Preparation method of polyamine-source benzoxazine film based on melamine

Abstract

The invention discloses a preparation method of a polyamine-source benzoxazine film based on melamine, and belongs to the technical field of high polymer materials. The preparation method comprises the following specific steps: S1, mixing benzotripolycyanamide and melamine to serve as an amine source, and stirring and reacting the amine source with a phenol source and paraformaldehyde in a solvent N-N dimethyl formamide to obtain a benzoxazine polymer hot solution; s2, the benzoxazine polymer hot solution is subjected to film forming through a solution pouring method, a benzoxazine film is obtained and then cooled, and the melamine-based polyamine-source benzoxazine film is obtained. The preparation technology is simple in process and obvious in effect, and large-scale production and application can be achieved. The polyamine-source benzoxazine resin prepared by the method has the characteristics of easiness in processing, high modulus, high strength, high bending strength, excellent hydrophobicity, excellent heat resistance, excellent chemical corrosion resistance, excellent mechanical strength and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and in particular to a method for preparing a melamine-based polyamine-source benzoxazine film. Background Art

[0002] Benzoxazine, a new type of phenolic resin, is a six-membered heterocyclic compound composed of oxygen and nitrogen atoms. The main characteristics of this type of compound are as follows:

[0003] ① Maintains the excellent electrical properties, flame retardant properties and mechanical properties of traditional phenolic resin.

[0004] ② The curing process does not require strong acid as a catalyst, Lewis acid or heating can cause polymerization.

[0005] ③The polymer has a high glass transition temperature and thermal oxidation stability.

[0006] ④ It overcomes the disadvantage of traditional phenolic resin that small molecules are volatilized during the polymerization process.

[0007] ⑤ Products prepared using raw materials with different structures can meet different practical needs.

[0008] Therefore, this resin has broad application prospects in aerospace, electronic information and other fields.

[0009] While benzoxazine resins have many advantages, they also present some challenges. For example, the bifunctional benzoxazine molecular structure can lead to poor polymer toughness. For example, patent application number CN201810330531.5 discloses a method for preparing benzoxazine resins using a polyamine source, but the type of amine source is not specified. Furthermore, the resin prepared using this method may sacrifice toughness, resulting in high brittleness in the cured resin, which could affect its application in dynamic load scenarios (such as impact-resistant composite materials). Summary of the Invention

[0010] The present invention aims to provide a method for preparing a melamine-based polyamine-source benzoxazine film, thereby effectively improving the toughness of the resin, while increasing the glass transition temperature of the benzoxazine resin, reducing the degree of polymerization reaction of benzoxazine, and alleviating the violent exothermic behavior of the benzoxazine resin (as can be seen from the DSC curve in the accompanying figure, the exothermic peak is shifted, and the gelation time proves that the violent exothermic behavior of the benzoxazine resin is alleviated), thereby facilitating production and processing.

[0011] The object of the present invention is achieved through the following technical solutions:

[0012] A method for preparing a polyamine-based benzoxazine film comprises the following steps:

[0013] S1. A mixture of benzoguanamine and melamine as an amine source is reacted with a phenol source and paraformaldehyde in a solvent of NN dimethylformamide with stirring to obtain a hot solution of a benzoxazine polymer;

[0014] S2. forming a film of the benzoxazine polymer hot solution by solution casting to obtain a benzoxazine film; and cooling the film to obtain a melamine-based polyamine source benzoxazine film.

[0015] Benzoxazine resin monomers are usually prepared by the reaction between phenols, primary amines and aldehyde compounds (usually formaldehyde). Melamine, as one of the amine sources, has the characteristics of low corrosion, low smoke generation, low cost, high thermal stability, and good synergistic effect. However, the reactivity of the benzoxazine resin prepared with melamine as the sole amine source is too high, resulting in the technical problems of the prepared benzoxazine resin such as short gelation time, narrow processing temperature window, and short product shelf life. The present invention introduces benzoguanamine (chemical formula C on the basis of melamine) into the benzoxazine resin. 12 H 16 N4), whose molecular structure contains benzene rings and melamine functional groups, can cross-link with other resins, thereby improving the material's durability, heat resistance, chemical resistance, and mechanical strength. This effectively overcomes the shortcomings of benzoxazine resins synthesized using melamine as an amine source, such as short gelation time, narrow processing temperature window, and storage difficulties.

