CN108641665B - Polyimide adhesive and preparation method thereof - Google Patents

Abstract

The invention relates to a polyimide adhesive and a preparation method thereof, belongs to the technical field of adhesives, and solves the problems that the polyimide adhesive is unstable in heat resistance and reduced in adhesive property when the temperature is higher than 350 ℃ in the prior art. A polyimide adhesive is obtained by curing a polyimide adhesive prepolymer, wherein the polyimide adhesive prepolymer is prepared from aromatic diamine containing a biphenyl structure, aromatic diamine containing a siloxane structure, aromatic dianhydride and a capping agent. Dissolving a polyimide adhesive prepolymer in an organic solvent to obtain a homogeneous solution; and coating the homogeneous solution on the surface of the bonded object, removing the organic solvent, and curing to obtain the polyimide adhesive to finish bonding of the bonded object. The polyimide adhesive disclosed by the invention can be applied to the bonding of high-temperature-resistant parts in the fields of aviation, aerospace, precision machinery, petrochemical industry and the like.

Description

A kind of polyimide adhesive and preparation method thereof

technical field

The invention relates to the technical field of adhesives, in particular to a polyimide adhesive and a preparation method thereof.

Background technique

With the rapid development of aerospace technology, organic high temperature resistant adhesives have been widely used in the manufacture of various aircraft.

Polyimide adhesives are more and more popular because of their excellent heat-resistant and high-temperature adhesive properties. Usually polyimide adhesives are classified according to processing and synthesis methods: condensation type, thermoplastic and addition type. For condensed polyimide adhesives, the curing process is the dehydration and cyclization process of polyamic acid, and the formation of water in the middle is easy to form pore defects, which is not suitable for large-area bonding. For thermoplastic polyimide adhesives, although the material can be bonded by direct hot melt to avoid the generation of pores, the heat resistance of such adhesives is insufficient, and its glass transition temperature (T _g ) generally does not exceed 250°C. For addition type polyimide adhesives, it is usually used in the form of a prepolymer with a reactive end capping agent. During the thermoforming process, the resin prepolymer first melts and infiltrates the adhesive material, and then solidifies to form a three-dimensional network structure. Polyimide adhesives have higher heat resistance and adhesion properties than the first two. Among them, addition-type polyimide adhesives terminated with phenylacetylene groups are the most widely used because of their rigid main chain structure, strong inter-molecular chain interactions, and high cross-linking density. However, the rigid main chain structure and strong interaction between molecular chains will increase the melt viscosity of the polyimide adhesive prepolymer, which will not be able to better wet the surface of the material to be bonded, thus reducing its bonding performance. . At the same time, the high crosslinking density in the structure will also bring about obvious curing shrinkage stress, thus affecting the bonding performance. In order to obtain a phenylacetylene-terminated addition type polyimide adhesive with both thermal stability and adhesive properties, researchers have carried out a series of research work. PETI-5 is an addition type polyimide adhesive developed earlier. It is composed of 3,3',4,4'-biphenyltetracarboxylic dianhydride (s-BPDA) and 15% of 1, 3-Bis(3-aminophenoxy)benzene (1,3,3-APB) and 85% of 3,4'-diaminodiphenyl ether (3,4'-ODA) were polymerized with 4-benzene The polyimide adhesive prepolymer prepared by end-capping with ethynyl phthalic anhydride (PEPA) has a designed molecular weight of 5000 g/mol. The glass transition temperature of the cured product is 270 ℃, and the titanium alloy after adhesive film bonding is made with E-112 fiber glass cloth as the carrier. The shear strength at room temperature is 49.0 MPa and 29.7 MPa at 177 ℃. The melt viscosity of the adhesive is relatively large, and the minimum melt viscosity is 10000Pa·s. The researchers further increased the branching degree of PETI-5 by introducing triamine monomer, and the minimum melt viscosity of modified PETI-5 was 60 Pa s. The shear strength of the titanium alloy bonded by it is 41MPa and 36MPa at room temperature and 177℃, respectively. Domestic researchers have also conducted a lot of research on the high-temperature bonding properties of polyimide adhesives. For example, the glass transition temperature of PEPA-terminated thermosetting polyimide adhesives developed by the Institute of Chemistry, Chinese Academy of Sciences exceeds 310 °C. The shear strength of the stainless steel sheet for bonding is 13MPa at room temperature and exceeds 10MPa at 316°C, but there is still a large melt viscosity (>300Pa·s), which is prone to bonding defects.

Based on the existing research results, polyimide adhesives still have the problems of unstable heat resistance and decreased bonding performance when used at high temperatures, which cannot meet the demand for higher temperature-resistant adhesives in the aerospace field in the future.

