Preparation and application method of metal ion coordination type epoxy resin latent curing accelerator

Abstract

The invention discloses a preparation method and an application method of a metal ion coordination type epoxy resin latent curing accelerator. The accelerant is prepared by catalyzing cationic polymerization of an epoxy monomer through a liquid metal complex. The structure takes metal ions as a dynamic coordination core and is combined with a flexible ether chain to form a functional unit. At room temperature, flexible chain physical wrapping and dynamic coordination bonds cooperate to stabilize metal ions, inhibit catalytic activity of the metal ions and realize latency; at high temperature, the flexible chain is stretched, the coordinate bond is dissociated, and released metal ions efficiently drive the epoxy resin to be rapidly cured. Besides, the accelerant can form a local coordination supramolecular network during curing, and curing internal stress is effectively relieved by means of reversible dissociation of coordination bonds and synergy of a rigid network and a flexible chain, so that the force and thermal properties of the resin are synchronously improved. According to the invention, collaborative optimization of curing efficiency and mechanical and thermal properties is realized, and the obtained reinforced epoxy resin has wide application prospects in the fields of aerospace bearing parts, automobile lightweight parts and the like.

Description

Technical Field

[0001] This invention provides a method for preparing and applying a metal ion-coordinated epoxy resin latent curing accelerator, belonging to the field of epoxy resin modification and application technology. Background Technology

[0002] Epoxy resins, due to their outstanding thermomechanical properties and processing applicability, have been widely used in various industrial fields such as coatings, adhesives, and fiber composites. However, epoxy resin curing systems face significant technical bottlenecks: the activation energy of the reaction between epoxy monomers and curing agents is high, requiring the reaction to be carried out at high temperatures, and the curing cycle is lengthy, which greatly limits the promotion of epoxy resins in rapid production applications. To solve this problem, curing accelerators are usually used to accelerate the crosslinking reaction between epoxy monomers and curing agents. Common curing accelerators include tertiary amine compounds, triphenylphosphine derivatives, organic carboxylates, and aryl isocyanates. However, these traditional curing accelerators exhibit high catalytic activity at room temperature. While optimizing reaction kinetic parameters, they inevitably bring defects such as short system pot life, poor storage stability, and narrow processing window, severely restricting continuous and rapid industrial production.

[0003] Developing latent accelerators is an effective way to solve the above-mentioned technical problems. The core feature of latent accelerators is that they remain chemically inert under normal conditions and only exhibit promoting activity under specific triggering conditions such as heat and light. Compared with other types of latent accelerators, thermal latent accelerators have the characteristics of strong universality and high process compatibility. They can achieve on-demand adjustment of curing rate while ensuring the storage stability of epoxy system, which has important engineering value for promoting intelligent continuous and rapid manufacturing of epoxy resin. At present, the research on thermal latent accelerators mainly focuses on two types of methods: (1) chemical modification method. By introducing large-volume substituents (benzene ring, aliphatic chain, etc.) or compounding with organic acids, metal salts and other compounds, the structure of traditional curing accelerators (such as imidazole) is modified to achieve latentness; (2) physical encapsulation method. Traditional accelerators are encapsulated in synthetic polymer microcapsules to keep them inert at room temperature, while the capsules rupture at high temperature to release the accelerator and efficiently catalyze the curing of resin.

