Branched polyaromatic amides, methods of making and using the same

Abstract

This invention relates to a branched polyaromatic amide, its preparation method, and its applications, belonging to the field of polymer synthesis technology. The method includes: dissolving m-phenylenediamine and 3,5-diaminobenzoic acid in an amide-based aprotic solvent containing Li₂CO₃ under an inert atmosphere; and adding isophthaloyl chloride at low temperature to carry out a polycondensation reaction. This invention successfully constructs a branched structure by introducing 3,5-diaminobenzoic acid as a branching precursor and employing specific subsequent reactions, effectively avoiding gelation side reactions. The prepared branched polyaromatic amide is soluble in common organic solvents such as N,N'-dimethylacetamide and N-methylpyrrolidone, exhibits excellent processing performance, and maintains high mechanical strength and good thermal stability. Its tensile strength can reach 256 MPa, and its 5% thermal decomposition temperature can reach above 480℃, solving the technical problem of decreased mechanical strength and thermal stability caused by the introduction of a third monomer in traditional modification methods.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, specifically to a branched polyaromatic amide, its preparation method, and its application. Background Technology

[0002] Currently, there are two main types of commercially available polyaromatic amides. One is poly(m-phenylene terephthalamide), commonly referred to as para-aramid, marketed by DuPont under the brand name Kevlar. It is a high-performance polymer fiber material combining high strength, high modulus, high temperature resistance, flame retardancy, and insulation. The poly(m-phenylene terephthalamide) molecular chain is a rigid linear molecule with numerous hydrogen bonds between molecules, resulting in strong intermolecular forces. Therefore, para-aramid paper or fibers possess extremely high strength and modulus. However, due to these excessive intermolecular forces, para-aramid is insoluble in common organic solvents. Industrially, highly corrosive 100% sulfuric acid is commonly used as a solvent, placing high demands on equipment and process conditions, thus affecting the processability of para-aramid. The other type of polyaromatic amide is poly(m-phenylene isophthalamide), commonly referred to as meta-aramid, marketed by DuPont under the brand name Nomex. Poly(m-phenylene isophthalamide) molecular chains possess a certain degree of flexibility, are soluble in common polar solvents, and exhibit good processability, but their strength is relatively low. Therefore, developing a polyaromatic material that simultaneously possesses high strength and good processability is of great significance.

[0003] In existing technologies, a common method to improve the processability of para-aramid fibers is to introduce a third monomer, such as 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl sulfone, 2,5-furandicarboxylic acid, or m-phenylenediamine sulfonate, into the main chain of poly(m-phenylene terephthalamide). The introduction of these monomers disrupts the regularity of the molecular chain, reducing the intermolecular forces between aramid molecules, thereby obtaining modified aramid fibers that are soluble in common organic solvents. However, a drawback of this method is that while improving the processability of aramid fibers, it significantly reduces their thermal stability and strength. Therefore, it is necessary to design a new polyaromatic amide molecular structure to meet the requirements of simultaneously possessing high strength, high heat resistance, and good processability. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a branched polyaromatic amide, its preparation method and application. The branched polyaromatic amide prepared in the present invention is soluble in common amide aprotic solvents such as N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone, and at the same time maintains thermal stability and strength close to that of para-aramid.

[0005] This invention is achieved through the following technical solution: A method for preparing branched polyaromatic amides includes the following steps: (1) Under an inert atmosphere, lithium salt is dissolved in an organic solvent, and then m-phenylenediamine and 3,5-diaminobenzoic acid are added and stirred until completely dissolved to obtain a mixed monomer solution; (2) Cool the mixed monomer solution obtained in step (1), add isophthaloyl chloride to carry out polycondensation reaction, and obtain a prepolymer solution; (3) Tris(o-methoxyphenyl)phosphine and iodine chloride were added sequentially to the prepolymer solution obtained in step (2) for activation reaction, followed by the addition of p-aminobenzoic acid for branching reaction. After the reaction was completed, the product was precipitated, filtered and dried to obtain the branched polyaromatic amide.

[0006] Further specified, the lithium salt in step (1) is Li2CO3, and its mass is 0.5% to 5% of the mass of the organic solvent; the organic solvent is N,N'-dimethylacetamide or N-methylpyrrolidone.

[0007] Further specified, in step (1), the molar ratio of intermediate phenylenediamine to 3,5-diaminobenzoic acid is 1:10 to 10:1; the total mass of intermediate phenylenediamine and 3,5-diaminobenzoic acid to the mass ratio of organic solvent is 0.1% to 5%.

