Preparation method of polyimide molding powder with recyclable solvent

Abstract

The invention discloses a preparation method of polyimide molding powder with a recyclable solvent, and belongs to the technical field of high polymer material synthesis. The preparation method comprises the following steps: adding dianhydride and diamine into a polar aprotic solvent, and carrying out condensation polymerization to generate polyamide acid; the preparation method comprises the following steps: heating polyamide acid under a vacuum condition to carry out imidization to obtain a solid-liquid mixture, separating, washing the separated solid, carrying out heat treatment to obtain polyimide molding powder, and recycling the separated filtrate as a polar aprotic solvent. Compared with a normal-pressure water-carrying system method in which methylbenzene, xylene and other aromatic solvents are used, the reduced-pressure azeotropic dehydration method ensures that an azeotropic system is formed by a polar aprotic solvent and water, moisture in the system is fully removed, anhydride hydrolysis caused by the fact that the recycled solvent contains moisture is avoided, and the yield of the product is improved. Therefore, the problems that the imidization degree is low during cyclization and the thermodynamic property is reduced are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material synthesis, and in particular relates to a method for preparing a solvent-recyclable polyimide molding powder. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] Polyimide (PI) generally refers to a class of high-performance aromatic heterocyclic polymers containing aromatic rings and imide ring structures in the repeating units. The PI molecular chain has good rigidity and strong interactions between the molecular chains. Therefore, its plastic products have very excellent mechanical properties, heat resistance and thermal stability, and are at the top of the polymer material pyramid. In addition, PI also has excellent electrical insulation (dielectric properties), resistance to chemical reagents, radiation resistance and other properties, so it has been widely used in many fields such as automobiles, aerospace, microelectronics, and electrical appliances. PI has great prospects as a structural material or a functional material, and is known as a "problem solver."

[0004] At present, the solution polycondensation method is the most commonly used method for synthesizing polyimide. Organic dianhydride and organic diamine monomers are subjected to polycondensation reaction at room temperature in a polar aprotic solvent to generate polyamic acid (PAA), and polyamic acid is dehydrated and cyclized to obtain polyimide. The currently disclosed technology shows that there are two methods for preparing polyimide molding powder: chemical imidization and normal pressure hydrothermal imidization. The chemical imidization method requires the addition of dehydrating agents such as acetic anhydride and propionic anhydride and catalysts such as pyridine and triethylamine to the solution system of polyamic acid. The normal pressure hydrothermal imidization method requires the addition of aromatic solvents such as toluene and xylene to the solution system of polyamic acid to remove the water generated by imidization from the system. The introduction of dehydrating agents and aromatic hydrocarbons changes the original single solvent system, resulting in impure polar aprotic solvents, and post-processing and recycling are very difficult. On the one hand, the production cost of polyimide resin is increased, and on the other hand, the amount of three wastes to be treated is increased, which is not conducive to green and environmentally friendly industrial production.

[0005] Patent CN109369915A reports a method for synthesizing polyimide, which uses an excess of pyridine and heats to make the imidization reaction more complete, thereby obtaining qualified polyimide. On the one hand, although this method does not add a dehydrating agent during the entire reaction process, the reaction system is simple and easy to recycle, but the solution system after the reaction still needs to be separated by means of distillation or rectification, the process is complicated and increases equipment investment. On the other hand, this technology does not carry out a synthetic experiment of solvent recovery and application, and the quality of the polyimide prepared after solvent recovery and application cannot be guaranteed.

[0006] Therefore, how to use the recycled solvent to synthesize polyimide molding powder with good thermodynamic properties to achieve cost-effective green and environmentally friendly development is an urgent problem to be solved. Summary of the invention

[0007] In order to solve the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing a polyimide molding powder with recoverable solvent. The preparation method provided by the present invention does not introduce other media such as dehydrating agents and aromatic hydrocarbons, thereby ensuring the original single solvent system. After the solvent is recovered, it can be directly used for continued production without any treatment, and does not affect the thermodynamic properties of the polyimide.

