Organosilicon cyclophosphazene modified epoxy resin and preparation method thereof

Abstract

The invention discloses organosilicone cyclophosphazene modified epoxy resin and a preparation method thereof, belongs to the field of flame-retardant materials, and particularly relates to a preparation method of an organosilicone cyclophosphazene flame retardant and a preparation method of the organosilicone cyclophosphazene modified epoxy resin. The invention aims to research and develop a synergistic composite flame retardant of three elements of N, P and Si by optimizing the structure of the flame retardant and solve the problem of low flame retardant efficiency of the flame retardant. The preparation method comprises the following steps: taking hexachlorotripolyphosphazene, p-hydroxybenzaldehyde, p-aminobenzoic acid, DOPO and triphenylsilanol as raw materials, and carrying out substitution, dehydration condensation, addition and esterification to obtain the organic silicon cyclophosphazene flame retardant. The modified epoxy resin is obtained by taking m-phenylenediamine as a curing agent and adding organosilicone cyclophosphazene flame retardants in different proportions. The organosilicone cyclophosphazene modified epoxy resin provided by the invention reaches the standard of a flame-retardant material, and the limit oxygen index is up to 31.6%, which passes a UL-94 test.

Description

Technical Field

[0001] The invention relates to an organosilicon cyclophosphazene modified epoxy resin and a preparation method thereof, and belongs to the field of flame retardant materials. Background Art

[0002] Epoxy resin has excellent comprehensive performance and has been widely used in many fields of production and life. However, epoxy resin is highly flammable, which seriously threatens people's lives and property safety. Therefore, the research and development of new, efficient and environmentally friendly flame retardants has become an important research topic in the field of flame retardancy. At present, the flame retardant industry is in a booming development trend, and there are many types of flame retardants. However, some problems are also highlighted during the use of flame retardants: in order to meet the flame retardant performance requirements, it is usually necessary to add a large amount of flame retardant to epoxy resin, and excessive addition often increases the difficulty and cost of preparing epoxy resin composite materials, and reduces the compatibility between flame retardants and epoxy resins, thereby reducing flame retardant efficiency.

[0003] In response to the above problems, researchers started from the compounding of flame retardants and the design of the two-phase interface to improve the flame retardant efficiency of flame retardants in epoxy resin matrix and meet the multifunctional requirements of epoxy resin for flame retardants. Studies have found that physical compounding of flame retardants, as a common way to improve the flame retardant effect in engineering, can significantly reduce the actual amount of flame retardants added while ensuring the excellent flame retardant properties of epoxy resin. However, the matching of specific flame retardant types and related addition ratios usually need to be based on a large number of experiments, and there is a certain degree of contingency. In addition, as an additive in the epoxy resin matrix, the problem of the combination of flame retardants with the epoxy resin matrix has always attracted the attention of researchers. Since the formation of an organic whole between the filler and the matrix usually depends on the interaction between the interfaces of the two, the molecular chain structure of the flame retardant and the position and number of active sites that can cross-link with epoxy resin will actually affect the compatibility between the flame retardant and the epoxy resin, and then affect the flame retardant efficiency. Therefore, how to adjust the composition and design the structure of the flame retardant, that is, to fundamentally improve the flame retardant efficiency in production applications, is of great significance. Summary of the invention

[0004] The present invention provides a method for preparing an organosilicon cyclophosphazene modified epoxy resin, aiming to solve the problem of low flame retardant efficiency of the flame retardant by optimizing the flame retardant structure. The invention mainly includes a method for preparing an organosilicon cyclophosphazene flame retardant and a method for preparing an organosilicon cyclophosphazene modified epoxy resin.

