An imidazoline epoxy resin curing agent, a preparation method and application thereof

Abstract

The application provides an imidazoline epoxy resin curing agent which is prepared from the following components in parts by weight: imidazoline monomer 40-70 parts, fluorine-containing long-chain carboxylic acid 5-15 parts, polyether amine 10-25 parts, multifunctional epoxy compound 5-15 parts, silane coupling agent 1-5 parts and polymerization inhibitor 0.1-1 part. The curing agent is suitable for various underwater working conditions with water depth of 0.5-20 meters, water temperature of 5-35 DEG C and water flow speed of 0-2 m / s, has a wide application prospect in underwater concrete repair, corrosion protection coating in tidal zone, marine structure grouting, submarine pipeline repair, reservoir dam reinforcement and the like, and has important significance for promoting the progress of marine engineering and water conservancy facility maintenance technology.

Description

Technical Field

[0001] This invention relates to the field of epoxy resin curing agent technology, and particularly to an imidazoline epoxy resin curing agent, its preparation method and application. Specifically, it relates to a novel imidazoline curing agent that can be used underwater, in humid or dry environments, its preparation method and its application in marine engineering, water conservancy and hydropower, underground structures and other scenarios. Background Technology

[0002] Epoxy resins are widely used in the repair and protection of infrastructure such as marine engineering, water conservancy facilities, and bridges due to their excellent bonding, mechanical, and chemical corrosion resistance. With the rapid development of the marine economy and the increasing prominence of aging infrastructure problems, the demand for underwater curing epoxy materials in fields such as underwater concrete structures, marine steel structures, anti-corrosion coatings in tidal zones, and subsea pipeline repair has increased dramatically. Statistics show that approximately 70% of ports and wharves, 40% of offshore platforms, and a large number of cross-sea bridges in my country's coastal areas are located in seawater or tidal zones. These facilities are subjected to multiple effects such as seawater erosion, wave impact, and biofouling year-round, resulting in cracks, peeling, and corrosion, necessitating the use of high-performance repair materials for maintenance.

[0003] The curing of epoxy resins depends on the chemical reaction between the curing agent and the epoxy groups. Traditional epoxy curing agents, such as aliphatic amines, aromatic amines, and acid anhydrides, are mainly designed for dry environments and have many limitations in underwater or humid conditions: (1) the curing reaction is severely affected by moisture, the epoxy groups are easily hydrolyzed, and the curing speed is significantly reduced; (2) the curing agent has poor affinity with water, making it difficult to effectively dissipate the water film on the substrate surface, leading to interfacial adhesion failure; (3) the cured product has a high water absorption rate, and its mechanical properties are greatly reduced after long-term immersion in water; (4) the cured product is brittle and is prone to cracking and falling off under the impact of water flow and temperature cycling. These problems seriously restrict the application of epoxy resins in underwater engineering.

[0004] Imidazole and imidazoline curing agents, due to the presence of strongly basic tertiary amine groups in their molecular structure, exhibit significant catalytic ring-opening effects on epoxy groups, enabling rapid curing of epoxy resins and producing cured products with excellent heat resistance and mechanical properties. However, conventional imidaazole curing agents (such as 2-methylimidazole, 2-ethyl-4-methylimidazole, etc.) still face the following problems in underwater environments: First, the curing agent molecules are highly polar and hydrophilic, resulting in poor compatibility with epoxy resins. They easily accumulate at the interface and are dissolved in water, leading to incomplete curing. Second, the curing agents lack hydrophobic modification, failing to effectively repel interfacial moisture, resulting in a significant water film barrier effect. Third, the crosslinking density of the cured product is too high, leading to insufficient toughness and easy brittle fracture at underwater stress concentration points. Fourth, they lack a chemical coupling mechanism with inorganic substrates (concrete, steel, etc.), resulting in underwater bonding strength generally below 15 MPa, which is insufficient to meet engineering requirements.

[0005] In recent years, researchers have attempted to improve the underwater adaptability of epoxy curing agents through various means, such as introducing hydrophobic groups, adding surfactants, and compounding flexible curing agents, achieving some success. For example, CN103360652A discloses a waterborne epoxy curing agent containing siloxane segments, which improves hydrophobicity through organosilicon modification, but its curing speed is slow, requiring more than 24 hours to reach practical strength. CN106832538A discloses a polyetheramine-modified flexible curing agent, which improves the toughness of the cured product, but its underwater curing activity is insufficient, and its water absorption rate is still higher than 1.5%. These technical solutions have shortcomings in terms of curing speed, bonding strength, or water resistance, and have not yet achieved an organic unity between rapid underwater curing and high-strength bonding.

[0006] Furthermore, underwater-cured epoxy materials also face the challenge of interfacial water film replacement. When epoxy resin is coated or poured onto the surface of an underwater substrate, a water film with a thickness of several micrometers to tens of micrometers typically exists on the substrate surface. This water film consists of physically adsorbed water and chemically bound water, exhibiting strong stability. If the curing agent cannot effectively displace or penetrate this water film, a "weak interfacial layer" will form between the epoxy resin and the substrate, severely weakening the bonding performance. Traditional curing agents lack surface migration and interfacial replacement capabilities, leading to a high failure rate of underwater bonding. Simultaneously, factors such as salinity, microorganisms, and temperature fluctuations in the marine environment further exacerbate the performance degradation of the cured material.

[0007] Therefore, developing an underwater-curing epoxy curing agent that combines rapid curing, high bond strength, low water absorption, and good toughness to enable reliable application of epoxy resins in underwater and humid environments is of great significance for marine engineering, water conservancy facilities, and infrastructure maintenance. This requires starting with the molecular design of the curing agent, and through reasonable component compatibility and preparation processes, endowing the curing agent with underwater curing activity, interfacial water film replacement capability, hydrophobic properties, and flexibility, while enhancing the chemical bonding with inorganic substrates, thereby comprehensively improving the overall performance of underwater-curing epoxy materials.

[0008] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0009] The purpose of this invention is to provide an imidazoline epoxy resin curing agent to solve or alleviate the problems existing in the prior art.

[0010] To achieve the above objectives, the present invention provides the following technical solution:

[0011] This invention provides an imidazoline epoxy resin curing agent, which is prepared from the following components by weight: 40-70 parts imidazoline monomer, 5-15 parts fluorinated long-chain carboxylic acid, 10-25 parts polyetheramine, 5-15 parts polyfunctional epoxy compound, 1-5 parts silane coupling agent, and 0.1-1 parts polymerization inhibitor.

[0012] Preferably, the imidazoline monomer is prepared by the following method: Step 1: 1 mol C 12 -C 18 Fatty acids and 1.0-1.4 mol of polyethylene polyamine are added to a reaction vessel, protected by nitrogen, and heated to 120-160℃ for amidation reaction for 2-4 hours; Step 2: The temperature is further increased to 180-220℃ for cyclization reaction for 4-8 hours, followed by vacuum dehydration to obtain imidazoline monomer; the fatty acid is at least one of lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid; the polyethylene polyamine is at least one of diethylenetriamine, triethylenetetramine, and tetraethylenepentamine.

[0013] Preferably, the fluorinated long-chain carboxylic acid is a perfluoroalkyl carboxylic acid with 8-12 carbon atoms in its fluorinated carbon chain and an acid value of 80-160 mg KOH / g; more preferably, the fluorinated long-chain carboxylic acid is at least one of perfluorooctylpropionic acid, perfluorodecylacetic acid, and perfluorododecylbutyric acid.

[0014] Preferably, the polyetheramine is polyoxypropylene amine or polyoxyethylene-polyoxypropylene copolyamine with a molecular weight of 230-600 and an amine value of 200-600 mgKOH / g; more preferably, the polyetheramine is at least one of Jeffamine D-230, D-400, T-403 and ED-600.

[0015] Preferably, the multifunctional epoxy compound is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and trifunctional epoxy resin TDE-85 with an epoxy equivalent of 100-250 g / eq.

[0016] Preferably, the polymerization inhibitor is at least one selected from p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, and hydroquinone.

[0017] The present invention also provides a method for preparing the above-mentioned imidazoline epoxy resin curing agent, comprising the following steps:

[0018] Step 1: Add the imidazoline monomer to the reaction vessel, heat to 70-90℃, and add the fluorinated long-chain carboxylic acid dropwise under nitrogen protection. The addition will be completed in 0.5-1h, and the reaction will be maintained at the temperature for 1-2h.

[0019] Step 2: Add polyetheramine, heat to 90-110℃, and react for 1-3 hours;

[0020] Step 3: Cool to 60-80℃, add the multifunctional epoxy compound in batches, and react for 2-4 hours;

[0021] Step 4: Add silane coupling agent and polymerization inhibitor, continue stirring for 0.5-1 hour, degas under vacuum, and the product is ready.

[0022] Preferably, in step 1, the fluorinated long-chain carboxylic acid is added at a temperature of 80°C and the reaction time is 1.5 h; in step 2, the polyetheramine is added at a reaction temperature of 100°C and the reaction time is 2 h; in step 3, the epoxy compound is added in 3 batches, with an interval of 20 min between each batch, at a reaction temperature of 70°C, for a total reaction time of 3 h.

[0023] The present invention also provides the application of the above-mentioned imidazoline epoxy resin curing agent for curing epoxy resin in underwater, humid or dry environments, wherein the epoxy resin is at least one of bisphenol A type, bisphenol F type, phenolic epoxy, and marine epoxy mortar system; the amount of curing agent is 8-25% of the mass of epoxy resin.

[0024] Preferably, the underwater curing conditions are: water temperature 5-35℃, water depth 0.5-20m, water flow velocity 0-2m / s, visibility ≥0.2m; curing time initial setting ≤4h, final setting ≤24h, and underwater shear bond strength ≥18MPa after 7 days.

[0025] Preferably, after the curing agent is mixed with the epoxy resin, the underwater contact angle is ≤65°, the interfacial water film replacement rate is ≥85%, the water absorption rate of the cured product is ≤0.8%, and the Shore D hardness is ≥75.

[0026] Beneficial effects:

[0027] In the imidazoline epoxy resin curing agent of the present invention, the imidazoline monomer is prepared by an amidation-cyclization reaction of long-chain fatty acids and polyethylenepolyamines. Its molecular structure contains both tertiary and secondary amine groups. The tertiary amine group has a strong catalytic ring-opening effect on the epoxy group, which can significantly accelerate the curing reaction. The secondary amine group directly participates in the curing reaction to form a cross-linked network. This synergistic effect of catalysis and curing allows the curing agent to maintain high activity in an underwater environment, achieving rapid curing of the epoxy resin. Simultaneously, the introduction of long-chain fatty acid segments endows the imidazoline monomer with certain hydrophobicity and flexibility, which helps improve the compatibility between the curing agent and the epoxy resin, avoiding phase separation and loss of active components due to excessive polarity.

[0028] The imidazoline epoxy resin curing agent of this invention, by introducing fluorinated long-chain carboxylic acids, utilizes the ultra-low surface energy of fluorocarbon chains to endow the curing agent with excellent surface migration and hydrophobic properties. When the epoxy resin and curing agent are mixed and coated onto the surface of an underwater substrate, the fluorinated segments preferentially migrate to the interface due to surface energy, forming a hydrophobic barrier layer. This effectively displaces or penetrates the physically adsorbed water film on the substrate surface, significantly improving the interfacial water film replacement rate. Simultaneously, the carboxyl groups in the fluorinated long-chain carboxylic acid and the amine groups in the imidazoline monomer form ion pairs through acid-base neutralization. This ionic bonding not only improves the dispersion stability of the fluorinated component in the curing agent system but also regulates the reactivity of the curing agent, avoiding excessively rapid exothermic reactions. Fluorine modification enables the curing agent to exhibit low contact angle characteristics in underwater environments, with the underwater contact angle reduced to below 65°. This significantly improves the wetting and spreading ability of the epoxy resin on damp substrates, laying the foundation for achieving high-strength interfacial adhesion.

[0029] The imidazoline epoxy resin curing agent of this invention constructs a flexible segment network through the introduction of polyetheramine. The polyetheramine molecular backbone is composed of flexible polyoxypropylene or polyoxyethylene segments with primary amine end groups. This allows it to participate in the epoxy curing reaction to form crosslinking points and also provides freedom of movement for molecular segments within the cured network, significantly improving the toughness and impact resistance of the cured product. At underwater stress concentration sites, the flexible segments effectively absorb and disperse stress through molecular chain orientation and deorientation processes, avoiding the brittle fracture problem caused by excessively high crosslinking density in traditional imidazoline curing agents. Simultaneously, the hydrophilicity of the polyether segments facilitates the emulsification and dispersion of the curing agent in aqueous media, improving the operability of underwater construction. The synergistic curing of polyetheramine and imidazoline monomers also produces a gradient crosslinking density structure, balancing the strength and toughness requirements of the cured product.

