Flame-retardant modified benzoxazine resin and preparation method thereof

Abstract

The invention discloses flame-retardant modified benzoxazine resin, and a preparation method of the flame-retardant modified benzoxazine resin comprises the following steps: blending a benzoxazine monomer with dihydric phenol which is used as a flame retardant and contains a boron acetal structure, and then curing the blend to obtain the flame-retardant modified benzoxazine resin, the preparation method of the dihydric phenol containing the boron acetal structure comprises the following steps: adding hydroxyphenylboronic acid, pentaerythritol and a water-carrying agent into a reaction container, adding an organic solvent, carrying out a stirring reaction at 80-100 DEG C for 4-8 h, and after the reaction is finished, carrying out rotary evaporation and drying to obtain the dihydric phenol, the water-carrying agent is any one of petroleum ether, benzene, cyclohexane and chloroform. The blending method of the benzoxazine monomer and the dihydric phenol is solution blending or melt blending, and the curing method is thermocuring or catalytic curing. The boron acetal structure in the used flame retardant can generate a condensed phase flame retardant and gas phase flame retardant synergistic effect, so that the flame retardant property of the benzoxazine resin reaches UL94V-0 level, and the boron acetal structure can promote char formation and improve the carbon residue rate of the benzoxazine resin.

Description

Technical Field

[0001] The invention relates to the technical field of polymer materials, in particular to a flame retardant modified benzoxazine resin and a preparation method thereof. Background Art

[0002] Benzoxazine is a class of benzo six-membered heterocyclic compounds containing oxygen and nitrogen atoms. It can undergo ring-opening polymerization under heating or catalyst conditions. Its monomers are obtained through Mannich condensation reaction with phenolic compounds, primary amine compounds and formaldehyde as raw materials. Compared with other thermosetting resins, polybenzoxazine resins have many excellent properties, with almost zero curing shrinkage, no small molecule release during the curing process, high heat resistance, residual carbon rate, and excellent mechanical properties. However, most benzoxazine resins cannot meet the flame retardant requirements, which limits the development of resins. Therefore, there is an urgent need to develop flame-retardant benzoxazine resins.

[0003] At present, the commonly used flame retardant method for organic polymer materials is to add flame retardants to the polymer. According to the method of use, flame retardants can be divided into reactive and additive types. Although the reactive type has little effect on the performance of the polymer, it is expensive, which is not conducive to cost saving and large-scale development. Among the additive flame retardants, halogen flame retardants can achieve the desired effect, but due to secondary pollution after combustion, they are gradually withdrawing from the stage of history, and flame-retardant polymer materials are developing in the direction of halogen-free and phosphorus-free. There are many literature reports on the flame retardancy of benzoxazine resins in the prior art, and there are still two main problems: one is that the flame retardant effect is limited and needs to be further improved; the other is that the preparation process of flame-retardant benzoxazine resins is complicated or the flame retardant composition is complicated, and the preparation is difficult. Summary of the invention

[0004] In view of the problem that the flame retardant performance of current benzoxazine resins still needs to be improved, the present invention provides a flame retardant modified benzoxazine resin and a preparation method thereof.

[0005] The invention provides a method for preparing a flame retardant modified benzoxazine resin. Firstly, pentaerythritol and hydroxyphenylboric acid are used as raw materials to synthesize a dihydric phenol containing a boron acetal structure, and then the dihydric phenol is blended with a benzoxazine monomer, and the mixture is heated and co-cured to obtain a flame retardant modified benzoxazine resin.

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

[0007]

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

[0009] Hydroxyphenylboric acid, pentaerythritol and a water-carrying agent are added to a reaction container, and an organic solvent is added. The mixture is stirred and reacted at 80-100° C. for 4-8 hours. After the reaction is completed, the mixture is rotary evaporated and dried to obtain a dihydric phenol containing a boron acetal structure.

[0010] The water-carrying 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 hydroxyphenylboric acid is any one of 2-hydroxyphenylboric acid, 3-hydroxyphenylboric acid and 4-hydroxyphenylboric acid.

[0013] The molar ratio of hydroxyphenylboric acid to pentaerythritol is 2:1, the amount of the organic solvent is calculated based on a solid content of 40%, and the amount of the water-carrying agent is twice the amount of the 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, and -C(CH3)3.

[0017] Wherein, the R2 substituent is 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 dihydric phenol is 100:(3-20).

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

[0023] The temperature of melt blending is 80-120°C, and the blending time is 0.5-3h.

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

[0025] The curing method is thermal curing or catalytic curing.

[0026] The thermal curing method is a multi-stage thermal curing, and the blend is cured in sequence according to the procedures of 120-130°C (2-4h), 140-150°C (2-4h), 160-170°C (2-4h), 180-190°C (2-4h), and 200-220°C (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 the benzoxazine monomer and the flame retardant.

