A piperazine-grafted polyimide type resin and a method for preparing the same

Abstract

The present application relates to the technical field of high molecular compound preparation, and more particularly to a kind of piperazine grafted polyimide resin and preparation method thereof.Preparation raw materials include: diamine, dianhydride, solvent, dehydrating agent, catalyst, piperazine monomer;The structure of the piperazine monomer is shown in formula 1: the R1 includes hydrogen atom or C1-C4 straight chain alkyl or branched alkyl, the R2 includes C1-C8 straight chain alkyl or branched alkyl, the R2 also includes amino group, only one primary amino group or secondary amine group in the piperazine monomer, and the piperazine monomer includes at least two kinds.The R1 includes hydrogen atom or methyl in the structure of the piperazine monomer, and the R2 includes C2 or C4 straight chain alkyl or branched alkyl, which can improve the water solubility of polyimide resin while maintaining thermal performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular compound preparation, and more particularly to a piperazine grafted polyimide resin and a preparation method thereof. BACKGROUND

[0002] Since the 1970s, the cathodic electrophoretic coating technology has been successfully applied to industrialization, the research of cathodic electrophoretic paint at home and abroad is more mature, and the application field is also expanding. The excellent thermodynamic performance, mechanical performance and electrical performance of aromatic polyimide make polyimide applied to various aspects of industrial production. However, the traditional aromatic polyimide is difficult to be dissolved in some conventional solvents, which causes difficulties for polyimide in the field of electrophoretic paint. In order to improve the solubility of polyimide, a series of modifications are usually carried out, such as introducing flexible groups into the main chain, grafting large size side groups, or introducing fluorine-containing groups. Especially, the fluorine-containing polyimide significantly improves the solubility.

[0003] CN111040450A discloses a low dielectric fluorine-containing polyimide composite film and a preparation method thereof. The low dielectric fluorine-containing polyimide composite film is obtained by adding 9,9-bis[4-(4-amino-3-trifluoromethyl phenoxy) phenyl] fluorene and dianhydride monomer into the dispersion liquid of cage-type polysilsesquioxane and then performing in-situ polymerization. The low dielectric fluorine-containing polyimide composite film has low dielectric constant, low dielectric loss and solubility. However, the fluorine-containing monomer is expensive and not suitable for large-scale production. In addition, the introduction of fluorine-containing groups increases the flexibility of the main chain, which causes a certain decrease in thermal performance and rigidity, and is not suitable for the field of electrophoretic paint. SUMMARY

[0004] In order to overcome the deficiencies in the background art, the present application provides a piperazine grafted polyimide resin and a preparation method thereof. By selecting a specific piperazine grafted polyimide, the prepared resin improves the solubility of polyimide while maintaining the thermal performance of polyimide.

[0005] To achieve the purpose of the present application, the first aspect of the present application provides a piperazine grafted polyimide resin. The preparation raw materials include diamine, dianhydride, solvent, dehydrating agent, catalyst and piperazine monomer. The structure of the piperazine monomer is shown in formula 1. Formula 1

[0006] R1 includes hydrogen atom or C1-C4 straight chain alkyl or branched alkyl, R2 includes C1-C8 straight chain alkyl or branched alkyl, and R2 also includes amino group. There is only one primary amino group or secondary amine group in the piperazine monomer, and the piperazine monomer includes at least two kinds.

[0007] Preferably, the piperazine monomers include at least two of N-methylpiperazine (CAS: 109-01-3), N-isopropylpiperazine (CAS: 137186-14-2), N-propylpiperazine (CAS: 21867-64-1), N-ethylpiperazine (CAS: 5308-25-8), 1-(2-dipropylaminoethyl)piperazine (CAS: 496808-01-6), 4-methyl-1-piperazineethylamine (CAS: 934-98-5), 1-(2-dimethylaminoethyl)piperazine (CAS: 3644-18-6).

