Preparation method and application of dynamic covalent bond dual-curing 3D printing organic silicon resin

Abstract

The invention relates to the technical field of 3D printing material manufacturing, and discloses a preparation method and application of dynamic covalent bond dual-curing 3D printing organic silicon resin. The preparation method comprises the following steps: mixing an organic silicon polyurethane acrylate prepolymer, a reactive diluent, a micromolecular organic silicon thermosetting crosslinking agent and a photoinitiator to obtain resin, carrying out photocuring printing to obtain an initial blank, and carrying out heat treatment on the initial blank to dissociate hindered urea bonds and carry out secondary crosslinking with the micromolecular organic silicon thermosetting crosslinking agent. According to the preparation method, a photo-thermal dual-curing strategy is adopted, isocyanate groups generated by thermal dissociation of hindered urea bonds react with a micromolecular organic silicon thermosetting cross-linking agent, so that a polymer network is evolved into a high-crosslinking interpenetrating / hybrid network from an initial loose single structure, interlayer defects are eliminated, the cross-linking density is improved, and the cross-linking property is improved. The isotropic mechanical property is endowed to the organic silicon elastomer.

Description

Technical Field

[0001] This invention relates to the field of 3D printing material manufacturing technology, specifically to a method and application for preparing and using dynamic covalent bond dual-curing 3D printing silicone resin. Background Technology

[0002] Silicon elastomers have been applied in the fields of flexible electronic devices, biomedical implants and soft robots due to their biocompatibility, resistance to high and low temperatures and excellent flexibility. Digital light processing 3D printing technology can use liquid photosensitive resin to quickly manufacture silicone elastomer structures with complex geometries, making up for the shortcomings of traditional molding or casting processes that are difficult to process complex internal flow channels and lattice structures.

[0003] Existing photopolymerization 3D printing technology for silicone mainly relies on the free radical photopolymerization reaction of acrylated silicone prepolymers for molding. During the layer-by-layer printing process, ultraviolet light induces rapid cross-linking and curing of liquid resin, forming a three-dimensional network structure. Due to the fast rate of free radical polymerization, the double bond conversion rate on the surface of the cured layer is high, and there are few residual active reaction sites. This makes it difficult for newly deposited liquid resin layers to form dense chemical bonds with the surface of the cured layer. The connection between layers mainly relies on physical stacking or weak chemical bonding. As a result, the tensile strength and tear resistance of photopolymerization 3D printed silicone elastomers in the layer stacking direction are lower than those in the planar direction, exhibiting anisotropic mechanical properties. This limits the service life and reliability of photopolymerization 3D printed silicone elastomers as load-bearing structural components. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for preparing and applying dynamic covalent bond dual-curing 3D printing silicone resin, which solves the problems of weak interlayer bonding, insufficient mechanical strength, and anisotropy in photocuring 3D printing silicone materials in existing technologies.

[0005] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a method for preparing a dynamically covalently bonded dual-curing 3D printing silicone resin, comprising the following steps: S1. Mix the organosilicon polymer, diisocyanate and catalyst, and carry out the polymerization reaction under heating conditions to obtain an isocyanate-terminated intermediate. Then add the terminator to carry out the termination reaction until the isocyanate content meets the standard, and obtain organosilicon polyurethane acrylate prepolymer. S2. Take organosilicon polyurethane acrylate prepolymer, reactive diluent, small molecule organosilicon thermosetting crosslinking agent and photoinitiator, mix them evenly and degas them under light-protected conditions to obtain dynamic covalent bond dual curing 3D printing organosilicon resin. S3. Inject the dynamic covalent bond dual-curing 3D printing silicone resin into the 3D printer, and perform layer-by-layer photocuring according to the model data to obtain a photocured silicone elastomer preform. S4. The photocurable silicone elastomer preform is subjected to constant temperature heat treatment at high temperature, so that dynamic covalent bond dissociation occurs inside the photocurable silicone elastomer preform and a secondary crosslinking reaction is completed with the small molecule silicone thermosetting crosslinking agent. After cooling, a dynamic covalent bond double-cured 3D printed silicone elastomer is obtained.

[0006] By adopting the above technical solution, the preparation method of dynamic covalent bond dual curing 3D printing silicone resin utilizes the synergistic mechanism of photocuring and thermal curing.

[0007] First, in step S1, isocyanate reacts with end-capping agent to introduce hindered urea bonds and acrylates into the backbone of silicone polyurethane prepolymer, thereby imparting photocurable groups to the silicone polyurethane.

[0008] Secondly, in the S3 step photocuring stage, ultraviolet light initiates the free radical polymerization of acrylate double bonds, constructing a preliminary cross-linked network to form a photocurable silicone elastomer preform.

