Modified polyvinyl alcohol, modified polyvinyl alcohol optical film and preparation method and application of modified polyvinyl alcohol optical film

Abstract

The invention provides modified polyvinyl alcohol, a modified polyvinyl alcohol optical film and a preparation method and application of the modified polyvinyl alcohol optical film, and belongs to the technical field of polyvinyl alcohol modification. The modified polyvinyl alcohol has a structure as shown in a formula (I) or a formula (II), wherein the formula (I) and the formula (II) are shown in the description; wherein n is equal to 1500 to 3000, m is equal to 100 to 1500, and n is greater than m; r is selected from any one of a polycyclic aromatic hydrocarbon group, a halogenated polycyclic aromatic hydrocarbon group, a crown ether group, a halogenated crown ether group, a calixarene / pillararene group, a halogenated calixarene / pillararene group, a heterocyclic aromatic hydrocarbon group, a halogenated heterocyclic aromatic hydrocarbon group, a halogenated phenyl group and a halogenated phenol group.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyvinyl alcohol modification, and in particular relates to a modified polyvinyl alcohol, a modified polyvinyl alcohol optical film, and a preparation method and application thereof. Background Art

[0002] With the rapid development of optics and optoelectronics, higher performance requirements are put forward for polymer materials, especially high refractive index (refractive index n>1.6), low dispersion, high transparency (transmittance>90%) and high thermal stability (glass transition temperature (T g )>150℃) to meet the application needs of cutting-edge technologies such as photonic crystals, photoresists and microlens arrays in precision optics.

[0003] The traditional material polyvinyl alcohol (PVA) has been widely used in basic optical devices due to its excellent properties: high transparency, with a transmittance of over 93%; excellent solution processing performance, capable of preparing ultra-thin and uniform film layers; and good biocompatibility. However, PVA has obvious performance defects that seriously limit its application in high-end optical systems: a low refractive index of only 1.50-1.53; a high birefringence value (Δn>0.01); insufficient thermal stability, T g These shortcomings make it difficult to apply to high-end fields such as high numerical aperture microlenses and metasurface photonic devices.

[0004] Currently, physical blending is often used to optimize the aforementioned performance deficiencies of PVA materials. However, this approach has significant drawbacks: it can significantly reduce the light transmittance of the PVA material, and it can easily cause phase separation during processing, resulting in whitening of the PVA material and other issues, which in turn reduces the mechanical properties and durability of the PVA material.

[0005] Another approach to improving the optical properties of PVA is chemical modification. Because PVA contains numerous hydroxyl side groups, it exhibits extremely high positive birefringence during stretching. Chemical modification can introduce groups with negative birefringence, aligning them with the hydroxyl groups, effectively reducing the birefringence of the modified product. Furthermore, the hydroxyl side groups in PVA serve as active sites for modification, allowing the introduction of groups with different structures (such as benzaldehyde) as needed. This can, to a certain extent, reduce the birefringence of the polyvinyl alcohol (PVA) while simultaneously increasing its refractive index. Unfortunately, the refractive index of the modified material still fails to break the 1.6 threshold, falling short of the requirements for high-refractive-index materials. This phenomenon is primarily attributed to the inherent refractive limitations of the PVA backbone. Achieving a balance between high refractive index and low birefringence through chemical modification is significantly more challenging. Summary of the Invention

[0006] In order to solve the above technical problems, the present application provides a modified polyvinyl alcohol, a modified polyvinyl alcohol optical film, a preparation method and application thereof, so as to at least partially solve the above technical problems, and the specific technical solutions provided by the present application are as follows.

[0007] As a first aspect of the present application, a modified polyvinyl alcohol is provided, having a structure as shown in formula (I) or formula (II):

[0008] Formula (I),

[0009] Formula (II);

[0010] Wherein, n=1500-3000, m=100-1500, n>m;

[0011] R is selected from any one of a fused ring aromatic hydrocarbon group, a halogenated fused ring aromatic hydrocarbon group, a crown ether group, a halogenated crown ether group, a calix / pillar aromatic hydrocarbon group, a halogenated calix / pillar aromatic hydrocarbon group, a heterocyclic aromatic hydrocarbon group, a halogenated heterocyclic aromatic hydrocarbon group, a halogenated phenyl group, and a halogenated phenol group.

[0012] As a second aspect of the present application, a preparation method of a modified polyvinyl alcohol optical film is provided, comprising: dissolving the above modified polyvinyl alcohol in a second polar solvent, performing solvent evaporation to form a film, to obtain a modified polyvinyl alcohol film; stretching the modified polyvinyl alcohol film, and quenching and setting to obtain a modified polyvinyl alcohol optical film.

[0013] As a third aspect of the present application, a modified polyvinyl alcohol optical film is provided, prepared by the above preparation method.

[0014] As a fourth aspect of the present application, an application of the above modified polyvinyl alcohol optical film in the field of optics is provided.

[0015] Based on the above technical solutions, the modified polyvinyl alcohol, the modified polyvinyl alcohol optical film, the preparation method and the application thereof provided by the present application at least have one of the following beneficial effects.

[0016] (1) In the embodiments of the present invention, the modified polyvinyl alcohol provided by the present invention has a structure of formula (I) or formula (II), wherein n=1500-3000, m=100-1500 (n>m), and R is selected from a variety of functional groups. The introduction of specific R groups (such as groups containing large conjugated structures such as condensed aromatic hydrocarbons) can effectively improve the refractive index of polyvinyl alcohol by virtue of their large conjugated properties. At the same time, the introduced large conjugated structure groups can regulate the stacking mode of the molecular chains through steric hindrance effects and intermolecular interactions, reduce the optical anisotropy caused by local orientation differences, make the molecular chains more evenly distributed and more coordinated in orientation in the material, thereby reducing the birefringence value and achieving a balance between high refractive index and low birefringence value; and after the large conjugated structure is grafted, the intermolecular force is enhanced, significantly improving T g To above 150℃, solving the problem of low T g The problem of easy deformation and decomposition during processing is solved, so that it can maintain rigidity at higher temperatures (above 120°C), suitable for high-temperature processes such as injection molding and hot pressing. It can also be stably used in high-temperature scenarios such as photoresist baking and reflow soldering, reducing the risk of thermal decomposition, providing support for the development of high-performance optical materials, and expanding its application potential in optics, electronic packaging and other fields.

