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Title:
LIQUID-CRYSTALLINE GLASSES
Document Type and Number:
WIPO Patent Application WO/1996/003476
Kind Code:
A1
Abstract:
The present invention is directed to stable liquid-crystalline glasses which have a high Tg and are readily orientable. Such glasses are suitable for use in optical applications. The glasses according to the invention are obtained by reacting a diamine with mesogenic group-containing epoxides. The liquid-crystalline glasses according to the invention are especially suitable for use in the retardation layers of displays, digital data storage such as CDs, analog data storage, and polarisers.

Inventors:
Wit DE.
Paulus
Pieter, Erdhuisen
Erwin
Wilhelmus
Petrus, Picken
Stephen
James
Application Number:
PCT/EP1995/002981
Publication Date:
February 08, 1996
Filing Date:
July 26, 1995
Export Citation:
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Assignee:
Akzo, Nobel N.
De Wit, Paulus Pieter Erdhuisen Erwin Wilhelmus Petrus Picken Stephen James
International Classes:
C07C225/22; C07D303/22; C08G59/22; C08G59/50; C09K19/22; C09K19/28; C09K19/30; C09K19/60; G02B5/30; G11B7/25; G02F1/13363; (IPC1-7): C09K19/22; C09K19/30; C09K19/28; C09K19/60; C09B23/00; C09K19/04; G11B7/24; G02F1/1337; G11B7/00; G11B7/26; C07C251/30
Foreign References:
EP0432735A21991-06-19
EP0478052A11992-04-01
US5112759A1992-05-12
EP0554627A11993-08-11
EP0475238A21992-03-18
EP0445401A21991-09-11
EP0568267A21993-11-03
Other References:
DATABASE WPI Week 8613, Derwent World Patents Index; AN 86-085022
DATABASE WPI Week 8801, Derwent World Patents Index; AN 88-003692
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Claims:
CLAIMS:
1. A l i qui dcrystal l i ne gl ass compri si ng a compound accordi ng to formul a 1 : wherein R»: represents an aromatic group having 5 to 24 carbon atoms, an aromatic groupcontaining aliphatic group having 6 to 24 carbon atoms, a heterocyclic group having 4 to 24 carbon atoms, or a cyclic aliphatic group having 6 to 24 carbon atoms; Ra: represents H, a nonmesogenic group or a mesogenic group with a spacer; R3 : may represent the same groups as R*. but may be chosen independently from R*. R* and R* ; R«: may represent the same groups as R*. but may be chosen independently from R*. R*. and R»; R>: may represent the same groups as R*. but may be chosen independently from R*. R* and R*, with not more than 25% of all R2, R3, R*, and R* groups representing H or a nonmesogenic group.
2. A liquidcrystalline glass according to claim 1, characterised in that Ri stands for a group according to the formulae below: C = C C = c / \ / \ C C (X)n C C \ / \ / C C c c c = c C C / \ / \ (CH2)m C C (CH2)m (CH2)m C C (CH2)m \ / C C c c C C C C c c / \ / \ / \ C C (X)n C C (CH2)m C C \ / \ / \ / C C C C , C C \ (CH2)m wherein X represents 0, SO2, CH2, S, C(0) or C(CH3)2, n represents 1 or 0, and m represents 0, 1, or 2.
3. A liquidcrystalline glass according to claim 1 or 2, characterised in that R*, R , R*. and/or Rs represent a mesogenic group according to the formulae below: CH2 R« CH2CH(CHRιo)t(0(CHRn)uCH2)v0 OH c c (R n (R')n C C c = c / \ / \ CH2 R« CH2CH(CHRio)t(0(CHRw)uCH2)v0 Ri OH CH2CH(CHRιo)t(0(CHR»ι)uCH2)v0 R« OH c = c c c I / \ / \ CH2CH(CHRιo)t(0(CHRι uCH2)v0C . C (Y)n C , C R« OH C C c c (ROn (ROn CH2 R« CH2CH(CHRιo)t(0(CHRιι)uCH2)v0 R« OH CH2 Ri wherein Y stands for C(0)0, OC, 0C(0), C=C, or NN; R stands for 0R», 0C0R» , C00R», CN, N02, or R»; R' stands for an alkyl group having 1 to 5 carbon atoms; R« stands for an alkyl group having 1 to 5 carbon atoms; R» stands for an alkyl group having 1 to 15 carbon atoms; t is 16; u is 17; v is 03; R»o stands for H or CH3; Rii stands forH or alkyl, and n has the same meaning as in the formulae above.
4. A l iquidcrystal l i ne glass accordi ng to any one of precedi ng claims 13, characteri sed in that the glass comprises a mixture of compounds according to formul a 1.
5. A liquidcrystalline glass according to anyone of the preceding claims 13, characterised in that different mesogenic groups are present within one glass molecule.
6. A liquidcrystalline glass according to any one of preceding claims 15, characterised in that the R*. RΪ, R*, and/or R= groups comprise a mesogenic group with positive dielectric anisotropy due to the presence of one or more permanent dipole moments directed along the long axis of the mesogenic group.*& 10.
7. A liquidcrystalline glass according to any one of preceding claims 16, characterised in that Ri is a croconium or squarilium fragment.
8. A liquidcrystalline glass according to any one of preceding 15 claims 16, characterised in that the glass comprises a dye.
9. A liquidcrystalline glass according to claim 8, characterised in that the dye is dichroic.*& 20.
10. Use of liquidcrystalline glass according to any one of preceding claims 16 in a retardation layer.
11. A retardation layer in which liquidcrystalline glass according to ?c. any one of preceding claims 16 is employed.
12. A retardation layer according to claim 11 wherein a liquid crystalline glass with a chiral centre is employed.
13. Use of l iquidcrystal l i ne gl ass accordi ng to any one of precedi ng 30 cl aims 19 i n a compact di sc .
14. A digital fi lm i n whi ch l iqui dcrystal l i ne gl ass accordi ng to any one of precedi ng cl aims 19 i s empl oyed .
15. Use of liquidcrystalline glass according to any one of preceding claims 19 in a digital film.
16. A compact disc in which liquidcrystalline glass according to any one of preceding claims 19 is employed.
17. A compact disc according to claim 16 wherein the liquid crystalline glass is homeotropically oriented and in which a dichroic dye is present.
18. An analog data storage medium wherein a liquidcrystalline glass according to any one of preceding claims 18 is employed.
19. Use of liquidcrystalline glass according to any one of preceding claims 18 in an analog data storage medium.
20. Use of liquidcrystalline glass according to any one of preceding claims 18 in a human readable, rewritable display.
21. A human readable, rewritable display wherein liquidcrystalline glass according to any one of preceding claims 18 is employed.
22. A polariser wherein a liquidcrystalline glass according to claim 7, 8 or 9 is employed.
23. Use of liquidcrystalline glass according to claim 7, 8 or 9 in a polariser.
24. A process for the preparation of a liquidcrystalline glass wherein a diamine is reacted with a mesogenic groupcontaining epoxide.
25. A crocon ium compound according to the formula below: wherein Rlϊ= .
26. A cholesteric reflector wherein a liquid crystalline glass according to anyone of the preceeding claiml 18 is employed.
27. A cholesteric polariser wherein a liquidcrystalline glass according to anyone of the preceding claims 18 is employed.
Description:
LIQUID-CRYSTALLINE GLASSES

The present invention is directed to liquid-crystalline glasses for optical applications and retardation layers.