[0009] Finally, in the S4 heat treatment stage, the hindered urea bonds undergo a reverse dissociation reaction under heating conditions, generating isocyanate groups and amino groups. The generated isocyanate groups diffuse and undergo addition reactions with the pre-embedded small-molecule organosilicon thermosetting crosslinking agent rich in hydroxyl or amino groups in the system, generating urethane bonds or urea bonds. This process increases the content of organosilicon segments in the crosslinking network, improves the crosslinking density, eliminates the internal stress generated during photocuring, promotes chemical bonding between the printing layer interfaces, and enables the finally prepared dynamic covalent bond dual-curing 3D printed organosilicon elastomer to obtain isotropic mechanical properties.

[0010] Preferably, in step S1, the organosilicon polymer is a silanol-terminated polydimethylsiloxane or an aminopropyl-terminated polydimethylsiloxane, and the degree of polymerization n of the organosilicon polymer is an integer from 0 to 200; the diisocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate and isophorone diisocyanate; the end-capping agent is selected from one or more of 2-(tert-butylamino)ethyl methacrylate, hydroxyethyl acrylate and hydroxyethyl methacrylate.

[0011] By employing the above technical solution, terminally active polydimethylsiloxanes of a specific molecular weight are used as soft segments to impart flexibility to the material. When 2-(tert-butylamino)ethyl methacrylate is selected as the end-capping agent, the steric hindrance effect of the tert-butyl group reduces the bond energy of the urea bond, causing the hindered urea bond to undergo reversible dissociation under heating conditions, thus stimulating a dynamic bond exchange mechanism.

[0012] Preferably, in step S1, the specific process of the polymerization reaction is as follows: first, the temperature is raised to 50 to 60 degrees Celsius and reacted for 1.5 to 2 hours, then the temperature is raised to 80 to 85 degrees Celsius and reacted for 2 to 3 hours; the specific method of the end-capping reaction is as follows: the reaction system is cooled to 50 to 55 degrees Celsius, the end-capping agent is added dropwise, and after the addition is completed, the temperature is raised to 65 to 75 degrees Celsius and reacted for 3 to 4 hours until the isocyanate content is less than 0.1%.

[0013] By adopting the above technical solution, the segmented heating process ensures the symmetry of the reaction between the diisocyanate and the organosilicon polymer at both ends, and the temperature control in the end-capping stage ensures that the end-capping agent is grafted to the end of the organosilicon polyurethane acrylate prepolymer, preventing the acrylate double bond from undergoing thermal self-polymerization at high temperature, and ensuring the storage stability of the organosilicon polyurethane acrylate prepolymer.

[0014] Preferably, in step S2, the raw materials for preparing the dynamic covalent bond dual-curing 3D printing silicone resin include, by weight, 100 parts of silicone polyurethane acrylate prepolymer; 20 to 50 parts of reactive diluent; 1 to 10 parts of small molecule silicone thermosetting crosslinking agent; and 0.8 to 1.8 parts of photoinitiator.

[0015] By adopting the above technical solution, the raw material ratio balances the viscosity of the printing resin and the mechanical properties after curing. The small molecule organosilicon thermosetting crosslinking agent is dispersed in the resin system as a dynamic bond acceptor and serves as a crosslinking site during the heat treatment stage, thereby increasing the content of organosilicon segments and improving the elasticity of the material.

[0016] Preferably, in step S2, the reactive diluent is selected from one or more of isobornyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, 4-acryloylmorpholine, N-vinylpyrrolidone, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, tricyclodecanediethanol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate.

[0017] By adopting the above technical solution, the reactive diluent adjusts the resin viscosity to adapt to the digital light processing 3D printing process, participates in photocuring crosslinking, and adjusts the rigidity of the cured network.

[0018] Preferably, in step S2, the small molecule organosilicon thermosetting crosslinking agent is selected from one or more of 1,1,3,3-tetramethyl-1,3-disilol, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, hydroxyalkyl-modified polysiloxane, and small molecule chain extenders containing hydroxyl or amino groups.

[0019] By employing the above technical solution, the small-molecule organosilicon thermosetting crosslinking agent contains active silanol or amino groups, which capture isocyanate groups generated by the dissociation of hindered urea bonds during the thermal activation stage. The small-molecule organosilicon thermosetting crosslinking agent has a small molecular size and strong diffusion ability, allowing it to penetrate into the crosslinking network and form urethane or urea bonds, thereby increasing the crosslinking density of the finished product.

[0020] Preferably, in step S3, the 3D printer is a digital light processing 3D printer, the printing parameters are set to a layer thickness of 0.05 to 0.1 mm, a single layer exposure time of 1.5 to 4 seconds, a light source wavelength of 405 nanometers, and the surface is cleaned with anhydrous ethanol after printing.

[0021] By adopting the above technical solution, the printing parameter settings ensure that the resin curing and molding dimensions conform to the model data, and a photocurable silicone elastomer preform is obtained.

[0022] Preferably, in step S4, the temperature of the isothermal heat treatment is 90 to 110 degrees Celsius, and the treatment time is 3 to 5 hours.

