Photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, and preparation method and application thereof

Abstract

The application discloses a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, which is composed of 4-6 parts of bio-based cinnamyl alcohol, 5-9 parts of hydroxyethyl methacrylate, 4-6 parts of pyromellitic dianhydride, 4-6.5 parts of bio-based epoxy soybean oil, 0.04-0.07 parts of a first catalyst, 0.07-0.09 parts of a polymerization inhibitor, 0.1-0.2 parts of a second catalyst and 0.4-0.7 parts of a photoinitiator in terms of weight parts; the first catalyst is at least one selected from 4-dimethylaminopyridine, p-toluenesulfonic acid, triethylamine and stannous octoate; and the second catalyst is triphenylphosphine. By introducing a rigid benzene ring structure (from PMDA) and multiple photosensitive groups (acrylate double bonds and cinnamyl double bonds), the application effectively solves the problems of low mechanical strength and poor thermal stability of a cured product of pure epoxy soybean oil-based resin. The obtained resin has excellent thermal performance, mechanical strength and high bio-based content.

Description

Technical Field

[0001] This invention belongs to the field of photocurable materials technology, specifically relating to a photo-thermal dual-curable resin based on pyromellitic dianhydride and cinnamyl alcohol, its preparation method and application. Background Technology

[0002] UV-curable resins are widely used in coatings, inks, adhesives, and 3D printing due to their advantages such as fast curing speed, high energy efficiency, and low volatile organic compound (VOC) emissions. Traditional ultraviolet (UV) curable resins mainly rely on the free radical polymerization of monomers such as acrylates or methacrylates to form a cross-linked network. However, such systems have some inherent drawbacks: firstly, the penetration depth of UV light is limited, resulting in incomplete curing of thick coatings or shaded areas; secondly, free radical polymerization is easily inhibited by oxygen, affecting surface properties; and thirdly, networks formed entirely by free radical polymerization often have high cross-linking density and high brittleness, resulting in insufficient flexibility and impact resistance of the material.

[0003] To overcome the limitations of free radical polymerization photocuring, photo-thermal dual curing technology can effectively solve this problem. This technology combines ultraviolet (UV) curing and thermal curing mechanisms by introducing thermally reactive groups (such as epoxy groups and isocyanate groups) and photosensitive groups (such as acrylate double bonds) into the resin system. Photocuring and thermal curing occur sequentially or simultaneously in a single material system, resulting in a denser and more stable final network structure, effectively improving deep curing problems and enhancing mechanical properties. Epoxidized soybean oil (ESO), as a widely available and inexpensive renewable bio-based raw material, has epoxy groups on its molecular chain that can serve as thermal curing sites, and is therefore often used to modify synthetic resins to increase their bio-based content and environmental properties. However, ESO itself has low reactivity, and its long aliphatic chain structure may lead to a decrease in material rigidity and strength. On the other hand, to improve the rigidity and heat resistance of resins, multifunctional rigid monomers are often used as crosslinking reinforcing agents. Pyromellitic anhydride (PMDA) is an aromatic rigid monomer containing four carboxyl functional groups, which can significantly improve the crosslinking density and heat distortion temperature of materials. However, when PMDA is directly introduced into bio-based systems, its extremely high functionality and rigid structure easily lead to a sharp increase in the brittleness of the crosslinking network, poor compatibility with flexible components such as ESO, and micro-phase separation, ultimately making it difficult to balance the strength and toughness of the material, resulting in an imbalance of mechanical properties.

[0004] In addition, most existing dual-curing systems rely on a single type of polymerization mechanism (such as free radical / cationic, free radical / epoxy) and have a relatively uniform network structure. Therefore, it is necessary to construct a composite cross-linking structure with multiple interpenetrating mechanisms. Summary of the Invention

[0005] The purpose of this invention is to provide a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, so as to solve the technical problems of strength-toughness imbalance, incomplete curing and micro-phase separation that are common in existing bio-based photocurable materials.

[0006] According to a first aspect of the present invention, a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol is provided, wherein, by weight, the raw materials consist of 4-6 parts of bio-based cinnamyl alcohol, 5-9 parts of hydroxyethyl methacrylate (HEMA), 4-6 parts of pyromellitic dianhydride (PDMA), 4-6.5 parts of bio-based epoxidized soybean oil (ESO), 0.04-0.07 parts of a first catalyst, 0.07-0.09 parts of a polymerization inhibitor, 0.1-0.2 parts of a second catalyst, and 0.8-1.4 parts of a photoinitiator; The first catalyst is selected from at least one of 4-dimethylaminopyridine (DMAP), p-toluenesulfonic acid (TsOH), triethylamine, and stannous octanoate (Sn(Oct)2); the second catalyst is triphenylphosphine (TPP).

