Crystallinity properties

I)(. p end ing upon the parameters chosen, simulations performed using the Gay-Berne potential show behaviour typical of liquid crystaUine materials. Moreover, by modifying the potential, 111. can determine what contributions affect the liquid crystalline properties and so help to suggest what types of molecule should be made in order to attain certain properties. 

Examples of polymers which form anisotropic polymer melts iaclude petroleum pitches, polyesters, polyethers, polyphosphaziaes, a-poly- -xyljlene, and polysdoxanes. Synthesis goals iaclude the iacorporation of a Hquid crystal-like entity iato the maia chaia of the polymer to iacrease the strength and thermal stabiHty of the materials that are formed from the Hquid crystal precursor, the locking ia of Hquid crystalline properties of the fluid iato the soHd phase, and the production of extended chain polymers that are soluble ia organic solvents rather than sulfuric acid. 

Both 4,5- and 3,6-disubstituted phthalonitriles are commonly used to prepare phthalocyanines with liquid crystalline properties. An example of the Rosenmund-von Braun reaction is shown below.107... 

Wholly aromatic polyesters, in which both R1 and R2 are aromatic, are either high-7 amorphous polymers or veiy high melting semicrystalline polymers that often exhibit liquid crystalline properties. 

Thermotropic liquid-crystalline properties of different metal alkanesulfonates are studied by microscopy and X-ray diffraction [59]. Sodium soaps show smectic polymorphism of smectic A and smectic B phases. Ammonium soaps only show smectic A phases but polymorphism in the crystalline state. Calcium soaps show columnar mesophases. In Figs. 32 and 33 some textures and x-ray diffraction patterns are depicted. 

A simple example of how molecular electronic structure can influence condensed phase liquid crystalline properties exists for molecules containing strongly dipolar units. These tend to exhibit dipolar associations in condensed phases which influence many thermodynamic properties [29]. Local structural correlations are usually measured using the Kirkwood factor g defined as... 

The first report on the liquid crystalline properties of these compounds was published by Gray and Mosley [44] in 1976. The series of 4 -n-alkyl-4-cyanobiphenyls (CBn) have been widely studied by different methods due to their readily accessible nematic ranges around room temperature. The compounds have the phase sequences crystal-nematic-isotropic for CBS, CBIO, and monotropic nematic for CBS, CB4 crystal-smectic A-nematic-isotropic for CB9 crystal-smectic A-isotropic for CBll. The lower homologous CB2 is nonmesogenic. The general chemical structure of the compounds CBn is presented in Fig. 1. 

The liquid crystalline state may be identified as a distinct and unique state of matter which is characterised by properties which resemble those of both solids and liquids. It was first recognised in the middle of the last century through the study of nerve myelin and derivatives of cholesterol. The research in the area really gathered momentum, however, when as a result of the pioneering work of Gray in the early 1970 s organic compounds exhibiting liquid crystalline properties were shown to be suitable to form the basis of display devices in the electronic products. 

Liquid-crystalline complexes (metallomesogens) containing platinum(II) are new types of materials that have been the subject of several studies. These have largely included complexes of the type trans-[PtX2L2] (X = C1, L = cyanobiphenyls 229 X = C1, carboxylate, L = 4-alkoxy-4 stilbazoles 230 X = C1, L = 2,4-, 3,4-, or 3,5-dialkoxystilbazoles, 2,3,4-, 2,4,5-, or 3,4,5-trialkoxystilbazoles).231,232 Their liquid-crystalline properties have also been reported. 

Mesomorphic dendrimers containing electroactive units have potential for construction of dendrimer based molecular switches. Deschenaux et al. reported [154] the synthesis and liquid-crystalline properties of a novel dendrimer containing six mesomorphic ferrocene units. Apart from exhibiting a broad enantiotropic smectic A phase as determined by polarized optical microscopy, DSC, and XRD studies, thermogravimetry revealed the excellent thermal stability of the macromolecule. 

Polyisocyanates have attracted much attention owing to their liquid crystalline properties, stiff-chain solution characteristics, and induced optical activities associated with helical chain conformation (Scheme 8). Pattern and Novak [39]... 

Acetals of L-galactono-1,4-lactone (an abundant byproduct of the sugar beet industry) have thermotropic liquid crystalline properties. Acetalization in DMF containing H2S04 in the presence of anhydrous CuS04 gave (after 12 to 24 h at 40 °C) yields of 20-35% (Scheme 8.27). 

G.S. Attard, P.N. Bartlett, N.R.B. Coleman, J.M. Elliott, and J.R. Owen, Lyotropic liquid crystalline properties of nonionic surfactant/H20/hexachloroplatinic acid ternary mixtures used for the production of nanostructured platinum. Langmuir 14, 7340-7342 (1998). 

The first reports on the liquid crystalline properties of pyramidal or cone-shaped materials appeared in 1985.65 It was discovered that compounds with... 

