LCP mesogens

TABLE 2.15 Building Blocks Used in Main-Chain Polyester LCP Mesogenic Units... 

Macromolecules dendritic, 285 hyperbranched, 284-286 Main-chain liquid crystalline polymers, 49 Main-chain polyester LCP mesogenic units, 50... 

Flexible polymers Lyotropic LCP Main-chain type LCP Mesogen-jacketed LCP... 

Both thermotropie and lyotropic liquid crystal polymers exhibit eharacteristic micro-strueture features [9,10]. Anisometrieal monomers such as rods or disks are conneeted to ehains in an appropriate manner. These anisometrieal monomers are considered the mesogens and may be part of main ehain LCP, side chain LCP, or of both types together (Fig. 6). Flexible spacers of nonmesogenic character are located between the mesogens. A sufficient flexibility is a prerequisite for the liquid crystal formation with an increase in temperature or solvent concentration. 

There is no consensus yet as far as the name of these materials is concerned. Some investigators use the name polymer(ic) liquid crystals (PLCs), others call them liquid crystalline polymers (LCPs) or mesogenic macromolecules. 

For polymers which, on heating, yield Mesophases (liquid crystal melts), the so-called mesogenic polymers or liquid crystal polymers (LCPs), the situation of phase transitions is much more complex. In this case the simple Volume-Temperature diagram, given in Fig. 4.2 is not valid anymore and has to be substituted by a more complicated one, which is shown in Fig. 6.12. 

All Liquid Crystal Polymers are characterised by the fact that they contain stiff meso-genic groups, often inserted in flexible chain systems (so called "spacers") and connected to them by linking functional groups the mesogenic unit is inserted either in the main chain or in the side chains or (in exceptional cases) in both. We shall discuss MCLCPs and SCLCPs. A schematic representation of common structures of LCPs is displayed in Fig. 6.14 (Jansen, 1996). An example of a SCLCP with disc-like mesogens is displayed in Fig. 6.15 (Franse et al., 2002, 2004). 

Estimate the characteristic temperatures of an LCP with mesogenic groups in main- and side-chain, of the following structure ... 

A great number of initiators and monomers are now available, allowing almost perfect control over most of the important parameters of LCPs main chain stiffness tacticity glass transition temperatures processabiUty from solution or melt mesogen density along the main chain combination with... 

The first thermotropic LCPs were reported in the mid-1970 s by Roviello and Sirigu (15) and Jackson and Kuhfuss (16). Since then, a large number of LCPs have been reported an excellent, though now dated, review of main-chain (i.e., the mesogen is in the polymer backbone) thermotropic LCPs was published by Ober et al. (17). In the 1980 s, several thermotropic aromatic copolyester LCPs were commercialized. 

Side-chain LCPs can be prepared by attaching a mesogen pendant to a flexible polymer backbone (18). These materials often have optical properties similar to low molar mass LCs and have generated interest for such applications as non-linear optics, filters and optical storage devices. 

This Is a copolymer where the "mesogen" Itself Is a seml-flexlble moiety of diphenyl ethane, which Is not LCP forming as a homopolymer, with (CH.) as a sole spacer, but Is turned Into LCP on copolymerization with (CHjJjq as the alkyl portion of the comonomer unit. The result Is shown by Figure 4. Ue see that a stable mesophase (T,>T ) results beyond a molar fraction of (CH )10 equal to 0.2 with Tr.-tf" being largest at around 1 1 (CH0)0/(CH ) molar ratio (15). m... 

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