[0004] While the methods described above can impart latent accelerator properties to epoxy resin prepolymers to some extent, chemically modified accelerators or polymer microcapsules still generally suffer from poor compatibility with epoxy monomers, complex synthesis processes, and high costs. Furthermore, the introduction of traditional accelerators or thermally latent accelerators exacerbates the inherent brittleness of epoxy resins: rapid cross-linking reactions in localized areas at high temperatures easily lead to microscopic stress concentrations, resulting in a decrease in the resin's tensile strength and fracture toughness. This inherent contradiction between catalytic efficiency and mechanical properties caused by accelerators has become a key scientific problem restricting the development of high-performance epoxy resin materials. Therefore, developing multifunctional thermally latent accelerators that combine high catalytic efficiency, high mechanical properties, and good process versatility is of great significance for both the theoretical research of high-performance epoxy resins and their engineering applications in rapid curing. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a metal ion coordination-type curing accelerator. This accelerator boasts advantages such as simple synthesis and good compatibility with epoxy resin compositions, while also possessing latent promoting function and enhancing toughening effects. It constructs a dynamic coordination system with metal ions as the core and introduces a flexible ether chain structure through the cationic polymerization of epoxy monomers. As it is a liquid derivative of epoxy monomers, this accelerator exhibits excellent compatibility with epoxy resin compositions. At room temperature, strong coordination and the physical coating effect of the flexible ether chains effectively inhibit the catalytic activity of metal ions, ensuring the storage stability of the epoxy resin composition at room temperature. Upon thermal activation, the reversible dissociation of the dynamic coordination bonds and the conformational unfolding of the flexible ether chains promote the release of active metal ions. The released metal ions activate epoxy groups, driving efficient curing of the resin system. Simultaneously, the presence of epoxy groups in the accelerator allows it to react with the curing agent, participating in the construction of a reversible coordination supramolecular network. The reversible dissociation of coordination bonds in the network and the synergistic effect of rigid coordination network and flexible chain segments can effectively alleviate the internal stress of resin curing and improve the energy dissipation capacity of the system, thereby strengthening and toughening epoxy resin.

[0006] The present invention provides a metal ion coordination type epoxy resin latent curing accelerator, the structural formula of which is as follows: Formula 1:

[0007]

[0008] n is the degree of polymerization, which is an integer from 2 to 10; m is the number of ligands, which is an integer from 1 to 6, preferably 3 to 4;

[0009] M is a metal salt containing Li. + Na + Zn 2+ Fe 2+ Fe 3+ Co 2+ Al3+ Cu + Cu 2+ One or more of the metal salts;

[0010] L is a metal ion ligand, including one or more of lactic acid, acetamide, acrylic acid, acrylamide, urea, thiourea, and nicotinamide;

[0011] R is a repeating unit formed by the cationic polymerization of epoxy monomers, wherein the epoxy monomers include one or more of bisphenol A glycidyl ether, 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester, 4-(diglycidylamino)phenyl glycidyl ether, and tetraglycidyl-4,4'-diaminodiphenylmethane.

[0012] [L] m →M is the coordinate bond structure obtained by the reaction of metal salt and ligand;

[0013] R–L is the structure obtained by the addition reaction of epoxy group and ligand reactive group.

[0014] The preparation method of the metal ion coordination type epoxy resin latent curing accelerator described in Formula 1 includes the following steps:

[0015] (1) Metal salt M and ligand L were mixed and reacted at 80–100 °C for 3–8 h to obtain the following...

[0016] The liquid coordination complex shown in Equation 2:

[0017]

[0018] M, L, and m are defined as in equation 1;

[0019] The molar ratio of metal salt M to ligand L in the liquid coordination complex is 1:1 to 1:5, preferably 1:1 to 1:3.

[0020] (2) The liquid coordination complex obtained in (1) is blended with the epoxy monomer and reacted at 100–180°C for 0.5–3 h to obtain a metal ion coordination type latent curing accelerator for epoxy resin as shown in Formula 1. The amount of the liquid metal coordination complex added is 1–10 parts by weight of the epoxy monomer.

[0021] This invention further provides a method for applying a metal ion-coordination type latent curing accelerator for epoxy resins, wherein the accelerator is used as a reactive accelerator in the curing of epoxy monomers and curing agents:

[0022] The epoxy monomer comprises one or more of the following: bisphenol A type epoxy monomer, 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester, 4-(diglycidylamino)phenylglycidyl ether, and tetraglycidyl-4,4'-diaminodiphenylmethane.

[0023] The curing agent is one or more of m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, and dicyandiamide;

[0024] The molar ratio between the epoxy group and the reactive hydrogen of the curing agent is 0.8 to 1.5, preferably 1;

[0025] The metal ion coordination type epoxy resin latent curing accelerator is 5 to 70 parts by weight of epoxy monomer, preferably 5 to 40 parts by weight.

