Solvent-free modified PI resin and preparation method thereof

Abstract

The invention relates to the technical field of high polymer materials, and discloses a solvent-free modified PI resin and a preparation method thereof, and the solvent-free modified PI resin comprises amino-terminated polyimide powder, acryloyl line, isobornyl acrylate, isocyano ethyl methacrylate and a photoinitiator. The preparation method comprises the following steps: firstly, synthesizing amino-terminated polyimide powder from fluorine-containing diamine and dianhydride, then dissolving the amino-terminated polyimide powder in acryloyl line and isobornyl acrylate, adding isocyano ethyl methacrylate to enable an isocyanate group to react with an amino-terminated group so as to introduce photoactive double bonds, and finally mixing an initiator. The PI solubility is improved through the fluorine-containing structure design, and zero VOC emission is achieved by replacing an organic solvent with the reactive diluent; a uniform cross-linked network is constructed through chemical bonding, so that the microscopic phase separation problem of a physical blending system is solved, second-level photocuring is realized, and the tensile strength and heat resistance of the cured resin are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a solvent-free modified PI resin and its preparation method. Background Technology

[0002] Polyimide materials are widely used in microelectronics manufacturing, aerospace and flexible display fields due to their excellent thermal stability, mechanical strength and dielectric properties.

[0003] Traditional polyimide resin processing typically relies on high-boiling-point polar solvents such as N-methylpyrrolidone and N,N-dimethylacetamide for dissolution and coating. This solvent-based processing method not only results in high emissions of volatile organic compounds during production, burdening the environment, but also requires prolonged high-temperature baking to remove the solvent and complete the imidization reaction. This not only consumes a lot of energy but also easily leads to volume shrinkage or defects in the coating due to solvent evaporation, limiting the application of polyimide in rapid prototyping and heat-sensitive substrates.

[0004] To address these issues, the industry has attempted to develop photocurable polyimide systems or physically blend polyimide with photosensitive monomers. However, due to solubility differences and polarity mismatches between rigid polyimide molecular chains and photosensitive monomers such as acrylates, physically blended systems are prone to macroscopic or microscopic phase separation during standing or curing. This phase separation results in an inhomogeneous network structure after curing, making it impossible for the final material to maintain both the original heat resistance and mechanical strength of polyimide. This often leads to decreased light transmittance, increased brittleness, and a significant drop in glass transition temperature, making it difficult to meet the performance requirements of high-end electronic packaging and precision manufacturing.

[0005] Therefore, developing a modified polyimide resin that can achieve solvent-free rapid photocuring and solve phase separation problems through chemical bonding, thereby maintaining excellent mechanical properties and heat resistance, has become a technical challenge to be solved in the field of polymer materials. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a solvent-free modified PI resin and its preparation method, which solves the problems of high volatile organic compound emissions and long thermal curing cycles caused by the reliance on high-boiling-point organic solvents in the traditional polyimide resin processing, as well as the micro-phase separation, decreased mechanical properties and heat resistance after curing caused by the physical blending method used in existing photocurable polyimide systems.

[0007] To achieve the above objectives, the present invention provides the following technical solution: In a first aspect, the present invention provides a solvent-free modified PI resin, employing the following technical solution: A solvent-free modified PI resin is made from raw materials comprising the following parts by weight: amino-terminated polyimide powder: 30.0-70.0 parts; acrylonitrile: 15.0-40.0 parts; isobornyl acrylate: 15.0-30.0 parts; isocyanate methacrylate: 1.5-5.0 parts; phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide: 1.0-5.0 parts.

[0008] By adopting the above technical solution, this invention utilizes an reactive diluent system to replace traditional volatile organic solvents such as N-methylpyrrolidone, achieving zero volatile organic compound emissions and rapid UV curing. The specific modification and enhancement mechanisms are as follows: Dissolution and dispersion mechanism: Acryloyl line and isobornyl acrylate are used as reactive diluents. On the one hand, the high solubility of acryloyl line completely dissolves the terminal amino polyimide powder to form a homogeneous system. On the other hand, acryloyl line and isobornyl acrylate themselves contain polymerizable double bonds, which directly participate in the polymerization reaction during the curing process and become part of the resin matrix. This avoids the solvent evaporation process and solves the problems of volume shrinkage and environmental pollution caused by solvent evaporation in traditional thermosetting processes.