[0023] By adopting the above technical solution, the temperature range and time range are matched to the thermal dissociation kinetics of hindered urea bonds. Under these conditions, the hindered urea bonds dissociate and recombine, thereby enhancing mechanical properties.

[0024] Preferably, the main chain of the organosilicon polyurethane acrylate prepolymer contains hindered urea bonds. In step S4, the hindered urea bonds dissociate under heating conditions to generate isocyanate groups, which react with hydroxyl or amino groups in the small molecule organosilicon thermosetting crosslinking agent.

[0025] By employing the above technical solution, during the heat treatment process, the hindered urea bonds in the organosilicon polyurethane acrylate prepolymer segments undergo a reverse reaction, breaking down into isocyanate groups and secondary amine groups. The small-molecule organosilicon thermosetting crosslinking agent containing hydroxyl or amino groups present in the system reacts with the dissociated isocyanate groups. This reaction process involves bond exchange and post-crosslinking, allowing the polymer network to rearrange its topology, releasing internal stress accumulated during printing, introducing siloxane segments, and enhancing the overall network toughness.

[0026] The second aspect of this invention provides the application of dynamically covalently bonded dual-curing 3D printing silicone resin in the preparation of silicone elastomers.

[0027] By employing the above technical solution, dynamic covalent bond dual-curing 3D printing silicone resin is applied to the manufacture of silicone elastomers, overcoming the limitations of traditional molding or casting processes in fabricating complex structures. The prepared silicone elastomers utilize dynamic covalent bond recombination technology to eliminate mechanical defects caused by 3D printing layer textures, thereby improving tensile strength and tear resistance.

[0028] This invention provides a method for preparing and applying dynamically covalently bonded dual-curing 3D printing silicone resin. It offers the following advantages: This invention employs a dual curing strategy of photocuring and thermocuring to synthesize organosilicon polyurethane acrylate prepolymers containing hindered urea bonds. By adding a small-molecule organosilicon thermosetting crosslinking agent containing active hydroxyl or amino groups, after photocuring, isothermal heat treatment causes the hindered urea bonds within the organosilicon polyurethane acrylate prepolymer to dissociate and generate isocyanate groups. These isocyanate groups diffuse and undergo a secondary crosslinking reaction with the small-molecule organosilicon thermosetting crosslinking agent, constructing a second crosslinking network. This secondary crosslinking reaction increases the crosslinking density of the system, eliminating interlayer interface defects generated by the layer-by-layer stacking in 3D printing. This results in a dynamically covalently bonded dual-cured 3D-printed organosilicon elastomer exhibiting isotropic mechanical properties and tensile strength superior to that of a single photocured material. Attached Figure Description

[0029] Figure 1 The NMR spectrum is shown for the final product of the reaction of hydroxyl-terminated polydimethylsiloxane with an average molecular weight of 2000 with isophorone diisocyanate and 2-(tert-butylamino)ethyl methacrylate.

[0030] Figure 2 The infrared spectra of the final product of the reaction between hydroxyl-terminated polydimethylsiloxane with an average molecular weight of 2000 and isophorone diisocyanate and 2-(tert-butylamino)ethyl methacrylate, are shown. Detailed Implementation

[0031] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to comparative examples and test cases. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0033] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below with reference to specific embodiments. The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher products.

[0034] The organosilicon prepolymers include silanol-terminated polydimethylsiloxane (CAS No.: 70131-67-8) and aminopropyl-terminated polydimethylsiloxane (CAS No.: 106214-84-0), with the degree of polymerization n being an integer from 0 to 200.

[0035] Diisocyanates include toluene diisocyanate (TDI, CAS No.: 584-84-9), diphenylmethane diisocyanate (MDI, CAS No.: 101-68-8), hexamethylene diisocyanate (HDI, CAS No.: 822-06-0) and isophorone diisocyanate (IPDI, CAS No.: 4098-71-9).

[0036] The end-capping agents are 2-(tert-butylamino)ethyl methacrylate (TBEMA, CAS No.: 3775-90-4), hydroxyethyl acrylate (HEA, CAS No.: 818-61-1) and hydroxyethyl methacrylate (HEMA, CAS No.: 868-77-9).

[0037] The photoinitiators include 2-hydroxy-2-methyl-1-phenyl-1-propanone (1173, CAS No.: 7473-98-5), 1-hydroxycyclohexylphenyl ketone (184, CAS No.: 947-19-3), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO, CAS No.: 75980-60-8), 2-methyl-1-[4-methylthiophenyl]-2-morpholino-1-propanone (907, CAS No.: 71868-10-5), bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (819, CAS No.: 162881-26-7), and ethyl 2,4,6-trimethylbenzoylphosphonate (TPO-L, CAS No.: 84434-11-7).

