BENZIL MONOKETALS AND THE USE THEREOF

Abstract

The present invention relates to the use of hydrophilic compounds of the formula I as photopolymerisation initiators of polymerisable substance mixtures which comprise unsaturated compounds, or for the photochemical crosslinking of linear polymers,

##STR00001##

in which the parameters have the meaning indicated in Claim 1, to sealants for liquid-crystal displays which comprise the hydrophilic photoinitiators, to novel hydrophilic photoinitiators of the formula I, and to the liquid-crystal displays produced using these sealants.

Claims

1. A photopolymerization or crosslinking process, comprising photopolymerization of polymerizable substance mixtures which comprise unsaturated compounds, or photochemical crosslinking of linear polymers, by subjecting said unsaturated compounds or linear polymers to photopolymerization or crosslinking conditions respectively in the presence of an initiator of formula I ##STR00039## in which R.sup.1, R.sup.2, independently of one another, denote a straight-chain or branched or cyclic alkyl, cycloalkylalkyl, arylalkyl, alkenyl or cycloalkylalkenyl radical having up to 20 C atoms or an arylalkenyl radical having 8 to 20 C atoms, in each of which one or more CH.sub.2 groups may be replaced by CO, O and/or S in such a way that no O or S atoms are adjacent and in which one or more hydrogen atoms may be replaced by halogen, or both radicals R.sup.1 and R.sup.2 together denote a divalent bridging group W, W denotes a divalent radical of an aliphatic, straight-chain or branched diol having 2 to 20 C atoms, Ar.sup.1, Ar.sup.2, independently of one another, denote aryl radicals which are each substituted by one or more substituents L and which may additionally be substituted by halogen, alkyl, alkoxy, each having 1 to 5 C atoms, or phenyl, L on each occurrence, identically or differently, denotes a hydrophilic radical.

2. The process according to claim 1, wherein, in formula I, R.sup.1, R.sup.2, independently of one another, denote a straight-chain or branched alkyl radical having 1 to 7 C atoms, Ar.sup.1, Ar.sup.2, independently of one another, denote 1,4-phenylene, which is in each case substituted by a substituent L, L denotes CH.sub.2-L, O-L or N(L).sub.2, L denotes a straight-chain or branched alkyl radical having 1 to 19 C atoms, in which one or more CH.sub.2 groups may be replaced by cycloalkanediyl radicals having 3 to 8 ring atoms and in which one or more non-adjacent CH.sub.2 groups may be replaced by O and in which one or more H atoms may be replaced by OH or ##STR00040##

3. The process according to claim 1, wherein, in formula I, R.sup.1, R.sup.2 denote W, W denotes a divalent radical of an aliphatic, straight-chain or branched diol having 2 to 10 C atoms, Ar.sup.1, Ar.sup.2, independently of one another, denote 1,4-phenylene, which is in each case substituted by a substituent L, L denotes CH.sub.2-L, O-L or N(L).sub.2, L denotes a straight-chain or branched alkyl radical having 1 to 19 C atoms, in which one or more CH.sub.2 groups may be replaced by cycloalkanediyl radicals having 3 to 8 ring atoms and in which one or more non-adjacent CH.sub.2 groups may be replaced by O and in which one or more H atoms may be replaced by OH or ##STR00041##

4. The process according to claim 1, wherein the compounds of the formula I are compounds of the following sub-formulae: ##STR00042## where L denotes CH.sub.2-L, O-L or N(L).sub.2, L denotes a straight-chain or branched alkyl radical having 1 to 19 C atoms, in which one or more CH.sub.2 groups may be replaced by cycloalkanediyl radicals having 3 to 8 ring atoms and in which one or more non-adjacent CH.sub.2 groups may be replaced by O and in which one or more H atoms may be replaced by OH or ##STR00043##