[0005] Advantage 1: It is usually difficult to achieve the desired effect by adding a single flame retardant to epoxy resin. The common method is to compound multiple flame retardants to produce a synergistic flame retardant effect. The specific ratio and addition method of traditional physical compound flame retardants often require a lot of experimental exploration, and the specific implementation is relatively complicated. Therefore, directly designing the combination of flame retardant elements in the molecular structure of the flame retardant is becoming an effective method to improve the flame retardant effect. The organosilicon cyclophosphazene flame retardant proposed in the present invention is based on hexachlorotripolyphosphazene as the core skeleton, which has a high content of N and P elements. It also uses the characteristics of easy derivatization of the side group to successfully introduce Si elements into its side chain structure through a simple esterification reaction. That is, through the design of the molecular structure of the flame retardant, the present invention successfully establishes a synergistic flame retardant system of the three elements of N, P, and Si, and then can reasonably utilize the flame retardant effects of gas-phase free radicals such as covering, heat absorption, dilution, and capture in the combustion process to exert the synergistic flame retardant effect of the three flame retardant elements.

[0006] Advantage 2: The flame retardant and the epoxy resin are combined with each other through the interface action, and the interfacial compatibility between the two directly affects the morphology, structure, thickness and dispersion uniformity of the interface of the epoxy resin composite material, and ultimately determines the quality of the epoxy resin composite material. Therefore, the organosilicon cyclophosphazene flame retardant proposed in the present invention is designed to have multiple active sites that can be cross-linked and cured with the epoxy resin, and these reactive anchor points participating in the curing reaction are evenly distributed on the six branches of the six-membered ring, located in the middle of each branch, which can improve the interaction between the flame retardant and the epoxy resin and increase the interfacial compatibility between the flame retardant and the epoxy resin. In addition, the present invention further introduces a high-stability DOPO group on its side chain to increase its steric hindrance. Studies have shown that DOPO has a significant effect on enhancing the compatibility between the flame retardant and the epoxy resin matrix.

[0007] Advantage 3: Since the structure of the material is closely related to its performance, the organosilicon cyclophosphazene flame retardant designed in the present invention mainly uses heat-resistant aromatic groups (benzene rings, etc.) such as groups corresponding to chemical bonds with higher bond energy as the main carbon structure on the extended skeleton branch of the flame retardant, and triphenylsilanol with a high thermal stability structure is selected in the process of introducing the Si element, so that the organosilicon cyclophosphazene flame retardant and the organosilicon cyclophosphazene modified epoxy resin themselves have good flame retardant properties.

[0008] The structural formula of organosilicon cyclophosphazene flame retardant is:

[0009] The preparation method of the organosilicon cyclophosphazene flame retardant provided by the present invention is carried out according to the following steps: firstly, tetrahydrofuran is used as a solvent, p-hydroxybenzaldehyde and hexachlorotripolyphosphazene undergo a substitution reaction to obtain an intermediate 1, then the intermediate 1 and p-aminobenzoic acid undergo a dehydration condensation reaction with dioxane as a solvent to obtain an intermediate 2 containing a Schiff base structure, then the intermediate 2 undergoes an addition reaction with DOPO to obtain an intermediate 3, and finally DMSO is used as a solvent, under the catalytic action of HOBT and EDCI, the intermediate 3 undergoes an esterification reaction with triphenylsilanol to obtain the organosilicon cyclophosphazene flame retardant.

[0010] The preparation method of the organosilicon cyclophosphazene modified epoxy resin provided by the present invention is carried out according to the following steps: heating the epoxy resin (E51 bisphenol A type glycidyl ether epoxy resin) to 100-120°C, adding a certain amount of organosilicon cyclophosphazene flame retardant until it is evenly stirred, lowering the temperature of the epoxy resin to 60-80°C, adding a curing agent (meta-phenylenediamine) calculated and weighed in advance, mixing evenly, vacuum degassing, pouring into a preheated mold, and curing at 60-80°C and 130-150°C for 1.5-2h respectively.