[0008] In order to achieve the above object, the technical solution of the present invention is:

[0009] The first aspect of the present invention provides a method for preparing a solvent-recyclable polyimide molding powder, comprising:

[0010] Adding dianhydride and diamine into a polar aprotic solvent to carry out polycondensation reaction to generate polyamic acid;

[0011] The polyamic acid is heated under vacuum conditions for imidization to obtain a solid-liquid mixture, which is separated. The separated solid is washed and heat-treated to obtain a polyimide molding powder. The separated filtrate is recycled as a polar aprotic solvent.

[0012] In some embodiments of the present invention, the polar aprotic solvent includes one or more of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

[0013] In some embodiments of the present invention, the dianhydride includes one or more of pyromellitic dianhydride, 4,4'-biphenyl ether dianhydride, 3,4'-biphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, bisphenol A diether dianhydride and hexafluoro dianhydride.

[0014] Preferably, the dianhydride is selected from one or more of pyromellitic dianhydride, 4,4'-biphenyl ether dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

[0015] In some embodiments of the present invention, the diamine includes one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 1,3-bis(4'-aminophenoxy)benzene, m-phenylenediamine and p-phenylenediamine.

[0016] Preferably, the diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene and p-phenylenediamine.

[0017] In some embodiments of the present invention, the molar ratio of the diamine to the dianhydride is 1:(1-1.1), and the mass ratio of the total mass of the diamine to the dianhydride to the polar aprotic solvent is (5-25):(75-95).

[0018] Preferably, the molar ratio of the diamine to the dianhydride is 1:(1-1.05), and the mass ratio of the total mass of the diamine to the dianhydride to the polar aprotic solvent is (10-20):(80-90).

[0019] In some embodiments of the present invention, the reaction temperature of the polycondensation reaction is 20-40° C., and the reaction time is 1-4 h.

[0020] In some embodiments of the present invention, the vacuum condition is -0.01 to -0.08 MPa, the imidization temperature is 130-150° C., and the time is 1-4 h.

[0021] In some embodiments of the present invention, the washing is performed using a cleaning agent, and the cleaning agent is at least one of water, ethanol, methanol and acetone, preferably at least one of ethanol and acetone.

[0022] In some embodiments of the present invention, the heat treatment conditions are 80°C-100°C-130°C-160°C-190°C-220°C-240°C-260°C for 2 hours each.

[0023] In some embodiments of the present invention, the filtrate obtained by separation is recycled as a polar aprotic solvent, and the preparation conditions of the polyimide molding powder remain unchanged.

[0024] The beneficial effects of the present invention are:

[0025] The present invention innovatively adopts a reduced pressure azeotropic dehydration method in the process of dehydration and cyclization to prepare polyimide, and heats and dehydrates under vacuum conditions. Compared with the atmospheric pressure water system method using aromatic hydrocarbon solvents such as toluene and xylene, the reduced pressure azeotropic dehydration method ensures that the polar aprotic solvent and water form an azeotropic system, fully removes the moisture in the system, and avoids the water contained in the recycled solvent to cause the anhydride hydrolysis, thereby affecting the generation of polyamic acid, resulting in a low degree of imidization during cyclization, and the problem of a decrease in thermodynamic properties. At the same time, the reduced pressure azeotropic dehydration method can also reduce the cyclization reaction temperature and time, and improve production efficiency.

[0026] The present invention does not introduce dehydrating agents and other media such as aromatic hydrocarbons in the process of preparing polyimide by dehydration and cyclization, thereby ensuring the original single solvent system. After the solvent is recovered, it can be directly applied to continue production without further treatment. While reducing the amount of waste liquid generated and the amount of treatment, it also reduces production costs and achieves cost-effective green and environmentally friendly development. In the process of preparing polyimide by dehydration and cyclization, the reduced pressure azeotropic dehydration method is innovatively adopted. Compared with the atmospheric pressure water system method using aromatic hydrocarbon solvents such as toluene and xylene, the azeotropic dehydration method can reduce the cyclization reaction temperature and time, and improve production efficiency.

[0027] The thermodynamic properties of the polyimide molding powder obtained by the preparation method of the present invention are stable, and the thermodynamic properties of the polyimide molding powder obtained are the same whether the powder is produced by using a polar aprotic solvent or a filtrate obtained by separation. DETAILED DESCRIPTION

[0028] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0029] Example 1

[0030] A method for preparing a solvent-recyclable polyimide molding powder comprises the following steps:

[0031] (1) 1 mol (218 g) of pyromellitic dianhydride and 1 mol (200 g) of 4,4'-diaminodiphenyl ether were added to 2369 g of N-methylpyrrolidone, and polycondensation reaction was carried out at 20° C. for 4 h to obtain polyamic acid.

