JPH0224297B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to liquid crystals, and more particularly to films made of polymeric liquid crystal materials having certain optical properties. The existence of liquid crystal materials has been recognized since the late 1800s. The term "liquid crystal" or "methodiene" refers to a state of matter that lies between a solid crystal and an isotropic liquid, the latter being randomly arranged. Liquid crystal materials have certain structural characteristics of crystals, yet are viscous or quite fluid liquids. The various degrees of order that liquid crystals have give rise to three different types of structures called mesophases. Liquid crystals in a crystalline state are directionally and positionally ordered.
It has a dimensionally uniform structure. When a crystal is heated, it first loses one dimension of its positional order. This is called a smectic mesophase, and the liquid crystal in this phase maintains the directional order and two-dimensional positional order of the crystalline state. Upon further heating, the liquid crystal can transform into a nematic mesophase. In this phase, the remaining positional order is lost and the liquid crystal maintains only unidirectional order of the crystalline state. The molecular arrangement (order) of the nematic mesophase is characterized by the orientation of the molecules along an axis that coincides with the long axis of the molecules. Since the molecular centers of gravity are randomly arranged, there is no long-range order of position. The molecular order in the cholesteric mesophase is such that the molecules are oriented along an axis that coincides with the long axis of the molecules as in the nematic phase, but that axis is continuously oriented along a second axis perpendicular to the first axis. It is characterized by changing. For this reason, the cholesteric mesophase is often called the twisted nematic mesophase. Optical activity is required for methodological materials to form cholesteric mesophases. The term "cholesteric" is historical in origin since the first discovered liquid crystal material exhibiting a cholesteric mesophase was cholesteryl benzoate. However, it has been recognized that the presence of a cholesterol moiety is not required and that non-cholesterol derivatives also exhibit cholesteric mesophases. There has been considerable interest in liquid crystal materials because they exhibit unique optical properties such as selectively reflecting visible light and exhibiting iridescence and circular dichroism.
For example, U.S. Pat. No. 3,720,623 discloses mixtures of cholesteric and nematic liquid crystals useful in temperature-sensitive visual displays;
No. 3,766,061 discloses a decorative film consisting of a proportion of solid materials whose composition exhibits cholesteric properties; U.S. Pat. No. 3,923,685 discloses a cholesteric material that transforms into a nematic state when exposed to an electric field; Mixtures of nematic and potentially cholesteric materials useful in imaging and display devices are disclosed. Although colored images obtained using cholesteric materials are very useful, such images are rarely permanent. Accordingly, there has been substantial interest in preparing cholesteric materials capable of fixing color. That is, the above-mentioned U.S. Patent No.
No. 3766061 discloses a decorative film whose color is fixed by cooling. Additionally, U.S. Patent No.
No. 4,293,435 discloses polymeric liquid crystals in which color is fixed by fixing the polymer in the solid state by lowering the temperature of the polymer below its glass transition temperature. However, it is not always practical to employ temperature changes to fix the color, and the color may be fixed by other means, such as photopolymerization.
There has been interest in the development of cholesteric materials whose fixed color is not sensitive to temperature. Applicants are aware of only one such polymer. This was reported by a group of Japanese researchers, who found that poly(gammabutyl-L-glutamate) in trimethylene glycol dimethacrylate photopolymerizes, making it insensitive to temperature. It is disclosed that it can be fixed. Accordingly, one object of the present invention is to provide a film of polymeric cholesteric liquid crystal material having a fixed color that is essentially temperature insensitive. Furthermore, another object of the present invention is to provide a polymeric film with a fixed color that is useful in a variety of optical devices. These and other objects of the invention will become apparent from the detailed description of the preferred embodiments set forth below. The present invention relates to new cholesteric liquid crystal monomers and mixtures of said monomers with materials that support the formation of mixtures exhibiting cholesteric liquid crystal properties. These materials are formed as films, exhibit the desired optical response when heated or cooled to a desired temperature, and when photopolymerized virtually fix the optical properties of the resulting polymer. In one embodiment, the present invention comprises a composition suitable for providing a polymeric film having certain optical properties, the composition comprising a photopolymerizable monomer having the following structure: (However, R ₁ is H or CH ₃ ; A is -R ₂ -, -
R ₃ O-, or -R ₄ O-; R ₂ is an alkylene chain having 3 to 14 methylene groups or lower alkyl substituted methylene groups; R ₃ is an alkylene chain having 2 to 14 methylene groups or lower alkyl substituted methylene groups chain; R ₄ is an alkylene or lower alkyl substituted alkylene ether, diether or triether having 3 to 14 total carbon atoms in the alkylene chain, provided that the terminal alkylene chain adjacent to the carbonate moiety consists of 2 or more carbons; and Y is 0 or 1); and a suitable photoinitiator. The invention in a second embodiment consists of a polymeric film with a certain optical response, and the film comprises a photopolymerizable monomer having the following structure: (However, R ₁ is H or CH ₃ ; A is -R ₂ -, -