[0026] Beneficial effects

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. The metal ion coordination type latent curing accelerator for epoxy resin involved in this invention is liquid at room temperature and has good compatibility with epoxy monomers;

[0029] 2. At room temperature, physical encapsulation and coordination bond binding reduce the activity of the accelerator, and the epoxy resin composition has a good pot life; after heating to 100℃, the oligomer chain segments in the accelerator expand, the coordination bonds gradually dissociate, the catalytic activity of metal ions is released, the curing rate is accelerated, and the degree of curing is increased.

[0030] 3. Thanks to the synergistic effect of reversible coordination bond dissociation and rigid coordination network-flexible segments, this accelerator can effectively promote the curing of epoxy resin while relieving stress concentration in the system and improving the strength, modulus, toughness and glass transition temperature of the resin.

[0031] 4. The preparation method of this invention is simple and safe, and it has latent promoting, strengthening and toughening effects on both amine and dicyandiamide curing systems. Attached Figure Description

[0032] Figure 1 This is a reaction mechanism diagram of the curing accelerator in Example 1 of the present invention;

[0033] Figure 2 This is the Fourier transform infrared spectrum of the curing accelerator in Example 1 of the present invention;

[0034] Figure 3 This is a transmission electron microscope image of the curing accelerator in Example 1 of the present invention;

[0035] Figure 4 The tensile stress-strain curves are for the cured products of Example 1 and Comparative Example 1. Detailed Implementation

[0036] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0037] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0038] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0039] Test method:

[0040] The gel time of the epoxy resin composition was measured using a rotational rheometer. After heating the epoxy resin composition to the test temperature, the test was started and the time was recorded. The time at which the loss modulus (G") and storage modulus (G') curves of the composition intersect is the gel time.

[0041] The degree of cure was calculated by measuring the exothermic peak during the curing reaction using differential scanning calorimetry (DSC) at a heating rate of 5 °C / min. Unreacted epoxy groups continue to react during heating, releasing heat; the residual enthalpy ΔH is also measured. 残余 With the theoretical total enthalpy ΔH 总 The ratio reflects the degree of curing:

[0042]

[0043] Tensile properties were tested according to GB / T 1040.2-2022 standard.

[0044] The glass transition temperature of the material was obtained by dynamic mechanical thermal analyzer using a three-point bending mode at a frequency of 1 Hz and a heating rate of 5 °C / min.

[0045] Example 1

[0046] (1) Preparation of liquid metal coordination complexes

[0047] Mix 10g of acetamide with 7.68g of zinc chloride and stir at 80℃ for 3 hours until a colorless and transparent solution is obtained.

[0048] (2) Preparation of metal ion coordination type epoxy resin latent curing accelerator

[0049] Add 3g of the liquid metal coordination complex obtained in (1) to 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and stir at 150℃ for 0.5h until a yellow transparent solution is obtained.

[0050] (3) Preparation of epoxy resin

[0051] 15g of the accelerator obtained in (2) was mixed with 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and 27.2g of m-phenylenediamine in an oil bath at 60℃ for 10min. After mixing evenly, the mixture was placed in a 30℃ oven for vacuum degassing to obtain an epoxy resin composition. The composition was poured into a mold and cured at 120℃ for 15min. After cooling, the epoxy resin was obtained.

[0052] Example 2

[0053] (1) Preparation of liquid metal coordination complexes

[0054] Mix 10g of acetamide with 7.68g of zinc chloride and stir at 80°C for 3 hours until a clear and transparent solution is obtained.

[0055] (2) Preparation of metal ion coordination type epoxy resin latent curing accelerator

[0056] 1g of the liquid metal coordination complex obtained in (1) was added to 100g of bisphenol A glycidyl ether and stirred at 150°C for 3h until a yellow transparent solution was obtained.

[0057] (3) Preparation of epoxy resin

[0058] 5g of the accelerator obtained in (2) was mixed with 100g of bisphenol A glycidyl ether and 30g of m-phenylenediamine in an oil bath at 60°C for 10 minutes. After mixing evenly, the mixture was placed in a 30°C oven for vacuum degassing to obtain an epoxy resin composition. The composition was poured into a mold and cured at 120°C for 15 minutes. After cooling, an epoxy resin was obtained.

