A special radical plasticizing-activator and low-temperature forming high-temperature resistant polyimide resin based on it, preparation method and use

Abstract

The application provides a special radical plasticizing-activating agent, a low-temperature forming high-temperature-resistant polyimide resin prepared based on the special radical plasticizing-activating agent, a preparation method and an application, and belongs to the field of advanced material technology. Based on the integrated molecular design idea with the synergistic effect of "viscosity reduction and flow increase-low temperature crosslinking", a low-viscosity polyimide oligomer capable of generating radicals is introduced as a radical plasticizing-activating agent, and in the co-curing with a polyimide oligomer containing a terminal alkyne group, the radicals generated in situ during heating promote the synergistic copolymerization of the terminal alkyne group and the internal alkyne group, so that the system has both low-temperature processability and high-temperature stability. The polyimide resin has both "low-temperature efficient curing" and "excellent heat resistance and mechanical properties", breaks through the bottleneck that traditional polyimide resins are difficult to balance between process temperature and high-temperature heat stability, and makes the polyimide resin have a wide application market in the fields of aerospace, electronic packaging, heat-resistant and heat-protection composites.

Description

Technical Field

[0001] This invention belongs to the field of advanced materials technology, specifically relating to a special free radical plasticizer-activator and a low-temperature molding high-temperature resistant polyimide resin prepared based thereon, its preparation method and uses. Background Technology

[0002] Polyimide (PI) is a class of high-performance engineering resins containing aromatic imide ring structures. It possesses excellent thermal stability, chemical inertness, and mechanical strength, and is widely used in aerospace, electronic packaging, and heat-resistant and thermal protection composite materials. Currently, the most widely used PI system internationally is the phenylethynyl-terminated imide (PETI) series developed by NASA, such as PETI-5, PETI-330, and PETI-375. However, existing phenylethynyl-terminated polyimide materials (such as PETI-5) generally suffer from technical bottlenecks such as a narrow processing window, high curing temperature, and insufficient temperature resistance; their curing process typically requires temperatures above 370°C.

[0003] To reconcile the inherent contradiction between low melt processing temperature and high heat resistance in PI systems, existing technologies focus on improving low-temperature molding performance through molecular structure modification. This is achieved by introducing non-coplanar structures and large-volume substituents to adjust the main chain structure, thereby reducing the viscosity of the processing system, improving processing flowability, and expanding the processing window. Li et al. (Li, X.; Zhang, P.; Dong, J.; Gan, F.; Zhao, X.; Zhang, Q. Preparation of flow-k-polyimides in outstanding stability of dielectric properties versus temperature by adding an active cardo-containing diluent. Compos. Part B-Eng. 2019, 177, 107401) introduced a reactive cardo-containing diluent into PETI oligomers, achieving a minimum viscosity of 1.65 Pa·s at 268°C, a curing temperature of 370°C, and obtaining a T... gA PETI oligomer based on bisphenol AF (BPAF) has been developed. This system has a bulky and highly twisted caloric structure, a cured Tg of up to 487°C, a 5% weight loss temperature in air (Td5%) exceeding 550°C, and a minimum melt viscosity. The resin has a curing temperature of up to 403°C. Meng et al. (Meng, X.; Wen, Y.; Wang, X.; Shen, D.; Yan, J.; Wang, Z. High-performance imide oligomers and thermosets derived from 9,9-bis(3,4-dicarboxyphenyl)fluorenedianhydride. Polymer 2023, 281, 126086) possesses a curing temperature of up to 403°C. Approximately 2 Pa·s (332°C); Hong et al. (Hong, W.; Yuan, L.; Ma, Y.; Cui, C.; Zhang, H.; Yang, S.; Sun, W.) synthesized fluorinated PETI oligomers based on 6FDA and different diamines, with a minimum melt viscosity below 1 Pa·s, a curing temperature of approximately 380°C, and a curing temperature of approximately 2 Pa·s (332°C). g The curing temperature ranges from 363 to 391°C. Hong et al. (Hong, W.; Yuan, L.; Yang, S. High-temperature phenylethynyl-terminated imide oligomers derived from asymmetric diphenyl etherdiamines for resin transfer molding. Polymer 2023, 269, 125635.) further designed asymmetric fluorinated PETI oligomers based on 6FDA and various asymmetric diamines, achieving a minimum melt viscosity below 0.15 Pa·s, a curing temperature of 380°C, and a Tg as high as 426°C. However, existing strategies still struggle to achieve an ideal balance between processing performance and heat resistance. Most PIs still require curing temperatures above 370°C, and there are also issues with insufficient thermal stability or low decomposition temperatures, limiting their application in large-size complex components.

[0004] In addition, existing technologies also use external initiators or catalysts to reduce the activation energy of the phenylethynyl crosslinking reaction by utilizing the decomposition products of the initiator or the catalytic effect of the catalyst, thereby reducing the curing temperature. Harbin Institute of Technology (Qian,Y.,Yang,J.,&Zhang,C.(2021). Phenylethynyl terminated polyimide resin / carbon fiber composite catalytic cured at 300°C and its performance. Journal of Adhesion Science and Technology,35(23),2652-2663) used a composite catalyst of isopropyl peroxide and cobalt naphthenate to catalyze the crosslinking reaction of phenylethynyl-terminated polyimide resin, reducing the curing temperature of phenylethynyl polyimide to 300°C. In subsequent research, a thiocarbonyl disulfide compound was introduced to achieve catalytic curing of phenylethynyl-terminated polyimide, reducing the curing temperature to 260.4°C. However, organic peroxides have poor thermal stability, and high processing temperatures cause them to decompose prematurely, rendering them ineffective. Furthermore, the small molecule products generated during decomposition can create pores within the material, negatively impacting its density and mechanical properties. Transition metal catalysts have also been attempted to lower curing temperatures, but they suffer from serious residue problems. These residues can act as catalysts for the thermal oxidative degradation of polymers at high temperatures, accelerating molecular chain breakage and oxidative aging, and ultimately reducing material performance.

