Liquid crystal polymers

Details Liquid crystal polymers Liquid crystal polymers

1998-05-26

2000-02-29

Wu, Shean C.

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

With charge transferring layer of specified composition

25229901, 25229961, 25229963, 25229964, 25229965, 25229966, 252 629, 349 2, 528396, C09K 1938, C09K 1942, G02F 1133, C08G 6104

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active

060306688

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention concerns novel liquid crystal polymers (LCP) materials, novel intermediates and methods for preparing them.
Liquid crystals can exist in various phases. In essence there are three different classes of liquid crystalline material, each possessing a characteristic molecular arrangement. These classes are nematic, chiral nematic (cholesteric) and smectic. A wide range of smectic phases exists, for example smectic A and smectic C. Some liquid crystal materials possess a number of liquid crystal phases on varying the temperature, others have just one phase. For example, a liquid crystal material may show the following phases on being cooled from the isotropic phase:--isotropic--nematic--smectic A--smectic C--solid. If a material is described as being smectic A then it means that the material possesses a smectic A phase over a useful working temperature range.
Materials possessing a smectic A (SA) phase may exhibit an electroclinic effect. The electroclinic effect was first described by S Garoff and R Meyer, Phys. Rev. Lett., 38, 848 (1977). An electroclinic device has also been described in UK patent application GB-2 244 566 A. This particular device helps to overcome the poor alignment problems of electroclinic (EC) devices using a surface alignment that gives a surface tilt within a small range of angles.
When a smectic A phase is composed of chiral molecules, it may exhibit an electroclinic effect, i.e. a direct coupling of molecular tilt to applied field. The origin of the electroclinic effect in a smectic A phase composed of chiral polar molecules has been described by Garoff and Meyer as follows. The application of an electric field parallel to the smectic layers of such a smectic A phase biases the free rotation of the transverse molecular dipoles and therefore produces a non-zero average of the transverse component of the molecular polarisation. When such a dipole moment is present and coupled to the molecular chirality, a tilt of the long molecular axis (the director) is induced in a plane perpendicular to the dipole moment.
In thin samples, for example 1-3 mm, and with the smectic layers tilted or perpendicular with respect to the glass plates the electroclinic effect is detectable at low applied fields.
In an aligned smectic A sample a tilt of the director is directly related to a tilt of the optic axis. The electroclinic effect results in a linear electro-optic response. The electro-optic effect can manifest itself as a modulation of the effective birefringence of the device.
Electroclinic (EC) devices are useful, for example, in spatial light modulators having an output that varies linearly with applied voltage. A further advantage of EC devices is that they have high speed response times, much faster than twisted nernatic type devices. One known type of ferroelectric device is bistable, in contrast the EC device is not bistable and has an output that varies linearly with applied voltage.
The electroclinic effect is sometimes referred to as the soft-mode effect see G Andersson et al in Appl. Phys. Lett., 51, 9, (1987).
In general terms, regarding the electroclinic effect, it is advantageous if on applying a small voltage there results a large induced tilt. An increase in induced tilt may result in an increase in contrast ratio. It is also advantageous if a large induced tilt can be obtained at as low a voltage as possible.
It is also advantageous if the relationship between molecular induced tilt and applied voltage is temperature independent. When an increase in applied voltage results in little or no change in induced tilt then the material being tested is generally referred to as exhibiting a saturation voltage effect.
By S.sub.A * is meant a S.sub.A phase which contains some proportion of chiral molecules.
Cholesteric or chiral nematic liquid crystals possess a twisted helical structure which is capable of responding to a temperature change through a change in the helical pitch length. Therefore as the temperature is changed, then the wavelength of th

REFERENCES:
patent: 5104956 (1992-04-01), Waymouth
Macromolecules, vol 26, No. 1, Jan. 4, 1993, pp. 155-166, XP000330544 Colr F R: "Side-Chain Liquid Crystalline Poly(N-Maleimides). 5. Dielectric Relaxation Behavior Of Liquid Crystalline Side-Chain And Amorphous Poly(N-Maleimides). A Comparative Structural Study".
Macromolecules, vol. 26, No. 7, Mar. 29, 1993, pp. 1487-1492, XP000355034 Sung-Ho Jin et al: "Synthesis And Characterization Of Novel Side-Chain Liquid Crystalline Polymers With a Poly(1,6-Heptadiyne) Main Chain" see the whole document.
Macromolecules, vol. 26, No. 6, Mar. 15, 1993, pp. 1387-1392, XP000355050 Zen Komiya et al: "Synthesis Of Side Chain Liquid Crystal Polymers By Living Ring-Opeining Metathesis Polymerization. 4. Synthesis of AB Block Copolymers Containing Amorphous and Side Chain Liquid Crystal Blocks" see the whole document.

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