Dense hydroxyl group-containing polyfluorene ether ketone polymer for toughening epoxy resin and preparation method of dense hydroxyl group-containing polyfluorene ether ketone polymer

Abstract

The invention discloses a dense hydroxyl-containing polyfluorene ether ketone polymer for toughening epoxy resin and a preparation method of the dense hydroxyl-containing polyfluorene ether ketone polymer, and belongs to the field of high polymer materials. The preparation method comprises the following steps: firstly, synthesizing a novel polymer monomer, namely 6, 12-dimethoxy-9, 9-bis (3, 5-dimethoxy-4-hydroxyl) fluorene, and then carrying out copolycondensation and hydroxylation to obtain the dense hydroxyl polyfluorene ether ketone polymer. Epoxy resin is a thermosetting polymer applied to the fields of adhesives, coatings, composite materials and the like, but the application of the epoxy resin is still limited by the characteristics of high brittleness, easiness in cracking and the like after curing. According to the synthesized polyfluorene ether ketone polymer containing the dense hydroxyl groups, the dense hydroxyl groups are spherically distributed in a polymer unit, so that the polymer has unique cross-linked network performance, and strong interface bonding can be formed among phases in modified epoxy resin. Therefore, a composite material with good toughness and thermal stability can be obtained by introducing the dense hydroxyl polyfluorene ether ketone polymer into an epoxy resin / anhydride system.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a densely hydroxyl-containing polyfluorene ether ketone polymer for toughening epoxy resin and a preparation method thereof. Technical Background

[0002] Due to the simplicity and effectiveness of epoxy resins, a large number of studies have been devoted to improving the toughness of epoxy resins. Among them, reactive functionalized rubbers have been widely studied. Commonly used reactive functionalized rubbers include: carboxyl-terminated butadiene acrylonitrile, amine-terminated butadiene acrylonitrile, and epoxy-terminated butadiene acrylonitrile. However, although reactive functionalized rubbers improve the toughness of epoxy resin composites, they also reduce the heat resistance and mechanical properties of epoxy resins, which limits their application in high-performance composites.

[0003] In order to solve this problem, active functionalized thermoplastic polymers are used to modify epoxy resins because of their good toughness and compatibility, high modulus and heat resistance. At present, active functionalized thermoplastic polymers used to toughen epoxy resins include: carboxyl-terminated polyadipate succinate, hydroxyl-terminated poly(ether ether ketone) and amino-terminated polycaprolactone. Liu (ACS Appl. Polym. Mater. 2024, 6, 6068-6076) et al. prepared hydroxyl-terminated phenolphthalein polyether sulfone (PESC-OH) to study the effect of PESC-OH modification on the heat resistance and mechanical properties of epoxy resin. PESC-OH modification improves the impact and flexural strength of epoxy resin to varying degrees, but does not significantly improve the glass transition temperature and thermal stability. In addition, the hydroxyl functional group content of PESC-OH is low and is only distributed at both ends of the polymer main chain, so the modification effect is limited. Summary of the invention

[0005] The purpose of the present invention is to provide a polyfluorene ether ketone polymer containing dense hydroxyl groups as a toughening agent for epoxy resin, through which the dense hydroxyl groups carried by the polymer directly or indirectly react with the epoxy groups in the epoxy resin to form strong interfacial bonding between the various phases inside the modified epoxy resin, thereby obtaining a composite material with good toughness and thermal stability.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned densely hydroxyl-containing polyfluorene ether ketone polymer.

[0007] A densely hydroxyl-containing polyfluorene ether ketone polymer, the structural formula of which is shown below:

[0008]

[0009] Wherein, m is an integer > 1, n is an integer > 1, and the sum of the ratios of m and n is 1.

