Polyamide type polycarboxylic acid water reducing agent and preparation method thereof

Abstract

The application provides a kind of polyamide type polycarboxylic acid water reducing agent and its preparation method, comprising: step one, binary acid, binary amine, caprolactam, molecular weight regulator, water are added to reactor and stirred to be mixed uniformly;Protective gas is introduced to replace the reactor, and the reaction body is heated to a certain temperature and is kept under different pressure conditions by stage pressure control, to obtain the first product;Step two, the first product and maleic anhydride are added to the reactor and stirred to be mixed uniformly;Keep warm for 0.5-1h, to obtain the second product;Step three, the second product, acrylic acid, catalyst, chain transfer agent, water are added to the reactor and stirred uniformly;Reaction obtains the final product polyamide type polycarboxylic acid water reducing agent.The scheme uses polyamide structure as side chain to replace the traditional polyether side chain, so that the water reducing agent has high water reducing rate, high slump retention and reinforcement.

Description

Technical Field

[0001] This invention belongs to the field of concrete admixture technology, specifically relating to a polyamide-type polycarboxylate superplasticizer and its preparation method. Background Technology

[0002] In recent years, polycarboxylate superplasticizers, as the third generation of high-performance superplasticizers, have become mainstream products in the field of concrete admixtures due to their high water reduction rate, low dosage, and environmentally friendly characteristics. Traditional polycarboxylate superplasticizers typically use polyether macromonomers (such as polyethylene glycol monomethyl ether) as the main raw material, introducing hydrophilic functional groups such as carboxylic acid groups through free radical copolymerization to form copolymers with a comb-like structure. However, polyether macromonomers have high molecular chain flexibility but insufficient high-temperature resistance, and are prone to chain segment breakage in high-temperature or high-alkali environments, leading to accelerated slump loss in concrete. Furthermore, the synthesis of polyether macromonomers depends on petrochemical raw materials such as ethylene oxide, resulting in problems such as large fluctuations in raw material prices and high environmental pressure. Therefore, developing new macromonomers to replace polyethers has become an important direction for improving the performance and sustainability of superplasticizers. Summary of the Invention

[0003] One objective of this invention is to provide a polyamide-type polycarboxylate superplasticizer, the structural formula of which is as follows: Where m:n = 3.5:1; a and b represent the number of methylene groups in different diamines and diacids, respectively, a≥2, b≥2; k represents the degree of polymerization of polyamide, k=5-7.

[0004] As a preferred embodiment, the polyamide-type polycarboxylate superplasticizer has a molecular weight of 20,000-30,000.

[0005] The second objective of this invention is to provide a method for preparing a polyamide-type polycarboxylate superplasticizer. Step 1: Add the diacid, diamine, caprolactam, molecular weight regulator, and water to the reactor and stir until homogeneous; introduce a protective gas to replace the gas in the reactor to control the pressure inside the reactor at 0.2-0.3 MPa, and then seal the reactor; heat the reaction system to a certain temperature, and maintain the reaction system under different pressure and temperature conditions through staged pressure control to obtain the first product; Step 2: Add the first product obtained in Step 1 and maleic anhydride into the reactor and stir to mix evenly; then start heating, and after the reactor is heated to a specific temperature, keep it at that temperature for 0.5-1 hour to obtain the second product; Step 3: Add the second product obtained in Step 2, acrylic acid, catalyst, chain transfer agent and water into the reactor and stir evenly; after reacting for a period of time, the final product, polyamide-type polycarboxylate superplasticizer, is obtained.

[0006] As a preferred embodiment, in step one, the dicarboxylic acid is at least one of adipic acid, sebacic acid, or dodecanoic acid; the diamine is at least one of pentanediamine, hexanediamine, decanediamine, or 1,12-diaminododecane; and the molecular weight regulator is at least one of pentanediamine, hexanediamine, decanediamine, or 1,12-diaminododecane.

[0007] As a preferred embodiment, in step one, the pressure inside the reactor is controlled at 0.2-0.3 MPa, the reactor is sealed, and then the temperature is raised to 190-200 ℃ and held for 1-2 h; then the pressure in the reactor is released to atmospheric pressure within 0.5-1 h; the reactor temperature is raised to 240-260 ℃ and held for 1-2 h; then the reactor is evacuated and the vacuum degree is maintained at 0-800 Pa and held for 0.5-1 h to obtain the first product.

