Halogen-free and phosphorus-free flame-retardant modified benzoxazine resin, and preparation method and application thereof

Abstract

The application discloses a halogen-free and phosphorus-free flame-retardant modified benzoxazine resin and a preparation method thereof, and relates to taking one or more benzoxazine monomers and one or more aldehyde-based compounds as raw materials, and obtaining the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin through blending and heating curing; the mass ratio of the benzoxazine monomers to the aldehyde-based compounds is 100:(1-40); the benzoxazine monomers are diphenol-type benzoxazine monomers, diamine-type benzoxazine monomers, triphenol-type benzoxazine monomers or triamine-type benzoxazine monomers. The application also provides application of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin in preparation of fiber-reinforced composite materials, rail transit interior trim parts, printed circuit boards, paints, adhesives and the like. The halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared by the application has excellent flame-retardant performance and heat resistance.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, and relates to benzoxazine resins, particularly to a halogen-free and phosphorus-free flame-retardant modified benzoxazine resin, its preparation method, and its application. Background Technology

[0002] Since their invention and application in daily life, polymers have exacerbated the fire hazards and dangers caused by combustion, making the development of flame-retardant polymer materials an urgent priority. Introducing halogen or phosphorus elements into polymers can achieve flame retardancy; however, polymers prepared in this way produce toxic gases or cause environmental problems during combustion, leading to a trend towards halogen-free and phosphorus-free flame-retardant polymers. Furthermore, synthesizing flame-retardant elements into resin structures carries risks of synthetic difficulties, as well as the challenges of scarce and expensive raw materials.

[0003] Benzoxazine monomers are benzo[a]heterocyclic compounds synthesized from primary amine compounds, phenolic compounds, and formaldehyde. Under heating or with a catalyst, they undergo ring-opening polymerization to obtain cross-linked cured products. Benzoxazine does not release small molecules during curing, exhibits low curing shrinkage, and the cured products possess high heat resistance, high strength, and low water absorption, attracting widespread attention and rapid development. They have already found applications in aerospace, electronics, and other fields. However, most benzo[a]oxazine resins cannot meet high-level flame retardant requirements, significantly limiting their further development.

[0004] The development of halogen-free and phosphorus-free flame-retardant benzoxazine has attracted widespread interest. Patent CN202010183622.8 discloses a halogen-free and phosphorus-free intrinsically flame-retardant benzoxazine, introducing an intrinsically flame-retardant benzoxazine prepared based on deoxybenzoin bisphenol. This benzoxazine exhibits excellent heat resistance and high char residue while maintaining V-0 flame retardancy. However, the phenol source used is expensive and difficult to prepare. Patent CN202111203283.6 discloses a high-heat-resistant, low-dielectric, flame-retardant benzoxazine resin, introducing alkynyl-containing benzoxazine monomers and alkynyl-containing imide benzoxazine monomers. These two monomers can synergistically improve the flame retardancy of the resin, but the preparation method is complex, and the alkynyl compounds are too expensive. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of high raw material costs and complex preparation methods in the preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resins. This invention provides a halogen-free and phosphorus-free flame-retardant modified benzoxazine resin and its preparation method. The method uses aldehyde compounds to blend and modify benzoxazine, which reduces the difficulty of preparing halogen-free and phosphorus-free flame-retardant modified benzoxazine resin while optimizing the flame-retardant properties and heat resistance of the resin.

[0006] Another object of the present invention is to provide the use of the above-mentioned halogen-free and phosphorus-free flame-retardant modified benzoxazine resin.

[0007] To achieve the above objectives, the present invention adopts the following technical solutions.

[0008] This invention provides a method for preparing halogen-free and phosphorus-free flame-retardant modified benzoxazine resin, which is obtained by blending and heating one or more benzoxazine monomers and one or more aldehyde compounds as raw materials; the mass ratio of the benzoxazine monomer to the aldehyde compound is 100:(1-40); the benzoxazine monomer is a diphenol type benzoxazine monomer, a diamine type benzoxazine monomer, a triphenol type benzoxazine monomer, or a triamine type benzoxazine monomer.

