Crosslinkable liquid crystalline compounds

Details Crosslinkable liquid crystalline compounds Crosslinkable liquid crystalline compounds

2001-04-05

2003-09-02

Huff, Mark F. (Department: 1756)

Compositions

Liquid crystal compositions

Containing nonsteryl liquid crystalline compound of...

C526S245000, C252S299660, C252S299670

Reexamination Certificate

active

06613245

ABSTRACT:

The present invention relates to crosslinkable, especially photocross-linkable, bi-reactive liquid crystalline compounds, to liquid crystalline mixtures comprising such compounds and to the use thereof in the crosslinked state as optical components.
Photocrosslinkable liquid crystals provided with a suitable amount of a photoinitiator can be oriented on a substrate or in a cell by means of suitable orientation layers or in a force field, and can then be crosslinked in that state by irradiation with light of-a suitable wavelength. The resulting structure is retained even at high temperatures. Thus, optical components, such as, for example, waveguides, optical gratings, filters and retarders, piezoelectric cells and cells having non-linear optical (NLO) properties, etc., can be produced. Such optical components can be used, for example, for frequency doubling (SHG) or in colour filters.
Further properties, such as, for example, the birefringence, the refractive index, the transparency, etc., must satisfy different requirements depending on the field of application. For example, materials for optical filters should have high birefringence &Dgr;n combined with low dispersion n=f(&lgr;).
In addition to the general utility of polymerisable i.e. crosslinkable liquid crystals for optical components, such liquid crystalline materials are suitable for cladding glass fibres for optical data transmission. The use of such materials increases the elastic modulus in the longitudinal axis of the fibre, lowers the thermal expansion coefficients and reduces microdistortion losses. This results in increased mechanical stability. Moreover, cross-linkable liquid crystals have an anisotropic thermal conductivity that enables heat to flow in specific directions.
The crosslinkable liquid crystals must have good chemical and thermal stability, good solubility in usual solvents and good stability towards electric fields and electromagnetic radiation. They should have a suitable mesophase in a temperature range from about 25° C. to about +100° C., especially from about 25° C. to about +80° C. It is also important that the components have good miscibility with one another since liquid crystals are generally used in the form of mixtures of several components.
For use in optical retarders, polarisation interference filters (for example Solc filters) etc., it is necessary, in addition, for the optical anisotropy to be as great as possible (&Dgr;n=|n
e
−n
o
|) while the absorption wavelength is as short as possible., In that manner, the desired optical retardation can be obtained with sufficiently thin LCP films (LCP stands for liquid crystalline polymer).The same applies also to use in cholesteric filters, since the band width of the selective reflection is proportional to the optical anisotropy &Dgr;n.
Conventional photochemically oligomerisable or polymerisable liquid crystals generally have a high melting point and a high clearing point and medium optical anisotropy. Firstly, the high melting point has the disadvantage that during processing spontaneous thermal polymerisation may occur prematurely at just above the melting point. This spontaneous polymerisation leads to the formation of domains, resulting in significant impairment of the optical and thermal properties of the crosslinked layers produced. Secondly, a small temperature difference between the melting point and the clearing point results in a low degree of ordering and thus in a low degree of optical anisotropy. The melting point can be lowered by producing complex mixtures having several components, which enables processing to be carried out at lower temperatures but entails the risk of crystallisation of conventional polymerisable liquid crystals. Photochemically oligomerisable or polymerisable compounds are described, for example, in EP-A-0 331 233.