[0008] As a preferred embodiment, in step one, the molar ratio of diacid, diamine, caprolactam, and molecular weight regulator is 1:1:1:0.15-0.3.

[0009] As a preferred embodiment, in step one, the molecular structure of the first product is as follows: Where a and b represent the number of methylene groups in different diamines and diacids, respectively, a≥2, b≥2; k represents the degree of polymerization of polyamide, k=5-7.

[0010] As a preferred embodiment, in step two, 1 mol of maleic anhydride and 2000g of the first product are added to the reactor and stirred until homogeneous.

[0011] As a preferred embodiment, the catalyst is at least one of hydrogen peroxide or ammonium persulfate; the chain transfer agent is at least one of mercaptoethanol, mercaptoacetic acid, or mercaptopropionic acid.

[0012] As a preferred embodiment, the structural formula of the second product is: Where a and b represent the number of methylene groups in different diamines and diacids, respectively, a≥2, b≥2; k represents the degree of polymerization of polyamide, k=5-7.

[0013] As a preferred embodiment, in step three, the catalyst accounts for 0.1%-1% of the total mass of the second product and acrylic acid.

[0014] As a preferred embodiment, in step three, the chain transfer agent accounts for 0.1%-0.5% of the total mass of the second product and acrylic acid.

[0015] To achieve the above objectives and address the aforementioned problems in the prior art, the polyamide-type polycarboxylate superplasticizer prepared using the raw materials and methods of this invention, by replacing the polyether macromonomer with a polyamide macromonomer, not only overcomes the technical bottlenecks of traditional superplasticizers in terms of high-temperature adaptability and durability, but also promotes the transformation of the concrete admixture industry towards green and low-carbon development. The strong polarity of the amide bonds and the hydrogen bonding in the polyamide molecular chain enhance the adsorption stability of the superplasticizer molecules with cement particles, thereby improving the slump retention and compressive strength of concrete. Simultaneously, the polyamide macromonomer can be synthesized from bio-based raw materials (such as vegetable oil derivatives) or renewable resources, reducing dependence on fossil fuels.

[0016] Beneficial effects Firstly, the polyamide-type polycarboxylate superplasticizer of this invention uses a polyamide structure as the side chain to replace the traditional polyether side chain. The unique amide bond and rigid molecular structure of the polyamide main chain form a multipolar synergistic system with the carboxylic acid groups. This system can strengthen the adsorption of Ca2+ in cement particles by constructing an adsorption network through the amide bond. 2 The anchoring of active sites can also delay the re-aggregation of cement particles through steric hindrance, achieving a dual improvement in adsorption efficiency and dispersion stability. Simultaneously, the stable molecular chain structure within the polyamide segments allows it to maintain the integrity of its molecular conformation in complex high-salt, alkaline media, avoiding the performance abrupt changes caused by the degradation of traditional polyether side chains.

[0017] Secondly, the polyamide-type polycarboxylate superplasticizer of the present invention has amide groups in the polyamide molecular chain that can selectively chelate harmful metal ions (such as Cl⁻), reduce the ion migration rate in concrete pore fluid, inhibit steel corrosion and improve structural durability; in addition, due to the chemical stability of the polyamide chain segments, it exhibits strong heat resistance and chemical corrosion resistance in high temperature or extreme environments, and can effectively cope with the challenges of different climates and construction environments.