R ₃ O-, or -R ₄ O-; R ₂ is an alkylene chain having 3 to 14 methylene groups or lower alkyl substituted methylene groups; R is an alkylene chain having 2 to 14 methylene groups or lower alkyl substituted methylene groups ; R ₄ is an alkylene or lower alkyl substituted alkylene ether, diether or triether having a total number of carbon atoms of 3 to 14 in the alkylene chain;
provided that the terminal alkylene chain adjacent to the carbonate moiety consists of two or more carbon atoms; Y is 0 or 1); and a suitable photoinitiator. In a third embodiment, the present invention comprises a method for preparing a film made of a polymeric liquid crystal material having a certain optical response, which method comprises a photopolymerizable monomer having the following structure: (However, R ₁ is H or CH ₃ ; A is -R ₂ -, -
R ₃ O- or -R ₄ O-; R ₂ is an alkylene chain having 3 to 14 methylene groups or lower alkyl-substituted methylene groups; R is an alkylene chain having 2 to 14 methylene groups or lower alkyl-substituted methylene groups; R ₄ is an alkylene or lower alkyl substituted alkylene ether, diether or triether having a total of 3 to 14 carbon atoms in the alkylene chain;
(wherein the terminal alkylene chain adjacent to the carbonate moiety consists of 2 or more carbon atoms; Y is 0 or 1); preparing a film consisting of a suitable photoinitiator; orienting said film; The method comprises adjusting the temperature of the film to obtain a desired optical response; and photopolymerizing the film. Derivatives of cholesterol that can be used in the practice of this invention include cholesterol (Y=0) and 5,6-
It is dihydrocholesterol (Y=1). Additionally, there are many choices for the side chains at the three positions. Thus, the polymerizable side chain consists of an acrylate or methacrylate moiety crosslinked to an ester or carbonate side chain. When an ester chain is present, it consists of an alkyl chain consisting of 3 to 14 methylene groups or lower alkyl substituted methylene groups. As used herein, lower alkyl refers to an alkyl group consisting of 1 to 4 carbon atoms. Methacrylate ester (R ₁ = CH ₃ , n = 5, 10 and
14) have been reported in Soviet literature, but these esters were prepared for solution polymerization reactions, and their use in the photopolymerized film disclosed herein was not recognized. On the other hand, bridges become more complex when carbonate chains are present. That is, it has 2 to 14 methylene groups or lower alkyl substituted methylene groups,
or consisting of an alkylene or alkyl-substituted alkylene ether, diether or triether having a total of 3 to 14 carbon atoms in the alkylene chain (provided that the terminal alkylene chain adjacent to the carbonate moiety consists of 2 or more carbon atoms). Examples of ether moieties utilized in the practice of this invention include ethylene glycol, diethylene glycol, triethylene glycol, tetramethylene glycol,
3,3'-oxybis-1-propanol, 4,
It is similar to 4'-oxybis-1-butanol, 1,1'-oxybis-2-propanol, etc. The compounds of the invention in their pure state are somewhat difficult to process because they tend to crystallize at inopportune times. Furthermore, it is difficult for pure monomers to obtain colored polymers, since most exhibit no colored cholesteric mesophase or a very narrow colored cholesteric mesophase. Therefore, the pure compounds of the present invention are limited in their ability to produce polymeric films with the desired optical response. Surprisingly, these limitations are overcome and colored and non-colored films comprising compounds of the invention and other compounds of the invention or a second material suitable for the formation of films exhibiting cholesteric liquid crystal properties are suitable photoinitiators. It has been discovered that photopolymerization can be tailored and photopolymerized in the presence of a polymer, thereby giving a film with certain optical properties. When the film is colored, it is desirable that the fixed color be substantially the same as the color of the unpolymerized film; however, in some cases it is desirable to obtain a polymerized film with a fixed color that is different from the color of the unpolymerized film. is desirable. That is, the present invention considers all such possibilities. A preferred method of practicing the invention involves preparing a film that exhibits desired optical properties at specific temperatures. For colored films, this involves preparing a mixture of the material providing the cholesteric film, a photoinitiator, and optionally a crosslinking agent; heating the mixture to a viscous liquid; Obtained by spreading and dispensing the liquid; submerging the plates in a constant temperature water bath; and adjusting the temperature to obtain the desired color. In the case of unpigmented films, the optical properties must be measured spectrophotometrically. The film is then irradiated with a suitable radiation source, such as a mercury lamp. The polymeric film thus obtained remains substantially unchanged even at elevated temperatures for several weeks, depending on the properties of the second component as detailed below. Photoinitiators useful in the practice of the invention include, for example, benzophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-acetophenone, 2-benzoyloxyacetophenone, 2-chlorothioxanthone. and 2-hydroxycyclohexyl phenyl ketone (all of these compounds are given by way of example and not by way of limitation). Optional crosslinking agents useful in the practice of this invention include, for example, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate,