Liquid-crystalline glasses are well-known. In the present patent application, the term glasses refers to compositions which when cooling (at a faster rate than 0.01°/s) from the melting point or from 3/2 Tg (if no melting point is observed) do not crystallise but are transformed into the glassy state and remain frozen in that state. By liquid-crystall ne glasses are meant, glasses where the liquid- crystalline phase is frozen in. The liquid-crystalline glasses described here all have a nematic structure. J. Mater. Chem. 1, 3 (1991), 347-356 provides an overview of the presently known liquid- crystalline glasses. The article shows that it is hard to prepare liquid-crystalline glasses which are stable and also have a high transition temperature (Tg above room temperature). The term stable glasses refers to glasses which are not subject to cold crystallisation upon being heated. In Liq. Cryst. 6 (1989), 47-62 dimeric li uid-crystalline molecules are described which are interconnected via a sulphinyl or sulphonyl bridge. These compounds having a Tg in the range of 12° to 50°C display cold crystallisation between Tg and Tc. DD-A1-242627 discloses the same compounds as described above, including mixtures thereof. In the mixtures the cold crystallisation is suppressed. Mol . Cryst. Liq. Cryst. 191 (1990), 269-276 describes naphthalene-containing liquid-crystalline glasses. These glasses are not stable. Crystallisation is suppressed in the mixtures. Liquid Crystals Vol. 11, No. 5 (1992), 785-789 describes a number of liquid-crystalline glasses based on a inopyrene which have a Tg (glass transition temperature) ranging from 35° to 66°C. Several of these glasses do not exhibit any crystallisation between Tg and Tc. However, it is clear from Chem. Mater. 4 (1992), 1246-1253 that these liquid-crystalline glasses have negative dielectric anisotropy and hence cannot be properly oriented in an electric field, which is a

drawback in the case of some optical applications. The same publication discloses other liquid-crystalline glasses based on aminopyrene of fairly high transition temperatures (Tg ranging from 29° to 54°C) . It was found that two of these glasses do not exhibit cold crystallisation. However, as the authors of this article report, these LC glasses were found to be hydrolytically unstable on account of the presence of Schiff's bases, and thus not suitable for use in commercial applications. This also holds for the glasses from Liq. Cryst. Vol. 11, No.5 (1992), 785-789.

The invention provides (hydrolytically and thermally) stable liquid- crystalline glasses which have a high Tg and are readily orientable.

To this end the liquid-crystalline glasses according to the invention comprise compounds according to formula 1:

R* R»

\ / N - Ri - N (formula 1)

/ \ R * R* wherein R*: represents an aromatic group having 5 to 24 carbon atoms, an aromatic group-containing aliphatic group having 6 to 24 carbon atoms, a heterocyclic group having 4 to 24 carbon atoms, or a cyclic aliphatic group having 6 to 24 carbon atoms;

R*: represents -H, a non-mesogenic group or a mesogenic group with a spacer;

Ra : may represent the same groups as R*, but may be chosen independently from R*, R* and R* ;

R * : may represent the same groups as R*. but may be chosen independently from R*, R^, and R»;

R»: may represent the same groups as R*, but may be chosen independently from R 2 , R* and R*. with not

more than 25% of all R*. R*, R«, and R* groups representing -H or a non-mesogenic group.

The liquid-crystalline glasses according to formula 1 were found to have a high transition temperature (the LC glasses in the examples all have a Tg above 50°C) . Furthermore, the viscosity of the glasses is sufficiently low between Tg and Tc to give trouble-free rapid orientation. In addition, the glasses are so stable that even after multiple heating cycles cold crystallisation does not occur. Moreover, these li uid-crystalline glasses do not contain any Schiff's bases and so are hydrolytically stable.

Consequently, the liquid-crystalline glasses according to the invention are pre-eminently suited for use in a wide range of optical applications, e.g., in optical data storage and retardation layers for LCDs.

The glasses according to the invention are obtained by reacting a dia ine of the Ri group with mesogenic group-containing epoxides.

Examples of suitable Ri groups are given in the formulae below. Diamines of these R» groups are used to prepare glasses containing these groups.

C = C \

/ \ C = C

- c c - / \

\ / C c -

\ C = C CH2 -

/ \ / c - CH 2

\ /

- CH 2 \

C - c / \ / C C - CH

\ / c - c

CH ? - CH2 C - C CH2 - CH2

\ / \ / CH2 - N N - CH

\ /

C - C

C - C C - C

/ \ / \ - C C - CH 2 - C C -

\ / \ /

C - C C - C

- CH 2

C = C \

/ \ / C = C

CH 2 - C C - CH / \ /

/ \ / C C - CH 2

C - c \ /

C - C

c - c

CH3 CH 3

/

C = C c = c / \ / \

- c c - c

\ / c - c c - c

/

CH 3 c*

CH 3 o 0CH3

/

C = c C = C

/ \ / \

- C C — C c c - c c - c

Cl Cl

\ / c = c C = c

/ \ / \

: c - c c -

C - C C - C

Cl Cl

/ /

C = C C = C

/ \ / \

- C C - C c -

\ / \ / c - c c - c

/ /

Cl Cl Cl Cl

/ \

C = C C = C

/ \ / \

- C C — C C -

\ / \ /

C - C C - C

/ \

CH30 0CH3

C = C C = C

/ \ / \

C C - CH 2 - C C

\ / \ /

C - C C - C

\ / c = c c = c

/ \ / \

C C - CH - C C

\ / \ / c - c c - c

C = C C = C

/ \ / \

- C C - CH 2 - CH -C C \ / \ /

C - C C - C

C = C c = c

/ \ / \

- C 0 - c c -

C - C C - C \ c = c c = c

/ \ / \ c c - 0 - c c

\ / \ / c - c c - c

c = c c = c

/ \ / \

C C - 0 - (CH 2 ) 3 - 0 - C C

\ / \ / c - c c - c

\ / c = c c = c

/ \ / \

C I C - 0 - (CH 2 ) n - 0 - C

\ / \ / c - c [n = 2, 3, 4]

