Photosensitive diamine monomer, photosensitive polyimide precursor, and film material preparation method and application thereof

Abstract

This invention provides a photosensitive diamine monomer, a photosensitive polyimide precursor containing the monomer, a method for preparing thin film materials using the photosensitive polyimide precursor, and the application of this material in patterned hydrophilic surfaces and humidity sensor substrates. The photosensitive diamine monomer has a triphenyldiamine backbone, and its side chain contains o-nitrobenzyl ether photosensitive groups. When polyamic acid or polyimide materials prepared from this diamine monomer are irradiated with ultraviolet light, the o-nitrobenzyl ether groups in the side chain undergo a photolysis reaction to generate o-nitrosobenzaldehyde and release phenolic hydroxyl groups. The phenolic hydroxyl groups are covalently fixed on the polymer backbone, which significantly improves the hydrophilicity of the irradiated area. This material can be used to prepare patterned hydrophilic surfaces and has potential application prospects in fields such as the integrated design of humidity sensor substrates and humidity-sensitive materials.

Description

Technical Field

[0001] This invention belongs to the field of organic functional materials technology, specifically relating to a photosensitive diamine monomer with an o-nitrobenzyl ether structure, a photosensitive polyimide precursor containing the monomer, a method for preparing thin film materials using the photosensitive polyimide precursor, and the application of the material in patterned hydrophilic surfaces and humidity sensor substrates. Background Technology

[0002] Polyimide (PI) is widely used in microelectronics, optoelectronics, and flexible sensing due to its excellent heat resistance, mechanical properties, and chemical stability. In recent years, research on the modulation of polyimide surface properties through light irradiation has attracted widespread attention, especially the controllable enhancement of hydrophilicity in irradiated areas, which has important application prospects in microfluidic chips, biosensors, and humidity sensors.

[0003] In the prior art, the methods for controlling the hydrophilicity of polyimide surfaces mainly include: (1) grafting hydrophilic polymers onto the surface, such as grafting polyethylene glycol after plasma treatment. This method is complex and has low patterning accuracy; (2) blending and adding hydrophilic small molecules or surfactants. This method has the problems of easy migration and precipitation of hydrophilic additives and poor long-term stability.

[0004] In recent years, researchers have attempted to introduce photosensitive groups into polyimides via copolymerization to achieve photosensitive hydrophilicity. Among these, side-chain suspended photosensitive polyimides have attracted attention due to their relatively simple synthesis and flexible design of photosensitive groups. These materials typically involve introducing photosensitive side chains onto a diamine monomer, with the photosensitive groups suspended outside the polyimide backbone after polymerization.

[0005] Existing literature reports on polyimide materials containing o-nitrobenzyl photosensitive groups and the photomodulation of their surface wettability (see: Tsuda et al., Journal of Photopolymer Science and Technology, 2016, 29(2), 265-268). This study reported that after irradiation with 365 nm ultraviolet light, the water contact angle of the polyimide film containing o-nitrobenzyl diamine decreased from approximately 90° (hydrophobic) to approximately 60° (hydrophilic), a change of approximately 30°. However, this existing technology has the following shortcomings: (1) the rigidity of the diamine backbone backbone used is relatively insufficient; (2) the improvement in hydrophilicity after irradiation is limited (Δ≈30°); (3) it does not involve a method for directly forming hydrophilic / hydrophobic patterns through mask exposure; and (4) it does not involve the application of this material in humidity sensors.

[0006] In addition, the existing side-chain suspended photosensitive polyimide still has the following shortcomings: (1) Some photosensitive groups undergo side chain breakage after light exposure. If the generated small molecular fragments cannot be effectively removed, they may remain in the film, affecting long-term stability; (2) Photosensitive side chains are usually connected to the main chain through long-chain flexible alkyl chains (such as C4-C12 alkylene chains). The free movement of the side chains may interfere with the regular stacking of the polymer main chain, affecting the mechanical properties and thermal stability of the film.