[0038] The diluents contain isobornyl acrylate (IBOA, CAS No.: 5888-33-5), hydroxyethyl acrylate (HEA, CAS No.: 818-61-1), hydroxyethyl methacrylate (HEMA, CAS No.: 868-77-9), 4-acryloylmorpholine (ACMO, CAS No.: 5117-12-4), N-vinylpyrrolidone (NVP, CAS No.: 88-12-0), 1,6-hexanediol diacrylate (HDDA, CAS No.: 13048-33-4), and tripropylene glycol diacrylate (…). TPGDA (CAS No.: 42978-66-5), dipropylene glycol diacrylate (DPGDA (CAS No.: 57472-68-1), tricyclodecanediethanol diacrylate (TCDDMA (CAS No.: 42594-17-2), trimethylolpropane triacrylate (TMPTA (CAS No.: 15625-89-5), pentaerythritol triacrylate (PETA (CAS No.: 3524-68-3)) and dipentaerythritol hexaacrylate (DPHA (CAS No.: 29570-58-9)).

[0039] Small molecule organosilicon thermosetting crosslinking agents include one or more of the following: 1,1,3,3-tetramethyl-1,3-disilol (CAS No.: 1118-15-6); 1,3-bis(3-aminopropyl)tetramethyldisiloxane (CAS No.: 2469-55-2); hydroxyalkyl-modified polysiloxanes; and small molecule chain extenders containing hydroxyl or amino groups (such as small molecule diols or diamines).

[0040] The catalyst contains dioctyltin dilaurate (CAS No.: 3648-18-8).

[0041] Reference Appendix Figure 1 and attached Figure 2 The present invention provides embodiments 1-5: Example 1: This embodiment provides a method for preparing a dynamically covalently bonded dual-curing 3D printing silicone resin, including the following steps: S1. In a four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and nitrogen protection port, add 200 parts by mass of hydroxyl-terminated polydimethylsiloxane with a number average molecular weight of 2000, 44.4 parts by mass of isophorone diisocyanate, and 0.16 parts by mass of dioctyltin dilaurate. Under a nitrogen atmosphere, start stirring and set the speed to 200 rpm. Heat to 50 degrees Celsius and react at a constant temperature for 2 hours, then heat to 80 degrees Celsius and react at a constant temperature for 3 hours. Lower the temperature of the reaction system to 50 degrees Celsius and add 37 parts by mass of 2-(tert-butylamino)ethyl methacrylate dropwise at a uniform rate over 30 minutes. After the dropwise addition is completed, heat to 70 degrees Celsius and react at a constant temperature for 3 hours until the isocyanate content is detected to be less than 0.1%, thus obtaining an organosilicon polyurethane acrylate prepolymer. S2. Weigh 100 parts by weight of silicone polyurethane acrylate prepolymer, 30 parts by weight of isobornyl acrylate, 5 parts by weight of 1,1,3,3-tetramethyl-1,3-disilol, and 1 part by weight of ethyl 2,4,6-trimethylbenzoylphosphonate. Mix them evenly using a homogenizer in a light-protected environment, and then place them in a vacuum drying oven for vacuum degassing treatment until no bubbles overflow, to obtain a dynamic covalent bond dual-cured 3D printing silicone resin. S3. Dynamic covalent bond double-cured 3D printing silicone resin is injected into the resin tank of the digital light processing 3D printer. The printing layer thickness is set to 0.05 mm, the single layer exposure time is 2 seconds, and the light source wavelength is 405 nm. The layer-by-layer photocuring is performed according to the preset three-dimensional model data. After printing, the uncured resin on the surface is cleaned with anhydrous ethanol to obtain the photocured silicone elastomer preform. S4. Place the photocurable silicone elastomer preform in a forced-air drying oven, set the temperature to 100 degrees Celsius, and heat-treat at a constant temperature for 4 hours to cause the hindered urea bonds inside the photocurable silicone elastomer preform to dissociate and complete a secondary cross-linking reaction with the small molecule silicone thermosetting cross-linking agent. After natural cooling to room temperature, the dynamic covalent bond double-cured 3D printed silicone elastomer product is obtained.

