A high-temperature-resistant polyimide adhesive based on dynamic boron-oxygen bond and a preparation method thereof

Abstract

The application discloses a high-temperature-resistant polyimide adhesive based on a dynamic boron-oxygen bond and a preparation method thereof. The application first synthesizes linear polyamide acid with boronic acid groups at the molecular terminals, and then forms polyimide crosslinked by boron-oxygen hexacyclic rings through high-temperature dehydration. The formation of the boron-oxygen hexacyclic rings as crosslinking points further improves the thermal stability and chemical stability of the polyimide adhesive. Meanwhile, based on the hydrolysis reaction of the boron-oxygen hexacyclic rings, the adhesive can be de-crosslinked under acidic conditions, and exhibits the characteristics of debonding and repeatable processing. The crosslinked polyimide can be used as a reversible adhesive, and has excellent bonding strength, high-temperature thermal stability, chemical stability and debonding reshaping property for metals such as stainless steel.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology and relates to a high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds and its preparation method. Background Technology

[0002] On-demand release adhesives constitute a rapidly developing class of materials that require high holding power during use to achieve reliable adhesion, while simultaneously offering simple and clean removability at the end of the application. On-demand release adhesives have a wide range of applications, including the selective removal of bonded components and repair of complex structures in automated production processes, wafer-level packaging in the microelectronics industry, and the recycling and regeneration of high-value materials at the end of the lifespan of automotive or smart products (laptops, mobile phones, etc.). However, conventional adhesives are unsuitable for high-temperature processes such as the assembly and sealing of thermal protection systems, the connection and repair of brake and engine system components, and wafer thinning processes. Abrasion or impact under high-temperature conditions can easily lead to bond failure. It is well known that the limiting temperature of most polymer adhesives is typically below 400°C, which significantly limits their application in high-temperature environments. Most commercial temporary adhesives are also low-melting-point, heat-sensitive polymers. Therefore, the development of advanced temporary adhesives with high bond strength and excellent heat resistance has become a priority.

[0003] In the field of high-temperature adhesives, polyimides are the preferred matrix for adhesives due to their high heat resistance, excellent mechanical properties, and good chemical stability. Generally, a polymer structure with intra-chain covalent bonds and inter-chain entanglement networks is crucial for achieving high adhesive strength. However, fully aromatic polyimides are characterized by high molecular weight and strong inter-chain interactions, resulting in high polymer viscosity, high crystallinity, and low solubility. These characteristics reduce their ability to penetrate the substrate, leading to shrinkage and defects after curing, resulting in poor adhesion and failing to meet the requirements for on-demand debonding. To reduce the cohesive energy of polyimides, flexible segments (-O-, -C=O-, and -Si-O-), aliphatic units (-CH3 and -CH2-), or asymmetric structures are often introduced, thereby reducing the rigidity of the polymer backbone, inhibiting close chain packing, and reducing inter-chain interactions. Furthermore, molecular weight can be controlled to reduce viscosity. However, these strategies often lead to a sharp decline in thermal stability, adhesive strength, and chemical stability. Therefore, the development of polyimide adhesives that combine high heat resistance, high adhesion, and chemical stability with on-demand debonding capability remains a significant challenge. Summary of the Invention

[0004] To address the problems mentioned in the background section, the present invention aims to provide a novel high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds and its preparation method.

[0005] The dynamically crosslinked polyimide adhesive provided by this invention first synthesizes PI-b with boric acid groups at the molecular end using diamine, dianhydride monomers, and boric acid monomers as raw materials; then, PI-b undergoes dehydration condensation to synthesize boron-oxygen bond crosslinked polyimide. The formation of boron-oxygen hexacyclic rings as crosslinking points further improves the thermal and chemical stability of the polyimide adhesive. Simultaneously, based on the hydrolysis reaction of boron-oxygen hexacyclic rings, this adhesive can decrosslink under acidic conditions, exhibiting debonding and reprocessable characteristics. This crosslinked polyimide can serve as a reversible adhesive, demonstrating excellent bonding strength, high-temperature thermal stability, chemical stability, and debonding and remodeling properties to metals such as stainless steel.

