A temperature-sensitive self-adjusting light intelligent polymethyl methacrylate composite material and a preparation method thereof

Abstract

The application provides a temperature-sensitive self-adjusting light intelligent polymethyl methacrylate composite material and a preparation method thereof, and belongs to the technical field of high polymer materials. The composite material aims to solve the problems of poor compatibility, slow response and insufficient stability of the existing temperature-sensitive polymethyl methacrylate material. The composite material comprises a polymethyl methacrylate matrix and temperature-sensitive polymer chain segments covalently bonded in the matrix; a nanoscale microphase separation structure composed of the temperature-sensitive polymer chain segments is formed in the composite material, so that the material is transparent when the temperature is lower than the phase transition temperature and is scattered when the temperature is higher than the phase transition temperature. The preparation method comprises the following steps: providing a mixture comprising methyl methacrylate, temperature-sensitive comonomers and an initiator. The composite material obtained by the application has the advantages of excellent optical performance, rapid response, cycle stability and integrated multifunction.

Description

Technical Field

[0001] This application belongs to the field of polymer materials technology, specifically relating to a temperature-sensitive self-adjusting smart polymethyl methacrylate composite material and its preparation method. Background Technology

[0002] Polymethyl methacrylate (PMMA) is widely used as an optical material due to its excellent transparency, weather resistance, and processability. However, the optical properties of traditional PMMA, such as transmittance and haze, are fixed and cannot be adaptively adjusted according to environmental changes, which limits its application in high-end fields such as smart windows and adaptive optics.

[0003] To endow materials with intelligent light-modulating properties, a common approach in existing technologies is to utilize thermosensitive polymers (such as poly(N-isopropylacrylamide)) with low critical dissolution temperatures. For example, Chinese patent CN113248731B discloses a PNIPAm / PPy composite hydrogel with poly(N-isopropylacrylamide) hydrogel as the matrix, which is applied to smart windows to achieve thermochromic effects. However, this type of technology mainly relies on hydrogel systems containing a large amount of water. Combining such typically hydrophilic thermosensitive polymers with hydrophobic polymethyl methacrylate rigid matrices presents serious compatibility problems. Simple physical blending methods easily lead to macroscopic phase separation, resulting in a cloudy final material at any temperature, significantly degrading both optical and mechanical properties, and rendering it impractical for solid-state optical devices.

[0004] Furthermore, to improve the microstructure and properties of polymer materials, existing technologies have also explored microgel composite methods. For example, Chinese patent CN102675549B discloses a method for preparing a high-strength hydrogel with a polymer microgel composite structure, which introduces a poly(N-isopropylacrylamide) microgel aqueous dispersion to construct a composite network. Although this approach modulates the polymer network to some extent, its preparation environment and products are still limited to hydrophilic aqueous systems. When faced with the challenge of uniformly and stably introducing temperature-sensitive microregions into solid transparent resins, existing technologies (including conventional methods attempting to combine two materials with mismatched thermo-optical coefficients) generally lack a preparation process capable of precisely controlling the internal microstructure of the material, resulting in limited dimming efficiency and difficulty in achieving rapid, reversible, and wide-range transmittance changes. Therefore, solving the compatibility problem between the temperature-sensitive functional component and the polymethyl methacrylate matrix, and establishing a preparation method capable of forming a stable and efficient temperature-sensitive dimming structure, is a pressing technical challenge in this field. Summary of the Invention

[0005] The purpose of this application is to provide a temperature-sensitive self-adjusting smart polymethyl methacrylate composite material and its preparation method, so as to solve the technical problems in the prior art, such as poor compatibility between the temperature-sensitive functional component and the polymethyl methacrylate matrix, resulting in poor optical performance, slow response speed and insufficient cycle stability of the material.

[0006] To achieve the above objectives, this application provides a temperature-sensitive self-adjusting smart polymethyl methacrylate composite material, comprising: a polymethyl methacrylate matrix; and temperature-sensitive polymer segments covalently bonded to the polymethyl methacrylate matrix, wherein the temperature-sensitive comonomer used to form the temperature-sensitive polymer segments accounts for 10%-25% of the total mass of the polymethyl methacrylate and the temperature-sensitive comonomer; The composite material forms a nanoscale microphase separation structure composed of the temperature-sensitive polymer chain segments. The average characteristic size of the microphase separation structure is 10-50 nm, so that the transmittance of the composite material at 550 nm wavelength at 25°C is not less than 88% and the haze is not more than 2.5%; and at 50°C, the transmittance at 550 nm wavelength is not more than 55% and the haze is not less than 50%.

