Mesogenic moiety, liquid

With these three different examples it has been demonstrated that the systematics observed for the polymorphism of m-l.c. s is also valid for the side chain polymers, provided that a flexible spacer connects the rigid mesogenic moieties to the polymer main chain. Deviations from this behavior are observed, when the mesogenic moieties are directly linked to the backbone. Under these conditions, normally no liquid crystalline behavior is to be expected, according to the model considerations mentioned in Chap. 2.1. Some examples, however, proved l.c. properties for such systems, which are characterized by two striking properties Very high glass transition temperatures and only smectic structures even in case of short substituents... 

Since their discovery in the nineteenth century [1], hquid crystals have fascinated scientists due to their unusual properties and their wide range of potential apphcations, especially in optoelectronics. LC systems can be divided into two categories thermotropic LC phases and lyotropic LC phases. Thermotropic LC systems result from anisotropic molecules or molecular parts (so called mesogens or mesogenic moieties, respectively), and form hquid crystalline phases between the soHd state and the isotropic hquid state, where they flow like liquids but possess some of the characteristic physical properties of crys-... 

SCLCPs combine liquid crystalline properties and polymeric behavior in one material. If the mesogenic unit is fixed directly to the polymer main chain, the motion of the liquid crystalline side chain is coupled with the motion of the polymer backbone, preventing the formation of a LC mesophase. Therefore, Finkelmann and Ringsdorf proposed that the introduction of a flexible spacer between the main chain and the mesogenic unit would decouple their motions, allowing the mesogenic moiety to build up an orientational order [29,30]. 

Complementary dendritic hexamers based on a central scaffold made up of linked pentaerythritol and tri(hydroxymethyl)amino methane units have been found to also exhibit liquid-crystalline properties. This star-shaped scaffold was used to create supermolecules containing two different hemispheres, referred to thereafter as Janus supermolecular Hquid crystals (Fig. 76) [323,324]. One of the hemisphere contains three cyanobiphenyl end-groups, whereas the other lobe consists of three chiral phenyl benzoate mesogenic moieties laterally attached. The type of mesophase observed (N ... 

Liquid-Crystalline Character of Novel Main-Chain Oligophosphates Bearing Lipophilic and/or Mesogenic Moieties... 

In a recent article we have established the liquid crystalline behavior exhibited by a, to diphosphate amphiphiles (20) Prompted by this investigation we decided to study the liquid crystalline character of their polymeric counterparts, i.e. of polyphosphates or rather oligophosphates ( Scheme I) prepared by the reaction of phosphorous oxychloride with 1,12 dodecanediol and 1,16 hexadecanediol respectively. In addition, the mesomorphic behavior of oligophosphates bearing the biphenyl mesogenic moiety was compared with the liquid crystalline behavior of the purely aliphatic oligophosphates. 

When the mesogen moiety is included into the main chain of the polymer, the obtained macromolecule contains inherently rigid units, which usually result in remarkable mechanical properties and thermal stability. Fibers made by these polymers compete with the best ceramic fibers and are far superior to metal fibers [83]. They therefore are ideal candidates as reinforcements for polymer-based composites. However, these materials often have a poor miscibility and adhesion to other polymeric substrates, limiting the range of their applications. This problem basically arises from weak intermolecular interactions either within the liquid-crystalline polymer itself or with the matrix of the composite. Strong ionic... 

The next family of materials, which are to be discussed all possess cyanobiphenyl moieties as the mesogenic units. The systematic studies of the liquid crystal properties are described in terms of spacer length and peripheral number density. The first material, 37, shown in Fig. 35, is an octamer based on the octasilsesquioxane core unit [86]. This material was prepared and purified in such a way that by HPLC and 29Si NMR spectroscopy it was shown to be a single compound without dispersity. The material was found to exhibit smectic polymorphism with SmC and SmA phases being formed. The incorporation of cyanobiphenyl mesogenic moieties means that the material has interesting... 

A PAP may be either amorphous or liquid crystalline and usually comprises suitably functionalized photochromic azobenzene and mesogenic moieties as side groups. The latter play an important cooperative or synergistic role with the photo-chromic group enhancing the overall birefringence (photoinduced anisotropy). 

For commercial TLCPs having their mesogenic moieties contained within the main chain of the polymer, this structure is often nematic. Nematic order in the liquid crystalline phase is shown schematically in Figure 3. The nematic phase is the LCP phase of lowest order, consisting of aggregates of rod-like molecules. Within each aggregate, or domain, the molecules have a distribution about a common axis, denoted by n.. No order exists, however. 

Kato T, Kondo G, Hanabusa K. 1998a. Thermoreversible self organized gels of a liquid crystal formed by aggregation of trans 1,2 bis(acylamino)cyclohexane containing a mesogenic moiety. Chem Lett 3 193 194. 

Liquid-crystalline (LC) silsesquioxanes having various mesogenic moieties were synthesized by the hydrosilylation reaction of octa(hydridosilsesquioxane) and terminal alkenes with mesogenic groups using hexachloroplatinic acid as a catalyst... 

These results show that the side chain polymers fit the model well. Furthermore they confirm the expected analogy of these spacer-group-containing polymers with conventional liquid crystals that nematic and smectic phases can be realized, depending on the para substituents of the mesogenic moieties. 

Liquid crystalline polymers in which the mesogenic moiety is incorporated into the polymer main chain are of two types i) rigid segments joined by flexible segments ii) totally rigid segments (with very little or no chain flexibility)... 

Various aspects of liquid crystallinity in flexible polymers with the mesogenic moiety in the side group are discussed in several articles. The focus here is on the liquid crystalline behavior in electric fields and possible applications of PLCs in electro-optical display and recording. The properties of a novel group of PLCs — liquid crystalline elastomers — obtained from mesogenic side group systems are also described. 

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