[0005] In summary, existing improvement methods for phenylacetylene-terminated polyimide systems suffer from narrow processing windows and high curing temperatures, making it difficult to meet the requirements of achieving both "low-temperature, high-efficiency curing" and "excellent heat resistance" in polyimide materials. Therefore, developing a technical solution that achieves low-temperature, high-efficiency curing while simultaneously imparting excellent heat resistance to polyimide resins is of great significance for expanding the application of aromatic thermosetting polyimide materials. Summary of the Invention

[0006] The purpose of this invention is to provide a special free radical plasticizer-activator and a low-temperature molding high-temperature resistant polyimide resin prepared based thereon, its preparation method and uses.

[0007] This invention provides a polyimide oligomer, which is obtained by reacting a polyamine compound with free radical generating ability and a twisted non-coplanar structure with a capping agent; the capping agent is a monoacid anhydride containing an alkynyl group.

[0008] Furthermore, the molar ratio of the polyamine compound to the capping agent is (2~8):(0.5~3);

[0009] The polyamine compound is a hydroxyl-containing cyclic polyamine compound with the structural formula (R). n1 -X-OH, wherein R is an amino-substituted cycloalgyl group, n1=2 or 3, and X is a straight-chain or branched C1~C6 alkylene group; preferably, R is an amino-substituted aryl group, n1=3;

[0010] The alkyne-containing monoacid anhydride includes at least one of 4-phenylethynyl phthalic anhydride, 3-phenylethynyl phthalic anhydride, 5-phenylethynyl naphthalene-1,8-dicarboxylic anhydride, 4-(1-propynyl)phthalic anhydride, 4-(4-tert-butylphenylethynyl)phthalic anhydride, and 4-(4-phenoxyphenylethynyl)phthalic anhydride.

[0011] Furthermore, the molar ratio of the polyamine compound to the capping agent is 5:1.5;

[0012] The hydroxyl-containing cyclic polyamine compounds include parapine alkaloids or 4,4'-diaminotriphenylmethanol.

[0013] This invention also provides a method for preparing polyimide oligomers, comprising the following steps:

[0014] (1) A polyamine compound with free radical generating ability and a twisted non-coplanar structure is reacted with a capping agent to obtain a reaction solution;

[0015] (2) Then add a dehydrating agent and a catalyst to the reaction solution, purify, heat treat, and obtain polyimide oligomer.

[0016] Furthermore, the molar ratio of the polyamine compound to the dehydrating agent and catalyst is (2~8):(2~6):(2~6).

[0017] Furthermore, the molar ratio of the polyamine compound, dehydrating agent, and catalyst is 5:4:4.

[0018] Further, the reaction solvent is an organic solvent; the reaction temperature in step (1) is 50~70℃, the reaction time is 6~10h, and the solid content of the reaction solution is 25~35wt%; the reaction temperature in step (2) is 90~130℃, and the reaction time is 20~28h; the purification steps include: alcohol precipitation, collecting solids, washing, and drying; the heat treatment temperature is 240~280℃, and the heat treatment time is 1~3h.

[0019] Further, the organic solvent includes at least one selected from N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the dehydrating agent includes at least one selected from trifluoroacetic anhydride, acetic anhydride, thionyl chloride, and organosilicon compounds; and the catalyst includes at least one selected from triethylamine and pyridine. This invention also provides the use of polyimide oligomers in the preparation of polyimide resins having low molding viscosity, low curing temperature, and / or high-temperature resistance.

[0020] The present invention also provides a polyimide resin, which is obtained by co-curing a polyimide oligomer containing terminal alkyne groups and a polyimide oligomer; wherein the polyimide oligomer containing terminal alkyne groups is prepared by using aromatic diamine and dianhydride as monomers and alkyne-containing monoacid anhydride as end-capping agent.

[0021] Furthermore, the mass ratio of the polyimide oligomer containing terminal alkyne groups to the polyimide oligomer is (0.5~2):(0.5~2);

[0022] The molar ratio of the aromatic diamine, dianhydride, and capping agent is (0.5~3):(0.2~2):(0.5~3);

[0023] The dianhydride mentioned is a dianhydride containing an alkyne group;

[0024] The aromatic diamine includes at least one of the following: fluorenyl-containing aromatic diamines, alkynyl-containing aromatic diamines, phenyl-containing aromatic diamines, and disulfide-containing aromatic diamines;

[0025] The alkyne-containing monoacid anhydride includes at least one of 4-phenylethynyl phthalic anhydride, 5-phenylethynyl naphthalene-1,8-dicarboxylic anhydride, 4-(1-propynyl)phthalic anhydride, 2-aminophenylethyn, 3-aminophenylethyn, and 4-ethynylaniline.

[0026] Furthermore, the mass ratio of the polyimide oligomer containing terminal alkyne groups to the polyimide oligomer is 1:1;

[0027] The molar ratio of the aromatic diamine, dianhydride, and capping agent is 2:1:2;

[0028] The alkynyl-containing dianhydrides include 4,4'-(acetylene-1,2-diyl)dibenzoic anhydride;

[0029] The fluorene-containing aromatic diamines include 9,9-bis(4-aminophenyl)fluorene, 9,9-bis(4-amino-3-methylphenyl)fluorene, 9,9-bis(4-amino-3,5-dimethylphenyl)fluorene, 9,9-bis(4-amino-3-trifluoromethylphenyl)fluorene, or 9,9-bis(4-amino-3-methoxyphenyl)fluorene;

[0030] The alkynyl-containing aromatic diamines include (3,3'-(acetylene-1,2-diyl)diphenylamine), 4,4'-(acetylene-1,2-diyl)diphenylamine, or 3,4'-(acetylene-1,2-diyl)diphenylamine;

[0031] The phenyl-containing aromatic diamines include o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 2-methyl-1,4-phenylenediamine, or 1,2-di(aminomethyl)benzene;

[0032] The disulfide-containing aromatic diamines include 4,4'-diaminodiphenyl disulfide, 2,2'-diaminodiphenyl disulfide, or 3,3'-diaminodiphenyl disulfide;

[0033] The present invention also provides a method for preparing polyimide resin, comprising the following steps:

[0034] (1) Aromatic diamine reacts with dianhydride, and a capping agent is added to continue the reaction;

[0035] (2) Add dehydrating agent and catalyst to react, purify, heat treat to obtain polyimide oligomers containing terminal alkyne groups;

[0036] (3) After mixing polyimide oligomers containing terminal alkyne groups with polyimide oligomers, polyimide resin is obtained by co-curing.

