Polycarboxylic acid slump retaining agent, preparation method and application thereof

Abstract

The application belongs to the field of building materials, and provides a polycarboxylic acid slump retaining agent, a preparation method and application thereof. The preparation method of the polycarboxylic acid slump retaining agent comprises the following steps: in the presence of water, a viscosity regulator, an initiator and an optional chain transfer agent, performing a polymerization reaction on comonomers including unsaturated polyether macromonomer, unsaturated carboxylic acid ester monomer, unsaturated monomer I and unsaturated esterification product to synthesize polycarboxylic acid, so as to obtain the polycarboxylic acid slump retaining agent. The preparation method can reduce the viscosity of the polycarboxylic acid slump retaining agent, and high-solid polycarboxylic acid slump retaining agent is obtained.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of building materials, and specifically provides a polycarboxylic acid slump retaining agent, a preparation method and application thereof. BACKGROUND

[0002] Slump retaining agent is an important additive in concrete, which can improve the fluidity of concrete and significantly reduce the slump loss, ensuring the operability and uniformity of concrete during construction. In recent years, polycarboxylic acid slump retaining agent has developed rapidly due to its superior performance and pollution-free production. The performance of polycarboxylic acid slump retaining agent is influenced by factors such as synthesis process, raw material quality and concrete mix proportion, and the solid content also directly affects the application performance in concrete. In addition, higher solid content not only saves the transportation cost of external additives over long distances, but also facilitates the application of external additives in large-scale construction.

[0003] Increasing the solid content of polycarboxylic acid slump retaining agent can save transportation costs, achieve energy saving and emission reduction, and be low-carbon and environmentally friendly. However, high solid content polycarboxylic acid slump retaining agent has problems such as high viscosity, difficulty in synthesis and pumping, and poor product performance. SUMMARY

[0004] In view of the above problems existing in the prior art, the purpose of the present application is to provide a polycarboxylic acid slump retaining agent, a preparation method and application thereof. The preparation method of the present application can reduce the viscosity of polycarboxylic acid slump retaining agent and obtain high solid content polycarboxylic acid slump retaining agent.

[0005] To achieve the above-mentioned purpose, the first aspect of the present application provides a preparation method of a polycarboxylic acid slump retaining agent, which comprises: in the presence of water, a viscosity regulator, an initiator and an optional chain transfer agent, polymerizing a comonomer comprising an unsaturated polyether macromonomer, an unsaturated carboxylic acid ester monomer, an unsaturated monomer I and an unsaturated esterification product to synthesize a polycarboxylic acid, to obtain a polycarboxylic acid slump retaining agent; wherein,

[0006] The structure of the unsaturated carboxylic acid ester monomer is shown in formula 1:

[0007]

[0008] In formula 1, R1 is hydrogen or methyl, and R2 is hydrogen or an alkyl group with 1-4 carbon atoms;

[0009] The unsaturated monomer I is at least one of an unsaturated carboxylic acid, an unsaturated carboxylic acid salt and an unsaturated carboxylic anhydride;

[0010] The unsaturated esterification product is the reaction product of an unsaturated monomer II and a hydroxyl polycarboxylic acid;

[0011] The unsaturated monomer II is an unsaturated carboxylic acid and / or an unsaturated carboxylic anhydride.

[0012] The viscosity regulator is a trivalent cation salt.

[0013] In the preparation method of the present application, the unsaturated esterification product is polymerized with the unsaturated carboxylic acid ester monomer, the unsaturated monomer I and the unsaturated polyether macromonomer, which can introduce polycarboxylic acid unit structure into the polycarboxylic acid molecular chain, and the trivalent cation salt is used as the viscosity regulator, which can introduce trivalent cation into the polycarboxylic acid molecular chain, and the combination of the carboxylate ion on the polycarboxylic acid molecular chain and the trivalent cation can make the conformation of the polycarboxylic acid molecule shrink in water, thereby reducing the viscosity of the polycarboxylic acid slump retaining agent itself. The method of the present application not only solves the problem of performance reduction caused by high viscosity in the synthesis process of the high solid content slump retaining agent, but also improves the production and transportation efficiency of the polycarboxylic acid slump retaining agent.

[0014] In some embodiments of the present application, the unsaturated polyether macromonomer is selected from at least one of 3-methylbut-3-enyl polyethylene glycol ether, 2-methylprop-2-enyl polyethylene glycol ether, ethylene glycol monovinyl polyethylene glycol ether and vinyl hydroxybutyl polyoxyethylene ether.

[0015] In some embodiments of the present application, the unsaturated carboxylic acid ester monomer is selected from at least one of hydroxyethyl acrylate, hydroxypropyl acrylate and hydroxyethyl methacrylate.

[0016] In some embodiments of the present application, the unsaturated carboxylic acid is selected from at least one of acrylic acid, methacrylic acid and itaconic acid; the unsaturated carboxylic acid salt is selected from at least one of sodium acrylate, potassium acrylate, sodium methacrylate, potassium methacrylate, sodium itaconate and potassium itaconate; and the unsaturated carboxylic acid anhydride is selected from at least one of maleic anhydride, itaconic anhydride and methacrylic anhydride.

[0017] In some embodiments of the present application, the hydroxyl polycarboxylic acid has the structure shown in Formula 2:

[0018]

[0019] wherein, L1, L2 and L3 are each independently a single bond or an alkylene group having 1-6 carbon atoms, and R is hydrogen or a carboxyl group.

[0020] Further, the hydroxyl polycarboxylic acid is selected from citric acid and / or malic acid.

[0021] In some embodiments of the present application, the unsaturated esterification product is prepared by a method comprising the following steps: esterification of the unsaturated monomer II and the hydroxyl polycarboxylic acid in the presence of a catalyst and optionally a polymerization inhibitor.

[0022] Further, the molar ratio of the unsaturated monomer to the hydroxyl polycarboxylic acid is (1-10) : 1.

[0023] Further, the temperature of the esterification reaction is 80-130℃, and the reaction time is 1-6h.

