Thermochromic aviation organic glass and preparation method thereof

Abstract

The invention relates to thermochromic aviation organic glass and a preparation method thereof. The thermochromic aviation organic glass comprises a polymethyl methacrylate matrix and a thermochromic compound distributed in the polymethyl methacrylate matrix, the thermochromic compound is distributed in the polymethyl methacrylate matrix in at least one of the following modes: the thermochromic compound is distributed in the polymethyl methacrylate matrix; the thermochromic compound is distributed in the polymethyl methacrylate matrix through a copolymerization reaction between an unsaturated unit and a methyl methacrylate monomer for preparing the polymethyl methacrylate matrix; the thermochromic compound is distributed in the polymethyl methacrylate matrix through ring-opening reaction of the functional monomer. The thermochromic aviation organic glass is stable, reliable and good in high temperature resistance.

Description

Technical Field

[0001] This application relates to the field of acrylic glass technology, specifically to a thermochromic aviation acrylic glass and its preparation method. Background Technology

[0002] Color plays an indispensable role in nature and human society, enhancing the visual presentation of both natural and artificial environments and providing crucial support for information transmission, target recognition, and environmental perception. Compared to traditional static color materials, color-changing materials exhibit superior stimulus-response characteristics, adjustable performance, and design flexibility, demonstrating more prominent application advantages and overcoming the functional limitations of static materials. In particular, the color of stimulus-responsive color-changing materials can change in response to external stimuli (such as heat, force, and light), showing broad prospects in optical sensors, smart coatings, and information storage. Taking thermochromic materials as an example, their reversible color or performance transformation characteristics in thermal response have significant application value in various scenarios. For instance, in intelligent control, they can be used for thermal response optical adjustment in smart windows and temperature-controlled coatings, breaking through the limitations of traditional materials and providing a new thermal response core module for the smart materials industry, driving related technologies towards precision and self-adaptation. However, despite significant progress in these areas, thermochromic materials still face some important challenges, such as the precipitation of color-changing materials during long-term use, which limits further applications.

[0003] Therefore, there is an urgent need to develop thermoresponsive color-changing materials that can overcome the aforementioned limitations, providing stable, reliable, and temperature-resistant color-changing performance to meet practical applications. Acrylic glass, scientifically known as polymethyl methacrylate (PMMA), is an advantageous matrix for color-changing materials due to its excellent light transmittance (>92%), good processing performance, and superior outdoor anti-aging properties. For aerospace materials with extremely stringent requirements in the industrial field, such as aerospace acrylic glass (e.g., cockpit canopies, windows, or windshields), as one of the core components of aircraft, the integrity of its function and the richness of its colors directly affect the passenger's flight experience. Therefore, developing thermoresponsive color-changing aerospace acrylic glass to achieve diversified color control and further enhance the passenger's flight experience has significant application value and extremely high technical challenges. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a stable and reliable thermochromic aviation acrylic glass.

[0005] To address the aforementioned technical problems, this application provides a thermochromic aviation acrylic glass, comprising a polymethyl methacrylate (PMMA) matrix and a thermochromic compound distributed within the PMMA matrix; wherein the thermochromic compound is distributed within the PMMA matrix through at least one of the following methods: The thermochromic compound is distributed in the polymethyl methacrylate matrix by copolymerization of unsaturated units with methyl methacrylate monomers used to prepare the polymethyl methacrylate matrix; The thermochromic compound is distributed in the polymethyl methacrylate matrix through a ring-opening reaction of a functional monomer.

[0006] In some embodiments, the functional monomer includes at least one of a first functional monomer and a second functional monomer, and the thermochromic compound undergoes a ring-opening reaction with the first functional monomer via an epoxy group unit; the thermochromic compound undergoes a ring-opening reaction with the second functional monomer via a tertiary amine group unit.

[0007] In some embodiments, the thermochromic compound accounts for ≤30% by mass, and the polymethyl methacrylate matrix accounts for ≥60% by mass.

[0008] In some embodiments, the first functional monomer is a compound containing a maleimide group, and the second functional monomer is an unsaturated compound containing an epoxy group.

[0009] This application also provides a method for preparing thermochromic aviation acrylic glass, comprising the following steps: S1: Provide methyl methacrylate monomer and prepolymerize the methyl methacrylate monomer to obtain a matrix material; S2: Prepare a homogeneous mixture, the homogeneous mixture comprising the matrix material, an initiator, and at least one of the following components: a thermochromic compound having unsaturated units; a thermochromic compound undergoing a ring-opening reaction via a functional monomer; S3: The homogeneous mixture is cured to distribute the thermochromic compound in the polymethyl methacrylate matrix in at least one of the following ways: by copolymerizing the unsaturated unit with the methyl methacrylate monomer in the matrix material to distribute the thermochromic compound in the polymethyl methacrylate matrix; or by performing a ring-opening reaction of the functional monomer to distribute the thermochromic compound in the polymethyl methacrylate matrix, thereby obtaining the thermochromic aviation acrylic glass.

[0010] In some embodiments, the functional monomer includes at least one of a first functional monomer and a second functional monomer, and the thermochromic compound that undergoes a ring-opening reaction through the functional monomer includes at least one of the following: a thermochromic compound having an epoxy group and a thermochromic compound having a tertiary amino group; wherein, the thermochromic compound having an epoxy group undergoes a ring-opening reaction with the first functional monomer through the epoxy group, and the thermochromic compound having a tertiary amino group undergoes a ring-opening reaction with the second functional monomer through the tertiary amino group.

[0011] In some embodiments, step S1, the prepolymerization of the methyl methacrylate monomer to obtain the matrix material, includes at least one of the following: The thermochromic compound with unsaturated units, the initiator, and the methyl methacrylate monomer are mixed and then subjected to a polymerization reaction to form a precursor mixture containing the polymerization precursor to obtain the matrix material. The thermochromic compound having epoxy units, the initiator, and the methyl methacrylate monomer are mixed and then subjected to a polymerization reaction to form a precursor mixture containing the polymerization precursor to obtain the matrix material. The thermochromic compound having tertiary amine units, the initiator, and the methyl methacrylate monomer are mixed and then subjected to a polymerization reaction to form a precursor mixture containing the polymerization precursor to obtain the matrix material. The ratio of the amount of at least one of the thermochromic compound having unsaturated units, the thermochromic compound having epoxy units, and the thermochromic compound having tertiary amine units to the amount of the methyl methacrylate monomer is less than or equal to 1:10.

[0012] In some embodiments, the method further includes a step of modifying and preparing a thermochromic compound, wherein the step of modifying and preparing a thermochromic compound includes: Prepare an organic solution containing initial molecules with thermochromic properties; The modified molecule is added to the organic solution, and the reaction is carried out under heat. After the reaction is completed, the mixture is washed, separated and purified to obtain a thermochromic compound with unsaturated units, a thermochromic compound with epoxy units, or a thermochromic compound with tertiary amine units.

[0013] In some embodiments, in the homogeneous mixture, at least one of the thermochromic compound having unsaturated units and the thermochromic compound undergoing a ring-opening reaction via a functional monomer is present in a mass ratio of (5~30):(60~90) to the matrix material; the molar ratio of the functional monomer to the thermochromic compound undergoing a ring-opening reaction via the functional monomer is 1:1; and the initiator has a mass percentage of ≤0.6% in the homogeneous mixture.

[0014] In some embodiments, the step of curing the homogeneous mixture includes: a water bath at 35-65°C for 12-120 h, followed by a forced-air bath at 105-135°C for 10-80 h.

[0015] In the thermochromic aviation acrylic glass of this application, the thermochromic compound co-phase participates in the polymerization reaction to form the acrylic glass, and / or the thermochromic compound is stably distributed in the polymethyl methacrylate matrix through a ring-opening reaction. Both of these bonding methods enable the thermochromic compound and the polymethyl methacrylate matrix to be chemically bonded to each other, forming a strong whole and eliminating the generation of free state. This effectively solves the problem of color-changing material precipitation under long-term use conditions in the prior art, and is stable and reliable.

