JP2005232345A - Polymer for birefringence-inducing material, polarization diffraction element, and liquid crystal alignment film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a polymer for bireringence-inducing materials from which a polarization diffraction element having light diffraction and polarizing beam conversion functions stable to external stimuli such as heat and light is prepared at a low cost. <P>SOLUTION: The polymer having a structure expressed by chemical formula (1) is manufactured which induces birefringence by the molecular movement caused by the irradiation of a light containing a straight polarizing component and heat and whose direction of molecular orientation is changed by 90° by the irradiation of light. The polarization diffraction element is manufactured by irradiating a film of the polymer with a light having periodically modulating polarization or intensity or both of them. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

The present invention relates to a birefringence inducing material polymer suitable for the production of a polarization diffraction element having both light wave diffraction and polarization conversion functions, a polarization diffraction element using the polymer, and a liquid crystal alignment film.

  As materials for producing diffraction gratings and holography using mask exposure and two-beam interference fringes, silver halide photosensitive materials, such as those used in photography, and gelatin films are immersed in an aqueous solution of ammonium dichromate. Examples thereof include dichromated gelatin imparted with photosensitivity, a photoresist used for manufacturing a semiconductor integrated circuit, a photopolymer utilizing refractive index modulation by photopolymerization of a monomer, and the like. Diffraction gratings and holograms using such materials include optical pickup elements for extracting various signals on optical disks, CDs, etc., elements for scanning beams such as barcode scanners, holographic memories for information processing, Applications to optical interconnects have been studied and are actually being used. However, these elements utilize refractive index modulation and surface irregularities, and thus cannot produce a polarization diffraction element having both light wave diffraction and polarization conversion functions.

  In order to produce a polarization diffraction element having both light wave diffraction and polarization conversion functions, it is necessary to highly control the periodic structure of optical anisotropy such as birefringence and the direction of the optical axis. Polyvinyl cinnamate (PVCi), which is a negative photoresist, is known as a material capable of this. When a PVCi film is irradiated with linearly polarized ultraviolet light, the carbon-carbon double bond of the cinnamoyl group arranged in a direction parallel to the direction of electric field vibration of the irradiated light is selectively light-dimerized and birefringent. It comes to occur. If this is utilized, it is possible to periodically control the optical anisotropy, but the induced birefringence is as small as 0.01 or less and is not practical.

  As other representative materials, use of a polymer material containing azobenzene has been studied. The azobenzene molecule undergoes photoisomerization between the cis and trans isomers due to external stimuli such as light and heat, and this can be used to control the molecular orientation. It can be done by irradiation. However, the polymer materials containing azobenzene, which have been studied in the past, not only exhibit a large optical anisotropy, but also change their characteristics due to the influence of external fields such as heat and light, resulting in high stability. It was difficult to apply to required optical devices.

  The present inventor also has a side chain including a structure in which a substituent such as biphenyl, terphenyl, and phenylbenzoate, which has been frequently used as a mesogenic component as a birefringence inducing material, and a photosensitive group are bonded. Has proposed a single polymer having a repeating unit having a structure bonded to the main chain, such as hydrocarbon, acrylate, methacrylate, siloxane, through a flexible portion such as monocarbon or alkyl ether. In this birefringence inducing material, when a film is formed by applying (spin coating) on a substrate and then irradiating the film with linearly polarized ultraviolet rays, cinnamoyl groups (along the electric field vibration direction of the irradiated linearly polarized light ( Alternatively, dimerization of a photosensitive group such as a derivative group thereof occurs selectively, and side chains that have not undergone photodimerization due to molecular movement due to subsequent heating are arranged in the same direction as the side chain that has undergone photodimerization, It is a material in which side chains are arranged in the direction of electric field vibration of linearly polarized light irradiated on the entire molecular coating film. As a method of producing a polarization diffraction element having both light wave diffraction and polarization conversion function using the material, a method of irradiating using a two-beam interference using a polarizing beam having good coherence such as laser light, or There is a method of irradiating linearly polarized light using a light-shielding mask having a desired periodic pitch.

