A POSS flame retardant containing phosphorus and nitrogen elements, preparation method and application

Abstract

The present invention discloses a POSS flame retardant containing phosphorus and nitrogen elements, a preparation method and an application thereof. The flame retardant of the present invention is prepared by randomly hydrolyzing and condensing a phosphaphenanthrene-type siloxane monomer and a triazine ring-type siloxane monomer; wherein the phosphaphenanthrene-type siloxane monomer is prepared from a vinyl siloxane and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; the triazine ring-type siloxane monomer is prepared from an aminopropyl siloxane and cyanuric chloride. The POSS flame retardant containing phosphorus and nitrogen elements prepared by the present invention adopts a method of first synthesizing monomers and then preparing POSS, which can effectively increase the content of phosphorus and nitrogen elements in the flame retardant, thereby better realizing the efficient synergistic flame retardancy of P, N and Si; at the same time, the cage structure in the flame retardant avoids intermolecular aggregation under the connection of the triazine ring, enabling the flame retardant to be uniformly dispersed in the epoxy matrix, and a large number of organic groups on the surface of POSS can enhance the interaction between the flame retardant and the epoxy resin matrix, improving the mechanical properties of the composite material; in addition, the inorganic skeleton composed of Si-O-Si has better stability at high temperatures, improving the thermal stability of the epoxy resin matrix.

Description

Technical Field

[0001] The present invention relates to the technical field of flame - retardant composite materials, and particularly relates to a POSS flame - retardant containing phosphorus and nitrogen elements, a preparation method and an application thereof. Background Art

[0002] As a common thermosetting material, epoxy resin has been widely used in many fields due to its excellent adhesion, electrical insulation and mechanical properties. However, epoxy resin is a flammable material, and when it burns, it will release a large amount of toxic gases, posing a great threat to the environment and people's health. Therefore, improving the flame retardancy of epoxy resin is of great significance for life and production.

[0003] As an environmentally friendly green flame - retardant, organosilicon compounds have received extensive attention in the field of flame retardancy due to their high efficiency, non - toxicity, low smoke, no melt - dripping, no pollution and other characteristics. At the same time, the lightweight molecular cage - type polyhedral oligomeric silsesquioxane (POSS) derived from it with an organic - inorganic hybrid structure has great application prospects in the field of designing new flame - retardants due to its special spatial size, performance characteristics and structure. The structural formula of POSS is shown in the following formula (a), where R, as a reactive group, can introduce flame - retardant elements such as phosphorus and nitrogen into the POSS molecule to play a synergistic role with silicon elements.

[0004]

[0005] Chinese Patent CN 106750317A grafts a phosphorus - containing monomer onto the surface of vinyl POSS by the addition reaction of P - H bond and vinyl to obtain phosphorus - containing POSS. This method needs to be carried out at a relatively high temperature, and the phosphorus content in the phosphorus - containing POSS is relatively low, which has limited improvement on the flame - retardant performance of materials. Chinese Patent CN 106220854 B synthesized a hyperbranched POSS flame - retardant for enhancing the flame - retardant performance, mechanical properties and heat - insulation and smoke - suppression performance of silicone rubber. The internal structure of POSS is mainly composed of Si - O - Si to form an inorganic skeleton, and there is still a weak interaction between it and the matrix. Therefore, a monomer with a flame - retardant element can be first synthesized using reactive siloxane, and then a condensation reaction is carried out to obtain POSS with more organic flame - retardant groups on the surface. This method not only improves the flame retardancy of POSS, but also is beneficial to enhancing the compatibility with the matrix. Summary of the Invention

[0006] Aiming at the deficiencies in the prior art, the present invention provides a POSS flame - retardant containing phosphorus and nitrogen elements, a preparation method and an application thereof. Among them, the POSS structures can be interconnected through triazine rings to form a POSS with a network structure, which has excellent improvement effects on the flame - retardant performance, mechanical properties and thermal stability of epoxy resin.

[0007] According to an embodiment of the present invention, a POSS flame retardant containing phosphorus and nitrogen elements is provided, which includes two siloxane monomers, namely a phosphaphenanthrene-type siloxane monomer and a triazine ring-type siloxane monomer; the phosphaphenanthrene-type siloxane monomer is prepared by an addition reaction of vinyl siloxane and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; the triazine ring-type siloxane monomer is prepared by a substitution reaction of aminopropyl siloxane and cyanuric chloride.