[0016] Furthermore, epoxy groups and maleimide groups are often used as functional additives for the temperature resistance modification of polymer materials, especially maleimide groups, which are particularly effective as temperature resistance modification units. In this technical solution, both epoxy groups and maleimide groups are uniformly distributed in the plexiglass matrix through chemical bonding, thus ensuring stability, reliability, and good improvement in high-temperature resistance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the ring-opening reaction process between the epoxy group unit and the first functional monomer in this application.

[0018] Figure 2 This is a schematic flowchart of the preparation method of the thermochromic aviation acrylic glass in this application.

[0019] Figure 3 This is a schematic diagram of the process for preparing thermochromic compounds by modification in this application.

[0020] Figure 4 This is a schematic diagram of the key reaction process involved in Example 1 of this application.

[0021] Figure 5 This is a schematic diagram of the key reaction process involved in Example 2 of this application.

[0022] Figure 6 This is a schematic diagram illustrating the mechanism of the thermochromic process of the thermochromic aviation acrylic glass in Examples 1 to 5 of this application. Detailed Implementation

[0023] The following specific embodiments illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification.

[0024] In the following description, reference is made to the accompanying drawings, which illustrate several embodiments of the present application. It should be understood that other embodiments may also be used, and changes in mechanical composition, structure, electrical and operational aspects may be made without departing from the spirit and scope of the present application. The following detailed description should not be considered limiting, and the terminology used herein is for describing particular embodiments only and is not intended to limit the present application.

[0025] Although the terms first, second, etc., are used in some instances to describe various elements herein, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0026] Furthermore, as used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context indicates otherwise. It should be further understood that the terms “comprising,” “including,” indicate the presence of the stated feature, step, operation, element, component, item, kind, and / or group, but do not preclude the presence, occurrence, or addition of one or more other features, steps, operations, elements, components, items, kinds, and / or groups. The terms “or” and “and / or” as used herein are to be interpreted inclusively, or mean any one or any combination thereof. Thus, “A, B, or C” or “A, B, and / or C” means “any one of: A; B; C; A and B; A and C; B and C; A, B, and C.” Exceptions to this definition occur only when combinations of elements, functions, steps, or operations are inherently mutually exclusive in some way.

[0027] Some embodiments of this application provide a thermochromic aviation acrylic glass, which includes a polymethyl methacrylate (PMMA) matrix and a thermochromic compound distributed in the PMMA matrix. The thermochromic compound is distributed in the PMMA matrix in at least one of the following ways: The thermochromic compound is distributed in the polymethyl methacrylate matrix through a copolymerization reaction between unsaturated units and methyl methacrylate monomers used to prepare the polymethyl methacrylate matrix; The thermochromic compound is distributed in the polymethyl methacrylate matrix through a ring-opening reaction of the functional monomer.

[0028] Thermochromic compounds are distributed in the polymethyl methacrylate matrix, giving the acrylic glass matrix thermochromic properties. When this thermochromic acrylic glass is applied to the aerospace field, it can achieve diversified color control of aerospace acrylic glass parts and improve the color richness of aerospace transparent parts.

[0029] Methyl methacrylate monomers possess unsaturated units. Thermochromic compounds, through these unsaturated units, directly copolymerize with the methyl methacrylate monomers used to prepare the polymethyl methacrylate matrix, thus distributing themselves within the polymethyl methacrylate matrix. This means the thermochromic compounds participate in the polymerization reaction to form the acrylic glass, and the thermochromic compounds and the polymethyl methacrylate matrix are chemically bonded together. This ensures the stable distribution of the thermochromic compounds within the polymethyl methacrylate matrix, effectively preventing or reducing the precipitation of thermochromic compounds under long-term use conditions. Therefore, this thermochromic aviation acrylic glass is stable and reliable.

[0030] Methyl methacrylate monomers have unsaturated units. One end of the functional monomer undergoes a ring-opening reaction with the thermochromic compound, while the other end can copolymerize with the methyl methacrylate monomer. This chemical bonding method also allows the thermochromic compound to be stably distributed in the polymethyl methacrylate matrix, resulting in stable and reliable thermochromic aerospace acrylic glass.

[0031] In some embodiments, the functional monomer includes at least one of a first functional monomer and a second functional monomer. The thermochromic compound has an epoxy group, which is distributed within a polymethyl methacrylate (PMMA) matrix through a ring-opening reaction with the first functional monomer and copolymerization with the PMMA monomer. Alternatively, the thermochromic compound has a tertiary amine group, which is distributed within a PMMA matrix through a ring-opening reaction with the second functional monomer and copolymerization with the PMMA monomer. In both methods, the thermochromic compound and the PMMA matrix are chemically bonded together, enabling the thermochromic compound to be stably distributed within the PMMA matrix, thus ensuring the stability and reliability of the thermochromic aerospace acrylic glass. Furthermore, epoxy groups and maleimide groups are commonly used as functional additives for the temperature resistance modification of polymer materials. Maleimide groups, in particular, are more effective as temperature resistance modification units, thereby improving the high-temperature resistance of the thermochromic aerospace acrylic glass.

[0032] It should be noted that thermochromic compounds can be distributed in the polymethyl methacrylate (PMMA) matrix solely through copolymerization, or solely through ring-opening reactions, or both copolymerization and ring-opening reactions can be used simultaneously to distribute different types of thermochromic compounds in the PMMA matrix. In both the single ring-opening reaction and the simultaneous copolymerization and ring-opening reaction methods, the reaction can be carried out with at least one of the first and second functional monomers.

[0033] It should also be noted that when both copolymerization and ring-opening reactions are used to distribute the thermochromic compound into the polymethyl methacrylate matrix, this application does not limit the ratio of copolymerization to ring-opening reactions, that is, it does not limit the mass ratio of the thermochromic compound containing unsaturated units, the thermochromic compound containing epoxy groups, and / or the thermochromic compound containing tertiary amine groups. When the thermochromic compound is distributed into the polymethyl methacrylate matrix using only a ring-opening reaction, there is no limitation on the mass ratio of the thermochromic compound containing epoxy groups to the thermochromic compound containing tertiary amine groups. For example, in a thermochromic compound, the mass percentage of the thermochromic compound containing epoxy groups can be 100%, and correspondingly, the mass percentage of the thermochromic compound containing tertiary amine groups can be 0%; conversely, the mass percentage of the thermochromic compound containing epoxy groups can be 0%, while the mass percentage of the thermochromic compound containing tertiary amine groups can be 100%; or, both the mass percentages of the thermochromic compound containing epoxy groups and the mass percentages of the thermochromic compound containing tertiary amine groups can be other percentages greater than 0% and less than 100%. Regardless of the type of thermochromic compound or the ratio of different types of thermochromic compounds, the thermochromic compound can be stably and reliably distributed in the polymethyl methacrylate matrix.

[0034] Simultaneously, copolymerization and ring-opening reactions are used to distribute different types of thermochromic compounds in the polymethyl methacrylate matrix. With the thermochromic compounds stably distributed in the polymethyl methacrylate matrix precursor, more different thermochromic compounds can be selected. Through appropriate ratios, the thermochromic properties can be better adjusted. For example, by combining RGB (red, green, blue), the color diversification of aerospace acrylic parts can be achieved.

[0035] In some embodiments, when the thermochromic compound itself has unsaturated units, the thermochromic compound is directly used to copolymerize with methyl methacrylate monomers and distributed in the polymethyl methacrylate matrix.

[0036] In some embodiments, the initial molecule having thermochromic function is unsaturated to obtain a thermochromic compound having unsaturated units.

[0037] In some embodiments, when the thermochromic compound itself has epoxy units or when the initial molecule with thermochromic function is epoxidized to obtain a thermochromic compound with epoxy units, the thermochromic compound is linked to the polymethyl methacrylate matrix by a ring-opening reaction through a first functional monomer.