[0007] o-Nitrobenzyl (ONB) derivatives are among the most widely studied photoresponsive functional groups. Under ultraviolet light irradiation, they undergo irreversible photolysis to generate o-nitrosobenzaldehyde and release a hydroxyl group or its derivative. The photolysis mechanism has been thoroughly investigated: upon photoexcitation, the nitro group is activated, undergoing intramolecular hydrogen transfer to form a quinone intermediate, which then cyclizes to form a five-membered isoxazole structure, ultimately opening the ring and releasing the leaving group. These photosensitive groups possess advantages such as simple synthesis, easy structural modification, and high photochemical quantum yield, and have been widely applied in photoresponsive polymers, photodegradable materials, and photoinduced micropatterning.

[0008] However, there are no reports in the prior art of using o-nitrobenzyl ether as a diamine monomer with a side chain and utilizing the generation of phenolic hydroxyl groups on the main chain after light irradiation to achieve a controllable hydrophilicity transition. Summary of the Invention

[0009] To achieve a significant improvement in hydrophilicity while maintaining the excellent thermal properties of polyimide, this invention provides a photosensitive diamine monomer with an o-nitrobenzyl ether structure, a photosensitive polyimide precursor containing the monomer, and a method and application for preparing thin film materials using the photosensitive polyimide precursor. By introducing a rigid terphenyl backbone and a short-chain (monomethylene) linkage, a significant improvement in hydrophilicity is achieved while maintaining the excellent thermal properties of polyimide. Furthermore, the hydrophilic groups are directly covalently linked to the polymer backbone, avoiding the migration and precipitation problems of small molecule additives.

[0010] This invention provides a photosensitive diamine monomer, the monomer having the structure shown in general formula (I):

[0011] H2N−Ar1−Ar2−Ar3−NH2 (I)

[0012] Ar1, Ar2, and Ar3 are each independently selected from substituted or unsubstituted phenyl, naphthyl, or biphenyl groups; the substituents are selected from one or more of C1-C6 alkyl, C1-C6 alkoxy, and halogen atoms.

[0013] Furthermore, at least one of Ar1, Ar2, or Ar3 has the following photosensitive side chain:

[0014] −O−CH2−Ar(NO2),

[0015] Ar is a substituted or unsubstituted phenyl group.

[0016] Preferably, the structure of the monomer is as follows: .

[0017] The present invention also provides a photosensitive polyimide precursor, comprising: a photosensitive diamine monomer structural unit as described above.

[0018] The photosensitive polyimide precursor also includes structural units derived from tetracarboxylic dianhydride.

[0019] The tetracarboxylic dianhydride is selected from one or more of pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), diphenyl ether dianhydride (ODPA), and hexafluorodianhydride (6FDA).

[0020] In the photosensitive polyimide precursor, the molar ratio of structural units derived from photosensitive diamine monomers to structural units derived from tetracarboxylic dianhydrides is 1:99-100:0 or 5:95-50:50.

[0021] This invention also provides a method for preparing a photosensitive polyimide film material, comprising the following steps:

[0022] (1) Dissolve the above-mentioned photosensitive polyimide precursor in an organic solvent to obtain a polyamic acid solution;

[0023] (2) The polyamic acid solution is coated onto the surface of the substrate and dried to form a polyamic acid film;

[0024] (3) The selected area of ​​the polyamic acid film is irradiated with ultraviolet light through a mask, so that the photosensitive diamine unit in the irradiated area undergoes a photolysis reaction to generate phenolic hydroxyl groups;

[0025] (4) Heat treatment is performed on the film after light exposure to imidize the polyamic acid and obtain polyimide film material.

[0026] In step (3), the wavelength of the ultraviolet light is 200-400 nm or 365 nm; the exposure energy is 50-2000 mJ / cm². 2 .