5. The process according to claim 1, wherein L denotes (CH.sub.2).sub.pOG, O(CH.sub.2).sub.m+1OG, (CH.sub.2).sub.n(OCH.sub.2CH.sub.2).sub.mOG, (O).sub.n(CH.sub.2).sub.mCH(OH)CH.sub.2OG, O(CH.sub.2CH.sub.2).sub.m+1OCH.sub.2CH(OG)CH.sub.2-OG, OC(CH.sub.2OG).sub.3, OC(CH.sub.2OG).sub.2(CH.sub.2).sub.nH, (CH.sub.2).sub.nOCH.sub.2CH(OH)CH.sub.2OG, (OCH.sub.2CH.sub.2).sub.mOCH.sub.2CH(OG)CH.sub.2OG, (CH.sub.2).sub.nOCH.sub.2(CH).sub.m((CH.sub.2).sub.mOG).sub.2, (CH.sub.2).sub.nOC(CH.sub.2OG).sub.3, (CH.sub.2).sub.mOC(CH.sub.2OG).sub.2(CH.sub.2).sub.nH, N((CH.sub.2).sub.m+1OG).sub.2, N((CH.sub.2CH.sub.2O).sub.mG).sub.2, N((CH.sub.2).sub.mCH(OG)CH.sub.2OG).sub.2 or ##STR00044## m denotes an integer from 1 to 10, n, p denote an integer from 0 to 10, G denotes H, ##STR00045## or a monosaccharide radical selected from glucopyranose and glucofuranose, with the proviso that G cannot be H if p is equal to 0.

6. The process according to claim 1, wherein the compounds of the formula I have an octan-1-ol/water partition coefficient of log P3.2.

7. (canceled)

8. A sealant for liquid-crystal displays, comprising a) one or more curable epoxide resins which comprise compounds which are each substituted by one or more epoxide groups and/or b) one or more (meth) acrylate compounds which are each substituted by one or more acrylate or methacrylate groups and/or c) one or more epoxide acrylate compounds which are substituted both by epoxide groups and by (meth)acrylate groups and d) a compound of the formula I ##STR00046## in which R.sup.1, R.sup.2, independently of one another, denote a straight-chain or branched or cyclic alkyl, cycloalkylalkyl, arylalkyl, alkenyl or cycloalkylalkenyl radical having up to 20 C atoms or an arylalkenyl radical having 8 to 20 C atoms, in each of which one or more CH.sub.2 groups may be replaced by CO, O and/or S in such a way that no O or S atoms are adjacent and in which one or more hydrogen atoms may be replaced by halogen, or both radicals R.sup.1 and R.sup.2 together denote a divalent bridging group W, W denotes a divalent radical of an aliphatic, straight-chain or branched diol having 2 to 20 C atoms, Ar.sup.1, Ar.sup.2, independently of one another, denote aryl radicals which are each substituted by one or more substituents L and which may additionally be substituted by halogen, alkyl, alkoxy, each having 1 to 5 C atoms, or phenyl, L on each occurrence, identically or differently, denotes a hydrophilic radical.

9. The sealant according to claim 8, that is photochemically curable.

10. The sealant according to claim 9, that is additionally thermally curable.

11. A compound of the formula I ##STR00047## in which R.sup.1, R.sup.2, independently of one another, denote a straight-chain or branched or cyclic alkyl, cycloalkylalkyl, arylalkyl, alkenyl or cycloalkylalkenyl radical having up to 20 C atoms or an arylalkenyl radical having 8 to 20 C atoms, in each of which one or more CH.sub.2 groups may be replaced by CO, O and/or S in such a way that no O or S atoms are adjacent and in which one or more hydrogen atoms may be replaced by halogen, or both radicals R.sup.1 and R.sup.2 together denote a divalent bridging group W, W denotes a divalent radical of an aliphatic, straight-chain or branched diol having 2 to 20 C atoms, Ar.sup.1, Ar.sup.2, independently of one another, denote aryl radicals which are each substituted by one or more substituents L and which may additionally be substituted by halogen, alkyl, alkoxy, each having 1 to 5 C atoms, or phenyl, L on each occurrence, identically or differently, denotes a hydrophilic radical with the proviso that compounds of the formula I-1-1a ##STR00048## are excluded.