c = c c = c c = c

- c / \ c - o-c / V-o- c / V t -

\ / \ / \ / c - c c - c c - c

c

/ \ c = c c c c = c

/ \ I II / \

-c c -o -c c - o - c c - v C - C / \ C / \ C -

\ / c \ / c = c c c c = c

/ \ I II / \ c c - o - c c -o -c c c - c c c

c = c c = c c = c c = c

/ \ / \ / \ / \

- c c - o - c c — c c - o - c c \ / \ / \ / \ / c - c c - c c - c c - c

c = c C = C CH 3 C = C C = C

/ \ / \ I / \ / \ c c c c-c-c c-o-c c

\ / \ / I \ / \ / c - c C - C CH 3 C - C C - C

c = c c = c o c = c c = c c / \ c - o - c / \ c — s I— c / \ c - o - c / \ c

\ c-c / \ c-c / o I \ c-c / \ c-c /

\ / c = c c = c 0 c = c c = c

/ \ / \ II / \ / \ c c c c -S-- c c c

\ / II \ \ / c - c c - c 0 c - c

C = C 0 c = c

/ \ II / \ c c-c-c c

\ / \ / c - c c - c

\ / c = c 0 c = c

/ \ II / \ c c-c-c c

\ / \ / c - c c - c

\

C = C 0 c = c

/ \ II / \ c c-c-c c

\ / \ / c - c c - c

C = c = c

/ / \

- C - c c -

\ \ /

C -

\ /

C = c = c

/ / \

- c

\ / c -

CH, CH,

V / c = c C = C

/ \ / \

C - O - C

C - C

S

/\

0 0

C = C C = C

/ \ / \ c - s - c c - c - c =

/ c -

\ c =

/

H 3 C - C C - CH 3

\

\ c = c c = c

/ \ / \ c - s - c c

\ / \ / c - c c - c c = c CH- c = c

/ \ I / \ c c-c c c -

\ I \ / c - c / I

CH 3 C - C

/ c \ / c \\ / c \\ / c w

C C C C C C

II I II II I II

C C C C C c

\ /\ / \ /\ / c c c c

c c

/ \ / \ c c c c II I II I c c c c

/\ /\ /\ / \ c c c c = c c = c c = c

/ \ / \ / \

- c c - c c - c c

\ c-c / \ c-c / V c-c /

C = C N-N C = C

/ \ / \ / \

- c c - c c - c C - \ / \ / \ / c - c 0 c - c

Preferred are the diamines of the Ri groups according to the formulae below.

\ (CH 2 )m-

C = C c = c / \ / \

C -(X) n - C C > / \ / c -c c-c

c = c C - C

/ \

-(CH2) m - C C - (CH2) m - (CH2)m- C C (CH2)m"

\ /

C - C C - C

" c \ / " c \ " c \

- C C -(X) n - C C - -(CH2) m - C C \ / \ / \ /

C-C c -c , c - c

\

(CH 2 )m-

wherein X stands for -0-, -S0 -, -CH -, -S-, -C(0)-, or

-C(CH3) 2 -, n stands for 1 or 0, and m stands for 0, 1, or 2.

Suitable mesogenic groups with spacers are depicted in the formulae below. Glasses having such mesogenic groups are obtained by reacting the epoxides corresponding to the groups below with a diamine.

C = C C = C

/ \ / \

-CH2-CH-(CHR>°) t -(-0(CHR' uCH2) v -°- c c " ( γ )n- C C - R«

I \ ; / \ I /

OH C -: C C -i C

(R n (R ' n

CH2-CH-(CHRιo) t -(-0(CHRn) u CH 2 )v-0-

OH

(R ' n (R-)n

-CH2- - R«

(R n (R-)ι

CH -CH-(CHR ι °) t -(-0(CHR ι uCH 2 )v-0- - R«

OH

c = c

/ \ f -

-CH2-CH-(CHR 1 o)t-(-0(CHR 1 u CH2)v-0-C C -(Y)n- C, R«

\ j / \ /

OH C → C C

(R-)n (R n

CH 2 -CH-(CHR 1 ) t -(-0(CHR 1 u CH 2 )v-0-C - R«

OH

(R n (R')n

-CH2-

C = C / \

-CH2-CH-(CHRι o ) t -(-0(CHR ii ) u CH2) v -0-C C -(Y) n - C r \ C - Ri

\ ! /

OH c -c

(R')n (R n

- R'

wherein Y stands for -C(0)-0-, -OC-, -O-C(O)-, -C=C-, or -N-N-; R stands for -0-R», -OCO-R>, -COOR» , -CN, -NO2, or

-R » ;

R' stands for an alkyl group having 1 to 5 carbon atoms; R» stands for an alkyl group having 1 to 5 carbon atoms; R» stands for an alkyl group having 1 to 15 carbon atoms; t is 1-6; u is 1-7; v is 0-3;

Rio stands for -H or -CH3; R11 stands for-H or alkyl, and n has the same meaning as in the formulae above.

It should be noted that groups which act as a mesogenic group in combination with a specific diamine, may act as a non- esogenic group in combination with another diamine. This unpredictability of liquid-

crystalline materials is known to the artisan. The artisan can easily choose the suitable side-groups for a specific diamine.

It is of advantage to intermix several of the compounds according to formula 1 or to have different mesogenic groups present within one compound according to formula 1. In this way the stability of the liquid-crystalline glass can be enhanced, and it is even possible to set the Tg and the Tc as desired. It was further noted that the use of certain mixtures will give a reduction of the scattering of single- domain films after heating during the orientation process.

Examples of R» groups include: -(CH 2 )χ-CH 3 ,

-CH 2 -CH(CH 3 )-(CH2) X -CH 3 , -CH(CH3)-(CH 2 ) X -CH 3 , wherein x = 1-14.

Some of these R» groups contain an asymmetrical carbon atom. The use of chiral (exclusively laevorotatory or dextrorotatory) R» groups is advantageous in a number of applications, e.g., in LCD retardation 1ayers.

Suitable non-mesogenic groups are groups obtained from the ring- opening reaction of epoxides of methoxy biphenyls, cyanobiphenyls, and biphenyls. It shouldnbe-noted that methoxy bephenyl epoxides can both act as mesogenics and as non-mesogenics depending on the diamine used.

