A large-volume easily deblocked methacrylate-terminated polyurethane prepolymer, photosensitive resin and preparation method

Abstract

The present invention provides a large-volume, easily deblocked methacrylate-terminated polyurethane prepolymer, a photosensitive resin, and a preparation method, relating to the field of 3D printing technology. The structural formula of the polyurethane prepolymer is shown in Formula III. The polyurethane prepolymer is prepared by reacting an isocyanate-terminated oligomer with an isocyanate blocking agent dissolved in a solvent. The present invention also provides a photosensitive resin comprising the polyurethane prepolymer shown in Formula III. Through dynamic chemical design, the present invention imparts high-temperature reconfiguration capabilities to the cross-linked network, thereby improving the mechanical properties of the material.

Description

Technical Field

[0001] The present invention relates to the technical field of 3D printing, and in particular to a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer, a photosensitive resin and a preparation method thereof. Background Art

[0002] In recent years, polyurethane materials have been widely used in flexible electronics, medical devices, the automotive industry, 3D printing, and other fields due to their excellent mechanical properties, wear resistance, chemical resistance, and controllable elasticity. Among them, photocurable polyurethane materials, which combine the high efficiency of UV curing technology with the excellent properties of polyurethane, have become a research hotspot. However, traditional photocurable polyurethane systems generally rely on a single free radical photopolymerization reaction, which has problems such as limited cure depth, difficulty curing in shadowed areas, and high volume shrinkage, limiting their application in complex structures or high-performance elastomers.

[0003] To overcome the limitations of single-photocuring systems, researchers have developed dual-cure systems, combining photocuring with other curing mechanisms (such as thermal, moisture, or chemical reaction curing). Among these, the use of polyurethane prepolymers with diamine chain extenders, combined with dual photocuring and thermal curing, can achieve a more uniform cured network structure, improving the mechanical properties and dimensional stability of the material. Diamine chain extenders react with isocyanate (-NCO) groups to form urea bonds, enhancing the material's crosslinking density and heat resistance while reducing cure shrinkage. Other studies have also used other chain extenders. Patent CN 116023597A discloses a plant-based reinforced 3D printing resin composition and molding method, incorporating reinforcing and / or toughening plant-based chain extenders in place of amine chain extenders. However, compared to amine chain extenders, the reactive groups of plant-based chain extenders have lower reactivity with the resin system and cannot simultaneously enhance both strength and toughness. Furthermore, the dual-component design optimizes storage stability and enables synergistic effects of rapid photocuring and subsequent thermal curing during use, making it suitable for high-end applications such as high-precision 3D printing, flexible sensors, and sealing materials. However, existing dual-cure photosensitive polyurethane elastomers still face challenges, such as matching the reaction rates of light and heat curing, the impact of chain extender selection on material flexibility and strength, and the adaptability of prepolymer viscosity to processing techniques. Therefore, developing a dual-cure polyurethane photosensitive resin elastomer with excellent mechanical properties, controllable curing characteristics, and good processing performance has important scientific research value and industrial application prospects. Summary of the Invention

[0004] The purpose of the present invention is to provide a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer, a photosensitive resin and a preparation method. The photosensitive resin of the present invention has excellent heat resistance, toughness and wear resistance, and can be used in the field of 3D printing.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The present invention first provides a large-volume, easily deblocked methacrylate-terminated polyurethane prepolymer, the structural formula of which is shown in Formula III:

[0007] Formula III;

[0008] In formula III, the value range of n is 20~50.

[0009] The present invention also provides a method for preparing a large-volume, easily deblocked methacrylate-terminated polyurethane prepolymer, comprising:

[0010] Step 1: Under nitrogen protection, polypropylene glycol, isophorone diisocyanate, a catalyst and a solvent are added to a reaction vessel to react to obtain an isocyanate-terminated oligomer represented by formula I;

[0011] Formula I;

[0012] Step 2: Add anhydrous tetrahydrofuran, a primary amine containing a large steric hindrance group, and anhydrous zinc chloride to a reaction vessel, cool to 10-15°C in an ice-water bath, and then slowly add ethylene oxide dropwise while controlling the temperature to below 25°C. After the addition is complete, remove the ice-water bath and react at room temperature for 5 hours. After the reaction is complete, remove THF by rotary evaporation to obtain a crude intermediate product, which is then added to a reaction vessel with methyl methacrylate and activated 4Å molecular sieves, heated to 90-95°C, and refluxed for 12 hours. After post-treatment, the isocyanate blocking agent shown in Formula II is obtained.