[0059] Example 3

[0060] (1) Preparation of liquid metal coordination complexes

[0061] Mix 10g of urea with 6.75g of ferric chloride and stir at 100℃ for 8 hours until a reddish-brown transparent solution is obtained.

[0062] (2) Preparation of metal ion coordination type epoxy resin latent curing accelerator

[0063] 10g of the liquid metal coordination complex obtained in (1) was added to 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and stirred at 180℃ for 0.5h until a dark brown transparent solution was obtained.

[0064] (3) Preparation of epoxy resin

[0065] 15g of the accelerator obtained in (2) was mixed with 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and 27.2g of m-phenylenediamine in an oil bath at 60℃ for 10min. After mixing evenly, the mixture was placed in a 30℃ oven for vacuum degassing to obtain an epoxy resin composition. The composition was poured into a mold and cured at 120℃ for 15min. After cooling, the epoxy resin was obtained.

[0066] Example 4

[0067] (1) Preparation of liquid metal coordination complexes

[0068] Mix 10g of urea with 8g of ferric chloride and stir at 100℃ for 8 hours until a reddish-brown transparent solution is obtained.

[0069] (2) Preparation of metal ion coordination type epoxy resin latent curing accelerator

[0070] Add 3g of the liquid metal coordination complex obtained in (1) to 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and stir at 100℃ for 3h until a dark brown transparent solution is obtained.

[0071] (3) Preparation of epoxy resin

[0072] 40g of the accelerator obtained in (2) was mixed with 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and 32g of m-phenylenediamine in an oil bath at 60℃ for 10min. After mixing evenly, the mixture was placed in a 30℃ oven for vacuum degassing to obtain an epoxy resin composition. The composition was poured into a mold and cured at 120℃ for 15min. After cooling, the epoxy resin was obtained.

[0073] Example 5

[0074] (1) Preparation of liquid metal coordination complexes

[0075] Mix 10g of lactic acid with 1.18g of lithium chloride and stir at 80°C for 5 hours until a clear and transparent solution is obtained.

[0076] (2) Preparation of metal ion coordination type epoxy resin latent curing accelerator

[0077] Add 5g of the liquid metal coordination complex obtained in (1) to 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and stir at 130℃ for 2h until a yellow transparent solution is obtained.

[0078] (3) Preparation of epoxy resin

[0079] 15g of the accelerator obtained in (2) was mixed with 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and 27.2g of m-phenylenediamine in an oil bath at 60℃ for 10min. After mixing evenly, the mixture was placed in a 30℃ oven for vacuum degassing to obtain an epoxy resin composition. The composition was poured into a mold and cured at 120℃ for 15min. After cooling, the epoxy resin was obtained.

[0080] Comparative Example 1

[0081] To demonstrate the importance of metal ion-coordination epoxy resin accelerators, this comparative example uses epoxy resin without the addition of a latent curing accelerator, as detailed below:

[0082] 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester and 21.7g of m-phenylenediamine were stirred in an oil bath at 60℃ for 10 minutes. After mixing evenly, the mixture was placed in a 30℃ oven for vacuum degassing to obtain an epoxy resin composition. The composition was poured into a mold and cured at 120℃ for 15 minutes. After cooling, the epoxy resin was obtained.

[0083] Comparative Example 2

[0084] To demonstrate the importance of metal ion-coordination epoxy resin accelerators, this comparative example uses epoxy resin without the addition of a latent curing accelerator, as detailed below:

[0085] 100g of bisphenol A glycidyl ether and 30g of m-phenylenediamine were stirred in an oil bath at 60℃ for 10 minutes. After mixing evenly, the mixture was placed in a 60℃ oven for vacuum degassing to obtain an epoxy resin composition. The composition was poured into a mold and cured at 120℃ for 40 minutes. After cooling, the epoxy resin was obtained.

[0086] Comparative Example 3

[0087] To demonstrate the importance of metal ion-coordination epoxy resin accelerators, this comparative example uses epoxy resins with added non-latent curing accelerators, as detailed below:

[0088] 100g of 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester, 21.7g of m-phenylenediamine, and 0.5g of imidazole were stirred in an oil bath at 60℃ for 10 minutes. After mixing evenly, the mixture was placed in a 30℃ oven for vacuum degassing to obtain an epoxy resin composition. The composition was poured into a mold and cured at 120℃ for 40 minutes. After cooling, the epoxy resin was obtained.

