Sulfate-resistant polycarboxylate water reducer and preparation method thereof

Abstract

The application relates to the technical field of concrete admixtures, in particular to a sulfate-resistant polycarboxylate superplasticizer and a preparation method thereof. The sulfate-resistant polycarboxylate superplasticizer is prepared by copolymerization of ethylene glycol monovinyl polyethylene glycol ether, a first unsaturated carboxylic acid, an unsaturated phosphate ester and a functional monomer XS under the action of an initiator and a chain transfer agent. The sulfate-resistant polycarboxylate superplasticizer provided by the application has excellent sulfate resistance and good working performance. The sulfate-resistant polycarboxylate superplasticizer is synthesized by adopting a normal-temperature free radical solution copolymerization synthesis technology, the preparation process does not need heating, the preparation steps are simple, raw materials are easy to obtain, and the equipment is conventional, so that the actual industrial application requirements can be met.

Description

Technical Field

[0001] This application relates to the field of concrete admixtures technology, and in particular to a sulfate-resistant polycarboxylate superplasticizer and its preparation method. Background Technology

[0002] With the development of the times, infrastructure construction both domestically and internationally has gradually increased, and the scale of projects has continued to expand. Consequently, the demand for various raw materials and admixtures used in cement concrete is also constantly growing. Polycarboxylate superplasticizers, as high-performance concrete admixtures, are widely used in the construction industry due to their excellent water-reducing effect and good adaptability.

[0003] However, when polycarboxylate superplasticizers are applied to cement concrete, their adsorption performance is limited by various factors, particularly the competitive adsorption of sulfate ions present in the concrete, which significantly weakens the dispersion effect of polycarboxylate superplasticizers on cement. In cement paste or fresh concrete, sulfate ions, due to their strong negative charge, rapidly occupy the positively charged sites on the surface of cement minerals, leading to the desorption of adsorbed polycarboxylate superplasticizers. The sensitivity of polycarboxylate superplasticizers to sulfates is closely related to their molecular structure.

[0004] To address the compatibility issue of polycarboxylate superplasticizers with sulfates, a common approach is to introduce more carboxyl groups into the main chain of the polycarboxylate superplasticizer to enhance its adsorption capacity and thus improve sulfate resistance. However, while this method improves sulfate resistance, it accelerates the loss of slurry fluidity, significantly reducing the workability of concrete.

[0005] Therefore, developing a sulfate-resistant polycarboxylate superplasticizer with excellent sulfate resistance and good workability is of great significance to the development of the construction industry. Summary of the Invention

[0006] To address the problems of the prior art mentioned in the background section, this application provides a sulfate-resistant polycarboxylate superplasticizer, the technical solution of which is as follows: This sulfate-resistant polycarboxylate superplasticizer is produced by copolymerization of ethylene glycol monovinyl polyethylene glycol ether, a first unsaturated carboxylic acid, an unsaturated phosphate ester, and a functional monomer XS under the action of an initiator and a chain transfer agent. The structural formula of the functional unit XS is as follows: ; Wherein, R1 is H or CH3.

[0007] In some embodiments, the preparation process of the functional monomer XS is as follows: 3-(3-aminophenoxy)propyltrimethoxysilane and a second unsaturated carboxylic acid are added to a reactor to form a mixture; wherein the molar ratio of 3-(3-aminophenoxy)propyltrimethoxysilane to the second unsaturated carboxylic acid is (1.0-1.2):1; an organic solvent and a catalyst are added to the mixture under a protective atmosphere; under the action of the catalyst, the mixture is heated to 40-60°C for 3-6 hours; finally, the reaction solution is filtered and the organic solvent is removed sequentially to obtain the functional monomer XS.

[0008] It should be noted that the amount of organic solvent used is based on the ability of 3-(3-aminophenoxy)propyltrimethoxysilane and the second unsaturated carboxylic acid to be dispersed in the solvent and react. Since the organic solvent will be removed by rotary evaporation later, there are no restrictions on the amount of organic solvent used.

[0009] In some embodiments, the second unsaturated carboxylic acid is at least one of acrylic acid and methacrylic acid.

[0010] In some embodiments, the organic solvent is at least one selected from dichloromethane, trichloromethane, methyl acetate, and tetrahydrofuran.