[0013] Formula II;

[0014] Step 3: Under nitrogen protection, the isocyanate-terminated oligomer prepared in step 1 and the isocyanate blocking agent prepared in step 2 are dissolved in a solvent and reacted to obtain a bulky, easily deblocked methacrylate-terminated polyurethane prepolymer represented by formula III;

[0015] Formula III;

[0016] In formula III, the value range of n is 20~50.

[0017] Preferably, the primary amine containing a large steric hindering group in step 2 includes aniline, cyclohexylamine, methylcyclohexylamine or cyclopentylamine.

[0018] Preferably, the molar ratio of the primary amine containing a large steric hindrance group, ethylene oxide and anhydrous zinc chloride in step 2 is 1: (1.1-1.2): (0.05-0.1).

[0019] Preferably, the molar ratio of the intermediate crude product to methyl methacrylate is 1:(2-3).

[0020] Preferably, the amount of the activated 4Å molecular sieve is 10-20% of the total mass of the crude product and methyl methacrylate.

[0021] Preferably, the molar ratio of the isocyanate-terminated oligomer to the isocyanate blocking agent in step three is 1:(1.1-1.5).

[0022] Preferably, the reaction temperature in step 3 is 50-70° C., and the reaction time is 3-6 hours.

[0023] The present invention also provides a photosensitive resin comprising the above-mentioned bulky and easily deblocked methacrylate-terminated polyurethane prepolymer, the structural formula of which is shown in Formula III:

[0024] Formula III;

[0025] In formula III, the value range of n is 20~50.

[0026] The present invention also provides a method for preparing a photosensitive resin, comprising:

[0027] The bulky and easily deblocked methacrylate-terminated polyurethane prepolymer shown in formula III, a reactive diluent and a photoinitiator constitute component A, and component B is a diamine compound. The two components are uniformly mixed at room temperature to obtain a photosensitive resin.

[0028] Beneficial effects of the present invention

[0029] The present invention provides a large-volume, easily deblocked methacrylate-terminated polyurethane prepolymer, a photosensitive resin, and a preparation method. This invention utilizes a blocking agent containing large steric hindrance groups to block isocyanates, forming an acrylate-containing polyurethane prepolymer, which serves as the resin matrix to ensure rapid curing and molding under ultraviolet light. During the subsequent thermal curing stage, the large sterically hindered urea bonds formed by the reaction of secondary amines with isocyanates are susceptible to partial thermal dissociation due to their poor thermal stability, regenerating the isocyanate-terminated prepolymer. A latent diamine chain extender is introduced, which remains inert during the photocuring stage to avoid interfering with molding precision. However, during the thermal curing stage, it reacts with the isocyanate to form a fully chain-extended, cross-linked polyurethane-urea network. Dynamic chemical design (such as thermally reversible urea bonds) imparts high-temperature reconfiguration capabilities to the cross-linked network, thereby improving the material's mechanical properties.

[0030] The dual-curing mechanism of the present invention gives the material excellent mechanical properties. The staged reaction strategy (photocuring molding followed by thermal curing) and the latent chain extender design improve process compatibility and production efficiency. At the same time, the recyclability brought by low volatility and dynamic bonds enhances its environmental protection characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is the infrared spectrum of the methacrylate-terminated polyurethane prepolymer prepared in Example 1 of the present invention;

[0032] Figure 2 This is the NMR spectrum of the methacrylate-terminated polyurethane prepolymer prepared in Example 1 of the present invention;

[0033] Figure 3 This is the NMR spectrum of the methacrylate-terminated polyurethane prepolymer prepared in Example 2 of the present invention;

[0034] Figure 4 This is the NMR spectrum of the methacrylate-terminated polyurethane prepolymer prepared in Example 3 of the present invention;

[0035] Figure 5 This is the NMR spectrum of the methacrylate-terminated polyurethane prepolymer prepared in Example 4 of the present invention;

[0036] Figure 6 This is the tensile strength curve of the 3D printed product prepared in Example 1 of the present invention;

[0037] Figure 7 This is the tensile strength curve of the 3D printed product prepared in Example 2 of the present invention;

[0038] Figure 8 This is the tensile strength curve of the 3D printed product prepared in Example 3 of the present invention;

[0039] Figure 9 This is the tensile strength curve of the 3D printed product prepared in Example 4 of the present invention;

[0040] Figure 10 This is the tensile strength curve of the 3D printed product prepared in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0041] The present invention first provides a large-volume, easily deblocked methacrylate-terminated polyurethane prepolymer, the structural formula of which is shown in Formula III:

[0042] Formula III;

[0043] In formula III, the value range of n is 20~50.