  Furthermore, the inventor has a side chain including a structure in which a substituent such as biphenyl, terphenyl, and phenylbenzoate, which is frequently used as a mesogenic component as a birefringence inducing material, and a photosensitive group are bonded, and the side chain is A copolymer of a repeating unit having a structure bonded to a main chain such as hydrocarbon, acrylate, methacrylate, siloxane, and the like and a non-liquid crystalline repeating unit through a flexible part such as monocarbon or alkyl ether has been proposed. In this copolymer, the photoisomerization of the side chain having a photosensitive group is superior to the photodimerization. When the amount of irradiation energy of linearly polarized light is relatively small, the photoisomerization is performed from the photoisomerized Z isomer. Since the side chain that was not present has a higher orientation, when heated after irradiation, the entire film is oriented in a direction perpendicular to the electric field oscillation direction of the linearly polarized light irradiated by molecular motion. Furthermore, when irradiation with linearly polarized ultraviolet light is performed and the amount of irradiation energy in which light dimerization is superior to photoisomerization, unreacted side chains are aligned along the side chain that has undergone light dimerization. The entire film becomes oriented. Even in the aforementioned homopolymer, when the irradiation energy amount of the linearly polarized light is relatively small, the whole film tends to be oriented in the direction perpendicular to the electric field vibration direction of the irradiated linearly polarized light, but the head- It has been found that the formation of a to-tail association (J association) or a head-to-head association (H association) inhibits molecular orientation and does not increase the degree of orientation. In view of this point, the non-liquid crystalline repeating unit is a copolymer in order to suppress the association between side chains, and methyl methacrylate or the like is used as the non-liquid crystalline repeating unit in a copolymerization ratio of 1 : Copolymerization at a ratio of about 1 has realized a material that can change the molecular orientation direction by 90 ° depending on the dose of linearly polarized ultraviolet light. However, such a copolymer has a problem that the degree of orientation of the whole film is lowered because the copolymerized non-liquid crystalline repeating unit is rich in flexibility at the molecular level.

In the polarization diffraction element, as known from the analysis by the Jones method of a polymer layer having a molecular orientation structure, it is advantageous to increase the phase difference in order to obtain high diffraction efficiency, and to increase the film thickness. Alternatively, the diffraction efficiency can be increased by increasing the anisotropy of the material itself. For this reason, when a polarization diffraction element is produced using the above-mentioned copolymer, which has a low degree of orientation, the diffraction efficiency can be improved to some extent by increasing the film thickness. Irradiation light does not reach the inside of the film due to the absorption of light, and the light dimerization density at that portion becomes low. As a result, the alignment regulating force of the unreacted side chain is reduced, and when a polarization diffraction element is produced, the haze is generated and the performance of the element is deteriorated. The problem was that it would grow.
R. C. Jones, J .; Opt. Soc. Am. , 31, 488, 1941

In view of such problems, the present invention provides a polarization diffractive element that is excellent in stability against external stimuli such as heat and light and that has both high light wave diffraction and polarization conversion functions at low cost. It is an object of the present invention to provide a birefringence inducing material polymer that can be produced.

  In a polarization diffractive element produced by a process including irradiation of light and heating / cooling to a birefringence inducing material polymer, the liquid crystalline mesogen of the birefringence inducing material polymer forms a periodic alignment structure. The above problem can be solved by using a compound having a structure represented by Chemical Formula 1 as a combination.

  According to the present invention, there is provided a birefringence inducing material polymer that is excellent in stability against external stimuli such as heat and light, and that can produce a polarization diffraction element having both high light wave diffraction and polarization conversion functions at low cost. Can be provided. In addition, a liquid crystal alignment film having excellent heat resistance can be manufactured using the same material.

  Details of the present invention will be described below. As a result of intensive studies by the present inventors, in a method for producing a polarization diffraction element having both a light wave diffraction and a polarization conversion function, which is produced by a process including light irradiation and heating and cooling operations on a birefringence inducing material polymer. The inventors have found that the above problem can be solved by using a material having a structure represented by Chemical Formula 1 for the birefringence inducing material polymer, and have completed the present invention. The birefringence-inducing material polymer has a side chain including a structure in which a substituent such as biphenyl, terphenyl, and phenylbenzoate, which are frequently used as a mesogenic component, and a photosensitive group are bonded, and the side chain is monocarbonized, A copolymer having a repeating unit of a structure bonded to a main chain such as hydrocarbon, acrylate, methacrylate, siloxane and the like and a repeating unit of N-phenylmaleimide or a derivative thereof through a flexible part such as alkyl ether. (Figure 1: Chemical formula 1)

