Cross-linked terminated polyimide with high residual carbon rate and its application

Abstract

The present invention belongs to the technical field of polymer materials, and in particular to a cross-linked end-capped polyimide with a high residual carbon rate and its application. 1,4,5,8-naphthalenetetracarboxylic anhydride and 4,4'-diaminobiphenyl-2,2-dicarboxylic acid are dissolved in N-N dimethylacetamide, maleic anhydride is added and reacted at room temperature under a nitrogen atmosphere to obtain PAA; PAA is evenly drop-coated on a glass plate for gradient temperature reaction to obtain PI. Polyurethane and guanidine phosphate are dissolved in N-N dimethylacetamide, and the prepared PI is dissolved therein to obtain a polyurethane mixed solution, and the mixed solution is then evenly drop-coated on a glass plate and dried to obtain a polyurethane composite material. The polyimide of the present invention is compounded with flame retardant GP for use in improving the flame retardant grade of thermoplastic polyurethane composite materials, and the obtained polyurethane composite materials have excellent mechanical properties and heat resistance, and have broad prospects in high-performance application fields.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer materials, and particularly relates to a cross-linked terminated polyimide with a high residual carbon rate and application thereof. Background Art

[0002] Thermoplastic polyurethane (TPU) is an important organic polymer material with advantages such as a wide hardness range, oil and moisture resistance, wear resistance, insulation, shock absorption, and high strength. It is widely used in wires and cables, furniture, building insulation, aerospace insulation, fire retardant coatings, clothing, and other fields. However, polyurethane materials have disadvantages such as a low oxygen index (approximately 18), flammability, and high smoke density, which limit their further application.

[0003] Polyimide (PI) is a high-performance polymer with excellent thermal stability, maintaining structural integrity at high temperatures. Its superior high-temperature resistance allows it to withstand the stress and thermal expansion of high-temperature environments without melting or decomposing easily. Furthermore, polyimides exhibit exceptional mechanical properties, including high strength and stiffness. They can withstand significant forces and stresses, exhibiting excellent structural stability and resistance to deformation. They also exhibit good chemical stability, resisting attack by chemicals, solvents, and corrosive substances.

[0004] In order to improve the flame retardancy, heat resistance and thermal stability of TPU, flame retardants are usually added to it. Guanidine phosphate (GP) is a phosphorus-based flame retardant that is halogen-free, non-toxic and environmentally friendly, and meets modern environmental protection requirements. It can also be used for flame retardant treatment of a variety of materials, including wood, paper products, plastics, etc., and has broad application prospects. In addition, guanidine phosphate can also enhance its mechanical properties by increasing the carbonization rate of the material. The increase in the carbonization rate means that the material can form more carbon layers during the combustion process. This carbon layer can not only isolate oxygen and heat, but also enhance the structural strength of the material to a certain extent, thereby improving its mechanical properties. However, the heat resistance of guanidine phosphate is relatively poor, which may limit its scope of application in high temperature environments. Summary of the Invention

[0005] The purpose of the present invention is to provide a cross-linked blocked polyimide with a high residual carbon rate, and use it as a carbonizing agent to prepare a polyurethane composite material with high flame retardancy and high mechanical properties. The blocked polyimide provided by the present invention also has good thermal stability and a high residual carbon rate, can maintain high-temperature strength, and can be used as a carbonizing agent.

[0006] The preparation method of the thermally cross-linked capped polyimide with a high carbon residue rate of the present invention is as follows:

[0007]

[0008] The specific preparation steps are as follows:

[0009] (1) Add the dehydrated N-N-dimethylacetamide (DMAc) solvent to a three-necked flask equipped with a mechanical stirrer, and add the diamine monomer 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB) at one time. After the diamine monomer is completely dissolved, add the dianhydride monomer 1,4,5,8-naphthalenetetracarboxylic anhydride (NTDA). Nitrogen is replaced 3 to 5 times to ensure that the air in the device is isolated and prevent the dianhydride monomer from hydrolyzing prematurely. After the diamine and dianhydride monomers are added, the end-capping agent MA is added, and an appropriate amount of DMAc is added to adjust the solid content of the system to 12%. React at room temperature for 8 to 12 hours to obtain PAA;

[0010] Wherein, the molar ratio of dianhydride, diamine and end-capping agent is 1:1.02:1-2;

[0011] (2) Using the thermal imidization method, the obtained PAA is evenly dropped on a glass plate and placed in a high-temperature oven for a gradient temperature reaction. After the reaction is complete, it is taken out and scraped off the glass plate to obtain PI.

