Preparation method and application of high-strength sulfonated long-carbon-chain polyamide

Abstract

The invention discloses a preparation method and application of high-strength sulfonated long-carbon-chain polyamide, and the preparation method of the high-strength sulfonated long-carbon-chain polyamide comprises the following steps: uniformly mixing dodecanedioic acid and water, then adding 1, 10-diaminodecane and 2, 4-diaminobenzenesulfonic acid sodium salt, and carrying out a salt forming reaction at 70-100 DEG C to obtain the high-strength sulfonated long-carbon-chain polyamide. After the salt forming reaction is finished, the temperature is raised to 170-220 DEG C under the protective atmosphere, auxiliaries are added, pre-polycondensation reaction is carried out, then the temperature is raised to 230-255 DEG C, vacuum polycondensation is carried out, cooling is carried out to the room temperature, granulation is carried out, and the high-strength sulfonated long carbon chain polyamide is obtained. The sulfonation rate of the high-strength sulfonated long carbon chain polyamide prepared through the melt polycondensation one-pot method can reach 25% or above; the prepared PA1012 has excellent mechanical properties, the yield strength of the PA1012 can be higher than 60MPa, the elongation at break of the PA1012 can reach 210.00%, and the piezoelectric property of the PA1012 is changed from nothing to thing.

Description

Technical Field

[0001] This invention belongs to the field of functional polymer materials technology, specifically relating to a method for preparing high-strength sulfonated long-chain polyamide and its application. Background Technology

[0002] Polyamide (PA), commonly known as nylon, is an important engineering plastic containing repeating amide groups (-CONH-) in its main chain. The amide groups between its macromolecular chains can form hydrogen bonds, serving as physical cross-linking points and significantly improving the material's mechanical strength, rigidity, and heat resistance. Based on the different lengths of the methylene (-CH2-) sequence in diamines and diacids (or lactams), polyamides can be divided into short-chain polyamides and long-chain polyamides, which exhibit significant and systematic differences in performance. Short-chain polyamides (such as PA6 and PA66) have advantages such as high strength, high rigidity, and high heat resistance, but also inherent disadvantages such as high water absorption, poor dimensional stability, and insufficient low-temperature toughness. Their high water absorption can cause significant changes in the dimensions and electrical properties of products in humid environments, limiting their application in precision parts and electronic and electrical fields. Long-chain polyamides (such as PA11, PA12, and PA1012) have more than 10 carbon atoms in their monomers. Due to the longer methylene sequences in their molecular chains, the density of amide groups is relatively low, and the spacing is large, resulting in a much smaller number of intermolecular hydrogen bonds compared to short-chain polyamides. The longer methylene segments impart greater flexibility to the molecular chains because the energy barrier for carbon-carbon single bond rotation to change conformation is lower. Therefore, long-chain polyamides exhibit characteristics such as low water absorption, excellent dimensional stability, high toughness, good impact resistance, and good flexibility. However, their strength, stiffness, and melting point are generally lower than those of short-chain polyamides.

[0003] Polyamide PA1012 is formed by the condensation polymerization of 1,10-diaminodecane (C10) and dodecanoic acid (C12) (total carbon number 22), belonging to the typical even-carbon polyamides. It is particularly important to note that the piezoelectric properties of polyamides are closely related to the polarization and crystal structure of their molecular chains, a fundamental difference between odd-carbon and even-carbon polyamides. For odd-carbon polyamide PA11, prepared by polymerization of 11-aminoundecanoic acid, because its monomer has an odd number of carbon atoms, the dipoles of all amide groups in its molecular chain can achieve cooperative alignment along the chain direction, thus exhibiting intrinsic piezoelectric properties macroscopically. Conversely, in even-carbon polyamides, adjacent amide groups in the crystal have opposite orientations, and their dipole moments cancel each other out, resulting in a very small net dipole moment for the entire molecular chain. Therefore, even-carbon polyamides are inherently non-piezoelectric or have extremely weak piezoelectricity. The symmetrical long carbon chain structure of PA1012 endows it with strong interchain van der Waals forces. While retaining the general advantages of long-chain polyamides, it also exhibits excellent flexibility, impact resistance, superior dimensional stability, and chemical resistance. However, its highly ordered molecular structure, strong intermolecular forces, and high crystallinity also lead to poor dyeability and processing performance. More importantly, as an even-chain long carbon polyamide, PA1012, limited by its inherent molecular structural symmetry, inherently lacks piezoelectric properties, completely excluding it from high-end functional materials fields such as smart sensing and energy harvesting. Therefore, functional modification of PA1012, especially endowing it with piezoelectricity, faces significant technical challenges but also holds immense application value.

