A glycourea polythiol curing agent composition and its application

Abstract

This application provides a glycourea polythiol curing agent composition, relating to the field of polymer materials technology. The composition comprises a mixture of a glycourea trithiol compound and a glycourea dithiol compound consisting of positional isomers. This composition, used as a curing agent for epoxy resin compositions, can form a highly uniform cross-linked network structure, enabling the cured epoxy resin composition to simultaneously possess a high glass transition temperature, high flexural modulus, and ultra-high fracture toughness, achieving an excellent balance between rigidity and toughness.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a glycourea-based polythiol curing agent composition and its application. Background Technology

[0002] Epoxy resins are widely used due to their excellent adhesion, mechanical strength, chemical resistance, and electrical insulation properties. Their performance largely depends on the curing agent used. Thiol-based curing agents have attracted attention for their advantages such as rapid curing at room temperature and low viscosity; however, traditional thiol curing agents often suffer from insufficient toughness or poor heat resistance.

[0003] Glycourea is a heterocyclic compound with a symmetrical rigid structure, and its derivatives can be used as crosslinking agents to improve the heat resistance and rigidity of materials. However, single glycourea derivatives often fail to achieve both toughness and heat resistance. Furthermore, in polymer network structure design, the uniformity of crosslinking points is a key factor affecting the final mechanical properties of materials, especially toughness; excessive regularity may lead to stress concentration.

[0004] Therefore, a new molecular design is needed that can actively introduce appropriate chemical heterogeneity to construct a uniform and rigid-tough balanced cross-linked network. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a glycourea polythiol curing agent composition and its application.

[0006] In a first aspect, this application provides a glycourea polythiol curing agent composition, the glycourea polythiol curing agent composition comprising a first component and a second component; the first component is prepared by the following preparation method: S1: Add intermediate compound, dehydrating agent and catalyst to organic solvent, cool to 0-5℃, add 3-mercaptobutyric acid, and continue stirring until the reaction is complete; S2: After the reaction is completed, the mixture is purified and processed to obtain the first component; The structural formula of the intermediate compound is shown in Formula I. Formula I; The molar ratio of the intermediate compound to 3-mercaptobutyric acid is 1:(1.8-2.2). The first component obtained includes compounds with structural formulas as shown in Formulas II-IV; the compounds with structural formulas as shown in Formulas II-IV are shown below: Formula II; Formula III; Formula IV; The structural formula of the second component is shown in formula V. Formula V; Based on the total mass of the glycourea polythiol curing agent composition, the mass fraction of the first component is 50%-60%, and the mass fraction of the second component is 40%-50%.

[0007] It should be understood that the first component is a mixture of compounds that are positional isomers of each other, namely compounds with structural formulas shown in Formula II, Formula III, and Formula IV.

[0008] Those skilled in the art will understand that in the glycourea polythiol curing agent composition of this application, the compounds represented by Formula II, Formula III, and Formula IV in the first component are a mixture of positional isomers resulting from their unique synthetic pathways. The composition of the first component is defined and non-random, as specifically described below: The first component is determined by the preparation method provided in this application. Specifically, it is determined by the regularity of the esterification reaction between the three primary hydroxyl groups with highly similar chemical environments in the intermediate compound as shown in Formula I and a limited amount of 3-mercaptobutyric acid. Under strictly fixed reaction conditions, the reaction results are deterministic and reproducible. To verify this, this application provides repeatability experimental data demonstrating a high degree of consistency in the composition of different batches of products.

[0009] Esterification was performed by selecting two of the three reaction sites (1,3,4) of the intermediate compound shown in Formula I. Chemically, there are only three combinations: 1,4-position (Formula II), 1,3-position (Formula III), and 3,4-position (Formula IV). Mass spectrometry confirmed the existence of this group of positional isomers.

[0010] Treating the compounds shown in Formula II, Formula III, and Formula IV as a bifunctional mixed component is based on the equivalence of their chemical functions. More importantly, the inherent micro-heterogeneity of the mixture composed of the compounds shown in Formula II, Formula III, and Formula IV is precisely the key design for forming a uniform cross-linked network and achieving the excellent rigidity-toughness balance performance of this application.

[0011] Furthermore, based on the total mass of the glycourea polythiol curing agent composition, the mass fraction of the first component is 55%, and the mass fraction of the second component is 45%.

[0012] Furthermore, in the preparation method of the first component, the molar ratio of the dehydrating agent to 3-mercaptobutyric acid in step S1 is 1:(1-1.2); preferably, the molar ratio of the dehydrating agent to 3-mercaptobutyric acid is 1:1.