Ethylene glycol diacrylate, ethylene glycol dimethacrylate, di- and tri-ethylene glycol diacrylate and dimethacrylate, 1,6-hexanediol diacrylate and dimethacrylate, 1,4-butanediol diacrylate and dimethacrylate , similar substituted acrylamides and methacrylamides (these are included for illustrative purposes and not as a limitation). Various combinations can be made to produce films with different optical properties, but these are a matter of choice for the engineer. However, a few generalizations can be made to the novel monomeric compound combinations described herein. First, a combination of similar monomers provides a film that exhibits a cholesteric mesophase over a temperature range that is comparable to the individual monomers. For example, if the paired acrylate and methacrylate cholesterol derivatives are prepared, where Y=0, A=-
(CH ₂ ) ₁₀ −), methacrylate (R ₁ = CH ₃ ) is
Shows color range (single only) at 55.8-55.3°C, while acrylate (R ₁ =H) shows 57.8-59.2
Color areas are shown in °C. A 1:1 mixture of both exhibits a colored intermediate range of 56.5-55.9°C. Second, the combination of similar monomers with very different alkyl side chain lengths provides a mixture with a substantially wider intermediate range compared to the individual components. for example,
A pair of acrylate monomers (R ₁ =H, Y=0)
is prepared (in the unlikely event that the monomer is A=-
(CH ₂ ) ₁₀ −, and other monomers have A=−(CH ₂ ) ₃
-), the former monomer exhibits a color range of 57.8-59.2°C, and the latter monomer exhibits colorlessness. A 1:1 mixture of both provides a virtually wide color range from 68 to -15°C
−15°C is the low detection limit of the test equipment used. Thus, by careful mixing of the monomers, it is possible to provide a mesophase that exhibits an overall optical response over various temperature ranges. Third, the optical response range can be changed considerably by adding small amounts of non-methodogenic materials to the methodical material. Thus, for example, by adding 2% of photoinitiator or crosslinking agent, the color range of a mixture of pure mesophase materials can be lowered by 10°C. As previously mentioned, another method of preparing photopolymerized films with certain optical properties is to mix the compounds of the present invention with a second material suitable for forming a film exhibiting cholesteric liquid crystal properties. Consisting of The second component need not be polymerizable or methodological, although it is desirable that it be photopolymerizable to provide a stable polymeric film. A variety of materials are suitable for providing the unique film. Such materials include
For example, cholesteryl oleyl carbonate and 2-methyl-1,4-phenylene-bis(4'-hexyloxybenzoate), which can produce mesophases but are nonpolymerizable, cannot produce mesophases. p-methoxyphenyl-p-(6-methacryloyloxyhexyloxy)benzoate, which is polymerizable, and cholesteryl 11-(methacrylamido)undecanoate, which forms a mesophase and is polymerizable. Examples of the use of these compounds are shown in Example 9 below. The color intensity and uniformity exhibited by the various combinations of the present invention is also influenced by orientation. Therefore, as is well known, some form of mechanical shear must be provided to produce color films. Such orientation has been successfully obtained by sandwiching the monomers between glass plates or polyester films. Although film polymerization is achieved by radical or thermal initiation in solution or in bulk, in virtually all cases no fixed color or optical response is observed. Instead, polymers formed in solution or in bulk tend to produce colorless smectic mesophases or amorphous polymers. Therefore, photopolymerization is required to achieve the objectives of the present invention. The method by which photopolymerization is obtained influences the optical properties of the resulting polymer. If replication of the response is required, it is desirable to use a high intensity light source that results in rapid polymerization. On the other hand, slow polymerization caused by low intensity light tends to produce polymeric films whose response shifts toward the red end of the spectrum. Multi-response films can also be made according to the present invention by sequentially photopolymerizing unpolymerized films. For example, a colored film can be placed under a mask and illuminated to fix the color of the exposed (light) areas. By removing the mask and changing the temperature of the partially cured film, a color change occurs in the unpolymerized portions of the film. During the next exposure, the second color is fixed, thereby providing a two-color film. Of course, this method can be extended to provide films with multiple optical responses, if desired. The unique film properties of the present invention, which reflect specific wavelengths of light ranging from the near ultraviolet region to the infrared region, make the film extremely useful. For example, insensitivity to temperature changes makes them particularly suitable for filters such as bandpass filters, notch filters, and circular polarizing filters in optical devices. Furthermore, the films are suitable for reflective displays and so-called "Scheffer cells".
Additionally, if the films reflect the visible spectrum and exhibit bright iridescent colors, they are useful as substitutes for dyes and pigments. They can therefore be used, for example, in floor coverings, wall coverings, textiles, mats, paper products and graphic art that is not ordinary ink. The advantages and contributions of the invention will become more apparent from the following examples, which are illustrative only and are not intended to limit the scope of the invention. Examples Compounds designated by Roman numerals have the structure: The temperature range used herein is the melting range unless otherwise specified with an asterisk (*) or bracket. The asterisk indicates the mesophase range, and the asterisk indicates the monotropic mesophase range. And the latter was measured when the temperature dropped. In materials with a discernible melting range, the monotropic mesophase range is often below the melting range.