12. A liquid-crystal display, containing a sealant according to claim 8.

13. A liquid-crystal display according to claim 12, been produced by an ODF process.

14. A liquid-crystal display according to claim 12, that is a PS-VA, PS-IPS, PS-FFS, PS-OCB or PS-TN display.

15. The process according to claim 1, comprising sealing a liquid crystalline display by said photopolymerization or crosslinking.

Description

EXAMPLES

[0117] The present invention is described in detail by the following, non-restrictive examples.

Example 1: 1,2-Bis[4-(2,3-dihydroxypropoxy)phenyl]-2,2-dimethoxyethanone

[0118] 1.1 4,4-Bis(allyloxy)benzil

##STR00024##

[0119] A solution of allyl bromide (23.0 g, 190 mmol) in 50 ml of dimethylformamide is added dropwise to a suspension of 4,4-dihydroxybenzil (16.8 g, 69.4 mmol) and potassium carbonate (21.1 g, 153 mmol) in 250 ml of dimethylformamide. The batch is left to stir overnight at 80 C., added to water and extracted with dichloromethane. The combined org. phases are washed with water, dried over sodium sulfate and evaporated in vacuo. The residue is chromatographed on silica gel with dichloromethane, giving 4,4-bis(allyloxy)benzil as a yellowish solid.

[0120] 1.2 1,2-Bis(4-allyloxyphenyl)-2,2-dimethoxyethanone

##STR00025##

[0121] 60 ml of methanol are slowly added dropwise to a suspension of 4,4-bis-(allyloxy)benzil (17.7 g, 55.0 mmol) and thionyl chloride (53.0 ml, 0.740 mol) at such a rate that the temperature is 5-10 C. When the addition is complete, the batch is heated at 50 C. for 6 h, carefully neutralised by addition of dil. sodium hydroxide solution and extracted with ethyl acetate. The combined org. phases are washed with water and dried over sodium sulfate. The solvent is removed in vacuo, and the residue is purified by chromatography on silica gel with dichloromethane/ethyl acetate (9:1), giving 1,2-bis(4-allyloxyphenyl)-2,2-dimethoxyethanone as a yellowish oil.

[0122] 1.3 1,2-Bis[4-(2,3-dihydroxypropoxy)phenyl]-2,2-dimethoxyethanone

##STR00026##

[0123] 6.4 ml of a 4 percent aqueous osmium tetraoxide solution are added dropwise to a solution of 1,2-bis(4-allyloxyphenyl)-2,2-dimethoxyethanone (7.6 g) and 4-methylmorpholine N-oxide (8.2 g) in 90 ml of acetone and 20 ml of water at such a rate that the temperature does not exceed 20 C. After stirring overnight, 0.6 g of sodium metabisulfite are added, and the batch is left to stir for 1 h. The solution is extracted with ethyl acetate, and the combined org. phases are purified by chromatography on silica gel with dichloromethane/methanol (9:1), giving 1,2-bis[4-(2,3-dihydroxypropoxy)-phenyl]-2,2-dimethoxyethanone as a wax-like solid.

[0124] .sup.1H-NMR (d.sub.6-DMSO, 500 MHz, with TFA exchange)

[0125] =7.79 ppm (d., 4H, ArH), 7.79 (d., 4H, ArH), 4.06-3.82 (br. m., 8H, 4CH.sub.2O), 3.45 (br. m., 2H, 2CH.sub.2CHOHCH.sub.2), 3.14 (s., 6H, 2OCH.sub.3).