[0037] Furthermore, the mixing method is one or more of the following: dry mixing, wet mixing, melt mixing, energy field enhanced dispersion, and stepwise / masterbatch method.

[0038] Furthermore, the molar ratio of the aromatic diamine to the dehydrating agent and catalyst is (0.5~3):(6~10):(6~10).

[0039] Furthermore, the molar ratio of the aromatic diamine to the dehydrating agent and catalyst is 2:8:8.

[0040] Further, the solvent for the reaction is an organic solvent; the reaction temperature in step (1) is 50~70℃, the reaction time is 6~10 hours, and the reaction time is 10~14 hours; the solid content of the solution obtained after the reaction is completed is 25~35 wt%; the reaction temperature in step (2) is 90~130℃, and the reaction time is 20~28 hours; the purification steps include: alcohol precipitation, solid collection, washing, and drying; the heat treatment temperature is 240~280℃, and the heat treatment time is 1~3 hours; the polyimide oligomer containing terminal alkyne groups and the curing method of the polyimide oligomer are vacuum hot pressing molding.

[0041] Further, the organic solvent includes at least one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, and dimethyl sulfoxide; the dehydrating agent includes at least one of trifluoroacetic anhydride, acetic anhydride, thionyl chloride, and organosilicon compound; the catalyst includes at least one of triethylamine and pyridine; the vacuum hot pressing conditions are: vacuuming to -85~110kPa, pressurizing to 8~12MPa, heating to 270~310℃ and holding for 15~45min, then heating to 300~330℃ and holding for 1~5h.

[0042] This invention also provides the use of polyimide resins in aerospace, electronic packaging, heat-resistant and thermal protection composite materials.

[0043] This invention involves reacting aromatic diamines and dianhydrides with an alkynyl-containing end-capping agent to obtain polyimide oligomers containing terminal alkynyl groups. The polyimide oligomers are then introduced as free radical plasticizers-activators. These free radical plasticizers-activators generate triphenylmethyl free radicals in situ during heating, utilizing their free radical activation effect to promote the self-curing reaction of the terminal alkynyl groups, thus giving the system both low-temperature processability and high-temperature stability. Furthermore, by reacting aromatic diamines and dianhydrides containing internal alkynyl groups with an alkynyl-containing end-capping agent, polyimide oligomers containing both terminal and internal alkynyl groups are obtained, achieving synergistic crosslinking of terminal and internal alkynyl groups. The introduction of the polyimide oligomers, which generate triphenylmethyl free radicals in situ during heating, can further activate the synergistic copolymerization of the terminal alkynyl groups and the alkynyl groups within the main chain, giving the system both low-temperature processability and superior high-temperature stability.

[0044] Experiments have shown that introducing polyimide oligomers into polyimide oligomers containing terminal alkyne groups for co-curing can significantly reduce the curing temperature of the system from 370℃ to 310~320℃, thereby greatly reducing the minimum viscosity of the system and expanding the processing window of the material; at the same time, the resulting product has excellent thermal stability and mechanical properties, with a Tc... g >490℃, T d The T-phase of the co-cured system of terminal alkyne-endoyne polyimide oligomers and free radical plasticizer-activator at >540℃ d The highest temperature reached was 579.2℃.

[0045] This invention enables polyimide resin to possess both "low-temperature and high-efficiency curing" and "excellent heat resistance and mechanical properties," breaking through the bottleneck of traditional polyimide resins' difficulty in balancing process temperature and thermal stability, thus enabling polyimide resins to have a larger application market.

[0046] Obviously, based on the above description of the present invention, and according to common technical knowledge and conventional methods in the field, various other modifications, substitutions or alterations can be made without departing from the basic technical concept of the present invention.

[0047] The following detailed embodiments further illustrate the above-described content of the present invention. However, this should not be construed as limiting the scope of the present invention to the following embodiments. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Attached Figure Description

[0048] Figure 1 A is a flowchart of the synthesis of polyimide oligomer (PI1) using α-BPDA, 6FDA and EBPA dianhydride as raw materials, aromatic diamine BAFL and active end-capping agent 4-PEPA. Figure 1 b is a flowchart of the preparation of trifunctional polyimide oligomer (PI2) formed by trifunctional aromatic diamine (MT) and terminal styrene anhydride PEPA; Figure 1 c is a schematic diagram of the catalyst-free molecular design mechanism, which features viscosity dilution and low-temperature cross-linking networks.

[0049] Figure 2 a is the FTIR spectrum of PI1; Figure 2 b is the FTIR spectrum of PI2; Figure 2 c1 is PI1. 1 H NMR spectrum; Figure 2 c2 is the proton coordination map of PI1; Figure 2 d1 is PI2 1 H NMR spectrum; Figure 2 d2 is the proton coordination diagram of PI2; Figure 2 e represents the DFT optimization results for MT, PB, αBPDA, 6FDA, EBPA, PEPA, and BAFL, revealing that the molecular structures of each unit exhibit a distorted, non-coplanar configuration.

