Aromatic diamine monomer and preparation method thereof, photosensitive polyimide and preparation method thereof and application thereof

Abstract

The present invention provides an aromatic diamine monomer and a preparation method thereof, as well as a photosensitive polyimide and its preparation method and application, relating to the technical field of polymer compounds. The aromatic diamine monomer provided by the present invention contains a photocurable ethyl methacrylate group. This monomer can be copolymerized with a commercial diamine monomer and a dianhydride monomer to produce a photosensitive polyimide with a controllable ratio of photocurable groups. The photosensitive polyimide provided by the present invention has good solubility and is easy to process, and can be used as a substrate for photocurable 3D printing.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer compounds, and in particular to an aromatic diamine monomer and a preparation method thereof, a photosensitive polyimide and a preparation method and application thereof. Background Art

[0002] Polyimide (PI) is a type of high-performance polymer containing an imide ring in the main chain. It has high mechanical strength, excellent thermal stability and good solvent resistance, and is widely used in the aerospace and automotive industries. Traditional processing methods require separate molds to prepare polymer parts, and generate a lot of waste during the cutting, chipping, drilling and other processing processes. 3D printing, which accumulates materials layer by layer, can produce polymer parts with higher precision while reducing material waste. Polyimide has been widely used in 3D printing. For example, thermoplastic polyimide can be used in fused deposition 3D printing, and self-supporting polyimide solutions can be used in direct writing 3D printing. These printing technologies have good precision, but are slightly inferior to digital light processing and stereolithography based on UV curing.

[0003] The ink used in photocurable 3D printing consists of a photosensitive polymer, a reactive diluent, a crosslinker, and an initiator. The polyimide commonly used lacks photocurable groups, limiting its application in the field of photocuring. Currently, most methods for preparing photocurable polyimides first synthesize polyimide or polyamic acid polymers and then introduce photosensitive groups into the molecule via pendant groups on the polymer. This method has the advantage of rapidly producing photocurable polymers, but it cannot precisely control the content of photosensitive groups in the polymer. Summary of the Invention

[0004] The present invention provides an aromatic diamine monomer and a method for preparing the same, as well as a photosensitive polyimide and its preparation method and application. The aromatic diamine monomer provided herein can be used to prepare a photosensitive polyimide with a controllable ratio of photocurable groups. The photosensitive polyimide exhibits excellent solubility, is easily processed, and can be used as a polymer matrix for photocurable 3D printing. Directly introducing photosensitive groups into monomer side chains through molecular design allows for precise control of the photocurable properties of polymers using photoactive monomers, which is of great research significance.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides an aromatic diamine monomer containing an ethyl methacrylate group, having a structure shown in Formula I:

[0007]

[0008] In the formula I, R1 is H, CF3 or CH3; R2 is H, F, CH3 or CH2CH3.

[0009] Preferably, when R1 is H, R2 is H, F, CH3 or CH2CH3; when R1 is CF3, R2 is H; when R1 is CH3, R2 is CH3 or CH2CH3.

[0010] The present invention provides a method for preparing the aromatic diamine monomer described in the above technical solution, comprising the following steps:

[0011] Mixing an aromatic diamine, di-tert-butyl dicarbonate, a first catalyst, and a first organic solvent to carry out a substitution reaction to obtain compound 1;

[0012] Mixing the compound 1 with isocyanoethyl methacrylate, a second organic solvent, and a second catalyst to carry out a nucleophilic addition reaction to obtain compound 2;

[0013] The compound 2 is mixed with a solvent containing trifluoroacetic acid to carry out a nucleophilic substitution reaction to obtain an aromatic diamine monomer having a structure shown in Formula I;

[0014] The structure of the aromatic diamine is

[0015] The structure of compound 1 is

[0016] The structure of compound 2 is

[0017] Preferably, the molar ratio of the aromatic diamine to di-tert-butyl dicarbonate is 10:20-25.

[0018] Preferably, the molar ratio of the compound 1 to isocyanoethyl methacrylate is 2:4-6.

[0019] The present invention provides a photosensitive polyimide having a structure shown in Formula II:

[0020]

[0021] In the formula II, R1 is H, CF3 or CH3; R2 is H, F, CH3 or CH2CH3;

[0022] for

[0023] for

[0024]

[0025] The present invention provides a method for preparing the photosensitive polyimide described in the above technical solution, comprising the following steps:

[0026] The aromatic diamine monomer containing ethyl methacrylate groups described in the above technical solution or the aromatic diamine monomer containing ethyl methacrylate groups prepared by the preparation method described in the above technical solution, a commercial diamine monomer, a commercial dianhydride monomer, and a third organic solvent are mixed to carry out a copolymerization reaction to obtain a polyamic acid;

[0027] The polyamic acid, a dehydrating agent and a third catalyst are mixed to perform a chemical imidization reaction to obtain a photosensitive polyimide having a structure shown in Formula II;

[0028] The structure of the commercial diamine monomer is

[0029] The structure of the commercial dianhydride monomer is

[0030] The present invention provides the use of the photosensitive polyimide described in the above technical solution or the photosensitive polyimide prepared by the preparation method described in the above technical solution in the preparation of polyimide films or polyimide parts.

[0031] Preferably, the application includes: mixing the photosensitive polyimide, an organic solvent and a photoinitiator to obtain a polyimide solution; and curing the polyimide solution with ultraviolet light to obtain a polyimide film.

[0032] Preferably, the application includes: mixing the photosensitive polyimide, a reactive diluent, a photocrosslinker and a photoinitiator to obtain ink; and performing photocuring 3D printing on the ink to obtain a polyimide part.

[0033] The present invention provides an aromatic diamine monomer containing an ethyl methacrylate group, having a structure shown in Formula I. The aromatic diamine monomer provided by the present invention contains a photocurable ethyl methacrylate group. The monomer is copolymerized with a commercial diamine monomer and a commercial dianhydride monomer to obtain a photosensitive polyimide with a controllable ratio of photoactive groups (ethyl methacrylate groups). The photosensitive polyimide provided by the present invention has good solubility and is easy to process, and can be used as a substrate for photocurable 3D printing.

[0034] The present invention provides a method for preparing an aromatic diamine monomer containing ethyl methacrylate groups. The method is simple and requires only three steps to introduce photocurable ethyl methacrylate groups into a commercial monomer. In a specific embodiment of the present invention, the amino groups on both sides of the commercial aromatic diamine are protected with di-tert-butyl dicarbonate. Subsequently, a nucleophilic addition reaction occurs between the phenolic hydroxyl groups on the side groups and the isocyanate groups in isocyanoethyl methacrylate to introduce photocurable acrylate groups into the molecule. Finally, the amino groups are deprotected with trifluoroacetic acid to obtain the aromatic diamine monomer containing ethyl methacrylate groups.

[0035] The photosensitive polyimide obtained by copolymerizing the aromatic diamine monomer provided by the present invention with a commercial diamine monomer and a commercial dianhydride monomer has good solubility. This is because the aromatic diamine monomer of the present invention introduces a bulky side group into the photosensitive polyimide, breaking the tight stacking of the polymer and reducing its crystallization performance, thereby improving the solubility.

[0036] The photosensitive polyimide provided by the present invention is readily soluble in acetone and chloroform, as well as in N-vinylpyrrolidone, the diluent required for photocuring. The photosensitive polyimide exhibits excellent film-forming properties. UV curing yields a uniform and tough photocurable polyimide film with high mechanical and thermal properties, extremely low water absorption, and excellent dielectric properties.