[0006] This invention also provides a method for synthesizing high-temperature resistant polyimide adhesives based on dynamic boron-oxygen bonds.

[0007] Includes the following steps:

[0008] (1) Synthesis of macromolecules PI-b with boric acid groups at the molecular end: Under nitrogen protection, diamine monomers are added to a solvent, and after dissolution, excess dianhydride monomers are added in batches to generate polyimide prepolymers with acid anhydride groups at the molecular end. Then, an amino-containing boric acid compound is added, and phenylboronic acid is linked to the molecular chain end of the prepolymer through the reaction of amino and acid anhydride to obtain PI-b with boric acid groups at the molecular end.

[0009] (2) Synthesis of high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds: The PI-b obtained in step (1) is cured under heating conditions and then dehydrated at high temperature to obtain the high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds.

[0010] Preferably, in step (1), the diamine monomer used is selected from at least one of 4,4'-diaminodiphenyl ether, 4,4-diaminodiphenyl sulfide, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, p-phenylenediamine, 4,4'-dichlorodiphenylmethane, and 4,4'-diaminodiphenyl sulfone;

[0011] The diamine monomer has a mass fraction of 10-15% in the solvent.

[0012] Preferably, in step (1), the dianhydride monomer used is selected from at least one of pyromellitic anhydride, 4,4-oxobisphthalic anhydride, 3,4-oxobisphthalic anhydride, 4,4-hexafluoroisopropylphthalic anhydride, and 2,3',3,4'-biphenyltetracarboxylic dianhydride.

[0013] The molar ratio of the dianhydride monomer to the diamine monomer is 1.03-1.2.

[0014] Preferably, in step (1), the amino-containing boric acid compound used is selected from at least one of 3-aminophenylboronic acid, 2-aminophenylboronic acid, 4-aminophenylboronic acid salt, 3-aminophenylboronic acid salt, 2-aminophenylboronic acid salt, 4-carbamoylphenylboronic acid, 3-carbamoylphenylboronic acid, and 2-carbamoylphenylboronic acid.

[0015] The proportion of the amino-containing boric acid compound added is 6-40% of the molar amount of the diamine monomer.

[0016] Preferably, in step (1), the solvent is selected from at least one of N,N′-dimethylformamide, N,N′-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

[0017] Preferably, in step (2), the curing step is: curing according to a step program of 80℃ / 3h, 120℃ / 1h, 150℃ / 1h, 180℃ / 1h, 250℃ / 1h and 300℃ / 1h;

[0018] Alternatively, pre-cur at 80-200℃ for 4 hours, followed by curing at 300℃ for 1 hour.

[0019] The high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds prepared by this invention has the following characteristics: the boron-oxygen bond crosslinking polyimide agent has the characteristics of reversible recycling and reprocessing. Specifically, the adhesive achieves decrosslinking and debonding under acidic conditions through a hydrolysis reaction, allowing for reuse; the hydrolysis reaction step is as follows: the adhesive is soaked in a mixed solvent containing acid for debonding.

[0020] Preferably, the acid is selected from at least one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, boric acid, perchloric acid, and hydrobromic acid.

[0021] Preferably, the solvent is selected from at least one of N,N′-dimethylformamide, N,N′-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, acetone, diethyl ether, chloroform, and dichloromethane.

[0022] This invention further investigates the mechanism and properties of the boron-oxygen bond crosslinked polyimide adhesive. The linear polyimide prepolymer synthesized in this invention has boric acid groups at the ends of its molecular chain. This linear polyimide prepolymer undergoes a trimerization reaction through the boric acid groups at the ends of its molecular chain to form boron-oxygen hexacycles, yielding a boron-oxygen bond crosslinked polyimide. Through the dynamic and reversible reaction of the boron-oxygen hexacycle, the network structure of this crosslinked polyimide polymer can be transformed and reorganized, thus exhibiting characteristics of on-demand debonding and reprocessability. Furthermore, the boron-oxygen hexacycle further improves the high-temperature thermal stability, adhesive strength, and chemical stability of the polyimide adhesive.