[0008] The present applicant has found that the piperazine monomer structure, in which R1 includes a hydrogen atom or a methyl group, and R2 includes a C2 or C4 straight-chain alkyl group or a branched-chain alkyl group, can improve the water solubility of the polyimide resin. The rigid structure and strong intermolecular forces of the polyimide reduce its solubility and processability. The primary amine or secondary amine on the piperazine molecule reacts with the polyamide group, thereby grafting the piperazine to the polyimide molecular chain. The presence of only one primary amine or secondary amine group in the piperazine monomer can control the smooth progress of the grafting reaction. If the activity of the primary amine or secondary amine group is too high, it can react with the polyimide. When multiple active amine groups are present in the piperazine monomer, crosslinking occurs, thereby producing a gel, making it difficult to maintain the reaction.

[0009] Further research has found that the piperazine monomers including 4-methyl-1-piperazineethylamine and 1-(2-dimethylaminoethyl)piperazine can reduce the color depth of the polyimide resin, thereby being applicable to the field of light-colored electrophoretic paint. It is possible that the presence of a conjugated π bond in the aromatic polyimide improves the mechanical properties while also showing a relatively deep color. The introduction of 4-methyl-1-piperazineethylamine and 1-(2-dimethylaminoethyl)piperazine as a side group destroys the conjugation effect on the molecular chain, cuts off the charge transfer between the macromolecular chains, and makes it difficult to form intermolecular and intramolecular charge transfer complexes, thereby reducing the color depth of the resin. At the same time, the introduction of the piperazine monomer can effectively improve the solubility of the resin without affecting the rigidity of the molecular chain. It is possible that the reduction in the packing degree of the polymer molecular chain makes it easier for solvent molecules to penetrate.

[0010] Preferably, R1 includes a hydrogen atom or a methyl group, and R2 includes a C2 or C4 straight-chain alkyl group or a branched-chain alkyl group.

[0011] Further preferably, the piperazine monomers include 4-methyl-1-piperazineethylamine and 1-(2-dimethylaminoethyl)piperazine, and the molar ratio of the 4-methyl-1-piperazineethylamine to the 1-(2-dimethylaminoethyl)piperazine is 1: (2-4).

[0012] More preferably, the piperazine monomer comprises 4-methyl-1-piperazine ethylamine (CAS: 934-98-5), 1-(2-dimethylaminoethyl)piperazine (CAS: 3644-18-6) at a molar ratio of 1:2.5.

[0013] The dianhydride comprises at least one of 3,4'-oxydibenzoic anhydride, trisphenol ether tetra carboxylic dianhydride, bisphenol A type diether dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic anhydride, hydrogenated pyromellitic anhydride, bisphenol A type diester dianhydride, 4,4-oxyphthalic anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride, pyromellitic dianhydride, 3,3',4,4'-diphenyl sulfone tetracarboxylic dianhydride, naphthalene-1,4,5,8-tetracarboxylic dianhydride, 3,4'-oxydibenzoic anhydride, and 3,4,9,10-perylenetetracarboxylic dianhydride.

[0014] Preferably, the dianhydride comprises at least one of 3,4'-oxydibenzoic anhydride, trisphenol ether tetra carboxylic dianhydride, bisphenol A type diether dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, hydrogenated pyromellitic anhydride, bisphenol A type diester dianhydride, 4,4-oxyphthalic anhydride.

[0015] Further preferably, the dianhydride comprises 4,4-oxyphthalic anhydride.

[0016] The diamine comprises at least one of 4,4'-diaminobenzophenone, p-phenylenediamine, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(3-aminophenoxy)phenyl]propane, 4,4'-diaminodiphenyl sulfone, 3,3'-dihydroxybenzidine, 3,3'-diaminobenzophenone, 3,4'-diaminodiphenyl methane, 3,3'-dimethyl-4,4'-diaminobenzophenone, 2,2'-dichloro-6,6'-dimethylbenzidine, 3,3'-diaminobenzophenone, 1,3-bis(3-aminophenoxy)benzene, 1,2-bis(4-aminophenoxy)benzene, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl disulfide, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl sulfone, 4,4'-bis(4-aminophenoxy)diphenyl sulfone.

