Mesogenic character

Note 4 The rigid units may, but often do not, possess intrinsic mesogenic character. 

Both thermotropic and lyotropic liquid crystal polymers exhibit characteristic features with regard to their microstructureJ Anisometrical monomers such as rods or discs are connected to chains in an appropiate manner. These anisometrical monomers are considered to be the mesogens and may be part of main chain LCP, side chain LCP, or of both types together (Fig. 6). Between the mesogens are located flexible spacers of non-mesogenic character. Sufficient flexibility is a prerequisite for liquid crystal formation, with an increase in either temperature or solvent concentration. 

All LC-polyimides discussed in this review possess at least one phthalimide unit in the mesogenic unit and most of them contain an AT-phenyl phthalimide moiety. For a better understanding of the potential mesogenic character of aromatic imide groups it is useful to discuss briefly their stereochemical and conformational properties. 

When compared to the homopolyester of 16b the homo PEI of 16a is a lower melting material (Tm=430-433 °C) [14,47] but its melt is isotropic as expected for a meta functionalization. Despite the non-mesogenic character of 16a this hydroxy acid can serve as a comonomer in LC-PEIs. Characteristic examples are the co PEIs containing 4-HBA (23a-h) or 2,6-HNA (25a-h) [47]. Two samples of LC-co PEIs of structure 23 were first described in a patent of Bayer AG [40]. 

At the same time the polycarbonates 54a-f (all of them with m=3,4,5,6) were prepared and characterized by Sato and coworkers [66,67]. All syntheses were conducted by transesterification of the corresponding diols with the biscar-bonates 55 in bulk. None of the four homo PEIs (54a, m=3-6) proved to be thermotropic. In the case of the copolycarbonates only those containing more than 50 mol% of the biphenylester unit (e.g. 54d-f, m=3) were apparently thermotropic. This thermotropic property was attributed to the mesogenic character of... 

In these derivatives, the substituted bipyridyl ligand has a mesogenic character. The derivative (rac)-(6.30) is obtained by the zinc reduction of Ru (acac)3 followed by addition of the bipyridyl ligand (L). The two enantiomers (A)-(6.30) and (A)-(6.30) are separated by chromatography on a column of synthetic laponite doped with [Ru(phen)3] " (Scheme 6.1). 

This paper describes novel approaches to the exploitation of both furan monomers and a specific facet of furan reactivity in order to synthesize either conjugated oligomers incorporating the heterocycle in their backbone, or polymeric structures which can be crosslinked and returned to linear structures through the reversible chemistry of the Diels-Alder reaction. The first family of compounds showed interesting features in terms of conductivity, luminescence, mesogenic character and photoactivity. The second class of materials owes its interest to the possibility of recycling otherwise intractable polymers, e.g. tires, thanks to a simple thermal process. 

Triblock partially fluorinated hydrocarbons F/nHiiFin(m = 12, n = 8 m = 10, n = 10 m = 12, n = 12) have also been examined and all are found to exhibit very narrow (< ) range of thermotropic smectic B phases between their crystalline and isotropic liquid phases [88]. When the polymethylene portions of such molecules are replaced by a much stiffer pam-substituted aromatic ring, the mesogenic character is lost [89]. 

Lyotropic main chain LCPs — forming liquid crystalline solutions due to the conformation of the polymer main chain rather than due to mesogenic character of substituents on the main chain — were first recognised in the case of poly(Y-benzyl-L-glutamate) [1],... 

Intrinsic viscosity [ ] - Polymerized for 3 h in water bath Solvent Mesogenic character (3)... 

Enamine carbonyl hydrogen bonding ring containing polymers can be made several ways. In the case of poly(amide enamine) prepared from piperazine no mesogenic character was observed. The new materials reported, synthesized... 

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