»

Particular preference i s given to l iquid-crystal l ine glass containing a pol abl e mesogeni c group . Polable groups contai n one or more permanent dipole moments di rected more or less along the l ong axi s of the mesogenic group , such that there i s positive di electri c anisotropy. Thi s makes it possible to orient fi lms of the l iquid-crystal l ine glass using a static electri c field. As R pol able

mesogenic groups contain, e.g., a -CN or -NO2 group. For more detailed information on polability reference may be had to Vertogen and en de Jeu, Thermotropic liquid crystals, fundamentals (Springer, 1987), pp. 195-201.

As was mentioned above, the liquid-crystalline glasses according to the invention are especially suited to be used in optical applications. For instance, the liquid-crystalline glasses according to the invention are pre-eminently suited to be used in LCD retardation layers. The functioning of retardation layers is described in EP-A1-0 565 182 and EP-A3-0380 338, which describe liquid-crystalline polymers for use in retardation layers. For further elucidation reference may be had to these patent publications. The liquid-crystalline glasses according to the invention have a low viscosity between Tg and Tc. This low viscosity permits rapid homogeneous arrangement of the liquid-crystalline glasses into a nematic structure having an angle of rotation as desired. In the case of an angle of rotation of 90° (or -90), the film is called "twisted nematic"; if the angle of rotation is greater, the film is called "supertwisted nematic." In addition, the liquid-crystalline glasses according to the invention are suitable for use in retardation layers without twist. In that case the arrangement of the liquid-crystalline layer will be homeotropical or uniform planar. At angles of rotation exceeding 360° the structure goes through more than one full rotation within a single layer. The length covered by the structure in a full rotation is called the pitch. The liquid-crystalline glasses according to the invention can be used to make retardation layers which have a thickness of more than five times the pitch. It was even found possible to make retardation layers which have a thickness of 20 times the pitch. The orientation of this type of layers is usually called cholesteric.

Because the liquid-crystalline glasses according to the invention have a Tg of well above room temperature, the liquid-crystalline glass does

not have to be incorporated into a rigid cell, as is the case with low-molecular weight liquid-crystalline material. Since the different compounds according to formula 1 are easily iscible, and also different mesogenic groups can be present within one compound according to formula 1, the birefringence and the dispersion of the retardation layers can be exactly matched with the appropriate active liquid-crystalline cell. By varying the mesogenic group the dispersion can be varied. In this way the use of mesogenic groups containing a cyclohexyl group or a bicyclooctane group instead of a phenyl group will make it possible to alter the dispersion. The birefringence can be lowered by reducing the mesogenic group density. The invention is also directed to retardation layers containing liquid-crystalline glasses according to the invention.

The retardation layers may be prepared as follows: a thin layer of liquid-crystalline glass is applied between two orienting substrates. Generally, a thin layer of liquid-crystalline glass will be provided on either or both of the orienting substrates by means of spin coating, screen printing, meter bar coating, melt coating, or some other conventional coating technique. The two substrates are then placed one on top of the other. To set the thickness of the retardation layer, spacers of a specific diameter may be provided between the two substrates. As a rule, spheres of glass, polymer or silica are used to this end. Next, the whole is heated to a temperature between Tg and Tc (usually to about 10°C below Tc), which causes the glass to start arranging itself. On cooling to room temperature the well-ordered structure is frozen in, and a stable film is obtained which retains its shape. The substrates may be of either glass or plastic. If they are of glass, it is preferred to use thin glass substrates of a thickness of 20 to 500 micrometers. This allows retardation layers to be made which are lightweight, thin, and somewhat flexible.

Various techniques are known for making an orienting substrate. For instance, the substrate itself may be rubbed in a single direction. The substrate in that case may be made of, e.g., polyimide, polyvinyl alcohol, glass, etc. Alternatively, the substrate may be provided with a thin orienting layer. This may be a thin polymer layer which can be rubbed, e.g., polyimide, polyvinyl alcohol, etc. Alternatively, this thin orienting layer may be a Si0 x layer evaporated at an angle of less than 90°, usually of 60° or 86°. Generally, a substrate of poor flexibility is used for SiO x evaporation, such as glass or quartz. These orienting techniques are known to the skilled person and require no further elucidation here. Of course, it is also possible to employ other orienting techniques.

A twisted structure is obtained by giving one of the two substrates a different orientation direction from that of the other substrate. To control the direction of rotation of the director (to the left or to the right) and/or to obtain an angle of rotation greater than 90°, the liquid-crystalline material is frequently mixed with a chiral material: the so-called chiral dopant. In principle, any optically active compound may be used to this end. As examples may be mentioned cholesterol derivatives and 4-(4-hexyloxy-benzoyloxy) benzene acid 2-octyl-ester. Ordinarily speaking, for application as retardation layers up to 5 wt.% of chiral dopant is employed in relation to the total amount of liquid-crystalline material. Alternatively, some of the compounds according to formula 1 may be provided with chiral centres. Preferably, this is done by providing the mesogenic group with a chiral chain (group Ri) or spacer, since in this way the transition temperatures will hardly if at all be adversely affected. Examples of mesogenic groups with chiral chains have already been described above. Since the carbon originally at the α-position of the epoxide group is asymmetrical also, its chiral version may be used as well. In that case, use is made of an epoxy-containing mesogenic group with a chiral centre in the epoxide group. Of course, the chiral centre may also be located in the diamine.

It is not necessary to use two substrates to make a retardation layer. If the liquid-crystalline assumes a sufficiently twisted structure of its own accord, a single orienting substrate will suffice. A sufficiently twisted structure can be obtained if the liquid-crystalline material contains a sufficient quantity of chiral dopant, and the layer thickness is accurately controlled.

As mentioned above, is it also possible to make layers with a very small pitch with the liquid-crystalline glass according to the invention. These so-called cholestric layers can also be used as cholesteric reflectors or cholesteric polarisers. In these cases, more chiral dopant is employed than for the application in retardation layers.

Further, the liquid-crystalline glasses according to the invention may be used for digital data storage such as in Compact Discs (CDs, both recordable and rewritable) or digital films. Digital films may be of different shapes, e.g., tape, cards, and disks which cannot be written or read as specified by the CD standard. The orientation in these CDs or films may be either ho eotropic or uniform planar. For digital media various read out principles may be employed. For instance, in the case of homeotropic orientation (i.e., perpendicular to the substrate), dichroic dye may be blended in, making it possible to read out data via the difference in absorption. Further, in the case of homeotropic as well as uniform planar orientation contrast results from an isotropic pit or trace giving a different optical path length from a homeotropic or uniform planar background. Because of this difference in path lengths, there is interference by the portion of the incident light beam which falls adjacent to the pit with the portion which falls within the pit. Generally, the different phenomena are active within the CD simultaneously, and it is impossible to state precisely where exactly the contrast originates.