[0050] Figure 3 a is the differential scanning calorimetry (DSC) curve of PI1; Figure 3 b is the DSC curve of PI2; Figure 3 c and Figure 3 d represents the HOMO / LUMO and band gap of PI1 and PI2, respectively. Figure 3 e is the variable-temperature electron paramagnetic resonance (EPR) spectrum of PB; Figure 3 f is the ESP and LEAE diagram of PEPA; Figure 3 g represents the A and B radical-initiated curing mechanism of the triphenylmethyl-assisted ethyl polymerization pathway; Figure 3 h, i1, and i2 are the potential energy surfaces and corresponding transition states and structures calculated by density functional theory (DFT), and the single-point energy represents the attack path of the free radical.

[0051] Figure 4 a and Figure 4 b represents the composite viscosity-temperature curves of PI1 and PI2, respectively; Figure 4 c and Figure 4 d represents the XRD patterns of PI1 and PI2, respectively; Figure 4 ef represents the molecular geometry optimized by DFT and the calculated structural dimensions of the corresponding system. Figure 4 g1 and Figure 4 g2 represents the molecular dynamics (MD) simulation free volume fraction (FFV) of PB / PEPA and MT / PEPA, respectively. Figure 4 h is the molecular diffusion coefficient used to calculate PI2 resin.

[0052] Figure 5 a is the DMA curve of PI1; Figure 5 b is the DMA curve of PB / PEPA; Figure 5 c is the DMA curve of MT / PEPA resin; Figure 5 d and Figure 5 e represents the TGA curves of PI1 and PI2, respectively; Figure 5 f represents the curing temperature and T of PI1 and PI2 compared to the previously reported PI system. g Comparison; Figure 5 g is the TMA curve of PI1 and PI2 after curing; Figure 5 h represents the compressive stress-strain curves of PI1 and PB / PEPA after heat exposure at 25℃ and 300℃ for 15 min. Figure 5 i is a schematic diagram of the dual-network design strategy for low-temperature processable and high-temperature resistant PI systems: Strategy 1: Multifunctional free radical-synergistic crosslinking; Strategy 2: Terminal end-ethyl co-crosslinking.

[0053] Figure 6 a is a schematic diagram of the catalytic activation mechanism by which the PB / PEPA system promotes the low-temperature curing, thermal stability and mechanical properties of PI1 resin; Figure 6 bd represents the DSC curves for PI1, PI2, and PI1-PB / PEPA (mass ratio = 1:1); Figure 6 e.g., the complex viscosity-temperature curves of PI1, PI2, and PI1-PI2 (mass ratio = 1:1); Figure 6 h is the potential energy distribution plot calculated by DFT for different reaction pathways; Figure 6 i is a schematic diagram of the mechanism by which PB / PEPA attacks ethynyl radicals within EBPA in the interpenetrating PI1 / PI2 cross-linked network; Figure 6 j represents the structure and single-point energy of the reactants, transition states, and products on the DFT-optimized reaction path C.

[0054] Figure 7 a is the DSC curve of polyimide resins co-cured with α-BPDA / BAFL / PEPA, PB / PEPA, and α-BPDA / BAFL / PEPA and PB / PEPA (mass ratio = 1:1). Figure 7b is the DSC curve of polyimide resins co-cured with 6FDA / BAFL / PEPA, PB / PEPA, and 6FDA / BAFL / PEPA and PB / PEPA (mass ratio = 1:1). Figure 7 c is the DSC curve of polyimide resins co-cured with EBPA / BAFL / PEPA, PB / PEPA, and EBPA / BAFL / PEPA and PB / PEPA (mass ratio = 1:1). Figure 7 d is the TG and DTG curve of the polyimide resin co-cured with α-BPDA / BAFL / PEPA and PB / PEPA (mass ratio = 1:1); Figure 7 e is the TG and DTG curve of the polyimide resin co-cured with 6FDA / BAFL / PEPA and PB / PEPA (mass ratio = 1:1); Figure 7 f is the TG and DTG curve of the polyimide resin co-cured with EBPA / BAFL / PEPA and PB / PEPA (mass ratio = 1:1); Figure 7 g is the TMA curve of PI1 and PI1-PB / PEPA (mass ratio = 1:1) co-cured resin; Figure 7 h is the compressive stress-strain curve of PI1-PB / PEPA (mass ratio = 1:1) co-cured resin after exposure to heat at room temperature and 300℃ for 15 min; Figure 7 i is the T value between the state-of-the-art low-temperature processable heat-resistant polyimide reported in the literature and the polyimide resin of this invention. g Comparison with curing temperature parameters. Detailed Implementation

[0055] The raw materials and equipment used in this invention are all known products, obtained by purchasing commercially available products.

[0056] The main raw materials used in the specific embodiments of this invention include: aromatic diamine 9,9-bis(4-aminophenyl)fluorene (BAFL), paraben (PB), 4',4',4'-triaminotriphenylmethane (MT), dianhydride 2,3',4,4'-biphenyltetracarboxylic dianhydride α-BPDA, 4,4'-(hexafluoroisopropene)phthalic anhydride 6FDA, 4,4'-(acetylene-1,2-diyl)dibenzoic anhydride EBPA, end-capping agent 4-phenylethynyl phthalic anhydride 4-PEPA, solvent anhydrous N-methyl-2-pyrrolidone (NMP), dehydrating agent acetic anhydride, and catalyst pyridine. All the above raw materials were purchased from Chengdu Kelong Chemical Co., Ltd. All raw materials were vacuum dried at 150°C for 8 hours to remove moisture.

[0057] Example 1: Preparation of polyimide oligomers

[0058] 1.1 Preparation of PB / PEPA

[0059] (1) Under nitrogen protection, 0.05 mol PB was weighed and dissolved in anhydrous NMP. After stirring at 25°C for 1 h, 0.15 mol 4-PEPA was added and stirred at 60°C for 8 h to make the solid content 30 wt% and obtain the reaction solution.