[0007] This invention relates to a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, using ESO, PDMA, HEMA, and cinnamyl alcohol as raw materials. This resin composition combines the free radical polymerization and photodimerization characteristics of cinnamyl alcohol, and is expected to synergistically work with the rigid network of PMDA and the thermal crosslinking network of ESO to construct a multi-mechanism interpenetrating composite crosslinking structure. This structure can achieve both photocuring and thermal curing through reaction with a photoinitiator, solving the technical problem of incomplete curing in existing bio-based photocurable materials. Simultaneously, by using bio-based cinnamyl alcohol and epoxidized soybean oil as raw materials, the resulting resin composition has a high bio-based content, making it environmentally friendly and enhancing the material's sustainability. Furthermore, the resin composition of this invention uses PDMA, cinnamyl alcohol, and HEMA to form a prepolymer, producing a unique "rigid-tough synergistic" modification effect on the ESO system. This solves the technical problem of microphase separation during resin curing caused by PDMA on the ESO system. The cured resin composition exhibits high hardness, excellent adhesion, good flexibility, and chemical resistance. Specifically, the double bonds of HEMA accelerate photocuring efficiency, while cinnamyl alcohol introduces a benzene ring structure that improves material rigidity and carbon-carbon double bonds that participate in photocuring. When used in conjunction with ESO, it balances the material's rigidity and toughness. Cinnamyl alcohol can introduce a unique [2+2] photocycloaddition curing mechanism, forming a synergistic and complementary dual curing network with the free radical polymerization of HEMA. This fundamentally solves the problems of oxygen inhibition and large volume shrinkage in traditional photocuring systems. The rigid benzene ring structure derived from PDMA and bio-based cinnamyl alcohol effectively addresses the issues of low mechanical strength and poor thermal stability in cured pure epoxy soybean oil-based resins.

[0008] In some embodiments, the photoinitiator is composed of a long-wavelength photoinitiator and a short-wavelength photoinitiator; the long-wavelength photoinitiator is selected from at least one of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator 819), 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO), and isopropylthioxanthone (ITX); the short-wavelength photoinitiator is selected from at least one of 1-hydroxycyclohexylphenyl ketone (photoinitiator 184), 2-hydroxy-2-methyl-1-phenyl-1-propanone (photoinitiator 1173), and 2-methyl-1-[4-methylthiophenyl]-2-morpholino-1-propanone (photoinitiator 907). Preferably, the long-wavelength photoinitiator is selected from 2,4,6-trimethylbenzoyl-diphenylphosphine oxide; and the short-wavelength photoinitiator is selected from 2-hydroxy-2-methyl-1-phenyl-1-propanone. The photocuring agent of the present invention combines long-wavelength photoinitiators with short-wavelength photoinitiators, utilizing their complementary ultraviolet light absorption characteristics to achieve uniform, efficient, and thorough curing of the resin composition from the surface to the depth, thereby overcoming the limitations that cannot be overcome by a single photoinitiator system.

[0009] In some embodiments, the amount of long-wavelength photoinitiator is 1%-5% of the total mass of bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, and bio-based epoxidized soybean oil. Preferably, the amount of long-wavelength photoinitiator is 3% of the total mass of bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, and bio-based epoxidized soybean oil.

[0010] In some embodiments, the amount of short-wavelength photoinitiator is 1%-5% of the total mass of bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, and bio-based epoxidized soybean oil. Preferably, the amount of short-wavelength photoinitiator is 3% of the total mass of bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, and bio-based epoxidized soybean oil.

[0011] In some embodiments, the molar ratio of pyromellitic dianhydride to hydroxyethyl methacrylate is 1:(2-5); the molar ratio of hydroxyethyl methacrylate to bio-based cinnamyl alcohol is 1:2 to 2:1.

[0012] It should be noted that the resin properties can be adjusted by regulating the molar ratio of hydroxyethyl methacrylate to bio-based cinnamyl alcohol. Since cinnamyl alcohol contains a benzene ring structure, increasing the amount of cinnamyl alcohol can appropriately increase the resin's rigidity and improve its thermal stability and resistance to yellowing. HEMA contains highly reactive double bonds; therefore, a slightly higher amount of HEMA can improve the resin's photocuring efficiency and give it greater toughness and abrasion resistance.

[0013] In some embodiments, the molar ratio of bio-based cinnamyl alcohol, hydroxyethyl methacrylate, and pyromellitic dianhydride is (0.02-0.06):(0.03-0.09):(0.01-0.03).

[0014] According to a second aspect of the present invention, a method for preparing a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol is provided, comprising the following steps: S1. Mix bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, the first catalyst and the polymerization inhibitor, and react at 60-85℃ for 2-5 hours to obtain the prepolymer; S2. The prepolymer, bio-based epoxidized soybean oil and the second catalyst are mixed and reacted at 70-90℃ for 0.5-2 hours to obtain the first intermediate; S3. Mix the first intermediate with the photoinitiator and irradiate with ultraviolet light to obtain the final product.

[0015] This invention first reacts bio-based cinnamyl alcohol, hydroxyethyl methacrylate, and pyromellitic dianhydride to prepare a prepolymer with cinnamate and acrylate structures in its side chains. Then, this prepolymer undergoes an epoxy-carboxyl addition reaction with bio-based epoxidized soybean oil (ESO) under a catalyst to crosslink, thereby introducing cinnamate and acrylate structures into the bio-based resin. Furthermore, cinnamyl alcohol contains a benzene ring structure, which can alter the rigidity of the product and improve its thermal stability and resistance to yellowing; while HEMA contains highly reactive double bonds, which is beneficial for improving the photocuring efficiency of the product and imparting higher toughness and wear resistance. This invention first reacts PMDA, cinnamyl alcohol, and HEMA to form a prepolymer possessing both an aromatic rigid structure and a reactive double bond structure. This prepolymer, in its molecular structure, simultaneously possesses polar ester bonds, flexible segments, and aromatic rigid structural units. Thermodynamically, this reduces the difference in solubility parameters between systems and decreases interaction parameters, thereby improving the compatibility between components. Subsequently, the prepolymer is reacted with ESO, which mitigates the reaction rate difference between the rigid anhydride structure and the epoxy group in curing kinetics, inhibits curing-induced phase separation, and forms a uniform three-dimensional cross-linked structure with covalent bonds. This allows the aromatic rigid units to be uniformly dispersed at the molecular level within the flexible aliphatic chain continuous phase, avoiding the formation of an independent hard phase. This achieves a "rigid-tough synergistic" modification effect and solves the technical problem of micro-phase separation during resin curing caused by PDMA in the ESO system.