[0009] The benzoxazine monomer is selected from one of the following structural formulas:

[0010]

[0011] In ac, the R1 substituent can be H, 1 to 2 -CH3 (when it is one -CH3, it can be at position 2, 3, 4, or 5; when it is two -CH3, the two -CH3 are located at positions 2 and 3, 2 and 4, 2 and 5, 3 and 4, or 3 and 5 respectively), or -C(CH3)3;

[0012] The R2 substituent in dh can be one of the following structural formulas:

[0013]

[0014] The aforementioned aldehyde compounds are aldehydes with benzene rings or heterocyclic structures, or benzoxazine monomers containing aldehyde groups.

[0015] The aldehyde containing a benzene ring or heterocyclic structure is selected from one of the following structural formulas:

[0016]

[0017] The aldehyde-containing benzoxazine monomer is selected from one of the following structural formulas:

[0018]

[0019] The R substituent can be one of the following structures:

[0020]

[0021] In the above-mentioned method for preparing halogen-free and phosphorus-free flame-retardant modified benzoxazine resin, the mass ratio of the benzoxazine monomer to the aldehyde compound is preferably 100:(3-25), more preferably 100:(5-20).

[0022] The preparation method of the above-mentioned halogen-free and phosphorus-free flame-retardant modified benzoxazine resin includes the following blending step: benzoxazine monomer and aldehyde compound are melt-blended or solution-blended together to obtain modified benzoxazine blend.

[0023] In one feasible embodiment, the melt blending temperature is 50-160°C, and the blending time is 0.5-3 hours. In a preferred embodiment, the melt blending temperature is 90-140°C, and more preferably 100-130°C.

[0024] In one feasible implementation, the organic solvent used for solution blending is at least one selected from acetone, butanone, toluene, xylene, chloroform, 1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and diethyl ether. The blending temperature is 25-90°C, and the blending time is 0.5-3 hours. In a preferred implementation, the solution blending time is 1-2 hours.

[0025] In one possible implementation, the blending step further includes adding a curing catalyst, which is melt-blended or solution-blended together with the benzoxazine monomer and the aldehyde compound. The catalyst is at least one selected from imidazole, benzimidazole, resorcinol, m-aminophenylacetylene, phenolic resin, acetic acid, oxalic acid, aluminum trichloride, and ferric chloride. The mass ratio of the catalyst to the benzoxazine monomer is (0.5-10):100; in a preferred implementation, the mass ratio is (0.5-3):100.

[0026] The preparation method of the above-mentioned halogen-free and phosphorus-free flame-retardant modified benzoxazine resin includes a heating and curing step of: the obtained modified benzoxazine blend is subjected to gradient thermocuring at 100-220℃ for 8-16 hours. In a preferred embodiment, the obtained modified benzoxazine blend is subjected to a heat-holding reaction in 4-6 temperature segments at 100-220℃ to achieve gradient thermocuring.

[0027] The above-mentioned heating and curing step is preferably performed by subjecting the obtained modified benzoxazine blend to gradient thermocuring at 120-200℃ for 8-12 hours. In a preferred embodiment, the obtained modified benzoxazine blend is subjected to a heat preservation reaction in 4-6 temperature segments at 120-200℃ to achieve gradient thermocuring.

[0028] The present invention also provides a halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared by the above method, which can achieve UL94 V-0 level flame retardancy and has excellent flame retardant performance; at the same time, the glass temperature of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin can reach 265℃, which has good heat resistance.

[0029] This invention also provides the application of the above-mentioned halogen-free and phosphorus-free flame-retardant modified benzoxazine resin in the preparation of fiber-reinforced composite materials, rail transit interior parts, printed circuit boards, coatings, adhesives, etc.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention uses benzoxazine and aldehyde compounds as raw materials, and can prepare halogen-free and phosphorus-free flame-retardant modified benzoxazine resin by blending and heating curing, which greatly simplifies the preparation method of flame-retardant resin.