[0060] (2) Then add 0.4 mol each of acetic anhydride and pyridine to the reaction solution and reflux at 110°C for 24 h. After cooling, slowly pour into 1 L of anhydrous ethanol and precipitate the product under stirring. The obtained solid is vacuum filtered, washed three times with ethanol and deionized water, dried under vacuum at 180°C for 24 h, and then heat-treated at 200°C for 8 h to obtain PB / PEPA, which is then ground into powder for later use.

[0061] Comparative Example 1: Preparation of MT / PEPA

[0062] Refer to 1.1, the only difference being that PB is replaced with MT.

[0063] PB / PEPA and MT / PEPA are both polyimide oligomers, collectively referred to as PI2; their synthetic routes are as follows: Figure 1 As shown in b.

[0064] Example 2: Preparation of polyimide resin

[0065] 2.1 Preparation of polyimide oligomers containing terminal alkyne groups

[0066] 2.1.1 Preparation of EBPA / BAFL / PEPA

[0067] Under a nitrogen atmosphere, 0.2 mol BAFL was dissolved in NMP and stirred at 25 °C for 0.5 h. Then, 0.1 mol EBPA was added and stirred at 60 °C for 8 h to form a polyamic acid solution. After cooling to room temperature, 0.2 mol 4-PEPA was added and the reaction continued for 12 h to obtain a precursor solution with a solid content of 30 wt%. Then, 0.8 mol acetic anhydride and 0.8 mol pyridine were added and refluxed at 110 °C for 24 h to complete the imidization reaction. After cooling, the reaction solution was slowly poured into 1 L of ethanol, and the product was precipitated under vigorous stirring. The obtained solid was collected by vacuum filtration, repeatedly washed with ethanol and deionized water, vacuum dried at 80 °C for 24 h, and then heat-treated at 260 °C for 2 h to obtain EBPA / BAFL / PEPA, which was then ground into powder for later use.

[0068] 2.1.2 Preparation of 6FDA / BAFL / PEPA

[0069] Refer to 2.1.1, the only difference being that EBPA is replaced with 6FDA.

[0070] 2.1.3 Preparation of α-BPDA / BAFL / PEPA

[0071] Refer to 2.1.1, the only difference being that EBPA is replaced with α-BPDA.

[0072] EBPA / BAFL / PEPA, 6FDA / BAFL / PEPA, and α-BPDA / BAFL / PEPA are all polyimide oligomers containing terminal alkyne groups, collectively referred to as PI1. The difference lies in that EBPA / BAFL / PEPA contains both internal and terminal alkyne groups, while 6FDA / BAFL / PEPA and α-BPDA / BAFL / PEPA contain terminal alkyne groups but not internal alkyne groups. Their synthetic routes are as follows: Figure 1 As shown in a.

[0073] 2.2 Preparation of polyimide resin

[0074] EBPA / BAFL / PEPA, 6FDA / BAFL / PEPA, and α-BPDA / BAFL / PEPA were mixed with PB / PEPA at a mass ratio of 1:1 in a high-speed mixer at 26,000 rpm for 5 minutes to obtain a homogeneous mixture. The mixture was then hot-pressed and cured in a vacuum hot press: a vacuum of -92 kPa was applied, a pressure of 10 MPa was applied, and the temperature was raised to 280°C and held for 0.5 hours to achieve melt flow and leveling. The temperature was then raised to 310°C and held for 3 hours to complete curing. After cooling, the resulting product was demolded and ground to obtain polyimide resins co-cured with EBPA / BAFL / PEPA+PB / PEPA, 6FDA / BAFL / PEPA+PB / PEPA, and α-BPDA / BAFL / PEPA+PB / PEPA.

[0075] The following experimental examples demonstrate the beneficial effects of the present invention.

[0076] Structural characterization of Experiment 1, PI1, PI2 and polyimide resin

[0077] 1.1 Characterization Methods

[0078] (1) The chemical structure of the sample was determined by Fourier transform infrared spectroscopy (FT-IR, Nicolet 570, Thermo Scientific, USA, 4000-400 cm⁻¹). -1 ) and hydrogen nuclear magnetic resonance spectrum ( 1 Characterized by 1H NMR (AVANCE NEO 500MHz, Bruker, Germany).

[0079] (2) Quantum chemical calculations (DFT) were performed using Gaussian 16 software. The geometry of the all-atom polyimide molecular fragments was optimized using the B3LYP method and the 6-31G(d,p) basis set level until the energy gradient converged to 10.- 5 Below Hartree. To further refine the energy distribution and verify the reaction intermediates, potential surface energy (PES) scans were performed using ORCA 5.0.2, and single-point electron energies were calculated at the M06-2X / def2-SVP level. The electronic properties of the optimized structure were analyzed using the Multiwfn program, mapping the electrostatic potential (ESP) and local electron attachment energy (LEAE) distributions on the molecular van der Waals surface to characterize the electrophilic / nucleophilic active regions in the molecule. The electronic density topology was visualized using VMD (Visual Molecular Dynamics).

[0080] 1.2 Characterization Results

[0081] Figure 2 The FTIR spectra of ab show that all PI1 and PI2 systems exhibit typical imide absorption peaks (1778 cm⁻¹). -1 1722 cm -1 1362 cm -1 720cm -1 ) and alkyne bond peak (2210 cm⁻¹) -1 ).

[0082] Figure 2 c1 and c2 1 ¹H NMR and proton coordination analysis showed that the proton chemical shifts of the aromatic rings in each PI1 system ranged from 7.3 to 8.2 ppm, confirming the presence of terminal phenylacetylene groups.

[0083] Figure 2 d1 and d2 1 ¹H NMR and proton coordination revealed a triphenylmethyl central proton peak of 5.9-6.9 ppm in PB / PEPA and MT / PEPA, proving the successful introduction of the trifunctional structure.

[0084] Figure 2 The DFT optimization results of e reveal that the molecular structure of each unit exhibits a distorted non-coplanar configuration.

