A method for the preparation of organic framework polymers for structural materials

Abstract

This invention relates to the field of organic framework polymer materials technology, and discloses a method for preparing organic framework polymers for structural materials, comprising the following steps: prepolymer preparation: polyfunctional amine monomers and dianhydride monomers undergo a polycondensation reaction in a polar solvent, and an end-capping agent is added. After dehydration and cyclization, a fusible and soluble polyisoimide oligomer is obtained. This method for preparing organic framework polymers for structural materials employs a two-step route of "prepolymer preparation—molding—thermosetting crosslinking," which differs from the traditional one-step method of directly crosslinking to generate insoluble and non-fusible powders. This method successfully prepares a bulk organic framework polymer with a continuous three-dimensional network structure, giving it practical mechanical properties and engineering application value, thus expanding the application boundaries of organic framework materials from traditional adsorption and catalysis to the field of high-performance structural materials.

Description

Technical Field

[0001] This invention relates to the field of organic framework polymer materials technology, specifically to a method for preparing an organic framework polymer for structural materials. Background Technology

[0002] In recent years, organic framework materials such as covalent organic frameworks (COFs), porous aromatic frameworks (PAFs), conjugated microporous polymers (CMPs), and self-contained microporous polymers (PIMs) have shown broad application prospects in gas adsorption, separation, catalysis, and energy storage due to their high specific surface area, designable pore structure, and excellent thermochemical stability. Among them, crystalline COFs form thermodynamically stable products through reversible reactions, while amorphous PAFs and CMPs are obtained through efficient and directional transformation via kinetically controlled coupling reactions (such as Yamamoto, Sonogashira-Hagihara, and Glaser reactions). Existing research mainly focuses on increasing specific surface area and controlling pore size distribution. Using rigid tetrahedra such as tetraphenylmethane and tetraphenylsilane as core structural units, porous organic materials with a specific surface area as high as 6461 m² / g (such as PPN-4) have been obtained by optimizing coupling reaction conditions.

[0003] However, the preparation of the aforementioned organic framework materials all employs a one-step direct crosslinking polymerization method. Due to the significant steric hindrance of rigid structural units during solution coupling and the tendency of oligomers to precipitate in the early stages of the reaction, the resulting products have low molecular weights, ultimately yielding only powdered materials. These powdered materials lack any mechanical strength and processing fluidity, making them unsuitable for fabrication into bulk structural components using conventional polymer molding processes such as compression molding and injection molding. Consequently, they have long been limited to functional materials applications such as adsorption and catalysis, and are difficult to use as structural materials in aerospace, electronic packaging, and other applications requiring stringent mechanical properties and heat resistance. Summary of the Invention

[0004] To address the problems mentioned in the background section, the present invention provides the following technical solution: a method for preparing an organic framework polymer for structural materials, comprising the following steps:

[0005] Prepolymer preparation: Polyfunctional amine monomers and dianhydride monomers are subjected to polycondensation reaction in a polar solvent, and end-capping agents are added. After dehydration and cyclization, molten and soluble polyisoimide oligomers are obtained.

[0006] Compression molding: The polyisoimide oligomer is filled into a mold, heated under pressure to melt and flow, and fills the mold cavity;

[0007] Thermosetting crosslinking: The molded part is cured by programmed temperature rise, which causes the oligomers to undergo isomerization and imidization and terminal functional group crosslinking reaction to form a three-dimensional crosslinked network structure of bulk organic framework polymer.

[0008] Preferably, the polyfunctional amine monomer is selected from trifunctional or tetrafunctional aromatic amine compounds, and is preferably one or more of 4,4',4''-triaminotriphenylmethane (TAPM), 1,3,5-tris(4-aminophenyl)benzene (TAPB), tetra(4-aminophenyl)methane (TEAPM), or 1,3,5,7-tetra(4-phenylmethylamino)adamantane (TAPAD).

[0009] Preferably, the dianhydride monomer is selected from one or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), or pyromellitic dianhydride (PMDA).

[0010] Preferably, the capping agent is a thermally crosslinkable acid anhydride compound with a phenylacetylene group, preferably 4-phenylacetyl phthalic anhydride (PEPA).

[0011] Preferably, the prepolymer preparation step specifically includes:

[0012] Polyfunctional amine monomers are dissolved in a polar solvent, and dianhydride monomers and end-capping agents are added sequentially under inert gas protection. The reaction is carried out at room temperature for 1 to 5 hours.