SUMMARY OF THE INVENTION

In view of the above analysis, the present invention aims to provide a polyimide adhesive and a preparation method thereof, which are used to solve the problem that the polyimide adhesive is thermally unstable and the adhesion performance is reduced when the temperature is higher than 350°C. question.

The object of the present invention is mainly achieved through the following technical solutions:

The invention provides a polyimide adhesive, which is obtained by curing a polyimide adhesive prepolymer, and the preparation raw material of the polyimide adhesive prepolymer is an aromatic diamine containing a biphenyl structure , Aromatic diamines containing siloxane structures, aromatic dianhydrides and end-capping agents.

The beneficial effects of the polyimide adhesive of the present invention are as follows:

On the one hand, the present invention selects aromatic diamine with siloxane structure as the preparation raw material of polyimide adhesive prepolymer, because the flexible siloxane structure is introduced into the rigid main chain structure of polyimide, thereby The melt viscosity of the prepolymer is greatly reduced, so that it can better infiltrate the surface of the bonded material to improve the bonding performance; on the other hand, because the polyimide adhesive prepolymer solidifies to form a three-dimensional network structure, The glass transition temperature of the adhesive after curing is increased, and the adhesive has excellent bonding performance and heat resistance at room temperature and high temperature.

On the basis of the above scheme, the present invention has also made the following improvements:

Further, the polyimide adhesive prepolymer has the structure of general formula I:

Wherein, Ar is selected from any one of the following aromatic structures:

R ₁ is a biphenyl structure, R ₂ is a siloxane structure, the ratio of x to y is (9:1)-(7:3), and n is 1-3.

Considering that the rigid main chain structure and the strong interaction between molecular chains will increase the melt viscosity of the polyimide adhesive prepolymer, it will not be able to better wet the surface of the bonded material, thus reducing its bonding performance. . Therefore, the present invention selects the polyimide adhesive prepolymer with the structure of general formula I, because the flexible siloxane structure is introduced into the rigid main chain structure, thereby greatly reducing the melt viscosity of the prepolymer, making its It can better wet the surface of the material to be bonded to improve the bonding performance.

When the ratio of x to y is (9:1)-(7:3) and n is 1-3, the number-average molecular weight (M _n ) of the polyimide adhesive prepolymer is 1100-2900 g/mol between. Appropriate molecular weight of polyimide adhesive prepolymer contributes to the compatibility of adhesive properties and heat resistance. The above-mentioned prepolymer molecular weight can ensure good melt viscosity and suitable crosslinking density.

Further, the aromatic diamine containing a siloxane structure is bis(4-aminophenoxy)tetramethyldisiloxane and/or bis(4-(4-aminophenoxy)benzene)tetramethyldisiloxane oxane.

The above-mentioned two aromatic diamines containing siloxane structure are preferred in the present invention because the long-chain segment disiloxane and aromatic structure in the structure endow the polyimide adhesive with excellent melt fluidity and heat resistance. Two aromatic diamines containing siloxane structure were used as raw materials for the preparation of polyimide adhesive prepolymers.

R ₂ is selected from any one of the following structures:

Further, the aromatic diamine of biphenyl structure is 4,4'-diamino-2,2'-dimethylbiphenyl and/or 4,4'-diamino-2,2'-bistrifluoromethyl biphenyl benzene.

Considering that the methyl substitution and trifluoromethyl substitution in the biphenyl structure can effectively reduce the stacking between molecular chains, thereby improving the wettability of the adhesive and the material to be bonded, and improving the bonding performance and heat resistance, the present invention is preferably the above-mentioned. Two aromatic diamines with biphenyl structure were used as raw materials for the preparation of polyimide adhesive prepolymers.

R ₁ is selected from any one of the following structures:

Further, the aromatic dianhydride is one of pyromellitic dianhydride, 3,3',4,4'-biphthalic dianhydride or 3,3',4,4'-benzophenone tetracarboxylic dianhydride. One or more; the end-capping agent is 4-phenylethynyl phthalic anhydride.

In the experiment, it was found that the dianhydride with rigid symmetrical structure can give the polyimide adhesive outstanding heat resistance, while the pyromellitic dianhydride, 3,3',4,4'-biphthalic dianhydride and 3,3',4,4'-benzophenone tetraacid dianhydride has a rigid symmetrical structure, so the present invention preferably uses the above-mentioned aromatic dianhydride as the raw material for the preparation of the adhesive prepolymer, and the obtained polyimide When the amine adhesive is used above 350 ℃, it not only has good heat resistance stability, but also has excellent adhesion performance.

It is worth noting that the phenylacetylene-based end-capping agent can endow the polyimide adhesive with a wider molding temperature window, and no small-molecule volatiles are generated during the curing and molding process. Therefore, in the present invention, 4-phenylethynyl phthalic anhydride is preferred as the end-capping agent.