[0032] (2) The present invention utilizes aldehyde compounds to modify benzoxazine monomers through blending. The copolymerization of aldehydes and benzoxazine can increase the crosslinking density of the system and improve the heat resistance of benzoxazine resin.

[0033] (3) In this invention, aldehyde compounds are used to modify benzoxazine by blending. When the solidified material is ignited, the aldehyde group can be oxidized to carboxyl group and decarboxylated, which increases the release of CO2 and water molecules and achieves the purpose of gas phase flame retardancy. At the same time, the co-crosslinking reaction between the aldehyde group and the benzoxazine monomer at high temperature can also promote the char formation of benzoxazine and achieve the purpose of solid phase flame retardancy.

[0034] (4) The halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared by the present invention has excellent flame-retardant and heat-resistant properties, and can be used to prepare flame-retardant fiber-reinforced composite materials, rail transit interior parts, printed circuit boards, coatings, adhesives and other application fields. Attached Figure Description

[0035] Figure 1 Standard vertical combustion test image of unmodified benzoxazine resin prepared for comparison;

[0036] Figure 2 Standard vertical burning test image of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 1;

[0037] Figure 3 The results of the heat resistance test of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 1 are as follows;

[0038] Figure 4 The results of the heat resistance test of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 2 are as follows;

[0039] Figure 5 The results of the heat resistance test of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 3 are as follows;

[0040] Figure 6 The results of the heat resistance test of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 4 are as follows;

[0041] Figure 7 The results of the heat resistance test of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 5 are as follows;

[0042] Figure 8 The results of the heat resistance test of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 6 are as follows;

[0043] Figure 9 The results of the heat resistance test of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 7 are shown. Detailed Implementation

[0044] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are part of the present invention.

[0045] In the following examples, unless otherwise specified, all solvents and raw materials used were purchased externally.

[0046] Example 1

[0047] The preparation steps of phenol / diaminodiphenylmethane type benzoxazine with structural formula (1) are as follows: phenol, paraformaldehyde and 4,4-diaminodiphenylmethane are added to the reaction vessel in a molar ratio of 2:4:1, toluene is added as solvent, so that the solid content of the reaction system is maintained at 60%, and the reaction is carried out at 80°C for 6 hours. After the reaction is completed, the mixture is washed with water to separate the layers, and the solvent is removed to obtain phenol / diaminodiphenylmethane type benzoxazine.

[0048] The preparation steps of the trimer-p-hydroxybenzaldehyde azine of structural formula (2) are as follows: p-hydroxybenzaldehyde and cyanuric chloride are added to the reaction vessel in a molar ratio of 3:1. Sodium hydroxide solution of 1M prepared with an equimolar amount of sodium hydroxide as p-hydroxybenzaldehyde is added to the reaction system. Tetrahydrofuran is used as the solvent, and its mass is half that of the sodium hydroxide solution. The reaction is carried out at 50°C for 6 hours. After the reaction is completed, the mixture is filtered, washed with methanol, and dried to obtain trimer-p-hydroxybenzaldehyde azine.

[0049]

[0050] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 200g of phenol / diaminodiphenylmethane type benzoxazine with structural formula (1), add 10g of trimeric p-hydroxybenzaldehyde azine with structural formula (2) and 1g of imidazole, melt-blend at 120℃ for 60min, and then use staged heating curing. The specific conditions are heating at 120℃ for 2h, heating at 140℃ for 2h, heating at 160℃ for 2h, heating at 180℃ for 2h, and heating at 200℃ for 2h.

[0051] Example 2

[0052] Structure (3) was purchased from Adamas, product number 75458D.

[0053] The preparation steps of the trimer salicylaldehyde azin with structural formula (4) are as follows: salicylaldehyde and cyanuric chloride are added to the reaction vessel in a molar ratio of 3:1. Sodium hydroxide solution of 1M with an equimolar amount of salicylaldehyde is added to the reaction system. Tetrahydrofuran is used as the solvent, and its mass is 1 / 4 of the sodium hydroxide solution. The reaction is carried out at 55°C for 6 hours. After the reaction is completed, the mixture is filtered and dried to obtain trimer salicylaldehyde azin.