Use Example

[0126] A nematic liquid-crystal mixture M-1 is prepared as follows:

TABLE-US-00002 Mixture M-1 Composition Compound Concentration/ No. Structural formula % by weight 1 [00027] 9.50 2 [00028] 5.00 3 [00029] 9.50 4 [00030] 10.50 5 [00031] 10.50 6 [00032] 9.50 7 [00033] 12.00 8 [00034] 9.00 9 [00035] 11.00 10 [00036] 13.50 100.00

[0127] A polymerisable liquid-crystal mixture P-1 consisting of [0128] 1. 99.7% by weight of the nematic liquid-crystal mixture M-1 and [0129] 2. 0.3% by weight of the polymerisable compound RM-1

##STR00037##

is prepared. Three samples of in each case 0.5 g of mixture P-1 are stored together with in each case 1 g of the commercially available sealant Unocol 2094 (APM Technica GmbH, PUrgen-Ummendorf), the latter in each case containing [0130] 1. no photoinitiator [0131] 2. 3.0% by weight of the photoinitiator according to the invention from Example 1 [0132] 3. 3.0% by weight of the commercially available photoinitiator Irgacure651 of the structure shown below
in a tightly sealed vial at 80 C. for 7 d with exclusion of air and light. A fourth sample of mixture P-1 is stored under the same conditions without the presence of sealant (blank experiment).

##STR00038##

TABLE-US-00003 TABLE 2 Initiator Ex. Mixture Sealant Photoinitiator concentration 0.1 (blank P-1 experiment) 0.2 (comparison) P-1 Unocol 2094 1 P-1 Unocol Irgacure651 3.0% by weight 2094 2 P-1 Unocol Ex. 1 3.0% by weight 2094

[0133] The mixtures are subsequently separated off from the sealant, in each case divided into two parts, introduced into PS-VA test cells and irradiated with a metal halide UV lamp with an intensity of 100 mW/cm.sup.2 at 40 C. for a duration of 60 s or 180 s.

[0134] The PS-VA test cells consist of two plane-parallel glass plates having a cell gap of 4 m, each of which are coated with an ITO electrode and with a polyimide alignment layer on top.

[0135] After the irradiation, the concentration of the polymerisable compound RM-1 is determined by HPLC. The results are shown in Table 3.

TABLE-US-00004 TABLE 3 Concentration of RM/rel % after Ex. t = 0 s t = 60 s t = 180 s 0.1 (blank experiment) 100 88 56 0.2 (comparison) 70 64 51 1 71 66 51 2 72 0 0

[0136] As can be seen from Table 3, approximately the same amount of the polymerisable compound RM-1 (70-72%) can be detected in the samples from Examples 0.2, 1 and 2 after the storage test. In the blank experiment (Ex. 0.1, without sealant), somewhat more RM-1 is detectable (relative 100%), which indicates dissolution of the RM out of the liquid crystal by the sealant or slow decomposition of RM-1 by components of the sealant in the other three samples during the storage test. As is furthermore evident, the presence of Irgacure651 during the storage test subsequently results in rapid polymerisation of RM-1 on UV irradiation of the liquid-crystal mixture; RM-1 is no longer detectable after only 60 s, which suggests that considerable amounts of photoinitiator have dissolved in the liquid-crystal mixture (Ex. 2).

[0137] The decrease in the RM concentration in the Examples 0.1 and 0.2 is due to the, albeit slight, reactivity of RM-1, which polymerises slowly even without photoinitiator.

[0138] As can be seen, the decrease in the concentration of RM-1 after contact of mixture P-1 with sealant comprising the photoinitiator according to the invention (Example 1) is comparable with the sample from Example 0.2 (without photoinitiator), which suggests that no photoinitiator according to the invention has been dissolved out of the sealant in the liquid crystal during the storage test, which means that the photoinitiator according to the invention is eminently suitable for the production of liquid-crystal displays, in particular if undesired reactions during curing of sealants during production are to be avoided.