[0044] The present invention also provides a method for preparing a large-volume, easily deblocked methacrylate-terminated polyurethane prepolymer, comprising:

[0045] Step 1: Under nitrogen protection, polypropylene glycol, isophorone diisocyanate, a catalyst and a solvent are added to a reaction vessel for reaction. The reaction is preferably performed by adjusting the reaction system to a reaction temperature range of 60-80°C in a programmed temperature manner, maintaining the constant temperature reaction for 2-4 hours. After the reaction is completed, the system is naturally cooled to room temperature, and then the organic solvent is removed by a reduced pressure distillation process to obtain an isocyanate-terminated oligomer represented by formula I; the catalyst is preferably dibutyltin dilaurate, the solvent is preferably anhydrous toluene, the molar ratio of polypropylene glycol to isophorone diisocyanate is preferably 1: (2.1~2.5), and the amount of catalyst added is preferably 0.01~0.1wt% of the mass of polypropylene glycol.

[0046] The reaction process is as follows:

[0047]

[0048] Step 2: Add anhydrous tetrahydrofuran, a primary amine containing a large steric hindrance group, and anhydrous zinc chloride to the reaction vessel, cool to 10-15°C in an ice-water bath, and slowly add ethylene oxide dropwise while controlling the temperature to below 25°C. After the addition is complete, remove the ice-water bath and react at room temperature for 5 hours. After the reaction is complete, remove THF by rotary evaporation to obtain a crude intermediate product, which is then added to the reaction vessel with methyl methacrylate and activated 4Å molecular sieves, heated to 90-95°C, and refluxed for 12 hours. Methanol is removed using a Dean-Stark water separator. After the reaction is complete, filter to remove the molecular sieves, and then remove excess methyl by vacuum distillation at 50°C. Methyl acrylate is then distilled at 120-125°C to collect a light yellow transparent liquid to obtain an isocyanate blocking agent of Formula II. The primary amine containing a large steric hindrance group preferably includes aniline, cyclohexylamine, methylcyclohexylamine, or cyclopentylamine. The molar ratio of the primary amine containing a large steric hindrance group, ethylene oxide, and anhydrous zinc chloride is preferably 1:(1.1-1.2):(0.05-0.1). The molar ratio of the crude intermediate product to methyl methacrylate is preferably 1:(2-3). The amount of activated 4Å molecular sieve used is 10-20% of the total mass of the crude intermediate product and methyl methacrylate. The activated 4Å molecular sieve is obtained by high-temperature treatment of commercially available 4Å molecular sieve at 400°C for 5-8 hours.

[0049] The reaction process is as follows:

[0050]

[0051] Step 3: Under nitrogen protection, the isocyanate-terminated oligomer prepared in Step 1 and the isocyanate blocking agent prepared in Step 2 are dissolved in a solvent and reacted. The reaction temperature is preferably 50-70°C and the reaction time is preferably 3-6 hours. After completion of the reaction, the product is poured into n-hexane for precipitation. After separation by filtration, the product is washed with n-hexane multiple times (3-5 times) for purification, and finally dried to obtain a bulky, easily deblocked methacrylate-terminated polyurethane prepolymer represented by Formula III. The molar ratio of the isocyanate-terminated oligomer to the isocyanate blocking agent is preferably 1:(1.1-1.5).

[0052] The reaction process is as follows:

[0053]

[0054] The present invention also provides a photosensitive resin, comprising a bulky and easily deblocked methacrylate-terminated polyurethane prepolymer represented by the above formula III;

[0055] Formula III;

[0056] In formula III, the value range of n is 20~50.

[0057] The present invention also provides a method for preparing a photosensitive resin, comprising:

[0058] The bulky and easily deblocked methacrylate-terminated polyurethane prepolymer shown in formula III, a reactive diluent and a photoinitiator constitute component A, and component B is a diamine compound. The two components are uniformly mixed at room temperature to obtain a photosensitive resin.