[0017] (2) In the embodiment of the present invention, the modified polyvinyl alcohol imparts excellent performance to the optical film by virtue of its unique structure: the modified polyvinyl alcohol optical film obtained by solvent volatilization film formation, stretching and quenching setting effectively improves the refractive index due to the introduction of R groups containing large conjugation and other characteristics into the molecular chain, while optimizing the molecular orientation and reducing the birefringence value, achieving a balance of optical performance; the large conjugated structure enhances the interaction between molecules and significantly increases the glass transition temperature, so that the film maintains rigidity and avoids deformation during high-temperature molding (such as injection molding auxiliary film formation), and maintains structural stability in high-temperature processing scenarios (such as high-temperature testing after optical device packaging), reducing the risk of thermal decomposition. The optical film can accurately control optical parameters and adapt to the needs of optical lenses, display modules and other fields for high refractive index, low birefringence and temperature resistance, providing material support for the miniaturization and high performance of optical devices, showing potential in applications such as optical filtering and polarization control, promoting material upgrades and product innovation in the optical field, and has significant technical value and industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Graph showing the average refractive index change of the modified polyvinyl alcohol optical films in Examples 1 to 3 of the present invention and Comparative Example 1;

[0019] Figure 2 The thermogravimetric analysis diagram of the modified polyvinyl alcohol optical film in Examples 1 to 3 of the present invention and Comparative Example 1;

[0020] Figure 3The differential scanning calorimetry diagrams of the modified polyvinyl alcohol optical films in Examples 1 to 3 of the present invention and Comparative Example 1 are shown;

[0021] Figure 4 This is a graph showing changes in birefringence values ​​of the modified polyvinyl alcohol optical film at different stretching ratios in Example 8 of the present invention;

[0022] Figure 5 This is a graph showing changes in birefringence values ​​of the modified polyvinyl alcohol optical film at different stretching ratios in Example 9 of the present invention;

[0023] Figure 6 This is a graph showing the change in birefringence value of the modified polyvinyl alcohol optical film at different stretching ratios in Example 10 of the present invention. DETAILED DESCRIPTION

[0024] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0025] In the process of realizing the concept of the present invention, it was found that it is difficult to achieve a balance between high refractive index and low birefringence when polyvinyl alcohol (PVA) material is used in the optical field, and due to T g The present invention provides a modified polyvinyl alcohol, which uses raw materials with large conjugated structural groups such as condensed aromatic hydrocarbons as modified raw materials. By leveraging the characteristics of the large conjugated structural groups, the refractive index of polyvinyl alcohol is increased while the birefringence value is effectively reduced, achieving a balance between the two properties. At the same time, the T is significantly improved by grafting the large conjugated structure. g , so that it maintains rigidity during high-temperature molding processes (such as injection molding and hot pressing), avoids uncontrolled deformation, and has a more stable structure during high-temperature processing (such as photoresist baking), reducing thermal decomposition problems, providing support for the development of high-performance optical materials and showing broad application potential.

[0026] As a first aspect of the present invention, a modified polyvinyl alcohol is provided, having a structure as shown in formula (1) or formula (2):

[0027] Formula (1),

[0028] Formula (2);

[0029] Among them, n=1500-3000, m=100-1500, n>m;

[0030] R is selected from any one of a condensed ring aromatic hydrocarbon group, a halogenated condensed ring aromatic hydrocarbon group, a crown ether group, a halogenated crown ether group, a cup / pillar aromatic hydrocarbon group, a halogenated cup / pillar aromatic hydrocarbon group, a heterocyclic aromatic hydrocarbon group, a halogenated heterocyclic aromatic hydrocarbon group, a halogenated phenyl group, and a halogenated phenol group.

[0031] In the embodiments of the present application, the polyvinyl alcohol is modified by introducing R groups containing large conjugated structures (such as fused ring aromatic hydrocarbons), the refractive index of the polyvinyl alcohol is improved by means of the large conjugated characteristics, the birefringence value is reduced by optimizing the molecular chain orientation, and the balance between the two is achieved; at the same time, the intermolecular force is enhanced, and the T g , solve the problem of traditional polyvinyl alcohol processing easy deformation, decomposition, make it resistant to injection molding, photoresist baking and other high temperature process, reduce the risk of thermal decomposition, provide support for the development of high performance optical materials, expand its application potential in the field of optics, electronic packaging and other fields.

[0032] According to the embodiments of the present application, the fused ring aromatic hydrocarbon includes any one of azulene, naphthalene, anthracene, phenanthrene, pyrene, benzopyrene, tetracene, chrysene, acenaphthene, fluorene. The crown ether includes 18-crown-6. The calixarene includes p-tert-butyl calix[4]arene, and the pillararene includes diethoxy pillar[5]arene. The heterocyclic aromatic hydrocarbon includes any one of thiophene, pyridine, indole, quinoline, acridine, benzothiazole. The halogen element in the halogenated phenyl group and the halogenated phenol group includes any one of fluorine, chlorine, bromine and iodine. By limiting the specific type of R group, different technical effects can be achieved on the basis of improving the refractive index and reducing the birefringence value: for example, crown ethers such as 18-crown-6 enhance the intermolecular force and optimize the processing performance; heterocyclic aromatic hydrocarbons such as thiophene improve solubility and chemical stability. In the actual application process, targeted selection can be made according to specific scenes and needs.

[0033] According to the embodiments of the present application, the modified polyvinyl alcohol shown in formula (I) can be prepared by the following method: an acidic catalyst and R-formaldehyde are sequentially added to a first polar solvent in which polyvinyl alcohol is dissolved, an acetal reaction is performed, and the modified polyvinyl alcohol shown in formula (I) is obtained. The reaction process is shown in formula I.

[0034] Formula I

[0035] Specifically, the molecular weight of the polyvinyl alcohol is 5-500 kDa, the molecular weight distribution range is 2-4, and the alcoholysis degree is 55-99%. The mass ratio of the polyvinyl alcohol to the first polar solvent is 1:1-50, preferably 1:1-15. The molar ratio of the polyvinyl alcohol to the acidic catalyst is 5-15:1; the molar ratio of the polyvinyl alcohol to R-formaldehyde is 1:0.1-10. The acidic catalyst is selected from any one of hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, and p-methylbenzenesulfonic acid. The first polar solvent is selected from any one of water, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and dioxane.

[0036] In an embodiment of the present invention, the method for preparing modified polyvinyl alcohol of formula (I) provided by the present invention realizes an efficient and controllable acetal reaction by optimizing raw material parameters and reaction conditions: limiting the molecular weight, alcoholysis degree and ratio of polyvinyl alcohol to solvent to ensure that it is fully dissolved in the first polar solvent to provide a uniform system for the reaction; accurately controlling the molar ratio of polyvinyl alcohol to acidic catalyst and R-formaldehyde, combined with the selection of acidic catalysts such as hydrochloric acid, can effectively promote the acetal reaction, improve the reaction conversion rate and product structural uniformity. The method is simple to operate, and by adjusting the raw material ratio and solvent type, the degree of modification can be flexibly controlled to ensure that the product is stable and has a high refractive index, low birefringence value, and high T brought by the large conjugated structure. g and thermal stability, providing reliable process support for the large-scale preparation of high-performance modified polyvinyl alcohol.

[0037] In some embodiments, the R-formaldehyde comprises any one of the compounds represented by Formulas I1-I8.

[0038]

[0039] According to an embodiment of the present invention, the modified polyvinyl alcohol represented by formula (II) can be prepared by the following method: a basic catalyst and R-formyl chloride are sequentially added to a first polar solvent containing polyvinyl alcohol, and an esterification reaction is performed to obtain the modified polyvinyl alcohol represented by formula (II). The reaction process is shown in formula II.