[0089] Table 1 Performance of Examples 1-5 and Comparative Examples 1-3

[0090]

[0091] As can be seen from the comparison of Examples 1-5 and Comparative Example 1 in Table 1, the gel time of the epoxy resin compositions with the latent accelerator of the present invention is not significantly affected, and all of them can improve the curing degree and mechanical and thermal properties of the fast-curing resin at the same curing temperature and time. The comparison of Example 2 and Comparative Example 2 shows that the composition without the latent accelerator of the present invention requires a longer curing time to be fully cured, and the mechanical and thermal properties of the fully cured product are lower than those of the composition with the latent accelerator. The comparison of Example 1, Comparative Example 1 and Comparative Example 3 shows that the gel time of the composition with the non-latent accelerator is significantly shortened, and the mechanical and thermal properties of the cured resin are lower than those of the composition without the accelerator (Comparative Example 1) and the composition with the latent accelerator of the present invention (Example 1).

Claims

1. A metal ion coordination type latent curing accelerator for epoxy resin, characterized in that: The accelerator is a cationic polymer derivative of epoxy resin with metal ion coordination bonds, and its chemical structural formula is as follows: Formula 1: n is the degree of polymerization, an integer from 2 to 10; m is the number of ligands, an integer from 1 to 6; M is a metal salt containing Li. + Na + Zn 2+ Fe 2+ Fe 3+ Co 2+ Al 3+ Cu + Cu 2+ One or more of the metal salts; L is a metal ion ligand, including one or more of lactic acid, acetamide, acrylic acid, acrylamide, urea, thiourea, and nicotinamide; R is a repeating unit formed by the cationic polymerization of epoxy monomers, wherein the epoxy monomers include one or more of bisphenol A glycidyl ether, 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester, 4-(diglycidylamino)phenyl glycidyl ether, and tetraglycidyl-4,4'-diaminodiphenylmethane. [L] m →M is the coordinate bond structure obtained by the reaction of metal salt and ligand; R–L is the structure obtained by the addition reaction of epoxy group and ligand reactive group.

2. The preparation method of the metal ion coordination type epoxy resin latent curing accelerator according to claim 1, characterized in that: The accelerator is generated by the cationic polymerization of epoxy monomers catalyzed by a liquid coordination complex, as follows: (1) Metal salt M and ligand L were mixed and reacted at 80–100 °C for 3–8 h to obtain a liquid coordination complex as shown in Formula 2: M, L, and m are defined as in equation 1; The molar ratio of metal salt M to ligand L in the liquid coordination complex is 1:1 to 1:

5. (2) The liquid coordination complex obtained in (1) is blended with the epoxy monomer and reacted at 100-180°C for 0.5-3 hours to obtain the metal ion coordination type epoxy resin latent curing accelerator as shown in Formula 1. The amount of the liquid metal coordination complex added is 1 to 10 parts by weight of the epoxy monomer.

3. The application method of the metal ion coordination type epoxy resin latent curing accelerator according to claim 1, characterized in that: The accelerator is a reactive latent accelerator used in the curing of epoxy monomers and curing agents. The epoxy monomer comprises one or more of the following: bisphenol A type epoxy monomer, 4,5-epoxyhexane-1,2-dicarboxylic acid diglycidyl ester, 4-(diglycidylamino)phenylglycidyl ether, and tetraglycidyl-4,4'-diaminodiphenylmethane. The curing agent comprises one or more of m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, and dicyandiamide; The molar ratio between the epoxy group and the reactive hydrogen of the curing agent is 0.8 to 1.5; The metal ion coordination type epoxy resin latent curing accelerator is 5 to 70 parts by weight of epoxy monomer.

4. The application method of the metal ion coordination type epoxy resin latent curing accelerator according to claim 3, characterized in that: The latent curing accelerator is suitable for rapid curing in fields such as aerospace load-bearing components, automotive lightweight parts, and electronic packaging.

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