[0004] To broaden the application areas of PA1012 and endow it with new functions, sulfonation modification is an effective technical path. Sulfonated polymers have broad prospects in fields such as polymer electrolyte fuel cells, evaporative permeation membranes, and hydrogels. However, the main methods for preparing sulfonated polymers currently have inherent defects: the sulfonation modification method after polymer polymerization is simple to operate, but the degree of sulfonation is low, the sulfonation is uneven, and the sulfonation process conditions are harsh, which can easily lead to polymer chain degradation and deterioration of mechanical properties, and the degree of sulfonation is not easy to control precisely; although the sulfonated monomer polymerization method can control the degree of sulfonation and obtain high molecular weight polymers by selecting monomers, the existing processes are usually lengthy, involving the use of a large amount of toxic solvents and the separation and purification of intermediate products. Not only are the processes cumbersome, inefficient, and costly, but they also cause great pollution, making it difficult to efficiently and industrially produce target products with high sulfonic acid content and high molecular weight. For example, patent CN108465386A discloses a sulfonated polyamide for retaining anionic dyes, which is prepared by ring-opening polymerization of 2-amino-5-sulfonyl-benzoic acid and ε-caprolactam. This preparation process is complex, cumbersome, and inefficient. Furthermore, the sulfonic acid groups result in a low molecular weight, poor mechanical properties, and poor color, limiting the maximum addition content to below 5 wt%. Therefore, this existing technology cannot yield sulfonated polyamides that combine high sulfonic acid content, high molecular weight, and excellent mechanical properties, nor can it effectively explore new functions such as piezoelectricity. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a high-strength sulfonated long-chain polyamide. Here, "sulfonation" refers to the process of directly attaching sulfonic acid groups (-SO3H) or their salts (such as -SO3Na) to the polymer molecular backbone through a chemical reaction. This is fundamentally different from simply physically blending additives containing sulfonates with polyamide: in physical blends, there is no chemical bond between sulfonates and the polyamide matrix, which is prone to migration and precipitation, resulting in unstable performance and difficulty in achieving synergistic effects at the molecular level, thus failing to endow the material with truly meaningful and durable new functionalities. In contrast, the "sulfonation modification" of this invention is a chemical copolymerization modification, introducing sulfonate groups into the PA1012 molecular chain to achieve a stable covalent bond between the sulfonic acid groups and the backbone, fundamentally changing the chemical structure and polarity of the polymer, and endowing the polymer with permanent functionality (piezoelectric properties).

[0006] Another objective of this invention is to provide a method for preparing the above-mentioned high-strength sulfonated long-chain polyamide. This method employs a one-pot melt polycondensation process, which introduces sodium 2,4-diaminobenzenesulfonate (MPDSA) to disrupt the regularity of the molecular structure of PA1012, weaken the intermolecular hydrogen bonding forces, reduce its crystallization rate, and improve its processability and mechanical properties.

[0007] Another object of the present invention is to provide the use of the above-mentioned high-strength sulfonated long-chain polyamide in improving the piezoelectric coefficient.

[0008] The objective of this invention is achieved through the following technical solutions.

[0009] A high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) has the following structural formula:

[0010] , where m∶n=(1~3)∶(3~19).

[0011] In the above technical solution, the intrinsic viscosity of high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) is 0.8~1.1 dL / g.

