A photosensitive functional monomer and a method for preparing a light-cured 3D printing polyurethane elastomer using the same

Abstract

A photosensitive functional monomer and a method for preparing a light-cured 3D-printed polyurethane elastomer using the same, relating to self-healing polymer functional materials. This method aims to address the technical issues of low repair efficiency and poor mechanical properties of existing self-healing polyurethane elastomers prepared by light-cured 3D printing. The functional monomer of the present invention has the chemical formula: wherein m is 1, 2, 3, or 4; R is 1,4-phenylenediboronic acid, 1,2,4-butanetriol, water, and anhydrous magnesium sulfate, and then reacts the intermediate with 2-isocyanatoethyl acrylate. A slurry of the photosensitive functional monomer, a photosensitive resin monomer, a reactive diluent, and a photoinitiator is mixed and then 3D printed to produce a polyurethane elastomer with a tensile strength of 3 to 8.6 MPa, a visible light transmittance of 85%, 100% healing upon heating at 80°C, and self-healing properties at room temperature, making it suitable for 3D printing.

Description

Technical Field

[0001] The invention relates to a self-repairing polymer functional material and a method for preparing a 3D-printed polyurethane elastomer using the same. Background Art

[0002] 3D printing, also known as additive manufacturing, is an emerging rapid prototyping technology that has gained significant traction in fields such as biomedicine, aerospace, and smart devices. Stereolithography 3D printing, with its high resolution and efficiency, and its ability to produce micro-sized and complex structures, has become a research hotspot and holds promising prospects.

[0003] Polyurethane elastomers are widely used in many fields due to their unique molecular structure. However, during use, they are inevitably subject to physical damage caused by light, heat, or mechanical stimulation, which ultimately leads to a significant reduction in their service life and reliability. On the other hand, the disposal of waste polyurethane elastomers (including landfill or incineration) usually leads to a large amount of resource waste and environmental pollution. Self-healing polyurethane elastomers that can be photocured and 3D printed are a new type of material that can self-repair after being damaged. Due to this special function, self-healing polyurethane elastomers that can be photocured and 3D printed have shown great potential in fields such as coatings and flexible electronic devices.

[0004] Borate esters are dynamic covalent bonds with a unique combination of high thermodynamic stability and kinetic tunability. The bond dissociation energy of borate ester bonds is -124 kcal / mol. This high bond dissociation energy can impart high strength and thermal stability to polyurethane elastomers. Chinese patent application number CN201811583121.8, "A Method for Preparing a Self-Healing Photocurable Reconfigurable System Based on Borate Ester Exchange," prepares a bifunctional thiol monomer containing a borate ester bond via a one-step reaction. This is then subjected to a thiol-ene photoinitiated click reaction with a multifunctional double-bond monomer to produce a crosslinked system containing a borate ester bond. Because borate ester bonds can undergo an exchange reaction when heated, the photocured crosslinked system exhibits a certain degree of plasticity when heated, enabling self-healing and repeated reprocessing. However, this method uses solid or high-viscosity fluids that require dilution with an inert organic solvent. Furthermore, the thiol-containing raw materials have a strong odor, making them unsuitable for photocurable 3D printing. In 2020, the University of Science and Technology of China published a paper titled "Preparation and Performance Research of Self-Healing Polyurethane Materials" that described a polyurethane elastomer containing borate bonds. The elastomer exhibited a tensile strength of 7.73 MPa. However, after 24 hours of healing in water at room temperature, the toughness-based healing efficiency was only 62.03%, and after 24 hours of healing in air at room temperature, the healing efficiency was only 2.56%. A photocurable borate-based polyurethane exhibited a tensile strength of 288 kPa and a healing efficiency of only 80.8% after 24 hours of healing at room temperature. Summary of the Invention

[0005] The present invention aims to solve the technical problems of low repair efficiency and poor mechanical properties of self-healing polyurethane elastomers prepared by existing photocuring 3D printing, and provides a photosensitive functional monomer and a method for preparing photocuring 3D printed polyurethane elastomers using the same. The introduction of the photosensitive functional monomer containing a borate bond of the present invention enables the polyurethane elastomer to achieve high-precision photocuring 3D printing of complex configurations and imparts excellent self-healing properties under mild conditions. At the same time, the introduction of dynamic borate bonds enables the polyurethane elastomer to be repeatedly formed and processed by hot pressing.