[0008] According to an embodiment of the present invention, a preparation method of a POSS flame retardant containing phosphorus and nitrogen elements is further provided, including the following steps:

[0009] Step 1, prepare the phosphaphenanthrene-type siloxane monomer. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and an initiator are stirred in a nitrogen atmosphere until both are completely dissolved; after heating to 75 °C, a certain amount of vinyl siloxane is slowly dropped into the mixed solution, the dropping time is 0.5 h to 1 h, and the reaction time is 4 to 6 h; after the reaction ends, rotary evaporation is carried out to obtain a light yellow viscous liquid, and it is washed several times with a solvent to obtain the target product, the phosphaphenanthrene-type siloxane monomer;

[0010] Step 2, prepare the triazine ring-type siloxane monomer. Cyanuric chloride is dissolved in 200 ml of dioxane, and a mixed liquid of equimolar amounts of aminopropyl siloxane and an acid-binding agent is added respectively in three temperature ranges of 10 to 20 °C, 50 to 60 °C, and 80 to 90 °C, and the reaction is carried out for 2 to 3 h in each temperature range; after the reaction ends, vacuum filtration is carried out to obtain a light yellow filtrate, and rotary evaporation is continued to obtain a yellow liquid, and it is washed several times with dioxane to obtain the target product, the triazine ring-type siloxane monomer;

[0011] Step 3, add the above two siloxane monomers to solvent A in a certain proportion and mix evenly; add catalyst B to make the pH of the reaction between 2 and 4, and heat to 45 to 60 °C, and react for 15 to 20 h; after the reaction ends, a light yellow viscous precipitate is obtained, which is washed several times with solvent C and then placed in a vacuum drying oven for drying to obtain a light yellow solid as the target product, the POSS flame retardant containing phosphorus and nitrogen elements.

[0012] Preferably, in the above step 1, the vinyl siloxane is one of vinyltrimethoxysilane and vinyltriethoxysilane; the initiator is one of azobisisobutyronitrile and azobisisoheptonitrile; the molar ratio of the reactants 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, vinyl siloxane and the initiator is 1 to 1.1:1:0.05.

[0013] Further preferably, in the second step, the acid-binding agent is an organic weak base such as triethylamine or pyridine; the aminopropylsiloxane is one of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane; the molar ratio of cyanuric chloride, aminopropylsiloxane and the acid-binding agent is 1:3:3.

[0014] Further preferably, in the third step, the mass ratio of the phosphaphenanthrene-type siloxane monomer to the triazine ring-type siloxane monomer is 1-1.5:1; the mass ratio of solvent A to the triazine ring-type siloxane is 25-30:1; the dosage of catalyst B is determined by the pH of the reaction.

[0015] Further preferably, in the third step, solvent A is a mixed solution of one of ethanol, n-propanol or isopropanol and water, and the mixing volume ratio is alcohol:water = 5:95; catalyst B is one of hydrochloric acid and sulfuric acid; solvent C is one of acetonitrile, dioxane and acetone.

[0016] According to the embodiments of the present invention, there is provided an application of a POSS flame retardant containing phosphorus and nitrogen elements in epoxy resin.

[0017] Preferably, the mass proportion of the POSS flame retardant containing phosphorus and nitrogen elements added in the epoxy resin is 5% - 20%.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The method of the present invention for preparing POSS by first synthesizing monomers and then performing hydrolysis and condensation can effectively improve the phosphorus content and nitrogen content of the flame retardant, and better realize the efficient synergistic flame retardancy among the three elements of P, N, and Si.

[0020] The cage structure of the POSS flame retardant containing phosphorus and nitrogen elements prepared by the present invention avoids intermolecular aggregation under the connection of the triazine ring, enabling the flame retardant to be evenly dispersed in the epoxy matrix. Moreover, a large number of organic groups on the surface of POSS can enhance the interaction between the flame retardant and the epoxy resin matrix, improving the mechanical properties of the composite material. In addition, the inorganic skeleton composed of Si-O-Si has better stability at high temperatures, improving the thermal stability of the epoxy resin matrix.