[0027] The present invention also provides an application of the aforementioned photosensitive polyimide precursor or the prepared polyimide film material in the preparation of patterned hydrophilic surfaces or humidity sensor substrates.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The photosensitive diamine monomer of this invention has a terphenyldiamine backbone, and its side chain contains an o-nitrobenzyl ether photosensitive group. The o-nitrobenzyl ether photosensitive group is linked to the rigid terphenyldiamine backbone via ether bonds to form a novel side-chain suspended photosensitive diamine monomer. The terphenyl backbone has high chain rigidity, which is beneficial for improving the heat resistance and dimensional stability of the polyimide film, while also providing stable connection sites for the photosensitive side chain. Compared with the prior art using long-chain flexible alkyl linkers, the side chain of this invention contains only one methylene unit, and its interference with the regular stacking of the main chain is negligible.

[0030] Upon light exposure, the o-nitrobenzyl ether groups on the side chains undergo photolysis, generating o-nitrosobenzaldehyde and diamine terphenyl. The diamine terphenyl is covalently fixed to the polymer backbone, with the generated phenolic hydroxyl groups directly attached to the backbone. Compared to the problem of easy migration and precipitation of hydrophilic additives in traditional blend systems, the hydrophilic groups of this invention are covalently fixed, resulting in expected superior long-term stability. The water contact angle changes by more than 40° before and after light exposure (reaching 43.8° in Example 6). A latent image can be formed on the surface of the polyamic acid film through mask exposure. After thermal imidization, the difference in water contact angle between the illuminated and unilluminated areas is significant, allowing for the acquisition of hydrophilic / hydrophobic patterns without the need for developing solutions or chemical post-treatment.

[0031] The photosensitive hydrophilic properties of this material make it promising for applications in patterned hydrophilic surfaces, microfluidic chips, and biochips, and it is expected to be used as a sensitive layer or substrate for humidity sensors. Attached Figure Description

[0032] Figure 1 The 1H NMR spectrum (¹H NMR) of the intermediate o-DMN prepared in Example 1 of this invention. Figure 2 The photosensitive diamine monomer prepared in Example 1 of this invention has a hydrogen nuclear magnetic resonance spectrum (¹H NMR).

[0033] Figure 3 The photolysis product diamine terphenyl prepared in Example 1B of this invention has a 1H NMR spectrum (¹H NMR). Figure 4 The UV-Vis absorption spectrum of the photosensitive diamine monomer prepared in Example 1 of this invention; Figure 5 Bar charts showing the water contact angles of polyamic acid films with different proportions of photosensitive diamine prepared in Examples 2-4 of this invention before and after light exposure. Figure 6 These are contact angle test photographs of the polyimide film prepared in Example 6 of the present invention, wherein: Figure 6 a is a photograph of the water droplet shape in the unlit area; Figure 6 b is a photograph of the water droplet shape in the illuminated area. Detailed Implementation

[0034] This invention provides a photosensitive diamine monomer, the monomer having the structure shown in general formula (I):

[0035] H2N−Ar1−Ar2−Ar3−NH2 (I)

[0036] Ar1, Ar2, and Ar3 are each independently selected from substituted or unsubstituted phenyl, naphthyl, or biphenyl groups; the substituents are selected from one or more of C1-C6 alkyl, C1-C6 alkoxy, and halogen atoms.

[0037] Furthermore, at least one of Ar1, Ar2, or Ar3 has the following photosensitive side chain:

[0038] −O−CH2−Ar(NO2),

[0039] Ar is a substituted or unsubstituted phenyl group.

[0040] Preferably, the structure of the monomer is as follows: .

[0041] The present invention provides a photosensitive polyimide precursor comprising the above-mentioned photosensitive diamine monomer, the photosensitive polyimide precursor further comprising structural units derived from tetracarboxylic dianhydride, wherein the molar ratio of structural units derived from photosensitive diamine monomer to structural units derived from tetracarboxylic dianhydride in the photosensitive polyimide precursor is 1:99 to 100:0 or 5:95 to 50:50.