[0013] Add trifluoroacetic anhydride and triethylamine to the reaction system and continue the reaction for 2 to 10 hours;

[0014] After the reaction was completed, the reaction solution was precipitated in isopropanol, filtered, washed and dried to obtain polyisoimide oligomer powder.

[0015] Preferably, in the compression molding step, the mold temperature is 150-250°C, and pressure is applied to melt the oligomer and fill the mold cavity.

[0016] Preferably, the programmed temperature curing conditions in the thermosetting crosslinking step are: segmented temperature holding within the range of 200 to 400°C, including holding at 200°C for 0.5 to 2 hours, holding at 250°C for 0.5 to 2 hours, holding at 300°C for 0.5 to 2 hours, and holding at 350°C for 1 to 4 hours.

[0017] Preferably, the molecular weight and terminal functionality of the polyisoimide oligomer are controlled by adjusting the molar ratio of polyfunctional amine monomers to dianhydride monomers, the amount of end-capping agent added, and the prepolymerization reaction time, thereby regulating the crosslinking density and mechanical properties of the final organic framework polymer.

[0018] Preferably, during the thermosetting crosslinking process, the oligomers simultaneously undergo isomerization to form a polyimide backbone and a thermosetting crosslinking reaction with end-capped phenylacetylene groups, forming a three-dimensional network structure.

[0019] Preferably, the organic framework polymer prepared by the method is a bulk structural material with an initial decomposition temperature of not less than 569°C, a tensile strength of not less than 69.8 MPa, and a long-term service temperature of 300–350°C.

[0020] Compared with the prior art, the present invention provides a method for preparing organic framework polymers for structural materials, which has the following beneficial effects:

[0021] 1. The preparation method of the organic framework polymer for structural materials adopts a two-step route of "prepolymer preparation - compression molding - thermosetting crosslinking", which is different from the traditional one-step method of directly crosslinking to generate insoluble and non-melting powder. It successfully prepares a bulk organic framework polymer with a continuous three-dimensional network structure, which enables it to have practical mechanical properties and engineering application value, and expands the application boundary of organic framework materials from the traditional adsorption and catalysis to the field of high-performance structural materials.

[0022] 2. The preparation method of the organic framework polymer for structural materials, by rationally selecting polyfunctional amine monomers and dianhydride monomers and controlling the crosslinking density by controlling the proportion of end-capping agents, yields bulk materials with tensile strength of 69.8–75.7 MPa, flexural strength of 60.9–74.1 MPa, and compressive strength of 69.3–100.2 MPa, which are far superior to existing powdered organic framework materials and meet the basic strength requirements of structural materials.

[0023] 3. The method for preparing organic framework polymers for structural materials yields organic framework polymers with initial decomposition temperatures as high as 569–589℃ and long-term service temperatures reaching 300–350℃. Furthermore, by selecting dianhydride monomers with higher rigidity (such as α-BPDA) and improving the degree of curing, the heat resistance can be further optimized. In contrast, the initial decomposition temperatures of traditional PAF-5 and PI-COF-2 powders are only 505℃ and 535℃, respectively, and they are prone to pulverization at high temperatures.

[0024] 4. The method for preparing the organic framework polymer for structural materials, due to the formation of a highly cross-linked three-dimensional network structure, shows that the material of this invention remains intact, without swelling, and exhibits a mass change rate of less than 0.5% after being immersed in strong acid (1 mol / L HCl), strong alkali (1 mol / L NaOH), and organic solvent (acetone) for 7 days, demonstrating excellent chemical stability and suitability for structural components in harsh environments.

[0025] 5. The method for preparing the organic framework polymer for structural materials obtains a soluble, meltable polyisoimide oligomer powder with appropriate flowability by controlling the monomer ratio, end-capping agent proportion, and prepolymerization degree. This oligomer can be directly filled into a mold and melt-molded under pressure without the use of any solvent, avoiding the porosity, volatile residues, and shrinkage defects easily generated by traditional solution casting methods. This improves part quality and production efficiency, and is adaptable to complex mold cavities such as irregularly shaped parts, large-sized parts, and thin-walled parts.