[0040] Formula II

[0041] Specifically, the polyvinyl alcohol has a molecular weight of 5-500 kDa, a molecular weight distribution range of 2-4, and a degree of alcoholysis of 55-99%. The mass ratio of polyvinyl alcohol to the first polar solvent is 1:1-50. The molar ratio of polyvinyl alcohol to the alkaline catalyst is 5-15:1; and the molar ratio of polyvinyl alcohol to R-formyl chloride is 1:0.1-10. The alkaline catalyst is selected from any one of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, triethylamine, and pyridine. The first polar solvent is selected from any one of water, dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and dioxane.

[0042] In an embodiment of the present invention, the present invention provides a method for preparing modified polyvinyl alcohol of formula (II), which achieves efficient modification through an esterification reaction under alkaline conditions: limiting the molecular weight, alcoholysis degree and ratio of polyvinyl alcohol to the first polar solvent to ensure that the raw materials are fully dissolved to form a uniform reaction system; regulating the molar ratio of polyvinyl alcohol to the alkaline catalyst and R-formyl chloride, combined with the selection of alkaline catalysts such as sodium hydroxide and triethylamine, can effectively promote the esterification reaction and improve the structural regularity and reaction conversion rate of the product. The method is simple to operate, and the degree of modification can be flexibly controlled by adjusting the raw material ratio and solvent type, stably giving the product a high refractive index, low birefringence value, and high T brought by a large conjugated structure. g and thermal stability, providing a reliable process path for the large-scale preparation of high-performance modified polyvinyl alcohol and ensuring the performance stability of subsequent optical films and other products.

[0043] In some embodiments, the R-formyl chloride comprises any one of the compounds represented by Formulae III-II8.

[0044]

[0045] Illustratively, the present invention provides a method for preparing a modified polyvinyl alcohol represented by formula (II), comprising: dissolving polyvinyl alcohol (PVA) in a first polar solvent to obtain a PVA solution; sequentially adding an alkaline catalyst and R-formyl chloride to the PVA solution to carry out an esterification reaction; after the reaction is completed, adding the reaction solution to a precipitation solvent to wash away excess catalyst and incompletely reacted monomers; performing solid-liquid separation on the obtained solid-liquid mixture, purifying it through repeated dissolution-precipitation washing steps, and then drying to obtain the modified polyvinyl alcohol represented by formula (II).

[0046] The temperature of the esterification reaction is 20-100°C, and the time of the esterification reaction is 1-10 hours. To avoid the occurrence of side reactions, the esterification reaction can be carried out under an inert gas atmosphere, including argon, nitrogen, etc. The precipitation solvent includes ethanol, methanol, petroleum ether, deionized water, etc. The mass ratio of the precipitation solvent to the reaction liquid is 1:5-500. After the reaction liquid is added to the precipitation solvent, it is stirred. Magnetic stirring or mechanical stirring can be selected, and the stirring speed is 100-1000rpm. Drying methods include: vacuum drying and forced air drying. The drying temperature is 50-180°C, and the drying time is 24-72h.

[0047] It should be noted that the specific preparation method of the modified polyvinyl alcohol represented by formula (1) can be adjusted accordingly with reference to the idea of ​​the preparation method of the modified polyvinyl alcohol represented by formula (2) above, and the specific details will not be repeated here.

[0048] In embodiments of the present invention, by adjusting parameters such as reaction time, reaction temperature, and the molar ratio of reactants to polyvinyl alcohol, the grafting rate of groups such as condensed aromatic hydrocarbons can be effectively controlled, thereby flexibly adjusting the refractive index and birefringence of the modified polyvinyl alcohol to adapt it to different application scenarios. Within a certain range, extending the reaction time, increasing the reaction temperature, or increasing the molar ratio of reactants to polyvinyl alcohol can all increase the grafting rate of the product. By regulating this grafting rate, the refractive index of PVA can be significantly increased while the birefringence can be reduced, thereby obtaining a polyvinyl alcohol material that meets diverse application needs.

[0049] As a second aspect of the present invention, a method for preparing a modified polyvinyl alcohol optical film is provided, comprising: dissolving the modified polyvinyl alcohol in a second polar solvent, volatilizing the solvent to form a film, and obtaining a modified polyvinyl alcohol film; stretching the modified polyvinyl alcohol film, and quenching and shaping it to obtain a modified polyvinyl alcohol optical film.

[0050] According to an embodiment of the present invention, the mass ratio of the modified polyvinyl alcohol to the second polar solvent is 1:1-20. The second polar solvent is selected from any one of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N-methylpyrrolidone (NMP), acetone, and diethyl ether. The stretching method includes any one of uniaxial stretching, constrained uniaxial stretching, asynchronous biaxial stretching, and simultaneous biaxial stretching.

[0051] Specifically, the present invention provides a method for preparing a modified polyvinyl alcohol optical film by uniaxial stretching, comprising: dissolving modified polyvinyl alcohol in a second polar solvent to form a modified polyvinyl alcohol solution, and obtaining a modified polyvinyl alcohol film by a solvent volatilization film-forming method; fixing the modified polyvinyl alcohol film in the length direction by a clamp, and preheating the modified polyvinyl alcohol film; after preheating, stretching the modified polyvinyl alcohol film in the length direction, and then quenching to obtain a modified polyvinyl alcohol optical film.

[0052] Among them, the solid content of the modified polyvinyl alcohol solution is 5-30wt%, preferably 10-30wt%, and more preferably 15-30wt%. The modified polyvinyl alcohol is dried before the preparation begins, and the drying method can be hot air drying or vacuum oven drying to reduce the water content of the modified polyvinyl alcohol particles to below 3wt%. In order to ensure that the subsequent dissolution process in the reactor is stable and not disturbed by moisture, it is more preferred to reduce the water content of the modified polyvinyl alcohol particles to below 1wt%. When dissolving the modified polyvinyl alcohol, the dissolution temperature is controlled to be 80-200°C. The stirring speed during dissolution will also affect the dissolution temperature. Under the premise of ensuring uniform stirring and stable temperature, the stirring speed can be increased. Hot air heating is used during preheating to preheat the film by a uniform thermal effect to ensure that the film temperature is uniform. The preheating temperature is T g -50℃~T g +50℃, where Tg is the glass transition temperature of the modified polyvinyl alcohol, preferably T g -20℃~T g The stretching temperature is +20°C. The stretching ratio during the stretching process is 1.5-3.0, and the stretching speed is 0.1-20 mm / s, preferably 1-5 mm / s. The quenching process involves rapidly cooling the stretched modified polyvinyl alcohol film from the stretching temperature environment to a liquid nitrogen temperature environment to quench and fix the orientation of the modified polyvinyl alcohol optical film.

[0053] As a third aspect of the present invention, a modified polyvinyl alcohol optical film is provided, which is prepared by the above preparation method.

[0054] In an embodiment of the present invention, the modified polyvinyl alcohol optical film is prepared using a solvent evaporation film-forming method. The modified polyvinyl alcohol exhibits a reduced birefringence value Δn and an increased refractive index. The resulting modified polyvinyl alcohol optical film exhibits a refractive index n of 1.5-1.9 and a birefringence value Δn of -0.01-0.01 within a wavelength range of 400-800 nm. By manipulating the degree of substitution of the substituent groups and stretching parameters, the refractive index and birefringence can be adjusted in various ways. This optical film exhibits excellent optical properties, a tunable refractive index, good processability, and stable properties, making it highly valuable for future applications.