[0018] Thirdly, this invention optimizes the preparation process. The synthesis of polyamide macromonomers does not require highly toxic catalysts, the reaction conditions are mild, and there are few byproducts, which conforms to the principles of green chemistry. Experiments show that the water-reducing agent based on polyamide macromonomers can still maintain a slump retention rate of over 90% under high temperature (above 40℃) conditions, and its adaptability to low-quality aggregates is significantly better than that of traditional products. By using polyamide structures as side chains to replace traditional polyether side chains, the water-reducing agent has high water reduction rate, high slump retention, and reinforcing properties. Compared with traditional polyether macromonomers, polyamide macromonomers are more flexible in molecular structure design: long-chain alkyl groups can be introduced into their main chain to improve the thermal stability and alkali resistance of the water-reducing agent; the side chains can optimize the dispersion effect on cement particles by controlling the density and distribution of amide groups. Detailed Implementation

[0019] To make the technical means, creative features, objectives, and beneficial effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0020] In addition, to better illustrate the present invention, numerous specific details are given in the following detailed embodiments. Those skilled in the art should understand that the present invention can be implemented even without certain specific details. In other embodiments, methods, means, equipment and steps well known to those skilled in the art are not described in detail in order to highlight the main points of the present invention.

[0021] Example 1 This embodiment provides a preparation process for a polyamide-type polycarboxylate superplasticizer, including the following steps: (1) 343 g hexamethylenediamine (2.95 mol), 431 g adipic acid (2.95 mol), 334 g caprolactam (2.95 mol), 65.3 g hexamethylenediamine (molecular weight adjuster, 0.56 mol), and 60 mL of water were added to the reactor and stirred until homogeneous. Nitrogen gas was purged three times, and then nitrogen gas was introduced into the reactor, and the reactor pressure was controlled at 0.2 MPa. The reactor was then sealed. The temperature was then raised to 200 °C and held for 1 h. The reactor pressure was then released to atmospheric pressure within 0.5 h. The reaction system was then heated to 250 °C and held for 1 h. The reactor was then evacuated and kept at a vacuum of 0-800 Pa for 0.5 h to obtain the first product. The first product was washed, crushed, and dried (mass yield: 88%). (2) Add 400 g of the first product and 19.6 g of maleic anhydride to the reactor and stir to mix evenly; then start heating, and when the reaction system reaches 180 °C, keep it at the temperature for 0.5 h to obtain the second product; wash, crush and dry the second product (mass yield: 95%). (3) Add 354 g of the second product, 44.8 g of acrylic acid, 0.8 g of hydrogen peroxide (27.5 wt%), 0.4 g of mercaptoethanol and 600 g of water to the reactor and stir until homogeneous; react for 2 h to obtain the final product, polyamide-type polycarboxylate superplasticizer.

[0022] In step one, step (1) adopts staged pressure control: initially, the reactor pressure is controlled at 0.2 MPa, and the volatilization of diamine is suppressed by pressurization to ensure that the amine reacts fully; in the middle stage, the pressure is released to atmospheric pressure, which can remove the water generated by condensation and promote the reaction; in the later stage, vacuum is drawn to further dehydrate, which can promote the increase of molecular weight of the final product.

[0023] The stirring rate in steps (1)-(3) is 50-60 r / min (unless otherwise specified, the stirring rate in each step of the following examples and comparative examples is 50-60 r / min).

[0024] Example 2 This embodiment provides a preparation process for a polyamide-type polycarboxylate superplasticizer, including the following steps: (1) 251 g pentanediamine (2.45 mol), 564 g dodecanoic acid (2.45 mol), 277 g caprolactam (2.45 mol), 58.6 g pentanediamine (molecular weight adjuster, 0.57 mol), and 60 mL water were added to the reactor and stirred until homogeneous. Nitrogen gas was purged three times, and then nitrogen gas was introduced into the reactor, and the reactor pressure was controlled at 0.2 MPa. The reactor was then sealed. The temperature was then raised to 200 °C and held for 1 h. The reactor pressure was then released to atmospheric pressure within 0.5 h. The reaction system was then heated to 250 °C and held for 1 h. The reactor was then evacuated and kept at a vacuum of 0-800 Pa for 0.5 h to obtain the first product. The first product was washed, crushed, and dried (mass yield: 86%). (2) Add 400 g of the first product and 19.6 g of maleic anhydride to the reactor and stir to mix evenly; then start heating, and when the reactor temperature reaches 180 °C, keep it at the temperature for 0.5 h to obtain the second product; wash, crush and dry the second product (mass yield: 95%). (3) Add 354 g of the second product, 44.8 g of acrylic acid, 0.8 g of hydrogen peroxide (27.5 wt%), 0.4 g of mercaptoethanol and 600 g of water to the reactor and stir until homogeneous; react for 2 h to obtain the final product, polyamide-type polycarboxylate superplasticizer.