  In this copolymer, N-phenylmaleimide or a derivative thereof is copolymerized. When N-phenylmaleimide or its derivative is introduced into the main chain as a copolymer at an appropriate ratio, the formation of side chain association can be suppressed without reducing the molecular orientation ability, and the amount of irradiation energy of linearly polarized light is compared. It was confirmed that the orientation in the direction perpendicular to the electric field oscillation direction of the irradiated linearly polarized light can be achieved. Although this N-phenylmaleimide or derivative thereof can suppress the formation of J-association when the copolymerization ratio is increased, it inhibits not only the orientation in the direction perpendicular to the electric field vibration direction but also the orientation in the electric field vibration direction. End up. If the copolymerization ratio is too small, the effect of suppressing the formation of J-association cannot be obtained sufficiently, and it is impossible to achieve the orientation in the direction perpendicular to the electric field vibration direction. From these viewpoints, the copolymerization ratio of N-phenylmaleimide or a derivative thereof is x: y = 95-50: 5-50 in the chemical formula (1), more preferably x: y = 90-70: 10. 30.

  When copolymerizing methyl methacrylate or the like as a non-liquid crystalline repeating unit for the purpose of suppressing the formation of side chain association, it is necessary to copolymerize at a high ratio of about 1: 1 as the copolymerization ratio. Although there was a problem that the degree of orientation of the entire film was lowered, N-phenylmaleimide or a derivative thereof can efficiently suppress the association of side chains because of its relatively rigid molecular structure. As a result, the effect of sufficiently suppressing the association of side chains can be obtained even at a relatively low copolymerization ratio, and the molecular orientation ability of the birefringence inducing material polymer is not lowered. As a result, with respect to the direction of electric field vibration of the linearly polarized light when irradiated with linearly polarized ultraviolet light and the orientation perpendicular to the direction of electric field vibration of the linearly polarized light when the irradiation energy amount of linearly polarized light is relatively small A high degree of orientation can be obtained in parallel orientation, and a polarization diffraction element having both high light wave diffraction and polarization conversion functions can be manufactured.

In order to proceed with the photoisomerization reaction or photodimerization reaction for inducing birefringence, it is necessary to irradiate light having a wavelength at which the photosensitive group portion can react. This wavelength varies depending on the type of -R ₁ represented by Chemical Formula 1, but is generally 200-500 nm, and in particular, the effectiveness of 250-400 nm is often high.

  As a method for producing a polarization diffraction element having both light wave diffraction and polarization conversion functions, a liquid obtained by dissolving the birefringence-inducing material polymer of the present invention in a solvent is applied on a transparent substrate and then dried, and the film is irradiated with laser light. Examples include a method of irradiating using two-beam interference using a polarizing beam having good coherence or a method of irradiating linearly polarized light using a light-shielding mask having a desired periodic pitch. As a method using a light-shielding mask, a light-shielding mask having a desired periodic pitch is used at least twice, and at least two regions are irradiated with linearly polarized light having different polarization characteristics or intensities, and a desired method. By irradiating linearly polarized light using a light-shielding mask having a periodic pitch, and then irradiating linearly polarized light without using a light-shielding mask, the irradiation energy amount can be reduced at a desired periodic pitch. There is a method of providing a periodic structure having different regions and molecular orientation directions different by 90 °. As a method using a light-shielding mask, the latter has an advantage that the apparatus can be simplified.

This orientation by molecular motion after irradiation is promoted by heating the coating film. The heating temperature of the coating film is preferably lower than the softening point of the photoreacted part and higher than the softening point of the side chain part not photoreacting and the side chain part having no photosensitive group. Further, the alignment can be promoted by irradiation under heating (from room temperature to T _i + 5 ° C.). Here, T _i indicates a phase transition temperature when the birefringence inducing material polymer changes from a liquid crystal phase to an isotropic phase. In this way, when the film heated after irradiation and oriented unreacted side chains or the film irradiated and oriented under heating is cooled below the softening point temperature of the material, the molecules are frozen. Furthermore, by irradiating the coating film cooled to below the softening point temperature with ultraviolet rays, the photoreaction of unreacted photosensitive groups can be promoted, and the orientation in the film can be firmly fixed, and the heat resistance and light stability. It is possible to obtain a polarization diffraction element having both excellent light wave diffraction and polarization conversion functions.