[0042] Example 2: This embodiment provides a method for preparing a dynamically covalently bonded dual-curing 3D printing silicone resin, including the following steps: S1. In a four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and nitrogen protection port, add 300 parts by mass of hydroxyl-terminated polydimethylsiloxane with a number average molecular weight of 3000, 44.4 parts by mass of isophorone diisocyanate, and 0.28 parts by mass of dioctyltin dilaurate. Under a nitrogen atmosphere, start stirring and set the speed to 350 rpm. Heat to 60 degrees Celsius and react at a constant temperature for 2 hours, then heat to 85 degrees Celsius and react at a constant temperature for 2 hours. Reduce the temperature of the reaction system to 55 degrees Celsius and add 37 parts by mass of 2-(tert-butylamino)ethyl methacrylate dropwise at a uniform rate over 45 minutes. After the dropwise addition is completed, heat to 75 degrees Celsius and react at a constant temperature for 3 hours until the isocyanate content is detected to be less than 0.1%, thus obtaining an organosilicon polyurethane acrylate prepolymer. S2. Weigh 100 parts by weight of silicone polyurethane acrylate prepolymer, 25 parts by weight of isobornyl acrylate, 4 parts by weight of 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and 1.2 parts by weight of ethyl 2,4,6-trimethylbenzoylphosphonate. Mix them evenly using a homogenizer in a light-protected environment, and then place them in a vacuum drying oven for vacuum degassing treatment until no bubbles overflow, to obtain a dynamic covalent bond dual-cured 3D printing silicone resin. S3. Dynamic covalent bond double-cured 3D printing silicone resin is injected into the resin tank of digital light processing 3D printer. The printing layer thickness is set to 0.05 mm, the single layer exposure time is 3 seconds, and the light source wavelength is 405 nm. According to the preset three-dimensional model data, the layer-by-layer photocuring is performed. After printing, the uncured resin on the surface is cleaned with anhydrous ethanol to obtain the photocured silicone elastomer preform. S4. Place the photocurable silicone elastomer preform in a forced-air drying oven, set the temperature to 110 degrees Celsius, and heat-treat at a constant temperature for 3 hours to cause the hindered urea bonds inside the photocurable silicone elastomer preform to dissociate and complete a secondary cross-linking reaction with the small molecule silicone thermosetting cross-linking agent. After natural cooling to room temperature, the dynamic covalent bond double-cured 3D printed silicone elastomer product is obtained.

[0043] Example 3: This embodiment provides a method for preparing a dynamically covalently bonded dual-curing 3D printing silicone resin, including the following steps: S1. In a four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and nitrogen protection port, add 200 parts by mass of hydroxyl-terminated polydimethylsiloxane with a number average molecular weight of 2000, 33.6 parts by mass of hexamethylene diisocyanate, and 0.15 parts by mass of dioctyltin dilaurate. Under a nitrogen atmosphere, start stirring and set the speed to 250 rpm. Heat to 55 degrees Celsius and react at a constant temperature for 1.5 hours, then heat to 80 degrees Celsius and react at a constant temperature for 2.5 hours. Lower the temperature of the reaction system to 50 degrees Celsius and add 37 parts by mass of 2-(tert-butylamino)ethyl methacrylate dropwise at a uniform rate over 40 minutes. After the dropwise addition is completed, heat to 65 degrees Celsius and react at a constant temperature for 4 hours until the isocyanate content is detected to be less than 0.1%, thus obtaining an organosilicon polyurethane acrylate prepolymer. S2. Weigh 100 parts by weight of silicone polyurethane acrylate prepolymer, 40 parts by weight of 4-acryloylmorpholine, 5 parts by weight of 1,1,3,3-tetramethyl-1,3-disilol, and 0.8 parts by weight of 2,4,6-trimethylbenzoylphosphonate ethyl ester. Mix them evenly using a homogenizer in a light-protected environment, and then place them in a vacuum drying oven for vacuum degassing treatment until no bubbles overflow, to obtain a dynamically covalently bonded dual-cured 3D printing silicone resin. S3. Dynamic covalent bond double-cured 3D printing silicone resin is injected into the resin tank of the digital light processing 3D printer. The printing layer thickness is set to 0.05 mm, the single layer exposure time is 2.5 seconds, and the light source wavelength is 405 nm. The printing is carried out layer by layer photocuring according to the preset three-dimensional model data. After printing, the uncured resin on the surface is cleaned with anhydrous ethanol to obtain the photocured silicone elastomer preform. S4. Place the photocurable silicone elastomer preform in a forced-air drying oven, set the temperature to 90 degrees Celsius, and heat-treat at a constant temperature for 5 hours to cause the hindered urea bonds inside the photocurable silicone elastomer preform to dissociate and complete a secondary cross-linking reaction with the small molecule silicone thermosetting cross-linking agent. After natural cooling to room temperature, the dynamic covalent bond double-cured 3D printed silicone elastomer product is obtained.