[0017] Preferably, the diamine comprises at least one of 4,4'-diaminobenzophenone, p-phenylenediamine, 4,4'-diaminodiphenyl methane, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone.

[0018] Further preferably, the diamine comprises 4,4'-diaminodiphenyl ether.

[0019] The solvent includes one of N-methyl pyrrolidone, dimethyl sulfoxide, hexamethylphosphoramide, N,N'-dimethylformamide, N,N'-dimethylacetamide, dimethyl sulfoxide.

[0020] Preferably, the solvent includes N-methyl pyrrolidone.

[0021] The dehydrating agent includes one or more of acetic anhydride, propionic anhydride, butyric anhydride and benzoic anhydride.

[0022] Preferably, the dehydrating agent includes acetic anhydride.

[0023] The catalyst includes one or more of trimethylamine, triethylamine, triethanolamine, beta-pyrroline, isoquinoline, triethylene diamine, 3-methylpyridine.

[0024] The present applicant finds that the molar ratio of the diamine to the catalyst is 1:(0.2-0.6), which can control the acylimination reaction rate and reduce the occurrence of side reactions. With the increase of the catalyst content, the acylimination reaction rate is accelerated, the content of the imide ring in the polymer molecular chain is increased in the same time, the order of the polyimide aggregate structure is increased, thereby the rigidity of the polyimide is improved. However, if the catalyst content is too high, the risk of gelation is easy to occur. Further research finds that when the catalyst is triethylamine, the occurrence of side reactions can be reduced. When the ortho-position of the carbonyl group in the dianhydride has a strong electron-withdrawing group, the possibility of generating such positional isomers is increased. This may be because the presence of the strong electron-withdrawing group increases the possibility of the attack on the carbonyl carbon atom. A certain amount of triethylamine can effectively prevent the generation of such positional isomers, which may be the result of the interaction between the configuration of triethylamine and the electron-withdrawing group. Meanwhile, triethylamine has a relatively low boiling point and is easy to escape from the system during the reaction, thereby reducing the degree of damage to the molecular chain caused by the strong basicity of triethylamine itself.

[0025] Preferably, the catalyst includes one of triethylamine, triethanolamine and 3-methylpyridine.

[0026] Further preferably, the catalyst includes triethylamine.

[0027] The molar ratio of the diamine to the catalyst is 1:(0.2-0.6).

[0028] Preferably, the molar ratio of the diamine to the catalyst is 1:0.4.

[0029] The molar ratio of the diamine to the dehydrating agent is 1:(0.1-0.3).

[0030] Preferably, the molar ratio of the diamine to the dehydrating agent is 1:0.15.

[0031] The neutralizing agent comprises organic acid, preferably lactic acid, acetic acid, citric acid.

[0032] Preferably, the neutralizing agent comprises lactic acid.

[0033] Preferably, the molar ratio of the diamine to dianhydride is 1: (1-1.02).

[0034] Further preferably, the molar ratio of the diamine to dianhydride is 1:1.

[0035] The second aspect of the present application provides a preparation method of a piperazine grafted polyimide resin, comprising the following steps:

[0036] Step 1: adding diamine and dianhydride into part of solvent to react, obtaining polyamic acid solution;

[0037] Step 2: adding dehydrating agent and catalyst into the polyamic acid solution to carry out imidization reaction, and obtaining polyimide powder after precipitation and washing;

[0038] Step 3: adding the polyimide powder into the remaining solvent, dissolving and heating to obtain polyimide solution;

[0039] Step 4: adding piperazine monomer into the polyimide solution to react, obtaining mixture 1;

[0040] Step 5: after cooling the mixture 1, adding organic acid to neutralize, obtaining mixture 2;

[0041] Step 6: adding water into the mixture 2 and stirring at high speed, obtaining the product.