[0016] The present application uses melamine and benzoguanamine as amine sources to synthesize a benzoxazine polymer hot solution with a phenol source and paraformaldehyde, and then forms a film by a solution casting method to obtain a polyamine-source benzoxazine resin that is easy to process, has high modulus, high strength, high flexural strength and excellent hydrophobicity. The entire preparation process is simple, the effect is obvious, and large-scale production and application can be achieved.

[0017] In the above-mentioned preparation process, the amino group in the amine source can effectively catalyze the cross-linking reaction of the oxazine ring, improving the cross-linking degree and thermal stability of the polymer, thereby enabling the wide application of this special polymer material in comprehensive fields. In addition, the introduction of the amino group can enhance the nucleophilicity of benzoxazine, making it exhibit stronger nucleophilicity in certain chemical reactions. The amino group is a strong electron donor and can increase the electron density of the benzene ring in benzoxazine through the conjugation effect. This electron donor effect affects the reactivity of benzoxazine, making it more susceptible to participating in some electrically sensitive chemical reactions. The amino group is a strong electron donor and can increase the electron density of the benzene ring in benzoxazine through the conjugation effect. This electron donor effect affects the reactivity of benzoxazine, making it more susceptible to participating in some electrically sensitive chemical reactions.

[0018] In the synthesis of benzoxazine resins, the amino groups of both amine sources participate in the Mannich reaction, combining with paraformaldehyde and bisphenol A to form benzoxazine monomers. During the curing process, the residual amino groups (regardless of the amine source) act as catalysts, promoting crosslinking reactions with cyano groups (or reactive groups formed after the opening of the oxazine ring), thereby increasing the polymer's crosslinking degree and thermal stability.

[0019] Through its unique phenyl-substituted structure, benzoguanamine forms multiple synergistic effects with melamine, bisphenol A, and paraformaldehyde in the system. The steric hindrance of its benzene ring modulates the density of the resin's crosslinking network, suppressing brittleness caused by excessive crosslinking. Simultaneously, the hydrophobicity and conjugation effects of the phenyl group synergize with the aromatic ring of bisphenol A to enhance the mechanical properties of the molecular chain. Furthermore, the retained amino groups (unsubstituted -NH2) in benzoguanamine act together with the amino groups of melamine as dynamic catalytic sites, activating cyano or oxazine ring-opening intermediates through an electron-donating effect during the curing process, promoting the efficient crosslinking reaction. This unique mechanism of action makes benzoguanamine a key functional component that balances the material's mechanical properties and reactivity.

[0020] In the above preparation process, curing under high temperature environment can more effectively improve the cross-linking reaction rate, mechanical properties and heat resistance of the system; at the same time, the benzene ring gives the polymer mechanical properties.

[0021] Preferably, in step S1, the molar ratio of the phenol source, paraformaldehyde and amine source is 1:1:(4-5). More preferably, the molar ratio of the phenol source, paraformaldehyde and amine source is 1:1:4.

[0022] Preferably, in step S1, the molar ratio of melamine to benzoguanamine is (9-6):(1-4). More preferably, the molar ratio of melamine to benzoguanamine is 9:1 or 8:2.

[0023] Preferably, in step S1, the stirring reaction temperature is 70-80° C., and the reaction time is 5-7 h.

[0024] Preferably, in step S1, the phenol source is bisphenol AF, biphenol, 1,4-butanediol, cardanol-based diol, bisphenol S or isosorbide.

[0025] Preferably, in step S1, benzoguanamine is replaced by a combination of benzoguanamine and any one or more of polyethyleneimine, aniline, p-toluidine, n-butylamine or ethylenediamine.

[0026] Preferably, in step S2, the temperature rising process of the solution casting method is: keeping warm at 80°C, 100°C, 120°C, 160°C, 180°C and 200°C for 1 to 3 hours respectively, and then keeping warm at 220°C for 2 to 4 hours.