[0037] The present invention can control the crosslinking degree of the photosensitive polyimide by adjusting the ratio of the photoactive groups (ethyl methacrylate groups), further accurately regulate the mechanical properties of the obtained parts, and solve the problem of unclear content of grafted photocurable groups in the existing method. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is the H NMR spectrum of compound 1 prepared in Example 1;

[0039] Figure 2 This is the H NMR spectrum of compound 2 prepared in Example 1;

[0040] Figure 3 This is the H-NMR spectrum of the aromatic diamine monomer containing ethyl methacrylate group having the structure shown in Formula III prepared in Example 1;

[0041] Figure 4 UV-Vis spectra of PI-0 and photosensitive PSPI;

[0042] Figure 5 XRD characterization diagrams of PI-0 and photosensitive PSPI;

[0043] Figure 6 FT-IR characterization of PSPI-100 before and after light curing;

[0044] Figure 7 is the gel fraction of PI-0 and light-cured UV-PSPI films;

[0045] Figure 8 FT-IR spectra of PI-0 and photocured UV-PSPI films;

[0046] Figure 9 XRD characterization of PI-0 and photocured UV-PSPI films;

[0047] Figure 10 Stress-strain curves (a) and tensile strength, elongation at break, and tensile modulus (b) of PI-0 and photocured UV-PSPI films;

[0048] Figure 11 TGA curves (a) and TMA curves (b) of PI-0 and photocured UV-PSPI films;

[0049] Figure 12 SEM images of the surface and tensile cross-section of PI-0 and photocured UV-PSPI films;

[0050] Figure 13 Transmittance (a), absorbance (b) and digital photos (c) of PI-0 and photocured UV-PSPI films;

[0051] Figure 14 The real part ε', imaginary part ε" and dielectric loss tanδ of the dielectric constant of PI-0 and photocured UV-PSPI films at different temperatures and frequencies;

[0052] Figure 15 This is a physical picture of the polyimide part obtained by light-curing 3D printing. DETAILED DESCRIPTION

[0053] The present invention provides an aromatic diamine monomer containing an ethyl methacrylate group, having a structure shown in Formula I:

[0054]

[0055] In formula I, R1 is H, CF3 or CH3; R2 is H, F, CH3 or CH2CH3.

[0056] In the present invention, when R1 is H, R2 is preferably H, F, CH3 or CH2CH3; when R1 is CF3, R2 is preferably H; when R1 is CH3, R2 is preferably CH3 or CH2CH3.

[0057] The present invention provides a method for preparing the aromatic diamine monomer described in the above technical solution, comprising the following steps:

[0058] Mixing an aromatic diamine, di-tert-butyl dicarbonate, a first catalyst, and a first organic solvent to carry out a substitution reaction to obtain compound 1;

[0059] Mixing the compound 1 with isocyanoethyl methacrylate, a second organic solvent, and a second catalyst to carry out a nucleophilic addition reaction to obtain compound 2;

[0060] The compound 2 is mixed with a solvent containing trifluoroacetic acid to carry out a nucleophilic substitution reaction to obtain an aromatic diamine monomer having a structure shown in Formula I;

[0061] The structure of the aromatic diamine is

[0062] The structure of compound 1 is

[0063] The structure of compound 2 is

[0064] In the present invention, an aromatic diamine, di-tert-butyl dicarbonate, a first catalyst, and a first organic solvent are mixed and subjected to a substitution reaction to obtain Compound 1. In the present invention, the aromatic diamine is preferably 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane. In the present invention, the molar ratio of the aromatic diamine to di-tert-butyl dicarbonate is preferably 10:20-25, more preferably 10:21. In the present invention, the first catalyst is preferably nano-ferrosoferric oxide. In the present invention, the ratio of di-tert-butyl dicarbonate to the first catalyst is preferably 21 mmol:0.2-0.4 g, more preferably 21 mmol:0.28 g. In the present invention, the first organic solvent is preferably anhydrous ethanol or methanol. In the present invention, the ratio of di-tert-butyl dicarbonate to the first organic solvent is preferably 21 mmol:40-100 mL, more preferably 21 mmol:60 mL.

[0065] In the present invention, the temperature of the substitution reaction is preferably room temperature; the time of the substitution reaction is preferably 6 to 15 hours, more preferably 12 hours. In the present invention, the atmosphere of the substitution reaction is preferably air atmosphere.

[0066] In the present invention, after the substitution reaction, the first catalyst is preferably removed by filtration using a 0.45 μm organic filter membrane, and the reaction liquid is spin-dried; the crude product is dissolved in ethyl acetate, washed with a saturated ammonium chloride solution to remove excess di-tert-butyl dicarbonate, and the liquids are separated and spin-dried to obtain Compound 1.

[0067] After obtaining compound 1, the present invention mixes the compound 1 with isocyanoethyl methacrylate, a second organic solvent and a second catalyst to carry out a nucleophilic addition reaction to obtain compound 2. In the present invention, the molar ratio of compound 1 and isocyanoethyl methacrylate is preferably 2:4 to 6, more preferably 2:5. In the present invention, the second organic solvent is preferably anhydrous acetone or ethyl acetate. In the present invention, the amount ratio of the compound 1 and the second organic solvent is preferably 10 mmol:30 to 60 mL, more preferably 10 mmol:50 mL. In the present invention, the second catalyst is preferably dibutyltin dilaurate (DBTL) or stannous octoate (SC). In the present invention, the amount ratio of the compound 1 and the second catalyst is preferably 10 mmol:0.05 to 0.3 g, more preferably 10 mmol:0.08 g.

[0068] In the present invention, mixing Compound 1 with isocyanoethyl methacrylate, a second organic solvent, and a second catalyst preferably includes: mixing isocyanoethyl methacrylate and a portion of the second organic solvent to obtain an isocyanoethyl methacrylate solution; mixing Compound 1 with the remaining second organic solvent to obtain a Compound 1 solution; dropwise adding the Compound 1 solution to the isocyanoethyl methacrylate solution, and then adding the second catalyst. In the present invention, the mixing is preferably performed in an ice bath. In the present invention, the Compound 1 solution is preferably added dropwise to the isocyanoethyl methacrylate solution at a rate of one drop per second.

[0069] In the present invention, the nucleophilic addition reaction preferably comprises: first reacting at room temperature for 0.5 to 3 hours, then heating to 35 to 60°C for 10 to 24 hours; more preferably, it comprises: first reacting at room temperature for 1 hour, then heating to 40°C for 12 hours. In the present invention, the nucleophilic addition reaction is preferably carried out in an argon atmosphere.

[0070] In the present invention, after the nucleophilic addition reaction, the resulting reaction system is preferably subjected to reduced pressure distillation to remove the organic solvent, and the compound 2 is purified by column chromatography. In the present invention, the eluents used in the column chromatography are preferably ethyl acetate and petroleum ether; the volume ratio of ethyl acetate to petroleum ether is preferably 1:6.

[0071] After obtaining compound 2, the present invention mixes compound 2 with a solvent containing trifluoroacetic acid and conducts a nucleophilic substitution reaction to obtain an aromatic diamine monomer having a structure represented by Formula I. In the present invention, the solvent containing trifluoroacetic acid is preferably a mixed solvent of trifluoroacetic acid and dichloromethane; the volume ratio of trifluoroacetic acid to dichloromethane in the mixed solvent of trifluoroacetic acid and dichloromethane is preferably 1:0.5-4, more preferably 1:1. In the present invention, the amount ratio of compound 2 to the solvent containing trifluoroacetic acid is preferably 5 mmol:20-40 mL, more preferably 5 mmol:30 mL.

[0072] In the present invention, the temperature of the nucleophilic substitution reaction is preferably room temperature; the time of the nucleophilic substitution reaction is preferably 1 to 4 hours, more preferably 2 hours. In the present invention, the atmosphere of the nucleophilic substitution reaction is preferably air atmosphere.

