history, different transitions may occur. The DSC curves of samples quenched from the melt may show the glass transition (positive ACp), cold crystallization (exotherm), melting (endotherm)and the mesophase-isotropic liquid transition (endotherm)[ Fig. I6]. ... 

Dobb, M.G., McIntyre, J.E. (1984) Properties and applications of liquid-crystaUine main chain polymers, in Liquid Crystals Polymers //////. Advances in Polymer Science 60/61, (ed. N.A. Plate), Springer Verlag, Berhn, pp. 61-91. 

Hydrated bilayers containing one or more lipid components are commonly employed as models for biological membranes. These model systems exhibit a multiplicity of structural phases that are not observed in biological membranes. In the state that is analogous to fluid biological membranes, the liquid crystal or La bilayer phase present above the main bilayer phase transition temperature, Ta, the lipid hydrocarbon chains are conforma-tionally disordered and fluid ( melted ), and the lipids diffuse in the plane of the bilayer. At temperatures well below Ta, hydrated bilayers exist in the gel, or Lp, state in which the mostly all-trans chains are collectively tilted and pack in a regular two-dimensional... 

Liquid crystals based on aliphatic isocyanides and aromatic alkynyls (compounds 16) show enantiotropic nematic phases between 110 and 160 °C. Important reductions in the transition temperatures, mainly in clearing points (<100 °C), areobtained when a branched octyl isocyanide is used. The nematic phase stability is also reduced and the complexes are thermally more stable than derivatives of aliphatic alkynes. Other structural variations such as the introduction of a lateral chlorine atom on one ring of the phenyl benzoate moiety or the use of a branched terminal alkyl chain produce a decrease of the transition temperatures enhancing the formation of enantiotropic nematic phases without decomposition. 

In general terms, high molar mass liquid crystals are classified according to the location of the mesogenic unit in the polymer. Thus, they are either incorporated into the main chain (main-chain liquid crystal polymers - MCLCP Fig. 5A) or they are pendant from the main chain (side-chain liquid crystal polymers - SCLCP Fig. 5B). 

Fig. 5 Schematic representation of the molecular arrangement in A main-chain and B side-chain liquid crystal polymers...

Phospholipids, which are one of the main structural components of the membrane, are present primarily as bilayers, as shown by molecular spectroscopy, electron microscopy and membrane transport studies (see Section 6.4.4). Phospholipid mobility in the membrane is limited. Rotational and vibrational motion is very rapid (the amplitude of the vibration of the alkyl chains increases with increasing distance from the polar head). Lateral diffusion is also fast (in the direction parallel to the membrane surface). In contrast, transport of the phospholipid from one side of the membrane to the other (flip-flop) is very slow. These properties are typical for the liquid-crystal type of membranes, characterized chiefly by ordering along a single coordinate. When decreasing the temperature (passing the transition or Kraft point, characteristic for various phospholipids), the liquid-crystalline bilayer is converted into the crystalline (gel) structure, where movement in the plane is impossible. 

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