[0013] Furthermore, in the preparation method of the first component, the amount of catalyst used in step S1 is 5%-10% of the mass of the intermediate compound.

[0014] Furthermore, in the preparation method of the first component, the dehydrating agent in step S1 is one or more of N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, or 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride.

[0015] Furthermore, in the preparation method of the first component, the catalyst in step S1 is an acylation reaction catalyst; preferably, the catalyst is 4-dimethylaminopyridine.

[0016] Furthermore, in the preparation method of the first component, the organic solvent in step S1 is one of acetonitrile, dichloromethane, or tetrahydrofuran.

[0017] Furthermore, in the preparation method of the first component, the reaction temperature in step S1 is 0-5℃; the stirring time is 14-18 hours.

[0018] Furthermore, in the preparation method of the first component, the specific steps of the purification and post-treatment in step S2 are as follows: Water was added dropwise to the mixture after the reaction was completed, and ethyl acetate was added for extraction. The aqueous layer was extracted again with an equal volume of ethyl acetate, and the organic layers were combined. The organic layers were washed sequentially with citric acid solution, saturated sodium bicarbonate aqueous solution, and water, then dried with anhydrous sodium sulfate and filtered. The solvent was evaporated under reduced pressure, and the residue was subjected to column chromatography to obtain the first component.

[0019] Furthermore, in some embodiments, during the extraction process, the volume ratio of the ethyl acetate initially added to the total volume of the reaction system is 1:1.

[0020] Furthermore, during the extraction process, the volume ratio of water to ethyl acetate was 1:2.

[0021] Furthermore, during the washing process, the concentration of the citric acid solution is 4-6%; the volume ratio of the citric acid solution, the saturated sodium bicarbonate aqueous solution, and water is 1:1:1.

[0022] Furthermore, column chromatography was performed using a silica gel column, with the eluent being ethyl acetate to petroleum ether in a volume ratio of 1:3.

[0023] In step S2, after purification, water is added to quench any residual active reagents or catalysts; ethyl acetate is used to extract the organic product from the aqueous phase, thus separating the product; washing with citric acid solution removes unreacted 3-mercaptobutyric acid (acidic) or basic byproducts; washing with saturated sodium bicarbonate solution neutralizes and removes any acidic impurities or residual citric acid that may be generated during the reaction; water washing removes water-soluble inorganic salts; and the product is dried and concentrated before being subjected to column chromatography to separate the target product from impurities with significantly different polarities, obtaining a high-purity first component.

[0024] Furthermore, the preparation method of the second component adopts the preparation method of the first component, the difference being that the molar ratio of the intermediate compound to 3-mercaptobutyric acid is at least 1:3; preferably, the molar ratio of the intermediate compound to 3-mercaptobutyric acid is 1:(3-5).

[0025] Secondly, this application provides a method for preparing the glycourea polythiol curing agent composition described in the first aspect, comprising the following steps: S1': Prepare the first component according to steps S1-S2 of the first aspect; S2': The first component obtained in step S1' is mixed with the second component with the structural formula shown in Formula V at a mass ratio of (50-60):(40-50) to obtain the glycourea polythiol curing agent composition.

[0026] The raw materials, solvents, other components, other reagents, parameters, and process conditions used in step S1' when preparing the first component according to steps S1-S2 of the first aspect are also the same as those used in the preparation of the first component in the first aspect.

[0027] Thirdly, this application provides a curing agent comprising the glycourea polythiol curing agent composition described in the first aspect.

[0028] Fourthly, this application provides the use of the glycourea polythiol curing agent composition described in the first aspect as an epoxy resin curing agent.

[0029] Compared with the prior art, this application includes the following beneficial technical effects: This application utilizes a specific intermediate compound with a molar ratio of 1:(1.8-2.2) to 3-mercaptobutyric acid, so that the compounds shown in Formula II, Formula III and Formula IV in the first component of the reaction product are identified. Independent batch experiments (batch A / B / C) have demonstrated that this process can stably and reproducibly prepare identified products, ensuring batch consistency.

