Transparent dynamic covalent cross-linked polyurethane plate capable of being processed and remolded and preparation method of transparent dynamic covalent cross-linked polyurethane plate

Abstract

The invention relates to a transparent dynamic covalent cross-linked polyurethane plate capable of being processed and remolded and a preparation method of the transparent dynamic covalent cross-linked polyurethane plate. The transparent dynamic covalent cross-linked polyurethane plate comprises the following raw material components: polyisocyanate, a polyol chain extender, a functional cross-linking agent, a solvent and a catalyst, the plate structurally comprises at least one of boric acid ester with a thermal stimulation response function, Diels-Alder reaction, thiocarbamate bonds, oxime urethane bonds, disulfide bonds, imine bonds and carbamate bonds. According to the invention, dynamic covalent bonds with thermal response characteristics are introduced into cross-linking points, and the cross-linked polyurethane plate with high transparency, high mechanical strength and reversible processability is constructed through interaction and synergy with rich hydrogen bonds in polyurethane.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane sheet technology, and specifically relates to a processable, reshapeable, transparent, dynamically covalently crosslinked polyurethane sheet and its preparation method. Background Technology

[0002] Traditional thermosetting polyurethanes, due to their irreversible three-dimensional cross-linked structure, cannot be reprocessed by heating after molding and are difficult to recycle efficiently. This results in products being difficult to regenerate once they are discarded, causing resource waste and increasing environmental burden. With the increasing demand for sustainable development and material recycling, the non-recyclability and non-remodelability of these materials have become major bottlenecks restricting their application and green transformation. Therefore, developing polyurethane materials that combine excellent performance with reversible processing characteristics has become an important research direction in the field of polymer materials.

[0003] Currently, common polyurethane materials on the market, especially formulations based on aliphatic or partially aromatic isocyanates, generally suffer from yellowing and unstable transparency. Under the influence of light, heat and oxygen, or humid environments, the aromatic rings in the polyurethane molecule cause the material to gradually yellow and its light transmittance to decrease, severely affecting its long-term performance in high-transparency applications. This defect significantly limits the application expansion of polyurethane in high-end fields such as transparent windows, optical components, and protective windows. Therefore, developing a polyurethane sheet that combines high strength, weather resistance, long-term transparency, and processability is of great significance in meeting these market demands, especially in applications requiring lightweight design, safety, and the ability to form complex curved surfaces. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a processable and reshapeable transparent dynamic covalent crosslinked polyurethane sheet and its preparation method. Dynamic covalent bonds with thermal response characteristics are introduced at the crosslinking points. Through synergistic interaction with the abundant hydrogen bonds in polyurethane, a crosslinked polyurethane sheet with high transparency, high mechanical strength and reversible processability is constructed.

[0005] This invention provides a processable, remodelable, transparent, dynamically covalently crosslinked polyurethane sheet, wherein the raw material components, by weight, include:

[0006] 1-100 parts of polyisocyanate;

[0007] 70-90 parts of polyol chain extender;

[0008] 1-20 parts of functional crosslinking agent;

[0009] Solvent: 10-100 parts;

[0010] 0-5 parts of catalyst;

[0011] The structure of the plate contains at least one of the following: boronic acid ester, Diels-Alder reaction, thiocarbamate bond, oxime ester bond, disulfide bond, imine bond, and carbamate bond, which have a heat-stimulated response function.

[0012] Preferably, the polyisocyanate includes at least one of 4,4'-methylene bis(phenyl isocyanate), toluene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane-diisocyanate, naphthalene diisocyanate, terephthalic diisocyanate, 1,4-cyclohexane diisocyanate, phenyl dimethylene diisocyanate, tetramethyl isophthalic diisocyanate, dimethyl biphenyl diisocyanate, polymethylene polyphenyl isocyanate, and modified diisocyanate (such as liquefied MDI from Yantai Wanhua).