[0009] Chemical bonding and network interpenetration mechanism: Isoethyl methacrylate in the raw material acts as a chemical bridge. One end of the isoethyl methacrylate molecule has a highly reactive isocyanate group (-NCO), and the other end has a photopolymerizable methacrylate double bond. During resin preparation, the isocyanate group undergoes a nucleophilic addition reaction with the amino group (-NH2) at the end of the amino-terminated polyimide powder molecular chain, generating a stable urea bond structure, thereby introducing the photopolymerizable double bond to the end of the polyimide molecular chain.

[0010] Network Construction: Under ultraviolet irradiation, the double bonds at the ends of the modified polyimide molecular chains are initiated, undergoing a free radical copolymerization reaction with acryloyl line and isobornyl acrylate monomers. This process allows the rigid polyimide skeleton to be tightly bonded to the acrylate crosslinked network through chemical bonds, forming a uniform organic network structure. This chemical bonding eliminates the interfacial tension between the polyimide and acrylate phases in the physical blend system, preventing microphase separation during the curing process and improving the tensile strength and glass transition temperature of the cured film.

[0011] Preferably, the amino-terminated polyimide powder is made from raw materials comprising the following parts by weight: 2,2'-bis(trifluoromethyl)biphenyldiamine: 30.0-34.0 parts; 4,4'-(hexafluoroisopropyl)diphthalic anhydride: 37.7-42.2 parts; N,N-dimethylacetamide: 250-350 parts; acetic anhydride: 9.0-12.0 parts; pyridine: 4.0-6.0 parts.

[0012] By employing the above technical solution, both 2,2'-bis(trifluoromethyl)biphenyldiamine and 4,4'-(hexafluoroisopropyl)phthalic anhydride contain large trifluoromethyl side groups. This fluorinated structure increases the free volume of the polyimide molecular chain, hinders the close packing of the molecular chain, and disrupts the formation of charge-transfer complexes. This molecular structure design endows the amino-terminated polyimide powder with excellent solubility in reactive diluents such as acryloyl phosphate, while maintaining the intrinsic properties of high heat resistance and high transparency of polyimide materials, providing the material basis for achieving solvent-free processing.

[0013] Preferably, the preparation process of the amino-terminated polyimide powder includes: dissolving 2,2'-bis(trifluoromethyl)biphenyldiamine in N,N-dimethylacetamide, adding 4,4'-(hexafluoroisopropyl)diphthalic anhydride for reaction, adding acetic anhydride and pyridine for chemical imidization, and finally obtaining the powder through precipitation, filtration and drying.

[0014] By employing the above-mentioned technical solution, the two-step process of first synthesizing polyamic acid and then performing chemical imidization can precisely control the molecular weight distribution of the polymer. Using an acetic anhydride and pyridine system for chemical imidization, compared to thermal imidization, yields a polyimide precursor with better solubility and lower isomerization, facilitating subsequent dissolution in reactive diluents.

[0015] Preferably, the drying temperature is 70-90℃.

[0016] By adopting the above technical solution, a drying temperature of 70-90℃ can remove residual precipitant (methanol) and detergent (ethanol), while avoiding excessive temperature that could cause oxidation or self-condensation of the amino groups at the ends of the amino-terminated polyimide powder, thus ensuring amino activity and providing sufficient reaction sites for subsequent grafting reaction with isocyanate methacrylate.

[0017] Preferably, in the raw materials, isocyanate methacrylate undergoes an addition reaction with the amino groups at the ends of the amino-terminated polyimide powder.

[0018] By adopting the above technical solution, the chemical reaction pathway within the resin system was clarified, the possibility of physical mixing was eliminated, and the consistency and superiority of the final cured product's performance were ensured.

