A 1,3,4-tris(3-mercapto butyryloxypropyl)-6-(3-methyl butyryloxypropyl) glycoluril compound, and a preparation method and application thereof

Abstract

The application discloses a 1,3,4-tris (3-mercapto butyryloxy propyl) -6- (3-methyl butyryloxy propyl) glycoluril compound and a preparation method and application thereof, and the 1,3,4-tris (3-mercapto butyryloxy propyl) -6- (3-methyl butyryloxy propyl) glycoluril compound has a rigid glycoluril nucleus, three 3-mercapto butyryloxy propyl flexible long chains with reactive thiol terminals are connected to the three nitrogen atoms of the glycoluril nucleus through ester bonds, and a 3-methyl butyryloxy propyl flexible long chain is connected to another nitrogen atom. Based on the chemical bond effect of the rigid node, the flexible long chain, the thiol and the epoxy group of the epoxy resin in the rigid glycoluril nucleus, the epoxy resin composition prepared by using the compound as a curing agent has good fracture toughness and impact resistance, and rigidity and heat resistance are maintained.

Description

A 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound, its preparation method and application Technical Field

[0001] This application belongs to the field of materials technology, specifically relating to a 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound, its preparation method and application. Background Technology

[0002] Epoxy resins, as important thermosetting materials, are widely used in electronic packaging, composite materials, coatings, and other fields due to their excellent bonding properties, mechanical strength, and chemical stability. However, traditional epoxy resin systems often face problems such as high brittleness and insufficient fracture toughness in cured products. Especially in high-performance applications, balancing the rigidity, heat resistance, and toughness of materials has become a technical bottleneck in the industry.

[0003] Thiol compounds, as highly efficient curing agents for epoxy resins, can achieve rapid curing under mild conditions through the click reaction between thiol and epoxy groups, imparting good flexibility and low shrinkage to the material. However, traditional small-molecule thiol curing agents suffer from insufficient curing efficiency and limited crosslinking density due to their low functionality. Although they can improve toughness, this often comes at the cost of sacrificing rigidity and heat resistance.

[0004] To improve the overall performance of materials, researchers have begun to explore multifunctional thiol compounds with rigid frameworks. Glycourea derivatives have attracted attention due to their inherent rigidity of bicyclic structure and multi-site reactivity. Symmetrical tetrathioglycourea curing agents (such as CN105764907A) have been reported in the prior art, which achieve good rigidity and heat resistance through high crosslinking density. However, due to their highly symmetrical homogeneous network structure, the improvement in toughness is limited. In addition, other rigid frameworks such as triazine ring derivatives (such as 1,3,5-tris(3-mercaptobutyryloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione) have also been used in the design of thiol curing agents. However, their monocyclic structure lacks sufficient rigidity and has weak constraint on chain segment movement, resulting in unsatisfactory rigidity and heat resistance, and limited improvement in fracture toughness.

[0005] Existing technologies for introducing thiol segments onto a glyceryl framework into glyceryl mercapto compounds lack the structural design to simultaneously impart rigidity, heat resistance, and toughness to the material. Furthermore, existing synthetic methods for glyceryl mercapto compounds often face challenges such as low reaction selectivity, numerous byproducts, and purification difficulties. Improper condition control can easily lead to incomplete functional group modification or product isomerization, affecting the consistency of the curing agent's performance.

[0006] Therefore, there is a need to develop a novel, highly functional, and robustly synthesized glycyrrhizin-based multithiolated compound that can balance the rigidity, heat resistance, and toughness of materials such as epoxy resins. Summary of the Invention

[0007] To address the aforementioned technical problems, this application provides a 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound, its preparation method, and its application.

[0008] In a first aspect, this application provides a 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound, the structural formula of which is shown in Formula I.

[0009] Formula I.

[0010] Secondly, this application provides a method for preparing the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound described in the first aspect, comprising the following steps:

[0011] The intermediate compound, dehydrating agent, and catalyst are added to an organic solvent, cooled to 0-5°C, and then 3-mercaptobutyric acid is added. Stirring continues until the reaction is complete. The structural formula of the intermediate compound is shown in Formula II.

[0012] Formula II;

[0013] The preparation route of the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound is as follows:

[0014] .

[0015] Furthermore, 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).

