A method for preparing a low viscosity polyamic acid slurry and a polyimide product

Abstract

The application relates to a preparation method of a low-viscosity polyamide acid slurry and a polyimide product, and belongs to the technical field of polyimide synthesis. In the application, a monocarboxylic anhydride is reacted with amino groups in part of diamine monomers to generate monoamino amide, then the monoamino amide is reacted with dianhydride, the end groups of the generated polyamide acid molecular chain are amide groups and anhydride groups, the molecular chain length is controlled, and finally the purpose of controlling the viscosity of the polyamide acid slurry is achieved. In the subsequent imidization process, the end amide groups are reacted with the end anhydride groups, the polyimide molecular chain is further lengthened, the molecular weight is further increased, and the performance of the polyimide product is improved, and meanwhile, the generated monocarboxylic anhydride is volatilized and removed at high temperature. The method has the advantages of large viscosity control range of the polyamide acid slurry, obvious effect, simple process and wide application range.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of polyimide synthesis, and particularly relates to a low-viscosity polyamide acid slurry and a preparation method of a polyimide product. BACKGROUND

[0002] Polyimide is a kind of high-performance polymer containing imide rings in the molecular main chain, and is widely used in the fields of aviation, aerospace, microelectronics, rail transportation and nuclear industry due to its excellent comprehensive performance. The products of polyimide are various, such as films and fibers, and the preparation method thereof is usually a two-step method, that is, a synthetic polyamide acid slurry is first synthesized by using dianhydride and diamine monomers to occur polycondensation reaction in an aprotic solvent, and then a final polyimide product is obtained through chemical imidization or thermal imidization. Therefore, the quality of the polyamide acid slurry is crucial for preparing the polyimide product.

[0003] In order to ensure the processability and the feasibility of synthesis of the polyamide acid slurry, the viscosity of the polyamide acid slurry is generally required to be moderate. The viscosity of the polyamide acid slurry is mainly determined by the solid content and the molecular weight. At present, the solid content of the polyamide acid slurry is usually 10-20%, and if the solid content is further increased, the viscosity of the polyamide acid will rapidly increase due to the strong hydrogen bond interaction between the polyamide acid molecular chains, and even gelation occurs, so that the processability is lost; if the solid content is reduced, the film thickness of the slurry will decrease, the film forming time will be prolonged, and the amount of organic solvent will be increased, thereby affecting the economic and environmental benefits of the product. On the other hand, if the molecular weight is too high, the viscosity of the polyamide acid solution will be too large, and the processability will be lost; if the molecular weight is too low, the viscosity of the polyamide acid slurry will be reduced, but the molecular weight of the polyimide obtained by corresponding solidification will also be low, thereby resulting in poor performance of the obtained polyimide product, such as poor heat resistance and mechanical properties. Therefore, developing a preparation method of a polyamide acid slurry with high solid content and controllable viscosity is one of the research focuses in the field.

[0004] Method I for preparing a polyimide product by regulating the viscosity of a polyamide acid solution is to introduce a capping agent capable of containing a functional group, to regulate the viscosity of the polyamide acid by regulating the length of the polyamide acid molecular chain, and to further crosslink the capping agent during or after imidization by high temperature, so as to increase the length of the polyimide molecular chain, thereby obtaining a high-performance polyimide product. Such patent documents include CN1127268A for preparing a polyimide resin by one-step method through unsaturated bond functional group capping; CN102532541A for forming a molecular chain with a carboxyl group at one end by capping with a tricarboxylic anhydride, and further increasing the molecular weight by the reaction of the amino group and the carboxyl group at the molecular end when heated; and CN104292459A for further increasing the molecular weight by addition reaction of the unsaturated bond when heated through unsaturated bond functional group capping.

