Polymerizable nematic monomer compositions

The present invention relates to new polymerizable nematic monomer compositions.

Liquid crystal monomers and mixtures of monomers in combination with photoinitiators can show nematic mesophases. Under ultraviolet (UV) radiation, these nematic mesophases can undergo rapid photopolymerization in the presence of UV photoinitiators in order to freeze the structure and orientation (orientation) of the nematic mesophase in a polymer matrix.

For example, JP-A-62-70.406 describes the polymerization of nematic monomers in the liquid crystal state in the presence of a polymerization initiator with ultraviolet rays. One or more of the monomers are heated to melt and then cooled to their nematic mesophase. This mesophase is aligned and photopolymerized to obtain an aligned polymer film. The disclosed monomers have the following structure:

wherein n is 2, 3, 4, 5, 6, 8 or 11, X -CN, H, Cl, etc., R CH & sub3; or H and Y are a covalent bond or -CO 2 -.

It has been found that the compositions disclosed in this patent are of limited utility in photopolymerization processes because some of the disclosed monomers or mixtures of the monomers undergo rapid crystallization from the monotropic nematic phase so that the desired oriented nematic structure is destroyed before the photopolymerization can be carried out.

It is therefore desirable to have polymerizable nematic monomer mixtures that resist crystallization at room temperature.

This object is achieved by a polymerizable nematic monomer composition with monomers of the general formula I:

in the R CH & sub3; or H and Y are a covalent bond or -CO 2 -, which is characterized in that (A) in 20 to 80% by weight of the monomers with the general formula (I) n = 10, 12 or 14 and (B ) in 80 to 20% by weight of the monomers with the general formula (1) n = 4, 6 or 8.

Two, three and four monomer mixtures are preferred which contain 30 to 70% by weight of the monomers of Part A and 70 to 30% by weight of the monomers of Part B. Two and three monomer mixtures which contain 30 to 70% by weight of a monomer of part A and 70 to 30% by weight of one or two of the monomers of part B are particularly preferred. Most preferred is a composition with equal amounts of the three monomers in which n is 6, 8 and 10 and R is CH 3. are.

The synthesis of these monomers is known in the prior art. For example, monomers in which Y is a covalent bond have been prepared by alkylating 4 '- (hydroxy) -4-cyanobiphenyl with omega-bromoalcohols and then esterifying the alcohol with acryloyl or methacryloyl chloride (VP Shibaev, SG Kostromin and NA Plate, Eur. Polym. J., 18, 651 (1982)).

Monomers in which Y is -CO₂- are prepared by alkylating 4-hydroxybenzoic acid with omega-chloroalcohols, esterifying the alcohol obtained with acrylic acid or methacrylic acid, converting the 4-substituted benzoic acid to an acid chloride and esterifying the acid chloride with 4-cyanophenol (M. Portugal, H. Ringsdorf, R. Zentel, Makromol. Chem., 183, 2311 (1982)).

These polymerizable nematic mesophases are useful in the formation of polymer films. They can be used to make films with multi-oriented mesogens.

The photopolymerization is initiated by UV radiation. A small amount of the photoinitiator, preferably 0.5 to 2% by weight, is added to the polymerizable monomer composition to increase the reactivity of the composition to UV radiation. Examples of photoinitiators useful for the purposes of the present invention are benzophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxyacetophenone, 2-benzoyloxyacetophenone, 2-chlorothioxanthone and 2-hydroxycyclohexylphenyl ketone.

Multifunctional monomers useful as crosslinking agents can be added to the monomeric liquid crystals, if desired. Conventional crosslinking agents are generally added in amounts from about 0.5 to about 5 percent by weight.

The compositions of the invention, when melted, show nematic mesophases when cooled to near room temperature. An advantage of the compositions of the present invention is their increased stability compared to the nematic monomers themselves and in other mixtures. The stability of the compositions of the present invention provides a significant processing advantage. Once the monomer has melted and cooled to the nematic phase, time is required to align the material on a substrate, fill a cell, or perform other processing. During this period it is important that the nematic phase is not subject to crystallization, since the crystallization of one or more monomers destroys the mesophase. The compositions of the present invention have been found to be stable over a period of 12 hours or more.

