JP2024086253A - Liquid Crystal Polyurethane Elastomer - Google Patents

Abstract

[Problem] To provide a liquid crystal polyurethane elastomer having a large contractile force. [Solution] A liquid crystal polyurethane elastomer having an orientation degree f of 0.08 to 0.3, calculated by wide-angle X-ray diffraction measurement and the Hermans method. The liquid crystal polyurethane elastomer can be produced, for example, by reacting a mesogen group-containing compound having an active hydrogen group, an isocyanate compound, a photopolymerizable group-containing compound having an active hydrogen group, and a crosslinking agent having three or more active hydrogen groups to produce a photocrosslinkable liquid crystal polyurethane, and then irradiating the photocrosslinkable liquid crystal polyurethane with light of a specific wavelength in a stretched state. [Selected Figure] None

Description

The present invention relates to liquid crystal polyurethane elastomers.

Liquid crystal polymers that have mesogenic groups in their molecular structure have physical properties that change with changes in the degree of orientation of the liquid crystals (mesogenic groups). Taking advantage of this property, attempts are being made to use liquid crystal polymers as elastomers in a variety of applications.

For example, there is a thermoresponsive material that contains a liquid crystal polymer as a matrix, the liquid crystal polymer being obtained by reacting a diisocyanate component, a high molecular weight polyol component, and a mesogenic diol (see, for example, Patent Document 1).

JP 2017-115036 A

The thermoresponsive material containing the liquid crystal polymer of Patent Document 1 as a matrix was developed by the present applicant and has rubber elasticity in the liquid crystal manifestation temperature range. This liquid crystal polyurethane elastomer has a lower liquid crystal manifestation temperature compared to conventional liquid crystal polyurethanes. When the liquid crystal molecules of such a liquid crystal polyurethane elastomer are uniaxially aligned and an isotropic phase-liquid crystal phase transition occurs, reversible deformation such as shrinkage occurs. However, depending on the application, a larger shrinkage force may be required.

The present invention was made in consideration of the above-mentioned circumstances, and its purpose is to provide a liquid crystal polyurethane elastomer having a large contractile force.

The above object can be achieved by the following configuration. That is, the present invention relates to a liquid crystal polyurethane elastomer having an orientation degree f of 0.08 to 0.3, calculated by wide-angle X-ray diffraction measurement and the Hermans method.

The liquid crystal polyurethane elastomer of the present invention has improved contractile force. The reason why such an effect is obtained is unclear, but the following reasons are considered, for example.

The liquid crystal polyurethane elastomer of the present invention is designed to have a high degree of orientation; specifically, the degree of orientation f calculated by the Hermans method using wide-angle X-ray diffraction measurement is designed to be 0.08 to 0.3, so that the entropy is low at room temperature. On the other hand, when the liquid crystal structure melts due to heating, the entropy increases, and it is believed that the contractile force of the liquid crystal polyurethane elastomer of the present invention also increases as the amount of entropy change increases.

The liquid crystal polyurethane elastomer according to the present invention is subjected to wide-angle X-ray diffraction measurement, and the degree of orientation f calculated by the Hermans method is 0.08 to 0.3. The degree of orientation f can be calculated by the Hermans method, and the calculation procedure will be described later.

The liquid crystal polyurethane elastomer having the degree of orientation f of 0.08 to 0.3 can be produced, for example, by reacting a mesogen group-containing compound having an active hydrogen group, an isocyanate compound, a photopolymerizable group-containing compound having an active hydrogen group, and a crosslinking agent having three or more active hydrogen groups to produce a photocrosslinkable liquid crystal polyurethane, and then irradiating the stretched liquid crystal polyurethane with light of a specific wavelength. The components that are the raw materials for the photocrosslinkable liquid crystal polyurethane (liquid crystal polyurethane elastomer) are described below.

[Mesogen group-containing compound]
As the mesogen group-containing compound, for example, a compound represented by the following general formula (1) is preferable.

