Silicon-phosphorus composite flame-retardant epoxy resin curing agent, preparation method and application thereof

Abstract

The present invention provides a silicon-phosphorus composite flame-retardant epoxy resin curing agent, comprising the following compound, wherein A is derived from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine, diphenylphosphine oxide, or diphenylphosphine sulfide. Replacing a portion of the epoxy resin curing agent with this compound can impart excellent mechanical properties, transparency, and flame retardancy to the epoxy resin. The present invention also provides a one-pot method for preparing the silicon-phosphorus composite flame-retardant epoxy resin curing agent. This method is simple to prepare, operates under mild reaction conditions, and avoids side reactions, making it suitable for large-scale industrial production. #imgabs0#

Description

Technical Field

[0001] The present invention relates to the technical field of epoxy resin flame retardants, and in particular to a silicon-phosphorus composite flame retardant epoxy resin curing agent, a preparation method thereof, and applications thereof. Background Art

[0002] At present, epoxy resin (EP), as an excellent resin material, has been widely used in the fields of fiber reinforcement materials, general adhesives, high-performance coatings and packaging materials. However, its flammability and brittleness limit the application of EP in high-end scenarios, so the epoxy resin needs to be flame-retardant modified. Adding halogen flame retardants is a traditional method to improve the flame retardant properties of EP, especially brominated flame retardants. The improvement of the flame retardant properties of EP is particularly prominent, but this type of flame retardant has adverse effects such as the release of toxic smoke and environmental hazards. Therefore, halogen-free and high-efficiency flame retardants have come into people's view. Among the existing halogen-free flame retardants, phosphorus-containing flame retardants have the characteristics of high efficiency, low smoke, low toxicity, etc., and have multiple flame retardant mechanisms.

[0003] As a new type of flame retardant material, derivatives of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide have become a research hotspot for halogen-free flame retardancy of epoxy resins in recent years due to their high thermal and chemical stability, remarkable flame retardant properties, and characteristics such as being halogen-free, smokeless, environmentally friendly, not easy to migrate, and having a high carbon residue rate. Chinese patent CN110183727A provides a method for preparing a sulfur-nitrogen-phosphorus ternary synergistic flame retardant containing di-DOPO and benzothiazole structural units. When the effective phosphorus content is 0.21wt%, the vertical combustion rating can reach UL-94V-0, but its production process is complicated and the final yield is low; Chinese patent CN110396219A provides a phosphorus-containing flame retardant with good optical properties and flame retardant properties, but its molecular weight is small, which may affect the thermal stability of the final cured product; Chinese patent CN105924674A provides a flame retardant synthesized from phosphaphenanthrene and toluene-2,4-diisocyanate, but its structure has many rigid structures, which reduces the toughness of epoxy resin and limits its application.

[0004] Based on the deficiencies in the prior art, the present application provides a novel silicon-phosphorus composite flame-retardant epoxy resin curing agent, a preparation method thereof, and applications thereof. Summary of the Invention

[0005] In view of the deficiencies in the prior art described above, the object of the present invention is to provide a silicon-phosphorus composite flame-retardant epoxy resin curing agent, a preparation method thereof, and an application thereof. The silicon-phosphorus composite flame-retardant epoxy resin curing agent of the present application has an amide bond, has high polarity and hydrogen bond forming ability, thereby improving the mechanical strength, rigidity and wear resistance of the material, and showing more excellent performance in terms of tensile strength and flexural strength. In addition, the introduction of an amide bond can improve the toughness of the epoxy resin, which can absorb and disperse energy, thereby reducing the tendency of the material to crack and break in stress concentration areas. Moreover, the present application adopts a one-pot preparation method, which is simple and has mild reaction conditions. Replacing a portion of the epoxy resin curing agent with it can make the epoxy resin have good mechanical properties, transparency and flame retardancy.