[0006] The chemical formula of the photosensitive functional monomer of the present invention is:

[0007] Where m is 1, 2, 3 or 4; R is

[0008]

[0009] The photosensitive functional monomer of the present invention contains dynamic borate bonds. Under mild room temperature or heating conditions, an ester exchange reaction occurs between the borate bonds, and the hydrogen bonds can be broken and reorganized. The combination of the two can give the cross-linked polymer excellent self-repairing properties and hot pressing recovery properties.

[0010] Preferably, the chemical formula of the photosensitive functional monomer is:

[0011]

[0012] The preparation method of the above-mentioned photosensitive functional monomer is carried out according to the following steps:

[0013] 1. Dissolve 1,4-phenylenediboronic acid and 1,2,4-butanetriol in a solvent, add deionized water and mix well, then add anhydrous magnesium sulfate and react under stirring for 20 to 26 hours to obtain an intermediate product;

[0014] 2. Dissolve the intermediate product and the catalyst in a solvent, add 2-isocyanatoethyl acrylate, and stir the reaction at a temperature of 70-75°C in an inert gas atmosphere. End the reaction after infrared monitoring indicates that the isocyanate group has reacted to obtain a photosensitive functional monomer.

[0015] Preferably, the solvent in step 1 is tetrahydrofuran or dichloromethane.

[0016] Preferably, the molar ratio of 1,4-phenylenediboronic acid, 1,2,4-butanetriol and anhydrous magnesium sulfate in step 1 is 1:(1.9-2.1):(2.9-3.1).

[0017] Preferably, the amount of deionized water added in step 1 is 0.1 ml to promote the reaction process.

[0018] Preferably, the solvent in step 2 is tetrahydrofuran or dichloromethane.

[0019] Preferably, the catalyst in step 2 is dibutyltin dilaurate.

[0020] Preferably, the molar ratio of the intermediate product to 2-isocyanatoethyl acrylate in step 2 is 1:(2-2.1).

[0021] The method for preparing a light-cured 3D printed polyurethane elastomer using the above-mentioned photosensitive functional monomer is carried out in the following steps:

[0022] 1. Mix 1% to 20% of a photosensitive functional monomer, 60% to 99% of a photosensitive resin monomer, and 0% to 20% of a reactive diluent by mass, then add a photoinitiator and mix well to obtain a slurry;

[0023] 2. Add the slurry into a 3D printer for 3D printing to obtain a polyurethane elastomer.

[0024] Preferably, the photosensitive resin monomer in step 1 is monofunctional polyurethane acrylate.

[0025] Preferably, the photoinitiator in step 1 is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, benzoin dimethyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone or 1-hydroxycyclohexyl phenyl ketone; the amount of the photoinitiator is 0.5% to 5% of the total mass of the photosensitive functional monomer, the photosensitive resin monomer and the reactive diluent.

[0026] Preferably, the reactive diluent in step 1 is hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylic acid, isobornyl acrylate, isobornyl methacrylate, 4-acryloylmorpholine, dicyclopentadienyl acrylate or benzyl acrylate.

[0027] Preferably, the 3D printing in step 2 is: using ultraviolet curing with a wavelength range of 265nm to 420nm, in the process of light-curing 3D printing, the number of overexposure layers is set to 1 to 6 layers, the layer thickness is set to 10 to 150μm, the curing time of each layer is 500ms to 2000ms, and the light intensity is 10mw / cm 2 ~55mw / cm 2 The thickness of the remaining layers is set to 10-150 μm, the curing time of each layer is 500ms-2000ms, and the light intensity is 10mw / cm 2 ~55mw / cm 2, obtaining a polyurethane elastomer having excellent self-repairing function and hot pressing recovery function.

[0028] Preferably, the ultraviolet light is ultraviolet light with a wavelength of 405 nm.