[0025] Example 3 This embodiment provides a preparation process for a polyamide-type polycarboxylate superplasticizer, including the following steps: (1) 362 g of decanediamine (2.1 mol), 484 g of dodecanoic acid (2.1 mol), 238 g of caprolactam (2.1 mol), 98.9 g of decanediamine (molecular weight adjuster, 0.57 mol), and 60 mL of water were added to the reactor and stirred until homogeneous. Nitrogen gas was purged three times, and then nitrogen gas was introduced into the reactor, and the pressure of the reaction system was controlled at 0.2 MPa. The reactor was then sealed. The temperature was then raised to 200 °C and held for 1 h. The pressure of the reactor was then released to atmospheric pressure within 0.5 h. The temperature of the reaction system was raised to 250 °C and held for 1 h. Then, a vacuum was drawn into the reactor and the vacuum degree was maintained at 0-800 Pa. The temperature was held for 0.5 h to obtain the first product. The first product was washed, crushed, and dried (mass yield: 92%). (2) Add 400 g of the first product and 19.6 g of maleic anhydride to the reactor and stir to mix evenly; then start heating, and when the reaction system reaches 180 °C, keep it at the temperature for 0.5 h to obtain the second product; wash, crush and dry the second product (mass yield: 94%). (3) Add 354 g of the second product, 44.8 g of acrylic acid, 0.8 g of hydrogen peroxide (27.5 wt%), 0.4 g of mercaptoethanol and 600 g of water to the reactor and stir until homogeneous; react for 2 h to obtain the final product, polyamide-type polycarboxylate superplasticizer.

[0026] Example 4 This embodiment provides a preparation process for a polyamide-type polycarboxylate superplasticizer, including the following steps: (1) 307 g pentanediamine (3.0 mol), 438 g adipic acid (3.0 mol), 340 g caprolactam (3.0 mol), 54.1 g pentanediamine (molecular weight adjuster, 0.53 mol), and 60 mL water were added to the reactor and stirred until homogeneous. Nitrogen gas was purged three times, and then nitrogen gas was introduced into the reactor, and the pressure of the reaction system was controlled at 0.2 MPa. The reactor was then sealed. The temperature was then raised to 200 °C and held for 1 h. The pressure of the reactor was then released to atmospheric pressure within 0.5 h. The temperature of the reaction system was raised to 250 °C and held for 1 h. Then, a vacuum was drawn into the reactor and the vacuum degree was maintained at 0-800 Pa. The temperature was held for 0.5 h to obtain the first product. The first product was washed, crushed, and dried (mass yield: 85%). (2) Add 400 g of the first product and 19.6 g of maleic anhydride to the reactor and stir to mix evenly; then start heating, and when the reaction system reaches 180 °C, keep it at the temperature for 0.5 h to obtain the second product; wash, crush and dry the second product (mass yield: 96%). (3) Add 354 g of the second product, 44.8 g of acrylic acid, 0.8 g of hydrogen peroxide (27.5 wt%), 0.4 g of mercaptoethanol and 600 g of water to the reactor and stir until homogeneous; react for 2 h to obtain the final product, polyamide-type polycarboxylate superplasticizer.

[0027] Example 5 This embodiment provides a preparation process for a polyamide-type polycarboxylate superplasticizer, including the following steps: (1) 491 g of 1,12-diaminododecane (2.45 mol), 358 g of adipic acid (2.45 mol), 277 g of caprolactam (2.45 mol), 115.1 g of 1,12-diaminododecane (molecular weight adjuster, 0.57 mol), and 60 mL of water were added to the reactor and stirred until homogeneous. Nitrogen gas was purged three times, and then nitrogen gas was introduced into the reactor, and the reactor pressure was controlled at 0.2 MPa. The reactor was then sealed. The temperature was then raised to 200 °C and held for 1 h. The reactor pressure was then released to atmospheric pressure within 0.5 h. The reaction system was then heated to 250 °C and held for 1 h. The reactor was then evacuated and kept at a vacuum of 0-800 Pa for 0.5 h to obtain the first product. The first product was washed, crushed, and dried (mass yield: 93%). (2) Add 400 g of the first product and 19.6 g of maleic anhydride to the reactor and stir to mix evenly; then start heating, and when the reactor temperature reaches 180 °C, keep it at the temperature for 0.5 h to obtain the second product; wash, crush and dry the second product (mass yield: 93%). (3) Add 354 g of the second product, 44.8 g of acrylic acid, 0.8 g of hydrogen peroxide (27.5 wt%), 0.4 g of mercaptoethanol and 600 g of water to the reactor and stir until homogeneous; react for 2 h to obtain the final product, polyamide-type polycarboxylate superplasticizer.

