A flame-retardant modified benzoxazine resin and a preparation method thereof

Abstract

The application discloses a kind of flame-retardant modified benzoxazine resin, its preparation method is, benzoxazine monomer is blended with the binary phenol of boron-containing acetal structure as flame retardant, then the blend is cured to obtain flame-retardant modified benzoxazine resin;The preparation method of the binary phenol of boron-containing acetal structure: take hydroxybenzene boronic acid, pentaerythritol and water agent into reaction vessel, add organic solvent, stir at 80-100 ℃ for 4-8 hours, after reaction, rotary evaporation, dry to obtain binary phenol;Water agent is any one in petroleum ether, benzene, cyclohexane, chloroform.The blending method of benzoxazine monomer and binary phenol is solution blending or melt blending, and the curing method is thermal curing or catalytic curing.The boron acetal structure in flame retardant used in the application can produce the synergistic effect of condensed phase flame retardant and gas phase flame retardant, so that the flame-retardant performance of benzoxazine resin reaches UL94V-0 level, and the boron acetal structure can also promote charring, improve the carbon residue rate of benzoxazine resin.

Description

A flame-retardant modified benzoxazine resin and its preparation method Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a flame-retardant modified benzoxazine resin and its preparation method. Background Technology

[0002] Benzoxazines are a class of benzo-6 heterocyclic compounds containing oxygen and nitrogen atoms. They can undergo ring-opening polymerization under heating or catalytic conditions. Their monomers are obtained through Mannich condensation reactions using phenolic compounds, primary amine compounds, and formaldehyde as raw materials. Compared to other thermosetting resins, polybenzoxazine resins possess many superior properties, including near-zero curing shrinkage, no release of small molecules during curing, high heat resistance, high char residue, and excellent mechanical properties. However, most benzoxazine resins cannot meet flame retardant requirements, limiting their development. Therefore, there is an urgent need to develop flame-retardant benzoxazine resins.

[0003] Currently, the most common flame-retardant method for organic polymer materials is to add flame retardants to the polymer. Based on the application method, flame retardants can be divided into reactive and additive types. While reactive flame retardants have less impact on polymer performance, they are expensive, hindering cost savings and large-scale development. Among additive flame retardants, halogenated flame retardants, although effective, are gradually being phased out due to secondary pollution after combustion, and flame-retardant polymer materials are developing towards halogen-free and phosphorus-free methods. Regarding the flame retardancy of benzoxazine resins, existing literature has reported on numerous technologies, but two main problems remain: firstly, the flame-retardant effect is limited and needs further improvement; secondly, the preparation process of flame-retardant benzoxazine resins is complex, or the flame retardant composition is complex, making preparation difficult. Summary of the Invention

[0004] To address the issue that the flame retardant properties of current benzoxazine resins still need improvement, this invention provides a flame-retardant modified benzoxazine resin and its preparation method.

[0005] The method for preparing flame-retardant modified benzoxazine resin provided by the present invention firstly uses pentaerythritol and hydroxyphenylboronic acid as raw materials to synthesize a diphenol with a boron acetal structure, then blends it with benzoxazine monomer, and co-cures it by heating to obtain flame-retardant modified benzoxazine resin.

[0006] The molecular structure of the diphenol containing the boron acetal structure is any one of the following three structural formulas:

[0007]

[0008] The preparation method of the boron-containing acetal structure of the diphenol is as follows:

[0009] Hydroxyphenylboronic acid, pentaerythritol, and a dehydrating agent were added to a reaction vessel, along with an organic solvent. The mixture was stirred at 80-100°C for 4-8 hours. After the reaction was completed, the mixture was rotary evaporated and dried to obtain a diphenol with a boron acetal structure.

[0010] The water-removing agent is at least one of petroleum ether, benzene, cyclohexane, and chloroform;

[0011] The organic solvent is at least one of 1,4-dioxane, N,N-dimethylformamide, dimethyl sulfoxide, and toluene.

[0012] The hydroxyphenylboronic acid is any one of 2-hydroxyphenylboronic acid, 3-hydroxyphenylboronic acid, and 4-hydroxyphenylboronic acid.

[0013] The molar ratio of hydroxyphenylboronic acid to pentaerythritol is 2:1. The amount of organic solvent is calculated based on a solid content of 40%, and the amount of dehydrating agent is twice the amount of organic solvent.

[0014] The structural formula of the benzoxazine monomer is shown in any one of the following three structural formulas:

[0015]

[0016] Wherein, the R1 substituent is any one of -H, –CH3, –C(CH3)3.

