A process for the preparation of melamine-based ternary benzoxazine resins

Abstract

The application belongs to the technical field of high polymer materials, and particularly relates to a preparation method of a ternary benzoxazine resin based on melamine. The method is characterized in that a ternary phenol containing Schiff base is synthesized by taking melamine and aldehyde-based phenol as raw materials through an aldehyde-amine reaction, then the ternary phenol is reacted with formaldehyde and monamine to obtain a ternary benzoxazine resin, and then polymerization is carried out at high temperature to obtain a resin based on tri-substituted benzoxazine. The method can greatly improve the cross-linking density, heat resistance and dielectric property of the resin while reducing the curing temperature of the benzoxazine.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically a method for preparing a ternary benzoxazine resin based on melamine. Background Technology

[0002] Benzoxazine is a thermosetting resin, a collective term for compounds containing six-membered oxazine rings (N and O) in their structure. It has attracted widespread attention due to its high modulus, high strength, and good heat resistance, as it does not release small molecules during curing and has almost zero curing shrinkage. However, its low crosslinking density and high brittleness limit its applications, and its dielectric properties are not particularly excellent, with a dielectric constant generally around 3.5. Therefore, its use as a next-generation low-dielectric electronic material still faces certain challenges.

[0003] Melamine is a triazine-based nitrogen-containing heterocyclic organic compound used as a chemical raw material. Initially used in the manufacture of melamine resin, its applications have gradually expanded to adhesives, crosslinking agents, flame retardants, and other fields. Its characteristics, including low corrosion, low smoke generation, low cost, high thermal stability, and good synergistic effects, have made its product research and development and improvement highly valued, indicating broad application prospects. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems existing in the prior art and provide a method for preparing ternary benzoxazine resin based on melamine. This invention first synthesizes a Schiff base-containing ternary phenol from melamine and an aldehyde-containing monohydric phenol as raw materials via an aldehyde-amine reaction. Then, the ternary phenol is reacted with formaldehyde and a monohydric amine to obtain the ternary benzoxazine resin. This method can significantly improve the resin's crosslinking density, heat resistance, and dielectric properties while lowering the curing temperature of benzoxazine resin. This will provide a reference for developing more low-cost, high-performance thermosetting resins and expanding the applications of high-performance thermosetting resins.

[0005] To achieve the objectives of the invention described above, the specific technical solution of the present invention is as follows:

[0006] A method for preparing a melamine-based ternary benzoxazine resin includes the following steps:

[0007] (1) Melamine, aldehyde-containing monohydric phenol and organic solvent are added to the reactor at room temperature;

[0008] (2) The reaction system is heated to a certain temperature and stirred for a period of time to carry out the synthesis reaction;

[0009] (3) The solution after the reaction in step (2) is added dropwise to a large amount of distilled water at room temperature. The mixture is stirred evenly during the addition, and a white flocculent precipitate is formed, resulting in a mixture containing the white flocculent precipitate.

[0010] (4) After the mixture obtained in step (3) is left to stand for a period of time, filter it, change the water and precipitate it. Soak the filter residue in a large amount of distilled water for a period of time.

[0011] (5) Filter the mixture in step (4), dry the filter residue in a vacuum oven to obtain triphenol; (6) Dissolve the triphenol obtained in step (5) in an organic solvent, stir and react with formaldehyde at a certain temperature, then add monoamine dropwise, stir and react at a certain temperature to obtain a tri-benzoxazine resin solution; that is, a melamine-based tri-benzoxazine resin solution;

[0012] (7) The ternary benzoxazine resin solution was obtained by removing the solvent.

[0013] The reaction formulas for the preparation steps are as follows:

[0014]

[0015] In the reaction formula, R1 can be an ether bond, etc.; R2 can be a benzene ring, phenylacetylene, methyl, ethyl, propyl or furan group.

[0016] Furthermore, the aldehyde-containing monohydric phenol is at least one of p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, vanillin, salicylaldehyde, and aldehyde naphthol;

[0017] The monoamine is at least one of aniline, m-aminophenylacetylene, p-aminophenylacetylene, methylamine, ethylamine, propylamine, and furanylmethylamine.

[0018] Preferably, in the preparation method, the molar ratio of melamine to aldehyde phenol in the reaction substrate added in step (1) is 1:3 to 1:3.5.

