Rigid rods mesogenic groups

Horie and his co-workers [131-135] have made extensive use of fluorescence spectroscopy to probe the microstructures of MCLC polymers. The first such polymer to be studied [131,135] was the all aromatic, rigid rod polyester, 65, with long, flexible side-chains attached to a pyromellitic ester mesogenic group. 

Ringsdorf s research group have prepared novel types of rigid-rod polyesters and polyamides 56 with a disc-like mesogen in tte mainchain [75]. Most polymers with six lateral substituents appear to be thermotropic liquid crystals. Polyamides with Z = H and having four substituents on the diamine component are not liquid crystalline. The two substituents on the diacid component seem to contribute to decrease further the intermolecular hydrogen bonding. 

Figure 1. Structures of liquid crystalline polymers (LCPs) (A) rigid rod LCP [25, 65] (B) main chain LCP with flexible spacer [26] (C) side group LCP with flexible spacer [27] (D) combined main/side group LCP [28] (E) side group LCP without flexible spacer or mesogen jacketed LCP [29], (F) well-defined three-arm star [30] (G) LC dendrimer [33].

Many polymers exhibiting liquid crystalline properties have been reported. From this work have come generalizations concerning the nature of the structural components or mesogenic groups necessary to impart liquid crystalline behavior to polymeric materials. These polymers are frequently rigid rods, and the groups which contribute... 

Liquid crystalline thermosets (LCT) with a rigid rod-like mesogenic group capped firom both ends by reactive fimctional groups can be used as matrices for production of advanced composites, coatings or adhesives (1, 2). hi this case ordering of the chains of the final network polymer is the only way to improve its physical and mechanical properties. 

Fig. 3.1 Building blocks of thermotropic and lyotropic liquid crystalline phases. The upper part of the figure shows two examples of typical thermotropic mesogens. Calamitic mesogens, such as terephthal-bis-(p-butylaniline) (TBBA) [2], can be represented by prolate ellipsoids or rigid rods, while discotic mesogens, such as benzene-hexa-n-octanoate (BH8) [4], are usually described by oblate ellipsoids or discs. The lower part of the figure shows the typical surfactant molecule sodium dodecyl sulfate (SDS), which forms lyotropic phases with water [5], Such a surfactant molecule is basically composed of a polar head group and a flexible hydrophobic tail. These amphiphilic molecules aggregate into different types of micelles, which are the actual mesogens of lyotropic liquid crystals. The shape of the micelles depends mainly on the solvent concentration...

Figure 4 Schematic representation of macromolecules of different rigidity (a) flexible chains (b) rigid-rod LC polymers (c) main-chain LC polymers with mesogenic groups (d) side-chain LC polymers with mesogenic groups (comb-shaped LC polymers).

The order parameter (S), defined below, characterizes the state of orientation of the rigid-rod main chains or, in the case of side-chain polymers, of the pendant mesogenic groups in a sample or in a part of a sample, e.g. a liquid-crystalline domain ... 

---