GB2314839A - Chiral reactive mesogens - Google Patents

Abstract

The invention relates to chiral reactive mesogens of formula I P-(SP-X)n-(A 1 -Z 1 ) m -G-(Z 2 -A 2 ) I -R I wherein P, Sp, X, n, Z 1 , Z 2 , A 1 , A 2 , m, I, G and R have the meaning given in claim 1, to compositions comprising chiral reactive mesogens of formula I, to linear or crosslinked (co)polymers obtainable by (co)polymerizing said chiral reactive mesogens or compositions and to the use of said chiral reactive mesogens or compositions for the preparation of linear or crosslinked polymers or polymer films for decorative pigments, cosmetics or security applications, active and passive optical elements, colour filters, liquid crystal displays, adhesives or synthetic resins with anisotropic mechanical properties.

Description

Chiral Reactive Mesogens The invention relates to chiral reactive mesogens of the formula I P-(Sp-X)n-(A' -Zl)m-G-(-Z2-A2-)I -R wherein P is CH2=CW-COO-, WCH=CH-O-,

or CH2=CH-Phenyl-(O)k- with W being H, CH3 or CI and k being 0 or 1, Sp is a spacer group having 1 to 20 C atoms, X is a group selected from -0-, -S-, -CO-,-COO-, -000-, -OCO-O-, -S-CO-, -CO-S- or a single bond, n isOori, Z1 and Z2 are each independently 400-, -000-, -CH2CHr, -OCHr, -CH20-, -CH=CH-, -CH=CH-COO-, -OCO-CH=CH-, -C~C-, or a single bond, A1 and A2 are each independently 1 ,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1,4 cyclohexylene in which, in addition, one or two non-adjacent CH2 groups may be replaced by 0 and/or S, 1,4 cyclohexenylene, 1,4-bicyclo(2,2,2)octylene, pi peridine-1 ,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2,6-diyl, or 1,2,3,4 tetrahydro-naphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or polysubstituted with halogen, cyano or nitro groups or alkyl, alkoxy or acyl groups having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, m and I are each independently 0, 1 or 2, G is the following structure element

with q being 0, 1, 2, 3 or 4 and L being in each case independently halogen, a cyano or nitro group or an alkyl, alkoxy or acyl group having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, and R is an alkyl radical with up to 25 atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH2 groups to be replaced, in each case independently from one another, by -O-, -S-, -NH-, -N(CH3)-, -CO-, -COO-, -000-, -OCO-O-, -S-CO-, -CO-S- or -C5C- in such a manner that oxygen atoms are not linked directly to one another, or altematively R is halogen, cyano or has independently one of the meanings given for P-(Sp-X)n-.

The invention furthermore relates to compositions comprising at least two reactive mesogenic compounds at least one of which is a chiral reactive mesogen of formula I as specified above or below.

Another aspect of the invention are linear or crosslinked (co)polymers obtainable by (co)polymerizing at least one chiral reactive mesogen of formula I or a composition as described above.

Yet another aspect of the invention is the use of chiral reactive mesogenic compounds or compositions as described above for the preparation of linear or crosslinked polymer materials or polymer films for decorative pigments, cosmetics or security applications, active and passive optical elements, colour filters, liquid crystal displays, in particular polymer stabilized cholesteric texture displays, adhesives or synthetic resins with anisotropic mechanical properties.

The chiral reactive mesogenic compounds of the present invention can be polymerized in situ alone or in mixture with achiral reactive mesogens when being macroscopically oriented in their liquid crystalline state to give anisotropic linear or crosslinked polymers or polymer films with a helically twisted molecular structure. These polymer films preferably have a uniform orientation of high quality.

Such materials can be used for example as optical elements like broad band cholesteric polarizers, such as described in EP 0,606,940.

For these applications as well for others like, for example polymerizable liquid crystalline mixtures for polymer stabilized cholesteric texture displays (PSCT) displays, it is often desired to have available polymerizable materials that show a strong helical twist, and thereby a pitch length which is short enough so that the maximum of the wavelength reflected by the cholesteric helix is in the range of visible light or even below, i.e. in the UV region.

Chiral reactive mesogenic compounds of various molecular structures are described for example in the Patent Applications EP O 562 681 and DE 195,04,224.

