Large-volume easy-to-unblock methacrylate-terminated polyurethane prepolymer, photosensitive resin and preparation method

Abstract

The invention provides a large-volume easy-to-unblock methacrylate-terminated polyurethane prepolymer, photosensitive resin and a preparation method, and relates to the technical field of 3D printing. The structural formula of the polyurethane prepolymer is shown as a formula III, and the polyurethane prepolymer is prepared by dissolving an isocyanate-terminated oligomer and an isocyanate sealing agent in a solvent to react. The invention also provides a photosensitive resin, which comprises the polyurethane prepolymer as shown in the formula III. Through dynamic chemical design, the cross-linked network is endowed with high-temperature reconstruction capability, so that the mechanical property of the material is improved.

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, automotive industry, 3D printing and other fields due to their excellent mechanical properties, wear resistance, chemical resistance and adjustable elasticity. Among them, photocurable polyurethane materials combine the high efficiency of UV curing technology and the excellent performance of polyurethane, becoming a research hotspot. However, traditional photocurable polyurethane systems usually rely on a single free radical photopolymerization reaction, and have problems such as limited curing depth, difficulty in curing shadow areas, and high volume shrinkage, which limits their application in complex structures or high-performance elastomers.

[0003] In order to overcome the limitations of a single photocuring system, researchers have developed a dual-curing system, which is a method that combines photocuring with other curing mechanisms (such as thermal curing, moisture curing, or chemical reaction curing). Among them, the use of polyurethane prepolymers with diamine chain extenders combined with light / heat dual curing technology can achieve a more uniform cured network structure and improve the mechanical properties and dimensional stability of the material. Diamine chain extenders can form urea bonds by reacting with isocyanate groups (-NCO), enhance the crosslinking density and heat resistance of the material, and reduce the curing shrinkage. There are also studies using other chain extenders. Patent CN 116023597A discloses a plant-based enhanced 3D printing resin composition and a molding method thereof, introducing an enhanced and / or toughened plant-based chain extender instead of an amine chain extender. However, compared with amine chain extenders, the active groups of plant-based chain extenders have lower reactivity with the resin system and cannot simultaneously achieve simultaneous improvement in strength and toughness. In addition, the two-component design can optimize storage stability and achieve the synergistic effect of rapid photocuring and subsequent thermal curing during use, which is suitable for high-end applications such as high-precision 3D printing, flexible sensors, and sealing materials. However, there are still some challenges in the existing dual-curing photosensitive polyurethane elastomers, such as the matching of photocuring and thermal curing reaction rates, the influence of chain extender selection on material flexibility and strength, and the adaptability of prepolymer viscosity to processing technology. Therefore, the development of a dual-curing 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 solution:

[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 into a reaction container to react to obtain an isocyanate-terminated oligomer as shown in 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, slowly add ethylene oxide dropwise and control the temperature to below 25°C, remove the ice-water bath after the addition is complete, react at room temperature for 5 hours, remove THF by rotary evaporation after the reaction to obtain a crude intermediate product, then add it, methyl methacrylate and activated 4Å molecular sieves to a reaction vessel, heat to 90-95°C and reflux for 12 hours, and obtain an isocyanate blocking agent shown in Formula II by post-treatment;

[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 large-volume easily deblocked methacrylate-terminated polyurethane prepolymer as shown in 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 dosage of the activated 4 Å 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 3 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, and the structural formula is as 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 preparation method of a photosensitive resin, comprising:

[0027] The bulky and easily deblocked methacrylate-terminated polyurethane prepolymer shown in Formula III, an active diluent and a photoinitiator are combined to form Component A, and Component B is a diamine compound. The two components are uniformly mixed at room temperature to obtain the photosensitive resin.

[0028] Advantages of the present invention

[0029] The present invention provides a bulky and easily deblocked methacrylate-terminated polyurethane prepolymer, a photosensitive resin and a preparation method. The present invention uses a blocking agent containing a large steric hindrance group to block isocyanate to form a polyurethane prepolymer containing acrylate, and uses it as a resin matrix to ensure rapid curing and forming under ultraviolet light. In the subsequent thermal curing stage, the large steric hindrance urea bond formed by the reaction of secondary amine and isocyanate is prone to partial thermal dissociation due to poor thermal stability, and the isocyanate-terminated prepolymer is regenerated. A latent diamine chain extender is introduced, which remains inert during the photocuring stage to avoid interfering with the forming accuracy, and reacts with isocyanate during the thermal curing stage to form a fully chain-extended and cross-linked polyurethane-urea network. Through dynamic chemical design (such as thermoreversible urea bond), the cross-linked network is endowed with high-temperature reconstruction ability, thereby improving the mechanical properties of the material.