[0024] Further, the catalyst is at least one selected from the group consisting of benzenesulfonic acid, p-toluenesulfonic acid, ethyl sulfonic acid, and concentrated sulfuric acid.

[0025] Further, the polymerization inhibitor is hydroquinone and / or phenothiazine.

[0026] In some embodiments of the present application, the amount of the unsaturated esterification product is 1-8 parts by weight, the amount of the unsaturated monomer I is 3-12 parts by weight, and the amount of the unsaturated carboxylic acid ester monomer is 15-40 parts by weight, with respect to 100 parts by weight of the unsaturated polyether macromonomer.

[0027] In some embodiments of the present application, the viscosity modifier is at least one selected from the group consisting of ferric citrate, ferric sulfate, and potassium aluminum sulfate.

[0028] In some embodiments of the present application, the amount of the viscosity modifier is 0.1%-2% of the total mass of the co-monomer.

[0029] In some embodiments of the present application, the temperature of the polymerization reaction is 5-90℃, and the reaction time is 1-8h.

[0030] In some embodiments of the present application, the amount of water is such that the solid content of the prepared polycarboxylic acid slump retaining agent is not less than 55%.

[0031] Further, the amount of water is such that the solid content of the prepared polycarboxylic acid slump retaining agent is not less than 60%.

[0032] In some embodiments of the present application, the initiator is a redox initiator.

[0033] Further, the oxidizing agent in the redox initiator is at least one selected from the group consisting of benzoyl peroxide, hydrogen peroxide, tert-butyl hydroperoxide, ammonium persulfate, sodium persulfate, and potassium persulfate; and the reducing agent in the redox initiator is at least one selected from the group consisting of ferrous sulfate, ferrous sulfate heptahydrate, BRUGGOLITE E51, and ascorbic acid.

[0034] Further, the mass ratio of the oxidizing agent to the reducing agent is 1:(0.2-2).

[0035] In some embodiments of the present application, the amount of the initiator is 0.1%-1% of the total mass of the co-monomer.

[0036] In some embodiments of the present application, the chain transfer agent is selected from at least one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, sodium formate and sodium hypophosphite.

[0037] In some embodiments of the present application, the mass amount of the chain transfer agent is 0.1% to 2% of the total mass of the co-monomer.

[0038] In some embodiments of the present application, the preparation method comprises the following steps:

[0039] (1) uniformly mixing the unsaturated polyether macromonomer, unsaturated esterification product, viscosity regulator, partial initiator and water, and dropping into the mixture an aqueous solution of the mixture of unsaturated monomer I and unsaturated carboxylic acid ester monomer, an aqueous solution of the remaining initiator and an aqueous solution of the molecular weight regulator; or

[0040] uniformly mixing the unsaturated polyether macromonomer, unsaturated esterification product, viscosity regulator, molecular weight regulator, partial initiator and water, and dropping into the mixture an aqueous solution of the mixture of unsaturated monomer I and unsaturated carboxylic acid ester monomer, an aqueous solution of the remaining initiator; wherein,

[0041] controlling the time of the dropping to be 0.5 to 3 hours, and the temperature of the reaction system during the dropping to be 10 to 60°C;

[0042] (2) after the dropping is completed, continuing the reaction at 10 to 60°C for 0.5 to 1 hour.

[0043] The second aspect of the present application provides a polycarboxylic acid slump retaining agent prepared by the preparation method of the first aspect of the present application. The polycarboxylic acid slump retaining agent of the present application has a relatively low viscosity under the condition of high solid content.

[0044] The third aspect of the present application provides the use of the polycarboxylic acid slump retaining agent of the second aspect of the present application in building materials.

[0045] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. DETAILED DESCRIPTION

[0046] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0047] The ranges disclosed herein are defined by their lower and / or upper limits. Ranges can either be inclusive or exclusive of their endpoints, and can be arbitrarily combined with other defined ranges to form new ranges, whether explicitly stated or not. In addition, individual endpoints of the ranges can be combined with other specified ranges or individual endpoints to form new ranges. Furthermore, the disclosure of a single point of a range or a single value is itself a disclosure of a range that includes that single point or value.

[0048] Unless otherwise indicated, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0049] In a first aspect, the present application provides a preparation method of a polycarboxylic acid slump retaining agent, which comprises: polymerizing a comonomer comprising an unsaturated polyether macromonomer, an unsaturated carboxylic acid ester monomer, an unsaturated monomer I and an unsaturated esterification product in the presence of water, a viscosity regulator, an initiator and an optional chain transfer agent to form a copolymerization product (i.e., a polycarboxylic acid), thereby obtaining a polycarboxylic acid slump retaining agent.

[0050] In the present application, the unsaturated polyether macromonomer can be selected from polyether alkylene macromonomers containing a hydrophilic group such as a carboxyl group and an optional amino group, a sulfonic acid group and other hydrophilic groups. Preferably, the unsaturated polyether macromonomer is at least one of 3-methylbut-3-enyl polyethylene glycol ether (IPEG), 2-methylprop-2-enyl polyethylene glycol ether (HPEG), ethylene glycol monovinyl polyethylene glycol ether (EPEG) and vinyl hydroxybutyl polyoxyethylene ether (VPEG).

[0051] In the present application, the number average molecular weight of the unsaturated polyether macromonomer can be 600-6000, such as 1000, 1500, 2400, 3000, 3500, 4000, 5000, etc.

[0052] As some examples, the unsaturated polyether macromonomer can be EPEG2400, EPEG3000, VPEG2400, VPEG3000, IPEG2400, etc.

[0053] The unsaturated polyether macromonomer of the present application can be obtained by commercial purchase, such as OXAC-608A, OXAC-609E, etc. polyether products from Jiangsu Oak Chemical Co., Ltd.

[0054] In the present application, the structure of the unsaturated carboxylic acid ester monomer is shown in formula 1:

[0055]

[0056] In Formula 1, R1 is hydrogen or methyl, and R2 is hydrogen or an alkyl group having 1 to 4 carbon atoms.

