Polymerisable compounds and the use thereof in liquid-crystal media and liquid-crystal displays

Abstract

The present invention relates to polymerizable compounds, to processes and intermediates for the preparation thereof, to the use thereof for optical, electro-optical and electronic purposes, in particular in liquid-crystal (LC) media and LC displays having a polymer-stabilized blue phase, and in LC media for LC displays of the PS or PSA type (polymer sustained or polymer sustained alignment), and to LC media and LC displays comprising these compounds.

Claims

1. Compounds of the formula I
P.sup.a-(Sp.sup.a).sub.s1-A.sup.2-CH.sub.2CH.sub.2-A.sup.1-CH.sub.2C.sub.2-A.sup.3-(Sp.sup.b).sub.s2-P.sup.bI wherein the individual radicals have the following meaning P.sup.a P.sup.b each, independently of one another, denote a polymerisable group, Sp.sup.a, Sp.sup.b on each occurrence, identically or differently, denote a spacer group, s1, s2 each, independently of one another, denote 0 or 1, A.sup.1, A.sup.2, A.sup.3 each, independently of one another, denote a radical selected from the following groups a) the group consisting of trans-1,4-cyclohexylene, 1,4-cyclohexenylene and 4,4-bicyclohexylene, wherein one or more non-adjacent CH.sub.2 groups may be replaced by O and/or S and wherein, one or more H atoms may be replaced by F, b) the group consisting of 1,4-phenylene and 1,3-phenylene, wherein, one or two CH groups may be replaced by N and wherein, one or more H atoms may be replaced by L, c) the group consisting of tetrahydropyran-2,5-diyl, 1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobut-1,3-diyl, piperidine-1,4-diyl, thiophene-2,5-diyl and selenophene-2,5-diyl, each of which may, in addition, be mono- or polysubstituted by L, d) the group consisting of saturated, partially unsaturated or fully unsaturated, and optionally substituted, polycyclic radicals having 5 to 20 cyclic C atoms, one or more of which may also be replaced by heteroatoms, preferably selected from the group consisting of bicyclo[1.1.1]pentane-1,3-diyl, bicyclo-[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, ##STR00258## where, in addition, one or more H atoms in these radicals may be replaced by L, and/or one or more double bonds may be replaced by single bonds, and/or one or more CH groups may be replaced by N, L on each occurrence, identically or differently, F denotes, Cl, CN, SCN, SF.sub.5 or straight-chain or branched, in each case optionally fluorinated alkyl, alkoxy, alkylcarbonyl, alkoxycarbonyl, alkylcarbonyloxy or alkoxycarbonyloxy having 1 to 12 C atoms, R.sup.0, R.sup.00 each, independently of one another, denote H, F or straight-chain or branched alkyl having 1 to 12 C atoms, wherein, one or more H atoms may be replaced by F, M denotes O, S, CH.sub.2, CHY or CY.sup.1Y.sup.2, Y and Y.sup.1 each, independently of one another, have one of the meanings indicated above for R.sup.0, or denote Cl or CN, and preferably denote H, F, Cl, CN, OCF.sub.3 or CF.sub.3, and in which one or more of the radicals A.sup.1, A.sup.2 and A.sup.3 are selected from the group d) consisting of saturated, partially unsaturated or fully unsaturated, and optionally substituted, polycyclic radicals having 5 to 20 cyclic C atoms, one or more of which may also be replaced by heteroatoms, preferably in which one or more of the radicals A.sup.1, A.sup.2 and A.sup.3 are selected from the group consisting of bicyclo[1.1.1]pentane-1,3-diyl, bicyclo[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, ##STR00259## where, in addition, one or more H atoms in these radicals may be replaced by L, and/or one or more double bonds may be replaced by single bonds, and/or one or more CH groups may be replaced by N.