[0059] According to the present invention, the mass ratio of the bulky, easily deblocked methacrylate-terminated polyurethane prepolymer represented by Formula III, the reactive diluent, the photoinitiator and the diamine compound is preferably (50-70): (10-20): (1-5): (5-15).

[0060] According to the present invention, the reactive diluent is preferably diethylene glycol dimethacrylate, the photoinitiator is preferably diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and the diamine compound is preferably hexamethylenediamine or benzyldiamine.

[0061] According to the present invention, the above-mentioned photosensitive resin is placed in the molding tank of a digital light processing 3D printer, and is irradiated layer by layer with a 405nm wavelength ultraviolet light source to initiate a photopolymerization reaction to obtain a photocured product; the photocured product comprises the structure shown in Formula IV:

[0062] Formula IV;

[0063] In formula IV, the value range of n is 20~50.

[0064] After the photocurable product is initially formed, it is preferably preheated at 80°C for 30 minutes, and then the temperature is raised to 140-150°C and maintained for 2 hours to complete the thermal curing process. During this thermal curing stage, the large sterically hindered urea bond formed by the reaction of the secondary amine and the isocyanate undergoes partial thermal dissociation due to poor thermal stability, regenerating the isocyanate-terminated prepolymer. This dynamic dissociation-recombination mechanism enables the generated prepolymer to further undergo a chain extension reaction with the diamine compound in component B to obtain the final 3D printed product, which comprises the structure shown in Formula V:

[0065] Formula V;

[0066] In formula V, the value range of n is 20~50, and the value range of m is 5~300.

[0067] The reaction process is as follows:

[0068]

[0069] a 1；

[0070]

[0071] a 2；

[0072]

[0073] a 3；

[0074] The present invention is further described in detail below with reference to specific examples, in which the raw materials involved are all commercially available.

[0075] Example 1

[0076] 1) Under nitrogen, polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (46.68 g), the catalyst dibutyltin dilaurate (0.02 g), and anhydrous toluene (15 mL) were added sequentially to a three-necked flask equipped with a thermometer, reflux condenser, and mechanical stirrer. With continuous stirring, the reaction system was temperature-programmed to 60°C and maintained at this temperature for 3 hours. After completion of the reaction, the system was naturally cooled to room temperature, and the organic solvent, toluene, was removed by vacuum distillation to obtain an isocyanate-terminated oligomer.

[0077] 2) In a fume hood, add anhydrous tetrahydrofuran (THF) (100 mL), aniline (9.3 g), and anhydrous zinc chloride (0.68 g) to a three-necked flask. Cool to 10°C in an ice-water bath. Slowly add ethylene oxide (5.3 g) dropwise while maintaining the temperature below 25°C. After the addition is complete, remove the ice-water bath and allow the reaction to proceed at room temperature for 5 hours. After the reaction, remove the THF by rotary evaporation to yield crude N-(2-hydroxyethyl)aniline. This crude product, along with methyl methacrylate (30.00 g) and activated 4Å molecular sieves (2.00 g), is then added to a round-bottom flask. The temperature is raised to 90°C and refluxed for 12 hours. Methanol is removed using a Dean-Stark trap. After the reaction is complete, the molecular sieves are removed by filtration. Excess methyl methacrylate is then removed by vacuum distillation at 50°C. The new isocyanate blocking agent is then collected as a pale yellow, transparent liquid by distillation at 120°C.

[0078] 3) The isocyanate-terminated oligomer (52.07 g) prepared above and the novel isocyanate blocking agent were dissolved in N,N-dimethylformamide solvent (95 mL) and placed in a three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser. Under nitrogen protection, the mixed system was heated to 60°C and reacted at a constant temperature for 4 hours. After the reaction was completed, the product was poured into n-hexane for precipitation. After filtration and separation, it was washed and purified with n-hexane, and finally dried to obtain a methacrylate-terminated polyurethane prepolymer. The infrared spectrum is shown in the figure below. Figure 1 As shown, the NMR spectrum is Figure 2 shown.

[0079] 4) Component A consists of a methacrylate-terminated polyurethane prepolymer (75.00 g), a reactive diluent (diethylene glycol dimethacrylate) (15.00 mL), and a photoinitiator (diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide (TPO)) (2.00 g). Component B consists of hexamethylenediamine (8.00 g). The two components are uniformly mixed at room temperature to produce a photosensitive resin.

