A retarder for improving the setting time of magnesium phosphate cement and its preparation method and application

Abstract

The present invention discloses a retarder for improving the setting time of magnesium phosphate cement, and its preparation method and application. The method comprises: (1) adding a reducing agent to a glucose solution in a protective atmosphere for hydroxylation treatment, and obtaining a hydroxylated glucose solution after the reaction is completed. (2) adjusting the pH of the hydroxylated glucose solution to alkaline, and then adding a mixed solution of NHS and EDC, and obtaining an activated glucose solution after the reaction is completed. (3) adding butenedioic acid and a catalyst to the activated glucose solution for esterification reaction, and then performing purification treatment after the reaction is completed to obtain a butenedioic acid esterified glucose derivative solution. (4) adjusting the pH of the butenedioic acid esterified glucose derivative solution to acidic, and then adding an acrylic acid monomer and an initiator, and performing a polymerization reaction under heating conditions, and then obtaining the retarder after the reaction is completed. The retarder of the present invention not only prolongs the setting time of magnesium phosphate cement, but also avoids the problem of strength loss.

Description

Technical Field

[0001] The present invention relates to the technical field of magnesium phosphate cement retarder preparation, and in particular to a retarder for improving the setting time of magnesium phosphate cement, and a preparation method and application thereof. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance understanding of the overall background of the invention and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to those skilled in the art.

[0003] Magnesium phosphate cement (MPC), a new type of fast-hardening cementitious material, shows great potential in engineering fields such as construction, roads, and bridges due to its excellent early mechanical properties and fire resistance. The hydration mechanism of magnesium phosphate cement (MPC) differs significantly from that of commonly used Portland cement. The hydration process of MPC first involves the dissolution of phosphates. This step occurs rapidly under the action of water, generating phosphate ions and releasing hydrogen ions, causing the pH value of the surrounding environment to drop and forming an acidic environment. Subsequently, the phosphate ions in the acidic environment react with magnesium oxide (one of the main components of magnesium phosphate cement) to form magnesium phosphate hydration products. As the reaction proceeds, the pH of the environment gradually increases.

[0004] When the pH exceeds 9, the hydration product in MPC transforms into struvite (Mg(NH4)PO4•6H2O). Its formation marks the beginning of the cement's loss of fluidity and the entry into the setting and hardening phase. The cement's setting time during this process is directly affected by the hydration rate. MPC's rapid setting and hardening properties limit its construction time, hindering both efficiency and widespread application. While existing retarders (such as borax and boric acid) can extend the setting time of magnesium phosphate cement, they can easily reduce the cement's later strength and durability, and may also pose environmental concerns. Summary of the Invention

[0005] To address the above-mentioned problems, the present invention provides a retarder for improving the setting time of magnesium phosphate cement, as well as its preparation method and application. The retarder not only prolongs the setting time of magnesium phosphate cement but also avoids the problem of strength loss. Specifically, the technical solution of the present invention is as follows.

[0006] First, the present invention provides a retarder for improving the setting time of magnesium phosphate cement, the structural formula of which is shown in formula (1):

[0007] Formula (1).

[0008] Furthermore, in the above formula (1), m=8-10n, so that the hydrolysis is carried out more quickly in an alkaline environment and the retarding effect is lost. The n is an integer not equal to 0.

[0009] Secondly, the present invention provides a method for preparing a retarder for improving the setting time of magnesium phosphate cement, comprising the following steps:

[0010] (1) In a protective atmosphere, a reducing agent is added to a glucose solution for hydroxylation. After the reaction is completed, a hydroxylated glucose solution is obtained.

[0011] (2) The pH of the hydroxylated glucose solution is adjusted to alkaline, and then a mixed solution of N-hydroxysuccinimide (NHS) and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) is added to perform an activation reaction, and an activated glucose solution is obtained after completion.

[0012] (3) Adding butenedioic acid and a catalyst into the activated glucose solution to carry out esterification reaction, and then performing purification treatment to obtain a butenedioic acid esterified glucose derivative solution.

[0013] (4) The pH of the butylated glucose derivative solution is adjusted to acidic, and then an acrylic acid monomer and an initiator are added, and a polymerization reaction is carried out under heating conditions to obtain the retarder.