[0054] The preparation steps of vanillin / furfurylamine type benzoxazine with structural formula (5) are as follows: vanillin, paraformaldehyde and furfurylamine are added to the reaction vessel in a molar ratio of 1:2:1, toluene is added as solvent, so that the solid content of the reaction system is maintained at 60%, and the reaction is carried out at 70°C for 12 hours. After the reaction is completed, the reaction vessel is washed with 1M sodium hydroxide aqueous solution of 1wt% of the reaction system mass, and then washed with water to separate the layers and remove the solvent to obtain vanillin / furfurylamine type benzoxazine.

[0055]

[0056] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 150g of phenol / diaminodiphenylmethane type benzoxazine with structure (1) (see Example 1 for preparation steps), add 8g of biphenyl dicarboxaldehyde with structure (3), 5g of tri-salicylaldehyde with structure (4), 3g of vanillin / furfurylamine type benzoxazine with structure (5), and 1g of resorcinol. Melt and blend at 130℃ for 40min, and then use staged heating curing: heat at 140℃ for 2h, heat at 160℃ for 2h, heat at 180℃ for 2h, heat at 200℃ for 2h, and heat at 220℃ for 2h.

[0057] Example 3

[0058] The preparation steps of phenol / diaminodiphenyl ether type benzoxazine with structural formula (6) are as follows: phenol, paraformaldehyde, and 4,4-diaminodiphenyl ether are added to the reaction vessel in a molar ratio of 2:4:1. Toluene is added as a solvent to keep the solid content of the reaction system at 50%. The reaction is carried out at 90°C for 5 hours. After the reaction is completed, the mixture is washed with 1M sodium hydroxide aqueous solution (1wt% of the mass of the reaction system), then washed with water to separate the layers, and the solvent is removed to obtain phenol / diaminodiphenyl ether type benzoxazine.

[0059] The structural formula (7) was purchased from Adamas, product number 85006D.

[0060] The preparation steps of the trimeric vanillin azin with structural formula (8) are as follows: vanillin and cyanuric chloride are added to the reaction vessel in a molar ratio of 3:1. Sodium hydroxide solution of 1M with an equimolar amount of vanillin is added to the reaction system. Tetrahydrofuran is used as the solvent, and its mass is 1 / 2 of the sodium hydroxide solution. The reaction is carried out at 40°C for 6 hours. After the reaction is completed, the mixture is filtered and dried to obtain trimeric vanillin azin.

[0061]

[0062] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 200g of phenol / diaminodiphenyl ether type benzoxazine with structure (6), add 10g of 2,5-furandicarboxaldehyde with structure (7), 10g of tri-vanillin azine with structure (8), and 2g of acetic acid. Melt and blend at 120℃ for 40min, and then use staged heating curing: heat at 120℃ for 2h, at 130℃ for 2h, at 150℃ for 2h, at 170℃ for 2h, and at 180℃ for 5h.

[0063] Example 4

[0064] The preparation steps of m-cresol / p-phenylenediamine type benzoxazine with structural formula (9) are as follows: m-cresol, paraformaldehyde and p-phenylenediamine are added to the reaction vessel in a molar ratio of 2:4:1, toluene is added as solvent, the solid content of the reaction system is 50%, and the reaction is carried out at 90°C for 8 hours. After the reaction is completed, the reaction vessel is washed with 1M sodium hydroxide aqueous solution of 1wt% of the reaction system mass, and then washed with water to separate the layers. The solvent is removed to obtain m-cresol / p-phenylenediamine type benzoxazine.

[0065]

[0066] The structural formula (10) was purchased from Adamas, product number 122528I.