[0013] Preferably, the polyol chain extender includes p-phenylenediethanol, dihydroxydiphenylsilane, resorcinol, catechol, 2,2-bis(4-hydroxyphenyl)propane, biphenyl, [1,1':4',1''-terphenyl]-4,4''-diol, 4-amino-4-hydroxybiphenyl, 4-(4-hydroxymethylphenyl)phenol, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxythiophenol, [1,1:3,1 [-terphenyl]-4,4'-diol, 1,5-pentanediol, 1,4-butanediol, p-aminophenol, [1,1-bisphenyl]-2,4-diol, p-hydroxybenzyl alcohol, 4,4'-(ethylene-1,1-diyl)biphenol, 4,4'-dihydroxymethylbiphenyl, 1,3-bis(4-hydroxyphenyl)propane, biphenyl-4,4'-dithiol, 2,6-dihydroxynaphthalene, bis(4-hydroxybenzene)1,4-diisopropylbenzene, 2,7-dihydroxynaphthalene, or one or more of these.

[0014] Preferably, the functional crosslinking agent comprises at least one of boric acid, 1,4-phenyldiboronic acid, trimethylolpropane tris(3-mercaptopropionic acid) ester, 4,4-biphenyldiboronic acid, diaminoglyoxime, pentaerythritol tetrakis(3-mercaptopropionic acid) ester, dipentaerythritol hexa(3-mercaptopropionic acid) ester, trimesonol, tris(3-mercaptopropionate), pentaerythritol tetra(mercaptoacetic acid) ester, diphenylmethane bismaleimide, and m-phenylene bismaleimide.

[0015] Preferably, the solvent includes one or more of acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, N,N'-dimethylformamide, N,N'-dimethylacetamide, N-methylpyrrolidone, ethyl acetate, butyl acetate, ethylene glycol ethyl ether acetate, and dichloromethane.

[0016] Preferably, the catalyst includes one or more of organometallic catalysts and tertiary amine catalysts.

[0017] This invention also provides a method for preparing a processable, remodelable, transparent, dynamically covalently crosslinked polyurethane sheet, comprising the following steps:

[0018] (1) The polyol chain extender was vacuum stirred and dehydrated at 80-100℃ for 1-5h, and then cooled to 50-70℃ to obtain the pretreated product;

[0019] (2) Add the solvent to the above pretreated product, stir evenly under inert protective gas, then add polyisocyanate and react at 50-120℃ for 1-24 hours, then add functional crosslinking agent and continue to react for 1-5 hours to obtain polyurethane product.

[0020] (3) Apply the polyurethane product onto an iron plate and place it in a vacuum oven at 50-110°C for 2-24 hours. Then, maintain the vacuum state for 2-24 hours to remove the solvent in the reaction system, and a transparent polyurethane board is obtained.

[0021] Beneficial effects

[0022] This invention introduces dynamic covalent bonds with thermally responsive characteristics into the crosslinking points of a polyurethane network structure, achieving the following beneficial effects: On the one hand, it endows traditional thermosetting polyurethane materials with reversible crosslinking properties, enabling partial dissociation and reconstruction of the network structure under heating conditions, thus possessing good processability and remodelability. This overcomes the technical bottlenecks of existing crosslinked polyurethane materials being unable to be thermally processed and recycled. This structural design provides the material with structural stability and environmental adaptability, facilitating its reuse in high-end transparent structural components and complex structural molding, thereby enhancing the material's comprehensive performance and application value. On the other hand, simultaneously, through the construction of a hydrogen bond network in the polyurethane molecule and the uniform distribution of dynamic crosslinking points, a high degree of order and synergistic effect in the material's internal structure is achieved, effectively enhancing the inter-segment forces and energy dissipation capacity. While enhancing the overall mechanical properties of the material, it avoids light scattering problems caused by phase separation or microphase structure, thus endowing the material with excellent optical transparency and high mechanical strength, achieving a harmonious unity between high transparency and mechanical properties. Attached Figure Description

[0023] Figure 1 Transmittance diagram (a), transparent physical image (b), and infrared spectrum (c) of the dynamically cross-linked polyurethane sheet prepared for the example.