[0007] In this application, the characteristic size d of the microphase-separated structure is strictly controlled to be below 50 nm. According to Rayleigh scattering law, the light scattering intensity I in the medium satisfies the relationship between the characteristic size d of the micro-region and the incident light wavelength λ. When the temperature is below the phase transition temperature, because the micro-area size d is much smaller than the wavelength λ (400 nm - 700 nm) in the visible light band, the Rayleigh scattering generated when light passes through the composite material is extremely weak, thus ensuring that the material has a macroscopic transparency of up to 92% and extremely low haze. If this is not limited by the specific three-stage temperature-controlled curing process of this application, and d increases, strong Mie scattering or Rayleigh scattering will occur, destroying the initial high transparency state of the material.

[0008] Optionally, the composite material further comprises surface-modified functional nanoparticles covalently bonded to the polymethyl methacrylate matrix; the average particle size of the functional nanoparticles is 10-50 nanometers, and the amount of the functional nanoparticles is 0.5%-8% of the total mass of the polymethyl methacrylate and the thermosensitive comonomer.

[0009] Optionally, the thermosensitive polymer segment is formed by polymerization of thermosensitive comonomers selected from the following: methacrylate, acrylamide, or methacrylamide monomers containing polyethylene glycol segments or N-substituted acrylamide groups.

[0010] Optionally, the thermosensitive comonomer is selected from at least one of methoxy polyethylene glycol methacrylate, N-isopropylmethacrylamide, or methoxytriethylene glycol methacrylate; wherein, when the thermosensitive comonomer is methoxy polyethylene glycol methacrylate, its average molecular weight is 750 g / mol.

[0011] Optionally, the functional nanoparticles are selected from silica nanoparticles or zinc oxide nanoparticles; and when the functional nanoparticles are zinc oxide nanoparticles, the composite material has a transmittance of less than 5% for ultraviolet light in the wavelength range of 320-400 nm.

[0012] This application also provides a method for preparing the aforementioned temperature-sensitive self-adjusting smart polymethyl methacrylate composite material, the method comprising the following steps: (a) Provide a mixture comprising methyl methacrylate, a thermosensitive comonomer and an initiator; (b) The mixture is subjected to in-situ copolymerization at a temperature of 70-85°C for 2.5-4 hours to form a prepolymer; (c) The prepolymer is subjected to multi-stage temperature-controlled curing, the curing process including: pre-curing at 40-60°C for 2-4 hours, main curing at 80-100°C for 4-6 hours, and post-curing at 120-140°C for 2-3 hours. In this process, the in-situ copolymerization and multi-stage temperature-controlled curing form a nanoscale microphase separation structure with an average feature size of 10-50 nm inside the resulting composite material, so that the composite material remains transparent below the phase transition temperature.

[0013] Optionally, the mixture in step (a) further comprises functional nanoparticles, which are pre-modified with a silane coupling agent to introduce copolymerizable functional groups.

[0014] Optionally, the amount of the thermosensitive comonomer is 10%-25% of the total mass of the methyl methacrylate and the thermosensitive comonomer.

[0015] Optionally, the amount of the functional nanoparticles is 0.5%-8% of the total mass of the methyl methacrylate and the thermosensitive comonomer.

[0016] Optionally, the thermosensitive comonomer is N-isopropylmethacrylamide, the functional nanoparticles are silica nanoparticles, and the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane.

[0017] Compared with the prior art, this application has the following beneficial effects: 1. The composite material prepared in this application can automatically and reversibly adjust its light transmittance according to the ambient temperature. It exhibits high transparency at low temperatures and milky white scattering at high temperatures, without the need for any external energy or control system, thus achieving intelligent energy saving.