[0019] Preferably, in the preparation method, the molar ratio of triphenol, monoamine and formaldehyde in the reaction substrate added in step (5) is between 1:3:4 and 1:3:8.

[0020] Preferably, in the preparation method, the organic solvents in steps (1) and (5) are DMF, DMSO, DMAc or NMP, or any one of the mixtures of DMF, DMSO, DMAc or NMP with ethanol, butanone, acetone, toluene, dioxane or dichloromethane.

[0021] Preferably, in the preparation method, the temperature of the synthesis reaction in step (2) is 120-130℃; and the stirring time is 5-6 hours.

[0022] Preferably, in the preparation method, the temperature for vacuum drying of the filter residue in step (5) is 50-70℃.

[0023] Preferably, in the preparation method, the dissolution temperature of the triphenol and the organic solvent in step (6) is 50±10℃, and the stirring reaction time is 0.5-1 hour; the reaction temperature after adding the monoamine is 80±10℃, and the stirring reaction time is 4-6 hours.

[0024] Another objective of this invention is to protect a melamine-based ternary benzoxazine resin prepared according to any of the methods described above.

[0025] Furthermore, the melamine-based ternary benzoxazine resin can be used as a low-dielectric electronic material.

[0026] Preferably, the application method of the melamine-based ternary benzoxazine resin is as follows: the ternary benzoxazine resin is directly applied to the coating or coating process.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] (I) Starting from the design of molecular structure, this invention uses melamine as the matrix to obtain benzoxazine resin with a three-membered oxazine ring structure. While ensuring the excellent performance of traditional benzoxazine resin, it also reduces costs, improves thermal stability and heat resistance, etc. The introduction of melamine reduces production costs and improves flame retardant performance, providing a new preparation method for the production of high-performance benzoxazine resin.

[0029] (II) This invention synthesizes trifunctional phenols from melamine and aldehyde phenols via Schiff base synthesis reaction; then reacts the trifunctional phenols with formaldehyde and a monoamine to obtain a tri-benzoxazine resin.

[0030] By changing the types of aldehydes, phenols, and amines, the chemical structure, reactivity, and heat resistance of the final synthesized resin can be controlled to meet the needs of different application scenarios and resin types.

[0031] (III) The melamine-based ternary benzoxazine resin obtained by the method described in this invention has a higher crosslinking density, higher heat resistance and thermal stability, and higher flame retardancy compared to ordinary benzoxazine resin and benzoxazine resin containing aldehyde groups.

[0032] (iv) The melamine-based ternary benzoxazine resin described in this invention has a lower dielectric constant and dielectric loss compared to ordinary benzoxazine resin and benzoxazine resin containing aldehyde groups. Attached Figure Description

[0033] Figure 1 The 1H NMR spectrum of the melamine-based ternary benzoxazine resin prepared in Example 1;

[0034] Figure 2The infrared spectrum of the melamine-based ternary benzoxazine resin prepared in Example 2 is shown below.

[0035] Figure 3 The DSC curve of the melamine-based ternary benzoxazine resin prepared in Example 3 is shown below.

[0036] Figure 4 The TGA curve of the melamine-based ternary benzoxazine resin prepared in Example 4 is shown. Detailed Implementation

[0037] The present invention will be further described below through specific embodiments, but this is not a limitation of the present invention. Those skilled in the art can make various modifications or variations based on the basic idea of ​​the present invention, as long as they do not depart from the basic idea of ​​the present invention, they are all within the scope of the present invention.

[0038] The reagents used in the following examples are all commercially available products and are commonly used chemicals.

[0039] Example 1:

[0040] Step 1: Add 0.1 mol of melamine, 0.35 mol of p-hydroxybenzaldehyde, and 150 g of DMSO to a three-necked flask;

[0041] Step 2: Reflux and stir the substance from Step 1 at 120°C for 5 hours, then cool to obtain a dark yellow liquid.

[0042] Step 3: Let the adhesive solution obtained in Step 2 stand at room temperature, filter it, and take the clear brown filtrate. Add the filtrate dropwise to water at room temperature, stirring evenly as you add it to precipitate a white flocculent precipitate.

[0043] Step 4: After letting the mixture obtained in Step 3 stand for a period of time, filter it, change the water and continue to settle. Finally, soak the filter residue (precipitate) in a large amount of distilled water for a period of time.