The present invention also provides a preparation method of the polyimide adhesive, the preparation method comprising the following steps:

Step 1: dissolving the polyimide adhesive prepolymer in an organic solvent to obtain a homogeneous solution;

Step 2: Coat the homogeneous solution on the surface of the adherend, remove the organic solvent, and cure to obtain a polyimide adhesive, which completes the bonding of the adherend.

In the preparation method of the above polyimide adhesive, the removal of the organic solvent is stepwise heating removal, and the specific process is: 60-80°C, 1-4 hours; 120-150°C, 0.5-4 hours; 180-200°C, 0.5-4 hours.

The organic solvents used in the preparation method of the above-mentioned polyimide adhesive are N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide ( One or more of DMF), dimethyl sulfoxide (DMSO) and cyclopentanone.

The beneficial effects of the preparation method of the polyimide adhesive of the present invention are as follows:

On the one hand, due to the introduction of a flexible siloxane structure into the rigid main chain structure of polyimide, the melt viscosity of the prepolymer is greatly reduced, so that it can better wet the surface of the bonded material and improve the viscosity. On the other hand, since siloxane has the organic-inorganic conversion characteristics of oxidative crosslinking at high temperature, during the curing process, the polyimide adhesive produces a silica-like inorganic structure, which further improves the Heat resistance of polyimide adhesives. The polyimide adhesive prepared by the above method still has excellent heat resistance stability and outstanding adhesive performance at high temperature above 350°C. The preparation method is simple in process and easy to operate.

Further, the solid content of the homogeneous solution in the above preparation method is 40wt.%-65wt.%.

In the experiment, it was found that if the solid content of the homogeneous solution in the above preparation method is too low, the solvent is easy to remain, which affects its bonding performance; if the solid content is too high, it is difficult to store. The invention controls the solid content of the homogeneous solution to be 40wt.%-65wt.%.

Further, the curing in step 2 of the above preparation method is heating and curing, and the heating and curing process is: at a heating rate of 2-6 °C/min, the temperature is raised to 350-400 °C, and the curing reaction time is 1-6 hours.

The heating rate of 2-6°C/min is conducive to better removal of the solvent and avoids solvent residues that affect the adhesive properties of the adhesive.

The temperature range of 350-400℃ is the reaction temperature of the thermal curing of the phenylacetylene group in the capping agent. If the temperature is too low, the curing will be incomplete, and if the temperature is too high, it may decompose, which is not conducive to the bonding performance of the adhesive. Therefore, the preferred curing temperature of the present invention is 350-400°C.

It is found in the experiment that the curing reaction is incomplete when the reaction time is less than 1 hour; when the reaction time is 6 hours, the curing reaction has been completed. Therefore, in the above preparation method, the curing reaction time is controlled to be 1-6 hours.

Further, the polyimide adhesive prepolymer is prepared by the following method:

The aromatic diamine containing biphenyl structure and the aromatic diamine containing siloxane structure are dissolved in an organic solvent, and completely dissolved under the protection of an inert gas to obtain a mixed solution; the aromatic dianhydride and the end-capping agent are sequentially added to the mixed solution , under the protection of inert gas to complete dissolution, stirring and reacting to obtain a homogeneous solution of prepolymer raw materials; adding a dehydrating agent to the homogeneous solution of prepolymer raw materials, azeotropic reaction occurs, removing the dehydrating agent, cooling, precipitation and separation to obtain a polymer Imide adhesive prepolymer.

In the above-mentioned preparation method of the polyimide adhesive prepolymer, the organic solvent used is the same as the organic solvent used in the preparation method of the polyimide adhesive.

In the preparation method of the above polyimide adhesive prepolymer, the stirring reaction is carried out at room temperature, and the stirring reaction time is 6-24 hours, and the solid content of the obtained prepolymer raw material homogeneous solution is 25wt.% -40wt.%.

Considering this range of solid content, it is beneficial to obtain the polyimide adhesive prepolymer with the expected structure and designed molecular weight, and the appropriate molecular weight of the polyimide adhesive prepolymer helps the adhesion performance and resistance. Thermal compatibility. Therefore, in the preparation method of the polyimide adhesive prepolymer of the present invention, the solid content of the homogeneous solution of the prepolymer raw material is controlled to be 25wt.%-40wt.%.

In the preparation method of the above-mentioned polyimide adhesive prepolymer, in order to realize the complete dehydration and cyclization of the polyamic acid, the dehydrating agent used is toluene or xylene, and the mass ratio of the dehydrating agent to the organic solvent is (0.5-1.5 ): 10. The azeotropic reaction is carried out under the protection of nitrogen at a temperature of 120-190 °C, and the azeotropic reaction time is 6-18 hours. After removing the dehydrating agent, the reaction solution was cooled to 80-120°C.