[0011] In some embodiments, the catalyst is at least one selected from 4-dimethylaminopyridine, dicyclohexylcarbodiimide, pyridine, and imidazole.

[0012] In some embodiments, the protective atmosphere is an N2 atmosphere.

[0013] In some embodiments, the reaction solution is filtered to obtain a filtrate, and then the filtrate is subjected to rotary evaporation to remove the organic solvent, thereby obtaining the functional monomer XS.

[0014] In some embodiments, under the action of an initiator and a chain transfer agent, the ethylene glycol monovinyl polyethylene glycol ether, the first unsaturated carboxylic acid, the unsaturated phosphate ester, and the functional monomer XS are copolymerized to obtain a sulfate-resistant polycarboxylic acid superplasticizer; wherein, the copolymerization reaction temperature is 15-35°C; and the weight ratio of the ethylene glycol monovinyl polyethylene glycol ether, the first unsaturated carboxylic acid, the unsaturated phosphate ester, and the functional monomer XS is 200:(5-10):(4-8):(8-14).

[0015] In some embodiments, the initiator is composed of a reducing agent and an oxidizing agent; the copolymerization process is as follows: the ethylene glycol monovinyl polyethylene glycol ether is dissolved in a certain amount of water; the reaction system temperature is controlled at 15-35°C, and then an oxidizing agent is added and stirred evenly; then the reaction system temperature is maintained at 15-35°C, and solutions A and B are added for constant temperature reaction; after the addition is complete, the reaction system temperature is kept at 15-35°C for 0.5-1 h; finally, a neutralizing agent is added to adjust the pH to 5.5-6.5 to obtain the sulfate-resistant polycarboxylate superplasticizer; wherein, solution A is prepared by mixing the functional monomer XS, the first unsaturated carboxylic acid, the unsaturated phosphate ester with a portion of water evenly; solution B is prepared by mixing the chain transfer agent, the reducing agent with a portion of water evenly.

[0016] In some embodiments, solution A and solution B are added by dropwise addition over a period of 0.5 to 2.5 hours. The raw material formulation for the copolymerization reaction, by weight, is as follows: 200 parts ethylene glycol monovinyl polyethylene glycol ether, 8 to 14 parts functional monomer XS, 5 to 10 parts first unsaturated carboxylic acid, 4 to 8 parts unsaturated phosphate ester, 1.0 to 2.5 parts oxidant, 0.2 to 0.6 parts reducing agent, 0.5 to 1.6 parts chain transfer agent, and a total of 200 to 230 parts water.

[0017] In some embodiments, the molecular weight of the ethylene glycol monovinyl polyethylene glycol ether is 1500 to 3000.

[0018] In some embodiments, the first unsaturated carboxylic acid is at least one of acrylic acid, methacrylic acid, and maleic anhydride.

[0019] In some embodiments, the unsaturated phosphate ester is at least one of hydroxyethyl methacrylate phosphate, dimethyl vinyl phosphate, and dimethyl allyl phosphate.

[0020] In some embodiments, the oxidant is at least one of a 27.5% (w / w) hydrogen peroxide solution, ammonium persulfate, and sodium persulfate.

[0021] In some embodiments, the chain transfer agent is at least one selected from sodium hypophosphite, mercaptoacetic acid, and mercaptopropionic acid. In some embodiments, the reducing agent is at least one of ascorbic acid, Bruggolite FF6, and Bruggolite E01.

[0022] In some embodiments, the neutralizing agent is a 32% sodium hydroxide solution by mass.

[0023] This application also provides a method for preparing the sulfate-resistant polycarboxylate superplasticizer as described above, wherein the initiator includes an oxidant and a reducing agent; the preparation method includes the following preparation steps: The ethylene glycol monovinyl polyethylene glycol ether is dissolved in a certain amount of water, and the temperature of the reaction system is controlled at 15-35°C. Then, an oxidant is added and stirred evenly to form a mixed solution. Solution A is prepared by mixing the functional monomer XS, the first unsaturated carboxylic acid, the unsaturated phosphate ester, and a portion of water evenly. Solution B is prepared by mixing the chain transfer agent, the reducing agent and a portion of water evenly. Then, maintaining the reaction system temperature at 15–35°C, solution A and solution B are added dropwise to the mixed solution to carry out a constant-temperature reaction for 0.5–2.5 hours. After the addition is complete, the reaction system is kept at a temperature of 15–35°C for 0.5–1 h. Finally, a neutralizing agent is added to adjust the pH to 5.5–6.5 to obtain the sulfate-resistant polycarboxylate superplasticizer.