[0030] The imidazoline epoxy resin curing agent of this invention significantly improves the compatibility between the curing agent and the epoxy resin matrix through the pre-chain extension reaction of a multifunctional epoxy compound. During the preparation process, the epoxy groups in the multifunctional epoxy compound undergo addition reactions with the active hydrogen in the imidazoline monomer and polyetheramine, forming an oligomer structure containing epoxy end groups. This pre-chain extended product retains the reactive sites of the curing agent and enhances its chemical and physical compatibility with the epoxy resin through the introduction of epoxy segments. The formation of the pre-chain extended structure also increases the molecular weight and viscosity of the curing agent, reduces the leaching risk of small molecule curing agents in underwater environments, and ensures the integrity of the curing reaction. The introduction of the multifunctional epoxy compound increases the crosslinking point density of the cured product, improves the integrity of the crosslinking network and thermal stability, enabling the cured product to maintain excellent mechanical properties even during long-term underwater immersion.

[0031] The imidazoline epoxy resin curing agent of this invention achieves chemical bridging between the organic curing agent and the inorganic substrate through the introduction of a silane coupling agent. One end of the silane coupling agent molecule contains a hydrolyzable alkoxysilane group, which hydrolyzes in an underwater environment to form a silanol group, which then undergoes a condensation reaction with hydroxyl groups on the surface of inorganic substrates such as concrete and steel to form a stable Si-OM chemical bond. The other end contains organic functional groups such as epoxy and amino groups, which can chemically react with epoxy resin and curing agent, covalently grafting them into the cured network. This two-way chemical bonding mechanism constructs a strong molecular bridge at the interface, significantly improving underwater adhesion strength. The hydrolysis-condensation reaction of the silane coupling agent utilizes water molecules in the underwater environment as reactants, transforming water from a harmful factor into a beneficial one. This unique chemical mechanism is key to achieving high-strength underwater adhesion. The silane-modified interface layer also possesses certain hydrophobicity and density, inhibiting water molecules from penetrating deeper into the interface and improving the long-term durability of the bonded interface.

[0032] The imidazoline epoxy resin curing agent of this invention effectively controls the stability of the curing agent during storage and transportation by adding a polymerization inhibitor. The phenolic hydroxyl groups in the polymerization inhibitor molecule can form hydrogen bonds with the active sites in the imidazoline monomer, temporarily shielding its catalytic activity and preventing self-polymerization or pre-reaction of the curing agent before use, thus ensuring a sufficiently long pot life. When the curing agent is mixed with epoxy resin, the high reactivity of the epoxy groups causes it to react preferentially with the curing agent, diluting and covering the effect of the polymerization inhibitor, and not significantly inhibiting the normal curing reaction. The precise control of trace amounts of polymerization inhibitor achieves a balance between the storage stability and the reactivity of the curing agent, meeting the dual requirements of material shelf life and application window in engineering applications.

[0033] The imidazoline epoxy resin curing agent of this invention exhibits excellent performance. In an underwater environment, the 7-day shear bond strength of the cured epoxy resin reaches 18-25 MPa, an improvement of over 80% compared to the 10-12 MPa of traditional imidazoline curing agents, fully meeting the high-strength bonding requirements of marine engineering and hydraulic facilities. The water absorption rate of the cured product is less than 0.8%, far lower than the 1.5-3% of traditional products. This excellent water absorption resistance ensures that the cured product maintains stable mechanical properties and dimensional stability even during long-term underwater immersion. The Shore D hardness of the cured product can reach over 75, indicating good surface hardness and wear resistance. More importantly, this curing agent exhibits excellent curing activity in both dry and underwater environments. Underwater curing, the initial setting time does not exceed 4 hours, and the final setting time does not exceed 24 hours, resulting in rapid curing and significantly shortening the construction cycle and traffic control time. The underwater contact angle of the curing agent mixed with epoxy resin can be reduced to below 65°, and the interfacial water film replacement rate is as high as 85% or more. This performance indicator shows that the curing agent system can effectively overcome the underwater interfacial water film barrier, achieving efficient wetting and strong adhesion of epoxy resin to damp substrates. The curing agent of this invention is suitable for various underwater working conditions with water depths of 0.5-20 meters, water temperatures of 5-35℃, and water flow velocities of 0-2 m / s. It has broad application prospects in underwater concrete repair, anti-corrosion coating in tidal zones, grouting of marine structures, subsea pipeline repair, and reservoir dam reinforcement, and is of great significance for promoting the advancement of marine engineering and water conservancy facility maintenance technologies. Detailed Implementation

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0035] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0036] This invention addresses at least one of the problems of current epoxy resin curing agents in underwater environments, including low curing activity, poor interfacial bonding strength, high water absorption, and high brittleness of cured products, by providing an imidazoline epoxy resin curing agent for underwater curing.

[0037] The inventors discovered that while traditional imidazole curing agents possess excellent catalytic activity, they face three major obstacles in underwater environments: first, excessive hydrophilicity leads to the loss of active components; second, they lack interfacial water film replacement capacity; and third, the high crosslinking density of the cured product results in high brittleness. Introducing long-chain hydrophobic groups into the imidazole molecule structure, and simultaneously compounding it with fluorinated surfactants, flexible curing components, and interfacial coupling components, can construct a multifunctional curing agent system possessing catalytic activity, hydrophobic properties, toughness, and interfacial bonding ability, which will help solve or improve the above problems. Furthermore, through molecular design of the imidazole monomer, it can simultaneously contain tertiary amine catalytic groups and secondary amine curing groups, achieving a synergistic effect of catalysis and curing, maintaining high curing activity in underwater environments.

[0038] The imidazoline epoxy resin curing agent of this invention is prepared from the following parts by weight: 40-70 parts of imidazoline monomer (e.g., 40, 45, 50, 55, 60, 65 or 70 parts), 5-15 parts of fluorinated long-chain carboxylic acid (e.g., 5, 7, 10, 12 or 15 parts), 10-25 parts of polyetheramine (e.g., 10, 13, 16, 19, 22 or 25 parts), 5-15 parts of polyfunctional epoxy compound (e.g., 5, 7, 10, 12 or 15 parts), 1-5 parts of silane coupling agent (e.g., 1, 2, 3, 4 or 5 parts), and 0.1-1 part of polymerization inhibitor (e.g., 0.1, 0.3, 0.5, 0.7 or 1 part).

[0039] In the imidazoline epoxy resin curing agent of this invention, the imidazoline monomer is the core active component. Its molecular structure contains both tertiary and secondary amine groups, thus possessing both catalytic and curing functions. The tertiary amine group exhibits a strong catalytic ring-opening effect on the epoxy group, significantly accelerating the curing reaction; the secondary amine group directly participates in the curing reaction to form a cross-linked network. The introduction of long-chain fatty acid segments endows the imidazoline monomer with certain hydrophobicity and flexibility, which helps improve the compatibility between the curing agent and the epoxy resin, avoiding phase separation due to excessive polarity and loss of active components in underwater environments.

[0040] In a preferred embodiment of the imidazoline epoxy resin curing agent of the present invention, the imidazoline monomer is prepared by the following method:

[0041] Step 1: Add 1 mol C 12 -C 18 Fatty acids and 1.0-1.4 mol of polyethylene polyamine are added to a reaction vessel, protected by nitrogen, and heated to 120-160℃ (e.g., 120℃, 130℃, 140℃, 150℃ or 160℃) for amidation reaction for 2-4 h (e.g., 2 h, 2.5 h, 3 h, 3.5 h or 4 h).

[0042] Step 2: Continue heating to 180-220℃ (e.g., 180℃, 190℃, 200℃, 210℃ or 220℃), cyclize for 4-8 hours (e.g., 4 hours, 5 hours, 6 hours, 7 hours or 8 hours), then dehydrate under vacuum to obtain the imidazoline monomer.

[0043] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the fatty acid is at least one selected from lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid; and the polyethylene polyamine is at least one selected from diethylenetriamine, triethylenetetraamine, and tetraethylenepentamine. The choice of fatty acid carbon chain length is crucial to the performance of the imidazoline monomer. 12 -C 18 The carbon chain length provides sufficient hydrophobicity without reducing molecular mobility due to excessive chain length. If the carbon chain is too short ( <C 12 If the carbon chain is too long (>C), the hydrophobicity is insufficient, making it difficult to effectively repel interfacial moisture; if the carbon chain is too long (>C), the hydrophobicity is insufficient, making it difficult to effectively repel interfacial moisture. 18 If the viscosity of the curing agent is too high, its compatibility with epoxy resin will decrease, affecting the mixing uniformity and curing speed. The multiple amine groups in polyethylene polyamines provide abundant reaction sites; diethylenetriamine contains 3 amine groups, triethylenetetramine contains 4, and tetraethylenepentamine contains 5. Increasing the number of amine groups is beneficial for improving the reactivity and crosslinking density of the curing agent, but it also increases the brittleness of the cured product. Therefore, it needs to be balanced by subsequently compounding flexible components.

[0044] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the molar ratio of polyethylene polyamine to fatty acid is 1.0-1.4:1. If the amount of polyethylene polyamine is too small (molar ratio <1.0:1), then: 1) the number of amine groups is insufficient, the amidation reaction is incomplete, and the residual free fatty acid will affect the stability of the curing agent; 2) the substrate for the cyclization reaction is insufficient, the imidazoline ring formation rate is low, and the catalytic activity decreases; 3) the content of secondary amine groups in the curing agent is insufficient, and the curing speed is slow; 4) the crosslinking density of the final cured product is low, and the mechanical properties are poor. If the amount of polyethylene polyamine is too large (molar ratio >1.4:1), then: 1) excessive free amine will cause the curing agent to be too hydrophilic and easily dissolve in the underwater environment; 2) the storage stability of the curing agent will decrease, and self-polymerization reaction will easily occur; 3) the crosslinking density of the cured product is too high, and the brittleness increases; 4) excessive amine will make the curing system too alkaline, which may corrode the substrate; 5) the water absorption rate of the cured product will increase, and the durability will decrease.

[0045] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the amidation reaction temperature in step 1 is 120-160℃, and the reaction time is 2-4h. If the reaction temperature is too low (<120℃), then: 1) the activation energy of the amidation reaction is insufficient, and the reaction rate is extremely slow; 2) fatty acids and polyethylene polyamines are difficult to fully react, resulting in low conversion rate; 3) the reaction time is significantly prolonged, reducing production efficiency; 4) there are many unreacted raw materials remaining in the product, affecting subsequent cyclization reactions. If the reaction temperature is too high (>160℃), then: 1) side reactions may occur, generating products that are not conducive to cyclization; 2) polyethylene polyamines are prone to oxidative degradation, reducing amine value; 3) excessively high temperatures may cause some amides to directly cyclize, making the reaction difficult to control; 4) energy consumption increases, requiring higher equipment standards. If the reaction time is too short (<2h), then: 1) the amidation reaction is incomplete, resulting in low conversion rate; 2) insufficient substrate for subsequent cyclization reactions, resulting in low imidazoline ring formation rate; 3) the product composition is uneven, leading to poor batch stability. If the reaction time is too long (>4h), then: 1) energy consumption and production costs will increase; 2) prolonged high temperature may cause the product color to darken; 3) some amides may degrade or undergo side reactions; 4) the production cycle will be extended and efficiency will be reduced.

[0046] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the cyclization reaction temperature in step 2 is 180-220℃, the reaction time is 4-8h, and vacuum dehydration is required. If the reaction temperature is too low (<180℃), then: 1) the cyclization reaction is difficult to start, and the imidazoline ring formation rate is extremely slow; 2) the reaction is incomplete, and the product contains a large amount of uncyclized amides; 3) the catalytic activity is significantly reduced, making it difficult to meet the requirements for rapid underwater curing; 4) the product viscosity is low, and the overall performance of the curing agent is poor. If the reaction temperature is too high (>220℃), then: 1) it may lead to ring-opening or thermal decomposition of the imidazoline ring; 2) the product color is severely darkened, or even carbonized; 3) excessively high temperature may trigger amine oxidation, reducing curing activity; 4) energy consumption increases significantly, equipment requirements are high, and safety hazards are significant. If the reaction time is too short (<4h), then: 1) the cyclization reaction is incomplete, resulting in a low imidazoline ring formation rate; 2) the product contains a mixture of amides and imidazolines, leading to unstable performance; 3) insufficient formation of tertiary amine catalytic sites, resulting in low curing activity; 4) the final curing agent quality is unstable, with large batch-to-batch variations. If the reaction time is too long (>8h), then: 1) excessive cyclization may lead to product cross-linking and a significant increase in viscosity; 2) prolonged high temperatures may cause partial decomposition, reducing product quality; 3) energy consumption and costs increase, reducing production efficiency; 4) high requirements are placed on the long-term high-temperature operation capability of the equipment. Vacuum dehydration is crucial for the cyclization reaction. The cyclization reaction is a dehydration condensation reaction, and timely removal of the generated water is beneficial for the reaction to proceed in the forward direction, increasing the imidazoline ring formation rate. Without vacuum dehydration, the reaction equilibrium is limited, cyclization is incomplete, and product activity is reduced.

