Polymer mesogenic

Griffin, A. C. and Havens, S. J. Mesogenic polymers. III. Thermal properties and synthesis of three homologous series of thermotropic liquid crystalline backbone polyesters. J. Polymer Sci., Polymer Phys. Ed. 19, 951 (1981)... 

Figure 14.25 Mesogenic polymers. The mesogenic groups may (a) form part of the main chain or (b) be attached as side chains.

The transition regions in liquid crystalline polymers or mesogenic polymers is much more complex. These transitions are referred to as mesomorphic transitions, and occur when one goes from a crystal to a liquid crystal, from a liquid crystal to another liquid... 

Finklemann, H., Laub, R.J., Roberts, W.E., and Smith, C.A., Use of mixed phases for enhanced gas chromatographic separation of polycychc aromatic hydrocarbons. II. Phase transition behavior, mass-transfer non-equilibrium, and analytical properties of a mesogen polymer solvent with silicone diluents, in Polynuclear Aromatic Hydrocarbons, Phys. Biol. Chem. 6th Int. Symp., Cooke, M., Ed., Battelle Press, Columbus, OH, 1982, p. 275. 

For polymers which, on heating, yield Mesophases (liquid crystal melts), the so-called mesogenic polymers or liquid crystal polymers (LCPs), the situation of phase transitions is much more complex. In this case the simple Volume-Temperature diagram, given in Fig. 4.2 is not valid anymore and has to be substituted by a more complicated one, which is shown in Fig. 6.12. 

Measurement techniques of the elastic moduli, 388 Mechanical behaviour and failure, 819 Mechanical comfort, 879 Mechanical properties of solid polymers, 383 various materials, 389 Melt/Melting, 167, 700 elasticity, 316 expansion, 97 flow index, 801, 802 flow rate diagram, 801 fracture, 578 number, 579 strength, 799, 812 Merkel number, 59 Mesogenic groups, 34 in the main chain, 177 side-chain, 179 Mesogenic polymers, 172... 

The orientation-dependent, soft interactions here considered doubtless play an important role in polymers and copolymers exhibiting mesomorphic behavior. Such polymers typically contain aromatic residues, having large anisotropies, as integral members of the chain backbone. These interactions are especially prominent in melts and concentrated solutions, as has been pointed out. Their influences in mesogenic polymers have received little attention. 

Fig. 2. A portion of the phase diagram for mesogenic polymer-solvent system...

Solid formulations for sustained drug release may contain mesogenic polymers as excipients. The mesogenic polymers form a matrix, which is usually compressed into tablets. Some of the most frequently used excipients for sustained release matrices include cellulose derivatives, which behave like lyotropic liquid crystals when they are gradually dissolved in aqueous media. Cellulose derivatives such as hydroxy-propyl cellulose or hydroxy-propylmethyl cellulose form gel-like lyotropic mesophases in contact with water, through which diffusion takes place relatively slowly. Increasing dilution of the mesophase with water transforms the mesophase to a highly viscous slime and then to a colloidal polymer solution. 

Table 23 demonstrates the mesogenicity of polymers containing biphenylene-S j -tetracarboxylic imide. A comparison of series 9 and 10 in the table shows that replacement of pyromellitic dianhydride with BPTA in a copolymer with two moles of m-aminophenol and an aromatic diacid does not lead to mesogenic polymers. The assignment of an MI score of 4 compared to 2 for pyromellitic anhydride does however raise the MI as far as the borderline condition of MI=9.5 when 2,6-naphthalene dicarboxylic acid is the co-monomer. 

An initial approach to supramolecular H-bonded mesogenic polymer complexes involves a polyacrylate with 4-oxybenzoic acid moieties via a hexamethylene spacer 29 [26]. The 1 1 complexation of the side chain of the polymer and stilbazole 3 n - 2) (nematic, 168-216 °C) results in the formation of an extended supramolecular mesogen in the side chain (Fig. 11). Side-chain polymer complex 30 exhibits a nematic phase up to 252 °C, which shows that a significantly stabilized mesophase is achieved by the complexation of two different components. Liquid-crystalline properties have been examined for the series of complexes formed between polyacrylates and trans-4-alkoxy-4 -stilbazoles [33, 78]. Figure 12 shows transition temperatures against the carbon number of the alkyl chain for the series of complexes 31 [33]. They exhibit thermally stable smectic liquid-crystalline phases. For example, smectic E, B, and A phases are observed until 192 °C after the glass transition at 38 °C for the complex with m = 6 [78a]. 

The 1-nylons or poly(alkyl isocyanates) give liquid crystalline polymers which may make them useful for electrical applications. These polymers are characterized as main-chain mesogenic polymers having a semirigid structure. 

Gu, D., and Jamieson, A. M., Rheological characterization of director dynamics in a nematic monodomain containing mesogenic polymers of differing architectures. Macromolecules, 27, 337-347 (1994a). 

Pashkovskii, E. E., and Litvina, T. G., Twist viscosity coefficient of a dilute solution of the main-chain mesogenic polymer in a nematic solvent an estimation of the anisotropy and the rotational relaxation time of polymer chains, J. Phys. II, 2, 521-528 (1992a). 

Alternate approaches to modeling semi-flexible PLC phases are now appearing.(30,31) Coarsely, these statistical theories address the influence of the intrinsic flexibility of the chain on the stability of ordered fluid phases. Such modeling may help define the prerequisites for PLC formation suggesting how non-mesogenic polymers may be modified to exhibit mesomorphisra and thereby help identify new classes of PLCs. 

CONFORMATIONAL PROPERTIES OF MACROMOLECULES OF MESOGENIC POLYMERS IN SOLUTIONS... 

The study of the entire complex of hydrodynamic properties as a function of molecular weight showed that the molecules of mesogenic polymers exhibit considerable equilibrium rigidity characterized by the length of the Kuhn segment A of several hundred angstroms (Table 1). 

Table 1. Optical Properties of Some Mesogenic Polymers. 

The data given in Table 1 conclusively show that mesogenic polymers exhibit a general property high op-... 

Fig. 2 shows the theoretical dependence of the relative value of FB A= (In] / [n] ) / ( [n] / [ri] ) 00 on x=2L/A for an assembly of rigid random coil molecules with the evaluation of the polydispersity of molecules according to conformations. The points represent experimental values of A at the corresponding molecular weights for one of the mesogenic polymers, polyamide benzimidazole, in concentrated sulfuric acid (o) and in dimethylacetamide ( ). 

Table 2. Intramolecular Orientational-Axial Order Degree S for Some Mesogenic Polymers. 

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