[0029] The present invention synthesizes a photosensitive functional monomer containing a dynamic borate ester bond through molecular design. By copolymerizing it with monofunctional polyurethane acrylate and reactive diluent free radicals, a photocurable 3D-printable polyurethane elastomer with self-repairing and recyclable functions can be prepared.

[0030] The photosensitive functional monomer containing a dynamic borate ester bond of the present invention has universal applicability, and any monofunctional photosensitive compound monomer or diluent can be used to prepare a photocurable 3D printing material with self-repairing and recyclable functions.

[0031] The self-healing properties of the polyurethane elastomer prepared by this invention are achieved through strong dynamic covalent bonds (borate bonds) and weak non-dynamic covalent bonds (hydrogen bonds). As non-covalent bonds, hydrogen bonds have a bond energy far less than borate bonds. However, introducing a large number of hydrogen bonds into the polyurethane molecular chain not only enhances the strength of the polyurethane elastomer but also imparts self-healing properties at room temperature, achieving 100% healing upon heating at 80°C. Compared to other strong dynamic covalent bonds, such as DA bonds (which generally have a healing temperature above 110°C), this type of elastomer has a mild healing temperature and high healing efficiency.

[0032] The polyurethane elastomer prepared by the present invention can achieve a self-repairing function without adding a catalyst, thereby reducing the use of additional toxic catalysts.

[0033] The polyurethane elastomer prepared by the present invention has excellent mechanical properties, with a tensile strength of 3 to 8.6 MPa. It is easily recyclable, reducing resource waste and environmental pollution. Furthermore, the polyurethane elastomer has a visible light transmittance of 85%. This high transmittance not only facilitates deep curing of the resin but also offers a wider range of applications compared to colored polyurethane elastomers. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the infrared reflection spectrum of the intermediate BDB prepared in Example 1.

[0035] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the intermediate BDB prepared in Example 1.

[0036] Figure 3 This is the infrared reflection spectrum of the photosensitive functional monomer ABDBA containing a borate bond prepared in Example 1.

[0037] Figure 4This is the hydrogen nuclear magnetic resonance spectrum of the photosensitive functional monomer ABDBA containing a borate bond prepared in Example 1.

[0038] Figure 5 This is a tensile test curve of polyurethane elastomers with different photosensitive functional monomer ABDBA contents in Application Examples 1 to 5.

[0039] Figure 6 This is a tensile test curve of the polyurethane elastomer prepared in Application Example 1 before and after self-repair.

[0040] Figure 7 This is the macroscopic healing tensile performance diagram of the polyurethane elastomer prepared in Application Example 1.

[0041] Figure 8 This is a graph showing the macroscopic healing performance of the polyurethane elastomer prepared in Application Example 1.

[0042] Figure 9 This is a photo of the hot pressing recovery of the polyurethane elastomer prepared in Application Example 1.

[0043] Figure 10 This is a transmittance curve of the polyurethane elastomer prepared in Application Example 1.

[0044] Figure 11 This is a transparent photo of the sheet-like polyurethane elastomer prepared in Application Example 1. DETAILED DESCRIPTION

[0045] In order to describe the technical solution of the present invention more clearly and completely, the present invention is further described in detail below through specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0046] Example 1: The preparation method of the photosensitive functional monomer of this embodiment is carried out according to the following steps:

[0047] 1. Add 3.0 g (18 mmol) of 1,4-phenylenediboronic acid to 80 mL of tetrahydrofuran, ultrasonically stir until 1,4-phenylenediboronic acid is completely dissolved, then add 3.816 g (36 mmol) of 1,2,4-butanetriol and 0.1 mL of deionized water, stir for 5 min, then add 6.48 g (54 mmol) of anhydrous MgSO4, stir and react at room temperature for 24 h, filter after the reaction, evaporate and concentrate the filtrate to obtain a white solid, then add the white solid to 60 ° C n-heptane and stir for 2 h to dissolve it, filter, evaporate and concentrate the filtrate to obtain a white product again, and finally dry the white product in a vacuum oven at a temperature of 50 ° C for 24 h to obtain an intermediate product, recorded as BDB;