[0080] 5) The photosensitive resin is then placed in the molding tank of a digital light processing 3D printer. Layer-by-layer irradiation with a 405nm wavelength ultraviolet light source initiates a photopolymerization reaction, resulting in a photocured product. After initial molding, the photocured product is preheated at 80°C for 30 minutes, then the temperature is raised to 140°C and maintained for 2 hours to complete the heat curing process. During this heat curing stage, the large hindered urea bond formed by the reaction of the secondary amine and isocyanate undergoes partial thermal dissociation due to its poor thermal stability, regenerating an isocyanate-terminated prepolymer. This dynamic dissociation-recombination mechanism enables the resulting prepolymer to undergo further chain extension reactions with the diamine compound in component B, resulting in the final 3D printed product.

[0081] Figure 6This is the tensile strength curve of the 3D-printed product prepared in Example 1 of the present invention. The resulting material has a tensile strength of 75.4 MPa and an elongation at break of 186%. This is due to the diamine chain extender triggering a chain extension reaction during the subsequent thermal curing stage, forming a fully extended and cross-linked polyurethane-urea network, significantly improving the mechanical strength of the material.

[0082] Example 2

[0083] 1) Under nitrogen, polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (51.13 g), the catalyst dibutyltin dilaurate (0.05 g), and anhydrous toluene (20 mL) were added sequentially to a three-necked flask equipped with a thermometer, reflux condenser, and mechanical stirrer. With continuous stirring, the reaction system was temperature-programmed to 60°C and maintained at this temperature for 3 hours. After completion of the reaction, the system was naturally cooled to room temperature, and the organic solvent, toluene, was removed by vacuum distillation to obtain an isocyanate-terminated oligomer.

[0084] 2) In a fume hood, add anhydrous tetrahydrofuran (THF) (100 mL), cyclohexylamine (9.3 g), and anhydrous zinc chloride (0.68 g) to a three-necked flask. Cool to 10°C in an ice-water bath. Slowly add ethylene oxide (5.3 g) dropwise while maintaining the temperature below 25°C. After the addition is complete, remove the ice-water bath and allow the reaction to proceed at room temperature for 5 hours. After the reaction, remove the THF by rotary evaporation to obtain the crude N-(2-hydroxyethyl)cyclohexylamine product. This product, along with methyl methacrylate (30.00 g) and activated 4Å molecular sieves (2.00 g), is then added to a round-bottom flask and heated to 90°C, refluxed for 12 hours, and methanol is removed using a Dean-Stark trap. After the reaction, the molecular sieves are removed by filtration. Excess methyl methacrylate is then removed by vacuum distillation at 50°C. The product, a new isocyanate blocking agent, cyclohexylaminoethyl methacrylate, is collected as a pale yellow, transparent liquid by distillation at 120°C.

[0085] 3) The isocyanate-terminated oligomer (52.07 g) and cyclohexylaminoethyl methacrylate (45.16 g) prepared above were dissolved in N,N-dimethylformamide solvent (100 mL) and placed in a three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser. Under nitrogen protection, the mixed system was heated to 60°C and reacted at a constant temperature for 4 hours. After the reaction was completed, the product was poured into n-hexane for precipitation. After filtration and separation, it was washed and purified with n-hexane, and finally dried to obtain a methacrylate-terminated polyurethane prepolymer. The nuclear magnetic spectrum is as follows Figure 3 shown.

[0086] 4) Component A consists of methacrylate-terminated polyurethane prepolymer (70.00 g), reactive diluent diethylene glycol dimethacrylate (19.00 mL), and photoinitiator diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) (1.00 g). Component B consists of hexamethylenediamine (10.00 g). The two components are uniformly mixed at room temperature to produce a photosensitive resin.

[0087] 5) The photosensitive resin is then placed in the molding chamber of a digital light processing (DLP) 3D printer. Layer-by-layer irradiation with a 405nm wavelength UV light source initiates a photopolymerization reaction, resulting in a photocured product. After initial molding, the photocured product is preheated at 80°C for 30 minutes, then the temperature is raised to 140°C and maintained for 2 hours to complete the thermal curing process. During this thermal curing stage, the large hindered urea bond formed by the reaction of the secondary amine with the isocyanate undergoes partial thermal dissociation due to its poor thermal stability, regenerating an isocyanate-terminated prepolymer. This dynamic dissociation-recombination mechanism enables the resulting prepolymer to undergo further chain extension reactions with the diamine compound in component B, resulting in the final 3D printed product.