[0012] The temperature gradient of thermal imidization is: first react at 80°C, 100°C, and 130°C for 1 hour each; after the solvent is basically evaporated to the film is dry, then react at 180°C for 2 hours, 230°C for 2 hours, and 300°C for 2 hours.

[0013] The present invention also provides a thermoplastic polyurethane composite material with high mechanical properties. By adding heat-crosslinked end-capped polyimide to TPU to construct a crosslinked structure, not only can the flexibility be improved, but the mechanical properties can also be greatly enhanced.

[0014] The polyurethane composite material comprises the following components in parts by mass: 100 parts of polyurethane, 5-10 parts of guanidine phosphate and 5 parts of the cross-linked blocked polyimide prepared by the present invention.

[0015] The preparation method of the polyurethane composite material is as follows: polyurethane and guanidine phosphate are dissolved in NN dimethylacetamide, and after complete dissolution, triethylamine is added to adjust the pH of the solution to alkaline, and then polyimide is added thereto. After complete dissolution, the obtained mixed solution is evenly dripped onto a glass plate and dried to obtain a TPU composite film with high flame retardancy and high mechanical properties.

[0016] Due to the adoption of the above technical solution, the present invention has the following advantages and beneficial effects:

[0017] The polyimide provided by the present invention exhibits a high residual carbon rate under oxygen and nitrogen atmospheres, as shown by thermogravimetric analysis, making it suitable for use as an excellent char-forming agent. When combined with the flame retardant GP, the flame retardancy rating of TPU composites can be effectively improved. Furthermore, the polyimide itself possesses excellent mechanical properties, including high strength and stiffness. After end-capping, the polyimide exhibits even better mechanical strength, such as tensile strength and impact strength. Furthermore, the processing properties of TPU composites can be improved, indicating a wide range of potential applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the thermogravimetric analysis spectrum of the polyimide NTDA-DCB synthesized in Example 1. DETAILED DESCRIPTION

[0019] In order to illustrate the present invention more clearly, the present invention is further described below in conjunction with embodiments. It should be understood by those skilled in the art that the following specific description is illustrative rather than restrictive and should not be used to limit the scope of protection of the present invention.

[0020] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. The experimental materials, reagents, etc. used in the following experimental examples can be obtained through commercial channels or known experimental methods.

[0021] Example 1

[0022] This embodiment provides a thermally cross-linked terminated polyimide with a high carbon residue rate, which has the following repeating structural units. The polyimide is named NTDA-DCB.

[0023]

[0024] The specific preparation method is as follows:

[0025] (1) Water removal and purification of N-dimethylacetamide (DMAc):

[0026] Place 100 ml of DMAc into a 250 ml single-necked flask, add a rotor and 0.6 g of CaH2, seal the flask with a balloon, and stir magnetically at room temperature for 24 hours to allow for complete reaction. After stirring, set the flask to a vacuum distillation apparatus. Since DMAc has a boiling point of 163°C, set the vacuum distillation temperature to 155°C. Separate the first and last fractions, and collect and seal the remaining fractions. Yield: 80%.

[0027] (2) Preparation of thermally cross-linked terminated polyimide NTDA-DCB:

[0028] The dianhydride monomer, 1,4,5,8-naphthalenetetracarboxylic anhydride (NTDA), was pretreated in an oven at 170°C for 12 hours. To a three-necked flask equipped with a mechanical stirrer, 38 ml of dehydrated DMAc was added, along with 4,4'-diaminobiphenyl-2,2-dicarboxylic acid (DCB) (2.7771 g, 10.2 mmol). The atmosphere was purged with nitrogen three times to ensure air removal, and the mixture was stirred until completely dissolved. The dianhydride monomer, 1,4,5,8-naphthalenetetracarboxylic anhydride (NTDA) (2.6422 g, 10 mmol), was added in four batches, with half the total amount added initially and half the amount added each time, with 40 minutes between each addition. After the addition of the dianhydride and diamine monomers, a capping agent (MA) (1.9612 g, 20 mmol) was added, and DMAc was added to adjust the solids content of the system to 12%. The mixture was stirred at room temperature for 8 hours to obtain a PAA acid solution.