However, chiral reactive mesogenic compounds of the prior art most often exhibit low values of the helical twisting power (HTP). The HTP is the ability of a chiral compound to induce or enhance a helically twisted molecular structure in a liquid crystalline medium. It is related to the concentration c of the chiral compound in the liquid crystalline medium and to the pitch p of the molecular helix in the first approximation, which is sufficient for most practical applications, according to the following equation: 11 P HTP C (1) This means that in case of chiral compounds with a low HTP value high amounts of these compounds have to be used to obtain the desired short cholesteric pitch values for many applications. This is a serious drawback because, as these compounds can be used only with a significant enantiomeric excess, they are expensive and difficult to synthesize.

Another drawback when using chiral compounds with a low HTP is that their high concentrations which are necessary to achieve the desired short pitch lengths are altering the properties of the liquid crystalline medium, or, in case of polymerizable liquid crystalline compositions containing chiral compounds, the properties of the resulting polymer.

Consequently there has been a considerable demand for chiral reactive mesogens with a high HTP which are easy to synthesize and which can be used in low amounts in combination together with achiral polymer precursors.

One of the aims of the present invention is to provide chiral reactive mesogenic compounds having these properties, but which do not have the disadvantages of the compounds of prior art discussed above.

Another aim of the invention is to extend the pool of reactive mesogenic compounds available to the expert and /or to provide cheap chiral reactive mesogens based on regrowing natural resources. Other aims of the present invention are immediately evident to the person skilled in the art from the following detailed description.

It has been found that these aims can be achieved by the provision of chiral reactive mesogenic compounds according to formula I as shown above.

The inventive compounds contain a chiral structure element based on 1,4:3,6-Dianhydro-D-sorbitol, which is cheap and easily available from sugars as natural source.

G. Wulff et al. in Makromolekulare Chemie, 188 (4), 731-40 (1987) describe non-mesogenic 1,4 :3,6-Dianhydro-D-sorbitol-2,5- dimethacrylate used as chiral crosslinking agent for templateimprinted vinyl and acrylic polymers.

The German laid open Patent Application DE 4342 280 discloses chiral polymerizable compounds with 1 ,4:3,6-Dianhydro-D-sorbitol which is linked directly to benzene rings as a chirality inducing structure element.

The chiral reactive mesogenic compounds according to the present invention in addition to the sorbitol group comprise a structure element based on cinnamic acid. This group induces further significantly advantageous properties of the chiral reactive mesogenic compounds compared to those of prior art, among which are e.g. a higher birefringence and a broader mesophase range.

The terms reactive mesogen, reactive mesogenic compound, reactive liquid crystal (compound) or reactive liquid crystalline compound as used in the foregoing and the following comprise compounds with a rodlike, boardlike or disklike mesogenic group.

These mesogenic compounds do not necessarily have to exhibit mesophase behaviour by themselves. In a preferred embodiment of the present invention they show mesophase behaviour in mixtures with other compounds or after polymerization of the pure mesogenic compounds or mixtures comprising the mesogenic compounds.

Preferably the reactive mesogenic compounds exhibit mesophase behaviour on their own.

The object of the present invention is to provide chiral reactive mesogens of formula I P-(Sp-X)n-(A-Z)m-G-(-Z-A-)i-R wherein P is CH2=CW-COO-, WCH=CH-O-,

or CH2=CH-Phenyl-(O)k- with W being H, CH3 or Cl and k being 0 or 1, Sp is a spacer group having 1 to 20 C atoms, X is a group selected from -0-, -S-, -CO-,-COO-, -000-, -OCO-O-, -S-CO-, -CO-S- or a single bond, n isOor1, Z1 and z2 are each independently -COO-1 -000-, -CH2CH=, -OCH2-, -CH20-, -CH=CH-, -CH=CH-COO-, -OCO-CH=CH-, -0=-C-, or a single bond, A and A2 are each independently 1 ,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1,4 cyclohexylene in which, in addition, one or two non-adjacent CH2 groups may be replaced by 0 andlor S, 1,4 cyclohexenylene, 1 ,4-bicyclo(2,2,2)octyl ene, pi peridine-1 ,4-diyl, naphthalene-2,6-diyl, decahydronaphthalene-2 ,6-diyl, or 1,2,3,4 tetrahydro-naphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or polysubstituted with halogen, cyano or nitro groups or alkyl, alkoxy or acyl groups having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, m and I are each independently 0, 1 or 2, G is the following structure element

withqbeingo, 1, 2, 3 or 4 and L being in each case independently halogen, a cyano or nitro group or an alkyl, alkoxy or acyl group having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, and R is an alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH2 groups to be replaced, in each case independently from one another, by -O-, -S-, -NH-, -N(CH3)-, -CO-, -COO- -OCO-, -OCO-O-, -S-CO-, -CO-S- or -C=-C- in such a manner that oxygen atoms are not linked directly to one another, or alternatively R is halogen, cyano or has independently one of the meanings given for P-(Sp-X)n-.