[0088] Figure 7 This is the tensile strength curve of the 3D printed product prepared in Example 2 of the present invention; it can be seen that the tensile strength of the obtained material is 69.6 MPa and the elongation at break is 188%.

[0089] Example 3

[0090] 1) Under nitrogen, polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (55.58 g), the catalyst dibutyltin dilaurate (0.10 g), and anhydrous toluene (25 mL) were added sequentially to a three-necked flask equipped with a thermometer, reflux condenser, and mechanical stirrer. With continuous stirring, the reaction system was temperature-programmed to 60°C and maintained at this temperature for 3 hours. After completion of the reaction, the system was naturally cooled to room temperature, and the organic solvent, toluene, was removed by vacuum distillation to obtain an isocyanate-terminated oligomer.

[0091] 2) In a fume hood, add anhydrous tetrahydrofuran (THF) (100 mL), methylcyclohexylamine (9.3 g), and anhydrous zinc chloride (0.68 g) to a three-necked flask. Cool to 10°C in an ice-water bath. Slowly add ethylene oxide (5.3 g) dropwise while maintaining the temperature below 25°C. After the addition is complete, remove the ice-water bath and allow the reaction to proceed at room temperature for 5 hours. After the reaction, remove the THF by rotary evaporation to yield the crude product N-(2-hydroxyethyl)methylcyclohexylamine. This crude product, along with methyl methacrylate (30.00 g) and activated 4Å molecular sieves (2.00 g), is then added to a round-bottom flask. The temperature is raised to 90°C and refluxed for 12 hours. Methanol is removed using a Dean-Stark trap. After the reaction is complete, the molecular sieves are removed by filtration. Excess methyl methacrylate is then removed by vacuum distillation at 50°C. Methylcyclohexylaminoethyl methacrylate, a novel isocyanate blocking agent, is then collected as a pale yellow, transparent liquid by distillation at 120°C.

[0092] 3) The isocyanate-terminated oligomer (52.07 g) and methylcyclohexylaminoethyl methacrylate (49.26 g) prepared above were dissolved in N,N-dimethylformamide solvent (105 mL) and placed in a three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser. Under nitrogen protection, the mixed system was heated to 60°C and reacted at a constant temperature for 4 hours. After the reaction was completed, the product was poured into n-hexane for precipitation. After filtration and separation, it was washed and purified with n-hexane, and finally dried to obtain a methacrylate-terminated polyurethane prepolymer. The nuclear magnetic spectrum is as follows Figure 4 shown.

[0093] 4) Component A consists of a methacrylate-terminated polyurethane prepolymer (78.00 g), a reactive diluent (diethylene glycol dimethacrylate) (12.00 mL), and a photoinitiator (diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide) (TPO) (2.00 g). Component B consists of hexamethylenediamine (8.00 g). The two components are uniformly mixed at room temperature to produce a photosensitive resin.

[0094] 5) The photosensitive resin is then placed in the molding chamber of a digital light processing (DLP) 3D printer. Layer-by-layer irradiation with a 405nm wavelength UV light source initiates a photopolymerization reaction, resulting in a photocured product. After initial molding, the photocured product is preheated at 80°C for 30 minutes, then the temperature is raised to 140°C and maintained for 2 hours to complete the thermal curing process. During this thermal curing stage, the large hindered urea bond formed by the reaction of the secondary amine with the isocyanate undergoes partial thermal dissociation due to its poor thermal stability, regenerating an isocyanate-terminated prepolymer. This dynamic dissociation-recombination mechanism enables the resulting prepolymer to undergo further chain extension reactions with the diamine compound in component B, resulting in the final 3D printed product.

[0095] Figure 8This is the tensile strength curve of the 3D printed product prepared in Example 3 of the present invention; it can be seen that the tensile strength of the obtained material is 52.2 MPa and the elongation at break is 191%.

[0096] Example 4

[0097] 1) Under nitrogen, add polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (55.58 g), the catalyst dibutyltin dilaurate (0.10 g), and anhydrous toluene (25 mL) sequentially to a three-necked flask equipped with a thermometer, reflux condenser, and mechanical stirrer. With continuous stirring, program the reaction system to a temperature range of 60-80°C and maintain the reaction at this temperature for 3 hours. After the reaction is complete, cool the system to room temperature, and then remove the toluene solvent by vacuum distillation to obtain an isocyanate-terminated oligomer.

