Chiral liquid-crystalline polymer

Differences in tacticity were also reflected by thermal data. While the iso-tropization temperature of (-)-poly-(IV-ll) and ( )-poly-(IV-ll),synthesized using initiator 1, stayed approximately unchanged, the isotropization temperatures for the chiral liquid crystalline polymers shifted to higher values when initiators 2 or 3 were used. The difference was up to 7 °C. If the decreased glass transition temperatures (Tg) for the chiral analogues were taken into account, the temperature range of the liquid crystalline phase was broadened by up to 12 °C. This means that a certain diad must be responsible for this behavior. The authors assumed that the diad cmHT was most suitable one for the formation of stable liquid crystalline phases in poly(norbornene) main chains. 

Dielectric and Electrooptical Properties of a Chiral Liquid Crystalline Polymer... 

It is worthy to note at this point that the polymerization of mesogenic monomers with chiral moieties does not necessarily result in polymers with the chiral liquid crystalline phase. For example, Finkelmann (1982) reported that homopolymers of chiral monomers yielded only smectic mesophases. On the other hand, copolymerization of chiral monomers with different spacers or of a chiral monomer and a nematic monomer has been proven effective and convenient for synthesizing chiral liquid crystalline polymers. 

Gipparone, G., Mazzulla, A., Kozlovsky, M. V, Palto, S. P., Yudin, S. G., and Blinov, L. M. Polarization gratings in photosensitive Langmuir-Blodgett films and chiral liquid crystalline polymers. Mol. Mat. 12, 359 (2000). 

The unspecific textures of evolutionary polydisperse DNAs a) W.-V. Meister, A.-M. Ladhoff, S. I. Kargov, G. Burckhardt, G. Luck, S.Hoffmann,Z Chem. 1990,i0,213 b)A.Leforestier, F. Livolant, Phase Transition in a Chiral Liquid Crystalline Polymer . Eur. Conf. Liq. Cryst. Sci. Technol., Conf. Abstr., Films 1993, 1-19, 24 see also [62],... 

Chiellini E., GaUi G., Po R., Chiral liquid-crystalline polymers. XII. New chiral polyesters by chemical modification of a nonmesophasic polymer, Polym. Bull., 23, 1990, 397-402. 

Chiellini, E., and Galli, G., Chiral liquid crystalline polymers recent trends and perspectives in synthesis and electrooptical applications. Mol. Cryst. Liq. Cryst., 254, 17-36 (1994). 

Bualek S, Kapitza H, Meyer J, Schmidt GF, Zentel R (1988) Orientability of crosslinked and of chiral liquid-crystalline polymers. Mol Cryst Liq Cryst 155 47-56. doi 10.1080/ 00268948808070351... 

Fouquey, C. Lehn, J.-M. Levelut, A.-M. Molecular recognition directed self-assembly of supramolecular liquid crystalline polymers from complementary chiral components. Adv. Mater. 1990, 2, 254-257. 

Alternating dark and bright bands observed, following shear, in a wide range of main-chain nematic and chiral nematic liquid-crystalline polymers. 

Gulikkrzywicki T, Fouquey C, Lehn JM. Electron-microscopic study of supramolecular liquid-crystalline polymers formed by molecular-recognition-directed self-assembly from complementary chiral components. Proc Natl Acad Sci USA 1993 90 163-167. 

Wulff, G. Schmidt, H. Witt, H. Zentel, R. Cooperativity and Transfer of Chirality in Liquid-Crystalline Polymers, Angew. Chem. Int. Ed. Engl. 1994, 23, 188-191. 

Scheme 6.9. Ringsdorf et al. s[434 preparation of hyperbranched liquid crystalline polymers possessing chiral capping units.

Scheme 7.6. Preparation of a hyperbranched liquid crystalline polymer possessing mesogenic building blocks and chiral termini.

A large number of azobenzene-based amorphous and liquid crystalline polymers, particularly polyacrylates and polymethacrylates with chiral azobenzene pendants, have been prepared for the development of data storage and photonic devices [1-3,11-14]. For instance, the introduction of optically active mesogenic azobenzene residues into the side groups of the polymers produces chiral nematic and cholesteric phases, which are regulated by photoisomerization of the azobenzene units [10,14]. In most cases, however, the optical activity and chiroptical... 