[0012] The preparation method of the above-mentioned high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) includes:

[0013] Dodecanoic acid is mixed evenly with water, and then 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) are added. A salt formation reaction is carried out at 70~100℃. After the salt formation reaction is completed, the temperature is raised to 170~220℃ under a protective atmosphere, and an auxiliary agent is added to carry out a pre-condensation reaction. The temperature is then raised to 230~255℃ for vacuum condensation. After cooling to room temperature, the mixture is granulated to obtain a high-strength sulfonated long-chain polyamide (PA1012 / MPDSA). The ratio of dodecanoic acid, 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) is 1:(0.75~0.95):(0.05~0.25) by molar amount.

[0014] In the above technical solution, the ratio of dodecanoic acid to water by mass is 1:(2~4).

[0015] In the above technical solution, the uniform mixing includes stirring at 70~90℃ for 15~30 minutes.

[0016] In the above technical solution, the stirring speed is 30~90 rpm.

[0017] In the above technical solution, the salt formation reaction time is 2-5 hours.

[0018] In the above technical solution, the pre-polymerization time is 2-4 hours.

[0019] In the above technical solution, the vacuum polycondensation time is 2~5h, and the vacuum degree of vacuum polycondensation is ≤100Pa.

[0020] In the above technical solution, the additive may be one or more of potassium phosphite, sodium phosphite, magnesium phosphite, potassium hypophosphite, sodium hypophosphite, and magnesium hypophosphite.

[0021] In the above technical solution, the ratio of dodecanoic acid to auxiliaries by mass is 1:(0.001~0.005).

[0022] In the above technical solution, the protective atmosphere includes nitrogen.

[0023] In the above technical solution, the granulation speed is 15~30 r / s.

[0024] The above-mentioned high-strength sulfonated long-chain polyamides are used to improve the piezoelectric coefficient.

[0025] In the above technical solution, the piezoelectric coefficient is 15*10. -12 ~58*10 -12 C / N.

[0026] The above-mentioned high-strength sulfonated long-chain polyamide is used to improve the elongation at break. The ratio of dodecanoic acid, 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) is 1:(0.85~0.95):(0.05~0.15) by weight.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] 1. The high-strength sulfonated long-chain polyamide prepared by the one-pot melt polycondensation method of this invention has a sulfonation rate (the proportion of sodium sulfonate groups introduced) of more than 25%, and its mechanical properties are excellent. The yield strength can be higher than 60MPa and the elongation at break can be as high as 210.00%. It also achieves a breakthrough in the piezoelectric properties of PA1012 from scratch.

[0029] 2. The preparation method of the present invention precisely controls the amount of sulfonating monomer (sodium 2,4-diaminobenzenesulfonate) to precisely introduce sodium sulfonate groups (-SO3Na) into the main chain of polyamide (PA1012) and synergistically regulates the hydrogen bond density, thereby realizing the multifunctional integration of the material, effectively improving the mechanical properties of the material, and endowing even-numbered polyamides with piezoelectric properties that they do not possess, solving the problem of weak flexible electronic compatibility caused by the low polarity of the molecular chain of traditional long carbon chain polyamides (such as PA12, PA1212 and PA1012).

[0030] 3. The monomers 1,10-diaminodecane and dodecanoic acid used in the preparation method of the present invention are both bio-based raw materials, which are in line with the current sustainable development strategy.

[0031] 4. The preparation method of the present invention is simple to operate, has universality, can effectively shorten the production cycle, and meet the actual needs of industrial scale-up production. Attached Figure Description

[0032] Figure 1 The diagram shows the piezoelectric properties of the polymer piezoelectric film, where a is Example 1, b is Example 2, c is Example 3, d is Example 4, e is Example 5, f is Comparative Example 1, g is Comparative Example 2, and h is Comparative Example 3.

[0033] Figure 2 Fourier transform infrared spectra of the high-strength sulfonated long-chain polyamides of Examples 1-5 and the long-chain polyamide of Comparative Example 1.