[0018] 2. Through in-situ copolymerization, all functional components are covalently linked to the polymethyl methacrylate backbone, achieving uniform dispersion at the molecular level. This effectively suppresses phase separation problems caused by physical blending, resulting in materials with extremely high light transmittance and low haze in a transparent state, maintaining optical-grade quality.

[0019] 3. A specific multi-stage temperature-controlled curing process creates nanoscale temperature-sensitive micro-regions. Phase transitions occur at this microscale, resulting in shorter heat transfer distances and thus faster response speeds. Simultaneously, chemical bonding and the physical confinement of the polymethyl methacrylate matrix effectively suppress the aggregation and destruction of these micro-regions, enabling the material to maintain stable optical properties and excellent service life even after hundreds of thermal cycles.

[0020] 4. By selecting different functional nanoparticles, it is easy to integrate a variety of additional functions into the material. For example, zinc oxide nanoparticles can be used to achieve efficient ultraviolet shielding, and silicon dioxide can be used to enhance the mechanical properties of the material. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 A schematic flowchart illustrating a method for preparing a temperature-sensitive, self-adjusting, intelligent polymethyl methacrylate composite material, provided in this application embodiment; Figure 2 This is a schematic diagram of the microstructure of a temperature-sensitive self-adjusting smart polymethyl methacrylate composite material in one embodiment of this application.

[0023] Explanation of reference numerals in the attached figures: 10, polymethyl methacrylate matrix; 20, thermosensitive polymer segment; 30, functional nanoparticles; 40, covalent bond. Detailed Implementation

[0024] To better understand the technical solutions of this application, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0025] This application provides a temperature-sensitive, self-adjusting, intelligent polymethyl methacrylate (PMMA) composite material and its preparation method. The technical concept lies in using in-situ copolymerization technology to firmly bind temperature-responsive functional monomers and surface-functionalized nanoparticles into the PMMA matrix via covalent bonds, thereby effectively improving the poor compatibility problems associated with traditional physical blending methods. Correspondingly, a three-stage, multi-stage temperature-controlled curing process is used to precisely regulate the microstructure within the material, thereby constructing a nanoscale, temperature-responsive microphase separation structure within the macroscopically homogeneous material.

[0026] Reference Figure 1 This document illustrates the overall process of a preparation method provided in an embodiment of this application. The method specifically includes the following steps: Step S10, synthesizing or selecting a specific temperature-sensitive comonomer; Step S20, surface-modifying functional nanoparticles to introduce polymerizable functional groups; Step S30, uniformly mixing the matrix monomer, temperature-sensitive comonomer, modified functional nanoparticles, and initiator, and performing an in-situ copolymerization reaction to form a viscous prepolymer containing the polymer and remaining monomers; and Step S40, subjecting the prepolymer to multi-stage temperature-controlled curing to form the final composite material.

[0027] Figure 2 This is a schematic diagram of the microstructure of the composite material in one embodiment of this application. In this schematic structure, the thermosensitive polymer segments 20 and functional nanoparticles 30 do not exist as independent aggregates, but are connected to the molecular chains of the polymethyl methacrylate matrix 10 via stable covalent bonds 40, achieving uniform dispersion at the molecular level. Figure 2 This diagram primarily illustrates the connection relationships between the functional components in the composite material of this application and their dispersion state within the matrix. Based on the optical test results and structural characterization results of the embodiments described below, it can be determined that the thermosensitive polymer segments form a nanoscale microphase-separated structure with an average characteristic size of 10-50 nm within the polymethyl methacrylate matrix. It should be noted that... Figure 2 This is an illustrative diagram and is not drawn to actual dimensions or scale, nor is it intended to define the precise geometry of the temperature-sensitive polymer segments, functional nanoparticles, and their microstructure. For embodiments without functional nanoparticles, the microstructure is similar to... Figure 2 The schematic diagram shown is similar, but does not include the functional nanoparticles 30.