[0006] To achieve the above-mentioned and other related purposes, the present invention is implemented through the following technical solutions:

[0007] The first aspect of the present invention provides a silicon-phosphorus composite flame-retardant epoxy resin curing agent, comprising the following compounds:

[0008]

[0009] A is derived from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenyl phosphine, diphenyl phosphine oxide or diphenyl phosphine sulfide; that is, it is prepared by reacting 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenyl phosphine, diphenyl phosphine oxide or diphenyl phosphine sulfide with acid anhydride and aminopropyl-terminated polydimethylsiloxane.

[0010] m is 0 or 1, n=0~400.

[0011] In some feasible examples, n may be selected from n=0, n=0-10, n=10-50, n=50-100, n=100-200, n=200-300 or n=300-400.

[0012] In some possible embodiments, A is

[0013]

[0014] In some feasible embodiments, the compounds include those represented by Formula I and / or Formula II:

[0015]

[0016] n = 0 to 400, where n can be selected from n = 0, n = 0 to 10, n = 10 to 50, n = 50 to 100, n = 100 to 200, n = 200 to 300, or n = 300 to 400. In some embodiments, the curing agent further comprises 4,4-diaminodiphenylmethane. The molar ratio of the silicon-phosphorus composite flame-retardant epoxy resin curing agent to 4,4-diaminodiphenylmethane is 0.1 to 5:1; the molar ratio can be selected from 0.1 to 1:1, 1 to 2:1, 2 to 3:1, 3 to 4:1, or 4 to 5:1.

[0017] A second aspect of the present invention provides a method for preparing a silicon-phosphorus composite flame-retardant epoxy resin curing agent, comprising the following steps:

[0018] 1) reacting a pH flame retardant compound with an acid anhydride to obtain a phosphorus-containing intermediate;

[0019] In a feasible embodiment, the reaction of the PH flame retardant compound and the acid anhydride is carried out under solvent conditions, and the solvent is selected from at least one of 1,4-dioxane, benzene, toluene, xylene, cyclohexane or chlorobenzene; preferably, the mass ratio of the PH flame retardant compound to the acid anhydride and the solvent is 0.6 to 1.5:1, and the ratio can be optionally 0.6 to 1.0:1 or 1.0 to 1.5:1.

[0020] In a feasible embodiment, the PH flame retardant compound reacts with the acid anhydride under the protection of an inert gas; preferably, the PH flame retardant compound and the acid anhydride powder are directly mixed, protected by an inert gas, and then a solvent is added to react.

[0021] In a feasible embodiment, the molar ratio of the pH flame retardant compound to the acid anhydride is 0.8-1.2:1, preferably 1:1.

[0022] In a feasible embodiment, the reaction temperature of the PH flame retardant compound and the acid anhydride is 70-120°C, and the temperature can be selected from 70-80°C, 80-90°C, 90-100°C, 100-110°C or 110-120°C.

[0023] In a feasible embodiment, the reaction time of the pH flame retardant compound and the acid anhydride is 12 to 24 hours, and the reaction time can be optionally 12 to 18 hours or 18 to 24 hours.

[0024] In a feasible example, the pH flame retardant is selected from at least one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine, diphenylphosphine oxide or diphenylphosphine sulfide.

[0025] In a feasible example, the acid anhydride is selected from at least one of maleic anhydride and itaconic anhydride.

[0026] 2) adding aminopropyl-terminated polydimethylsiloxane to the phosphorus-containing intermediate product for reaction, and post-treating to obtain a silicon-phosphorus composite flame-retardant epoxy resin curing agent.

[0027] In one feasible embodiment, in step 2), water is removed by fractional distillation during the reaction, and the solvent is removed by post-treatment by reduced pressure distillation to obtain a silicon-phosphorus composite flame-retardant epoxy resin curing agent.

[0028] In one possible embodiment, the aminopropyl-terminated polydimethylsiloxane is 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane.

[0029] In a feasible embodiment, the molar ratio of aminopropyl-terminated polydimethylsiloxane to the phosphorus-containing intermediate is 2 to 2.5:1, and the molar ratio is preferably 2:1; the reaction temperature is 80 to 160°C, and the temperature can be optionally 80 to 90°C, 90 to 100°C, 100 to 120°C, 120-140°C or 140 to 160°C; the reaction time is 6 to 12h, and the reaction time can be optionally 6 to 8h or 8 to 12h.