  A polarization diffraction element having both a light wave diffraction and a polarization conversion function using such a birefringence inducing material polymer is an optically transparent functional polymer layer in which the molecular orientation structure is periodically controlled. The optical properties of the polymer layer having such a molecular orientation structure can be analyzed by the Jones method (RC Jones, J. Opt. Soc. Am., 31, 488, 1941). For example, in the polymer layer having the alignment structure shown in FIG. 2, when linearly polarized light is considered as incident light, the light is diffracted as ± first order light and simultaneously output by rotating the polarized light by 90 °, and is incident as incident light. When the circularly polarized light is considered, it is understood that the light is diffracted as ± first-order light and is simultaneously output as the counterclockwise circularly polarized light. In this way, by using a polymer layer having a periodically oriented molecular orientation structure, it is possible to form a polarization diffractive element in which a diffraction function and a polarization conversion function are combined. Whether to have a polarization conversion function can be controlled by the periodic structure and the magnitude of anisotropy.

  Further, when a material having a structure represented by the chemical formula 1 of the present invention is applied to a glass substrate and irradiated with light containing linearly polarized light, the linearly polarized light irradiated in a direction perpendicular to the traveling direction of the irradiated light is irradiated. Photoisomerization or photodimerization of the photosensitive group proceeds selectively in a direction parallel to the electric field vibration direction of light, and as a result, the film surface becomes anisotropic. When liquid crystal molecules come into contact with this film, the liquid crystal molecules are aligned by the interaction with the film. When the amount of irradiation energy of the linearly polarized light is relatively small, the liquid crystal molecules are aligned in a direction perpendicular to the electric field vibration direction of the irradiated linearly polarized light. The liquid crystal molecules are aligned in a direction parallel to the electric field vibration direction of polarized light. In the material of the present invention, N-phenylmaleimide or a derivative thereof having a relatively rigid structure in the main chain is copolymerized, so that a molecularly flexible structure such as methyl methacrylate is copolymerized. Since the glass transition temperature can be increased as compared with the case, a liquid crystal alignment film having excellent heat resistance can be obtained. Such a liquid crystal alignment film is effective as a liquid crystal alignment film when producing a non-rubbing light alignment film or an optical compensation film in which liquid crystal molecules are aligned in a liquid crystal display device.

The synthesis method for the raw material compound of the photosensitive (birefringence inducing material) polymer used in the examples of the polarization diffraction element having both the light wave diffraction and polarization conversion functions of the present invention or the examples of the liquid crystal alignment film is shown below. (Monomer 1) 4,4-Diphenyldiol was reacted with 1,6-dibromohexane under alkaline conditions to synthesize 4- (6-bromohexyloxy) -4′-hydroxybiphenyl. Next, lithium methacrylate was reacted to synthesize 6- (4′-hydroxybiphenyl-4-yloxy) -1-hexyl methacrylate. Finally, 4-methoxycinnamoyl chloride was added under basic conditions to synthesize a methacrylic acid ester represented by Chemical Formula 2.

(Monomer 2) 4,4-Diphenyldiol was reacted with 1,6-dibromohexane under alkaline conditions to synthesize 4- (6-bromohexyloxy) -4′-hydroxybiphenyl. Next, lithium methacrylate was reacted to synthesize 6- (4′-hydroxybiphenyl-4-yloxy) -1-hexyl methacrylate. Finally, 4-methylcinnamoyl chloride was added under basic conditions to synthesize a methacrylic acid ester represented by Chemical Formula 3.

(Polymer 1) Monomer 1 (2.25 mmol) and commercially available N-phenylmaleimide (0.249 mmol) are dissolved in 12 ml of anisole, and AIBN (azobisisobutyronitrile) is added as a reaction initiator. A photosensitive polymer 1 was obtained by polymerization. The copolymer 1 had a copolymerization ratio of x: y = 82: 18 and exhibited liquid crystallinity.

(Polymer 2) Monomer 2 (2.20 mmol) and commercially available N-phenylmaleimide (0.252 mmol) are dissolved in 12 ml of anisole, and AIBN (azobisisobutyronitrile) is added as a reaction initiator. The photosensitive polymer 2 was obtained by polymerization. The copolymer 2 had a copolymerization ratio of x: y = 81: 19 and exhibited liquid crystallinity. (Polymer 3) Monomer 1 (2.25 mmol) is dissolved in 12 ml of anisole, and AIBN (azobisisobutyronitrile) is added as a reaction initiator for polymerization to obtain photosensitive polymer 3. It was. This polymer 3 exhibited liquid crystallinity. (Polymer 4) Monomer 1 (2.34 mmol) and commercially available N-phenylmaleimide (0.073 mmol) are dissolved in 12 ml of anisole, and AIBN (azobisisobutyronitrile) is added as a reaction initiator. The photosensitive polymer 4 was obtained by polymerization. The copolymer 4 had a copolymerization ratio of x: y = 96: 4 and exhibited liquid crystallinity.