[0034] Figure 3 A represents the 1H NMR spectrum of the high-strength sulfonated long-chain polyamides of Examples 1-5 and the long-chain polyamide of Comparative Example 1. Figure 3 b is Figure 3 A magnified view of the area within the red box in image a. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to the embodiments and accompanying drawings.

[0036] In the following examples, the water used is deionized water.

[0037] The purity and source of the reagents used in the following examples are as follows:

[0038] Dodecanoic acid (99.8%), 1,10-diaminodecane (99.8%), sodium 2,4-diaminobenzenesulfonate (MPDSA, 99.5%), sodium hypophosphite (99.9%), potassium hypophosphite (99.9%), potassium phosphite (99.9%), magnesium phosphite (99.9%), and sodium phosphite (99.9%) were all purchased from the same supplier: Aladdin Reagent Co., Ltd., Shanghai, China.

[0039] The instrument models and manufacturers used in the following examples are as follows:

[0040] Bruker ALPHA Fourier Transform Infrared Spectrometer, Bruker Corporation;

[0041] Bruker AVIII 400 liquid nuclear magnetic resonance spectrometer, Bruker Corporation;

[0042] JJ-TEST cantilever beam impact testing machine, manufactured by Shenzhen Sansi Company, China;

[0043] Instron 1122 Electronic Universal Testing Machine, Shenzhen Sanshi Company, China;

[0044] LQ-25 high-speed pelletizer, Jiangsu Zhenghong Rubber & Plastic Machinery Manufacturing Co., Ltd.

[0045] R3221 Flat Plate Vulcanizer, Wuhan Qien Technology Development Co., Ltd.;

[0046] SZS-20 injection molding machine, Wuhan Ruiming Experimental Instrument Co., Ltd.;

[0047] Ubbelohde viscometer (inner diameter 0.8~0.9mm), Shuniu Glass Instrument Co., Ltd.;

[0048] JJANM-21 Notch Sample Preparation Machine, Chengde Jinjian Testing Instruments Co., Ltd.;

[0049] Pressure applicator, Changsha Micro-Nano Instrument Technology Co., Ltd.;

[0050] ZJ-3 piezoelectric d33 tester, Institute of Acoustics, Chinese Academy of Sciences.

[0051] In the following embodiments, the granulation is performed using an LQ-25 high-speed pelletizer with a granulation speed of 15 r / s.

[0052] Example 1

[0053] A method for preparing a high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) includes:

[0054] Dodecanoic acid was mixed with water and stirred at 30 rpm at 75°C for 30 min. Then, 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) were added, and a salt-forming reaction was carried out at 70°C for 4 h. After the salt-forming reaction was completed, the temperature was raised to 170°C under a protective atmosphere (nitrogen), and an auxiliary agent was added for a pre-condensation reaction for 3 h. Then, the temperature was raised to 230°C, and vacuum condensation was carried out for 3 h under a vacuum of ≤100 Pa. After cooling to room temperature, the mixture was granulated to obtain high-strength sulfonated long... Carbon chain polyamide (PA1012 / MPDSA), wherein, by mass parts, the ratio of dodecanoic acid to water is 1:2, and by molar parts, the ratio of dodecanoic acid, 1,10-diaminodecane, and sodium 2,4-diaminobenzenesulfonate (MPDSA) is 1:0.95:0.05; the auxiliary agent is sodium hypophosphite, and by mass parts, the ratio of dodecanoic acid to the auxiliary agent is 1:0.005; the structural formula of high-strength sulfonated long carbon chain polyamide (PA1012 / MPDSA) is:

[0055] , where m∶n=1∶19.