[0098] 2) In a fume hood, add anhydrous tetrahydrofuran (THF) (100 mL), cyclopentylamine (9.3 g), and anhydrous zinc chloride (0.68 g) to a three-necked flask. Cool to 10°C in an ice-water bath. Slowly add ethylene oxide (5.3 g) dropwise while maintaining the temperature below 25°C. After the addition is complete, remove the ice-water bath and allow the reaction to proceed at room temperature for 5 hours. After the reaction, remove the THF by rotary evaporation to yield the crude N-(2-hydroxyethyl)cyclopentylamine product. This product, along with methyl methacrylate (30.00 g) and activated 4Å molecular sieves (2.00 g), is then added to a round-bottom flask. The temperature is raised to 90°C and refluxed for 12 hours. Methanol is removed using a Dean-Stark trap. After the reaction is complete, the molecular sieves are removed by filtration. Excess methyl methacrylate is then removed by vacuum distillation at 50°C. The product, a new isocyanate blocking agent, cyclopentylaminoethyl methacrylate, is collected as a pale yellow, transparent liquid by distillation at 120°C.

[0099] 3) The isocyanate-terminated oligomer (52.07 g) and cyclopentylaminoethyl methacrylate (49.26 g) prepared above were dissolved in N,N-dimethylformamide solvent (105 mL) and placed in a three-necked flask equipped with a mechanical stirrer, a thermometer and a reflux condenser. Under nitrogen protection, the mixed system was heated to 60°C and reacted at a constant temperature for 4 hours. After the reaction was completed, the product was poured into n-hexane for precipitation. After filtration and separation, it was washed and purified with n-hexane, and finally dried to obtain a methacrylate-terminated polyurethane prepolymer. The nuclear magnetic spectrum is as follows Figure 5 shown.

[0100] 4) Component A consists of a methacrylate-terminated polyurethane prepolymer (78.00 g), a reactive diluent (diethylene glycol dimethacrylate) (12.00 mL), and a photoinitiator (diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide) (TPO) (2.00 g). Component B consists of hexamethylenediamine (8.00 g). The two components are uniformly mixed at room temperature to produce a photosensitive resin.

[0101] 5) The photosensitive resin is then placed in the molding chamber of a digital light processing (DLP) 3D printer. Layer-by-layer irradiation with a 405nm wavelength UV light source initiates a photopolymerization reaction, resulting in a photocured product. After initial molding, the photocured product is preheated at 80°C for 30 minutes, then the temperature is raised to 140°C and maintained for 2 hours to complete the thermal curing process. During this thermal curing stage, the large hindered urea bond formed by the reaction of the secondary amine with the isocyanate undergoes partial thermal dissociation due to its poor thermal stability, regenerating an isocyanate-terminated prepolymer. This dynamic dissociation-recombination mechanism enables the resulting prepolymer to undergo further chain extension reactions with the diamine compound in component B, resulting in the final 3D printed product.

[0102] Figure 9 This is the tensile strength curve of the 3D printed product prepared in Example 4 of the present invention; it can be seen that the tensile strength of the obtained material is 56.8 MPa and the elongation at break is 190%.

[0103] Comparative Example 1

[0104] The isocyanate blocking agent containing a large steric hindrance (such as a six-membered ring, a five-membered ring or a benzene ring) secondary amine and a methacrylate or acrylate structure is replaced with a hindered amine methacrylate blocking agent (TBEMA) containing a tert-butyl structure. The specific process is as follows:

[0105] 1) Under nitrogen, polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (55.58 g), the catalyst dibutyltin dilaurate (0.10 g), and anhydrous toluene (25 mL) were added sequentially to a three-necked flask equipped with a thermometer, reflux condenser, and mechanical stirrer. With continuous stirring, the reaction system was temperature-programmed to 60°C and maintained at this temperature for 3 hours. After completion of the reaction, the system was naturally cooled to room temperature, and the organic solvent, toluene, was removed by vacuum distillation to obtain an isocyanate-terminated oligomer.

[0106] 2) Dissolve the isocyanate-terminated oligomer (52.00 g) and tert-butylaminoethyl methacrylate (49.00 g) prepared above in N,N-dimethylformamide (100 mL) in a three-necked flask equipped with a mechanical stirrer, thermometer, and reflux condenser. Heat the mixture to 60°C under nitrogen for 4 hours. After the reaction, precipitate the product in n-hexane. After filtration, wash with n-hexane for purification, and finally dry to obtain a methacrylate-terminated polyurethane prepolymer.