[0024] The sulfate-resistant polycarboxylate superplasticizer provided in this application has the following advantages compared with existing technologies: The sulfate-resistant polycarboxylate superplasticizer provided in this application combines excellent sulfate resistance with good performance. It is synthesized using room-temperature free radical solution copolymerization technology, requiring no heating during preparation. The preparation steps are simple, the raw materials are readily available, and the equipment is conventional, meeting the needs of practical industrial applications. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0026] This application also provides the following embodiments and comparative examples: Example 1: Preparation of functional monomer XS: (1) By mass, 132 parts of 3-(3-aminophenoxy)propyltrimethoxysilane and 31 parts of acrylic acid were added to the reactor; wherein the molar ratio of 3-(3-aminophenoxy)propyltrimethoxysilane to acrylic acid was 1.13:1; (2) Under N2 atmosphere, add 500 mL of tetrahydrofuran and react at 50 °C for 4 h under the catalysis of 4-dimethylaminopyridine (DMAP) to obtain the reaction solution; The amount of catalyst 4-dimethylaminopyridine used was 1.29 parts.

[0027] (3) Filter the reaction solution and evaporate the filtrate to remove the organic solvent, thereby obtaining the functional monomer XS.

[0028] Preparation of sulfate-resistant polycarboxylate superplasticizer: (1) Add 200 parts of ethylene glycol monovinyl polyethylene glycol ether and 160 parts of water to a three-necked flask, keep at 15-35°C, and stir to form a mixed solution; (2) Mix 12.0 parts of functional monomer XS, 7.2 parts of acrylic acid, 5.4 parts of allyl phosphate dimethyl ester and 30 parts of water evenly to prepare solution A; (3) Mix 0.7 parts mercaptopropionic acid, 0.35 parts ascorbic acid and 34 parts water evenly to prepare solution B; (4) Add 1.5 parts of 27.5% hydrogen peroxide to the flask and stir well; (5) Add the above solutions A and B dropwise to a three-necked flask over a period of 1.5 hours and react at a constant temperature of 15–35°C. (6) After the addition is completed, keep warm at 15-35℃ for 1 hour, then add 32% sodium hydroxide solution to the three-necked flask and adjust the pH of the mixed solution to 5.5-6.5 to obtain the sulfate-resistant polycarboxylate superplasticizer.

[0029] Example 2: Preparation of functional monomer XS: (1) By mass, 138 parts of 3-(3-aminophenoxy)propyltrimethoxysilane and 37 parts of methacrylic acid were added to the reactor; wherein the molar ratio of 3-(3-aminophenoxy)propyltrimethoxysilane to methacrylic acid was 1.18:1.

[0030] (2) Under N2 atmosphere, add 500 mL of tetrahydrofuran and react at 54 °C for 4 h under the catalysis of 4-dimethylaminopyridine (DMAP) to obtain the reaction solution; The amount of catalyst 4-dimethylaminopyridine used was 1.38 parts.

[0031] (3) Filter the reaction solution and evaporate the filtrate to remove the organic solvent, thereby obtaining the functional monomer XS.

[0032] Preparation of sulfate-resistant polycarboxylate superplasticizer: (1) Add 200 parts of ethylene glycol monovinyl polyethylene glycol ether and 156 parts of water to a three-necked flask, keep at 15-35°C, and stir to form a mixed solution; (2) Mix 13.2 parts of functional monomer XS, 6.8 parts of acrylic acid, 6.00 parts of hydroxyethyl methacrylate phosphate and 32 parts of water evenly to prepare solution A; (3) Mix 1.2 parts sodium hypophosphite, 0.28 parts Bruggolite FF6 and 33 parts water evenly to prepare solution B; (4) Add 1.3 parts of 27.5% hydrogen peroxide to the flask and stir well; (5) Add the above solutions A and B dropwise to a three-necked flask over a period of 1.5 hours and react at a constant temperature of 15–35°C. (6) After the addition is completed, keep warm at 15-35℃ for 1 hour, then add 32% sodium hydroxide solution to the three-necked flask and adjust the pH of the mixed solution to 5.5-6.5 to obtain the sulfate-resistant polycarboxylate superplasticizer.