[0021] The raw materials required by the present invention are inexpensive, the preparation process is simple, there is no complex reaction equipment and strict reaction conditions, which is conducive to large-scale production. Description of the Drawings

[0022] Figure 1 is the structural formula of the POSS flame retardant containing phosphorus and nitrogen elements of the present invention;

[0023] Figure 2 is the infrared spectrum of the POSS flame retardant containing phosphorus and nitrogen elements of the present invention;

[0024] Figure 3 The limiting oxygen index and vertical burning rating of the epoxy resin added with the phosphorus- and nitrogen-containing POSS flame retardant;

[0025] Figure 4 The impact strength of the epoxy resin added with the phosphorus- and nitrogen-containing POSS flame retardant. Specific embodiments

[0026] The technical solutions in the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] The present invention provides a phosphorus- and nitrogen-containing POSS flame retardant, which includes two siloxane monomers, namely a phosphaphenanthrene-type siloxane monomer and a triazine ring-type siloxane monomer; the phosphaphenanthrene-type siloxane monomer is prepared by the addition reaction of vinyl siloxane and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide; the triazine ring-type siloxane monomer is prepared by the substitution reaction of aminopropyl siloxane and cyanuric chloride;

[0028] As Figure 1 shown, one of its structures is as Figure 1 shown, and the R groups in the figure are randomly distributed with phosphaphenanthrene groups and triazine ring groups.

[0029] Example 1: Preparation of the phosphorus- and nitrogen-containing POSS flame retardant;

[0030] Preparation of the phosphaphenanthrene-type siloxane monomer: 13 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 0.1 g of initiator azobisisobutyronitrile are added to a four-necked flask containing 200 ml of toluene, stirred until dissolved under a nitrogen atmosphere, and the temperature is raised to 75 °C; 7.5 g of vinyltrimethoxysilane is slowly dropped into the mixture, the dropping time is 1 h, and the reaction is carried out for 6 h; after the reaction is completed, rotary evaporation is carried out to obtain a light yellow viscous liquid, which is washed several times with toluene to obtain the target product;

[0031] Preparation of the triazine ring-type siloxane monomer: 9.2 g of cyanuric chloride is dissolved in 200 ml of dioxane, and a mixed solution of 11 g of 3-aminopropyltriethoxysilane and 5.05 g of triethylamine is added at 20 °C, 50 °C and 80 °C respectively for reaction, and the reaction is carried out for 2 h at each temperature; after the reaction is completed, rotary evaporation is carried out to obtain a yellow liquid, which is washed several times with dioxane to obtain the target product;

[0032] The above two kinds of siloxane monomers were added to a mixed solution of 100 ml of ethanol and water in a ratio of 1:1 and mixed evenly. Concentrated hydrochloric acid was added dropwise until the pH reached 3, and the temperature was raised to 50 °C. The reaction was carried out for 15 h. After the reaction, a pale yellow viscous precipitate was obtained. After washing several times with acetone, it was placed in a vacuum drying oven to dry to obtain a pale yellow solid, which was the POSS flame retardant containing phosphorus and nitrogen elements;

[0033] As Figure 1 shown, it is the infrared spectrum of the preparation of the POSS flame retardant containing phosphorus and nitrogen elements. The characteristic absorption peaks of P-Ph, P-O, and P=O in DOPO are at 1585 cm -1 , 1485 cm -1 and 1267 cm -1 . The absorption peaks of C=N and C-N in the triazine ring are at 1560 cm -1 , 1267 cm -1 . The stretching vibration peak of -CH 2 - in vinyl siloxane and aminopropyl siloxane appears at 2933 cm -1 . The absorption peak of N-H in aminopropyl siloxane is at 3301 cm -1 , and the absorption peak of Si-O-Si in the regular cage-type and semi-cage-type structures is at 1112 cm -1 .

