Rigid side-group liquid crystal polymer

Fig. 1. Examples of three types of liquid crystal polymer molecule I, chain made up from rigid aromatic units joined by relatively stiff ester groups II, chain containing rigid units separated by flexible aliphatic sequences DI, chain with a flexible backbone but rigid side-groups.

Figure 20. Structures of molecules of some liquid crystal polymers. The rod-like and disk-like mesogenic groups can be included as main groups in rigid or flexible polymeric chains, or can be attached as side groups of flexible chains. Cross-linking gives the liquid crystal elastomers or thermosets. (By courtesy of Adamczyk [355]).

In one type of liquid crystal polymer (LCP) the rigid cores (or even disks) are connected head-to-tail leading to a main-chain LCP in the second type they are connected via a linking group onto a polymer backbone giving a side-group LCP (Figure 2.14). 

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). 

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