2. Compounds of the formula IA
G-O-(Sp.sup.a).sub.s1-A.sup.2-CH.sub.2CH.sub.2-A.sup.1-CH.sub.2CH.sub.2-A.sup.3-(Sp.sup.b).sub.s2-O-GIA wherein Sp.sup.a, Sp.sup.b, A.sup.1, A.sup.2, A.sup.3, s1 and s2 have the following meaning, Sp.sup.a, Sp.sup.b on each occurrence, identically or differently, denote a spacer group, s1, s2 each, independently of one another, denote 0 or 1, A.sup.1, A.sup.2, A.sup.3 each, independently of one another, denote a radical selected from the following groups a) the group consisting of trans-1,4-cyclohexylene, 1,4-cyclohexenylene and 4,4-bicyclohexylene, wherein, one or more non-adjacent CH.sub.2 groups may be replaced by O and/or S and wherein, one or more H atoms may be replaced by F, b) the group consisting of 1,4-phenylene and 1,3-phenylene, wherein, one or two CH groups may be replaced by N and wherein, one or more H atoms may be replaced by L, c) the group consisting of tetrahydropyran-2,5-diyl, 1,3-dioxane-2,5-diyl, tetrahydrofuran-2,5-diyl, cyclobut-1,3-diyl, piperidine-1,4-diyl, thiophene-2,5-diyl and selenophene-2,5-diyl, each of which may, in addition, be mono- or polysubstituted by L, d) the group consisting of saturated, partially unsaturated or fully unsaturated, and optionally substituted, polycyclic radicals having 5 to 20 cyclic C atoms, one or more of which may also be replaced by heteroatoms, preferably selected from the group consisting of bicyclo[1.1.1]pentane-1,3-diyl, bicyclo-[2.2.2]octane-1,4-diyl, spiro[3.3]heptane-2,6-diyl, ##STR00260## where, in addition, one or more H atoms in these radicals may be replaced by L, and/or one or more double bonds may be replaced by single bonds, and/or one or more CH groups may be replaced by N, and G and G each, independently of one another, denote an H atom or a protecting group.

3. The compounds of formula I of claim 1 wherein, A.sup.1 is selected from a group consisting of: ##STR00261##

4. The compounds of formula IA of claim 2 wherein, A.sup.1 is selected from a group consisting of: ##STR00262##

Description

EXAMPLE 1

6-(4-{2-[3-Methyl-4-(2-{4-[6-(2-methylacryloyloxy)hexyl]phenyl}ethyl)-phenyl]ethyl}hexyl 2-methacrylate (1)

(1) Compound (1) according to the invention, 6-(4-{2-[3-methyl-4-(2-{4-[6-(2-methylacryloyloxy)hexyl]phenyl}ethyl)phenyl]ethyl}phenyl)hexyl 2-methacrylate (1), is synthesised as described below.

(2) ##STR00242##

1.1 Preparation of 1,4-bis[2-(4-bromophenyl)vinyl]-2-methylbenzene (E/Z mixture)

(3) ##STR00243##

(4) 6.30 g (42.5 mmol) of 2-methylbenzenedicarbaldehyde are initially introduced in 150 ml of dichloromethane together with 50.0 g (97.6 mmol) of 4-bromobenyzltriphenylphosphonium bromide and 2.50 g (9.47 mmol) of 18-crown-6. 11.0 g (0.20 mol) of powdered KOH are added in portions at 70 C. The mixture is stirred at 70 C. for 2 h, and the batch is warmed to room temperature. After 1 h at this temperature, water is added, and the organic phase is separated off.

(5) The aqueous phase is extracted with dichloromethane, and the combined organic phases are washed with sat. ammonium chloride soln. The solution is filtered absorptively (SiO.sub.2, CH.sub.2Cl.sub.2), and the filtrate is concentrated to dryness. The crude product is purified by column chromatography (SiO.sub.2, toluene:n-heptane=1:1). E/Z-1,4-bis-[2-(4-bromophenyl)vinyl]-2-methylbenzene is obtained as a yellow oil.

