Monoreactive mesogenic compounds

Details Monoreactive mesogenic compounds Monoreactive mesogenic compounds

2000-07-03

2002-12-10

Wu, Shean C. (Department: 1756)

Stock material or miscellaneous articles

Liquid crystal optical display having layer of specified...

C428S001530, C428S001550, C252S299640, C560S076000, C560S083000, C570S129000, C528S192000

Reexamination Certificate

active

06491990

ABSTRACT:

The invention relates to monoreactive mesogenic compounds, to polymerizable liquid crystal compositions comprising the monoreactive mesogenic compounds, to linear or crosslinked liquid crystal polymers obtainable from the monoreactive mesogenic compounds and the polymerizable compositions comprising them, and to the use of the monoreactive mesogenic compounds and the polymerizable compositions and polymers obtainable thereof in optical elements, liquid crystal displays, adhesives, synthetic resins with anisotropic mechanical properties, cosmetics, diagnostics, liquid crystal pigments, decorative and security applications, nonlinear optics and optical information storage:
BACKGROUND OF THE INVENTION
Polymerizable mesogenic compounds, which are also known as reactive mesogenic compounds, have been described in prior art for various purposes. For example, they can be aligned in their liquid crystal phase and subsequently polymerized in situ, to give linear or crosslinked liquid crystal polymer films with uniform orientation of high quality. These films can be used for example as optical elements, like polarization filters as described in EP 0 397 263, broadband circular polarizers as described in EP 0 606 940 and WO 97/35219, or compensation or retardation films as described in WO 98/00475, WO 98/04651 and WO 98/12584.
The polymerizable mesogenic compounds described in prior art, however, do often exhibit liquid crystalline phases only in a small temperature range or do not show mesophase behavior at all.
Therefore, often mixtures of two or more polymerizable compounds are used for the preparation of oriented liquid crystal polymer films.
When preparing oriented liquid crystal polymer films for the uses as described above, it is especially desired to have available polymerizable compositions exhibiting a nematic liquid crystal phase at room temperature, so that it is possible to carry out aligment and polymerization of the composition at low temparatures. For this purpose, it is advantageous if the single polymerizable components exhibit broad liquid crystalline phases, too.
Thus, there is a demand for polymerizable mesogenic compounds with a broad liquid crystalline phase, which can be used for the preparation of oriented liquid crystal polymer films for optical applications.
Furthermore, regarding the broad range of applications for polymerizable mesogenic compounds it is desirable for the expert to have available further compounds of this type which are easy to synthesize and fulfill the various requirements as described above.
SUMMARY OF THE INVENTION
It was an aim of the invention to provide polymerizable mesogenic compounds with advantageous properties, thus extending the pool of reactive mesogenic compounds available to the expert. Other aims of the present invention are immediately evident to the person skilled in the art from the following detailed description.
It was now found that these aims can be achieved by providing monoreactive mesogenic compounds according to the present invention.
The terms reactive or polymerizable mesogenic compound as used in the foregoing and the following comprise compounds with a rod-shaped, board-shaped or disk-shaped mesogenic group, i.e. a group with the ability to induce mesophase behavior. These compounds do not necessarily have to exhibit mesophase behavior by themselves. It is also possible that these compounds show mesophase: behavior only in mixtures with other compounds or when the polymerizable mesogenic compounds or the mixtures comprising them are polymerized.
The compounds according to the present invention are characterized by a mesogenic core which comprises three phenylene rings linked via ester groups, and which is laterally monosubstituted and terminally substituted by polar groups.
Monoreactive mesogenic compounds having a mesogenic core that is substituted with polar groups are disclosed in DE 38 37 936 and EP 0 648 827.
DE 38 37 936 shows monoreactive methacrylates with a mesogenic core that consists of a hydroquinone dibenzoate being laterally substituted with alkyl or alkoxy groups having two or more C atoms and carries a terminal cyano or alkoxy group. However, monoreactive compounds according to the present invention are not disclosed in DE 38 37 936. Furthermore, the compounds shown in DE 38 37 936 do exhibit only narrow or even monotropic nematic phases.
EP 0 648 827 discloses mono- and direactive mesogenic compounds having a mesogenic core with three phenylene rings linked directly or via ester groups, and optionally being laterally substituted with polar groups. However, the monoreactive ester compounds of the present invention are not disclosed in EP 0 648 827, whereas e.g. the compounds of EP 0 648 827 with directly linked phenylene groups (terphenyls) show a tendency to smectic phase behavior .
A particularly preferred aspect of the invention relates to the use of the inventive monoreactive mesogenic compounds in polymerizable compositions for the preparation of a liquid crystalline polymer retardation or compensation film with a planar or tilted structure.
In this connection, the term ‘tilted structure’ means that the optical axis of the retardation film forms a tilt angle between 0 and 90° with the plane of the film. The term ‘planar structure’ means that the optical axis of the retardation film is oriented substantially parallel to the plane of the film. For sake of simplicity, an optical retardation film (ORF) with a tilted structure or a planar structure is hereinafter shortly referred to as ‘tilted ORF’, and ‘planar ORF’, respectively.
A tilted ORF is described for example in WO 98/12584, a planar ORF is described for example in WO 98/04651, the entire disclosure of these documents being incorporated into this application by way of reference.
Planar and tilted ORFs as described above are usually prepared from a polymerizable liquid crystal composition by coating a thin layer of the composition onto a substrate, aligning the liquid crystal molecules in the layer in the desired orientation, and fixing the orientation by polymerization.
Thus, in case of a planar ORF, it is required to achieve highly uniform alignment of the polymerizable compounds, with the mesogenic groups oriented substantially parallel to the substrate, i.e. with a low tilt angle or preferably without any tilt, whereas in case of a tilted ORF, the polymerizable compounds have to be aligned such that the mesogenic groups form the desired tilt angle with the plane of the substrate.
The inventors have found that, when using a monoreactive prior art mesogenic compound with a polar terminal group in a polymerizable composition, such as e.g. the compound
the methacrylate homologue of which is described in EP 0 445 629, the resulting composition has a relatively narrow nematic phase with a low nematic isotropic phase transition temperature (clearing temperature), and shows a relatively low tilt angle.
On the other hand, when adding a monoreactive prior art compound with an non-polar terminal alkyl group to the polymerizable composition, such as e.g. the compound
which is known from WO 97/34862 and exhibits a broad nematic phase, the clearing temperature of the composition is increased, however at the same time the tilt angle is increased.
Therefore, due to the above described arbitrating effects it is difficult, by using known compounds, to increase the clearing temperature of a polymerizable composition without altering the tilt angle.
The inventors now found that, when using one or more monoreactive mesogenic compounds according to the present invention in a polymerizable liquid crystal composition as described above, it is possible at the same time to increase the clearing point of the composition whereas the tilt angle remains substantially the same.
Thus, the inventive monoreactive mesogenic compounds can be used in a polymerizable liquid crystal composition that shows planar orientation with low tilt when coated onto a substrate, in order to improve the nematic phase behavior of the composition. On the other hand, the inventive comp

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