[0016] Because pyromellitic dianhydride has very large steric hindrance, the prepolymer obtained after the reaction of bio-based cinnamyl alcohol, hydroxyethyl methacrylate and pyromellitic dianhydride still contains carboxyl groups that can react with ESO.

[0017] In some embodiments, in step S1, bio-based cinnamyl alcohol, hydroxyethyl methacrylate (HEMA), and pyromellitic dianhydride (PMDA) are reacted at 70°C for 3 hours. This condition can effectively inhibit gelation or color deepening while ensuring the reaction rate.

[0018] In some embodiments, the acid value of the prepolymer is 120-180 mg KOH / g. Preferably, the acid value of the prepolymer is 130-180 mg KOH / g. An acid value within this range indicates that each PMDA unit in the prepolymer retains an average of approximately 1.6-2.0 carboxyl groups, providing suitable reaction sites for subsequent reactions with ESO.

[0019] In some embodiments, the acid value of the first intermediate is 54.6-58.6 mg KOH / g.

[0020] In some embodiments, the molar ratio of the first catalyst to pyromellitic dianhydride is (4~6):(1~2). Preferably, the molar ratio of the first catalyst to pyromellitic dianhydride is 5:2.

[0021] In some embodiments, the polymerization inhibitor is selected from at least one of hydroquinone (HQ), 2,6-di-tert-butyl-p-methylphenol, and p-hydroxyanisole (MEHQ).

[0022] In some embodiments, the amount of polymerization inhibitor used is 0.3%-0.8% of the total mass of pyromellitic dianhydride, bio-based cinnamyl alcohol, hydroxyethyl methacrylate, and bio-based epoxidized soybean oil.

[0023] In some embodiments, the epoxidation equivalent of the bio-based epoxidized soybean oil is 240-260 g / eq.

[0024] In some embodiments, the molar ratio of epoxy groups in the bio-based epoxidized soybean oil to carboxyl groups in the prepolymer is 0.5:1 to 0.8:1. Preferably, the molar ratio of epoxy groups in the bio-based epoxidized soybean oil to carboxyl groups in the prepolymer is 0.6:1 to 0.7:1. This ratio ensures sufficient reaction between the carboxyl and epoxy groups while avoiding excessive epoxy groups that could lead to an overly brittle cured film.

[0025] In some embodiments, the amount of the second catalyst is 0.5%-3.5% of the total mass of the prepolymer and bio-based epoxidized soybean oil.

[0026] In some implementations, the structural formula of the first intermediate is: In the formula, R is or R1, R2, and R3 are straight-chain or branched alkane groups of C5 to C7.

[0027] In some embodiments, in step S2, the prepolymer, bio-based epoxidized soybean oil, and the second catalyst are mixed at 40-60°C, then heated to 70-79°C and stirred for 10-15 minutes, followed by heating to 80-90°C and continuing the reaction for 0.5-1.8 hours. Because the addition of ESO can easily lead to uneven stirring and localized gelation, a lower temperature (70-79°C) is used first to allow the raw materials to be stirred evenly before the reaction is raised to 80-90°C.

[0028] In some embodiments, step S3 further includes mixing the first intermediate with the reactive diluent and then with the photoinitiator.

[0029] Reactive diluents have active double bond structures that can adjust the viscosity of the system and facilitate coating. Their own acrylate double bonds can also participate in photocuring crosslinking, increasing the crosslinking density.

[0030] In some embodiments, the reactive diluent is isobornyl acrylate (IBOA). The amount of reactive diluent used is 20%-50% of the total mass of the prepolymer and ESO.

[0031] In some embodiments, in step S3, the wavelength of ultraviolet light used for irradiation is 365 nm, and the light intensity is 80-120 mW / cm². 2 The irradiation time is 30-90 seconds.

[0032] According to a third aspect of the present invention, another method for preparing a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol is provided, comprising the following steps: S1. Mix bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, the first catalyst and the polymerization inhibitor, and react at 60-85℃ for 2-5 hours to obtain the prepolymer; S2. The prepolymer is mixed with a photoinitiator and irradiated with ultraviolet light to obtain the second intermediate; S3. Mix the second intermediate, bio-based epoxidized soybean oil and the second catalyst, and react at 70-90℃ for 0.5-2 hours to obtain the final product.

[0033] In this invention, the role of the polymerization inhibitor is to prevent the double bonds of the reactants from self-polymerizing in step S1; the role of the first catalyst is to promote the reaction between the hydroxyl groups of bio-based cinnamyl alcohol and hydroxyethyl methacrylate and pyromellitic dianhydride; and the role of the second catalyst is to promote the ring-opening reaction between the prepolymer and ESO or the second intermediate.