[0028] Compared with the prior art, the present invention is beneficial in that:

[0029] (1) The boron acetal diphenol used in the present invention contains two flame retardant structures, boron and acetal, which can greatly improve the flame retardancy of benzoxazine resin through the synergistic effect of condensed phase flame retardancy and gas phase flame retardancy; the main flame retardant mechanism is that during the high temperature cracking process, the boron element will migrate to the surface, and boron oxide will form on the surface of the carbon layer, and the boron oxide will be coated on the surface of the carbon layer to form a dense carbonized layer, which not only plays a solid phase flame retardant role, but also improves the residual carbon rate of benzoxazine resin. At the same time, the diacetal structure will dehydrate and carbonize, releasing CO2 gas, which plays a gas phase flame retardant role.

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

[0031] (3) The flame retardant properties of the benzoxazine resin obtained in 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, and have broad application prospects in the fields of aerospace, rail transportation, electronic communications, etc.

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

[0033] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The DSC results of benzoxazine before and after modification in Example 1 are shown.

[0035] Figure 2 These are the TGA results of the benzoxazine resin before and after modification in Example 1. DETAILED DESCRIPTION

[0036] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0037] Example 1

[0038] Take 200g of phenol / diaminodiphenylmethane type benzoxazine monomer, add 10g of diphenol (p-PHB) containing boron acetal structure, melt blend at 120°C for 30min, and then cure at 120-200°C for 10h, specifically, cure in the order of 120°C (2h), 140°C (2h), 160°C (2h), 180°C (2h), 200°C (2h) to obtain flame retardant modified benzoxazine resin. The structural formula of 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 container, N,N-dimethylformamide is added as a solvent, and the mixture is heated and stirred at 100°C for 5 hours. After the reaction is completed, the mixture 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] The prepared flame-retardant modified benzoxazine resin was subjected to a standard vertical combustion test of 5 specimens. The results are shown in Table 1. The results show that the modified benzoxazine resin has UL94 V-0 flame retardancy. Similarly, a benzoxazine resin without p-PHB was prepared by taking a phenol / diaminodiphenylmethane type benzoxazine monomer without adding p-PHB according to the same curing procedure. The standard vertical combustion test was carried out, and the results showed that it was only UL94 V-1 flame retardant. This shows that the addition of p-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0042] Table 1. Standard vertical burning test results of modified benzoxazine resin of Example 1

[0043]

[0044] DSC tests were performed on the blend of phenol / diaminodiphenylmethane benzoxazine monomer and p-PHB and single phenol / diaminodiphenylmethane benzoxazine monomer before curing. The results are as follows: Figure 1It can be seen that compared with the sample without adding p-PHB, after adding p-PHB, the curing peak temperature is reduced from 240°C to 222°C, proving that p-PHB has a catalytic effect on benzoxazine resin.

[0045] The flame retardant modified benzoxazine resin obtained after curing and the benzoxazine resin without p-PHB were subjected to TGA test. The results are as follows: Figure 2 As shown in the figure, it can be seen that the carbon residue rate of the resin after adding p-PHB is 52.1%, and the carbon residue rate of the resin without adding p-PHB is only 46.9%. This shows that the addition of p-PHB in the present invention can increase the carbon residue rate of the benzoxazine resin.

[0046] Example 2

[0047] Take 200g of phenol / aniline benzoxazine monomer, add 15g of diphenol (m-PHB) containing boron acetal structure, melt blend at 110℃ for 1h, and then cure at 120-200℃ for 12h. Specifically, the curing is carried out in the order of 120℃ (2h), 140℃ (2h), 160℃ (2h), 180℃ (2h), and 200℃ (4h) to obtain flame retardant modified benzoxazine resin. The structural formula of phenol / aniline 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 container, 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] The prepared flame retardant modified benzoxazine resin was subjected to a standard vertical combustion test of 5 specimens. The test results are shown in Table 2. The results show that the modified benzoxazine resin has UL94 V-0 flame retardancy. Similarly, the phenol / aniline benzoxazine monomer was taken, and m-PHB was not added. The benzoxazine resin without m-PHB was prepared according to the same curing procedure. The standard vertical combustion test was carried out, and the results showed that it was not flame retardant. This shows that the addition of m-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0051] Table 2. Standard vertical burning test results of modified benzoxazine resin of 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°C for 1.5h, and then cure at 120-200°C for 10h. Specifically, the curing is carried out in accordance with the procedure of 130°C (2h), 150°C (2h), 170°C (2h), 180°C (2h), and 200°C (2h) to obtain a flame retardant modified benzoxazine resin.

