Polyesters Nematic

The even-odd effect was first detected in the series of nematic polyesters prepared by Griffin and Havens, the mesogenic structure of which is listed as 35 in Table 1 They also found that the temperature range for mesophase stability decreased as the spacer length increased, and the copolymer with the longest spacers in their series (10 and 12 methylene groups) had the lowest transition temperatures . 

Blumstein, R. B., Stickles, E. M., Gauthier, M. M., Blmnstein, A., and Vohno, R, Influence of molecular weight on phase transitions and alignment of a thermotropic nematic polyester, Macwmolecules, 17,177-183 (1984). 

ORDER AND ODD-EVEN EFFECTS IN THERMOTROPIC NEMATIC POLYESTERS... 

Thermotropic liquid crystals, 15 86-98 bent-core, 15 98 discotic phases of, 15 96 frustrated phases of, 15 94-96 metallomesogens, 15 97 nematic liquid crystals, 15 86-92 smectic liquid crystals, 15 92-94 Thermotropic mesophases, 20 79 Thermotropic polycarbonates, 19 804 Thermotropic polyesters, liquid-crystalline, 20 34... 

NMR spectra and Tj measurements at different temperatures. The local polymer chain motion varies over a frequency range of 104-106 Hz in the nematic phase. The activation energy of this motion is found to increase with decreasing number ( ) of methylene units in the spacer, and exhibits odd-even fluctuations. In a study of a homologous series of main-chain LC polyesters, 13C CP/MAS and variable-temperature experiments reveal a conformation-ally more homogeneous and a less dynamic nature for the even-chained than for the odd-chained polymer structures.300... 

Recent work focuses on non-classical mesogenes which are built up by self-assembly. One example is a family of polymers containing disk-like groups which form no liquid crystalline phase, but ean act as an electron acceptor or donor. Charge transfer complexation with a complementary low molecular mass compound induces nematic or columnar discotic liquid crystalline order [153,154]. Figure 13 demonstrates this with the example of a polyester, bearing electron-rich tetra(alkoxy)tri-phenylene-units in the main chain, mixed with the electron deficient aromatic 2,4,7-trinitro-9-fluorenone (TNF). While the pure polymer shows a non-ordered isotropic melt, a columnar phase appears on addition of TNF. 

In contrast, a racemic mixture of the 3-methyladipic acid residues in the polyester resulted in the formation of a nematic phase. Similar cholesteric polyesters based on azobenzene mesogenic units and (-f) 3-methyladipic acid were reported by Japanese workers... 

In order to investigate the influence of chemical structure on the melt viscosity, polyesters A1.A2.B1 and B2 were compared in the steady mode in plate and plate-geometry at 300°C. A2 and B2 should be in the isotropic region, whereas Al, B1 would be in the nematic state. Prior to steady shear measurements a transient step from... 

The thermal characterization of 3,4 - and 4.4 -dicarboxy diphenyl ether containing polyesters has shown better thermal-stability than the corresponding 3,4 - and 4,4 -dicarboxy diphenyl ketone polyesters. Furthermore, higher degrees of substitution with the kinked monomer is necessary in case of the ketone containing polyesters to achieve the same depression of the melt transitions, compared to the ether polyesters. Crystalline-nematic transitions may be as low as approx. 200°C. 

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