[0044] Example 4: This embodiment provides a method for preparing a dynamically covalently bonded dual-curing 3D printing silicone resin, including the following steps: S1. In a four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and nitrogen protection port, add 200 parts by mass of amino-terminated polydimethylsiloxane with a number average molecular weight of 2000, 44.4 parts by mass of isophorone diisocyanate, and 0.16 parts by mass of dioctyltin dilaurate. Under a nitrogen atmosphere, start stirring and set the speed to 220 rpm. Heat to 50 degrees Celsius and react at a constant temperature for 2 hours, then heat to 80 degrees Celsius and react at a constant temperature for 3 hours. Lower the temperature of the reaction system to 50 degrees Celsius and add 37 parts by mass of 2-(tert-butylamino)ethyl methacrylate dropwise at a uniform rate over 20 minutes. After the dropwise addition is completed, heat to 70 degrees Celsius and react at a constant temperature for 3 hours until the isocyanate content is detected to be less than 0.1%, thus obtaining an organosilicon polyurethane acrylate prepolymer. S2. Weigh 100 parts by weight of silicone polyurethane acrylate prepolymer, 40 parts by weight of N-vinylpyrrolidone, 5 parts by weight of 1,3-bis(3-aminopropyl)tetramethyldisiloxane, and 1.5 parts by weight of ethyl 2,4,6-trimethylbenzoylphosphonate. Mix them evenly using a homogenizer in a light-protected environment, and then place them in a vacuum drying oven for vacuum degassing treatment until no bubbles overflow, to obtain a dynamically covalently bonded dual-cured 3D printing silicone resin. S3. Dynamic covalent bond double-cured 3D printing silicone resin is injected into the resin tank of digital light processing 3D printer. The printing layer thickness is set to 0.1 mm, the single layer exposure time is 4 seconds, and the light source wavelength is 405 nm. According to the preset three-dimensional model data, the layer is photocured and formed layer by layer. After printing, the uncured resin on the surface is cleaned with anhydrous ethanol to obtain the photocured silicone elastomer preform. S4. Place the photocurable silicone elastomer preform in a forced-air drying oven, set the temperature to 105 degrees Celsius, and heat-treat at a constant temperature for 3.5 hours. This causes the hindered urea bonds inside the photocurable silicone elastomer preform to dissociate and complete a secondary crosslinking reaction with the small molecule silicone thermosetting crosslinking agent. After natural cooling to room temperature, the dynamic covalent bond double-cured 3D printed silicone elastomer product is obtained.

[0045] Example 5: This embodiment provides a method for preparing a dynamically covalently bonded dual-curing 3D printing silicone resin, including the following steps: S1. In a four-necked flask equipped with a mechanical stirrer, reflux condenser, thermometer, and nitrogen protection port, add 200 parts by mass of hydroxyl-terminated polydimethylsiloxane with a number average molecular weight of 2000, 44.4 parts by mass of isophorone diisocyanate, and 0.16 parts by mass of dioctyltin dilaurate. Under a nitrogen atmosphere, start stirring and set the speed to 280 rpm. Heat to 50 degrees Celsius and react at a constant temperature for 2 hours, then heat to 80 degrees Celsius and react at a constant temperature for 3 hours. Lower the temperature of the reaction system to 50 degrees Celsius and add 37 parts by mass of 2-(tert-butylamino)ethyl methacrylate dropwise at a uniform rate over 60 minutes. After the dropwise addition is completed, heat to 70 degrees Celsius and react at a constant temperature for 3 hours until the isocyanate content is detected to be less than 0.1%, thus obtaining an organosilicon polyurethane acrylate prepolymer. S2. Weigh 100 parts by weight of silicone polyurethane acrylate prepolymer, 30 parts by weight of isobornyl acrylate, 10 parts by weight of 1,1,3,3-tetramethyl-1,3-disilol, and 1.8 parts by weight of ethyl 2,4,6-trimethylbenzoylphosphonate. Mix them evenly using a homogenizer in a light-protected environment, and then place them in a vacuum drying oven for vacuum degassing treatment until no bubbles overflow, to obtain a dynamically covalently bonded dual-cured 3D printing silicone resin. S3. Dynamic covalent bond double-cured 3D printing silicone resin is injected into the resin tank of the digital light processing 3D printer. The printing layer thickness is set to 0.05 mm, the single layer exposure time is 1.5 seconds, and the light source wavelength is 405 nm. The layer-by-layer photocuring is performed according to the preset three-dimensional model data. After printing, the uncured resin on the surface is cleaned with anhydrous ethanol to obtain the photocured silicone elastomer preform. S4. Place the photocurable silicone elastomer preform in a forced-air drying oven, set the temperature to 95 degrees Celsius, and heat-treat at a constant temperature for 4.5 hours. This causes the hindered urea bonds inside the photocurable silicone elastomer preform to dissociate and complete a secondary crosslinking reaction with the small molecule silicone thermosetting crosslinking agent. After natural cooling to room temperature, the dynamic covalent bond double-cured 3D printed silicone elastomer product is obtained.

[0046] Comparative Examples 1-4: Comparative Example 1: Compared with Example 1, the difference is that in step S1, 37 parts by mass of 2-(tert-butylamino)ethyl methacrylate is replaced with 26 parts by mass of hydroxyethyl methacrylate to ensure that the molar ratio of isocyanate to hydroxyl group is consistent, thereby forming a static urethane bond instead of a dynamic hindered urea bond. All other aspects are the same.

[0047] Comparative Example 2: Compared with Example 1, the difference is that no small molecule organosilicon thermosetting crosslinking agent was added in step S2. Instead, 100 parts by weight of organosilicon polyurethane acrylate prepolymer, 30 parts by weight of isobornyl acrylate, and 1 part by weight of ethyl 2,4,6-trimethylbenzoylphosphonate were weighed and mixed. All other steps were the same.