[0073] In the present invention, after the nucleophilic substitution reaction, a saturated NaHCO3 solution is preferably added to the obtained reaction system to adjust the pH value of the system to 8, and the liquid is separated. After the organic layer is collected and dehydrated, the solvent is removed by reduced pressure distillation to obtain an aromatic diamine monomer with a structure shown in Formula I.

[0074] The present invention provides a photosensitive polyimide having a structure shown in Formula II:

[0075]

[0076] In the formula II, R1 is H, CF3 or CH3; R2 is H, F, CH3 or CH2CH3;

[0077] for

[0078] for

[0079]

[0080] In the present invention, when R1 is H, R2 is preferably H, F, CH3 or CH2CH3; when R1 is CF3, R2 is preferably H; when R1 is CH3, R2 is preferably CH3 or CH2CH3.

[0081] In the present invention, in Formula II, x is the molar percentage of units containing ethyl methacrylate groups. In the present invention, x is preferably 2.5 to 50%, more preferably 5 to 10%. In the present invention, in Formula II, x + y = 1.

[0082] The present invention provides a method for preparing the photosensitive polyimide described in the above technical solution, comprising the following steps:

[0083] The aromatic diamine monomer containing ethyl methacrylate groups described in the above technical solution or the aromatic diamine monomer containing ethyl methacrylate groups prepared by the preparation method described in the above technical solution, a commercial diamine monomer, a commercial dianhydride monomer, and a third organic solvent are mixed to carry out a copolymerization reaction to obtain a polyamic acid;

[0084] The polyamic acid, a dehydrating agent and a third catalyst are mixed to perform a chemical imidization reaction to obtain a photosensitive polyimide having a structure shown in Formula II;

[0085] The structure of the commercial diamine monomer is

[0086] The structure of the commercial dianhydride monomer is

[0087] The present invention comprises mixing an aromatic diamine monomer containing ethyl methacrylate groups, a commercial diamine monomer, a commercial dianhydride monomer, and a third organic solvent, and performing a copolymerization reaction to obtain polyamic acid. In the present invention, the commercial diamine monomer is preferably 4,4'-diaminodiphenyl ether (ODA). In the present invention, the molar ratio of the aromatic diamine monomer containing ethyl methacrylate groups to the commercial diamine monomer is preferably 0.08-2.5:1.406-6.65, more preferably 0.114-0.35:2.5-3.22, and specifically preferably 0.08:3.22, 0.35:6.65, 0.114:1.406, 0.3:2.7, or 2.5:2.5. In the present invention, the commercial dianhydride monomer is preferably hexafluorodianhydride (6FDA). In the present invention, the molar ratio of the aromatic diamine monomer containing ethyl methacrylate groups to the commercial dianhydride monomer is preferably 0.08-2.5:2-9, more preferably 0.114-0.35:4-7, and specifically preferably 0.08:4.3, 0.35:9, 0.114:2, 0.3:4, or 2.5:7. In the present invention, the third organic solvent is preferably N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide. In the present invention, the usage ratio of the aromatic diamine monomer containing ethyl methacrylate group and the third organic solvent is preferably 0.08-2.5 mmol:14-31.5 mL, more preferably 0.114-0.35 mmol:14.13-30 mL, specifically preferably 0.08 mmol:14.36 mL, 0.35 mmol:31.5 mL, 0.114 mmol:14.13 mL, 0.3 mmol:14 mL or 2.5 mmol:30 mL.

[0088] In the present invention, the mixing of the aromatic diamine monomer containing ethyl methacrylate groups, the commercial diamine monomer, the commercial dianhydride monomer, and the third organic solvent preferably comprises: mixing the aromatic diamine monomer containing ethyl methacrylate groups, the commercial diamine monomer, and the third organic solvent, and then adding the commercial dianhydride monomer in batches. In the present invention, the mixing is preferably performed in an ice bath.

[0089] In the present invention, the temperature of the copolymerization reaction is preferably room temperature; the time of the copolymerization reaction is preferably 8 to 12 hours, more preferably 10 hours.

[0090] After obtaining the polyamic acid, the present invention mixes the polyamic acid with a dehydrating agent and a third catalyst to undergo a chemical imidization reaction to obtain a photosensitive polyimide having the structure represented by Formula II. In the present invention, the dehydrating agent is preferably acetic anhydride, more preferably anhydrous acetic anhydride. In the present invention, the molar ratio of the total amino group molar amount of the aromatic diamine monomer containing ethyl methacrylate groups and the commercial diamine monomer to the dehydrating agent is preferably 1:0.5-1, more preferably 1:0.66. In the present invention, the third catalyst preferably comprises triethylamine or pyridine, more preferably anhydrous triethylamine or anhydrous pyridine. In the present invention, the molar ratio of the dehydrating agent to the third catalyst is preferably 1:1. In the present invention, the mixing is preferably carried out at room temperature. In the present invention, the chemical imidization reaction temperature is preferably 90-120°C, more preferably 100°C, and the chemical imidization reaction time is preferably 8-12 hours, more preferably 10 hours.

[0091] In the present invention, after the chemical imidization reaction, the obtained reaction solution is preferably poured into ethanol to precipitate an off-white flocculent solid; the polymer is washed with ethanol and the solvent is removed by centrifugation; the washing is repeated until the supernatant is colorless and transparent, and the obtained solid is vacuum-dried at 100° C. to obtain a photosensitive polyimide with a structure represented by Formula II.

[0092] The present invention provides the use of the photosensitive polyimide described in the above technical solution or the photosensitive polyimide prepared by the preparation method described in the above technical solution in the preparation of polyimide films or polyimide parts.

[0093] In the present invention, the application preferably includes: mixing the photosensitive polyimide, an organic solvent, and a photoinitiator to obtain a polyimide solution; and subjecting the polyimide solution to ultraviolet light curing to obtain a polyimide film. In the present invention, the organic solvent is preferably N-methylpyrrolidone, N,N-dimethylformamide, or N,N-dimethylacetamide. In the present invention, the photoinitiator is preferably phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator 819). In the present invention, the mass ratio of the photosensitive polyimide, organic solvent, and photoinitiator is preferably 0.25:3.5-5:0.08-0.1, more preferably 0.25:4:0.086. In the present invention, the mixing is preferably ultrasonic mixing. In the present invention, the ultraviolet light curing preferably includes: pouring the polyimide solution onto a substrate and subjecting it to ultraviolet light curing. In the present invention, the power of the UV lamp for UV curing is preferably 15 to 30 W, more preferably 20 W; the wavelength of the UV lamp is preferably 405 nm; and the time for UV curing is preferably 2 to 5 minutes, more preferably 3 minutes.

[0094] The present invention preferably further comprises heat treatment, water immersion and drying in sequence after the UV curing. In the present invention, the heat treatment preferably comprises: heating at a rate of 1°C / min, heating at 80°C, 180°C, 280°C and 290°C for 120min, 120min, 120min and 10min respectively. In the present invention, the water immersion is preferably carried out in hot water, and the temperature of the hot water is preferably 70°C. The present invention allows the polymer film to fall off naturally through water immersion. In the present invention, the drying is preferably vacuum drying; the drying temperature is preferably 120°C; and the drying time is preferably 10h.

[0095] In the present invention, the thickness of the polyimide film is preferably 30 to 40 μm.

[0096] In the present invention, the application preferably includes: mixing the photosensitive polyimide, a reactive diluent, a photocrosslinker, and a photoinitiator to obtain an ink; and subjecting the ink to photocuring 3D printing to obtain a polyimide part. In the present invention, the reactive diluent is preferably N-vinyl pyrrolidone; the photocrosslinker is preferably trimethylolpropane triacrylate (TMPTA); and the photoinitiator is preferably photoinitiator 819. In the present invention, the mass ratio of the photosensitive polyimide, reactive diluent, photocrosslinker, and photoinitiator is preferably 40 to 50:40 to 50:8:2. In the present invention, the photocuring 3D printing is preferably cured under ultraviolet light conditions; the wavelength of the ultraviolet light is preferably 405 nm.