[0042] The present applicant finds that in the step 1, the part of solvent accounts for 50-70% of the mass percentage of the polyamic acid solution, which can improve the reaction efficiency, balance the solubility and molecular weight of the polyimide polymer, and the forward reaction of generating polyamic acid is a bimolecular reaction, and the reverse reaction is the degradation of polyamic acid into dianhydride and diamine, which is a monomolecular reaction. From the reaction equilibrium, increasing the reaction monomer concentration is beneficial to the forward reaction, but too high reaction monomer concentration reduces the molecular weight of polyamic acid to some extent, thereby affecting the mechanical properties of the prepared resin. It is possible that the dianhydride is added in solid form, and the solvent content is too low, which is prone to poor mass transfer. With the reaction of diamine, the water concentration around the dianhydride ion increases relatively, thereby increasing the hydrolysis rate of the acid anhydride, resulting in a decrease in the polymerization degree.

[0043] In the step 1, the part of solvent accounts for 50-70% of the mass percentage of the polyamic acid solution.

[0044] Preferably, in the step 1, the part of solvent accounts for 61% of the mass percentage of the polyamic acid solution.

[0045] Preferably, the weight ratio of the piperazine monomer to the polyimide powder is 1: (4-8).

[0046] Further preferably, the weight ratio of the piperazine monomer to the polyimide powder is 3:20.

[0047] The present applicant has found that the piperazine monomer includes 4-methyl-1-piperazine ethylamine and 1-(2-dimethylaminoethyl) piperazine, the molar ratio of the 4-methyl-1-piperazine ethylamine and 1-(2-dimethylaminoethyl) piperazine is 1: (2-4), and the weight ratio of the piperazine monomer to the polyimide powder is 1: (4-8), which can improve the thermal performance of the polyimide, the 4-methyl-1-piperazine ethylamine piperazine ring has higher activity, the piperazine ring heterocycle has certain steric hindrance, the grafting rate can be controlled, the thermal performance of the resin is maintained, the piperazine ring can reduce the polarization degree of the molecular chain, thereby reducing the dielectric constant of the polyimide and improving the insulation performance of the resin, the secondary amine group in the 1-(2-dimethylaminoethyl) piperazine participates in the reaction, and the alkyl side chain further weakens the conjugated structure of the aromatic ring. Further research has found that when the temperature of the grafting reaction is 80-130℃ and the reaction time is 2-6h, the reaction efficiency and uniformity of the polyimide can be improved. It is possible that too high a temperature makes the primary amine group have too high reactivity, which affects the grafting rate of the secondary amine group, resulting in a decrease in the comprehensive performance of the resin.

[0048] Preferably, the temperature of the reaction in step 4 is 80-130℃, and the reaction time is 2-6h.

[0049] The temperature of the reaction in step 4 is 110℃, and the reaction time is 4h.

[0050] Further preferably, the temperature of the reaction in step 4 is 110℃, and the reaction time is 4h.

[0051] Preferably, the pH of the mixed solution 2 is 5-6.5.

[0052] Further preferably, the pH of the mixed solution 2 is 6.

[0053] Beneficial effects:

[0054] 1. In the structure of the piperazine monomer, R1 includes a hydrogen atom or a methyl group, and R2 includes a C2 or C4 straight-chain alkyl group or a branched-chain alkyl group, which can improve the water solubility of the polyimide resin while maintaining the thermal performance.

[0055] 2. The molar ratio of the diamine to the catalyst is 1: (0.2-0.6), which can control the imidization reaction rate and reduce the occurrence of side reactions, thereby improving the thermal performance.

[0056] 3、The piperazine monomer has only one primary amino group or secondary amine group, which can avoid the occurrence of gel reaction.

[0057] 4、In step 1, the mass percentage of the solvent is 50-70%, which can improve the reaction efficiency and improve the thermal performance of the polyimide polymer.

[0058] 5、The molar ratio of 4-methyl-1-piperazine ethylamine, 1-(2-dimethylaminoethyl) piperazine is 1: (2-4), and the weight ratio of the piperazine monomer to the polyimide powder is 1: (4-8), the grafting reaction temperature is 80-130℃, and the reaction time is 2-6h, which can improve the thermal performance and insulation performance of the polyimide resin. BRIEF DESCRIPTION OF DRAWINGS

[0059] Figure 1 TGA of the piperazine grafted polyimide resin electrophoretic film prepared in Example 1.