[0017] Wherein, the R2 substituent can be any one of the following structural formulas:

[0018] -CH3-CH2CH2CH3

[0019]

[0020] The R3 substituent is any one of –CH2–, –C(CH3)2–, –O–, -C=O-, and SO2.

[0021] Preferably, the mass ratio of the benzoxazine monomer to the diphenol is 100:(3-20).

[0022] The blending method is solution blending or melt blending.

[0023] The melt blending temperature is 80–120℃, and the blending time is 0.5–3 h.

[0024] The organic solvent used for solution blending is one or more of the following: acetone, toluene, xylene, chloroform, dioxane, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide. The blending temperature is 25–90℃ and the blending time is 0.5–2 h.

[0025] The curing method is either thermosetting or catalytic curing.

[0026] The thermosetting method is a multi-stage thermosetting process, in which the blend is cured sequentially at 120-130℃ (2-4h), 140-150℃ (2-4h), 160-170℃ (2-4h), 180-190℃ (2-4h), and 200-220℃ (2-4h).

[0027] The catalyst used in the catalytic curing method is one or more of AlCl3, FeCl2, imidazole, oxalic acid, adipic acid, resorcinol, p-phenylenediamine, p-toluenesulfonic acid, and acetic anhydride, and the amount used is 0.2% to 8% of the total mass of benzoxazine monomer and flame retardant.

[0028] Compared with the prior art, the advantages of the present invention are:

[0029] (1) The boron acetal diol used in this invention contains both boron and acetal flame-retardant structures. Through the synergistic effect of condensed-phase flame retardancy and gas-phase flame retardancy, the flame retardancy of benzoxazine resin can be significantly improved. The main flame retardant mechanism is as follows: During high-temperature pyrolysis, boron migrates to the surface, and boron oxide is formed on the surface of the char layer. The boron oxide coats the surface of the char layer, thereby forming a dense char layer, which not only plays a role in solidified-phase flame retardancy but also improves the char residue of benzoxazine resin. At the same time, the bisacetal structure dehydrates and carbonizes, releasing CO2 gas, which plays a role in gas-phase flame retardancy.

[0030] (2) The phenolic hydroxyl groups in the boron-containing acetal structure of the diphenol used in this invention can catalyze the curing reaction of benzoxazine resin and reduce the curing reaction temperature.

[0031] (3) The flame retardant properties of the benzoxazine resin obtained by the present invention all reach UL94 V-0 level, and can be used as a resin matrix to prepare fiber-reinforced composite materials with excellent flame retardant properties. It has broad application prospects in aerospace, rail transportation, electronic communication and other fields.

[0032] (4) The method of preparing the boron acetal-containing diphenol flame retardant of the present invention is simple, easy to operate, and the raw materials are readily available and the cost is low.

[0033] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0034] Figure 1 shows the DSC results of benzoxazine before and after modification in Example 1.

[0035] Figure 2 shows the TGA results of the benzoxazine resin before and after modification in Example 1. Detailed Implementation

[0036] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0037] Example 1

[0038] 200g of phenol / diaminodiphenylmethane type benzoxazine monomer was added to 10g of a diphenol (p-PHB) containing a boron acetal structure. The mixture was melt-blended at 120℃ for 30min, and then cured at 120-200℃ for 10h. Specifically, the curing was performed sequentially at 120℃ (2h), 140℃ (2h), 160℃ (2h), 180℃ (2h), and 200℃ (2h) to obtain a flame-retardant modified benzoxazine resin. The structural formula of the phenol / diaminodiphenylmethane type benzoxazine monomer is as follows:

[0039]

[0040] The synthesis method of p-PHB is as follows: 4-hydroxyphenylboronic acid, pentaerythritol, and petroleum ether are added to a reaction vessel, and N,N-dimethylformamide is added as a solvent. The mixture is heated and stirred at 100°C for 5 hours. After the reaction is completed, it is rotary evaporated and dried to obtain a white solid powder. The molar ratio of 4-hydroxyphenylboronic acid to pentaerythritol is 2:1. The amount of N,N-dimethylformamide is calculated based on a solid content of 40%, and the amount of petroleum ether is twice the amount of N,N-dimethylformamide.