[0067] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 100g of m-cresol / p-phenylenediamine type benzoxazine with structure (9), add 5g of tri-salicylaldehyde with structure (4) (see Example 2 for preparation steps), 5g of tri-vanillin with structure (8) (see Example 3 for preparation steps), 1g of pyromellitic trimethylaldehyde with structure (10), and 0.5g of oxalic acid. Melt and blend at 140℃ for 30min, and then use staged heating curing: heat at 140℃ for 2h, heat at 150℃ for 2h, heat at 170℃ for 2h, heat at 190℃ for 2h, and heat at 200℃ for 2h.

[0068] Example 5

[0069] The preparation steps of the m-tert-butylphenol / diaminodiphenyl ether type benzoxazine with structural formula (11) are as follows: m-tert-butylphenol, paraformaldehyde, and 4,4-diaminodiphenyl ether are added to the reaction vessel in a molar ratio of 2:4:1. Toluene is added as a solvent to make the solid content of the reaction system reach 50%. The reaction is carried out at 90°C for 7 hours. After the reaction is completed, the mixture is washed with 1M sodium hydroxide aqueous solution (1wt% of the mass of the reaction system), then washed with water to separate the layers, and the solvent is removed to obtain m-tert-butylphenol / diaminodiphenyl ether type benzoxazine.

[0070] The preparation steps of salicylaldehyde / furfurylamine type benzoxazine with structural formula (12) are as follows: salicylaldehyde, paraformaldehyde and furfurylamine are added to the reaction vessel in a molar ratio of 1:2:1, toluene is added as solvent, so that the solid content of the reaction system reaches 50%, and the reaction is carried out at 85°C for 6 hours. After the reaction is completed, the reaction vessel is washed with 1M sodium hydroxide aqueous solution of 1wt% of the reaction system mass, and then washed with water to separate the layers and remove the solvent to obtain salicylaldehyde / furfurylamine type benzoxazine.

[0071]

[0072] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 150g of m-tert-butylphenol / diaminodiphenyl ether type benzoxazine with structure (11), add 10g of salicylaldehyde / furfurylamine type benzoxazine with structure (12), 3g of biphenyl dicarboxaldehyde with structure (3) (see Example 2 for preparation steps), 2g of trimeric salicylaldehyde with structure (4) (see Example 2 for preparation steps), and 1g of imidazole. Melt and blend at 120℃ for 60min, and then use staged heating curing: heat at 140℃ for 2h, heat at 160℃ for 2h, heat at 180℃ for 2h, and heat at 200℃ for 2h.

[0073] Example 6

[0074] The preparation steps of vanillin / m-aminophenylacetylene type benzoxazine with structural formula (13) are as follows: vanillin, paraformaldehyde, and m-aminophenylacetylene are added to the reaction vessel in a molar ratio of 1:2:1, toluene is added as a solvent, so that the solid content of the system is 60%, and the reaction is carried out at 90°C for 6 hours. After the reaction is completed, the reaction vessel is washed with 1M sodium hydroxide aqueous solution of 1wt% of the reaction system mass, and then washed with water to separate the layers. The solvent is removed to obtain vanillin / m-aminophenylacetylene type benzoxazine.

[0075] The preparation steps of salicylaldehyde / m-aminophenylacetylene type benzoxazine with structural formula (14) are as follows: salicylaldehyde, paraformaldehyde and m-aminophenylacetylene are added to the reaction vessel in a molar ratio of 1:2:1, toluene is added as solvent, so that the solid content of the system is 60%, and the reaction is carried out at 85°C for 7 hours. After the reaction is completed, the reaction vessel is washed with 1M sodium hydroxide aqueous solution of 1wt% of the reaction system mass, and then washed with water to separate the layers. The solvent is removed to obtain salicylaldehyde / m-aminophenylacetylene type benzoxazine.

[0076]

[0077] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 100g of phenol / diaminodiphenylmethane type benzoxazine with structure (1) (see Example 1 for preparation steps), add 10g of vanillin / m-aminophenylacetylene type benzoxazine with structure (13), 5g of salicylaldehyde / m-aminophenylacetylene type benzoxazine with structure (14), 2g of tri-vanillin azine with structure (8) (see Example 3 for preparation steps), and 1g of oxalic acid. Melt and blend at 90°C for 60min, and then use staged heating curing: heat at 120°C for 2h, at 140°C for 2h, at 160°C for 2h, at 180°C for 2h, at 200°C for 2h, and at 220°C for 2h.