[0019] Secondly, the present invention provides a method for preparing solvent-free modified PI resin, employing the following technical solution: A method for preparing a solvent-free modified PI resin, used to prepare the solvent-free modified PI resin according to any of the above-mentioned first aspect, includes the following steps: S1. 2,2'-bis(trifluoromethyl)biphenyldiamine was dissolved in N,N-dimethylacetamide, and 4,4'-(hexafluoroisopropyl)diphthalic anhydride was added in batches under nitrogen protection to carry out the reaction, thereby obtaining an amino-terminated polyamic acid solution. S2. Acetic anhydride and pyridine were added to the amino-terminated polyamic acid solution, and the mixture was heated and stirred to carry out chemical imidization, resulting in a soluble polyimide solution. S3. The soluble polyimide solution was poured into methanol for precipitation. After filtration, washing with ethanol and vacuum drying, amino-terminated polyimide powder was obtained. S4. Dissolve the amino-terminated polyimide powder in a mixture of acryloxyline and isobornyl acrylate. After complete dissolution, add ethyl isocyanate methacrylate and stir in the dark to react, so that ethyl isocyanate methacrylate reacts with the amino groups at the ends of the amino-terminated polyimide powder to obtain a photosensitive modified polyimide resin base. S5. Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide was added to the photosensitive modified polyimide resin base and dispersed evenly by high-speed stirring under light-protected conditions to obtain solvent-free modified PI resin.

[0020] By employing the above technical solution, this preparation method designs a complete route from monomer synthesis to resin formulation. Steps S1 to S3, through molecular structure design, yielded terminal amino polyimide powders with specific solubility due to the introduction of fluorine-containing groups. Step S4 is the core innovation of this preparation method, employing an in-situ reaction strategy of dissolution followed by modification. Specifically, the high molecular weight terminal amino polyimide powder is first fully dissolved using acryloyl line and isobornyl acrylate to form a homogeneous liquid phase environment.

[0021] Subsequently, small-molecule isocyanate methacrylate is introduced into the liquid phase for grafting. This process sequence ensures that the modifier can fully contact the ends of the polymer chains, improving grafting efficiency, while avoiding the problem of uneven reaction in the solid state. Step S5 finally completes the construction of the photosensitive system. The entire preparation process does not require the removal of any solvent, and the prepared resin can be directly used for coating or 3D printing.

[0022] Preferably, in step S1, the reaction temperature is 20-30°C and the reaction time is 4-8 hours.

[0023] By adopting the above technical solution, the low-temperature and long-term polymerization conditions are beneficial to controlling the reaction rate, preventing local gelation caused by the accumulation of reaction heat, and ensuring that the generated polyamic acid has a suitable molecular weight and a narrow molecular weight distribution.

[0024] Preferably, in step S2, the temperature for chemical imidization is 50-70°C and the time is 3-5 hours.

[0025] By adopting the above technical solution, the temperature range and time range ensure the complete execution of the imidization ring-closing reaction, while avoiding side reactions caused by high temperature, thus ensuring the quality of the soluble polyimide solution.

[0026] Preferably, in step S3, the amount of methanol used is 1200-1800 parts by weight.

[0027] By adopting the above technical solution, a sufficient amount of precipitant (methanol) can quickly replace the good solvent (N,N-dimethylacetamide) in the polymer solution, causing the polymer to precipitate out in a loose powder form, which facilitates subsequent filtration and washing, and effectively removes unreacted monomers and catalyst residues.

[0028] Preferably, in step S4, the temperature of the reaction with stirring in the dark is 30-50°C, and the time is 4-6 hours.

[0029] By employing the above technical solution and controlling the reaction temperature at 30-50℃, the addition reaction rate between the isocyanate groups and amino groups can be promoted, while the thermal polymerization of the double bonds in isocyanate methacrylate can be prevented. Simultaneously, the light-shielding conditions prevent photopolymerization of the double bonds. This process window achieves a balance between the end-group functionalization of polyimide and the stability of the system.

[0030] This invention provides a solvent-free modified PI resin and its preparation method. It has the following beneficial effects: 1. This invention uses acryloyl line and isobornyl acrylate as reactive diluents, replacing traditional high-boiling-point organic solvents such as N-methylpyrrolidone. Acryloyl line and isobornyl acrylate directly participate in the polymerization reaction to build a crosslinked network during ultraviolet curing, which not only avoids the emission of volatile organic compounds, but also eliminates the volume shrinkage and long baking time required by solvent evaporation in traditional thermosetting processes, achieving a balance between green environmental protection and efficient processing.

[0031] 2. This invention utilizes ethyl isocyanate methacrylate as a chemical bridging agent. Urea bonds are generated by the reaction of isocyanate groups with the amino groups at the ends of amino-terminated polyimide powder, introducing photoactive double bonds into the polyimide molecular chain. This chemical modification allows the polyimide backbone to be tightly bound to the acrylate network formed by the reactive diluent during curing via chemical bonds, preventing microphase separation and thus improving the tensile strength and glass transition temperature of the solvent-free modified PI resin after curing.