[0044] Step 5: Filter the mixture from Step 4, and dry the precipitate in a vacuum oven at 65°C to obtain a brown solid resin, namely a trifunctional phenol (trihydric phenol).

[0045] Step 6: Dissolve 10g of the brown solid resin obtained in Step 5 in 10g of DMF in a three-necked flask, add formaldehyde, and stir at 50℃ for 1 hour; then add aniline and stir at 80℃ for 5 hours to obtain a ternary benzoxazine resin solution. The molar ratio of the trifunctional phenol, formaldehyde, and aniline is 1 mol: 4.5 mol: 3 mol.

[0046] Step 7: Cur the obtained adhesive solution (ternary benzoxazine resin solution) into a coating film in an oven at 200°C.

[0047] Melamine was supplied by Sichuan Jinxiang Chemical Co., Ltd., paraformaldehyde, p-hydroxybenzaldehyde and benzylamine were purchased from the Tansuo Reagent Platform, and DMSO and DMF were purchased from Chengdu Kelong Chemical Co., Ltd.

[0048] The tested resin had an initial curing temperature of 100℃, an enthalpy of 179 J / g, a CTE of 57 ppm / ℃ for the film cured at 200℃, a glass transition temperature of 189℃, an initial decomposition temperature of 390℃, a dielectric constant of 3.21 at 1MHz, a dielectric loss tangent of 0.009, and a saturated water absorption rate of 1.1% (GB 1738-1979).

[0049] Example 2:

[0050] Step 1: Add 0.1 mol melamine, 0.31 mol m-hydroxybenzaldehyde and 150 g DMF / ethanol (volume ratio 1:1) mixed solvent into a three-necked flask.

[0051] Step 2: Reflux and stir the substance from Step 1 at 123°C for 5 hours, then cool to obtain a dark yellow liquid.

[0052] Step 3: Let the adhesive solution obtained in Step 2 stand at room temperature, filter it, and take the clear brown filtrate. Add the filtrate dropwise to water at room temperature, stirring evenly as you add it to precipitate a white flocculent precipitate.

[0053] Step 4: After letting the mixture obtained in Step 3 stand for a period of time, filter it a second time, change the water and let it settle. Finally, soak the filter residue (sediment) in a large amount of distilled water for a period of time.

[0054] Step 5: Filter the mixture from Step 4, and dry the precipitate in a vacuum oven at 70°C to obtain a brown solid resin, namely trifunctional phenol (trihydric phenol).

[0055] Step 6: Dissolve 10g of the brown solid resin obtained in Step 5 in 12g of NMP in a three-necked flask, then add formaldehyde, and stir the mixture at 50°C for 0.8 hours. Next, add methylamine to the reactants and stir at 80°C for 6 hours to obtain a ternary benzoxazine resin solution. The molar ratio of the trifunctional phenol, formaldehyde, and methylamine is 1 mol: 8 mol: 3 mol.

[0056] Step 7: The obtained adhesive solution (ternary benzoxazine resin solution) is cured and coated in an oven at 200°C to obtain the cured resin.

[0057] Melamine was supplied by Sichuan Jinxiang Chemical Co., Ltd., paraformaldehyde, vanillin and methylamine were purchased from the Tansuo Reagent Platform, and DMF, NMP and ethanol were purchased from Chengdu Kelong Chemical Co., Ltd.

[0058] Tests showed that the initial curing temperature of the cured resin was 120℃; the enthalpy was 235 J / g; and the curing temperature was 200℃. ℃ The cured film has a CTE of 65 ppm / ℃, a glass transition temperature of 176℃, an initial decomposition temperature of 378℃, a dielectric constant of 3.40 at 1 MHz, a dielectric loss tangent of 0.011, and a saturated water absorption rate of 1.12% (GB 1738-1979).

[0059] Example 3:

[0060] Step 1: Add 0.1 mol of melamine, 0.3 mol of salicylaldehyde, and 100 g of DMF to a three-necked flask.

[0061] Step 2: Reflux and stir the substance from Step 1 at 126°C for 4.5 hours, and then cool to obtain a dark yellow liquid.