[0030] The third aspect of the present invention is a silicon-phosphorus composite flame-retardant epoxy resin curing agent prepared by the preparation method.

[0031] The fourth aspect of the present invention is the use of the above silicon-phosphorus composite flame-retardant epoxy resin curing agent in epoxy resin.

[0032] The present invention has the following technical effects including but not limited to:

[0033] 1) The silicon-phosphorus composite flame-retardant epoxy resin curing agent of the present invention can replace a part of the epoxy resin curing agent to enable the epoxy resin to have good mechanical properties, transparency and flame retardancy.

[0034] 2) The silicon-phosphorus composite flame-retardant epoxy resin curing agent prepared by the present invention has a fixed raw material ratio, a simple one-pot preparation method, mild reaction conditions, no other side reactions, and is suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The structural formula of the silicon-phosphorus composite flame-retardant epoxy resin curing agent prepared by the present invention is as follows:

[0036] Figure 2 This is the nuclear magnetic resonance spectrum of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, maleic anhydride, and silicon-phosphorus composite flame retardant epoxy resin curing agent.

[0037] Figure 3This is the infrared spectrum of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, maleic anhydride, phosphorus-containing intermediate, and silicon-phosphorus composite flame retardant epoxy resin curing agent. DETAILED DESCRIPTION

[0038] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0039] In addition, for numerical ranges in the present invention, it is understood that each intervening value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any stated value or intervening value in a stated range and any other stated value or intervening value in the stated range is also included in the present invention. The upper and lower limits of these smaller ranges may independently be included or excluded in the range.

[0040] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0041] All raw materials used in the following examples and effect verifications of the present invention are commercially available products.

[0042] Preparation Example 1

[0043] Preparation of silicon-phosphorus composite flame-retardant epoxy resin curing agent (D-2-3):

[0044] 1) 69.39 mmol (15 g) of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 69.39 mmol (6.80 g) of maleic anhydride were added to a two-necked flask. After nitrogen displacement, 236.59 mmol (21.8 g) of toluene was added via syringe and the temperature was raised to 80°C and maintained for 6 h to generate a phosphorus-containing intermediate.

[0045] 2) Add 138.75 mmol (34.49 g) of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane to the previous two-necked flask. Connect the two-necked flask to a distillation receiver and a condenser, raise the temperature to 160°C, and maintain the temperature for 12 hours while continuously fractionating and removing water.

[0046] 3) After completion, the product is subjected to reduced pressure distillation to recover the solvent to obtain the final product, a silicon-phosphorus composite flame-retardant epoxy resin curing agent.

[0047] The structural formula of the prepared silicon-phosphorus composite flame retardant epoxy resin curing agent is shown in Figure 1 .

[0048] Effect verification

[0049] In the specific implementation method, the applicant uses the following four examples and comparative examples to explain in detail the effects of each component and dosage on the flame retardant properties, mechanical properties and thermal stability of the epoxy resin product, so that those skilled in the art can adjust it within the scope defined by the above technical features as needed.

[0050] Example 1

[0051] To 5g of epoxy resin E-51, add 0.5051g of a silicon-phosphorus composite flame-retardant epoxy resin curing agent (D-2-3) and 1.1367g of 4,4-diaminodiphenylmethane curing agent (DDM). See Table 1 for details. After mixing thoroughly, remove any bubbles and pour the mixture into a mold. Curing was carried out at 100°C / 2h, 130°C / 2h, and 160°C / 2h to obtain a cured product (D-2-3-10%).

[0052] Example 2

[0053] To 5g of E-51, add 1.0103g of a silicon-phosphorus composite flame-retardant epoxy resin curing agent (D-2-3) and 1.0104g of DDM (see Table 1 for details). After mixing thoroughly, remove any bubbles and pour the mixture into a mold. Curing was carried out at 100°C / 2h + 130°C / 2h + 160°C / 2h to obtain a cured product (D-2-3-20%).

