Phenylene ether moiety

Nevertheless remarkable is the failure of the diphenols 10a and 10b to yield LC-homo PEIs. Computer modelling of 9b, 10a and 10b in their energy minimum conformations (Fig. 5) revealed the following differences. The diphenyl ether moiety has a relatively wide bond angle (124 1°) and requires little activation energy to adopt a nearly coplanar conformation of the phenylene rings. 

Chemical modifications of copoly[methylsilylene(alkylene)/l,4-phenylene] bearing Si—H moieties as well as poly(methylhydrosiloxane) are readily performed through Pt-catalyzed graft hydrosilylation with functionalized allyl ethers, 3-cyano-l-propene, and allyl carbamates in a manner similar to the process shown in equation 107 (vide supra)290,291. 

Four donor acceptor [2]catenanes possessing cyclobis(paraquat-p-phenylene), as the 7i-electron acceptor, and 1,5-dioxynaphthalene-containing macrocyclic polyethers, as the 7i-electron donor moieties, have been constructed employing Cu+-catalyzed Huisgen 1,3-dipolar cycloaddition and Cu+2-mediated Eglinton coupling condition in the final step <07JA8236>. Desymmetrized [2]catenanes were synthesized by means of a template synthesis of pseudorotaxanes between 7i-rich crown ethers and a 7i-deficient pyromellitic subunit,... 

As is for low mass liquid crystals, incorporation of kinked moieties will result in destructive effects on the liquid crystallinity of polymers (Figure 3.4). 2,2-diphenylpropane, diphenylmethane, diphenyl ether, diphenyl ketone, 1,2-phenylene, 1,3-phenylene, and 1,2-naphthalene are examples of kinked moieties used in the modification of liquid crystalline polymers. They are very effective in destroying the linearity of rigid rods. Polymers with kinked units have less crystallinity and lower phase transition temperatures. Appropriate use of kinked units is thus of help from case to case. However, the type and amount of kinked units should be carefully determined so as to maintain desirable liquid crystallinity. 

Other components of the design [138—142] include the choice of the crown size or even the use of open-chain metalloclefts, not necessarily polyether armed. The issue of special importance for extraction and transport applications is the selection of substituents ensuring a necessary lipo-philicity-solubility balance. For example, use of a cyclohexano moiety as shown above, instead of the more common o-phenylene bridge between nitrogens, enhances solubility in the membrane phase. The modification of the polyether chain with binaphthyl or calixarene substituents provides high membrane transport rates due to increased ionophore lipophilicity [138,142]. Some representative examples (initial fluxes, in 10 mol cm h , through o-nitrophenyloctyl ether-impregnated Accurel membrane 1 M source urea [138]) are as follows. 

A series of diamide-based cryptands derived from bis(m-phenylene)-[32]crown-10 have been synthesized to complex divalent salts such as paraquat (N,N-dimethyl-4,4 -bipyridinium) dichloride. The synthetic project started from the observation that readily prepared bicyclic crown ether 23 containing two 1,3,5-phenylene units linked by three tetra(ethyleneoxy) units forms a pseudorotaxane-like inclusion complex with Af,Af-dimethyl-4,4-bipyridinium bis(hexafluorophosphate), with an association constant /fa = 6.1 X 1() M that is 100-fold greater than that of the analogous simple crown ether. On this basis, additional anion-binding moieties, such as isophthalamide or 2,6-pyridinedicarboxamide unit, were intfoduced in the third chain of the cryptand receptor. The anion-assisted complexation of bypyridinium dications was analyzed by a combination of different techniques ( H NMR,... 

Figure 15 (Left) Bicyclic crown ether containing two 1,3,5-phenylene units linked by three tetra(ethyleneoxy) units. (Right) Derivative in which one chain contains anion-binding moieties. (Reproduced from Ref. 33. Wiley-VCH, 2010.)...

Another wide family of purely organic interlocked systems has been developed by Stoddart s group, based on hydrogen bonding and on donor-acceptor interactions. Suitably sized crown ethers can form pseudorotaxane complexes with appropriate secondary dialkylammonium ions which rely on N —H - 0 and C—H - 0 hydrogen bonds for stabiUzation. Similarly, a r-electron rich component, in interaction with a r-electron deficient moiety (traditionally cyclobis(paraquat-p-phenylene), CBPQ T, 21, ... 

---