[0047] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the fluorinated long-chain carboxylic acid is at least one selected from perfluorooctylpropionic acid, perfluorodecylacetic acid, and perfluorododecylbutyric acid, with an acid value of 80-160 mgKOH / g (e.g., 80 mgKOH / g, 100 mgKOH / g, 120 mgKOH / g, 140 mgKOH / g, or 160 mgKOH / g). The introduction of the fluorinated long-chain carboxylic acid is key to achieving underwater curing. Fluorocarbon chains have extremely low surface energy (approximately 6-10 mN / m), far lower than hydrocarbon chains (20-30 mN / m) and water (72 mN / m), giving the fluorinated component excellent hydrophobic and oleophobic properties. In the epoxy resin curing agent system, the fluorinated long-chain carboxylic acid preferentially migrates to the interface due to surface energy, forming a hydrophobic barrier layer on the substrate surface, effectively displacing physically adsorbed water films and improving the epoxy resin's wetting ability on damp substrates. The carboxyl groups in fluorinated long-chain carboxylic acids and the amine groups in imidazoline monomers form ion pairs through acid-base neutralization reactions. This ionic bonding not only improves the dispersion stability of the fluorinated components in the curing agent system but also regulates the reactivity of the curing agent. If the acid value is too low (<80 mg KOH / g), then: 1) the carboxyl content is insufficient, resulting in weak ionic bonding with the imidazoline monomer; 2) the interfacial migration ability is reduced, and the hydrophobic barrier layer is not fully formed; 3) the water film replacement rate is low, resulting in insufficient underwater bonding strength; 4) the storage stability of the curing agent is poor. If the acid value is too high (>160 mg KOH / g), then: 1) excessive carboxyl groups will over-neutralize the alkalinity of the imidazoline monomer, reducing catalytic activity; 2) the curing agent is too acidic, which may corrode the metal substrate; 3) the curing speed is significantly reduced, making it difficult to meet the requirements for rapid curing; 4) the formation of excessive ion pairs will lead to an increase in the viscosity of the curing agent, affecting its application performance.

[0048] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the selection of the fluorocarbon chain length of the fluorinated long-chain carboxylic acid is crucial. Perfluorooctyl (C8F) 17 ), perfluorodecyl (C 10 F 21 ), perfluorododecyl (C 12 F 25 () represents different hydrophobicities and surface activities. C8F 17 With a moderate chain length, it possesses both good hydrophobicity and maintains good solubility and dispersibility, making it a cost-effective choice. 10 F 21 and C 12 F 25 Longer chain lengths result in greater hydrophobicity but decreased solubility, potentially affecting the uniformity of the curing agent. The choice of carboxylic acid linkages (propionic acid, acetic acid, butyric acid) influences the flexibility of the fluorinated segments and their compatibility with the system. Propionic and butyric acid chains provide appropriate flexible spacers, which are beneficial for the surface migration and interfacial arrangement of fluorocarbon chains.

[0049] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the polyetheramine is at least one of Jeffamine D-230, D-400, T-403, and ED-600, with an amine value of 200-600 mgKOH / g (e.g., 200 mgKOH / g, 300 mgKOH / g, 400 mgKOH / g, 500 mgKOH / g, or 600 mgKOH / g). The introduction of the polyetheramine aims to construct a flexible chain segment network, improving the toughness of the cured product. The Jeffamine series are typical polyetheramines, with a main chain composed of polyoxypropylene (PO) or polyoxyethylene (EO) segments and primary amine groups at the end groups. D-230 has a molecular weight of approximately 230 and contains relatively short polyether segments; D-400 has a molecular weight of approximately 400 and longer polyether segments; T-403 is a trifunctional polyether amine, providing more crosslinking points; ED-600 has a molecular weight of approximately 600 and contains EO and PO copolymer segments, exhibiting both hydrophilicity and flexibility. If the amine value is too low (<200mgKOH / g), then: 1) the amine content is insufficient, resulting in fewer active sites participating in the curing reaction; 2) the crosslinking density of the cured product is low, leading to insufficient mechanical properties; 3) the curing speed is slow, making it difficult to meet the requirements for rapid underwater curing; 4) the proportion of flexible segments is too high, potentially resulting in an overly soft cured product with insufficient hardness. If the amine value is too high (>600mgKOH / g), then: 1) the polyether segments are too short, providing limited flexibility; 2) the amine group density is too high, which may lead to excessive local crosslinking density, thus increasing brittleness; 3) the hydrophilicity is enhanced, and the water absorption rate of the cured product increases; 4) it contradicts the hydrophobic properties of the fluorinated components, affecting the overall performance balance.

[0050] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the molecular weight and structure selection of the polyetheramine embodies the art of balancing toughness and strength. D-230 has a relatively small molecular weight, offering limited flexibility, but its high amine value and fast curing speed make it suitable for applications requiring rapid curing and high hardness. D-400 has a moderate molecular weight and is the most commonly used flexible agent, providing sufficient flexible segments while maintaining a reasonable curing speed and strength. T-403's trifunctional structure can form a branched crosslinking network, improving crosslinking density and mechanical strength while maintaining toughness, but its dosage needs to be controlled to avoid over-crosslinking. ED-600 has the largest molecular weight and the best flexibility, making it particularly suitable for applications requiring high toughness and impact resistance, but its strong hydrophilicity necessitates its use in conjunction with hydrophobic components. The synergistic curing of polyetheramine and imidazoline monomers also produces a gradient crosslinking density structure, achieving a balance of rigidity and flexibility at the molecular scale.

[0051] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the multifunctional epoxy compound is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and trifunctional epoxy resin TDE-85 with an epoxy equivalent of 100-250 g / eq (e.g., 100 g / eq, 130 g / eq, 160 g / eq, 190 g / eq, 220 g / eq, or 250 g / eq). The pre-chain extension reaction of the multifunctional epoxy compound is key to improving the compatibility between the curing agent and the epoxy resin. During the curing agent preparation process, the epoxy groups in the multifunctional epoxy compound undergo addition reactions with the active hydrogen (secondary amine, primary amine) in the imidazoline monomer and polyether amine to form an oligomer structure containing epoxy end groups. This pre-chain extended product retains the reactive sites of the curing agent and enhances the chemical and physical compatibility with the epoxy resin matrix through the introduction of epoxy segments. If the epoxy equivalent is too low (<100 g / eq), then: 1) the epoxy group density is too high, the pre-chain extension reaction is too fast and difficult to control; 2) it may lead to excessive cross-linking of the curing agent, a significant increase in viscosity, or even gelation; 3) the storage stability of the curing agent decreases, and the pot life is shortened; 4) it may react rapidly when mixed with epoxy resin, resulting in a short operating time window. If the epoxy equivalent is too high (>250 g / eq), then: 1) the epoxy group density is too low, and the pre-chain extension reaction is insufficient; 2) the compatibility improvement effect between the curing agent and epoxy resin is limited; 3) the cross-linking density of the cured product is low, resulting in insufficient mechanical properties; 4) the molecular weight of the pre-chain extended product is too large, which may affect the flowability and permeability of the curing agent.

[0052] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, bisphenol A epoxy resin is the most commonly used epoxy compound, possessing good mechanical properties and chemical stability, with an epoxy equivalent typically between 180-190 g / eq. Bisphenol F epoxy resin has a lower viscosity, with an epoxy equivalent of approximately 160-180 g / eq, which helps reduce the overall viscosity of the curing agent and improves its application performance. Trifunctional epoxy resin TDE-85 has an epoxy equivalent of approximately 100-110 g / eq and high functionality, which can significantly improve the crosslinking density and heat resistance of the cured product; however, its dosage needs to be controlled to avoid excessively high curing agent viscosity. The formation of the pre-extended chain structure also increases the molecular weight and viscosity of the curing agent, reducing the risk of leaching of small molecule curing agents in the underwater environment and ensuring the integrity of the curing reaction.

[0053] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the silane coupling agent is at least one selected from γ-glycidoxypropyltrimethoxysilane (KH-560), γ-aminopropyltriethoxysilane (KH-550), and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (KH-792). The introduction of the silane coupling agent achieves chemical bridging between the organic curing agent and the inorganic substrate, which is crucial for high-strength underwater adhesion. Silane coupling agents possess a dual-functional structure: one end contains a hydrolyzable alkoxysilane group (methoxy or ethoxy), which hydrolyzes in an underwater environment to form a silanol group (Si-OH), which then undergoes a condensation reaction with hydroxyl groups (-OH) on the surface of inorganic substrates such as concrete and steel, forming a stable Si-OM chemical bond (M representing a metal or silicon atom in the substrate); the other end contains organic functional groups (epoxy, amino, etc.), which can chemically react with epoxy resins and curing agents, covalently grafting them into the cured network. This bidirectional chemical bonding mechanism constructs a robust molecular bridge at the interface, significantly improving underwater adhesion strength.

[0054] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, KH-560 contains epoxy groups, which can undergo copolymerization with epoxy resin to achieve chemical grafting with the matrix. Simultaneously, its epoxy groups can also be ring-opened and cured by the curing agent to form a dense interfacial network. KH-550 contains primary amino groups, which can directly participate in the epoxy curing reaction, exhibiting high reactivity and strong interfacial bonding ability, making it particularly suitable for scenarios requiring rapid curing. KH-792 contains two amino groups (primary and secondary amino groups), providing more reaction sites and stronger basicity, combining catalytic and curing effects, but the dosage needs to be controlled to avoid over-reaction. The hydrolysis-condensation reaction of the silane coupling agent utilizes water molecules in the underwater environment as reactants, transforming water from a harmful factor into a beneficial one. This unique chemical mechanism is a key innovation for achieving high-strength underwater adhesion.

[0055] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the amount of silane coupling agent is 1-5 parts. If the amount is too low (<1 part), then: 1) there are insufficient chemical bonding sites at the interface, resulting in limited improvement in bonding strength; 2) the silane-modified interface layer is discontinuous, allowing water molecules to easily penetrate; 3) the coupling effect with the inorganic substrate is insufficient, resulting in poor long-term durability; 4) the underwater bonding strength is difficult to reach the target of 18 MPa or higher. If the amount is too high (>5 parts), then: 1) excessive silane accumulates at the interface, which may form a weak interface layer; 2) excessive release of silane hydrolysis products (methanol or ethanol) generates bubbles, affecting interface quality; 3) the viscosity of the curing agent increases significantly, affecting workability and permeability; 4) the cost increases, reducing economic efficiency; 5) excessive silicon-oxygen network may cause the interface layer to be too rigid, making it prone to cracking under stress.

[0056] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the polymerization inhibitor is at least one selected from p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, and hydroquinone. The addition of the polymerization inhibitor aims to control the stability of the curing agent during storage and transportation, and to extend its pot life. The phenolic hydroxyl groups in the polymerization inhibitor molecule can form hydrogen bonds with the active sites (tertiary and secondary amines) in the imidazoline monomer, temporarily shielding its catalytic activity and preventing self-polymerization or pre-reaction of the curing agent when not in use. When the curing agent is mixed with the epoxy resin, the high concentration and high reactivity of the epoxy groups cause it to react preferentially with the curing agent, breaking the hydrogen bond association of the polymerization inhibitor, diluting and covering its effect, and not significantly inhibiting the normal curing reaction. p-hydroxyanisole is a mild polymerization inhibitor with moderate inhibition effect and minimal impact on the curing speed. 2,6-Di-tert-butyl-p-cresol (BHT) is a commonly used antioxidant and polymerization inhibitor. It has high steric hindrance and good stability, and can both inhibit polymerization and prevent the curing agent from oxidizing and deteriorating. Hydroquinone has a strong polymerization inhibitory effect, but the dosage needs to be strictly controlled; excessive dosage will significantly reduce the curing speed.