[0054] Example 3

[0055] To 5g of E-51, add 1.5154g of a silicon-phosphorus composite flame-retardant epoxy resin curing agent (D-2-3) and 0.8841g of DDM (see Table 1 for details). After mixing thoroughly, remove any bubbles and pour the mixture into a mold. Curing is carried out at 100°C / 2h + 130°C / 2h + 160°C / 2h to obtain a cured product (D-2-3-30%).

[0056] Example 4

[0057] To 5g of E-51, add 2.0205g of a silicon-phosphorus composite flame-retardant epoxy resin curing agent (D-2-3) and 0.7578g of DDM (see Table 1 for details). After mixing thoroughly, remove any bubbles and pour the mixture into a mold. Curing is carried out at 100°C / 2h, 130°C / 2h, and 160°C / 2h to obtain a cured product (D-2-3-40%).

[0058] Comparative Example

[0059] Add 1.2630 g of DDM to 5 g of E-51 (see Table 1 for details). Mix thoroughly and remove air bubbles. Pour the mixture into a mold and cure it at 100°C / 2 h + 130°C / 2 h + 160°C / 2 h to obtain the cured product DGEPA.

[0060] Table 1 Silicon-phosphorus composite flame-retardant epoxy resin curing agent and DDM addition content

[0061]

[0062] The solidified materials of Example 1, Example 2, Example 3, Example 4, and Comparative Example were obtained, and the following experiments were performed.

[0063] (1) According to GB / T2408-1996, the UL-94 test was performed on the above-mentioned cured product. The test results are shown in Table 2.

[0064] Table 2 Limiting oxygen index and UL-94 test results of cured products

[0065]

[0066] As shown in Table 2, DGEBA is a relatively flammable material, with an LOI value of only 22.6%. Replacing a portion of DDM with the silicon-phosphorus composite flame-retardant epoxy resin curing agent of the present invention significantly improved the LOI value of the cured product, exceeding 27%. In the UL-94 test, DGEBA burned violently after ignition and remained extinguished even after 120 seconds, failing the UL-94 test. In contrast, the cured products of Examples 1-4, incorporating the silicon-phosphorus composite flame-retardant epoxy resin curing agent, exhibited excellent flame retardancy, achieving the UL-94 V-0 rating. For example, D-2-3-30% spontaneously extinguished within 4 seconds after initial ignition and within 1 second after subsequent reignition. During the combustion of D-2-3-30%, a noticeable blowout phenomenon was observed, particularly during the second reignition, where the flame was quickly extinguished by gas ejected from the substrate. This can be explained by the formation of a protective carbon layer on the surface of the sample during ignition, preventing further combustion. Polysiloxane can also decompose to form Si-O-Si, Si-C and Si-OC structures, which can provide cross-linking points to react with phosphoric acid to obtain a continuous and stable carbon layer. In addition, the SiO2 structure can further improve stability. At the same time, the gas produced by pyrolysis accumulates inside the carbon layer. When the continuous combustion makes it difficult to maintain the carbon layer, the pyrolysis gas containing phosphorus radicals (P· and PO·) is ejected and terminates the combustion reaction by quenching H· and OH· radicals. This can well explain the phenomenon that the solidified material automatically extinguishes in a very short time when it is ignited for the second time after the addition of additives.

[0067] (2) According to GB / T2567-2008 standard, the mechanical properties of the above-mentioned cured product were tested. The test results are shown in Table 3.

[0068] Table 3 Mechanical properties of cured products

[0069] sample Tensile strength (MPa) Elongation at break (%) <![CDATA[Impact strength (kJ / m 2 )]]> Example 1 56.2 3.1 24.5 Example 2 55.4 3.6 26.9 Example 3 54.9 4.3 27.7 Example 4 54.1 5.6 30.2 Comparative Example 56.7 2.8 14.5