[0097] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0098] Example 1

[0099] (1) Compound 1, a commercial monomer protected by di-tert-butyl dicarbonate, has the following structural formula:

[0100]

[0101] The preparation method of compound 1 is:

[0102] 10 mmol of 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (6FOHA), 21 mmol of di-tert-butyl dicarbonate (Boc anhydride), and 0.28 g of nano-ferrosoferric oxide were added to 60 mL of anhydrous ethanol and reacted at room temperature for 12 hours. After the reaction was confirmed to be complete by thin-layer chromatography (TLC), the nano-ferrosoferric oxide was removed by filtration using a 0.45 μm organic filter membrane, and the reaction solution was spin-dried. The crude product was dissolved in ethyl acetate and washed with saturated ammonium chloride solution to remove excess Boc anhydride. After separation, the solution was spin-dried to obtain compound 1 as a white solid with a yield of 96.8%.

[0103] Characterization results of compound 1: 1 HNMR (400MHz, DMSO-d6) δ10.32(s,2H),7.84(s,2H),7.77(s,2H),6.86(d,J=8.7Hz,2H),6.79(d,J=8.4Hz,2H),1.42(s,18H); 13 C NMR (101MHz, DMSO-d6) δ153.11,148.06,126.58,125.58,123.19,122.20,115.05,79.98,28.45.

[0104] IR(KBr,cm -1 ):3427,3379,3280,3108,2935,2874,2754,2599,2291,2171,2109,1854,1709,1673,1609,1543,1518,1439,1394,1370,1320,1254,1162,1132,1080,1056,997,962,887,850,810,776,736,714,638,548,528,470.

[0105] HRMS:C 25 H 28 F6N2NaO6 for[M+Na] + , calculated 589.1744, found 589.1740.

[0106] (2) Compound 2 containing a photocurable acrylate group was prepared, and the structural formula is as follows:

[0107]

[0108] The preparation method of compound 2 is:

[0109] 25 mmol of isocyanoethyl methacrylate was added to 30 mL of anhydrous acetone. A mixture of 10 mmol of the compound 1 and 20 mL of anhydrous acetone was added dropwise to the flask using a constant pressure dropping funnel under ice bath conditions. 0.08 g of dibutyltin dilaurate (DBTL) was added to catalyze the reaction. The reaction was allowed to react at room temperature for 1 h, then the temperature was raised to 40°C for 12 h. The entire reaction was carried out under argon protection. After the reaction was completed as determined by TLC analysis, the reaction solvent was removed by distillation under reduced pressure, and the compound 2 was purified by column chromatography (eluent: ethyl acetate: petroleum ether = 1:6 (V / V)) to obtain a light yellow solid compound 2 with a yield of 62.4%.

[0110] Characterization results of compound 2: 1 H NMR (400MHz, DMSO-d6) δ8.49(s,2H),7.96–7.86(m,4H),7.22(d,J=8.8Hz,2H),6.89(dd,J=8.5,3.0Hz,2H),6.06(t, J=1.5Hz,2H),5.67–5.63(m,2H),4.14(t,J=5.5Hz,4H),3.34(q,J=5.6Hz,4H),1.85(t,J=1.3Hz,6H),1.38(s,18H); 13 C NMR(101MHz,DMSO-d6)δ167.11,153.96,153.08,142.35,136.33,131.37,129.03,126.49,125 .26,123.37,123.12,128.90–119.88(m),80.38,64.88–63.79(m),63.62,40.19,28.47,18.46.

[0111] IR(KBr,cm -1):3369,2982,2934,1722,1638,1604,1535,1477,1467,1433,1394,1369,1318,1299,1236,1158,1050,1030,1010,981,966,918,891,816,770,742,723,647,595,463.

[0112] HRMS:C 39 H 46 F6N4NaO 12 for[M+Na] + , calculated 899.2909, found 899.2934.

[0113] (3) Preparation of an aromatic diamine monomer containing an ethyl methacrylate group having a structure shown in Formula III:

[0114]

[0115] The preparation method of the aromatic diamine monomer containing ethyl methacrylate group is as follows:

[0116] 5 mmol of the compound 2 was added to 30 mL of a mixed solution of trifluoroacetic acid:dichloromethane = 1:1 (V / V). A bubbler was connected to the bottle mouth to monitor the reaction and stirred at room temperature for 2 h. After no bubbles escaped from the bubbler, TLC was used to confirm. After completion of the reaction, saturated NaHCO3 solution was added to the flask in small amounts and multiple times. The system was adjusted to pH = 8 for separation. The organic layer was collected and dehydrated, and the solvent was removed by distillation under reduced pressure to obtain an aromatic diamine monomer containing an ethyl methacrylate group having the structure represented by Formula III, with a yield of 83.6%.

[0117] Characterization results of the aromatic diamine monomer containing ethyl methacrylate groups having the structure shown in Formula III: 1 H NMR (400MHz, DMSO-d6) δ7.79(t,J=5.8Hz,2H),6.93(d,J=8.6Hz,2H),6.73(s,2H),6.46(d,J=7.9Hz,2H),6.08–6. 03(m,2H),5.65(p,J=1.6Hz,2H),5.03(s,4H),4.14(t,J=5.5Hz,4H),3.32(q,J=5.6Hz,4H),1.86(t,J=1.3Hz,6H); 13C NMR(101MHz,DMSO-d6)δ167.16,154.64,141.05,138.20,136.35,130.18,126.49,124.7 7(q,J=287.0,286.6Hz),122.68,117.55,117.46,64.53–63.82(m),63.61,40.25,18.47.

[0118] IR(KBr,cm -1 ):3460,3361,3064,2962,2934,1724,1700,1630,1549,1515,1439,1405,1371,1321,1297,1256,1240,1219,1157,1133,1038,1003,977,957,942,864,815,792,767,742,722,704,654,632,542,506,464.

[0119] HRMS:C 29 H 30 F6N4NaO8 for[M+Na] + , calculated 699.1860, found 699.1874;

[0120] Example 2

[0121] Preparation of a photosensitive polyimide having a structure shown in Formula IV:

[0122]

[0123] The preparation method of the photosensitive polyimide is:

[0124] To a 50 mL three-necked flask equipped with mechanical stirring and under an argon atmosphere, 3.22 mmol of 4,4'-diaminodiphenyl ether (ODA) and 0.08 mmol of an aromatic diamine monomer containing an ethyl methacrylate group (Formula III) were added. The mixture was thoroughly dissolved in 6.5 mL of anhydrous N-methylpyrrolidone (NMP). Once completely dissolved, the flask was cooled in an ice bath for 10 min. 4.3 mmol of hexafluorodianhydride (6FDA) was added in four portions, each rinsed with a small amount of NMP. After the final addition of 6FDA, the remaining NMP was added, for a total of 14.36 mL of NMP. The resulting mixture was allowed to react in an ice bath for an additional hour, after which the ice bath was removed and the reaction continued at room temperature for 10 hours. Subsequently, a mixed solution of 2.18 mL of anhydrous acetic anhydride and 3.17 mL of anhydrous triethylamine was added to the system via a constant pressure dropping funnel at room temperature. After the addition was complete, the temperature was raised to 100°C and the reaction continued for 10 hours. After the reaction, the resulting reddish-brown solution was poured into ethanol, resulting in the precipitation of an off-white, flocculent solid. The polymer was then washed with ethanol and the solvent removed by centrifugation. Washing was repeated until the supernatant became colorless and transparent. The resulting solid was then vacuum-dried at 100°C to yield a photosensitive polyimide (FMADA) having the structure represented by Formula IV. The molar percentage of units containing ethyl methacrylate groups in the photosensitive polyimide was 2.5%, designated PSPI-2.5. The number average molecular weight was 5000 g / mol.