[0014] Furthermore, in step (1), the molar ratio of glucose to reducing agent is 8 to 10:1. Optionally, the protective atmosphere includes any one of nitrogen, argon, etc., whose main function is to prevent oxygen from participating in the reaction and destroying the reducing atmosphere, oxidizing aldehyde groups and alcohol groups. The reducing agent includes at least one of sodium borohydride, lithium aluminum hydride, diisobutylaluminum hydride, etc.

[0015] Furthermore, in step (1), the reaction time is 0.5 to 3 hours. Preferably, stirring is performed continuously during the reaction. In this step, the aldehyde group on the glucose undergoes a hydroxylation reaction under the action of NaBH4 to form hydroxylated glucose, which facilitates the subsequent esterification reaction with acrylic acid. The reaction process is shown in formula (2):

[0016] Formula (2).

[0017] Furthermore, in step (2), the pH is adjusted to 8-9. Optionally, the pH is adjusted by adding an alkali solution (such as sodium hydroxide, potassium hydroxide, saturated lime water, etc.).

[0018] Furthermore, in step (2), the molar ratio of the hydroxylated glucose in the hydroxylated glucose solution to the N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide is 10:1~2:1~2.

[0019] Furthermore, in step (2), the activation reaction time is 0.5 to 2 hours. As shown in formula (3), during this process, the hydroxylated glucose, under alkaline conditions and the action of NHS and EDC, makes the alcoholic hydroxyl group more active, and can preferentially undergo polymerization reaction with acrylic acid:

[0020] Formula (3).

[0021] Furthermore, in step (3), the molar ratio of the activated glucose in the activated glucose solution to the butenedioic acid and the catalyst is 1:1-1.5:0.01-0.05. Optionally, the catalyst comprises at least one of toluenesulfonic acid (TsOH), concentrated sulfuric acid, concentrated hydrochloric acid, thionyl chloride, and the like.

[0022] Furthermore, in step (3), the esterification reaction time is 4 to 8 hours. As shown in formula (4), during this process, the activated glucose is endowed with a carbon-carbon double bond for polymerization reaction, so as to undergo polymerization reaction with the acrylic acid:

[0023] Formula (4).

[0024] Furthermore, in step (3), the obtained reaction solution is purified by dialysis to remove the unreacted butenedioic acid and catalyst.

[0025] Furthermore, in step (4), the pH is adjusted to 3.5-4.5. Optionally, the pH is adjusted by adding any one of hydrochloric acid, sulfuric acid, acetic acid, etc.

[0026] Furthermore, in step (4), the mass ratio of the butylated glucose derivative in the butylated glucose derivative solution to the acrylic acid monomer and the initiator is 1:8-12:0.01-0.03. Optionally, the initiator comprises at least one of ammonium persulfate, sodium persulfate, potassium persulfate, and benzoyl peroxide.

[0027] Furthermore, in step (4), the heating temperature is 65-85°C, and the reaction time is 1-4 hours. As shown in formula (5), in this process, the butylated glucose derivative is given a longer carbon chain to form a retarder, which not only increases the adsorption effect, but also the abundant carboxyl groups on the carbon chain are easily hydrolyzed under alkaline conditions, destroying the structure of the retarder, playing the role of acidic stable adsorption and retarding, and alkaline hydrolysis failure:

[0028] Formula (5).

[0029] Optionally, in step (4), in order to adjust the molecular weight and molecular weight distribution of the retarder generated by the polymerization reaction (i.e., to control the values ​​of n and m in the retarder shown in the above formulas (1) and (5)), a chain transfer agent, sodium thiosulfate (STS), may be added to the reaction system to achieve the above purpose.

[0030] Finally, the present invention discloses the use of the retarder for improving the setting time of magnesium phosphate cement in magnesium phosphate cement-based materials. Optionally, the retarder is added in an amount of 5-10% by mass of the magnesium phosphate cement (magnesium oxide and ammonium dihydrogen phosphate) in the magnesium phosphate cement-based material.