1.2 Preparation of 6-{4-[(2-(4-{2-[4-(6-hydroxyhex-1-ynyl)phenyl]vinyl}-3-methylpheny)vinyl]phenyl}hex-5-yn-1-ol (E/Z mixture)

(6) ##STR00244##

(7) A mixture of 18.0 g (39.6 mmol) of E/Z-1,4-bis-[2-(4-bromophenyl)vinyl]-2-methylbenzene, 2.78 g (3.96 mmol) of bis(triphenylphosphine)palladium(II) chloride, 755 mg (3.96 mmol) of copper(I) iodide and 28.0 ml (0.20 mol) of triethylamine in 150 ml of DMF is warmed to 60 C. 15.3 ml of 5-hexyn-1-ol dissolved in 50 ml of DMF are metered in. When the addition is complete, the batch is stirred at 75 C. for 18 h. After cooling, the mixture is diluted with THF/MTBE and neutralised using dil. hydrochloric acid. The organic phase is separated off, and the aqueous phase is extracted with MTBE. The combined organic phase is washed with sodium chloride solution and dried using sodium sulfate. The solution is concentrated to dryness, and the residue is purified by column chromatography (SiO.sub.2, toluene:ethyl acetate=1:1).

1.3 Preparation of 6-{4-[2-(4-{2-[4-(6-hydroxyhexyl)phenyl]ethyl}-2-methyl-phenyl)ethyl]phenyl}hexan-1-ol

(8) ##STR00245##

(9) 9.5 g (19.4 mmol) of 6-{4-[(2-(4-{2-[4-(6-hydroxyhex-1-ynyl)phenyl]vinyl}-3-methylphenyl)vinyl]phenyl}hex-5-yn-1-ol (E/Z mixture) are hydrogenated at room temperature for 19 h in the presence of Pd/C (5% of Pd) in THF. The solution is filtered and concentrated to dryness. The residue is recrystallised from n-heptane/MTBE (1:1), giving 6-{4-[2-(4-{2-[4-(6-hydroxyhexyl)phenyl]ethyl}-2-methylphenyl)ethyl]phenyl}hexan-1-ol as a colourless solid.

1.4 Preparation of 6-(4-{2-[3-methyl-4 (2-{4-[6-(2-methylacryloloxy)hexyl]-phenyl}ethyl)phenyl]ethyl}phenyl)hexyl 2-methacrylate

(10) ##STR00246##

(11) 600 mg of (6-{4-[2-(4-{2-[4-(6-hydroxyhexyl)phenyl]ethyl}-2-methylphenyl)ethyl]phenyl}hexan-1-ol are initially introduced in 15 ml of dichloromethane together with 0.30 ml (3.54 mol) of methacrylic acid and 10 mg (0.08 mmol) of DMAP. 3.5 ml (3.5 mmol, 1 M soln. in CH.sub.2Cl.sub.2) of DCC in are metered in, and the batch is stirred for 3 h. 100 mg (0.79 mmol) of oxalic acid dihydrate are added, and the mixture is filtered. The filtrate is concentrated to dryness, and the residue is purified by column chromatography (SiO.sub.2, pentane:MTBE=9:1), giving 6-(4-{2-[3-methyl-4-(2-{4-[6-(2-methylacryloyloxy)hexyl]phenyl}ethyl)phenyl]ethyl}phenyl)hexyl 2-methyacrylate (1) as a colourless solid having a melting point of 38 C.

(12) Phase sequence: C 38 I

(13) .sup.1H-NMR (400 MHz, CHCl.sub.3): =7.15-7.07 (m, 9H, H.sub.aryl.), 7.01-6.47 (m, 2H, H.sub.aryl.), 6.10-6.08 (m, 2H, CMe=CH.sub.2), 5.55-5.53 (m, 2H, CMe=CH.sub.2), 4.14 (t, 4H, J=6.7 Hz, 2CH.sub.2OC(O)CMe=CH.sub.2), 2.89-2.79 (m, 8H, H.sub.benzyl.), 2.61-2.56 (m, 4H, H.sub.benzyl.), 2.28 (s, 3H, Me), 1.95 (bs, 6H, Me.sub.acryl.), 1.71-1.59 (m, 8H, CH.sub.2), 1.46-1.34 (m, 8H, CH.sub.2).

(14) MS (EI): m/e (%)=636 (62, M.sup.+), 69 (100).

EXAMPLE 2

6-(4-{2-[4-(2-{4-[6-(2-Methylacryloyloxy)hexyl]phenyl}ethyl)phenyl]ethyl}phenyl)hexyl 2-methacrylate (2)

(15) Compound (2) according to the invention, 6-(4-{2-[4-(2-{4-[6-(2-methylacryloyloxy)hexyl]phenyl}ethyl)phenyl]ethyl}phenyl)hexyl 2-methacrylate, is synthesised analogously to compound (1) from Example 1.