In the above general formula (1), X is an active hydrogen group, R ₁ is a single bond forming a part of an adjacent bonding group, -N=N-, -CO-, -CO-O-, or -CH=N-, R ₂ is a single bond forming a part of an adjacent bonding group, or -O-, and R ₃ is a single bond forming a part of an adjacent bonding group, or an alkylene group having 1 to 20 carbon atoms. However, this does not include cases where R ₂ is -O- and R ₃ is a single bond forming a part of an adjacent bonding group.) Note that "a single bond forming a part of an adjacent bonding group" means a state in which the single bond is shared with a part of an adjacent bonding group. For example, in the above general formula (1), when R ₁ is a single bond forming a part of an adjacent bonding group, R ₁ , which is a single bond, is shared with the benzene rings on both sides, and forms a biphenyl structure together with the benzene rings on both sides. Examples of X include OH, SH, NH ₂ , COOH, and secondary amines. The amount of the mesogen group-containing compound is adjusted to 20 to 80% by mass, preferably 40 to 70% by mass, in the raw materials constituting the liquid crystal polyurethane elastomer. If the amount of the mesogen group-containing compound is less than 20% by mass, the liquid crystal polyurethane elastomer produced is unlikely to exhibit liquid crystallinity. If the amount of the mesogen group-containing compound is more than 80% by mass, the phase transition temperature (Ti) between the liquid crystal phase and the isotropic phase becomes high, making it difficult to mold the liquid crystal polyurethane elastomer in a low temperature range including room temperature.

It is preferable to use an alkylene oxide and/or styrene oxide in combination with the mesogen group-containing compound. Since the alkylene oxide and/or styrene oxide function to lower the temperature at which the liquid crystal phase appears in the liquid crystal polyurethane elastomer, the liquid crystal polyurethane elastomer produced by using the alkylene oxide and/or styrene oxide in combination with the mesogen group-containing compound can be a product with excellent practicality at room temperature. For example, ethylene oxide, propylene oxide, or butylene oxide can be used as the alkylene oxide. The alkylene oxides listed above may be used alone or in combination. Styrene oxide may have a substituent such as an alkyl group, an alkoxy group, or a halogen on the benzene ring. It is also possible to use a mixture of the alkylene oxides listed above and the styrene oxide listed above. The amount of alkylene oxide and/or styrene oxide is adjusted so that 1 to 10 moles, preferably 2 to 6 moles, of alkylene oxide and/or styrene oxide are added per mole of the mesogen group-containing compound. If the number of moles of alkylene oxide and/or styrene oxide added is less than 1 mole, it becomes difficult to sufficiently lower the temperature range in which the liquid crystal phase of the liquid crystal polyurethane elastomer is expressed, and therefore it becomes difficult to continuously mold the photocrosslinkable liquid crystal polyurethane without a solvent and in a state in which the liquid crystal phase is expressed. If the number of moles of alkylene oxide and/or styrene oxide added exceeds 10 moles, it may become difficult for the liquid crystal polyurethane elastomer to express the liquid crystal phase.

[Isocyanate compound]
As the isocyanate compound, for example, the diisocyanate compounds shown below can be used. Examples of the diisocyanate compound include aromatic diisocyanates such as 2,4-toluene diisocyanate, 2,6-toluene diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, p-phenylene diisocyanate, m-phenylene diisocyanate, p-xylylene diisocyanate, and m-xylylene diisocyanate; ethylene diisocyanate; aliphatic diisocyanates such as 1,5-pentamethylene diisocyanate, 2,2,4-trimethylhexamethylene-1,6-diisocyanate, 2,4,4-trimethylhexamethylene-1,6-diisocyanate, and 1,6-hexamethylene diisocyanate; and alicyclic diisocyanates such as 1,4-cyclohexane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, isophorone diisocyanate, and norbornane diisocyanate. The diisocyanate compounds exemplified above may be used alone or in combination. In the present invention, a trifunctional or higher isocyanate compound may be used in combination as the isocyanate compound, but in order to ensure the thermoplasticity of the resulting photocrosslinkable liquid crystal polyurethane, when the total amount of the isocyanate compounds used is taken as 100 mass%, the ratio of the diisocyanate compound is preferably 98 mass% or more, more preferably 99 mass% or more, and even more preferably approximately 100 mass%. Examples of trifunctional or higher isocyanate compounds include triisocyanates such as triphenylmethane triisocyanate, tris(isocyanatephenyl)thiophosphate, lysine ester triisocyanate, 1,3,6-hexamethylene triisocyanate, 1,6,11-undecane triisocyanate, 1,8-diisocyanate-4-isocyanate methyloctane, and bicycloheptane triisocyanate, and tetraisocyanates such as tetraisocyanate silane.