[0010] The preparation method of the polyfluorene ether ketone polymer containing dense hydroxyl groups comprises the following steps:

[0011] (1) First, dissolve 2,7-dihydroxy-9-fluorenone and methyl iodide in 250 - 300 mL of N,N'-dimethylformamide, then add anhydrous potassium carbonate, and raise the temperature to 50 - 80 °C for reaction for 8 - 12 h. After the reaction is completed, add toluene to dilute the reaction mixture, then filter and collect the liquid, extract it with pure water 2 - 3 times, add anhydrous sodium sulfate for drying, and finally filter the product using a chromatography column to obtain pure dimethoxyfluorenone. The reaction formula is as follows:

[0012]

[0013] (2) Take dimethoxyfluorenone and 2,6-dimethoxyphenol and dissolve them in 30 - 60 mL of toluene, then add 3-mercaptopropionic acid. Raise the temperature of the system to 30 - 60 °C, and slowly add 98% concentrated sulfuric acid dropwise. Subsequently, raise the temperature to 50 - 80 °C for reaction for 12 - 16 h. After the reaction is completed, precipitate the solid in pure water and then obtain the pure new polymer monomer: 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy)fluorene through recrystallization. The reaction formula is as follows:

[0014]

[0015] (3) Under nitrogen protection, dissolve bisphenol fluorene, 4,4-difluorobenzophenone and 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy)fluorene in 10 - 15 mL of N,N'-dimethylacetamide, then add anhydrous potassium carbonate and toluene, raise the temperature to 130 - 160 °C for reaction for 4 - 8 h. Subsequently, remove the water generated in the reaction through a water separator and distill out the toluene. Raise the temperature to 170 - 200 °C and continue the reaction for 10 - 14 h. After the reaction is completed, pour the reactant into pure water to precipitate the solid, and then obtain the polyfluorene ether ketone polymer containing dense methoxy groups with a yield of 98% through filtration, washing with methanol and drying. The reaction formula is as follows:

[0016]

[0017] (4) Dissolve the polyfluorene ether ketone polymer containing dense methoxy groups in 50 - 80 mL of chloroform, lower the temperature to -45 - 0 °C, then add boron tribromide, and then react at room temperature for 24 - 36 h. After the reaction is completed, pour the reactant into methanol to precipitate, and then obtain the polyfluorene ether ketone polymer containing dense hydroxyl groups with a yield of 98% through filtration, washing with water and drying. The reaction formula is as follows:

[0018]

[0019] To better implement the present invention, in step (1), the molar ratio of 2,7-dihydroxy-9-fluorenone, methyl iodide, and anhydrous potassium carbonate is 1:(2-5):(0.1-0.5);

[0020] In step (2), the molar ratio of dimethoxyfluorenone, 2,6-dimethoxyphenol, and 3-mercaptopropionic acid is 1:(3-6):(0.0005-0.001).

[0021] In step (3), the molar ratio of 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy) and potassium carbonate is 1:(7-10);

[0022] In the hydroxylation process of step (4), the molar ratio of polyfluorene ether ketone containing dense methoxy groups and boron tribromide is 1:(10-15).

[0023] A cured product of epoxy resin modified with a polyfluorene ether ketone polymer containing dense hydroxyl groups is mainly composed of epoxy resin, curing agent methyltetrahydrophthalic anhydride, toughening agent polyfluorene ether ketone containing dense hydroxyl groups, and curing accelerator 2-methylimidazole. The mass ratio of epoxy resin to the polyfluorene ether ketone polymer containing dense hydroxyl groups is 1:(0.03-0.5), the mass ratio of epoxy resin to the curing agent is 1:(0.5-0.8), and the mass ratio of epoxy resin to the curing accelerator is 1:(0.01-0.05). The specific preparation method includes the following steps:

[0024] (1) Dissolve the polyfluorene ether ketone polymer containing dense hydroxyl groups in tetrahydrofuran solvent to obtain a solution with a mass percentage ≥5%, then add epoxy resin, curing agent methyltetrahydrophthalic anhydride, and curing accelerator 2-methylimidazole, and stir at 70-90°C for 2-3 h.

[0025] (2) Stir and evacuate the solvent and defoam the mixed solution obtained in step (1) at 70-90°C, then pour it into a self-made mold, then cure it at 60-90°C under vacuum for 16-20 h, then cure it at 100-120°C for 2-4 h, and finally demold it after natural cooling to obtain the cured product of modified epoxy resin.

[0026] Through the above design scheme, the beneficial effects of the present invention are:

[0027] The raw materials used in the present invention are all common chemical reagents, which are easy to obtain and inexpensive.

[0028] The polymer monomers used have relatively rigid molecular structures, endowing the polyfluorene ether ketone polymer containing dense hydroxyl groups with good thermal stability.