[0125] Characterization results of the photosensitive polyimide having the structure shown in Formula IV: 1 HNMR(400MHz, DMSO-d6)δ8.16(dd,J=8.1,3.2Hz,2H),7.94(d,J=7.9Hz,2H),7.74(s,2H),7.51–7.43(m,4H),7.26–

[0126] 7.18 (m, 4H). 13 C NMR (101MHz, DMSO-d6) δ166.73,166.60,156.61,137.84,136.32,133.58,133.18,129.87,127.69,124.90,124.10,119.63.

[0127] IR(KBr,cm -1):3491,3116,3079,2927,2726,2444,2198,2082,2017,1944,1890,1785,1728,1624,1597,1501,1436,1377,1296,1245,1209,1192,1171,1145,1112,1015,984,963,913,879,862,846,829,798,777,755,745,722,674,636,606,592,566,545,518,449.

[0128] Example 3

[0129] The preparation method was basically the same as that in Example 2, except that the amount of ODA was adjusted to 6.65 mmol, the amount of the aromatic diamine monomer containing ethyl methacrylate groups having the structure represented by Formula III was adjusted to 0.35 mmol, the amount of 6FDA was adjusted to 9 mmol, and the total amount of NMP used in the entire process was adjusted to 31.5 mL; the amount of anhydrous acetic anhydride was adjusted to 4.62 mL, and the amount of anhydrous triethylamine was adjusted to 6.72 mL. A photosensitive polyimide having a molar percentage of units containing ethyl methacrylate groups of 5% was obtained, which was designated as PSPI-5.

[0130] Example 4

[0131] The preparation method was basically the same as that in Example 2, except that the amount of ODA was adjusted to 1.406 mmol, the amount of the aromatic diamine monomer containing ethyl methacrylate groups having the structure represented by Formula III was adjusted to 0.114 mmol, the amount of 6FDA was adjusted to 2 mmol, and the total amount of NMP used in the entire process was adjusted to 14.13 mL; the amount of anhydrous acetic anhydride was adjusted to 1.00 mL, and the amount of anhydrous triethylamine was adjusted to 1.46 mL. A photosensitive polyimide having a molar percentage of units containing ethyl methacrylate groups of 7.5% was obtained, which was recorded as PSPI-7.5.

[0132] Example 5

[0133] The preparation method was basically the same as that in Example 2, except that the amount of ODA was adjusted to 2.7 mmol, the amount of the aromatic diamine monomer containing ethyl methacrylate groups having the structure represented by Formula III was adjusted to 0.3 mmol, the amount of 6FDA was adjusted to 4 mmol, and the total amount of NMP used in the entire process was adjusted to 14 mL; the amount of anhydrous acetic anhydride was adjusted to 1.98 mL, and the amount of anhydrous triethylamine was adjusted to 2.88 mL. A photosensitive polyimide having a molar percentage of units containing ethyl methacrylate groups of 10% was obtained, which was designated as PSPI-10.

[0134] Example 6

[0135] The preparation method was basically the same as that in Example 2, except that the amount of ODA was adjusted to 2.5 mmol, the amount of the aromatic diamine monomer containing ethyl methacrylate groups having the structure represented by Formula III was adjusted to 2.5 mmol, the amount of 6FDA was adjusted to 7 mmol, and the total amount of NMP used in the entire process was adjusted to 30 mL; the amount of anhydrous acetic anhydride was adjusted to 3.3 mL, and the amount of anhydrous triethylamine was adjusted to 4.8 mL. A photosensitive polyimide having a molar percentage of units containing ethyl methacrylate groups of 50% was obtained, which was designated as PSPI-50.

[0136] Comparative Example 1

[0137] The preparation method is basically the same as that of Example 2, except that the aromatic diamine monomer containing ethyl methacrylate group having the structure represented by Formula III is not added. The obtained polyimide is recorded as PI-0.

[0138] Comparative Example 2

[0139] The preparation method was substantially the same as that in Example 2, except that the amount of the aromatic diamine monomer containing ethyl methacrylate groups having the structure represented by Formula III was adjusted to 3.5 mmol, the amount of 6FDA was adjusted to 4.5 mmol, and the total amount of NMP used in the entire process was adjusted to 24.75 mL; the amount of anhydrous acetic anhydride was adjusted to 5.28 mL, and the amount of anhydrous triethylamine was adjusted to 7.68 mL. A photosensitive polyimide having a molar percentage content of units containing ethyl methacrylate groups of 100% was obtained, which was designated PSPI-100.

[0140] Application Examples

[0141] Preparation of photocurable polyimide film

[0142] 0.25 g of the polyimide prepared in Examples 2 to 6 and Comparative Example 1 was weighed respectively, and dissolved in 4 g of N-methylpyrrolidone to obtain a polyimide solution; 0.086 g of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (photoinitiator 819) was added to the polyimide solution and completely dissolved by ultrasound. The polymer solution was centrifuged to allow the insoluble matter to settle at the bottom; the solution was then poured onto a 76 mm × 26 mm glass slide, placed in a muffle furnace, and irradiated with an ultraviolet lamp with a wavelength of 405 nm and a power of 20 W for 3 min; after the irradiation was completed, the temperature was increased at a rate of 1 ° C / min, and heated at 80 ° C, 180 ° C, 280 ° C, and 290 ° C for 1 min, respectively. 20min, 120min, 120min and 10min; after the muffle furnace is cooled to room temperature, the glass slide is immersed in 70°C hot water, the polymer film falls off naturally, and the film is dried in a vacuum drying oven at 120°C for 10h to remove moisture to obtain a photocurable polyimide film having a thickness of 35 to 37μm, recorded as UV-PSPI-x, where x represents the molar percentage of the unit containing ethyl methacrylate groups in the polyimide (the photocurable polyimide films corresponding to Examples 2 to 6 and Comparative Example 1 are UV-PSPI-2.5, UV-PSPI-5, UV-PSPI-7.5, UV-PSPI-10, UV-PSPI-50, and PI-0 films, respectively).

[0143] Test Example 1 Characterization of light transmittance of polyimide

[0144] Figure 4 The following are UV-visible absorption spectra of photosensitive polyimides in NMP. The results show that PI-0 has a maximum absorption peak at 265 nm, while the maximum absorption peaks of photosensitive polyimide PSPI-5 and PSPI-10 are at 272 nm and 264 nm, respectively. This indicates that the introduction of photosensitive groups into the polymer does not significantly affect the UV absorption wavelength of the polymer. The C=O group in the polyimide structure possesses a π-electron chromophore, and the n→π* transition results in an absorption peak in the near-UV region. In practical applications, photosensitive polyimides require the use of a photoinitiator, and the polymer and photoinitiator compete for UV light absorption. Based on the absorption peak position of the photosensitive polymer, photoinitiator 819, which absorbs at a wavelength of 405 nm, was selected. When the polymer solution was illuminated with a UV lamp at a wavelength of 405 nm, photoinitiator 819 underwent homolytic cleavage to generate free radicals, which subsequently opened the carbon-carbon double bonds of the methacrylates, promoting polymerization. The peak position of the ultraviolet spectrum of photosensitive polyimide plays a key role in the selection of irradiation wavelength and photoinitiator.