[0029] The glass sheet was placed in a high-temperature oven for preheating, and then the PAA acid solution obtained above was drop-coated on the glass sheet for thermal imidization to obtain a PI film with a thickness of 200 μm.

[0030] The temperature gradient of thermal imidization is: first react at 80℃, 100℃, and 130℃ for 1 hour each; after the solvent is basically evaporated to the film is dry, then react at 180℃-2h, 230℃-2h, and 300℃-2h. After the reaction is complete, take it out and scrape it from the glass plate to obtain polyimide PI.

[0031] (3) Preparation of TPU composite film:

[0032] Thermoplastic polyurethane (TPU, 3.1578 g) and guanidine phosphate (GP, 0.3158 g) were weighed into a 50 ml beaker, 32.09 mL of DMAc was added, and the mixture was placed on a stirring platform and heated to 90°C for stirring and dissolving. The mixture was stirred vigorously for 6 h to obtain a 10 wt% TPU solution.

[0033] Triethylamine was added to the TPU solution to adjust the pH value of the solution to 10 to facilitate the dissolution of polyimide. Then, polyimide (PI, 0.1579 g) was weighed into the TPU solution and stirred for 8 h. After the solution was completely dissolved, the relevant TPU composite solution was obtained.

[0034] The amount of guanidine phosphate (GP) added, expressed as a percentage by weight of the thermoplastic polyurethane (TPU), was 10 wt %. The amount of polyimide (PI) added, expressed as a percentage by weight of the thermoplastic polyurethane (TPU), was 5 wt %.

[0035] The TPU composite solution obtained in the above steps was placed in an ultrasonic cleaner and vibrated for 45 minutes. It was then allowed to stand for 6 hours to remove any bubbles that may have been contained during stirring. After standing completely, it was placed in a vacuum oven to evacuate the solution and completely remove any bubbles. The treated TPU composite solution was then evenly drop-coated on a glass plate and dried in an oven at 60°C for 10 hours to remove excess moisture, thereby obtaining a TPU composite film.

[0036] Example 2

[0037] The difference between this embodiment and embodiment 1 is that the molar ratio of dianhydride, diamine and end-capping agent in the prepared composite film is 1:1.02:1, and other treatment methods are consistent with those in embodiment 1.

[0038] Example 3

[0039] The difference between this embodiment and embodiment 1 is that the ratio of the prepared composite film is 1:1.02:1.5, and the other processing methods are consistent with those in embodiment 1.

[0040] Example 4

[0041] The difference between this embodiment and embodiment 1 is that the content of flame retardant GP in the prepared composite film is 5 wt %. Other processing methods are the same as those in embodiment 1.

[0042] Example 5

[0043] The difference between this embodiment and embodiment 1 is that the content of flame retardant GP in the prepared composite film is 7.5 wt %. Other processing methods are the same as those in embodiment 1.

[0044] Comparative Example 1

[0045] The difference between this comparative example and Example 1 is that no thermally cross-linked terminated polyimide is added to the TPU composite solution, and other treatment methods are the same as those in Example 1.

[0046] Comparative Example 2

[0047] The difference between this comparative example and Example 1 is that the dianhydride monomer in the cross-linked terminated polyimide is replaced with hexafluorodianhydride (6FDA) as a carbon-forming agent, and the other treatment methods are the same as those in Example 1.

[0048] Comparative Example 3

[0049] The difference between this comparative example and Example 1 is that no end-capping agent MA is added to synthesize the thermally cross-linked end-capped polyimide, and other processing methods are consistent with those in Example 1.

[0050] Comparative Example 4

[0051] The difference between this comparative example and Example 1 is that the flame retardant GP is not added, and other treatment methods are the same as those in Example 1.