[0055] As a fourth aspect of the present invention, there is provided an application of the modified polyvinyl alcohol optical film in the optical field.

[0056] In an embodiment of the present invention, the modified polyvinyl alcohol provided herein is chemically modified to introduce substituents into the polyvinyl alcohol side chains. The resulting modified polyvinyl alcohol has a refractive index (n) of 1.5-1.9 within the wavelength range of 400-800 nm, a birefringence value (Δn) controlled between -0.01 and 0.01, and near-zero birefringence in the unstretched state, meeting the requirements of applications such as aspheric lenses for mobile phone cameras and multilayer coatings. This modified polyvinyl alcohol combines excellent optical performance with an adjustable refractive index. For example, in aspheric lenses for mobile phone cameras, a high refractive index of 1.7 enables the design of thinner lenses (such as periscope lenses), aligning with the trend toward thinner and lighter mobile phones. In lens coatings, it can be used as an antireflection coating (in conjunction with high and low refractive index layers), effectively reducing lens surface reflections and improving image contrast, providing strong support for optimizing optical device performance.

[0057] The present application is further illustrated by the following examples and related test experiments. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the application. However, it will be apparent to one skilled in the art that one or more embodiments can be practiced without these specific details. In other instances, well-known methods have not been described in detail in order to avoid unnecessarily obscuring the present application. Unless otherwise noted, all instruments, materials, and reagents, etc. used in the following examples, were obtained from commercial suppliers such as Sigma-Aldrich (St. Louis, Missouri, United States of America) and Alfa Aesar (Ward Hill, Massachusetts, United States of America) which refer to the products as of the date of filing this patent, and used without further purification, except for those that are otherwise noted.

[0058] Example 1

[0059] In this Example 1, a modified polyvinyl alcohol was prepared by modifying polyvinyl alcohol with 1-pyrene carboxaldehyde, and a modified polyvinyl alcohol optical film was prepared.

[0060] Specifically, the reaction equation is shown in Formula III.

[0061] Formula III

[0062] The specific process for synthesizing the modified polyvinyl alcohol is described as follows.

[0063] S1: 0.03 mol of PVA 1799 was weighed and added to 25 mL of anhydrous DMSO. The oil bath was heated to 90°C, a stirring rotor was placed in the reaction container, the condensing water device was connected, the remaining bottle opening was sealed with a rubber plug, and then a sealing rubber was wrapped around the opening to reinforce the seal. After stirring for 5 h in this state, the stirring was stopped, and the system was naturally cooled to room temperature to obtain a PVA solution.

[0064] S2: A stirring rod was placed in the reaction container containing the PVA solution, and the stirring speed was adjusted to 300 rpm. Then, 0.003 mol of p-toluenesulfonic acid was dissolved in 2.5 mL of DMSO and added dropwise to the dissolved PVA solution at 20°C. After stirring for 5 min, 1-pyrene carboxaldehyde solution (0.006 mol of 1-pyrene carboxaldehyde dissolved in 20 mL of DMSO, i.e., the molar ratio of polyvinyl alcohol to 1-pyrene carboxaldehyde was 1:0.2) was slowly added through a constant pressure dropping funnel, and the dropwise addition time was controlled to be 30 min. After the dropwise addition was completed, the acetal reaction was carried out.

[0065] S3: The temperature and time program for the acetal reaction was set as follows: 90 min at 20°C; then programmed heating was carried out to slowly increase the temperature from 20°C to 60°C within 180 min; after reaching 60°C, the temperature was maintained for 120 min.

[0066] S4: After the reaction is completed, the reaction solution is added dropwise to deionized water to terminate the reaction by precipitation. The yellow solid product is then filtered to obtain a yellow solid product. For further purification, the yellow solid product is repeatedly subjected to the "dissolution (using NMP) - precipitation (using deionized water) - washing (using ethanol)" operation. Finally, the purified product is placed in a vacuum drying oven at 60°C to obtain 1-pyrene formaldehyde-modified polyvinyl alcohol.

[0067] Furthermore, the specific process of preparing the modified polyvinyl alcohol optical film by using the above method to prepare 1-pyrene formaldehyde modified polyvinyl alcohol is as follows.

[0068] Q1: Weigh 1 g of 1-pyrene formaldehyde-modified polyvinyl alcohol and dissolve it in 20 mL of NMP.

[0069] Q2: Preheat the vacuum oven to 60°C and pour 1-pyrene formaldehyde-modified polyvinyl alcohol dissolved in NMP into a 15 cm diameter glass dish.

[0070] Q3: The film-forming procedure is set as follows: first, the temperature is raised to 80°C and kept warm for 2 hours; then, the temperature is raised to 106°C within 2 hours, and then the solution is placed under vacuum conditions and kept warm at 106°C for 4 hours; then, the temperature is raised to 150°C within 2 hours to finally obtain 1-pyrene formaldehyde-modified polyvinyl alcohol film.

[0071] Q4: After the modified polyvinyl alcohol film is cut into rectangular shapes of preset sizes, it is fixed in the length direction by a clamp and the 1-pyrene formaldehyde modified polyvinyl alcohol film is preheated at a preheating temperature of T g ±20℃.

[0072] Q5: After preheating, stretching is performed in the length direction, and then quenching is performed (the stretched modified polyvinyl alcohol film is suddenly cooled from the stretching temperature environment to the liquid nitrogen temperature environment, and the orientation state of the modified polyvinyl alcohol optical film is suddenly cooled and fixed) to obtain a 1-pyrene formaldehyde modified polyvinyl alcohol optical film.

[0073] Example 2

[0074] The method for synthesizing modified polyvinyl alcohol in Example 2 is the same as that in Example 1, except that the molar ratio of polyvinyl alcohol to 1-pyrene formaldehyde is 1:0.5. The specific process for preparing the modified polyvinyl alcohol optical film in Example 2 is the same as that in Example 1.

[0075] Example 3

[0076] The method for synthesizing modified polyvinyl alcohol in Example 3 is the same as that in Example 1, except that the molar ratio of polyvinyl alcohol to 1-pyrenecarboxaldehyde is 1:1. The specific process for preparing the modified polyvinyl alcohol optical film in Example 3 is the same as that in Example 1.

[0077] Example 4

[0078] The method for synthesizing modified polyvinyl alcohol in Example 4 is the same as that in Example 1, except that the molar ratio of polyvinyl alcohol to 1-pyrene carboxaldehyde is 1:1.25. The specific process for preparing the modified polyvinyl alcohol optical film in Example 4 is the same as that in Example 1.

[0079] Example 5

[0080] The method for synthesizing modified polyvinyl alcohol in Example 5 is the same as that in Example 3, except that the temperature is slowly raised from 20° C. to 40° C. and then kept warm. The specific process for preparing the modified polyvinyl alcohol optical film in Example 5 is the same as that in Example 1.