[0145] Test Example 2 XRD Characterization of Polyimide

[0146] The photosensitive polyimide was characterized by XRD. Figure 5 As shown in the figure, all photosensitive polyimides exhibit a broad peak near 2θ = 15.2°, indicating poor polymer crystallinity and amorphous state. The peak of the photosensitive polyimide PSPI-7.5 is relatively sharp, suggesting some crystallinity. Overall, the synthesized photosensitive polyimide does not exhibit good crystallinity, which would make subsequent processing difficult.

[0147] Test Example 3 Polyimide Solubility Test

[0148] In 3D printing, the ink used in fused deposition modeling (FDM) 3D printing is a filamentous material that is molten at high temperatures, while the ink used in direct writing (DIW) 3D printing must be self-supporting. Both methods utilize the principle of polymer shear thinning when squeezing the ink from a needle, making them capable of processing highly viscous molten polymers and polymer solutions with high solids content. However, in stereolithography 3D printing, the ink must quickly spread across the platform after the previous layer has cured, allowing for the next light-curing step. Therefore, the ink used must have a lower viscosity. Furthermore, the polymer must be fully soluble in the solvent and reactive diluent, and the larger the proportion of the polymer matrix, the better. Therefore, the molecular weight of the polymer generally used is approximately 4000 to 6000 g / mol. Reducing the molecular weight increases its solubility and reduces the viscosity of the dissolved ink, making it easier to process. The number average molecular weight of the photosensitive polyimide prepared by the present invention is 5000 g / mol, and the solubility of PI-0 and photosensitive polymers PSPI-5, PSPI-10, and PSPI-50 in different solutions at 25°C was explored. The results are shown in Table 1. Test method: 5 mg of fully dried photosensitive polyimide was weighed, added to 1 mL of solvent, and its dissolution at room temperature was observed. High-boiling point aprotic solvents such as NMP, N,N-dimethylformamide (DMF) and photocurable active diluents N-vinylpyrrolidone (NVP), N-vinylformamide (NVF), polyethylene glycol diacrylate (PEGDA) and commonly used polar solvents such as toluene, acetone, tetrahydrofuran, and chloroform were selected to qualitatively analyze the changes in the solubility of the polymer before and after the introduction of photosensitive side groups.

[0149] PI-0 and photosensitive PSPI have excellent solubility in the high-boiling-point aprotic solvents NMP and DMF. Among the UV-curable reactive diluents NVP, NVF, and PEGDA required for photocurable 3D printing, photosensitive PSPI has better solubility than PI-0. The solubility of photosensitive PSPI in the three solvents is ranked as NVP > NVF > PEGDA, and the solubility of the polymer gradually increases with increasing photosensitive diamine monomer content. Photosensitive PSPI also has better solubility than PI-0 in commonly used polar solvents. Photosensitive PSPI has good solubility in chloroform, followed by acetone, tetrahydrofuran, and toluene. The present invention introduces large system side groups containing photocurable groups into the polyimide, effectively increasing the solubility of the polymer. The prepared photosensitive polyimide also has good solubility in reactive diluents, demonstrating promising application prospects in the field of photocuring.

[0150] Table 1 Solubility properties of PI-0 and photosensitive polymers PSPI-5, PSPI-10, and PSPI-50

[0151]

[0152] In Table 1, the experiments were performed at 25°C. ++: Completely soluble, +-: Partially soluble, -: Almost insoluble. NMP: N-methylpyrrolidone, DMF: N,N-dimethylformamide, NVP: N-vinylpyrrolidone, NVF: N-vinylformamide, PEGDA: polyethylene glycol diacrylate, Toluene: Toluene, Acetone: Acetone, THF: Tetrahydrofuran, CHCl3: Chloroform.

[0153] Test Example 4: Polyimide photosensitivity test

[0154] In order to determine the photocuring ability of the photosensitive polyimide, its photosensitivity was tested. The double bond infrared peak cannot be clearly observed in the infrared image of the polymer, so PSPI-100 with a photosensitive monomer content of 100% was synthesized and the photosensitivity of the polymer was tested. Take 0.05g of photosensitive polyimide PSPI-100, dissolve it in 2gNMP, and add 0.041g of photoinitiator 819 to prepare it into a photosensitive polymer solution. Pour the solution onto a glass slide, and after leveling, irradiate it with an ultraviolet lamp with a wavelength of 405nm for 3 minutes, and then dry the solvent in a vacuum drying oven at 60°C to obtain a photocurable polymer film UV-PSPI-100. The infrared spectra of the polymer before and after irradiation are shown as follows: Figure 6 As shown. It can be seen that the polymer and film have a peak at 1621 cm -1 The peak at has obvious intensity changes, which proves that PSPI can be photocured by photoinitiator 819 under ultraviolet light, indicating the application potential of photosensitive polyimide in the field of photocuring.

[0155] Gel fraction test:

[0156] Test method: Weigh W1 of UV-PSPI-x photocurable polyimide film and extract it in a Soxhlet extractor using NMP as the solvent. After 12 hours of extraction, dry the remaining film in a vacuum drying oven at 120°C for 10 hours. Record the remaining film mass as W2. The percentage of the remaining film mass to the initial film mass is the gel fraction. The gel fraction is calculated as shown in Equation (1).

[0157]

[0158] The gel fraction of the polyimide film was calculated according to formula (1). The results are as follows: Figure 7 As shown. The results show that PI-0 is readily soluble in NMP. The higher the amount of photosensitive diamine monomer added to the photosensitive polymer, the higher the gel fraction of the photocurable polyimide film. This indicates that, using the same preparation method, a higher content of photosensitive double bonds in the system leads to a tighter crosslinked structure when irradiated with UV light. Moderate crosslinking helps improve mechanical strength and thermal properties. These results indicate that all UV-PSPI-x polyimide films are crosslinked, and the degree of crosslinking increases with increasing double bond content in the system.

[0159] Test Example 5 Structural Characterization of Photocured PI Film

[0160] (1) Infrared characterization of photocurable PI films

[0161] The infrared spectrum of polyimide after light curing is as follows Figure 8 As shown in the figure, there are several obvious groups of polyimide characteristic peaks, located at 1782cm -1 The peak at 1725 cm is the asymmetric stretching vibration peak of the C=O bond. -1 The position is the symmetrical stretching vibration peak of C=O bond. -1 The stretching vibration peak of the CN bond is 721cm -1 The presence of these peaks indicates that after UV irradiation, the polymer is still polyimide and no other changes have occurred. -1 The disappearance of the hydroxyl peak at 37° indicates that the prepared photocurable film has been fully imidized.

[0162] (2) XRD characterization of photocured PI film

[0163] Figure 9XRD characterization of the photocured polyimide films revealed that all PI films exhibited an amorphous state. The photocured PI films and the PI-0 film exhibited similar molecular stacking morphologies, with a broad peak between 15° and 16° and another, less pronounced, broad peak between 25° and 26°. The photocured films UV-PSPI-7.5 and UV-PSPI-10 exhibited a small peak at 16°, indicating that the more photosensitive monomers added, the denser the crosslinking network, and the more likely it is to form a regular structure.

[0164] Test Example 6 Mechanical Properties of Photocured PI Film

[0165] Mechanical properties of PI-0 film and photocurable polyimide film were tested using an EZ-Test SHIMADZU universal materials testing machine. Testing conditions: Room temperature, 1 mm / min. Test method: Polymer film was cut into rectangular strips measuring 40 mm x 5 mm and tensile tested on the testing machine. At least five specimens were tested for each sample group, and the average of the appropriate data was calculated.