[0031] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0032] The retarder of the present invention can stably exist in the early stage of magnesium phosphate cement hydration, reduce the rate of the hydration reaction, and prolong the setting time of magnesium phosphate cement. As the hydration reaction proceeds, when the pH of the system environment increases to a certain level, the retarder of the present invention gradually loses its effect, allowing hydration to continue, thereby avoiding the problem of traditional retarders easily causing strength loss and having broad application prospects. That is, the present invention utilizes the change in the pH of the cement environment caused by the hydration reaction of magnesium phosphate cement and the unique pH sensitivity of the retarder of the present invention, not only effectively prolonging the setting time of magnesium phosphate cement, but also effectively avoiding the problem of traditional retarders easily causing strength loss. The reason for this is:

[0033] As mentioned above, in the early stage of the hydration reaction of magnesium phosphate cement, the phosphate first dissolves under the action of water to release hydrogen ions, which will cause the pH value of the environment to drop and form an acidic environment. The retarder prepared by the present invention can stably exist in the form of a macromolecular in an acidic environment and cover the surface of magnesium oxide particles through physical adsorption, slowing down the contact reaction between magnesium oxide and water, thereby slowing down the dissolution of magnesium oxide, and then slowing down the hydration reaction between phosphate and magnesium ions to form a gelled product, thereby delaying the setting time. As the hydration reaction proceeds, when the pH value of the environment rises above 9, the retarder of the present invention hydrolyzes under the action of an alkaline environment and gradually loses its effect on the covered magnesium oxide. At this time, magnesium oxide can continue to undergo hydration reaction, causing magnesium phosphate cement to quickly coagulate and form hydration products, avoiding the problem that traditional retarders prevent the hydration reaction for a long time, resulting in insufficient strength development of magnesium phosphate concrete and shrinkage, ensuring the long-term durability and mechanical properties of the material, and having better environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0035] Figure 1 This is a sample diagram of the retarder for improving the setting time of magnesium phosphate cement prepared in Example 1. DETAILED DESCRIPTION

[0036] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples, for which specific conditions are not specified, are generally performed under conventional conditions or as recommended by the manufacturer.

[0037] Unless otherwise defined, all professional and scientific terms used in the present invention have the same meanings as those familiar to those skilled in the art. The reagents and raw materials used in the present invention can be purchased through conventional channels. Unless otherwise specified, the reagents and raw materials used in the present invention are used in accordance with conventional methods in the art or in accordance with the product instructions.

[0038] In addition, any methods and materials similar or equivalent to those described herein can be applied to the method of the present invention. The technical solution of the present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0039] Example 1

[0040] A method for preparing a retarder for improving the setting time of magnesium phosphate cement comprises the following steps:

[0041] (1) In a nitrogen atmosphere, NaBH4 is added to a 0.5 M glucose solution, wherein the molar ratio of glucose to NaBH4 is 10:1. The glucose is then stirred for 2 hours to perform hydroxylation, and a hydroxylated glucose solution is obtained for later use.

[0042] (2) Sodium hydroxide solution was added dropwise to the hydroxylated glucose solution to adjust the pH of the system to 8, and then a mixed solution of N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide was added dropwise, wherein the molar ratio of hydroxylated glucose to NHS and EDC in the hydroxylated glucose solution was 10:1:1. The mixture was stirred for 1 hour to perform an activation reaction, and an activated glucose solution was obtained after completion, which was set aside.

[0043] (3) Adding butenedioic acid and a catalyst (toluenesulfonic acid) to the activated glucose solution, the molar ratio of the activated glucose to butenedioic acid and the catalyst in the activated glucose solution is 1:1.5:0.02. Then, the reaction is stirred for 4 hours to carry out the esterification reaction. After completion, the obtained reaction solution is dialyzed and purified: a phosphate buffer with a molecular weight cutoff (MWCO) of 3500 and a pH value of 7.4 is selected as the dialysate to maintain the stability of the glucose derivative. The dialysis process lasts for 48 hours, and the dialysate is replaced every 8 hours to promote the removal of small molecular impurities. During the dialysis process, a magnetic stirrer is used to continuously stir at a speed of 100 rpm to ensure effective exchange of the dialysate with the solution in the bag. After the dialysis is completed, the purified butenedioic acid-esterified glucose derivative solution is collected from the dialysis bag and stored at 4°C for future use.