Here also it was found that because of the low viscosity of the liquid-crystalline glass according to the invention it is possible to attain rapid and, above all, homogeneous orientation.

When the film or CD contains dichroic dye, its orientation will be along the same lines as that of the mesogenic groups of the liquid- crystalline glass. The term dichroic dye refers to a dye which in an oriented medium (e.g., a nematic liquid-crystalline phase) will have a dichroic ratio (absorption |i/absorption α.) > 1 in the desired wavelength range, absorption | standing for the absorption of light which is polarised parallel with the orientation direction of the medium, and absorption J. standing for the absorption of light which is polarised perpendicularly. Dichroic dyes, in other words, will absorb one polarisation direction of linearly polarised light to a much greater extent than the other one.

In a virgin homeotroppically oriented film or CD the mesogenic groups, and hence the dichroic dye molecules, are oriented perpendicular to the film's surface, and there is only low absorption of the incident light by the dichroic dye molecules. (It should be noted that the polarisation direction of the light is perpendicular to its propagation direction as the incident light travels in many cases perpendicularly towards the film ' s surface). In the case of local heating or irradiation (e.g., with a laser) of the film or CD to above Tc, the homeotropic orientation is converted into an isotropic one. Rapid cooling causes this local isotropic orientation to be frozen in. In the case of such an isotropically written trace or pit, the dichroic dye molecules will likewise be isotropically oriented, resulting in a substantially higher absorption of the incident light. In the isotropic state 2/3 of the dichroic dye molecules -on average- is positioned with the long axis parallel with the CD surface (i.e. on average 1/3 along the x-axis of the plane of the film, and 1/3 along the y-axis ). The polarisation direction of the incident light (either x_ or y-polarised) is now parallel with the long axis of the dichroic dye molecules, and thus a high absorption is realised.

The dichroic dye may be mixed or incorporated into the liquid- crystalline glass. In the case of incorporation, an epoxy- functionalised dichroic dye may be co-reacted with the other mesogenic group-containing epoxides. In principle, any dichroic dye may be employed, providing it is sufficiently stable to be mixed or incorporated into the liquid-crystalline glass. For instance azo dyes, anthraquinone dyes, croconium and squarilium based dyes are suitable. The invention is also directed to novel croconium compounds with mesogenic groups.

If other read out princples are used than the difference in absorption of dichrioc dyes in a homeotropic medium, dichrioc dyes are not necessary and the liquid-crystalline glass may be oriented differently, e.g. uniform planar.

Writing out data with the aid of a solid state laser requires that the liquid-crystalline glass film be, or be rendered, near-infrared light absorbing. Generally, this is done by blending in or incorporating a near-infrared absorbing dye. Preferably, the same (diode) laser can be employed for writing as well as reading. CDs as specified by the CD standard are read out by a solid state laser. In the case of a CD wherein the read out principle is based in the difference in absorption of dichroic dye in a homeotropic medium, use is made of a dichroic dye which absorbs the laser light during writing and creates a difference in absorption during reading. In such cases it is advisable that the dichroic dye be greatly dichroic but not fully oriented, so that a sufficient quantity of light will be absorbed during the writing. The objective is a light absorption percentage in the range of 2 to 40% of the incident light in the homeotropic (virgin) state. Dichroic near-infrared dyes which can be blended in are, among others, anthraquinone dyes: IR-750 ® , ex Nippon Kayaku Co. Ltd, squarilium dyes: NK-2772®, ex Nippon Kankoh - Shikiso Kenkyusho Co. Ltd.,3-(7-isopropyl-l-methyl)azulene-4-yl-2-ethyl-propionic acid-

n-butylester, and the dyes mentioned in EP-A2-0310080 , croconium dyes: ST 172 ® , ex Syntec.

For high-density CDs lasers having a wavelength in the range of 620 to 680 nm are employed for reading. The liquid-crystalline glasses according to the invention can be employed also to make high-density CDs based on the difference in absorption principle when dichroic dyes having an absorption maximum in this range are used. Examples of dichroic dyes having an absorption maximum in this range include: azo dyes: SI-361 ® , ex Mitsui Toatsu Chemicals GmbH, anthraquinone dyes: LCD 116 ® and LCD 118 ® , ex Nippon Kayaku Co. Ltd.,M-137 ®, M-483 ®, SI-497 ® , ex Mitsui Toatsu Chemicals GmbH., squarilium dyes: ST 6/2 ® and ST 5/3 ® , ex Syntec. When other read out principles are used, the 620-680 nm absorbing dyes need not be dichroic.

In principle, the reading out and writing of data in the liquid- crystalline glass/dye system can take place at different wavelengths. In the case of reading out with the difference in absorption principle, use will be made of a dichroic dye, as mentioned-above, in combination with a writing light absorbing dye. It is advisable that said writing light absorbing dye is hardly susceptible to orientation, or is not very dichroic, since otherwise absorption during the writing would be unsatisfactory. For that reason preference is given to dyes which are not elongated in shape (e.g., molecules in platelet form or spherical molecules). These writing light absorbing dyes may be incorporated into the liquid-crystalline glass by co-reacting the dye diamines with the other diamines.

Ordinarily speaking, a film or CD is made by applying a solution of the glass onto a substrate and evaporating the solvent. Suitable substrates include PET, PET-ITO, metal, glass, cellulose acetate, polycarbonate, polycarbonate-Al , silicon, amorphous polyolefins, etc. Generally, these substrates are provided with a thin layer of metal

such as aluminium or gold or a layer of material with a high dielectric constant such as silicium nitride, silicium oxide or ZNSe. Usually, films having a thickness of 0.2 to 10 micrometers are employed.

Homeotropic orientation of the liquid-crystalline material can be attained in several ways:

1. By treating the surface of the substrate with homeotropic orientation inducing surfactants. These may be, int. al., silanes, higher alcohols, and the like, e.g., n-dodecanol and Liquicoat® PA, ex Merck.

2. By poling the liquid-crystalline layer in a magnetic or electric field. The electric field may be generated by corona poling (using a sharp needle or a thin wire as electrode). There will have to be a counter-electrode on the other side of the liquid-crystalline layer (e.g., an ITO-layer, a metal layer, or a conductive polymer layer), so that the poling field will be positioned over the liquid-crystalline layer. Alternatively, the liquid-crystalline layer may be provided with a conductive layer on either side, and an electric field applied thereto.