[0166] according to Figure 10 As shown in (a), adding a small amount of photosensitive diamine monomer can improve the mechanical properties of the photocurable film. When the addition amount is 5%, the tensile strength reaches the maximum, reaching 110MPa. When the monomer addition amount is further increased, the tensile strength will decrease. The tensile strength of UV-PSPI-10 is lower than that of PI-0 film. Figure 10 (b), the elongation at break of UV-PSPI-5 reached 10.9%, the highest among all films. This result shows that moderate cross-linking is beneficial to the improvement of the mechanical strength of the polymer, among which UV-PSPI-5 has the highest strength and toughness. From the perspective of material application, a copolymer with the best comprehensive mechanical properties has been found, which can be used as a polymer matrix for photocuring 3D printing to formulate ink. What is more special is that UV-PSPI-7.5 has the lowest elongation at break and the highest tensile modulus, indicating that the photosensitive polymer film has greater rigidity, which is presumably caused by crystallization. The crystallinity of PSPI-7.5 copolymer and UV-PSPI-7.5 is the best among all materials, which leads to a decrease in elongation at break and an increase in tensile modulus.

[0167] Test Example 7 Thermal Properties of Photocurable PI Film

[0168] Thermal stability is one of the important application parameters of polyimide films. All polyimide films were tested for thermal weight loss and thermal dimensional stability. The results are as follows: Figure 11 and as shown in Table 2.

[0169] Thermogravimetric Analysis (TGA): Instrument model: NETZSCH-STA449F3 Synchronous Thermal Analyzer. Test conditions: Nitrogen atmosphere, heating from 25°C to 800°C at a rate of 10°C / min. Test method: 3-5 mg of sample was placed in an alumina crucible and tested. Thermal stability was measured based on the change in mass.

[0170] Thermomechanical Analyzer (TMA): Instrument model: TMAQ400EM. Test conditions: Tensile test mode, preload force 0.05N. Test method: Heating at a rate of 5°C / min in a nitrogen flow to 300°C, then holding for 30 minutes and cooling to room temperature to eliminate thermal history. A second run was then initiated, heating at a rate of 5°C / min to 400°C, and the average CTE value was obtained.

[0171] according to Figure 11 (a) shows that when the content of added photosensitive diamine monomer is 2.5%, the thermal stability of the photocurable polyimide film is higher than that of the PI-0 film. When the content of photosensitive diamine monomer continues to increase, the thermal stability of the film continues to decrease. Due to the presence of ester groups and -NH- groups in the photosensitive polymer that are unstable at high temperatures, the thermal stability is worse than that of PI-0. According to the data in Table 2, UV-PSPI-2.5 has the best thermal performance, with a residual amount of 54% at 800°C. The carbon residue rates of other photocurable polyimide films are higher than that of PI-0 film, but the temperature of 5% thermal weight loss (T d5％ ) decreased significantly, and the T d5％ Compared with PI-0, it dropped by 110℃. Figure 13 (c) The polymer film exhibits a unique black color and can be used in the optoelectronic field to prevent light from damaging the circuit. Further testing of its coefficient of thermal expansion (CTE) shows the following results: Figure 11 This test can measure the glass transition temperature (T g ), which are listed in Table 2. According to the test results, the T g The relationship between the thermal expansion coefficient and the diamine monomer content is not linear, which may be due to the different molecular weights of the polymers produced in different batches. In the high-elastic range of 300-320°C, the thermal expansion coefficient of PI-0 is 66.35μm / °C, while that of UV-PSPI-5 is reduced to 48.69μm / °C. UV-PSPI-10 has the lowest thermal expansion coefficient, at 38.37μm / °C. This result also indirectly supports the formation of a cross-linked structure in the photosensitive polyimide film, making it less susceptible to deformation and having better overall thermal dimensional stability than PI-0.

[0172] Table 2 Thermal performance data of PI-0 and light-cured UV-PSPI films

[0173]

[0174] Test Example 8 Morphology Characterization of Photocured PI Film

[0175] like Figure 12 Shown are the surface morphology and tensile cross-sectional morphology of a photocured polyimide film. Instrument model: JEOL JSM-IT200(LA) desktop scanning electron microscope. Test conditions: Room temperature, test voltage 5.0 kV. Test method: The polymer film was mounted on a sample stage with the surface or tensile cross-sectional surface facing up. A gold coating was applied for 15 seconds, and the surface and tensile cross-sectional morphology of the polymer film were observed.

[0176] Scanning electron microscopy results show that the film's surface is relatively smooth, with occasional scratches and impurities, but overall it is relatively uniform. When a polymer film breaks under tension, the PI-0 cross-section is the smoothest, while the photocured film's tensile cross-section is relatively rough, with an uneven fracture surface. PI-0 is a linear polymer, and it breaks when the polymer backbone reaches its limit of tensile strength, a result of changes in backbone bond length, resulting in a relatively smooth cross-section. In photocured polyimide films, however, the short-chain structures in the cross-linked network become stress concentration points and are the first to generate microcracks. The stress concentration effect causes defects in these areas of the film, which then spreads to the entire material, causing fracture, resulting in a relatively rough cross-section.

[0177] Test Example 9 Characterization of Transmittance and Absorbance of Photocured PI Film

[0178] like Figure 13 As shown in (c), the photocurable polyimide film prepared by the present invention has a unique black color. The color of the PI film is related to the charge transfer complex (CTC) formed between the electron-donating diamine monomer and the electron-accepting dianhydride monomer. Usually, the polyimide films prepared are yellow. In order to obtain a colorless and transparent PI film, the formation of CTC in the film can be weakened. Conversely, strengthening the formation of CTC in the film will deepen the color of the polymer film. Increasing the electron density of the diamine unit and ensuring the presence of a conjugated molecular skeleton for electron transfer in the molecule are effective ways to enhance the formation of CTC. Nitrogen-containing diamines have electron-rich properties and are widely used to adjust the color of PI films. The photosensitive diamine monomer of the present invention contains an -NH- electron-rich group, and after ultraviolet light irradiation, the photosensitive polymer undergoes a polymerization reaction, and there is a conjugated structure with alternating single and double bonds, which promotes the formation of CTC in the photosensitive polyimide film. In the process of forming CTC between or within polyimide molecules, visible light is strongly absorbed, thereby deepening the color of the polyimide film, changing it from the commonly seen yellow-brown to black. As Figure 13As shown in (c), the films with added photosensitive diamine monomers are all black and almost opaque, and it is impossible to judge the effect of the amount of monomer added on the color of the photocurable film with the naked eye. Figure 13 As shown in (a) and (b), the film thickness is between 33 and 36 μm. As can be seen from the figure, the introduction of photosensitive diamine monomers into polyimide greatly reduces the optical transmittance of the film. In the wavelength range of 250 to 650 nm, all photocurable polyimide films are almost opaque. In the wavelength range of 650 to 800 nm, the film with the highest transmittance is UV-PSPI-10, followed by UV-PSPI-2.5, UV-PSPI-5 and UV-PSPI-7.5. Even the UV-PSPI-10 film with the highest transmittance only shows a transmittance of 7.15% at 800 nm. This result shows that the transmittance of films with an added monomer content of 2.5% and 10% is higher than that of films with an added content of 5% and 7.5%. Figure 13 The results of (b) also show that UV-PSPI-5 and UV-PSPI-7.5 have the strongest absorption of ultraviolet light and therefore have the lowest transmittance.