When the total amount of the mesogen group-containing compounds constituting the liquid crystal polyurethane elastomer is taken as 100 parts by mass, the proportion of the isocyanate compound is preferably 20 to 70 parts by mass, and more preferably 30 to 60 parts by mass. If the amount of the isocyanate compound is less than 20 parts by mass, the polymerization by the urethane reaction becomes insufficient, making it difficult to continuously mold the liquid crystal polyurethane elastomer. On the other hand, if the proportion of the isocyanate compound exceeds 70 parts by mass, the amount of the mesogen group-containing compounds in the total raw materials of the liquid crystal polyurethane elastomer becomes relatively small, and the liquid crystallinity of the liquid crystal polyurethane elastomer decreases.

The isocyanate group of the isocyanate compound can react with active hydrogen groups such as hydroxyl groups of the mesogen group-containing compound and active hydrogen groups such as hydroxyl groups of the photopolymerizable group-containing compound. The NCO INDEX (NCO/OH), which is the theoretical amount of isocyanate groups of the isocyanate compound relative to the theoretical amount of active hydrogen groups of the mesogen group-containing compound and the photopolymerizable group-containing compound, is preferably 0.95 to 1.10, and more preferably 1.00 to 1.05.

[Photopolymerizable group-containing compound]
Examples of photopolymerizable group-containing compounds having active hydrogen groups include acryloyl group-containing compounds, methacryloyl group-containing compounds, and allyl compounds. Examples of acryloyl group-containing compounds include propylene glycol diglycidyl ether acrylic acid adduct, ethylene glycol diglycidyl ether methacrylic acid adduct, tripropylene glycol diglycidyl ether acrylic acid adduct, glycerin diglycidyl ether acrylic acid adduct, and bisphenol A. Examples of the PO 2 mol adduct include diglycidyl ether acrylic acid adduct, 2-acryloyloxyethyl succinate, β-carboxyethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxybutyl acrylate, 2-hydroxy-3-phenoxypropyl acrylate, 2-acryloyloxyethyl succinic acid, 2-acryloyloxyethyl hexahydrophthalic acid, 2-acryloyloxyethyl phthalic acid, 2-acryloyloxyethyl-2-hydroxyethyl phthalic acid, 2-acryloyloxyethyl acid phosphate, 2-hydroxy-3-acryloyloxypropyl methacrylate, and pentaerythritol triacrylate. Examples of methacryloyl group-containing compounds include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 2-hydroxybutyl methacrylate, 2-methacryloyloxyethyl succinic acid, 2-methacryloyloxyethyl hexahydrophthalic acid, 2-methacryloyloxyethyl acid phosphate, glycerin dimethacrylate, bisphenol A PO 2 mol adduct diglycidyl ether methacrylic acid adduct, bisphenol A diglycidyl ether methacrylic acid adduct, 2-hydroxy-3-acryloyloxypropyl methacrylate, 2-methacryloyloxyethyl succinate, etc. Examples of allyl group-containing compounds include glycerin monoallyl ether, trimethylolpropane diallyl ether, pentaerythritol triallyl ether, etc.