Both when homeotropic films are produced by means of a surface treatment and in the case of poling, the viscosity and the layer thickness of the glass film are of importance.

Uniform planar orientation can likewise be obtained by surface treatment. Since the liquid-crystalline glasses according to the invention have a low viscosity between Tg and Tc, they can be made into fine uniform planar films or CDs.

Since poling is one of the easiest ways of obtaining homogeneous homeotropic orientation, the use of polable liquid-crystalline glasses is preferred for digital data storage. Such glasses have been described hereinbefore.

The liquid-crystalline glasses according to the invention can easily be made into homogeneously scattering films which permit local isotropic writing after the addition of suitable dyes, with a laser or some other source of heat. Thus, the liquid-crystalline glasses according to the invention are rendered serviceable also for low density digital storage and analog data storage. The term analog data storage refers both to human readable rewritable displays such as smart cards and thermal paper and to machine readable media (such as media which can be read with a bar code reader). The films can be prepared by spin coating, meter bar coating, melt coating, screen printing, and any other conventional technique for coating on a substrate. Suitable substrates are of PET, glass, polycarbonate, PVC, ABS, polystyrene, metal, and paper. The films may have different formats, such as .disks, cards, and tape.

A homogeneously scattering film is obtained by heating the film to above Tc and then leaving it to cool to room temperature. The creation of small domains gives a scattering texture. It was found that films of liquid-crystalline glasses according to the invention can be initialised within 2 seconds in this way. This, in its turn, means that written films can be erased within 2 seconds in this way and prepared for rewriting.

To increase the contrast between the written and the virgin sections, a contrast layer can be applied beneath the liquid-crystalline glass layer. This may be a refelecting layer, which may be of any material reflecting light. Examples include metal substrates or foils of copper, aluminium, gold, silver, nickel, steel, metallised plastic substrates or foils such as aluminised PET, metallised paper, metal coated metal or plastic substrates such as used in the car industry. Alternatively, the contrast layer may be made up of a layer having a low index of refraction, e.g., a thin layer of air. The liquid- crystalline glass layer may be provided with a protective coating.

If epoxy-functionalised and/or diamine-functionalised dye are co- reacted with the mesogenic group-containing epoxides and/or diamines, or if dyes are blended in, glass is formed which can be used as a polariser. the dyes, of course, should be dichroic and co-oriented with the liquid-crystalline glass. To this end the liquid-crystalline glass according to the invention is applied onto an optically transparant substrate, after which the liquid-crystalline glass layer is oriented uniformly planarly. The invention is also directed to polarisers comprising a liquid-crystalline glass containing dye according to the invention.

To enhance the glasses' UV-stability it is possible to add UV-stabilisers. Alternatively, epoxy-functionalised UV-stabilisers may be incorporated into the glasses. An example of such an epoxy- functionalised UV-stabiliser is listed in Macromol . 26 (1993), 3227-3229.

The invention will be further illustrated with reference to a number of purely illustrative, non-limitative examples.

EXAMPLES

Example 1

Synthesis of LC glasses (general method):

A mixture of 1 eq. of diamine and 4 eq. of epoxy was heated for 5-20 hours, depending on the diamine used, under a nitrogen atmosphere at a temperature of 130°C. When two or more different diamines or epoxides are used, 40 % of weight of chlorobenzene was added for obtaining a homogeneous melt. After 1 hour at 130 °C the chlorobenzene was distilled off. The melt was cooled down and dissolved in THF, and the solution of approximately 20% (m/M) was precipitated in a 10-fold excess of ethanol . The yields were in the range of 75 to 90%.

Synthesis of epoxide monomers:

Example 2

epoxide van cyanobiphenyl (epoxide 1)

A mixture of 39.0 g (0.20 mole) of hydroxycyanobiphenyl, 100 ml (1.25 moles) of epichlorohydrin, and 0.44 g (2.4 mmoles) of benzyl trimethyl ammonium chloride was heated to 70°C. Next, a solution of 17 g (0.42

10 mole) of sodium hydroxide in 100 ml water was dispensed in 3 hours. Following this addition there was one extra hour of stirring at 70°C. The reaction mixture was cooled to 20°C, and 200 ml of dichloromethane were added. The organic layer was separated from the aqueous one and washed with, successively, NaCl solution (twice) and water (twice).

._ After drying on magnesium sulphate and concentration by evaporation lb the crude product was converted to the crystallised form from 450 ml of methanol. The yield was 38,30 g (76%).

The epoxide of cyanobi phenyl was used to prepare glasses by the 0 general method for the synthesi s of LC glasses specified above, using: m-xylyl ene diamine (m-XDA) , ex Fluka® m-phenylene diamine (m-PDA) , ex Jansen Chimi ca® 4,4 ' -oxydi ani l i ne (ODA) , ex Fl uka ® methyl ene diamine (MDA) , ex Fluka® 5 p-phenylene diamine (p-PDA) , ex Jansen Chimica® 1,3-bi smethylaminocyclohexane (CHDA) , ex Al drich® 3,3 ' -sul phonyl dianil ine (3-SDA) , ex Aldri ch® 4,4 ' -sul phonyl di ani l ine (4-SDA) , ex Fl uka®

0 The properties of the resulting glasses are compiled in TABLE I. It was found that the obtained liquid-crystalline glasses remained stable even after multiple heating cycles.

Example 3

epoxide of nitrobiphenyl (epoxide 2)

In a manner analogous to that for the synthesis of the epoxide of cyanobiphenyl, the epoxide of nitrobiphenyl (epoxide 2) was prepared. Using various diamines glasses were prepared by the general method for the synthesis of LC glasses specified above.

The properties of the resulting glasses are compiled in TABLE I. It was found that the obtained liquid-crystalline glasses remained stable even after multiple heating cycles.

Example 4

epoxide of nitrostilbene (epoxide 3)

In a manner analogous to that for the synthesis of the epoxide of cyanobiphenyl, the epoxide of nitrostilbene (epoxide 3) was prepared. Using various diamines glasses were prepared by the general method for the synthesis of LC glasses specified above.

The properties of the resulting glasses are compiled in TABLE I. It was found that the obtained liquid-crystalline glasses remained stable even after multiple heating cycles.

Example 5

epoxide of methoxyphenyl benzoate (epoxide 4)

In a manner analogous to that for the synthesis of the epoxide of cyanobiphenyl, the epoxide of methoxyphenyl benzoate (epoxide 4) was prepared, except that only half the amount of caustic solution was

used for epoxide 4. Using various diamines glasses were prepared by the general method for the synthesis of LC glasses specified above.