The invention is explained in more detail below with the aid of the examples, all parts, percentages or the like being based on the weight, unless stated otherwise.

example 1

This example shows the formation of intermediates used in the synthesis of monomers 1a, 1b, 1c, 1d, 1e, 1f and 1g.

1a - Formation of 4 '- (6-bromohexyloxy) -4-cyanobiphenyl

A mixture of 4'-hydroxy-4-cyanobiphenyl (7.8 g, 40 mmol), potassium carbonate (8.3 g, 60 mmol), 1,6-dibromohexane (29.8 g, 120 mmol) and acetone (80 ml) was heated under reflux for 6 hours under a nitrogen atmosphere. The acetone was concentrated and the residue was dissolved in ether / dichloromethane (4: 1, 400 ml). The solution was filtered through a glass fiber. The filtrate was washed with water and brine, dried over magnesium sulfate and concentrated. Excess 1,6-dibromohexane was removed by Kugelrohr distillation up to 75 ° C at 13.3 Pa (0.1 mm Hg). The material remaining in the pot was recrystallized from ethanol (100 ml), filtered hot and cooled in a freezer to form bromide crystals (9.6 g, 67%): mp 65.5-66 ° C, mesophase at 63 ° C at Cooling down; NMR (CDCl₃) 7.55 (s, 4H), 7.49 (d, 2H), 6.82 (d, 2H), 3.91 (t, 2H), 2.0-1.3 (m , 8H); IR (CH2 Cl2) 2222, 1602 cm-1.

1b - Formation of 4 '- (8-bromooctyloxy) -4-cyanobiophenyl

Treatment of 4'-hydroxy-4-cyanobiphenyl with 1,8-dibromoctane as described above gave the bromide crystals (10.9 g, 69%): mp 79-80 ° C; NMR (CDCl₃) 7.55 (s, 4H), 7.50 (d, 2H), 6.85 (d, 2H), 3.9 (t, 2H), 3.35 (t, 2H), 1.9-1.3 (m, 12H).

1c - Formation of 4 '- (10-bromodecyloxy) -4-cyanobiphenyl

Treatment of 4'-hydroxy-4-cyanobiphenyl with 1,10-dibromodecane as described above gave the bromide crystals (13.0 g, 78%): mp 69-71 ° C; NMR (CDCl 3) 7.6 (s, 4H), 7.5 (d, 2H), 6.9 (d, 2H), 3.95 (t, 2H), 3.35 (t, 2H), 1.95-1.3 (m, 16H); IR (KBr) 2238, 2222, 1605 cm-1.

1d - Formation of 4 '- (12-bromododecyloxy) -4-cyanobiphenyl

Treatment of 4'-hydroxy-4-cyanobiphenyl with 1,12-dibromododecane as described above gave the bromide crystals.

1e - Formation of 4 '- (5-bromopentyloxy) -4-cyanobiphenyl

Treatment of 4'-hydroxy-4-cyanobiphenyl with 1,5-dibromopentane as described above gave the bromide crystals.

1f - Formation of 4 '- (9-bromononyloxy) -4-cyanobiphenyl

Treatment of 4'-hydroxy-4-cyanobiphenyl with 1,9-dibromononane as described above gave the bromide crystals.

1g - Formation of 4 '- (11-bromundecyloxy) -4-cyanobiphenyl

Treatment of 4'-hydroxy-4-cyanobiphenyl with 1,11-dibromundecane as described above gave the bromide crystals.

Example 2

This example shows the formation of methacrylate monomers 1a, 1b, 1c, 1d, 1e, 1f and 1g.

Methacrylate monomer 1a

A mixture of 4 '- (6-bromohexyloxy) -4-cyanobiphenyl (7.0 g, 20 mmol) prepared according to Example 1, potassium methacrylate (4.8 g, 40 mmol), hydroquinone (10 mg) and distilled dimethylformamide (40 ml) was heated to 70-80 ° C for 3 hours. The mixture was diluted with water (200 ml) and extracted with ether / dichloromethane (4: 1, 200 ml portions, 2 x). The extract was washed with water, dried over magnesium sulfate and concentrated. The solid obtained was recrystallized from absolute ethanol (90 ml), filtered and cooled in a freezer to give crystals of 1a (5.5 g, 76%): mp 74-76 ° C; NMR (CDCl₃) 7.55 (s, 4H), 7.45 (d, 2H), 6.88 (d, 2H), 6.0 (s, 1H), 5.45 (s, 1H), 1.95-1.3 (m, 11H); IR (KBr) 2225, 1708 cm-1.