Another object of the present invention are compositions comprising at least two reactive mesogens at least one of which is a compound of formula I as described above.

In a preferred embodiment of the invention the chiral reactive mesogens acccording to formula I are compounds of formula I a

wherein P, Sp, X, n, L, q and R have the meanings given in formula I.

In another preferred embodiment of the invention the chiral reactive mesogens are selected according to formula I or I a, wherein R has one of the meanings of P-(Sp-X)n- given above.

In another preferred embodiment of the invention the chiral reactive mesogens are compounds of formula I or I a, wherein R is halogen, cyano or an optionally fluorinated achiral or chiral alkyl or alkoxy group with 1 to 15 C atoms.

In another preferred embodiment of the invention the chiral reactive mesogens are compounds of formula I or I a, wherein n is 1 and Sp is alkylene with 1 to 15 C atoms.

Halogen is preferably F, Cl or Br, especially preferably F.

In yet another preferred embodiment the composition comprising chiral reactive mesogens as described above is characterized in that it comprises at least one reactive mesogenic compound of formula I having two or more polymerizable terminal groups.

Another aspect of the invention are linear or crosslinked (co)polymers obtainable by (co)polymerizing at least one chiral reactive mesogen of formula I or a composition comprising a chiral reactive mesoogen of formula I.

Yet another aspect of the invention is the use of chiral reactive mesogens or compositions as described above for the preparation of linear or crosslinked polymers or polymer films for decorative pigments, cosmetics or security applications, active and passive optical elements, colour filters, anisotropic gels, liquid crystal displays in particular polymer stabolized cholesteric texture displays, adhesives or synthetic resins with anisotropic mechanical properties.

Of the compounds of formula I the following are preferred: P-Sp-X-G-R 11 P-Sp-X-A1 X -G-Z2-A2-R 12 P-Sp-X-A1 -Z1 -G-R 13 P-S p-X-G-Z2-A2-R 14 P-SP-X-A' -Z'-A'-Z1-G-R IS P-S p-X-G-Z2-A2-Z2-A2-R 16 P-Sp-X-A'-Z'-A'-Z'-G-Z2-A2-R 1 7 P-Sp-X-A1-Z1-G-Z2-A2-Z2-A2-R 1 8 P-Sp-X-A'-Z'-A' Z' -G-Z-A-Z-A-R 19 wherein P, Sp, X, Aa, A2, Z1, Z2, G and R have the meanings given for formula I as described above.

Of these compounds, particularly preferred are those of formula II to 1 4, very particularly preferred those of formula 11 and 1 2.

Particularly preferred mesogenic compounds of the formula 11 are those wherein n is 1 and R is alkyl or alkoxy with 1 to 15 C atoms or has the meaning of P-Sp-X-. Furthermore -Sp-X- in the compounds of formula 11 is preferably alkylene or alkyleneoxy with 1 to 12 C atoms.

Of the compounds of formula 1 2 to I 9 especially preferred are those in which R is alkyl or alkoxy or has the meaning given for P-Sp-Xand Z1 and z2 are each independently -COO-, -OCO-, -CHCHr or a single bond.

Of the mesogenic compounds wherein A1 and A2 denote a heterocyclic group, those containing a pyridine-2,5-diyl group, pyrimidine-2,5-diyl group or 1 ,3-dioxane-2,5-diyl group are particularly preferred.

A smaller group of particularly preferred mesogenic compounds of the formulae 1 2, 1 3 and 1 4 is listed below. For reasons of simplicity, PheS is 1,4-phenylene, which is substituted in 2- and/or 3-position with S, wherein S has one of the meanings of L as given in formula I as described above. Furthermore, Pyd is pyridine-2,5-diyl, Pyr is pyrimidine-2,5-diyl, Cyc is 1 ,4-cyclohexylene, Dio is trans-1,3dioxane-2,5-diyl, Dit is trans-I ,3-dithiane-2,5-diyl and Nap is a tetraor decahydronaphthalene-2,6-diyl or naphthalene-2,6-diyl group. The notations Pyd, Pyr, Dio and Dit in each case include the 2 possible positional isomers.