[0032] (2) Under a vacuum condition of -0.08 MPa, the polyamic acid obtained in step (1) was heated to 150° C. for imidization for 1 hour to obtain a solid-liquid mixture.

[0033] (3) The solid-liquid mixture obtained in step (2) is separated by suction filtration, and the obtained solid is poured into an ethanol cleaning agent for washing to obtain a polyimide crude material, and the obtained N-methylpyrrolidone recovery liquid is collected for later use.

[0034] (4) The polyimide crude material obtained in step (3) is placed in an oven for further heat treatment at 80-100-130-160-190-220-240-260° C. for 2 h each to obtain polyimide molding powder PI-A1.

[0035] (5) According to the process and parameters of steps (1) to (4), the N-methylpyrrolidone recovery liquid obtained in step (3) is used to re-synthesize the polyimide molding powder to obtain the polyimide molding powder PI-B1.

[0036] Example 2

[0037] A method for preparing a solvent-recyclable polyimide molding powder comprises the following steps:

[0038] (1) 1.05 mol (325.5 g) of 4,4'-biphenyl ether dianhydride and 1 mol (292 g) of 1,3-bis(4'-aminophenoxy)benzene were added to 5557.5 g of N,N-dimethylacetamide, and polycondensation reaction was carried out at 40° C. for 1 hour to obtain polyamic acid.

[0039] (2) Under a vacuum condition of -0.04 MPa, the polyamic acid obtained in step (1) was heated to 130° C. for imidization for 4 hours to obtain a solid-liquid mixture.

[0040] (3) The solid-liquid mixture obtained in step (2) is separated by suction filtration, and the obtained solid is poured into an acetone cleaning agent for washing to obtain a polyimide crude material, and the obtained N,N-dimethylacetamide recovery liquid is collected for later use.

[0041] (4) The polyimide crude material obtained in step (3) is placed in an oven for further heat treatment at 80-100-130-160-190-220-240-260° C. for 2 h each to obtain polyimide molding powder PI-A2.

[0042] (5) According to the process and parameters of steps (1) to (4), the N,N-dimethylacetamide recovery liquid obtained in step (3) is used to re-synthesize the polyimide molding powder to obtain the polyimide molding powder PI-B2.

[0043] Example 3

[0044] A method for preparing a solvent-recyclable polyimide molding powder comprises the following steps:

[0045] (1) 1.02 mol (300 g) of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 1 mol (108 g) of p-phenylenediamine were added to 1632 g of N,N-dimethylformamide, and polycondensation reaction was carried out at 30° C. for 2.5 h to obtain polyamic acid;

[0046] (2) heating the polyamic acid obtained in step (1) to 140° C. for imidization for 3 h under a vacuum degree of −0.01 MPa to obtain a solid-liquid mixture;

[0047] (3) filtering the solid-liquid mixture obtained in step (2) to separate the solid, pouring the obtained solid into an ethanol cleaning agent for washing to obtain a polyimide crude material, and collecting the obtained N,N-dimethylformamide recovery liquid for later use;

[0048] (4) The polyimide crude material obtained in step (3) is placed in an oven for further heat treatment at 80-100-130-160-190-220-240-260° C. for 2 h each to obtain polyimide molding powder PI-A3.

[0049] (5) According to the process and parameters of steps (1) to (4), the N,N-dimethylformamide recovery liquid obtained in step (3) is used to re-synthesize the polyimide molding powder to obtain the polyimide molding powder PI-B3.

[0050] Comparative Example 1

[0051] A method for preparing a polyimide molding powder for solvent recovery and application, comprising the following steps:

[0052] (1) 1 mol (218 g) of pyromellitic dianhydride and 1 mol (200 g) of 4,4'-diaminodiphenyl ether were added to 2369 g of N-methylpyrrolidone, and polycondensation reaction was carried out at 20° C. for 4 h to obtain polyamic acid.

[0053] (2) The polyamic acid obtained in step (1) is heated to 150° C. under normal pressure for imidization for 1 hour to obtain a solid-liquid mixture.