[0023] It is evident that, compared with the prior art, the present invention has the following advantages:

[0024] (1) The boron-oxygen bond crosslinked polyimide adhesive prepared by this invention has excellent high-temperature thermal stability, bonding strength, and chemical stability. At the same time, this dynamically crosslinked polyimide adhesive can be debonded, recycled, and reused under acidic conditions, achieving reversible bonding, which is of positive significance for the development of high-temperature resistant reversible adhesives.

[0025] (2) The boron-oxygen bond crosslinked polyimide adhesive provided by the present invention has the advantages of easy operation, cheap and readily available raw materials, and flexible and diverse formulations and products. Attached Figure Description

[0026] Figure 1 The diagram shows the synthetic route for the polyimide adhesive prepared according to the present invention. In the diagram, A is a diamine monomer, B is a dianhydride monomer, C is aminophenylboronic acid, D is a polyimide prepolymer PI-b with an anhydride terminal, and E is a polyimide crosslinked with boron-oxygen bonds.

[0027] Figure 2 The image shows the appearance of the boron-oxygen crosslinked polyimide film prepared in Example 1.

[0028] Figure 3 The infrared spectrum of the boron-oxygen crosslinked polyimide film prepared in Example 1 is shown.

[0029] Figure 4 The adhesive strength of the crosslinked polyimide adhesive prepared in Example 2.

[0030] Figure 5 The thermogravimetric curve of the boron-oxygen bond crosslinked polyimide film prepared in Example 3.

[0031] Figure 6 The adhesion strength of the boron-oxygen bond crosslinked polyimide adhesive prepared in Example 3 at different temperatures.

[0032] Figure 7 The debonding of the boron-oxygen bond crosslinked polyimide adhesive prepared in Example 3 in different solvents.

[0033] Figure 8 The adhesion strength of the boron-oxygen bond crosslinked polyimide adhesive prepared in Example 3 in different solvents.

[0034] Figure 9 The debonding of the boron-oxygen bond crosslinked polyimide adhesive prepared in Example 4 was observed in a mixed solvent of NMP / DCM / HCl.

[0035] Figure 10 The adhesion strength of the boron-oxygen bond crosslinked polyimide adhesive prepared in Example 4 after four dissolution-bonding cycles is shown. Detailed Implementation

[0036] To more clearly illustrate the present invention, the following description, in conjunction with preferred embodiments, further clarifies the invention. Those skilled in the art should understand that the specific descriptions below are illustrative rather than restrictive, and should not be construed as limiting the scope of protection of the present invention.

[0037] Example 1

[0038] 4.1 g (10 mmol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane was weighed and dissolved in 34.3 g of N-methylpyrrolidone. After dissolution, 3.42 g (11 mmol) of 4,4-oxobisphthalic anhydride was added in batches. The mixture was stirred at room temperature for 6 h under nitrogen protection until a transparent viscous solution with a solid content of 18% was obtained. 0.274 g (2 mmol) of 3-aminophenylboronic acid was added, and stirring was continued for 4 h to obtain a pale yellow solution. The solution was then coated onto a glass plate and cured into a film according to a stepwise program of 80℃ / 3 h, 120℃ / 1 h, 150℃ / 1 h, 180℃ / 1 h, 250℃ / 1 h, and 300℃ / 1 h to obtain the boron-oxygen bond crosslinked polyimide sample 1.

[0039] The appearance of sample 1 is shown below. Figure 2 As shown, from Figure 2 It can be seen that the boron-oxygen bond crosslinked polyimide film has good transparency.

[0040] The infrared spectrum of sample 1 is as follows Figure 3 As shown, from Figure 3 It can be seen that at 719cm -1 The presence of characteristic peaks for BO at this location confirms the formation of boron-oxygen hexacyclic crosslinks.