Particularly preferred mesogenic compounds of the formula 1 2 are those of the following formulae: P-Sp-X-Phe-Z1 -G-Z2-Phe-R I 2-1 P-Sp-X-Phe-Z'-G-Z2-PheS-R 12-2 P-Sp-X-PheS-Z'-G-Z2-Phe-R 1 2-3 P-Sp-X-PheS-Z'-G-Z2-PheS-R I 24 P-Sp-X-Cyc-Z'-G-Z2-Cyc-R I 2-5 P-S p-X-Phe-Z1 -G-Z2-Cyc-R I 24 P-Sp-X-Cyc-Z'-G-Z2-Phe-R 2-7 P-Sp-X-PheS-Z1-G-Z2-Oyc-R I 2-8 P-Sp-X-Cyc-Z1-G-Z2-PheS-R I 29 P-Sp-X-Phe-Z1 -G-Z2-Pyr-R 12-10 P-Sp-X-Phe-Z1 -G-Z2-Pyd-R 12-11 P-Sp-X-Pyd-Z-G-Z-Pyd-R 12-12 P-Sp-X-Pyd-Z1 -G-Z2-PheS-R I 2-13 P-Sp-X-Pyr-Z-G-Z-PheS-R 12-14 P-Sp-X-Phe-Z'-G-Z2-Dio-R I 2-15 P-Sp-X-Phe-Z-G-Z-Dit-R 12-16 P-Sp-X-Dio-Z1-G-Z2-Dio-R I 2-17 P-Sp-X-Dit-Z1 -G-Z2-Dit-R 12-18 P-Sp-X-Phe-Z-G-Z-Nap-R I 2-19 P-Sp-X-Nap-Z1-G-Z2-Cyc-R I 2-20 In the compounds of formula 1 2-1 to 1 2-20, P, Sp, X, G, z', Z2 and R have, unless otherwise indicated, the meanings given for formula I described above.

In the compounds of formula 1 2-1 to 1 2-20, R is very particularly preferably P-Sp-X- or an alkyl or alkoxy group having 1 to 15 C atoms. Furthermore, Z' in these compounds is very particularly preferably an ester group (-CO-O- or 4-CO-), -CH2CHr or a single bond.

Of the compounds of formula 1 2-1 to 1 2-20, those of formula 1 2-1 to 1 2-9 are preferred. Especially preferred are the compounds of formula 1 2-1 to 1 2-4.

Particularly preferred mesogenic compounds of the formula 1 3 are those of the following formulae: P-S p-X-Phe-Z1 -G-R I 3-1 P-S p-X-PheS-Z1 -G-R I 3-2 P-Sp-X-Cyc-Z-G-R 1 3-3 P-Sp-X-Dio-Z-G-R I 3-4 P-Sp-X-Dit-Z1 -G-R 1 3-5 P-Sp-X-Pyr-Z-G-R 1 3-6 P-Sp-X-Pyd-Z-G-R I 3-7 P-Sp-X-Nap-Z1 -G-R 1 3-8 Particularly preferred mesogenic compounds of formula 1 4 are those of the following formulae: P-Sp-X-G-Z2-Phe-R I 4-1 P-S p-X-G-Z2-PheS-R I 4-2 P-Sp-X-G-Z2-Cyc-R I 4-3 P-Sp-X-G-Z2-Dio-R I 4-4 P-Sp-X-G-Z2-Dit-R I 4-5 P-Sp-X-G-Z2-Pyr-R I 4-6 P-Sp-X-G-Z2-Pyd-R I 4-7 P-Sp-X-G-Z2-Nap-R I 4-8 In the compounds of formula 1 3-1 to 1 3-8 and 1 4-1 to 1 4-8 P. Sp, X G, z', z2 and R, unless otherwise indicated, have the meanings given for formula I as described above.

Of the preferred compounds of the formulae 1 3-1 to 1 3-8 and 1 4-1 to I 4-8 in particular preferred are those in which R is P-Sp-X- or an alkyl or alkoxy group having 1 to 15 C atoms and Z' is -COO-, -OCO-, -CH2CHr or a single bond.