[0016] Furthermore, the molar ratio of the dehydrating agent to 3-mercaptobutyric acid is 1:(1-1.2).

[0017] Preferably, the molar ratio of the dehydrating agent to 3-mercaptobutyric acid is 1:1.

[0018] Furthermore, the amount of catalyst used is 5%-10% of the mass of the intermediate compound, preferably 10% of the mass of the intermediate compound.

[0019] Furthermore, the dehydrating agent is one or more of N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, or 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride.

[0020] Furthermore, the catalyst is an acylation reaction catalyst; preferably, the catalyst is 4-dimethylaminopyridine.

[0021] Furthermore, the solvent for the reaction is one of acetonitrile, dichloromethane, or tetrahydrofuran.

[0022] Furthermore, the reaction is stirred for 14-18 hours.

[0023] Furthermore, the preparation method of the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound also includes a post-processing step, which is specifically as follows:

[0024] Water was slowly 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 amount of ethyl acetate, and the organic layers were combined.

[0025] The organic layer was washed sequentially with citric acid solution, saturated sodium bicarbonate aqueous solution and water, then dried with anhydrous sodium sulfate and filtered. The solvent was removed under reduced pressure, and the residue was subjected to column chromatography to obtain the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound.

[0026] Furthermore, during the extraction process, water is slowly added dropwise to the mixed system after the reaction is completed, and ethyl acetate is added for extraction. The volume ratio of the added ethyl acetate to the total volume of the reaction system is 1:1; the volume ratio of water to ethyl acetate is 1:2.

[0027] Furthermore, the concentration of the citric acid solution is 4-6%, preferably 5%; the volume ratio of the citric acid solution, the saturated sodium bicarbonate aqueous solution, and water is 1:1:1.

[0028] Furthermore, the eluent for column chromatography was ethyl acetate to petroleum ether in a volume ratio of 1:3.

[0029] Thirdly, this application provides a curing agent comprising the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound described in the first aspect.

[0030] Furthermore, the curing agent also includes a curing accelerator; the amount of the curing accelerator is 0.5%-5% of the mass of the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound.

[0031] Furthermore, the curing accelerator includes tertiary amine compounds or organophosphorus compounds; preferably, the curing accelerator includes at least one of 1,4-diazabicyclo[2.2.2]octane (DABCO), triphenylphosphine (TPP), and 2,4,6-tris(dimethylaminomethyl)phenol (DMP-30).

[0032] It should be noted that the curing accelerators provided in this application are not limited to the types of curing accelerators mentioned above, and those skilled in the art can also select other curing accelerators known in the art as needed.

[0033] Furthermore, the curing agent also includes at least one component selected from diluent, filler, storage stabilizer, and coupling agent.

[0034] Furthermore, the diluent is an active diluent containing epoxy or thiol groups; preferably, the diluent is at least one of octyl glycidyl ether, butyl glycidyl ether, and ethylene glycol dimercaptopropionate.

[0035] Furthermore, the filler is fumed silica or calcium carbonate.

[0036] Furthermore, the coupling agent is a silane coupling agent.

[0037] Diluents can reduce the viscosity of the main curing agent, improving its flowability and wettability when mixed with epoxy resin; fillers can reduce costs, change density, adjust thermal or electrical conductivity, improve hardness, abrasion resistance, or reduce curing shrinkage; storage stabilizers can prevent the curing agent from undergoing slow reactions or performance changes during storage; coupling agents can improve the adhesion between the curing agent and the substrate being bonded (such as metal, glass, ceramic).

[0038] Compared with the prior art, this application includes the following beneficial technical effects:

[0039] The 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound provided in this application possesses a rigid glycourea core. Three flexible 3-mercaptobutyryloxypropyl chains with reactive thiol ends are linked to three nitrogen atoms on the glycourea core via ester bonds, and a single flexible 3-methylbutyryloxypropyl chain is linked to the other nitrogen atom. When this molecular structure is used as a primary curing agent in epoxy resin compositions, it exhibits good fracture toughness and impact resistance while maintaining rigidity and heat resistance, as detailed below:

[0040] 1,3,4-Tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compounds form a highly functional, extremely rigid bicyclic structure with a glycourea molecule as the core and four tetrafunctional substituents on the nitrogen atoms. In the epoxy resin curing network, the rigid glycourea core enhances the network's structural stability, which is fundamental to maintaining high modulus and heat resistance. The three flexible long chains connected to the rigid glycourea core and the reactive thiol ends via ester bonds can absorb mechanical energy through rotation, extension, and conformational changes of C-C and CO bonds when the epoxy resin composition is subjected to impact or stress, giving the epoxy resin composition good fracture toughness and impact resistance. Furthermore, the ester group (-C(O)-O-) in the acyloxy group has a certain polarity, which allows it to form a good interaction with the polar epoxy resin matrix, enabling it to be uniformly dispersed in the crosslinked network after curing. The thiol (-SH) at the molecule's end forms a stable thioether bond with the epoxy resin through a chemical reaction between the thiol and the epoxy group. The high reactivity of the thiol ensures that each 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound molecule can be uniformly and quantitatively chemically bonded to the epoxy crosslinking network, avoiding the phase separation or aggregation problems that may occur with traditional physical blending toughening agents, thereby achieving comprehensive and efficient toughening. The other 3-methylbutyryloxypropyl chain in the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound possesses a large volume and flexibility. When the material is subjected to impact or stress, this non-crosslinking, free, flexible chain can effectively absorb and dissipate mechanical energy through significant conformational changes, rotation, and torsion. Synergistically with the three mercapto chains, it significantly improves fracture toughness and impact resistance. Furthermore, the 3-methylbutyryloxypropyl chain exhibits a certain degree of hydrophobicity and volume, which can adjust the polarity and solubility parameters of the entire molecule, resulting in better compatibility with the epoxy resin matrix. Simultaneously, it also acts as an internal lubricant, potentially moderately reducing the viscosity of the mixture system before curing.

[0041] This application describes an intermediate compound designed for the synthesis of 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea, the structure of which is itself innovative. This intermediate compound is key to the successful construction of the specific asymmetric structure of the target product, ensuring the structural regularity and high purity of the final product. The three hydroxyl groups in the intermediate compound prepare for the introduction of three thiol chains via an efficient esterification reaction; while a pre-formed ester group acts as a protected inert site, ensuring the presence of the non-reactive flexible 3-methylbutyryloxypropyl chain in the final product. This route strategy avoids the direct synthesis of molecules with four identical thiol chains, or the synthesis of mixtures with uncertain numbers and positions of functional groups, thus guaranteeing the structural regularity of the final product from the outset.

[0042] In preparing the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound, this application employs a pathway involving the reaction of an intermediate compound with 3-mercaptobutyric acid in the presence of a dehydrating agent and a catalyst. Specifically, Steglich esterification conditions (such as DCC / DMAP) are preferred. These conditions are mild and neutral, effectively protecting the acid-sensitive reactants and the glycourea core and ester bonds in the product, and avoiding oxidation side reactions of the thiol groups. An excess of 3-mercaptobutyric acid, combined with an equimolar amount of dehydrating agent, ensures complete esterification of the three hydroxyl groups on the intermediate compound, thereby driving the reaction towards completion and maximizing the yield of the final product.

[0043] The purification process can systematically and efficiently remove byproducts, excess reactants, catalyst residues, and various water-soluble or ionic impurities generated during the reaction. The water to ethyl acetate extraction ratio of 1:2 (volume ratio) ensures that the target product can be more fully distributed in the organic phase, and the presence of an appropriate amount of water phase can effectively dissolve and remove highly water-soluble byproducts and ionic impurities. This ratio significantly improves the separation efficiency of a single extraction.

[0044] A three-step washing method using citric acid, sodium bicarbonate, and water in a specific ratio can remove both alkaline and acidic impurities. A 4%-6% citric acid solution neutralizes and removes alkaline impurities, primarily unreacted catalyst DMAP and other possible alkaline byproducts. A saturated sodium bicarbonate aqueous solution neutralizes and removes acidic impurities, including excess 3-mercaptobutyric acid, trace amounts of acidic byproducts that may be generated during the reaction, and residues from the previous citric acid washing step. Water washing removes all water-soluble salts and other residues introduced in the first two washing steps. This washing process achieves a systematic and stepwise removal of both acidic and alkaline impurities.