【table】

【table】

Here A=R ₃ O=(CH ₂ ) _o O, or R ₄ O=(CH ₂ CH ₂ O) _o

【table】

TABLE Example 1 This example shows the color range of various monomeric esters V of the invention as measured with a Leitz optical microscope at 250x magnification using cross-polar transmitted light.
Temperature control was performed using a Mettler FP5 temperature controller and a Mettler FP52 hot stage; cooling was achieved by passing a nitrogen gas stream to a copper coil cooled with dry ice, followed by an FP52 hot stage. I did this by passing it through. Compound color range (℃) Va 57.8−59.2 Vb (55.8−55.3) Vc (48.5−33.0) Vd (51.0−26.5) Ve Colorless Vf Colorless example 2 This example shows the monomer weight of the above pair having the same alkyl chain length. The colored mesophase range obtained in the mixture of bodies is illustrated. The measurements were carried out using the apparatus described in Example 1 by heating, melting and cooling the monomer mixture. The components were a 1:1 mixture by weight.

Table Example 3 This example shows the range of colored mesophases obtained with binary mixtures of the monomers described above with different alkyl chain lengths.
Color measurements were carried out as described in Example 1. The components were a 1:1 mixture by weight.

[Table] Low temperature limits for baths.
Example 4 This example illustrates the colored mesophase range obtained with mixtures of the above monomers having different alkyl chain lengths. The mixture includes a photoinitiator under the trade name Irgacure 651;
Free from any other listed ingredients. Irgacure651 is 2,2-dimethoxy-2-phenyl acetophenone. Color measurements were performed using a thermostatically controlled water bath.