[0038] In some embodiments, when the thermochromic compound itself has a tertiary amine unit or when the initial molecule with thermochromic function is modified by tertiary amineization to obtain a thermochromic compound having a tertiary amine unit, the connection between the thermochromic compound and the polymethyl methacrylate matrix is ​​achieved by ring-opening reaction through a second functional monomer.

[0039] In some embodiments, the initial molecule having thermochromic properties is selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons, and triarylmethanes.

[0040] In some embodiments, the initial molecule with thermochromic function is N,N'-bis(salicylylene)-1,2-propanediamine (Schiff base), 1,3-dihydro-8-methoxy-1,3,3-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2-(2H)-indole] (spirocyclic compound), salicylates aniline (Schiff base), dianthrone (fused-ring aromatic hydrocarbon), and crystal violet lactone (triarylmethane).

[0041] In some embodiments, the thermochromic compound having an unsaturated unit, an epoxy unit, or a tertiary amine unit is also selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons, and triarylmethanes.

[0042] In some embodiments, the thermochromic compound having a tertiary amine unit is selected from at least one of 1',3'-dihydro-8-methoxy-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-[2H]indole] and crystal violet lactone. Thermochromic compounds having epoxy or unsaturated units are preferably obtained through modification.

[0043] In some embodiments, the first functional monomer is a compound containing a maleimide group. The first functional monomer can react with methyl methacrylate (MMA) and the epoxy unit of the thermochromic compound, respectively. That is, one end of the first functional unit is connected to the thermochromic compound and the other end is connected to the polymethyl methacrylate matrix, so that the thermochromic compound is stably distributed in the polymethyl methacrylate matrix.

[0044] The ring-opening reaction process of the epoxy group unit with the first functional monomer is as follows: Figure 1 As shown, since the nitrogen atom in the maleimide group is connected by three single bonds, it belongs to the tertiary amine class. Although tertiary amines lack active hydrogen, they catalyze the ring-opening of epoxy groups, and therefore can also be used as catalysts for epoxides. The suitable temperature for this ring-opening reaction is 70-80 °C, and the reaction conditions are relatively mild.

[0045] Furthermore, since the first functional monomer contains maleimide groups, when it is selected as the linking medium, a cyclic structure is introduced into the main chain of the polymethyl methacrylate matrix. This strongly inhibits the movement of matrix chain segments, thereby increasing the glass transition temperature of polymethyl methacrylate and improving the heat resistance of the acrylic glass. In addition, because the volume shrinkage rate during the epoxy compound curing process is extremely low and high transparency can be maintained, the above reaction not only improves heat resistance but also enhances the dimensional stability of the product.

[0046] Furthermore, the maleimide group also contains unsaturated units, which can directly copolymerize with methyl methacrylate to achieve chemical bonding, thus improving the anti-precipitation stability of thermochromic aerospace acrylic glass.

[0047] In some embodiments, the first functional monomer is selected from at least one of N-methylmaleimide, N-cyclohexylmaleimide, N-phenylmaleimide, N-benzylmaleimide, N-(4-fluorophenyl)maleimide, N-(2-hydroxyethyl)maleimide and N-(methoxycarbonyl)maleimide.

[0048] In some embodiments, the second functional monomer is an unsaturated compound containing an epoxy group. The second functional monomer can react with methyl methacrylate (MMA) and the tertiary amine unit of the thermochromic compound, respectively. That is, one end of the second functional unit is connected to the thermochromic compound and the other end is connected to the polymethyl methacrylate matrix, so that the thermochromic compound is stably distributed in the polymethyl methacrylate matrix.

[0049] In one embodiment, the second functional monomer is selected from at least one of glycidyl methacrylate, allyl glycidyl ether, 4-hydroxybutyl acrylate glycidyl ether, and glycidyl acrylate.

[0050] In the above embodiments, the ring-opening reaction occurs between the epoxy unit and the tertiary amine unit; that is, one of the thermochromic compound and the functional monomer has an epoxy unit, and the other has a tertiary amine unit. Since the conditions (temperature and time) for the ring-opening reaction between the epoxy unit and the tertiary amine unit are completely covered by the polymerization process of the methyl methacrylate monomer, the entire ring-opening reaction can be completed during the bulk polymerization of the methyl methacrylate monomer, thus allowing for a more efficient overall polymerization process. In other embodiments, the ring-opening reaction may not be limited to the epoxy unit and the tertiary amine unit; for example, it may occur between the epoxy unit and an anhydride compound.

[0051] In some embodiments, the mass percentage of the thermochromic compound is ≤30%, and the mass percentage of the polymethyl methacrylate matrix is ​​≥60%. Preferably, the mass percentage of the thermochromic compound is ≤6%, and the mass percentage of the polymethyl methacrylate matrix is ​​≥90%, in order to balance the thermochromic function and optical performance of the acrylic glass. Since the thermochromic compound is distributed in the polymethyl methacrylate matrix in a chemically bonded form, its presence has very little interference with the physical and mechanical properties of the acrylic glass. The limited range of the mass percentage takes into account the impact on light transmittance (which needs to meet the application requirements of aerospace acrylic glass).

[0052] Please see Figure 2 This application also provides a method for preparing thermochromic aviation acrylic glass, comprising the following steps: S1: Provide methyl methacrylate monomer and prepolymerize the methyl methacrylate monomer to obtain the matrix material.

[0053] In this step, methyl methacrylate monomers are first prepolymerized (the reaction temperature is maintained at 60-80 °C until the required viscosity is reached, at which point heating is stopped and the mixture is cooled to end the prepolymerization process), forming a precursor mixture containing the polymerization precursors to obtain the matrix material. Prepolymerization, resulting in a matrix material with a certain viscosity, allows for the pre-release of some of the heat of reaction compared to direct polymerization and curing. This helps improve the overall heat release process during polymerization, prevents violent reactions caused by instantaneous overheating (i.e., explosive polymerization), and facilitates control over the quality of the finished product.

[0054] In some embodiments, a thermochromic compound is also added in step S1. The thermochromic compound, initiator, and methyl methacrylate monomer are mixed and then subjected to a polymerization reaction to form a precursor mixture containing the polymerization precursor to obtain the matrix material.

[0055] In some embodiments, the viscosity of the matrix material is such that the flow time at 25°C is 20 to 120 s for the Coat 4 cup.

[0056] In some embodiments, the initiator (in this case, only a low-temperature initiator is used) accounts for less than or equal to 0.2% by mass in the mixture of the thermochromic compound, the initiator, and methyl methacrylate.

[0057] In some embodiments, the low-temperature initiator is selected from at least one of benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), and azobisisoheptanenitrile (ABVN).

[0058] In some embodiments, the conversion rate of methyl methacrylate in the precursor mixture comprising the polymerization precursor is 5 to 20%.

[0059] In the prepolymerization step, a thermochromic compound is also added, and methyl methacrylate and the thermochromic compound are reacted to obtain a precursor mixture. By introducing the thermochromic compound into the polymer chain of the partially polymerized precursor, the thermochromic compound can be more uniformly distributed in the final board.

[0060] In some embodiments, the molar ratio of the thermochromic compound to the methyl methacrylate monomer is less than or equal to 1:10. At this ratio, the thermochromic compound can achieve a substantially complete reaction.

[0061] The thermochromic compound is selected from at least one of thermochromic compounds containing unsaturated units, thermochromic compounds containing epoxy units, and thermochromic compounds containing tertiary amine units.

[0062] That is, in step S1, the operation of prepolymerizing methyl methacrylate monomer to obtain the matrix material includes at least one of the following: A thermochromic compound with unsaturated units, an initiator, and methyl methacrylate monomer are mixed and polymerized to form a precursor mixture containing the polymerization precursor to obtain the matrix material. A thermochromic compound with epoxy units, an initiator, and a methyl methacrylate monomer are mixed and polymerized to form a precursor mixture containing the polymerization precursor to obtain a matrix material. A thermochromic compound with tertiary amino units, an initiator, and methyl methacrylate monomer are mixed and polymerized to form a precursor mixture containing the polymerization precursor to obtain the matrix material.