[0055] The structural formula of 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, dioxane is added as a solvent, heated and stirred at 80°C for 7 hours, and after the reaction is completed, rotary evaporation is performed 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] The prepared flame retardant modified benzoxazine resin was subjected to a standard vertical burning test for 5 specimens. The results are shown in Table 3. The results show that the modified benzoxazine resin has UL94 V-0 flame retardancy. Similarly, bisphenol A / methylamine benzoxazine monomers were taken, and o-PHB was not added. The benzoxazine resin without o-PHB was prepared according to the same curing procedure. The standard vertical burning test was carried out, and the results showed that it was not flame retardant. This shows that the addition of o-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0059] Table 3. Standard vertical burning test results of modified benzoxazine resin of Example 3

[0060]

[0061] Example 4

[0062] Take 200g of phenol / m-aminophenylacetylene benzoxazine monomer, add 10g of boron-containing diacetal diphenol (p-PHB), mix the solution at 80°C with toluene as solvent (toluene dosage 20g) for 1h, and then cure at 120-200°C for 14h. Specifically, the curing is carried out in accordance with the procedures of 130°C (3h), 150°C (3h), 170°C (3h), 180°C (3h), and 200°C (2h) to obtain a flame-retardant modified benzoxazine resin. The structural formula of phenol / m-aminophenylacetylene benzoxazine monomer is as follows:

[0063]

[0064] The prepared flame-retardant modified benzoxazine resin was subjected to a standard vertical combustion test of 5 specimens. The results are shown in Table 4. The results show that the modified benzoxazine resin has UL94 V-0 flame retardancy. Similarly, a benzoxazine resin without p-PHB was prepared by taking a phenol / m-aminophenylacetylene type benzoxazine monomer without adding p-PHB according to the same curing procedure. The standard vertical combustion test was carried out, and the results showed that it was not flame retardant. This shows that the addition of p-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0065] Table 4. Standard vertical burning test results of modified benzoxazine resin of Example 4

[0066]

[0067]

[0068] Example 5

[0069] Take 200g of phenol / diaminodiphenyl sulfone type benzoxazine monomer, add 15g of diphenol (p-PHB) containing boron acetal structure, and mix the solution at 50°C with tetrahydrofuran as solvent (30g of tetrahydrofuran) for 1h, then add 2.15g of AlCl3 as catalyst, and cure at 120-200°C for 16h. Specifically, the curing is carried out in accordance with the procedures of 130°C (4h), 150°C (3h), 170°C (4h), 180°C (3h), and 200°C (2h) to obtain flame retardant modified benzoxazine resin. The structural formula of phenol / diaminodiphenyl sulfone type benzoxazine monomer is as follows:

[0070]

[0071] The prepared flame retardant modified benzoxazine resin was subjected to a standard vertical combustion test of 5 specimens. The results are shown in Table 5. The results show that the modified benzoxazine resin has UL94 V-0 flame retardancy. Similarly, a benzoxazine resin without p-PHB was prepared by taking a phenol / diaminodiphenyl sulfone type benzoxazine monomer without adding p-PHB according to the same curing procedure. The standard vertical combustion test was carried out, and the results showed that it was not flame retardant. This shows that the addition of p-PHB can significantly improve the flame retardancy of benzoxazine resin.

[0072] Table 5. Standard vertical burning test results of modified benzoxazine resin of Example 5

[0073]

[0074] The above description is only a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as a preferred embodiment as above, it is not intended to limit the present invention. Any technician familiar with the profession can make some changes or modifications to equivalent embodiments of equivalent changes using the technical contents disclosed above without departing from the scope of the technical solution of the present invention. However, any simple modification, equivalent change and modification made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a flame retardant modified benzoxazine resin, characterized in that: Blending a benzoxazine monomer with a dihydric phenol having a boron acetal structure as a flame retardant, and then curing the blend to obtain a flame retardant modified benzoxazine resin; The molecular structural formula of the dihydric phenol is any one of the following three structural formulas:

2. The method for preparing the flame retardant modified benzoxazine resin according to claim 1, characterized in that: The preparation method of the dihydric phenol is as follows: Hydroxyphenylboric acid, pentaerythritol and a water-carrying agent are added to a reaction container, and an organic solvent is added, and the mixture is stirred and reacted at 80-100° C. for 4-8 hours. After the reaction is completed, the mixture is rotary evaporated and dried to obtain a dihydric phenol containing a boron acetal structure; The water-carrying 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 according to claim 2, characterized in that: The hydroxyphenylboric acid is any one of 2-hydroxyphenylboric acid, 3-hydroxyphenylboric acid and 4-hydroxyphenylboric acid.

4. The method for preparing the flame retardant modified benzoxazine resin according to claim 2, characterized in that: The molar ratio of hydroxyphenylboric acid to pentaerythritol is 2:1, the amount of organic solvent is calculated based on a solid content of 40%, and the amount of water-carrying agent is twice the amount of organic solvent.

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

6. The method for preparing the flame retardant modified benzoxazine resin according to 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 according to claim 1, characterized in that: The curing method is thermal curing or catalytic curing.

8. A flame retardant modified benzoxazine resin, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

Images