[0005] The method II for preparing polyimide product by regulating the viscosity of polyamic acid solution is to add a less reactive tetracarboxylic acid or tetracarboxylic ester compound to regulate the viscosity of polyimide acid slurry. During the subsequent high-temperature imidization process, the carboxyl or ester group further reacts with the amino group to form an amide bond to increase the molecular weight of polyimide. Such patent documents include CN101558102A, which hydrolyzes part of the anhydride-terminated polyamic acid by adding water or using a water-containing solvent to obtain a diacid-terminated polyamic acid solution, and then further adding dianhydride and diamine to polymerize to obtain a high-concentration and low-viscosity polyamic acid solution; CN110117362A is a method for preparing a high-modulus and high-toughness polyimide film by combining a phenyl ester-containing aromatic dianhydride with a general aromatic dianhydride; CN106589370A regulates the viscosity by first adding a dicarboxylic acid diester and then adding dianhydride in batches; CN106589370A and CN110753715A regulate the viscosity by using a tetracarboxylic aromatic carboxylic acid; CN111087619A adds a polycarboxylic acid compound to a low-viscosity polyamic acid solution to prepare a high-strength polyimide film; and CN112029099A regulates the viscosity of the polyimide acid slurry by adding an acid ester compound three or more times under the condition of staged temperature rise.

[0006] In addition, CN110253904A discloses a polyimide thick film or super-thick film and a preparation method thereof, the preparation of the polyimide thick film or super-thick film is realized by adding a flow promoter in a high-viscosity PAA. CN110655650A discloses a benzoxazine-bridged polyimide precursor and a preparation method thereof, first, an amino-terminated polyamic acid is formed by reacting an excess of diamine monomer with dianhydride monomer, then bisphenol A and polyformaldehyde are added and heated to form an amino-terminated polyester ammonium salt solution, and finally imidization is performed by heating to form a benzoxazine-bridged polyimide. CN114181394A discloses a low-viscosity polyimide precursor solution and a preparation method thereof, first, ether-containing diester diacid and ether-containing monoester monoacid solutions are prepared by reacting ethylene glycol monomethyl ether with cyclic dianhydride and monocarboxylic anhydride end-capping agents, respectively, then the ether-containing diester diacid solution is mixed with aromatic diamine and the ether-containing monoester monoacid solution in an organic solvent to finally obtain the precursor solution; CN112876680A obtains an ester-terminated polyamic acid composition by reacting an excess of dianhydride with an imidazole-containing diamine, then adding an alcohol, and subsequently sequentially adding other remaining diamine and dianhydride monomers, and performing chemical imidization to obtain a block-structured polyimide film; CN114479073A relates to a polyamic acid resin composition, an anhydride-terminated polyamic acid resin is synthesized by reacting an excess of dianhydride with diamine, and an amino-protected aromatic diamine is formed by reacting a special amino-protecting mixture with diamine, then polycondensation reaction is performed to prepare a low-viscosity polyimide acid solution, and finally an amino-protecting group removing agent is used to remove the amino-protecting group, so that the molecular chain is polymerized and grown again to prepare a polyimide film;

[0007] The above-mentioned works can effectively adjust the viscosity of the polyamic acid solution, but still have some limitations and deficiencies. In method I, the polyamic acid molecular chain formed is short, and the introduction of crosslinking groups reduces the toughness and solubility of the final product, and has limitations in multiple processing; in method II, the added tetracarboxylic acid or tetracarboxylic ester compound has low reactivity, which reduces the molecular weight of the polyamic acid to some extent, and the uniformity and stability of the slurry are poor, and the obtained polyimide product after solidification is unstable, in addition, there are special limitations on the emission of small molecule compounds in some application fields, which also limits its application. Other works introduce special structure components or specific mixtures, which increase the complexity of the process. SUMMARY

[0008] In order to overcome the deficiencies of the prior art, the present application provides a low-viscosity polyamic acid slurry and a preparation method of a polyimide product.

[0009] The purpose of the present application is achieved by the following technical solutions:

[0010] One of the purposes of the present application is to provide a preparation method of low viscosity polyamic acid slurry, which is carried out in the following steps:

[0011] S1: Dissolve diamine in aprotic polar solvent under inert atmosphere, then add monocarboxylic anhydride, heat and react to obtain a mixed solution of monoamino amide and residual unreacted diamine;

[0012] S2: Add dianhydride to the above mixed solution to carry out polycondensation reaction to generate polyamic acid slurry with amide group and anhydride group as molecular chain end groups.