[0070] Table 3 shows that the addition of the aforementioned additives resulted in substantially no decrease in the tensile strength of the cured product. In contrast, the addition of most existing additives affects the mechanical properties of epoxy resin systems because they are unable to participate in the curing process, leading to phase separation. The additives of the present invention do not significantly affect tensile strength because they participate in the curing process, and both 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and the cyclic organosilicon structure provide rigidity. Elongation at break and impact strength indicate that the additives prepared in this invention significantly improve the toughness of the cured epoxy resin. The Si-O-Si cyclic structure provides a buffer against external impacts. Furthermore, Si-O bonds have larger bond angles and longer bond lengths than C-C and C-O bonds. Furthermore, the presence of amide bonds promotes energy dissipation, enhancing the toughness of the epoxy resin. The unique morphology of the additives of the present invention also significantly contributes to improving the toughness of the cured product. Therefore, the additives of the present invention can significantly enhance the toughness of the epoxy resin while maintaining good rigidity.

[0071] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A silicon-phosphorus composite flame-retardant epoxy resin curing agent, comprising the following compounds: A is derived from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine, diphenylphosphine oxide or diphenylphosphine sulfide; m is 0 or 1, n=0~400.

2. The silicon-phosphorus composite flame-retardant epoxy resin curing agent according to claim 1, characterized in that: A is or or or .

3. The silicon-phosphorus composite flame-retardant epoxy resin curing agent according to claim 1 or 2, characterized in that: Including compounds shown in formula I and / or formula II: Formula I Formula II n=0~400； And / or, the curing agent further comprises 4,4-diaminodiphenylmethane; the molar ratio of the silicon-phosphorus composite flame-retardant epoxy resin curing agent to 4,4-diaminodiphenylmethane is 0.1-5:

1.

4. The method for preparing the silicon-phosphorus composite flame-retardant epoxy resin curing agent according to claim 1, comprising the steps of: 1) reacting a pH flame retardant compound with an acid anhydride to obtain a phosphorus-containing intermediate; 2) adding aminopropyl-terminated polydimethylsiloxane to the phosphorus-containing intermediate product for reaction, and post-treating to obtain a silicon-phosphorus composite flame-retardant epoxy resin curing agent; The PH flame retardant is selected from at least one of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, diphenylphosphine, diphenylphosphine oxide or diphenylphosphine sulfide.

5. The preparation method according to claim 4, characterized in that Step 1) includes at least one of a1) to a5): a1) The reaction of the pH flame retardant compound with the acid anhydride is carried out under solvent conditions; a2) The molar ratio of the pH flame retardant compound to the acid anhydride is 0.8-1.2:1; a3) The reaction temperature of the PH flame retardant compound and the acid anhydride is 70~120℃; a4) The reaction time of the pH flame retardant compound and the acid anhydride is 12 to 24 hours; a5) The acid anhydride is selected from at least one of maleic anhydride and itaconic anhydride.

6. The preparation method according to claim 5, characterized in that a1), wherein the solvent is selected from at least one of 1,4-dioxane, benzene, toluene, xylene, cyclohexane or chlorobenzene; and / or, the mass ratio of the pH flame retardant compound to the acid anhydride and the solvent is 0.6-1.5:1; And / or, the pH flame retardant compound reacts with the acid anhydride under the protection of an inert gas.

7. The preparation method according to claim 6, characterized in that In step 1), the pH flame retardant compound and the acid anhydride powder are directly mixed, protected by an inert gas, and then a solvent is added to react.

8. The preparation method according to claim 4, characterized in that Step 2) includes at least one of b1) to b4): b1) fractional distillation to remove water during the reaction; b2) post-processing by removing the solvent by distillation under reduced pressure to obtain a silicon-phosphorus composite flame-retardant epoxy resin curing agent; b3) aminopropyl-terminated polydimethylsiloxane is 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane; b4) The molar ratio of aminopropyl-terminated polydimethylsiloxane to the phosphorus-containing intermediate is 2-2.5:1, the reaction temperature is 80-160°C, and the reaction time is 6-12 h.

9. The silicon-phosphorus composite flame-retardant epoxy resin curing agent prepared by the preparation method according to any one of claims 4 to 8.

10. Use of the silicon-phosphorus composite flame-retardant epoxy resin curing agent according to any one of claims 1 to 3 or 9 in epoxy resin.

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