[0045] An eluent with a volume ratio of ethyl acetate to petroleum ether of 1:3 can accurately separate the target product from impurities with significantly different polarities, which is key to obtaining high-purity, high-performance final products. The target product contains multiple polar ester bonds and thiol groups, but has a large molecular weight and contains nonpolar alkane chains, exhibiting overall moderate polarity. The 1:3 volume ratio of ethyl acetate to petroleum ether eluent has moderate polarity, enabling the target product to migrate at an appropriate rate on the chromatographic column, thereby achieving effective separation from impurities with stronger polarity (such as incompletely esterified hydroxyl byproducts) or weaker polarity (such as hydrocarbon impurities). Attached Figure Description

[0046] The present application will be described in further detail below with reference to the accompanying drawings and preferred embodiments. However, those skilled in the art will understand that these drawings are drawn only for the purpose of explaining the preferred embodiments and therefore should not be construed as limiting the scope of this disclosure. Furthermore, unless specifically indicated, the drawings are only schematic representations of the composition or structure of the described objects and may contain exaggerated depictions, and the drawings are not necessarily drawn to scale.

[0047] Figure 1 shows a product image of 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound.

[0048] Figure 2 shows the 1H NMR spectrum of the compound 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea.

[0049] Figure 3 shows the cured epoxy resin composition prepared in Application Example 1. Detailed Implementation

[0050] 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.

[0051] Chemicals and reagents

[0052] Epoxy resin: Model CYD-128, liquid, epoxy equivalent 184g / mol, manufacturer: Hunan Yueyang Baling Petrochemical.

[0053] 1,4-Diazabicyclo[2.2.2]octane: purchased from Hunan Huibaishi Biotechnology Co., Ltd.

[0054] Pentaerythritol tetrakis(3-mercaptopropionic acid) ester: purchased from Aladdin Reagents.

[0055] 1,3,5-Tris(3-mercaptobutyryloxyethyl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione: CAS No. 928339-75-7, purchased from Shanghai Xibo New Materials Technology Co., Ltd.

[0056] DCC: N,N'-dicyclohexylcarbodiimide, purchased from Aladdin Reagents.

[0057] DMAP: 4-Dimethylaminopyridine, purchased from Aladdin Reagents.

[0058] Unless otherwise specified, all other reagents used in the embodiments of this application are from conventional commercially available products.

[0059] Test method:

[0060] Glass transition temperature

[0061] Glass transition temperature testing shall be performed in accordance with ISO 11357-2-2020.

[0062] fracture toughness

[0063] Fracture toughness was tested in accordance with ISO 13586:2018, using compact tensile bending specimens and measuring their stress intensity factor (KIC).

[0064] Impact strength

[0065] 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.

[0066] Flexural modulus

[0067] The flexural modulus is tested according to ISO 178:2019.

[0068] Viscosity test

[0069] 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).

[0070] Example 1

[0071] This embodiment provides the preparation of the intermediate compound 1,3,4-tris(3-hydroxypropyl)-6-(3-methylbutyryloxypropyl)glycourea (compound 2) with the structure of Formula II, and the preparation route is as follows:

[0072]

[0073] Compound 1 was prepared in accordance with the patent application published JP2017-43571A.

[0074] Add 5.1 g (0.05 M) of isovaleric acid to 100 ml of dichloromethane, and slowly add 8.3 g (0.07 M) of thionyl chloride dropwise. After the addition is complete, heat and reflux for 2 hours. After the solvent is evaporated, add another 100 ml of dichloromethane to dissolve it, and obtain a dichloromethane solution of isovaleryl chloride.

[0075] 18.7 g (0.05 M) of compound 1, 1,3,4,6-tetra(3-hydroxypropyl)glyurea was added to 100 mL of dichloromethane, followed by 10 g (0.1 M) of triethylamine. The isovaleryl chloride solution prepared in the previous step was slowly added dropwise at room temperature, and stirring was continued for 18 hours after the addition was complete. 100 mL of water was slowly added dropwise, and the layers separated. The aqueous layer was extracted with 200 mL of dichloromethane. The organic layers were combined and washed successively with 100 mL of saturated sodium bicarbonate solution and 100 mL of water. The solvent was concentrated and evaporated to obtain 18.1 g of the intermediate compound 1,3,4-tris(3-hydroxypropyl)-6-(3-methylbutyryloxypropyl)glyurea.