[0033] Comparative Example 1: Point-S, a commercially available polycarboxylate superplasticizer.

[0034] Comparative Example 2: (Functional monomer XS is replaced with acrylic acid) The only difference from the example is that the functional monomer XS in Example 1 is replaced with acrylic acid in equal mass, and the rest is the same as Example 1.

[0035] Comparative Example 3: (Functional monomer XS is replaced with acrylamide) The only difference from the example is that the functional monomer XS in Example 1 is replaced with acrylamide by mass, and the rest is the same as Example 1.

[0036] Comparative Example 4: (Functional monomer XS is replaced with vinyltrimethoxysilane) The only difference from the example is that the functional monomer XS in Example 1 is replaced by vinyltrimethoxysilane in equal mass, and the rest is the same as Example 1.

[0037] Comparative Example 5: (Unsaturated phosphate esters are replaced with acrylic acid) The only difference from the example is that the unsaturated phosphate ester in Example 1 is replaced with acrylic acid by mass, and the rest is the same as Example 1.

[0038] Comparative Example 6: (The proportions of the first unsaturated carboxylic acid, unsaturated phosphate ester, and functional monomer XS are outside the acceptable range) The only difference from the example is that in the copolymerization process, there are 200 parts of ethylene glycol monovinyl polyethylene glycol ether, 14 parts of acrylic acid, 9 parts of allyl phosphate dimethyl ester, and 18 parts of functional monomer XS. The rest is the same as in Example 1.

[0039] Performance testing of examples and comparative examples: To further illustrate the performance of the sulfate-resistant polycarboxylate superplasticizer provided in this application, the above-mentioned examples and comparative examples were tested for cement paste fluidity under different sulfate concentrations according to GB8076-2008 "Concrete Admixtures" standard; the superplasticizer dosage was 0.12%, and the test results are shown in Table 1.

[0040] Table 1. Results of Cement Paste Flowability Test

[0041] In Table 1, the smaller the difference in the fluidity of the paste under different sulfate concentrations, the better the adaptability of the polycarboxylate superplasticizer to sulfate.

[0042] Experimental results show that: Under the same dosage conditions, the polycarboxylate superplasticizer of this application embodiment has better adaptability to sulfate, dispersion and dispersion retention performance than comparative examples 1 to 6.

[0043] In Comparative Example 1, the existing polycarboxylate superplasticizer Point-S exhibits poor adaptability to sulfate concentration, dispersion, and retention performance.

[0044] In Comparative Example 2, after replacing the functional monomer with acrylic acid, the adaptability to sulfate concentration decreased significantly, and the dispersion and retention performance was poor.

[0045] In Comparative Example 3, replacing the functional monomer with acrylamide significantly reduced the adaptability to sulfate concentration and the dispersibility.

[0046] In Comparative Example 4, replacing the functional monomer with vinyltrimethoxysilane resulted in a decrease in adaptability to sulfate concentration and a significant decrease in dispersion retention performance.

[0047] In Comparative Example 5, replacing unsaturated phosphate ester with acrylic acid resulted in decreased adaptability to sulfate concentration and poorer dispersion performance.

[0048] In Comparative Example 6, the amounts of the first unsaturated carboxylic acid, unsaturated phosphate ester, and functional monomer XS exceeded the recommended amounts in the technical solution. This imbalance in monomer ratios easily affected the polymerization process, leading to changes in the polymer's molecular weight and distribution. Simultaneously, the imbalance between the hydrophobicity and hydrophilicity of the polymer segments affected the polymer's stability and dispersibility, hindering the free distribution of water-reducing agent molecules on cement particles. Furthermore, the synergistic effect between the phosphate ester monomer and the functional monomer XS was affected by the imbalance in monomer ratios. The phosphate ester monomer's effect of promoting dispersion by providing negative charges was poor, while the functional monomer XS's improvement effect on the adhesion and plasticity of cement particles was not significant, thus affecting the fluidity and stability of the cement paste. Therefore, the polycarboxylic acid water-reducing agent's adaptability to sulfate concentrations decreased, and its dispersion and dispersion retention performance significantly declined.