[0063] The ratio of the amount of thermochromic compound to the amount of methyl methacrylate monomer mentioned above is less than or equal to 1:10. Specifically, this means that when only one type of thermochromic compound is used, the ratio of the amount of that thermochromic compound to the amount of methyl methacrylate monomer is less than or equal to 1:10; when two or more different types of thermochromic compounds are used, the ratio of the sum of the amounts of the two or more different types of thermochromic compounds to the amount of methyl methacrylate monomer is less than or equal to 1:10.

[0064] In some embodiments, at least one of the following is selected: a thermochromic compound having an unsaturated unit, a thermochromic compound having an epoxy unit, or a thermochromic compound having a tertiary amine unit.

[0065] In some embodiments, the initial molecule having thermochromic function can be modified to obtain a thermochromic compound having an unsaturated unit, a thermochromic compound having an epoxy group unit, or a thermochromic compound having a tertiary amine group unit, thereby selecting at least one of the above three modified products.

[0066] like Figure 3 As shown, in some embodiments, the steps for modifying and preparing thermochromic compounds include: S11: An organic solution for preparing initial molecules with thermochromic properties.

[0067] An organic solution is prepared by dissolving the initial molecule with thermochromic properties in an organic solvent.

[0068] In some embodiments, the initial molecule having thermochromic properties is selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons, and triarylmethanes.

[0069] In some embodiments, the organic solvent is selected from at least one of ethyl acetate, ethanol, butyl acetate, methanol, acetone, and isobutanol.

[0070] In some embodiments, the mass concentration of the organic solution is 5%, that is, the mass concentration of the initial molecule with thermochromic function in the solution is 5%.

[0071] S12: Add the modified molecule to the organic solution, keep it at a constant temperature for the reaction, and after the reaction is complete, wash, separate and purify to obtain a thermochromic compound with unsaturated units or a thermochromic compound with epoxy units.

[0072] In some embodiments, the process further includes adding an acid-binding agent. The acid-binding agent is used to adsorb and capture acidic leaving products and precipitated salt compounds generated during the substitution reaction, thereby promoting the forward progress of the reaction.

[0073] The acid-binding agent is an organic amine. In some embodiments, the acid-binding agent is selected from at least one of triethylamine, diisopropylethylamine, and pyridine. In some embodiments, the mass of the acid-binding agent is 0.5% to 2% of the mass of the organic solution.

[0074] Specifically, an acid-binding agent is added to the organic solution obtained in step S11, and the mixture is mixed evenly to obtain a mixed solution. After adjusting the mixed solution to a preset temperature, a modified molecule is added to the mixed solution, and a heat-preserving reaction is carried out. After purification, a thermochromic compound is obtained.

[0075] In some embodiments, the chemical structure of the modified molecule includes an active group and an unsaturated unit, or includes an active group and an epoxy group. The active group includes one of acyl chloride, acyl bromide, acid anhydride, methoxysilane, ethoxysilane, chlorosilane, and isocyanate groups.

[0076] In some embodiments, the chemical structure of the modified molecule includes an active group and an unsaturated unit.

[0077] When the active group is an acyl chloride or acyl bromide, the modified molecule is selected from one of methacryloyl chloride, but-3-enoyl chloride, 10-undecenoyl chloride, oxalyl chloride monoallyl ester, allyl chloroformate, hexaallyl chloride, acryloyl chloride, acryloyl bromide and methacryloyl bromide.

[0078] When the active group is an acid anhydride, the modified molecule is selected from one of methacrylic anhydride, maleic anhydride, allyl succinic anhydride, (2-methyl-2-propenyl) succinic anhydride, 2-buten-1-yl succinic anhydride, (2,7-octadien-1-yl) succinic anhydride, 2-octenyl succinic anhydride, and octadecenyl succinic anhydride.

[0079] When the active group is methoxysilane, ethoxysilane, or chlorosilane, the modified molecule is selected from one of the following: methyl methacrylate (triethoxysilyl), methyl methacrylate (dimethoxy(methyl)silyl), propyl 3-[dimethoxy(methyl)silyl]methacrylate, propyl 3-(trimethoxysilyl)acrylate, propyl 3-[diethoxy(methyl)silyl]methacrylate, allyltrimethoxysilane, propyl 3-(trimethoxysilyl)propyl vinylcarbamate, propyl 3-(ethoxydimethylsilyl)methacrylate, allyldimethylchlorosilane, allyl(dichloro)methylsilane, allyltrichlorosilane, norbornene-alkenylethyltrichlorosilane, and methylphenylvinylchlorosilane.

[0080] When the active group is an isocyanate group, the modified molecule is selected from allyl isocyanate, 3-isopropenyl-α,α-dimethylbenzyl isocyanate and isocyanoethyl methacrylate.

[0081] In some embodiments, the chemical structure of the modified molecule includes an active group and an epoxy unit.

[0082] Wherein, when the active group is methoxysilane, ethoxysilane or chlorosilane, the modified molecule is selected from one of the following: triethoxy(3-epoxypropyloxypropyl)silane, trimethoxy(3-epoxypropyloxypropyl)silane, 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane, 3-[(2,3)-epoxypropoxy]propylmethyldiethoxysilane, [8-(epoxypropyloxy)-n-octyl]trimethoxysilane, [8-(epoxypropyloxy)-n-octyl]triethoxysilane, diethoxy(3-glycidyloxypropyl)methylsilane, dimethoxy(3-glycidyloxypropyl)methylsilane, 3-glycidyloxypropyltrimethoxysilane and 3-glycidyloxypropyltriethoxysilane.

[0083] In some embodiments, the mass ratio of the modified molecule to the initial molecule having thermochromic properties is 2:1 to 1:1.

[0084] In some embodiments, the preset temperature is 30~50 ℃.

[0085] In some embodiments, the reaction time is 30 to 60 minutes.

[0086] It should be noted that the thermochromic compounds used in this step can be of a single type or multiple types. For example, the thermochromic compound can be only a thermochromic compound with unsaturated units, or it can include at least one of thermochromic compounds with unsaturated units, thermochromic compounds with epoxy groups, and thermochromic compounds with tertiary amine groups. When using multiple thermochromic compounds, the ratio of the various types of thermochromic compounds is not limited, as long as the mass of the various thermochromic compounds meets the requirements.

[0087] S2: Preparation of a homogeneous mixture; the homogeneous mixture includes a matrix material, an initiator, and at least one of the following components: a thermochromic compound having unsaturated units or a thermochromic compound undergoing a ring-opening reaction via a functional monomer.

[0088] In some embodiments, the homogeneous mixture includes a matrix material, a thermochromic compound having unsaturated units, and an initiator. In other embodiments, the homogeneous mixture includes a matrix material, a thermochromic compound undergoing a ring-opening reaction via a functional monomer, and an initiator.

[0089] When the homogeneous mixture includes a thermochromic compound that undergoes a ring-opening reaction via a functional monomer, it also includes a functional monomer to allow the functional monomer to react with the thermochromic compound and a methyl methacrylate monomer.

[0090] Regardless of whether a thermochromic compound is added in step S1, a thermochromic compound is added in step S2. When a thermochromic compound is added in step S1, the thermochromic compound added in step S2 can be the same as or different from the thermochromic compound in step S1.

[0091] In some embodiments, regardless of the type of thermochromic compound added, the mass ratio of the thermochromic compound added in step S2 to the matrix material in the homogeneous mixture is (5~30):(60~90). That is, the mass ratio of at least one of the thermochromic compound having unsaturated units and the thermochromic compound undergoing ring-opening reaction through a functional monomer to the matrix material is (5~30):(60~90). More specifically, the thermochromic compound having unsaturated units or the thermochromic compound undergoing ring-opening reaction through a functional monomer:matrix material = (5~30):(60~90); or, (thermochromic compound having unsaturated units + thermochromic compound undergoing ring-opening reaction through a functional monomer):matrix material = (5~30):(60~90).