[0048] Comparative Example 3: Compared with Example 1, the difference is that in step S2, 5 parts by weight of 1,1,3,3-tetramethyl-1,3-disilol are replaced with 5 parts by weight of dimethyl silicone oil (with a viscosity similar to that of 1,1,3,3-tetramethyl-1,3-disilol), while the rest are the same.

[0049] Comparative Example 4: Compared with Example 1, the difference is that the isothermal heat treatment operation in step S4 was not performed. The finished product was obtained directly after printing and cleaning in step S3. All other aspects are the same.

[0050] Test Example 1-2: Test Example 1: Mechanical performance testing The experimental steps are as follows: Sample preparation: In accordance with GB / T528-2009 "Determination of tensile stress-strain properties of vulcanized rubber or thermoplastic rubber", the dynamically covalently bonded double-cured 3D-printed silicone elastomer products obtained in Examples 1 to 5 and Comparative Examples 1 to 4 were prepared into dumbbell-shaped Type IV standard samples. Five parallel samples were prepared for each set of examples or comparative examples, and the final test results were taken as the arithmetic mean.

[0051] Initial tensile property test: The dumbbell-shaped Type IV standard specimen was subjected to tensile testing using a universal testing machine. The tensile rate was set to 100 mm / min, the gauge length to 12 mm, and the test was conducted under the conditions of ambient temperature of 25 degrees Celsius and relative humidity of 50%. The tensile strength (MPa) and elongation at break (%) of the specimen were recorded.

[0052] The experimental results are as follows: The test results of the samples prepared in each embodiment and comparative example are recorded in Table 1.

[0053] Table 1. Summary of mechanical property data for each group of samples The results are analyzed as follows: As shown in Table 1, Example 1 used 2-(tert-butylamino)ethyl methacrylate for end-capping, introducing hindered urea bonds based on the tertiary amine structure into the polymer chain. Compared with Comparative Example 1 without hindered urea bonds, Example 1 showed a significant improvement in tensile properties after thermosetting. This is because the dynamic covalent bonds undergo reversible dissociation and recombination reactions under thermal stimulation at 100 degrees Celsius. The free isocyanate groups recombine with the added organosilicon thermosetting crosslinking agent to form a more robust organosilicon interpenetrating network, increasing the adhesion between layers during photocuring.

[0054] The comparison between Example 1 and Comparative Examples 2 and 3 reveals the dual function of the small-molecule organosilicon thermosetting crosslinking agent. Comparative Example 2, which did not contain the small-molecule organosilicon thermosetting crosslinking agent, retained hindered urea bonds, but its initial tensile strength was only 2.38 MPa, far lower than the 7.82 MPa of Example 1. This indicates that the small-molecule organosilicon thermosetting crosslinking agent participates in the secondary crosslinking reaction during the heat treatment stage, increasing the crosslinking density and enhancing the mechanical strength of the material.

[0055] Comparative Example 3, with the addition of inactive dimethyl silicone oil, resulted in a further decrease in the tensile strength of the material to 1.67 MPa. This is because the inactive silicone oil cannot participate in chemical crosslinking, acting as a plasticizer and disrupting the integrity of the crosslinking network. Compatibility issues hindered the diffusion and recombination of molecular chains at the fracture surface. This conversely demonstrates the necessity of using small-molecule organosilicon monomers rich in active hydroxyl or amino groups in this invention. The active groups can react with isocyanate groups generated by the dissociation of hindered urea bonds, or directly participate in transesterification or urethane-transesterification reactions.

[0056] The comparison between Example 1 and Comparative Example 4 confirms the indispensability of the dual mechanism of photocuring and thermocuring reinforcement. Comparative Example 4 only underwent photocuring without subsequent heat treatment, and its tensile strength was only 3.15 MPa. This is because photocuring only constructs a preliminary cross-linking network. At this point, the hindered urea bonds have not yet been thermally activated to undergo chain segment rearrangement, and the small molecule organosilicon thermocuring cross-linking agent has not fully reacted and entered the main network. Only through the high-temperature heat treatment in step S4 can the dynamic bond exchange mechanism be activated and the active small molecules be prompted to complete secondary cross-linking, thereby obtaining a high-strength 3D-printed organosilicon elastomer product with dual curing of dynamic covalent bonds.

[0057] This invention successfully solves the problems of poor interlayer bonding and insufficient mechanical strength of traditional 3D printed silicone resins by introducing hindered urea dynamic bonds into the silicone polyurethane backbone and combining it with a small molecule silicone thermosetting crosslinking agent rich in active groups, using a photothermal dual curing strategy.