[0034] Example 2: Preparation of the POSS flame retardant containing phosphorus and nitrogen elements;

[0035] Preparation of phosphaphenanthrene-based siloxane monomer: 13 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 0.1 g of initiator azobisisobutyronitrile were added to a four-necked flask containing 200 ml of toluene. Under a nitrogen atmosphere, it was stirred until both were dissolved, and the temperature was raised to 75 °C; 9.5 g of vinyltriethoxysilane was slowly added dropwise to the mixed solution. The dropping time was 1 h, and the reaction was carried out for 6 h. After the reaction, it was rotary evaporated to obtain a light yellow viscous liquid, which was washed several times with toluene to obtain the target product;

[0036] Preparation of triazine ring-based siloxane monomer: 9.2 g of cyanuric chloride was dissolved in 200 ml of dioxane, and a mixed solution of 11 g of 3-aminopropyltriethoxysilane and 5.05 g of triethylamine was added and reacted at 20 °C, 50 °C, and 80 °C respectively, and the reaction was carried out for 2 h at each temperature; after the reaction, it was rotary evaporated to obtain a yellow liquid, which was washed several times with dioxane to obtain the target product;

[0037] The above two kinds of siloxane monomers were added to a mixed solution of 100 ml of ethanol and water in a mass ratio of 1:1, and mixed evenly; concentrated hydrochloric acid was added dropwise until the pH reached 3, the temperature was raised to 50 °C, and the reaction was carried out for 15 h. After the reaction ended, a pale yellow viscous precipitate was obtained. After washing several times with acetone, it was placed in a vacuum drying oven to dry to obtain a pale yellow solid, which was the POSS flame retardant containing phosphorus and nitrogen elements.

[0038] Example 3: Preparation of POSS flame retardant containing phosphorus and nitrogen elements;

[0039] Preparation of phosphaphenanthrene-based siloxane monomer: 13 g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and 0.1 g of initiator azobisisobutyronitrile were added to a four-necked flask containing 200 ml of toluene. Under a nitrogen atmosphere, it was stirred until both were dissolved, and the temperature was raised to 75 °C; 7.5 g of vinyltrimethoxysilane was slowly dropped into the mixed solution, and the dropping time was 1 h, and the reaction was carried out for 6 h. After the reaction ended, rotary evaporation was carried out to obtain a light yellow viscous liquid, which was washed several times with toluene to obtain the target product;

[0040] Preparation of triazine ring-based siloxane monomer: 9.2 g of cyanuric chloride was dissolved in 200 ml of dioxane, and a mixed solution of 11 g of 3-aminopropyltriethoxysilane and 5.05 g of triethylamine was added at 20 °C, 50 °C and 80 °C respectively for reaction, and the reaction was carried out for 2 h at each temperature; after the reaction ended, rotary evaporation was carried out to obtain a yellow liquid, which was washed several times with dioxane to obtain the target product;

[0041] The above two kinds of siloxane monomers were added to a mixed solution of 100 ml of n-propanol and water in a mass ratio of 1:1, and mixed evenly; concentrated sulfuric acid was added dropwise until the pH reached 3, the temperature was raised to 50 °C, and the reaction was carried out for 15 h. After the reaction ended, a pale yellow viscous precipitate was obtained. After washing several times with acetone, it was placed in a vacuum drying oven to dry to obtain a pale yellow solid, which was the POSS flame retardant containing phosphorus and nitrogen elements.

[0042] Example 4: Preparation of flame-retardant epoxy resin;

[0043] Epoxy resin was selected as the material matrix, and the POSS flame retardant containing phosphorus and nitrogen elements prepared in Example 1 was added, and the incorporated mass percentages of the flame retardant were 5%, 10%, 15%, and 20% respectively. The specific steps were as follows: The flame retardant was dispersed in 25 g of acetone, and after ultrasonic treatment for 1 h, it was added to 30.0 g of preheated epoxy resin. After stirring at 80 °C for 30 min until the acetone completely volatilized, 6.0 g of curing agent 4,4-diaminodiphenylmethane was added. After stirring for 5 min, the mixture was quickly transferred to a preheated mold and placed in an oven for curing. The curing program was set as 80 °C / 1.5 h, 120 °C / 2 h, 150 °C / 2 h; after the curing ended, a flame-retardant epoxy resin material was obtained.