[0092] In some embodiments, when the thermochromic compound added in step S2 includes at least two types, there are no requirements on the ratio of different types of thermochromic compounds. It is only necessary that the total amount of the added thermochromic compound meets certain requirements so that the thermochromic aviation plexiglass prepared subsequently has the function of thermo-responsive color change and meets the corresponding performance requirements.

[0093] When the thermochromic compound added in step S2 includes only thermochromic compounds with unsaturated units, the thermochromic compound with unsaturated units is mixed with the matrix material and the initiator to prepare a homogeneous mixture.

[0094] In some embodiments, the functional unit includes a first functional unit and a second functional unit, which are the same as the first functional unit and the second functional unit described above, and will not be repeated here.

[0095] When the thermochromic compound added in step S2 includes at least one of a thermochromic compound having an epoxy group and a thermochromic compound having a tertiary amine group, and includes a thermochromic compound having an unsaturated unit; or when the thermochromic compound added in step S2 includes only at least one of a thermochromic compound having an epoxy group and a thermochromic compound having a tertiary amine group, at least one of the first functional unit and the second functional unit is mixed with the matrix material and the initiator to prepare a homogeneous mixture.

[0096] The general principle is that when the mixed system for preparing thermochromic aviation acrylic glass contains thermochromic compounds with epoxy groups, a first functional unit is required to react with it; when the mixed system for preparing thermochromic aviation acrylic glass contains thermochromic compounds with tertiary amine groups, a second functional unit is required to react with it; so that the thermochromic compounds can be stably and reliably distributed in the prepared thermochromic aviation acrylic glass.

[0097] In some embodiments, the molar ratio of at least one of the first and second functional monomers in step S2 to the thermochromic compound added in this step that undergoes a ring-opening reaction via the functional monomer is 2:1 to 1:2. That is, taking a 1:1 molar ratio as an example, when only the first functional monomer is included, the ratio of the first functional monomer to the thermochromic compound containing an epoxy group is 1:1 (molar amount); when only the second functional monomer is included, the ratio of the second functional monomer to the thermochromic compound containing a tertiary amine group is 1:1 (molar amount); when both the first and second functional monomers are included, the ratio of (first functional monomer + second functional monomer) to (thermochromic compound containing an epoxy group + thermochromic compound containing a tertiary amine group) is 1:1 (molar amount). When only one type of thermochromic compound and corresponding functional monomer is used, the amounts of substances in the ratio are the amounts of the single thermochromic compound and the corresponding functional monomer, respectively. When at least two types of thermochromic compounds and corresponding functional monomers are used simultaneously, the amounts of substances in the ratio are the sum of the amounts of the functional monomers corresponding to the sum of the amounts of the at least two types of thermochromic compounds.

[0098] The above description illustrates the ratio of functional monomer to thermochromic compound using the example of the functional monomer being selected from at least one of the first and second functional monomers. It can be understood that in other embodiments, the above ratio also applies when the functional monomer is selected from other functional monomers different from the first and second functional monomers.

[0099] In some embodiments, the initiator accounts for ≤0.6% of the mass of the homogeneous mixture.

[0100] In some embodiments, the initiator includes a low-temperature initiator and a high-temperature initiator. The low-temperature initiator is selected from at least one of benzoyl peroxide (BPO), azobisisobutyronitrile (AIBN), and azobisisoheptanenitrile (ABVN); the high-temperature initiator is selected from at least one of dicumyl peroxide, di-tert-butyl peroxide, and tert-butyl peroxide.

[0101] It should be noted that when the thermochromic compound is not required in step S1, or the thermochromic compound to be added does not need to be obtained through modification, and the thermochromic compound obtained through modification is required in step S2, the order of the above-mentioned steps for preparing the thermochromic compound through modification and step S1 is not limited. The thermochromic compound can be prepared through modification first, or the prepolymerization in step S1 can be performed first, or the modification and prepolymerization can be performed simultaneously.

[0102] S3: The homogeneous mixture is cured to distribute the thermochromic compound in the polymethyl methacrylate matrix in at least one of the following ways: by copolymerizing the thermochromic compound with the methyl methacrylate monomer in the matrix material through unsaturated units; or by performing a ring-opening reaction with a functional monomer to distribute the thermochromic compound in the polymethyl methacrylate matrix, thereby obtaining thermochromic aerospace acrylic glass.

[0103] The homogeneous mixture obtained in step S2 is cured. During the curing process, the thermochromic compound with unsaturated units undergoes a copolymerization reaction with the methyl methacrylate monomer in the matrix material. At the same time, the matrix material polymerizes to form a polymethyl methacrylate matrix, thereby distributing the thermochromic compound in the polymethyl methacrylate matrix to obtain thermochromic aviation acrylic glass.

[0104] And / or, during the curing process, the matrix material polymerizes to form a polymethyl methacrylate matrix. Simultaneously, a thermochromic compound with epoxy units undergoes a ring-opening reaction with a first functional monomer through the epoxy units. One end of the first functional monomer undergoes a ring-opening reaction with the thermochromic compound, while the other end can copolymerize with the methyl methacrylate monomer. This allows the first functional monomer to act as a connecting medium, linking the thermochromic compound to the polymethyl methacrylate, thereby distributing the thermochromic compound within the polymethyl methacrylate matrix and obtaining thermochromic aerospace acrylic glass.

[0105] And / or, during the curing process, the matrix material polymerizes to form a polymethyl methacrylate matrix. Simultaneously, the thermochromic compound having tertiary amine units undergoes a ring-opening reaction with a second functional monomer through the tertiary amine units. One end of the second functional monomer undergoes a ring-opening reaction with the thermochromic compound, while the other end can copolymerize with the methyl methacrylate monomer. This allows the second functional monomer to act as a connecting medium, linking the thermochromic compound to the polymethyl methacrylate, thereby distributing the thermochromic compound on the polymethyl methacrylate matrix and obtaining thermochromic aerospace acrylic glass.

[0106] The first and second functional monomers have unsaturated bonds and can copolymerize with methyl methacrylate. Therefore, by reacting at least one of the first and second functional monomers with the thermochromic compound and the methyl methacrylate matrix, the thermochromic compound can be reliably attached to the polymethyl methacrylate matrix. Furthermore, by utilizing the physical properties of the introduced maleimide or epoxy groups (which can improve heat resistance and dimensional stability) after using the first and second functional monomers, the heat resistance and dimensional stability of polymethyl methacrylate acrylic glass during storage can be improved.

[0107] In some embodiments, the step of curing the homogeneous mixture includes: water bath at 35-65°C for 12-120 h, followed by forced air bath at 105-135°C for 10-80 h.

[0108] In some embodiments, the step of a forced-air bath at 105-135°C for 10-80 h includes a continuous forced-air bath at 100°C for 5-60 h, a continuous forced-air bath at 120°C for 3-15 h, and a continuous forced-air bath at 135°C for 2-5 h.

[0109] The above-mentioned method for preparing thermochromic aerospace acrylic glass involves distributing thermochromic compounds within a polymethyl methacrylate (PMMA) matrix through copolymerization and / or ring-opening reactions. This method not only reliably links the thermochromic compounds to PMMA but also preserves the thermo-responsive color-changing functional structure of the compounds themselves (the highest temperature condition during the entire reaction process is 135 °C for several hours, which does not damage the structure of the thermochromic compounds selected in this scheme). Therefore, it can produce thermochromic aerospace acrylic glass with stable and reliable performance.

[0110] When the above-mentioned method for preparing thermochromic aviation acrylic glass uses a thermochromic compound that is coordinated with at least one of the first and second functional monomers, the entire ring-opening reaction can be completed during the bulk polymerization reaction of methyl methacrylate monomer. This method can efficiently prepare thermochromic aviation acrylic glass with stable and reliable performance and superior high-temperature resistance.

[0111] The following more specific embodiments further illustrate the thermochromic aviation organic glass and its preparation method of this application.

[0112] Example 1 The initial molecule with thermochromic function is selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons and triarylmethanes. In this embodiment, Schiff bases are selected.