[0085] The above characterization results demonstrate that the structures of both PI1 and PI2 systems were successfully synthesized. The endoyne of EBPA and the triphenylmethyl center of PB can provide more sites for crosslinking activity, laying the foundation for subsequent low-temperature curing and high crosslinking degree.

[0086] Energy levels and reaction mechanisms of systems PI1 and PI2 in Experimental Example 2

[0087] 2.1 Experimental Methods

[0088] (1) The thermal transformation behavior of polyimide resin was studied using a differential scanning calorimeter (DSC, DSC 25, TA Instruments, USA) under a nitrogen atmosphere at 10°C·min. -1 The heating rate increases from room temperature to 400-500°C.

[0089] (2) Electron paramagnetic resonance (EPR) testing was performed on an X-band EPR spectrometer heated to a specified temperature. The resin sample was placed in a quartz tube and tested in an air atmosphere. The microwave frequency was approximately 9.8 GHz and the modulation frequency was 100 kHz. The microwave power and modulation amplitude were adjusted according to the actual situation to avoid signal saturation.

[0090] (3) DFT is the same as in Experiment 1.

[0091] 2.2 Experimental Results

[0092] Figure 3 The DSC curve of α shows that the exothermic peak of the EBPA / BAFL / PEPA system is 366℃, which is significantly lower than that of the α-BPDA / BAFL / PEPA system (391℃) and the 6FDA / BAFL / PEPA system (379℃).

[0093] Figure 3 The DSC curve of b shows that the curing temperature of the PB / PEPA system is 323°C, which is significantly lower than the curing temperature of the MT / PEPA system, which is 365°C.

[0094] Figure 3 DFT calculations of c show that the HOMO-LUMO gaps of α-BPDA / BAFL / PEPA, 6FDA / BAFL / PEPA, and EBPA / BAFL / PEPA are 3.196 eV, 3.196 eV, and 2.924 eV, respectively. The EBPA / BAFL / PEPA system has a smaller HOMO-LUMO gap and higher reactivity.

[0095] Figure 3 DFT calculations showed that the HOMO-LUMO gaps of PB / PEPA and MT / PEPA were 3.475 eV and 3.499 eV, respectively. The PB / PEPA system had a smaller HOMO-LUMO gap and higher reactivity.

[0096] Figure 3 The EPR experimental structure of e showed that the PB / PEPA system generated stable triphenylmethyl radicals at 150~200℃.

[0097] Figure 3DFT simulations of f-i2 show that the reaction barrier for radical attack on the α-C of the alkyne bond is the lowest (16.7 kcal•mol). -1 ).

[0098] The experimental results above show that the PI1 and PI2 systems have low curing temperatures and high reactivity. Among them, the EBPA / BAFL / PEPA system prepared by acetylinic dianhydride EBPA has a lower curing temperature and higher reactivity than the α-BPDA / BAFL / PEPA and 6FDA / BAFL / PEPA systems. The PB / PEPA system containing hydroxyl groups has a lower curing temperature and higher reactivity than the MT / PEPA system. This indicates that the EBPA / BAFL / PEPA and PB / PEPA systems can achieve better low-temperature curing and crosslinking reactions. At the same time, the PB group can generate free radicals in situ, triggering acetylinic bond addition reactions, realizing free radical-induced synergistic crosslinking of terminal and internal acetylinic groups, and significantly reducing its reaction activation energy.

[0099] Example 3: Viscosity-temperature behavior, XRD and molecular dynamics simulations of PI1 and PI2 systems.

[0100] 3.1 Experimental Methods

[0101] (1) Rheological properties were tested using a rotational rheometer (AR2000, TA Instruments, USA). Circular specimens (25 mm in diameter, 1.5 mm in thickness) were prepared by compression molding at 1 MPa using a 25 mm parallel plate fixture and a strain of 0.5% and an angular frequency of 10 rad·s. -1 Oscillating shear tests were conducted under the following conditions, with a heating rate of 4°C·min. -1 (Composite viscosity-temperature curve).

[0102] (2) The molecular packing and phase structure of the sample were analyzed using an X-ray diffractometer (XRD, Ultima IV, Rigaku, Japan).

[0103] (3) DFT is the same as in Experiment 1.

[0104] 3.2 Experimental Results

[0105] Figure 4 The viscosity-temperature curves of EBPA / BAFL / PEPA exhibit a typical "U-shape". In the PI1 system, EBPA / BAFL / PEPA shows the lowest viscosity, at only 412 Pa•s; in the PI2 system, PB / PEPA has an even lower viscosity, at only 2.8 Pa•s.

[0106] Figure 4 The XRD patterns of cd show that both PI1 and PI2 systems have amorphous structures, and the shift in the PB / PEPA peak position indicates an increase in interchain spacing.

[0107] Figure 4 The DFT simulation results for f show that PB / PEPA has a larger aspect ratio and a twisted configuration.

[0108] Figure 4 MD simulations of g1-h showed that PB / PEPA and MT / PEPA have similar free volume fractions (21.2% and 21.23%, respectively) and polymeric diffusivity (1.8%, respectively). 10 -7 cm 2 / s and 2.05 10 -7 cm 2 / s).

[0109] The above experimental results show that EBPA / BAFL / PEPA and PB / PEPA have lower viscosity. At the same time, PB / PEPA has a non-coplanar structure. This non-coplanar structure, together with its free radical properties, can significantly reduce the viscosity of the system while maintaining high fluidity and rapid crosslinking reactivity.

[0110] Experimental Example 4: Thermal and Mechanical Properties of PI1 and PI2 Systems

[0111] 4.1 Experimental Methods

[0112] (1) Dynamic mechanical analysis (DMA, Q800, TA Instruments, USA) was performed in three-point bending mode with a heating rate of 5℃•min. -1 It is used to determine the energy storage modulus and glass transition behavior.