[0026] 6. This method for preparing organic framework polymers for structural materials allows for the control of oligomer molecular weight, terminal functionality, and final crosslinking density by adjusting the molar ratio of polyfunctional amine monomers to dianhydride monomers, the amount of end-capping agent added, and the prepolymerization reaction time. This enables the tailoring and design of the material's toughness, heat resistance, and modulus. The entire process is simple, uses versatile equipment, requires no stringent synthesis conditions, is easy to scale up for production, and has significant industrial application prospects. Attached Figure Description

[0027] Figure 1 This is the 1H NMR spectrum of the oligomer in Example 1 of the present invention;

[0028] Figure 2 The following are the Fourier Transform Infrared (FT-IR) spectra of the oligomers and polymers in Example 1 of this invention;

[0029] Figure 3 This is the 1H NMR spectrum of the oligomer in Example 2 of the present invention;

[0030] Figure 4 The following are the Fourier Transform Infrared (FT-IR) spectra of the oligomers and polymers in Example 2 of this invention;

[0031] Figure 5 This is the 1H NMR spectrum of the oligomer in Example 2 of the present invention;

[0032] Figure 6 The following are the Fourier Transform Infrared (FT-IR) spectra of the oligomers and polymers in Example 3 of this invention;

[0033] Figure 7 This is a graph showing the material properties of the present 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. 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] Please see Figure 1-7 The present invention provides a technical solution:

[0036] Example 1

[0037] This embodiment provides a method for preparing an organic framework polymer that can be used as a structural material, comprising the following steps:

[0038] (1) Preparation of prepolymer

[0039] 1 mol (approximately 2.91 g) of 4,4',4''-triaminotriphenylmethane (TAPM) was weighed and added to a three-necked flask containing 50 mL of N,N-dimethylacetamide (DMAc). The mixture was stirred at room temperature until completely dissolved. Under nitrogen protection, 1.8 mol (approximately 5.25 g) of pyromellitic dianhydride (PMDA) and 0.4 mol (approximately 1.06 g) of 4-phenylethynyl phthalic anhydride (PEPA) were added sequentially, and the reaction was continued with stirring at room temperature for 3 hours. Subsequently, trifluoroacetic anhydride (3.0 mL) and triethylamine (2.0 mL) were added to the reaction system, and the reaction was continued for 5 hours. After the reaction was completed, the reaction solution was slowly poured into 200 mL of isopropanol to precipitate the product. The precipitate was filtered, washed three times with isopropanol, and dried under vacuum at 120 °C for 12 hours to obtain a light yellow polyisoimide oligomer powder.

[0040] (2) Compression molding

[0041] The obtained oligomer powder was ground and passed through a 100-mesh sieve. 10 g of the powder was weighed and evenly filled into a square mold with an inner cavity size of 60 mm × 60 mm × 4 mm. The mold was placed on a flat vulcanizing machine, and the pressure was gradually increased to 10 MPa at room temperature and held for 5 minutes to compact the powder. Then the temperature was raised to 180°C and held at 10 MPa for 30 minutes to melt the oligomer and completely fill the mold cavity.

[0042] (3) Thermosetting crosslinking

[0043] Maintaining a molding pressure of 10 MPa, the following staged temperature-curing procedure was followed: heating to 250℃ and holding for 1 hour; heating to 300℃ and holding for 1 hour; heating to 350℃ and holding for 2 hours. During curing, the oligomers underwent isomerization and imidization to form a polyimide backbone, while the end-capped phenylacetylene groups underwent thermal crosslinking to form a three-dimensional network structure.

[0044] (4) Demolding

[0045] After curing, the material was allowed to cool naturally to room temperature, and then the pressure was released and the mold was removed to obtain a black block organic framework polymer structure material, which was designated as Sample 1.

[0046] Example 2

[0047] This embodiment is basically the same as Embodiment 1, except that the types and proportions of raw materials are different.

[0048] (1) Preparation of prepolymer

[0049] Weigh 1 mol (approximately 3.51 g) of 1,3,5-tris(4-aminophenyl)benzene (TAPB) and dissolve it in 50 mL of DMAc. Under nitrogen protection, add 1.7 mol (approximately 5.61 g) of 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA) and 0.6 mol (approximately 1.59 g) of PEPA sequentially. After reacting at room temperature for 3 hours, add trifluoroacetic anhydride (3.5 mL) and triethylamine (2.2 mL) and continue reacting for 5 hours. Precipitate with isopropanol, wash, and dry under vacuum at 120 °C to obtain oligomeric powder.

[0050] (2) Molding is the same as in Example 1.

[0051] (3) Thermosetting crosslinking is the same as in Example 1.