[0028] Specifically, when the ambient temperature is below the phase transition temperature of the material, the thermosensitive polymer segments form swollen thermosensitive microregions in the matrix. These microregions have a refractive index highly matched to that of the polymethyl methacrylate matrix, allowing incident light to pass through the material with extremely low scattering loss, forming transmitted light. At this point, the material exhibits high transparency. When the ambient temperature rises above the phase transition temperature, the thermosensitive polymer segments undergo a conformational transformation and dehydrate and shrink, forming collapsed thermosensitive microregions with a significantly different refractive index from the matrix. These microregions transform into numerous nanoscale light scattering centers, causing the incident light to be strongly scattered as it passes through the material, forming scattered light. This results in the material appearing macroscopically as a milky white or translucent scattering state. It should be noted that because this process is a physical phase transition, it is completely reversible.

[0029] Understandably, the process is not a single isothermal curing process, but is divided into three stages with specific temperature and time ranges. As an optional implementation, the process includes: a first stage, pre-curing, which involves maintaining a low pre-curing temperature (e.g., 40-60°C) for a specified time to gently induce microphase separation of temperature-sensitive segments while the system still retains some fluidity, forming uniformly sized nanoscale regions. It should be noted that this 40-60°C temperature range covers or is close to the low critical dissolution temperature of the selected temperature-sensitive monomer, effectively promoting aggregation and phase separation of the temperature-sensitive segments through thermodynamic instability. The second stage, main curing, involves raising the temperature to the main curing temperature (e.g., 80-100°C) and maintaining the main curing time, aiming to rapidly polymerize most of the remaining monomers to form a robust polymethyl methacrylate matrix, thereby "freezing" or "locking" the microphase separation structure formed in the first stage within it. The third stage, post-curing, further raises the temperature to the post-curing temperature (e.g., 120-140°C) and maintains the post-curing time, primarily to eliminate internal stresses generated during polymerization and curing, and to improve the regularity of the polymer chains, ensuring excellent dimensional stability and mechanical properties in the final product.

[0030] The pre-curing stage is used to induce the formation of size-constrained initial microphase regions of thermosensitive polymer segments while the system still has a certain degree of fluidity; the main curing stage is used to increase the degree of polymerization and fix the microphase separation structure; the post-curing stage is used to reduce internal stress and improve the dimensional stability and cycle stability of the resulting composite material.

[0031] In this application, transmittance was measured using a visible-ultraviolet spectrophotometer at a wavelength of 550 nm, and haze was measured using a haze meter; unless otherwise specified, the sample thickness was 3 mm. The microphase separation structure dimensions were characterized by transmission electron microscopy and / or small-angle X-ray scattering. Response time was defined as the time required for the transmittance to reach 90% of its total change after the sample reached the target temperature.

[0032] The technical solution of this application will be described in more detail below through specific embodiments.

[0033] Example 1

[0034] This embodiment provides a method for preparing a composite material that combines excellent temperature-sensitive light-modulating properties with enhanced mechanical properties. In this embodiment, the temperature-sensitive comonomer is N-isopropylmethacrylamide, the functional nanoparticles are silica nanoparticles, and the silane coupling agent used for surface modification is γ-methacryloyloxypropyltrimethoxysilane.

[0035] Its preparation process follows Figure 1 The process shown is explained in detail below: Surface modification of functional nanoparticles (corresponding to step S20). Take 5 g of spherical silica nanoparticles with an average particle size of 30 nm and place them in a 500 mL three-necked flask. Add 200 mL of anhydrous ethanol and disperse the mixture magnetically and ultrasonically for 30 minutes to ensure a uniform suspension. Then, slowly add 5 mL of γ-methacryloyloxypropyltrimethoxysilane to the suspension. After the addition is complete, heat the reaction system to 60 °C and stir continuously for 4 hours under nitrogen protection. During this reaction, one end of the γ-methacryloyloxypropyltrimethoxysilane molecule undergoes hydrolytic condensation with the hydroxyl groups on the surface of the silica nanoparticles to form a stable siloxane bond, while the other end retains the polymerization-active methacryloyloxy functional group. After the reaction, separate the mixture by high-speed centrifugation (10,000 rpm, 15 minutes) and discard the supernatant. Wash the precipitate three times with anhydrous ethanol to remove unreacted silane coupling agent and byproducts. Finally, the product was dried in a vacuum oven at 60°C for 12 hours to obtain modified silica nanoparticle powder with polymerizable functional groups grafted onto its surface.