If R is an alkyl or alkoxy radical, i.e. where the terminal CH2 group is replaced by -0-, this may be straight-chain or branched. It is preferably straight-chain, has 2, 3, 4, 5, 6, 7 or 8 carbon atoms and accordingly is preferably ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, ethoxy, propoxy, butoxy, pentoxy, hexoxy, heptoxy, or octoxy, furthermore methyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, nonoxy, decoxy, undecoxy, dodecoxy, tridecoxy or tetradecoxy, for example.

Oxaalkyl, i.e. where one CH2 group is replaced by -O-, is preferably straight-chain 2-oxapropyl (=methoxymethyl), 2- (=ethoxymethyl) or 3-oxabutyl (=2-methoxyethyl), 2-, 3-, or 4-oxapentyl, 2-, 3-, 4-, or 5oxahexyl, 2-, 3-, 4-, 5-, or 6-oxaheptyl, 2-, 3-, 4-, 5-, 6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl or 2-, 3-, 4-, 5-, 6-,7-, 8- or 9oxadecyl, for example.

L and S are preferably F, Cl, CN, NO2, CH3, C2H5, OCH3, OC2H5, COCH3, COC2H5, CF3, OCF3, in particular F, CI, CN, CH3, C2H5, OCH3, COCH3 and OCF3, most preferably F, CH3, OCH3 and COCH3.

In the compounds of formula I P is CH2=CW-COO-,

WCH=CH-O- or CH2=CH-Phenyl-(O)k- with W being H, CH3 or Cl and k being 0 or 1.

P is preferably a vinyl group, an acrylate group, a methacrylate group, a propenyl ether group or an epoxy group, especially preferably an acrylate or a methacrylate group.

As for the spacer group Sp all groups can be used that are known for this purpose to the skilled in the art. The spacer group Sp is preferably linked to the polymerizable group P by an ester or ether group or a single bond. The spacer group Sp is preferably a linear or branched alkylene group having 1 to 20 C atoms, in particular 1 to 12 C atoms, in which, in addition, one or more non-adjacent CH2 groups may be replaced by -O-, -S-, -NH-, -N(CH3)-, -CO-, -O-CO-, -S-CO-, -O-COO-, -CO-S-, -CO-O-, -CH(halogen)-, -CH(CN)-, -CH=CH- or -0=-C-.

Typical spacer groups are for example -(CH2)o-, -(CH2CH20)r-, -CH2CH, -CH2CH2-S-CH2CHr or -C H2CHrN H-OH2CHr,with o being an integer from 2 to 12 and r being an integer from 1 to 3.

Preferred spacer groups are ethylene, propylene, butylene, pentyl ene, hexylene, heptyl ene, octylene, nonyl ene, decylene, undecylene, dodecylene, octadecylene, ethyl eneoxyethylene, methyl eneoxybutyl ene, ethylene-thioethylene, ethylene-N-methyliminoethylene and 1-methyl al kyl ene, for example.

In particular preferred are compounds of formula I wherein n is 1.

In a preferred embodiment, the polymers are copolymers obtained by copolymerizing mixtures comprising compounds of formula I wherein n is 0 and compounds of formula I wherein n is 1.

In the event that R or Q2 is a group of formula P-Sp-X- or P-Sprespectively, the spacer groups on each side of the mesogenic core may be identical or different.

The chiral reactive mesogenic compounds of formula I can be prepared for example according to or in analogy to the following reaction scheme.

Scheme 1:

MEK = methyl ethyl ketone, IMS = industrial methylated spirits, PTSA = p-toluenesulfonic acid, DCM = dichioromethane.

Corresponding monoreactive compounds can be prepared by using in the last reaction step a mixture of a cinnamic acid as indicated in scheme 1 and a cinnamic acid which is substituted in para position with R, wherein R is F, Cl, CN or an alkyl or alkoxy group with 1 to 12 C atoms.

Furthermore, reactive mesogenic compounds according to formula I can be prepared by methods which are known per se and which are described, for example, in standard works of organic chemistry such as, for example, Houben-Weyl, Methoden der organischen Chemie, Thieme-Verlag, Stuttgart.