[0049] In summary, the sulfate-resistant polycarboxylate superplasticizer provided in this application has at least the following design concept and beneficial effects: 1. The sulfate-resistant polycarboxylate superplasticizer provided in this application possesses excellent sulfate resistance. The siloxane and hydration product C in the superplasticizer molecule... S The silanol groups on the H-gel bind to form stable silicon-oxygen bonds (Si-O-Si). These silicon-oxygen bonds have a good barrier effect on sulfate ions, improving their ability to compete with sulfate adsorption on the surface of cement particles. Meanwhile, phosphate esters can form stable complexes with metal ions, preventing sulfate ions from reacting with water-reducing agents or cement, thereby improving the sulfate resistance of water-reducing agents.

[0050] 2. The sulfate-resistant polycarboxylate superplasticizer provided in this application has excellent workability. The alkoxy hydrolysis of silane in the superplasticizer molecule reduces the interaction forces between cement particles, lowers the viscosity and yield stress of the cement paste, and ensures that the amide group can slowly hydrolyze in the concrete environment. Combined with the steric hindrance effect, this further prevents the aggregation and sedimentation of cement particles and releases the trapped free water, ensuring the required fluidity of the concrete over time.

[0051] 3. The sulfate-resistant polycarboxylate superplasticizer provided in this application is produced by copolymerizing functional monomer XS and unsaturated phosphate with ethylene glycol monovinyl polyethylene glycol ether and a first unsaturated carboxylic acid. The comonomers work synergistically with each other, rather than simply adding up their functions. The structural selection and proportion design of each monomer will affect the structure of the final polycarboxylate superplasticizer, thereby affecting its performance and effect.

[0052] The unsaturated carboxylic acid, functional monomer XS, and unsaturated phosphate ester exhibit a synergistic effect. If the monomer ratio is outside the range specified in this application, the imbalance in the monomer ratio can easily affect the polymerization process, leading to changes in the polymer's molecular weight and distribution. Simultaneously, an imbalance in the hydrophobicity and hydrophilicity of polymer segments affects the polymer's stability and dispersibility, hindering the free distribution of water-reducing agent molecules on cement particles. Furthermore, the synergistic effect between the phosphate ester monomer and the functional monomer XS is affected by the imbalance in the monomer ratio. The phosphate ester monomer's effect of promoting dispersion by providing negative charges is poor, while the functional monomer XS's improvement effect on the adhesion and plasticity of cement particles is not significant, thus affecting the fluidity and stability of the cement paste. Therefore, the adaptability of polycarboxylic acid water-reducing agents to sulfate concentration decreases, and their dispersion and dispersion retention performance significantly declines.

[0053] 4. The EPEG-type polycarboxylate superplasticizer provided in this application introduces functional monomers XS, thereby introducing silane alkoxy groups, benzene rings, amide groups, etc., into the superplasticizer to achieve the corresponding effects. However, simply introducing the corresponding silane alkoxy groups, benzene rings, and amide groups into the superplasticizer molecule is not sufficient to achieve the effects described in this application. The specific method of introducing silane alkoxy groups, benzene rings, amide groups (whether different groups are introduced through copolymerization of different monomers, or multiple groups are integrated into a single functional monomer for polymerization, the two methods differ), and the specific structure of the functional monomer used to integrate silane alkoxy groups, benzene rings, and amide groups for polymerization, will all lead to different side chain structures in the resulting polycarboxylate superplasticizer, resulting in different molecular structures and ultimately affecting its performance and effects.

[0054] This application uses a functional monomer XS with a specific structure integrating alkoxy and amide groups. This functional monomer XS with a specific structure is then introduced into the side chain of the polycarboxylate superplasticizer through a copolymerization reaction to obtain the desired polycarboxylate superplasticizer structure and achieve the desired effect of this application.

[0055] If unsaturated amide monomers containing amide groups, silane monomers containing alkoxy groups, and monomers containing benzene rings are used as comonomers to copolymerize with monomers such as ethylene glycol monovinyl polyethylene glycol ether, unsaturated carboxylic acid monomers, and unsaturated phosphate esters, the monomers with different groups will compete for the reaction due to differences in reactivity and solubility. As a result, the side chains of polycarboxylic acid will have an uneven distribution of groups, which is different from the evenly distributed structure of the side chains in this application. Consequently, the structure of the resulting polycarboxylic acid water-reducing agent will be different, and this approach will not achieve the effect of this application.