[0013] Further limitation, the structural general formula of monocarboxylic anhydride in S1 is:

[0014]

[0015] In which: R1 and R2 are each independently selected from one of alkyl, cycloalkyl, aromatic group.

[0016] Further limitation, the structural general formula of diamine in S1 is: In the formula, R3 is selected from one or more of the following structures:

[0017]

[0018]

[0019] Further limitation, the molar ratio of monocarboxylic anhydride to diamine in S1 is (0.1-30):100.

[0020] Further limitation, the molar ratio of monocarboxylic anhydride to diamine in S1 is (0.5-10):100.

[0021] Further limitation, the heating in S1 is to 40-130℃ for 0.5-6h.

[0022] Further limitation, the aprotic polar solvent in S1 includes one or more of N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAc).

[0023] Further limitation, the structural general formula of dianhydride in S2 is:

[0024]

[0025] at least one of pyromellitic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-biphenyl tetracarboxylic dianhydride, 2,3,3'4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3'4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, and 4,4'-(4,4'-isopropyl diphenyloxy) bis(phthalic anhydride).

[0026] Further limited, the molar ratio of the dianhydride in S2 to the diamine in S1 is 1:(0.99-1.01).

[0027] Further limited, the reaction temperature in S2 is -10-100℃, and the time is 0.5-12h.

[0028] The second object of the present application is to provide a polyamic acid slurry prepared by the above method, wherein the polyamic acid slurry comprises two types of molecular chains, which are formula (I) and (II) respectively.

[0029]

[0030]

[0031] In the formula, m and n are 1-20 respectively, A and B are each independently selected from R1, R2 in the general formula of monocarboxylic anhydride, R3 is R3 in the general formula of diamine, and R4 is R4 in the general formula of dianhydride.

[0032] Further limited, the solid content of the polyamic acid slurry is 2-50wt%, and the room temperature viscosity is 100-200000cP.

[0033] Further limited, the solid content of the polyamic acid slurry is 15-35wt%.

[0034] The third object of the present application is to provide an application of the polyamic acid slurry prepared by the above method in the preparation of polyimide film.

[0035] The fourth object of the present application is to provide a high-performance polyimide film, which is prepared by coating the above polyamic acid slurry and then performing thermal imidization or chemical imidization.

[0036] Further limited, the thermal imidization temperature is 300-500℃.

[0037] Further limited, the catalyst for chemical imidization comprises a tertiary amine catalyst.

[0038] More specifically, the tertiary amine catalyst includes at least one of pyridine, p- pyrroline, dimethylpyridine, trimethylpyridine, and quinoline.

[0039] More specifically, the chemical imidization dehydrating agent includes at least one of trifluoroacetic anhydride, acetic anhydride, and propionic anhydride.

[0040] Compared with the prior art, the present application has the following remarkable effects:

[0041] (1) The present application uses monocarboxylic anhydride to react with part of the amino groups to form mono-amino amide, so that part of the polyamic acid molecule chains in the synthesized polyamic acid slurry are capped by amide groups, thereby realizing the control of the molecular chain length and ultimately achieving the purpose of controlling the viscosity of the polyamic acid slurry.

[0042] (2) During the high-temperature imidization process of the polyamic acid slurry prepared by the present application, the end anhydride groups in the PAA further react with the end amide groups, so that two molecular chains are connected and polymerized again, and the molecular weight is further increased, thereby improving the performance of the polyimide product. At the same time, the monocarboxylic anhydride generated is volatilized and removed at high temperature.

[0043] (3) The method of the present application has a wide application range and does not require additional complex compounds, and also saves the preparation process. At the same time, the viscosity adjustment range is large, and the removal of the end amide groups occurs during the imidization process, without the need to introduce special structure monomers and additional heating process steps, the process is simple, and is suitable for industrial production. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 The infrared spectra of the polyimide films obtained from Examples 1-5 and Comparative Example 1 are shown in the following figures. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present application clearer, the following embodiments are further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0046] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained by commercial channels by those skilled in the art.

[0047] The terms "comprising," "including," "having," "containing," or "encompassing," and any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, step, method, article, or apparatus.