[0057] In a preferred embodiment of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the amount of polymerization inhibitor is 0.1-1 part. If the amount is too low (<0.1 part), then: 1) the polymerization inhibition effect is insufficient, and the storage stability of the curing agent is poor; 2) the viscosity is prone to increase or partial gelation when the temperature fluctuates or during long-term storage; 3) the performance consistency between batches decreases, affecting quality control; 4) the pot life is too short, which is not conducive to transportation and use. If the amount is too high (>1 part), then: 1) excessive polymerization inhibition leads to a significant reduction in curing speed; 2) even after mixing with epoxy resin, the residual polymerization inhibitor will still inhibit the curing reaction; 3) the underwater curing time is prolonged, making it difficult to meet the requirements for rapid curing (initial setting ≤4h); 4) the curing is incomplete, and the mechanical properties and bond strength of the cured product decrease; 5) excessive phenolic compounds may affect the weather resistance and color of the cured product. The precise control of trace amounts of polymerization inhibitor achieves the best balance between the storage stability of the curing agent (pot life ≥6 months) and the reactivity in use (rapid underwater curing).

[0058] This invention also provides a method for preparing an imidazoline epoxy resin curing agent for underwater curing. The method for preparing the imidazoline epoxy resin curing agent for underwater curing according to an embodiment of this invention includes the following steps: Step 1: Adding imidazoline monomer to a reaction vessel, heating to 70-90℃ (e.g., 70℃, 75℃, 80℃, 85℃, or 90℃), and adding fluorinated long-chain carboxylic acid dropwise under nitrogen protection over 0.5-1h (e.g., 0.5h, 0.6h, 0.7h, 0.8h, 0.9h, or 1h) until the addition is complete, and maintaining the reaction temperature for 1-2h (e.g., 1h, 1.2h, 1.5h, 1.8h, or 2h); Step 2: Adding polyetheramine and heating... Step 1: React at 90-110℃ (e.g., 90℃, 95℃, 100℃, 105℃, or 110℃) for 1-3 hours (e.g., 1 hour, 1.5 hours, 2 hours, 2.5 hours, or 3 hours); Step 2: Cool down to 60-80℃ (e.g., 60℃, 65℃, 70℃, 75℃, or 80℃), add the multifunctional epoxy compound in batches, and react for 2-4 hours (e.g., 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours); Step 3: Add silane coupling agent and polymerization inhibitor, continue stirring for 0.5-1 hour (e.g., 0.5 hours, 0.6 hours, 0.7 hours, 0.8 hours, 0.9 hours, or 1 hour), degas under vacuum, and discharge the product.

[0059] The steps in the preparation method of the underwater curing imidazoline epoxy resin curing agent of the present invention are designed to: (1) ensure the orderliness and controllability of the reaction (correct feeding sequence and temperature control can ensure that each component reacts in a predetermined manner to form an ideal curing agent structure; if the sequence is disrupted, it may lead to an increase in side reactions and a decrease in product performance); (2) help achieve uniform dispersion of fluorine-containing components (in step 1, fluorine-containing long-chain carboxylic acids are added dropwise to avoid excessively high local concentrations leading to agglomeration or phase separation; the tertiary amine group of the imidazoline monomer and The carboxyl groups of fluorinated carboxylic acids gradually form ion pairs, achieving stable dispersion of fluorinated components in the system; if added all at once, the performance of the curing agent may be unstable due to uneven mixing); (3) It helps to control the degree of pre-chain extension reaction (the timing and temperature setting of the addition of polyetheramine and multifunctional epoxy compounds in steps 2 and 3 precisely control the pre-chain extension reaction; polyetheramine is added first, and reacts initially with imidazoline monomer and fluorinated carboxylic acid ion pairs at a higher temperature to form an intermediate containing flexible segments; then the multifunctional epoxy compound is added at a lower temperature). (3) Pre-chain extension of the compound at a lower temperature to avoid over-reaction and gelation; this stepwise temperature control strategy ensures that the curing agent has a suitable molecular weight distribution and viscosity); (4) Strategy of adding multifunctional epoxy compounds in batches (adding in batches rather than all at once in step 3 helps to control the exothermic reaction and reaction rate; the reaction between epoxy groups and amine groups is a strongly exothermic reaction, and adding in batches can avoid local over-crosslinking caused by a sudden temperature rise; after each batch is added, there is sufficient mixing and reaction time to ensure product uniformity); (5) Timing of adding silane coupling agent and polymerization inhibitor (adding in step 4 after the pre-chain extension reaction is basically completed to avoid its participation in the complex reaction in the early stage; adding silane coupling agent at a lower temperature to prevent premature hydrolysis or self-polymerization; adding polymerization inhibitor last to play a stabilizing role after the curing agent is basically formed and not to interfere with the main reaction in the early stage); (6) Necessity of vacuum degassing (stirring and reaction during the preparation process will introduce bubbles, and vacuum degassing can effectively remove bubbles and improve the quality of curing agent; the presence of bubbles will become a defect point of the cured product, reducing mechanical properties and interfacial bonding strength).

[0060] In a preferred embodiment of the preparation method of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the fluorinated long-chain carboxylic acid is added at a temperature of 80°C and the reaction time is 1.5 h in step 1. This temperature and time are the optimal conditions for the formation of the imidazoline monomer and the fluorinated carboxylic acid ion pair, ensuring sufficient reaction while avoiding excessive temperature that could lead to ring opening of the imidazoline ring or decomposition of the fluorinated component. In step 2, the polyetheramine is reacted at a temperature of 100°C and the reaction time is 2 h. Under these conditions, the primary amino group of the polyetheramine reacts moderately with the imidazoline monomer and the fluorinated carboxylic acid ion pair to form an intermediate containing flexible segments, laying the foundation for subsequent pre-chain extension. In step 3, the epoxy compound is added in three batches, with an interval of 20 min between each batch, at a reaction temperature of 70°C, for a total reaction time of 3 h. Adding the product in three batches allowed for precise control of the pre-chain extension reaction. Each batch was followed by 20 minutes of mixing and reaction time to ensure that the epoxy groups and active hydrogen reacted fully. The temperature of 70°C maintained a reasonable reaction rate while avoiding excessive cross-linking. The total reaction time of 3 hours ensured that the pre-chain extension reaction reached the ideal level, and the viscosity and molecular weight of the curing agent were appropriate.

[0061] This invention also provides the application of an imidazoline epoxy resin curing agent for underwater curing, used for curing epoxy resins in underwater, humid, or dry environments. The epoxy resin is at least one of bisphenol A, bisphenol F, phenolic epoxy, or marine epoxy mortar systems. The curing agent dosage is 8-25% of the epoxy resin mass (e.g., 8%, 10%, 12%, 15%, 18%, 20%, 22%, or 25%). The curing agent dosage needs to be adjusted according to the epoxy value of the epoxy resin and the application scenario. For epoxy resins with high epoxy values ​​(>0.5 eq / 100g), the curing agent dosage can be at the lower limit (8-12%) to maintain the toughness of the cured product; for epoxy resins with low epoxy values ​​(<0.45 eq / 100g), the curing agent dosage needs to be at the upper limit (20-25%) to ensure sufficient curing and adequate crosslinking density. For rapid underwater repairs, the curing agent dosage should be at the upper-middle level (15-20%) to accelerate the curing speed; for large-volume grouting, the curing agent dosage should be at the lower limit (8-12%) to control heat release and shrinkage. Marine epoxy mortar systems usually also contain fillers and additives, and the curing agent dosage should be calculated based on the actual formula, using the epoxy resin dosage as a benchmark.

[0062] In a preferred embodiment of the application of the imidazoline epoxy resin curing agent for underwater curing of the present invention, the underwater curing conditions are: water temperature 5-35℃ (e.g., 5℃, 10℃, 15℃, 20℃, 25℃, 30℃, or 35℃), water depth 0.5-20m (e.g., 0.5m, 2m, 5m, 8m, 10m, 15m, or 20m), water flow velocity 0-2m / s (e.g., 0m / s, 0.5m / s, 1m / s, 1.5m / s, or 2m / s), and visibility ≥0.2m. This range of conditions covers the actual working conditions of most underwater engineering projects. The water temperature range of 5-35℃ covers sea temperatures from frigid to tropical zones, as well as most inland water temperatures; the water depth range of 0.5-20m encompasses shallow water repair, tidal zone construction, and general underwater operations; the water flow velocity range of 0-2m / s includes still water, slow-moving, and moderate flow conditions; and visibility of ≥0.2m is a basic requirement for underwater manual operations. Under these conditions, the initial setting time is ≤4h, the final setting time is ≤24h, and the 7-day underwater shear bond strength is ≥18MPa, fully meeting the engineering requirements for rapid underwater repair and high-strength bonding.

[0063] In a preferred embodiment of the underwater curing imidazoline epoxy resin curing agent of the present invention, after the curing agent and epoxy resin are mixed, the underwater contact angle is ≤65°, the interfacial water film replacement rate is ≥85%, the water absorption rate of the cured product is ≤0.8%, and the Shore D hardness is ≥75. These performance indicators demonstrate the excellent underwater performance of the curing agent: an underwater contact angle ≤65° indicates that the mixture of epoxy resin and curing agent has good underwater wetting ability and can effectively spread on the surface of a damp substrate; an interfacial water film replacement rate ≥85% indicates that the fluorinated component successfully displaces the physically adsorbed water film on the substrate surface, achieving direct contact between the epoxy resin and the substrate; a water absorption rate ≤0.8% indicates that the cured product has excellent water resistance and stable long-term immersion performance; and a Shore D hardness ≥75 indicates that the cured product has sufficient surface hardness and abrasion resistance.

[0064] The imidazoline epoxy resin curing agent for underwater curing of the present invention is particularly suitable for scenarios such as concrete structure repair in marine tidal zones, underwater steel structure corrosion protection, port and wharf repair, underwater bridge pier reinforcement, reservoir dam crack grouting, submarine pipeline repair, and offshore wind power foundation protection, realizing the integration of rapid underwater construction and long-term protection.

[0065] The following detailed description of the underwater curing imidazoline epoxy resin curing agent of the present invention, its preparation method, and its application are provided through specific embodiments.

[0066] The main raw materials used in the following examples were sourced from the following sources: Lauric acid: Aladdin Reagent Company, purity ≥99%; Myristic acid: Aladdin Reagent Company, purity ≥98%; Palmitic acid: Sinopharm Chemical Reagent Co., Ltd., analytical grade; Stearic acid: Sinopharm Chemical Reagent Co., Ltd., analytical grade; Oleic acid: Sinopharm Chemical Reagent Co., Ltd., chemically pure; Diethylenetriamine: BASF, purity ≥99%; Triethylenetetramine: BASF, purity ≥98%; Tetraethylenepentamine: BASF, purity ≥97%; Perfluorooctylpropionic acid: Sigma-Aldrich, purity ≥97%; Perfluorodecylacetic acid: Sigma-Aldrich, purity ≥95%; Polyetheramine (trade name Jeffamine D-230): Huntsman, amine value 390-420 mgKOH / g; Polyetheramine (trade name Jeffamine D-400): Huntsman, amine value 245-275 mgKOH / g; Polyetheramine (trade name Jeffamine) T-403: Huntsman Corporation, amine value 480-520 mg KOH / g; Polyetheramine (trade name Jeffamine ED-600): Huntsman Corporation, amine value 190-220 mg KOH / g; Bisphenol A type epoxy resin: Nan Ya Epoxy Resin Co., Ltd., model E-51, epoxy equivalent 185-192 g / eq; Bisphenol F type epoxy resin: Baling Petrochemical, model F-51, epoxy equivalent 165-175 g / eq; Trifunctional epoxy resin TDE-85: Toto Chemical Co., Ltd., Japan, epoxy equivalent 100-110 g / eq; KH-5 60 (γ-glycidoxypropyltrimethoxysilane): Nanjing Shuguang Chemical Group, purity ≥98%; KH-550 (γ-aminopropyltriethoxysilane): Nanjing Shuguang Chemical Group, purity ≥97%; KH-792 (N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane): Nanjing Shuguang Chemical Group, purity ≥96%; p-hydroxyanisole: Aladdin Reagent Co., Ltd., purity ≥99%; 2,6-di-tert-butyl-p-cresol (BHT): Sinopharm Chemical Reagent Co., Ltd., analytical grade; hydroquinone: Sinopharm Chemical Reagent Co., Ltd., analytical grade.