[0036] Preparation of the polymerization reaction solution (corresponding to the preparation stages of steps S10 and S30). In a clean, dry beaker, accurately weigh 75 g of methyl methacrylate main monomer purified by vacuum distillation, 20 g of N-isopropylmethacrylamide thermosensitive comonomer, and 0.5 g of initiator azobisisobutyronitrile (AIBN). Mix and stir until completely dissolved. Then, add 5 g of modified silica nanoparticle powder prepared in step 1 to the mixed solution. To ensure sufficient dispersion of the nanoparticles, place the mixture in a 300 W ultrasonic cell disruptor for 30 minutes, cooling it with an ice-water bath during treatment to prevent premature polymerization of the monomers. After ultrasonic treatment, a uniform, semi-transparent polymerization reaction solution is obtained. According to calculations, in this embodiment, the amount of thermosensitive comonomer used is approximately 21.1% of the total mass (95 grams) of methyl methacrylate and N-isopropylmethacrylamide, which falls within the range of 10%-25%; the amount of functional nanoparticles used is approximately 5.3% of the total mass of methyl methacrylate and thermosensitive comonomer, which falls within the range of 0.5%-8%.

[0037] In-situ copolymerization and multi-stage temperature-controlled curing (corresponding to steps S30 and S40). The prepared polymerization reaction solution is transferred to a 3 mm thick mold. The filled mold is placed in a 75°C water bath for prepolymerization for 3 hours, until the system gradually thickens to form a prepolymer slurry. Subsequently, the mold is transferred to a programmable temperature-controlled oven for multi-stage temperature-controlled curing. Curing procedure: First, curing is carried out at a pre-curing temperature of 55°C for 3 hours; then, the temperature is increased to 95°C at a rate of 5°C / min and cured at this main curing temperature for 5 hours; finally, the temperature is increased to 135°C at a rate of 5°C / min and heat-treated at this final curing temperature for 2 hours.

[0038] Demolding and Finished Product. After the curing process is complete, turn off the oven power and allow the mold to cool slowly to room temperature inside the oven. After it has completely cooled, carefully disassemble the mold and remove a transparent, hard sheet, which is the reinforced thermosensitive self-adjusting polymethyl methacrylate composite material prepared in this embodiment.

[0039] The composite material sheet prepared in this embodiment was subjected to performance testing. At 25°C, the material exhibited a transmittance of up to 90% in the visible light band (550 nm) and a haze of less than 2%, demonstrating excellent optical transparency. According to optical scattering theory (such as Rayleigh scattering), if the size of the phase-separated structure inside the material is larger than one-tenth of the visible light wavelength (i.e., larger than approximately 50 nm), it will cause strong static light scattering, leading to a sharp increase in haze and a cloudy appearance. The extremely low haze (<2%) and high transmittance exhibited in this embodiment below the phase transition temperature directly confirms from macroscopic test data that the temperature-sensitive polymer segments do indeed form a 'nanoscale microphase-separated structure' in the matrix with a size much smaller than the visible light wavelength, and that this structure is highly matched to the refractive index of the matrix at low temperatures. When the sample was heated to 50°C and tested again, its transmittance rapidly decreased to 35%, while the haze increased sharply to 75%, exhibiting a significant dimming effect. Continuous temperature variation testing determined the phase transition temperature of this material to be approximately 42°C, and its dimming response time was less than 1 minute. Furthermore, mechanical property testing showed that compared to pure thermosensitive copolymer without added silica nanoparticles, its tensile strength and surface hardness increased by approximately 10% and 15%, respectively. These results demonstrate that by introducing surface-modified silica nanoparticles, not only can thermosensitive dimming be achieved, but the mechanical properties of the material can also be effectively enhanced. The structure of this material is similar to... Figure 2 The microstructure shown is consistent.

[0040] Example 2

[0041] This embodiment provides a composite material that combines temperature-sensitive dimming and high-efficiency ultraviolet shielding functions, making it suitable for outdoor applications. In this embodiment, methoxytriethylene glycol methacrylate is selected as the temperature-sensitive comonomer, which has a relatively high phase transition temperature; the functional nanoparticles are zinc oxide nanoparticles, which have a strong absorption effect on ultraviolet light.