[0057] As some examples, R2 can be hydrogen, methyl, ethyl, n-propyl, isopropyl, or n-butyl.

[0058] Preferably, the unsaturated carboxylate monomer is selected from at least one of hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), and hydroxyethyl methacrylate (HEMA).

[0059] In some embodiments, the unsaturated carboxylate monomer is used in an amount of 15 to 40 parts by weight, for example 15 parts by weight, 18 parts by weight, 20 parts by weight, 22 parts by weight, 23 parts by weight, 24 parts by weight, 25 parts by weight, 30 parts by weight, 32 parts by weight, 34 parts by weight, 35 parts by weight, 36 parts by weight, 38 parts by weight, 40 parts by weight, etc., relative to 100 parts by weight of the unsaturated polyether macromonomer.

[0060] In the present application, the unsaturated monomer I is at least one of an unsaturated carboxylic acid, an unsaturated carboxylic acid salt, and an unsaturated carboxylic anhydride.

[0061] In the present application, the unsaturated esterification product is a reaction product of the unsaturated monomer II and a hydroxyl polycarboxylic acid, wherein the unsaturated monomer II is one or more of an unsaturated carboxylic acid, an unsaturated carboxylic anhydride.

[0062] In the present application, the unsaturated carboxylic acid can be a carboxylic acid having 3 to 8 carbon atoms with a double bond. Preferably, the unsaturated carboxylic acid is at least one of acrylic acid (AA), methacrylic acid (MAA), and itaconic acid (IA).

[0063] In the present application, the unsaturated carboxylic anhydride can be a carboxylic anhydride having 3 to 10 carbon atoms with a double bond. Preferably, the unsaturated carboxylic anhydride is at least one of maleic anhydride (MA), itaconic anhydride (ITA), and methacrylic anhydride.

[0064] In the present application, the unsaturated carboxylic acid salt can be a metal salt of an unsaturated carboxylic acid. Preferably, the unsaturated carboxylic acid salt is selected from at least one of sodium acrylate, potassium acrylate, sodium methacrylate, potassium methacrylate, sodium itaconate, and potassium itaconate.

[0065] As one preferred embodiment, the unsaturated monomer I is selected from one or more of acrylic acid, methacrylic acid, maleic anhydride, sodium acrylate, and sodium methacrylate.

[0066] As a preferred embodiment, the unsaturated monomer II is selected from one or more of acrylic acid, methacrylic acid and maleic anhydride.

[0067] In the present application, the unsaturated esterification product can be an esterification product having a double bond and multiple carboxyl groups, wherein the double bond can be provided by the unsaturated monomer II and the multiple carboxyl groups can be provided by the hydroxyl polycarboxylic acid, for example, in the esterification reaction, the carboxyl group in the unsaturated monomer II and the hydroxyl group in the hydroxyl polycarboxylic acid are removed with a water molecule to form the unsaturated esterification product.

[0068] In some embodiments, the hydroxyl polycarboxylic acid can be at least one of a hydroxyl dicarboxylic acid and a hydroxyl tricarboxylic acid.

[0069] Preferably, the hydroxyl polycarboxylic acid has a structure as shown in Formula 2:

[0070]

[0071] wherein L1, L2 and L3 are each independently a single bond or an alkylene group having a carbon number of 1 to 6 (e.g., methylene, ethylene, etc.), and R is hydrogen or a carboxyl group.

[0072] As some examples, L1 is a single bond, L2 is a single bond, methylene or ethylene, and L3 is methylene or ethylene.

[0073] It can be understood that a single bond represents a direct connection between the two groups associated therewith, for example, when L2 is a single bond, the structure of Formula 2 is

[0074] More preferably, the hydroxyl polycarboxylic acid is at least one of citric acid and malic acid.

[0075] In some embodiments, the unsaturated esterification product is prepared by a method comprising the step of: esterifying the unsaturated monomer II and the hydroxyl polycarboxylic acid in the presence of a catalyst and optionally a polymerization inhibitor.

[0076] In the present application, the molar ratio of the unsaturated monomer II to the hydroxyl polycarboxylic acid can be (1 to 10) : 1, for example, 1:1, 1.5:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 9:1, 10:1, etc.

[0077] In the present application, the catalyst can be an acid catalyst. Preferably, the catalyst is selected from at least one of benzene sulfonic acid, p-toluene sulfonic acid, ethyl sulfonic acid and concentrated sulfuric acid.

[0078] In the present application, the amount of the catalyst used can be selected according to the total amount of the reactants. According to some embodiments, the mass amount of the catalyst used is 0.5% to 3%, such as 0.8%, 0.9%, 1.0%, 1.1%, 1.3%, 1.5%, 1.6%, 1.8%, 1.9%, 2.2%, 2.5%, 2.8%, 3%, etc. of the total mass of the unsaturated monomer II and the hydroxyl polycarboxylic acid.

[0079] In the present application, a polymerization inhibitor can or can not be added in the esterification reaction, which can be selected according to the type of the unsaturated monomer II, aiming to reduce the possibility of self-polymerization of the unsaturated monomer II under the esterification reaction conditions. Preferably, the polymerization inhibitor is selected from hydroquinone and / or phenothiazine.

[0080] In some embodiments, the mass amount of the polymerization inhibitor used is 0 to 1%, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, etc. of the total mass of the unsaturated monomer II and the hydroxyl polycarboxylic acid.

[0081] In some embodiments, the temperature of the esterification reaction is 80 to 130°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 120°C, 125°C, 130°C, etc.; and the time of the esterification reaction is 1 to 6 hours, such as 1 hour, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, 5 hours, etc.

[0082] In the present application, in order to improve the yield of the esterification product, it is preferred to perform a dehydration operation during the esterification reaction, such as vacuum dehydration or dehydration with an inert gas as the carrier gas. The inert gas is, for example but not limited to, nitrogen.