[0081] Example 6

[0082] The method for synthesizing modified polyvinyl alcohol in Example 6 is the same as that in Example 3, except that the temperature is slowly raised from 20° C. to 80° C. and then kept warm. The specific process for preparing the modified polyvinyl alcohol optical film in Example 6 is the same as that in Example 1.

[0083] Example 7

[0084] The method for synthesizing modified polyvinyl alcohol in Example 7 is the same as that in Example 3, except that the temperature is slowly raised from 20° C. to 100° C. and then kept warm. The specific process for preparing the modified polyvinyl alcohol optical film in Example 7 is the same as that in Example 1.

[0085] Comparative Example 1

[0086] Unmodified polyvinyl alcohol was completely dissolved in DMSO, and an unmodified polyvinyl alcohol optical film was prepared using the same method as in Example 1.

[0087] Comparative Example 2

[0088] Benzaldehyde-modified polyvinyl alcohol was completely dissolved in DMSO, and a benzaldehyde-modified polyvinyl alcohol optical film was prepared using the same method as in Example 1.

[0089] The reaction conditions and basic performance parameters of the modified polyvinyl alcohols prepared in Examples 1-7 and Comparative Examples 1-2 are shown in Table 1. The glass transition temperature was measured using a differential scanning calorimeter (DSC Q2000, manufactured by TA Instruments, USA). The degree of acetalization represents the ratio of hydroxyl groups modified with 1-pyrenecarboxaldehyde to the unmodified hydroxyl groups in the polyvinyl alcohol, i.e., m / n in Formula III.

[0090] Table 1 Reaction conditions and basic performance parameters of Examples 1-7 and Comparative Examples 1-3

[0091]

[0092] From Table 1, we can see that the glass transition temperature (T g ) is significantly improved compared with the comparative example. The embodiment is much higher than 79°C of comparative example 1 and 124°C of comparative example 2. In a certain range, it increases with the increase of reaction degree (which can be reflected by feed ratio). For example, when the reaction temperature of Example 1 to Example 4 is 60°C, the feed ratio increases, T g From 156 ° C to 213 ° C; at the same time, the degree of modification of polyvinyl alcohol (represented by acetalization degree) is positively correlated with the feed ratio. The larger the feed ratio, the higher the degree of modification. For example, in Examples 1 to 4, the acetalization degree increases with the increase of the feed ratio, and the degree of modification is related to the reaction temperature. Too high a temperature will affect the reaction efficiency. For example, in Examples 3, 5, 6, and 7, when the feed ratio is the same, the acetalization degree is relatively higher at 60 ° C. The glass transition temperature and the acetalization degree are related to each other. When the degree of modification is high, T g It also tends to be higher, reflecting the effect of modification on improving the thermal properties of polyvinyl alcohol and the regulation of reaction conditions.

[0093] In order to further understand the present invention, in the context of industrial production of optical films often involving stretching treatment, stretching treatments similar to the industrial production process were carried out on all embodiments and comparative examples. The specific operations are as follows: using a unidirectional stretching device, the modified polyvinyl alcohol films in Examples 1 to 3 and Comparative Examples 1 and 2 were stretched. When preparing the modified polyvinyl alcohol optical film, the stretching process parameters were set as follows: preheating for 5 minutes, the stretching temperature was controlled at 10±0.5°C above the glass transition temperature, the stretching rate was 1mm / s, and an unrestricted unidirectional stretching method was adopted. After the stretching was completed, the film thickness d of the modified polyvinyl alcohol optical film prepared in Examples 1 to 3 and Comparative Examples 1 and 2 was measured by a screw micrometer. The relevant stretching process parameters and the test results of the film thickness after stretching are shown in Table 2.

[0094] Table 2 Stretching process parameters and film thickness test results after stretching of Examples 1-3 and Comparative Examples 1-2

[0095]

[0096] When optical tests were performed on the modified polyvinyl alcohol optical films with different stretching ratios in Examples 1 to 3 and Comparative Examples 1 and 2, the refractive index was measured using an ellipsometer, and the in-plane retardation value R at a specific wavelength was measured using a phase difference meter. in and out-of-plane retardation R th , and calculate the in-plane birefringence value Δn based on this in and out-of-plane birefringence Δn th , the relevant test results are shown in Table 3.

[0097] The draw ratio (DR) is defined as: , where L is the length of the stretched spline.

[0098] About R in and Δn in 、R th and Δn th The calculation involves the following parameters and methods: R in (λ) represents the in-plane retardation at wavelength λ, R th (λ) represents the out-of-plane retardation at wavelength λ, and the measurement wavelength λ is in the visible light region (400-800 nm, preferably 400-750 nm, more preferably 420-720 nm). Unless otherwise specified, R in the present invention is in and R th Refers to the value measured or calculated at 500-600nm. In-plane retardation (R in ) is measured using a RETS-100L (manufactured by Otsuka Electronics Co., Ltd.) by allowing light of wavelength λ to enter the surface of a modified polyvinyl alcohol optical film perpendicularly. Light of wavelength λ is introduced at an angle of 30-70 degrees relative to the normal direction of the film surface, and the in-plane slow axis (determined by the RETS-100L) is taken as the tilt axis. Based on the measured retardation value, average refractive index, and thickness of the film, the RETS-100L calculates R according to the following equations (1) and (2). th (λ) value. The average refractive index can be obtained by an Abbe refractometer (for example, trade name NAR-1T; ATAGO, Japan). in and Δn in 、R th and Δn th The calculation formulas are shown in formulas (1) to (4).

[0099] (1)

[0100] (2)

[0101] (3)

[0102] (4)

[0103] Among them, R in (θ) is the retardation value in the direction making an angle θ with the normal direction, nx is the refractive index in the slow axis direction in the plane, ny is the refractive index in the direction orthogonal to nx in the plane, nz is the refractive index in the direction orthogonal to nx and ny, d is the film thickness, and λ is the wavelength.

[0104] Table 3 Optical performance test results of Examples 1-3 and Comparative Examples 1-2

[0105]

[0106] As can be seen from Table 3, the modified polyvinyl alcohol optical film has good performance after treatment. The stretching ratio of the modified polyvinyl alcohol optical film prepared in Examples 1 to 3 is 1.0-3.0, and it can meet 1.6≤n≤1.9 and -0.01≤Δn in the wavelength range of 400nm-1200nm. in ≤0.01, -0.01≤Δn th ≤0.01, Δn when not stretched in and Δn th Close to zero, Δn at 3 times the stretching ratio in ≤0.01, Δn th ≤0.01. The refractive index (589nm) of Example 1 is 1.655, and that of Example 3 reaches 1.694, which is much higher than that of Comparative Example 1 (1.520) and Comparative Example 2 (1.542). It can be seen that the refractive index of the modified polyvinyl alcohol optical film is significantly higher than that of the unmodified polyvinyl alcohol ester optical film, and the refractive index is related to the reaction conditions. Keeping the reaction temperature and time unchanged, increasing the feed ratio can increase the degree of reaction, thereby increasing the refractive index. The birefringence value is mainly regulated by stretching, and the birefringence value of the unstretched optical film is relatively small, basically close to 0. Comparing the above examples with the comparative examples, it can be seen that the birefringence value of the modified polyvinyl alcohol optical film is significantly lower than that of the unmodified polyvinyl alcohol optical film. The modified polyvinyl alcohol optical film provided by the present invention has a significantly higher refractive index than the unmodified one, and the birefringence value can be adjusted by regulating the reaction conditions (such as feed ratio, etc.) and stretching parameters (such as stretch ratio), which can meet the requirements of the optical field for the performance of modified polyvinyl alcohol optical films.

