Thermotropic liquid crystals preparation

The raw materials from which di-D-fructose dianhydrides can be obtained in appreciable yield are readily available from comparatively inexpensive agricultural feedstocks. Thus, these compounds are attractive as chiral-starting materials for chemical synthesis. Their stability to acid and heat, and their relative rigidity, because of the conformational constraints covered here, are also features that might be exploited during syntheses.119 A series of variously substituted di-D-fructose dianhydrides has been prepared,119 starting from 6,6 -dideoxy-6,6 -di-halosucroses. The properties of these and other derivatives of di-D-fructose dianhydrides are summarized in Tables XIV-XX. Two of these derivatives, 48 and 56, exhibit thermotropic liquid-crystal properties.119... 

Several cyclopropanated organofullerene materials have been synthesized for the preparation of fullerene-containing thermotropic liquid crystals. A wide variety of such liquid-crystalline materials were synthesized possessing mono-140-42], hexa-addition [43] pattern, or even dendritic addends [44-46]. 

The cyclopentane ring has already been used to prepare thermotropic liquid crystals [23]. In 17, the bulky ferrocene core, due to its depth, acts as a spacer... 

It should be mentioned that crystal structure data are often obtained from co-solvent systems (Desai and Klibanov, 1995). For example, crystals of ubiqui-tin, papain and a heptapeptide were grown from 30% polyethylene glycol (PEG) 4000, 62% MeOH and a DMSO/isopropanol mixture, respectively (Kamphius et al., 1984 Karle et al., 1993 Love et al., 1997). The orthogonal and tetratogonal crystal forms of cyclosporine were prepared from 25% PEG 300 and acetone, respectively (Petcher et al., 1976 Kessler et al., 1985 Loosli et al., 1985 Verheyden et al., 1994a). Furthermore, cyclosporine and leuprolide form thermotropic liquid crystals when dried from EtOH and lyotropic liquid crystals when solubilized in PG, respectively (Tan et al., 1998 Lechuga-Ballesteros et al., 2003 Stevenson et al., 2003). 

Techniques for phase identification are similar to those employed for thermotropic liquid crystals, although there are differences. Thus, optical microscopy is the most common technique used, but rather than prepare multiple samples at a range of concentrations it is more common to perform Lawrence Penetration Experiments [189]. In this experiment, some solid surfactant (maybe up to 50 mg) is placed on a microscope slide and a cover slip placed on the top. Water (or which ever solvent is to be used) is placed at the end of the cover slip and proceeds from one end to the other by capillary action, thus, setting up a concentration gradient across the sample. Now, at any given temperature, it is possible to have a snapshot of the whole phase diagram, and clear phase boundaries can often be seen. This experiment can be very... 

The interest of 2,6-dialkylnaphthalenes as starting materials in the production of polyester fibers and plastics with superior properties [1, 2] and of thermotropic liquid crystal polymers [3] is clearly shown by the increasing number of recent patents relevant to their preparation and separation[3.5]. However, the selective formation of 2,6-dialkylnaphthalenes is not obvious, not only with conventional Friedel-Crafts catalysts [6-8], but also over solid catalysts such as silica-alumina [9-11] or zeolites. 

Ringsdorf s research group have prepared novel types of rigid-rod polyesters and polyamides 56 with a disc-like mesogen in tte mainchain [75]. Most polymers with six lateral substituents appear to be thermotropic liquid crystals. Polyamides with Z = H and having four substituents on the diamine component are not liquid crystalline. The two substituents on the diacid component seem to contribute to decrease further the intermolecular hydrogen bonding. 

To our knowledge, this is the first example of the coexistence of both twisted smectic and cholesteric phases in thermotropic liquid crystal polymers. Previous preparations of thermotropic polymers by the use of chiral derivatives both incorporated in the macromolecular backbone and pendant to it as side chain substituents (comb-like polymers) resulted in either cholesteric or smectic " polymeric products. 

Only a few examples of optically active ferrocene-containing thermotropic liquid crystals have been reported. Compounds (304) and (305) have been prepared by functionalizing ferrocene with a chiral fragment bearing an asymmetric carbon atom. Ferrocene derivative (304) showed an SmC phase, while for (305), SmC, SmA, TGBA, N, and blue phases (blue phases are referred to in Section 7.9.4.3.3) were obtained. " Ferrocene has also been substituted with a cholesterol derivative but the mesophases were not identified. ... 

A new set of carbohydrate-based thermotropic liquid crystals (17) have been prepared via reaction of the oxetan (18)(derived from glucose) with lithium acetylide reagents followed by catalytic hydrogenation. A related series of 2,5-anhydro-hexitol derivatives (19) have been prepared by a similar route, reacting the oxetan with long-chain alcohols in presence of trifluoroacetic... 

According to the phase diagram schematically shown in Fig. 4.7, two types of liquid crystal ordering with different preparation methods can be categorized. One is the lyotropic liquid crystal approached by changing the concentration in solutions. The other is the thermotropic liquid crystal approached by changing the... 

Fig. 4.7 Schematic picture of typical phase diagram of polymer solutions combining L-L binodal (Iso), L-S coexistence (Cr), and L-liquid crystal-S coexistences (LC). The two arrows in the picture show the preparation methods of thermotropic liquid crystal and lyotropic liquid crystal, respectively (Keller 1992)...

Even the first thermotropic liquid crystals (cholesterol benzoate and cholesterol acetate) were chiral molecules, and their chiral mesophases were observed [2]. Here, the chirality is taken from the chiral pool. Because liquid crystals are needed in gram scales for physical research and technical applications, they should be prepared by short synthetic pathways using easily available starting materials. Thus, synthetic strategies based on the chiral pool are more often used than asymmetric synthesis or chiral separation techniques. 

Donnio B, Wermter H, Finkelmann H (2000) A simple and versatile synthetic route for the preparation of main-chain liquid-crystalline elastomers. Macromolecules 33 7724—7729 Finkelmann H (1987) Liquid crystal polymers. Chap 1. In Gray GW (ed) Thermotropic liquid crystals. Wiley, Chichester, pp 1-27... 

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