[0056] Example 2

[0057] A method for preparing a high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) includes:

[0058] Dodecanoic acid was mixed with water and stirred at 30 rpm at 80°C for 30 min. Then, 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) were added, and a salt-forming reaction was carried out at 80°C for 3 h. After the salt-forming reaction was completed, the temperature was raised to 180°C under a protective atmosphere (nitrogen), and an auxiliary agent was added for a pre-condensation reaction for 2.5 h. The temperature was then raised to 240°C, and vacuum condensation was carried out for 2.5 h under a vacuum degree ≤100 Pa. After cooling to room temperature, granulation was performed to obtain high-strength sulfonate. The high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) contains, by mass, dodecanoic acid and water in a ratio of 1:2, and by molar amount, dodecanoic acid, 1,10-diaminodecane, and sodium 2,4-diaminobenzenesulfonate (MPDSA) in a ratio of 1:0.90:0.10. The additive is potassium hypophosphite, and by mass, the ratio of dodecanoic acid to the additive is 1:0.005. The structural formula of the high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) is as follows:

[0059] , where m∶n=1∶9.

[0060] Example 3

[0061] A method for preparing a high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) includes:

[0062] Dodecanoic acid was mixed with water and stirred at 30 rpm at 85°C for 30 min. Then, 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) were added, and a salt-forming reaction was carried out at 90°C for 3 h. After the salt-forming reaction was completed, the temperature was raised to 190°C under a protective atmosphere (nitrogen), and an auxiliary agent was added for a pre-condensation reaction for 2 h. Then, the temperature was raised to 245°C, and vacuum condensation was carried out for 2 h under a vacuum of ≤100 Pa. After cooling to room temperature, granulation was performed to obtain high-strength sulfonated long carbon. The high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) contains, by mass, dodecanoic acid and water in a ratio of 1:2, and by molar, dodecanoic acid, 1,10-diaminodecane, and sodium 2,4-diaminobenzenesulfonate (MPDSA) in a ratio of 1:0.85:0.15; the auxiliary agent is potassium phosphite, and by mass, the ratio of dodecanoic acid and the auxiliary agent is 1:0.005; the structural formula of the obtained high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) is as follows:

[0063] , where m∶n=3∶17.

[0064] Example 4

[0065] A method for preparing a high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) includes:

[0066] Dodecanoic acid was mixed with water and stirred at 30 rpm at 90°C for 30 min. Then, 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) were added, and a salt-forming reaction was carried out at 100°C for 3 h. After the salt-forming reaction was completed, the temperature was raised to 210°C under a protective atmosphere (nitrogen), and an auxiliary agent was added for a pre-condensation reaction for 2 h. Then, the temperature was raised to 250°C, and vacuum condensation was carried out for 2 h under a vacuum of ≤100 Pa. After cooling to room temperature, granulation was performed to obtain high-strength sulfonated long carbon. The high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) contains, by mass, dodecanoic acid and water in a ratio of 1:2, and by molar, dodecanoic acid, 1,10-diaminodecane, and sodium 2,4-diaminobenzenesulfonate (MPDSA) in a ratio of 1:0.80:0.20; the auxiliary agent is magnesium phosphite, and by mass, the ratio of dodecanoic acid and the auxiliary agent is 1:0.005; the structural formula of the obtained high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) is as follows:

[0067] , where m∶n=1∶4.

[0068] Example 5

[0069] A method for preparing a high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) includes:

[0070] Dodecanoic acid was mixed with water and stirred at 30 rpm at 90°C for 15 min. Then, 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) were added, and a salt-forming reaction was carried out at 100°C for 3 h. After the salt-forming reaction was completed, the temperature was raised to 220°C under a protective atmosphere (nitrogen), and an auxiliary agent was added for a pre-condensation reaction for 2 h. Then, the temperature was raised to 255°C, and vacuum condensation was carried out for 2 h under a vacuum of ≤100 Pa. After cooling to room temperature, granulation was performed to obtain high-strength sulfonated long carbon. The high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) contains, by mass, dodecanoic acid and water in a ratio of 1:2, and by molar, dodecanoic acid, 1,10-diaminodecane, and sodium 2,4-diaminobenzenesulfonate (MPDSA) in a ratio of 1:0.75:0.25; the additive is sodium phosphite, and by mass, the ratio of dodecanoic acid and the additive is 1:0.005; the structural formula of the obtained high-strength sulfonated long-chain polyamide (PA1012 / MPDSA) is as follows:

[0071] , where m∶n=1∶3.