[0042] The tetracarboxylic dianhydride is selected from one or more of pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), diphenyl ether dianhydride (ODPA), and hexafluorodianhydride (6FDA).

[0043] This invention provides a method for preparing a photosensitive polyimide thin film material using the above-mentioned photosensitive polyimide precursor, comprising the following steps:

[0044] (1) Dissolve the photosensitive polyimide precursor prepared above in an organic solvent to obtain a polyamic acid solution;

[0045] (2) The polyamic acid solution is coated onto the surface of the substrate and dried to form a polyamic acid film;

[0046] (3) The selected area of ​​the polyamic acid film is irradiated with ultraviolet light through a mask, so that the photosensitive diamine unit in the irradiated area undergoes a photolysis reaction to generate phenolic hydroxyl groups;

[0047] (4) Heat treatment is performed on the film after light exposure to imidize the polyamic acid and obtain polyimide film material.

[0048] In step (3), the wavelength of the ultraviolet light is 200-400 nm or 365 nm; the exposure energy is 50-2000 mJ / cm². 2 .

[0049] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. All raw materials used in the embodiments are commercially available analytical grade products, or synthesized according to methods known in the art.

[0050] Example 1: Synthesis of photosensitive diamine monomer

[0051] This embodiment provides a method for synthesizing a photosensitive diamine monomer (denoted as compound A), and the specific synthetic route is as follows:

[0052] (1) Synthesis of intermediate o-DMN

[0053] Add anhydrous N,N-dimethylformamide (DMF, 200 mL, 2.60 mol) to a two-necked flask. While stirring magnetically, add o-nitrobenzyl bromide (23.763 g, 0.11 mol). After complete dissolution, slowly add cesium carbonate (Cs₂CO₃, 40.728 g, 0.125 mol) and cesium iodide (CsI, 25.981 g, 0.11 mol) in three portions. After each addition, rinse the flask neck with a small amount of DMF (approximately 5 mL). Install a reflux condenser and a constant-pressure dropping funnel, and heat the flask to 70°C in an oil bath.

[0054] 3,5-Dibromophenol (27.719 g, 0.11 mol) was dissolved in 150 mL of anhydrous DMF and added to a constant-pressure dropping funnel. Under nitrogen protection, the solution was added dropwise to the reaction flask at a rate of approximately 1 drop per second. After the addition was complete, the reaction was continued at 70 °C under nitrogen protection for 12 hours.

[0055] After the reaction was complete, the mixture was filtered while hot, and the filtrate was collected. The filtrate was slowly poured into 4 L of deionized water and allowed to stand overnight. The precipitated solid was filtered, and the filter cake was dried in a vacuum oven at 55 °C for 24 hours to obtain the intermediate o-DMN.

[0056] The ¹H NMR (500 MHz, DMSO-d6) data of the obtained intermediate are as follows: δ 8.14 (d, J = 8.2 Hz, 1H), 7.82–7.78 (m, 1H), 7.76 (d, J = 6.2 Hz, 1H), 7.67–7.62 (m, 1H), 7.43 (s, 1H), 7.32 (s, 2H), 5.52 (s, 2H).

[0057] (2) Synthesis of the target photosensitive diamine monomer

[0058] Add the above intermediate o-DMN (19.35 g) and tetrahydrofuran (THF, 200 mL) to a 100 mL double-necked flask. Add tetratriphenylphosphine palladium (Pd(PPh3)4, 0.6 g) and potassium carbonate (K2CO3, 20.73 g) under magnetic stirring. Wash the mouth of the flask with a small amount of THF and reflux at 70 °C for 10 minutes.

[0059] Add p-aminophenylborate acid salt (27.710 g), THF (200 mL), and water (100 mL) in portions to a 50 mL centrifuge tube. Sonicate until the solid is completely dissolved, and transfer the solution to a constant-pressure dropping funnel. Evacuate the reaction flask and purge with nitrogen for protection. Slowly add the solution dropwise through the constant-pressure dropping funnel at 70 °C. After the addition is complete, continue the reaction for 24 hours.