[0032] 3. In the synthesis of amino-terminated polyimide powder, this invention selects 2,2'-bis(trifluoromethyl)biphenyldiamine and 4,4'-(hexafluoroisopropyl)phthalic anhydride, which contain large-volume trifluoromethyl side groups, as monomers. The introduction of fluorinated groups increases the intermolecular distance, hinders the close packing of molecular chains, and endows the amino-terminated polyimide powder with excellent solubility in reactive diluents such as acryloyl phosphate, providing a material basis for achieving a solvent-free photocuring system with high solids content and low viscosity. Attached Figure Description

[0033] Figure 1 This is a flowchart of the method of the present invention; Figure 2 This is a bar chart comparing the curing times of Example 1 and Comparative Example 1 in this invention; Figure 3 This is a bar chart comparing the VOC content of Example 1 and Comparative Example 1 in this invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings, examples, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Examples 1-3: Example 1

[0036] Reference Appendix Figure 1 S1. Dissolve 32.0 parts by weight of 2,2'-bis(trifluoromethyl)biphenyldiamine in 300 parts by weight of N,N-dimethylacetamide. Under nitrogen protection, add 39.9 parts by weight of 4,4'-(hexafluoroisopropyl)phthalic anhydride in batches. Stir and react at 25°C for 6 hours to obtain an amino-terminated polyamic acid solution. S2. Add 10.2 parts by weight of acetic anhydride and 5.0 parts by weight of pyridine to the amino-terminated polyamic acid solution, heat to 60°C and stir for 4 hours to carry out chemical imidization, and obtain a soluble polyimide solution. S3. The soluble polyimide solution was poured into 1500 parts by weight of methanol for precipitation. After filtration, washing with ethanol and vacuum drying at 80°C for 24 hours, amino-terminated polyimide powder was obtained. S4. Dissolve 50.0 parts by weight of amino-terminated polyimide powder in a mixture of 30.0 parts by weight of acryloxyline and 20.0 parts by weight of isoborneol acrylate. After complete dissolution, add 3.1 parts by weight of isocyanate methacrylate and stir at 40°C in the dark for 5 hours to allow the isocyanate methacrylate to undergo an addition reaction with the amino groups at the ends of the amino-terminated polyimide powder, thus obtaining a photosensitive modified polyimide resin base material. S5. Add 3.0 parts by weight of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide to the photosensitive modified polyimide resin base, and stir at high speed under light-protected conditions to disperse evenly, thus obtaining solvent-free modified PI resin. Example 2

[0037] S1. 34.0 parts by weight of 2,2'-bis(trifluoromethyl)biphenyldiamine were dissolved in 350 parts by weight of N,N-dimethylacetamide. Under nitrogen protection, 42.2 parts by weight of 4,4'-(hexafluoroisopropyl)diphthalic anhydride were added in batches. The mixture was stirred at 30°C for 8 hours to obtain an amino-terminated polyamic acid solution. S2. Add 12.0 parts by weight of acetic anhydride and 6.0 parts by weight of pyridine to the amino-terminated polyamic acid solution, heat to 70°C and stir for 5 hours to carry out chemical imidization, and obtain a soluble polyimide solution. S3. The soluble polyimide solution was poured into 1800 parts by weight of methanol for precipitation. After filtration, washing with ethanol and vacuum drying at 90°C for 24 hours, amino-terminated polyimide powder was obtained. S4. Dissolve 70.0 parts by weight of amino-terminated polyimide powder in a mixture of 15.0 parts by weight of acryloxyline and 15.0 parts by weight of isoborneol acrylate. After complete dissolution, add 1.5 parts by weight of isocyanate methacrylate and stir at 50°C in the dark for 6 hours to allow the isocyanate methacrylate to undergo an addition reaction with the amino groups at the ends of the amino-terminated polyimide powder, thus obtaining a photosensitive modified polyimide resin base material. S5. Add 5.0 parts by weight of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide to the photosensitive modified polyimide resin base, and stir at high speed under light-protected conditions to disperse evenly, to obtain solvent-free modified PI resin. Example 3