[0034] The resin prepared by this invention introduces a combination of cinnamic acid ester structure and acrylate structure. It is not simply adding a photocurable double bond to the system, but rather based on its unique [2+2] cycloaddition reaction mechanism, forming an essential complementary and synergistically enhanced dual photocuring design with the existing free radical chain polymerization path of acrylate in the system. Specifically, it is reflected in the following three aspects: (1) The curing mechanisms of cinnamic acid ester and acrylate are different. Acrylate forms a three-dimensional network of "long chain connection" through free radical chain polymerization, while cinnamic acid ester directly forms a rigid cyclobutane ring crosslinking point between the two functional groups through photo-excited stepwise [2+2] cycloaddition. (2) Cinnamic acid ester and acrylate synergistically solve the inherent defects of traditional photocuring. The former provides toughness, and the latter introduces rigid short crosslinking points. The combination of the two achieves a network structure with a rigid-toughness balance. Acrylate curing is easily affected by oxygen inhibition, resulting in sticky surface and large polymerization shrinkage (about 10%-20%) and high internal stress. The [2+2] cycloaddition of cinnamic acid esters is not inhibited by oxygen and has minimal volume shrinkage (approximately 1%-3%). The combined effect of both ensures rapid deep curing and significantly improves surface quality, reducing internal stress and edge warping risk in the cured film. (3) Acrylic acid ester systems commonly use 365 nm for photocuring, while the characteristic absorption of cinnamic acid esters is ≤320 nm (e.g., 302 nm). By introducing acrylate and cinnamic acid esters into the system, different wavelengths of UV can be used sequentially. First, 365 nm is used to initiate the formation of a primary network of acrylate, and then short-wave UV is used to selectively strengthen the crosslinking of cinnamic acid esters, thereby achieving spatiotemporally controllable dual photocuring. This forms a denser interpenetrating network with subsequent thermal curing (epoxy-carboxyl reaction), comprehensively improving the modulus, thermal stability, and dimensional stability of the material.

[0035] A fourth aspect of the present invention provides the application of photo-thermal dual-curing resins based on pyromellitic dianhydride and cinnamyl alcohol in the preparation of coatings, electronic packaging and 3D printing composite materials.

[0036] In some embodiments, the method involves coating a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol onto the surface of a substrate, followed by curing under ultraviolet light.

[0037] In some embodiments, the substrate is metal, plastic, polytetrafluoroethylene, wood, or glass.

[0038] The beneficial effects of this invention are as follows: (1) High bio-based content, with bio-based cinnamyl alcohol and epoxidized soybean oil as the main raw materials, the bio-based carbon content can reach more than 50%, reducing dependence on fossil resources and being environmentally friendly.

[0039] (2) Excellent overall performance. Through the multifunctional modification of PMDA and cinnamyl alcohol, rigid benzene rings and reactive carboxyl groups are introduced; then combined with the flexible long chain of ESO, the hardness and flexibility of the coating are balanced; HEMA provides photocuring activity, the curing speed is fast, and the coating has high hardness, excellent adhesion, good flexibility and chemical resistance.

[0040] (3) The process is simple and the conditions are mild. Both the ring-opening esterification and the epoxy-carboxyl addition reaction are carried out at a low temperature, without the need for complicated post-processing, making it suitable for large-scale production.

[0041] (4) Wide range of applications: This product can be widely used in coatings, electronic packaging and 3D printing composite materials. Attached Figure Description

[0042] Figure 1 FT-IR images of samples 1-5 of this invention; Figure 2 The rheological diagrams are of samples 1-5 of this invention. Detailed Implementation

[0043] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0044] Example 1 This embodiment provides a method for preparing a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, comprising the following steps: (1) 0.032 mol (4.294 g) of bio-based cinnamyl alcohol, 0.048 mol (6.247 g) of HEMA, 0.020 mol (4.362 g) of PMDA, 0.050 g of DMAP and 0.080 g of HQ were added to a four-necked flask equipped with a stirrer, thermometer and condenser. The mixture was stirred in an oil bath at 70 °C for 3 hours to obtain the prepolymer. The acid value was measured every 30 minutes during the reaction. At the end of the reaction, the acid value of the prepolymer was measured to be 172.8 mg KOH / g.

[0045] (2) Cool the prepolymer to below 50°C, add 0.20 g TPP (1% of the total mass of the prepolymer and ESO), and stir for 5 minutes to disperse it evenly. Then slowly add 5.37 g of bio-based epoxidized soybean oil (ESO, epoxy equivalent 250 g / eq, molar ratio of epoxy groups to carboxyl groups in the prepolymer is 0.6:1), controlling the dropping rate to keep the reaction temperature below 60°C. After the addition is complete, first heat to 75°C and stir for 15 minutes, then heat to 85°C and continue stirring for 1 hour to obtain a light yellow transparent viscous liquid, which is the resin intermediate.

[0046] (3) Add 4.5 g of isobornyl acrylate (IBOA, reactive diluent, with a mass of 20% of the total mass of prepolymer and ESO) to the resin intermediate, stir at 45°C for 15 minutes, mix evenly, then add 0.608 g of TPO and 0.608 g of photoinitiator 1173, mix evenly, and obtain a photocurable resin composition.

[0047] (4) The resin composition is coated onto a polished and cleaned aluminum plate, with a wet film thickness of approximately 50 μm. The coated sample is then placed in a UV curing machine (365 nm, light intensity 100 mW / cm²). 2 Irradiate for 60 seconds to obtain a milky white, smooth cured coating.