T. Gulik-Krzywicki, C. Fouquey, J.-M. Lehn, Electron Microscopic Study of Supramolecular Liquid Crystalline Polymers Formed by Molecular-Recognition-Directed Self-Assembly from Complementary Chiral Components , Proc. Natl. Acad. Sci. USA, 90, 163 (1993)... 

Chirality in Liquid-Crystalline Polymers, Chem. Int. Ed. Engl. 1994,... 

There have been many papers concerning liquid-crystalline polymers having azobenzenes in their side chains (Figure 14) because of the mesogenic nature of the azo chromophore. Liquid-crystalline polymers incorporating azobenzene moieties in their main chains (30) have also been prepared.102 A family of poly(acrylates) substituted with azobenzenes having chiral alkyl groups (31) showed smectic A as well as cholesteric phases.103 The photochromic behavior... 

Han, W.H. Rey, A.D. Dynamic simulations of shear-flow-induced chirality and twisted-texture transitions of a liquid-crystalline polymer. Phys. Rev. E. 1994, 49, 597-613. 

A similar approach has been used to produce materials with a chiral (cholesteric) structure by performing the experiments described above in the presence of a low molecular weight chiral liquid crystalline material (Figure 9.6). The chiral material is not covalently attached to the network and can be removed subsequently to produce an imprinted chiral structure. As before, the polymer displays a nematic mesophase between the glass transition (Tg 33°C) and the transition to an isotropic fluid (rN, 128°C). 

The ease of forming the smectic mesophase by this class of side-group type liquid crystalline polymers has rendered a great possibility in synthesizing polymeric chiral smectic materials useful in non-linear optics, transducers, pyroelectric detectors and display devices (Chapter 6). The first polymer forming a chiral smectic-C phase was synthesized by Shibaev et al. (1984). It has a polymethacrylate main chain, a long polymethylene spacer, and a mesogenic unit attached at the end with a chiral moiety (polymer (3.60)). Since then, a lot of polymers with chiral mesophases have been synthesized and studied (Le Barny and Dubois, 1989). 

The texture of polymeric chiral liquid crystalline phases. The chiral liquid crystalline phases include the chiral smectics and the chiral nematic or cholesteric phase. Poly(7-benzyl-L-glutamate) and derivatives of cellulose are popular examples of polymers that form a chiral mesophase. Side-chain type copolymers of two chiral monomers with flexible spacers of different, lengths and copolymers of one chiral and the other non-chiral mesogenic monomers may also form a cholesteric phase (Finkelmann et al., 1978 1980). In addition, a polymeric nematic phase may be transformed to a cholesteric phase by dissolving in a chiral compound (Fayolle et al., 1979). The first polymer that formed a chiral smectic C phase was reported by Shibaev et al. (1984). It has the sequence of phase transition of g 20-30 Sc 73-75 Sa 83-85 I with the Sc phase at the lower temperature side of Sa- More examples of Sc polymers are given by Le Barny and Dubois (1989). 

In addition to the above mentioned lyotropic cholesteric liquid crystalline polymers composed of rigid polymers, there is a diversity of thermotropic cholesteric liquid crystalline polymers which consist of a flexible chain incorporated with a mesogenic and chiral units. The thermotropic cholesteric liquid crystalline polymers are classified into two categories main chain and side chain. 

In main chain cholesteric liquid crystalline polymers, the mesogenic groups and flexible spacers are linked alternatively. The flexible units contain asymmetrical carbon atoms which enable the polymers to possess chirality and thus form cholesteric liquid crystals. By varying the ratio of chiral to non-chiral parts, the cholesteric temperature range and pitch can be changed. The cholesteric range depends on the mol fraction of the polymers. A typical main chain cholesteric liquid crystalline polymer is shown in Figure 6.27. 

D-3-methyl-glyoxal is a common chiral spacer. In addition, D-butane-1, 3-diphenol, L-propane-1, 2-diphenol, and their dimers and trimers are used as the chiral spacers in cholesteric liquid crystalline polymers as well. 

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