[0083] In some embodiments, the amount of the unsaturated esterification product used is 1 to 8 parts by weight, such as 1 part by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.1 parts by weight, 4 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 8 parts by weight, etc. relative to 100 parts by weight of the unsaturated polyether macromonomer.

[0084] In some embodiments, the amount of the unsaturated monomer I used is 3 to 12 parts by weight, such as 3 parts by weight, 5 parts by weight, 6 parts by weight, 7 parts by weight, 7.2 parts by weight, 7.5 parts by weight, 8 parts by weight, 9 parts by weight, 10 parts by weight, 11.5 parts by weight, 12 parts by weight, etc. relative to 100 parts by weight of the unsaturated polyether macromonomer.

[0085] In the present application, the viscosity modifier is a trivalent cation salt. The trivalent cation salt refers to a salt that can provide trivalent cations after being dissolved in water, which can be a simple salt or a complex salt. During the preparation of the polycarboxylic acid slump retaining agent, the cations on the trivalent cation salt can combine with the carboxylate ions on the polycarboxylic acid molecules, effectively reducing the viscosity of the polycarboxylic acid slump retaining agent. According to some embodiments, the viscosity modifier is at least one of ferric citrate, ferric sulfate, and potassium aluminum sulfate.

[0086] In the present application, the amount of the viscosity modifier can be selected according to the amount of the comonomer. According to some embodiments, the mass amount of the viscosity modifier is 0.1% to 2% of the total mass of the comonomer (i.e., the total amount of the unsaturated polyether macromonomer, the unsaturated monomer I, the unsaturated carboxylate monomer, and the unsaturated esterification product), such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.7%, 1.8%, etc. Generally, a lower amount of the viscosity modifier can not be sufficient to form enough combinations with the carboxylate ions, and the viscosity reduction effect on the slump retaining agent is limited, and a higher amount of the viscosity modifier can affect the use effect of the slump retaining agent. Preferably, the mass amount of the viscosity modifier is 0.3% to 1% of the total mass of the comonomer.

[0087] In the present application, the temperature of the polymerization reaction can be 5 to 90°C, such as 5°C, 10°C, 13°C, 15°C, 18°C, 30°C, 32°C, 35°C, 40°C, 50°C, 55°C, 60°C, 70°C, 80°C, etc. In some embodiments, the temperature of the polymerization reaction can be controlled within any temperature range within the above range, such as between 10 and 40°C, between 13 and 25°C, between 15 and 30°C, between 40 and 60°C, etc.

[0088] In the present application, the time of the polymerization reaction can be determined according to the conversion degree of the reactants, which can generally be 1 to 8 hours, such as 1 hour, 2 hours, 3.5 hours, 5 hours, 6 hours, 7 hours, 8 hours, etc.

[0089] In the present application, after the polymerization reaction, an alkali can or can not be added to adjust the pH, which can be determined according to the type of monomer, and preferably the pH of the product is slightly acidic or neutral. As some specific embodiments, the preparation method further comprises: after the polymerization reaction, adding an alkali to adjust the pH of the product to 3 to 7.5. Preferably, the mass amount of the alkali can be 0 to 1% of the total mass of the comonomer.

[0090] In the present application, the alkali can include but is not limited to sodium hydroxide and potassium hydroxide. Preferably, the alkali is added in the form of an alkali solution. As one specific example, the alkali solution is a sodium hydroxide aqueous solution with a mass concentration of 15% to 35%.

[0091] In the present application, the initiator can be selected from various water-soluble initiators, for example, can be selected from one or more of redox system initiators, persulfate initiators, peroxide initiators, preferably the initiator is a redox system initiator.

[0092] In the present application, specific examples of the persulfate initiator include, but are not limited to, one or several of ammonium persulfate, sodium persulfate, potassium persulfate.

[0093] In the present application, specific examples of the peroxide initiator include, but are not limited to, one or several of hydrogen peroxide, tert-butyl hydroperoxide, benzoyl peroxide.

[0094] In the present application, the redox system initiator includes an oxidizing agent and a reducing agent. Preferably, the oxidizing agent is selected from at least one of benzoyl peroxide, hydrogen peroxide, tert-butyl hydroperoxide, ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent is selected from at least one of ferrous sulfate, ascorbic acid, BRUGGOLITE E51, and ascorbic acid.

[0095] As some examples, the redox system initiator can be hydrogen peroxide-ascorbic acid, hydrogen peroxide-ascorbic acid, hydrogen peroxide-BRUGGOLITE E51, hydrogen peroxide-ascorbic acid-ferrous sulfate, hydrogen peroxide-ascorbic acid-ferrous sulfate, hydrogen peroxide-BRUGGOLITE E51-ferrous sulfate.

[0096] It can be understood that in the description of the redox system initiator, the expression "A-B" means the combination of A and B, and the expression "A-B-C" means the combination of A, B, and C. For example, "hydrogen peroxide-ascorbic acid" means using the combination of hydrogen peroxide and ascorbic acid as the redox initiator, and "hydrogen peroxide-ascorbic acid-ferrous sulfate" means using the combination of hydrogen peroxide, ascorbic acid, and ferrous sulfate as the redox initiator. The hydrogen peroxide in the initiator can generally be used in the form of hydrogen peroxide water, and the mass content of hydrogen peroxide in the hydrogen peroxide water can be, for example, 27.5%.

[0097] In some embodiments, in the redox system initiator, the mass ratio of the oxidizing agent to the initiator can be 1:(0.2-2), for example, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:1, 1:2, etc.

[0098] In the present application, the amount of the initiator can be selected according to the total amount of the comonomer. According to some embodiments, the mass amount of the initiator is 0.1% to 1% of the total mass of the comonomer, such as 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0099] In some embodiments, the chain transfer agent can be selected from at least one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, sodium formate, and sodium hypophosphite.

[0100] In some embodiments, the mass amount of the chain transfer agent is 0.1% to 2% of the total mass of the comonomer, such as 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 1%, 1.1%, 1.5%, 1.7%, 1.8%, etc.