[0078] Example 7

[0079] The preparation steps of m-cresol / diaminodiphenylmethane type benzoxazine with structural formula (15) are as follows: m-cresol, paraformaldehyde, and 4,4-diaminodiphenylmethane are added to the reaction vessel in a molar ratio of 2:4:1. Toluene is added as a solvent to make the solid content of the reaction system 50%. The reaction is carried out at 90°C for 8 hours. After the reaction is completed, the mixture is washed with 1M sodium hydroxide aqueous solution (1wt% of the mass of the reaction system), then washed with water to separate the layers, and the solvent is removed to obtain m-cresol / diaminodiphenylmethane type benzoxazine.

[0080]

[0081] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 150g of m-cresol / diaminodiphenylmethane type benzoxazine with structural formula (15), add 5g of vanillin / m-aminophenylacetylene type benzoxazine with structural formula (13), 5g of 2,5-furandicarboxaldehyde, 5g of biphenyldicarboxaldehyde, and 2g of benzimidazole, melt-blend at 120℃ for 30min, and then use staged heating curing: heat at 120℃ for 2h, heat at 140℃ for 2h, heat at 160℃ for 2h, heat at 180℃ for 2h, and heat at 200℃ for 2h.

[0082] Example 8

[0083] The preparation steps of bisphenol F / furfurylamine type benzoxazine with structural formula (16) are as follows: bisphenol F, paraformaldehyde and furfurylamine are added to the reaction vessel in a molar ratio of 1:4:2, toluene is added as solvent, so that the solid content of the reaction system is 55%, and the reaction is carried out at 70°C for 12 hours. After the reaction is completed, the reaction system is washed with 1M sodium hydroxide aqueous solution of 1wt% of the reaction system mass, and then washed with water to separate the layers and remove the solvent to obtain bisphenol F / furfurylamine type benzoxazine.

[0084]

[0085] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 100g of bisphenol F / furfurylamine type benzoxazine with structure (16), add 10g of biphenyl dicarboxaldehyde with structure (3), 15g of vanillin / furfurylamine type benzoxazine with structure (5), and 2g of imidazole. Melt and blend at 120℃ for 40min, and then use staged heating curing: heat at 120℃ for 2h, heat at 140℃ for 2h, heat at 160℃ for 2h, heat at 180℃ for 2h, and heat at 200℃ for 2h.

[0086] Example 9

[0087] The preparation steps of bisphenol F / aniline type benzoxazine with structural formula (17) are as follows: bisphenol F, paraformaldehyde and aniline are added to the reaction vessel in a molar ratio of 1:4:2, toluene is added as solvent, so that the solid content of the reaction system is 50%, and the reaction is carried out at 75°C for 10h. After the reaction is completed, the reaction vessel is washed with 1M sodium hydroxide aqueous solution of 1wt% of the reaction system mass, and then washed with water to separate the layers and remove the solvent to obtain bisphenol F / aniline type benzoxazine.

[0088]

[0089] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 150g of bisphenol F / aniline type benzoxazine with structure (17), add 20g of trimeric p-hydroxybenzaldehyde azine with structure (2) and 10g of vanillin / m-aminophenylacetylene type benzoxazine with structure (13), melt-blend at 110℃ for 60min, and then use staged heating curing: heat at 140℃ for 2h, heat at 160℃ for 2h, heat at 180℃ for 2h, and heat at 200℃ for 2h.

[0090] Example 10

[0091] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 200g of phenol / diaminodiphenylmethane type benzoxazine with structure (1), add 1g of pyromellitic trimethylolpropoxide with structure (10), 1g of trimeric p-hydroxybenzaldehyde with structure (2), and 6g of imidazole. Melt and blend at 120℃ for 60min, and then use staged heating curing. The specific conditions are: heating at 120℃ for 2h, heating at 140℃ for 2h, heating at 160℃ for 2h, heating at 180℃ for 2h, and heating at 200℃ for 2h.