Further, the epoxide of cyanostilbene (epoxide 5), and the epoxide of nitrotolane (ph≡ph-N02, epoxide 6) were prepared in a manner analogous to that for the synthesis of the epoxide of cyanobiphenyl.

The properties of the obtained glasses are compiled in TABLE I. It was found that the obtained liquid-crystalline glasses remained stable even after multiple heating cycles.

TABLE I

epoxide diamine Mw Tg Tc Tm

1-(2,3-epoxypropyloxy)-4-(p-methoxyphenyl)bicyclo[2,2,2]o ctane (epoxide 7)

3-Acetyl-1,5-dicyano-3-(p-methoxyphenyl)pentane

Cyanoethylene (53 g, 1.0 mole) was added dropwise to a stirred solution of 82 g (0.5 mole) p-methoxyphenyl acetone and 5.5 ml of a 40% w/v solution of benzyl trimethyl ammonium hydroxide (Triton B) in methanol in 100 g of t-butanol, while the temperature of the solution was maintained between 10 and 15 °C. After stirring the reaction for 4 hours, the almost solid mixture of product was filtered off, washed with methanol, and dried. Yield: 99.2 g (73%).

3-Acetyl-3-(p-methoxyphenyl)pentane-l,5-dicarboxylic acid

A mixture of 17.8 g (0.44 mole) of NaOH, 175 g of water and 40 g (0.15 mol) of 3-acetyl-1,5-dicyano-3-(p-methoxyphenyl)pentane was refluxed overnight. Concentrated hydrochloric acid was added to the cooled solution and the product separated as an oil. The oil was taken up in 100 ml of dichloromethane. Upon standing and cooling to 0 °C the pure acid precipitated as a white solid. Yield: 39.5 g (87%).

4-Acetyl-4-(p-methoxyphenyl)cyclohexanone

A solution of 38.0 g (0.14 mole) of 3-acetyl-3-(p-methoxyphenyl)pentane- 1,5-dicarboxylic acid and 0.31 g of potassium acetate in 140 ml of acetic anhydride was refluxed for 2 hours. The excess acetic acid was removed at reduced pressure, after which the temperature was raised to 250 °C in order to pyrolyze the residue and to distill the formed cyclohexanone (pressure 0.05 bar) . 23.0 g (79%) of distillate were collected which rapidly solidified. The product was used without further purification.

l-Hydroxy-4-(p-methoxyphenyl)bicyclo[2,2, ]octan-3-one

A solution of 23.0 g (0.11 mole) of 4-acetyl-4-(p-methoxyphenyl)cyclo- hexanone and 19.2 g (0.29 mole) of KOH in 200 ml of water was heated

at 70 oC for 6 hours. After cooling the precipated product was filtered off, washed with water, and dried in vacuo. Yield: 18.9 g (82%), m.p. 159-160 °C.

l-Hydroxy-4-(p-methoxyphenyl)bicyclo[2, ,2]octane

A solution of 10.0 g (0.048 mole) of l-hydroxy-4-(p-methoxyphenyl)bicyclo[2,2,2]octan-3-one and 7.36 g (0.15 mole) of hydrazine monohydrate in 40 ml of triethylene glycol was subsequently heated at 100 °C (3 hrs) and 165 °C (15 min.). The solution was cooled to 60 °C and an equally warm solution of 9.28 g (0.14 mole) of K0H in 40 ml of triethylene glycol was added. The vessel was equipped with a Dean-Stark trap, and the mixture was heated at 105 °C for one hour and then at 185 °Cfor half an hour. The cooled solution was added to 150 ml of water and washed with dichloromethane (3 x 100 ml). The combined organic layers were washed with 50 ml 2 N HCI and 50 ml of water, dried and evaporated to dryness. Yield: 7.83 g (84%). The product was purified by recrystallization from toluene.

1-A11yloxy-4-(p-methoxyphenyl)bicyclo[2,2, ]octane

To a solution of 2.0 g (10 mmoles) of l-hydroxy-4-(p-methoxyphenyl)bicyclo[2,2,2]octane in 15 ml of sieve dried DMF under N2 was added 0.52 g (13 mmoles) of a 60 % NaH dispersion in oil. After stirring at room temperature for 4 hours the evolution of hydrogen had stopped. There was added 70 mg (0.19 mmol) of tetrabutyl ammonium iodide and (dropwise) 1.56 g (13 mmoles) of a solution of allyl bromide in 5 ml DMF. The resultant reaction mixture was stirred for an additional 2 hours, poured into 150 ml of water, and washed with diethyl ether (3 x 50 ml). The combined organic layers were washed with 50 ml of water and 50 ml of brine, dried and evaporated to dryness. The crude product was purified by column

chromatography (Si0 2 , eluent diethyl ether), and there was obtained 1.0 g (43%) of l-allyloxy-4-(p-methoxyphenyl)bicyclo[2.2.2]-octane, m.p. 62-63 °C.

1-( ,3-epoxypropyloxy)-4-(p-methoxyphenyl )bicyclo[2,2,2]octane

A solution of 1.0 g (4.2 mmoles) of l-allyloxy-4-(p-methoxyphenyl)bicyclo[2,2,2]octane and 1.9 g of 50% (5.4 mmoles) of -chloroperbenzoic acid in 10 ml of sieve dried dichloromethane was stirred at room temperature overnight. The reaction mixture was diluted with 10 ml of dichloromethane, washed with a 10% aqueous solution of sodium carbonate (2 x 20 ml), water (20 ml), and brine (20 ml), dried and evaporated to dryness. The crude product was recrystallized from methanol, yield 0.15 g (14 %) .

Example 7

l-bromo-4-(p-2,3-epoxypropyloxyphenyl )bicyclo[2,2,2] octane (epoxide 8)

l-Bromo-4-(p-hydroxyphenyl)bicyclo[2,2,2]octane

To a solution of 2.7 g (0.14 mmoles) of l-hydroxy-4-(p-methoxyphenyl)bicyclo[2.2.2]octane in 50 ml of sieve dried dichloromethane was added dropwise a solution of 8.8 g (0.35 mmoles) of boron tribromide in 50 ml of sieve dried dichloromethane at 0 °C. The solution was stirred overnight and allowed to re-attain room temperature. The solution was poured in 400 ml of water, and the aqueous phase was extracted with dichloromethane (2 x 100 ml). The combined organic layers were washed with a 10% aqueous solution of sodium carbonate (100 ml) and water (100 ml), dried and evaporated to dryness. Yield 3.2 g (93%). The product was used without further purification.

l-Bromo-4-(p- ,3-epoxypropyloxyphenyl)bicyclo[2, ,2]octane

A solution of 3.0 g (0.12 mmoles) of l-bromo-4-(p-hydroxyphenyl)bicy- clo[2,2,2]octane and 0.023 g (0.012 mmoles) of benzyl trimethyl ammoniumchloride in 9.0 g (0.99 mmoles) of epichlorohydrin was stirred at 70 °C. A solution of 1.0 g (0.26 mmoles) of NaOH in 7.5 ml of water was gradually added during 2.5 hours and the mixture was stirred overnight. 10 ml of water and 25 ml of dichloromethane were added, the organic layer was separated off, and the aqueous layer was extracted with dichloromethane (2 x 25 ml). The combined organic layers were washed with water (25 ml) and brine (25 ml), dried, and evaporated to dryness. The crude product was crystallized from methanol; yield 3.2 g (86%), m.p. 112-115 °C.