[0101] In order to improve the effect of the polymerization reaction, according to some preferred embodiments, the preparation method of the polycarboxylic acid slump retaining agent comprises the following steps:

[0102] (1) uniformly mixing the unsaturated polyether macromonomer, unsaturated esterification product, viscosity regulator, partial initiator, and water, and dropping into the mixture an aqueous solution of the mixture of unsaturated monomer I and hydroxyl carboxylic acid ester, an aqueous solution of the remaining initiator, and an aqueous solution of the molecular weight regulator; or

[0103] uniformly mixing the unsaturated polyether macromonomer, unsaturated esterification product, viscosity regulator, molecular weight regulator, partial initiator, and water, and dropping into the mixture an aqueous solution of the mixture of unsaturated monomer I and hydroxyl carboxylic acid ester, an aqueous solution of the remaining initiator; wherein,

[0104] controlling the time of the dropping to be 0.5 to 3 hours, and controlling the temperature of the reaction system during the dropping to be 10 to 60°C;

[0105] (2) after the dropping is completed, continuing the reaction at 10 to 60°C for 0.5 to 1 hour.

[0106] Optionally, further comprising:

[0107] (3) adding an aqueous solution of the base to the product obtained in step (2) to adjust the pH to be 3 to 7.5.

[0108] In step (1), when the initiator is selected from the redox system initiator, the partial initiator can be one component thereof, and the remaining initiator can be another component thereof.

[0109] In step (1), the time for the dropping is 0.5-3 hours, and the temperature of the reaction system during the dropping is 10-60℃. Under this condition, the conversion rate of the reactants can be improved, and the mass and heat transfer can be facilitated, which is beneficial to the stability of the product.

[0110] In step (2), the holding after the dropping can further improve the conversion degree of the reactants.

[0111] In the present application, the amount of water can be selected according to the solid content and the viscosity of the polycarboxylic acid slump retaining agent. Generally, with the increase of the amount of water, the viscosity of the polycarboxylic acid slump retaining agent decreases, which is beneficial to the pumping and mass and heat transfer, but the solid content also decreases, which can cause the decrease of the production and transportation efficiency. In particular, the preparation method of the present application can reduce the viscosity of the polycarboxylic acid slump retaining agent, and is particularly suitable for the preparation of high solid content polycarboxylic acid slump retaining agent. In other words, the preparation method of the present application can increase the solid content of the polycarboxylic acid slump retaining agent while maintaining the low viscosity of the slump retaining agent.

[0112] In some embodiments, the amount of water is such that the solid content of the polycarboxylic acid slump retaining agent is not less than 55%, preferably not less than 60%.

[0113] In the second aspect, the present application provides a polycarboxylic acid slump retaining agent prepared by the preparation method of the first aspect of the present application. Compared with the traditional polycarboxylic acid slump retaining agent, the polycarboxylic acid slump retaining agent of the present application has lower viscosity at the same solid content, or has higher solid content at the same viscosity.

[0114] In some embodiments, the solid content of the polycarboxylic acid slump retaining agent is ≥60%, and the viscosity at 20℃ is <600cP.

[0115] In the third aspect, the present application provides the use of the polycarboxylic acid slump retaining agent of the second aspect of the present application in building materials. The polycarboxylic acid slump retaining agent of the present application has the characteristics of low viscosity, and has high slump retaining effect on building materials, especially concrete.

[0116] The following examples illustrate the present application. The examples described below are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0117] In the following examples and comparative examples, the concentration of hydrogen peroxide in hydrogen peroxide is 27.5wt%, and the mass concentration of NaOH in sodium hydroxide aqueous solution is 32%.

[0118] Example 1

[0119] (1) Put 192.00 g of citric acid, 288.00 g of acrylic acid, 5.90 g of p-toluenesulfonic acid and 2.00 g of hydroquinone into a reactor and stir, heat to 105°C, remove water by passing nitrogen, react for 3h to obtain unsaturated esterification product A-1.

[0120] (2) Take 12 g of unsaturated esterification product A-1, 480 g of EPEG3000, 5.00 g of iron citrate, 0.016 g of ferrous sulfate and 293.00 g of water into a reactor, start the stirrer and temperature control device, mix the materials evenly, start dropping the mixed aqueous solution of acrylic acid and hydroxyethyl acrylate (acrylic acid 36.00 g, hydroxyethyl acrylate 173.00 g, water 127.60 g), hydrogen peroxide aqueous solution (hydrogen peroxide 4.30 g, water 15.00 g), mercaptopropionic acid aqueous solution (mercaptopropionic acid 2.40 g, water 15.00 g), BRUGGOLITE E51 aqueous solution (BRUGGOLITE E51 0.70 g, water 15.00 g), the initial reaction temperature is 15°C, the dropping time is 1h, the material temperature is controlled ≤30°C during dropping, after dropping, heat for 1h to obtain copolymerization product;

[0121] (3) Add 6 g of sodium hydroxide aqueous solution to the copolymerization product obtained in step (2) to obtain polycarboxylic acid slump retaining agent KZJ-1.

[0122] Example 2

[0123] (1) Put 134.00 g of malic acid, 43.00 g of methacrylic acid, 288.00 g of acrylic acid, 8.80 g of p-toluenesulfonic acid, 1.00 g of hydroquinone, and 0.50 g of phenothiazine into a reactor and stir, heat to 110°C, remove water by vacuum, react for 4h to obtain unsaturated esterification product A-2.