[0054] (3) The solid-liquid mixture obtained in step (2) is separated by suction filtration, and the obtained solid is poured into an ethanol cleaning agent for washing to obtain a polyimide crude material, and the obtained N-methylpyrrolidone recovery liquid is collected for later use.

[0055] (4) The polyimide crude material obtained in step (3) was placed in an oven for further heat treatment at 80-100-130-160-190-220-240-260° C. for 2 h each to obtain polyimide molding powder PI-A1′.

[0056] (5) According to the process and parameters of steps (1) to (4), the N-methylpyrrolidone recovery liquid obtained in step (3) is used to re-synthesize polyimide molding powder to obtain polyimide molding powder PI-B1'.

[0057] Comparative Example 2

[0058] A method for preparing a polyimide molding powder for solvent recovery and application, comprising the following steps:

[0059] (1) 1.05 mol (325.5 g) of 4,4'-biphenyl ether dianhydride and 1 mol (292 g) of 1,3-bis(4'-aminophenoxy)benzene were added to 5557.5 g of N,N-dimethylacetamide, and polycondensation reaction was carried out at 40° C. for 1 hour to obtain polyamic acid.

[0060] (2) The polyamic acid obtained in step (1) is heated to 130° C. under normal pressure for imidization for 4 hours to obtain a solid-liquid mixture.

[0061] (3) The solid-liquid mixture obtained in step (2) is separated by suction filtration, and the obtained solid is poured into an acetone cleaning agent for washing to obtain a polyimide crude material, and the obtained N,N-dimethylacetamide recovery liquid is collected for later use.

[0062] (4) The polyimide crude material obtained in step (3) is placed in an oven for further heat treatment at 80-100-130-160-190-220-240-260° C. for 2 h each to obtain polyimide molding powder PI-A2′.

[0063] (5) According to the process and parameters of steps (1) to (4), the N,N-dimethylacetamide recovery liquid obtained in step (3) is used to re-synthesize polyimide molding powder to obtain polyimide molding powder PI-B2'.

[0064] Comparative Example 3

[0065] A method for preparing a polyimide molding powder for solvent recovery and application, comprising the following steps:

[0066] (1) 1.02 mol (300 g) of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 1 mol (108 g) of p-phenylenediamine were added to 1632 g of N,N-dimethylformamide, and polycondensation reaction was carried out at 30° C. for 2.5 h to obtain polyamic acid.

[0067] (2) The polyamic acid obtained in step (1) is heated to 140° C. under normal pressure for imidization for 3 hours to obtain a solid-liquid mixture.

[0068] (3) The solid-liquid mixture obtained in step (2) is separated by suction filtration, and the obtained solid is poured into an ethanol cleaning agent for washing to obtain a polyimide crude material, and the obtained N,N-dimethylformamide recovery liquid is collected for later use.

[0069] (4) The polyimide crude material obtained in step (3) was placed in an oven for further heat treatment at 80-100-130-160-190-220-240-260° C. for 2 h each to obtain polyimide molding powder PI-A3′.

[0070] (5) According to the process and parameters of steps (1) to (4), the N,N-dimethylformamide recovery liquid obtained in step (3) is used to re-synthesize polyimide molding powder to obtain polyimide molding powder PI-B3'.

[0071] The mechanical properties test method of the polyimide molding powder obtained in the above examples and comparative examples is GB / T 2567-208, and the test results are shown in Tables 1 and 2 below.

[0072] Table 1 Mechanical properties test results of polyimide molding powder obtained in Examples 1-3

[0073] serial number 5wt% thermal weight loss temperature (℃) Tensile strength(MPa) Bending strength(MPa) PI-A1 572 70 100 PI-B1 572 70 100 PI-A2 568 100 150 PI-B2 568 100 150 PI-A3 555 80 130 PI-B3 555 80 130

[0074] Table 2 Mechanical properties test results of polyimide molding powder obtained in Comparative Examples 1-3

[0075] serial number 5wt% thermal weight loss temperature (℃) Tensile strength(MPa) Bending strength(MPa) PI-A1' 565 65 90 PI-B1' 560 60 80 PI-A2' 550 90 135 PI-B2' 540 80 125 PI-A3' 530 70 120 PI-B3' 520 60 110

[0076] It can be seen from the data in the embodiment of Table 1 that compared with the PI-A series molding powder, the performance of the molding powder PI-B prepared by the reduced pressure azeotropic dehydration method with the recovered solvent has not changed, indicating that the solvent recovered by the reduced pressure azeotropic dehydration method does not affect the formation of polyamic acid during the polycondensation reaction nor the subsequent dehydration and cyclization process to prepare polyimide.