[0060] After the reaction was completed, the insoluble matter was removed by filtration, the filtrate was extracted with ethyl acetate (200 mL), the organic phase was separated, the organic phase was washed three times with saturated brine (50 mL each time), dried with anhydrous sodium sulfate, filtered, and the solvent was removed by rotary evaporation. The obtained solid was dried in a vacuum oven at 50 °C for 24 hours to obtain the target photosensitive diamine monomer.

[0061] The ¹H NMR (400 MHz, DMSO-d6) data of the obtained target product are as follows: δ 8.11 (d, J = 8.2 Hz, 1H), 7.87 (d, J = 7.7 Hz, 1H), 7.79 (t, J = 6.6 Hz, 1H), 7.62 (t, J = 6.6 Hz, 1H), 7.42 (d, J = 6.5 Hz, 4H), 7.29 (s, 1H), 7.00 (s, 2H), 6.64 (d, J = 6.4 Hz, 4H), 5.57 (s, 2H), 5.23 (s, 4H).

[0062] The UV-Vis absorption spectrum (UV-Vis, DMAc solution) shows that the monomer has a characteristic absorption peak at λmax = 325 nm.

[0063] Example 1B: Isolation and structural characterization of photolysis products of photosensitive diamine monomers

[0064] 0.5 g of the photosensitive diamine monomer (compound A) prepared in Example 1 was dissolved in 20 mL of N,N-dimethylacetamide (DMAc) and placed in a quartz reaction flask. The mixture was irradiated with 365 nm ultraviolet light (high-pressure mercury lamp) at an exposure energy of 500 mJ / cm². After irradiation, the reaction solution was concentrated under reduced pressure to approximately 5 mL, and 50 mL of deionized water was added, causing a solid to precipitate. The solid was filtered, dried, and purified by column chromatography (200-300 mesh silica gel powder, eluent: ethyl acetate / petroleum ether = 1:1) to obtain the photolysis product, diamine terphenyl.

[0065] The ¹H NMR (500 MHz, DMSO-d6) data of the obtained photolysis products are as follows: δ 9.36 (s, 1H), 7.36 (d, J = 8.5 Hz, 4H), 7.11 (s, 1H), 6.80 (s, 2H), 6.65 (d, J = 8.5 Hz, 4H), 5.22 (s, 4H).

[0066] With pre-illuminated monomers ( Figure 2 A comparison of the NMR spectra of the two compounds shows that the methylene (−O−CH2−Ar) signal at δ 5.57 ppm completely disappeared before illumination, and the proton signals originally attributed to the ortho-nitrobenzene ring (δ 8.11, 7.87, 7.79, 7.62) also completely disappeared. A new singlet signal appeared at δ 9.36 ppm, attributed to the phenolic hydroxyl (−OH) proton. The chemical shifts of the aromatic proton region changed accordingly (7.36, 7.11, 6.80, 6.65), which is consistent with the structural characteristics of the diamine terphenylphenol. The amino proton signal (δ 5.22) remained unchanged, indicating that the terphenyl diamine skeleton was not affected.

[0067] The above results directly prove that after ultraviolet light irradiation, the o-nitrobenzyl ether side chain of the photosensitive diamine monomer undergoes photolytic cleavage, generating diamine terphenyl containing a phenolic hydroxyl group.

[0068] Examples 2-4: Preparation of photosensitive polyamic acid (PAA) with different component ratios

[0069] Example 2 (photosensitive diamine content 10 mol%)

[0070] Weigh 0.9 mmol of 4,4'-diaminodiphenyl ether (ODA) and 0.1 mmol of the photosensitive diamine monomer prepared in Example 1, dissolve them in 10 mL of N,N-dimethylacetamide (DMAc), add 1.0 mmol of pyromellitic dianhydride (PMDA) in portions under nitrogen protection, and stir the mixture in an ice-water bath for 12 hours to obtain a polyamic acid solution with a solid content of approximately 10 wt%.