[0008] Further specified, in step (2), the temperature is lowered to -5 to 0℃, the polycondensation reaction is first carried out at -5 to 0℃ for 2 to 4 hours, and then raised to room temperature for 2 to 4 hours; the molar ratio of the total amount of m-phenylenediamine and 3,5-diaminobenzoic acid to the amount of isophthaloyl chloride is 0.9:1 to 1.1:1.

[0009] Further specified, in step (3), the molar ratio of tris(o-methoxyphenyl)phosphine to iodine chloride is 1:1; the molar ratio of tris(o-methoxyphenyl)phosphine to 3,5-diaminobenzoic acid is 1.5:1 to 10:1.

[0010] Further specifying, the molar ratio of p-aminobenzoic acid to 3,5-diaminobenzoic acid in step (3) is 1:1 to 50:1.

[0011] Further, the activation reaction time in step (3) is 20 to 40 minutes, and the branching reaction time is 10 to 14 hours.

[0012] A branched polyaromatic amide is prepared by the above-described method. It is soluble in N,N'-dimethylacetamide, N,N'-dimethylformamide, or N-methylpyrrolidone solvents, and its 5% thermal decomposition temperature under a nitrogen atmosphere is not lower than 500°C.

[0013] And it can be used to prepare polymer films, fibers or composite materials.

[0014] The beneficial effects of this invention are as follows: 1. The preparation method provided by this invention does not produce gelation side reactions during the preparation of branched polyaromatic amides.

[0015] 2. The branched polyaromatic amide prepared by this invention is readily soluble in common polar aprotic solvents such as N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone, making it easy to perform subsequent processing such as solution spinning and coating, thus avoiding the use of 100% sulfuric acid.

[0016] 3. The 5% thermal decomposition temperature of the branched polyaromatic amide prepared by the present invention is about 480℃, which is slightly lower than that of para-aramid (Kevlar 29) at 520℃, and significantly better than that of meta-aramid (Nomex paper).

[0017] 4. The branched polyaromatic amide prepared by the present invention has better mechanical properties than para-aramid film and significantly better mechanical properties than meta-aramid film (Nomex paper) after film formation.

[0018] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0019] Figure 1 The chemical structural formula of the branched polyaromatic amide prepared in this invention is shown below. Figure 2 TG curves of the branched polyaromatic amide prepared in this invention, commercial Kevlar 29 fiber, and Nomex paper; Figure 3 The stress-strain curves of the branched polyaromatic amide film, the para-aramid film, and the Nomex paper prepared in this invention are shown. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments.

[0021] This invention provides a technical solution: a method for preparing branched polyaromatic amides, comprising the following steps: (1) Under an inert atmosphere, lithium salt is dissolved in an organic solvent, and then m-phenylenediamine and 3,5-diaminobenzoic acid are added and stirred until completely dissolved to obtain a mixed monomer solution; (2) Cool the mixed monomer solution obtained in step (1), add isophthaloyl chloride to carry out polycondensation reaction, and obtain a prepolymer solution; (3) Tris(o-methoxyphenyl)phosphine and iodine chloride were added sequentially to the prepolymer solution obtained in step (2) for activation reaction, followed by the addition of p-aminobenzoic acid for branching reaction. After the reaction was completed, the product was precipitated, filtered and dried to obtain the branched polyaromatic amide.

[0022] In step (1), the lithium salt is Li2CO3, and its mass is 0.5% to 5% of the mass of the organic solvent; the organic solvent is N,N'-dimethylacetamide or N-methylpyrrolidone.

[0023] In step (1), the molar ratio of intermediate phenylenediamine to 3,5-diaminobenzoic acid is 1:10 to 10:1; the total mass of intermediate phenylenediamine and 3,5-diaminobenzoic acid is 0.1% to 5% of the mass of organic solvent.

[0024] In step (2), the temperature is lowered to -5 to 0℃, the polycondensation reaction is first carried out at -5 to 0℃ for 2 to 4 hours, and then raised to room temperature for 2 to 4 hours; the molar ratio of the total amount of m-phenylenediamine and 3,5-diaminobenzoic acid to the amount of isophthaloyl chloride is 0.9:1 to 1.1:1.

[0025] In step (3), the molar ratio of tris(o-methoxyphenyl)phosphine to iodine chloride is 1:1; the molar ratio of tris(o-methoxyphenyl)phosphine to 3,5-diaminobenzoic acid is 1.5:1 to 10:1.