[0044] (4) Add hydrochloric acid to adjust the pH of the butylated glucose derivative solution to 4.5, then add acrylic acid monomer and initiator (ammonium persulfate) and heat to 70°C for polymerization reaction. The mass ratio of the butylated glucose derivative to the acrylic acid monomer and initiator in the butylated glucose derivative solution is 1:10:0.01. After reacting for 2 hours, cool to room temperature and add ascorbic acid to terminate the reaction, thereby obtaining a retarder, such as Figure 1 shown.

[0045] Performance test: Take magnesium phosphate cement (300 parts of magnesium oxide, 200 parts of ammonium dihydrogen phosphate), 200 parts of fly ash, 35 parts of the retarder prepared in this embodiment, and 140 parts of water. Mix the above raw materials for 3 minutes and pour them into a 40×40×40 mm steel mold, and then test the initial setting time. In addition, according to the "Test Method for Strength of Cement Mortar (ISO Method)" GB / T17671-2021, the compressive strength of the test pieces prepared by the above method at the age of 1d and 28d was tested. In addition, borax retarder was used instead of the retarder of this embodiment as a comparison, and the initial setting time, 1d, and 3d compressive strength of the magnesium phosphate cement obtained were tested. The results are shown in the following table:

[0046] .

[0047] Example 2

[0048] A method for preparing a retarder for improving the setting time of magnesium phosphate cement comprises the following steps:

[0049] (1) In a nitrogen atmosphere, NaBH4 is added to a 0.5 M glucose solution, wherein the molar ratio of glucose to lithium aluminum hydride (LiAlH4) is 8:1. The glucose is then stirred for 0.5 hours to perform a hydroxylation treatment on the glucose. Upon completion, a hydroxylated glucose solution is obtained, which is set aside.

[0050] (2) Sodium hydroxide solution was added dropwise to the hydroxylated glucose solution to adjust the pH of the system to 8, and then a mixed solution of N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide was added dropwise. The molar ratio of hydroxylated glucose to NHS and EDC in the hydroxylated glucose solution was 10:1.5:2. The mixture was stirred for 0.5 hours to perform an activation reaction. After completion, an activated glucose solution was obtained and set aside.

[0051] (3) Adding butenedioic acid and a catalyst (concentrated hydrochloric acid) to the activated glucose solution, the molar ratio of activated glucose to butenedioic acid to catalyst being 1:1:0.01. The reaction was then stirred for 5 hours to carry out an esterification reaction. After completion, the resulting reaction solution was dialyzed and purified (same as in Example 1). A butenedioic acid-esterified glucose derivative solution was obtained for later use.

[0052] (4) Sulfuric acid was added to adjust the pH of the butylated glucose derivative solution to 4.0, and then an acrylic acid monomer and an initiator (sodium persulfate) were added. The mixture was heated to 65° C. to carry out a polymerization reaction. The mass ratio of the butylated glucose derivative to the acrylic acid monomer and the initiator in the butylated glucose derivative solution was 1:8:0.02. After reacting for 4 hours, the mixture was cooled to room temperature and ascorbic acid was added to terminate the reaction, thereby obtaining a retarder.

[0053] The same method as in Example 1 was used to test the initial setting time, 1d, and 28d compressive strength of the magnesium phosphate cement containing the retarder prepared in this example. The results are shown in the following table:

[0054] .

[0055] Example 3

[0056] A method for preparing a retarder for improving the setting time of magnesium phosphate cement comprises the following steps:

[0057] (1) In a nitrogen atmosphere, NaBH4 was added to a 0.5 M glucose solution, wherein the molar ratio of glucose to diisobutylaluminum hydride (C8HAl) was 9:1. The glucose was then stirred for 3 hours to perform a hydroxylation treatment. After completion, a hydroxylated glucose solution was obtained, which was set aside.