[0071] Example 3 (photosensitive diamine content 20 mol%)

[0072] Weigh 0.8 mmol of ODA and 0.2 mmol of photosensitizing diamine monomer, and the rest are the same as in Example 2.

[0073] Example 4 (photosensitive diamine content 30 mol%)

[0074] Weigh 0.7 mmol of ODA and 0.3 mmol of photosensitizing diamine monomer, and the rest are the same as in Example 2.

[0075] Example 5: Preparation and Photolysis Performance Testing of Polyamic Acid Films

[0076] The polyamic acid solution prepared in Examples 2-4 was spin-coated onto a quartz glass substrate and vacuum dried at 80°C for 2 hours to obtain a polyamic acid film with a thickness of about 10 μm.

[0077] The thin film was irradiated with 365 nm ultraviolet light (high-pressure mercury lamp) at an exposure energy of 500 mJ / cm². The water contact angle of the thin film surface before and after irradiation was measured using a contact angle meter.

[0078] The contact angle test conditions were as follows: a Dataphysics OCA100 contact angle meter was used; the test solution was deionized water with a droplet volume of 3 µL; the ambient temperature was 25℃; the relative humidity was 63%; and the droplet settling time was 5-10 seconds. Each sample was measured 5 times at different locations, and the arithmetic mean was taken as the final contact angle value. The test results are shown in Table 1.

[0079] Table 1. Changes in water contact angle of PAA films with different compositions before and after light irradiation.

[0080]

[0081] The results showed that the contact angle of all PAA films containing photosensitive diamine units decreased after light irradiation, indicating that the photolysis reaction had been successfully carried out and phenolic hydroxyl groups were generated on the main chain, thus improving the hydrophilicity of the PAA films.

[0082] Example 6: Preparation and Photolysis Performance Testing of Polyimide Films

[0083] The polyamic acid solution prepared in Example 4 was spin-coated onto a quartz glass substrate and dried at 80°C for 2 hours to obtain a polyamic acid film with a thickness of about 10 μm.

[0084] Selected areas of the film were irradiated with 365 nm ultraviolet light (high-pressure mercury lamp) through a mask at an exposure energy of 500 mJ / cm². The irradiated film was then placed in a nitrogen atmosphere and heated to 300 °C at a heating rate of 5 °C / min, and held at that temperature for 1 hour to perform thermal imidization, yielding a polyimide film.

[0085] The water contact angles in the illuminated and unilluminated areas were tested using the same contact angle test conditions as in Example 5. The results are as follows: Figure 6 The water contact angle in the unlit area was 88.3°, while it decreased to 44.5° in the illuminated area, a change of 43.8°. This indicates that the hydrophilicity of the polyimide film is significantly improved in the illuminated area, achieving high-contrast hydrophilic / hydrophobic pattern construction. In contrast, the ordinary polyimide film in Comparative Example 1, which does not contain photosensitive diamine, showed almost no change in contact angle under the same treatment conditions (change <2°), proving that the improved hydrophilicity of the present invention does indeed originate from the photolysis reaction of the photosensitive diamine monomer.

[0086] Analysis of the differences between the results of Example 5 and Example 6

[0087] In Example 5, the water contact angle of the polyamic acid film containing 30% photosensitive diamine decreased from 71.9° to 58.4° after irradiation with 365 nm ultraviolet light (500 mJ / cm²), a change of 13.5°. In Example 6, after further thermal imidization at 300°C under the same illumination conditions, the water contact angle in the illuminated area further decreased to 44.5°, a difference of 43.8° compared to the unilluminated area (88.3°).

[0088] This difference is mainly due to the following factors:

[0089] (1) Removal of byproducts: The small molecule byproduct o-nitrosobenzaldehyde generated by photolysis is completely volatilized and released under heat treatment at 300℃. In contrast, after exposure to light at room temperature, some byproducts may remain on the surface or inside of the polyamic acid film, which has a certain shielding effect on hydrophilicity. After removing the byproducts, the phenolic hydroxyl groups are fully exposed, and the hydrophilicity is further enhanced.

