Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Liquid crystalline state side chains

A block copolymer composed of liquid crystalline polymer (LCP) segments or that composed of segments having an LCP unit in their main chain or side chain was synthesized [67,68]. The latter showed partial compatibility and second-phase separation even when in a melt liquid crystalline state. [Pg.763]

Properties have been determined for a series of block copolymers based on poly[3,3-bis(ethoxymethyl)oxetane] and poly [3,3-bis(methoxymethyl)oxetane]-(ro-tetrahydrofuran. The block copolymers had properties suggestive of a thermoplastic elastomer (308). POX was a good main chain for a well-developed smectic liquid crystalline state when cyano- or fluorine-substituted biphenyls were used as mesogenic groups attached through a four-methylene spacer (309,310). Other side-chain liquid crystalline polyoxetanes were observed with a spacer-separated azo moiety (311) and with laterally attached mesogenic groups (312). [Pg.368]

Schematically the arrangement of a macromolecule with side-chain mesogenic groups in the liquid crystalline state is shown in Fig. 13. Flexible spacers give the mesogenic group its mobility. It is of interest to note that in such liquid crystals all positional mobility of the mesogen is based on conformational motion of the flexible spacer and backbone. Restricting this mobility either prohibits ordering, or freezes the order into the glassy state. Schematically the arrangement of a macromolecule with side-chain mesogenic groups in the liquid crystalline state is shown in Fig. 13. Flexible spacers give the mesogenic group its mobility. It is of interest to note that in such liquid crystals all positional mobility of the mesogen is based on conformational motion of the flexible spacer and backbone. Restricting this mobility either prohibits ordering, or freezes the order into the glassy state.
Attaching non amphiphilic or amphiphilic liquid crystalline molecules as side chains to linear, branched or crosslinkedpolymers yields liquid crystal (l.c.) side chain polymers, which can exhibit the liquid crystalline state analogously to the conventional low molar mass liquid crystals. The l.c.-side chain polymers combine the specific, anisotropic properties of the liquid crystalline state with the specific properties of polymers. [Pg.99]

There have been a lot of studies of cholesteric films and gels in order to exploit their potential as specific optical media and as other functional materials. Most of the preparations were achieved by modification or improvement of previous attempts to immobilize the cholesteric structure of cellulose derivatives into the bulky networks either by crosslinking of cellulosic molecules with functional side-chains in the liquid-crystalline state [203], or by polymerization of monomers as lyotropic solvents for cellulose derivatives [204-206],... [Pg.138]

Liquid crystals can be in the smectic, nematic, or isotropic states. In the smectic liquid crystalline state there is a long-range order in the direction of the long axis of the molecules. These molecules may be in single- or bilayer conformation, have molecular axis normal or tilted to the plane of the layer, and frozen or melted chains. In the nematic liquid crystalline state the molecules are aligned side by side but not in specific layers. The isotropic liquid crystalline state is more or less a liquid state, but where clusters with short-range order persist (Small, 1986, pp. 49-51). [Pg.35]

Physically, the membrane may exist in two states the "solid" gel crystalline and the "liquid" fluid crystalline states. For each type of membrane, there is a specific temperature at which one changes into the other. This is the transition temperature (Tc). The Tc is relatively high for membranes containing saturated fatty acids and low for those with unsaturated fatty acids. Thus, bilayers of phosphatidylcholine with two palmitate residues have a Tc = 41°C but that with two oleic acid residues has a Tc = -20°C. The hybrid has a Tc = -5°C. Sphingomyelin bilayer, on the other hand, may have a Tc of close to body temperature. In the gel crystalline state, the hydrophobic tails of phospholipids are ordered, whereas in the fluid crystalline state they are disordered. At body temperature, all eukaryotic membranes appear to be in the liquid crystalline state, and this is caused, in part, by the presence of unsaturated fatty acids and in part by cholesterol. The latter maintains the fatty acid side chains in the disordered state, even below the normal Tc. There is thus no evidence that membranes regulate cellular metabolic activity by changing their physical status from the gel to the fluid state,... [Pg.250]

The transition moment directions of some of the absorption bands of PBLG in liquid crystalline state have been investigated in a CaF2 cell by means of the infra-red dichroic ratio (56). All the transition moment directions measured at 1 °C are very similar to those observed 32) on mechanically oriented films of PBLG (Table 2), verifying that all the polymer molecules present a parallel or nearly parallel orientation in the molecular cluster and that the main chain and the side chains of the polymer molecule are fixed as in the solid film. No significant difference is observed between the systems of solution testing. The orientation of the solvent molecules (methylene moletules) is detected in an electric field in accordance with the NMR observation (56). [Pg.86]