[0028] In this scheme, the molecular weight of the first product mentioned in step (1) is 1800-2400. When feeding, the molecular weight of the first product is calculated to be 2000, and the molar ratio of the first product to maleic anhydride is approximately 1:1. The molecular weight of the second product is calculated to be 2098. The molar ratio of the second product to acrylic acid is 1:3.5-4.

[0029] Comparative Example 1 The preparation of polyether-type polycarboxylate superplasticizer includes the following steps: 360 g of HPEG polyether macromonomer (Liaoning Kelong Fine Chemical Co., Ltd., model: F-1088), 300 g of water, and 4 g of hydrogen peroxide (27.5 wt%) were added to a reactor and stirred. After the macromonomer was completely dissolved, 38 g of acrylic acid and 1.8 g of mercaptopropionic acid were added to the reactor and reacted at room temperature (20 ℃) ​​for 3.5 h, followed by holding at this temperature for 1 h to obtain the water-reducing agent.

[0030] Comparative Example 2 The preparation conditions were the same as in Example 1, except that in step (1), after displacement in the reactor at the beginning of the reaction, the pressure was not applied to 0.2 MPa (that is, atmospheric pressure was used for heat preservation instead).

[0031] Specifically, step (1) involves adding 343 g hexamethylenediamine (2.95 mol), 431 g adipic acid (2.95 mol), 334 g caprolactam (2.95 mol), 65.3 g hexamethylenediamine (molecular weight adjuster, 0.56 mol), and 60 mL of water to a reactor and stirring until homogeneous. Nitrogen gas is then introduced to purge the mixture three times, and the reactor is sealed. The temperature is then raised to 200 ℃ and maintained for 1 h. The temperature is then raised to 250 ℃ and maintained for 1 h. A vacuum is then drawn into the reactor, maintaining a vacuum of 0-800 Pa, and the temperature is maintained for 0.5 h to obtain the first product. The first product is then washed, crushed, and dried (yield: 75%).

[0032] Comparative Example 3 The preparation conditions are the same as in Example 1, except for step (2): 400 g of the first product and 29.4 g of maleic anhydride (0.3 mol) were added to the reactor and stirred until homogeneous. Then the temperature was raised to 180 °C and held for 0.5 h to obtain the second product. The second product was then washed, crushed and dried.

[0033] Comparative Example 4 The preparation conditions are the same as in Example 1, except for step (1): 343 g hexamethylenediamine (2.95 mol), 431 g adipic acid (2.95 mol), 334 g caprolactam (2.95 mol), 65.3 g hexamethylenediamine (molecular weight adjuster, 0.56 mol), and 60 mL of water were added to a reactor and stirred until homogeneous. Nitrogen gas was purged three times, and then nitrogen gas was introduced into the reactor, maintaining the reactor pressure at 0.2 MPa. The reactor was then sealed. The temperature was then increased to 200 °C and held for 1 h. Within 0.5 h, the reactor pressure was reduced to atmospheric pressure. The reaction system was then heated to 250 °C and held for 1 h to obtain the first product. The first product was then washed, crushed, and dried.

[0034] Comparative Example 5 The preparation conditions are the same as in Example 1, except for step (2): 600 g of the first product and 19.6 g of maleic anhydride (0.2 mol) were added to the reactor and stirred until homogeneous. Then the temperature was raised to 180 °C and held for 0.5 h to obtain the second product. The second product was then washed, crushed and dried.