[0048] When equivalent, concentration, or other values or parameters are expressed in ranges, preferred ranges, or a series of upper preferred values and lower preferred values, it is to be understood that all ranges formed by any pair of an upper or preferred value and a lower or preferred value of any range, whether or not the range is expressly disclosed, are specifically disclosed. For example, where a range "1 to 5" is disclosed, the described range is to be construed as including the range "1 to 4," "1 to 3," "1 to 2," "1 to 2 and 4 to 5," "1 to 3 and 5," etc. When numerical ranges are described herein, unless the context indicates otherwise, the range is intended to include the end values and all the integers and fractions within that range. In the application specification and claims, range limitations can be combined and / or interchanged, unless the context indicates otherwise, and the ranges include all sub-ranges contained therein.

[0049] The indefinite articles "a" and "an," as used herein in the specification, unless clearly indicated to the contrary, should be understood to mean one or at least one. The use of the negative "not" in the claims, unless clearly indicated to the contrary, should be understood to mean the absence of the feature or characteristic being negated.

[0050] As used herein, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. "Coupled" means directly or indirectly connected, coupled, or linked, either chemically or physically.

[0051] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The endpoints of the ranges and any values are intended to be approximate, unless otherwise indicated. It is intended that the application encompass all such ranges and values unless otherwise indicated. For numerical ranges which include endpoints, each intervening value between the endpoints is also specifically included. For ranges which include endpoints, each intervening point between the endpoints is specifically included. For ranges which include endpoints, each intervening point between the endpoints is specifically included. For ranges which include endpoints, each intervening point between the endpoints is specifically included. For ranges which include endpoints, each intervening point between the endpoints is specifically included.

[0052] The following examples and comparative examples were measured by the following methods.

[0053] (1) The solid content of the polyamic acid slurry was calculated by the following formula.

[0054] The following examples and comparative examples were measured by the following methods.

[0055] (2) The viscosity of polyamide acid slurry was tested by Physica MCR 301 rotary rheometer.

[0056] (3) The thickness of the film was determined by using the digital display micrometer thickness gauge of Aipu Measuring Instrument Co., Ltd.

[0057] (4) The tensile strength and tensile elastic modulus were determined according to GB / T 1040-2008 by using a universal material testing machine.

[0058] (5) The 5% thermal decomposition temperature was determined by using a thermogravimetric analyzer device under a nitrogen atmosphere at a temperature rising speed of 10 ℃ / min, and the temperature at which the weight loss reached 5% was calculated.

[0059] Example 1

[0060] The preparation method of the high-performance polyimide film of the present example was carried out according to the following steps:

[0061] Step (1) Under a nitrogen atmosphere, 3.0279 g of p-phenylenediamine was dissolved in 30 ml of N,N-dimethylacetamide solvent at -10 ℃, and after stirring until completely dissolved, 0.0587 g of acetic anhydride was added, and then the temperature was raised to 60 ℃ for 2 h to obtain a mixture of mono-phenylamine acetamide and residual unreacted diamine; the reaction process is shown in the following formula:

[0062]

[0063] Step (2) Again, the temperature was lowered to -10 ℃, and 8.2386 g of 3,3'4,4'-diphenyl tetracarboxylic dianhydride was added, and after stirring for 0.5 h, the temperature was raised to 40 ℃ for 6 h to obtain a polyamide acid slurry with a solid content of 20 wt%;

[0064] Step (3) The polyamide acid slurry was uniformly coated on a clean and smooth glass plate by casting method, and then the coated glass plate was placed in an imidization furnace under a nitrogen atmosphere for staged temperature rising, with a temperature rising rate of 5 ℃ / min, wherein the temperature was kept constant at 80 ℃ for 0.5 h, at 160 ℃ for 0.5 h, at 350 ℃ for 0.5 h, and at 450 ℃ for 0.5 h, and then naturally cooled. Finally, the polyimide film with a thickness of 38 microns was peeled off from the glass plate.