[0052] The vertical combustion performance test of the prepared TPU composite film was carried out, and the test results are shown in Table 1

[0053] Table 1

[0054]

[0055] The mechanical properties of the prepared TPU composite film were tested, and the test results are shown in Table 2

[0056] Table 2

[0057] sample Elongation at break / % Tensile strength / MPa Elastic modulus / MPa Example 1 596 36 7.2 Example 2 1053 29 5.3 Example 3 917 34 4.4 Example 4 604 33 6.5 Example 5 653 33 6.9 Comparative Example 1 594 22 3.8 Comparative Example 2 580 25 6.8 Comparative Example 3 517 27 4.9 Comparative Example 4 612 26 5.1

[0058] In summary, the thermally cross-linked capped polyamide-imide resin prepared in this application has a high residual carbon rate and can be used as a carbon-forming agent. When used in combination with the flame retardant GP, it can effectively improve the flame retardant grade and mechanical properties of the TPU composite film.

[0059] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed as above in terms of a preferred embodiment, it is not intended to limit the present invention. Any technician familiar with this patent can make slight changes or modifications to equivalent embodiments using the above technical content without departing from the scope of the technical solution of the present invention. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention are still within the scope of the solution of the present invention.

Claims

1. A cross-linked terminated polyimide with a high residual carbon rate, characterized in that: The cross-linked terminated polyimide has the following repeating structural units:

2. The cross-linked terminated polyimide with a high residual carbon rate according to claim 1, wherein The preparation method of the cross-linked blocked polyimide comprises the following steps: (1) Dissolve 1,4,5,8-naphthalenetetracarboxylic anhydride (NTDA) and 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid (DCB) in N,N-dimethylacetamide and stir until completely dissolved under a nitrogen atmosphere to obtain a transparent solution; then add a capping agent (MA) and DMAc to adjust the solid content of the system; stir and react at room temperature to obtain a PAA solution; (2) The obtained PAA solution is evenly dropped onto a glass plate for a gradient temperature reaction. After the reaction is complete, it is taken out and scraped off the glass plate to obtain polyimide PI.

3. The cross-linked terminated polyimide with a high carbon residue rate according to claim 2, wherein The molar ratio of 1,4,5,8-naphthalenetetracarboxylic anhydride, 4,4'-diaminobiphenyl-2,2'-dicarboxylic acid and end-capping agent MA in step (1) is 1:1.02:1-2; during the reaction, the solid content of the solution is 12%.

4. The cross-linked terminated polyimide with a high carbon residue rate according to claim 2, wherein The reaction conditions of step (1) are: stirring at room temperature for 8 to 12 hours.

5. The cross-linked terminated polyimide with a high residual carbon rate according to claim 2, wherein The gradient temperature increase reaction in step (2) is as follows: first react at 80°C, 100°C, and 130°C for 1 hour each; after the solvent evaporates to dry the film, react at 180°C for 2 hours, 230°C for 2 hours, and 300°C for 2 hours.

6. An application of the cross-linked terminated polyimide with a high carbon residue rate according to claim 1, characterized in that: The cross-linked blocked polyimide with a high residual carbon rate is used as a carbon-forming agent for preparing a polyurethane composite material with flame retardancy and mechanical properties.

7. The use of the cross-linked terminated polyimide with a high carbon residue rate according to claim 6, characterized in that: The polyurethane composite material is composed of 100 parts by mass of polyurethane, 5-10 parts by mass of guanidine phosphate, and 5 parts by mass of the cross-linked terminated polyimide according to claim 1.

8. The use of the cross-linked terminated polyimide with a high carbon residue rate according to claim 6, characterized in that: The preparation method of the polyurethane composite material comprises the following steps: dissolving polyurethane and guanidine phosphate in NN dimethylacetamide, adding triethylamine to adjust the pH of the solution to alkaline after complete dissolution, adding polyimide thereto, and evenly dripping the obtained mixed solution onto a glass plate after complete dissolution, and drying the mixed solution to obtain a TPU composite film with flame retardancy and mechanical properties.

Images