[0030] The first component is a mixture of compounds that are positional isomers of glycoureodithiol compounds—compounds shown in Formula II, Formula III, and Formula IV. The -(CH2)3-OC(=O)-CH(SH)-CH2-CH3 linkages in the molecular structure are long chains linked by freely rotatable C / C and CO single bonds. These chains do not contain any rigid cyclic structures or highly polar, densely packed groups capable of forming strong hydrogen bonds. This structure allows the first component to adopt countless coiled and extended conformations in space, exhibiting excellent flexibility. Each compound in the first component has two -(CH2)3-OC(=O)-CH(SH)-CH2-CH3 linkages. In the solidified network, their main role is to connect two crosslinking points using their two long chains. They do not constitute network nodes themselves but rather form connecting bridges between crosslinking nodes. These connecting bridges possess flexible properties, determining the mobility of the chain segments between the two crosslinking nodes. The two flexible linkages of each compound in the first component fill the network, providing significant deformability. In the first component, the compounds shown in Formula II, Formula III, and Formula IV are used together as a mixture of positional isomers. This ensures the random and uniform distribution of flexible segments in the three-dimensional network from the source, avoiding local weaknesses or stress concentrations in the network that may be caused by a single connection site, and laying a chemical foundation for constructing a uniform and toughened network.

[0031] The second component is a glycourea trithiol compound. Each molecule has three long flexible chains -(CH2)3-OC(=O)-CH(SH)-CH2-CH3, which are connected to the same glycourea core. In the solidified network, the second component acts as a multi-arm crosslinking point. The three arms can react with different epoxy molecules, thus becoming rigid crosslinking nodes in the network. The rigidity of this node mainly comes from the rigid heterocyclic structure of the glycourea core and the spatial constraint brought about by its high functionality.

[0032] A curing agent composition consisting of 50%-60% by weight of the first component and 40%-50% by weight of the second component, formulated with glyceryl polythiol, is used as a curing agent for epoxy resin compositions, exhibiting a synergistic effect. The second component, with its high-density rigid crosslinking points, constructs a robust network framework, providing load-bearing capacity, high Tg, and high modulus. The compounds in the second component act as flexible connecting chains, filling the network and providing significant deformability. The coexistence of positional isomers in the second component ensures that flexible segments are randomly and uniformly distributed at positions 1, 3, and 4 of the glyceryl core, avoiding localized regularity or weaknesses in the network caused by single connecting sites, creating a uniform stress field where stress can be uniformly transmitted. When subjected to impact or stress, the rigid framework initially resists deformation, and the stress is dissipated through the significant extension and rearrangement of the flexible segments and the induction of numerous small shears, hindering crack propagation. Through the aforementioned synergistic effect, the epoxy resin cured product maintains high heat resistance and high rigidity while significantly improving fracture toughness and impact strength, successfully resolving the contradiction between high toughness and high heat resistance that is difficult to achieve simultaneously in traditional technologies.

[0033] In summary, this application provides a glycourea polythiol curing agent composition comprising a mixture of a glycourea trithiol compound and a glycourea dithiol compound composed of positional isomers. This composition, used as a curing agent for epoxy resin compositions, can form a highly uniform cross-linked network structure, enabling the cured epoxy resin composition to simultaneously possess a high glass transition temperature, high flexural modulus, and ultra-high fracture toughness, achieving an excellent balance between rigidity and toughness. This successfully solves the long-standing contradiction in this field of achieving both high toughness and high heat resistance. Detailed Implementation

[0034] The present invention will be further illustrated below with examples, but the implementation of this application is not limited thereto. The following embodiments should not be construed as limiting the scope of protection of this application. If those skilled in the art make some non-essential improvements and adjustments to this application based on the above content, they shall still fall within the scope of protection of this application.

[0035] Chemicals and reagents Epoxy resin: Model CYD-128, liquid, epoxy equivalent 184g / mol, manufacturer: Hunan Yueyang Baling Petrochemical.

[0036] 1,4-Diazabicyclo[2.2.2]octane: purchased from Hunan Huibaishi Biotechnology Co., Ltd.

[0037] DCC: N,N'-dicyclohexylcarbodiimide, purchased from Aladdin Reagents.

[0038] DMAP: 4-Dimethylaminopyridine, purchased from Aladdin Reagents.

[0039] Unless otherwise specified, all other reagents used in the embodiments of this application are from conventional commercially available products.

[0040] Test method: Glass transition temperature Glass transition temperature testing shall be performed in accordance with ISO 11357-2-2020.

[0041] fracture toughness Fracture toughness was tested in accordance with ISO 13586:2018, using compact tensile bending specimens and measuring their stress intensity factor (KIC).

[0042] Impact strength Impact strength testing was conducted in accordance with ISO 179-1-2023, using a cantilever beam impact testing machine to measure the impact strength of unnotched samples.