(Polymer 5) Monomer 1 (2.10 mmol) and commercially available N-phenylmaleimide (1.96 mmol) are dissolved in 12 ml of anisole, and AIBN (azobisisobutyronitrile) is added as a reaction initiator. The photosensitive polymer 5 was obtained by polymerization. The copolymer 5 had a copolymerization ratio of x: y = 53: 47 and exhibited liquid crystallinity.

(Polymer 6) Monomer 1 (2.31 mmol) and commercially available methyl methacrylate (2.35 mmol) are dissolved in 12 ml of THF, and AIBN (azobisisobutyronitrile) is added as a reaction initiator for polymerization. As a result, a photosensitive polymer 6 was obtained. The copolymer 6 had a copolymerization ratio of x: y = 51: 49 and exhibited liquid crystallinity.

  Examples 1 to 3 evaluate the orientation when the film of the birefringence inducing material polymer of the present invention is irradiated with linearly polarized ultraviolet rays, and further, use a light-shielding mask to diffract light waves. It is the Example which produced the polarization | polarized-light diffraction element which has a polarization conversion function together.

Polymer 1 was dissolved in dichloroethane at a concentration of 1% by weight and applied on a glass substrate to a thickness of about 0.3 μm using a spin coater. This film was irradiated with ultraviolet light from a high-pressure mercury lamp as linearly polarized light through a Grand Taylor prism for various times, and then the degree of orientation (S) calculated from the change in polarized UV-vis absorption spectrum when heat-treated at 180 ° C. [S = (A _// −A _⊥ ) / (A _large + 2A _smallr ), where A _// is the absorbance in the direction parallel to the electric field vibration direction of the irradiated linearly polarized ultraviolet light, and A _⊥ is the absorbance perpendicular to the electric field vibration direction of the linearly polarized light of the ultraviolet light _{irradiated, a larger} is, a _// or larger absorbance of a _{⊥, a Smaller} absorbance of a _// or a _⊥ The smaller of Is shown in FIG. In FIG. 3, when the degree of orientation is a negative value, the direction is perpendicular to the electric field oscillation direction of the irradiated linearly polarized ultraviolet light. When the degree of orientation is a positive value, the irradiated linearly polarized ultraviolet light is It shows that the mesogenic component is oriented in a direction parallel to the electric field oscillation direction. As shown in FIG. 3, when the amount of irradiation energy of linearly polarized light is relatively small, the orientation of the irradiated linearly polarized light is perpendicular to the electric field vibration direction, and the degree of orientation (S) is a high value of −0.6 or more. Furthermore, when the irradiation energy amount of the linearly polarized light is increased, it shows an orientation parallel to the electric field vibration direction of the irradiated linearly polarized light, and the degree of orientation (S) is also when the irradiation energy amount of the linearly polarized light is relatively small. Similarly, it was found that a high value of 0.6 or more can be obtained.

The following is an example in which a polarization diffraction element was produced using this polymer 1. Polymer 1 was dissolved in dichloromethane at a concentration of 1% by weight and applied on a glass substrate to a thickness of about 0.3 μm using a spin coater. A light-shielding mask with a pitch of 40 μm (20 μm transmission part and 20 μm non-transmission part) is arranged on this film, and ultraviolet light from a high-pressure mercury lamp whose electric field oscillation direction is 45 ° with respect to the lattice direction of the mask. Light having a linear polarization property was irradiated through a Taylor prism at 1.5 J / cm ² . Subsequently, the light-shielding mask was removed and irradiation was performed at 0.3 J / cm ² . After the irradiation, heat treatment was performed at 180 ° C., and finally, ultraviolet light from a high-pressure mercury lamp was irradiated with 3.0 J / cm ² without passing through the Grand Taylor prism to fix the orientation, thereby producing a polarization diffraction element. When the produced polarization diffraction element was observed with a polarization microscope, it was confirmed that the molecular orientation structure of FIG. 2 was taken.