When the total amount of the mesogen group-containing compounds constituting the liquid crystal polyurethane elastomer is taken as 100 parts by mass, the ratio of the photopolymerizable group-containing compound is preferably 0.1 to 10 parts by mass, and more preferably 0.3 to 7 parts by mass. If the ratio of the photopolymerizable group-containing compound is less than 0.1 parts by mass, the raw material will not be sufficiently cured even when irradiated with light, and the resulting liquid crystal polyurethane elastomer will be less likely to exhibit thermal responsiveness. If the ratio of the photopolymerizable group-containing compound is more than 10 parts by mass, the crosslink density in the liquid crystal polyurethane elastomer will be too high, and in this case too, the resulting liquid crystal polyurethane elastomer will be less likely to exhibit thermal responsiveness.

[Crosslinking agent]
A crosslinking agent having three or more active hydrogen groups can be used as a raw material for the liquid crystal polyurethane elastomer. Examples of the crosslinking agent include polyol compounds and amine compounds having three or four active hydrogen groups. Examples of the polyol compounds include trimethylolpropane, glycerin, 1,2,6-hexanetriol, diglycerin, methyl glucoside, pentaerythritol, tetramethylolcyclohexane, and polyether polyols obtained by adding an ether compound to a trifunctional initiator (trimethylolpropane, glycerin, etc.) or a tetrafunctional initiator (pentaerythritol, diglycerin, diethyleneamine, etc.). Examples of the amine compounds include methanetriamine, diethylenetriamine, and 2-(2-aminoethylamino)ethanol.

[Other ingredients]
In addition to the mesogen group-containing compound having an active hydrogen group, the isocyanate compound, the photopolymerizable group-containing compound having an active hydrogen group, and the crosslinking agent, an active hydrogen group-containing compound may be used as a raw material for the liquid crystal polyurethane elastomer. Examples of the active hydrogen group-containing compound include polyol compounds and amine compounds. Examples of the polyol compound include polyether polyol, polyester polyol, polycarbonate polyol, polyester polycarbonate polyol, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,2-butanediol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, 1,6-hexanediol, neopentyl glycol, 1,4-cyclohexanedimethanol, 3-methyl-1,5-pentanediol, diethylene glycol, triethylene glycol, and 1,4-bis(2-hydroxyethoxy)benzene. The above-listed active hydrogen group-containing compounds may be used alone or in combination of two or more kinds.

In addition, when reacting a mesogen group-containing compound having an active hydrogen group, an isocyanate compound, a photopolymerizable group-containing compound having an active hydrogen group, and a crosslinking agent, a urethane polymerization catalyst known to those skilled in the art may be used. Examples of such polymerization catalysts include organic titanium catalysts such as titanium tetra-n-butoxide, titanium tetra-2-ethylhexoxide, titanium tetraacetylacetonate, and titanium diisopropoxybis(ethylacetoacetate), organic zirconium catalysts such as zirconium tetra-n-butoxide, zirconium dibutoxybis(ethylacetoacetate), zirconium tetraacetylacetonate, and zirconium tetraacetylacetonate, organic zinc catalysts such as zinc naphthenate, dibutyltin dilaurate, and octyl Examples of suitable catalysts include organotin catalysts such as tin oxide, triethylenediamine and its derivatives, tertiary amine catalysts such as N-methylmorpholine, N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethylhexamethylenediamine, 1,8-diazabicyclo[5,4,0]undecene-7 (DBU), bis(N,N-dimethylamino-2-ethyl)ether, and bis(2-dimethylaminoethyl)ether, carboxylate metal salt catalysts such as potassium acetate and potassium octylate, and imidazole catalysts. Among these, triethylenediamine and its derivatives are preferably used.

When producing a reaction product of a mesogen group-containing compound having an active hydrogen group, an isocyanate compound, a photopolymerizable group-containing compound having an active hydrogen group, and a crosslinking agent having three or more active hydrogen groups, it is preferable to add a photoreaction initiator.