【table】

[Table] Example 5 This example shows a single monomer of the present invention and 1%
A colored polymeric film obtained from a film composed of Irgacure 651 photoinitiator is shown. The table shows the film and the maximum apparent absorbance (λmax) and transmittance (%) of the polymer obtained when the film is photopolymerized at the indicated temperature.
T), and the half width at half height (HW−
HH). Polymerization in this and other examples involves placing the film in a 450 watt mercury arc lamp.
This was achieved by exposing for 30 seconds.

TABLE EXAMPLE 6 This example shows a few colored polymeric films obtained from the indicated monomer compositions. All films are 1%
Contained Irgacure 651 photoinitiator. All four films contained 3% trimethylolpropane triacrylate, except for the pair Vb:IXb, which contained trimethylolpropane trimethacrylate.

[Table] *: Example of colorless mixture 7 This example shows polymer films of different colors obtained by bringing monomer mixtures to different temperatures and then exposing the colored films to ultraviolet light. The monomer mixture described in this example is compound Vb and
Consisting of a 1:1 weight ratio mixture of Vf. The maximum apparent absorbance and color are shown for each film.

[Table] Comparative experiments performed on a 1:1 mixture of compounds Va and Ve gave the following results:

Table: Example 8 This example shows the influence of non-methodogenic materials on a mixture of monomers. Compounds Vc and Vd 1:
A 1 weight ratio mixture gave a colored mesophase range as shown in Example 2. Addition of 2% by weight photoinitiator shifted the colored mesophase range from 43° to 20°C. Example 9 This example demonstrates polymeric films that can be prepared from compounds of the invention and unrelated materials such as: Compound A is a nematic liquid crystal material that cannot participate in the photopolymerization process. Compound B is a non-methodogenic material that can participate in photopolymerization reactions. Compound C is a cholesteric liquid crystal material that cannot participate in photopolymerization reactions. All 3 are suitable for forming films exhibiting cholesteric liquid crystal properties. To demonstrate this, films were prepared and photopolymerized using 1% Irgacure 651 photoinitiator and 3% trimethylolpropane trimethacrylate.

Table Vb: The film obtained from A exhibits suitable optical properties, but not as suitable as other films in which both components of the pair are polymerizable. For example, when this polymer film was heated at 60° C. for one day, it crystallized into an opaque, colorless film. The present invention is not limited to the above description and description, but includes all modifications and variations contemplated by the claims.

Claims (1)

[Claims] 1 (a) A photopolymerizable monomer having the following structure: (However, R ₁ is H or CH ₃ ; A is -R ₂ -,
-R ₃ O-, or -R ₄ O-; R ₂ is a 3 to 14 methylene group or a lower alkyl-substituted methylene group;
R ₃ is a methylene group of 2 to 14 or a lower alkyl substituted methylene group; R ₄ is an alkylene ether, diether or triether having a total number of carbon atoms of 3 to 14 in the alkylene chain, provided that the terminal alkylene chain adjacent to the carbonate moiety is consisting of 2 or more carbon atoms; and Y is 0 or 1);
and (b) a polymeric film with a fixed optical response obtained by photopolymerizing a composition consisting of a suitable photoinitiator. 2 (a) (a) Photopolymerizable monomer having the following structure: (However, R ₁ is H or CH ₃ ; A is -R ₂
−, −R ₃ O−, or −R ₄ O−; R ₂ is 3 to 14
methylene group or lower alkyl substituted methylene group; R ₃ is a methylene group of 2 to 14 or a lower alkyl substituted methylene group; R ₄ is an alkylene group having 3 to 14 total carbon atoms in the alkylene chain;
ether, diether or triether,
provided that the terminal alkylene chain adjacent to the carbonate moiety consists of two or more carbon atoms; and Y is 0 or 1), and (b) a step of preparing a film comprising a suitable photoinitiator; (c) adjusting the temperature of the film to obtain a desired optical response; and (d) photopolymerizing the film to form a polymer having a fixed optical response. A method of adjusting a film made of liquid crystal material.