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

[0028] 1. This application uses melamine and benzoguanamine as amine sources, and synthesizes a benzoxazine polymer hot solution with a phenol source and paraformaldehyde. Then, a film is formed by a solution casting method to obtain a melamine-based polyamine source benzoxazine film. The entire preparation process is simple, the effect is obvious, and it can be achieved in large-scale production and application.

[0029] The melamine-based polyamine-source benzoxazine film prepared in this application has the characteristics of easy processing, high modulus, high strength, high flexural strength, excellent hydrophobicity, excellent heat resistance, excellent chemical corrosion resistance and excellent mechanical strength.

[0030] 2. Compared with the use of melamine alone as an amine source, the present invention uses melamine and benzoguanamine as a common amine source, which can effectively improve the shortcomings of the benzoxazine resin synthesized using melamine as an amine source, such as short gelation time, narrow processing temperature window, and difficulty in storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 is the structural formula of the benzoxazine hot solution prepared in Example 1-3;

[0032] Figure 2 The DSC curves of the polyamine-derived benzoxazine monomers prepared in Examples 1-4 are shown;

[0033] Figure 3 The DSC curves of the polyamine-derived benzoxazine films prepared in Examples 1-4 are shown;

[0034] Figure 4 This is a contact angle test diagram of the polyamine-source benzoxazine film prepared in Example 1-4;

[0035] Figure 5 This is a graph showing the impact strength test of the polyamine-derived benzoxazine films prepared in Examples 1-4;

[0036] Figure 6 This is a graph showing the bending strength test of the polyamine-derived benzoxazine films prepared in Examples 1-4. DETAILED DESCRIPTION

[0037] Example 1

[0038] A method for preparing a polyamine-based benzoxazine film comprises the following steps:

[0039] S1. Stir melamine, benzoguanamine, bisphenol A, paraformaldehyde and NN dimethylformamide at 80°C for 5 hours to obtain a benzoxazine polymer hot solution with the structural formula shown below. Figure 1As shown; wherein the molar ratio of melamine to benzoguanamine is 9:1; the molar ratio of bisphenol A, paraformaldehyde and amine source (i.e., a mixture of melamine and benzoguanamine) is 1:1:4;

[0040] S2. The benzoxazine polymer hot solution is subjected to a solution casting method to form a film to obtain a polyamine-based benzoxazine film; wherein the temperature rise process of the solution casting method is: keeping the temperature at 80°C, 100°C, 120°C, 160°C, 180°C and 200°C for 1 hour respectively, and then keeping the temperature at 220°C for 2 hours. Thereafter, the cured benzoxazine film is naturally cooled to room temperature to obtain a melamine-based benzoxazine film [poly(ML-BG10)].

[0041] The properties of the melamine-based polyamine-source benzoxazine film obtained in Example 1 are as follows:

[0042] The gelation temperature is 140℃ for 6min, Td5 is 419℃, and the residual carbon rate is 53.9%.

[0043] Example 2

[0044] The difference between this embodiment and embodiment 1 is that in step S1, the molar ratio of melamine to benzoguanamine is 8:2. The remaining steps are exactly the same as those in embodiment 1.

[0045] The properties of the melamine-based polyamine-source benzoxazine film [poly(ML-BG20)] obtained in Example 2 are as follows:

[0046] The gelation temperature is 140℃ for 10min, Td5 is 421℃, and the residual carbon rate is 53.95%.

[0047] Example 3

[0048] The difference between this embodiment and embodiment 1 is that in step S1, the molar ratio of melamine to benzoguanamine is 7:3. The remaining steps are exactly the same as those in embodiment 1.

[0049] The properties of the melamine-based polyamine-source benzoxazine film [poly(ML-BG30)] obtained in Example 3 are as follows:

[0050] The gelation temperature is 140℃ for 13min, Td5 is 422℃, and the residual carbon rate is 54.43%.

[0051] Example 4

[0052] The difference between this embodiment and embodiment 1 is that in step S1, the molar ratio of melamine to benzoguanamine is 6:4. The remaining steps are exactly the same as those in embodiment 1.

[0053] The performance of the melamine-based polyamine source benzoxazine film [poly(ML-BG40)] obtained in Example 4 is as follows:

[0054] The gelation temperature is 140℃ for 14min, Td5 430℃, and the carbon residue rate is 54.69%.