[0124] (2) Take 15.00 g of unsaturated esterification product A-2, 380 g of EPEG3000, 100.00 g of VPEG3000, 4.60 g of iron sulfate, 0.012 g of ferrous sulfate and 290.00 g of water into a reactor, start the stirrer and temperature control device, mix the materials evenly, start dropping the mixed aqueous solution of acrylic acid and hydroxypropyl acrylate (acrylic acid 34.00 g, hydroxypropyl acrylate 163.00 g, water 122.30 g), hydrogen peroxide aqueous solution (hydrogen peroxide 3.80 g, water 15.00 g), mercaptoacetic acid aqueous solution (mercaptoacetic acid 2.20 g, water 15.00 g), white block aqueous solution (white block 1.20 g, water 15 g), the initial reaction temperature is 17°C, the dropping time is 50 min, the material temperature is controlled ≤30°C during dropping, after dropping, heat for 1h to obtain copolymerization product;

[0125] (3) Add 12 g of sodium hydroxide aqueous solution into the copolymerization product prepared in step (2) to obtain polycarboxylic acid slump retaining agent KZJ-2.

[0126] Example 3

[0127] (1) Put 32.00 g of citric acid, 33.00 g of malic acid, 196.00 g of maleic anhydride, 86.00 g of methacrylic acid, 72.00 g of acrylic acid, 6.80 g of p-toluenesulfonic acid and 1.20 g of hydroquinone into a reactor, stir, heat to 100℃, remove water by vacuumizing, and react for 3 h to obtain unsaturated esterification product A-3.

[0128] (2) Put 24.00 g of unsaturated esterification product A-3, 400 g of EPEG2400, 80.00 g of IPEG2400, 4.00 g of ferric citrate, 2.00 g of potassium aluminum sulfate, 7.50 g of sodium hypophosphite, 0.015 g of ferrous sulfate and 314.00 g of water into a reactor, start the stirrer and temperature controller, mix the materials evenly, start dropping the mixed aqueous solution of acrylic acid and hydroxyethyl methacrylate (24.00 g of acrylic acid, 115.00 g of hydroxyethyl methacrylate, 88.00 g of water), aqueous hydrogen peroxide solution (5.70 g of hydrogen peroxide, 15.00 g of water), and aqueous ascorbic acid solution (1.50 g of ascorbic acid, 15.00 g of water), the initial reaction temperature is 13℃, the dropping time is 1 h, the material temperature is controlled to be ≤30℃ during the dropping process, after the dropping is completed, heat for 1 h to obtain a copolymerization product;

[0129] (3) Add 2 g of sodium hydroxide aqueous solution into the copolymerization product prepared in step (2) to obtain polycarboxylic acid slump retaining agent KZJ-3.

[0130] Example 4

[0131] Put 15.00 g of unsaturated esterification product A-1 prepared in Example 1, 480 g of EPEG3000, 6.0 g of ferric sulfate, 0.012 g of ferrous sulfate and 310.00 g of water into a reactor, start the stirrer and temperature controller, mix the materials evenly, start dropping the mixed aqueous solution of acrylic acid, sodium acrylate, maleic anhydride and hydroxyethyl acrylate (18.00 g of acrylic acid, 12.00 g of sodium acrylate, 6.00 g of maleic anhydride, 173.00 g of hydroxyethyl acrylate, 124.70 g of water), aqueous hydrogen peroxide solution (4.00 g of hydrogen peroxide, 10.00 g of water), aqueous mercaptoacetic acid solution (2.00 g of mercaptoacetic acid, 10.00 g of water), and aqueous erioglaucine solution (1.30 g of erioglaucine, 15.00 g of water), the initial reaction temperature is 20℃, the dropping time is 1 h, the material temperature is controlled to be ≤25℃ during the dropping process, after the dropping is completed, heat for 1.5 h to obtain a copolymerization product;

[0132] (3) Add 4 g of sodium hydroxide aqueous solution to the copolymerization product prepared in step (2) to obtain a polycarboxylic acid slump retaining agent KZJ-4.

[0133] Example 5

[0134] (1) Stir 192.00 g of citric acid, 144.00 g of acrylic acid, 2.90 g of p-toluenesulfonic acid and 1.30 g of hydroquinone in a reactor, heat to 105°C, remove water by passing nitrogen, and react for 3 h to obtain an unsaturated esterification product A-4.

[0135] (2) Take 12 g of the unsaturated esterification product A-4, 480 g of EPEG3000, 5.00 g of potassium aluminum sulfate, 0.016 g of ferrous sulfate and 300.00 g of water, and add them to a reactor. Start the stirrer and temperature controller, and mix the materials uniformly. Then start dropping a mixed aqueous solution of acrylic acid, sodium methacrylate and hydroxyethyl acrylate (33.00 g of acrylic acid, 5.00 g of sodium methacrylate, 183.00 g of hydroxyethyl acrylate and 137.20 g of water), hydrogen peroxide (4.1 g of hydrogen peroxide and 10.00 g of water), an aqueous solution of mercaptopropionic acid (2.20 g of mercaptopropionic acid and 10.00 g of water), and an aqueous solution of BRUGGOLITE E51 (0.70 g of BRUGGOLITE E51 and 15.00 g of water). The initial reaction temperature is 15°C, the dropping time is 1.0 h, the material temperature is controlled at ≤40°C during dropping, and the reaction is maintained for 1 h after dropping is completed to obtain a copolymerization product.

[0136] (3) Add 5.00 g of sodium hydroxide aqueous solution to the copolymerization product prepared in step (2) to obtain a polycarboxylic acid slump retaining agent KZJ-5.

[0137] Comparative Example 1

[0138] (1) Stir 480.00 g of EPEG3000, 5.00 g of ferric citrate, 0.016 g of ferrous sulfate and 293.00 g of water in a reactor, heat to 105°C, remove water by passing nitrogen, and react for 3 h to obtain an unsaturated esterification product A-4.

[0139] (2) In the copolymerization product prepared in step (1), 6 g of sodium hydroxide aqueous solution was added to obtain a polycarboxylic acid slump retaining agent, which was denoted as comparative sample PCE-1.

[0140] Comparative Example 2

[0141] (1) 192.00 g of citric acid, 288.00 g of acrylic acid, 5.90 g of p-toluenesulfonic acid, and 2.00 g of hydroquinone were added into a reactor and stirred, and then heated to 105°C, and water was removed by nitrogen blowing, and reacted for 3 h to obtain an esterification product A-1.