[0029] The hydroxyl groups of the polyfluorene ether ketone polymer containing dense hydroxyl groups can react directly or indirectly with the epoxy groups in the epoxy resin, thereby improving the interfacial properties between the phases inside the modified epoxy resin.

[0030] The hydroxyl groups of the polyfluorene ether ketone polymer containing dense hydroxyl groups can be not only located at the end of the main chain, but also easily regulated in content.

[0031] The polyfluorene ether ketone polymer containing dense hydroxyl groups can improve the mechanical properties such as the impact strength and flexural fracture strain of the epoxy resin, and can also improve the thermal stability of the modified epoxy resin. Description of the Drawings

[0032] Figure 1 is the nuclear magnetic resonance hydrogen spectrum of the novel polymer monomer in Example 1 of the present invention: 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy)fluorene.

[0033] Figure 2 is the nuclear magnetic resonance hydrogen spectrum of the polyfluorene ether ketone polymer containing dense methoxy groups (PFEKs-hOMe) in Example 2 and the polyfluorene ether ketone polymer containing dense hydroxyl groups (PFEKs-hOH) in Example 3 of the present invention.

[0034] Figure 3 is the infrared-visible spectrum of the polyfluorene ether ketone polymer containing dense methoxy groups (PFEKs-hOMe) in Example 2 and the polyfluorene ether ketone polymer containing dense hydroxyl groups (PFEKs-hOH) in Example 3 of the present invention.

[0035] Figure 4 is the polyfluorene ether ketone polymer containing dense methoxy groups (PFEKs-hOMe) in Example 2 of the present invention, and the differential scanning calorimetry curve of the polyfluorene ether ketone polymer containing dense hydroxyl groups (PFEKs-hOH) in Example 3.

[0036] Figure 5 is the thermogravimetric curve of the polyfluorene ether ketone polymer containing dense methoxy groups (PFEKs-hOMe) in Example 3 and the polyfluorene ether ketone polymer containing dense hydroxyl groups (PFEKs-hOH) in Example 4 of the present invention. Detailed Embodiments

[0037] The following examples provide general descriptions and definitions of how the present invention is made and evaluated, so that those of ordinary skill in the art can understand, but the present invention is not limited to these examples.

[0038] Synthesis of the Novel Polymer Monomer in Example 1

[0039] First, dissolve 21.20 g (0.10 mol) of 2,7-dihydroxy-9-fluorenone and 35.48 g (0.25 mol) of methyl iodide in 250 mL of N,N'-dimethylformamide. Then, add 34.58 g (0.25 mol) of anhydrous potassium carbonate and heat the mixture to 60 °C for 12 h. After the reaction, add 10 mL of toluene to dilute the reaction mixture, then filter and collect the liquid. Extract it three times with pure water, add anhydrous sodium sulfate for drying, and finally filter the product through a chromatography column to obtain pure dimethoxyfluorenone.

[0040] Dissolve 24.02 g (0.10 mol) of dimethoxyfluorenone and 61.6 g (0.4 mol) of 2,6-dimethoxyphenol in 30 mL of toluene. Then, add 0.1 mL of 3-mercaptopropionic acid. Raise the temperature of the system to 30 °C and slowly add 8 mL of 98% sulfuric acid dropwise. Subsequently, heat the mixture to 50 °C for 12 h. After the reaction, precipitate the solid in pure water and recrystallize it to obtain the pure novel polymer monomer: 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy)fluorene.

[0041] Example 2 Synthesis of Polyfluorene Ether Ketone Polymer with Dense Methoxy Groups (PFEKs-hOMe)

[0042] Under nitrogen protection, dissolve 1.0513 g (3 mmol) of bisphenol fluorene, 0.8728 g (4 mmol) of 4,4-difluorobenzophenone, and 0.5306 g (1 mmol) of 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy)fluorene in 12 mL of N,N'-dimethylacetamide. Then, add 1.1056 g (8 mmol) of anhydrous potassium carbonate and 5 mL of toluene. Raise the temperature to 145 °C and react for 4 h. Subsequently, remove the water generated during the reaction through a water separator and distill off the toluene. Raise the temperature to 165 °C and continue the reaction for 12 h. After the reaction, pour the reactant into pure water to precipitate the solid, and then obtain the polyfluorene ether ketone polymer with dense methoxy groups with a yield of 98% through filtration, washing with methanol, and drying.