[0076] The structural characterization of the intermediate compound is as follows:

[0077] MS [M+1] + 458.27.

[0078] 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).

[0079] Example 2

[0080] This embodiment provides the preparation of 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound (compound 3) of formula I, and the preparation route is as follows:

[0081]

[0082] 4.6 g (0.01 M) of intermediate compound 1,3,4-tris(3-hydroxypropyl)-6-(3-methylbutyryloxypropyl)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 over 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 obtain 4.2 g of 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound of formula I, as shown in Figure 1.

[0083] The structure of 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea (compound 3) of formula I is characterized as follows:

[0084] MS [M+1] + 764.32.

[0085] 1 ¹H-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), as shown in Figure 2.

[0086] Based on Example 2, this application investigated the molar ratio of the intermediate compound to 3-mercaptobutyric acid, and the specific parameters are shown in Table 1.

[0087] Table 1. Molar ratio of intermediate compound to 3-mercaptobutyric acid.

[0088]

[0089] The yields and purities of the mercaptoglycourea derivatives prepared in Examples 2-4 and Comparative Example 1 are shown in Table 2. Purity was determined by high-performance liquid chromatography (HPLC), and product purity was calculated using the area normalization method.

[0090] Table 2. Results of the molar ratio study of intermediate compound and 3-mercaptobutyric acid.

[0091]

[0092] The intermediate compound 1,3,4-tris(3-hydroxypropyl)-6-(3-methylbutyryloxypropyl)glycourea has three primary hydroxyl groups. During the DCC / DMAP-catalyzed esterification reaction with 3-mercaptobutyric acid, each hydroxyl group requires one equivalent of 3-mercaptobutyric acid for complete reaction. Therefore, theoretically, 1 mol of the intermediate compound requires 3 mol of 3-mercaptobutyric acid. In Example 3, the molar ratio of the intermediate compound to 3-mercaptobutyric acid was 1:3, representing the theoretical amount. In Example 2, the molar ratio was 1:4, with approximately 33% excess 3-mercaptobutyric acid. In Example 4, the molar ratio was 1:5, with approximately 67% excess 3-mercaptobutyric acid. In Comparative Example 1, the molar ratio was 1:2, with only 2 / 3 of the theoretical amount of 3-mercaptobutyric acid.

[0093] As shown in Table 2, the yield of Comparative Example 1 was extremely low because it contained insufficient 3-mercaptobutyric acid. The molar ratio of the intermediate compound to 3-mercaptobutyric acid was 1:2, resulting in mainly disubstituted products and some monosubstituted products. These could not be fully converted into the target trisubstituted final product. The disubstituted and monosubstituted products were separated during purification, resulting in a very small amount of the final target product. The product yields of Examples 2-4 were between 45% and 56%. In Example 2, an excess of 3-mercaptobutyric acid helped improve the yield. In Example 4, even more 3-mercaptobutyric acid was used, but the yield increase compared to Example 2 was not significant, indicating that the molar ratio of the intermediate compound to 3-mercaptobutyric acid of 1:4 was close to the upper limit of the yield under these reaction conditions.

[0094] As shown in Table 2, the purity of the products after column chromatography is all above 96.7%, indicating high purity.

[0095] Application Example 1

[0096] In this application example, the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound prepared in Example 2 is used as an epoxy resin curing agent to prepare an epoxy resin composition. The epoxy resin composition further includes CYD-128 type epoxy resin, 1,4-diazabicyclo[2.2.2]octane curing accelerator, and the equivalent ratio of mercapto groups in the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound to epoxy groups in the epoxy resin is 1:1; the mass of the 1,4-diazabicyclo[2.2.2]octane curing accelerator is 1% of the mass of the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound.

[0097] The preparation method of the epoxy resin composition is as follows:

[0098] The CYD-128 epoxy resin and the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound prepared in Example 2 were heated to achieve a flowability that allows for easy mixing.

[0099] The heated 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound was slowly added to the heated epoxy resin while stirring. After the addition was complete, stirring was continued until the mixture was homogeneous. Vacuum degassing was then performed. During this process, the above heating temperature was maintained to keep the mixture in a fluid state.

[0100] The degassed composition is injected into a mold or coated onto a substrate and then cured, as shown in Figure 3.