Methacrylate monomer 1b

The bromide described in Example 1 was treated with potassium methacrylate as described above to give 1b as crystals (4.9 g, 63%): mp 71-73 ° C; NMR (CDCl₃) 7.6 (s, 4H), 7.48 (d, 2H), 6.9 (d, 2H), 6.03 (s, 1H), 5.5 (s, 1H), 4.02 (m, 4H), 2.0-1.3 (m, 12H).

Methacrylate monomer 1c

The bromide described in Example 1 was treated with potassium methacrylate as described above to give 1c as crystals (5.9 g, 66%): mp 69-70 ° C, mesophase at 47 ° C in the cooling cycle; NMR (CDCl₃) 7.53 (s, 4H), 7.4 (d, 2H), 6.85 (d, 2H), 5.95 (s, 1H), 5.45 (s, 1H), 4.0 (m, 4H), 2.0-1.3 (m, 19H)

Methacrylate monomers 1d, 1e, 1f and 1g

The bromides prepared in Example 1 were treated with potassium methacrylate as described above to give 1d, 1e, 1f and 1g. Their melting points are listed in Table 1.

Example 3

This example shows the formation of 4- (10-hydroxydecyloxy) benzoic acid and 4 (6-hydroxyhexyloxy) benzoic acid, intermediates in the preparation of monomers 2a and 2b.

4- (10-Hydroxydecyloxy) benzoic acid

A mixture of 4-hydroxybenzoic acid (69.0 g, 0.5 mol), 10-chloro-1-decanol (106 g, 0.55 mol), potassium hydroxide (75 g, 1.15 mol), potassium iodide (0, 1 g) and absolute ethanol (300 ml) was refluxed with stirring for 18 hours. The mixture was diluted with water (800 ml) and stirred at room temperature for 0.5 hours. The mixture was acidified with 12N hydrochloric acid (125 ml) and the mixture was stirred for 5 hours. The material was allowed to settle overnight and filtered. The solid was washed with water and air dried for 4 days. The solid was recrystallized from tetrahydrofuran (300 ml) to give 4- (10-hydroxydecyloxy) benzoic acid (85.2 g, 58%): mp 115-117 ° C; NMR (CDCl3 + d6-DMSO) 7.93 (d, 2H), 6.85 (d, 2H), 4.0 (t, 2H), 3.52 (t, 2H), 3.48 (bs , 1H), 1.9-1.2 (m, 16H).

4- (6-hydroxyhexyloxy) benzoic acid

A mixture of 4-hydroxybenzoic acid (138 g, 1.0 mol) and 6-chloro-1-hexanol (150 g, 1.1 mol) was treated as described above to give a solid (101.2 g, mp 127 - 132 ° C) was obtained. Recrystallization of part of the solid from tetrahydrofuran gave pure 4- (6-hydroxyhexyloxy) benzoic acid: mp 132-135 ° C.

Example 4

This example shows the formation of 4- (10-methacryloxydecyloxy) benzoic acid and 4- (6-methacryloyloxyhexyloxy) benzoic acid, intermediates in the preparation of monomers 2a and 2b.