[0092] Example 11

[0093] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 100g of m-tert-butylphenol / diaminodiphenyl ether type benzoxazine with structural formula (11), add 15g of vanillin / furfurylamine type benzoxazine with structural formula (5), 10g of vanillin / m-aminophenylacetylene type benzoxazine with structural formula (13), and 10g of benzimidazole. Melt and blend at 100℃ for 40min, and then use staged heating curing. The specific conditions are: heating at 120℃ for 2h, heating at 140℃ for 2h, heating at 160℃ for 2h, heating at 180℃ for 2h, heating at 200℃ for 2h, and heating at 220℃ for 1h.

[0094] Example 12

[0095] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 100g of phenol / diaminodiphenyl ether type benzoxazine with structural formula (6), add 30g of vanillin / furfurylamine type benzoxazine with structural formula (5), 10g of vanillin / m-aminophenylacetylene type benzoxazine with structural formula (13), and 0.5g of acetic acid. Melt and blend at 90℃ for 30min, and then use staged heating curing. The specific conditions are heating at 140℃ for 2h, heating at 160℃ for 2h, heating at 180℃ for 2h, heating at 200℃ for 2h, and heating at 220℃ for 2h.

[0096] Example 13

[0097] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 200g of phenol / diaminodiphenylmethane type benzoxazine with structure (1), add 1g of 2,5-furandicarboxaldehyde with structure (7) and 5g of tri-salicylaldehyde with structure (4), melt-blend at 120℃ for 60min, and then use staged heating curing. The specific conditions are heating at 140℃ for 2h, heating at 160℃ for 2h, heating at 180℃ for 2h, and heating at 200℃ for 2h.

[0098] Example 14

[0099] Preparation of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin: Take 100g of phenol / diaminodiphenylmethane type benzoxazine with structure (1), dissolve it in 200mL of acetone at 40℃, add 3g of biphenyl dicarboxaldehyde with structure (3) and 5g of tri-vanillin with structure (8), mix the solution for 60min, then remove the acetone by rotary evaporation at 60℃, and further dry in a vacuum oven at 120℃ for 10min; then use staged heating curing, specifically heating at 120℃ for 2h, heating at 140℃ for 2h, heating at 160℃ for 2h, heating at 180℃ for 2h, and heating at 200℃ for 2h.

[0100] Comparative Example

[0101] Preparation of unmodified benzoxazine resin: 100g of phenol / diaminodiphenylmethane type benzoxazine with structural formula (1) was used as raw material and cured by staged heating. The specific conditions were: heating at 120℃ for 2h, heating at 140℃ for 2h, heating at 160℃ for 2h, heating at 180℃ for 2h, and heating at 200℃ for 2h.

[0102] Performance testing

[0103] 1. Standard vertical burning tests were conducted on unmodified benzoxazine resin and the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Examples 1-7 (5 specimens were taken for each sample, with dimensions of 125mm × 13mm × 3mm). The test procedure was as follows: the sample was vertically clamped on the testing instrument using a clamp. Timing began from the moment the flame source touched the bottom of the sample. After ignition for 10 seconds, the flame source was removed, and the duration of the flame at the bottom of the sample, t1, was recorded. After the sample extinguished, it was ignited again, and after 10 seconds, the flame source was removed, and the duration of the flame at the bottom of the sample, t2, was recorded. When both t1 and t2 were less than 10 seconds, and the total burning time ∑(t1+t2) of the 5 specimens after the flame source was removed was less than 50 seconds, the sample was considered to have a V-0 flame retardancy rating. When both t1 and t2 were less than 30 seconds, and the total burning time ∑(t1+t2) of the 5 specimens after the flame source was removed was less than 250 seconds, the sample was considered to have a V-1 flame retardancy rating. The results are shown in Table 1-8.