[0090] (2) Surface reconstruction induced by imidization: During the conversion of polyamic acid to polyimide, the molecular chain undergoes cyclization, rigidification and rearrangement. The polar phenolic hydroxyl group, as a hydrophilic group, tends to migrate to the surface at high temperatures, resulting in its enrichment on the surface of the film, thereby significantly reducing the water contact angle.

[0091] The above explanation is consistent with the significant decrease in contact angle observed in Example 6 (43.8°) and the more moderate decrease (13.5°) observed in Example 5. Therefore, the complete technical solution of the present invention can achieve a more significant hydrophilic / hydrophobic contrast, which is beneficial for the construction of high-resolution patterned hydrophilic surfaces.

[0092] Expected changes in the hydrophilicity of polyimide films with different photosensitizing diamine contents

[0093] The polyamic acid films in Examples 2-4 all exhibited a decrease in contact angle after illumination at different photosensitive diamine contents (10%, 20%, and 30%), with the decrease increasing with increasing photosensitive diamine content (Table 1). Example 6 further confirmed that when the photosensitive diamine content was 30%, the water contact angle of the thermally imidized polyimide film in the illuminated area decreased from 88.3° in the unilluminated area to 44.5°, a change of 43.8°. Based on the trend in the polyamic acid state, those skilled in the art can reasonably expect that after thermal imidization, polyimide films with 10% and 20% photosensitive diamine contents can also achieve a significant decrease in water contact angle, with the decrease increasing with increasing content. Therefore, the technical solution of the present invention can achieve a controllable improvement in hydrophilicity within a limited range of 1:99 to 100:0.

[0094] Comparative Example 1: Control experiment of ordinary polyimide film without photosensitive diamine

[0095] Weigh 1.0 mmol of 4,4'-diaminodiphenyl ether (ODA) and 1.0 mmol of pyromellitic dianhydride (PMDA), and prepare a polyamic acid solution using the same polymerization method as in Example 2. Spin-coat the solution onto a quartz glass substrate and dry under vacuum at 80°C for 2 hours to obtain a polyamic acid film with a thickness of approximately 10 μm.

[0096] The film was irradiated with ultraviolet light (365 nm, exposure energy 500 mJ / cm²) under the same conditions as in Example 6, and then placed in a nitrogen atmosphere and heated to 300°C at a heating rate of 5°C / min, and held at that temperature for 1 hour to perform thermal imidization, thus obtaining a common polyimide film.

[0097] Using the same contact angle testing conditions as in Example 5, the water contact angle of the film before and after illumination (i.e., the exposed area and the unexposed area) was measured. The results showed that the water contact angle in the unexposed area was 76.0°, and the water contact angle in the illuminated area was 74.2°, a change of only 1.8°, within the instrument measurement error range (±2°). The contact angle of the unexposed area was 76.0°, different from the 88.3° in the unexposed area of ​​Example 6. This is because the introduction of the photosensitive diamine monomer altered the chemical structure of the polymer backbone, leading to an increase in the intrinsic contact angle. These results indicate that ordinary polyimide films without the photosensitive diamine monomer do not show significant changes in surface hydrophilicity under the same illumination and heat treatment conditions. Therefore, the significant decrease in contact angle observed in Example 6 can be attributed to the introduction of the photosensitive diamine monomer of this invention and the phenolic hydroxyl groups generated by the photolysis of the side chains after illumination.