(16) ##STR00247##

(17) 6-(4-{2-[4-(2-{4-[6-(2-Methylacryloyloxy)hexyl]phenyl}ethyl)phenyl]ethyl}-phenyl)hexyl 2-methacrylate (2) is obtained as a colourless solid having an m.p. of 80 C.

(18) Phase sequence: C 80 S.sub.B (60) I

(19) .sup.1H-NMR (400 MHz, CHCl.sub.3): =7.13-7.06 (m, 12H, H.sub.aryl.), 6.09-6.08 (m, 2H, CMe=CH.sub.2), 5.55-5.52 (m, 2H, CMe=CH.sub.2), 4.13 (t, 4H, J=6.7 Hz, 2CH.sub.2OC(O)CMe=CH.sub.2), 2.87 (s, 8H, H.sub.benzyl.), 2.61-2.56 (m, 4H, H.sub.benzyl.), 1.95 (bs, 6H, Me.sub.acryl.), 1.72-1.57 (m, 8H, CH.sub.2), 1.46-1.34 (m, 8H, CH.sub.2).

(20) MS (EI): m/e (%)=622 (11, M.sup.+), 104 (100).

EXAMPLE 3

6-(4-{2-[4-(2-{4-[6-(2-Methylacrloyloxy)hexyl]phenyl}ethyl)naphthalen-1-yl]ethyl}phenyl)hexyl 2-methacrylate (3)

(21) Compound (3) according to the invention, 6-(4-{2-[4-(2-{4-[6-(2-methylacryloyloxy)hexyl]phenyl}ethyl)naphthalen-1-yl]ethyl}phenyl)hexyl 2-methylacrylate, is synthesised as described below.

(22) ##STR00248##

3.1 Preparation of naphthalene-1,4-dicarbaldehyde

(23) ##STR00249##

(24) 80.0 g (0.28 mol) of 1,4-dibromonaphthalene are initially introduced in 800 ml of THF at 70 C., and 200 ml (0.32 mmol, 15% soln. in hexane) of n-BuLi are added. After 1 h, 24 ml (0.31 mol) of DMF are slowly added dropwise, and the mixture is stirred for 30 min. 500 ml (0.80 mmol, 15% soln. in hexane) of n-BuLi are subsequently metered in, and the mixture is left at 70 C. for 2 h. 110 ml (1.4 mol) of DMF are added. After 30 min., the batch is slowly warmed and hydrolysed using dilute hydrochloric acid. The mixture is extracted a number of times with MTBE, and the combined organic phases are washed with sat. antrium chloride solution. The solution is dried using sodium sulfate and concentrated to dryness. The residue is digested in MTBE and filtered off with suction.

3.2 Preparation of 1,4-bis-[(E,Z)-2-(4-bromophenyl)vinyl]naphthalene

(25) ##STR00250##

(26) 20.0 g (0.11 mol) of naphthalene-1,4-dicarbaldehyde are initially introduced in 500 ml of dichloromethane together with 125.0 g (0.24 mol) of 4-bromobenyzltriphenylphosphonium bromide and 6.50 g (24.6 mmol) of 18-crown-6. 30.0 g (0.53 mol) of powdered KOH are added in portions at 70 C. The mixture is stirred at 70 C. for 2 h, and the batch is warmed to room temperature. After 1 h at this temperature, water is added, and the organic phase is separated off.

(27) The aqueous phase is extracted with dichloromethane, and the combined organic phases are washed with sat. ammonium chloride soln. The solution is filtered absorptively (SiO.sub.2, CH.sub.2Cl.sub.2), and the filtrate is concentrated to dryness. The crude product is purified by column chromatography (SiO.sub.2, toluene:n-heptane=1:1), giving 1,4-bis-[(E,Z)-2-(4-bromophenyl)vinyl]naphthalene as a semicrystalline solid.