[0065] The reaction processes of steps (2) to (3) are shown in the following formula:

[0066]

[0067] The viscosity of the polyamide acid slurry and the thickness, mechanical and heat resistance properties of the polyimide film thus obtained are shown in Table 1. The infrared spectrum of the polyimide film is shown in Fig. 1. Figure 1

[0068] Example 2

[0069] The preparation method of the high performance polyimide film of this example is carried out in the following steps:

[0070] Step (1) 3.0279 g of p-phenylenediamine is dissolved in 30 ml of N,N-dimethylacetamide solvent under nitrogen atmosphere at -10°C, after stirring to complete dissolution, 0.8378 g of acetic anhydride is added, then warmed to 60°C for 2 h to obtain a mixture of monoaniline acetamide and residual unreacted diamine;

[0071] Steps (2)-(3): same as Example 1.

[0072] The viscosity of the polyamide acid slurry and the thickness, mechanical and heat resistance properties of the polyimide film thus obtained are shown in Table 1. The infrared spectrum of the polyimide film is shown in Fig. 1. Figure 1

[0073] Example 3

[0074] The preparation method of the high performance polyimide film of this example is carried out in the following steps:

[0075] Step (1) 3.0279 g of p-phenylenediamine is dissolved in 30 ml of N,N-dimethylacetamide solvent under nitrogen atmosphere at -10°C, after stirring to complete dissolution, 0.8378 g of acetic anhydride is added, then warmed to 60°C for 2 h to obtain a mixture of monoaniline acetamide and residual unreacted diamine;

[0076] Steps (2)-(3): same as Example 1.

[0077] The viscosity of the polyamide acid slurry and the thickness, mechanical and heat resistance properties of the polyimide film thus obtained are shown in Table 1. The infrared spectrum of the polyimide film is shown in Fig. 1. Figure 1

[0078] Example 4

[0079] The preparation method of the high performance polyimide film of this example is carried out in the following steps:

[0080] ​​​Step (1) 3.0279 g of p-phenylenediamine was dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C, 0.0139 g of acetic anhydride was added after stirring until complete dissolution, and then the temperature was increased to 60°C for 2 h to obtain a mixture of monoanilinoacetamide and remaining unreacted diamine;

[0081] Steps (2)-(3) were the same as in Example 1.

[0082] The viscosity of the polyamic acid syrup thus obtained and the thickness, mechanical and heat resistance properties of the polyimide film were tested and the results are shown in Table 1. The infrared spectrum of the polyimide film is shown in FIG. 1. Figure 1

[0083] Example 5

[0084] The preparation method of the high-performance polyimide film of this example was carried out in the following steps:

[0085] Step (1) 3.0279 g of p-phenylenediamine was dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C, 0.0139 g of acetic anhydride was added after stirring until complete dissolution, and then the temperature was increased to 60°C for 2 h to obtain a mixture of monoanilinoacetamide and remaining unreacted diamine;

[0086] Steps (2)-(3) were the same as in Example 1.

[0087] The viscosity of the polyamic acid syrup thus obtained and the thickness, mechanical and heat resistance properties of the polyimide film were tested and the results are shown in Table 1. The infrared spectrum of the polyimide film is shown in FIG. 1. Figure 1

[0088] Comparative Example 1

[0089] The preparation method of the polyimide film of this comparative example was carried out in the following steps:

[0090] Step (1) 3.0279 g of p-phenylenediamine was dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C, 8.2386 g of 3,3'4,4'-diphenyltetracarboxylic dianhydride was added after stirring for 0.5 h, and then the temperature was increased to 40°C for 6 h to obtain a polyamic acid syrup;

[0091] Step (2) was the same as in Example 1, step (3).

[0092] The viscosity of the polyamic acid syrup thus obtained and the thickness, mechanical and heat resistance properties of the polyimide film were tested and the results are shown in Table 1. The infrared spectrum of the polyimide film is shown in FIG. 1. Figure 1

[0093] ​​​By comparing the infrared spectra of the polyimide films of Examples 1-5 and Comparative Example 1, it was found that the infrared spectra of the polyimide film obtained after adjusting the concentration with acetic anhydride was identical to that of the film without acetic anhydride, which indicated that the acetic anhydride was completely removed and did not remain in the film.