[0060] Figure 2 Infrared spectrum of the piperazine grafted polyimide resin electrophoretic film prepared in Example 1.

[0061] Figure 3 Piperazine grafted polyimide resin emulsion prepared in Example 1. DETAILED DESCRIPTION

[0062] Example 1

[0063] A piperazine grafted polyimide resin, the preparation raw materials are: diamine, dianhydride, solvent, dehydrating agent, catalyst, piperazine monomer.

[0064] The dianhydride is 4,4-oxophthalic anhydride.

[0065] The diamine is 4,4'-diamino diphenyl ether.

[0066] The solvent is N-methyl pyrrolidone.

[0067] The dehydrating agent is acetic anhydride.

[0068] The catalyst is triethylamine.

[0069] The molar ratio of the diamine to the catalyst is 1:0.4, and the molar ratio of the diamine to the dehydrating agent is 1:0.15.

[0070] The neutralizing agent is lactic acid.

[0071] The molar ratio of the diamine to the dianhydride is 1:1, and the diamine is 1 mol.

[0072] The piperazine monomer is 4-methyl-1-piperazine ethylamine (CAS: 934-98-5), 1-(2-dimethylaminoethyl) piperazine (CAS: 3644-18-6), and the molar ratio of the 4-methyl-1-piperazine ethylamine, 1-(2-dimethylaminoethyl) piperazine is 1:2.5.

[0073] A preparation method of a piperazine grafted polyimide type resin is the following steps:

[0074] Step 1: diamine and dianhydride are added to 800g solvent, and reacted at 25℃ for 8h to obtain a polyamide acid solution;

[0075] Step 2: a dehydrating agent and a catalyst are added to the polyamide acid solution to carry out an imidization reaction (170℃, 1h), and then poured into a methanol solution to precipitate and separate out, and then washed with water to obtain a polyimide powder;

[0076] Step 3: 100g of the polyimide powder is added to 400g of solvent, heated to 80℃ to dissolve, and a polyimide solution is obtained;

[0077] Step 4: a piperazine monomer is added to the polyimide solution to carry out a reaction, and a mixed solution 1 is obtained;

[0078] Step 5: the mixed solution 1 is cooled to 60℃, an organic acid is added for neutralization, and a mixed solution 2 is obtained;

[0079] Step 6: 100g of water is added to the mixed solution 2, and stirred uniformly at 2000rpm, as shown in the following formula, and the product is obtained. Figure 3

[0080] The weight ratio of the piperazine monomer to the polyimide powder is 3:20.

[0081] The pH of the mixed solution 2 is 6.

[0082] The reaction temperature in step 4 is 110℃, and the reaction time is 4h.

[0083] Example 2

[0084] The specific implementation is the same as that in Example 1, except that the molar ratio of the 4-methyl-1-piperazine ethylamine, 1-(2-dimethylaminoethyl) piperazine in Example 2 is 1:3.

[0085] Example 3

[0086] The specific implementation is the same as that in Example 1, except that the weight ratio of the piperazine monomer to the polyimide powder in Example 3 is 3.5:20, and the reaction temperature in step 4 is 105℃, and the reaction time is 4h.

[0087] Comparative Example 1 ​

[0088] The specific implementation is the same as Example 1; except that the molar ratio of 4-methyl-1-piperazine ethylamine to 1-(2-dimethylaminoethyl) piperazine in Comparative Example 1 is 1:1.

[0089] Comparative Example 2

[0090] The specific implementation is the same as Example 1; except that the molar ratio of 4-methyl-1-piperazine ethylamine to 1-(2-dimethylaminoethyl) piperazine in Comparative Example 2 is 1:6.

[0091] Comparative Example 3

[0092] The specific implementation is the same as Example 1; except that the piperazine monomer in Comparative Example 3 is piperazine (CAS: 110-85-0).