[0035] Neat pulp fluidity The fluidity of cement paste was tested according to GB / T 8076-2023, with a water-cement ratio of 0.29. The dosage of water-reducing agent prepared in each example and comparative example was 0.3% of the cement mass. The test results are shown in Table 1.

[0036] Table 1. Test results of cement paste Concrete effect Referring to the experimental methods of GB 8076-2008 and GB / T 50081-2019, samples prepared by the examples and comparative examples with a total mass of cement, fly ash and mineral powder of 0.3wt% were tested for concrete slump, spread and compressive strength. The results are shown in Table 3, and the concrete mix proportions are shown in Table 2.

[0037] Table 2 Concrete Mix Proportion The cement is Southern Cement, and the fineness modulus of the manufactured sand is 2.8.

[0038] Table 3 Concrete Test Results Concrete durability test According to the test method of GB / T 50082-2024, the concrete samples prepared by the examples and comparative examples with a total mass of cement, fly ash and mineral powder of 0.3wt% were tested for frost resistance and chloride ion penetration resistance. The results are shown in Table 4.

[0039] Table 4 Concrete mass loss rate (%) and chloride ion diffusion coefficient (10) -12 mm 2 / s) According to the test results in Tables 1-4, the polyamide-type water-reducing agents in Examples 1-5 exhibit superior performance in terms of water reduction rate, slump retention, reinforcement, and durability compared to traditional polyether water-reducing agents. Comparative Example 2 showed poor water reduction; the lack of pressure during the initial polymerization of the polyamide led to the loss of amine components, uneven molecular weight distribution, and a low degree of polymerization, resulting in shorter side chains and ultimately affecting dispersion and slump retention. While Comparative Example 3 showed a high initial water reduction rate, its slump retention was significantly insufficient. Excessive maleic anhydride was added during the synthesis stage with the first product and maleic anhydride. Although this enhanced the water reduction effect, it significantly weakened the slump retention, ultimately leading to a decrease in concrete strength and durability. Comparative Example 4 was slightly inferior to Example 1 in terms of water reduction rate, slump retention, reinforcement, and durability. This was because vacuuming was not performed during the polyamide synthesis stage, resulting in a lower and more unevenly distributed polyamide molecular weight. The side chains of the water-reducing agent molecular chain were also shorter, leading to a lower water reduction rate, poor dispersibility, and rapid loss of fluidity. Comparative Examples 2-4 verified the necessity of staged pressure control during the polyamide synthesis stage. Comparative Example 5 exhibited poor water reduction rate and slump retention. During the synthesis stage of the first product and maleic anhydride, the first product was over-added. Since the first product lacks double bond reactivity, it could not participate in polymerization, introducing a large amount of impurities into the water-reducing agent system. This not only directly resulted in low water reduction efficiency but also affected the slump retention, strength development, and durability of the concrete.

[0040] This invention involves the condensation polymerization of adipic acid and hexamethylenediamine to form a polyamide, introducing a polymerizable double bond structure to form an active polyamide macromonomer. Subsequently, under the action of an initiator, it is copolymerized with an acrylic monomer, and the target water-reducing agent is obtained by controlling the molecular weight. Compared to polyether water-reducing agents with ether bonds as side chains, this invention utilizes the amide bonds in the polyamide macromonomer and the Ca in the hydration products (Ca(OH)2 and CSH gel)... 2The strong chelating effect and synergistic effect of hydrogen bonds enhance the adsorption stability of water-reducing agent molecules on the surface of cement particles. This property not only significantly improves slump retention but also delays the re-aggregation of cement particles through steric hindrance, achieving a high water reduction rate (water reduction rate can be increased by 2%-7.6%). Furthermore, this water-reducing agent can improve concrete strength (3-day strength can be increased by 0.4 MPa-4.0 MPa, and 7-day strength can be increased by 1.6 MPa-6.7 MPa). In addition, due to the chemical stability of the polyamide segments, it exhibits strong heat resistance and chemical resistance under high temperature or extreme environments, effectively addressing the challenges of different climates and construction environments.