[0056] For example, the scheme disclosed in patent publication number CN104592457A involves preparing a terpolymer from 2-acrylamide-2-methylpropanesulfonic acid, vinyl aromatic monomer A, and unsaturated amide monomer B under the action of sodium dodecyl sulfate and an initiator. Then, the terpolymer, polyoxyethylene polyoxypropylene ether comonomer C, unsaturated carboxylic acid monomer D, and silane coupling agent monomer E are subjected to an aqueous free radical polymerization reaction at 40℃~45℃ under the action of an initiator and chain transfer agent in a redox system to obtain a sulfate-compatible polycarboxylic acid superplasticizer. This scheme does not provide corresponding proof of its effectiveness in high sulfate concentration environments (sulfate concentration greater than 70 mmol / L, sulfate content about 2% of cement mass). The test results show that it has better cement paste fluidity and time loss only in low sulfate concentration environments (sulfate content of 0~1.0% of cement mass).

[0057] 5. The sulfate-resistant polycarboxylate superplasticizer provided in this application has excellent compatibility with polycarboxylate molecules, supports independent use or compound application with conventional superplasticizers, and has significant market potential.

[0058] 5. The sulfate-resistant polycarboxylate superplasticizer provided in this application can be prepared at room temperature. The process is simple and mild, requiring no complicated temperature control steps, and has low energy consumption, making it highly efficient in production and practical applications.

[0059] In summary, this application introduces unsaturated amide-phenylsilane functional monomers and can synergize with some common unsaturated carboxylic acids and unsaturated phosphate esters. Using room temperature free radical solution copolymerization technology, without heating, a sulfate-resistant polycarboxylic acid superplasticizer with excellent performance and can meet the needs of actual industrial applications is prepared.

[0060] It should be noted that: In this article, “~” is used to represent the range of values, and the range of values ​​represented by this expression includes two endpoint values.

[0061] Apart from the specific choices embodied in the above embodiments, any formulation range described above may be used in the specific implementation of this application, including but not limited to the above embodiment schemes.

[0062] The specific parameters or some commonly used reagents or raw materials in the above embodiments are specific embodiments or preferred embodiments under the concept of this application, and are not intended to limit them; those skilled in the art can make adaptive adjustments within the concept and protection scope of this application.

[0063] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A sulfate-resistant polycarboxylate superplasticizer, characterized in that: It is produced by copolymerization of ethylene glycol monovinyl polyethylene glycol ether, first unsaturated carboxylic acid, unsaturated phosphate ester and functional monomer XS under the action of initiator and chain transfer agent; The structural formula of the functional unit XS is as follows: ； Wherein, R1 is H or CH3; The weight ratio of the ethylene glycol monovinyl polyethylene glycol ether, the first unsaturated carboxylic acid, the unsaturated phosphate ester, and the functional monomer XS is 200:(5-10):(4-8):(8-14).

2. The sulfate-resistant polycarboxylate superplasticizer according to claim 1, characterized in that: The preparation process of the functional monomer XS is as follows: 3-(3-aminophenoxy)propyltrimethoxysilane and a second unsaturated carboxylic acid are added to a reactor to form a mixture; wherein the molar ratio of 3-(3-aminophenoxy)propyltrimethoxysilane to the second unsaturated carboxylic acid is (1.0–1.2):1; An organic solvent and a catalyst are added to the mixture under a protective atmosphere; the mixture is heated to 40–60°C and reacted for 3–6 hours under the action of the catalyst; finally, the reaction solution is filtered to remove the organic solvent, thereby obtaining the functional monomer XS.

3. The sulfate-resistant polycarboxylate superplasticizer according to claim 2, characterized in that: The second unsaturated carboxylic acid is at least one of acrylic acid and methacrylic acid; The organic solvent is at least one of dichloromethane, trichloromethane, methyl acetate, and tetrahydrofuran; The catalyst is at least one of 4-dimethylaminopyridine, dicyclohexylcarbodiimide, pyridine, and imidazole.

