Liquid crystalline side group polymers

H-C- C00(CH2)60 -< )-COO-< )-och3 FIGURE 21.13. Scheme of the side group liquid crystalline polymer. 

For a combined main chain side group liquid crystalline polymer (Fig. 21.17) two librational (3-relaxations are observed [9] originating from the two different mesogenic units (Fig. 21.18). 

First, we will consider the design of polyphosphazenes as side-chain liquid-crystalline materials.241 248 Side-chain liquid-crystalline polymers are a subclass of species described earlier as structure 3.72. Liquid crystallinity occurs when the rigid side groups become organized, usually in the semi-liquid state. The organization may be nematic (oriented but unlayered) or smectic (layered) as illustrated in Figure 3.25. 

Figure 4 Vinyl ethers with pendant mesogenic groups for side-chain liquid-crystalline polymers. The numerals in brackets attached to each entry indicate reference numbers.

Experimental results of the order parameter Sa of side groups of side chain liquid crystalline polymers are shown in Figure 2.28, where the chemical formulae of the side group polymers are... 

If the side chain liquid crystalline polymers goes into the smectic A phase from the nematic phase, the backbone chain is confined between two successive smectic layers, occasionally jumping into the neighboring layer gap. See Figure 2.30 where the cylinders denote side groups and thick lines represent backbones. The mean square end-to-end distances parallel and perpendicular to the director differs more than that in the nematic phase. 

In the side chain liquid crystalline polymers the nematogenic side groups and chiral side groups are attached respectively to a polymer backbone to form a copolymer. They exhibit the cholesteric phase. A typical example is shown below. One is the homopolymer (shown in Figure 6.28) and the other is the copolymer (Figure 6.29). 

To overcome the drawback, copolymers are proposed for the NLO purpose. In a side chain liquid crystalline polymer some side mesogenic groups are replaced by NLO active groups. In this method, the concentration of... 

Apply the concept of liquid crystal networks crosslink the backbone of NLO side chain liquid crystalline polymers when they are in the liquid crystal phase. In the presence of a mechanical force the resultant sample may be well aligned because of the interaction between the network strands and the side groups. The mechanical effect is equivalent to the electric or magnetic field. The re-orientation response of the liquid crystal is a quadratic function of the applied electric field, but it is linearly proportional to the mechanical stress. Thus, the mechanical stress is more effective in aligning the liquid crystals and is expected to produce less defects and hence to promote the transparency of the sample. 

It has been found experimentally that the spontaneous polarization Ps of side chain liquid crystalline polymers is more or less the same as that of small molecular mass liquid crystals, i.e., so far as the chemical formula of the side group of a side chain liquid crystalline polymer is the same as that of a small molecular mass liquid crystal. This phenomenon illustrates that either the side groups in the side chain liquid crystalline polymer or the small molecular mass ferroelectric liquid crystal in their Sc phase are aligned in same way. The dependence of Ps on temperature for the three small molecular mass ferroelectric liquid crystals LI, L2 and L3 and their polymer counterparts PI, P2 and P3 are depicted in Figure 6.40. 

Boemlburg et al. (1991) first discovered the anti-ferroelectric liquid crystal phase in the chiral side chain liquid crystalline polymer, Sca phase. Several other research groups followed with more such side chain liquid crystalline polymers. Boemlburg et al. (1992) reported an anti-ferroelectric liquid crystal in the molecule... 

Side-chain liquid crystalline polymers containing disk-like pendant mesogenic groups are well known to exhibit thermotropic columnar mesophases [65], the... 

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