In the preparation method of the above-mentioned polyimide adhesive prepolymer, the precipitating agent used in the precipitation separation is any one or several arbitrary proportions in water, methanol, ethanol, propanol, isopropanol or butanol. mixture. After precipitation and separation, resin precipitation is obtained, which is repeatedly washed, filtered and then dried to obtain a polyimide adhesive prepolymer. The washing of the resin precipitation can use any one of hot water, methanol, ethanol or other low-boiling alcohol solvents or a mixture of several in any proportion.

When the polyimide adhesive of the present invention is used to bond objects, the polyimide resin prepolymer is first dissolved in an organic solvent to prepare a homogeneous solution with a certain solid content; the homogeneous solution is uniformly coated On the surface of the object to be bonded, the solvent is removed by step heating, and then a solid bonding body is obtained through the heating and curing process.

The adherends in the present invention can be common metals such as stainless steel, aluminum alloys, titanium alloys, etc., as well as high-temperature-resistant resin-based composite materials.

In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination solutions. Additional features and advantages of the invention will be set forth in the description which follows, and some of the advantages may become apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention may be realized and attained by the things particularly pointed out in the description, claims and drawings.

Description of drawings

The drawings are for the purpose of illustrating specific embodiments only, and are not to be considered limiting of the present invention.

Fig. 1 is the rheological curve of the polyimide adhesive prepolymer prepared in Example 1.

2 is the DMA curve of the polyimide adhesive prepared in Example 1.

3 is a TEM image of the polyimide adhesive prepared in Example 1 after a single lap shear test at a high temperature of 380°C.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments. The following examples select representative monomer raw materials such as diamine, dianhydride, and end-capping agent to prepare addition-type polyimide adhesives with different structures, and select representative stainless steel as the adherend to conduct adhesion performance In the test, the raw material monomers or the adherends in the examples were replaced with other raw material monomers or other types of adherends described in the content of the present invention, and the polyimide prepared by the preparation method and conditions described in the content of the present invention was used. The amine adhesive has the same effect as this embodiment.

The percentage content and percentage concentration in the present invention are both the mass percentage content and the mass percentage concentration unless otherwise specified. The raw materials can be obtained from commercial sources unless otherwise specified.

Example 1

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 28.82 g (0.09 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 3.49 g (0.01 mol) of bis(4-aminophenoxy)tetramethyldisiloxane and 110 g of N-methylpyrrolidone were stirred under nitrogen protection until completely dissolved. Then, 16.11 g (0.05 mol) of 3,3',4,4'-benzophenone tetraacid dianhydride and 24.82 g (0.10 mol) of 4-phenylethynylphthalic anhydride were added, and the mixture was stirred under a nitrogen atmosphere until it was completely dissolved. Stir at room temperature for 12 hours to obtain a homogeneous solution with a solids content of 40 wt.%.

(2) 16 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 175°C, reacted under nitrogen protection for 12 hours, then heated to 200°C to steam out toluene and stop heating.

(3) cooling the reaction solution to 100°C, pouring it into ethanol to obtain a resin precipitate, repeatedly washing with ethanol and hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer Solid powder, 97% yield (prepolymer structure x:y=9:1, n=1.0, _Mn =1410 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N-methylpyrrolidone to obtain a resin solution with a solid content of 65wt.%, and the homogeneous solution was evenly coated on the surface of the stainless steel sheet, and first passed 80°C/2 hours , 120°C/1 hour, 200°C/1.5 hours step heating process to remove the solvent, then raise the temperature to 370°C at a heating rate of 2°C/min, and solidify for 2 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Example 2

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 25.62 g (0.08 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 6.97 g (0.02 mol) of bis(4-aminophenoxy)tetramethyldisiloxane and 215 g of N,N-dimethylacetamide were stirred under nitrogen protection until completely dissolved. Then, 19.33 g (0.06 mol) of 3,3',4,4'-benzophenone tetraacid dianhydride and 19.86 g (0.08 mol) of 4-phenylethynylphthalic anhydride were added, and the mixture was stirred under nitrogen atmosphere until it was completely dissolved. Stir at room temperature for 12 hours to obtain a homogeneous solution with a solids content of 25 wt.%.

(2) 11 grams of xylene was added to the above homogeneous solution, the reaction system was heated to 150° C., reacted under nitrogen protection for 12 hours, then heated to 166° C. to steam out xylene and stop heating.