[0026] In step (3), the molar ratio of p-aminobenzoic acid to 3,5-diaminobenzoic acid is 1:1 to 50:1.

[0027] In step (3), the activation reaction time is 20 to 40 minutes and the branching reaction time is 10 to 14 hours.

[0028] Example 1 Under a nitrogen atmosphere, 300 mL of N,N'-dimethylacetamide and 8 g of Li₂CO₃ were added to a 500 mL flask and stirred until completely dissolved. Then, 1.5 g of m-phenylenediamine and 1.52 g of 3,5-diaminobenzoic acid were added and stirred until completely dissolved. The temperature was lowered to -5°C, and 4.06 g of isophthaloyl chloride was added. The reaction was maintained at -5°C with stirring for 3 h, followed by a 3 h reaction at room temperature. Then, 10.5 g of tris(o-methoxyphenyl)phosphine and 4.86 g of iodine chloride were added and stirred for 30 min. Finally, 5.48 g of p-aminobenzoic acid was added and stirred for 12 h until the reaction was complete. The reaction solution was poured into a large amount of water, the precipitate was precipitated, filtered, and dried to obtain the branched polyaromatic amide (product 1).

[0029] Example 2 Under a nitrogen atmosphere, 300 mL of N,N'-dimethylacetamide and 15 g of Li₂CO₃ were added to a 500 mL flask and stirred until completely dissolved. Then, 1.08 g of m-phenylenediamine and 2.28 g of 3,5-diaminobenzoic acid were added and stirred until completely dissolved. The temperature was lowered to -5°C, and 5.08 g of isophthaloyl chloride was added. The reaction was maintained at -5°C with stirring for 3 h, followed by a 3 h reaction at room temperature. Then, 7.92 g of tris(o-methoxyphenyl)phosphine and 3.65 g of iodine chloride were added, and the reaction was stirred for 30 min. Finally, 10.96 g of p-aminobenzoic acid was added, and the reaction was stirred for 12 h until the reaction was complete. The reaction solution was poured into a large amount of water, the precipitate precipitated, filtered, and dried to obtain the branched polyaromatic amide. The obtained branched polyaromatic amide is soluble in N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone (product 2).

[0030] Example 3 Under a nitrogen atmosphere, 300 mL of N,N'-dimethylacetamide and 12 g of Li₂CO₃ were added to a 500 mL flask and stirred until completely dissolved. Then, 1.08 g of m-phenylenediamine and 0.76 g of 3,5-diaminobenzoic acid were added and stirred until completely dissolved. The temperature was lowered to -5°C, and 3.06 g of isophthaloyl chloride was added. The reaction was maintained at -5°C with stirring for 3 h, followed by a 3 h reaction at room temperature. Then, 35.2 g of tris(o-methoxyphenyl)phosphine and 16.2 g of iodine chloride were added, and the reaction was stirred for 30 min. Finally, 2.06 g of p-aminobenzoic acid was added, and the reaction was stirred for 12 h until the reaction was complete. The reaction solution was poured into a large amount of water, the precipitate precipitated, filtered, and dried to obtain the branched polyaromatic amide. The obtained branched polyaromatic amide is soluble in N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone (product 3).

[0031] The branched polyaromatic amides obtained in the above examples are soluble in N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone. In contrast, linear poly(p-phenylene terephthalamide) (Kevlar 29 fiber) is insoluble in N,N'-dimethylacetamide, N,N'-dimethylformamide, and N-methylpyrrolidone. This demonstrates that the branched polyaromatic amides prepared in this invention possess good solubility and solution processability.

[0032] To test the heat resistance of the branched polyaromatic amide products 1, 2, and 3 prepared in this invention, thermogravimetric analysis was performed on the branched polyaromatic amide products 1, 2, and 3 obtained in the above examples. The results are as follows: Figure 2As shown, under a N2 atmosphere, the 5% thermal decomposition temperatures of the branched polyaromatic amide products 1, 2, and 3 prepared in the examples were 482°C, 480°C, and 479°C, respectively. For comparison, the 5% thermal decomposition temperature of poly(p-phenylene terephthalamide) (Kevlar 29 fiber) was 520°C, and the 5% thermal decomposition temperature of poly(m-phenylene isophthalamide) (Nomex paper) was 370°C. This indicates that the thermal stability of the branched polyaromatic amides prepared in this invention is slightly lower than that of poly(p-phenylene terephthalamide) (Kevlar 29 fiber), but significantly higher than that of poly(m-phenylene isophthalamide) (Nomex paper).