[0094] Example 6

[0095] The method for preparing the high-performance polyimide film of this example was carried out in the following steps:

[0096] Step (1) 10.6281 g of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 0.9209 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl were dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C. After stirring until complete dissolution, 0.1574 g of cyclohexanecarbonyl anhydride was added, and then the temperature was raised to 60°C for 2 h to obtain a mixture of monoamino amide and residual unreacted diamine;

[0097] Step (2) The temperature was again lowered to -10°C, and 5.6423 g of cyclobutane tetracarboxylic dianhydride was added. After stirring for 0.5 h, the temperature was raised to 40°C for 6 h to obtain a polyamic acid slurry having a solid content of 35 wt%;

[0098] Step (3) The polyamic acid slurry was uniformly coated on a clean and smooth glass plate by casting, and the coated glass plate was placed in an imidization furnace under a nitrogen atmosphere for staged temperature increase at a rate of 5°C / min. The temperature was held constant at 80°C for 0.5 h, at 160°C for 0.5 h, and at 350°C for 0.5 h, after which the temperature was naturally lowered. The polyimide film having a thickness of 38 microns was finally peeled off from the glass plate.

[0099] The viscosity of the polyamic acid slurry thus obtained and the thickness, mechanical and heat resistance test results of the polyimide film are shown in Table 2.

[0100] Example 7

[0101] The method for preparing the high-performance polyimide film of this example was carried out in the following steps:

[0102] Step (1) 10.6281 g of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 0.9209 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl were dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C. After stirring until complete dissolution, 0.1574 g of cyclohexanecarbonyl anhydride was added, and then the temperature was raised to 60°C for 2 h to obtain a mixture of monoamino amide and residual unreacted diamine;

[0103] Steps (2)-(3): Same as Example 6.

[0104] The viscosity of the polyamic acid slurry and the thickness, mechanical and heat resistance properties of the polyimide film thus obtained are shown in Table 2.

[0105] Example 8

[0106] The preparation method of the high performance polyimide film of this example was carried out in the following steps:

[0107] Step (1) 10.6281 g of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 0.9209 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl were dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C, 0.3360 g of cyclohexanecarbonyl anhydride was added after stirring to complete dissolution, and then the temperature was raised to 60°C for 2 h to obtain a mixture of monoamino amide and remaining unreacted diamine;

[0108] Steps (2)-(3) were the same as in Example 6.

[0109] The viscosity of the polyamic acid slurry and the thickness, mechanical and heat resistance properties of the polyimide film thus obtained are shown in Table 2.

[0110] Example 9

[0111] The preparation method of the high performance polyimide film of this example was carried out in the following steps:

[0112] Step (1) 10.6281 g of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 0.9209 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl were dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C, 0.3360 g of cyclohexanecarbonyl anhydride was added after stirring to complete dissolution, and then the temperature was raised to 60°C for 2 h to obtain a mixture of monoamino amide and remaining unreacted diamine;

[0113] Steps (2)-(3) were the same as in Example 6.

[0114] The viscosity of the polyamic acid slurry and the thickness, mechanical and heat resistance properties of the polyimide film thus obtained are shown in Table 2.

[0115] Example 10

[0116] The preparation method of the high performance polyimide film of this example was carried out in the following steps:

[0117] Step (1) 10.6281 g of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 0.9209 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl were dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C, and after stirring until complete dissolution, 1.4071 g of cyclohexanecarbonyl anhydride was added, and then warmed to 60°C for 2 h to obtain a mixture of monoaminoamide and remaining unreacted diamine;

[0118] Steps (2) and (3) were the same as in Example 6.

[0119] The viscosity of the polyamic acid syrup thus obtained and the thickness, mechanical and heat resistance of the polyimide film were tested and the results are shown in Table 2.

[0120] Comparative Example 2

[0121] The preparation method of the high-performance polyimide film of the present example was carried out in the following steps:

[0122] Step (1) 3.5428 g of 2,2'-bis[4-(4-aminophenoxyphenyl)]propane and 0.3067 g of 2,2'-bis(trifluoromethyl)diaminobiphenyl were dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C, and after stirring until complete dissolution, 1.8808 g of cyclobutane tetracarboxylic dianhydride was added, and after stirring for 0.5 h, warmed to 40°C for 6 h to obtain a polyamic acid syrup having a solid content of 15 wt%;

[0123] Step (2) was the same as in Example 6, step (3).

