Rigid biphenyl moiety

The phase behavior of related polymers and monomers containing the rigid biphenyl moiety are studied in a later paper [131]. The phase behavior of the monomeric surfactants is generally compatible with that of common nonionic surfactants (especially ethylene oxide alkyl ethers). They exhibit Ii (sometimes two), Hj and L phases as well as clouding. The polymers, which have an average degree of polymerization of 55, nearly all exhibit H, and L phases, whereas the Ij phase is only seen in one (PC3BiE i)55. One major difference between the polymer and monomer phase behavior is the appearance of a nematic phase (Nc) built up of rod-like micelles in a num-... 

Interestingly, the hydroformylation results obtained with ligands 2b and 2d, which have conformationally flexible axially chiral biphenyl moieties, are similar to those obtained with ligand 2m, which have conformationally rigid binaphthyl moieties. This indicates that diphosphite ligands that contain the conformationally flexible axially chiral biphenyl moieties predominantly exist as single atropoisomer in the [RhH(CO)2 (diphosphite)] complexes... 

When the side chain is modified to include a rigid rod-like biphenyl moiety [ 130] [(CH2)3-0-0-0-(CH2CH20)9CH3] and the degree of polymerization reduced to 55 (P55C3BiE9), subtle differences are seen in the phase behavior. H, (34-75%, -2 -> 68 °C) and La (60-95%, 20- 100 °C) phases are still seen but with no Vj phase between them. Clouding is observed up to 58% polymer between 66 and 82 °C. Above this a biphasic Li-i-La region is seen to 80%. ... 

Rigid rods (a), laths (b) and disks (c) have no conformational degree of freedom. They are very convenient for theoretical discussions and computer simulations of the mesophase structure. Closer to reality are rods (or disks) with flexible tails (hydrocarbon chains) shown in Fig. 3.2a, which facilitate formation of layered liquid crystal phases. As an example of conformational degrees of freedom of flexible molecular fragments is the trans-cis isomerization. In sketch 3.2b transform is on the left, cis-form in the middle, a combination of the two on the right. The rotational isomerization is another example in sketch 3.2c the internal rotation of phenyl rings about the single bond in a biphenyl moiety is sketched. 

Fig. 3.2 Different degrees of freedom for non-rigid mesogenic molecules molecules with flexible tails (a), tram-, cis- and combined tram-cis isomerisation of the flexible chains (b) rotational isomerism of biphenyl moiety (c)...

Actually, such bowl phases are still to be found. However, polar achiral phases have been observed in the so-called polyphilic compounds [8]. The rod-like molecules of these compounds consist of distinctly different chemical parts, a hydrophilic rigid core (a biphenyl moiety) and hydrophobic perlluoroalkyl- and alkyl-chains at opposite edges. Such molecules form polar blocks that, in turn, form a polar phase manifesting pyroelectric and piezoelectric properties with a field-induced hysteresis characteristic of ferroelectric phases. 

Amphiphilic systems containing an extended rigid-rod block, rather than a more flexible linear chain, have also been shown to self-assemble into well-defined structures. Stupp s group explored a series of rod-dendron and dendron-rod-dendron hybrids containing two to three biphenyl ester moieties as a rigid rod that was capped by one or two 3,4,5-tra-alkoxy benzoate dendrons (Lecommandoux et al. 2003). The... 

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