[0093] Comparative Example 4

[0094] The specific implementation is the same as Example 1; except that the preparation method in Comparative Example 4 does not include steps 4-6.

[0095] Performance test method

[0096] The polyurea resin emulsion prepared by Example 1-3 and Comparative Example 1-4 is diluted to a solid content of 12wt%, and electrophoretic film forming is carried out, with a control voltage of 110V and a film thickness of 20μm. The film is tested for the following performance, and the test data is shown in Table 1, wherein Figure 1 TGA analysis of electrophoretic film, Figure 2 Infrared spectrum of electrophoretic film.

[0097] 1. Heat resistance: test voltage DC 1000V, test time 60s, record insulation resistance value (GΩ) at 150℃.

[0098] 2. Voltage resistance: test voltage DC 2700V, test time 60s, record leakage current (mA).

[0099] 3. Hardness performance: refer to standard GB / T 6739-2006, "Pencil Hardness Method for Coating Film Hardness" test.

[0100] Wherein "-" is not tested because it cannot form a film during preparation.

[0101] Performance test data

[0102] Table 1

[0103] Thermal resistance (GΩ) Voltage resistance (mA) Hardness Example 1 60 0.01 2H Example 2 58 0.02 2H Example 3 60 0.02 2H Comparative Example 1 60 0.01 2H Comparative Example 2 48 0.08 H Comparative Example 3 - - - Comparative Example 4 - - -

Claims

1. A piperazine-grafted polyimide type resin characterized by comprising: The raw materials include: diamine, dianhydride, solvent, dehydrating agent, catalyst, piperazine monomer; The piperazine monomer includes 4-methyl-1-piperazine ethylamine and 1-(2-dimethylaminoethyl) piperazine, and the molar ratio of the 4-methyl-1-piperazine ethylamine and 1-(2-dimethylaminoethyl) piperazine is 1:(2-4). The molar ratio of the diamine and the catalyst is 1:(0.2-0.6), and the catalyst includes one of triethylamine, triethanolamine and 3-methylpyridine.

2. The piperazine grafted polyimide resin according to claim 1, wherein The molar ratio of the diamine and the dianhydride is 1:(1-1.02).

3. The piperazine grafted polyimide resin according to claim 1, wherein The solvent includes one of N-methylpyrrolidone, dimethyl sulfoxide, hexamethylphosphoramide, N,N'-dimethylformamide, N,N'-dimethylacetamide and dimethyl sulfoxide.

4. A method for preparing the piperazine-grafted polyimide resin according to claim 1, The method is characterized in that, The method includes the following steps: Step 1: reacting the diamine and the dianhydride in part of the solvent to obtain a polyamic acid solution; Step 2: adding the dehydrating agent and the catalyst to the polyamic acid solution to perform imidization reaction, and then precipitating, washing and obtaining polyimide powder; Step 3: adding the polyimide powder to the remaining solvent, dissolving and then heating to obtain a polyimide solution; Step 4: adding the piperazine monomer to the polyimide solution to perform reaction and obtain a mixed solution 1; Step 5: cooling the mixed solution 1, adding an organic acid to perform neutralization and obtain a mixed solution 2; Step 6: adding water to the mixed solution 2 and stirring at high speed to obtain the product.

5. The method for preparing piperazine-grafted polyimide resin according to claim 4, characterized in that, The reaction temperature in the step 4 is 80-130℃, and the reaction time is 2-6h.

6. The method for preparing piperazine-grafted polyimide resin according to claim 5, characterized in that, The weight ratio of the piperazine monomer and the polyimide powder is 1:(4-8).

7. The method for preparing piperazine-grafted polyimide resin according to claim 6, characterized in that, In the step 1, the part of the solvent accounts for 50-70% of the mass percentage of the polyamic acid solution.

8. The method for preparing piperazine-grafted polyimide resin according to claim 7, characterized in that, The pH of the mixed solution 2 is 5-6.5.

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