Liquid crystal polymers with mesogen

Shibaev, V.P. Freidzon, Ya.S. Kostromin, S.G. Molecular Architecture and Structure of Thermotropic Liquid Crystal Polymers with Mesogenic Side Groups Shibaev, V.P. Freidzon, Ya.S. Kostromin, S.G., Ed. Springer-Verlag New York, 1994, pp 77-120. 

A preparation of new liquid crystal polymers with bilaterally linked mesogens in main-chain was reported [57]. Such materials exhibit biaxial fluctuation in the nematic phase. This is interesting because most commonly encountered polymeric liquid crystals have mesogens linked at their ends to the polymer backbone by flexible spacers. On the other hand, liquid crystal polymers with mesogens linked bilaterally by flexible spacers are not common and only a few examples were reported [58]. One such material can be illustrated as follows ... 

Shibaev, V.P., Freidzon, S., Kostromin, S.G. Molecular architecture and structure of thermotropic liquid crystal polymers with mesogenic side chain groups. In Shibaev, V.P., Lam, L. (eds.) Liquid Crystalline and Mesomorphic Polymers, pp. 77-120. Springer-Verlag, New York (1993)... 

Thermotropic liquid-crystal polymers with mesogenic groups in the main chain only began to be intensely studied in recent years due to their limited solubility and relative infusibility. 

THERMOTROPIC LIQUID-CRYSTAL POLYMERS WITH MESOGENIC GROUPS IN THE MAIN CHAIN... 

Thermotropic Liquid-Crystal Polymers with Mesogenic Groups in the Main Chain 165... 

Thermotropic Liquid-Crystal Polymers with Mesogenic Groups in the Main Chain 181 TABLE 5.2. Data from the x-ray Structural Analysis of LC Polyethers [64-67]... 

Zhang D, Zhou QF, Ma YG, Wan XH, Feng XD (1997) Mesogen-jacketed liquid crystal polymers with mesogens of aromatic amide structure. Polym Adv Technol 8 227-233... 

FIG. 6. Liquid crystal polymers with the mesogen within the main chain, the side chain, and both the main and side chain. From Muller-Goymaim, C.C., Flussigkristalline Systeme in der Pharmazeutischen Technologic, PZ Prisma, 5 129-140 (1998). 

Figure 2. Schematic structure of side chain liquid crystal polymers with dichroic dyes (imparting nonlinear optical properties) and mesogenic side groups.

Copolymerization reactions can use many other combinations, but one interesting reaction involves the modification of poly(ethylene terephthalate) by reacting the preformed polymer with -acetoxybenzoic acid. This has the effect of introducing a mesogenic unit to the structure at the points where the two units combine, producing a thermotropic liquid crystal polymer with a flexible spacer. 

Studied siloxane-based side-chain liquid crystal polymers with cyano-terminated phenyl benzoate mesogenic groups. The technqiues involve the computer-fitting of various Fuoss-Kirkwood lineshapes to the experimental spectra. From a detailed analysis, values for (fi(cos or)) are obtained. Although this is a complex procedure, it provides an attractive route to the measurement of the quality of homeotropic (i.e. normal to the sample surface) orientation in thin films. 

Instead of an isotropic polymer we can use a side-chain liquid crystal polymer with pendant mesogenic groups [256]. The droplets in the polymer matrix are prepared during the polymerization of the prepolymer, containing a low weight nematic. The size of the droplets can be varied upon the rate of polymerization. 

An interesting area, which involves chiral liquid crystal properties, is that of temperature sensors, used, for example, in the diagnosis of skin cancer, as well as in peripheral blood circulation problems. Another application in the medical field is represented by nematic elastomer films or fibers of liquid crystalline polymers with mesogene in the side chain, that can be used in the manufacture of muscle prosthesis [28]. To optimize their performance for different applications, the current knowledge on the relationship between the structure and properties of liquid crystals should be extended. In addition to further development of liquid crystals and their applications, the liquid crystal theories represent a sound basis for other areas of interest. For example, liquid crystals can be used as model compounds for the study of molecular interactions and of their effects on self-organization in supramolecular chemistry. 

Figure 5. Schematic diagram of a SANS experiment on a side group liquid crystal polymer with the mesogenic units aligned by the magnetic field B. Some of the backbones are deuterium labeled so that the area detector measures an anisotropic scattering pattern which is used to determine the dimensions of the backbones.

Vasanthi BJ, Ravikumar L (2013) Synthesis and characterization of poly(azomethine ester)s with a pendent dimethoxy benzylidene group. Open J Polym Chem 3 70-77 Zifa L, Zhang S, Shaokui CAO, Chen Z, Zhou Q (1996) Synthesis and characterization of liquid crystal polymers with T-shaped two-dimensional mesogenic units. Chin J Polym Sci 14 (l) 71-79... 

Shibaev V, Plate NA (1984) Thermotropic liquid-crystalline polymers with mesogenic side groups. Liquid Crystal Polymers II/III. Adv Polym Sci 60/61 173-252 Shibaev VP, Plate NA (1985) Synthesis and structure of liquid-crystalline side-chain polymers. Pure Appl Chem 57 1589-1602... 

Both thermotropie and lyotropic liquid crystal polymers exhibit eharacteristic micro-strueture features [9,10]. Anisometrieal monomers such as rods or disks are conneeted to ehains in an appropriate manner. These anisometrieal monomers are considered the mesogens and may be part of main ehain LCP, side chain LCP, or of both types together (Fig. 6). Flexible spacers of nonmesogenic character are located between the mesogens. A sufficient flexibility is a prerequisite for the liquid crystal formation with an increase in temperature or solvent concentration. 

This polymer suffered thermal degradation only above 400 C, before melting. For molecular weights higher than about 20,000, it showed a lyotropic liquid-crystal behaviour in N-metnypyrrolidone containing LiCl. This is the first reported example of a furanic polymer with mesogenic properties. 

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