[0043] Flexural modulus The flexural modulus is tested according to ISO 178:2019.

[0044] Viscosity test Viscosity testing was conducted in accordance with standard GB / T 2794-2022, using a rotational viscometer to measure the viscosity of the mixture at a specific temperature (e.g., 40°C).

[0045] Example 1 This embodiment provides the preparation of the first component, and the preparation route is as follows:

[0046] Among them, compound 3 is the compound shown in formula II, compound 4 is the compound shown in formula III, and compound 5 is the compound shown in formula IV.

[0047] The preparation process is as follows: Compound 1 was prepared in accordance with the patent application published JP2017-43571A.

[0048] Preparation of compound 2 5.1 g (0.05 M) of isovaleric acid was added to 100 mL of dichloromethane, and 8.3 g (0.07 M) of thionyl chloride was slowly added dropwise. After the addition was complete, the mixture was heated to reflux for 2 hours. After the solvent was evaporated, another 100 mL of dichloromethane was added to dissolve the solvent, yielding a dichloromethane solution of isovaleryl chloride. 18.7 g (0.05 M) of compound 1, 1,3,4,6-tetra(3-hydroxypropyl)glycourea was added to 100 mL of dichloromethane, and 10 g (0.1 M) of triethylamine was added. The isovaleryl chloride solution prepared in the previous step was slowly added dropwise at room temperature, and the mixture was stirred for 18 hours after the addition was complete. Slowly add 100ml of water, separate the layers, extract the aqueous layer with 200ml of dichloromethane, combine the organic layers, wash successively with 100ml of saturated sodium bicarbonate solution and 100ml of water, concentrate and evaporate the solvent to obtain 18.1g of intermediate compound 1,3,4-tris(3-hydroxypropyl)-6-(3-methylbutyrylpropyl)glycourea (compound 2).

[0049] The structure of the intermediate compound (compound 2) is characterized as follows: MS [M+1] + 458.27; 1 H-NMR (CDCl3) δ: 5.15(s,2H), 4.12-4.15(t,2H), 3.60-3.66(m,6H), 3.41-3.44(m,5H), 3.36-3.40(m,6H), 2.19-2.23(q,2H), 1.94-2.09(m,3H), 1.72-1.78(d,6H), 0.98-1.00(d,3H), 0.93-0.95(d,3H).

[0050] Preparation of the first component 4.6 g (0.01 M) of intermediate compound 1,3,4-tris(3-hydroxypropyl)-6-(3-methylbutyrylpropyl)glycourea, 4.1 g (0.02 M) of DCC, and 0.4 g of DMAP were added to 200 mL of acetonitrile. After cooling to 0 °C, 2.4 g (0.02 M) of 3-mercaptobutyric acid was added. The mixture was stirred for 16 hours after the addition was complete. 100 mL of water was slowly added dropwise, followed by extraction with 200 mL of ethyl acetate. The aqueous layer was extracted again with 200 mL of ethyl acetate. The organic layers were combined and washed successively with 100 mL of 5% citric acid solution, 100 mL of saturated sodium bicarbonate aqueous solution, and 100 mL of water. The mixture was then dried over anhydrous sodium sulfate and filtered. The solvent was removed under reduced pressure, and the residue was subjected to column chromatography (silica gel column, ethyl acetate:petroleum ether = 1:3) to give a first fraction of 3.7 g containing compound II (compound 3), compound III (compound 4), and compound IV (compound 5).

[0051] The mass spectrometric characterization of the first component is as follows: MS [M+1] + 662.30. This data is consistent with the theoretical molecular weights calculated based on the compounds shown in Formula II, Formula III, and Formula IV of the first component, indicating that the target reaction product, the first component, was successfully obtained through the preparation method of the first component.

[0052] Repeatable experiments To demonstrate the reproducibility of the preparation method of this application, three batches of synthesis experiments were repeated under the exact same conditions as in the examples (labeled as batches A, B, and C, respectively).

[0053] The structures of the first component obtained in three batches were characterized, and the results were consistent with those of Example 1, fully demonstrating the excellent reproducibility of the preparation method of this application. The yields and purities of the products prepared in each batch of the repeatability experiment are shown in Table 1. Purity was determined by high performance liquid chromatography area normalization, which is the percentage of the peak area of ​​the compounds with structural formulas shown in Formulas II, III and IV in the first component relative to the total peak area.