[0042] Its preparation process also follows Figure 1 The process shown specifically includes: Surface modification of functional nanoparticles (step S20). 7 g of zinc oxide nanoparticles with an average particle size of 20 nm were taken and surface modified using the same reagents and methods as in Example 1, reacting at 60 °C for 4 hours in ethanol medium. After centrifugation, washing, and drying, modified zinc oxide nanoparticles with methacryloyloxy functional groups grafted onto their surface were obtained.

[0043] Preparation of the polymerization reaction solution. 78 g of methyl methacrylate monomer, 15 g of methoxytriethylene glycol methacrylate thermosensitive comonomer, and 0.4 g of initiator azobisisobutyronitrile were accurately weighed and mixed thoroughly. Then, 7 g of modified zinc oxide nanoparticles prepared in step 1 were added to the mixture, and the mixture was dispersed by ultrasonication to obtain the final polymerization reaction solution. In this embodiment, the amount of thermosensitive comonomer accounted for approximately 16.1% of the total mass (93 g) of methyl methacrylate and thermosensitive comonomer, falling within the range of 10%-25%; the amount of functional nanoparticles accounted for approximately 7.5% of the total mass of methyl methacrylate and thermosensitive comonomer, falling within the range of 0.5%-8%, further verifying the effectiveness of the technical solution of this application.

[0044] In-situ copolymerization and multi-stage temperature-controlled curing (steps S30 and S40). The polymerization reaction solution was injected into the mold and prepolymerized in an 80°C water bath for 4 hours to obtain the prepolymer. Subsequently, the mold was transferred to a programmable temperature-controlled oven and the following curing program was executed: a pre-curing temperature of 60°C was maintained for 3 hours; the temperature was increased to the main curing temperature of 100°C and maintained for 6 hours; finally, the temperature was increased to the post-curing temperature of 140°C and maintained for 2 hours.

[0045] Demolding and finished product. After the process is cured and slowly cooled to room temperature, the product is demolded to obtain a slightly yellowish transparent sheet, which is the UV-shielded temperature-sensitive self-adjusting polymethyl methacrylate composite material prepared in this embodiment.

[0046] The composite material sheet prepared in this embodiment was subjected to performance tests. At 25°C, its visible light (550 nm) transmittance was measured to be 88%, and its haze was 2.5%. When heated to 50°C, the transmittance decreased to 40%, and the haze increased to 70%, exhibiting good temperature-sensitive light-modulating characteristics. Its phase transition temperature was measured to be approximately 48°C. More importantly, the ultraviolet transmittance test results showed that the material's transmittance of ultraviolet light in the 320 nm to 400 nm wavelength range was less than 5%, achieving excellent ultraviolet shielding effect. This ultraviolet shielding function is attributed to the efficient absorption of ultraviolet light by zinc oxide nanoparticles 30 uniformly dispersed in the polymethyl methacrylate matrix 10. The results of this embodiment demonstrate that, within the technical framework of this application, by selecting different functional nanoparticles, additional functions can be conveniently integrated into materials, thereby preparing multifunctional integrated smart composite materials.

[0047] Example 3

[0048] This embodiment discloses a basic formula that does not contain functional nanoparticles but only achieves the core temperature-sensitive dimming function, which has lower cost and simpler process.

[0049] Its preparation process includes: Preparation of the polymerization solution (corresponding to the preparation stages of steps S10 and S30, step S20 is omitted). In a beaker, mix 80 g of methyl methacrylate monomer, 20 g of methoxy polyethylene glycol methacrylate with an average molecular weight of 750 g / mol, and 0.5 g of initiator azobisisobutyronitrile. Stir magnetically at room temperature for 30 minutes until all components are completely dissolved, forming a clear and transparent polymerization reaction solution. In this embodiment, the amount of thermosensitive comonomer accounts for 20% of the total mass (100 g) of both methyl methacrylate and thermosensitive comonomer, falling within the range of 10%-25%.