Polymers or copolymers can be prepared from the inventive reactive mesogenic compounds by solution polymerization or by in-situ polymerization. Solution polymerization can be carried out for example in a solvent like dichloromethane, tetrahydrofuran or toluene using AIBN (Azobisisobutyronitril) as an initiator and heating for 24 hours at 30 to 60 "C. However, in order to obtain polymers with macroscopic uniform orientation, which is desired for most applications, the polymers prepared by solution polymerization have to be aligned afterwards e.g. by mechanical shear forces or electric or magnetic fields and high temperatures.

On the other hand, the inventive reactive mesogenic monomers can easily be aligned by conventional techniques and the alignment can subsequently be frozen in by in-situ polymerization to give well aligned anisotropic polymers. A detailed description of this method can be found in D.J.Broer et al., Makromol.Chem. 190, 2255 (1989).

The reactive mesogens and compositions according to this invention are preferably polymerized in situ as described in the foregoing and the following.

Polymerization of reactive mesogens or compositions comprising compounds with only one polymerizable functional group leads to linear polymers or copolymers, whereas in the presence of compounds with more than one polymerizable functional group crosslinked polymers are obtained.

In particular crosslinked polymers show very high thermal stability of the optical and mechanical properties, depending on the degree of crosslinking, when compared to linear polymers.

Linear or crosslinked polymers or copolymers can be obtained for example by exposure of the inventive reactive mesogenic compounds or compositions to actinic radiation in the presence of an initiator having an absorbing at the wavelength of said radiation.

For example, one can use UV light and a photoinitiator that decomposes under UV irradiation to produce free radicals that start the polymerization reaction. In another preferred embodiment a cationic photoinitiator is used that photocures with cations instead of free radicals. The polymerization may also be started by an initiator that decomposes when heated above a certain temperature.

As a photoinitiator for example the commercially available Irgacure 651 (from Ciba Geigy AG) can be used.

In addition to light- or temperature-sensitive initiators the compositions according to the present invention may also comprise one or more other suitable components such as, for example, catalysts, stabilizers, sensitizers, co-reacting monomers or surface- active compounds.

It is also possible to add, for example, a quantity of up to 20% by weight of a nonpolymerizable liquid-crystalline material to adapt the optical properties of the polymer.

It is also further possible to add altematively and/or additionally up to 20% of a non mesogenic compound with two or more polymerizable functional groups to increase crosslinking of the polymers. Typical examples for difunctional non mesogenic monomers are alkyldiacrylates or alkyldimethacrylates with alkyl groups of 1 to 20 C atoms. Typical examples for non mesogenic monomers with more than two polymerizable groups are trimethylpropanetrimethacrylate or pentaerythritoltetraacrylate.

To prepare anisotropic polymer films with uniform orientation the inventive reactive mesogenic compounds or compositions, for example, are coated onto a substrate, aligned and cured by irradiation as described above. Alignment and curing are carried out in the mesophase of the reactive mesogenic compounds.

As a substrate for example a glass plate or a plastic film can be used. To achieve uniform alignment, the film can be sheared for example by means of a doctor blade. In another preferred embodiment, a second substrate is put on top of the coated material.

In this case, the shearing caused by putting together the two substrates is sufficient to give good alignment.

In some embodiments it is of advantage to apply a second substrate to exclude oxygen that may inhibit the polymerization. Alternatively the curing can be carried out under an atmosphere of inert gas, for example under a nitrogen atmosphere. In this case shearing of the mesogenic material prior to polymerization is necessary to cause sufficient alignment of the mesophase. When using a cationic photoinitiator oxygen exclusion is not needed, but water should be excluded.

The compounds of the present invention can be used in mixtures with other reactive mesogenic compounds to give mixtures with low melting points. This is of importance especially when anisotropic polymer films are prepared. To obtain highly oriented films the polymerization has to be carried out in the liquid crystal phase of the reactive liquid crystal mixture. Thus by using mixtures of the compounds of this invention the polymerization temperature can be lowered significantly and the polymerization process is made easier.

When polymerizing the inventive reactive mesogenic compounds with propenyl ether groups as polymerizable groups preferably an initiator is used that decomposes when exposed to heat or actinic radiation to produce cations that start the polymerization reaction, like for example, the commercially available photoinitiator Cyracure UVI 6974 (from Union Carbide). In this case, water should be excluded during the polymerization.