The epoxides 7 and 8 were used in the liquid-crystalline glasses according to the invention to alter the dispersion of retardation layers made of these liquid-crystalline glasses.

Example 8

Liquid-crystalline cyanobiphenyl glasses containing different diamines were intermixed. The results in TABLE II show that by varying the diamines the Tg and the Tc can be set as desired. Further, the use of mixtures in optimal mixing ratios was found to promote the stability of the liquid-crystalline glasses.

TABLE II

after the material had been melted in a first heating cycle, no cold crystallisation could be observed even with heating at lK/min cold crystallisation could be observed with heating at lK/min Tm in first heating cycle

Example 9

Blends were made of liquid-crystalline glasses of epoxide 1 and 3-SDA (glass 1) and liquid-crystalline glasses of epoxide 6 and m-XDA (glass 2). The results are given in TABLE III. From the results it can be seen that the Tg and Tc can be set by using blends of liquid- crystalline glasses.

Liquid-crystalline glasses were obtained by reacting ODA with epoxide 1 and another epoxy. The results in TABLE IV show that the incorporation of different epoxides in one liquid-crystalline glass molecule does not destroy the liquid-crystalline behaviour and the Tg and TC can be set by varying the amount of epoxides of a specific ty e-

Liquid-crystalline glasses were obtained by reacting 3-SDA with epoxide 1 and another epoxy. The results in TABLE V again show that the incorporation of different epoxides in one liquid-crystalline glass molecule does not destroy the liquid-crystalline behaviour and the Tg and Tc can be set by varying the amount of a specific epoxide.

TABLE V

Liquid-crystalline glasses were obtained by reacting SDA with epoxide 1 and a non-mesogenic group-containing epoxy. The non-mesogenicBepoxides were obtained in a manner analogous to the preparation of epoxide 1. The results in TABLE VI show that by incorporating non-mesogenic groups in the liquid-crystalline glass the liquid crystalline behaviour is not destroyed. It was further noticed that a reduction of the scattereing of single domain films of these liquid-crystalline glasses was obtained after heating during the orientation process.

TABLE VI

wt.% epoxide 1 wt.% R-epoxide Tg Tc Tm

90 90 95 90

ph is a phenyl group

Example 13

Synthesis of croconium dyes in a manner analogous to that for LC glasses

A mixture of 0.54 g (5 mmoles) of m-aminophenol and 10 mmoles of epoxide was melted under nitrogen at a temperature of 130°C. After 4 hours at 130°C the melt was dissolved in DMF, and the solution of about 20% (m/M) was precipitated in a 10-fold excess of ethanol .

0.50 mmole of the product from the above step (phenol derivative) was dissolved under a nitrogen atmosphere in a mixture of 1 ml of DMSO and 50 ml of n-butanol . Next, at reflux temperature 53 mg (0.25 mmole) of croconic acid were added in one go. After 1 hour of refluxing the mixture was cooled down and the precipitated product was filtered and washed with ethanol. The product was purified with the aid of column chromatography. In TABLE VII the properties of croconium dyes with various π groups according to the formula of claim 25 are comprised.

TABLE VI I

R1 group Tg Tc Tm λmax

829 160 000

238

Example 10

Appl i cation i n retardation l ayer:

Used were two glass substrates of a thickness of 100 micrometers. These substrates were coated with a thin layer of Merck Liquicoat ® PA, which was precured at 60°C for 15 minutes, cured at 300°C for one hour, and then rubbed in the desired direction with a felt cloth in accordance with the Merck® instructions. To ensure proper adhesion of the PI layer the glass substrates were cleaned in advance, using the following procedure:

- ultra-sonic cleaning with a detergent (Q9, Purum GmbH)

- KOH (1 M), 50 °C/1 hr

- HN0 3 /H 2 S04/H 2 0 (1:1:2), 60 C/l hr

- refluxing in isopropyl alcohol vapour for 30 minutes.

There was flushing with demineralised water between all of the cleaning steps. This is a variation of the method described by W.H. de Jeu in Physical Properties of Liquid Crystals, 1st ed., Gordon and Breach Science Publishers, p. 23.

Liquid-crystalline glass of m-XDA and epoxide 1 was dissolved in cyclopentanone together with 5 wt.% of chiral dopant (Merck CB 15®). To the filtered solution 0.5 wt.% (calculated on LC glass) of cross- linked polymer spheres (Dynospheres DL-1060 ® , ex JSR) was added as spacers. The solution of liquid-crystalline glass with spacers was spin coated onto the two pretreated glass substrates. The layer thickness obtained was 4 micrometers. The two glass films were dried in a vacuum oven for 16 hours at 20°C. They were then placed one on top of the other under a 60° difference in orientation direction and moulded at a temperature of 160°C. Next, the sample was cooled to 115°C, and after 5 minutes to room temperature. The quality of the resulting retardation film was determined with the aid of various optical techniques such as described in E.P. Raynes, "Molecular Crystals," Liquid Crystals Letters 4(3-4) (1987), 69-75.

Application for analog data storage:

Liquid-crystalline glass of m-XDA and epoxide 1 was dissolved in cyclopentanone and filtered. Using a meter bar, the solution was applied onto a 100 micrometers thick Alu-PET substrate (based on Melinex 401®, ex ICI). The solvent was removed by drying at room temperature for 5 minutes and heating to 60°C for 15 minutes. Obtained was a film with a thickness of about 6 micrometers. The liquid- crystalline layer was provided with a protective coating based on Actilane 200®, ex Akcros Chemicals.

The film was rendered homogeneously light scattering by heating to 134°C, followed immediately by cooling to about 20°C in >2 seconds. Writing with a thermal printing head gave a very good contrast. The film was erased by the same method.