[0104] Table 1. Standard vertical combustion test results of unmodified benzoxazine resin in the comparative examples.

[0105]

[0106] Table 2. Standard vertical burning test results of halogen-free and phosphorus-free flame-retardant modified benzoxazine resin in Example 1.

[0107]

[0108] Table 3 Standard vertical combustion test results of Example 2

[0109]

[0110] Table 4. Standard vertical combustion test results of Example 3

[0111]

[0112] Table 5. Standard vertical combustion test results of Example 4

[0113]

[0114]

[0115] Table 6. Standard vertical combustion test results of Example 5

[0116]

[0117] Table 7 Standard Vertical Combustion Test Results of Example 6

[0118]

[0119] Table 8. Standard vertical combustion test results of Example 7

[0120]

[0121] The results showed that the unmodified benzoxazine resin only had a UL94 V-1 flame retardancy rating, while the modified benzoxazine resin had a UL94 V-0 flame retardancy rating.

[0122] also, Figure 1 and Figure 2 Standard vertical burning test images of the unmodified benzoxazine resin prepared in the comparative example and the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 1 are provided. The images clearly show that the unmodified benzoxazine resin remained ignited for 20 seconds after the second ignition and removal of the flame, while the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared in Example 1 extinguished itself within 2 seconds after the second ignition and removal of the flame. Therefore, the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin prepared by the method of this invention exhibits better flame retardancy.

[0123] 2. The heat resistance tests were conducted on the halogen-free and phosphorus-free flame-retardant modified benzoxazine resins prepared in Examples 1-7, and the results are as follows: Figures 3-9 As shown.

[0124] The glass transition temperatures of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resins prepared in Examples 1-7 are 230-265℃. It can be seen that the halogen-free and phosphorus-free flame-retardant modified benzoxazine resins prepared in this invention have good heat resistance.

[0125] Those skilled in the art will recognize that the embodiments described herein are intended to help the reader understand the principles of the invention, and should be understood that the scope of protection of the invention is not limited to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations based on the technical teachings disclosed in this invention without departing from the spirit of the invention, and these modifications and combinations are still within the scope of protection of this invention.

Claims

1. A method for preparing a halogen-free and phosphorus-free flame-retardant modified benzoxazine resin, characterized in that, The product is obtained by blending and heating benzoxazine monomer and aldehyde compound as raw materials; the mass ratio of benzoxazine monomer to aldehyde compound is 100:(1-40); the structural formula of aldehyde compound is: ； The structural formula of the benzoxazine monomer is: 。 2. The method for preparing the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin according to claim 1, characterized in that, The mass ratio of the benzoxazine monomer to the aldehyde compound is 100:(3-25).

3. The method for preparing the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin according to claim 1 or 2, characterized in that, The blending step is as follows: benzoxazine monomer and aldehyde compound are melt-blended or solution-blended together to obtain modified benzoxazine blends.

4. The preparation method of the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin according to claim 3, characterized in that, The melt blending temperature is 50-160℃, and the blending time is 0.5-3h.

5. The method for preparing the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin according to claim 3, characterized in that, In the blending step, a curing catalyst is also added, and the catalyst, benzoxazine monomer, and aldehyde compound are melt-blended or solution-blended together; the catalyst is imidazole; the mass ratio of the catalyst to the benzoxazine monomer is (0.5-10):

100.

6. The method for preparing the halogen-free and phosphorus-free flame-retardant modified benzoxazine resin according to claim 1 or 2, characterized in that, The heating and curing steps are as follows: the obtained modified benzoxazine blend is subjected to gradient heat curing in 4-6 temperature ranges at 100-220℃, and the curing time is 8-20h.

7. A halogen-free and phosphorus-free flame-retardant modified benzoxazine resin, characterized in that, It is prepared by any one of the methods described in claims 1 to 6.

8. The halogen-free and phosphorus-free flame-retardant modified benzoxazine resin of claim 7 is used in the preparation of fiber-reinforced composite materials, rail transportation, printed circuit boards, coatings, and adhesives.

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