[0072] Comparative Example 1

[0073] A method for preparing a long-chain polyamide, comprising:

[0074] A mixture of dodecanoic acid aqueous solution and 1,10-diaminodecane aqueous solution was subjected to a salt-forming reaction at 90°C for 3 hours. Under a protective atmosphere (nitrogen), the temperature was raised to 190°C, an additive was added, and a pre-condensation reaction was carried out for 3 hours. The temperature was then raised to 250°C, and vacuum condensation was performed for 2 hours under a vacuum of ≤100 Pa. After cooling to room temperature, granulation was performed to obtain a long-chain polyamide. The ratio of dodecanoic acid in the dodecanoic acid aqueous solution to 1,10-diaminodecane in the 1,10-diaminodecane aqueous solution was 1:1 by weight. The additive was potassium phosphite, and the ratio of dodecanoic acid to the additive by weight was 1:0.005. The structural formula of the long-chain polyamide (PA1012 / MPDSA) is as follows:

[0075] .

[0076] The method for preparing a dodecanoic acid aqueous solution includes: mixing dodecanoic acid with water and stirring at 30 rpm at 70°C for 30 min, wherein the ratio of dodecanoic acid to water in the dodecanoic acid aqueous solution is 1:2 by mass.

[0077] A method for preparing an aqueous solution of 1,10-diaminodecane includes: mixing 1,10-diaminodecane with water and stirring at 30 rpm at 70°C for 30 min, wherein the ratio of 1,10-diaminodecane to water in the aqueous solution of 1,10-diaminodecane is 1:2 by mass.

[0078] Comparative Example 2

[0079] Hiprolon 400 NN polyamide 1012 pure resin (PA1012) purchased from Arkema, France, was used as Comparative Example 2. This grade is a general injection molding grade and is a standard long carbon chain polyamide produced from renewable resources.

[0080] Comparative Example 3

[0081] A general-purpose polyvinylidene fluoride resin (PVDF resin) of Solef® 60000 purchased from Solvay was used as Comparative Example 3 (this grade is pure PVDF resin without special polarization treatment). The structural formula of the PVDF resin is as follows:

[0082] .

[0083] The high-strength sulfonated long-chain polyamides of Examples 1-5, the long-chain polyamide of Comparative Example 1, and PA1012 of Comparative Example 2 were used as copolymers. The copolymers were dissolved in concentrated sulfuric acid (the concentration of H2SO4 in the concentrated sulfuric acid was 18 mol / L) at (25±0.01)℃ to prepare copolymer solutions with a copolymer concentration of 1 mg / dL. The intrinsic viscosity of the copolymer solutions was measured using an Ubbelohde viscometer, and the results are shown in "Intrinsic Viscosity" in Table 1.

[0084] At (25±0.01)℃, the PVDF resin of Comparative Example 3 was dissolved in N-N'-dimethylformamide (DMF) to prepare a PVDF solution with a PVDF resin concentration of 1 mg / dL. The intrinsic viscosity of the PVDF solution was measured using an Ubbelohde viscometer, and the results are shown in Table 1 under "Intrinsic Viscosity".

[0085] The copolymers of Examples 1-5 and Comparative Examples 1-2, as well as the PVDF resin of Comparative Example 3, were used to make dumbbell-shaped specimens of 75.0 mm × 5.0 mm × 2.0 mm using an SZS-20 injection molding machine. The yield strength, breaking strength and elongation at break of the dumbbell-shaped specimens were tested according to the method of standard ISO 527-1:2019. The results are shown in Table 1.

[0086] Rectangular strips of 80.0 mm × 10.0 mm × 4.0 mm were made from the copolymers of Examples 1-5 and Comparative Examples 1-2 and the PVDF resin of Comparative Example 3 using an SZS-20 injection molding machine. The bending strength of the rectangular strips was tested according to the method of standard ISO 178:2019. The results are shown in Table 1.