[0113] (1) Specifically, the Schiff base compound N,N'-bis(salicylic acid)-1,2-propanediamine was used as the initial molecule with thermochromic function. N,N'-bis(salicylic acid)-1,2-propanediamine was chemically modified to obtain a thermochromic compound with unsaturated units. The modification method is as follows: N,N'-bis(salicylic acid)-1,2-propanediamine was dissolved in ethyl acetate to prepare a 5% (w / w) organic solution. Diisopropylethylamine (an acid-binding agent) was added to the organic solution and stirred until homogeneous, yielding a mixture. The mass of diisopropylethylamine was 0.5% of the mass of the organic solution. The temperature of the mixture was adjusted to 50°C, and oxaloyl chloride monoallyl ester (a modifying molecule) was added, with a mass ratio of oxaloyl chloride monoallyl ester to N,N'-bis(salicylic acid)-1,2-propanediamine of 1:1. The mixture was then reacted at 50°C for 60 min. Finally, the mixture was washed, separated, and purified to obtain a thermochromic compound with unsaturated units.

[0114] Simultaneously, using the Schiff base compound N,N'-bis(salicylicyl)-1,2-propanediamine as the initial molecule possessing thermochromic properties, N,N'-bis(salicylicyl)-1,2-propanediamine was chemically modified to obtain a thermochromic compound with epoxy groups. The modification method is as follows: N,N'-bis(salicylic acid)-1,2-propanediamine was dissolved in ethyl acetate to prepare a 5% (w / w) organic solution. Diisopropylethylamine was added to the organic solution and stirred until homogeneous, yielding a mixture. The mass of diisopropylethylamine was 0.5% of the mass of the organic solution. The temperature of the mixture was adjusted to 50°C, and 3-glycidyloxypropyltrimethoxysilane was added, with a mass ratio of 3-glycidyloxypropyltrimethoxysilane to N,N'-bis(salicylic acid)-1,2-propanediamine of 1:1. The mixture was then reacted at 50°C for 60 min. Finally, the mixture was washed, separated, and purified to obtain a thermochromic compound with epoxy groups.

[0115] The above reaction process is as follows Figure 4 As shown.

[0116] (2) Under the action of the initiator benzoyl peroxide, methyl methacrylate and a thermochromic compound with unsaturated units were prepolymerized (the reaction temperature was maintained at 60 °C until the required viscosity was reached, then heating was stopped and the mixture was cooled to end the prepolymerization process), forming a precursor mixture containing a portion of the polymerization precursor, thus obtaining the matrix material. The amount of the thermochromic compound with unsaturated units accounted for 10% of the molar amount of methyl methacrylate. The viscosity of the precursor mixture was such that the flow time at 25 °C in a Forte 4 cup was 20 s.

[0117] (3) A homogeneous mixture was prepared by mixing the matrix material, the thermochromic compound with epoxy groups, the first functional monomer, and the initiator. The first functional monomer was N-(2-hydroxyethyl)maleimide, and the mass ratio of the matrix material to the thermochromic compound with epoxy groups was 90:5. The molar ratio of the thermochromic compound with epoxy groups to the first functional monomer was 1:1. The initiator was azobisisobutyronitrile and di-tert-butyl peroxide in a mass ratio of 1:1, and the initiator accounted for 0.6% of the mass of the homogeneous mixture.

[0118] (4) The obtained homogeneous mixture was placed in a water bath at 45 °C for 100 h, and then subjected to continuous forced-air baths at 100 °C, 120 °C and 135 °C in sequence. The mixture was placed in an air bath at 100 °C for 60 h, at 120 °C for 15 h, and at 135 °C for 5 h. After natural cooling to below 60 °C, it was taken out to obtain thermochromic aviation organic glass with a thickness of 40 mm.

[0119] The thermochromic aviation acrylic sheet obtained in this embodiment changes color from pale yellow to red when heated to 80-120°C. The color-changing mechanism is proton tautomerism. The thermochromic compound exists stably at room temperature in the enol-imine form (pale yellow). When heated above 80°C, protons migrate from the phenolic hydroxyl group to the imine nitrogen, forming a ketone-enamine form (red). Intramolecular hydrogen bond rearrangement alters the electron delocalization range.

[0120] Example 2 The initial molecule with thermochromic function is selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons and triarylmethanes. In this embodiment, Schiff bases are selected.

[0121] The thermochromic compound is also selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons and triarylmethanes. In this embodiment, a spirocyclic compound is selected.

[0122] (1) Specifically, the Schiff base compound N,N'-bis(salicylic acid)-1,2-propanediamine was used as the initial molecule with thermochromic function. N,N'-bis(salicylic acid)-1,2-propanediamine was chemically modified to obtain a thermochromic compound with unsaturated units. The modification method is as follows: N,N'-bis(salicylic acid)-1,2-propanediamine was dissolved in ethyl acetate to prepare a 5% (w / w) organic solution. Diisopropylethylamine (an acid-binding agent) was added to the organic solution and stirred until homogeneous, yielding a mixture. The mass of diisopropylethylamine was 0.5% of the mass of the organic solution. The temperature of the mixture was adjusted to 50°C, and 2-buten-1-ylsuccinic anhydride (a modifying molecule) was added, with a molar ratio of 2-buten-1-ylsuccinic anhydride to N,N'-bis(salicylic acid)-1,2-propanediamine of 1:1. The mixture was then reacted at 50°C for 60 min. Finally, the mixture was washed, separated, and purified to obtain a thermochromic compound with unsaturated units.

[0123] The above reaction process is as follows Figure 5 As shown.

[0124] Meanwhile, following the same modification method as in Example 1, [8-(epoxypropyloxy)-n-octyl]trimethoxysilane was used as the modifying molecule to modify N,N'-bis(salicylene)-1,2-propanediamine into a thermochromic compound with epoxy units.

[0125] (2) Under the action of the initiator azobisisobutyronitrile, methyl methacrylate and the thermochromic compound with unsaturated units obtained in step (1) were prepolymerized (the reaction temperature was maintained at 80 °C until the viscosity reached the required level, at which point heating was stopped and the mixture was cooled to end the prepolymerization process), forming a precursor mixture containing a portion of the polymerization precursor, thus obtaining the matrix material. The amount of the thermochromic compound with unsaturated units accounted for 10% of the molar amount of methyl methacrylate. The viscosity of the precursor mixture was 120 s at 25 °C using a Forte 4 cup flow time of 120 s. The specific polymerization process was the same as in Example 1.

[0126] (3) The matrix material, thermochromic compound, first functional monomer, second functional monomer and initiator are mixed to prepare a homogeneous mixture. The thermochromic compound includes a thermochromic compound with an epoxy group and a thermochromic compound with a tertiary amine group. The thermochromic compound with an epoxy group is obtained by modification in step (1). The thermochromic compound with a tertiary amine group is 1,3-dihydro-8-methoxy-1,3,3-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2-(2H)-indole]. The first functional monomer is N-benzylmaleimide and the second functional monomer is glycidyl acrylate. The mass ratio of the sum of the two types of thermochromic compounds to the mass of the matrix material is 30:60. The ratio of the sum of the amounts of the first functional monomer and the second functional monomer to the sum of the amounts of the two types of thermochromic compounds is 1:1. The mass ratio of the first functional monomer to the second functional monomer is 1:1.

[0127] The initiator is azobisisobutyronitrile and diisopropylbenzene peroxide in a mass ratio of 1:1, and the mass percentage of the initiator in the homogeneous mixture is 0.3%.

[0128] (4) The homogeneous mixture was cured using the same process as in Example 1 to obtain a thermochromic aviation organic glass with a thickness of 40 mm.

[0129] The thermochromic aviation acrylic sheet obtained in this embodiment contains three thermochromic compounds. Its thermochromic process involves changing from pale yellow to red when heated to 80-120 °C. The color-changing mechanism is proton tautomerism. At room temperature, the thermochromic compounds exist stably in the enol-imine form (pale yellow). When heated above 80 °C, protons migrate from the phenolic hydroxyl group to the imine nitrogen, forming a ketone-enamine form (red). Intramolecular hydrogen bond rearrangement alters the electron delocalization range.