[0107] 3) Component A consists of a methacrylate-terminated polyurethane prepolymer (78.00 g), a reactive diluent (diethylene glycol dimethacrylate) (12.00 mL), and a photoinitiator (diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide) (TPO) (2.00 g). Component B consists of hexamethylenediamine (8.00 g). The two components are uniformly mixed at room temperature to produce a photosensitive resin.

[0108] 4) The photosensitive resin is then placed in the molding chamber of a digital light processing (DLP) 3D printer. Layer by layer, it is irradiated with a 405nm UV light source to initiate a photopolymerization reaction, resulting in a photocured product. After the initial molding process, the photocured product is preheated at 80°C for 30 minutes, then the temperature is raised to 140°C and maintained for 2 hours to complete the thermal curing process. This results in the final 3D printed product.

[0109] Figure 10 This is the tensile strength curve of the 3D printed product prepared in Comparative Example 1 of the present invention; it can be seen that the tensile strength of the obtained material is 29 MPa and the elongation at break is 160%.

Claims

1. A bulky, easily deblocked methacrylate-terminated polyurethane prepolymer, characterized in that: The structural formula is shown in Formula III: Formula III; In formula III, the value range of n is 20~50.

2. The method for preparing a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer according to claim 1, characterized in that: include: Step 1: Under nitrogen protection, polypropylene glycol, isophorone diisocyanate, a catalyst and a solvent are added to a reaction vessel to react to obtain an isocyanate-terminated oligomer represented by formula I; Formula I; Step 2: Add anhydrous tetrahydrofuran, a primary amine containing a large steric hindrance group, and anhydrous zinc chloride to a reaction vessel, cool to 10-15°C in an ice-water bath, and then slowly add ethylene oxide dropwise while controlling the temperature to below 25°C. After the addition is complete, remove the ice-water bath and react at room temperature for 5 hours. After the reaction is complete, remove THF by rotary evaporation to obtain a crude intermediate product, which is then added to a reaction vessel with methyl methacrylate and activated 4Å molecular sieves, heated to 90-95°C, and refluxed for 12 hours. After post-treatment, the isocyanate blocking agent shown in Formula II is obtained. Formula II; Step 3: Under nitrogen protection, the isocyanate-terminated oligomer prepared in step 1 and the isocyanate blocking agent prepared in step 2 are dissolved in a solvent and reacted to obtain a bulky, easily deblocked methacrylate-terminated polyurethane prepolymer represented by formula III; Formula III; In formula III, the value range of n is 20~50.

3. The method for preparing a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer according to claim 2, characterized in that: The primary amine containing a large steric hindrance group in step 2 includes aniline, cyclohexylamine, methylcyclohexylamine or cyclopentylamine.

4. The method for preparing a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer according to claim 2, characterized in that: The molar ratio of the primary amine containing a large steric hindrance group, ethylene oxide and anhydrous zinc chloride in step 2 is 1: (1.1-1.2): (0.05-0.1).

5. The method for preparing a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer according to claim 2, characterized in that: The molar ratio of the intermediate crude product to methyl methacrylate is 1:(2-3).

6. The method for preparing a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer according to claim 2, characterized in that: The amount of the activated 4Å molecular sieve is 10-20% of the total mass of the crude product and methyl methacrylate.

7. The method for preparing a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer according to claim 2, characterized in that: The molar ratio of the isocyanate-terminated oligomer to the isocyanate blocking agent in step three is 1:(1.1-1.5).

8. The method for preparing a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer according to claim 2, characterized in that: The reaction temperature in step 3 is 50-70° C., and the reaction time is 3-6 hours.

9. A photosensitive resin, characterized in that: It includes a large-volume, easily deblocked methacrylate-terminated polyurethane prepolymer, the structural formula of which is shown in Formula III: Formula III; In formula III, the value range of n is 20~50.

10. The method for preparing a photosensitive resin according to claim 9, characterized in that: include: The bulky and easily deblocked methacrylate-terminated polyurethane prepolymer shown in formula III, a reactive diluent and a photoinitiator constitute component A, and component B is a diamine compound. The two components are uniformly mixed at room temperature to obtain a photosensitive resin.

Images