[0087] Rectangular specimens of 80.0 mm × 10.0 mm × 4.0 mm were prepared from the copolymers of Examples 1-5 and Comparative Examples 1-2, and the PVDF resin of Comparative Example 3, using an SZS-20 injection molding machine. A V-shaped notch with a depth of 2.0 mm and an angle of 45° was milled at the center of the rectangular specimen along its length using a JJANM-21 notch sampler. The tip radius of the notch was 0.25 mm. The notched impact strength of the copolymers of Examples 1-5 and Comparative Examples 1-2, and the PVDF resin of Comparative Example 3 was tested according to standard GB / T 1043.1-2008. The results are shown in Table 1.

[0088] 0.5g of the copolymers from Examples 1-5 and Comparative Examples 1-2, as well as the PVDF resin from Comparative Example 3, were hot-pressed using an R3221 flat vulcanizing apparatus. The hot-pressing temperature was 230℃, the hot-pressing time was 5 minutes, and the hot-pressing pressure was 2MPa, respectively, to obtain polymer piezoelectric films. The piezoelectric coefficients of the polymer piezoelectric films from Examples 1-5 and Comparative Examples 1-3 were tested using a ZJ-3 type piezoelectric d33 tester. The test method followed the standard GB / T 3389-2008, and the results are shown in Table 1.

[0089] Table 1

[0090]

[0091] As shown in Table 1, compared with Comparative Example 1, the high-strength sulfonated long-chain polyamides in Examples 1-5, after introducing different proportions of MPDSA into PA1012, significantly improved its yield strength, fracture strength, flexural strength, and notched impact strength. This is because sodium sulfonate groups can form ionic clusters as physical crosslinking points. By controlling their proportion, PA1012 can be simultaneously strengthened and toughened under the synergistic effect of intermolecular electrostatic forces and hydrogen bonds.

[0092] The elongation at break of the high-strength sulfonated long-chain polyamides in Examples 1-5 first increased and then decreased with the addition of MPDSA. This is because the physical cross-linking of ionic clusters formed between sodium sulfonate groups causes phase separation between molecules, thereby reducing the elongation at break.

[0093] In Examples 1-5, the sodium sulfonate groups introduced into PA1012 of the high-strength sulfonated long-chain polyamides exhibit strong polarity. These groups disrupt the regularity of the PA1012 molecular chain, weaken intermolecular hydrogen bonds, reduce the crystallization rate, and significantly increase the dipole moment of the molecular structure. This transforms PA1012 from a non-piezoelectric material into a piezoelectric material, resulting in novel and stable piezoelectric properties. The piezoelectric constant of Example 5 reached 58 × 10⁻⁶. -12 C / N not only far exceeds 2*10 of Comparative Example 1 and Comparative Example 2, but also... -12 The C / N ratio also significantly surpasses that of Comparative Example 3 (commercially available PVDF resin) at 23*10. -12 C / N.

[0094] Example 6

[0095] The piezoelectric properties of the polymer piezoelectric films from Examples 1-5 and Comparative Examples 1-3 were tested: Copper sheets were attached to both sides of the polymer piezoelectric film as electrodes (the electrodes were used for electrical connection with the electrochemical workstation), and the films were encapsulated with PET encapsulation tape to obtain piezoelectric components. Piezoelectric testing was performed on the piezoelectric components using a pressure applicator: The piezoelectric components were mounted on a stable support, and a compressive impact of 10N and 1.5Hz was applied to the piezoelectric components by controlling the pressure applicator. The voltage and current output by the piezoelectric components were recorded in real time using the electrochemical workstation (CHI 660E). The results are as follows: Figure 1 As shown. By Figure 1 It can be seen that as the content of sulfonic acid groups in the macromolecular backbone increases in Examples 1 to 5, the open-circuit piezoelectric voltage gradually increases. For example, the open-circuit voltage of Example 5 can reach 35V, which is higher than that of Comparative Example 3 (open-circuit voltage 28V).