[0107] Figure 1 This is a graph showing the average refractive index change of the modified polyvinyl alcohol optical film in Examples 1 to 3 of the present invention and Comparative Example 1.

[0108] like Figure 1 As shown, in the wave number range of 400-1200nm, the average refractive index (n av ) are significantly higher than those of comparative example 1 (unmodified polyvinyl alcohol optical film). For example, at a wave number of 589 nm, the average refractive index of Example 3 is 1.694, that of Example 2 is 1.679, that of Example 1 is 1.655, and that of comparative example 1 is only 1.520, indicating that the average refractive index of the modified polyvinyl alcohol optical film is significantly increased, and the average refractive index of different embodiments is different due to differences in modification conditions, etc. As the wave number changes, the average refractive index of each modified polyvinyl alcohol optical film shows an overall downward trend, further illustrating that modification can effectively increase the average refractive index of the polyvinyl alcohol optical film and improve its optical properties.

[0109] Figure 2 The thermogravimetric analysis diagram of the modified polyvinyl alcohol optical film in Examples 1 to 3 of the present invention and Comparative Example 1; Figure 3 3 and Comparative Example 1 of the present invention are differential scanning calorimetry graphs of the modified polyvinyl alcohol optical films.

[0110] from Figure 2 Thermogravimetric analysis (TG) diagram shows that each modified polyvinyl alcohol optical film shows mass loss during the heating process, and the thermal decomposition behavior is different. At lower temperatures (100-300 ° C), the mass change is slow, mainly due to the volatilization of light components; 300-500 ° C is the stage of large-scale decomposition and weight loss. Compared with other samples, Example 3 has a higher thermal decomposition starting temperature and a different weight loss rate, reflecting that its thermal stability may be better. Different preparation methods affect the thermal stability of modified polyvinyl alcohol optical films. The residual mass at high temperature (above 700 ° C) is similar, indicating that the difference in inorganic residues is small, and the modification mainly acts on the thermal decomposition of the organic phase. Then from Figure 3 It can be seen from the differential scanning calorimetry (DSC) graph that the heat flow of each modified polyvinyl alcohol optical film changes differently with temperature. Comparative Example 1 has an endothermic transition at 79°C, and Examples 1-3 have characteristic temperatures at 156°C, 203°C, and 213°C, respectively. This shows that the thermal transition temperatures of the examples are different from those of the comparative examples due to chemical modification, indicating that the chemical modification changes the internal structure and thermal phase change characteristics of polyvinyl alcohol. Combining the TG and DSC graphs, it can be seen that chemical modification can regulate the thermal stability and thermal phase change behavior of polyvinyl alcohol optical films.

[0111] Example 8

[0112] In this Example 8, polyvinyl alcohol was modified with 4-bromo-3-indolecarboxaldehyde to obtain modified polyvinyl alcohol, and a modified polyvinyl alcohol optical film was prepared.

[0113] Specifically, the reaction equation is shown in Formula IV.

[0114] Formula IV

[0115] The specific process of synthesizing modified polyvinyl alcohol is described as follows.

[0116] S1: Weigh 0.03 mol of PVA1799 and add it to 25 mL of H2O. Heat an oil bath to 90°C. Place a stirring rotor in the reaction vessel and connect a condenser. Seal the remaining bottle opening with a rubber stopper and then wrap with sealing tape to reinforce the seal. Stir and dissolve for 5 hours, then stop stirring and allow the system to cool naturally to room temperature to obtain a PVA solution.

[0117] S2: Place a stirring rod in the reaction vessel containing the PVA solution and adjust the stirring speed to 300 rpm. Next, add 0.003 mol of hydrochloric acid dropwise to the dissolved PVA solution at 10°C. After stirring for 5 minutes, slowly add 4-bromo-3-indolecarboxaldehyde solution (0.006 mol of 4-bromo-3-indolecarboxaldehyde dissolved in 20 mL of dioxane) dropwise using a constant pressure dropping funnel. Control the addition time to 30 minutes. After the addition is complete, proceed with the acetalization reaction.

[0118] S3: The temperature and time program of the acetalization reaction was set as follows: keep at 10°C for 90 minutes; then perform a temperature program to slowly increase the temperature from 10°C to 60°C within 180 minutes; after reaching 60°C, maintain this temperature for another 120 minutes.

[0119] S4: After the reaction is completed, the reaction solution is added dropwise to deionized water to terminate the reaction by precipitation. The product is then filtered to obtain a white solid. For further purification, the white solid product is repeatedly subjected to the "dissolution (using NMP) - precipitation (using deionized water) - washing (using ethanol)" operation. Finally, the purified product is dried in a vacuum drying oven at 60°C to obtain 4-bromo-3-indolecarboxaldehyde-modified polyvinyl alcohol.

[0120] Furthermore, the specific process of preparing a modified polyvinyl alcohol optical film by using the above method to prepare 4-bromo-3-indolecarboxaldehyde-modified polyvinyl alcohol is as follows.

[0121] Q1: Weigh 1 g of 4-bromo-3-indolecarboxaldehyde-modified polyvinyl alcohol and dissolve it in 20 mL of DMF.

[0122] Q2: Preheat the vacuum oven to 60°C and pour 4-bromo-3-indolecarboxaldehyde-modified polyvinyl alcohol dissolved in DMF into a 15 cm diameter glass dish.

[0123] Q3: The film formation procedure is set as follows: first, the temperature is raised to 80°C and kept warm for 2 hours; then, the temperature is raised to 106°C within 2 hours, and then the solution is placed under vacuum conditions and kept warm at 106°C for 4 hours; then, the temperature is raised to 150°C within 2 hours to finally obtain 4-bromo-3-indolecarboxaldehyde-modified polyvinyl alcohol film.

[0124] Q4: After the modified polyvinyl alcohol film is cut into rectangular shapes of preset sizes, it is fixed in the length direction by a clamp and the 4-bromo-3-indolecarboxaldehyde modified polyvinyl alcohol film is preheated at a preheating temperature of T g ±20℃.

[0125] Q5: After preheating, the film is stretched in the length direction and then quenched to obtain a 4-bromo-3-indolecarboxaldehyde-modified polyvinyl alcohol optical film.

[0126] Example 9

[0127] This Example 9 uses 4-iodobenzoyl chloride to modify polyvinyl alcohol to obtain modified polyvinyl alcohol, and a modified polyvinyl alcohol optical film is prepared.

[0128] Specifically, the reaction equation is shown in Formula V.

[0129] Formula V

[0130] The specific process for synthesizing the modified polyvinyl alcohol is described as follows.