[Photoinitiator]
Photoinitiators include, for example, 1-hydroxy-cyclohexyl-phenyl-ketone, bis(2,4,6-trimethylbenzoyl)-phenylphosphonoxide, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide, 2,2-dimethoxy-1,2-diphenylethane-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, 1-hydroxy-cyclohexyl-phenyl-ketone/benzophenone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy ... hydroxy-2-methyl-1-propan-1-one, 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methyl-propan-1-one, oxy-phenyl-acetic acid 2-[2-oxo-2-phenyl-acetoxy-ethoxy]-ethyl ester/oxy-phenyl-acetic acid 2-[2-hydroxy-ethoxy]-ethyl ester, phenylglyoxylic acid methyl ester, 2-methyl-1-[4-(methylthio)furan phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1, 2-dimethylamino-2-(4-methyl-benzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, bis(η5-2,4-cyclopentadien-1-yl)-bis(2,6-difluoro-3-(1H-pyrrol-1-yl)-phenyl)titanium, 1,2-octanedione, 1-[4-(phenylthio)phenyl-, 2-(O-benzoyl oxime)], ethanone, 1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(O-acetyloxime), iodonium, (4-methylphenyl) [4-(2-methylpropyl)phenyl]-hexafluorophosphate (1-)/propylene carbonate, triarylsulfonium hexafluorophosphate, triarylsulfonium tetrakis-(pentafluorophenyl)borate, and oxime sulfonate-based photoacid generators can be used. The proportion of the photoinitiator is preferably 0.1 to 10 parts by mass, and more preferably 0.1 to 8 parts by mass, when the total amount of the mesogen group-containing compounds constituting the photocrosslinkable liquid crystal polyurethane is taken as 100 parts by mass. If the amount of the photoinitiator is less than 0.1 part by mass, the polymerization reaction does not proceed uniformly during light irradiation or curing becomes insufficient, making it difficult for the liquid crystal polyurethane elastomer produced to exhibit thermal responsiveness. If the amount of the photoinitiator exceeds 10 parts by mass, the content of mesogen groups in the resulting liquid crystal polyurethane elastomer decreases, making it difficult to develop a liquid crystal phase. The photoinitiator preferably has an absorption wavelength of 200 to 600 nm. If the photoinitiator has an absorption wavelength in the above range, even if the transparency (transmittance of visible light) of the photocrosslinkable liquid crystal polyurethane or its raw material is low, the photoinitiator can absorb light and reliably proceed with the photocrosslinking reaction.

The photocrosslinkable liquid crystal polyurethane, which is the precursor (raw material) of the liquid crystal polyurethane elastomer, can be produced by reacting a mesogen group-containing compound having an active hydrogen group, an isocyanate compound, a photopolymerizable group-containing compound having an active hydrogen group, and a crosslinking agent having three or more active hydrogen groups in the presence of a photoinitiator. The reaction conditions for the reaction include, for example, a method in which the mesogen group-containing compound having an active hydrogen group, the isocyanate compound, the photopolymerizable group-containing compound having an active hydrogen group, and the crosslinking agent having three or more active hydrogen groups are fed into an extrusion molding machine together with the photoinitiator, and reacted while being heated and melted at, for example, 60 to 150°C.

The heated and melted liquid crystal polyurethane elastomer composition containing the photocrosslinkable liquid crystal polyurethane and the photoreaction initiator may be cooled, pulverized and molded into pellets, and the pelletized raw material may be molded into a predetermined shape using an extrusion molding machine, and then extruded while stretching in a temperature range where the liquid crystal phase is expressed (i.e., a temperature range from the glass transition temperature (Tg) or higher to the phase transition temperature (Ti) or lower). Alternatively, in the presence of a photoreaction initiator, the reaction product (photocrosslinkable liquid crystal polyurethane) of a mesogen group-containing compound having an active hydrogen group, an isocyanate compound, a photopolymerizable group-containing compound having an active hydrogen group, and a crosslinker having three or more active hydrogen groups may be extruded while stretching in a temperature range where the liquid crystal phase is expressed (i.e., a temperature range from the glass transition temperature (Tg) or higher to the phase transition temperature (Ti) or lower). In this case, the mesogen group contained in the mesogen group-containing compound moves along the stretching direction, so that a molded product of photocrosslinkable liquid crystal polyurethane with high orientation can be produced.