Size and shape Certain steric effects can be achieved using characteristically wedge-shaped dendrons. Thus, self-assembling dendrons have been connected to supramolecular aggregates with defined dimeric or hexameric structures. Such aggregates can form columnar superstructures which reveal liquid-crystalline properties. Spherical superstructures arise from the self-assembly process when conical dendrons are used14 14,161 Similar... 

Thermotropic liquid crystalline (LC) phases or mesophases are usually formed by rod-like (calamitic) or disk-like (discotic) molecules. Spheroidal dendrimers are therefore incapable of forming mesophases unless they are flexible, because this would allow them to deform and subsequently line up in a common orientation. However, poly(ethyleneimine) dendrimers were reported to exhibit lyotropic liquid crystalline properties as early as 1988 [123],... 

Totally synthetic bilayers show liquid crystalline properties similar to those of lecithin bilayers (Nagamura et al., 1978 Kano et al., 1979). Bilayer formation has also been observed for dialkyl compounds with anionic head groups such as [2] and [3] (Kunitake and Okahata, 1978a Mortara et al., 1978), and with nonionic and zwitterionic head groups as in [4] and [5] (Okahata et al., 1978a). 

Kim reported on liquid crystalline properties observed for hyperbranched aromatic amides obtained from 3,5-diaminobenzoic acid and derivatives thereof. The resulting polymers exhibited nematic liquid crystalline phases [89]. 

Sonochemistry affords a technology which can be used to generate ultrafine powders and nanostructured materials of significant commercial interest which encompass both amorphous and crystalline properties [152]. 

A third reason for interest in copolymers is crystallinity. Transparency and translucency are greatly affected by crystalline properties, which can be regulated by copolymerizatiOn. "... 

Dynamic combinatorial nitroaldol libraries were also used to illustrate iDCR [5,6], In this case, one of the library components was selected for its possibility to undergo an irreversible tandem cyctizafion reaction following equilibrium formation. This provided an internal kinetic selection pressure on the library, subsequently forcing the library to complete amplification of this novel reaction product. Furthermore, interesting crystalline properties were observed for one of the diastereoisomers of this isoindolinone-type product, providing a route to demonstrate consecutive resolution processes resolving coupled DCLs in a one-pot experiment. 

Further studies of the isolated isoindolinone structure (lactam 57) showed that one of the diastereoisomers had interesting crystalline properties. This was used in order to demonstrate how a DCR process could further be directed and diastereomerically amplified through a selection pressure caused hy a phase change. Systems where DCLs are driven by crystallization have previously been reported [50-52], and have recently received new attention [53-56]. 

This transformation of alkyl 2-chloro-2-cyclopropylideneacetates has been applied for the preparation of compounds of type 83 containing a czs-configurated disubstituted cyclopropane moiety [25] with potential liquid crystalline properties [52]. In the first approach to such compounds, 2-chloro-2-cyclopropylide-neacetic acids 2b-H, 2i-H were coupled with the linear diaryl components 81 fol-... 

Scheme 21. Preparation of biaryl derivatives of type 83 with potential liquid crystalline properties from 2-chloro-2-cyclopropylideneacetic acid. Conditions A DCC, CH2CI2, 0°C, 5 h. B DEAD, Ph3P, Et20,20°C, 14 h [25]...

As compared to the cholesteric LC, the lyotropic LC consists of two or more components that exhibit liquid-crystalline properties (dependent on concentration, temperature, and pressure). In the lyotropic phases, solvent molecules fill the space around the compounds (such as soaps) to provide fluidity to the system. In contrast to thermotropic liquid crystals, these lyotropics have another degree of freedom of concentration that enables them to induce a variety of different phases. A typical lyotropic liquid crystal is surfactant-water-long-chain alcohol. 

The structure of these spherites is uncertain Bradford assumes that they consist of a regular crystalline growth formed by multiple twinning of minute crystals. Scherrer s examination of gold sols, however, has revealed the fact that the crystal interference lines are well developed when the particle contains as few as eighty molecules arranged in the cube lattice, a spherite of OTju. diameter would probably show crystalline properties even if excessive twinning has taken place. 

Acyclic carbohydrates with two alkyl chains have been studied in detail in the case of dialkyldithioacetals 9. It is one of the more complete series whose results have been cross-checked and compiled [43]. Their liquid crystalline properties were compared with those of dodecyl a- and -D-glucofuranosides [50] depending on their structures, they form either hexagonal disordered columnar phases or a new rectangular columnar phase [77]. 

Alkyl chain(s) with carbohydrates at both termini (bolaamphiphiles) have also been reported since they are potential building blocks for the construction of membrane mimetics with a single monolayer [78]. Bisgluconamide and lactobionamides 6b (sug=Glc-A or Lac-A, X=NH) were studied for their crystalline properties and their arrangements in water [39, 40]. Alkyl-a,cc)-dimannitol 6b (sug=Man-ol, n=16-22) [66] or bolaamphiphiles with identical or different carbohydrates at both ends of the alkyl chain 6a (sug=D-Glc/, D-Galp, DL-Xyl-oI) were found to form micelles and lyotropic liquid crystals as well [41]. 

---