[0048] Example 2 This embodiment provides a method for preparing a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, comprising the following steps: (1) 0.032 mol (4.294 g) of bio-based cinnamyl alcohol, 0.048 mol (6.247 g) of HEMA, 0.020 mol (4.362 g) of PMDA, 0.050 g of DMAP and 0.080 g of HQ were added to a four-necked flask equipped with a stirrer, thermometer and condenser. The mixture was stirred in an oil bath at 70 °C for 3 hours to obtain the prepolymer. The acid value was measured every 30 minutes during the reaction. At the end of the reaction, the acid value of the prepolymer was measured to be 172.5 mg KOH / g.

[0049] (2) Cool the prepolymer to below 50°C, add 0.20 g TPP (1% of the total mass of the prepolymer and ESO), and stir for 5 minutes to disperse it evenly. Then slowly add 6.28 g of bio-based epoxidized soybean oil (ESO, epoxy equivalent 250 g / eq, molar ratio of epoxy groups to carboxyl groups in the prepolymer is 0.7:1), controlling the dropping rate to keep the reaction temperature below 60°C. After the addition is complete, first heat to 75°C and stir for 15 minutes, then heat to 85°C and continue stirring for 1 hour to obtain a light yellow transparent viscous liquid, which is the resin intermediate.

[0050] (3) Add 4.5 g of isobornyl acrylate (IBOA, reactive diluent, with a mass of 20% of the total mass of prepolymer and ESO) to the resin intermediate, stir at 45°C for 15 minutes, mix evenly, then add 0.608 g of TPO and 0.608 g of photoinitiator 1173, mix evenly, and obtain a photocurable resin composition.

[0051] (4) The resin composition is coated onto a polished and cleaned aluminum plate, with a wet film thickness of approximately 50 μm. The coated sample is then placed in a UV curing machine (365 nm, light intensity 100 mW / cm²).2 Irradiate for 60 seconds to obtain a milky white, smooth cured coating.

[0052] Example 3 This embodiment provides a method for preparing a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, comprising the following steps: (1) 0.032 mol (4.294 g) of bio-based cinnamyl alcohol, 0.048 mol (6.247 g) of HEMA, 0.020 mol (4.362 g) of PMDA, 0.050 g of DMAP and 0.080 g of HQ were added to a four-necked flask equipped with a stirrer, thermometer and condenser. The mixture was stirred in an oil bath at 80 °C for 3 hours to obtain the prepolymer. The acid value was measured every 30 minutes during the reaction. At the end of the reaction, the acid value of the prepolymer was measured to be 153.6 mg KOH / g.

[0053] (2) Cool the prepolymer to below 50°C, add 0.20 g TPP (1% of the total mass of the prepolymer and ESO), and stir for 5 minutes to disperse it evenly. Then slowly add 5.37 g of bio-based epoxidized soybean oil (ESO, epoxy equivalent 250 g / eq, molar ratio of epoxy groups to carboxyl groups in the prepolymer is 0.6:1), controlling the dropping rate to keep the reaction temperature below 60°C. After the addition is complete, first heat to 75°C and stir for 15 minutes, then heat to 85°C and continue stirring for 1 hour to obtain a light yellow transparent viscous liquid, which is the resin intermediate.

[0054] (3) Add 4.5 g of isobornyl acrylate (IBOA, reactive diluent, with a mass of 20% of the total mass of prepolymer and ESO) to the resin intermediate, stir at 45°C for 15 minutes, mix evenly, then add 0.608 g of TPO and 0.608 g of photoinitiator 1173, mix evenly, and obtain a photocurable resin composition.

[0055] (4) The resin composition is coated onto a polished and cleaned aluminum plate, with a wet film thickness of approximately 50 μm. The coated sample is then placed in a UV curing machine (365 nm, light intensity 100 mW / cm²). 2 Irradiate for 60 seconds to obtain a milky white, smooth cured coating.

[0056] Example 4 This embodiment provides a method for preparing a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, comprising the following steps: (1) 0.04 mol (5.367 g) of bio-based cinnamyl alcohol, 0.06 mol (7.804 g) of HEMA, 0.020 mol (4.362 g) of PMDA, 0.050 g of DMAP, and 0.080 g of HQ were added to a four-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was stirred in an oil bath at 70 °C for 3 hours to obtain a prepolymer. The acid value was measured every 30 minutes during the reaction. After the reaction, the acid value of the prepolymer was measured to be 134.8 mg KOH / g. Infrared spectroscopy was used to detect the acid value at 1780 cm⁻¹. - The disappearance of the characteristic peaks of the acid anhydride near ¹ indicates that the acid anhydride has been completely opened.

[0057] (2) Cool the prepolymer to below 50°C, add 0.20 g TPP (1% of the total mass of the prepolymer and ESO), and stir for 5 minutes to disperse it evenly. Then slowly add 5.37 g of bio-based epoxidized soybean oil (ESO, epoxy equivalent 250 g / eq, molar ratio of epoxy groups to carboxyl groups in the prepolymer is 0.6:1), controlling the dropping rate to keep the reaction temperature below 60°C. After the addition is complete, first heat to 75°C and stir for 15 minutes, then heat to 85°C and continue stirring for 1 hour to obtain a light yellow transparent viscous liquid, which is the resin intermediate.