[0044] Example 5: Preparation of pure epoxy resin;

[0045] 6.0 g of the curing agent 4,4-diaminodiphenylmethane was added to 30.0 g of preheated epoxy resin, and the mixture was stirred for 5 min. Then the mixture was transferred to a preheated mold and cured in an oven. The curing program was set as 80 °C / 1.5 h, 120 °C / 2 h, 150 °C / 2 h; after curing, a flame-retardant epoxy resin material was obtained;

[0046] As Figure 3 shown, the limiting oxygen index and vertical burning rating of the flame-retardant epoxy resin are presented. In the figure, when the addition amount of the POSS flame retardant containing phosphorus and nitrogen elements reaches more than 10%, the vertical burning rating of the epoxy resin can reach V0 level, and its limiting oxygen index also increases significantly, reaching the highest value of 33.2% when the addition amount is 15%;

[0047] As Figure 4 shown, the impact strength of the epoxy resin and the flame-retardant epoxy resin is presented. It can be seen from the figure that the impact strength of the pure epoxy resin is 65.13 MPa. After adding the POSS flame retardant containing phosphorus and nitrogen elements, the impact strength of the epoxy material is significantly improved, and it shows a trend of first increasing and then decreasing with the increase of the filler; when the addition amount of the flame retardant is 10%, the impact strength of the material reaches the maximum, which is 88.64 MPa; the good compatibility between the flame retardant and the epoxy matrix and the inorganic structure composed of Si-O-Si endow the material with excellent impact resistance.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing a POSS flame retardant containing phosphorus and nitrogen elements, characterized in that: The steps include: Step 1, preparing a phosphaphenanthrene-type siloxane monomer, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and an initiator are stirred under a nitrogen atmosphere until both are completely dissolved; after heating to 75° C., a certain amount of vinyl siloxane is slowly dripped into the mixed solution, the dripping time is 0.5h to 1h, and the reaction time is 4 to 6h; after the reaction is completed, rotary evaporation is performed to obtain a light yellow viscous liquid, and the liquid is washed several times with a solvent to obtain the target product, the phosphaphenanthrene-type siloxane monomer; Step 2, preparing a triazine cyclic siloxane monomer, dissolving cyanuric chloride in 200 ml of dioxane, and adding an equimolar amount of a mixed liquid of aminopropyl siloxane and an acid binding agent at three temperature ranges of 10-20° C., 50-60° C., and 80-90° C., respectively, and reacting for 2-3 hours in each temperature range; after the reaction is completed, filtering under reduced pressure to obtain a light yellow filtrate, continuing rotary evaporation to obtain a yellow liquid, and washing with dioxane several times to obtain the target product, a triazine cyclic siloxane monomer; Step three, adding the above two siloxane monomers into solvent A in a certain proportion and mixing evenly; adding catalyst B to make the reaction pH between 2 and 4, and heating to 45 to 60° C. and reacting for 15 to 20 hours; after the reaction, a light yellow viscous precipitate is obtained, which is washed several times with solvent C, and then placed in a vacuum drying oven to obtain a light yellow solid as the target product, a POSS flame retardant containing phosphorus and nitrogen elements.

2. The preparation method of the POSS flame retardant containing phosphorus and nitrogen elements according to claim 1, characterized in that, In the step 1, the vinyl siloxane is one of vinyl trimethoxy silane and vinyl triethoxy silane; the initiator is one of azobisisobutyronitrile and azobisisoheptanenitrile; the molar ratio of the reactant 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, the vinyl siloxane and the initiator is 1-1.1:1:0.

05.

3. The preparation method of the POSS flame retardant containing phosphorus and nitrogen elements according to claim 1, characterized in that, In the step 2, the acid binding agent is triethylamine or pyridine; the aminopropylsiloxane is one of 3-aminopropyltrimethoxysilane and 3-aminopropyltriethoxysilane; and the molar ratio of cyanuric chloride, aminopropylsiloxane and the acid binding agent is 1:3:

3.

4. The preparation method of the POSS flame retardant containing phosphorus and nitrogen elements according to claim 1, characterized in that, In the step 3, the mass ratio of the phosphaphenanthrene siloxane monomer to the triazine ring siloxane monomer is 1-1.5:1; the mass ratio of the solvent A to the triazine ring siloxane is 25-30:1; and the amount of the catalyst B is determined by the pH of the reaction.

5. The preparation method of the POSS flame retardant containing phosphorus and nitrogen elements according to claim 1, characterized in that, In the step three, solvent A is a mixed solution of ethanol, n-propanol or isopropanol and water, and the mixed volume ratio is alcohol: water = 5:95; catalyst B is one of hydrochloric acid and sulfuric acid; solvent C is one of acetonitrile, dioxane, and acetone.

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