[0030] The dual curing mechanism of the present invention endows the material with excellent mechanical properties. The staged reaction strategy (first photocuring and forming, then thermal curing) and the design of latent chain extender improve the process compatibility and production efficiency. At the same time, the low volatility and recyclability brought by the dynamic bond enhance the environmental protection characteristics. 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, add polypropylene glycol, isophorone diisocyanate, a catalyst, and a solvent into a reaction vessel for reaction. Preferably, the reaction system is adjusted to a reaction temperature range of 60 - 80°C in a programmed temperature increase manner, and the constant temperature reaction is maintained 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 vacuum distillation to obtain the isocyanate-terminated oligomer shown in 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 addition amount of the catalyst is preferably 0.01 - 0.1 wt% 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 bulky hindrance group, and anhydrous zinc chloride into a reaction vessel. After cooling to 10 - 15°C in an ice-water bath, slowly add ethylene oxide and control the temperature 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 completed, rotary evaporate to remove THF to obtain a crude intermediate product. Then, add it together with methyl methacrylate and activated 4Å molecular sieve into the reaction vessel, heat up to 90 - 95°C and reflux for 12 hours, use a Dean-Stark water separator to remove methanol. After the reaction is completed, filter to remove the molecular sieve, then distill under reduced pressure at 50°C to remove the excess methyl methacrylate, and then distill at 120 - 125°C to collect a light yellow transparent liquid to obtain the isocyanate blocking agent shown in Formula II. The primary amine containing a bulky hindrance group preferably includes aniline, cyclohexylamine, methylcyclohexylamine, or cyclopentylamine; the molar ratio of the primary amine containing a bulky 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 dosage of the activated 4Å molecular sieve is 10 - 20% of the total mass of the crude intermediate product and methyl methacrylate. The activated 4Å molecular sieve is obtained by subjecting the commercially available 4Å molecular sieve to high-temperature treatment at 400°C for 5 - 8 hours;

[0049] The reaction process is as follows:

[0050]

[0051] Step 3: Under nitrogen protection, react the isocyanate-terminated oligomer prepared in Step 1 and the isocyanate blocking agent prepared in Step 2 in a solvent. The reaction temperature is preferably 50-70°C, and the reaction time is preferably 3-6 hours. After the reaction is completed, pour the product into n-hexane for precipitation. After filtration and separation, wash it with n-hexane several times (3-5 times) for purification, and finally obtain the large-volume easily deblocked methacrylate-terminated polyurethane prepolymer shown in Formula III after drying; 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 the large-volume easily deblocked methacrylate-terminated polyurethane prepolymer shown in Formula III above;

[0055] Formula III;

[0056] In Formula III, the value range of n is 20-50.

[0057] The present invention also provides a preparation method of the photosensitive resin, comprising:

[0058] Form Component A by mixing the large-volume easily deblocked methacrylate-terminated polyurethane prepolymer shown in Formula III, an active diluent and a photoinitiator. Component B is a diamine compound. Uniformly mix the two components at room temperature to obtain the photosensitive resin.

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

[0060] According to the present invention, the active 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 benzidine diamine.

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

[0062] Formula IV;

[0063] In Formula IV, the value range of n is 20-50.

[0064] After the above-mentioned photocured product is preliminarily formed, it is preferably first 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 steric hindrance urea bonds formed by the reaction of secondary amine and isocyanate partially thermally dissociate due to poor thermal stability, and the isocyanate-terminated prepolymer is regenerated. 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, and the 3D printed product includes 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 will be further described in detail below with specific embodiments, and the raw materials involved in the embodiments are all commercially available.

[0075] Example 1

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

[0077] 2) In a fume hood, anhydrous tetrahydrofuran (THF) (100 mL), aniline (9.3 g), and anhydrous zinc chloride (0.68 g) were added to a three-necked flask. After cooling to 10 °C in an ice-water bath, ethylene oxide (5.3 g) was slowly added dropwise while controlling the temperature below 25 °C. After the addition was complete, the ice-water bath was removed, and the reaction was carried out at room temperature for 5 hours. After the reaction, THF was removed by rotary evaporation to obtain the crude product of N-(2-hydroxyethyl)aniline. Subsequently, it was added to a round-bottom flask together with methyl methacrylate (30.00 g) and activated 4 Å molecular sieve (2.00 g). The temperature was raised to 90 °C and refluxed for 12 hours. Methanol was removed using a Dean-Stark water separator. After the reaction was completed, the molecular sieve was removed by filtration. Subsequently, excess methyl methacrylate was removed by distillation under reduced pressure at 50 °C, and then the light yellow transparent liquid product, the novel isocyanate blocking agent, was collected by distillation at 120 °C.