[0038] S1. Dissolve 30.0 parts by weight of 2,2'-bis(trifluoromethyl)biphenyldiamine in 250 parts by weight of N,N-dimethylacetamide, and under nitrogen protection, add 37.7 parts by weight of 4,4'-(hexafluoroisopropyl)diphthalic anhydride in batches. Stir and react at 20°C for 4 hours to obtain an amino-terminated polyamic acid solution. S2. Add 9.0 parts by weight of acetic anhydride and 4.0 parts by weight of pyridine to the amino-terminated polyamic acid solution, heat to 50°C and stir for 3 hours to carry out chemical imidization, and obtain a soluble polyimide solution. S3. The soluble polyimide solution was poured into 1200 parts by weight of methanol for precipitation. After filtration, washing with ethanol and vacuum drying at 70°C for 24 hours, amino-terminated polyimide powder was obtained. S4. Dissolve 30.0 parts by weight of amino-terminated polyimide powder in a mixture of 40.0 parts by weight of acryloxyline and 30.0 parts by weight of isoborneol acrylate. After complete dissolution, add 5.0 parts by weight of isocyanate methacrylate and stir at 30°C in the dark for 4 hours to allow the isocyanate methacrylate to undergo an addition reaction with the amino groups at the ends of the amino-terminated polyimide powder, thus obtaining a photosensitive modified polyimide resin base material. S5. Add 1.0 part by weight of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide to the photosensitive modified polyimide resin base, and stir at high speed under light-protected conditions to disperse evenly, to obtain solvent-free modified PI resin.

[0039] Comparative Examples 1-2: Comparative Example 1: Compared with Example 1, the difference is that in step S4, 50.0 parts by weight of terminal amino polyimide powder was dissolved in 50.0 parts by weight of N-methylpyrrolidone (replacing acryloxyline and isobornyl acrylate in Example 1, keeping the total weight of the liquid medium consistent), and ethyl isocyanate methacrylate was not added. The mixture was stirred evenly to obtain a polyimide resin solution. Also, in step S5, phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide was not added. All other steps were the same.

[0040] Comparative Example 2: Compared with Example 1, the difference is that ethyl isocyanate methacrylate was not added in step S4, and only the terminal amino polyimide powder was physically dissolved in a mixture of acrylonitrile and isoborneol acrylate. All other steps are the same.

[0041] Test example: To verify the actual performance of the solvent-free modified PI resin and its preparation method, performance tests were conducted on the resins and cured films prepared in Examples 1, 2, 3, Comparative Example 1, and Comparative Example 2.

[0042] Experimental procedure: Using a Brookfield DV-II+Pro rotational viscometer with a No. 25 rotor, the viscosity of the resins prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2 were measured at 25°C and 50 rpm.

[0043] The resins prepared in Examples 1, 2, 3, and Comparative Example 2 were coated onto glass substrates, with the wet film thickness controlled at 50 μm. The films were then tested at a dominant wavelength of 395 nm and a light intensity of 100 mW / cm². 2 Irradiate the resin under an LED ultraviolet light source and record the time required for the resin to change from a liquid state to a solid state without fingerprint imprints on the surface; place the resin prepared in Comparative Example 1 in an oven and heat it until the solvent evaporates and imidization is completed, and record the time required.

[0044] According to GB / T1040.3-2006 standard, the resins prepared in Examples 1, 2, 3 and Comparative Example 2 were photocured into films, and the resin prepared in Comparative Example 1 was thermocured into films. The films were cut into dumbbell-shaped strips, and the maximum stress value at the time of fracture was determined by a universal testing machine at a tensile rate of 5 mm / min. Each group was tested 5 times and the average value was taken.

[0045] Using a dynamic thermomechanical analyzer in tensile mode, the temperature of the cured film sample was scanned from 50℃ to 350℃ at a heating rate of 5℃ / min and a frequency of 1Hz. The temperature corresponding to the peak value of the loss factor was recorded as the glass transition temperature.

[0046] According to GB / T23985-2009 standard, the resin sample was heated at 105℃ for 1 hour, and the percentage of mass loss before and after heating was calculated as the content of volatile organic compounds.

