Polymerisable liquid crystalline compounds

Details Polymerisable liquid crystalline compounds Polymerisable liquid crystalline compounds

1999-11-19

2002-05-28

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C252S299630, C252S299640, C252S299650, C252S299660, C252S299670, C560S064000, C560S118000, C560S130000, C560S144000

Reexamination Certificate

active

06395351

ABSTRACT:

This invention relates to new photo-crosslinkable liquid crystalline compounds, liquid crystalline mixtures which contain such compounds, and their use in the cross-linked condition as optical components.
Photo cross-linkable liquid crystals, which are provided with an appropriate amount of a photoinitiator, can be oriented on a substrate or in a cell by suitable orienting layers or in a field and then in this state can be cross-linked by irradiation with light of a suitable wavelength. The liquid crystal orientation in the structure thus produced is maintained, even at high temperatures. Optical components, such as waveguides, optical grids, filters and retarders, piezoelectric cells and cells with non-linear optical (NLO) properties etc. may therefore be produced using this procedure. Such optical elements may be used, for example, for frequency doubling (SHG) or in colour filters.
The optical properties of the liquid crystal materials used in the manufacture of the aforementioned optical components such as birefringence, refractive indices, transparency, etc. are selected according to the field of application in which they are to be used. Thus materials for optical filters, for example, must exhibit a high birefringence &Dgr;n at low dispersion n=f(&lgr;).
In addition to the use of photo-crosslinkable liquid crystals in the manufacture of optical components, such liquid crystalline materials are also suitable as glass fibre cladding for optical data transmission. Photo-crosslinkable liquid crystals exhibit anisotropic thermal conductivity, enabling heat to flow in certain directions. The use of such materials reduces the thermal coefficients of expansion and reduces microdistortion losses. This results in increased mechanical stability.
Liquid crystal media used in the manufacture of optical components are generally used in the form of liquid crystal mixtures. It is desirable that liquid crystal components are chemically and thermally stable, readily soluble in conventional solvents, and stable to electrical fields and electromagnetic radiation. They should have a suitable mesophase in the temperature range of from approx. 25° to approx. +100° C., particularly from approx. 25° C. to approx. +80° C. Moreover, since liquid crystals are usually used as mixtures of several components, it is important for the components to be well miscible with one another.
Conventional photochemically oligomerisable or polymerisable liquid crystals generally have a high melting and clearing point. The disadvantage of this is that spontaneous, thermal polymerisation may occur prematurely during processing, this polymerisation occurring at temperatures just below the clearing point where the viscosity is low and therefore favourable for a good orientability. This spontaneous polymerisation represents a significant problem as it results in the formation of domains, which substantially impairs the optical and thermal properties in the crosslinked layers produced. In an attempt to overcome this problem, complicated liquid crystal mixtures having several components have been used. Although the lower melting and clarifying points of these mixtures means that they can be processed at lower temperatures it presents the risk of crystallisation of the liquid crystal components.
There is, therefore, a need for photochemically oligomerisable or polymerisable compounds exhibiting relatively lower melting and higher clearing points. Such compounds can be satisfactorily processed in the liquid crystalline condition at temperatures above room temperature, and also in solution. These compounds find particular application in the manufacture of optical components. There is also a need for compounds that can be readily orientated and structured without the formation of domains, and which also exhibit excellent thermal and long-term stability in the crosslinked condition. There is also a need for liquid crystal mixtures with an adjustable optical anisotropy. Liquid crystal mixtures having an adjustable anisotropy are considered to be particularly suitable for the manufacture of optical retarders, for example, in which the optical retardation may be adjusted.