[0078] 3) The isocyanate-capped oligomer (52.07 g) and the novel isocyanate blocking agent prepared above 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, a methacrylate-terminated polyurethane prepolymer was obtained after drying. The infrared spectrum is as Figure 1 shown, and the NMR spectrum is as Figure 2 shown.

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

[0080] 5) Subsequently, the photosensitive resin was placed in the forming tank of a digital light processing type 3D printer. Through the layer-by-layer irradiation of a 405 nm wavelength ultraviolet light source, a photopolymerization reaction was initiated to obtain a photocured product. After the preliminary forming of the photocured product, first, a preheating treatment was carried out at 80 °C for 30 minutes, and then the temperature was raised to 140 °C and maintained for 2 hours to complete the thermal curing process. During this thermal curing stage, the large steric hindrance urea bonds formed by the reaction of secondary amine and isocyanate underwent partial thermal dissociation due to poor thermal stability, and the isocyanate-capped prepolymer was regenerated. This dynamic dissociation-recombination mechanism enabled the generated prepolymer to further undergo a chain extension reaction with the diamine compound in Component B to obtain the final 3D printed finished product.

[0081] Figure 6Tensile strength curve of the 3D printed finished product prepared in Example 1 of the present invention; it can be seen that the tensile strength of the obtained material is 75.4 MPa and the elongation at break is 186%. This is due to the chain extension agent diamine triggering a chain extension reaction in the subsequent thermal curing stage, forming a fully chain-extended and crosslinked polyurethane-urea network, which significantly improves the mechanical strength of the material.

[0082] Example 2

[0083] 1) Under a nitrogen protection environment, polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (51.13 g), catalyst dibutyltin dilaurate (0.05 g), and anhydrous toluene (20 mL) were successively added to a three-necked flask equipped with a thermometer, a reflux condenser, and a mechanical stirrer. Under continuous stirring, the reaction system was adjusted to a reaction temperature range of 60 °C in a programmed heating manner, and the constant temperature reaction was maintained for 3 hours. After the reaction was completed, the system was naturally cooled to room temperature, and then the organic solvent toluene was removed by vacuum distillation. Finally, an isocyanate-terminated oligomer was obtained.

[0084] 2) In a fume hood, anhydrous tetrahydrofuran (THF) (100 mL), cyclohexylamine (9.3 g), and anhydrous zinc chloride (0.68 g) were added to a three-necked flask. After cooling to 10 °C in an ice-water bath, ethylene oxide (5.3 g) was slowly added dropwise while controlling the temperature below 25 °C. After the dropwise addition was completed, the ice-water bath was removed, and the reaction was carried out at room temperature for 5 hours. After the reaction was completed, THF was removed by rotary evaporation to obtain a crude product of N-(2-hydroxyethyl)cyclohexylamine. Subsequently, it was added to a round-bottom flask together with methyl methacrylate (30.00 g) and activated 4 Å molecular sieve (2.00 g). The temperature was raised to 90 °C and refluxed for 12 hours. Methanol was removed using a Dean-Stark water separator. After the reaction was completed, the molecular sieve was removed by filtration. Subsequently, excess methyl methacrylate was removed by vacuum distillation at 50 °C, and then a light yellow transparent liquid product, a novel isocyanate blocking agent, cyclohexylaminoethyl methacrylate, was collected 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 obtained a methacrylate-terminated polyurethane prepolymer after drying. The NMR spectrum is as Figure 3 shown.

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

[0087] 5) Subsequently, the photosensitive resin is placed in the forming tank of a digital light processing (DLP) type 3D printer. Through layer-by-layer irradiation with a 405 nm wavelength ultraviolet light source, a photopolymerization reaction is initiated to obtain a photocured product. After preliminary shaping of the photocured product, it is first subjected to a preheating treatment at 80 °C for 30 minutes, and 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 steric hindrance urea bonds formed by the reaction of secondary amines and isocyanates undergo partial thermal dissociation due to poor thermal stability, regenerating the isocyanate-capped 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.