[0062] Step 3: Let the adhesive solution obtained in Step 2 stand at room temperature, filter it, and take the clear brown filtrate. Add the filtrate dropwise to water at room temperature, stirring evenly as you add it to precipitate a white flocculent precipitate.

[0063] Step 4: After letting the mixture obtained in Step 3 stand for a period of time, filter it a second time, change the water and let it settle. Soak the filter residue in a large amount of distilled water for a period of time.

[0064] Step 5: Filter the mixture from Step 4, and dry the precipitate in a vacuum oven at 68°C to obtain triphenol;

[0065] Step 6: Dissolve 10g of the brown solid resin obtained in Step 5 in 14g of DMAc in a three-necked flask. Add formaldehyde at 55℃ and stir the mixture in the three-necked flask for 1 hour. Then add aniline and stir the mixture at 80℃ for 6 hours to obtain a ternary benzoxazine resin solution. The molar ratio of the trifunctional phenol, formaldehyde, and aniline is 1 mol: 6 mol: 3 mol.

[0066] Step 7: Cure the adhesive solution (ternary benzoxazine resin solution) from Step 6 in an oven at 200°C to obtain a melamine-based ternary benzoxazine resin.

[0067] Melamine was supplied by Sichuan Jinxiang Chemical Co., Ltd., paraformaldehyde, vanillin and aniline were purchased from the Tansuo Reagent Platform, and DMF and DMAc were purchased from Chengdu Kelong Chemical Co., Ltd.

[0068] Tests showed that the initial curing temperature of the obtained resin was 140℃; the enthalpy was 132 J / g; and the curing temperature was 200℃. ℃ The cured film has a CTE of 55 ppm / ℃, a glass transition temperature of 176℃, an initial decomposition temperature of 377℃, a dielectric constant of 3.56 at 1MHz, a dielectric loss tangent of 0.008, and a saturated water absorption rate of 0.9% (GB 1738-1979).

[0069] Example 4:

[0070] Step 1: Add 0.1 mol melamine, 0.35 mol vanillin and 90 g DMAc / dioxane (volume ratio 3:1) to a three-necked flask.

[0071] Step 2: Reflux and stir the substance from Step 1 at 130°C for 5 hours, then cool to obtain a dark yellow liquid.

[0072] Step 3: Let the adhesive solution obtained in Step 2 stand at room temperature, filter it, and take the clear brown filtrate. Add the filtrate dropwise to water at room temperature, stirring evenly as you add it to precipitate a white flocculent precipitate.

[0073] Step 4: After letting the mixture obtained in Step 3 stand for a period of time, filter it a second time, change the water and let it settle. Soak the filter residue in a large amount of distilled water for a period of time.

[0074] Step 5: Filter the mixture from Step 4, and dry the precipitate in a vacuum oven at 69°C to obtain triphenol;

[0075] Step 6: Dissolve 10g of the brown solid resin obtained in Step 5 in 13g of DMSO in a three-necked flask, and react with formaldehyde at 50°C for 1 hour. Then add furanylmethylamine and react at 80°C for 4 hours to obtain a ternary benzoxazine resin solution. The molar ratio of the trifunctional phenol, formaldehyde, and furanylmethylamine is 1 mol: 7 mol: 3 mol.

[0076] Step 7: Cur the adhesive from Step 4 into a coating film in a 200°C oven.

[0077] Melamine was supplied by Sichuan Jinxiang Chemical Co., Ltd., paraformaldehyde, vanillin and furanyl methylamine were purchased from the Tansuo Reagent Platform, and DMSO, DMAc and dioxane were purchased from Chengdu Kelong Chemical Co., Ltd.

[0078] The tested results show that the resin has an initial curing temperature of 162℃, an enthalpy of 201 J / g, a CTE of 53 ppm / ℃ for the film cured at 200℃, a glass transition temperature of 173℃, an initial decomposition temperature of 369℃, a dielectric constant of 3.55 at 1MHz, a dielectric loss tangent of 0.009, and a saturated water absorption rate of 1.13% (GB 1738-1979).

[0079] Comparative Example 1:

[0080] The preparation method of melamine-based ternary benzoxazine resin is the same as in Example 1. However, during the research and development process, it was found that due to the significant steric hindrance effect in the melamine synthesis process, it is difficult for the three amino groups to react completely. If the amount of aromatic aldehyde is less than three times the molar amount of melamine, the yield of the synthesized ternary phenol is low, and a large amount of monophenol and diphenol are present in the product, which are difficult to separate and purify and affect the subsequent resin performance.