[0041] Example 2

[0042] Weigh 8.2 g (20 mmol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane and dissolve it in 67.9 g of N-methylpyrrolidone. After dissolution, add 6.7 g (21.6 mmol) of 4,4-oxobisphthalic anhydride in batches. Stir at room temperature for 6 hours under nitrogen protection until a transparent viscous solution with a solid content of 18% is obtained. Add 0.44 g (3.2 mmol) of 3-aminophenylboronic acid and continue stirring for 4 hours to obtain a pale yellow solution. Coat the pale yellow solution onto a polished steel sheet with a coating area of ​​20 × 12.5 mm and a coating thickness of 0.2 mm. Pre-cure at 250 °C for 4 hours, then adhere and fix the steel sheet, and cure at 300 °C for 1 hour to obtain an adhesive part bonded with cross-linked polyimide sample 2. Test the shear adhesion strength of the adhesive part using a tensile testing machine. The results are as follows: Figure 4 As shown, Sample 2 exhibits higher bond strength compared to a linear polyimide adhesive cured in the same steps with the same diamine and dianhydride ratio (without added phenylboronic acid).

[0043] Example 3

[0044] 4.1 g (10 mmol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane was weighed and dissolved in 33.5 g of N-methylpyrrolidone. After dissolution, 3.26 g (10.5 mmol) of 4,4-oxobisphthalic anhydride was added in batches. The mixture was stirred at room temperature for 6 hours under nitrogen protection until a transparent viscous solution with a solid content of 18% was obtained. 0.14 g (1 mmol) of 3-aminophenylboronic acid was added, and stirring was continued for 4 hours to obtain a pale yellow solution. The solution was then cured under the heating conditions described in Example 1 to obtain the boron-oxygen bond crosslinked polyimide sample 3.

[0045] The thermogravimetric curve of sample 3 is as follows Figure 5 As shown, the 5% decomposition temperature is above 500℃, exhibiting excellent heat resistance; the 23℃ increase in decomposition temperature after crosslinking indicates that boron-oxygen hexacyclic further improves thermal stability.

[0046] The bonded steel sheets of sample 3 were placed at different temperatures, and their shear adhesion strength was tested using a tensile testing machine. The results are as follows: Figure 6 As shown. From Figure 6 It can be seen that the initial adhesive strength of sample 3 reached 26 MPa, and it exhibited excellent adhesion performance at high temperatures. Below 300℃, the adhesive strength was almost unaffected. After heat treatment at 350℃ for 1 hour, the lap shear strength still reached over 20 MPa.

[0047] The steel sheets bonded in sample 3 were immersed in different single solvents for 1 hour, then suspended with weights again. Finally, the shear strength was tested using a tensile testing machine, and the results are as follows: Figure 7 and Figure 8 As shown, after solvent treatment, the bonded parts can still stably withstand a weight of 2.5 kg in the solvent, and the adhesion strength remains above 22 MPa, demonstrating excellent chemical stability.

[0048] Example 4

[0049] 8.2 g (20 mmol) of 2,2-bis[4-(4-aminophenoxy)phenyl]propane was weighed and dissolved in 67.1 g of N-methylpyrrolidone. After the diamine dissolved, 6.52 g (21 mmol) of 4,4-oxobisphthalic anhydride was added in batches. The mixture was stirred at room temperature for 6 h under nitrogen protection until a transparent viscous solution with a solid content of 18% was obtained. 0.28 g (2 mmol) of 3-aminophenylboronic acid was added, and stirring was continued for 4 h to obtain a pale yellow solution. After curing at the above temperature, the initial cross-linked polyimide adhesive sample 4 was obtained.

[0050] The bonded steel sheets of sample 4 were immersed in a mixed solvent of NMP / DCM / HCl to detach. Shear adhesion strength was tested using a tensile testing machine. The changes in adhesion strength with immersion time are shown below. Figure 9 As the soaking time increased, the adhesive strength of the boron-oxygen bond crosslinked polyimide adhesive gradually decreased, proving that the adhesive of the present invention can achieve the goal of on-demand debonding.