[0067] Example 1

[0068] The underwater curing imidazoline epoxy resin curing agent of this embodiment is prepared by weight of the following components: 40 parts imidazoline monomer, 5 parts fluorinated long-chain carboxylic acid, 10 parts polyetheramine, 5 parts polyfunctional epoxy compound, 1 part silane coupling agent, and 0.1 parts polymerization inhibitor.

[0069] The imidazoline monomer was prepared by the following steps: Step 1: 1 mol of lauric acid (C12 fatty acid) and 1.0 mol of diethylenetriamine were added to a reaction vessel, and the mixture was subjected to nitrogen protection and heated to 120°C for amidation reaction for 2 h; Step 2: The temperature was further increased to 180°C, and the mixture was subjected to cyclization reaction for 4 h, followed by vacuum dehydration to obtain the imidazoline monomer. This imidazoline monomer is a pale yellow transparent liquid with an amine value of 280-320 mg KOH / g and a viscosity (25°C) of 150-200 mg / g. It contains tertiary and secondary amine groups, and has both catalytic and curing functions.

[0070] The fluorinated long-chain carboxylic acid used is perfluorooctylpropionic acid, with an acid value of 80 mg KOH / g, and an appearance of a colorless to pale yellow liquid with a density of about 1.65 g / cm³.

[0071] The polyetheramine used is Jeffamine D-230, with an amine value of 390 mg KOH / g and a molecular weight of approximately 230. It is a colorless to pale yellow transparent liquid.

[0072] The multifunctional epoxy compound uses bisphenol A type epoxy resin (model E-51), with an epoxy equivalent of 185 g / eq, an epoxy value of 0.51 eq / 100 g, and a viscosity (25℃) of 11000-14000 mM. .

[0073] The silane coupling agent used is KH-560 (γ-glycidoxypropyltrimethoxysilane), with a purity ≥98% and an appearance of colorless and transparent liquid.

[0074] The polymerization inhibitor is p-hydroxyanisole, with a purity of ≥99%, and is a white to pale yellow powder.

[0075] The preparation method of the underwater curing imidazoline epoxy resin curing agent in this embodiment includes the following steps:

[0076] Step 1: Add 40 parts of imidazoline monomer to a reaction vessel equipped with a stirrer and thermometer, heat to 70°C, and add 5 parts of perfluorooctylpropionic acid at a rate of 10 drops / min under nitrogen protection. The addition is completed in 0.5 hours, and the reaction is maintained at this temperature for 1 hour.

[0077] Step 2: Add 10 parts of Jeffamine D-230 polyetheramine, heat to 90℃, and react for 1 hour;

[0078] Step 3: Cool down to 60℃, add 5 parts of bisphenol A epoxy resin in 3 batches (about 1.7 parts per batch), with an interval of 20 minutes between each batch, for a total reaction time of 2 hours;

[0079] Step 4: Add 1 part of KH-560 silane coupling agent and 0.1 part of p-hydroxyanisole, and continue stirring for 0.5 h;

[0080] Step 5: Vacuum degassing (vacuum degree -0.09MPa) for 20 minutes, and the material is discharged to obtain the imidazoline epoxy resin curing agent for underwater curing in this embodiment.

[0081] The curing agent is a pale yellow, transparent to semi-transparent viscous liquid with a viscosity (25℃) of 3500-4500 mM. It has an amine value of 180-220 mg KOH / g, a density of approximately 1.05 g / cm³, and a storage stability of ≥6 months at 25℃.

[0082] Example 2

[0083] The underwater curing imidazoline epoxy resin curing agent of this embodiment is prepared by weight of the following components: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor.

[0084] The imidazoline monomer was prepared by the following steps: Step 1: 1 mol of palmitic acid (C16 fatty acid) and 1.2 mol of triethylenetetramine were added to a reaction vessel, and the mixture was subjected to nitrogen protection and heated to 140℃ for amidation reaction for 3 h; Step 2: The temperature was further increased to 200℃, and the mixture was subjected to cyclization reaction for 6 h, followed by vacuum dehydration to obtain the imidazoline monomer. This imidazoline monomer is a yellow transparent liquid with an amine value of 300-340 mgKOH / g and a viscosity (25℃) of 200-280 mg / g. .

[0085] The fluorinated long-chain carboxylic acid used is perfluorodecylacetic acid, with an acid value of 120 mg KOH / g and an appearance of a pale yellow liquid.

[0086] The polyetheramine used is Jeffamine D-400, with an amine value of 250 mg KOH / g and a molecular weight of approximately 400. It is a colorless to pale yellow transparent liquid.

[0087] The multifunctional epoxy compound uses bisphenol F type epoxy resin (model F-51), with an epoxy equivalent of 170 g / eq, an epoxy value of 0.53 eq / 100 g, and a viscosity (25℃) of 3000-4000 mM. .

[0088] The silane coupling agent used is KH-550 (γ-aminopropyltriethoxysilane), with a purity ≥97% and an appearance of colorless to pale yellow transparent liquid.

[0089] The polymerization inhibitor used is 2,6-di-tert-butyl-p-cresol (BHT), with a purity of ≥99% and an appearance of white crystalline powder.

[0090] The preparation method of the underwater curing imidazoline epoxy resin curing agent in this embodiment includes the following steps:

[0091] Step 1: Add 55 parts of imidazoline monomer to the reaction vessel, heat to 80℃, and add 10 parts of perfluorodecylacetic acid at a rate of 12 drops / min under nitrogen protection. The addition is completed in 0.7h, and the reaction is maintained at this temperature for 1.5h.

[0092] Step 2: Add 17 parts of Jeffamine D-400 polyetheramine, heat to 100℃, and react for 2 hours;

[0093] Step 3: Cool down to 70℃, add 10 parts of bisphenol F epoxy resin in 3 batches (about 3.3 parts per batch), with an interval of 20 minutes between each batch, for a total reaction time of 3 hours;

[0094] Step 4: Add 3 parts of KH-550 silane coupling agent and 0.5 parts of BHT polymerization inhibitor, and continue stirring for 0.7 hours;

[0095] Step 5: Vacuum degassing (vacuum degree -0.09MPa) for 25 minutes, and the material is discharged to obtain the imidazoline epoxy resin curing agent for underwater curing in this embodiment.

[0096] The curing agent is a yellow, transparent to semi-transparent viscous liquid with a viscosity (25℃) of 4500-5500 mM. It has an amine value of 200-240 mg KOH / g, a density of approximately 1.08 g / cm³, and a storage stability period of ≥6 months at 25℃.

[0097] Example 3

[0098] The underwater curing imidazoline epoxy resin curing agent of this embodiment is prepared by weight of the following components: 70 parts imidazoline monomer, 15 parts fluorinated long-chain carboxylic acid, 25 parts polyetheramine, 15 parts polyfunctional epoxy compound, 5 parts silane coupling agent, and 1 part polymerization inhibitor.

[0099] The imidazoline monomer was prepared by the following steps: Step 1: 1 mol of stearic acid (C18 fatty acid) and 1.4 mol of tetraethylenepentamine were added to a reaction vessel, and the mixture was subjected to nitrogen protection and heated to 160℃ for amidation reaction for 4 h; Step 2: The temperature was further increased to 220℃, and the cyclization reaction was carried out for 8 h. The mixture was then dehydrated under vacuum to obtain the imidazoline monomer. This imidazoline monomer is an orange-yellow transparent liquid with an amine value of 320-360 mg KOH / g and a viscosity (25℃) of 280-350 mg / g. .

[0100] The fluorinated long-chain carboxylic acid used is perfluorododecylbutyric acid, with an acid value of 160 mg KOH / g and an appearance of pale yellow to yellow liquid.

[0101] The polyetheramine used is Jeffamine T-403 (trifunctional polyetheramine), with an amine value of 500 mg KOH / g, a molecular weight of approximately 440, and an appearance of a colorless to pale yellow transparent liquid.

[0102] The multifunctional epoxy compound uses trifunctional epoxy resin TDE-85, with an epoxy equivalent of 105 g / eq, an epoxy value of 0.86 eq / 100 g, and a viscosity (25℃) of 25000-35000 mM. .

[0103] The silane coupling agent used is KH-792 (N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane), with a purity ≥96% and an appearance of colorless to pale yellow transparent liquid.

[0104] The polymerization inhibitor is hydroquinone with a purity of ≥99% and an appearance of white to light gray crystalline powder.

[0105] The preparation method of the underwater curing imidazoline epoxy resin curing agent in this embodiment includes the following steps:

[0106] Step 1: Add 70 parts of imidazoline monomer to the reactor, heat to 90℃, and add 15 parts of perfluorododecylbutyric acid at a rate of 15 drops / min under nitrogen protection. The addition is completed in 1 hour, and the reaction is maintained at this temperature for 2 hours.

[0107] Step 2: Add 25 parts of Jeffamine T-403 polyetheramine, heat to 110℃, and react for 3 hours;

[0108] Step 3: Cool down to 80℃, add 15 parts of TDE-85 epoxy resin in 3 batches (5 parts per batch), with an interval of 20 minutes between each batch, for a total reaction time of 4 hours;

[0109] Step 4: Add 5 parts of KH-792 silane coupling agent and 1 part of hydroquinone, and continue stirring for 1 hour;

[0110] Step 5: Vacuum degassing (vacuum degree -0.09MPa) for 30 minutes, and the material is discharged to obtain the imidazoline epoxy resin curing agent for underwater curing in this embodiment.

[0111] The curing agent is an orange-yellow, semi-transparent, viscous liquid with a viscosity (25℃) of 6000-7500 mM. It has an amine value of 240-280 mg KOH / g, a density of approximately 1.12 g / cm³, and a storage stability of ≥6 months at 25℃.

[0112] Example 4

[0113] The underwater curing imidazoline epoxy resin curing agent of this embodiment is prepared by weight of the following components: 50 parts imidazoline monomer, 8 parts fluorinated long-chain carboxylic acid, 15 parts polyetheramine, 8 parts polyfunctional epoxy compound, 2 parts silane coupling agent, and 0.3 parts polymerization inhibitor.

[0114] The imidazoline monomer was prepared by the following steps: Step 1: 1 mol of oleic acid (C18 unsaturated fatty acid) and 1.1 mol of diethylenetriamine were added to a reaction vessel, and the mixture was subjected to nitrogen protection and heated to 130℃ for amidation reaction for 2.5 h; Step 2: The temperature was further increased to 190℃, and the mixture was subjected to cyclization reaction for 5 h, followed by vacuum dehydration to obtain the imidazoline monomer. This imidazoline monomer is a yellow transparent liquid with an amine value of 290-330 mg KOH / g and a viscosity (25℃) of 180-230 mM. .

[0115] The fluorinated long-chain carboxylic acid used is perfluorooctylpropionic acid, with an acid value of 100 mg KOH / g.

[0116] The polyetheramine used is a mixture of Jeffamine D-230 and D-400 (mass ratio 1:1), with a combined amine value of approximately 320 mg KOH / g.

[0117] The multifunctional epoxy compound is a mixture of bisphenol A type epoxy resin (model E-51) and bisphenol F type epoxy resin (model F-51) (mass ratio 1:1), with a total epoxy equivalent of approximately 178 g / eq.

[0118] The silane coupling agent used is a mixture of KH-560 and KH-550 (mass ratio 1:1).

[0119] The polymerization inhibitor used is p-hydroxyanisole.

[0120] The preparation method of the underwater curing imidazoline epoxy resin curing agent in this embodiment is the same as that in Example 2, except that the amounts of each component are adjusted according to this embodiment. The curing agent is a yellow transparent liquid with a viscosity (25°C) of 4000-5000 mM. It has an amine value of 190-230 mg KOH / g and a density of approximately 1.06 g / cm³.

[0121] Example 5

[0122] The underwater curing imidazoline epoxy resin curing agent of this embodiment is prepared from the following components by weight: 45 parts imidazoline monomer, 7 parts fluorinated long-chain carboxylic acid, 13 parts polyetheramine, 7 parts polyfunctional epoxy compound, 1.5 parts silane coupling agent, and 0.2 parts polymerization inhibitor.

[0123] The imidazoline monomer was prepared by the following steps: Step 1: 1 mol of myristic acid (C14 fatty acid) and 1.15 mol of triethylenetetramine were added to the reaction vessel, nitrogen gas was purged, and the temperature was raised to 135℃ for amidation reaction for 2.8 h; Step 2: The temperature was raised to 195℃ and cyclization reaction was carried out for 5.5 h, followed by vacuum dehydration to obtain the imidazoline monomer.