[0033] To compare the tensile strength of branched polyaromatic amide films, meta-aramid films, and para-aramid films, a 2% (w / w) solution of N,N'-dimethylacetamide from branched polyaromatic amide products 1, 2, and 3 was coated onto a glass substrate to form a liquid film. The film was then immersed in water for a solvent-free phase inversion, and dried to obtain the branched polyaromatic amide film. For comparison, commercially available Nomex paper was used for the meta-aramid film. The para-aramid film was prepared by first dispersing Kevlar 29 fibers in dimethyl sulfoxide containing potassium hydroxide (1% (w / w)) to form a 2% (w / w) nano-para-aramid dispersion. This dispersion was then coated onto a glass substrate to form a liquid film, immersed in water for a solvent-free phase inversion, and dried to obtain the para-aramid film. Tensile test results are shown below. Figure 3 As shown, the tensile strengths of branched polyaromatic amide membrane products 1, 2, and 3 are 240 MPa, 252 MPa, and 256 MPa, respectively. The tensile strength of the para-aramid membrane is 222 MPa, while the tensile strength of the meta-aramid membrane is only 90 MPa. This indicates that the branched polyaromatic amide membrane not only has good processability but also higher mechanical properties, superior to the para-aramid membrane and far exceeding the meta-aramid membrane, proving that the branched polyaromatic amide prepared in this invention has excellent overall performance.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing branched polyaromatic amides, characterized in that: Includes the following steps: (1) Under an inert atmosphere, lithium salt is dissolved in an organic solvent, and then m-phenylenediamine and 3,5-diaminobenzoic acid are added and stirred until completely dissolved to obtain a mixed monomer solution; (2) Cool the mixed monomer solution obtained in step (1), add isophthaloyl chloride to carry out polycondensation reaction, and obtain a prepolymer solution; (3) Tris(o-methoxyphenyl)phosphine and iodine chloride were added sequentially to the prepolymer solution obtained in step (2) for activation reaction, followed by the addition of p-aminobenzoic acid for branching reaction. After the reaction was completed, the product was precipitated, filtered and dried to obtain the branched polyaromatic amide.

2. The method for preparing branched polyaromatic amide according to claim 1, characterized in that: The lithium salt mentioned in step (1) is Li2CO3, and its mass is 0.5% to 5% of the mass of the organic solvent; the organic solvent is N,N'-dimethylacetamide or N-methylpyrrolidone.

3. The method for preparing branched polyaromatic amide according to claim 1, characterized in that: Step (1) The molar ratio of intermediate phenylenediamine to 3,5-diaminobenzoic acid is 1:10 to 10:1; the total mass of intermediate phenylenediamine and 3,5-diaminobenzoic acid to the mass ratio of organic solvent is 0.1% to 5%.

4. The method for preparing branched polyaromatic amide according to claim 1, characterized in that: In step (2), the temperature is lowered to -5 to 0℃, and the polycondensation reaction is first carried out at -5 to 0℃ for 2 to 4 hours, and then raised to room temperature for 2 to 4 hours; the molar ratio of the total amount of m-phenylenediamine and 3,5-diaminobenzoic acid to the amount of isophthaloyl chloride is 0.9:1 to 1.1:

1.

5. The method for preparing branched polyaromatic amide according to claim 1, characterized in that: In step (3), the molar ratio of tris(o-methoxyphenyl)phosphine to iodine chloride is 1:1; the molar ratio of tris(o-methoxyphenyl)phosphine to 3,5-diaminobenzoic acid is 1.5:1 to 10:

1.

6. The method for preparing branched polyaromatic amide according to claim 1, characterized in that: In step (3), the molar ratio of p-aminobenzoic acid to 3,5-diaminobenzoic acid is 1:1 to 50:

1.

7. The method for preparing branched polyaromatic amide according to claim 1, characterized in that: In step (3), the activation reaction time is 20 to 40 minutes, and the branching reaction time is 10 to 14 hours.

8. A branched polyaromatic amide, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 7.

9. The branched polyaromatic amide according to claim 8, characterized in that: It is soluble in N,N'-dimethylacetamide, N,N'-dimethylformamide or N-methylpyrrolidone solvents; and its 5% thermal decomposition temperature under nitrogen atmosphere is not lower than 500℃.

10. The use of the branched polyaromatic amide as described in claim 8 or 9 in the preparation of polymer films, fibers or composite materials.

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