[0124] The viscosity of the polyamic acid syrup thus obtained and the thickness, mechanical and heat resistance of the polyimide film were tested and the results are shown in Table 2.

[0125] Example 11

[0126] The preparation method of the high-performance polyimide film of the present example was carried out in the following steps:

[0127] Step (1) 2.8498 g of 2,2'-dimethyl-4,4'-diaminobiphenyl was dissolved in 30 ml of N,N-dimethylacetamide solvent under a nitrogen atmosphere at -10°C, and after stirring until complete dissolution, 0.4376 g of propionic anhydride was added, and then warmed to 60°C for 2 h to obtain a mixture of monoaminoamide and remaining unreacted diamine;

[0128] Step (2) was again cooled to -10°C, and 2.9283 g of pyromellitic dianhydride was added, and after stirring for 0.5 h, warmed to 40°C for 6 h to obtain a polyamic acid syrup having a solid content of 15 wt%;

[0129] Step (3) The polyamide acid slurry was uniformly coated on a clean and smooth glass plate by a casting method, and then the coated glass plate was placed in an imidization furnace under a nitrogen atmosphere and subjected to staged heating at a heating rate of 5°C / min, wherein the temperature was kept constant at 80°C for 0.5 h, at 160°C for 0.5 h, at 350°C for 0.5 h, and at 420°C for 0.5 h, and then naturally cooled. Finally, the polyimide film with a thickness of 38 microns was peeled off from the glass plate.

[0130] The viscosity of the polyamide acid slurry thus obtained and the thickness, mechanical and heat resistance performance test results of the polyimide film are shown in Table 3.

[0131] Example 12

[0132] The preparation method of the high-performance polyimide film of the present example was carried out in the following steps:

[0133] Step (1) Under a nitrogen atmosphere, 2.8498 g of 2,2'-dimethyl-4,4'-diaminobiphenyl was dissolved in 30 ml of N,N-dimethylacetamide solvent at -10°C, and after stirring until complete dissolution, 0.1308 g of propionic anhydride was added, and then the temperature was raised to 60°C for 2 h of reaction, to obtain a mixture of monoamino amide and residual unreacted diamine;

[0134] Steps (2)-(3): The same as in Example 11.

[0135] The viscosity of the polyamide acid slurry thus obtained and the thickness, mechanical and heat resistance performance test results of the polyimide film are shown in Table 3.

[0136] Example 13

[0137] The preparation method of the high-performance polyimide film of the present example was carried out in the following steps:

[0138] Step (1) Under a nitrogen atmosphere, 2.8498 g of 2,2'-dimethyl-4,4'-diaminobiphenyl was dissolved in 30 ml of N,N-dimethylacetamide solvent at -10°C, and after stirring until complete dissolution, 0.1308 g of propionic anhydride was added, and then the temperature was raised to 60°C for 2 h of reaction, to obtain a mixture of monoamino amide and residual unreacted diamine;

[0139] Steps (2)-(3): The same as in Example 11.

[0140] The viscosity of the polyamide acid slurry thus obtained and the thickness, mechanical and heat resistance performance test results of the polyimide film are shown in Table 3.

[0141] Example 14

[0142] The preparation method of the high performance polyimide film of the present example was carried out according to the following steps:

[0143] Step (1) 2.8498 g of 2,2'-dimethyl-4,4'-diaminobiphenyl was dissolved in 30 ml of N,N-dimethylacetamide solvent under nitrogen atmosphere at -10°C, after stirring to complete dissolution, 0.0752 g of propionic anhydride was added, then warmed to 60°C for 2h to obtain a mixture of monoamino amide and residual unreacted diamine;

[0144] Steps (2)-(3) were the same as in Example 11.

[0145] The viscosity of the polyamic acid slurry and the thickness, mechanical and heat resistance performance test results of the polyimide film thus obtained are shown in Table 3.

[0146] Example 15

[0147] The preparation method of the high performance polyimide film of the present example was carried out according to the following steps:

[0148] Step (1) 2.8498 g of 2,2'-dimethyl-4,4'-diaminobiphenyl was dissolved in 30 ml of N,N-dimethylacetamide solvent under nitrogen atmosphere at -10°C, after stirring to complete dissolution, 0.0752 g of propionic anhydride was added, then warmed to 60°C for 2h to obtain a mixture of monoamino amide and residual unreacted diamine;

[0149] Steps (2)-(3) were the same as in Example 11.