[0048] 2. Dissolve 2.5 g (8.2 mmol) of BDB prepared in step 1 in 40 mL of tetrahydrofuran. Dissolve the BDB by sonication. Add 0.005 g of dibutyltin dilaurate as a catalyst to obtain a mixed solution. Then, raise the temperature of the mixed solution to 70°C and slowly add 2.3124 g (16.4 mmol) of 2-isocyanatoethyl acrylate to the mixed solution. Monitor the reaction progress by infrared spectroscopy. When the infrared reflectance monitor indicates the absence of isocyanate groups, terminate the reaction. Remove the tetrahydrofuran solvent by rotary evaporation to obtain a photosensitive functional monomer, designated ABDBA. The entire preparation of ABDBA was carried out under an N2 atmosphere. ABDBA is a photosensitive functional monomer containing a borate ester bond.

[0049] The synthetic route of the intermediate product BDB in step 1 of this embodiment 1 is:

[0050]

[0051] The infrared reflection spectrum of the intermediate product BDB is shown in Figure 1 As shown, from Figure 1 It can be seen that at 1300cm -1 The asymmetric stretching vibration peak of the -BO group appears at 1170 cm -1 The bending vibration peak of the -B-OH group disappeared, indicating that the intermediate product BDB was successfully synthesized.

[0052] The H NMR spectrum of the intermediate product BDB is as follows Figure 2 As shown, Figure 2 The attribution of each peak is given in Figure 2 As you can see, 1 HNMR (400 MHz, DMSO-d6) δ7.70 (s, 2H), 4.96–4.63 (m, 1H), 4.47–3.91 (m, 3H), 3.65–3.47 (m, 2H), 2.10–1.70 (m, 2H), further indicating that the intermediate product BDB was successfully synthesized.

[0053] The synthetic route of ABDBA in step 2 of this embodiment 1 is as follows:

[0054]

[0055] The infrared reflection spectrum of the photosensitive functional monomer ABDBA is shown in the figure below: Figure 3 As shown, from Figure 3 It can be seen that at 2265cm -1 The characteristic peak of -N=C=O at 1722cm -1 The C=C vibration peak appears at 1600~1650cm-1 At 1300cm -1 The asymmetric stretching vibration peak of the -BO- group appeared at , indicating that the photosensitive functional monomer ABDBA containing a borate ester bond was successfully synthesized.

[0056] The H NMR spectrum of the photosensitive functional monomer ABDBA is as follows: Figure 4 As shown, Figure 4 The attribution of each peak is given in Figure 4 As you can see, 1 H NMR (400 MHz,) δ7.69 (d, J = 14.2 Hz, 2H), 6.36 (d, J = 17.4 Hz, 1H), 6.05 (dd, J = 17.2, 10.7 Hz, 1H), 5.79 (dd, J = 10.4, 3.9 Hz, 1H), 5.39 (dt, J = 71.8, 6.1 Hz, 1H), 4.33–3.97 (m, 7H), 3.47–3.33 (m, 2H), 2.01–1.82 (m, 2H), indicating that the dynamic cross-linker based on boronate bond was successfully synthesized.

[0057] Application Example 1: A light-curable 3D printing polyurethane elastomer is prepared using the photosensitive functional monomer prepared in Example 1. The specific method is as follows:

[0058] 1. Mix 12% of the photosensitive functional monomer ABDBA prepared in Example 1, 68% of the monofunctional polyurethane acrylate, and 20% of hydroxyethyl acrylate to obtain a mixed solution; then add 1% of the mass of the mixed solution as photoinitiator I-819, and mix again to obtain a slurry;

[0059] Second, the slurry was added to the DLP printer for photocuring 3D printing of dumbbell-shaped samples and sheet samples. The laser wavelength of the photocuring was 405nm, the number of overexposure layers was 3, each layer was 80μm thick, and the light intensity of the first layer was 15mw / cm 2 , the illumination time is 1000ms; the thickness of the remaining layers is 80μm, and the light intensity is 15mw / cm 2 , the illumination time is 900ms, and the printing is completed to obtain the light-cured 3D printed dumbbell-shaped polyurethane elastomer sample and sheet sample.

