A polysulfide-type epoxy curing agent and its synthesis method

Abstract

This invention relates to the field of curing agent technology, specifically disclosing a polysulfide-type epoxy curing agent and its synthesis method. The composition, by mass percentage, is: 20-40 wt% olefin monomer, 20-50 wt% elemental sulfur, 20-40 wt% accelerator, and 0.1-0.8 wt% catalyst. Polysulfide is synthesized through the reaction of elemental sulfur with olefins. The method of this invention features mild reaction conditions, wide monomer compatibility, simple operation, and low cost. The prepared polysulfide-type epoxy curing agent exhibits good chemical stability. It cures epoxy through a dynamic exchange reaction of sulfur-sulfur bonds, avoiding the odor problem associated with thiol curing agents. When combined with epoxy resin, it achieves low-temperature rapid drying, and the cured film has high hardness, good adhesion, and excellent anti-corrosion properties, making it suitable for outdoor packaging at room temperature. Furthermore, the cured resin can be degraded and recycled, facilitating the updating and adjustment of packaging operations.

Description

Technical Field

[0001] This invention relates to the field of curing agent technology, and specifically discloses a polysulfide-type epoxy curing agent and its synthesis method. Background Technology

[0002] Epoxy resin refers to a general term for compounds containing two or more epoxy groups in a single molecule that can form a three-dimensional cross-linked network with a curing agent. Uncured epoxy resin is a high-molecular-weight prepolymer with thermoplasticity and almost no practical use; it cannot be used directly. Only after undergoing a cross-linking reaction with different curing agents at room temperature or under heating conditions to form a three-dimensional cross-linked, insoluble, and infusible thermosetting polymer can it become an applicable material with practical value. After curing, epoxy resin possesses advantages such as electrical insulation, high adhesion, dimensional stability (low shrinkage during the curing reaction), corrosion resistance, and excellent mechanical properties. As coatings, adhesives, electronic and electrical materials, and civil engineering materials, it is widely used in mechanical and electronic, aerospace, chemical, shipbuilding, automotive, military, metallurgical, and light industries.

[0003] Amines, acid anhydrides, and thiols are among the most common and effective epoxy resin curing agents. Amines and acid anhydrides can cure epoxy resins at room temperature and medium to high temperatures; however, due to the reactive characteristics of amines, they often suffer from severe exothermic reactions. Thiols can effectively achieve low-temperature curing, but compared to amines, their preparation cost is high, and they produce a strong odor during actual production, causing production safety and environmental pollution. Therefore, there is a current need for a new type of epoxy curing agent that is highly efficient, convenient, easy to operate, and inexpensive. Summary of the Invention

[0004] To address the shortcomings of existing epoxy curing agents, this invention proposes a simple synthesis method for preparing polysulfide epoxy resin curing agents directly from elemental sulfur, along with the resulting curing agent. The obtained curing agent can cure epoxy resins at room temperature, and the synthesis method is simple, allows for long-term storage, has no irritating odor, and uses inexpensive elemental sulfur as the raw material. It avoids the complex process of synthesizing mercapto monomers, making it a novel and highly efficient curing agent for room-temperature curing epoxy resins.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] The polysulfide-type epoxy curing agent has the following composition by mass percentage: 20-40 wt% olefin monomer, 20-50 wt% elemental sulfur, 20-40 wt% accelerator, and 0.1-0.8 wt% catalyst.

[0007] The olefin monomer is one or a mixture of ethyl acrylate (EA), benzyl acrylate (BA), and N,N-dimethylacrylamide (DMAA).

[0008] The accelerator is one or more of the following: triethylamine (TEA), ethyl 2-(dimethylamino)acrylate (DMAEA), and dimethylaminopropylacrylamide (DMAPAA).

[0009] The catalyst is one of 1,8-diazobisspirocyclic [5.4.0]undec-7-ene (DBU), triethylenediamine (DACH), sodium hydroxide (NaOH), and potassium hydroxide (KOH).