[0058] (3) Add 4.5 g of isobornyl acrylate (IBOA, reactive diluent, accounting for 20% of the total mass of prepolymer and ESO) to the resin intermediate, stir at 45°C for 15 minutes, mix evenly, then add 0.687 g of TPO and 0.687 g of photoinitiator 1173, mix evenly, and obtain a photocurable resin composition.

[0059] (4) The resin composition is coated onto a polished and cleaned aluminum plate, with a wet film thickness of approximately 50 μm. The coated sample is then placed in a UV curing machine (365 nm, light intensity 100 mW / cm²). 2 Irradiate for 60 seconds to obtain a milky white, smooth cured coating.

[0060] Furthermore, this application found that when the molar ratio of the total hydroxyl groups of cinnamyl alcohol and HEMA to PMDA is adjusted to 5:1, compared with other embodiments (the molar ratio of the total hydroxyl groups of cinnamyl alcohol and HEMA to PMDA is 4:1), the viscosity of the reaction system in step (1) can be reduced and the gel point of the reactants can be delayed.

[0061] Example 5 This embodiment provides a method for preparing a photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, comprising the following steps: (1) 0.032 mol (4.294 g) of bio-based cinnamyl alcohol, 0.048 mol (6.247 g) of HEMA, 0.020 mol (4.362 g) of PMDA, 0.050 g of DMAP, and 0.080 g of HQ were added to a four-necked flask equipped with a stirrer, thermometer, and condenser. The mixture was stirred in an oil bath at 70 °C for 3 hours to obtain a prepolymer. The acid value was measured every 30 minutes during the reaction. At the end of the reaction, the acid value of the prepolymer was measured to be 172.7 mg KOH / g. Infrared spectroscopy was used to detect the acid value at 1780 cm⁻¹. -1 The disappearance of the characteristic peaks of the nearby anhydride indicates that the anhydride has been completely ring-opened.

[0062] (2) Cool the prepolymer to below 50°C, add 0.20 g TPP (1% of the total mass of the prepolymer and ESO), and stir for 5 minutes to disperse it evenly. Then slowly add 5.37 g of bio-based epoxidized soybean oil (ESO, epoxy equivalent 250 g / eq, molar ratio of epoxy groups to carboxyl groups in the prepolymer is 0.6:1), controlling the dropping rate to keep the reaction temperature below 60°C. After the addition is complete, first heat to 75°C and stir for 15 minutes, then heat to 85°C and continue stirring for 1 hour to obtain a light yellow transparent viscous liquid, which is the resin intermediate.

[0063] (3) Add 6.75g of isobornyl acrylate (IBOA, reactive diluent, with a mass of 30% of the total mass of prepolymer and ESO) to the resin intermediate, stir at 45°C for 15 minutes, mix evenly, then add 0.608g of TPO and 0.608g of photoinitiator 1173, mix evenly, and obtain a photocurable resin composition.

[0064] (4) The resin composition is coated onto a polished and cleaned aluminum plate, with a wet film thickness of approximately 50 μm. The coated sample is then placed in a UV curing machine (365 nm, light intensity 100 mW / cm²). 2 Irradiate for 60 seconds to obtain a milky white, smooth cured coating.

[0065] Performance testing: The photo-thermal dual-curing resins based on pyromellitic dianhydride and cinnamyl alcohol prepared in Examples 1-5 were named Example 1, Example 2, Example 3, Example 4 and Example 5, respectively.

[0066] Infrared spectral analysis was performed on samples 1-5, ESO, and PMDA using a Thermo Scientific / Nicolet iS50 Fourier transform infrared spectrometer. The test results are as follows: Figure 1 As shown. By Figure 1 It can be seen that 1766-1806cm-1 The characteristic peak at 843 cm⁻¹ represents the infrared absorption peak of the acid anhydride. The disappearance of this infrared absorption peak in the product indicates that the acid anhydride has completely reacted, and cinnamyl alcohol and HEMA have been successfully grafted onto it. -1 The infrared absorption peaks of the epoxy groups can reflect the reaction status of the epoxy groups in the product. The infrared absorption peaks of the epoxy groups at the result point have almost disappeared, indicating that the carboxyl groups in the prepolymer can effectively react with the epoxy groups in the ESO.

[0067] Viscosities of samples 1-5 were measured using an MCR502 modular intelligent advanced rheometer under constant temperature conditions of 25℃ and a CP25-2 rotor with a diameter of 25 mm. The experimental setup was an air pressure of 5 bar and a range of 0.01-100 s⁻¹. -1 25 data points were collected logarithmically within the range of shear rate and recorded.

[0068] Test results are as follows Figure 2 As shown in the figure. The results indicate that all groups exhibit low viscosity and flowability at room temperature (25℃), facilitating product discharge. Furthermore, the viscosity of the product gradually increases with increasing ESO dosage or reaction temperature.

[0069] The molecular weight of the products of samples 1-5 was determined using a Waters e2695 gel permeation chromatography instrument. The test results are shown in Table 1. The results show that the molecular weight of the products is 2136±60 g / mol and the polydispersity is around 1.51, indicating that the prepared photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol has a relatively pure structure and few by-products.

