Mesogenic Group Effects

The structural features of the mesogenic groups affect the onset, nature, and stability of the liquid-crystalline mesophases through their rigidity, their polarizability along either the main or minor axis direc- 

It is practically impossible to draw definite correlations between these structural 

The effect of substituents other than the methyl group on the mesophase behavior was investigated in very few studies. In general, it appears that small substituents such as Br or Cl do not substantially affect the 

2 Main Chain Liquid Crystalline Semiflexible Polymers 

The effect of the introduction of lateral alkyl chains of variable length on the mes-ogenic group was systematically studied for a polyester [70] with structure 2. 

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In summary the results of our 2H NMR investigation illustrate the spacer model for liquid crystalline polymers, indicating, however, that the decoupling of the mesogenic groups from the main chain, while effective, is not complete. 

Investigations in the past years have proved that applying the concept of flexible spacer, polymers can be synthesized systematically, which exhibit the l.c. state. Owing to the flexible linkage of the mesogenic molecules to the polymer main chain, very similar relations can be expected with respect to 1-l.c., like chemical constitution and phase behavior, or dielectric properties and field effects for the l.c. side chain polymers. This will be in contrast to main chain polymers, where the entire macromolecule, or in case of semiflexible polymers parts of the macromolecules, form the l.c. structure. The introduction of a flexible spacer between backbone and mesogenic group can be performed in a broad variety of chemical reactions. Some arbitrarily... 

With the I.c. side chain polymers a new class of I.c. material was realized and this poses the question, whether this new material also exhibits field effects in analogy to conventional I.c. s and whether the covalent bonding of the mesogenic groups to the polymer backbone changes the material parameters. In this chapter we therefore will compare the behavior of l-l.c. s and chemically very similar polymers in the electric and magnetic field. 

The only general statement that might be made is that the specific features of the structure of polymeric nematics are provided for by the ordering effect of the main chain on the packing of mesogenic groups in LC phase. 

The effect of POCS-4 molecular mass on the phase states is detected. Among works devoted to the study of MM effect on isotropization temperature variation, Tiso, in organic LC-polymers, the ones by Blumstein et al. should be outlined [45, 46], These works show that Tiso increases with MM, for organic LC-polymers with mesogenic groups in the backbone in a quite narrow range of molecular masses. 

Table 4. Effect of Mesogenic Group and Flexible Spacer on Entropy of Clearing, AS , of LC Polyesters...

Fig. 51 Schematic structures of the hexagonal tubular nematic and rectangular tubular nematic phases. The mesogenic groups are roughly parallel to the columns but their positions are disordered. Thus the columns effectively act as the directors of the nematic phase...

Fig. 13a Charge carrier hopping between chromophores connected to the side chain, and the effect on molecular alignment of the introduction of mesogenic groups, b Resulting energy level distribution of the chromophores. Molecular alignment should result in narrower distribution of molecular orbital energy levels...

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