[0051] Sample 4 was dissolved by immersing it in a mixed solvent of NMP / DCM / HCl, and then recoated onto a clean steel sheet for re-curing and bonding. The above steps were repeated to obtain a boron-oxygen bond crosslinked polyimide adhesive that had been recycled multiple times.

[0052] The steel sheets bonded with the adhesives of different recycling cycles were subjected to shear adhesion strength tests using a tensile testing machine. The results are as follows: Figure 10 The adhesive maintained a bond strength of 25 MPa during four cycles of dissolution-bonding, indicating that sample 4 has good recyclability and reusability.

Claims

1. A method for synthesizing a high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds, characterized in that, Includes the following steps: (1) Under nitrogen protection, diamine monomer is added to solvent, and after dissolution, excess dianhydride monomer is added in batches to generate polyimide prepolymer with anhydride at the molecular end. Then, an amino-containing boric acid compound is added, and phenylboronic acid is linked to the molecular chain end of the prepolymer through the reaction of amino and anhydride to obtain a pale yellow solution. (2) Synthesis of high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds: The pale yellow solution obtained in step (1) is cured under heating conditions, and after high-temperature dehydration, the high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds is obtained. The molar ratio of the dianhydride monomer to the diamine monomer is 1.03-1.2; The proportion of the amino-containing boric acid compound added is 6-40% of the molar amount of the diamine monomer; In step (2), the curing step is: curing according to a step program of 80℃ / 3h, 120℃ / 1h, 150℃ / 1h, 180℃ / 1h, 250℃ / 1h and 300℃ / 1h; Alternatively, pre-cur at 80-200℃ for 4 hours, followed by curing at 300℃ for 1 hour.

2. The synthesis method according to claim 1, characterized in that, In step (1), the diamine monomer used is selected from at least one of 4,4'-diaminodiphenyl ether, 4,4-diaminodiphenyl sulfide, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, p-phenylenediamine, 4,4'-dichlorodiphenylmethane, and 4,4'-diaminodiphenyl sulfone; The mass fraction of the diamine monomer in the solvent is 10-15%.

3. The synthesis method according to claim 1, characterized in that, In step (1), the dianhydride monomer used is selected from at least one of pyromellitic anhydride, 4,4-oxobisphthalic anhydride, 3,4-oxobisphthalic anhydride, 4,4-hexafluoroisopropylphthalic anhydride, and 2,3',3,4'-biphenyltetracarboxylic dianhydride.

4. The synthesis method according to claim 1, characterized in that, In step (1), the amino-containing boric acid compound used is selected from at least one of 3-aminophenylboronic acid, 2-aminophenylboronic acid, 4-aminophenylboronic acid salt, 3-aminophenylboronic acid salt, 2-aminophenylboronic acid salt, 4-carbamoylphenylboronic acid, 3-carbamoylphenylboronic acid, and 2-carbamoylphenylboronic acid.

5. The synthesis method according to claim 1, characterized in that, In step (1), the solvent is selected from at least one of N,N′-dimethylformamide, N,N′-dimethylacetamide, dimethyl sulfoxide, and N-methylpyrrolidone.

6. A high-temperature resistant polyimide adhesive based on dynamic boron-oxygen bonds, prepared by any one of the synthesis methods of claims 1-5.

7. The adhesive according to claim 6, characterized in that, The adhesive is de-crosslinked and de-adhesive under acidic conditions through a hydrolysis reaction, and can be reused. The hydrolysis reaction involves immersing the adhesive in a mixed solvent containing acid to de-adhesive.

8. The adhesive according to claim 7, characterized in that, The acid is selected from at least one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, boric acid, perchloric acid, and hydrobromic acid.

9. The adhesive according to claim 8, characterized in that, The solvent is selected from at least one of N,N′-dimethylformamide, N,N′-dimethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetrahydrofuran, acetone, diethyl ether, chloroform, and dichloromethane.

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