[0070] Table 1. Molecular weight and dispersibility of resins in Examples 1-5

[0071] The coating adhesion of samples 1-5 was tested using the following steps: First, a 500μm four-sided coating applicator was used to evenly coat the sample onto the surface of an A3 iron plate to form a wet film, which was then placed under a UV curing machine for full curing. On the cured coating surface, test spindles were bonded using 3M off-white DP420 two-component AB adhesive and allowed to stand under standard conditions for at least 24 hours to ensure strong adhesion. Finally, a pull-out test was performed using a fully automatic pull-out adhesion tester with a range of 0.7-20 MPa. The tensile force when the coating was pulled off was recorded. Five parallel samples were prepared, and the final result was the average value.

[0072] Gloss testing was performed on samples 1-5 as follows: First, the gloss meter (MN60) was calibrated using a standard calibration plate to ensure accurate instrument readings. Then, the instrument's measurement angle was set to 60°, and the surface of the cured film was measured. Five parallel measurements were performed at different locations for each sample, and the final result was the average.

[0073] The gelation rate of samples 1-5 was tested using the following method: First, approximately 0.5 g (denoted as W0) of each sample was weighed and immersed in 15 mL of each of the five organic solvents at room temperature, and allowed to stand for 2 days. Then, the samples were removed, and the residual solvent on the surface was gently blotted dry with filter paper before weighing to obtain the weight W1 after swelling. Finally, the samples were dried in a 60℃ oven until constant weight, and the final weight W2 was obtained. The gelation rate was calculated using Formula 2.1.

[0074]

[0075] The results of adhesion, gloss, and gelation rate tests are shown in Table 2. As can be seen from Table 2, the adhesion of the photo-thermal dual-curing resins based on pyromellitic dianhydride and cinnamyl alcohol prepared in Examples 1-5 ranged from 0.99 to 1.25 MPa. When the molar ratio of ESO epoxy groups to carboxyl groups in the prepolymer was adjusted from 0.6:1 to 0.7:1, the adhesion decreased. This is attributed to the increased epoxy group ratio leading to a significant consumption of highly polar carboxyl groups in the prepolymer, which significantly weakens the hydrogen and chemical bonding between the coating and the substrate (such as metal or glass). Secondly, the closer stoichiometric ratio of the reaction increases the crosslinking density and network rigidity, while simultaneously increasing the curing shrinkage stress, generating higher internal stress at the interface and making it easier to peel off. Adjusting the molar ratio of total hydroxyl groups of HEMA and bio-based cinnamyl alcohol to PDMA from 4:1 to 5:1 reduced the adhesion from 1.25 to 1.03. This is due to the synergistic changes in the prepolymer molecular structure, network crosslinking density, and interfacial internal stress. First, excess hydroxyl groups act as "end-capping agents," inhibiting the full condensation polymerization between PMDA and hydroxyl groups, leading to a decrease in the molecular weight of the prepolymer and insufficient cohesive strength of the network after curing. Second, excess hydroxyl groups from cinnamyl alcohol relatively increase the density of polymerizable double bonds in the system, forming a brittle network with a higher degree of cross-linking after photocuring, increasing curing shrinkage stress, and making the coating interface easier to peel off under stress. The gloss level is 101°±6°, indicating high light transmittance of the cured film surface. The gel rate of the photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol is above 95%, indicating a high degree of cross-linking and relatively complete and uniform curing.

[0076] Table 2 Adhesion, gloss and gelation rate tests for Examples 1-5

[0077] The acid value determination of the products from steps (1) and (2) in Examples 1-5 was performed as follows: Accurately weigh 0.1-0.2 g of sample into an Erlenmeyer flask and record its accurate mass. Then add a mixed solvent of toluene and ethanol (volume ratio 1:1) to completely dissolve the sample. Add 4-5 drops of phenolphthalein indicator to the solution, shake well, and then use 0.5 mol·L⁻¹ acid value determination solution. -1 Titrate with a standard potassium hydroxide (KOH) solution to a pink endpoint and record the volume consumed. The calculation formula is shown in 2.2.

[0078]

[0079] In addition, the theoretical acid value is calculated as follows: Hypothesis 1: Each PMDA molecule retains one carboxyl group (consuming all 3 equivalent hydroxyl groups), one anhydride group undergoes ring-opening and complete esterification (consuming 2 hydroxyl groups, generating a diester, with no carboxyl group), and the other anhydride group undergoes ring-opening to form a half-ester (consuming 1 hydroxyl group, generating one carboxyl group and one ester group). In total, 3 hydroxyl groups are consumed, 1 carboxyl group is generated, and there is no free alcohol. M avg =(M 肉桂醇 +M HEMA ) ÷ 2 = 132.155 g / mol.

[0080] Product molecular weight: M=M PMDA +3×M avg 1×M H2O =218.12+3×132.155 18.015 = 596.57 g / mol.

[0081] Theoretical acid value (based on carboxyl group, KOH molar mass 56.11 g / mol): AV=56.11×1000÷596.57≈94.1 mg KOH / g Hypothesis 2: Each PMDA molecule retains 2 carboxyl groups. Sub-hypothesis A: Unreacted alcohol is removed (purified product), each of the two anhydride groups undergoes ring opening once, each generating a half-ester (each consuming 1 hydroxyl group and contributing 1 carboxyl group), for a total consumption of 2 hydroxyl groups. The remaining 1 equivalent hydroxyl group (from the alcohol) is removed during purification.

[0082] Molecular weight of pure product (dihalester, without anhydrous loss): M=M PMDA +2×M avg =218.12+2×132.155=482.43 g / mol; Theoretical acid value: AV = 2 × 56.11 × 1000 ÷ 482.43 ≈ 232.6 mg KOH / g.