[0054] Table 1

[0055] As shown in Table 1, the yields and purities of the three batches of experiments (A, B, and C) independently repeated according to the method of Example 1 were highly similar to those of Example 1, with yields fluctuating between 52.7% and 56.2% and purity fluctuating between 94.7% and 95.9%. This indicates that the preparation method of this application has good reproducibility and process stability, and can reliably obtain the expected high-quality product. Furthermore, the high purity of the first component (94.7%-95.9%) in Table 1 indicates that the first component can be directly used for subsequent compounding with the second component without the need for complex separation and purification of the positional isomers in the first component.

[0056] Example 2 This embodiment provides the preparation of the compound (compound 6) shown in the second component formula V, and the preparation route is as follows:

[0057] The preparation process is as follows: Compound 1 was prepared in accordance with patent JP2017 / 43571.

[0058] The intermediate compound (compound 2) was prepared according to Example 1.

[0059] Preparation of the second component (compound 6) 4.6 g (0.01 M) of intermediate compound 1,3,4-tris(3-hydroxypropyl)-6-(3-methylbutyrylpropyl)glycourea, 8.2 g (0.04 M) of DCC, and 0.4 g of DMAP were added to 200 ml of acetonitrile. After cooling to 0 °C, 4.8 g (0.04 M) of 3-mercaptobutyric acid was added. After the addition was complete, the mixture was stirred for 16 hours. 100 ml of water was slowly added dropwise, and 200 ml of ethyl acetate was added for extraction. The aqueous layer was extracted again with 200 ml of ethyl acetate. The organic layers were combined and washed successively with 100 ml of 5% citric acid solution, 100 ml of saturated sodium bicarbonate aqueous solution, and 100 ml of water. The mixture was then dried with anhydrous sodium sulfate and filtered. The solvent was evaporated under reduced pressure, and the residue was purified by column chromatography (on silica gel, ethyl acetate: petroleum ether = 1:3) to give 4.2 g of the second component, 1,3,4-tris(3-mercaptobutylcarbonylpropyl)-6-(3-methylbutylcarbonylpropyl)glycourea.

[0060] The structure of the second component is characterized as follows: MS [M+1] + 764.32; 1 H-NMR (CDCl3) δ: 5.15(s,2H), 4.12-4.15(t,8H), 3.57-3.63(m,4H), 3.40-3.44(m,4H), 3.09-3.14(m,3H), 2.59-2.63(m,3H), 2.50-2.55(m,3H), 2.17-2.24(q,2H), 1.95-2.05(m,9H), 1.84-1.85(d,3H), 1.35-1.36(d,9H), 0.98-1.00(d,3H), 0.93-0.95(d,3H).

[0061] Based on Example 1, this application investigated the molar ratio of the intermediate compound to 3-mercaptobutyric acid. The specific parameters are shown in Table 2. Other processes and parameters are the same as in Example 1.

[0062] Table 2

[0063] The yields and purities of the products prepared in Examples 1, 3-4, and Comparative Examples 1-2 are shown in Table 3.

[0064] Table 3

[0065] As shown in Table 3 and in conjunction with Table 2, when the molar ratio of the intermediate compound to 3-mercaptobutyric acid is within the range of 1:(1.8-2.2), the yield (54.5-56.0%) and purity (95.0-96.0%) remain excellent and stable. Example 1 exhibits the best reaction completion and product separation. In Example 3, a slight reduction in acid content slightly decreases the reaction driving force, resulting in a very small amount of incomplete conversion of the starting material, leading to a slight decrease in yield of approximately 1% compared to Example 1. In Example 4, a slight increase in acid content drives the reaction more thoroughly, relatively reducing monosubstituted residues, resulting in a slight increase in yield of approximately 0.4% compared to Example 1. However, excess acid may introduce trace amounts of byproducts, leading to a slight decrease in purity. When acid is relatively insufficient, as seen in Comparative Example 1 where the yield decreases significantly, this is because insufficient acid causes most of the starting material to remain in the monosubstituted stage, resulting in a low inherent formation rate of the target disubstituted product, which is difficult to separate, leading to a significant decrease in yield (approximately 17%) and purity. The yield also decreased when acid was in excess (Comparative Example 2), but the decrease was less severe than that in Comparative Example 1. This is because when acid is in excess, a small number of side reactions are aggravated, such as DCC decomposition and excessive esterification leading to polarity changes. The yield of the main product decreased by about 7.6% compared to Example 1, but the decrease was less than that when acid was insufficient. The purity was less affected than that in Comparative Example 1.