[0081] When synthesizing a trifunctional benzoxazine from trifunctional phenols, formaldehyde, and furanyl methylamine, the molar ratio of the trifunctional phenol, monofunctional amine, and formaldehyde is between 1:3:4 and 1:3:8. If the formaldehyde content is lower, the resin polymerization will be difficult and the heat resistance will be poor. If the formaldehyde content is higher, gelation is likely to occur during the synthesis process.

[0082] Comparative Example 2:

[0083] The preparation method of melamine-based ternary benzoxazine resin is the same as in Example 1, except that the temperature in step 6 is adjusted to above 90°C. As a result, the reaction system is prone to gel precipitation, and the target resin product cannot be obtained.

[0084] The embodiments described above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. It should be noted that, for those skilled in the art, several improvements and modifications can be made based on the technical solution and patent concept of the present invention without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A process for the preparation of melamine-based ternary benzoxazine resin, characterized by: The method comprises the following steps: (1) adding melamine, aldehyde group-containing monohydric phenol and organic solvent into a reactor at room temperature; the aldehyde group-containing monohydric phenol is at least one of p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, vanillin, salicylaldehyde and aldehyde group-containing naphthol; the molar ratio of melamine to aldehyde group-containing phenol in the reaction substrate is 1:3 to 1:3.5; (2) heating the reaction system to a certain temperature and stirring for a period of time to perform the synthesis reaction; (3) dropping the solution after the reaction in step (2) into a large amount of distilled water at room temperature, uniformly stirring during the dropping, and precipitating white flocculent precipitate to obtain a mixture containing the white flocculent precipitate; (4) filtering and replacing water of the mixture obtained in step (3) after standing for a period of time, and soaking the filter residue in a large amount of distilled water for a period of time; (5) filtering the mixture in step (4), vacuum oven drying the filter residue to obtain a triphenol; (6) dissolving the triphenol obtained in step (5) in an organic solvent, stirring with formaldehyde at a certain temperature, then dropping monohydric amine and stirring at a certain temperature to obtain a melamine-based triphenyl benzoxazine resin solution; (7) removing the solvent from the triphenyl benzoxazine resin solution to obtain a triphenyl benzoxazine resin.

2. The process for the preparation of melamine-based ternary benzoxazine resin according to claim 1, characterized by the fact that: The monohydric amine is at least one of aniline, m-aminophenylacetylene, p-aminophenylacetylene, methylamine, ethylamine, propylamine and furanmethylamine.

3. The method for preparing a melamine-based ternary benzoxazine resin according to claim 1, characterized in that: In the preparation method, the molar ratio of triphenol, monohydric amine and formaldehyde in the reaction substrate in step (6) is 1:3:4 to 1:3:

8.

4. The process for the preparation of melamine based ternary benzoxazine resin according to claim 1, characterized by: The organic solvent in steps (1) and (6) is any one of DMF, DMSO, DMAc or NMP, or a mixture of DMF, DMSO, DMAc or NMP and any one of ethanol, butanone, acetone, toluene, dioxane or dichloromethane.

5. The process for the preparation of melamine based ternary benzoxazine resin according to claim 1, characterized by: The temperature of the synthesis reaction in step (2) is 120-130℃; the stirring time is 5-6 hours.

6. The process for the preparation of melamine based ternary benzoxazine resin according to claim 1, characterized by: The temperature of the vacuum drying of the filter residue in step (5) is 50-70℃.

7. The method of preparing melamine-based ternary benzoxazine resin according to claim 1, characterized by: In step (6), the dissolution temperature of the triphenol and the organic solvent is 50±10℃, the stirring time is 0.5-1 hour; the reaction temperature after dropping the monohydric amine is 80±10℃, and the stirring time is 4-6 hours.

8. The melamine-based triphenyl benzoxazine resin prepared by the method according to any one of claims 1-7.

9. Application of the melamine-based triphenyl benzoxazine resin according to claim 8 in low-dielectric electronic materials.

10. The method of using melamine-based terbenzoxazine resin according to claim 8, characterized by: The obtained triphenyl benzoxazine resin is directly coated or applied, and then cured and formed.

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