[0050] In-situ copolymerization and multi-stage temperature-controlled curing (steps S30 and S40). The polymerization reaction solution was injected into a 3 mm thick glass mold, sealed, and placed in a 70°C constant temperature water bath for 4 hours to form a viscous prepolymer. This 70°C prepolymerization process provides the initial activation energy required for initiator decomposition, rapidly establishing the polymer network framework. Subsequently, the mold was transferred to a programmable temperature oven and cured according to the following procedure: 4 hours at 50°C (pre-curing temperature), which is lower than the prepolymerization temperature and close to the phase transition critical point of the temperature-sensitive segments. Utilizing the thermodynamic compatibility at this low temperature, the macroscopic phase separation tendency of the temperature-sensitive polymer segments in the early stage of polymerization can be effectively suppressed, freezing the temperature-sensitive micro-region size below 50 nm; the temperature was then increased to 90°C (main curing temperature) and held for 6 hours; finally, the temperature was increased to 130°C (post-curing temperature) and held for 2 hours.

[0051] Demolding and Finished Product. After curing, the material is slowly cooled and demolded to obtain a colorless, highly transparent sheet. Its internal structure is similar to... Figure 2 Similar, but the difference is that this embodiment does not contain functional nanoparticles 30, that is, it only contains temperature-sensitive polymer segments 20 connected to the polymethyl methacrylate matrix 10 by covalent bonds 40.

[0052] The composite material prepared in this embodiment was subjected to performance testing. The "phase transition temperature" mentioned in this application refers to the lower critical solution temperature of the thermosensitive copolymer system, which macroscopically ranges from 25°C to 50°C. Within this range, as the temperature increases, the thermosensitive polymer chains transform from a hydrophilic extended coil state to a hydrophobic contracted spherical state, resulting in a sudden change in the refractive index of the micro-regions, thereby exciting strong light scattering. At 25°C (below the phase transition temperature), its visible light transmittance is as high as 92%, and the haze is only 1%. Its initial transparency fully demonstrates that there is no macroscopic phase separation within this pure thermosensitive copolymer system, and the size of the thermosensitive micro-regions induced by in-situ copolymerization and multi-stage temperature-controlled curing is strictly limited to the nanoscale, which does not cause visible light scattering. When the temperature rises to 50°C (above or equal to the upper limit of the phase transition temperature), its transmittance decreases to 45%, while the haze increases to 65%, exhibiting a typical thermosensitive dimming phenomenon, with a phase transition temperature of approximately 38°C. To verify its cycling stability, the sample was subjected to 100 cycles of thermal cycling between 25°C and 50°C, and the transmittance variation at both high and low temperatures was less than 5%. This excellent cycling stability is attributed to the fact that the temperature-sensitive polymer segment 20 is firmly anchored in the polymethyl methacrylate matrix 10 by covalent bonds, and the nanoscale regions formed therein are physically confined by the rigid matrix, thereby effectively preventing irreversible macroscopic aggregation or destruction during repeated phase transitions.

[0053] Example 4

[0054] This embodiment is used to verify that within the parameter range defined in this application, adjusting the raw material ratio and process parameters can still yield composite materials with excellent performance.

[0055] The preparation process is summarized as follows: First, 2 grams of silica nanoparticles were surface modified according to the method in Example 1.

[0056] Next, the polymerization reaction solution was prepared. 83 g of methyl methacrylate, 15 g of methoxy polyethylene glycol methacrylate (molecular weight 750), 2 g of the above-mentioned modified silica nanoparticles, and 0.5 g of initiator azobisisobutyronitrile were mixed and ultrasonically dispersed uniformly. The amount of the thermosensitive comonomer accounted for approximately 15.3% of the total mass of methyl methacrylate and the thermosensitive comonomer (98 g), falling within the range of 10%-25%; the amount of the functional nanoparticles relative to the total mass of methyl methacrylate and the thermosensitive comonomer was approximately 2.0%, falling within the range of 0.5%-8%.

[0057] Then, in-situ copolymerization and multi-stage temperature-controlled curing were performed. The polymer solution was polymerized at 85°C for 2.5 hours to obtain the prepolymer. It was then poured into a mold and subjected to multi-stage temperature-controlled curing: pre-curing at 60°C for 2 hours, primary curing at 100°C for 4 hours, and finally post-curing at 140°C for 2 hours. All process parameters are within the range defined in this application.