[0060] Application Example 2: This application example differs from Application Example 1 in that in step 1, 9% of the photosensitive functional monomer ABDBA prepared in Example 1, 71% of the monofunctional polyurethane acrylate, and 20% of hydroxyethyl acrylate are mixed uniformly by mass to obtain a mixed liquid; then, a photoinitiator I-819 is added at 1% of the mass of the mixed liquid, and the mixture is mixed uniformly again to obtain a slurry; the other steps and parameters are the same as those in Application Example 1.

[0061] Application Example 3: This application example differs from Application Example 1 in that in step 1, 6% of the photosensitive functional monomer ABDBA prepared in Example 1, 74% of the monofunctional polyurethane acrylate, and 20% of hydroxyethyl acrylate are mixed uniformly by mass to obtain a mixed liquid; then, a photoinitiator I-819 is added at 1% of the mass of the mixed liquid, and the mixture is mixed uniformly again to obtain a slurry; the other steps and parameters are the same as those in Application Example 1.

[0062] Application Example 4: This application example differs from Application Example 1 in that in step 1, 3% of the photosensitive functional monomer ABDBA prepared in Example 1, 77% of the monofunctional polyurethane acrylate, and 20% of hydroxyethyl acrylate are mixed uniformly by mass to obtain a mixed liquid; then, photoinitiator I-819 is added at 1% of the mass of the mixed liquid, and the mixture is mixed uniformly again to obtain a slurry; the other steps and parameters are the same as those in Application 1.

[0063] Application Example 5: This application example differs from Application Example 1 in that in step 1, 80% of monofunctional polyurethane acrylate and 20% of hydroxyethyl acrylate are mixed uniformly by mass to obtain a mixed liquid; then, photoinitiator I-819 is added at 1% of the mass of the mixed liquid, and the mixture is mixed uniformly again to obtain a slurry; the other steps and parameters are the same as those in Application 1.

[0064] The tensile test curves of the dumbbell-shaped polyurethane elastomer samples printed in Application Examples 1 to 5 are shown in the figure below. Figure 5 The tensile strength and elongation at break of each sample are shown in Table 1.

[0065] Table 1 Tensile strength and elongation at break of dumbbell-shaped polyurethane elastomer samples printed in Application Examples 1 to 5

[0066] sample ABDBA content Tensile strength (MPa) Elongation at break (%) Application Example 1 12％ 8.64 285 Application Example 2 9％ 7.43 278 Application Example 3 6％ 5.68 463 Application Example 4 3％ 4.68 654 Application Example 5 0 3.25 1261

[0067] from Figure 5 As can be seen from Table 1, with the increase of the content of the photosensitive functional monomer ABDBA containing a borate bond, the tensile strength of the polyurethane elastomer sample increased from 3.25 MPa to 8.64 MPa, while the elongation at break gradually decreased from 1261% to 285%.

[0068] The dumbbell-shaped polyurethane elastomer sample printed in Application Example 1 was cut, and then the cross-sections were tightly fitted and placed in an oven at 80°C for 12 hours to allow the cut dumbbell-shaped sample to heal. The strength of the healed dumbbell-shaped sample was tested and compared with the strength of the undamaged dumbbell-shaped polyurethane elastomer sample. The comparison chart is as follows: Figure 6 As shown, from Figure 6As can be seen in the figure, the tensile properties of the polyurethane elastomer after healing at 80°C for 12 hours are similar to those of the original elastomer. This is because after the cut surface is reconnected, the borate bonds can exchange under heating conditions, hydrogen bonds break and reorganize, and the network topology is re-arranged, achieving a healing efficiency of 100%. This proves that the polyurethane elastomer has excellent self-healing properties.

[0069] The dumbbell-shaped polyurethane elastomer sample printed in Application Example 1 was cut into two sections, and then the sections were tightly butted together at room temperature of 25°C for 1 hour. The macroscopic healing performance was as follows: Figure 7 and Figure 8 As shown, from Figure 7 It can be seen that no obvious cut surface can be seen after healing, and the healed sample still does not break after experiencing large deformation; Figure 8 It can be seen that the healed sample can withstand a weight of 600g without breaking, indicating that the sample has good room temperature healing ability.