[0043] Example 3 Synthesis of Polyfluorene Ether Ketone Polymer with Dense Methoxy Groups (PFEKs-hOMe)

[0044] Dissolve 5.06 g (4 mmol) of the polyfluorene ether ketone with dense methoxy groups in 72 mL of chloroform. After cooling the temperature to -45 °C, add (40 mmol) of boron tribromide, and then react at room temperature for 24 - 36 h. After the reaction, pour the reactant into methanol to precipitate it, and then obtain the polyfluorene ether ketone polymer with dense hydroxyl groups with a yield of 98% through filtration, washing with water three times, and drying.

[0045] Example 4 Preparation of Unmodified Epoxy Resin Curing Agent

[0046] Dissolve 10 g of bisphenol A epoxy resin E51, 6.0 g of curing agent methyltetrahydrophthalic anhydride, and 0.02 g of curing accelerator 2-methylimidazole in 8 mL of tetrahydrofuran solvent, and stir at 70 °C for 2 h to obtain a mixed solution. While stirring, evacuate the solvent and defoam the obtained mixed solution at 70 °C, then pour it into a self-made mold, then cure at 80 °C under vacuum for 16 h, then cure at 100 °C for 2 h, and finally demold after natural cooling to obtain an unmodified epoxy resin cured product. As shown in Table 1, the glass transition temperature (T g ) of the obtained unmodified epoxy resin cured product is 127 °C, the 5% thermal weight loss temperature (T d5％ ) is 315 °C, the notched impact strength is 2.51 KJ / m 2 , the flexural modulus is 3.04 MPa, the flexural strength is 90.25 MPa, the fracture flexural strain is 3.03%, and the critical stress intensity factor (K IC ) is 1.49 MN / m 3 / 2 , and the critical strain energy release rate (GIC) is 0.55 KJ / m 2 .

[0047] Preparation of Densely Hydroxylated Polyfluorene Ether Ketone Polymer-Modified Epoxy Resin Cured Product in Example 4

[0048] Dissolve 0.5 g of densely hydroxylated polyfluorene ether ketone polymer, 10 g of bisphenol A epoxy resin E51, 6.0 g of curing agent methyltetrahydrophthalic anhydride, and 0.02 g of curing accelerator 2-methylimidazole in 8 mL of tetrahydrofuran solvent, and stir at 70 °C for 2 h to obtain a mixed solution. While stirring, evacuate the solvent and defoam the obtained mixed solution at 70 °C, then pour it into a self-made mold, then cure at 80 °C under vacuum for 16 h, then cure at 100 °C for 2 h, and finally demold after natural cooling to obtain a modified epoxy resin cured product. As shown in Table 1, the glass transition temperature (T g ) of the obtained modified epoxy resin cured product is 135 °C, the 5% thermal weight loss temperature (T d5％ ) is 347 °C, the notched impact strength is 3.64 KJ / m 2 , the flexural modulus is 2.85 MPa, the flexural strength is 98.97 MPa, the fracture flexural strain is 5.92%, and the critical stress intensity factor (K IC ) is 2.09 MN / m 3 / 2 , and the critical strain energy release rate (GIC) is 1.02 KJ / m 2 .

[0049] Table 1 Properties of Unmodified Epoxy Resin Cured Product and Densely Hydroxylated Polyfluorene Ether Ketone Polymer-Modified Epoxy Resin Cured Product.

[0050] The above are only some embodiments of the present invention. All equivalent changes made according to the scope of the patent application of the present invention shall fall within the scope covered by the present invention.

Claims

1. A densely hydroxylated polyfluorene ether ketone polymer for toughening epoxy resin, characterized in that: The structural formula of the densely hydroxylated polyfluorene ether ketone polymer is as follows: Wherein, m is an integer > 1, n is an integer > 1, and the sum of the ratios of m and n is 1.