[0011] Technical effects of the present invention:

[0012] 1. The organic silicon cyclophosphazene flame retardant proposed in the present invention is a flame retardant of three elements, N, P, and Si, which effectively improves the flame retardant efficiency of the flame retardant, and there are multiple active sites in the corresponding molecular structure of the flame retardant that can be cross-linked and cured with the epoxy resin, which increases the compatibility between the flame retardant and the epoxy resin;

[0013] Second, the present invention uses hexachlorotripolyphosphazene as the skeleton material of the organosilicon cyclophosphazene flame retardant. This structure not only has good stability, but also the six symmetrical introduction sites are conducive to the introduction of more carbon chains, thereby promoting the organosilicon cyclophosphazene modified epoxy resin to form more covering carbon layers during the combustion process, thereby improving its flame retardant properties;

[0014] 3. The organosilicon cyclophosphazene modified epoxy resins prepared by the present invention meet the standards of flame retardant materials. When the addition amount of the organosilicon cyclophosphazene flame retardant is 8% and 12%, the corresponding modified epoxy resins reach the V-0 grade in the UL-94 test, and the limiting oxygen index is 31.1% and 31.6%, respectively, that is, the organosilicon cyclophosphazene modified epoxy resin has good flame retardant properties; BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a screenshot of the video of the vertical combustion experiment process of silicone cyclophosphazene modified epoxy resin.

[0016] Figure 2 Schematic diagram of the sample dimensions for the vertical burning test (UL-94).

[0017] Figure 3Schematic diagram of the limiting oxygen index test (LOI) specimen size. DETAILED DESCRIPTION

[0018] The preparation method of the organosilicon cyclophosphazene flame retardant and the preparation method of the organosilicon cyclophosphazene modified epoxy resin proposed in the present invention are specifically described by the following examples. The present invention is specifically described by the following examples, but the implementation mode is not limited thereto, and the examples should not be regarded as limiting the present invention.

[0019] Example 1

[0020] The preparation process of organosilicon cyclophosphazene flame retardant includes four steps: substitution, dehydration condensation, addition and esterification.

[0021] 1. Substitution reaction: With tetrahydrofuran as solvent, add p-hydroxybenzaldehyde and anhydrous potassium carbonate to a three-necked flask respectively, the molar ratio of p-hydroxybenzaldehyde to anhydrous potassium carbonate is 1:1~1:1.5, in addition, 100ml of tetrahydrofuran solvent is required for each 0.01~0.02mol of p-hydroxybenzaldehyde to dissolve, and stir continuously for 1~2h. Add hexachlorotrimer phosphazene to a beaker, 100ml of tetrahydrofuran is required for each 0.06~0.07mol of hexachlorotrimer phosphazene to dissolve, the molar ratio of hexachlorotrimer phosphazene to p-hydroxybenzaldehyde is 1:6~1:7, after complete dissolution, slowly add the hexachlorotrimer phosphazene solution dropwise to the above three-necked flask, heat in an oil bath and stir continuously, and react at 60~66℃ for 20~24h. After the reaction is completed, cool to room temperature, pour the reaction solution into a large amount of water, filter the precipitate, and dry it in vacuum at 60-70°C for 10-12 h. Recrystallize the crude product from ethyl acetate, let it stand and cool, filter it, and dry it in vacuum at 70-85°C for 10-12 h to obtain intermediate 1 as a light yellow solid.

[0022] 2. Dehydration condensation: add intermediate 1 and p-aminobenzoic acid into a three-necked flask in a molar ratio of 1:6~1:7, use dioxane as solvent, and dissolve 100 ml of dioxane for every 0.008~0.009 mol of intermediate 1. Vacuum and pass nitrogen, heat in an oil bath and stir continuously, react at 90~101℃ for 20~24h, cool to room temperature after the reaction is completed, pour the reaction solution into ethanol diluent, filter the precipitate, wash twice with ethanol, and vacuum dry at 60~70℃ for 10~12h to obtain intermediate 2 as a white solid.