(3) cooling the reaction solution to 80°C, pouring it into methanol to obtain a resin precipitate, washing with ethanol repeatedly, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer solid powder, The yield was 98% (prepolymer structure x:y=8:2, n=1.5, _Mn =1721 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N,N-dimethylacetamide to obtain a resin solution with a solid content of 50 wt. ℃/2 hours, 150°C/2 hours, 200°C/1.5 hours step heating process to remove the solvent, then raise the temperature to 350°C at a heating rate of 3°C/min, and solidify for 6 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Example 3

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 22.42 g (0.07 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 10.46 g (0.03 mol) of bis(4-aminophenoxy)tetramethyldisiloxane and 165 g of N,N-dimethylformamide were stirred under nitrogen protection until completely dissolved. Then, 21.49 g (0.067 mol) of 3,3',4,4'-benzophenone tetraacid dianhydride and 16.56 g (0.067 mol) of 4-phenylethynyl phthalic anhydride were added, and the mixture was stirred under nitrogen atmosphere until completely dissolved. Stir at room temperature for 8 hours to obtain a homogeneous solution with a solid content of 30 wt.%.

(2) 8 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 140° C., reacted under nitrogen protection for 12 hours, then heated to 153° C. to steam out toluene and stop heating.

(3) cooling the reaction solution to 120°C, pouring it into propanol to obtain a resin precipitate, washing with methanol repeatedly, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer solid powder , the yield was 96% (prepolymer structure x:y=7:3, n=2.0, _Mn =2034 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N,N-dimethylformamide to obtain a resin solution with a solid content of 40wt.%, and the homogeneous solution was evenly coated on the surface of the stainless steel sheet, and the ℃/2 hours, 120°C/4 hours, 200°C/2 hours step heating process to remove the solvent, then raise the temperature to 400°C at a heating rate of 5°C/min, and cure for 2 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Example 4

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 22.42 g (0.07 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 10.46 g (0.03 mol) of bis(4-aminophenoxy)tetramethyldisiloxane and 162 g of N-methylpyrrolidone were stirred under nitrogen protection until completely dissolved. Then, 24.17 g (0.075 mol) of 3,3',4,4'-benzophenone tetraacid dianhydride and 12.41 g (0.05 mol) of 4-phenylethynyl phthalic anhydride were added, and the mixture was stirred under a nitrogen atmosphere until it was completely dissolved. Stir at room temperature for 8 hours to obtain a homogeneous solution with a solid content of 30 wt.%.

(2) 16 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 180° C., reacted under nitrogen protection for 12 hours, then heated to 200° C. to steam out toluene and stop heating.

(3) cooling the reaction solution to 120°C, pouring it into propanol to obtain a resin precipitate, repeatedly washing with ethanol and hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer The solid powder was obtained in 96% yield (prepolymer structure x:y=7:3, n=3.0, _Mn =2649 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N,N-dimethylformamide to obtain a resin solution with a solid content of 40wt.%, and the homogeneous solution was evenly coated on the surface of the stainless steel sheet, and the ℃/4 hours, 120°C/3 hours, 200°C/1 hour step heating process to remove the solvent, then raise the temperature to 400°C at a heating rate of 6°C/min, and cure for 2 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Example 5

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 22.42 g (0.07 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 16.70 g (0.03 mol) of bis(4-(4-aminophenylesteryl)benzene)tetramethyldisiloxane and 176 g of dimethyl sulfoxide were stirred under nitrogen protection until completely dissolved. Then, 24.17 g (0.075 mol) of 3,3',4,4'-benzophenone tetraacid dianhydride and 12.41 g (0.05 mol) of 4-phenylethynyl phthalic anhydride were added, and the mixture was stirred under a nitrogen atmosphere until it was completely dissolved. Stir at room temperature for 6 hours to obtain a homogeneous solution with a solids content of 30 wt.%.

(2) 18 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 160° C., reacted under nitrogen protection for 18 hours, then heated to 177° C. to steam out toluene and stop heating.

(3) cooling the reaction solution to 80°C, pouring it into ethanol to obtain a resin precipitate, repeatedly washing with ethanol and hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer Solid powder, 97% yield (prepolymer structure x:y=7:3, n=3.0, _Mn =2867 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in dimethyl sulfoxide to obtain a resin solution with a solid content of 50 wt.%, and the homogeneous solution was evenly coated on the surface of the stainless steel sheet, and the temperature was 80°C/4 hours. , 150°C/2 hours, 200°C/4 hours step heating process to remove the solvent, then increase the temperature to 400°C at a heating rate of 2°C/min, and solidify for 1 hour to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1

Example 6

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 28.82 g (0.09 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 5.5676 g (0.01 mol) of bis(4-(4-aminophenylesteryl)benzene)tetramethyldisiloxane and 172 g of N-methylpyrrolidone were stirred under nitrogen protection until completely dissolved. Then, 14.71 g (0.05 mol) of 3,3',4,4'-biphtalic dianhydride and 24.82 g (0.10 mol) of 4-phenylethynylphthalic anhydride were added, and the mixture was stirred under a nitrogen atmosphere until it was completely dissolved. , and stirred at room temperature for 12 hours to obtain a homogeneous solution with a solid content of 30 wt.%.