[0101] Equivalent refers to the number of moles of functional groups that can participate in the reaction. The epoxy equivalent of an epoxy resin refers to the number of grams of epoxy resin required to contain 1 mole of epoxy groups, expressed in g / eq. The mercapto equivalent of a compound such as 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea refers to the number of grams of that derivative required to contain 1 mole of mercapto groups, also expressed in g / eq.

[0102] Based on Application Example 1, this application also conducted a comparative study on epoxy resin curing agents in the prior art. The parameters of different epoxy resin curing agents are shown in Table 3.

[0103] The preparation of the epoxy resin curing agent in Comparative Example 3 was carried out in accordance with the patent application publication number JP1975106881A, entitled "Preparation of Stabilized Organic Material Composition".

[0104] Comparative Example 5: The epoxy resin curing agent (1,3,4,6-tetra(3-mercaptopropyl)glycourea) was prepared according to CN105764907A.

[0105] Table 3 Parameters of different epoxy resin curing agents

[0106]

[0107] The epoxy resin compositions prepared in accordance with Example 1 and Comparative Examples 2-5 of this application were subjected to performance testing, and the results are shown in Table 4.

[0108] Table 4. Performance test results of the epoxy resin compositions prepared in Application Example 1 and Comparative Examples 2-5

[0109]

[0110] As shown in Table 4, the mercaptoglycourea derivatives provided in this application have excellent comprehensive properties.

[0111] Compared to Application Example 1, the curing agent in Comparative Example 2 is pentaerythritol tetrakis(3-mercaptopropionic acid) ester, which consists of freely rotating and bending pentaerythritol and four mercaptopropionic acid chains. The entire molecule is flexible, resulting in a softer and more resilient epoxy resin solid material, but with poor rigidity and heat resistance. The epoxy resin composition of Comparative Example 2 had a viscosity of 8000 mPa·s before curing, exhibiting low viscosity and good flowability, which is attributed to its small molecular size and flexible structure.

[0112] Compared to Application Example 1, the curing agent in Comparative Example 3 has four long alkyl thiol chains. These long alkyl chains act as intramolecular plasticizers, increasing chain mobility and significantly lowering the glass transition temperature (Tg). Flexible chains can absorb impact energy through conformational changes, thus significantly improving fracture toughness. However, excessively long flexible chains dilute the effective crosslinking density per unit volume and, due to their low modulus characteristics, lead to a decrease in modulus. Furthermore, excessive flexibility can impair stress transfer efficiency, resulting in decreased toughness. The epoxy resin composition in Comparative Example 3 had a viscosity of 18000 mPa·s before curing. Its long aliphatic chains and high symmetry in its molecular structure resulted in stronger intermolecular interactions and a higher melt viscosity, making mixing and degassing relatively more difficult than in Application Example 1, and resulting in relatively poor processability.

[0113] Compared to Application Example 1, the curing agent in Comparative Example 4 employed a triazine-2,4,6-trione triazine core monocyclic structure. Despite containing a triazine ring, its inherent resonance stabilization and lower ring strain resulted in lower inherent rigidity and steric hindrance of its molecular skeleton compared to glycourea. The triazine ring's ability to restrict the movement of the three 3-mercaptobutyryloxyethyl chain segments was weaker, leading to lower Tg and modulus. The lower rigidity of the triazine ring compared to glycourea meant that under stress, the triazine ring crosslinking points might experience slight deformation or rotation, dissipating some of the transmitted stress and resulting in a less uniform stress distribution. This simultaneously weakened its load-bearing capacity (modulus) and energy dissipation efficiency (toughness). Therefore, the rigid bicyclic structure of glycourea played a crucial supporting role in maintaining high heat resistance and rigidity while simultaneously toughening the resin. The epoxy resin composition in Comparative Example 4 had a viscosity of 13000 mPa·s before curing, exhibiting good processability.