It is accordingly an object of the present invention to provide oligomerisable or polymerisable i.e. crosslinkable compounds that, on their own or in mixtures, have an optical anisotropy that is as great as possible while the absorption wavelength is as short as possible, especially for use in optical components. They should also have low melting points and high clearing points so that during processing as high a degree of ordering as possible and thus a high degree of optical anisotropy of the LCP film is obtained at just above the melting point. It should further be possible to orient and structure the compounds without domains, and they should also have excellent thermal stability and long-term stability in the crosslinked state. Conventional photochemically oligomerisable or polymerisable liquid crystals generally have only medium optical anisotropy.
The present invention now provides compounds that are outstandingly suitable as individual components or as components of liquid crystal mixtures for the above-mentioned applications.
The present invention relates to compounds of the general formula I:
wherein
R
1
, R
2
each independently of the other represents a crosslinkable group, such as CH
2
═CH—, CH
2
═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—, (R′OOC)—CH
2
—C═CH
2
—COO—, CH
2
═CH—O—, CH
2
═CH—OOC—, CH═CH—Ph—, cis- or trans-—HOO—CR′═CR′—COO—, siloxane,
wherein (Ph) represents phenyl, Ph represents phenylene, R′ represents lower alkyl and R″ represents methyl, methoxy, cyano or halogen;
S
1
, S
2
each independently of the other represents a spacer unit, such as a straight-chain or branched alkylene grouping —(CH
2
)
r
— which may optionally be mono- or poly-substituted by fluorine, or —((CH
2
)
2
—O)
r
—, or a chain of the formula —(CH
2
)
r
—Y—(CH
2
)
s
— which may optionally be mono- or poly-substituted by fluorine, wherein Y is a single bond or a linking functional group, such as —O—, —COO—, —OOC—, —NR
3
—, —NR
3
—CO—, —CO—NR
3
—, —NR
3
—COO—, —OCO—NR
3
—, —NR
3
—CO—NR
3
—, —O—OC—O—, —CH═CH—, —C≡C—, wherein R
3
represents hydrogen or lower alkyl and r and s are each an integer from 0 to 20, with the proviso that 2≦r+s≦20, or —(Si[(CH
3
)
2
]O)
u
—, —O(CH
2
)
t
(Si[(CH
3
)
2
]O)
u
Si[(CH
3
)
2
](CH
2
)
t
O—, or —NH(CH
2
)
t
(Si[CH
3
)
2
]O)
u
Si[(CH
3
)
2
](CH
2
)
t
NH—, wherein t is an integer from 1 to 12 and u is an integer from 1 to 16, with the proviso that 2t+u≦20;
with the proviso that R
1
—S
1
and R
2
—S
2
do not contain any —O—O— or —N—O— groups;
A, C and D represent
B represents
wherein also at least one of the phenylene rings in A, B, C or D may be replaced by a 1,4-phenylene ring in which one or two non-adjacent CH groups have been replaced by nitrogen; and
L
1
, L
2
, L
3
each independently of the others represent hydrogen, C
1
-C
20
-allyl, C
2
-C
20
-alkenyl, C
1
-C
20
-alkoxy, C
2
-C
20
-alkenylpxy, C
1
-C
20
-alkoxycarbonyl, formyl, C
1
-C
20
-alkylcarbonyl, C
1
-C
20
-alkylcarbonyloxy or nitro,
with the proviso that in at least one phenylene ring in A, B, C or D one of the mentioned substituents is other than hydrogen;
k, l, m are O or 1, wherein k+I+m must be equal to 1 or 2; and
Z
1
, Z
2
, Z
3
each independently of the others represents a single bond, —CH
2
CH
2
—, —CH
2
O—, —OCH
2
—, —COO—, —OOC—, —CH═CH—COO—, —OOC—CH═CH—, —(CH
2
)
4
—, —O(CH
2
)
3
—, —(CH
2
)
3
O— or —C≡C—.
In the structural formulae of the present Application, broken lines ( - - - or—) are used to denote linkages with the adjacent element by a single bond.
Where necessary, the above-used terms will be explained hereinafter.
“Halogen” embraces, in the context of the present invention, fluorine, chlorine, bromine, iodine, especially fluorine and chlorine.
“Lower alkyl” represents, in the context of the present invention, a straight-chain or branched alkyl group having from 1 to 4 car

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