(2) 9 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 190° C., reacted under nitrogen protection for 6 hours, then heated to 200° C. to steam out toluene and stop heating.

(3) cooling the reaction solution to 100° C., pouring it into isopropanol to obtain a resin precipitate, washing with methanol and hot water repeatedly, filtering, pulverizing and drying in an oven to obtain a pre-polyimide adhesive Polymer solid powder in 98% yield (prepolymer structure x:y=9:1, n=1.0, _Mn =1400 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N,N-dimethylacetamide to obtain a resin solution with a solid content of 50 wt. ℃/1 hour, 150 ℃/4 hours, 200 ℃/1 hour step heating process to remove the solvent, then raise the temperature to 350 ℃ at a heating rate of 2 ℃/min, and solidify for 3 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1

Example 7

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 25.62 g (0.08 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 6.97 g (0.02 mol) of bis(4-aminophenoxy)tetramethyldisiloxane and 130 g of N,N-dimethylacetamide were stirred under nitrogen protection until completely dissolved. Then, 17.65 g (0.06 mol) of 3,3',4,4'-biphtalic dianhydride and 19.86 g (0.08 mol) of 4-phenylethynylphthalic anhydride were added, and the mixture was stirred under a nitrogen atmosphere until it was completely dissolved. Stir at room temperature for 10 hours to obtain a homogeneous solution with a solids content of 35 wt.%.

(2) 7 grams of xylene was added to the above homogeneous solution, the reaction system was heated to 150°C, reacted under nitrogen protection for 10 hours, then heated to 166°C to steam out toluene and stop heating.

(3) cooling the reaction solution to 80°C, pouring it into butanol to obtain a resin precipitate, repeatedly washing with hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer solid Powder, 96% yield (prepolymer structure x:y=8:2, n=1.5, _Mn =1665 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N,N-dimethylacetamide to obtain a resin solution with a solid content of 50 wt. ℃/4 hours, 150°C/2 hours, 200°C/2 hours step heating process to remove the solvent, then increase the temperature to 370°C at a heating rate of 3°C/min, and cure for 2 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1

Example 8

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 22.42 g (0.07 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl, 16.70 g (0.03 mol) of bis(4-(4-aminophenylesteryl)benzene)tetramethyldisiloxane and 112 g of N-methylpyrrolidone were stirred under nitrogen protection until completely dissolved. Then, 19.62 g (0.067 mol) of 3,3',4,4'-biphtalic dianhydride and 16.56 g (0.067 mol) of 4-phenylethynylphthalic anhydride were added, and the mixture was stirred under nitrogen atmosphere until it was completely dissolved. Stir at room temperature for 10 hours to obtain a homogeneous solution with a solid content of 40 wt.%.

(2) 17 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 175° C., reacted under nitrogen protection for 8 hours, then heated to 200° C. to steam out toluene and stop heating.

(3) cooling the reaction solution to 100°C, pouring it into hot water to obtain a resin precipitate, repeatedly washing with ethanol and hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer The solid powder was obtained in 97% yield (prepolymer structure x:y=7:3, n=2.0, _Mn =2120 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N,N-dimethylacetamide to obtain a resin solution with a solid content of 50 wt. ℃/4 hours, 150°C/0.5 hours, 200°C/2 hours step heating process to remove the solvent, then raise the temperature to 390°C at a heating rate of 3°C/min, and solidify for 4 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Example 9

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 19.11 g (0.09 mol) of 4,4'-diamino-2,2'-dimethylbiphenyl, 3.49 g (0.01 mol) bis(4-aminophenoxy)tetramethyldisiloxane and 136 g of cyclopentanone, stirred under nitrogen protection until completely dissolved. Then, 10.91 g (0.05 mol) of phthalic dianhydride and 24.82 g (0.10 mol) of 4-phenylethynyl phthalic anhydride were added, and the mixture was stirred under nitrogen atmosphere until completely dissolved. Stir at room temperature for 24 hours to obtain a homogeneous solution with a solids content of 30 wt.%.

(2) 6.8 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 120° C., reacted under nitrogen protection for 6 hours, then heated to 130° C. to steam out toluene and stop heating.