3.3 Preparation of 6-{4-[(E,Z)-2-(4-{(E,Z)-2-[4-(6-hydroxyhex-1-ynyl)-phenyl]vinyl}naphthalen-1-yl)vinyl]phenyl}hex-5-yn-1-ol

(28) ##STR00251##

(29) A mixture of 50.0 g (0.1 mol) of 1,4-bis-[(E,Z)-2-(4-bromophenyl)vinyl]-naphthalene, 7.3 g (10 mmol) of bis(triphenylphosphine)palladium(II) chloride, 2.0 mg (11 mmol) of copper(I) iodide and 75 ml (0.54 mol) of triethylamine in 300 ml of DMF is warmed to 60 C. 40.0 g (0.41 mol) of 5-hexyn-1-ol dissolved in 400 ml of DMF are metered in. When the addition is complete, the batch is stirred at 75 C. for 19 h. After cooling, the mixture is diluted with dichloromethane and neutralised using dil. hydrochloric acid. The organic phase is separated off, and the aqueous phase is extracted with dichloromethane. The combined organic phase is washed with sodium chloride solution and dried using sodium sulfate. The solution is concentrated to dryness, and the residue is purified by column chromatography (SiO.sub.2, dichloromethane:MTBE=8:2.fwdarw.1:1).

3.4 Preparation of 6-{4-[2-(4-{2-[4-(6-hydroxyhexyl)phenyl]ethyl}naphthalen-1-yl)ethyl]phenyl}hexan-1-ol

(30) ##STR00252##

(31) 25.0 g (47.7 mmol) of 6-{4-[2-(4-{2-[4-(6-hydroxyhex-1-ynyl)phenyl]vinyl}-naphthalen-1-yl)vinyl]phenyl}hex-5-yn-1-ol (E/Z mixture) are hydrogenated at room temperature for 17 h in the presence of Pd/C (5% of Pd) in THF. The solution is filtered and concentrated to dryness. The residue is recrystallised from n-heptane/MTBE (1:1), giving 6-{4-[2-(4-{2-[4-(6-hydroxyhexyl)phenyl]ethyl}naphthalen-1-yl)ethyl]phenyl}hexan-1-ol as a colourless solid.

3.5 Preparation of 6-(4-{2-[4-(2-{4-[6-(2-methlacryoloxy)hexyl]phenyl}-ethyl)naphthalen-1-yl]ethyl}phenyl)hexyl 2-methacrylate

(32) ##STR00253##

(33) 10.0 g (18.6 mmol) of 6-{4-[2-(4-{2-[4-(6-hydroxyhexyl)phenyl]ethyl}naphthalen-1-yl)ethyl]phenyl}hexan-1-ol are initially introduced in 100 ml of dichloromethane together with 50 ml (0.62 mol) of pyridine and 200 mg (1.64 mmol) of DMAP. 8.0 g (51.6 mmol) of methacrylic anhydride in 100 ml of DCM are metered in (ice cooling), and the batch is stirred for 19 h. The batch is washed with dil. hydrochloric acid and sat. sodium chloride solution, and the organic phase is dried using sodium sulfate. The solution is concentrated to dryness, and the residue is purified by column chromatography (SiO.sub.2, pentane:DCM=1:1.fwdarw.DCM), giving 6-(4-{2-[4-(2-{4-[6-(2-methylacryloyloxy)hexyl]phenyl}ethyl)naphthalen-1-yl]ethyl}-phenyl)hexyl 2-methacrylate (3) as a colourless solid having a melting point of 47 C.

(34) Phase sequence: T.sub.g 45 C 47 I

(35) .sup.1H-NMR (300 MHz, CHCl.sub.3): =8.16-8.11 (m, 2H, H.sub.aryl.), 7.56-7.50 (m, 2H, H.sub.aryl.), 7.24-7.09 (m, 10H, H.sub.aryl.), 6.11-6.08 (m, 2H, CMe=CH.sub.2), 5.54-5.52 (m, 2H, CMe=CH.sub.2), 4.14 (t, 4H, J=6.7 Hz, 2CH.sub.2OC(O)CMe=CH.sub.2), 3.38-3.31 (m, 4H, H.sub.aliph.), 3.05-2.98 (m, 4H, H.sub.aliph.), 2.64-2.56 (m, 4H, H.sub.aliph.), 1.95 (bs, 6H, Me.sub.acryl.), 1.73-1.57 (m, 8H, CH.sub.2), 1.47-1.33 (m, 8H, CH.sub.2).

