Compositions – Liquid crystal compositions – Containing nonsteryl liquid crystalline compound of...
Patent
1996-08-23
1998-11-10
Kelly, C. H.
Compositions
Liquid crystal compositions
Containing nonsteryl liquid crystalline compound of...
25229901, 25229967, C09K 1920, C09K 1952
Patent
active
058338802
DESCRIPTION:
BRIEF SUMMARY
This application is filed under 37 U.S.C. .sctn. 371 and claims benefit to PCT/EP95/00707 filed Feb. 27, 1995.
As known for molecules which are anisotropic in shape, liquid-crystalline phases, known as mesophases, can form on warming. The individual phases differ in the spatial arrangement of the major parts of the molecules on the one hand and in the molecular arrangement with respect to the long axes on the other hand (G. W. Gray, P. A. Winsor, Liquid Crystals and Plastic Crystals, Ellis Horwood Limited, Chichester, 1974). The nematic liquid-crystalline phase is distinguished by the fact that there is only one alignment long-distance order due to the long molecular axes lining up in parallel. Under the prerequisite of the molecules making up the nematic phase being chiral, a cholesteric phase forms, in which the long axes of the molecules form a helical superstructure perpendicular thereto (H. Baessler, Festkoperprobleme XI, 1971). The chiral moiety may either be present in the liquid-crystalline molecule itself or be added to the nematic phase as a dope, with induction of the cholesteric phase. This phenomenon was first studied in cholesterol derivatives (eg. H. Baessler, M. M. Labes, J. Chem. Phys., 52 (1970) 631; H. Baessler, T. M. Laronge, M. M. Labes, J. Chem. Phys., 51 (1969) 799; H. Finkelmann, H. Stegemeyer, Z. Naturforschg. 28a (1973) 799; H. Stegemeyer, K. J. Mainusch, Naturwiss., 58 (1971) 599, H. Finkelmann, H. Stegemeyer, Ber. Bunsenges. Phys. Chem. 78 (1974) 869).
The cholesteric phase has remarkable optical properties: a large optical rotation value and pronounced circular dichroism caused by selective reflection of circular-polarized light within the cholesteric layer. The different colors observed depending on the viewing angle depend on the pitch of the helical superstructure, which is itself dependent on the twisting power of the chiral component. The pitch and thus the wavelengths range of the selectively reflected light of a cholesteric layer can be varied, in particular by changing the concentration of a chiral dope. Cholesteric systems of this type offer interesting opportunities for practical use. For example, incorporation of chiral moieties into mesogenic acrylic esters and alignment in the cholesteric phase, for example after photocrosslinking, allows the production of a stable, colored network, but the concentration of the chiral component therein can then no longer be changed (G. Galli, M. Laus, A. Angelon, Makromol. Chemie, 187 (1986) 289). Furthermore, admixing of non-crosslinkable, chiral compounds wit:h nematic acrylic esters and photocrosslinking allows the production of a colored polymer still containing high proportions of soluble components (I. Heyndricks, D. J. Broer, Mol. Cryst. Liq. Cryst. 203 (1991) 113). Furthermore, the random hydrosilylation of mixtures of cholesterol derivatives and acrylate-containing mesogens using defined cyclic siloxanes followed by photopolymerization allows the production of a cholesteric network in which the chiral component can have a proportion of up to 50% of the material employed; however, these polymers still contain significant amounts of soluble components (F. H. Kreuzer, R. Maurer, C. Muller-Rees, J. Stohrer, Paper No. 7, 22nd Freiburg congress on liquid crystals, Freiburg, 1993).
DE-A-35 35 547 describes a process in which a mixture of cholesterol-containing monoacrylates can be converted into cholesteric layers by photocrosslinking. However, the total proportion of the chiral component in the mixture is about 94%. Although, as a pure side-chain polymer, a material of this type is not very mechanically stable, an increase in the stability can, however, be achieved by means of highly crosslinking diluents.
EP-A 331 233 describes mixtures of liquid-crystalline compounds which are symmetrically substituted by aliphatic side chains.
In addition to the nematic and cholesteric networks described above, smectic networks are also known and can be prepared, in particular, by photopolymerization/photocrosslinking of smectic liquid-crysta
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Delavier Paul
Etzbach Karl-Heinz
Meyer Frank
Siemensmeyer Karl
BASF - Aktiengesellschaft
Kelly C. H.
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