[0023] 3. Addition reaction: add intermediate 2 and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) into a three-necked flask, the molar ratio of intermediate 2 to DOPO is 1:6~1:7, use dioxane as solvent, 100 ml of dioxane is required to dissolve every 0.0006~0.0007 mol of intermediate 2, under nitrogen protection, heat in an oil bath and stir continuously, react at 90~101℃ for 20~24h, cool to room temperature after the reaction is completed, pour the reaction solution into ethanol diluent, filter the precipitate, wash twice with hot water and anhydrous ethanol respectively, and dry in a vacuum at 60~70℃ for 10~12h to obtain intermediate 3 as a white solid.

[0024] Example 2

[0025] Weigh a certain amount of epoxy resin, heat it to 100~110℃ with a constant temperature heating stirrer, add 4% (the added mass is the percentage of the total mass of the system, the same below) of organosilicon cyclophosphazene flame retardant to the epoxy resin until it is evenly stirred, adjust the heater temperature to 60~80℃, wait for the epoxy resin temperature to drop to the corresponding temperature, add the pre-calculated and weighed curing agent (m-phenylenediamine) to the epoxy resin, stir and mix evenly, vacuum for 3~5min, and then pour it into a silicone mold that has been preheated and brushed with a release agent (dimethyl silicone oil), and cure it in a constant temperature vacuum drying oven at 60~80℃ and 130~150℃ for 1.5~2h respectively, and take it out after the resin material cools naturally, and finally obtain a sample strip, which is marked as EP2. The reference sample is an epoxy resin without flame retardant added, and the sample is marked as EP1.

[0026] Example 3

[0027] Compared with Example 2, this embodiment has the following characteristics: the addition amount of the organosilicon cyclophosphazene flame retardant in the modified epoxy resin is 8%, the sample is marked as EP3, and the rest is the same as Example 2.

[0028] Example 4

[0029] Compared with Example 2, this embodiment has the following characteristics: the addition amount of the organosilicon cyclophosphazene flame retardant in the modified epoxy resin is 12%, the sample is marked as EP4, and the rest is the same as Example 2.

[0030] Example 5

[0031] Compared with Example 2, this embodiment has the following characteristics: the addition amount of the organosilicon cyclophosphazene flame retardant in the modified epoxy resin is 16%, the sample is marked as EP5, and the rest is the same as Example 2.

[0032] The flame retardant properties of organosilicon cyclophosphazene modified epoxy resin were studied by conducting vertical combustion (UL-94) and limiting oxygen index (LOI) tests on the samples prepared in Examples 2-5. Video screenshots of organosilicon cyclophosphazene modified epoxy resin during vertical combustion experiments are shown in the figure below. Figure 1 The specific test results are shown in Table 1.

[0033] Table 1 Flame retardant properties of samples in various embodiments

[0034] The test results show that pure epoxy resin (EP1) is highly flammable, with an LOI value of only 21.0%. It continued to burn in the UL-94 test, and a melting drop phenomenon occurred at the 33rd second of the combustion process, failing the UL-94 test. The addition of organosilicon cyclophosphazene flame retardant gradually increased the LOI of the epoxy resin, and showed a trend of first increasing and then decreasing, but the organosilicon cyclophosphazene modified epoxy resins all met the standards of flame-retardant materials. The UL-94 test results also show that the organosilicon cyclophosphazene modified epoxy resins are self-extinguishing within a certain time range. Among them, the organosilicon cyclophosphazene modified epoxy resins EP3 and EP4 obtained in Example 3 and Example 4 have the best flame retardant properties, and both reach the V-0 grade in the UL-94 test, and the limiting oxygen index is 31.1% and 31.6% respectively, with the best flame retardant effect.

[0035] The determination of vertical combustion and limiting oxygen index is carried out according to the following standards (the relevant specimen dimensions are as follows: Figure 2-3 shown):

[0036] Vertical burning (UL-94) test: GB / T 2408-2021;

[0037] Limiting Oxygen Index (LOI) test: GB / T 2406.2-2009.