When the photocrosslinkable liquid crystal polyurethane molding with high orientation obtained above is molded into an appropriate shape and cooled, and irradiated with light of wavelengths of 200 to 600 nm while maintaining the stretched state, a crosslinking reaction proceeds between the raw materials while maintaining the orientation, and a liquid crystal polyurethane elastomer is completed that exhibits thermal responsiveness and has both the expression of a liquid crystal phase at low temperatures and elasticity. The liquid crystal polyurethane elastomer produced in this way exhibits a unique thermal responsive behavior in which the mesogen groups are oriented in the stretching direction in the low temperature region, but when heated and the phase transition temperature (Ti) is exceeded, the orientation of the mesogen groups breaks down (becomes irregular) and the elastomer shrinks in the stretching direction, and when cooled and the temperature falls below the phase transition temperature (Ti), the orientation of the mesogen groups is restored and the elastomer stretches in the stretching direction. In particular, the liquid crystal polyurethane elastomer according to the present invention has a large contractile force when the degree of orientation f calculated by the Hermans method in wide-angle X-ray diffraction measurement is 0.08 to 0.3, more preferably 0.09 to 0.28, and even more preferably 0.1 to 0.27.

The liquid crystal polyurethane elastomer of the present invention may be used in fields such as clothing products (textiles), actuators, and filters.

Below, we will explain examples that specifically demonstrate the configuration and effects of the present invention. The evaluation items in the examples were measured as follows.

<Method for measuring the degree of orientation f>
A wide-angle X-ray diffraction image was taken using a Bruker X-ray diffractometer (DISCOVER D8). The light source used was CuKα radiation with a wavelength of 1.5460 Å, generated at a tube voltage of 50 kV and a tube current of 1000 μA. Next, the sample and background were imaged for 10 minutes with a camera length of 30 cm, a slit diameter of 1.0 mm, a collimator diameter of 0.5 mm, and transmission measurement (collimator and detector angles of 0°). In the direct beam measurement for absorption correction, the detector angle was set to 2°, imaging was performed for 10 seconds, and the maximum intensity per 68 μm × 68 μm was extracted. The absorption correction coefficient (δ) was calculated using the following formula.
Absorption correction factor (δ) = average value of direct beam measurement of sample (n = 5) / average value of direct beam measurement of background (n = 5)

Next, using a Bruker DIFFRAC. EVA, the diffraction image of the sample was azimuth-angle integrated at 10-26°, diffraction angle 75°-100°, and step width 0.02°. The diffraction angle showing the maximum peak of the obtained intensity profile was designated as A, and the diffraction angle was integrated at diffraction angles A-1.5° to A+1.5° and azimuth angles 0-360°. The obtained diffraction angle intensity profile was multiplied by an absorption correction factor, and the background intensity profile was subtracted to calculate the degree of orientation f using the Hermans method (Equation 1). The diffraction angle β at the peak top of the intensity profile was substituted as 0 into Equation (1).

Equation 1

<Contraction force>
The liquid crystal polyurethane elastomer was produced by light irradiation, and then stored at 20°C, with a sample shape of "width 4 mm, thickness 0.3 mm, length 30 mm", and a UBM "DVE-V4 Rheospectrolar" was used as a measuring device to calculate the shrinkage force (MPa) based on the load and cross-sectional size of the sample. The shrinkage forces at 37°C and 60°C in Table 1 were read from the measurement results and evaluated as an index, with the shrinkage force of the liquid crystal polyurethane elastomer obtained in Comparative Example 1 being set to 1. A higher index means a higher shrinkage force.
The conditions for measuring the contractile force using the measuring device are shown below.
(Temperature increase rate) 1°C/min
(Measurement temperature range) 20 to 60°C
(Distance between chucks) 15mm
(Initial strain) 0.1 mm
(Strain) 0.10%
(Frequency) 100Hz