[0070] The dumbbell-shaped polyurethane elastomer sample printed in Application Example 1 was cut into pieces with scissors, placed in a mold, and hot-pressed in a hot press at a temperature of 120°C for 3 hours and a pressure of 20 MPa. After cooling to room temperature and being taken out, the polyurethane elastomer fragments were restored to a sheet-like whole. The photos before and after hot pressing are shown in the figure. Figure 9 As shown, it shows that polyurethane elastomer can be recycled by hot pressing.

[0071] The transmittance of the dumbbell-shaped polyurethane elastomer sample printed in Application Example 1 was tested, and the transmittance curve obtained is shown in the figure below. Figure 10 As shown, from Figure 10 It can be seen that the visible light transmittance of the polyurethane elastomer reaches 85%. Good transmittance is not only conducive to the deep curing of the resin, but also compared with colored polyurethane elastomers, polyurethane elastomers with better transparency have a wider range of applications.

[0072] Place the polyurethane elastomer sheet sample printed in Application Example 1 on the color plate to test the transmittance of the polyurethane elastomer sheet sample. Figure 11 As shown, from Figure 11 It can be seen that the picture of the 1 mm thick polyurethane film superimposed on the colored paper card has almost no loss of clarity, which intuitively demonstrates the good transparency of the prepared polyurethane elastomer.

Claims

1. A photosensitive functional monomer, characterized in that: The chemical formula of the photosensitive functional monomer is: or 。 2. A method for preparing a photosensitive functional monomer according to claim 1, characterized in that: The method proceeds as follows:

1. Dissolve 1,4-phenylenediboronic acid and 1,2,4-butanetriol in a solvent, add deionized water and mix well, then add anhydrous magnesium sulfate and react under stirring for 20-26 hours to obtain an intermediate product; 2. Dissolve the intermediate product and the catalyst in a solvent, add 2-isocyanatoethyl acrylate, and stir the reaction at 70-75°C in an inert gas atmosphere. End the reaction after infrared monitoring indicates that the isocyanate group has reacted to obtain a photosensitive functional monomer.

3. The method for preparing a photosensitive functional monomer according to claim 2, wherein: The solvent in step 1 is tetrahydrofuran or dichloromethane.

4. The method for preparing a photosensitive functional monomer according to claim 2 or 3, characterized in that: The molar ratio of 1,4-phenylenediboronic acid, 1,2,4-butanetriol and anhydrous magnesium sulfate described in step 1 is 1:(1.9-2.1):(2.9-3.1).

5. The method for preparing a photosensitive functional monomer according to claim 2 or 3, characterized in that: The molar ratio of the intermediate product in step 2 to 2-isocyanatoethyl acrylate is 1:(2-2.1).

6. A method for preparing a light-cured 3D printing polyurethane elastomer using a photosensitive functional monomer according to claim 1, characterized in that: The method proceeds as follows:

1. Mix 1% to 20% of a photosensitive functional monomer, 60% to 99% of a monofunctional polyurethane acrylate, and 0% to 20% of a reactive diluent by mass, then add a photoinitiator and mix well to obtain a slurry; 2. Add the slurry into a 3D printer for 3D printing to obtain a polyurethane elastomer.

7. The method for preparing a light-cured 3D printing polyurethane elastomer using a photosensitive functional monomer according to claim 6, characterized in that: The photoinitiator described in step 1 is phenyl bis (2,4,6-trimethylbenzoyl) phosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, benzoin dimethyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone or 1-hydroxycyclohexyl phenyl ketone; the amount of the photoinitiator is 0.5% to 5% of the total mass of the photosensitive functional monomer, the photosensitive resin monomer and the reactive diluent.

8. The method for preparing a light-cured 3D printing polyurethane elastomer using a photosensitive functional monomer according to claim 6, characterized in that: The active diluent in step 1 is hydroxyethyl acrylate, hydroxyethyl methacrylate, acrylic acid, isobornyl acrylate, isobornyl methacrylate, 4-acryloylmorpholine, dicyclopentadienyl acrylate or benzyl acrylate.

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