[0096] Fourier transform infrared spectroscopy was used to measure the Fourier transform infrared spectra of the high-strength sulfonated long-chain polyamides of Examples 1-5 and the long-chain polyamide of Comparative Example 1. The results are as follows: Figure 2 As shown. By Figure 2 It can be seen that long-chain polyamides at 1640 cm⁻¹ -1 A C=O tensile vibration peak in the amide I band appears at 1540 cm⁻¹. -1 An amide II band NH bend appears at 1250 cm⁻¹ in the fingerprint area. -1 and 1025 cm -1 The presence of sulfonic acid groups indicates that the sulfonic acid groups have been successfully incorporated into the macromolecular backbone of PA1012.

[0097] The proton NMR spectra of the high-intensity sulfonated long-chain polyamides of Examples 1-5 and the long-chain polyamide of Comparative Example 1 were measured using a liquid nuclear magnetic resonance spectrometer. The results are as follows: Figure 3 As shown, where, Figure 3 'a' is the proton NMR spectrum. Figure 3 b is Figure 3 A magnified view of the area within the dashed box in image 'a'. (From...) Figure 3It can be seen that the NMR of the high-strength sulfonated long-chain polyamide is in good agreement with the theoretical structure, and no cross-linking or branched structures were observed. Among them, the peak at 2.6 ppm is caused by the hydrogen atom on the methylene group connected to the carboxyl group of the dodecanoic acid, while the resonance peaks of the hydrogen atoms on the remaining methylene groups are located around 1.2~1.3 ppm; the resonance peak of the α-methylene hydrogen atom connected to the amino group in 1,10-diaminodecane appears at 3.5 ppm, and the resonance peaks of the β and γ-methylene hydrogen atoms appear at 1.6 ppm; the methylene hydrogen atoms in the middle of the macromolecular chain are less affected by the shielding effect, and their resonance peaks overlap with the resonance peaks of the methylene hydrogen atoms from the dodecanoic acid that are not connected to the carboxyl group, located around 1.2~1.3 ppm; the multiple peaks between 7.5 and 8.25 ppm are formed by hydrogen atoms on the benzene ring of MPDSA under different electronic environments.

[0098] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A high-strength sulfonated long-chain polyamide, characterized in that, It has the following structural formula: , where m∶n=(1~3)∶(3~19).

2. A method for preparing a high-strength sulfonated long-chain polyamide, characterized in that, include: Dodecanoic acid is mixed evenly with water, and then 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate are added. A salt formation reaction is carried out at 70~100℃. After the salt formation reaction is completed, the temperature is raised to 170~220℃ under a protective atmosphere, and an auxiliary agent is added to carry out a pre-condensation reaction. The temperature is then raised to 230~255℃ for vacuum condensation. After cooling to room temperature, the mixture is granulated to obtain a high-strength sulfonated long-chain polyamide. The ratio of dodecanoic acid, 1,10-diaminodecane and sodium 2,4-diaminobenzenesulfonate (MPDSA) is 1:(0.75~0.95):(0.05~0.25) by molar amount.

3. The preparation method according to claim 2, characterized in that, The ratio of dodecanoic acid to water by mass is 1:(2~4).

4. The preparation method according to claim 2, characterized in that, The process of achieving uniform mixing includes stirring at 70-90°C for 15-30 minutes.

5. The preparation method according to claim 2, characterized in that, The salt formation reaction takes 2 to 5 hours.

6. The preparation method according to claim 2, characterized in that, The pre-polymerization time is 2-4 hours.

7. The preparation method according to claim 2, characterized in that, The vacuum polycondensation time is 2~5 hours, and the vacuum degree of vacuum polycondensation is ≤100Pa.

8. The preparation method according to claim 2, characterized in that, The additive may be one or more of potassium phosphite, sodium phosphite, magnesium phosphite, potassium hypophosphite, sodium hypophosphite, and magnesium hypophosphite; The ratio of dodecanoic acid to auxiliaries by mass is 1:(0.001~0.005).

9. Use of the high-strength sulfonated long-chain polyamide as described in claim 1 in improving the piezoelectric coefficient.

10. The use of the high-strength sulfonated long-chain polyamide as described in claim 1 in improving elongation at break, characterized in that, m∶n=1∶(5~19).

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