[0024] Figure 2 The mechanical properties (a) and hardness and Young's modulus data (b) of the dynamically cross-linked polyurethane sheet prepared for the example are shown.

[0025] Figure 3 The image shows the effect of hot-pressing remolding of the dynamically cross-linked polyurethane sheet prepared in the example. Detailed Implementation

[0026] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0027] raw material:

[0028] 1,4-Butanediol was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., trimethylolpropane tris(3-mercaptopropionic acid) ester was purchased from Sinopharm Chemical Reagent Co., Ltd., and 4,4'-dicyclohexylmethane diisocyanate was purchased from Wanhua Chemical Group Co., Ltd.

[0029] Relevant test content:

[0030] Structural characterization: The structures of the crosslinked polyurethane before and after synthesis were characterized using Fourier transform infrared spectroscopy (FTIR). Attenuated total reflectance (ATR) spectroscopy was used for testing, with 32 scans performed and a wavelength range of 4000-400 cm⁻¹. -1 Spectral resolution of 4 cm -1 .

[0031] Transmittance Characterization: The transmittance of cross-linked polyurethane sheets was characterized using a UV-Vis spectrophotometer (model: UV-3600, Shimadzu Corporation). The scanning mode was set to transmission spectroscopy, with 16 scans, a wavelength range of 200-800 nm, a spectral resolution of 1 nm, and a scanning speed of medium (240 nm / min). Air was used as a reference for instrument calibration before testing, and a standard quartz cuvette (10 mm optical path) was used as a blank control. Three different regions of each sample were selected for testing, and the final results were averaged. Data processing and analysis were performed according to GB / T2410-2008 "Determination of transmittance and haze of transparent plastics".

[0032] Characterization of mechanical properties of transparent polyurethane sheets: In the following examples, the mechanical properties of transparent polyurethane sheets were characterized using a universal testing machine. Rectangular strips were cut from the prepared samples, and the mechanical properties of the materials were tested at room temperature. The uniaxial tensile rate was set to 50 mm / min.

[0033] Characterization of polyurethane sheet remolding performance: The test was conducted using a flatbed hot press: the crushed sheet was placed in the mold and hot-pressed for 15 min at a temperature of 100℃ and a pressure of 5 MPa. After cooling and demolding, the tensile strength, elongation at break and other mechanical properties of the remolded sheet were tested, and the performance retention rate with the original sheet was calculated to evaluate the reprocessing capability of the material. At the same time, temperature gradients such as 80℃ and 120℃ and time gradients of 10 min and 20 min can be set to optimize the best remolding process parameters.

[0034] Example 1

[0035] By mass, 70 parts of 1,4-butanediol were placed under vacuum at 110°C for 2 hours to remove water, and then cooled to 50°C to obtain a pretreated product. Then, 100 parts of dicyclohexylmethane diisocyanate and 100 parts of dimethylformamide were added, and the mixture was reacted under nitrogen protection at 80°C for 4 hours. Then, 30 parts of trimethylolpropane tris(3-mercaptopropionic acid) ester were added and reacted for 1 hour to obtain a polyurethane product. The product was then coated onto an iron plate, placed in an oven at 50°C, and reacted for another 24 hours. The solvent was then removed under vacuum at 75°C to obtain a dynamically cross-linked polyurethane board, which was designated as DCPU-1.

[0036] Example 2

[0037] By mass fraction, 80 parts of 1,4-butanediol were placed under vacuum at 110°C for 2 hours to remove water. Then, 100 parts of dicyclohexylmethane diisocyanate and 100 parts of dimethylformamide were added and reacted under nitrogen protection at 80°C for 4 hours. Then, 20 parts of trimethylolpropane tris(3-mercaptopropionic acid) ester were added and reacted for 1 hour to obtain a polyurethane product. Subsequently, the product was coated onto an iron plate and placed in an oven at 50°C for 24 hours to continue the reaction. After that, the solvent was removed under vacuum at 75°C to obtain a dynamically cross-linked polyurethane board, which was designated as DCPU-2.