4- (10-Methacryloxydecyloxy) benzoic acid

A mixture of 4- (10-hydroxydecyloxy) benzoic acid (11.75 g, 40 mmol, prepared as described in Example 7), methacrylic acid (34.4 g, 0.4 mol), hexane (90 ml), toluene ( 130 ml), p-toluenesulfonic acid (1.0 g) and hydroquinone (0.2 g) were refluxed in a Dean-Stark apparatus for 4.5 hours. The mixture was cooled to room temperature and insoluble solids were filtered off. The filtrate was washed several times with water (1 liter in total), dried over magnesium sulfate and concentrated. Excess methacrylic acid was removed by bulb tube distillation up to 70 ° C at 13.3 Pa (0.1 mm Hg). The remaining residue was dissolved in tetrahydrofuran (40 ml) and diluted with hexane (300 ml). A small amount of insoluble material was filtered off and the solution was cooled to give a white solid (6.5 g, mp 62-102 ° C). Column chromatography (silica gel; hexane: ethyl acetate, 4: 1) gave a purified sample (5.2 g, 36%): mp 61-103 ° C, smectic mesophase in the cooling cycle, 103 ° C; NMR (CDCl 3) 9.45 (bs, 1H), 8.03 (d, 2H), 6.9 (d, 2H), 6.03 (s, 1H), 5.5 (s, 1H), 4.1 (t, 2H), 3.97 (t, 2H), 1.9 (s, 3H), 1.8-1.2 (m, 16H).

4- (6-methacryloyloxyhexyloxy) benzoic acid

A solution of 4- (6-hydroxyhexyloxy) benzoic acid (24.0 g, 0.10 mol, prepared as described in Example 3) was treated with methacrylic acid as described above, after recrystallization from tetrahydrofuran: hexane (1: 2) 4- (6-methacryloylhexyloxy) benzoic acid (19.9 g, 67%) was obtained: mp 81-94 ° C, nematic mesophase; NMR (CDCl₃) 9.82 (bs, 1H), 8.0 (d, 2H), 6.87 (d, 2H), 6.05 (s, 1H), 4.15 (t, 2H), 4.0 (t, 2H), 1.9 (s, 3H), 1.85 (m, 8H).

Example 5

This example shows the formation of monomers 2a and 2b.

Monomer 2a

A solution of 4- (10-methacryloyloxydecyloxy) benzoic acid (3.62 g, 10 mmol) in toluene (30 ml) was stirred with oxalyl chloride (15 mmol, 1.91 g) and 1 drop of diethylethylamide for 3 hours at room temperature. Excess oxalyl chloride and toluene (10 ml) were distilled off under reduced pressure. 4-Cyanophenol (1.43 g, 12 mmol), dichloromethane (10 ml) and triethylamine (21 mmol) were gradually added to this acid chloride solution. The mixture was heated to 60-65 ° C in an oil bath for 1 hour. The mixture was cooled, diluted with ether (150 ml) and washed with 1N hydrochloric acid, water and brine. The ether solution was dried over magnesium sulfate, concentrated and recrystallized from ethanol to give a solid (3.90 g). Further purification by column chromatography (silica, hexane: ether, 4: 1) and recrystallization from ethanol gave monomer 2a (3.6 g, 78%): mp. 59.5-59.7 ° C, crystallizes in the cooling cycle at 53aC; NMR (CDCl₃) 8.03 (d, 2H), 7.62 (d, 2H), 7.25 (d, 2H), 6.88 (d, 2H), 6.0 (s, 1H), 5.45 (s, 1H), 4.2-3.9 (m, 4H), 1.9 (s, 3H), 1.8-1.2 (m, 16H); IR (KBr) 2225, 1730, 1720, 1712, 1640, 1603 cm-1.

Monomer 2b

A solution of 4- (6-methacryloyloxyhexyloxy) benzoic acid (8.9 g, 30 mmol, prepared as described in Example 4) was treated as described above, giving a white solid (6.75 g, 55%, mp 54 -57 ° C) was obtained. Further purification by silica gel chromatography (hexane-ether, 3: 1) and recrystallization from ethanol gave pure monomer 2b: mp. 64.3-65.3 ° C, nematic phase in the cooling cycle, 40.2 ° C; NNR (CDCl₃) 8.05 (d, 2H), 7.67 (d, 2H), 7.28 (d, 2H), 6.90 (d, 2H), 6.02 (s, 1H), 5.5 (s, 1H), 4.25-3.9 (m, 4H), 1.9 (s, 3H), 1.85-1.30 (m, 8H); IR (CHCl₃) 2225, 1738, 1715, 1635, 1600 cm sup¹. Table 1 Compound No. Melting Point (° C) Table 2 Compound No. Melting Point (° C)

The information in brackets relates to the cooling cycle.

Example 6

This example shows the mixing of the monomers to obtain formulations that show monotropic nematic mesophases.