(3) cooling the reaction solution to 100°C, pouring it into ethanol to obtain a resin precipitate, repeatedly washing with ethanol and hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer Solid powder, 95% yield (prepolymer structure x:y=9:1, n=1.0, _Mn =1116 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in cyclopentanone to obtain a resin solution with a solid content of 40 wt. ℃/4 hours, 200 ℃/0.5 hours step heating process to remove the solvent, then increase the temperature to 400 ℃ at a heating rate of 6 ℃/min, and obtain a firm bond after curing for 2 hours.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Example 10

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 16.98 g (0.08 mol) of 4,4'-diamino-2,2'-dimethylbiphenyl, 6.97 g (0.02 mol) bis(4-aminophenoxy)tetramethyldisiloxane and 128 g of N,N-dimethylacetamide were stirred under nitrogen protection until completely dissolved. Then, 14.55 g (0.067 mol) of pyromellitic dianhydride and 16.56 g (0.067 mol) of 4-phenylethynylphthalic anhydride were added, and the mixture was stirred under nitrogen atmosphere until completely dissolved. Stir at room temperature for 10 hours to obtain a homogeneous solution with a solid content of 30 wt.%.

(2) 13 grams of toluene was added to the above-mentioned homogeneous solution, the reaction system was heated to 145° C., reacted under nitrogen protection for 8 hours, then heated to 166° C. to steam out toluene and stop heating.

(3) cooling the reaction solution to 120°C, pouring it into hot water to obtain a resin precipitate, repeatedly washing with ethanol and hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer The solid powder was obtained in 97% yield (prepolymer structure x:y=8:2, n=2.0, _Mn =1550 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N-methylpyrrolidone to obtain a resin solution with a solid content of 60wt.%, and the homogeneous solution was evenly coated on the surface of the stainless steel sheet, and the temperature was 60°C/4 hours. , 150°C/2 hours, 180°C/4 hours step heating process to remove the solvent, then increase the temperature to 400°C at a heating rate of 2°C/min, and solidify for 2 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Example 11

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet, and a thermometer, add 16.98 g (0.08 mole) of 4,4'-diamino-2,2'-dimethylbiphenyl, 11.14 g (0.02 mol) bis(4-(4-aminophenylesteryl)benzene)tetramethyldisiloxane and 138 g of N,N-dimethylacetamide were stirred under nitrogen protection until completely dissolved. Then, 14.55 g (0.067 mol) of pyromellitic dianhydride and 16.56 g (0.067 mol) of 4-phenylethynylphthalic anhydride were added, and the mixture was stirred under nitrogen atmosphere until completely dissolved. Stir at room temperature for 12 hours to obtain a homogeneous solution with a solids content of 30 wt.%.

(2) 14 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 145°C, reacted under nitrogen protection for 10 hours, then heated to 166°C to steam out toluene and stop heating.

(3) cooling the reaction solution to 100°C, pouring it into hot water to obtain a resin precipitate, repeatedly washing with ethanol and hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer The solid powder was obtained in 97% yield (prepolymer structure x:y=8:2, n=2.0, _Mn =1655 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N-methylpyrrolidone to obtain a resin solution with a solid content of 65wt.%, and the homogeneous solution was evenly coated on the surface of the stainless steel sheet, and the temperature was 60°C/4 hours. , 150°C/2 hours, 200°C/4 hours step heating process to remove the solvent, then increase the temperature to 370°C at a heating rate of 4°C/min, and solidify for 3 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Comparative Example 1

(1) In a three-necked flask equipped with a mechanical stirring, a water separator, a nitrogen inlet and outlet and a thermometer, add 12.81 g (0.04 mol) of 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl and 64 g of N-methylpyrrolidone was stirred under nitrogen protection until completely dissolved. Then, 9.67 g (0.03 mol) of 3,3',4,4'-benzophenone tetraacid dianhydride and 4.96 g (0.02 mol) of 4-phenylethynylphthalic anhydride were added, and the mixture was stirred under nitrogen atmosphere until completely dissolved. Stir at room temperature for 12 hours to obtain a homogeneous solution with a solids content of 30 wt.%.

(2) 6 grams of toluene was added to the above homogeneous solution, the reaction system was heated to 180° C., reacted under nitrogen protection for 12 hours, then heated to 200° C. to steam out toluene and stop heating.

(3) cooling the reaction solution to 100°C, pouring it into ethanol to obtain a resin precipitate, repeatedly washing with ethanol and hot water, filtering, pulverizing and drying in an oven to obtain a polyimide adhesive prepolymer Solid powder, 97% yield (prepolymer structure x:y=10:0, n=3.0, _Mn =2619 g/mol).

Adhesion experiment of polyimide adhesive and stainless steel sheet:

The above-mentioned polyimide adhesive solid powder was dissolved in N-methylpyrrolidone to obtain a resin solution with a solid content of 65wt.%, and the homogeneous solution was evenly coated on the surface of the stainless steel sheet, and first passed 80°C/2 hours , 120°C/1 hour, 200°C/1.5 hours step heating process to remove the solvent, then raise the temperature to 370°C at a heating rate of 2°C/min, and solidify for 2 hours to obtain a firm bond.

The main properties of the polyimide adhesive prepared in this example are shown in Table 1.