  Linear polarization He—Ne laser light (wavelength: 633 nm) was incident on the polarization diffraction element thus fabricated, and the characteristics of the polarization conversion function were examined. When the electric field oscillation direction of the He—Ne laser beam is made parallel to the grating direction of the polarization diffraction element, the polarization state of the ± first-order diffracted light is the electric field oscillation with respect to the electric field oscillation direction of the incident light. It was confirmed that the direction was linearly polarized light rotated by 90 °. In addition, when the polarization of the incident light is right-handed circularly polarized light, it is confirmed that the polarization state of the ± first-order diffracted light is left-handed circularly polarized light, and the characteristics of these polarization conversions are calculated by the above-described Jones method. Consistent with the results. The produced polarization diffraction element shows no change in properties even when left at 130 ° C. for over a week, confirming that the molecular orientation is fixed and has practical heat resistance. It was. The diffraction efficiency was as high as about 5%, and it was found that the diffraction efficiency was sufficient for practical use.

  Polymer 2 was dissolved in dichloromethane at a concentration of 1% by weight and applied on a glass substrate to a thickness of about 0.3 μm using a spin coater. Ultraviolet light from a high-pressure mercury lamp was applied to this film with a Grand Taylor prism. As in the case of the polymer 1, the change in the degree of orientation when irradiated for various times as linearly polarized light through the film is similar to that of the polymer 1 when the irradiation energy amount of the linearly polarized light is relatively small. The orientation in the direction perpendicular to the electric field vibration direction is shown (the degree of orientation (S) is −0.6 or more). It was found that the degree of orientation (S) was 0.6 or more. In this polymer 2, as in the case of polymer 1, after the polarized light irradiation through the light-shielding mask, the polarization diffraction element that agrees with the theoretical calculation result using the Jones method only by removing the light-shielding mask and irradiating the polarized light. Was able to be produced. The diffraction efficiency was as high as about 5%.

  Polymer 2 was dissolved in dichloromethane at a concentration of 0.15% by weight and applied on a glass substrate to a thickness of about 600 angstroms using a spin coater. Ultraviolet light from a high-pressure mercury lamp was applied to this film to Grand Taylor Using two substrates prepared by irradiating for various periods of time as linearly polarized light through a prism, an anti-parallel type liquid crystal cell with a thickness of 5.0 μm was prepared and filled with liquid crystal E7 (Merck Japan Co., Ltd.) did. When this liquid crystal cell was observed with crossed Nicols, the orientation of the liquid crystal molecules was confirmed, and when the irradiation energy amount of the linearly polarized light was relatively small, the orientation of the irradiated linearly polarized light was perpendicular to the electric field vibration direction, and the linearly polarized light was shown. It was found that when the irradiation energy amount increases, the irradiation is oriented in a direction parallel to the electric field vibration direction of the linearly polarized light. When this liquid crystal cell was allowed to stand in an atmosphere of 100 ° C. for 100 hours, it was confirmed that the orientation of the liquid crystal was maintained and it had high heat resistance.

(Comparative Example 1) Polymer 3 was dissolved in dichloromethane at a concentration of 1% by weight and applied on a glass substrate to a thickness of about 0.3 µm using a spin coater. This film was irradiated with ultraviolet light from a high-pressure mercury lamp as linearly polarized light through a Grand Taylor prism for various times, and the degree of orientation calculated from the change in polarized UV-vis absorption spectrum when heat-treated at 180 ° C. is shown in FIG. Shown in As shown in FIG. 4, when the amount of irradiation energy of linearly polarized light increases, it is aligned in a direction parallel to the direction of electric field oscillation of the irradiated linearly polarized light (orientation degree (S) is 0.7). When it was relatively small, the degree of orientation (S) was as small as -0.2. This is because the maximum absorption wavelength of the polarized UV-vis absorption spectrum after heating is red-shifted to the long wavelength side, so that the formation of a head-to-tail association (J association) between side chains during heating It is considered that the orientation is inhibited.

(Comparative Example 2) Polymer 4 was dissolved in dichloromethane at a concentration of 1% by weight, and applied on a glass substrate to a thickness of about 0.3 µm using a spin coater. The degree of orientation calculated from the change in polarized UV-vis absorption spectrum when the film was irradiated with ultraviolet light from a high pressure mercury lamp through a Grand Taylor prism for various times as linearly polarized light and then heat-treated at 180 ° C. As in the case of the union 3, when the amount of irradiation energy of linearly polarized light is large, it is oriented in the direction of electric field oscillation of the irradiated linearly polarized light (degree of orientation (S) was 0.6), but the amount of irradiation energy of linearly polarized light is compared. The orientation degree was as small as -0.3 when the target was small. Similarly to the polymer 3, since the maximum absorption wavelength of the polarized UV-vis absorption spectrum after heating is red-shifted to the longer wavelength side, the head-to-tail association (J It is thought that molecular orientation was inhibited by the formation of (association).