[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 a nitrogen protection environment, polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (55.58 g), the catalyst dibutyltin dilaurate (0.10 g), and anhydrous toluene (25 mL) are successively added to a three-necked flask equipped with a thermometer, a reflux condenser, and a mechanical stirring device. Under continuous stirring, the reaction system is adjusted to a reaction temperature range of 60 °C in a programmed heating manner and maintained at a constant temperature for 3 hours. After the reaction is completed, the system is naturally cooled to room temperature, and then the organic solvent toluene is removed by vacuum distillation to finally obtain an isocyanate-capped oligomer.

[0091] 2) In a fume hood, add anhydrous tetrahydrofuran (THF) (100 mL), methylcyclohexylamine (9.3 g), and anhydrous zinc chloride (0.68 g) into a three-necked flask. After cooling to 10 °C in an ice-water bath, slowly add ethylene oxide (5.3 g) while controlling the temperature below 25 °C. After the addition, remove the ice-water bath and react at room temperature for 5 hours. After the reaction is completed, rotary evaporate to remove THF to obtain the crude product of N-(2-hydroxyethyl)methylcyclohexylamine. Subsequently, add it, methyl methacrylate (30.00 g), and activated 4 Å molecular sieve (2.00 g) into a round-bottom flask, heat to 90 °C and reflux for 12 hours, remove methanol using a Dean-Stark water separator. After the reaction is completed, filter to remove the molecular sieve, then distill under reduced pressure at 50 °C to remove the excess methyl methacrylate, and then distill at 120 °C to collect the light yellow transparent liquid product, the novel isocyanate blocking agent, methylcyclohexylaminoethyl methacrylate.

[0092] 3) Dissolve the isocyanate-capped oligomer (52.07 g) and methylcyclohexylaminoethyl methacrylate (49.26 g) prepared above in N,N-dimethylformamide solvent (105 mL), and place it in a three-necked flask equipped with a mechanical stirrer, thermometer, and reflux condenser. Under nitrogen protection, heat the mixed system to 60 °C and react at a constant temperature for 4 hours. After the reaction is completed, pour the product into n-hexane for precipitation. After filtration and separation, wash and purify with n-hexane, and finally obtain the methacrylate-terminated polyurethane prepolymer after drying. The NMR spectrum is as Figure 4 shown.

[0093] 4) Component A consists of the methacrylate-terminated polyurethane prepolymer (78.00 g), the reactive diluent diethylene glycol dimethacrylate (12.00 mL), and the photoinitiator diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) (2.00 g), and component B is hexamethylenediamine (8.00 g). Mix the two components evenly at room temperature to obtain the photosensitive resin.

[0094] 5) Subsequently, place the photosensitive resin in the forming tank of a digital light processing (DLP) type 3D printer. Through the layer-by-layer irradiation of a 405 nm wavelength ultraviolet light source, initiate the photopolymerization reaction to obtain the photocured product. After the preliminary forming of the photocured product, first perform a preheating treatment at 80 °C for 30 minutes, and then raise the temperature to 140 °C and maintain it for 2 hours to complete the thermal curing process. During this thermal curing stage, the large steric hindrance urea bonds formed by the reaction of secondary amine and isocyanate undergo partial thermal dissociation due to poor thermal stability, and the isocyanate-capped prepolymer is regenerated. 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 finished product.

[0095] Figure 8Tensile strength curve of the 3D printed finished 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 a nitrogen protection environment, polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (55.58 g), catalyst dibutyltin dilaurate (0.10 g), and anhydrous toluene (25 mL) were successively added to a three-necked flask equipped with a thermometer, a reflux condenser, and a mechanical stirring device. Under continuous stirring, the reaction system was adjusted to a reaction temperature range of 60 - 80 °C in a programmed heating manner and maintained at a constant temperature for 3 hours. After the reaction was completed, the system was naturally cooled to room temperature, and then the organic solvent toluene was removed by vacuum distillation, and finally an isocyanate-terminated oligomer was obtained.

[0098] 2) In a fume hood, anhydrous tetrahydrofuran (THF) (100 mL), cyclopentylamine (9.3 g), and anhydrous zinc chloride (0.68 g) were added to a three-necked flask. After cooling to 10 °C in an ice-water bath, ethylene oxide (5.3 g) was slowly added dropwise while controlling the temperature below 25 °C. After the addition was completed, the ice-water bath was removed, and the reaction was carried out at room temperature for 5 hours. After the reaction was completed, THF was removed by rotary evaporation to obtain a crude product of N-(2-hydroxyethyl)cyclopentylamine. Subsequently, it was added to a round-bottom flask together with methyl methacrylate (30.00 g) and activated 4 Å molecular sieve (2.00 g), heated to 90 °C and refluxed for 12 hours, and methanol was removed using a Dean-Stark water separator. After the reaction was completed, the molecular sieve was removed by filtration, and then the excess methyl methacrylate was removed by vacuum distillation at 50 °C, and then the light yellow transparent liquid product, cyclopentylaminoethyl methacrylate, a novel isocyanate blocking agent, was collected 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 maintained 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 a methacrylate-terminated polyurethane prepolymer was obtained after drying. The NMR spectrum is as Figure 5 shown.