[0038] Example 3

[0039] By mass fraction, 90 parts of 1,4-butanediol were placed under vacuum at 110°C for 2 hours to remove water. Then, 100 parts of dicyclohexylmethane diisocyanate and 100 parts of dimethylformamide were added and reacted under nitrogen protection at 80°C for 4 hours. Then, 10 parts of trimethylolpropane tris(3-mercaptopropionic acid) ester were added and reacted for 1 hour to obtain a polyurethane product. Subsequently, the product was coated onto an iron plate and placed in an oven at 50°C for 24 hours to continue the reaction. After removing the solvent under vacuum at 75°C, a dynamically cross-linked polyurethane board was obtained, which was designated as DCPU-3.

[0040] Test case

[0041] like Figure 1The ultraviolet spectra shown in Figure a indicate that the light transmittance of the plates prepared in Examples 1-3 at a wavelength of 550 nm reaches over 91%, with Example 3 achieving a transmittance of 92.58% at 550 nm. Within the visible light wavelength range of 400-760 nm, the average transmittance of the samples from the above examples is all >90%, meeting the optical performance requirements of high-transmittance materials and achieving high optical transparency in the visible light region. Under natural sunlight, the materials exhibit beneficial transparency effects, such as... Figure 1 b indicates that the material of the present invention has significant application value in fields such as optical devices and transparent structural components.

[0042] like Figure 1 The infrared spectrum shown in c indicates that the plates prepared in Examples 1-3 have an infrared spectrum at a wavelength of 3335 cm⁻¹. -1 The stretching vibration peak of NH was observed in all samples, with a peak at 1698 cm⁻¹. -1 The presence of C=O stretching vibrations indicates the successful synthesis of the carbamate bond, bound to 2265 cm⁻¹. -1 The absence of stretching vibration peaks of isocyanate groups (N=C=O) indicates that the raw materials have reacted sufficiently, and the dynamic crosslinked polyurethane has been successfully synthesized.

[0043] like Figure 2 As shown in the mechanical curve diagram, the mechanical strength of the plates prepared in Examples 1-3 all reached above 50 MPa, with Example 1 reaching a strength of 61 MPa. Figure 2 As shown in b, the Young's modulus reaches 1.3 GPa and the Shore D hardness reaches 82D. Compared with the hardness of traditional ordinary glass (50-70 Shore D), the plate of this invention achieves a synergistic improvement in tensile strength, rigidity and surface hardness while maintaining high light transmittance. It has significant technical advantages and industrial application potential in replacing traditional transparent materials.

[0044] like Figure 3 The results of the hot-pressing reshaping test of the plates prepared in Examples 1-3 are shown. After pulverizing the dynamically cross-linked polyurethane glass samples, they were hot-pressed for 5 minutes under a pressure of 10 MPa and a temperature of 110°C. The results show that the plates prepared in Examples 1-3 can all achieve effective reshaping. The reshaped material maintains high transparency, and the light transmittance, as tested, remains above a specific value, such as 90%. Combined with the light transmittance test data, it meets the optical performance standards for high-transmittance materials. The plates of this invention, while maintaining high light transmittance, exhibit excellent hot-pressing reshaping capabilities. Compared with traditional transparent materials (such as ordinary glass which cannot be hot-pressed and reshaping, and acrylic glass which is prone to yellowing and a significant decrease in light transmittance after hot-pressing), this invention has outstanding technical advantages and promising prospects for industrial application in replacing traditional transparent materials. It can be widely used in aerospace, building curtain walls, automotive windows, and other fields with stringent requirements for material transparency, repairability, and mechanical properties.

Claims

1. A processable, reshapeable, transparent, dynamically covalently cross-linked polyurethane sheet, characterized in that, According to parts by mass, its raw material components include: 1-100 parts of polyisocyanate; 70-90 parts of polyol chain extender; 1-20 parts of functional crosslinking agent; Solvent: 10-100 parts; 0-5 parts of catalyst; The structure of the plate contains at least one of the following: boronic acid ester, Diels-Alder reaction, thiocarbamate bond, oxime ester bond, disulfide bond, imine bond, and carbamate bond, which have a heat-stimulated response function.