[0041] Five samples of the prepared flame-retardant modified benzoxazine resin were subjected to a standard vertical burning test. The results are shown in Table 1. The results show that the modified benzoxazine resin has a UL94 V-0 flame retardancy rating. Similarly, using phenol / diaminodiphenylmethane type benzoxazine monomer without adding p-PHB, a benzoxazine resin without p-PHB was prepared according to the same curing procedure. A standard vertical burning test was then performed, and the results showed that it only had a UL94 V-1 flame retardancy rating. This indicates that the addition of p-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0042] Table 1. Standard vertical combustion test results of the modified benzoxazine resin in Example 1

[0043]

[0044] DSC tests were performed on the samples before curing of the blend of phenol / diaminodiphenylmethane benzoxazine monomer and p-PHB, and the samples of phenol / diaminodiphenylmethane benzoxazine monomer alone. The results are shown in Figure 1. It can be seen that compared with the sample without p-PHB, the peak curing temperature decreased from 240℃ to 222℃ after adding p-PHB, proving that p-PHB has a catalytic effect on benzoxazine resin.

[0045] The flame-retardant modified benzoxazine resin and the benzoxazine resin without p-PHB were subjected to TGA testing after curing, and the results are shown in Figure 2. It can be seen that the char residue of the resin with p-PHB added was 52.1%, while the char residue of the resin without p-PHB was only 46.9%. This indicates that adding p-PHB in this invention can improve the char residue of the benzoxazine resin.

[0046] Example 2

[0047] 200g of phenol / aniline type benzoxazine monomer was added to 15g of a diphenol (m-PHB) containing a boron acetal structure. The mixture was melt-blended at 110℃ for 1 hour, and then cured at 120–200℃ for 12 hours. Specifically, the curing was carried out sequentially at 120℃ (2 hours), 140℃ (2 hours), 160℃ (2 hours), 180℃ (2 hours), and 200℃ (4 hours) to obtain the flame-retardant modified benzoxazine resin. The structural formula of the phenol / aniline type benzoxazine monomer is as follows:

[0048]

[0049] The synthesis method of m-PHB is as follows: 3-hydroxyphenylboronic acid, pentaerythritol, and petroleum ether are added to a reaction vessel, benzene is added as a solvent, and the mixture is heated and stirred at 100°C for 4 hours. After the reaction is completed, the mixture is rotary evaporated and dried to obtain a white solid powder. The molar ratio of 3-hydroxyphenylboronic acid to pentaerythritol is 2:1, the amount of benzene is calculated based on a solid content of 40%, and the amount of petroleum ether is twice the amount of benzene.

[0050] Five samples of the prepared flame-retardant modified benzoxazine resin were subjected to a standard vertical burning test. The test results are shown in Table 2. The results show that the modified benzoxazine resin has a UL94 V-0 flame retardancy rating. Similarly, phenol / aniline type benzoxazine monomers were used without the addition of m-PHB, and a benzoxazine resin without m-PHB was prepared according to the same curing procedure. A standard vertical burning test was conducted, and the results showed that it was not flame-retardant. This indicates that the addition of m-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0051] Table 2. Standard vertical combustion test results of the modified benzoxazine resin in Example 2

[0052]

[0053] Example 3

[0054] Take 200g of bisphenol A / methylamine type benzoxazine monomer, add 12g of diphenol (o-PHB) containing boron acetal structure, melt blend at 100℃ for 1.5h, and then cure at 120-200℃ for 10h. Specifically, cure in sequence at 130℃ (2h), 150℃ (2h), 170℃ (2h), 180℃ (2h), and 200℃ (2h) to obtain flame-retardant modified benzoxazine resin.

[0055] The structural formula of the bisphenol A / methylamine type benzoxazine monomer is as follows:

[0056]

[0057] The synthesis method of o-PHB is as follows: 2-hydroxyphenylboronic acid, pentaerythritol, and cyclohexane are added to a reaction vessel, and dioxane is added as a solvent. The mixture is heated and stirred at 80°C for 7 hours. After the reaction is completed, the mixture is rotary evaporated and dried to obtain a white solid powder. The molar ratio of 2-hydroxyphenylboronic acid to pentaerythritol is 2:1. The amount of dioxane is calculated based on a solid content of 40%, and the amount of cyclohexane is twice the amount of dioxane.

[0058] Five samples of the prepared flame-retardant modified benzoxazine resin were subjected to a standard vertical burning test. The results are shown in Table 3. The results show that the modified benzoxazine resin has a UL94 V-0 flame retardancy rating. Similarly, bisphenol A / methylamine type benzoxazine monomer was used without the addition of o-PHB, and a benzoxazine resin without o-PHB was prepared according to the same curing procedure. A standard vertical burning test was conducted, and the results showed that it was not flame-retardant. This indicates that the addition of o-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0059] Table 3. Standard vertical combustion test results of the modified benzoxazine resin in Example 3

[0060]