[0179] Test Example 10 Dielectric Properties and Water Absorption of Photocured PI Film

[0180] Previous research on the dielectric constant of polyimides has primarily focused on reducing it. However, due to polyimide's excellent thermal stability, mechanical properties, and good molecular design, numerous studies have also explored molecular design to achieve intrinsically high-dielectric-constant polyimide dielectrics that combine thermal stability and dielectric properties. Polarization in dielectric materials includes electronic polarization, atomic polarization, dipole polarization, ionic polarization, and interfacial polarization. The more polarization types a dielectric possesses, the higher the molar polarizability, leading to a larger dielectric constant. Analysis of the structure of photosensitive polyimide reveals that methyl groups disrupt the close packing of molecular chains, thereby increasing free volume and reducing the dielectric constant. Carbonyl groups, acting as permanent dipoles, increase dipole polarization, resulting in a higher dielectric constant. Hexafluoroisopropyl groups similarly disrupt the close packing of molecular chains, reducing the density of polar groups. Their strong electron-withdrawing effect also reduces electronic polarization, resulting in a lower dielectric constant. Para-linked ether bonds facilitate effective orientation under alternating electric fields, resulting in a higher dielectric constant. The dielectric constant of the present invention is better than that of the PDMS film. The dielectric constant of the PDMS film is better than that of the PDMS film. The dielectric constant of the PDMS film is better than that of the PDMS film. The dielectric constant of the PDMS film is better than that of the PDMS film. The dielectric constant of the PDMS film is better than that of the PDMS film. The dielectric constant of the PDMS film is better than that of the PDMS film. The dielectric constant of the PDMS film is better than that of the PDMS film. The dielectric constant of the PDMS film is better than that of the PI-0 film. The dielectric constant of the PDMS film is better than that of the PI-0 film. Figure 14 The real part ε', imaginary part ε", and dielectric loss tanδ of the dielectric constant of PI-0 and light-cured UV-PSPI films at different temperatures and frequencies are shown. The photosensitive polyimide in the present invention has good thermal stability, mechanical properties, and a high dielectric constant. Although the dielectric loss of the film currently made is relatively high, its potential for use as a high-temperature film capacitor is still seen.

[0181] Water absorption test:

[0182] Test method: Dry the polyimide film in a vacuum drying oven at 120°C for 12 hours and weigh the film mass as W. dry Immerse it in distilled water for 24 hours, then take out the film and wipe the surface moisture with filter paper, and record the mass of the film as W wet The calculation method of the water absorption rate of the film is shown in formula (2).

[0183]

[0184] The water absorption of the polyimide film was calculated according to formula (2), and the results are shown in Table 3. As can be seen from the table, the water absorption of both the PI-0 and photosensitive polyimide films remains very low, with a maximum water absorption of 2.5%. This is because the polyimide molecular chain contains a large number of hydrophobic groups such as trifluoromethyl and benzene rings. Since water molecules have a high polarizability, the dielectric constant of the material is very sensitive to moisture. The photosensitive polyimide film prepared by the present invention has a very low water absorption rate, which can minimize the impact of moisture on the dielectric constant of the material.

[0185] Table 3 Water absorption of PI-0 and photosensitive UV-PSPI films at room temperature

[0186]

[0187] According to the above test results, it can be seen that the present invention designed and synthesized a new photosensitive diamine monomer FMADA from the perspective of molecular structure, copolymerized it with commercial monomers 4,4'-diaminodiphenyl ether (ODA) and hexafluorodianhydride (6FDA), and successfully synthesized a polyimide with a photosensitive double bond in the molecule, and obtained the UV-PSPI-x series polyimide film by photocuring. Characterization of it yielded the following conclusions: (1) Compared with the PI-0 film, the mechanical properties of the photocured PI films UV-PSPI-2.5, UV-PSPI-5 and UV-PSPI-7.5 were improved, among which the tensile strength and elongation at break of the UV-PSPI-5 film were the highest, and it can be used as a polymer matrix for photocured 3D printing ink for subsequent exploration. (2) Compared with the PI-0 film, the thermal stability of the photocured PI film UV-PSPI-2.5 was improved, while the thermal stability of PI films with other ratios was reduced. The more diamine monomers are added, the tighter the cross-linking structure and the lower the thermal expansion coefficient. (3) The infrared spectrum shows that after being exposed to ultraviolet light, the photosensitive polyimide undergoes photocuring. At the same time, the photosensitive polyimide has good solubility in reactive diluents and can be used in photocuring 3D printing. (4) Compared with the PI film of the classic system, the prepared photocurable PI film exhibits a unique black color. The UV transmittance of UV-PSPI-5 and UV-PSPI-7.5 is the lowest in the wavelength range of 250-800nm, and can be used as a light-absorbing film in an optical fixed attenuator or a mask layer for a printed circuit board.

[0188] Test Example 11

[0189] In parts by weight, 45 parts of the photosensitive polyimide prepared in Example 2, 2 parts of the photoinitiator 819, 8 parts of the photocrosslinker TMPTA and 45 parts of N-vinyl pyrrolidone were mixed to obtain ink; the ink was subjected to photocuring 3D printing and cured under ultraviolet light to obtain the following: Figure 15 Polyimide part shown.

[0190] Depend on Figure 15 It can be seen that the photosensitive polyimide provided by the present invention can be used to prepare light-curing 3D printing ink to obtain polyimide parts with higher precision.

[0191] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A photosensitive polyimide, characterized in that: It has the structure shown in formula II: In the formula II, R1 is H, CF3 or CH3; R2 is H, F, CH3 or CH2CH3; In the formula II, x is 5 to 10%, and x+y=1; for for 2. The method for preparing the photosensitive polyimide according to claim 1, comprising the following steps: An aromatic diamine monomer containing an ethyl methacrylate group, a commercial diamine monomer, a commercial dianhydride monomer, and a third organic solvent are mixed and copolymerized to obtain polyamic acid; the aromatic diamine monomer containing an ethyl methacrylate group has a structure shown in Formula I: In the formula I, R1 is H, CF3 or CH3; R2 is H, F, CH3 or CH2CH3; The polyamic acid, a dehydrating agent and a third catalyst are mixed to perform a chemical imidization reaction to obtain a photosensitive polyimide having a structure shown in Formula II; The structure of the commercial diamine monomer is The structure of the commercial dianhydride monomer is 3. The preparation method according to claim 2, characterized in that When the R1 is H, the R2 is H, F, CH3 or CH2CH3; when the R1 is CF3, the R2 is H; when the R1 is CH3, the R2 is CH3 or CH2CH3.

4. The preparation method according to claim 2 or 3, characterized in that The preparation method of the aromatic diamine monomer comprises the following steps: Mixing an aromatic diamine, di-tert-butyl dicarbonate, a first catalyst, and a first organic solvent to carry out a substitution reaction to obtain compound 1; Mixing the compound 1 with isocyanoethyl methacrylate, a second organic solvent, and a second catalyst to carry out a nucleophilic addition reaction to obtain compound 2; The compound 2 is mixed with a solvent containing trifluoroacetic acid to carry out a nucleophilic substitution reaction to obtain an aromatic diamine monomer having a structure shown in Formula I; The structure of the aromatic diamine is The structure of compound 1 is The structure of compound 2 is 5. The preparation method according to claim 4, characterized in that The molar ratio of the aromatic diamine to di-tert-butyl dicarbonate is 10:20-25.

6. The preparation method according to claim 4, characterized in that The molar ratio of the compound 1 to isocyanoethyl methacrylate is 2:4-6.

7. Use of the photosensitive polyimide according to claim 1 or the photosensitive polyimide prepared by the preparation method according to any one of claims 2 to 6 in the preparation of polyimide films or polyimide parts.

8. The use according to claim 7, characterized in that The application comprises: mixing the photosensitive polyimide, an organic solvent and a photoinitiator to obtain a polyimide solution; and subjecting the polyimide solution to ultraviolet light curing to obtain a polyimide film.

9. The use according to claim 7, characterized in that The application includes: mixing the photosensitive polyimide, a reactive diluent, a photocrosslinker and a photoinitiator to obtain ink; and performing photocuring 3D printing on the ink to obtain a polyimide part.

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