[0077] From the data in the comparative example of Table 2, it can be seen that compared with the PI-A series molding powder in Table 1, the thermodynamic properties of the PI-A' molding powder obtained by atmospheric pressure dehydration are reduced. This is because the boiling point of the solvent used in the present invention is higher than 150°C, and the atmospheric pressure cyclization temperature is not higher than 150°C, and it cannot form an azeotropic system with water, resulting in a high water content in the system, affecting the forward reaction, and a low degree of imidization. If the solvent obtained by this method is further recovered and reused, because there is still a certain amount of water in the solvent, the acid anhydride will be partially hydrolyzed, affecting the formation of polyamic acid, resulting in a further low degree of imidization during cyclization, and the thermodynamic properties will be further reduced.

[0078] Therefore, compared with the atmospheric pressure dehydration method, the reduced pressure azeotropic dehydration method not only greatly reduces the production cost of polyimide resin while obtaining products with better thermodynamic properties, but also the synthesis process is more green and environmentally friendly, which is conducive to industrial production.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a solvent-recyclable polyimide molding powder, characterized in that: include: Adding dianhydride and diamine into a polar aprotic solvent to carry out polycondensation reaction to generate polyamic acid; The polyamic acid is heated under vacuum conditions for imidization to obtain a solid-liquid mixture, which is separated. The separated solid is washed and heat-treated to obtain a polyimide molding powder. The separated filtrate is recycled as a polar aprotic solvent.

2. The preparation method according to claim 1, characterized in that The polar aprotic solvent includes one or more of N-methylpyrrolidone, N,N-dimethylacetamide and N,N-dimethylformamide.

3. The preparation method according to claim 1, characterized in that: The dianhydride includes one or more of pyromellitic dianhydride, 4,4'-biphenyl ether dianhydride, 3,4'-biphenyl ether dianhydride, 3,3',4,4'-biphenyltetracarboxylic dianhydride, bisphenol A type diether dianhydride and hexafluoro dianhydride; Preferably, the dianhydride is selected from one or more of pyromellitic dianhydride, 4,4'-biphenyl ether dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride.

4. The preparation method according to claim 1, characterized in that: The diamine includes one or more of 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 3,4'-diaminodiphenyl sulfone, 1,3-bis(4'-aminophenoxy)benzene, m-phenylenediamine and p-phenylenediamine; Preferably, the diamine is selected from one or more of 4,4'-diaminodiphenyl ether, 1,3-bis(4'-aminophenoxy)benzene and p-phenylenediamine.

5. The preparation method according to claim 1, characterized in that: The molar ratio of the diamine to the dianhydride is 1:(1-1.1), and the mass ratio of the total mass of the diamine to the dianhydride to the polar aprotic solvent is (5-25):(75-95); Preferably, the molar ratio of the diamine to the dianhydride is 1:(1-1.05), and the mass ratio of the total mass of the diamine to the dianhydride to the polar aprotic solvent is (10-20):(80-90).

6. The preparation method according to claim 1, characterized in that: The reaction temperature of the polycondensation reaction is 20-40° C., and the reaction time is 1-4 hours.

7. The preparation method according to claim 1, characterized in that: The vacuum condition is -0.01 to -0.08 MPa, the imidization temperature is 130-150° C., and the time is 1-4 hours.

8. The preparation method according to claim 1, characterized in that: The washing is performed using a cleaning agent, and the cleaning agent is at least one of water, ethanol, methanol and acetone, preferably at least one of ethanol and acetone.

9. The preparation method according to claim 1, characterized in that: The heat treatment conditions are 80°C-100°C-130°C-160°C-190°C-220°C-240°C-260°C for 2 hours each.

10. The preparation method according to any one of claims 1 to 9, characterized in that: The separated filtrate is recycled as a polar aprotic solvent, and the preparation conditions of the polyimide molding powder remain unchanged.