Monomers 1a (45 mg) and 1c (45 mg) were mixed and melted in a hot air stream to give a nematic fluid. A sample of this mixture was made between a microscope slide and a coverslip and heated above the isotropic point in a Mettler FP5 hot stage using a Mettler FP52 temperature controller. The sample was cooled by 3 ° C per minute. A nematic phase was seen from 43.8 ° C to room temperature. The nematic phase crystallized over a period of about 1 day at room temperature.

Example 7

This example further shows the mixing of the monomers to obtain monotropic nematic mesophases.

Monomers 1a (90 mg), 1b (90 mg) and 1c (90 mg) were mixed and melted to give a nematic fluid. A sample of this material showed a nematic phase in the cooling cycle from 43 ° C to room temperature. The sample crystallized in about 2 days at room temperature.

Example 8

This example further shows the mixing of the monomers to obtain monotropic nematic mesophases.

Monomers 2a (102 mg) and 2b (102 mg) were mixed and melted to give a nematic fluid which showed a nematic phase in the cooling cycle from 44.0 ° C to room temperature. The material crystallized in about 1 day at room temperature.

Example 9

This example shows the effect of the added photoinitiator on the temperature range of the nematic mesophase.

2,2-Dimethoxy-2-phenylacetophenone (Irgacure 651, Ciba-Geigy, Ardsley, New York) (5 mg, 2.5% by weight) was added to the mixture described in the previous example. The mixture was heated until a homogeneous mixture was formed. The mixture showed a nematic phase in the cooling cycle from 36.5 ° C to room temperature. The material crystallized over a period of about 1 day at room temperature.

Example 10

This example shows the mixing of the monomers using a homolog with an odd number of carbon atoms at the alkylene end.

Monomers 1a (50 mg), 1b (50 mg) and 1f (50 mg) were mixed and melted in a hot air stream to give a nematic fluid. A sample of this mixture was made between a microscope slide and a coverslip and heated above the isotropic point in a Mettler FP5 hot stage using a Mettler FP52 temperature controller. The sample was cooled by 3 ° C per minute. A nematic phase was seen from 44.5 ° C to room temperature. The nematic phase crystallized over a period of about 20 minutes at room temperature.

Example 11

This example shows the mixing of the monomers using a homolog with an odd number of carbon atoms at the alkylene end.

Monomers 1f (50 mg) and Ig (50 mg) were mixed and melted in a hot air stream to give a nematic fluid. The nematic fluid immediately crystallized at room temperature.

Example 12

This example shows the mixing of the monomers using a homolog with an odd number of carbon atoms at the alkylene end.

Monomers 1e (50 mg), 1f (50 mg) and 1g (50 mg) were mixed and melted in a hot air stream to give a nematic fluid. A sample of this mixture was made between a microscope slide and a coverslip and heated above the isotropic point in a Mettler FP5 hot stage using a Mettler FP52 temperature controller. The sample was cooled by 3 ° C per minute. A nematic phase was seen from 47 ° C to room temperature. The nematic phase crystallized within 10 minutes at room temperature.

The above examples show that compositions in which n is an even number according to the present invention have a remarkably higher stability than the comparative samples in which n is an odd number of carbon atoms which crystallize rapidly from the nematic phase.

Example 13

This example shows the polymerization of a nematic monomer mesophase in a homeotropic orientation, giving a polymer phase that shows the same orientation.

Glass microscope slides were sonicated for 0.5 hour in a 50:50 mixture of RBS-35 nonionic surfactant (Pierce Chemical Co., Rockford, 11, 61105) and deionized distilled water, followed by successive sonication for 0.5 Hours (each) cleaned with acetone, methanol and deionized distilled water.

1% by weight of Irgacure 651 was added to the nematic monomer mixture described in Example 7. Then the nematic monomer composition was applied to a cleaned glass microscope slide at 50-60 ° C while being shielded from light. The sample was covered with a second clean carrier using 10 micron glass fiber spacers. The sample was cooled to room temperature and allowed to stand to develop a uniform homeotropic orientation. The sample was then exposed to UV light (200 watts Hg arc, 15.24-22.86 cm (6-9 inches) from the source) for 1 minute. A frozen homeotropic orientation was obtained. The plates were removed to give a free-standing film.