(Comparative Example 3) The polymer 5 was dissolved in dichloromethane at a concentration of 1% by weight and applied on a glass substrate to a thickness of about 0.3 μm using a spin coater. The degree of orientation calculated from the change in polarized UV-vis absorption spectrum when the film was irradiated with ultraviolet light from a high-pressure mercury lamp as linearly polarized light through a Grand Taylor prism for various times and then heat-treated at 180 ° C. is shown in FIG. Shown in From FIG. 5, a large degree of orientation (S) was not obtained regardless of the amount of irradiation energy. Since the maximum absorption wavelength of the polarized UV-vis absorption spectrum after heating when the irradiation energy amount is relatively small is not shifted, head-to-tail association (J association) between side chains during heating is suppressed. It is thought that the molecular orientation was inhibited. From Comparative Example 2 and Comparative Example 3, the copolymerization ratio of N-phenylmaleimide or a derivative thereof is perpendicular to the electric field vibration direction because the effect of suppressing the formation of J-association cannot be sufficiently obtained when the copolymerization ratio is too small. Directional orientation cannot be achieved. It has been found that when the copolymerization ratio increases, the formation of J-association can be suppressed, but not only the orientation in the direction perpendicular to the electric field vibration direction but also the orientation in the electric field vibration direction. From this, it was found that the copolymerization ratio of N-phenylmaleimide or a derivative thereof must be appropriately adjusted in order to obtain good alignment characteristics.

(Comparative Example 4) The polymer 6 was dissolved in dichloromethane at a concentration of 1% by weight, and applied on a glass substrate to a thickness of about 0.3 μm using a spin coater. The degree of orientation calculated from the change in polarized UV-vis absorption spectrum when the film was irradiated with ultraviolet light from a high pressure mercury lamp through a Grand Taylor prism for various times as linearly polarized light and then heat-treated at 180 ° C. As in the case of the united body 1, when the irradiation energy amount of the linearly polarized light is relatively small, it indicates an orientation perpendicular to the electric field vibration direction of the irradiated linearly polarized light, and the degree of orientation (S) is −0.45, It was found that when the irradiation energy amount was increased, the orientation was parallel to the direction of electric field vibration of the irradiated linearly polarized light, and the degree of orientation (S) was 0.48. Also with this polymer 6, a polarization diffraction element could be produced in the same manner as the polymer 1. This polarization diffraction element had characteristics that coincided with the theoretical calculation result using the Jones method, but the diffraction efficiency was as low as about 2.7%. As described above, this is considered to be because the degree of orientation of the entire film was lowered because the copolymerized methyl methacrylate repeating unit was rich in flexibility at the molecular level.

Chemical structure of the polymer of the present invention Schematic diagram of the molecular orientation structure of the polarization diffraction element produced in Example 1 Relationship between time irradiation of linearly polarized ultraviolet light and degree of orientation in polymer 1 of Example 1 Relation between time irradiation of linearly polarized ultraviolet light and degree of orientation in polymer 3 of Comparative Example 1 Relation between time irradiation of linearly polarized ultraviolet light and degree of orientation in polymer 5 of comparative example 3

Explanation of symbols

10 Polymer layers 11 and 13 having an oriented structure Oriented layers 12 and 14 oriented perpendicular to the electric field vibration direction of irradiated linearly polarized light Parallel to the electric field vibration direction of irradiated linearly polarized light Oriented layer oriented in the direction

Claims (4)

A birefringence-inducing material polymer having a structure represented by Chemical Formula 1.

The birefringence inducing material polymer according to claim 1, wherein x: y = 95 to 50: 5 to 50. A polarization diffraction element characterized in that a birefringence inducing material polymer having a structure represented by Chemical Formula 1 is irradiated with light containing a linearly polarizing component to give a periodic molecular orientation structure. A liquid crystal alignment film obtained by irradiating a birefringence-inducing material polymer having a structure represented by Chemical Formula 1 with light containing a linearly polarizing component to impart liquid crystal alignment ability.

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