Structure−Property Correlations in Model Compounds of Oligomer Liquid Crystals

Abstract

Structure−property correlations of the following model compounds for oligomer liquid crystals (LCs) have been investigated: monomers, C6H5O(CH2) x CH3 (x = 4 and 5); dimers, C6H5O(CH2) x OC6H5 (x = 3, 4, 5, and 6); and tetramers, C6H5O(CH2) x OC6H4O(CH2) x OC6H4O(CH2) x OC6H5 (x = 5 and 6). Deuterium NMR quadrupolar splittings observed from the deuterated model compounds dissolved in a nematic solvent, 4‘-methoxybenzylidene-4-n-butylaniline (MBBA) or p-azoxyanisole (PAA), were analyzed by the rotational isomeric state scheme with the maximum entropy method to yield the orientational order parameters, bond conformations, and molecular dimensions. For the dimers in particular, the solute shapes were estimated from phase diagrams of the dimer/MBBA systems, the crystal structures were determined by X-ray diffraction, and the melting points and enthalpies of fusion were evaluated from DSC measurements. From the dimers, the so-called odd−even effect was clearly observed in not only the orientational order and molecular shape in the nematic solution but also the crystal structure and thermal properties; that is, the dimers of x = 4 and 6 have larger order parameters, more anisotropic shapes, better-arranged crystal structures, higher melting points, and larger enthalpies of fusion than those of x = 3 and 5. In the nematic solution, the model compounds preserve the inherent conformational preferences of the ether chain and enhance the shape anisotropy by increasing the trans fractions. As the orientational correlation is expected to persist only within a short range, conformations of the tetramers may represent those of polymer LCs with the same ethereal spacers. The chainlike molecules adjust their spatial configuration to the LC environment, and consequently, physical properties of the LC system are affected.

Chemistry of aromatic polythioesters and polydithioesters

“…The thioesters weakly show the odd-even oscillation in T m , whereas the dithioesters do show strongly. In our previous study, 29 the similar odd-even effect was clearly observed in crystal and mesophase stabilities of the model compounds of liquid crystalline polyethers.…”

1,3-Bis(3,5-dimethylphenoxy)propane

“…The aliphatic linker between the aromatic rings is not in a fully stretched conformation, but has adopted an (anti, Àgauche,Àgauche,anti) conformation. This is directly comparable to the published (Sasanuma et al, 2004) nonderivatized ligand, viz. 1,3-diphenoxypropane, (II), which adopts a nearly identical conformation (Fig.…”

Conformational Characteristics of Poly(trimethylene sulfide) and Structure−Property Relationships of Representative Polysulfides and Polyethers

“…As found for PEO and PPO, the polyethers often form the (C-H)‚‚‚O attractions, whose strengths depend on the number of carbon atoms between ether linkages. 74,75 In some polyethers, the former factor appears predominantly, and the latter is often superior in other polyethers. These tendencies, being sensitive to the environment, are changeable.…”