[0130] Example 3 The thermochromic compound is also selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons and triarylmethanes. In this embodiment, a spirocyclic compound is selected.

[0131] (1) Specifically, 1',3'-dihydro-8-methoxy-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-[2H]indole] was selected as the thermochromic compound.

[0132] (2) Methyl methacrylate was prepolymerized under the action of the initiator azobisisobutyronitrile (the reaction temperature was maintained at 70 °C until the viscosity reached the required level, at which point heating was stopped and the temperature was lowered to end the prepolymerization process), forming a precursor mixture containing some of the polymerization precursors, to obtain the matrix material. The viscosity of the matrix material was such that the flow time in a Forte 4 cup at 25 °C was 50 s. The specific polymerization process was the same as in Example 1.

[0133] (3) Mix the matrix material, thermochromic compound, second functional monomer and initiator to prepare a homogeneous mixture. The second functional monomer is glycidyl methacrylate, the mass ratio of matrix material to thermochromic compound is 60:18, and the molar ratio of thermochromic compound to second functional monomer is 1:1.

[0134] The initiator is benzoyl peroxide and tert-butyl peroxide in a mass ratio of 1:1, and the mass percentage of the initiator in the homogeneous mixture is 0.1%.

[0135] (4) The homogeneous mixture was cured using the same process as in Example 1 to obtain a thermochromic aviation organic glass with a thickness of 40 mm.

[0136] The thermochromic aviation acrylic sheet obtained in this embodiment changes color from colorless to purple when heated to 60-80 °C. The color-changing mechanism is an open-ring-closed-ring isomerization. At low temperatures, it has a closed-ring colorless spiropyran structure. When heated above 60 °C, the spiro-CO bonds break to form an open-ring cyanine structure (purple), and the expansion of the π-conjugated system leads to a red shift of the absorption peak.

[0137] Example 4 The thermochromic compound is also selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons and triarylmethanes. In this embodiment, polycyclic aromatic hydrocarbons are selected.

[0138] (1) A polycyclic aromatic hydrocarbon compound, namely 1,4-dihydroxyanthraquinone, was selected as the initial molecule of the thermochromic compound. 3-[(2,3)-epoxypropoxy]propylmethyldimethoxysilane was selected as the modifying molecule, and the initial molecule was epoxidized to obtain a thermochromic compound with epoxy units. The modification process was the same as in Example 1.

[0139] (2) Methyl methacrylate was prepolymerized under the action of the initiator azobisisobutyronitrile to form a precursor mixture containing some of the polymerization precursors, thus obtaining the matrix material. The viscosity of the matrix material was such that the flow-out time at a Forte 4 cup at 25 °C was 90 s. The specific polymerization process was the same as in Example 1.

[0140] (3) A homogeneous mixture is prepared by mixing the matrix material, the thermochromic compound with epoxy groups, the first functional monomer, and the initiator. The first functional monomer is N-(4-fluorophenyl)maleimide, the mass ratio of the matrix material to the thermochromic compound is 60:30, and the molar ratio of the thermochromic compound to the first functional monomer is 1:1.

[0141] The initiator is azobisisobutyronitrile and di-tert-butyl peroxide in a mass ratio of 1:1, and the mass percentage of the initiator in the homogeneous mixture is 0.2%.

[0142] (4) The homogeneous mixture was cured using the same process as in Example 1 to obtain a thermochromic aviation organic glass with a thickness of 40 mm.

[0143] The thermochromic aviation acrylic sheet obtained in this embodiment changes color from pale yellow to dark green when heated to 100-120 °C. The color-changing mechanism is a conformational transformation. At room temperature, it has an inverse conformation (pale yellow), and when heated above 100 °C, it transforms into a twisted conformation (dark green). The disruption of molecular planarity leads to a weakening of π-electron delocalization, causing the absorption spectrum to shift to longer wavelengths.

[0144] Example 5 The thermochromic compound is also selected from at least one of spirocyclic compounds, Schiff bases, polycyclic aromatic hydrocarbons and triarylmethanes. In this embodiment, triarylmethanes are selected.

[0145] (1) Crystal violet lactone was specifically selected as the thermochromic compound.

[0146] (2) Methyl methacrylate was polymerized under the action of the initiator benzoyl peroxide to form a precursor mixture containing some of the polymerization precursors, thus obtaining the matrix material. The matrix material had a flow-out time of 45 s at 25 °C using a Forte 4 cup. The specific polymerization process was the same as in Example 1.

[0147] (3) The matrix material, thermochromic compound, second functional monomer and initiator are mixed to prepare a homogeneous mixture. The second functional monomer is 4-hydroxybutyl acrylate glycidyl ether, the mass ratio of matrix material to thermochromic compound is 60:5, the molar ratio of thermochromic compound to second functional monomer is 1:1, the initiator is azobisisobutyronitrile and di-tert-butyl peroxide in a mass ratio of 1:1, and the mass percentage of initiator in the homogeneous mixture is 0.5%.

[0148] (4) The homogeneous mixture was cured using the same process as in Example 1 to obtain thermochromic aviation organic glass with a thickness of 8 mm.

[0149] The thermochromic aviation acrylic sheet obtained in this embodiment changes color from colorless to blue when heated to 40-60°C. The color-changing mechanism involves the opening of the lactone ring. At room temperature, the lactone ring is closed (colorless). Heating to above 40°C causes the crystal violet lactone to open, forming a quinone structure (blue), and the delocalization of electrons leads to the color change.

[0150] The mechanism of the thermochromic process of the thermochromic aviation acrylic glass in Examples 1-5 is as follows: Figure 6 As shown, it exhibits stable and reliable thermochromic properties.

[0151] control group A liquid polymethyl methacrylate (PMMA) matrix material (polymerized from MMA monomers under the action of an initiator, with the specific process the same as in Example 3) was provided. This liquid matrix material consisted only of a prepolymerized liquid formed by bulk polymerization of MMA, crystal violet lactone and oil-soluble initiator ABVN in the same amounts as in Example 5, with a mass ratio of prepolymerized liquid to crystal violet lactone of 90:5. A polymerization reaction was carried out to form a solid matrix from the liquid matrix material. The viscosity of the prepolymerized liquid was 120 s. The mass percentage of the oil-soluble initiator ABVN in the liquid matrix material was 0.5%. In this control group, a thickness of 40 mm was used. The polymerization process specifically involved a water bath at 45 °C for 100 h, followed by continuous forced-air baths at 100 °C / 60 h, 120 °C / 15 h, and 135 °C / 5 h. Finally, the heating power was turned off, and the material was allowed to cool naturally to below 60 °C before being removed from the oven and ready for use. Crystal violet lactone is a thermochromic compound with tertiary amine units. It is chemically bonded to the polymethyl methacrylate matrix through a ring-opening reaction with a second functional monomer. In the control group, there is no second functional monomer, and the connection between crystal violet lactone and polymethyl methacrylate is not through chemical bonding.

[0152] The following is a performance evaluation of the thermochromic aviation acrylic glass prepared in Examples 1-5 and the control group. The specific testing process is as follows: the shape, size and quantity of the test strips used in Examples 1-5 and the control group meet the standard requirements of the corresponding tests, and the results are taken as the average value.