2. The processable, remodelable, transparent, dynamically covalently cross-linked polyurethane sheet according to claim 1, characterized in that, The polyisocyanate includes at least one of 4,4'-methylene bis(phenyl isocyanate), toluene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane-diisocyanate, naphthalene diisocyanate, terephthalic diisocyanate, 1,4-cyclohexane diisocyanate, phenyl diisocyanate, tetramethyl isophthalic diisocyanate, dimethyl biphenyl diisocyanate, polymethylene polyphenyl isocyanate, and modified diisocyanate.

3. The processable, remodelable, transparent, dynamically covalently cross-linked polyurethane sheet according to claim 1, characterized in that, The polyol chain extender includes p-phenylenediamine, dihydroxydiphenylsilane, resorcinol, catechol, 2,2-bis(4-hydroxyphenyl)propane, biphenyl, [1,1':4',1''-terphenyl]-4,4''-diol, 4-amino-4-hydroxybiphenyl, 4-(4-hydroxymethylphenyl)phenol, 4,4'-dihydroxydiphenyl sulfone, 4-hydroxythiophenol, [1,1:3,1 [-terphenyl]-4,4'-diol, 1,5-pentanediol, 1,4-butanediol, p-aminophenol, [1,1-bisphenyl]-2,4-diol, p-hydroxybenzyl alcohol, 4,4'-(ethylene-1,1-diyl)biphenol, 4,4'-dihydroxymethylbiphenyl, 1,3-bis(4-hydroxyphenyl)propane, biphenyl-4,4'-dithiol, 2,6-dihydroxynaphthalene, bis(4-hydroxybenzene)1,4-diisopropylbenzene, 2,7-dihydroxynaphthalene, or one or more of these.

4. The processable, remodelable, transparent, dynamically covalently cross-linked polyurethane sheet according to claim 1, characterized in that, The functional crosslinking agent includes at least one of boric acid, 1,4-phenyldiboronic acid, trimethylolpropane tris(3-mercaptopropionic acid) ester, 4,4-biphenyldiboronic acid, diaminoglyoxime, pentaerythritol tetrakis(3-mercaptopropionic acid) ester, dipentaerythritol hexa(3-mercaptopropionic acid) ester, pyromellitic methyl ester, tris(3-mercaptopropionate), pentaerythritol tetra(mercaptoacetic acid) ester, diphenylmethane bismaleimide, and m-phenylene bismaleimide.

5. The processable, reconfigurable, transparent, dynamically covalently cross-linked polyurethane sheet according to claim 1, characterized in that, The solvent includes one or more of acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, N,N'-dimethylformamide, N,N'-dimethylacetamide, N-methylpyrrolidone, ethyl acetate, butyl acetate, ethylene glycol ethyl ether acetate, and dichloromethane.

6. The processable, remodelable, transparent, dynamically covalently cross-linked polyurethane sheet according to claim 1, characterized in that, The catalyst includes one or more of organometallic catalysts and tertiary amine catalysts.

7. A method for preparing a processable, remodelable, transparent, dynamically covalently cross-linked polyurethane sheet as described in any one of claims 1-6, characterized in that, Includes the following steps: (1) The polyol chain extender was vacuum stirred and dehydrated at 80-100℃ for 1-5h, and then cooled to 50-70℃ to obtain the pretreated product; (2) Add the solvent to the above pretreated product, stir evenly under inert protective gas, then add polyisocyanate and react at 50-120℃ for 1-24 hours, then add functional crosslinking agent and continue to react for 1-5 hours to obtain polyurethane product. (3) Apply the polyurethane product onto an iron plate and place it in a vacuum oven at 50-110°C for 2-24 hours. Then, maintain the vacuum state for 2-24 hours to remove the solvent in the reaction system, and a transparent polyurethane board is obtained.

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