[0131] S1: Take 0.03 mol of PVA1788 and add it to 25 mL of NMP. Heat the oil bath pot to 90°C, place a stirring rotor in the reaction vessel, connect the condensing water device, seal the remaining bottle opening with a rubber plug, and then wrap the sealing glue to reinforce the sealing. After stirring for 5 h in this state, stop stirring and allow the system to cool naturally to room temperature to obtain a PVA solution.

[0132] S2: Place a stirring rod in the reaction vessel containing the PVA solution and adjust the stirring speed to 300 rpm. Then, take 0.003 mol of pyridine and add it dropwise to the dissolved PVA solution at 10°C. After stirring for 5 min, slowly add the 4-iodobenzoyl chloride solution (0.006 mol of 4-iodobenzoyl chloride dissolved in 20 mL of NMP) using a constant-pressure dropping funnel, control the dropwise addition time for 30 min, and perform esterification after the dropwise addition is complete.

[0133] S3: The temperature and time program for the esterification reaction is set as follows: 60°C for 180 min.

[0134] S4: After the reaction is complete, add the reaction solution dropwise to deionized water to terminate the reaction by precipitation, and then obtain white solid product by suction filtration. To further purify, repeatedly perform the "dissolution (using NMP) - precipitation (using deionized water) - washing (using ethanol)" operation on the white solid product, and finally place the purified product in a 60°C vacuum drying oven for drying, to obtain 4-iodobenzoyl chloride modified polyvinyl alcohol.

[0135] Further, the specific process for preparing a modified polyvinyl alcohol optical film using the 4-iodobenzoyl chloride modified polyvinyl alcohol prepared by the above method is described as follows.

[0136] Q1: Take 1 g of 4-iodobenzoyl chloride modified polyvinyl alcohol and dissolve it in 20 mL of NMP.

[0137] Q2: Preheat the vacuum oven to 60°C, and pour the 4-iodobenzoyl chloride modified polyvinyl alcohol dissolved in NMP into a 15 cm diameter glass dish.

[0138] Q3: The film-forming procedure is set as follows: first, the temperature is raised to 80°C and kept warm for 2 hours; then, the temperature is raised to 106°C within 2 hours, and then the solution is placed under vacuum conditions and kept warm at 106°C for 4 hours; then, the temperature is raised to 150°C within 2 hours to finally obtain 4-iodobenzoyl chloride-modified polyvinyl alcohol film.

[0139] Q4: After the modified polyvinyl alcohol film is cut into rectangular shapes of preset sizes, it is fixed in the length direction by a clamp and the 4-iodobenzoyl chloride modified polyvinyl alcohol film is preheated at a preheating temperature of T g ±20℃.

[0140] Q5: After preheating, the film is stretched in the length direction and then quenched to obtain a 4-iodobenzoyl chloride modified polyvinyl alcohol optical film.

[0141] Example 10

[0142] In this Example 10, polyvinyl alcohol was modified using 3,4-methylenedioxybenzoyl chloride to obtain modified polyvinyl alcohol, and a modified polyvinyl alcohol optical film was prepared.

[0143] Specifically, the reaction equation is shown in Formula VI.

[0144] Formula VI

[0145] The specific process of synthesizing modified polyvinyl alcohol is described as follows.

[0146] S1: Weigh 0.03 mol of PVA1788 and add it to 25 mL of NMP. Heat the oil bath to 90°C, place a stirring rotor in the reaction vessel, and connect the condenser. Seal the remaining bottle opening with a rubber stopper and then wrap with sealing tape to reinforce the seal. Stir and dissolve for 5 hours, then stop stirring and allow the system to cool naturally to room temperature to obtain a PVA solution.

[0147] S2: Place a stirring rod in the reaction vessel containing the PVA solution and adjust the stirring speed to 300 rpm. Next, add 0.003 mol of pyridine dropwise to the dissolved PVA solution at 10°C. After stirring for 5 minutes, slowly add 3,4-methylenedioxybenzoyl chloride solution (0.006 mol of 3,4-methylenedioxybenzoyl chloride dissolved in 20 mL of NMP) dropwise using a constant pressure dropping funnel. Control the addition time to 30 minutes. After the addition is complete, proceed with the esterification reaction.

[0148] S3: The temperature and time program of the esterification reaction was set as follows: keeping warm at 60°C for 180 min.

[0149] S4: After the reaction is completed, the reaction solution is added dropwise to deionized water to terminate the reaction by precipitation. A white solid product is then obtained by filtration. For further purification, the white solid product is repeatedly subjected to the "dissolution (using NMP) - precipitation (using deionized water) - washing (using ethanol)" operation. Finally, the purified product is dried in a vacuum drying oven at 60°C to obtain 3,4-methylenedioxybenzoyl chloride-modified polyvinyl alcohol.

[0150] Furthermore, the specific process of preparing a modified polyvinyl alcohol optical film by using the above method to prepare 3,4-methylenedioxybenzoyl chloride-modified polyvinyl alcohol is as follows.

[0151] Q1: Weigh 1 g of 3,4-methylenedioxybenzoyl chloride-modified polyvinyl alcohol and dissolve it in 20 mL of NMP.

[0152] Q2: Preheat the vacuum oven to 60°C and pour 3,4-methylenedioxybenzoyl chloride-modified polyvinyl alcohol dissolved in NMP into a 15 cm diameter glass dish.

[0153] Q3: The film-forming procedure is set as follows: first, the temperature is raised to 80°C and kept warm for 2 hours; then, the temperature is raised to 106°C within 2 hours, and then the solution is placed under vacuum conditions and kept warm at 106°C for 4 hours; then, the temperature is raised to 150°C within 2 hours to finally obtain 3,4-methylenedioxybenzoyl chloride-modified polyvinyl alcohol film.

[0154] Q4: After the modified polyvinyl alcohol film is cut into rectangular shapes of preset sizes, it is fixed in the length direction by a clamp and the 3,4-methylenedioxybenzoyl chloride modified polyvinyl alcohol film is preheated at a preheating temperature of T g ±20℃.

[0155] Q5: After preheating, the film is stretched in the length direction and then quenched to obtain a 3,4-methylenedioxybenzoyl chloride modified polyvinyl alcohol optical film.

[0156] After stretching, the film thickness d of the modified polyvinyl alcohol optical films prepared in Examples 8-10 and Comparative Examples 1-2 was measured by a micrometer. The relevant stretching process parameters and the test results of the film thickness after stretching are shown in Table 4.

[0157] Table 4 Stretching process parameters and film thickness test results after stretching of Examples 8-10 and Comparative Examples 1-2

[0158]

[0159] Furthermore, optical tests were performed on the modified polyvinyl alcohol optical films with different stretching ratios in Examples 8 to 10 and Comparative Examples 1 and 2 according to the above method. The test results are shown in Table 5.