2. A method for preparing a densely hydroxylated polyfluorene ether ketone polymer for toughening epoxy resin, which is used to prepare the densely hydroxylated polyfluorene ether ketone polymer for toughening epoxy resin according to claim 1, characterized in that: The following steps are involved: (1) First, 2,7-dihydroxy-9-fluorenone and iodomethane are dissolved in 250-300 mL of N,N'-dimethylformamide, then anhydrous potassium carbonate is added, and the temperature is raised to 50-80°C for reaction for 8-12 hours. After the reaction is completed, toluene is added to dilute the reaction mixture, and then the liquid is filtered and collected, extracted with pure water for 2-3 times, and then anhydrous sodium sulfate is added to dry, and finally the product is filtered using a chromatography column to obtain pure dimethoxyfluorenone; (2) Take dimethoxyfluorenone and 2,6-dimethoxyphenol and dissolve them in 30-60 mL toluene, then add 3-mercaptopropionic acid. The system temperature rises to 30-60°C, and 98% concentrated sulfuric acid is added dropwise. Then, the temperature is raised to 50-80°C and reacted for 12-16 hours. After the reaction is completed, a solid is precipitated in pure water and then recrystallized to obtain a pure new polymer monomer: 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy)fluorene; (3) Under nitrogen protection, bisphenol fluorene, 4,4-difluorobenzophenone and 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy)fluorene are dissolved in 10-15 mL N,N'-dimethylacetamide, followed by addition of anhydrous potassium carbonate and toluene, and the temperature is raised to 130-160°C for reaction for 4-8 hours. The water generated in the reaction is then removed through a water separator and the toluene is evaporated. The temperature is raised to 170-200°C and the reaction is continued for 10-14 hours. After the reaction is completed, the reactants are poured into pure water to precipitate solids, which are then filtered, washed with methanol and dried to obtain a densely methoxylated polyfluorene ether ketone polymer with a yield of 98%; (4) Dissolve the densely methoxylated polyfluorene ether ketone in 50-80 mL of chloroform, add boron tribromide after the temperature drops to -45-0°C, and then react at room temperature for 24-36 hours. After the reaction is completed, pour the reactant into methanol for precipitation, and then filter, wash with water and dry to obtain a densely hydroxylated polyfluorene ether with a yield of 98%.

3. The method for preparing a novel polymer monomer in the method for preparing a densely hydroxylated polyfluorene ether ketone according to claim 2, characterized in that: In step (1), the molar ratio of 2,7-dihydroxy-9-fluorenone, methyl iodide and anhydrous potassium carbonate is 1:(2-5):(0.1-0.5); Preferably, in step (2), the molar ratio of dimethoxyfluorenone, 2,6-dimethoxyphenol and 3-mercaptopropionic acid is 1:(3-6):(0.0005-0.001).

4. The method for preparing the densely hydroxylated polyfluorene ether ketone according to claim 2, characterized in that: In step (3), the molar ratio of 6,12-dimethoxy-9,9-bis(3,5-dimethoxy-4-hydroxy) to potassium carbonate is 1:(7-10); Preferably, during the hydroxylation process of step (4), the molar ratio of densely packed methoxy polyfluorene ether ketone to boron tribromide is 1:(10-15).

5. A cured epoxy resin modified with a densely hydroxylated polyfluorene ether ketone polymer prepared by the preparation method of claim 2, characterized in that: It is mainly composed of epoxy resin, curing agent methyltetrahydrophthalic anhydride, toughening agent densely hydroxylated polyfluorene ether ketone and curing accelerator 2-methylimidazole, wherein the mass ratio of epoxy resin to the mass ratio of densely hydroxylated polyfluorene ether ketone polymer is 1:(0.03-0.5), the mass ratio of epoxy resin to the mass ratio of curing agent is 1:(0.5-0.8), and the mass ratio of epoxy resin to the mass ratio of curing accelerator is 1:(0.01-0.05).

6. The method for preparing the epoxy resin modified by the densely hydroxyl-containing polyfluorene ether ketone polymer according to claim 5, characterized in that: The following steps are involved: (1) dissolving a densely hydroxyl-containing polyfluorene ether ketone polymer in tetrahydrofuran solvent to obtain a solution with a mass percentage of ≥5%, then adding epoxy resin, curing agent methyl tetrahydrophthalic anhydride and curing accelerator 2-methylimidazole, and stirring at 70-90° C. for 2-3 hours; (2) The mixed solution obtained in step (1) is stirred at 70-90° C. and vacuumed to remove the solvent and degas, then poured into a homemade mold, and then cured at 60-90° C. in vacuum for 16-20 h, and then cured at 100-120° C. for 2-4 h. Finally, it is naturally cooled and demolded to obtain a modified epoxy resin cured product.

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