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

[0101] 5) Subsequently, the photosensitive resin is placed in the forming tank of a digital light processing (DLP) type 3D printer. Through layer-by-layer irradiation with a 405 nm wavelength ultraviolet light source, a photopolymerization reaction is initiated to obtain a photocured product. After preliminary shaping of the photocured product, it is first preheated at 80 °C for 30 minutes, and 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 steric hindrance urea bonds formed by the reaction of secondary amines and isocyanates undergo partial thermal dissociation due to poor thermal stability, and the isocyanate-capped prepolymer is regenerated. 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 finished product.

[0102] Figure 9 It is the tensile strength curve of the 3D printed finished 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 secondary amine with a large steric hindrance (such as a six-membered ring, a five-membered ring or a benzene ring) 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 a nitrogen protection environment, polypropylene glycol (PPG2000) (20.00 g), isophorone diisocyanate (IPDI) (55.58 g), the catalyst dibutyltin dilaurate (0.10 g), and anhydrous toluene (25 mL) are successively added to a three-necked flask equipped with a thermometer, a reflux condenser and a mechanical stirring device. Under continuous stirring conditions, the reaction system is adjusted to a reaction temperature range of 60 °C in a programmed heating manner and maintained at a constant temperature for 3 hours. After the reaction is completed, the system is naturally cooled to room temperature, and then the organic solvent toluene is removed by vacuum distillation to finally obtain an isocyanate-capped oligomer.

[0106] 2) The above-prepared isocyanate-terminated oligomer (52.00 g) and tert-butylaminoethyl methacrylate (49.00 g) 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 obtained a methacrylate-terminated polyurethane prepolymer after drying treatment.

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

[0108] 4) Subsequently, the photosensitive resin was placed in the forming tank of a digital light processing (DLP) type 3D printer. Through the layer-by-layer irradiation of a 405 nm wavelength ultraviolet light source, a photopolymerization reaction was initiated to obtain a photocured product. After the preliminary forming of the photocured product, it was first preheated at 80 °C for 30 minutes, and then the temperature was raised to 140 °C and maintained for 2 hours to complete the thermal curing process. The final 3D printed finished product was obtained.

[0109] Figure 10 It is the tensile strength curve of the 3D printed finished 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 and easily deblocked methacrylate-terminated polyurethane prepolymer, characterized in that: The structural formula is as 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: It includes: Step 1: Under nitrogen protection, polypropylene glycol, isophorone diisocyanate, a catalyst and a solvent are added to a reaction vessel for reaction to obtain an isocyanate-terminated oligomer shown in Formula I; Formula Ⅰ; Step 2: Anhydrous tetrahydrofuran, a primary amine containing a large steric hindrance group and anhydrous zinc chloride are added to the reaction vessel. After cooling to 10 - 15 °C in an ice-water bath, ethylene oxide is slowly added dropwise while controlling the temperature below 25 °C. After the addition is completed, the ice-water bath is removed, and the reaction is carried out at room temperature for 5 hours. After the reaction is completed, THF is removed by rotary evaporation to obtain a crude intermediate product. Subsequently, it, methyl methacrylate and activated 4 Å molecular sieve are added to the reaction vessel, and the temperature is raised to 90 - 95 °C for reflux for 12 hours. After post-treatment, an 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 for reaction to obtain a large-volume easily deblocked methacrylate-terminated polyurethane prepolymer shown in 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 described 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 described 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 crude intermediate product and 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 dosage of the activated 4 Å 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 and the isocyanate blocking agent described in Step 3 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 described in Step 3 is 50 - 70 °C, and the reaction time is 3 - 6 hours.

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

10. The preparation method of a photosensitive resin according to claim 9, wherein It includes: The large-volume easily deblocked methacrylate-terminated polyurethane prepolymer shown in Formula III, an active diluent and a photoinitiator are composed into Component A, and Component B is a diamine compound. The two components are uniformly mixed at room temperature to obtain a photosensitive resin.

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