[0098] Application of polyimide film materials in the preparation of patterned hydrophilic surfaces or humidity sensor substrates: Because the polyimide film of this invention exhibits significantly improved hydrophilicity in the illuminated region (contact angle decreased from 88.3° to 44.5° in Example 6), and the hydrophilic groups are covalently fixed to the polymer backbone, this material has application value in the field of humidity sensors. For example, traditional humidity sensors typically involve coating or depositing a humidity-sensitive material (such as a hydrophilic polymer) onto a separate substrate (such as ceramic, silicon wafer, or ordinary polyimide film). Due to differences in material properties, insufficient adhesion may exist between the humidity-sensitive layer and the substrate. In this invention, the illuminated region (hydrophilic) and the non-illuminated region (hydrophobic) belong to the same continuous film, and their chemical compositions are identical (only the side chain functional groups differ), thus avoiding adhesion problems caused by heterogeneous material interfaces.

[0099] Furthermore, multiple independent hydrophilic regions can be defined on the same polyimide film through mask exposure, and each region can be used to fabricate an electrode for the preparation of a humidity sensor array.

[0100] Another feasible application is to fabricate interdigitated electrodes on the surface of a polyimide film (using inkjet printing, screen printing, or photolithography), and then irradiate selected sensitive areas with ultraviolet light (through a mask) to create a hydrophilic pattern in those areas. When the ambient humidity changes, the hydrophilic areas adsorb or desorb water molecules, causing changes in the dielectric constant or capacitance. Humidity detection can be achieved by monitoring the changes in capacitance / impedance between the electrodes.

Claims

1. A photosensitive diamine monomer, characterized in that, The monomer has the structure shown in the following general formula (I): H2N−Ar1−Ar2−Ar3−NH2 (I) Ar1, Ar2, and Ar3 are each independently selected from substituted or unsubstituted phenyl, naphthyl, or biphenyl groups; the substituents are selected from one or more of C1-C6 alkyl, C1-C6 alkoxy, and halogen atoms. Furthermore, at least one of Ar1, Ar2, or Ar3 has the following photosensitive side chain: −O−CH2−Ar(NO2), Ar is a substituted or unsubstituted phenyl group.

2. The photosensitive diamine monomer according to claim 1, characterized in that, The structure of the monomer is as follows: 。 3. A photosensitive polyimide precursor, characterized in that, include: The photosensitive diamine monomer structural unit as described in claim 1 or 2.

4. The photosensitive polyimide precursor according to claim 3, characterized in that, The photosensitive polyimide precursor also includes structural units derived from tetracarboxylic dianhydride.

5. The photosensitive polyimide precursor according to claim 4, characterized in that, The tetracarboxylic dianhydride is selected from one or more of pyromellitic dianhydride (PMDA), biphenyl dianhydride (BPDA), diphenyl ether dianhydride (ODPA), and hexafluorodianhydride (6FDA).

6. The photosensitive polyimide precursor according to claim 5, characterized in that, In the photosensitive polyimide precursor, the molar ratio of structural units derived from photosensitive diamine monomers to structural units derived from tetracarboxylic dianhydrides is 1:99-100:0 or 5:95-50:

50.

7. A method for preparing a photosensitive polyimide thin film material, characterized in that, Includes the following steps: (1) Dissolve the photosensitive polyimide precursor of any one of claims 3 to 6 in an organic solvent to obtain a polyamic acid solution; (2) The polyamic acid solution is coated onto the surface of the substrate and dried to form a polyamic acid film; (3) The selected area of ​​the polyamic acid film is irradiated with ultraviolet light through a mask, so that the photosensitive diamine unit in the irradiated area undergoes a photolysis reaction to generate phenolic hydroxyl groups; (4) Heat treatment is performed on the film after light exposure to imidize the polyamic acid and obtain polyimide film material.

8. The method for preparing a photosensitive polyimide film material according to claim 7, characterized in that, In step (3), the wavelength of the ultraviolet light is 200-400 nm or 365 nm; the exposure energy is 50-2000 mJ / cm². 2 .

9. The use of the photosensitive polyimide precursor according to any one of claims 3-6 or the polyimide film material prepared according to claim 7 or 8 in the preparation of patterned hydrophilic surfaces or humidity sensor substrates.

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