Claims

1. An organosilicon cyclophosphazene modified epoxy resin, the resin is composed of E51 bisphenol A type glycidyl ether epoxy resin, organosilicon cyclophosphazene flame retardant and m-phenylenediamine, wherein the structural formula of the organosilicon cyclophosphazene flame retardant is:

2. An organosilicon cyclophosphazene modified epoxy resin as claimed in claim 1, characterized in that The organosilicon cyclophosphazene flame retardant is based on hexachlorotripolyphosphazene as the core skeleton, which contains N and P elements, and Si elements in the side chain structure. There are multiple active sites in the middle of the side chain that can be cross-linked and cured with epoxy resin.

3. A method for preparing an organosilicon cyclophosphazene modified epoxy resin, characterized in that Follow these steps: Step 1: Using tetrahydrofuran as solvent, p-hydroxybenzaldehyde and hexachlorotriphosphazene undergo substitution reaction to prepare intermediate 1; Step 2: Intermediate 1 is subjected to dehydration condensation with p-aminobenzoic acid using dioxane as solvent to obtain intermediate 2 containing a Schiff base structure; Step 3: Intermediate 2 reacts with DOPO to obtain intermediate 3; Step 4: Using DMSO as solvent, the intermediate 3 undergoes an esterification reaction with triphenylsilanol under the catalysis of HOBT and EDCI to obtain an organosilicon cyclophosphazene flame retardant; Step 5: Heat E51 bisphenol A glycidyl ether epoxy resin to 100-120°C, add a certain amount of organosilicon cyclophosphazene flame retardant, stir until evenly, reduce the temperature of the epoxy resin to 60-80°C, add the pre-calculated and weighed m-phenylenediamine, mix evenly, vacuum defoam, pour into a preheated mold, cure at 60-80°C and 130-150°C for 1.5-2h, respectively, and obtain organosilicon cyclophosphazene modified epoxy resin after cooling; wherein the mass fraction of the organosilicon cyclophosphazene flame retardant added to the modified epoxy resin is 4-16%.

4. An organosilicon cyclophosphazene modified epoxy resin and a preparation method thereof according to claim 3, characterized in that In step 1: using anhydrous calcium carbonate as an acid-binding agent, p-hydroxybenzaldehyde and anhydrous calcium carbonate are dissolved in tetrahydrofuran at a molar ratio of 1:1 to 1:1.5; dissolving hexachlorotrimer phosphazene alone, and then slowly adding it dropwise to the p-hydroxybenzaldehyde solution, the molar ratio of hexachlorotrimer phosphazene to p-hydroxybenzaldehyde being 1:6 to 1:7; then, reacting at 60 to 66°C for 20 to 24 hours.

5. An organosilicon cyclophosphazene modified epoxy resin and a preparation method thereof according to claim 3 or 4, characterized in that As described in step 2: intermediate 1, p-aminobenzoic acid and dioxane are added to a three-necked flask, reacted at 90-101° C. for 20-24 hours, and the molar ratio of intermediate 1 to p-aminobenzoic acid is 1:6-1:

7.

6. An organosilicon cyclophosphazene modified epoxy resin and a preparation method thereof according to claim 3, 4 or 5, characterized in that As described in step 3: intermediate 2, DOPO and dioxane are added to a three-necked flask, and reacted at 90-101° C. for 20-24 hours. The molar ratio of intermediate 2 to DOPO is 1:6-1:

7.

7. An organosilicon cyclophosphazene modified epoxy resin and a preparation method thereof according to claim 3, 4, 5 or 6, characterized in that As described in step 4: using 1-hydroxybenzotriazole (HOBT) and 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDCI) as catalysts, the intermediate 3 / HOBT, EDCI and triphenylsilanol are dissolved in DMSO respectively. After complete dissolution, the EDCI solution and the triphenylsilanol solution are slowly added dropwise to the intermediate 3 solution in sequence, and the reaction is carried out at 100-110° C. for 20-24 hours. The molar ratio of the intermediate 3 to the triphenylsilanol is 1:6-1:

7.

8. As described in claim 7, the mass fraction of the organosilicon cyclophosphazene flame retardant added to the modified epoxy resin in step 5 is 4%, 8%, 12% or 16% respectively.

Images