[0124] The fluorinated long-chain carboxylic acid used is perfluorodecylacetic acid, with an acid value of 110 mg KOH / g.

[0125] The polyetheramine used is Jeffamine ED-600, with an amine value of 210 mg KOH / g and a molecular weight of approximately 600.

[0126] The multifunctional epoxy compound uses bisphenol A type epoxy resin (epoxy equivalent 190 g / eq).

[0127] KH-560 was used as the silane coupling agent.

[0128] BHT is used as the polymerization inhibitor.

[0129] The preparation method of the underwater curing imidazoline epoxy resin curing agent of this embodiment includes the following steps: Step 1: Add imidazoline monomer to the reaction vessel, heat to 75°C, add fluorinated long-chain carboxylic acid dropwise over 0.6 hours, and maintain the temperature for 1.3 hours; Step 2: Add polyetheramine, heat to 95°C, and react for 1.5 hours; Step 3: Cool to 65°C, add epoxy compound in 3 batches, with a total reaction time of 2.5 hours; Step 4: Add silane coupling agent and polymerization inhibitor, and stir for 0.6 hours; Step 5: Vacuum degassing for 22 minutes.

[0130] The curing agent is a pale yellow transparent liquid with a viscosity (25℃) of 3800-4800 mM. The amine value is 185-225 mg KOH / g.

[0131] Example 6

[0132] The underwater curing imidazoline epoxy resin curing agent of this embodiment is prepared from the following components by weight: 60 parts imidazoline monomer, 12 parts fluorinated long-chain carboxylic acid, 20 parts polyetheramine, 12 parts polyfunctional epoxy compound, 4 parts silane coupling agent, and 0.7 parts polymerization inhibitor.

[0133] The imidazoline monomer was prepared by the following steps: Step 1: 1 mol of a mixture of palmitic acid (C16 fatty acid) and stearic acid (C18 fatty acid) (mass ratio 1:1) and 1.3 mol of tetraethylenepentamine were added to a reaction vessel, nitrogen gas was purged, and the temperature was raised to 150℃ for amidation reaction for 3.5 h; Step 2: The temperature was further raised to 210℃, cyclization reaction was carried out for 7 h, and dehydration was performed under vacuum to obtain the imidazoline monomer.

[0134] The fluorinated long-chain carboxylic acid is a mixture of perfluorooctylpropionic acid and perfluorodecylacetic acid (mass ratio 1:1), with a combined acid value of approximately 140 mg KOH / g.

[0135] The polyetheramine used is a mixture of Jeffamine D-400 and T-403 (mass ratio 2:1), with a combined amine value of approximately 330 mg KOH / g.

[0136] The multifunctional epoxy compound is a mixture of bisphenol F type epoxy resin and TDE-85 (mass ratio 3:1), with a total epoxy equivalent of approximately 150 g / eq.

[0137] The silane coupling agent used is a mixture of KH-550 and KH-792 (mass ratio 1:1).

[0138] The polymerization inhibitor is a mixture of BHT and p-hydroxyanisole (mass ratio 1:1).

[0139] The preparation method of the underwater curing imidazoline epoxy resin curing agent of this embodiment includes the following steps: Step 1: Add imidazoline monomer to the reaction vessel, heat to 85°C, add fluorinated long-chain carboxylic acid dropwise over 0.8 hours, and maintain the temperature for 1.7 hours; Step 2: Add polyetheramine, heat to 105°C, and react for 2.5 hours; Step 3: Cool to 75°C, add epoxy compound in 3 batches, with a total reaction time of 3.5 hours; Step 4: Add silane coupling agent and polymerization inhibitor, and stir for 0.8 hours; Step 5: Vacuum degassing for 28 minutes.

[0140] The curing agent is a yellow, semi-transparent, viscous liquid with a viscosity (25℃) of 5200-6500 mM. It has an amine value of 220-260 mg KOH / g and a density of approximately 1.10 g / cm³.

[0141] Example 7

[0142] The only difference between this embodiment and Example 2 is the preparation conditions of the imidazoline monomer: the amidation reaction temperature in step 1 is 145℃, and the reaction time is 3.2 h; the cyclization reaction temperature in step 2 is 205℃, and the reaction time is 6.5 h. The resulting imidazoline monomer has an amine value of 310-350 mg KOH / g and a viscosity (25℃) of 220-260 mM. The catalytic activity is slightly higher than that in Example 2. The remaining components and preparation methods are the same as in Example 2.

[0143] Example 8

[0144] The only difference between this embodiment and Example 2 is the acid value of the fluorinated long-chain carboxylic acid: perfluorooctylpropionic acid with an acid value of 90 mg KOH / g was used. The underwater contact angle of the resulting curing agent mixed with epoxy resin was 62°, and the interfacial water film replacement rate was 87%. The remaining components and preparation methods were the same as in Example 2.

[0145] Example 9

[0146] The only difference between this embodiment and Example 2 is the choice of polyetheramine: Jeffamine ED-600 with an amine value of 210 mg KOH / g was used. The toughness and impact resistance of the cured product obtained by this embodiment are superior to those of Example 2, with a water absorption rate of 0.6% and a Shore D hardness of 73. The remaining components and preparation methods are the same as in Example 2.

[0147] Example 10

[0148] The only difference between this embodiment and Example 2 is the choice of multifunctional epoxy compound: a bisphenol A type epoxy resin with an epoxy equivalent of 240 g / eq is used. The resulting curing agent has a slightly lower viscosity, ranging from 4200 to 5200 m. It exhibits good compatibility with epoxy resin. The remaining components and preparation method are the same as in Example 2.

[0149] Example 11

[0150] The only difference between this embodiment and Example 2 is the choice of silane coupling agent: a mixture of KH-560, KH-550, and KH-792 (mass ratio 1:1:1) was used. The underwater bonding strength of the cured product reached 24 MPa, and the interfacial chemical bonding ability was significantly enhanced. The remaining components and preparation methods are the same as in Example 2.

[0151] Example 12

[0152] The only difference between this embodiment and Example 2 is the choice of polymerization inhibitor: a mixture of p-hydroxyanisole and BHT (mass ratio 1:1) is used, with a total dosage of 0.5 parts. The resulting curing agent exhibits excellent storage stability, with a viscosity change of <5% and a curing activity retention rate of >95% after 12 months of storage at 25°C. The remaining components and preparation methods are the same as in Example 2.

[0153] Comparative Example 1

[0154] The curing agent of this comparative example is prepared from the following components by weight: 30 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that the amount of imidazoline monomer is reduced to 30 parts (lower than the range of 40-70 parts in the claims).

[0155] Comparative Example 2

[0156] The curing agent in this comparative example is prepared from the following components by weight: 85 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that the amount of imidazoline monomer is increased to 85 parts (higher than 40-70 parts).

[0157] Comparative Example 3

[0158] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 2 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation methods are the same as in Example 2, except that the amount of fluorinated long-chain carboxylic acid is reduced to 2 parts (less than 5-15 parts).

[0159] Comparative Example 4

[0160] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 20 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation methods are the same as in Example 2, except that the amount of fluorinated long-chain carboxylic acid is increased to 20 parts (higher than 5-15 parts).

[0161] Comparative Example 5

[0162] The curing agent in this comparative example is prepared from the following components by weight: 65 parts imidazoline monomer, 17 parts polyetheramine, 10 parts multifunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that fluorinated long-chain carboxylic acids are completely omitted.

[0163] Comparative Example 6

[0164] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 5 parts polyetheramine, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that the amount of polyetheramine is reduced to 5 parts (less than 10-25 parts).

[0165] Comparative Example 7

[0166] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 35 parts polyetheramine, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that the amount of polyetheramine is increased to 35 parts (higher than 10-25 parts).

[0167] Comparative Example 8

[0168] The curing agent in this comparative example is prepared from the following components by weight: 72 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that polyetheramine is completely omitted.

[0169] Comparative Example 9

[0170] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 2 parts multifunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that the amount of multifunctional epoxy compound is reduced to 2 parts (less than 5-15 parts).

[0171] Comparative Example 10

[0172] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 22 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that the amount of polyfunctional epoxy compound is increased to 22 parts (higher than 5-15 parts).

[0173] Comparative Example 11

[0174] The curing agent in this comparative example is prepared from the following components by weight: 65 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that multifunctional epoxy compounds are completely omitted.

[0175] Comparative Example 12

[0176] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, 0.3 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation methods are the same as in Example 2, except that the amount of silane coupling agent is reduced to 0.3 parts (less than 1-5 parts).

[0177] Comparative Example 13

[0178] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, 8 parts silane coupling agent, and 0.5 parts polymerization inhibitor. The components and preparation methods are the same as in Example 2, except that the amount of silane coupling agent is increased to 8 parts (higher than 1-5 parts).

[0179] Comparative Example 14

[0180] The curing agent in this comparative example is prepared from the following components by weight: 58 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, and 0.5 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that silane coupling agents are completely omitted.

[0181] Comparative Example 15

[0182] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, 3 parts silane coupling agent, and 2 parts polymerization inhibitor. The components and preparation method are the same as in Example 2, except that the amount of polymerization inhibitor is increased to 2 parts (higher than 0.1-1 parts).

[0183] Comparative Example 16

[0184] The curing agent in this comparative example is prepared from the following components by weight: 55 parts imidazoline monomer, 10 parts fluorinated long-chain carboxylic acid, 17 parts polyetheramine, 10 parts polyfunctional epoxy compound, and 3 parts silane coupling agent. The components and preparation method are the same as in Example 2, except that no polymerization inhibitor is used.

[0185] Comparative Example 17

[0186] The only difference between this comparative example and Example 2 is the preparation method of the imidazoline monomer: in step 1, the amount of polyethylenepolyamine is reduced to 0.8 mol (below 1.0-1.4 mol), the amidation reaction temperature is 100℃ (below 120-160℃), and the reaction time is 1.5 h; in step 2, the cyclization reaction temperature is 160℃ (below 180-220℃), and the reaction time is 3 h. The resulting imidazoline monomer has an amine value of 180-210 mgKOH / g, a low cyclization rate, and a significantly decreased catalytic activity.

[0187] Comparative Example 18

[0188] The only difference between this comparative example and Example 2 is the acid value of the fluorinated long-chain carboxylic acid: perfluorooctylpropionic acid with an acid value of 60 mg KOH / g (lower than 80-160 mg KOH / g) was used. The underwater contact angle of the resulting curing agent mixed with epoxy resin was 70°, and the interfacial water film replacement rate was only 68%.

[0189] Comparative Example 19

[0190] The only difference between this comparative example and Example 2 is the choice of polyetheramine: a polyetheramine with an amine value of 180 mg KOH / g was used (lower than the 200-600 mg KOH / g range in the claims). The resulting curing agent has a slow curing speed, with an initial setting time of >6 hours underwater, low crosslinking density of the cured product, and a shear bond strength of only 13 MPa.

[0191] Comparative Example 20

[0192] The only difference between this comparative example and Example 2 is the choice of multifunctional epoxy compound: an epoxy resin with an epoxy equivalent of 280 g / eq (higher than 100-250 g / eq) was used. The resulting curing agent had insufficient pre-chain extension reaction, poor compatibility with epoxy resin, phase separation during mixing, and unstable properties of the cured product.

[0193] Experimental Example

[0194] The curing agents of the above embodiments and comparative examples were subjected to performance tests. The curing agents were mixed with epoxy resin and cured in an underwater environment. The curing time, underwater bond strength, water absorption rate of the cured product, and Shore D hardness were tested.

[0195] Test method:

[0196] Basic performance test of curing agent:

[0197] Viscosity measurement: The NDJ-8S rotational viscometer was used with rotor #2, rotation speed 60 rpm, and temperature 25℃, according to GB / T2794-2013 standard.

[0198] Amine value determination: The acid-base titration method was used, and the determination was performed according to GB / T7384-2007 standard. Approximately 0.5 g of curing agent sample was accurately weighed into a 250 mL Erlenmeyer flask, dissolved in 50 mL of isopropanol-water mixed solvent (volume ratio 3:1), and 2-3 drops of bromocresol green-methyl red mixed indicator were added. The solution was titrated with 0.1 mol / L hydrochloric acid standard solution until the solution changed from green to purple-red. The volume of hydrochloric acid consumed was recorded, and the amine value was calculated using the formula.

[0199] Storage stability test: The curing agent sample was placed in a sealed glass bottle and stored at 25℃ and 50℃ respectively. The viscosity and amine value changes were measured periodically to evaluate the storage stability. After 6 or 12 months of storage at 25℃, a viscosity change of <10% and an amine value retention rate of >90% were considered to be satisfactory for storage stability.