[0058] (2) Saturated lime water was added dropwise to the hydroxylated glucose solution to adjust the pH of the system to 9, and then a mixed solution of N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide was added dropwise. The molar ratio of hydroxylated glucose to NHS and EDC in the hydroxylated glucose solution was 10:2:1.5. The mixture was stirred for 2 hours to perform an activation reaction. After completion, an activated glucose solution was obtained and set aside.

[0059] (3) Adding butenedioic acid and a catalyst (concentrated sulfuric acid) to the activated glucose solution, wherein the molar ratio of activated glucose to butenedioic acid to catalyst in the activated glucose solution is 1:1.3:0.05. The reaction is then stirred for 8 hours to carry out an esterification reaction. After completion, the resulting reaction solution is dialyzed and purified (same as in Example 1). A butenedioic acid-esterified glucose derivative solution is obtained and set aside.

[0060] (4) Acetic acid was added to adjust the pH of the butylated glucose derivative solution to 3.5, and then acrylic acid monomer and initiator (benzoyl peroxide) were added. The mixture was heated to 85° C. to carry out polymerization reaction. The mass ratio of the butylated glucose derivative to the acrylic acid monomer and initiator in the butylated glucose derivative solution was 1:12:0.03. After reacting for 1 hour, the mixture was cooled to room temperature and ascorbic acid was added to terminate the reaction, thereby obtaining a retarder.

[0061] The same method as in Example 1 was used to test the initial setting time, 1d, and 28d compressive strength of the magnesium phosphate cement containing the retarder prepared in this example. The results are shown in the following table:

[0062] .

[0063] Example 4

[0064] A method for preparing a retarder for improving the setting time of magnesium phosphate cement comprises the following steps:

[0065] (1) In a nitrogen atmosphere, NaBH4 is added to a 0.5 M glucose solution, wherein the molar ratio of glucose to NaBH4 is 10:1. The glucose is then stirred for 2 hours to perform hydroxylation, and a hydroxylated glucose solution is obtained for later use.

[0066] (2) Adding butenedioic acid and a catalyst (toluenesulfonic acid) to the hydroxylated glucose solution, wherein the molar ratio of hydroxylated glucose to butenedioic acid and catalyst in the hydroxylated glucose solution is 1:1.5:0.02. The esterification reaction is then carried out by stirring for 4 hours. After completion, the obtained reaction solution is dialyzed and purified (same as in Example 1). After completion, a butenedioic acid-esterified glucose derivative solution is obtained, which is set aside.

[0067] (3) Hydrochloric acid was added to adjust the pH of the butylated glucose derivative solution to 4.5, and then acrylic acid monomer and initiator (ammonium persulfate) were added. The mixture was heated to 70° C. to carry out polymerization reaction. The mass ratio of the butylated glucose derivative to the acrylic acid monomer and initiator in the butylated glucose derivative solution was 1:10:0.01. After reacting for 2 hours, the mixture was cooled to room temperature and ascorbic acid was added to terminate the reaction, thereby obtaining a retarder.

[0068] The same method as in Example 1 was used to test the initial setting time, 1d, and 28d compressive strength of the magnesium phosphate cement containing the retarder prepared in this example. The results are shown in the following table:

[0069] .

[0070] Example 5

[0071] A method for preparing a retarder for improving the setting time of magnesium phosphate cement comprises the following steps:

[0072] (1) A sodium hydroxide solution was added dropwise to a 0.5 M glucose solution to adjust the pH of the system to 8, and then a mixed solution of N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide was added dropwise, wherein the molar ratio of hydroxylated glucose to NHS and EDC in the hydroxylated glucose solution was 10:1.5:2. The reaction was then stirred for 0.5 hours to perform an activation reaction. After completion, an activated glucose solution was obtained and set aside.

[0073] (2) Adding butenedioic acid and a catalyst (concentrated hydrochloric acid) to the activated glucose solution, wherein the molar ratio of activated glucose to butenedioic acid to catalyst in the activated glucose solution is 1:1:0.01. The reaction is then stirred for 5 hours to carry out an esterification reaction. After completion, the resulting reaction solution is dialyzed and purified (same as in Example 1). A butenedioic acid-esterified glucose derivative solution is obtained and set aside.