[0114] Compared to Application Example 1, Comparative Example 5 has four 3-mercaptopropyl chains, forming a highly functional and highly symmetrical homogeneous network. All connection points are rigid glycourea nuclei and reactive mercapto chains. The network has a high and uniform cross-linking density. It relies on the restriction of glycourea as a chemical cross-linking point and the stretching of the four 3-mercaptopropyl chains to toughen it. The energy dissipation mechanism is simple, and the performance improvement has an upper limit. The thiol derivative constructed in this application contains both a rigid phase composed of a glycinyl core providing modulus and Tg, and a dispersed flexible phase composed of a 3-methylbutyryloxypropyl inert flexible long chain and three thiol chains. When subjected to external force, the inert flexible long chain acts as a stress concentration point, inducing crazes and shear yielding, and inducing large-scale plastic deformation of the surrounding epoxy matrix. The flexible long chain that can cross both sides of the crack is stretched, generating closing stress on the crack and bridging the crack. The flexible chain absorbs energy through its own plastic deformation and viscous flow. The heterogeneous network of this application achieves fracture toughness far superior to that of the homogeneous network through multiple mechanisms. Compared with Comparative Example 5, since it contains only one inert long chain, the weakening of the overall crosslinking density and rigid framework is minimal, thus the modulus and Tg are maintained. Therefore, the asymmetric design of the trithiol-inert arm in this application (Application Example 1) has an advantage in toughness compared to the symmetric design of the tetrathiol group (Comparative Example 5), while the loss of rigidity and heat resistance is minimal. The inert flexible arm in this application acts as an intramolecular toughening agent. The viscosity of the epoxy resin composition in Comparative Example 6 before curing is 16000 mPa·s, which indicates that its molecular structure (high symmetry) leads to a higher melt viscosity, making mixing and degassing relatively more difficult than in Application Example 1, and resulting in poorer processability.

[0115] In summary, the mercaptoglycourea derivative provided in this application can form a mixture with epoxy resin of moderate viscosity and easy processing under mild processing conditions, exhibiting excellent processability. Its cured product combines fracture toughness with high levels of rigidity and heat resistance. In particular, compared to the structurally closest symmetric tetramercaptoglycourea, this application demonstrates significant advantages in both toughness and processing flowability, fully showcasing the superiority of the rigid core-flexible arm asymmetric molecular design.

[0116] 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 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound, characterized in that, The structural formula of the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound is shown in Formula I. Equation I.

2. The method for preparing the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound as described in claim 1, characterized in that, The process includes the following steps: adding an intermediate compound, a dehydrating agent, and a catalyst to an organic solvent, cooling to 0-5°C, adding 3-mercaptobutyric acid, and continuing stirring until the reaction is complete; wherein the structural formula of the intermediate compound is shown in Formula II. Formula II; the molar ratio of the intermediate compound to 3-mercaptobutyric acid is 1:(3-5).

3. The method for preparing the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound as described in claim 2, characterized in that, The amount of catalyst used is 5%-10% of the mass of the intermediate compound.

4. The method for preparing the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound as described in claim 2, characterized in that, The molar ratio of the dehydrating agent to 3-mercaptobutyric acid is 1:(1-1.2).

5. The method for preparing the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound as described in claim 2, characterized in that, The dehydrating agent is one or more of N,N'-dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, or 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride; the catalyst is 4-dimethylaminopyridine; and the organic solvent is one of acetonitrile, dichloromethane, or tetrahydrofuran.

6. The method for preparing the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound as described in claim 2, characterized in that, The preparation method further includes a post-treatment step, which is as follows: water is slowly added dropwise to the mixed system after the reaction is completed, and ethyl acetate is added for extraction; the aqueous layer is extracted again with an equal amount of ethyl acetate, and the organic layers are combined; the organic layer is washed sequentially with citric acid solution, saturated sodium bicarbonate aqueous solution and water, then dried with anhydrous sodium sulfate and filtered, the solvent is evaporated under reduced pressure, and the residue is subjected to column chromatography to obtain the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound.

7. A curing agent, characterized in that, The curing agent comprises the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound as described in claim 1.

8. The curing agent as described in claim 7, characterized in that, The curing agent further includes a curing accelerator; the amount of the curing accelerator is 0.5%-5% of the mass of the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound.

9. The curing agent as described in claim 8, characterized in that, The curing accelerator includes at least one of 1,4-diazabicyclo[2.2.2]octane, triphenylphosphine, and 2,4,6-tris(dimethylaminomethyl)phenol.

10. The use of the 1,3,4-tris(3-mercaptobutyryloxypropyl)-6-(3-methylbutyryloxypropyl)glycourea compound as described in claim 1 as an epoxy resin curing agent.

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