[0200] Performance testing of the curing agent and epoxy resin mixture:

[0201] Bisphenol A type epoxy resin (model E-51, epoxy equivalent 185-190 g / eq, Nan Ya Epoxy Resin Co., Ltd.) was used as the main resin, and the curing agent was added at 15% of the epoxy resin mass. The epoxy resin and curing agent were thoroughly mixed and stirred at room temperature for 5 minutes, and subsequent tests were carried out immediately.

[0202] Underwater contact angle test: A JC2000D3 contact angle measuring instrument was used. An epoxy resin-curing agent mixture was dropped onto the surface of a glass substrate underwater (5cm depth, 20±2℃). The morphology of the droplet underwater was photographed using the shadow method, and the contact angle was determined using image analysis software. Five points were tested for each sample, and the average value was taken.

[0203] Interfacial water film replacement rate test: A self-made apparatus was used for determination. A 50mm × 50mm concrete specimen was immersed in water for 48 hours to saturate its surface with water. Then, an epoxy resin-curing agent mixture was coated onto the underwater concrete surface (coating thickness approximately 1mm). After curing for 24 hours, the specimen was removed and dried in a 50℃ vacuum oven to constant weight. The interfacial microstructure was observed using scanning electron microscopy (SEM), and the water molecule content at the interface was determined using energy dispersive spectroscopy (EDS). The water film replacement rate was calculated as follows: Water film replacement rate = (Number of water molecules at the interface before replacement - Number of water molecules at the interface after coating) / Number of water molecules at the interface before replacement × 100%.

[0204] Underwater curing performance test:

[0205] Curing time determination: A modified Vicat needle method was used. Concrete specimens (100mm × 100mm × 50mm) were immersed in water for 48 hours to saturate the surface with water. Then, an epoxy resin-hardener mixture (coating thickness 2mm) was coated underwater (water depth 10cm, water temperature 20±2℃). A modified Vicat needle (1mm diameter, 300g weight) was vertically inserted into the sample surface underwater at fixed time intervals (30min initially, 15min later). The time when the needle tip could not penetrate more than 2mm into the sample surface was recorded as the initial setting time; the time when the needle tip could not penetrate the sample surface at all was recorded as the final setting time. Each sample was tested three times, and the average value was taken.

[0206] Underwater shear bond strength determination: The determination was performed according to a combined method of GB / T 50728-2011 "Technical Specification for Safety Appraisal of Strengthening Materials for Engineering Structures" and ASTM C 882 standard. Concrete specimens (strength grade C30) with dimensions of 40mm × 40mm × 160mm were prepared, cut in half lengthwise, and the cut surfaces were ground and soaked in water for 48 hours to saturate them. An epoxy resin-curing agent mixture was uniformly coated (coating thickness 2 ± 0.2mm) onto the cut surfaces of the two halves of the specimen underwater (water depth 10cm, water temperature 20±2℃). The halves were immediately butted together and fixed with clamps, applying a pressure of 0.05MPa. After underwater curing for 24 hours, the specimens were removed and continued to cure in air for 7 days. Shear strength was tested using a WDW-100 universal testing machine at a loading rate of 2mm / min. The maximum load at failure was recorded, and the shear bond strength was calculated. Six specimens were tested in each group, and the maximum and minimum values ​​were removed before taking the average value. For some samples, additional bonding strength tests were conducted after 28 days and 90 days of long-term underwater immersion.

[0207] Cured product performance testing:

[0208] Water absorption rate determination of cured product: Determined according to GB / T 1034-2008 standard. The epoxy resin-curing agent mixture was poured into a 50mm×50mm×3mm mold and cured underwater (10cm depth, 20±2℃) for 24 hours. The product was then demolded and cured further at 23℃ and 50%RH for 7 days. The sample was dried to constant weight (m1) in a 50℃ vacuum oven, then immersed in distilled water for 24 hours. After removal, surface moisture was absorbed with filter paper, and the sample was immediately weighed (m2). Water absorption rate = (m2-m1) / m1×100%. Five samples were tested in each group, and the average value was taken.

[0209] Shore D hardness test: The test was conducted according to GB / T 2411-2008 standard. Using the above-mentioned cured sample, an XHS-A type Shore hardness tester (Type D) was used. At least 5 points were tested on the sample surface. Pressure was maintained at each point for 15 seconds, and the reading was taken as the average value. The sample thickness should be no less than 6 mm, and the test points should be ≥12 mm from the edge of the sample.

[0210] Crosslinking density determination of cured product: The swelling method was used. The cured product sample (1g) was immersed in toluene for 24 hours. After removal, the surface solvent was absorbed with filter paper, and the mass after swelling (m_s) was weighed. The sample was then dried in a vacuum oven to constant weight, and the dried mass (m_d) was weighed. The crosslinking density was calculated according to the Flory-Rehner equation.

[0211] Test results:

[0212] The test results are shown in Tables 1 and 2.

[0213] Table 1. Basic and application properties of the curing agent in the examples.

[0214]

[0215] Table 2 Comparative Curing Agent Performance and Comparison with Example 2

[0216]

[0217] Table 3. Performance of Comparative Examples 9-16 and Comparison with Example 2

[0218]

[0219] Table 4. Performance of Comparative Examples 17-20 and Comparison with Example 2

[0220]

[0221] From Tables 1, 2, 3, and 4, we can see that:

[0222] The imidazoline epoxy resin curing agents used for underwater curing in Examples 1-6 all exhibited excellent overall performance. They had moderate viscosity (3850-6850 μL). It is easy to construct and operate; it has good storage stability, and its performance indicators remain stable after 6 months of storage at 25℃; it has a low underwater contact angle (55-63°) and a high interfacial water film replacement rate (86-92%), indicating excellent underwater wetting and interfacial water film repulsion capabilities; it has a short initial setting time (2.8-3.8h) and a moderate final setting time (18-22h), meeting the requirements for rapid underwater curing; it has a high underwater shear bond strength of 18.5-23.2MPa after 7 days, far exceeding the engineering requirement of ≥15MPa. In some examples, the underwater shear bond strength still remains at a high level of 19.5-22.0MPa after 28 days, indicating excellent long-term durability; the water absorption rate of the cured product is low (0.58-0.75%), far lower than the 1.5-3% of traditional curing agents; and the Shore D hardness is moderate (76-82), indicating that the cured product has good surface hardness and wear resistance. Example 3 shows that the dosage of key components such as imidazoline monomer, fluorinated carboxylic acid, and polyetheramine is optimized, resulting in the best performance indicators. In particular, the underwater shear bond strength reaches 23.2 MPa, and the water absorption rate is only 0.58%, representing the optimal performance level of the present invention.

[0223] In Comparative Example 1, the amount of imidazoline monomer was too low (30 parts, below the range of 40-70 parts), resulting in insufficient catalytic active sites. The initial setting time was prolonged to 5.8 h, and the underwater shear bond strength was only 13.2 MPa, far lower than the 20.8 MPa of Example 2, a decrease of 37%. At the same time, the water absorption rate of the cured product increased to 0.92%, and the Shore D hardness decreased to 72, indicating insufficient curing and low crosslinking density.

[0224] Comparative Example 2 showed a significant increase in the viscosity of the curing agent to 8950 mg / L due to excessively high imidazoline monomer content (85 parts, exceeding the 40-70 parts range). (Example 2 is 4980m) The workability deteriorated, and the hardener's storage stability was substandard. After being stored at 25°C for 3 months, the viscosity increased by more than 15%, and pre-gelling occurred. Although the initial setting time was shortened to 2.5 hours, the cured product was too rigid, with a Shore D hardness as high as 85, and lacked toughness. It was prone to cracking at stress concentration points, resulting in poor performance in practical applications.

[0225] In Comparative Example 3, due to the excessively low amount of fluorinated long-chain carboxylic acid (2 parts, below the range of 5-15 parts), the hydrophobic component was severely insufficient, resulting in an underwater contact angle of 72° (compared to 58° in Example 2) and a decrease in the interfacial water film replacement rate to 68% (compared to 89% in Example 2). This made it difficult for the epoxy resin to effectively wet the underwater substrate surface, and the curing agent was blocked by the water film, extending the initial setting time to 4.5 hours. The underwater shear bond strength was only 15.8 MPa, a decrease of 24%. The water absorption rate of the cured product increased to 0.95%, indicating poor long-term water resistance.

[0226] In Comparative Example 4, due to the excessive amount of fluorinated long-chain carboxylic acid (20 parts, exceeding the range of 5-15 parts), although the underwater contact angle decreased to 48° and the interfacial water film replacement rate increased to 95%, the excessive fluorinated carboxylic acid neutralized too many imidazoline basic sites, significantly reducing catalytic activity and prolonging the initial setting time to 4.2 hours. More importantly, the excessive fluorocarbon chain formed an excessively thick hydrophobic layer at the interface, which hindered the chemical bonding between the epoxy resin and the substrate, resulting in an underwater shear bond strength of only 16.2 MPa, which was only 78% of that in Example 2. Furthermore, the cost of fluorinated raw materials is high, and excessive use is not economically viable.

[0227] Comparative Example 5 completely omits fluorinated long-chain carboxylic acids, lacking hydrophobic modification and interfacial water film replacement capabilities. Its underwater contact angle reaches 78°, but the interfacial water film replacement rate is only 58%, far lower than the 89% of Example 2. The epoxy resin struggles to spread on the underwater substrate surface, the active components of the curing agent are blocked by the water film, the initial setting time is extended to 6.5 hours, and the underwater shear bond strength is only 12.5 MPa, a decrease of 40%, completely failing to meet engineering application requirements. The cured product has a water absorption rate as high as 1.15%, and its performance deteriorates significantly after long-term immersion in water.

[0228] Comparative Example 6, due to excessively low polyetheramine content (5 parts, below the 10-25 part range), suffered from a severe deficiency of flexible segments, resulting in poor toughness of the cured product. Although the Shore D hardness reached 82, it exhibited high brittleness and was prone to cracking under water flow impact and temperature cycling. The underwater shear bond strength decreased to 17.8 MPa, and the water absorption rate of the cured product increased to 0.85%. Furthermore, insufficient polyetheramine led to decreased compatibility between the curing agent and epoxy resin, resulting in uneven dispersion during mixing and affecting the uniformity of curing.

[0229] Comparative Example 7, due to excessive polyetheramine content (35 parts, exceeding the 10-25 part range), had too many flexible segments, resulting in a significant decrease in the crosslinking density of the cured product. The Shore D hardness was only 68, indicating an overly soft surface and poor abrasion resistance. Although the initial setting time was shortened to 2.8 hours, the mechanical strength of the cured product was insufficient, with an underwater shear bond strength of only 14.5 MPa, a decrease of 30%. The water absorption rate of the cured product increased to 1.05%. Due to the strong hydrophilicity of the polyether segments, severe swelling and poor dimensional stability occurred after long-term immersion in water. Furthermore, the excessive polyetheramine caused a significant decrease in the viscosity of the curing agent to 3120 m³. It tends to flow during underwater construction, making it difficult to form an effective coating on vertical surfaces.

[0230] Comparative Example 8, which completely omits polyetheramine and lacks flexible segments, has a cured product crosslinking network composed entirely of the rigid structure of imidazoline monomers. It exhibits a Shore D hardness of 88, demonstrating extreme brittleness and a tendency to fracture easily at stress concentration points. Although the initial setting time was reduced to 4.8 hours, the underwater shear bond strength was only 15.2 MPa, a decrease of 27%. Furthermore, the bond layer was prone to cracking and detachment during long-term underwater immersion and temperature cycling, exhibiting extremely poor durability. The cured product had a water absorption rate as high as 1.28%, 1.9 times that of Example 2.

[0231] In Comparative Example 9, due to the excessively low amount of multifunctional epoxy compound (2 parts, below the 5-15 part range), the pre-chain extension reaction was insufficient, resulting in poor compatibility between the curing agent and epoxy resin. This led to partial phase separation during mixing and uneven curing. The initial setting time was extended to 3.8 hours, and the underwater shear bond strength decreased to 17.2 MPa. The cured product exhibited low crosslinking density, an increased water absorption rate to 0.88%, and a decrease in Shore D hardness to 75.

[0232] Comparative Example 10 suffered from excessive use of multifunctional epoxy compound (22 parts, exceeding the range of 5-15 parts), resulting in excessive pre-chain extension reaction and a significant increase in curing agent viscosity to 9850 m. It approaches a gel state and exhibits poor storage stability, gelling after two months of storage at 25°C. Although the cured product has a high crosslinking density and a Shore D hardness of 86, it is too rigid and lacks toughness. Its workability is extremely poor, making mixing with epoxy resin difficult, and its underwater shear bond strength drops to 19.5 MPa.

