Cholesteric phase-forming polymers, process for their preparatio

Details Cholesteric phase-forming polymers, process for their preparatio Cholesteric phase-forming polymers, process for their preparatio

1998-06-16

2000-08-22

Hampton-Hightower, P.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

528176, 528190, 528193, 528195, 528272, 528288, 528289, 528322, 428 1, 428357, 428394, 428395, 428480, C08G 63197, C08G 63193, C08G 63672, C08G 6344

Patent

active

061074470

DESCRIPTION:

BRIEF SUMMARY
The invention is in the area of liquid-crystalline, macromolecular compounds. In particular, the invention relates to polymers and oligomers which are capable of forming cholesteric phases. In addition, the invention indicates advantageous processes for the preparation of such substances. In addition, the invention also relates to the use of cholesteric polymers and oligomers.
It is known that molecules which are anisotropic in shape can form liquid-crystalline phases, known as mesophases (from the Greek meso=in between, meaning between an isotropic liquid and an anisotropic crystal), on warming. Molecules which are anisotropic in shape are therefore also referred to as mesogens (adj.=mesogenic); in particular, the term mesogen denotes the rigid moiety without the wing groups usually attached to the ends thereof in low-molecular-weight liquid-crystal molecules or flexible spacer segments in semiflexible liquid-crystalline main-chain polymers. The individual mesophases differ through the spatial arrangement of the major parts of the molecules on the one hand and through 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 ordering due to the long molecular axes lining up in parallel. Under the prerequisite that the molecules making up the nematic phase are chiral, a so-called cholesteric phase forms, in which the long axes of the molecules form a helical superstructure perpendicular thereto (H. Baessler, Festkorperprobleme XI, 1971). The chiral moiety may either be present in the liquid-crystalline molecule itself or added to the nematic phase as a dopant. Phases produced by doping are referred to as induced cholesteric phases. This phenomenon was first studied on cholesterol derivatives (H. Baessler, M. M. Labes, J. Chem. Phys. 52 (1970) 631; H. Baessler, T. M. Laronge, M. M. Labes, J. Chem. Phys. 51 (1969) 3213; H. Finkelmann, H. Stegemeyer, Z. Naturforschg. 28a (1973) 799). The induction of cholesteric phases later also became possible through addition of other chiral substances which are not themselves liquid-crystalline (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, namely large optical rotation and pronounced circular dichroism caused by selective reflection of circular-polarized light within the cholesteric phase. 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 wavelength range of the light selectively reflected by a cholesteric phase can be varied, in particular, by changing the concentration of a chiral dopant (J. E. Adams, W. E. L. Haas, Mol. Cryst. Liq. Cryst. 16 (1972) 33).
Such cholesteric systems offer interesting opportunities for practical use.
For more details on the prior art, the following documents and publications are also mentioned: 565-574; 1990, pp. 779, 780; and
D1 describes cyclosiloxanes which form cholesteric phases and which can carry side chains which can be categorized in three groups. Firstly, the side chains are conventional (monofunctional) side-chain mesogens. However, (mesogenic) cholesteryl esters are also discussed as side chains. Finally, (mesogenic) vinyl derivatives which are polymerizable and consequently crosslinkable are presented. The cholesteric siloxanes in D1 exhibit a strong temperature dependence of the reflection color, which is utilized in thermography (for example mammography). For most applications, however, this temperature dependence of the reflection color is undesired.
D2 discloses pigments whose color depends on the viewing angle. The pigments consist of aligned, three-dimensionally crosslinked substances having a li

REFERENCES:
patent: 4891418 (1990-01-01), Hara et al.
patent: 5766679 (1998-06-01), Siemensmeyer et al.
Kricheldorf et al., Macromolecular Rapid Com., vol. 16, No. 4, 1995, pp. 231-237.
Braun et al., Applied Macromolecular Chemistry and Physics, vol. 210, Aug. 1993, pp. 173-196.
Storbeck et al., Makromol. Chem., vol. 194, 1993, pp. 53-64.

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