[0153] Referring to the requirements and methods in relevant standards such as GB / T 7134-2008 Cast Industrial Acrylic Glass Sheets, GB / T 40911.3-2021 Types, Dimensions and Properties of Polymethyl methacrylate Sheets for Plastic Products Part 3: Continuously Cast Sheets, GB / T 2411-2008 Determination of Indentation Hardness (Shore Hardness) of Plastics and Hard Rubber Using a Hardness Tester, and GJB 1251A Specification for Cast Aviation Acrylic Glass, the basic physical properties were tested and characterized, and the results are shown in Table 1. The results show that, compared with the control group, Examples 1-5 exhibited better consistency in tensile strength, tensile modulus of elasticity, impact strength, tensile fracture strain, flexural modulus of elasticity, flexural strength, and hardness, while the resistance to exudation and heat distortion temperature were significantly improved. Specifically, the evaluation process for anti-precipitation ability involves immersing the sample in MMA solvent for 48 hours, performing UV-Vis spectral characterization on the solvent, and comparing the characteristic peaks of the MMA solution spectrum at different concentrations of the corresponding thermochromic compound to determine whether and how much the thermochromic compound precipitates. Furthermore, this application conducted stability analysis on the tensile strength, tensile modulus of elasticity, flexural strength, and flexural modulus of elasticity in the data. The coefficients of variation were all less than 2%, indicating minimal data fluctuation. Therefore, compared to the untreated control group 1 (ordinary PMMA), Examples 1-5 did not show statistically significant changes in physical and mechanical properties, indicating good consistency between the two. All the above indicators of Examples 1-5 and the control group meet the technical requirements of the "GJB1251A Casting Aviation Acrylic Glass Specification," meaning they fall within the application scope of aviation acrylic glass. In addition, the test samples rapidly undergo color change after heating with a specific temperature heat source (see the above examples for details). The molecular mechanism of the color change process of the samples obtained in Examples 1-5 is illustrated below. Figure 6 Meanwhile, the control group showed a corresponding color change, but in the anti-precipitation ability test, the control group showed precipitation, while Examples 1-5 showed no precipitation, indicating that the implementation effect of the technical solution of this application is quite ideal, giving aviation plexiglass a stable and reliable thermochromic function.

[0154] Table 1. Statistics on basic physical properties

[0155] Note: a. Impact strength refers to the unnotched impact strength of a simply supported beam. Examples 1, 2, 3, 4, and 5 correspond to Example 1, Example 2, Example 3, Example 4, and Example 5, respectively.

[0156] It should be noted that while the thermochromic aerospace acrylic glass provided in this application emphasizes its significant application value in the aerospace field, thermochromic materials also possess core application value in multiple other fields due to their reversible color and performance transformation characteristics in thermal response. For example, in the field of temperature sensing, it can achieve precise temperature measurement and visual monitoring of the environment, industrial systems, and biological tissues; in the field of intelligent control, it can be used for thermal response optical adjustment of temperature control coatings and smart windows; in the field of anti-counterfeiting, it endows labels with dynamic anti-counterfeiting functions, improving the reliability of identification; and as a thermal control functional unit, it adapts to the temperature adaptation requirements of energy storage displays and flexible electronic devices. Its significance lies in breaking through the limitations of the static functions of traditional materials, providing new thermal response core modules for fields such as sensing and detection, smart materials, and anti-counterfeiting technology, and promoting the upgrading of related technologies towards precision, adaptability, and multi-functionality. Therefore, the scope of protection of the thermochromic technology involved in this application includes not only the aerospace field but also the aforementioned many other fields.

[0157] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered by the claims of this application.

Claims

1. A thermochromic aviation acrylic glass, characterized in that, The invention comprises a polymethyl methacrylate (PMMA) matrix and a thermochromic compound distributed within the PMMA matrix; wherein the thermochromic compound is distributed within the PMMA matrix in at least one of the following ways: The thermochromic compound is distributed in the polymethyl methacrylate matrix by copolymerization of unsaturated units with methyl methacrylate monomers used to prepare the polymethyl methacrylate matrix; The thermochromic compound is distributed in the polymethyl methacrylate matrix through a ring-opening reaction of a functional monomer.

2. The thermochromic aviation acrylic glass according to claim 1, characterized in that, The functional monomer includes at least one of a first functional monomer and a second functional monomer, and the thermochromic compound undergoes a ring-opening reaction with the first functional monomer through an epoxy group unit; the thermochromic compound undergoes a ring-opening reaction with the second functional monomer through a tertiary amine group unit.

3. The thermochromic aviation acrylic glass according to claim 1, characterized in that, The thermochromic compound accounts for ≤30% by mass, and the polymethyl methacrylate matrix accounts for ≥60% by mass.

4. The thermochromic aviation acrylic glass according to claim 2, characterized in that, The first functional monomer is a compound containing a maleimide group, and the second functional monomer is an unsaturated compound containing an epoxy group.

5. A method for preparing thermochromic aviation acrylic glass, characterized in that, Includes the following steps: S1: Provide methyl methacrylate monomer and prepolymerize the methyl methacrylate monomer to obtain a matrix material; S2: Prepare a homogeneous mixture, the homogeneous mixture comprising the matrix material, an initiator, and at least one of the following components: a thermochromic compound having unsaturated units; Thermochromic compounds that undergo ring-opening reactions via functional monomers; S3: The homogeneous mixture is cured to distribute the thermochromic compound in the polymethyl methacrylate matrix in at least one of the following ways: by copolymerizing the unsaturated unit with the methyl methacrylate monomer in the matrix material to distribute the thermochromic compound in the polymethyl methacrylate matrix; or by performing a ring-opening reaction of the functional monomer to distribute the thermochromic compound in the polymethyl methacrylate matrix, thereby obtaining the thermochromic aviation acrylic glass.

6. The method for preparing thermochromic aviation acrylic glass according to claim 5, characterized in that, The functional monomer includes at least one of a first functional monomer and a second functional monomer, and the thermochromic compound that undergoes a ring-opening reaction through the functional monomer includes at least one of the following: a thermochromic compound having an epoxy group and a thermochromic compound having a tertiary amino group; wherein, the thermochromic compound having an epoxy group undergoes a ring-opening reaction with the first functional monomer through the epoxy group, and the thermochromic compound having a tertiary amino group undergoes a ring-opening reaction with the second functional monomer through the tertiary amino group.

7. The method for preparing thermochromic aviation acrylic glass according to claim 6, characterized in that, In step S1, the prepolymerization of the methyl methacrylate monomer to obtain the matrix material includes at least one of the following: The thermochromic compound with unsaturated units, the initiator, and the methyl methacrylate monomer are mixed and then subjected to a polymerization reaction to form a precursor mixture containing the polymerization precursor to obtain the matrix material. The thermochromic compound having epoxy units, the initiator, and the methyl methacrylate monomer are mixed and then subjected to a polymerization reaction to form a precursor mixture containing the polymerization precursor to obtain the matrix material. The thermochromic compound having tertiary amine units, the initiator, and the methyl methacrylate monomer are mixed and then subjected to a polymerization reaction to form a precursor mixture containing the polymerization precursor to obtain the matrix material. The ratio of the amount of at least one of the thermochromic compound having unsaturated units, the thermochromic compound having epoxy units, and the thermochromic compound having tertiary amine units to the amount of the methyl methacrylate monomer is less than or equal to 1:

10.

8. The method for preparing thermochromic aviation acrylic glass according to claim 5, characterized in that, It also includes a step of modifying and preparing a thermochromic compound, wherein the step of modifying and preparing a thermochromic compound includes: Prepare an organic solution containing initial molecules with thermochromic properties; The modified molecule is added to the organic solution, and the reaction is carried out under heat. After the reaction is completed, the mixture is washed, separated and purified to obtain a thermochromic compound with unsaturated units, a thermochromic compound with epoxy units, or a thermochromic compound with tertiary amine units.

9. The method for preparing thermochromic aviation acrylic glass according to claim 5, characterized in that, In the homogeneous mixture, at least one of the thermochromic compound having unsaturated units and the thermochromic compound undergoing ring-opening reaction through functional monomers, is present in a mass ratio of (5 ~ 30): (60 ~ 90) to the matrix material. The molar ratio of the functional monomer to the thermochromic compound that undergoes a ring-opening reaction through the functional monomer is 1:1; the initiator has a mass percentage of ≤0.6% in the homogeneous mixture.

10. The method for preparing thermochromic aviation acrylic glass according to claim 5, characterized in that, The step of curing the homogeneous mixture includes: water bath at 35-65°C for 12-120 h, and then air bath at 105-135°C for 10-80 h.

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