[0047] The test results are as follows: Table 1. Performance test data of the examples and comparative examples Test Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Viscosity 1240 3850 420 1350 1180 Curing time 6 seconds 9 seconds 3 seconds 14 hours 5 seconds Tensile strength 94.6 101.3 78.2 108.5 46.7 Glass transition temperature 243 261 218 278 182 VOC content 0.42 0.38 0.55 50 0.45 Among them, viscosity is measured in mPa·s at 25℃; tensile strength is measured in MPa; glass transition temperature is measured in Tg (℃); and VOC content is measured in _____.

[0048] Reference Appendix Figure 1-2 , Figure 1-2 The following are bar charts comparing the curing time and VOC content of Example 1 and Comparative Example 1, respectively.

[0049] Figure 1 Example 1 (6 seconds): represents the solvent-free photocuring system of the present invention.

[0050] Comparative Example 1 (14 hours / 50400 seconds): Represents a traditional solvent-based thermosetting polyimide system.

[0051] Figure 1 This invention demonstrates that it transforms the traditional thermally induced phase change (solvent evaporation + thermal imidization) into a photo-initiated free radical chain polymerization reaction, thereby achieving second-level curing and improving processing efficiency.

[0052] Figure 2 In Example 1 (0.42%), the VOC content was close to zero.

[0053] Comparative Example 1 (50.0%): Half of the mass consisted of volatile organic compounds.

[0054] Although Comparative Example 1 maintained the same solids content as Example 1 (both 50%), it relied on N-methylpyrrolidone as a solvent, and the solvent had to evaporate completely during the film formation process, resulting in higher VOCs.

[0055] Example 1 used acryloyl line and isobornyl acrylate as reactive diluents. These monomers not only dissolved the polyimide powder, but also directly participated in the crosslinking reaction under ultraviolet light, becoming part of the cured film structure instead of evaporating into the air. Figure 2 This confirms that the present invention achieves the environmental goal of zero solvent emissions.

[0056] Table 1 shows that the viscosity range of the resins prepared in Examples 1, 2, and 3 is between 420 mPa·s and 3850 mPa·s. In Example 2, the terminal amino polyimide powder has a larger molecular weight and a higher addition amount, resulting in the highest viscosity of the resin prepared in Example 2. In Example 3, the terminal amino polyimide powder has a smaller molecular weight and a lower addition amount, and a higher proportion of reactive diluent, resulting in the lowest viscosity of the resin prepared in Example 3. Comparative Example 1, because the terminal amino polyimide powder was dissolved in the good solvent N-methylpyrrolidone, and the solid content was the same as in Example 1, had a viscosity of 1350 mPa·s, which is on the same order of magnitude as in Example 1, thus eliminating the influence of viscosity difference on coating performance.

[0057] The VOC content of the resins prepared in Examples 1 to 3 was less than 1%, while the VOC content of the resin prepared in Comparative Example 1 was 50.0%, indicating that the use of an active diluent system in Examples 1 to 3 avoided the volatilization of organic solvents.

[0058] Regarding the curing rate, the resins prepared in Examples 1, 2, and 3 cured within 3 to 9 seconds under ultraviolet light irradiation, while the resin prepared in Comparative Example 1 required 14 hours of heating to cure. The difference stems from the fact that Examples 1 to 3 used free radical photopolymerization to replace the solvent evaporation and thermal cyclization process of Comparative Example 1.

[0059] Regarding mechanical and thermal properties, the resin-cured film prepared in Example 1 had a tensile strength of 94.6 MPa and a glass transition temperature of 243 °C. The resin-cured film prepared in Comparative Example 2 had a tensile strength of 46.7 MPa and a glass transition temperature of 182 °C. The difference between Example 1 and Comparative Example 2 is that isocyanate methacrylate was introduced in the preparation process of Example 1. In the system of Example 1, the isocyanate groups of isocyanate methacrylate react with the terminal amino groups of the amino-terminated polyimide powder to form urea bonds, grafting photoactive double bonds onto the ends of the polyimide molecular chains. During photocuring, the modified polyimide molecular chains chemically bond with the crosslinking network formed by acryloyl phosphate and isobornyl acrylate through double bonds, forming a uniform network structure, which improves stress transfer efficiency and restricts chain segment movement. In Comparative Example 2, the mid-amino polyimide powder was not chemically modified and was only physically suspended or dissolved in an active diluent. During the curing process, the polyimide molecular chains did not participate in the construction of the cross-linked network, resulting in micro-phase separation. Consequently, the mechanical strength and heat resistance of Comparative Example 2 were lower than those of Example 1.