[0074] (3) Sulfuric acid was added to adjust the pH of the butylated glucose derivative solution to 4.0, and then an acrylic acid monomer and an initiator (sodium persulfate) were added. The mixture was heated to 65° C. to carry out a polymerization reaction. The mass ratio of the butylated glucose derivative to the acrylic acid monomer and the initiator in the butylated glucose derivative solution was 1:8:0.02. After reacting for 4 hours, the mixture was cooled to room temperature and ascorbic acid was added to terminate the reaction, thereby obtaining a retarder.

[0075] The same method as in Example 1 was used to test the initial setting time, 1d, and 28d compressive strength of the magnesium phosphate cement containing the retarder prepared in this example. The results are shown in the following table:

[0076] .

[0077] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A retarder for improving the setting time of magnesium phosphate cement, the structural formula of the retarder is shown below: ； The m=8-10n, and the n is an integer not equal to 0; the retarder is prepared by the following steps: (1) In a protective atmosphere, a reducing agent is added to a glucose solution for hydroxylation treatment, and after the reaction is completed, a hydroxylated glucose solution is obtained; the molar ratio of the glucose to the reducing agent is 8 to 10:1; and the reaction time of the hydroxylation treatment is 0.5 to 3 hours; (2) adjusting the pH of the hydroxylated glucose solution to alkaline, and then adding a mixed solution of N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide to carry out activation reaction for 0.5 to 2 hours, and obtaining an activated glucose solution after completion; the molar ratio of hydroxylated glucose to N-hydroxysuccinimide and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide in the hydroxylated glucose solution is 10:1-2:1-2; (3) adding butenedioic acid and a catalyst to the activated glucose solution to carry out esterification reaction for 4 to 8 hours, and then performing purification treatment to obtain a butenedioic acid esterified glucose derivative solution; the molar ratio of the activated glucose in the activated glucose solution to the butenedioic acid and the catalyst is 1:1-1.5:0.01-0.05; (4) The pH of the butylated glucose derivative solution is adjusted to acidic, and then an acrylic acid monomer and an initiator are added, and a polymerization reaction is carried out at a heating condition of 65 to 85° C. for 1 to 4 hours to obtain the retarder; the mass ratio of the butylated glucose derivative to the acrylic acid monomer and the initiator in the butylated glucose derivative solution is 1:8 to 12:0.01 to 0.

03.

2. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that In step (1), the reducing agent includes at least one of sodium borohydride, lithium aluminum hydride, and diisobutylaluminum hydride.

3. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that In step (1), the protective atmosphere includes any one of nitrogen and argon.

4. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that In step (1), continuous stirring is performed during the reaction process.

5. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that: In step (2), the pH is adjusted to 8-9.

6. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that: In step (2), the pH is adjusted by adding an alkali solution.

7. The retarder for improving the setting time of magnesium phosphate cement according to claim 6, characterized in that: In step (2), the alkali solution includes at least one of sodium hydroxide, potassium hydroxide, and saturated lime water.

8. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that: In step (3), the catalyst includes at least one of toluenesulfonic acid, concentrated sulfuric acid, concentrated hydrochloric acid, and thionyl chloride.

9. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that: In step (3), the obtained reaction solution is purified by dialysis.

10. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that: In step (4), the pH is adjusted to 3.5-4.

5.

11. The retarder for improving the setting time of magnesium phosphate cement according to claim 10, characterized in that: The pH is adjusted by adding any one of hydrochloric acid, sulfuric acid, and acetic acid.

12. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that: The initiator includes at least one of ammonium persulfate, sodium persulfate, potassium persulfate, and benzoyl peroxide.

13. The retarder for improving the setting time of magnesium phosphate cement according to claim 1, characterized in that: In step (4), a chain transfer agent, sodium thiosulfate, is added to the reaction system to control the molecular weight and molecular weight distribution of the retarder generated by the polymerization reaction.

14. Use of the retarder for improving the setting time of magnesium phosphate cement according to any one of claims 1 to 13 in magnesium phosphate cement-based materials.

15. The use according to claim 14, characterized in that The dosage of the retarder is 5-10% of the mass of the magnesium phosphate cement in the magnesium phosphate cement-based material.

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