To obtain amphiphilic polymers, different concepts are conceivable to introduce amphiphilic moieties into the polymer backbone. They are schematically summarized in Figure 5. Polymers of type A and B can be realized, if a polymerizable group is introduced into the hydrophobic group (type A) or hydrophilic group (type B) of a conventional surfactant, which exhibit the liquid crystalline state in solution. Copolymerization of a hydrophilic and a hydrophobic comonomer yields amphiphilic copolymers of type C. According to the convention, these polymers may be called "amphiphilic side-chain polymers"... [Pg.8]

To function properly, cell membranes must exist primarily in the liquid-crystalline state. Model studies using synthetic lipids have demonstrated that the presence of a (9Z)-olefinic fatty acyl side chain in a diacylphospholipid lowers its gel-liquid phase temperature (T ) by some 50° C relative to its fully saturated analog (4). The presence of the A fatty acyl side chain lowers the T even more and constitutes an important adaptation to chilling for plants. The regulation of the response to chilling temperatures has been studied in some detail in various organisms (4). [Pg.493]

The two-step synthesis process shown in Figure 2 affords several possibilities for preparing new side-chain liquid crystal polymers. The polymerization process allows one to vary the molecular weight and molecular weight distribution (MWD), and potentially change the properties of the liquid crystalline state. Most of the polyphosphazenes reported in the literature, including the examples in this paper, are derived from the bulk uncatalyzed process this... [Pg.186]

At 80°C, the polymers with more than 10 carbon atoms are in the liquid crystalline state. Low mobility of the side chain prevents the polymers of n 9 to be in the thermotropic liquid crystal. The existence of the discontinuity is evidence for the solvent like nature of the side chains in the thermotropic liquid crystalline phase. [Pg.286]

Poly(aspartates) and poly(glutamates) with -alkyl chains as the side chains take on the liquid crystalline state under any conditions such as temperature variation, the side-chain length variation, etc., as the macroscopic structure, and also take various main-chain conformations. In poly(aspartates) and poly(glutamates) with long -alkyl side groups such as -octadecyl groups, between which the difference is the number of CH2 carbons between the C and ester carbonyl carbons, i.e., the former has one CH2 carbon and the latter two CH2 carbons. By elevating the temperature the latter forms a... [Pg.828]

Mesogens in the side-chain have not yet lead to clearly identified condis states of the flexible spacers, probably because of the need of longer spacers. Usually the liquid crystalline state changes on cooling directly to the LC glass. [Pg.95]

In the preceding chapters the synthesis properties of linear liquid crystalline polymers are described, where different approaches exist to obtain the liquid crystalline state rod-like or disc-like mesogenic units are either incorporated in the polymer backbone or are attached as side groups to the monomer units of the main chain. Following conventional synthetic techniques these linear polymers can be converted to polymer networks. Compared to low molar mass liquid crystals and linear liquid crystalline polymers, these liquid crystalline elastomers exhibit exceptional new physical and material properties due to the combination and interaction of polymer network elasticity with the anisotropic liquid crystalline state. [Pg.277]

Polymers with side chain structure similar to that of low molecular weight liquid crystalline compounds can achieve various levels of organization in the bulk. These polymers are sometimes formed by polymerization of vinyl monomers that themselves exhibit mesomorphic behavior. In other cases, they can be obtained from monomers that do not form liquid crystalline states. At one extreme the structure of the polymer is highly organized, approaching that of crystalline polymers and giving rise to a number of x-ray diffraction peaks. At the other extreme the polymer chains are disorganized, with x-ray diffraction patterns that resemble those from amorphous polymers. [Pg.1]

Let us emphasize the main facts for alkyl-substituted stiff macromolecules. The conformation of the main chain is affected by side groups and depends critically on the chain length. For relatively short side chains hexagonal packing of macromolecules is possible, whereas for longer chains the boardlike shape of the molecules leads to formation of a highly ordered layered structure. In the crystal state the coplanar arrangement of the fully extended aromatic backbone for polyesters is possible. In the liquid crystalline state both a well-ordered layered structure and a nematic structure are observed. Because of the boardlike shape of the molecules, the nematic phase is biaxial. [Pg.149]


See other pages where Liquid crystalline state side chains is mentioned: [Pg.431]    [Pg.285]    [Pg.399]    [Pg.124]    [Pg.459]    [Pg.30]    [Pg.105]    [Pg.240]    [Pg.41]    [Pg.130]    [Pg.92]    [Pg.354]    [Pg.81]    [Pg.504]    [Pg.52]    [Pg.198]    [Pg.199]    [Pg.194]    [Pg.289]    [Pg.829]    [Pg.93]    [Pg.85]    [Pg.198]    [Pg.199]    [Pg.92]    [Pg.432]    [Pg.486]    [Pg.114]    [Pg.424]    [Pg.24]    [Pg.280]    [Pg.374]    [Pg.39]   
See also in sourсe #XX -- [ Pg.336 , Pg.337 ]




SEARCH



Crystalline state

Liquid crystalline state

Liquid side-chain

Liquid-side

Side chain crystallinity

© 2024 chempedia.info