[0055] In the above examples, the benzoxazine polymer hot solution in Examples 1-4 is respectively dropped into water to obtain white precipitates, and the corresponding polyamine source benzoxazine polymer monomers are obtained after drying at 80℃ (the DSC curve diagrams of the four monomers named as ML-BG10, ML-BG20, ML-BG30 and ML-BG40 respectively are shown in Figure 2

[0056] Comparative Example

[0057] A preparation method of a melamine-based polyamine source benzoxazine film, comprising the following steps:

[0058] S1, melamine, bisphenol A, paraformaldehyde and N-N dimethylformamide are stirred and reacted at 80℃ for 5h to obtain a benzoxazine polymer hot solution; wherein the mass ratio of bisphenol A, paraformaldehyde and melamine is 1:1:4;

[0059] S2, the benzoxazine polymer hot solution is cast into a film by solution casting method, to obtain a benzoxazine film; wherein the temperature rising process of the solution casting method is: respectively keeping at 80℃, 100℃, 120℃, 160℃, 180℃ and 200℃ for 1h, and then keeping at 220℃ for 2h, after that, the cured benzoxazine film is naturally cooled to room temperature, to obtain the melamine-based benzoxazine film [poly(PB-A)].

[0060] The performance of the melamine-based benzoxazine film obtained in the comparative example is as follows:

[0061] The gelation temperature is 140℃ for 1min, Td5 369℃, and the carbon residue rate is 34.9%.

[0062] It can be known from the comparison of Examples 1-4 and Comparative Example 1 that the reaction time is effectively prolonged by the addition of benzyl melamine, which is convenient for production and processing, and improves the thermal stability and decomposition temperature.

[0063] The DSC curve diagram of the melamine-based polyamine source benzoxazine film obtained in Examples 1-4 is shown in Figure 3 The contact angle test diagram is shown in Figure 4 The impact strength test diagram is shown in Figure 5 The bending strength test diagram is shown in Figure 6 ​​

[0064] pass Figure 2-6 It can be seen that the addition of benzoguanamine improves mechanical properties. Due to the steric hindrance effect, intermolecular reactions are more difficult, and the resin tends to polymerize linearly in the early stages. Through mechanical load-bearing and energy dissipation mechanisms, both rigidity and impact strength are increased.

Claims

1. A method for preparing a polyamine-based benzoxazine film, characterized in that: The steps include: S1. A mixture of benzoguanamine and melamine as an amine source is reacted with a phenol source and paraformaldehyde in a solvent of NN dimethylformamide with stirring to obtain a hot solution of a benzoxazine polymer; S2. forming a film of the benzoxazine polymer hot solution by solution casting to obtain a benzoxazine film, and then cooling the film to obtain a melamine-based polyamine source benzoxazine film.

2. The method for preparing a polyamine-based benzoxazine film according to claim 1, wherein: In the step S1, the molar ratio of the phenol source, paraformaldehyde and amine source is 1:1:(4-5).

3. The method for preparing a polyamine-based benzoxazine film according to claim 1, wherein: In the step S1, the molar ratio of melamine to benzoguanamine is (9-6):(1-4).

4. The method for preparing a polyamine-based benzoxazine film according to claim 1, wherein: In step S1, the stirring reaction temperature is 70-80° C., and the reaction time is 5-7 hours.

5. The method for preparing a polyamine-based benzoxazine film according to claim 1, wherein: In step S1, the phenol source is bisphenol AF, biphenol, 1,4-butanediol, cardanol-based diol, bisphenol S or isosorbide.

6. The method for preparing a polyamine-based benzoxazine film according to claim 1, wherein: In step S1, benzoguanamine is replaced by a combination of benzoguanamine and any one or more of polyethyleneimine, aniline, p-toluidine, n-butylamine or ethylenediamine.

7. The method for preparing a polyamine-based benzoxazine film according to claim 1, wherein: In step S2, the temperature rising process of the solution casting method is: keeping the temperature at 80°C, 100°C, 120°C, 160°C, 180°C and 200°C for 1 to 3 hours respectively, and then keeping the temperature at 220°C for 2 to 4 hours.

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