[0113] (2) Thermogravimetric analysis (TGA, TG209F1, Netzsch, Germany) is used to evaluate the thermal stability of the resin under nitrogen and air atmospheres.

[0114] (3) Thermomechanical analysis (TMA, Q400EM, TA Instruments, USA) was performed in compression mode, with the temperature increased from 30°C to 500°C under a static load of 0.1N to evaluate dimensional stability.

[0115] (4) Compressive stress-strain curve: The compressive properties were tested according to GB / T 2567-2008 standard on a universal testing machine (Instron 5567, USA), with rectangular specimens (10×10×25mm). 3 ) at 1mm•min -1 The loading rate was tested at room temperature and after heat treatment at 300°C for 15 min; tensile properties were tested according to ASTM D638 standard, using Type V specimens, at room temperature with a loading rate of 5 mm·min.-1 The constant tensile rate test was performed, with no fewer than 5 samples in each group, and the average value was taken as the result.

[0116] 4.2 Experimental Results

[0117] Figure 5 The DMA curves of ac show that the EBPA / BAFL / PEPA, PB / PEPA, and MT / PEPA systems all exhibit no obvious glass transition characteristics (>500℃) and have a highly cross-linked network structure.

[0118] Figure 5 The TGA curves of de show that the Td values ​​of each PI1 system are... 5% All exceeded 540℃, and the Td values ​​of each PI2 system were... 5% Both exceeded 525℃, indicating that both PI1 and PI2 systems have high thermal stability.

[0119] Figure 5 f's Curing-T g The comparison chart shows that both PI1 and PI2 systems achieved "low curing-high T". g "Decoupling."

[0120] Figure 5 The TMA curves of g show that the thermal expansion of each PI1 and PI2 system is less than 25µm (below 400℃).

[0121] Figure 5 The compressive stress-strain curves of h show that EBPA / BAFL / PEPA has a compressive strength of 178 MPa at 25℃ and still 93 MPa after 300℃; α-BPDA / BAFL / PEPA has a compressive strength of 142 MPa at 25℃ and 70 MPa after 300℃; 6FDA / BAFL / PEPA has a compressive strength of 159 MPa at 25℃ and 65 MPa after 300℃; and PB / PEPA has a compressive strength of 160 MPa at 25℃ and 75 MPa after 300℃.

[0122] Figure 5 The schematic diagram of i illustrates the dual-network solidification mechanism: free radical-assisted cross-linking with terminal and internal alkynes.

[0123] The above experimental results show that both PI1 and PI2 systems possess high modulus, low thermal expansion, and excellent heat compression resistance. g >500℃, T d >540℃; among them, EBPA / BAFL / PEPA has better heat-pressing resistance than other PI2 systems.

[0124] Experimental Example 5: Co-curing mechanism and viscosity-thermal behavior of PI1 and PI2

[0125] 5.1 Experimental Methods

[0126] DSC is the same as in Experiment 2; rheological properties are the same as in Experiment 3; DFT is the same as in Experiment 1.

[0127] 5.2 Experimental Results

[0128] Figure 6 The schematic diagram of a illustrates that PB / PEPA acts as a "free radical plasticizer-activator" to promote the co-crosslinking of terminal and internal alkyne groups.

[0129] Figure 6 The DSC curves of bd show that the exothermic peaks of the polyimide resins formed by co-curing each PI1 system with PB / PEPA at a mass ratio of 1:1 are 329℃~345℃. Compared with each PI1 system, the exothermic peaks of the polyimide resins after adding PB / PEPA decreased by 35~60℃.

[0130] Figure 6 The viscosity curves of eg show that, compared with the various PI1 systems, the viscosity of the polyimide resins formed by co-curing the various PI1 systems with PB / PEPA at a mass ratio of 1:1 decreased from 412 Pa•s to 118 Pa•s (290℃, α-BPDA / BAFL / PEPA), 13 Pa•s (284℃, 6FDA / BAFL / PEPA), and 127 Pa•s (283℃, EBPA / BAFL / PEPA), respectively.

[0131] Figure 6 hj's DFT calculations revealed that the energy barrier of the new pathway C (radical attack on EBPA endyne) is only 16.2 kcal / mol, which is lower than that of pathways A and B.

[0132] The above experimental results show that PB / PEPA can act on both terminal and internal alkynes to achieve multi-center free radical crosslinking, construct a dense interpenetrating network, and significantly reduce the curing temperature.

[0133] Experimental Example 6: Thermal stability and mechanical strengthening performance of co-cured polyimide resin

[0134] 6.1 Experimental Methods

[0135] The DMA, TGA, TMA, and compressive stress-strain curve tests are the same as in Experiment 4.

[0136] 6.2 Experimental Results

[0137] Figure 7The DMA curves of ac showed that all polyimide resins exhibited no obvious glass transition characteristics, with modulus retention rates exceeding 70%, indicating high mechanical properties. Specifically, at 400°C, the modulus retention rate of EBPA / BAFL / PEPA was 71.47%, the modulus retention rate of the EBPA / BAFL / PEPA co-cured system with PB / PEPA was 83.11%, and the modulus retention rate of PB / PEPA was 81.71%.

[0138] Figure 7 The TGA curve of df shows that the T of polyimide resin g >490℃, T d5% The temperature reached 545.2℃~579.2℃. The T value of the EBPA / BAFL / PEPA and PB / PEPA co-cured system was also mentioned. d5% Ideally, it reaches 579.2℃; the T of the αBPDA / BAFL / PEPA and PB / PEPA co-cured system. d5% The temperature is 545.2°C; the T value of the 6FDA / BAFL / PEPA and PB / PEPA co-curing system is... d5% The temperature is 548.2°C.