[0066] Application Example 1 In this application example, the glycourea polythiol curing agent composition composed of the first component prepared in Example 1 and the second component prepared in Example 2 is used as an epoxy resin curing agent to prepare an epoxy resin composition; based on the total mass of the glycourea polythiol curing agent composition, the mass fraction of the first component is 55% and the mass fraction of the second component is 45%.

[0067] The epoxy resin composition includes CYD-128 type epoxy resin, a glycourea polythiol curing agent composition, and a 1,4-diazabicyclo[2.2.2]octane curing accelerator; the equivalent ratio of mercapto groups in the glycourea polythiol curing agent composition to epoxy groups in the epoxy resin is 1:1; the amount of 1,4-diazabicyclo[2.2.2]octane curing accelerator is 1% of the mass of the glycourea polythiol curing agent composition.

[0068] The preparation method of the epoxy resin composition is as follows: The CYD-128 epoxy resin and glycourea polythiol curing agent composition were heated to a point where they had a fluidity that made them easy to mix. The heated urethane polythiol curing agent composition is slowly added to the heated epoxy resin while stirring. After the addition is complete, stirring is continued until the mixture is homogeneous. Vacuum degassing is then performed. During this process, the heating temperature is maintained to ensure the fluidity of the mixture. The degassed composition is injected into a mold or coated onto a substrate and then cured.

[0069] Equivalent refers to the molar number of functional groups that can participate in the reaction. The epoxy equivalent of epoxy resin refers to the number of grams of epoxy resin required to contain 1 mole of epoxy groups, measured in g / eq. The mercapto equivalent refers to the number of grams of glycourea-polythiol curing agent composition required to contain 1 mole of mercapto groups, also measured in g / eq.

[0070] Based on Application Example 1, this application investigated the dosage of the first component prepared in Example 1 and the second component prepared in Example 2 when using the glycourea polythiol curing agent composition composed of the first component prepared in Example 1 and the second component prepared in Example 2 as an epoxy resin curing agent to prepare an epoxy resin composition. The specific parameters are shown in Table 4. The remaining experimental procedures and parameters are the same as in Application Example 1.

[0071] Table 4

[0072] The performance of the epoxy resin compositions corresponding to Examples 1-3 and Comparative Examples 3-6 in this application was tested, and their structures are shown in Table 5.

[0073] Table 5

[0074] Table 5 shows that the viscosity of the epoxy resin composition before curing is positively correlated with the amount of the second component prepared in Example 2. The second component prepared in Example 2 is the main contributor to the system viscosity. The viscosity (10000-11000) of Application Examples 1-3 ensures good wettability and workability while avoiding problems such as filler sedimentation caused by excessively low viscosity. The reason for the viscosity change is that the second component has a larger molecular weight than the compounds in the first component, and its three long side chains are more extended in space, resulting in a larger hydrodynamic volume and a significant increase in flow resistance. In addition, the second component contains three polar ester groups and three thiol groups, which have stronger intermolecular dipole-dipole interactions and hydrogen bonding than the dithiol-substituted products of the first component, further hindering flow. Therefore, the system viscosity is positively correlated with the content of the second component. The viscosity of Application Examples 1-3 is moderate, achieving a balance between the dilution effect of reducing viscosity and maintaining network performance between large-size, high-polarity molecules (second component) and small-size, low-polarity molecules (first component).

[0075] As shown in Table 5, the fracture toughness exhibits a parabolic trend of rapid initial increase followed by slow decrease in KIC as the proportion of the first component prepared in Example 1 increases, with the peak value appearing in Application Example 1 (KIC = 3.9). In Application Example 2, the KIC drops to 3.6; with a 5% increase in the second component, the toughness decreases by approximately 8%. In Application Example 3, the KIC drops to 3.8; with a 5% increase in the first component prepared in Example 1, the toughness decreases only slightly. Comparative Example 6 shows a sharp decrease in toughness. The reason for the change in fracture toughness is that the network in Comparative Example 6 is rigid, with poor chain segment mobility. When subjected to impact, stress cannot be effectively dispersed through chain segment movement, quickly concentrating at micro-defects and leading to catastrophic brittle crack propagation, resulting in low energy dissipation capacity. The network in Comparative Example 5 is loose and relatively lacks a rigid skeleton. Although the chain segments are easy to move, they cannot bear and transmit high stress, making the material prone to large-scale plastic flow or direct tearing, and the energy absorbed per unit volume is also limited. In Application Examples 1-3, the second component, as a high-density rigid crosslinking point, constructs a strong network skeleton, providing load-bearing capacity. The first component, acting as a flexible connecting chain, fills the network, providing significant deformability. The coexistence of positional isomers within the first component ensures that the flexible segments are randomly and uniformly distributed at positions 1, 3, and 4 of the glycourea core. This avoids localized regularity or weaknesses in the network caused by a single connection site, creating a uniform stress field. Stress can be uniformly transmitted. When subjected to impact or stress, the rigid skeleton initially resists deformation. Stress is dissipated through the significant extension and rearrangement of the flexible segments, as well as the induction of numerous small shear bands, which hinder crack propagation.

