Liquid crystalline polymers monomers

Figure 7. DSC Thermograms of liquid crystalline polymer and its monomer.

A third mesogenic monomer, (III), was also used to prepare liquid crystalline polymer networks and is illustrated below. 

Liquid crystalline polymer networks were prepared by Kelly et al. (1) with mesogenic monomers, (IV), and used in forming networks charge-transporting or luminescent materials. 

Scheme 6.12. Monomer preparation for the construction of liquid crystalline polymers.

Komiya et al. described the living ROMP synthesis of AB-type block copolymers that contain side chain liquid crystalline polymer blocks and amorphous blocks [62]. Norbornene (NBE), 5-cyano-2-norbornene (NBCN) and methyl-tetracyclododecene (MTD) were used for the amorphous polymer blocks, while I-n (n=3,6) were used for the SCLCP block (see Fig. 9). Initiator 1 was used for the ROMP. Block copolymers with monomer ratios from 75/25 to 20/80 (amor-... 

In this chapter lyotropic liquid crystalline polymers are considered, where micelle-like organizations of the macromolecules cause the formation of mesophases in defined concentration and temperature regions. For these polymers it has to be assumed that the polymer backbone or the monomer units must contain an amphiphilic character. 

To summarize our results on side-chain all-hydrocarbon LC polymers [I], we found that they displayed Smectic E phases at lower temperatures and Smectic B phases at higher temperatures. The corresponding LC monomers exhibited only Smectic B phases. The presence of tails seems to enhance and stabilize liquid crystallinity. The monomers and polymers that do not have tails are not liquid crystalline. All of the substituted biphenyl hydrocarbon liquid crystals found in the literature are disubstituted. Examples of monosubstituted biphenyl hydrocarbon liquid crystals have not been found. The results obtained from this work support the idea that disubstitution of the biphenyl moiety is necessary to obtain a liquid crystalline phase. 

The next step of the investigation deals with the study of the behaviour of still larger molecules, namely mono and dimethyl naphthalenes. It was observed that the smaller naphthalenes could diffuse into the tube, while the larger naphthalenes is unable to enter the mouth of the tube. 2,6-dimethyl naphthalene (DMN) is a valuable intermediate for the preparation of monomer to produce thermotropic liquid crystalline polymers, altho-... 

Liquid crystalline polymers containing ferrocene in their side chains have been reported.235-240 Deschenaux used free-radical synthesis to prepare thermotropic liquid crystalline polymethacrylates containing ferrocene (Scheme 2.46).235 Polarized light microscopy showed that monomer 171 and its corresponding polymer 172 exhibited enantiotropic smectic A and C phases. 

The basic structure of low molecular mass liquid crystals or monomers of liquid crystalline polymers is schematically shown below... 

In the smectic A phase, molecules tend to be perpendicular to the smectic layers. The layer thickness d is roughly the same as the molecular length l. The thickness of the layers in the case of liquid crystalline polymers is about the order of the monomer s length. But in the smectic C phase, the molecules in the layers are parallel and tilted in arrangement with respect to the normal of the layers by a tilt angle 0. The layer thickness of the smectic C phase is d = l cos 6. The ordering of the smectic A and C phases are both higher than the nematic phase so that they appear at a lower temperature than the nematics do. The smectic A phase appears first as the temperature decreases if a compound shows both the smectic A and C phases. 

While main-chain type liquid crystalline polymers are made by step-wise polymerizations, side-group type polymers have been synthesized by both step and chain polymerizations of monomers with desired mesogenic side groups. In addition, mesogenic side groups can be introduced to polymers... 

It is worthy to note at this point that the polymerization of mesogenic monomers with chiral moieties does not necessarily result in polymers with the chiral liquid crystalline phase. For example, Finkelmann (1982) reported that homopolymers of chiral monomers yielded only smectic mesophases. On the other hand, copolymerization of chiral monomers with different spacers or of a chiral monomer and a nematic monomer has been proven effective and convenient for synthesizing chiral liquid crystalline polymers. 

For liquid crystalline polymers, the elastic constants are determined not only by the chemical composition but also by the degree of polymerization, i.e., the length of the molecular chain. One main aim of this section is to address the effects of molecular chain length on the elastic constants of liquid crystalline polymers. Figure 6.1 shows the three typical deformations of nematic liquid crystalline polymers. The length and flexibility of liquid crystalline polymers make the elastic constants of liquid crystalline polymers quite different from those of monomer liquid crystals. 

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