(Production Examples of Photocrosslinkable Liquid Crystalline Polyurethane and Liquid Crystalline Polyurethane Elastomer)
Example 1
In a reaction vessel, BH6 (500 g) in which R ¹ of formula (1) is a single bond as a mesogen group-containing compound having an active hydrogen group, potassium hydroxide (19 g), and N,N-dimethylformamide (3000 ml) as a solvent were mixed, and further, propylene oxide was added as an alkylene oxide in an amount of 5 equivalents per mole of BH6, and the mixture was reacted at 120° C. under pressure for 2 hours (addition reaction). Next, oxalic acid (15 g) was added to the reaction vessel to stop the addition reaction, and insoluble salts in the reaction solution were removed by suction filtration, and N,N-dimethylformamide in the reaction solution was removed by reduced pressure distillation to obtain mesogen diol A. The synthesis scheme of mesogen diol A is shown in formula (3). Note that mesogen diol A shown in formula (3) is a representative one and may include various structural isomers.

100 parts by mass of the obtained mesogen diol A were mixed with 27.5 parts by mass of 1,5-pentamethylene diisocyanate (manufactured by Mitsui Chemicals) as an isocyanate compound, 2 parts by mass of 2-hydroxyethyl acrylate (manufactured by Kyoeisha Chemicals) as a photopolymerizable group-containing compound, 0.1 parts by mass of 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide (TPO) (manufactured by IGM Resins) as a photoreaction initiator, and 0.03 parts by mass of trimethylolpropane (active hydrogen group number 3) as a crosslinking agent to prepare a raw material for photocrosslinkable liquid crystal polyurethane. The raw material was heated and melted at 80°C while stirring, and the mesogen diol A, the isocyanate compound, the photopolymerizable group-containing compound, and the trimethylolpropane were reacted to produce a liquid crystal polyurethane elastomer composition containing a photocrosslinkable liquid crystal polyurethane and a photoreaction initiator. The resulting product was cooled and then crushed using a plastic crusher (product name: ZI-420, manufactured by Horai Co., Ltd.).

Examples 2 to 4 and Comparative Example 1
A liquid crystal polyurethane elastomer composition containing a photocrosslinkable liquid crystal polyurethane and a photoreaction initiator was produced in the same manner as in Example 1, except that the type of crosslinking agent (trimethylolpropane or pentaerythritol (number of active hydrogen groups: 4)) and the amount of the crosslinking agent were changed to those shown in Table 1.

(Production Example of Liquid Crystal Polyurethane Elastomer)
Resin pellets of the liquid crystal polyurethane composition according to Examples 1 to 4 and Comparative Example 1 were fed into a single screw extruder (product name: SZW25GT-24MG-STD, manufactured by Technovel Co., Ltd.) set at 80 to 120°C, and molded into a resin sheet having a thickness of 1.0 mm. The resin sheet was passed through a cooling roll set at 15°C to be cooled to a temperature above the glass transition temperature (Tg) and below the phase transition temperature (Ti), and then taken up by a take-up roll. At this time, the resin sheet was stretched 1.5 to 10 times by providing a rotation difference between the cooling roll and the take-up roll. Furthermore, a tabletop UV curing device (product name: imini Grandage (ESC-1511U), manufactured by iGraphics Co., Ltd.) was installed between the cooling roll and the take-up roll, and the stretched resin sheet was irradiated with light from a high-pressure mercury lamp or a metal halide lamp as a light source to obtain a photocrosslinked (cured) liquid crystal polyurethane elastomer.

Compared to the liquid crystal polyurethane elastomer produced in Comparative Example 1 using a liquid crystal polyurethane composition containing a photocrosslinkable liquid crystal polyurethane as a raw material, the liquid crystal polyurethane elastomers produced in Examples 1 to 4 using a liquid crystal polyurethane composition containing a photocrosslinkable liquid crystal polymer as a raw material have a dramatically improved contractile force.

Claims (1)

A liquid crystal polyurethane elastomer with a degree of orientation f of 0.08 to 0.3, as calculated using wide-angle X-ray diffraction measurements and the Hermans method.