Segmented-chain polymer liquid crystals

Linear chain polymers with repeating sequences of hard and soft segments Possibility of formation of liquid crystal polymers and thermoplastic elastomers... 

The fluorescence polarization technique is a very powerful tool for studying the fluidity and orientational order of organized assemblies (see Chapter 8) aqueous micelles, reverse micelles and microemulsions, lipid bilayers, synthetic non-ionic vesicles, liquid crystals. This technique is also very useful for probing the segmental mobility of polymers and antibody molecules. Information on the orientation of chains in solid polymers can also be obtained. 

Polymer Melts. When a rigid, polarizable monomer forms wither a mainchtiin polymer with flexible segments in belween or a side-chain polymer with flexible segments between the rigid segments and the flexible main chain, liquid-crystal phases are usually viable. 

The main part of the side group in these macromolecules consists of the alkoxy-benzoic acid moiety. This acid may form thermotropic liquid crystals. The investigation of the hydrodynamic properties of PPhEAA molecules in dilute solutions has revealed that the equilibrium rigidity of their main chains is relatively low (Table 12). Hence, since for all flexible-chain polymers, the shear optical coefficient An/Ar in PPhEAA solutions is independent of molecular weight the segmental anisotropy - tt2 and the anisotropy of the monomer unit Aa may be determined by use ofEq. (67). 

In a very crude sense, liquid crystalline polymers can be regarded as a freely-jointed-rod chain, shown in Figure 2.16. The freely-jointed-rod chain consists of a series of repeated segments of length lo- Each segment is able to rotate freely. It is assumed that the freely-jointed-rod chain is a replica of its small molecular mass liquid crystal counterpart in the liquid crystalline properties. 

The substitution effect on liquid crystals has been discussed for low mass and fully aromatic polymers. The comparison of (3.28) with (3.27) shows the effect of substitution in mesogenic units on the properties of polymers with flexible segments in main chains. Again, the substituted polymer has a lower melting point, a lower clearing temperature, and a narrower temperature... 

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