[0150] The viscosity of the polyamic acid slurry and the thickness, mechanical and heat resistance performance test results of the polyimide film thus obtained are shown in Table 3.

[0151] Comparative Example 3

[0152] The preparation method of the high performance polyimide film of the present example was carried out according to the following steps:

[0153] Step (1) 2.8498 g of 2,2'-dimethyl-4,4'-diaminobiphenyl was dissolved in 30 ml of N,N-dimethylacetamide solvent under nitrogen atmosphere at -10°C, after stirring to complete dissolution, 0.0752 g of propionic anhydride was added, then warmed to 60°C for 2h to obtain a mixture of monoamino amide and residual unreacted diamine;

[0154] Step (2) was the same as step (3) of Example 11.

[0155] The viscosity of the polyamic acid slurry and the thickness, mechanical and heat resistance performance test results of the polyimide film thus obtained are shown in Table 3.

[0156] Table 1 Test results of polyimide films obtained from Examples 1-5 and Comparative Example 1

[0157]

[0158] Table 2 Test results of polyimide films obtained from Examples 6-10 and Comparative Example 2

[0159]

[0160]

[0161] Table 3 Test results of polyimide films obtained from Examples 11-15 and Comparative Example 3

[0162]

[0163] The above descriptions are only preferred embodiments of the present application, which are based on different implementations of the overall concept of the present application. The protection scope of the present application is not limited to this, and any changes or replacements within the technical scope disclosed by the present application can be easily thought by those skilled in the art, which should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for preparing a low viscosity polyamic acid syrup, characterized by, The following steps are taken: S1: Dissolve the diamine in an aprotic polar solvent under an inert atmosphere, then add the monocarboxylic anhydride, heat the reaction to obtain a mixture of monoamino amide and residual unreacted diamine; The molar ratio of monocarboxylic anhydride to diamine in S1 is (0.1-30):100; S2: Add dianhydride to the above mixture to perform polycondensation reaction to generate polyamic acid slurry with molecular chain end groups of amide and anhydride groups.

2. The method of claim 1, wherein, The general structure of the monocarboxylic anhydride in S1 is: Wherein: R1 and R2 are each independently selected from one of alkyl, cycloalkyl, and aromatic group.

3. The method of claim 1, wherein, The general structure of the diamine in S1 is: wherein R3is selected from one or more of the following structures: 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 、 ， The aprotic polar solvent in S1 includes one or more of N-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), and N,N-dimethylacetamide (DMAc).

4. The method of claim 1, wherein, In S1, heating is performed to 40-130°C for 0.5-6h.

5. The method of claim 1, wherein, The general structure of the dianhydride in S2 is: ， At least one of pyromellitic dianhydride, 3,3',4,4'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-biphenyl tetracarboxylic dianhydride, 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, 1,2,3,4-cyclobutane tetracarboxylic dianhydride, 1,2,4,5-cyclohexane tetracarboxylic dianhydride, and 4,4'-(4,4'-isopropyl diphenyloxy) bis(phthalic anhydride).

6. The method of claim 1, wherein, In S2, the molar ratio of dianhydride to diamine in S1 is 1:(0.99-1.01), and the reaction temperature in S2 is -10-100°C for 0.5-12h.

7. The polyamic acid slurry prepared by the method of any one of claims 1 to 6, characterized in that, It contains two types of molecular chains, which are (I) and (II) respectively: （I） (II) In the formula, m and n are each independently 1-20, A and B are each independently selected from R1 and R2 in the general structure of the monocarboxylic anhydride in claim 2, R3 is R3 in the general structure of the diamine in claim 3, and R4 is R4 in the general structure of the dianhydride in claim 6.

8. The polyamic acid syrup of claim 7, wherein, The polyamic acid slurry has a solid content of 2-50wt% and a room temperature viscosity of 100-200000cP.

9. Use of the polyamic acid slurry prepared by the method of any one of claims 1-6 in the preparation of a polyimide film.

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