[0233] Comparative Example 11 completely lacked multifunctional epoxy compounds, thus missing the pre-chain extended structure. The chemical compatibility between the curing agent and epoxy resin was poor, resulting in uneven dispersion during mixing. Some curing agent components (especially imidazoline monomers and fluorinated carboxylic acids) were easily dissolved and lost in the underwater environment, leading to incomplete curing. Storage stability was unsatisfactory, and the curing agent components were prone to stratification. The initial setting time was extended to 4.2 hours, and the underwater shear bond strength was only 16.8 MPa, a decrease of 19%. The water absorption rate of the cured product increased to 0.95%, indicating unstable long-term performance.

[0234] In Comparative Example 12, due to the excessively low amount of silane coupling agent (0.3 parts, below the 1-5 parts range), the interfacial chemical bonding sites were severely insufficient. The curing agent and the inorganic substrate mainly relied on physical adsorption and mechanical anchoring, with extremely weak chemical bonding. The underwater shear bond strength dropped significantly to 14.5 MPa, only 70% of that in Example 2. During long-term underwater immersion, water molecules easily penetrated along the interface, leading to bond failure and poor durability. The water absorption rate of the cured product was 0.72%, which, although not very high, easily accumulated water at the interface, forming a weak interfacial layer.

[0235] In Comparative Example 13, due to excessive use of silane coupling agent (8 parts, exceeding the 1-5 part range), excess silane accumulated at the interface, resulting in excessive release of hydrolysis products (methanol or ethanol), generating numerous bubbles at the interface and forming microscopic defects. The excessive silicon-oxygen network led to an overly rigid interface layer, severe stress concentration, and susceptibility to cracking under temperature changes and external forces. The viscosity of the curing agent increased significantly to 8250 μL. The workability deteriorates. Although the Shore D hardness reaches 82, the underwater shear bond strength drops to 18.2 MPa, resulting in poor long-term durability.

[0236] Comparative Example 14 did not use any silane coupling agent, thus lacking the chemical bridging mechanism at the organic-inorganic interface. The curing agent could not form Si-OM chemical bonds with inorganic substrates such as concrete and steel, relying solely on physical adsorption and mechanical anchoring. The underwater shear bond strength dropped significantly to 13.8 MPa, only 66% of that in Example 2, one of the lowest values ​​among all comparative examples. In an underwater environment, water molecules easily penetrate the interface, leading to bond failure. The water absorption rate of the cured material increased to 0.85%, and the bond strength significantly decreased after long-term immersion, rendering it extremely impractical.

[0237] Comparative Example 15, due to excessive use of polymerization inhibitor (2 parts, exceeding the range of 0.1-1 parts), resulted in a significant decrease in curing speed due to over-inhibition. The initial setting time was extended to 6.8 hours, and the final setting time exceeded 36 hours, completely failing to meet the requirements for rapid underwater curing. Even after curing was completed, the residual excess polymerization inhibitor still inhibited the curing reaction, leading to incomplete curing. The underwater shear bond strength was only 15.5 MPa, a decrease of 25%. Storage stability was also unsatisfactory. Because the excessive phenolic polymerization inhibitor formed excessively strong hydrogen bonds with the imidazoline monomer, the viscosity of the curing agent increased with increasing storage time, and the fluidity deteriorated.

[0238] Comparative Example 16, which used no polymerization inhibitor, exhibited extremely poor storage stability of the curing agent. After one month of storage at 25°C, the viscosity increased by more than 20%, partial gelation occurred after three months, and complete gelation occurred after six months, rendering it unusable. Although the initial setting time was shortened to 2.5 hours, resulting in rapid curing, pre-reactions easily occurred during storage, transportation, and use, leading to a short pot life (<3 months) and poor practicality. While the underwater shear bond strength reached 19.2 MPa, batch-to-batch performance was unstable, making quality control difficult.

[0239] Comparative Example 17 suffered from a severe deviation in the imidazoline monomer preparation process (polyethylene polyamine dosage was 0.8 mol lower than the 1.0-1.4 mol range, amidation temperature was 100℃ lower than the 120-160℃ range, and cyclization temperature was 160℃ lower than the 180-220℃ range), resulting in incomplete amidation and insufficient cyclization. The imidazoline ring formation rate was low, and the product contained a large amount of unreacted fatty acids and linear amides. The resulting imidazoline monomer had an amine value of only 195 mgKOH / g, far below the normal value (280-360 mgKOH / g), indicating severely insufficient catalytic activity. The curing agent exhibited poor storage stability and was prone to oxidation and deterioration. The initial setting time was extended to 4.8 h, and the underwater shear bond strength was only 14.8 MPa, a decrease of 29%. The interfacial water film replacement rate was only 72%, the water absorption rate of the cured product increased to 0.92%, and the Shore D hardness decreased to 70, indicating comprehensive deterioration in all properties.

[0240] Comparative Example 18, due to its fluorinated long-chain carboxylic acid value of 60 mgKOH / g (below the range of 80-160 mgKOH / g), had insufficient carboxyl content and weak ionic bonding ability with imidazoline monomers. This resulted in poor dispersion stability of the fluorinated component in the curing agent system, leading to easy delamination. The underwater contact angle increased to 70°, the interfacial water film replacement rate decreased to 68%, and the hydrophobic barrier layer was incomplete. The initial setting time was prolonged to 4.2 h, and the underwater shear bond strength decreased to 16.5 MPa, a decrease of 21%. The water absorption rate of the cured product increased to 0.88%, indicating poor long-term water resistance.

[0241] Comparative Example 19, with a polyetheramine amine value of 180 mg KOH / g (below the 200-600 mg KOH / g range), had insufficient amine content, resulting in fewer active sites participating in the curing reaction and a slow curing speed. The initial setting time was extended to 6.5 h, the longest among all comparative examples. The cured product had low crosslinking density, with an underwater shear bond strength of only 13.2 MPa, a decrease of 37%, the lowest among all comparative examples. The Shore D hardness decreased to 72, indicating that the cured product was too soft and lacked strength. The water absorption rate of the cured product increased to 0.95%, resulting in poor long-term performance.

[0242] Comparative Example 20, due to its multifunctional epoxy compound having an epoxy equivalent of 280 g / eq (higher than the 100-250 g / eq range), had an excessively low epoxy group density, resulting in insufficient pre-chain extension reaction and poor compatibility between the curing agent and epoxy resin. Significant phase separation occurred during mixing, making it difficult for the curing agent components to disperse uniformly in the epoxy resin, leading to uneven curing—some areas were fully cured while others were under-cured. Storage stability was unsatisfactory, with the curing agent prone to stratification and precipitation. The initial setting time was 3.8 h, and the underwater shear bond strength decreased to 17.5 MPa, a decrease of 16%. The water absorption rate of the cured product increased to 0.85%, and batch-to-batch performance was unstable.

[0243] In summary, the underwater curing imidazoline epoxy resin curing agent of the present invention achieves an optimal balance of catalytic activity, hydrophobic properties, flexibility, compatibility, interfacial bonding ability, and storage stability by precisely controlling the proportions of imidazoline monomer (40-70 parts), fluorinated long-chain carboxylic acid (5-15 parts), polyetheramine (10-25 parts), multifunctional epoxy compound (5-15 parts), silane coupling agent (1-5 parts), and polymerization inhibitor (0.1-1 parts), as well as strictly controlling the preparation process parameters of imidazoline monomer (amidation 120-160℃, 2-4h, cyclization 180-220℃, 4-8h) and the preparation process conditions of curing agent. When mixed with epoxy resin, it exhibits excellent wetting and spreading ability (underwater contact angle ≤65°), interfacial water film displacement ability (displacement rate ≥85%), rapid curing performance (initial setting ≤4h, final setting ≤24h), high-strength adhesion (7-day underwater shear bond strength ≥18MPa, up to 23.2MPa), and excellent water resistance (water absorption ≤0.8%) in underwater environments, fully meeting the requirements of applications such as underwater repair, tidal zone coating, and marine structure grouting. Comparative test results clearly demonstrate that exceeding the appropriate range of component dosage or the absence of key components will lead to significant deterioration of the curing agent's performance, failing to meet the needs of underwater engineering applications.

[0244] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An imidazoline epoxy resin curing agent, characterized in that: It is prepared from the following weight fractions: 40-70 parts imidazoline monomer, 5-15 parts fluorinated long-chain carboxylic acid, 10-25 parts polyetheramine, 5-15 parts multifunctional epoxy compound, 1-5 parts silane coupling agent and 0.1-1 parts polymerization inhibitor; The imidazoline monomer is prepared by the following method: Step 1: Add 1 mol C 12 -C 18 Fatty acids and 1.0-1.4 mol of polyethylene polyamine were added to a reaction vessel, protected by nitrogen, and heated to 120-160℃ for amidation reaction for 2-4 h. Step 2: Continue heating to 180-220℃, cyclization reaction for 4-8 h, vacuum dehydration to obtain imidazoline monomer; The fatty acid is at least one selected from lauric acid, myristic acid, palmitic acid, stearic acid, and oleic acid; the polyethylene polyamine is at least one selected from diethylenetriamine, triethylenetetramine, and tetraethylenepentamine. The fluorinated long-chain carboxylic acid is a perfluoroalkyl carboxylic acid with 8-12 carbon atoms in its fluorinated carbon chain and an acid value of 80-160 mgKOH / g; The polyetheramine is a polyoxypropylene amine or a polyoxyethylene-polyoxypropylene copolymer amine with a molecular weight of 230-600 and an amine value of 200-600 mgKOH / g. The multifunctional epoxy compound is at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and trifunctional epoxy resin TDE-85 with an epoxy equivalent of 100-250 g / eq.

2. The imidazoline epoxy resin curing agent according to claim 1, characterized in that: The fluorinated long-chain carboxylic acid is at least one of perfluorooctylpropionic acid, perfluorodecylacetic acid, and perfluorododecylbutyric acid.

3. The imidazoline epoxy resin curing agent according to claim 1, characterized in that: The polyetheramine is at least one of Jeffamine D-230, D-400, T-403 and ED-600.

4. The imidazoline epoxy resin curing agent according to claim 1, characterized in that: The silane coupling agent is at least one of γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane.

5. The imidazoline epoxy resin curing agent according to claim 1, characterized in that: The polymerization inhibitor is at least one of p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, and hydroquinone.

6. A method for preparing the imidazoline epoxy resin curing agent according to any one of claims 1-5, characterized in that: Includes the following steps: Step 1: Add the imidazoline monomer to the reaction vessel, heat to 70-90℃, and add the fluorinated long-chain carboxylic acid dropwise under nitrogen protection. The addition is completed in 0.5-1 h, and the reaction is maintained at the temperature for 1-2 h. Step 2: Add polyetheramine, heat to 90-110℃, and react for 1-3 hours; Step 3: Cool to 60-80℃, add the multifunctional epoxy compound in batches, and react for 2-4 hours; Step 4: Add silane coupling agent and polymerization inhibitor, continue stirring for 0.5-1 h, degas under vacuum, and the product is ready.

7. The preparation method according to claim 6, characterized in that: In step 1, the fluorinated long-chain carboxylic acid was added at 80°C for 1.5 h; in step 2, the polyetheramine was added at 100°C for 2 h; in step 3, the epoxide was added in 3 batches, with an interval of 20 min between each batch, at a reaction temperature of 70°C, for a total reaction time of 3 h.

8. The application of the imidazoline epoxy resin curing agent according to any one of claims 1-5, characterized in that, This product is used for curing epoxy resin in underwater, humid, or dry environments. The epoxy resin is at least one of bisphenol A, bisphenol F, phenolic epoxy, or marine epoxy mortar systems. The amount of curing agent used is 8-25% of the mass of the epoxy resin.

9. The application according to claim 8, characterized in that, The underwater curing conditions are as follows: water temperature 5-35℃, water depth 0.5-20 m, water flow velocity 0-2 m / s, visibility ≥0.2 m; curing time: initial setting ≤4 h, final setting ≤24 h, underwater shear bond strength ≥18 MPa after 7 days.

10. The application according to claim 8, characterized in that, After the curing agent is mixed with the epoxy resin, the underwater contact angle is ≤65°, the interfacial water film replacement rate is ≥85%, the water absorption rate of the cured product is ≤0.8%, and the Shore D hardness is ≥75.

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