[0010] This invention also provides a method for synthesizing a polysulfide epoxy curing agent, specifically: dried olefin monomers, elemental sulfur, an accelerator, and a catalyst are thoroughly stirred in a dry reaction vessel, and then a polymerization reaction is carried out at a copolymerization temperature above 25°C for 12-24 hours to obtain the polysulfide epoxy curing agent. The obtained product is directly packaged, dried, and stored.

[0011] The obtained polysulfide-type epoxy curing agent is used for curing epoxy resin, and its curing conditions are: room temperature curing for 12-36 hours.

[0012] For curing epoxy resin, the mass ratio of polysulfide-type epoxy curing agent to epoxy resin is 1:2 to 1:6.

[0013] Beneficial effects:

[0014] The polysulfide-type epoxy curing agent provided by this invention is synthesized in one step under mild reaction conditions, with no release of toxic gases, and uses inexpensive raw materials. The curing agent is non-thiol type, has no pungent odor, and cures the epoxy resin through dynamic exchange of sulfur-sulfur bonds. This greatly reduces the operational difficulty, time, and economic costs of curing agent synthesis.

[0015] A polysulfide-type epoxy curing agent prepared from elemental sulfur is used to cure epoxy resins. It achieves low-temperature, rapid drying, and produces a cured film with high hardness, good adhesion, and excellent corrosion resistance, making it suitable for outdoor encapsulation work at room temperature. The cured epoxy resin can be degraded and recycled through simple solvent treatment, further facilitating encapsulation operations. Attached image description:

[0016] Figure 1 This is a schematic diagram of the polysulfide-type epoxy curing agent in Example 1.

[0017] Figure 2 This is a schematic diagram of the curing mechanism of the curing agent of the present invention.

[0018] Figure 3 The curing agent of Example 1 1 H-NMR test.

[0019] Figure 4FTIR tests of E-51 before and after curing in Example 1.

[0020] Figure 5 Temperature scanning test of the curing agent in Example 1.

[0021] Figure 6 The XRD patterns are those of epoxy resin E-51 after curing in Example 3.

[0022] Figure 7 The degradation curve of epoxy resin E-51 after curing in Example 1 is shown. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments and accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] Example 1

[0025] Weigh 4g of elemental sulfur powder, 2g of DMAA, 2g of DMAEA, and 0.05g of DBU into a 100mL flask, mix and stir at room temperature for 24h. After the reaction is complete, a polysulfide curing agent is obtained with a yield of 99%.

[0026] Degradation test instructions: The epoxy resin cured in Example 1 (with a mass ratio of curing agent: E-51 = 1:4, the curing agent and E-51 were mixed evenly and cured at room temperature) was subjected to degradation tests in benzyl mercaptan (1 ml / 10 mL) and tetrahydrofuran containing sodium hydroxide (1 mg / mL). The mass loss of epoxy resin was measured over time.

[0027] Recycling Instructions: Take the degraded solution components, dry them at 40°C to evaporate the solvent, and obtain reusable epoxy resin oligomers.

[0028] Example 2

[0029] Weigh 3g of elemental sulfur powder, 2g of EA, 2g of DMAEA, and 0.07g of DBU into a 100mL flask, mix and stir at room temperature for 24h, and after the reaction is complete, a polysulfide curing agent is obtained with a yield of 99%.

[0030] Example 3

[0031] Weigh 5g of elemental sulfur powder, 4g of BA, 1g of DMAEA, and 0.09g of DBU into a 100mL flask, mix and stir at room temperature for 24h, and after the reaction is complete, a polysulfide curing agent is obtained with a yield of 99%.

[0032] Example 4

[0033] Weigh 5g of elemental sulfur powder, 4g of BA, 1g of TEA, and 0.09g of DBU into a 100mL flask, mix and stir at room temperature for 24h, and after the reaction is complete, a polysulfide curing agent is obtained with a yield of 99%.

[0034] Example 5

[0035] Weigh 4g of elemental sulfur powder, 2g of DMAA, 2g of DMAEA, and 0.10g of DACH into a 100mL flask, mix and stir at room temperature for 24h. After the reaction is complete, a polysulfide curing agent is obtained with a yield of 99%.