[0058] Finally, the material is cooled and demolded to obtain the composite material sheet.

[0059] The material prepared in this embodiment was subjected to performance testing, and its phase transition temperature was approximately 39°C. At 25°C, its transmittance was measured to be approximately 91%, and its haze to be 1.5%. At 50°C, its transmittance decreased to approximately 55%, and its haze increased to 50%. Although its high-temperature scattering ability was weakened compared to Example 3 due to the lower content of the temperature-sensitive monomer, it still exhibited a significant and practical temperature-sensitive dimming effect. The results of this embodiment strongly demonstrate that by adjusting the raw material ratio range (e.g., 10%-25% of the temperature-sensitive monomer and 0.5%-8% of the nanoparticles) and process conditions range (e.g., pre-curing temperature 40-60°C, main curing temperature 80-100°C, and post-curing temperature 120-140°C) disclosed in this application, the technical solution of this application can be successfully implemented, and a temperature-sensitive self-dimming composite material with the aforementioned beneficial effects can be obtained.

[0060] The above description is merely a preferred embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A temperature-sensitive, self-adjusting, intelligent polymethyl methacrylate composite material, characterized in that, Include: A polymethyl methacrylate (PMMA) matrix; and a thermosensitive polymer segment covalently bonded to the PMMA matrix, wherein the thermosensitive comonomer used to form the thermosensitive polymer segment accounts for 10%-25% of the total mass of both the PMMA and the thermosensitive comonomer; The composite material forms a nanoscale microphase separation structure composed of temperature-sensitive polymer segments. The average characteristic size of the microphase separation structure is 10-50 nm, so that the transmittance of the composite material at 550 nm wavelength is not less than 88% and the haze is not more than 2.5% at 25°C; and the transmittance at 550 nm wavelength is not more than 55% and the haze is not less than 50% at 50°C. The thermosensitive comonomer is selected from at least one of methoxy polyethylene glycol methacrylate, N-isopropylmethacrylamide, or methoxytriethylene glycol methacrylate; wherein, when the thermosensitive comonomer is methoxy polyethylene glycol methacrylate, its average molecular weight is 750 g / mol. The composite material is prepared by a method comprising the following steps: (a) Provide a mixture comprising methyl methacrylate, a thermosensitive comonomer and an initiator; (b) The mixture is subjected to in-situ copolymerization at a temperature of 70-85°C for 2.5-4 hours to form a prepolymer; (c) The prepolymer is subjected to multi-stage temperature-controlled curing, the curing process including: pre-curing at 40-60°C for 2-4 hours, main curing at 80-100°C for 4-6 hours, and post-curing at 120-140°C for 2-3 hours. In this process, the in-situ copolymerization and multi-stage temperature-controlled curing form a nanoscale microphase separation structure with an average feature size of 10-50 nm inside the resulting composite material, so that the composite material remains transparent below the phase transition temperature.

2. The composite material according to claim 1, characterized in that, It also includes surface-modified functional nanoparticles covalently bonded to the polymethyl methacrylate matrix; the average particle size of the functional nanoparticles is 10-50 nanometers, and the amount of the functional nanoparticles is 0.5%-8% of the total mass of the polymethyl methacrylate and the thermosensitive comonomer.

3. The composite material according to claim 2, characterized in that, The functional nanoparticles are selected from silica nanoparticles or zinc oxide nanoparticles. Furthermore, when the functional nanoparticles are zinc oxide nanoparticles, the transmittance of the composite material to ultraviolet light in the wavelength range of 320-400nm is less than 5%.

4. The composite material according to claim 1, characterized in that, The mixture in step (a) also contains functional nanoparticles, which are pre-modified with a silane coupling agent to introduce copolymerizable functional groups.

5. The composite material according to claim 4, characterized in that, The amount of the functional nanoparticles is 0.5%-8% of the total mass of the methyl methacrylate and the thermosensitive comonomer.

6. The composite material according to claim 4, characterized in that, The thermosensitive comonomer is N-isopropylmethacrylamide, the functional nanoparticles are silica nanoparticles, and the silane coupling agent is γ-methacryloyloxypropyltrimethoxysilane.

Images