[0142] (2) 12.00 g of the esterification product A-1 obtained in step (1), 480.00 g of EPEG3000, 0.016 g of ferrous sulfate, and 293.00 g of water were added into a reactor, and the stirrer and temperature controller were turned on, and then the materials were mixed uniformly, and then an aqueous solution of acrylic acid and hydroxyethyl acrylate (36.00 g of acrylic acid, 173.00 g of hydroxyethyl acrylate, and 127.60 g of water), an aqueous solution of hydrogen peroxide (4.30 g of hydrogen peroxide and 15.00 g of water), an aqueous solution of mercaptopropionic acid (2.40 g of mercaptopropionic acid and 15.00 g of water), and an aqueous solution of BRUGGOLITE E51 (0.70 g of BRUGGOLITE E51 and 15.00 g of water) were added dropwise, the initial reaction temperature was 15°C, the dropwise addition time was 1.0 h, the material temperature was controlled to be ≤30°C during the dropwise addition, and after the dropwise addition was completed, the reaction was maintained for 1 h to obtain a copolymerization product.

[0143] (3) In the copolymerization product prepared in step (2), 6 g of sodium hydroxide aqueous solution was added to obtain a polycarboxylic acid slump retaining agent, which was denoted as comparative sample PCE-2.

[0144] Comparative Example 3

[0145] (1) 480.00 g of EPEG3000, 0.016 g of ferrous sulfate, and 293.00 g of water were added into a reactor, and the stirrer and temperature controller were turned on, and then the materials were mixed uniformly, and then an aqueous solution of acrylic acid and hydroxyethyl acrylate (36.00 g of acrylic acid, 173.00 g of hydroxyethyl acrylate, and 127.60 g of water), an aqueous solution of hydrogen peroxide (4.30 g of hydrogen peroxide and 15.00 g of water), an aqueous solution of mercaptopropionic acid (2.40 g of mercaptopropionic acid and 15.00 g of water), and an aqueous solution of BRUGGOLITE E51 (0.70 g of BRUGGOLITE E51 and 15.00 g of water) were added dropwise, the initial reaction temperature was 15°C, the dropwise addition time was 1.0 h, the material temperature was controlled to be ≤30°C during the dropwise addition, and after the dropwise addition was completed, the reaction was maintained for 1 h to obtain a copolymerization product.

[0146] (2) In the copolymerization product prepared in step (1), 6 g of sodium hydroxide aqueous solution was added to obtain a polycarboxylic acid slump retaining agent, which was denoted as comparative sample PCE-3.

[0147] Comparative Example 4

[0148] (1) 480.00 g of EPEG3000, 0.016 g of ferrous sulfate, and 513.00 g of water were added to a reactor, the stirrer and temperature controller were turned on, and the materials were mixed uniformly. Then, an aqueous solution of acrylic acid and hydroxyethyl acrylate (36.00 g of acrylic acid, 173.00 g of hydroxyethyl acrylate, and 127.60 g of water), an aqueous solution of hydrogen peroxide (4.30 g of hydrogen peroxide and 15.00 g of water), an aqueous solution of mercaptopropionic acid (2.40 g of mercaptopropionic acid and 15.00 g of water), and an aqueous solution of BRUGGOLITE E51 (0.70 g of BRUGGOLITE E51 and 15.00 g of water) were added dropwise. The initial reaction temperature was 15°C, the dropwise addition time was 1.0 h, the temperature of the materials was controlled at ≤30°C during the dropwise addition, and the dropwise addition was maintained for 1 h after completion. A copolymer product was obtained.

[0149] (2) 6 g of an aqueous solution of sodium hydroxide was added to the copolymer product obtained in step (1) to obtain a polycarboxylic acid slump retaining agent as a comparative sample PCE-4.

[0150] Test Example

[0151] The following test example was used to illustrate the performance of the polycarboxylic acid slump retaining agents KZJ-1 to KZJ-5 and the comparative samples PCE-1 to PCE-4 prepared in the above examples and comparative examples.

[0152] 1. Viscosity test: The viscosity of each polycarboxylic acid slump retaining agent at 20°C was tested using a rotary viscometer NDJ-8T (No. 2 rotor, 30 rpm), and the test results are shown in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] 2. Slump retaining performance test: The slump retaining agent was mixed with a water reducing agent PC (Point-S type polycarboxylic acid water reducing agent, Kozhijie New Materials Co., Ltd.) at a mass ratio of 3:7 to prepare an admixture sample having a solid content of 20%, and a concrete performance comparison test was performed. The specific proportions of the concrete are shown in Table 2, and the test results are shown in Table 3.

[0157] Table 2

[0158] Cement (kg / m 3 )]]> Sand (kg / m 3 )]]> Stone (kg / m 3 )]]> Water (kg / m 3 )]]> 360 865 980 175

[0159] Table 3

[0160]

[0161] In combination with Table 1 and Table 3, the results of KZJ-1 and PCE-1 show that PCE-1 (Comparative Example 1) without adding unsaturated esterification product A-1 has smaller slump retention performance and larger viscosity than KZJ-1 prepared in Example 1, which is mainly because the unsaturated esterification product A-1 is not used, so that the number of carboxylic acid structures in the molecular structure of the copolymer is less, and the carboxylic acid structures that can form a combination with the viscosity regulator are also less, so the viscosity is larger, and the larger viscosity will affect the mass and heat transfer effect, resulting in the product having poorer slump retention performance.

[0162] The comparison results of KZJ-1 and PCE-2 show that PCE-2 (Comparative Example 2) without adding a viscosity regulator has poorer slump retention performance than KZJ-1 and a viscosity that is significantly larger than KZJ-1, indicating that in the case of the same copolymer monomer composition, the viscosity is larger without adding a viscosity regulator, and because the viscosity is large during synthesis, it will affect the mass and heat transfer effect, resulting in the synthesized product having poorer slump retention performance.