Conventional photochemically oligomerisable or polymerisable liquid crystals, such as those described in EP-A-0 331 233, ACS Symp. Ser. (1996)), 632, 182-189 and in Chem. Mater. (1996), 8 (10), 2451-2460, for example, consist mainly of aromatic rings, and therefore generally exhibit a very high optical anisotropy.
The present invention seeks to address at least some of these problems. A first aspect of the present invention provides compounds with the general formula I:
R—S
1
—A—Z
1
—B—S
2
—R  I
where
A and B are independent ring systems with the formulae a
1
, a
2
or b,
wherein, in teh trans-1,4-cyclohexylene ring, one or two non-adjacent CH
2
groups may be replaced by oxygen, and whereby, in the 1,4-phenylene ring, one or two non-adjacent CH groups may be replaced by nitrogen;
L
1
, L
2
, L
3
represent, independently, hydrogen, C
1
-C
20
-alkyl, C
1
-C
20
-alkenyl, C
1
-C
20
-alkoxy, C
1
-C
20
-alkyoxycarbonyl, formyl, C
1
-C
20
-alkylcarbonyl, C
1
-C
20
-alkylcarbonyloxy, halogen, cyano or nitro;
Z
1
, Z
2
, Z
3
represent, independently, a single bond, —CH
2
CH
2
—, —CH
2
O—, —OCH
2
—, —COO—, —OOC—, —(CH
2
)
4
—, —O(CH
2
)
3
—, —(CH
2
)
3
O— or —C≡C—;
S
1
, S
2
represent, independently, a spacer unit, such as a straight chain or branched alkylene grouping —(CH
2
)
r
, substituted if necessary singly or multiply with, for example, fluorine, or —((CH
2
)
2
—O)
r
—, or a chain with the formula —(CH
2
)
r
—Y—(CH
2
)
s
—, where Y represents a single bond or a linking functional group such as —O—, —COO—, —OOC—, —NR
1
—, NR
1
—CO—, —CO—NR
1
—, —NR
1
—COO—, —OCO—NR
1
—, —NR
1
—CO—NR
1
—, —O—OC—O—, —CH≡CH—, —C≡C—; where R
1
represents hydrogen or low alkyl, and where r and s each represent a whole number from 0 to 20 on condition that 2≦(r+s)≦20;
R represents crosslinkable groups with the structure CH
2
═CH—, CH2═CH—COO—, CH
2
═C(CH
3
)—COO—, CH
2
═C(Cl)—COO—, CH
2
═C(Ph)—COO—, CH
2
═CH—COO—Ph—, CH
2
═CH—CO—NH—, CH
2
═C(CH
3
)—CONH—, CH
2
═C(Cl)—CONH—, CH
2
═C(Ph)—CONH—, CH
2
═C(COOR′)—CH
2
—COO—, CH
2
═CH—O—, CH
2
═CH—OOC—, Ph—CH═CH—, CH
3
—C(═NR′)—, cis- or trans-HOOC—R′═CR′—COO—,
Ph represents a phenyl group,
R′ represents methyl, ethyl, propyl, butyl or pentyl;
R″ represents methyl, methoxy, cyano or halogen,
with the proviso that at least one of the ring systems A or B represents a ring system with the formula a
1
or a
2
, Z
1
and/or Z
2
represents a single bond, and —R—S
1
and R—S
2
do not contain —O—O— or —N—O— groups.
Compounds containing a structural unit with the formulae a
1
or a
2
in the molecule
(that is to say, a structural unit with the above-mentioned formulae a
1
and a
2
and in which Z
2
represents a single bond) have been found to exhibit relatively high clearing points and can be processed at room temperature, preferably as components of liquid crystal mixtures. It is also possible to orientate and structure the compounds or mixtures thereof without the formation of domains. As a component of a LC mixture, they are able to improve the orientability of the liquid crystal mixture on orientation layers thereby improving the contrast of optical display devices. In addition they exhibit extremely good thermal and long-term stability.
By the expression C
1
-C
20
-alkyl, C
1
-C
20
-alkoxy, C
1
-C
20
-alkoxycarbonyl, C
1
-C
20
-alkylcarbonyl, C
1
-C
20
-alkylcarbonyloxy it should be understood to mean, in the context of this invention, straight or branched chain saturated hydrocarbon residues, with up to 20 carbon atoms, e.g. methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, methoxy, ethoxy, n-propoxy, i-propoxy, butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, nonyloxy, decyloxy, undecyloxy, dodecyloxy, methoxycarbonyl, ethox

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