[0139] Figure 7 The TMA curve for g shows that the thermal expansion of the polyimide resin is <25µm. The thermal expansion of α-BPDA / BAFL / PEPA is 20µm at ≤400℃ and 25µm at 500℃; the thermal expansion of 6FDA / BAFL / PEPA is 25µm at ≤400℃ and 48µm at 500℃; the thermal expansion of EBPA / BAFL / PEPA is 18µm at ≤400℃ and 30µm at 500℃; the thermal expansion of the EBPA / BAFL / PEPA and PB / PEPA co-cured system is 15µm at ≤400℃ and 32µm at 500℃; the thermal expansion of αBPDA / BAFL / PEPA and PB / PEPA co-cured system is 18µm at ≤400℃ and 26µm at 500℃; and the thermal expansion of 6FDA / BAFL / PEPA and PB / PEPA co-cured system is 20µm at ≤400℃ and 45µm at 500℃.

[0140] Figure 7The compressive stress-strain curves of h show that the compressive strength of the polyimide resin αBPDA / BAFL / PEPA co-cured system with PB / PEPA is 193.6 MPa at 25℃ and 57 MPa at 300℃; the compressive strength of the 6FDA / BAFL / PEPA co-cured system with PB / PEPA is 147 MPa at 25℃ and 92 MPa at 300℃; and the compressive strength of the EBPA / BAFL / PEPA co-cured system with PB / PEPA is 170 MPa at 25℃ and 75 MPa at 300℃.

[0141] Figure 7 i's low-curing-high T g The comparison chart shows that the polyimide resin system of the present invention is superior to existing high-performance polyurethane resins.

[0142] The above experimental results show that all PI1 systems and PB / PEPA can achieve low-temperature curing at 310℃, while simultaneously obtaining high mechanical stability and T g >490℃, T d High thermal stability of >540℃. Meanwhile, the Tc of the EBPA / BAFL / PEPA and PB / PEPA co-cured system... d5% Ideally, it should reach 579.2℃.

[0143] In summary, this invention utilizes an integrated molecular design mechanism of "viscosity dilution-low temperature crosslinking" under catalytic-free conditions to form a "spider web"-like interpenetrating crosslinked network (e.g., Figure 1 (The molecular design mechanism of polyimide resin shown in c) is achieved by co-curing polyimide oligomers containing terminal alkyne groups with polyimide oligomers. The polyimide oligomers generate triphenylmethyl free radicals in situ during heating to promote the self-curing of terminal phenylacetylene groups or the synergistic copolymerization of terminal phenylacetylene groups and alkyne groups inside the main chain, so that the system has low-temperature processability and high-temperature stability.

[0144] Experiments have shown that EBPA / BAFL / PEPA and PB / PEPA have lower curing temperatures, lower viscosity, and higher reactivity than other PI1 and PI2 compounds, enabling better low-temperature curing and crosslinking reactions; they also possess high modulus, low thermal expansion, and excellent heat compression resistance (T). g >500℃, T d>540℃); Simultaneously, PB / PEPA possesses a non-coplanar structure and can generate triphenylmethyl free radicals in situ. In co-curing with EBPA / BAFL / PEPA, these two properties significantly reduce the system viscosity while maintaining high flowability and rapid crosslinking reactivity. Furthermore, PB / PEPA can act on both terminal and internal alkynes, achieving multi-center free radical crosslinking, constructing a dense interpenetrating network, and significantly reducing the curing temperature. The PI1 systems and PB / PEPA of this invention can achieve low-temperature curing at 310℃, resulting in a polyimide resin that simultaneously exhibits high mechanical stability and T... g >490℃, T d High thermal stability of >540℃, especially the Tc of the EBPA / BAFL / PEPA and PB / PEPA co-cured system. d The optimal temperature reached 579.2℃, breaking through the bottleneck of traditional polyimide resins struggling to balance process temperature and thermal stability.

Claims

1. A polyimide resin, characterized in that, It is obtained by co-curing polyimide oligomers containing terminal alkyne groups and polyimide oligomers; the mass ratio of the polyimide oligomers containing terminal alkyne groups to the polyimide oligomers is 1:1; the curing method is vacuum hot pressing, and the conditions for vacuum hot pressing are: vacuuming to -92kPa, pressurizing to 10MPa, heating to 280℃ and holding for 0.5h, and then heating to 310℃ and holding for 3h; The polyimide oligomer containing terminal alkyne groups is prepared using aromatic diamine and dianhydride as monomers and alkyne-containing monoacid anhydride as a capping agent; the molar ratio of the aromatic diamine, dianhydride, and capping agent is 2:1:2; the dianhydride is 2,3',4,4'-biphenyltetracarboxylic dianhydride, 4,4'-(hexafluoroisopropene)phthalic anhydride, or 4,4'-(acetylene-1,2-diyl)dibenzoic anhydride; the aromatic diamine is 9,9-bis(4-aminophenyl)fluorene; and the alkyne-containing monoacid anhydride is 4-phenylacetylenyl phthalic anhydride. The polyimide oligomer is prepared using alkali and 4-phenylethynyl phthalic anhydride as raw materials; the molar ratio of alkali and 4-phenylethynyl phthalic anhydride is 5:

15.

2. The polyimide resin according to claim 1, characterized in that, The preparation method of the polyimide oligomer includes the following steps: (1) reacting the red alkali with 4-phenylethynyl phthalic anhydride to obtain a reaction solution; (2) then adding a dehydrating agent and a catalyst to the reaction solution, purifying, and heat-treating to obtain the polyimide oligomer.

3. A method for preparing the polyimide resin according to any one of claims 1 to 2, characterized in that, Includes the following steps: (1) Aromatic diamine reacts with dianhydride, and a capping agent is added to continue the reaction; (2) Add dehydrating agent and catalyst to react, purify, heat treat to obtain polyimide oligomers containing terminal alkyne groups; (3) After mixing polyimide oligomers containing terminal alkyne groups with polyimide oligomers, polyimide resin is obtained by co-curing.

4. Use of the polyimide resin according to any one of claims 1 to 2 in the fields of aerospace, electronic packaging, heat-resistant and thermal protection composite materials.

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