[0052] (4) The black block organic framework polymer was obtained by demolding and is referred to as sample 2.

[0053] Example 3

[0054] This embodiment is basically the same as Embodiment 1, except that the raw material ratio is different, and a higher proportion of end-capping agent is used to reduce the crosslinking density and improve toughness.

[0055] (1) Preparation of prepolymer

[0056] Weigh 1 mol (approximately 3.51 g) of TAPB and dissolve it in 50 mL of DMAc; under nitrogen protection, add 1.5 mol (approximately 4.38 g) of PMDA and 1.0 mol (approximately 2.65 g) of PEPA sequentially; after reacting at room temperature for 3 hours, add trifluoroacetic anhydride (4.0 mL) and triethylamine (2.5 mL) and continue reacting for 5 hours; precipitate with isopropanol, wash, and vacuum dry at 120 °C to obtain oligomeric powder.

[0057] (2) Molding is the same as in Example 1.

[0058] (3) Thermosetting crosslinking is the same as in Example 1.

[0059] (4) The black block organic framework polymer was obtained by demolding and is referred to as sample 3.

[0060] Comparative Example 1 (Conventional one-step synthesis of PAF-5)

[0061] Following the method reported in the literature (Ben T, et al. Angew. Chem. Int. Ed. 2009, 48: 9457-9460), tetrakis(4-bromophenyl)methane was used as a monomer and directly polymerized in one step via Yamamoto coupling reaction to obtain porous aromatic framework PAF-5 powder, which was designated as control sample 1.

[0062] Comparative Example 2 (Conventional COF powder material PI-COF-2)

[0063] Following the method reported in the literature (Fang Q, et al. J. Am. Chem. Soc. 2014, 136: 6045-6048), covalent organic framework PI-COF-2 powder was obtained by one-step solvothermal polycondensation using pyromellitic dianhydride and 1,3,5-tris(4-aminophenyl)benzene as monomers, and was designated as control sample 2.

[0064] Comparative Example 3 (Comparison Experiment Without End-Capping Agent)

[0065] The steps are the same as in Example 1, but the prepolymer preparation does not include the end-capping agent PEPA; that is, the molar ratio of TAPM to PMDA is 1:2. The remaining steps are the same. The resulting product cannot form an effective cross-linked network during the thermosetting process after molding, resulting in a brittle and low-strength material that cannot be used as a structural material.

[0066] Performance testing

[0067] The following performance tests were performed on the materials obtained in each embodiment and comparative example:

[0068] Thermal stability: The initial decomposition temperature (the temperature at which 5% weight loss occurs) was determined using a thermogravimetric analyzer (TGA) under a nitrogen atmosphere.

[0069] Mechanical properties: The block material from the examples was cut into standard test strips, and tensile strength (ASTM D638), flexural strength (ASTM D790), and compressive strength (ASTM D695) were tested using a universal testing machine. Mechanical properties could not be tested for the comparative example powder material.

[0070] Long-term operating temperature: Evaluated by thermal aging test (the highest temperature at which the mechanical properties retain ≥80% after being placed in an air atmosphere at 300℃ for 100 hours).

[0071] Chemical corrosion resistance: The sample was immersed in 1 mol / L HCl, 1 mol / L NaOH and acetone for 7 days, and the appearance changes were observed and the mass change rate was tested.

[0072] Test results are summarized in Figure 7Note: "—" indicates that the mechanical properties of the powder sample cannot be tested; "Excellent" indicates that there is no swelling or mass loss after soaking in acid, alkali and organic solvents for 7 days (mass change rate <0.5%); Comparative Example 3 showed surface powdering after soaking in acid.

[0073] Results Analysis

[0074] from Figure 7 It can be seen that:

[0075] The organic framework polymers prepared in the various embodiments of the present invention are all dense bulk materials with excellent mechanical properties (tensile strength 69.8-75.7 MPa, flexural strength 60.9-74.1 MPa, compressive strength 69.3-100.2 MPa), while traditional methods (Comparative Examples 1 and 2) can only obtain powder materials, which do not have actual mechanical properties and cannot be used as structural materials.

[0076] The material of this invention has an initial decomposition temperature as high as 569-589℃ and a long-term service temperature of 305-335℃, which is far superior to the comparative materials (comparative examples 1 and 2 have initial decomposition temperatures of 505℃ and 535℃ respectively, and are powders; comparative example 3 has an initial decomposition temperature of only 480℃ due to lack of cross-linking), demonstrating excellent thermal stability.