[0041] The above results demonstrate that polyamide-based water-reducing agents possess excellent water reduction rate, slump retention, reinforcement, and durability. The water reduction rate is significantly improved compared to ordinary water-reducing agents; the slump retention and compressive strength are also superior. Furthermore, freeze-thaw tests and chloride ion penetration tests further validated the promoting effect of polyamide-based water-reducing agents on concrete durability.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A polyamide-type polycarboxylate superplasticizer, characterized in that: Its structural formula is as follows: Where m:n = 3.5:1; a and b represent the number of methylene groups in different dicarboxylic acids and diamines, respectively, 4 ≤ a ≤ 10, 5 ≤ b ≤ 12; k represents the degree of polymerization of polyamide, k = 5-7.

2. The polyamide-type polycarboxylate superplasticizer according to claim 1, characterized in that: The polyamide-type polycarboxylate superplasticizer has a molecular weight of 20,000-30,000.

3. A method for preparing a polyamide-type polycarboxylate superplasticizer according to claim 1 or 2, characterized in that: Step 1: Add the diacid, diamine, caprolactam, molecular weight regulator, and water to the reactor and stir until homogeneous; introduce a protective gas to replace the gas in the reactor to control the pressure inside the reactor at 0.2-0.3 MPa, and then seal the reactor; heat the reaction system to a certain temperature, and maintain the reaction system under different pressure and temperature conditions through staged pressure control to obtain the first product; Step 2: Add the first product obtained in Step 1 and maleic anhydride into the reactor and stir to mix evenly; then start heating, and after the reactor is heated to a specific temperature, keep it at that temperature for 0.5-1 hour to obtain the second product; Step 3: Add the second product obtained in Step 2, acrylic acid, catalyst, chain transfer agent and water into the reactor and stir evenly; after reacting for a period of time, the final product, polyamide-type polycarboxylate superplasticizer, is obtained.

4. The preparation method of a polyamide-type polycarboxylate superplasticizer according to claim 3, characterized in that: In step one, the dicarboxylic acid is at least one of adipic acid, sebacic acid, or dodecanoic acid; the diamine is at least one of pentanediamine, hexanediamine, decanediamine, or 1,12-diaminododecane; and the molecular weight regulator is at least one of pentanediamine, hexanediamine, decanediamine, or 1,12-diaminododecane.

5. The method for preparing a polyamide-type polycarboxylate superplasticizer according to claim 3, characterized in that: In step one, the pressure inside the reactor is controlled at 0.2-0.3 MPa, the reactor is sealed, and then the temperature is raised to 190-200 ℃ and held for 1-2 h. Then, the pressure inside the reactor is released to atmospheric pressure within 0.5-1 h. The reactor temperature is raised to 240-260 ℃ and held for 1-2 h. Then, the reactor is evacuated and the vacuum degree is maintained at 0-800 Pa and held for 0.5-1 h to obtain the first product.

6. The method for preparing a polyamide-type polycarboxylate superplasticizer according to claim 3, characterized in that: In step one, the molar ratio of dicarboxylic acid, diamine, caprolactam, and molecular weight regulator is 1:1:1:0.15-0.

3.

7. The method for preparing a polyamide-type polycarboxylate superplasticizer according to claim 3, characterized in that: In step one, the molecular structure of the first product is as follows: Where a and b represent the number of methylene groups in different dicarboxylic acids and diamines, respectively, 4 ≤ a ≤ 10, 5 ≤ b ≤ 12; k represents the degree of polymerization of the polyamide, k = 5-7.

8. The method for preparing a polyamide-type polycarboxylate superplasticizer according to claim 3, characterized in that: In step two, 1 mol of maleic anhydride and 2000g of the first product are added to the reactor and stirred until homogeneous.

9. The method for preparing a polyamide-type polycarboxylate superplasticizer according to claim 3, characterized in that: The catalyst is at least one of hydrogen peroxide or ammonium persulfate; the chain transfer agent is at least one of mercaptoethanol, mercaptoacetic acid or mercaptopropionic acid.

10. The method for preparing a polyamide-type polycarboxylate superplasticizer according to claim 3, characterized in that: The structural formula of the second product is: Where a and b represent the number of methylene groups in different dicarboxylic acids and diamines, respectively, 4 ≤ a ≤ 10, 5 ≤ b ≤ 12; k represents the degree of polymerization of the polyamide, k = 5-7.

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