[0160] Table 5 Optical performance test results of Examples 8-10 and Comparative Examples 1-2

[0161]

[0162] As shown in Table 5, the refractive index of polyvinyl alcohol optical films modified with various large benzene rings and heteroatom-containing benzene ring structures is significantly higher than that of unmodified polyvinyl alcohol ester optical films. For example, the refractive indices (589 nm) of Examples 8-10 are 1.68, 1.67, and 1.63, respectively, significantly higher than those of Comparative Example 1 (1.520) and Comparative Example 2 (1.542). Birefringence is primarily regulated by stretching; the birefringence of unstretched optical films is relatively low, essentially close to zero. Comparing all of the above Examples with the Comparative Examples shows that the birefringence of the modified polyvinyl alcohol optical films is significantly lower than that of the unmodified polyvinyl alcohol optical films. The birefringence of the modified polyvinyl alcohol optical films can be switched between positive and negative values ​​compared to the unmodified polyvinyl alcohol optical films. The modified polyvinyl alcohol optical films provided by the present invention have a significantly higher refractive index than the unmodified polyvinyl alcohol optical films, and their birefringence can be adjusted by controlling the reaction conditions and stretching parameters.

[0163] Figure 4 This is a graph showing changes in birefringence values ​​of the modified polyvinyl alcohol optical film at different stretching ratios in Example 8 of the present invention; Figure 5 This is a graph showing changes in birefringence values ​​of the modified polyvinyl alcohol optical film at different stretching ratios in Example 9 of the present invention; Figure 6 This is a graph showing the change in birefringence value of the modified polyvinyl alcohol optical film at different stretching ratios in Example 10 of the present invention.

[0164] like Figure 4-Figure 6 As shown, in the wave number range of 400-800nm, the in-plane birefringence value (Δn in ) shows a certain pattern with the change of stretch ratio (DR): the in-plane birefringence curves of different embodiments (8, 9, 10) are different. Under the same embodiment, the in-plane birefringence values ​​and change trends are different with different stretch ratios. For example, when DR=1.0, the in-plane birefringence value is relatively stable. As the DR increases (1.5, 2.0, 2.5, 3.0), the change amplitude and trend of the in-plane birefringence value change, reflecting the regulatory effect of the stretch ratio on the in-plane birefringence, and this regulation shows different performances in different embodiments due to differences in modification, etc., indicating that the in-plane birefringence performance of the modified polyvinyl alcohol optical film can be adjusted by adjusting the stretch ratio to adapt to different optical application requirements.

[0165] In summary, the modified polyvinyl alcohol prepared by the method provided by the present invention has excellent comprehensive performance and significant application value in the field of optics: it can achieve precise control of the refractive index, flexibly match the optical path requirements, eliminate interface reflection loss, and synergistically optimize the refractive index and mechanical properties. It can not only replace multi-material assembly by controlling the refractive index of a single material, reduce the steps such as coating or bonding to simplify the processing flow and reduce costs, but also allow the same optical effect to be achieved with a thinner material thickness, reducing the consumption of raw materials; at the same time, the modified polyvinyl alcohol maintains excellent mechanical properties and thermal stability (high T g The characteristics enhance thermal stability, improve dimensional accuracy and broaden process compatibility, optimize processing controllability and product reliability, and meet the technical needs of high-end fields such as precision optics for high-performance devices. At the same time, it has excellent optical performance and can be widely used in optical imaging and lens design, photonic integrated circuits and optical communications and other fields; in addition, it has good processing performance and stable properties, can be prepared into thin film materials, has a wide stretching temperature range and good ductility, and can select appropriate processing conditions such as uniaxial stretching, restricted uniaxial stretching, asynchronous biaxial stretching and synchronous biaxial stretching according to needs, further adapting to diversified application scenarios.

[0166] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A modified polyvinyl alcohol, characterized in that The modified polyvinyl alcohol has a structure as shown in formula (1) or formula (2): Formula (1), Formula (2); Among them, n=1500-3000, m=100-1500, n>m; R is selected from any one of a condensed ring aromatic hydrocarbon group, a halogenated condensed ring aromatic hydrocarbon group, a crown ether group, a halogenated crown ether group, a cup / pillar aromatic hydrocarbon group, a halogenated cup / pillar aromatic hydrocarbon group, a heterocyclic aromatic hydrocarbon group, a halogenated heterocyclic aromatic hydrocarbon group, a halogenated phenyl group, and a halogenated phenol group.

2. The modified polyvinyl alcohol according to claim 1, characterized in that The condensed ring aromatic hydrocarbons include any one of azulene, naphthalene, anthracene, phenanthrene, pyrene, benzopyrene, tetracene, chrysene, acenaphthene, acenaphthene, and fluorene; The crown ether includes 18-crown-6; The calixarene includes p-tert-butylcalix[4]arene; The pillar aromatic hydrocarbons include diethoxy pillar[5] aromatic hydrocarbons; The heterocyclic aromatic hydrocarbon includes any one of thiophene, pyridine, indole, quinoline, acridine, and benzothiazole.

3. The modified polyvinyl alcohol according to claim 2, characterized in that The modified polyvinyl alcohol is obtained by the following method: An acidic catalyst and R-formaldehyde are sequentially added to a first polar solvent in which polyvinyl alcohol is dissolved to carry out an acetal reaction to obtain a modified polyvinyl alcohol as shown in formula (1): Formula (1); or An alkaline catalyst and R-formyl chloride are sequentially added to a first polar solvent in which polyvinyl alcohol is dissolved, and an esterification reaction is carried out to obtain a modified polyvinyl alcohol as shown in formula (II): Formula (2).

4. The modified polyvinyl alcohol according to claim 3, characterized in that The molecular weight of the polyvinyl alcohol is 5-500 kDa, the molecular weight distribution range is 2-4, and the alcoholysis degree is 55-99%.

5. The modified polyvinyl alcohol according to claim 4, characterized in that The mass ratio of the polyvinyl alcohol to the first polar solvent is 1:1-50; The molar ratio of the polyvinyl alcohol to the acidic catalyst or the basic catalyst is 5-15:1; The molar ratio of the polyvinyl alcohol to R-formaldehyde or R-formyl chloride is 1:0.1-10.

6. The modified polyvinyl alcohol according to claim 4, characterized in that The acidic catalyst is selected from any one of hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, and p-toluenesulfonic acid; The alkaline catalyst is selected from any one of sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, triethylamine, and pyridine; The first polar solvent is selected from any one of water, dimethyl sulfoxide, N,N-dimethylformamide, and dioxane.

7. A method for preparing a modified polyvinyl alcohol optical film, characterized in that: include: dissolving the modified polyvinyl alcohol according to any one of claims 1 to 6 in a second polar solvent, and performing solvent volatilization to form a film to obtain a modified polyvinyl alcohol film; The modified polyvinyl alcohol film is stretched, quenched and shaped to obtain a modified polyvinyl alcohol optical film.

8. The preparation method according to claim 7, characterized in that The mass ratio of the modified polyvinyl alcohol to the second polar solvent is 1:1-20; The second polar solvent is selected from any one of N,N-dimethylformamide, dimethyl sulfoxide, N,N-dimethylformamide, acetone, and diethyl ether.

9. A modified polyvinyl alcohol optical film, characterized in that: Prepared by the preparation method according to any one of claims 7-8.

10. Use of the modified polyvinyl alcohol optical film according to claim 9 in the field of optics.

Images