Claims

1. A solventless modified PI resin characterized in that, The end-amino polyimide powder is made from raw materials comprising the following weight parts: End-amino polyimide powder: 30.0-70.0 parts; Acrylonitrile: 15.0-40.0 parts; Isobornyl acrylate: 15.0-30.0 parts; Isocyanatoethyl methacrylate: 1.5-5.0 parts; Phenyl bis (2, 4, 6-trimethyl benzoyl) phosphine oxide: 1.0-5.0 parts.

2. The solventless modified PI resin according to claim 1, characterized in that, The end-amino polyimide powder is made from raw materials comprising the following weight parts: 2, 2'-bis (trifluoromethyl) diphenyl diamine: 30.0-34.0 parts; 4, 4'- (hexafluoroisopropyl) diphthalic anhydride: 37.7-42.2 parts; N, N-dimethylacetamide: 250-350 parts; Acetic anhydride: 9.0-12.0 parts; Pyridine: 4.0-6.0 parts.

3. The solventless modified PI resin according to claim 2, characterized in that, The preparation process of the end-amino polyimide powder comprises: Dissolving the 2, 2'-bis (trifluoromethyl) diphenyl diamine in the N, N-dimethylacetamide, adding the 4, 4'- (hexafluoroisopropyl) diphthalic anhydride for reaction, adding the acetic anhydride and the pyridine for chemical imidization, and finally obtaining through precipitation, filtration and drying.

4. The solventless modified PI resin according to claim 3, characterized in that, The temperature of the drying is 70-90℃.

5. The solventless modified PI resin according to claim 1, characterized in that, In the raw materials, the isocyanatoethyl methacrylate and the amino group at the end of the end-amino polyimide powder undergo addition reaction.

6. A process for the preparation of a solvent-free modified PI resin, characterized by, A solvent-free modified PI resin according to any one of claims 1-5, comprising the following steps: S1, dissolving 2, 2'-bis (trifluoromethyl) diphenyl diamine in N, N-dimethylacetamide, adding 4, 4'- (hexafluoroisopropyl) diphthalic anhydride in batches under nitrogen protection, and reacting to obtain an end-amino polyamide acid solution; S2, adding acetic anhydride and pyridine to the end-amino polyamide acid solution, and stirring to react at elevated temperature to perform chemical imidization, thereby obtaining a soluble polyimide solution; S3, pouring the soluble polyimide solution into methanol for precipitation, and then filtering, washing with ethanol and vacuum drying to obtain an end-amino polyimide powder; S4, dissolving the end-amino polyimide powder in a mixture of acrylonitrile and isobornyl acrylate, adding isocyanatoethyl methacrylate after complete dissolution, and stirring to react in the dark, so that the isocyanatoethyl methacrylate and the amino group at the end of the end-amino polyimide powder undergo addition reaction, thereby obtaining a photosensitive modified polyimide resin base; S5, adding phenyl bis (2, 4, 6-trimethyl benzoyl) phosphine oxide to the photosensitive modified polyimide resin base, and stirring uniformly at high speed in the dark, thereby obtaining a solvent-free modified PI resin.

7. The method for preparing a solvent-free modified PI resin according to claim 6, characterized in that, In the S1 step, the reaction temperature is 20-30℃, and the reaction time is 4-8 hours.

8. The method for preparing a solvent-free modified PI resin according to claim 6, characterized in that, In the S2 step, the chemical imidization temperature is 50-70℃, and the chemical imidization time is 3-5 hours.

9. The method for preparing a solvent-free modified PI resin according to claim 6, characterized in that, In the S1 step, the amount of the 2, 2'-bis (trifluoromethyl) diphenyl diamine is 30.0-34.0 parts by weight, the amount of the 4, 4'- (hexafluoroisopropyl) diphthalic anhydride is 37.7-42.2 parts by weight, and the amount of the N, N-dimethylacetamide is 250-350 parts by weight. In the S2 step, the amount of acetic anhydride is 9.0-12.0 parts by weight, and the amount of pyridine is 4.0-6.0 parts by weight; In the S3 step, the amount of methanol is 1200-1800 parts by weight.

10. The method for preparing a solvent-free modified PI resin according to claim 6, characterized in that, In the S4 step, the temperature for stirring the reaction in the dark is 30-50℃, and the time is 4-6 hours.

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