[0036] Example 6

[0037] Weigh 4g of elemental sulfur powder, 2g of DMAA, 2g of DMAEA, and 0.10g of KOH into a 100mL flask, mix and stir at room temperature for 24h. After the reaction is complete, a polysulfide curing agent is obtained with a yield of 99%.

[0038] Example 7

[0039] Weigh 4g of elemental sulfur powder, 2g of DMAA, 2g of DMAPAA, and 0.05g of DBU into a 100mL flask, mix and stir at room temperature for 24h. After the reaction is complete, a polysulfide curing agent is obtained with a yield of 99%.

[0040] Example 8

[0041] Weigh 4g of elemental sulfur powder, 2g of BA, 2g of DMAEA, and 0.05g of DBU into a 100mL flask, mix and stir at room temperature for 24h, and after the reaction is complete, a polysulfide curing agent is obtained with a yield of 85%.

[0042] Example 9

[0043] Weigh 5g of elemental sulfur powder, 2g of DMAA, 2g of DMAEA, and 0.05g of DBU into a 100mL flask, mix and stir at room temperature for 24h. After the reaction is complete, a polysulfide curing agent is obtained with a yield of 90%.

[0044] Comparative Example 1

[0045] To remove the elemental sulfur component from Example 1, a sulfur-free epoxy curing agent was prepared using DMAA, DMAEA, and DBU. It was made from the following raw materials in the indicated mass percentages: 2g of olefin (DMAA), 2g of accelerator (DMAEA), and 0.05g of catalyst (DBU). All raw materials were mixed and stirred at room temperature for 24 hours. After the reaction was complete, the curing agent was obtained.

[0046] Table 1. Basic properties of epoxy resins cured by curing agents obtained in each embodiment.

[0047] Example Surface drying time (25℃) Actual working time (25℃) Adhesion force (MPa) hardness 1 2h 24h 9±1.02 4H 2 2 h 24h 8±0.80 4H 3 2 h 24h 8±1.21 4H 4 3 h 30h 9±0.81 4H 5 3 h 32h 7±0.80 3H 6 4 h 40h 7±0.69 3H 7 3 h 33h 8±0.88 3H 8 4 h 30h 6±0.56 3H 9 2 h 24h 8±1.62 4H Comparative Example 1 24 h 72h 0.5±0.16 H

[0048] Note: Curing epoxy resin: Mix curing agent and E-51 at a mass ratio of 1:4 and cure at room temperature.

[0049] Hardness was tested according to the method specified in national standard GB / T6739-1996; adhesion was tested according to the method specified in ASTM D1002.

[0050] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. An application of a polysulfide-type epoxy curing agent, characterized in that, The polysulfide-type epoxy curing agent is used for curing epoxy resin; the polysulfide-type epoxy curing agent has the following composition by mass percentage: 20-40 wt% olefin monomer, 20-50 wt% elemental sulfur, 20-40 wt% accelerator, and 0.1-0.8 wt% catalyst. The accelerator is one or more of the following: triethylamine (TEA), ethyl 2-(dimethylamino)acrylate (DMAEA), and dimethylaminopropylacrylamide (DMAPAA).

2. The application of the polysulfide-type epoxy curing agent according to claim 1, characterized in that, The olefin monomer is one or a mixture of ethyl acrylate (EA), benzyl acrylate (BA), and N,N-dimethylacrylamide (DMAA).

3. The application of the polysulfide-type epoxy curing agent according to claim 1, characterized in that, The catalyst is one of 1,8-diazobis-spirocyclic [5.4.0]undecyl-7-ene (DBU), triethylenediamine (DACH), sodium hydroxide, and potassium hydroxide.

4. The application of the polysulfide-type epoxy curing agent according to claim 1, characterized in that, When curing epoxy resin, the mass ratio of polysulfide-type epoxy curing agent to epoxy resin is 1:2 to 1:6, and the curing conditions are: room temperature curing for 12-36 hours.

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