[0077] The material of this invention exhibits excellent chemical corrosion resistance in strong acids, strong alkalis and organic solvents, while Comparative Example 3 has poor corrosion resistance due to incomplete cross-linking network.

[0078] Example 2 (using α-BPDA and TAPB) has the best overall performance, with a compressive strength of 100.2 MPa and a long-term operating temperature of 335℃.

[0079] Example 3 shows that due to the higher proportion of end-capping agent, the crosslinking density is reduced, the tensile strength is slightly improved, but the compressive strength and heat resistance are slightly reduced, indicating that the performance can be flexibly controlled by the monomer ratio.

[0080] Industrial application

[0081] The organic framework polymer structural material obtained by this invention has excellent processability: the oligomeric powder can be directly molded into complex shapes without solvents, making the process environmentally friendly and suitable for large-scale production. The resulting material possesses high mechanical strength, high heat resistance, and excellent chemical stability, and can be widely used in aerospace lightweight structural components, high-temperature insulating components, electronic packaging materials, corrosion-resistant equipment components, and high-performance composite resin matrices.

[0082] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing an organic framework polymer for structural materials, characterized in that, Includes the following steps: Prepolymer preparation: Polyfunctional amine monomers and dianhydride monomers are subjected to polycondensation reaction in a polar solvent, and end-capping agents are added. After dehydration and cyclization, molten and soluble polyisoimide oligomers are obtained. Compression molding: The polyisoimide oligomer is filled into a mold, heated under pressure to melt and flow, and fills the mold cavity; Thermosetting crosslinking: The molded part is cured by programmed temperature rise, which causes the oligomers to undergo isomerization and imidization and terminal functional group crosslinking reaction to form a three-dimensional crosslinked network structure of bulk organic framework polymer.

2. The method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, The polyfunctional amine monomer is selected from trifunctional or tetrafunctional aromatic amine compounds, preferably one or more of 4,4',4''-triaminotriphenylmethane (TAPM), 1,3,5-tris(4-aminophenyl)benzene (TAPB), tetra(4-aminophenyl)methane (TEAPM), or 1,3,5,7-tetra(4-phenylmethylamino)adamantane (TAPAD).

3. The method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, The dianhydride monomers are selected from one or more of 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA), 2,3,3',4'-biphenyltetracarboxylic dianhydride (α-BPDA), or pyromellitic dianhydride (PMDA).

4. The method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, The capping agent is a thermally crosslinkable acid anhydride compound with a phenylacetylene group, preferably 4-phenylacetylene phthalic anhydride (PEPA).

5. The method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, The prepolymer preparation steps specifically include: Polyfunctional amine monomers are dissolved in a polar solvent, and dianhydride monomers and end-capping agents are added sequentially under inert gas protection. The reaction is carried out at room temperature for 1 to 5 hours. Add trifluoroacetic anhydride and triethylamine to the reaction system and continue the reaction for 2 to 10 hours; After the reaction was completed, the reaction solution was precipitated in isopropanol, filtered, washed and dried to obtain polyisoimide oligomer powder.

6. The method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, In the compression molding step, the mold temperature is 150-250°C, and pressure is applied to melt the oligomers and fill the mold cavity.

7. The method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, The programmed temperature curing conditions in the thermosetting crosslinking step are as follows: segmented temperature holding within the range of 200 to 400°C, including holding at 200°C for 0.5 to 2 hours, holding at 250°C for 0.5 to 2 hours, holding at 300°C for 0.5 to 2 hours, and holding at 350°C for 1 to 4 hours.

8. The method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, By adjusting the molar ratio of polyfunctional amine monomers to dianhydride monomers, the amount of end-capping agent added, and the prepolymerization reaction time, the molecular weight and terminal functionality of polyisoimide oligomers can be controlled, thereby regulating the crosslinking density and mechanical properties of the final organic framework polymer.

9. The method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, During the thermosetting crosslinking process, the oligomers simultaneously undergo isomerization to form a polyimide backbone and a thermosetting crosslinking reaction with end-capped phenylacetylene groups, forming a three-dimensional network structure.

10. A method for preparing an organic framework polymer for structural materials according to claim 1, characterized in that, The organic framework polymer prepared by the method is a bulk structural material with an initial decomposition temperature of not less than 569℃, a tensile strength of not less than 69.8 MPa, and a long-term service temperature of 300-350℃.

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