[0076] Table 5 shows that the heat resistance (Tg) of the epoxy resin composition increases with the increase of the proportion of the second component. However, from Application Example 1 to Application Example 3, the Tg decreases gradually (118°C to 115°C). Compared with Comparative Example 5, Application Example 1 shows a significant decrease in Tg (118°C to 85°C). This indicates that in Application Example 1, the mass ratio of the first component prepared in Example 1 to the second component prepared in Example 2 is around 55:45. The prepared epoxy resin composition can sacrifice very little heat resistance but gain a huge increase in toughness.

[0077] Application Example 2 provides a high-rigidity, high-toughness solution. Its Tg (120℃) and modulus (2.8 GPa) are close to the high level of Comparative Example 6, while its toughness (KIC=3.6) far exceeds that of Comparative Example 6, reaching 92% of Application Example 1. It is suitable for scenarios with extreme requirements for heat resistance and rigidity, while also requiring good toughness. Application Example 3 provides an ultra-high toughness, high heat resistance solution. Its toughness (KIC=3.8) is almost on par with Application Example 1, while its heat resistance (115℃) and modulus (2.65 GPa) remain at a high level, far exceeding Comparative Example 5. It is suitable for scenarios with stringent requirements for impact resistance and crack resistance, and with slightly lower operating temperatures.

[0078] The changes in Tg and modulus are mainly affected by the crosslinking density of the epoxy resin composition. The chemical crosslinking points in the epoxy resin composition restrict the freedom of movement and space of the polymer chain segments. The higher the crosslinking density, the more difficult the chain segment movement, and the higher the energy required to transition from the glassy state to the elastic state (corresponding to Tg), resulting in stronger resistance to elastic deformation (modulus). In Comparative Example 6, the second component acts as a curing agent, with each molecule being a trifunctional crosslinking point, forming a rigid network with extremely high crosslinking density, thus resulting in the highest Tg and modulus. In Comparative Example 5, the first component acts as a curing agent, with each molecule providing only two connection points, mainly forming long chain or macroring structures. The crosslinking density is relatively low, the network is loose, and the flexible long chains can move at lower temperatures, thus resulting in the lowest Tg and modulus. From Application Example 3 to Application Example 1 and then to Application Example 2, as the proportion of the second component increases, the density of trifunctional crosslinking points in the network increases linearly, thus increasing Tg and modulus.

[0079] Data from Comparative Example 3 shows that when the proportion of the second component exceeds 50%, the fracture toughness of the system is significantly reduced. In Comparative Example 6, when the proportion of the first component prepared in Example 1 exceeds 60%, the rigidity of the system is significantly reduced, and its heat resistance is also significantly reduced.

[0080] Table 5 shows that, within the range of 50%-60% proportion of the first component prepared in Example 1, the epoxy resin compositions of Application Examples 1-3 exhibit the best overall performance. Application Example 1 has the highest fracture toughness value, while sacrificing only a small amount in heat resistance and rigidity, achieving the optimal balance of rigidity / toughness / heat resistance, making it the most versatile and preferred option. When the amount of the second component decreases, the rigid skeleton is insufficient, and the overall network strength is weak; even with a large number of flexible segments, efficient energy dissipation cannot be achieved. When the amount of the second component increases, the flexible segments are insufficient, the network is relatively rigid, and stress cannot induce sufficient plastic deformation to dissipate energy, increasing brittle fracture. Application Example 1 achieves the optimal match between the rigid skeleton strength and the number of flexible dissipation units, maximizing energy dissipation efficiency and thus exhibiting peak toughness.

[0081] This application uses three batches of products from repeatability experiments to prepare epoxy resin compositions according to Application Example 1. Batch A is Application Example 4, batch B is Application Example 5, and batch C is Application Example 6. Performance tests were conducted corresponding to Examples 4-6, and the results are shown in Table 6. Other process conditions and parameters are the same as in the Application Example.