(36) MS (EI): m/e (%)=673 (100, M.sup.+).

EXAMPLE 4

6-{4-[2-(4-{2-[4-(6-Acryloyloxyhexyl)phenyl]ethyl}naphthalen-1-yl)ethyl]-phenyl}hexyl acrylate (4)

(37) Compound (4) according to the invention, 6-{4-[2-(4-{2-[4-(6-acryloyloxy-hexyl)phenyl]ethyl}naphthalen-1-yl)ethyl]phenyl}hexyl acrylate, is synthesised analogously to Examples 1 and 3 from 6-{4-[2-(4-{2-[4-(6-hydroxyhexyl)phenyl]ethyl}naphthalen-1-yl)ethyl]phenyl}hexan-1-ol (see Example 3, step 3.4).

(38) ##STR00254##

(39) Phase sequence: T.sub.g 47 C 55 I

(40) MS (EI): m/e (%)=644 (83, M.sup.+), 105 (100).

(41) Use Example 1

(42) The following monomers are used:

(43) ##STR00255##

Monomer (1) from Example 1

(44) ##STR00256##
RM257 has the phase sequence C 66 N 127 I.
RM-CC has the phase sequence C 14 SmB 33 I.

(45) The following additives are used:

(46) (Dp: chiral dopant, In: polymerisation initiator)

(47) ##STR00257##

(48) TABLE-US-00005 TABLE 1 Composition of the base mixture (host) H1 before addition of the polymerisation components: Composition Component Proportion Acronym % by weight PUQU-3-F 5.00 AGUQU-3-F 13.00 AUUQU-2-F 6.00 AUUQU-3-F 10.00 AUUQU-4-F 6.00 AUUQU-5-F 9.00 AUUQU-7-F 6.00 AUUQU-3-T 8.00 AUUQU-3-OT 12.00 PUZU-2-F 6.00 PUZU-3-F 10.00 PUZU-5-F 9.00 100.00 Properties T(N, I): 66.6 C. n (20 C., 589 nm): 0.148
Description of the Polymerisation

(49) Before the polymerisation of a sample, the phase properties of the medium are established in a test cell having a thickness of about 10 microns and an area of 22.5 cm.sup.2. The filling is carried out by capillary action at a temperature of 75 C. The measurement is carried out a polarising microscope with heating stage with a temperature change of 1 C./min.

(50) The polymerisation of the media is carried out by irradiation with a UV lamp (Dymax, Bluewave 200, 365 nm interference filter) having an effective power of about 3.0 mW/cm.sup.2 for 180 seconds. The polymerisation is, carried out directly in the electro-optical test cell.

(51) The polymerisation is carried out initially at a temperature at which the medium is in the blue phase I (BP-I). The polymerisation is carried out in a plurality of part-steps, which gradually result in complete polymerisation. The temperature range of the blue phase generally changes during the polymerisation. The temperature is therefore adapted between each part-step so that the medium is still in the blue phase. In practice, this can be carried out by observing the sample under the polarising microscope after each irradiation operation of about 5 s or longer. If the sample becomes darker, this indicates a transition into the isotropic phase. The temperature for the next part-step is reduced correspondingly.

(52) The entire irradiation time which results in maximum stabilisation is typically 180 s at the irradiation power indicated. Further polymerisations can be carried out in accordance with an optimised irradiation/temperature programme.

(53) Alternatively, the polymerisation can also be carried out in a single irradiation step, in particular broad if a blue phase is already present before the polymerisation.

(54) Electro-Optical Characterisation

(55) After the above-described polymerisation and stabilisation of the blue phase, the phase width of the blue phase is determined. The electro-optical characterisation is carried out subsequently at various temperatures within and if desired also outside this range. The test cells used are fitted on one side with interdigital electrodes on the cell surface. The cell gap, the electrode separation and the electrode width are typically each 10 microns. This uniform dimension is referred to below as the gap width. The area covered by electrodes is about 0.4 cm.sup.2. The test cells do not have an alignment layer.