Inventive reactvie mesogenic compounds carrying a propenyl ether group can be synthesized by catalyzed rearrangement of the corresponding allyl ether compound.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to ist fullest extent. The following examples are, therefore, to be construed as merely illustrative and not limitative of the remainder of the disclosure in any way whatsoever.

In the foregoing and in the following examples, unless otherwise indicated, all temperatures are set forth uncorrected in degrees Celsius and all parts and percentages are by weight. The following abbreviations are used to illustrate the liquid crystalline phase behaviour of the compounds: K = crystalline; N = nematic; S = smectic; Ch = cholesteric; I = isotropic. The numbers between these symbols indicate the phase transition temperatures in degree Celsius.

ExamPle 1 The following compound was prepared according to scheme 1.

Claims (9)

Patent Claims

1. Chiral reactive mesogens of formula I P-(Sp-X)n-(A-Z)m-G-(Z-A)i-R wherein P is CH2=CW-COO-, WCH=CH-O-,

or CH2=CH-Phenyl-(O)k- with W being H, CH3 or Cl and k being 0 or 1, Sp is a spacer group having 1 to 20 C atoms, X is a group selected from -0-, -S-, -C 0-, -COO-, -000-, -OCO-O-, -S-CO-, -CO-S- or a single bond, n isOor1, Z' and Z are each independently -COO-, -000-, -CH2CHr, -OCH2-, -CH20-, -CH=CH-, -CH=CH-COO-, -OCO-CH=CH-, -C-C- or a single bond, A1 and A2 are each independently 1,4-phenylene in which, in addition, one or more CH groups may be replaced by N, 1 ,4-cydohexylene in which, in addition, one or two non adjacent CH2 groups may be replaced by 0 and/or S, 1,4 cyclohexenylene, 1 ,4-bicyclo(2,2,2)octyl ene, piperidine- 1 ,4-diyl, naphthalene-216-diyl, decahydronaphthalene-2,6 diyl, or 1,2,3,4-tetrahydronaphthalene-2,6-diyl, it being possible for all these groups to be unsubstituted, mono- or polysubstituted with halogen, cyano or nitro groups or alkyl, alkoxy or acyl groups having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, m and I are each independently 0, 1 or 2, G is the following structure element

with q being 0, 1, 2, 3 or 4 and L being each independently halogen, a cyano or nitro group or an alkyl, alkoxy or acyl group having 1 to 7 C atoms wherein one or more H atoms may be substituted by F or Cl, and R is an alkyl radical with up to 25 C atoms which may be unsubstituted, mono- or polysubstituted by halogen or CN, it being also possible for one or more non-adjacent CH2 groups to be replaced, in each case independently from one another, by -O-, -S-, -NH-, -N(CH3)-, -CO-, -COO-, ECO-, -OCO-O-, -S-CO-, -CO-S- or -C=C-- in such a manner that oxygen atoms are not linked directly to one another, or altematively R is halogen, cyano or has independently one of the meanings given for P-(Sp-X),-.

2. Chiral reactive mesogens according to claim 1 of the formula I a

wherein P, Sp, X, n, L, q and R have the meanings given in claim 1.

3. Chiral reactive mesogens according to claim 1 or 2, wherein R has one of the meanings given for P-(Sp-)Qn-.

4. Chiral reactive mesogens according to claim 1, 2 or 3, wherein R is halogen, cyano or an optionally fluorinated achiral or chiral alkyl or alkoxy group with 1 to 15 C atoms.

5. Chiral reactive mesogens according to any of the claims 1 to 4, wherein n is I and Sp is alkylene with 1 to 15 C atoms.

6. A composition comprising at least two reactive mesogenic compounds at least one of which is a chiral reactive mesogen of formula I according to any of the claims 1 to 5.

7. A composition according to claim 6 characterized in that it comprises at least one reactive mesogenic compound having two polymerizable terminal groups.

8. A linear or crosslinked (co)polymer obtainable by (co)polymerizing at least one chiral reactive mesogen or a composition comprising chiral reactive mesogenic compounds according to any of the claims 1 to 7.

9. Use of chiral reactive mesogens or compositions as described in any of the claims 1 to 8 for the preparation of linear or crosslinked polymers or polymer films for decorative pigments, cosmetics, security applications, active and passive optical elements, colour filters, liquid crystal displays like for example polymer stabilized cholesteric texture displays, adhesives or synthetic resins with anisotropic mechanical properties.