[0082] Table 6

[0083] As shown in Table 6, the RSD of all performance indicators in Application Examples 4-6 is less than 1%, indicating excellent repeatability. The average performance of the three batches is consistent with that of Application Example 1, with minor differences within the allowable range of testing error. This indicates that the preparation method of the first component provided in this application has process stability and reproducibility, and the compositional differences of the first component between different batches are minor and do not have an observable impact on the performance of the final material. Therefore, the chemical composition of the first component prepared in different batches is deterministic and non-random.

[0084] The present application has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present application. The descriptions of the embodiments above are only for the purpose of helping to understand the present disclosure. It should be noted that those skilled in the art can make several improvements and modifications to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A glycourea-based polythiol curing agent composition, characterized in that, The glycourea-polythiol curing agent composition comprises a first component and a second component; the first component is prepared by the following method: S1: Add intermediate compound, dehydrating agent and catalyst to organic solvent, cool to 0-5℃, add 3-mercaptobutyric acid, and continue stirring until the reaction is complete; S2: After the reaction is completed, the mixture is purified and processed to obtain the first component; The structural formula of the intermediate compound is shown in Formula I. Formula I; The molar ratio of the intermediate compound to 3-mercaptobutyric acid is 1:(1.8-2.2). The first component obtained includes compounds with structural formulas as shown in Formulas II-IV; the compounds with structural formulas as shown in Formulas II-IV are shown below: Formula II; Formula III; Formula IV; The structural formula of the second component is shown in formula V. Formula V; Based on the total mass of the glycourea polythiol curing agent composition, the mass fraction of the first component is 50%-60%, and the mass fraction of the second component is 40%-50%.

2. The glycourea-polythiol curing agent composition according to claim 1, characterized in that, In the preparation method of the first component, the dehydrating agent in step S1 is one or more of N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, or 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride; the molar ratio of the dehydrating agent to 3-mercaptobutyric acid is 1:(1-1.2).

3. The glycourea-polythiol curing agent composition according to claim 1, characterized in that, In the preparation method of the first component, the catalyst in step S1 is an acylation reaction catalyst; the amount of the catalyst used is 5%-10% of the mass of the intermediate compound.

4. The glycourea-polythiol curing agent composition according to claim 1, characterized in that, In the preparation method of the first component, the organic solvent in step S1 is one of acetonitrile, dichloromethane or tetrahydrofuran.

5. The glycourea-polythiol curing agent composition according to claim 1, characterized in that, In the preparation method of the first component, the reaction temperature in step S1 is 0-5℃; the stirring time is 14-18 hours.

6. The glycourea-polythiol curing agent composition according to claim 1, characterized in that, In the preparation method of the first component, the specific steps of purification and post-treatment in step S2 are as follows: Water was added dropwise to the mixture after the reaction was completed, and ethyl acetate was added for extraction. The aqueous layer was extracted again with an equal volume of ethyl acetate, and the organic layers were combined. The organic layers were washed sequentially with citric acid solution, saturated sodium bicarbonate aqueous solution, and water, then dried with anhydrous sodium sulfate and filtered. The solvent was evaporated under reduced pressure, and the residue was subjected to column chromatography to obtain the first component.

7. The glycourea-polythiol curing agent composition according to claim 6, characterized in that, During the extraction process, the volume ratio of the ethyl acetate added initially to the total volume of the reaction system was 1:1; The volume ratio of water to ethyl acetate is 1:2; The concentration of the citric acid solution is 4-6%, and the volume ratio of the citric acid solution, saturated sodium bicarbonate aqueous solution, and water is 1:1:

1. Column chromatography was performed using a silica gel column, with the eluent being ethyl acetate to petroleum ether in a volume ratio of 1:

3.

8. A method for preparing the glycourea-polythiol curing agent composition according to any one of claims 1-7, characterized in that, Includes the following steps: S1': Prepare the first component according to steps S1-S2 in claim 1; S2': The first component obtained in step S1' is mixed with the second component with the structural formula shown in Formula V at a mass ratio of (50-60):(40-50) to obtain the glycourea polythiol curing agent composition.

9. A curing agent, characterized in that, The curing agent comprises the glycourea polythiol curing agent composition according to any one of claims 1-7.

10. Use of the glycourea polythiol curing agent composition according to any one of claims 1-7 as an epoxy resin curing agent.

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