(56) For the electro-optical characterisation, the cell is located between crossed polarising filters, where the longitudinal direction of the electrodes adopts an angle of 45 to the axes of the polarising filter. The measurement is carried out using a DMS301 (Autronic-Melchers) at a right angle to the cell plane, or by means of a highly sensitive camera on the polarising microscope. In the voltage-free state, the arrangement described gives an essentially dark image (definition 0% transmission).

(57) Firstly, the characteristic operating voltages and then the response times are measured on the test cell. The operating voltage is applied to the cell electrodes in the form of rectangular voltage having an alternating sign (frequency 100 Hz) and variable amplitude, as described below.

(58) The transmission is measured while the operating voltage is increased. The reaching of the maximum value of the transmission defines the characteristic quantity of the operating voltage V.sub.100. Equally, the characteristic voltage V.sub.10 is determined at 10% of the maximum transmission. These values are measured at various temperatures in the range of the blue phase.

(59) Relatively high characteristic operating voltages V.sub.100 are observed at the upper and lower end of the temperature range of the blue phase. In the region of the minimum operating voltage, V.sub.100 generally only increases slowly with temperature. This temperature range, limited by T.sub.1 and T.sub.2, is referred to as the usable, flat temperature range (FR). The width of this flat range (FR) is (T.sub.2T.sub.1) and is known as the width of the flat range (WFR).

(60) The precise values of T.sub.1 and T.sub.2 are determined by the intersections of tangents on the flat curve section FR and the adjacent steep curve sections in the V.sub.100/temperature diagram.

(61) In the second part of the measurement, the response times during switching on and off (.sub.on, .sub.off) are determined. The response time .sub.on is defined by the time to achievement of 90% intensity after application of a voltage at the level of V.sub.100 at the selected temperature. The response time .sub.off is defined by the time until the decrease by 90% starting from maximum intensity at V.sub.100 after reduction of the voltage to 0 V. The response time is also determined at various temperatures in the range of the blue phase.

(62) As further characterisation, the transmission at continuously increasing and falling operating voltage between 0 V and V.sub.100 is measured at a temperature within the FR. The difference between the two curves is known as hysteresis. The difference in the transmissions at 0.5.Math.V.sub.100 and the difference in the voltages at 50% transmission are, for example, characteristic hysteresis values and are known as T.sub.50 and V.sub.50 respectively. Furthermore, the contrast during the first switching-on and during the subsequent switching off is distinguished as the ratio of the respective maximum and minimum transmission.

(63) Use Examples M1 to M

(64) Use Example Mixture M1 and Comparative Examples C1 and C2

(65) TABLE-US-00006 M1 C1 C2 Component Proportion [% by weight] H1 85.0 85.0 86.3 Dp 3.8 3.8 2.5 In 0.2 0.2 0.2 (1) 6.0 RM257 5.0 5.0 RM-CC 5.0 6.0 6.0

(66) The media are characterised as described before the polymerisation. The RM components are then polymerised by single irradiation (180 s) in the blue phase, and the media obtained are re-characterised.

(67) TABLE-US-00007 Measurement values M1 C1 C2 Transition point before 44.1 49.5 the polymerisation Temperature range of the blue phase V.sub.10 (20 C.) 34.9 V 25.7 V 22.2 V.sub.100 (20 C.) 78.0 V 64.0 V 55.0 V V.sub.50 (20 C.) 4.2 V 6.2 V 4.2 Contrast, switching on 569 503 45.0 Contrast, switching off 543 32 50.1 Gap width 10 m 10 m 10 m

(68) The polymer-stabilised medium M1, prepared using monomer (1) according to the invention, exhibits a reduction in hysteresis (V.sub.50) and a significant increase in the contrast during switching on and off compared with the polymer-stabilised medium C1, prepared using monomer RM257 from the prior art. Furthermore, it is evident that the contrast during switching off in the case of the polymer-stabilised medium C1 is much lower than during switching on. In the case of mixture C2, which is analogous to mixture C1, but comprises less chiral dopant, the contrast during switching on and off is very similar. The lower contrast compared with M1 and C1 is therefore-due to the fact that a visible blue phase is present in the case of C2. This means that the monomer mixture presented in this invention is particularly suitable for the stabilisation of blue phases with a high concentration of chiral dopant.