Claims

1. A method for preparing a dynamically covalently bonded dual-curing 3D printing silicone resin, characterized in that, Includes the following steps: S1. Mix the organosilicon polymer, diisocyanate and catalyst, and carry out the polymerization reaction under heating conditions to obtain an isocyanate-terminated intermediate. Then add the terminator to carry out the termination reaction until the isocyanate content meets the standard, and obtain organosilicon polyurethane acrylate prepolymer. S2. Take the organosilicon polyurethane acrylate prepolymer, reactive diluent, small molecule organosilicon thermosetting crosslinking agent and photoinitiator, mix them evenly and degas them under light-protected conditions to obtain dynamic covalent bond dual-curing 3D printing organosilicon resin. S3. Inject the dynamic covalent bond dual-curing 3D printing silicone resin into the 3D printer, and perform layer-by-layer photocuring according to the model data to obtain a photocured silicone elastomer preform. S4. The photocurable silicone elastomer preform is subjected to constant temperature heat treatment at high temperature, so that dynamic covalent bond dissociation occurs inside the preform and a secondary crosslinking reaction is completed with the small molecule silicone thermosetting crosslinking agent. After cooling, the dynamic covalent bond double-cured 3D printing silicone resin is obtained.

2. The method for preparing the dynamic covalent bond dual-curing 3D printing silicone resin according to claim 1, characterized in that, In step S1, the organosilicon polymer is a silanol-terminated polydimethylsiloxane or an aminopropyl-terminated polydimethylsiloxane, and its degree of polymerization n is an integer from 0 to 200. The diisocyanate is selected from one or more of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate; The capping agent is selected from one or more of 2-(tert-butylamino)ethyl methacrylate, hydroxyethyl acrylate, and hydroxyethyl methacrylate.

3. The method for preparing the dynamic covalent bond dual-curing 3D printing silicone resin according to claim 1, characterized in that, In step S1, the specific process of the polymerization reaction is as follows: first, the temperature is raised to 50-60 degrees Celsius and reacted for 1.5-2 hours, then the temperature is raised to 80-85 degrees Celsius and reacted for 2-3 hours; The specific method for the end-capping reaction is as follows: cool the reaction system to 50-55 degrees Celsius, add the end-capping agent dropwise, and after the dropwise addition is completed, raise the temperature to 65-75 degrees Celsius and react for 3-4 hours until the isocyanate content is less than 0.1%.

4. The method for preparing the dynamic covalent bond dual-curing 3D printing silicone resin according to claim 1, characterized in that, In step S2, the raw materials for preparing the dynamic covalent bond dual-curing 3D printing silicone resin include, by weight, the following: Organosilicon polyurethane acrylate prepolymer: 100 parts; Reactive diluent: 20-50 parts; Small molecule organosilicon thermosetting crosslinking agent: 1-10 parts; Photoinitiator: 0.8-1.8 parts.

5. The method for preparing the dynamic covalent bond dual-curing 3D printing silicone resin according to claim 1, characterized in that, In step S2, the reactive diluent is selected from one or more of isobornyl acrylate, hydroxyethyl acrylate, hydroxyethyl methacrylate, 4-acryloylmorpholine, N-vinylpyrrolidone, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, dipropylene glycol diacrylate, tricyclodecanediethanol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, and dipentaerythritol hexaacrylate.

6. The method for preparing the dynamic covalent bond dual-curing 3D printing silicone resin according to claim 1, characterized in that, In step S2, the small molecule organosilicon thermosetting crosslinking agent is selected from one or more of 1,1,3,3-tetramethyl-1,3-disilol, 1,3-bis(3-aminopropyl)tetramethyldisiloxane, hydroxyalkyl-modified polysiloxane, and small molecule chain extenders containing hydroxyl or amino groups.

7. The method for preparing the dynamic covalent bond dual-curing 3D printing silicone resin according to claim 1, characterized in that, In step S3, the 3D printer is a digital light processing 3D printer, and the printing parameters are set to a layer thickness of 0.05-0.1 mm, a single layer exposure time of 1.5-4 seconds, a light source wavelength of 405 nanometers, and the surface is cleaned with anhydrous ethanol after printing.

8. The method for preparing the dynamic covalent bond dual-curing 3D printing silicone resin according to claim 1, characterized in that, In step S4, the constant temperature heat treatment is performed at a temperature of 90-110 degrees Celsius for 3-5 hours.

9. The method for preparing the dynamic covalent bond dual-curing 3D printing silicone resin according to claim 1, characterized in that, The main chain of the organosilicon polyurethane acrylate prepolymer contains hindered urea bonds. In step S4, the hindered urea bonds dissociate under heating conditions to generate isocyanate groups. The isocyanate groups react with the hydroxyl or amino groups in the small molecule organosilicon thermosetting crosslinking agent.

10. The application of dynamically covalently bonded dual-curing 3D printing silicone resin, characterized in that, The application of the dynamic covalent bond dual-curing 3D printing silicone resin according to any one of claims 1-9 in the preparation of silicone elastomers.

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