[0061] Example 4

[0062] 200g of phenol / m-aminophenylacetylene type benzoxazine monomer was added to 10g of boron-containing bisacetal diphenol (p-PHB). The mixture was then co-mixed at 80℃ with toluene as solvent (20g of toluene) for 1 hour, followed by curing at 120–200℃ for 14 hours. Specifically, curing was carried out sequentially at 130℃ (3 hours), 150℃ (3 hours), 170℃ (3 hours), 180℃ (3 hours), and 200℃ (2 hours) to obtain flame-retardant modified benzoxazine resin. The structural formula of the phenol / m-aminophenylacetylene type benzoxazine monomer is as follows:

[0063]

[0064] Five samples of the prepared flame-retardant modified benzoxazine resin were subjected to a standard vertical burning test. The results are shown in Table 4. The results show that the modified benzoxazine resin has a UL94 V-0 flame retardancy rating. Similarly, phenol / m-aminophenylacetylene type benzoxazine monomers were used without the addition of p-PHB, and a benzoxazine resin without p-PHB was prepared according to the same curing procedure. A standard vertical burning test was conducted, and the results showed that it was not flame-retardant. This indicates that the addition of p-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0065] Table 4. Standard vertical combustion test results of the modified benzoxazine resin in Example 4

[0066]

[0067]

[0068] Example 5

[0069] 200g of phenol / diaminodiphenyl sulfone type benzoxazine monomer was added, along with 15g of a diphenol (p-PHB) containing a boron acetal structure. The mixture was then stirred at 50℃ with tetrahydrofuran as the solvent (30g of tetrahydrofuran) for 1 hour. Then, 2.15g of AlCl3 was added as a catalyst, and the mixture was cured at 120–200℃ for 16 hours. Specifically, the curing was carried out sequentially at 130℃ (4 hours), 150℃ (3 hours), 170℃ (4 hours), 180℃ (3 hours), and 200℃ (2 hours) to obtain the flame-retardant modified benzoxazine resin. The structural formula of the phenol / diaminodiphenyl sulfone type benzoxazine monomer is as follows:

[0070]

[0071] Five samples of the prepared flame-retardant modified benzoxazine resin were subjected to a standard vertical burning test. The results are shown in Table 5. The results show that the modified benzoxazine resin has a UL94 V-0 flame retardancy rating. Similarly, phenol / diaminodiphenyl sulfone type benzoxazine monomer was used without the addition of p-PHB, and a benzoxazine resin without p-PHB was prepared according to the same curing procedure. A standard vertical burning test was conducted, and the results showed that it was not flame-retardant. This indicates that the addition of p-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0072] Table 5. Standard vertical combustion test results of the modified benzoxazine resin in Example 5

[0073]

[0074] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a flame-retardant modified benzoxazine resin, characterized in that, A benzoxazine monomer is blended with a boron-containing acetal-structured diphenol used as a flame retardant, and the blend is then cured to obtain a flame-retardant modified benzoxazine resin; the diphenol has any one of the following three molecular structural formulas:

2. The method for preparing the flame-retardant modified benzoxazine resin as described in claim 1, characterized in that, The preparation method of the diphenol is as follows: hydroxyphenylboronic acid, pentaerythritol and a dehydrating agent are added to a reaction vessel, an organic solvent is added, and the mixture is stirred and reacted at 80-100℃ for 4-8 hours. After the reaction is completed, the mixture is rotary evaporated and dried to obtain a diphenol with a boron acetal structure. The dehydrating agent is at least one of petroleum ether, benzene, cyclohexane and chloroform. The organic solvent is at least one of 1,4-dioxane, N,N-dimethylformamide, dimethyl sulfoxide and toluene.

3. The method for preparing the flame-retardant modified benzoxazine resin as described in claim 2, characterized in that, The hydroxyphenylboronic acid is any one of 2-hydroxyphenylboronic acid, 3-hydroxyphenylboronic acid, and 4-hydroxyphenylboronic acid.

4. The method for preparing the flame-retardant modified benzoxazine resin as described in claim 2, characterized in that, The molar ratio of hydroxyphenylboronic acid to pentaerythritol is 2:

1. The amount of organic solvent used is calculated based on a solid content of 40%, and the amount of dehydrating agent used is twice the amount of organic solvent used.

5. The method for preparing the flame-retardant modified benzoxazine resin as described in claim 1, characterized in that, The mass ratio of the benzoxazine monomer to the diphenol is 100:(3-20).

6. The method for preparing the flame-retardant modified benzoxazine resin as described in claim 1, characterized in that, The blending method is solution blending or melt blending.

7. The method for preparing the flame-retardant modified benzoxazine resin as described in claim 1, characterized in that, The curing method is either thermosetting or catalytic curing.

8. A flame-retardant modified benzoxazine resin, characterized in that, It is prepared by the method described in any one of claims 1-7.

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