Table 1 Main properties of the polyimide adhesives prepared in Examples 1-11 and Comparative Example 1

Table 1 lists the melt fluidity, heat resistance and adhesive properties of the polyimide adhesives prepared in Examples 1-11 and Comparative Example 1, specifically including: The number-average molecular weight and melt flowability of polymers and the heat resistance and bonding properties of cured polyimide adhesives. It can be seen from Table 1 that the number-average molecular weight of the polyimide adhesive prepolymer prepared by the method provided by the present invention is 1100-2900 g/mol, and the minimum melt viscosity at 353-375 ° C is 1.7-18.5 Pa·s, The glass transition temperature (T _g ) of the adhesive after curing is greater than or equal to 360°C. The shear strength of the adhesive to stainless steel is 18-25MPa at room temperature, 15-18MPa and 7-10MPa at 350°C and 380°C, respectively. Compared with Comparative Example 1 without the addition of diamine containing siloxane structure, the melt viscosity of the polyimide adhesive prepared in Examples 1-11 was greatly reduced, and the shear strength after bonding with stainless steel was greatly improved. The excellent high-temperature adhesive performance of the adhesive is closely related to the organic-inorganic conversion characteristics of siloxane oxidative crosslinking at high temperature. The appearance of inorganic phase in the adhesive structure at high temperature improves its thermal stability. The above data show that the polyimide adhesive prepared by the method provided by the present invention has excellent melt fluidity, heat resistance and high temperature bonding properties, and can be applied to high temperature resistance in the fields of aviation, aerospace, precision machinery, petrochemical and other fields. Bonding of components.

The above description is only a preferred embodiment of the present invention, but the protection scope of the present invention is not limited to this. Substitutions should be covered within the protection scope of the present invention.

Claims (7)

1. a polyimide adhesive, is characterized in that, adopts polyimide adhesive prepolymer to solidify and obtains, and the preparation raw material of described polyimide adhesive prepolymer is to contain biphenyl structure aromatic diamines, aromatic diamines containing siloxane structures, aromatic dianhydrides and end-capping agents; The polyimide adhesive is used in the aerospace field; The polyimide adhesive prepolymer has the structure of general formula I:

Wherein, Ar is selected from any one or more in the following aromatic structures:

R ₁ is a biphenyl structure, R ₂ is a siloxane structure, the ratio of x to y is (9:1)-(7:3), and n is 1-3; The aromatic diamine containing siloxane structure is bis(4-aminophenoxy) tetramethyldisiloxane and/or bis(4-(4-aminophenoxy) benzene) tetramethyldisiloxane oxane; R ₂ is selected from any one or more of the following structures:

The end-capping agent is 4-phenylethynyl phthalic anhydride. 2. The polyimide adhesive according to claim 1, wherein the aromatic diamine of the biphenyl structure is 4,4'-diamino-2,2'-dimethylbiphenyl and / or 4,4'-diamino-2,2'-bistrifluoromethylbiphenyl; R ₁ is selected from any one or more of the following structures:

3. a preparation method of polyimide adhesive is characterized in that, for preparing polyimide adhesive as claimed in claim 1 or 2, described preparation method comprises the following steps: Step 1: dissolving the polyimide adhesive prepolymer in an organic solvent to obtain a homogeneous solution; Step 2: coating the homogeneous solution on the surface of the adherend, removing the organic solvent, and curing to obtain a polyimide adhesive, and completing the bonding of the adherend. 4 . The method for preparing a polyimide adhesive according to claim 3 , wherein the solid content of the homogeneous solution is 40wt.%-65wt.%. 5 . 5. The preparation method of the polyimide adhesive according to claim 3, wherein the curing in the step 2 is heating and curing, and the heating and curing process is: at a temperature of 2-6 °C/min The heating rate is increased to 350-400 ° C, and the curing reaction time is 1-6 hours. 6. The preparation method of polyimide adhesive according to claim 3, wherein the polyimide adhesive prepolymer is prepared by the following method: The aromatic diamine containing biphenyl structure and the aromatic diamine containing siloxane structure are dissolved in an organic solvent, and completely dissolved under the protection of an inert gas to obtain a mixed solution; the aromatic dianhydride and the end-capping agent are sequentially added to the mixed solution , under the protection of inert gas to complete dissolution, stirring and reacting to obtain a homogeneous solution of prepolymer raw materials; adding a dehydrating agent to the homogeneous solution of prepolymer raw materials, azeotropic reaction occurs, removing the dehydrating agent, cooling, precipitation and separation to obtain a polymer Imide adhesive prepolymer. 7 . The method for preparing a polyimide adhesive according to claim 6 , wherein the solid content of the homogeneous solution of the prepolymer raw material is 25wt.%-40wt.%. 8 .

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