4. The sulfate-resistant polycarboxylate superplasticizer according to claim 2, characterized in that: The protective atmosphere is an N2 atmosphere; The reaction solution was filtered to obtain a filtrate, which was then subjected to rotary evaporation to remove the organic solvent, thereby obtaining the functional monomer XS.

5. The sulfate-resistant polycarboxylate superplasticizer according to claim 1, characterized in that: Under the action of an initiator and a chain transfer agent, the ethylene glycol monovinyl polyethylene glycol ether, the first unsaturated carboxylic acid, the unsaturated phosphate ester, and the functional monomer XS are copolymerized to obtain a sulfate-resistant polycarboxylic acid superplasticizer. The copolymerization reaction temperature is 15–35°C.

6. The sulfate-resistant polycarboxylate superplasticizer according to claim 1, characterized in that: The initiator consists of a reducing agent and an oxidizing agent; the copolymerization process is as follows: The ethylene glycol monovinyl polyethylene glycol ether was dissolved in a certain amount of water; the reaction system temperature was controlled at 15-35°C, and then an oxidant was added and stirred evenly; then, the reaction system temperature was maintained at 15-35°C, and solutions A and B were added for constant temperature reaction; after the addition was completed, the reaction system temperature was kept at 15-35°C for 0.5-1 hour; finally, a neutralizing agent was added to adjust the pH to 5.5-6.5 to obtain the sulfate-resistant polycarboxylate superplasticizer. Solution A is prepared by uniformly mixing the functional monomer XS, the first unsaturated carboxylic acid, the unsaturated phosphate ester, and a portion of water; solution B is prepared by uniformly mixing the chain transfer agent, the reducing agent, and a portion of water.

7. The sulfate-resistant polycarboxylate superplasticizer according to claim 6, characterized in that: Solution A and solution B are added by dripping over a period of 0.5 to 2.5 hours. The raw material formulation for the copolymerization reaction, by weight, is as follows: 200 parts of ethylene glycol monovinyl polyethylene glycol ether, 8-14 parts of functional monomer XS, 5-10 parts of the first unsaturated carboxylic acid, 4-8 parts of unsaturated phosphate ester, 1.0-2.5 parts of oxidant, 0.2-0.6 parts of reducing agent, 0.5-1.6 parts of chain transfer agent, and a total of 200-230 parts of water.

8. The sulfate-resistant polycarboxylate superplasticizer according to claim 1, characterized in that: The molecular weight of the ethylene glycol monovinyl polyethylene glycol ether is 1500-3000; The first unsaturated carboxylic acid is at least one of acrylic acid, methacrylic acid, and maleic anhydride; The unsaturated phosphate ester is at least one of hydroxyethyl methacrylate phosphate, dimethyl vinyl phosphate, and dimethyl allyl phosphate.

9. The sulfate-resistant polycarboxylate superplasticizer according to claim 6, characterized in that: The oxidant is at least one of the following: a 27.5% (w / w) hydrogen peroxide solution, ammonium persulfate, and sodium persulfate. The chain transfer agent is at least one of sodium hypophosphite, mercaptoacetic acid, and mercaptopropionic acid; The reducing agent is at least one of ascorbic acid, Bruggolite FF6, and Bruggolite E01; The neutralizing agent is a 32% sodium hydroxide solution.

10. A method for preparing a sulfate-resistant polycarboxylate superplasticizer as described in any one of claims 1-9, characterized in that, The initiator includes an oxidizing agent and a reducing agent; the preparation method includes the following preparation steps: The ethylene glycol monovinyl polyethylene glycol ether is dissolved in a certain amount of water, and the temperature of the reaction system is controlled at 15-35°C. Then, an oxidant is added and stirred evenly to form a mixed solution. Solution A is prepared by mixing the functional monomer XS, the first unsaturated carboxylic acid, the unsaturated phosphate ester, and a portion of water evenly. Solution B is prepared by mixing the chain transfer agent, the reducing agent and a portion of water evenly. Then, maintaining the reaction system temperature at 15–35°C, solution A and solution B are added dropwise to the mixed solution to carry out a constant-temperature reaction for 0.5–2.5 hours. After the addition is complete, the reaction system is kept at a temperature of 15–35°C for 0.5–1 h. Finally, a neutralizing agent is added to adjust the pH to 5.5–6.5 to obtain the sulfate-resistant polycarboxylate superplasticizer.

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