[0083] Sub-hypothesis B: Unreacted alcohol remains in the reaction mixture (4 equivalents of alcohol are added, 2 equivalents are consumed), forming a dihaloester (2 hydroxyl groups are consumed), but the remaining 1 equivalent of alcohol remains unreacted and is mixed in the product. Total mass of the mixture (1 mol of PMDA corresponds to 1 mol of free alcohol): M=(M PMDA +2×M avg )+2×M avg =482.43+264.31=746.74 g / mol; Theoretical acid value (containing 2 mol of carboxyl groups in the mixture): AV=2×56.11×1000÷746.74≈150.3 mg KOH / g.

[0084] The acid value test results are shown in Table 3. Comparing the theoretical acid value with the actual measured acid value in Table 3, the acid value of the prepolymer ranges from 134.8 to 172.8 mg KOH / g, indicating that the vast majority of the prepolymer has two carboxyl groups, and a very small amount contains only one carboxyl group. The acid value test results of the resin intermediate obtained in step (2) are 54.6 to 58.6, indicating that the carboxyl groups in the resin intermediate successfully undergo a ring-opening reaction with the epoxy groups on the ESO, successfully grafting onto the ESO.

[0085] Table 3 Acid Value Test

[0086] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. A photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol, characterized in that, By weight, the raw material consists of 4-6 parts of bio-based cinnamyl alcohol, 5-9 parts of hydroxyethyl methacrylate, 4-6 parts of pyromellitic dianhydride, 4-6.5 parts of bio-based epoxidized soybean oil, 0.04-0.07 parts of the first catalyst, 0.07-0.09 parts of the polymerization inhibitor, 0.1-0.2 parts of the second catalyst, and 0.8-1.4 parts of the photoinitiator; The first catalyst is selected from at least one of 4-dimethylaminopyridine, p-toluenesulfonic acid, triethylamine, and stannous octoate; the second catalyst is triphenylphosphine.

2. The photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol according to claim 1, characterized in that, The photoinitiator is composed of a long-wavelength photoinitiator and a short-wavelength photoinitiator. The long-wavelength photoinitiator is selected from at least one of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and isopropylthioxanthone. The short-wavelength photoinitiator is selected from at least one of 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2-methyl-1-[4-methylthiophenyl]-2-morpholino-1-propanone. The amount of the long-wavelength photoinitiator is 1%-5% of the total mass of bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, and bio-based epoxidized soybean oil; the amount of the short-wavelength photoinitiator is 1%-5% of the total mass of bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, and bio-based epoxidized soybean oil. The amount of the polymerization inhibitor is 0.3%-0.8% of the total mass of pyromellitic dianhydride, bio-based cinnamyl alcohol, hydroxyethyl methacrylate, and bio-based epoxidized soybean oil.

3. The photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol according to claim 1, characterized in that, The molar ratio of pyromellitic dianhydride to hydroxyethyl methacrylate is 1:(2-5); the molar ratio of hydroxyethyl methacrylate to bio-based cinnamyl alcohol is 1:2 to 2:

1.

4. The photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol according to claim 3, characterized in that, The molar ratio of the bio-based cinnamyl alcohol, hydroxyethyl methacrylate, and pyromellitic dianhydride is (0.02-0.06):(0.03-0.09):(0.01-0.03).

5. The method for preparing the photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Mix bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, the first catalyst and the polymerization inhibitor, and react at 60-85℃ for 2-5 hours to obtain the prepolymer; S2. The prepolymer, bio-based epoxidized soybean oil and the second catalyst are mixed and reacted at 70-90℃ for 0.5-2 hours to obtain the first intermediate; S3. Mix the first intermediate with the photoinitiator and irradiate with ultraviolet light to obtain the final product.

6. The preparation method according to claim 5, characterized in that, Step S3 also includes mixing the first intermediate with the reactive diluent and then mixing it with the photoinitiator; The active diluent is isobornyl acrylate; the amount of the active diluent is 20%-50% of the total mass of the prepolymer and bio-based epoxidized soybean oil.

7. The preparation method according to claim 5, characterized in that, The amount of the second catalyst is 0.5%-3.5% of the total mass of the prepolymer and the bio-based epoxidized soybean oil; the molar ratio of the epoxy groups of the bio-based epoxidized soybean oil to the carboxyl groups of the prepolymer is 0.5:1 to 0.8:

1.

8. The method for preparing the photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Mix bio-based cinnamyl alcohol, hydroxyethyl methacrylate, pyromellitic dianhydride, the first catalyst and the polymerization inhibitor, and react at 60-85℃ for 2-5 hours to obtain the prepolymer; S2. The prepolymer is mixed with a photoinitiator and irradiated with ultraviolet light to obtain the second intermediate; S3. Mix the second intermediate, bio-based epoxidized soybean oil and the second catalyst, and react at 70-90℃ for 0.5-2 hours to obtain the final product.

9. The preparation method according to claim 5 or 8, characterized in that, The wavelength used for ultraviolet light irradiation is 365 nm, and the light intensity is 80-120 mW / cm². 2 The irradiation time is 30-90 seconds.

10. The application of the photo-thermal dual-curing resin based on pyromellitic dianhydride and cinnamyl alcohol according to any one of claims 1-4 in the preparation of coatings, electronic packaging and 3D printing composite materials.

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