[0163] The comparison results of KZJ-1 and PCE-3 show that PCE-3 without adding unsaturated esterification product A-1 and a viscosity regulator has poorer slump retention performance than KZJ-1 and a higher viscosity than KZJ-1.

[0164] The comparison results of PCE-3 and PCE-4 show that when the solid content of PCE-4 is reduced from 60.0% to 50.0% by adding more water under the same material ratio, the viscosity is significantly reduced and the slump retention performance is improved to a certain extent, but the low solid content will result in high transportation cost.

[0165] In summary, the preparation method of the present application can effectively reduce the viscosity of the product while increasing the solid content of the polycarboxylic acid slump retaining agent and improve the slump retention performance of the product.

[0166] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should be covered in the scope of the claims and description of the present application. Especially, as long as there is no structural conflict, each technical feature mentioned in each embodiment can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing a polycarboxylic acid slump retaining agent, characterized by, The application relates to a polycarboxylic acid slump retaining agent, a preparation method thereof and application thereof. The copolymerization of a comonomer including an unsaturated polyether macromonomer, an unsaturated carboxylate monomer, an unsaturated monomer I and an unsaturated esterification product in the presence of water, a viscosity regulator, an initiator and an optional chain transfer agent is carried out to synthesize a polycarboxylic acid, so as to obtain the polycarboxylic acid slump retaining agent; wherein, The structure of the unsaturated carboxylate monomer is shown in formula 1: Formula 1, In formula 1, R1 is hydrogen or methyl, and R2 is hydrogen or an alkyl group with 1-4 carbon atoms; The unsaturated monomer I is at least one of an unsaturated carboxylic acid, an unsaturated carboxylic acid salt and an unsaturated carboxylic anhydride; The unsaturated esterification product is a reaction product of an unsaturated monomer II and a hydroxyl polycarboxylic acid; The unsaturated monomer II is an unsaturated carboxylic acid and / or an unsaturated carboxylic anhydride; The viscosity regulator is a trivalent cation salt.

2. The production method according to claim 1, characterized by, The unsaturated polyether macromonomer is at least one of 3-methylbut-3-enyl polyethylene glycol ether, 2-methylprop-2-enyl polyethylene glycol ether, ethylene glycol monovinyl polyethylene glycol ether and vinyl hydroxybutyl polyoxyethylene ether.

3. The preparation method according to claim 1, characterized in that, The unsaturated carboxylate monomer is at least one of hydroxyethyl acrylate, hydroxypropyl acrylate and hydroxyethyl methacrylate.

4. The method of claim 1, wherein, The unsaturated carboxylic acid is at least one of acrylic acid, methacrylic acid and itaconic acid; the unsaturated carboxylic acid salt is at least one of sodium acrylate, potassium acrylate, sodium methacrylate, potassium methacrylate, sodium itaconate and potassium itaconate; and the unsaturated carboxylic anhydride is at least one of maleic anhydride, itaconic anhydride and methacrylic anhydride.

5. The method of any one of claims 1-4, wherein, The structure of the hydroxyl polycarboxylic acid is shown in formula 2: Formula 2, In formula 2, L1, L2 and L3 are each independently a single bond or an alkylene group with 1-6 carbon atoms, and R is hydrogen or a carboxyl group.

6. The method of any one of claims 1-4, wherein, The hydroxyl polycarboxylic acid is citric acid and / or malic acid.

7. The method of any one of claims 1-4, wherein, The unsaturated esterification product is prepared by a method including the following steps: The unsaturated monomer II and the hydroxyl polycarboxylic acid are subjected to esterification in the presence of a catalyst and an optional polymerization inhibitor.

8. The preparation method according to claim 7, characterized in that, The molar ratio of the unsaturated monomer II to the hydroxyl polycarboxylic acid is (1-10):

1.

9. The preparation method according to claim 7, characterized in that, The esterification is carried out at a temperature of 80-130 DEG C for 1-6 hours.

10. The preparation method according to claim 7, characterized in that, The catalyst is at least one of benzene sulfonic acid, p-toluene sulfonic acid, ethyl sulfonic acid and concentrated sulfuric acid.

11. The preparation method according to claim 7, characterized in that, The polymerization inhibitor is hydroquinone and / or phenothiazine.

12. The method of any one of claims 1-4, wherein, The amount of the unsaturated esterification product is 1-8 parts by weight, the amount of the unsaturated monomer I is 3-12 parts by weight, and the amount of the unsaturated carboxylate monomer is 15-40 parts by weight, relative to 100 parts by weight of the unsaturated polyether macromonomer.

13. The method of any one of claims 1-4, wherein, The viscosity regulator is at least one of ferric citrate, ferric sulfate and potassium aluminum sulfate.

14. The method of any one of claims 1-4, wherein, The mass amount of the viscosity regulator is 0.1%-2% of the total mass of the comonomer.

15. The method of any one of claims 1-4, wherein, The polymerization is carried out at a temperature of 5-90 DEG C for 1-8 hours.

16. The method of making according to any one of claims 1-4, wherein, The amount of water is such that the prepared polycarboxylic acid slump retaining agent has a solid content of not less than 55%.

17. The method of claim 16, wherein, The amount of water is such that the prepared polycarboxylic acid slump retaining agent has a solid content of not less than 60%.

18. The method of making according to any one of claims 1-4, wherein, The initiator is a redox initiator.

19. The method of claim 18, wherein, The oxidizing agent in the redox initiator is selected from at least one of benzoyl peroxide, hydrogen peroxide, tert-butyl hydroperoxide, ammonium persulfate, sodium persulfate and potassium persulfate; the reducing agent in the redox initiator is selected from at least one of ferrous sulfate, sodium dithionite, BRUGGOLITE E51 and ascorbic acid.

20. The method of claim 19, wherein, The mass ratio of the oxidizing agent to the reducing agent is 1:(0.2-2).

21. The method of any one of claims 1-4, wherein, The mass amount of the initiator is 0.1%-1% of the total mass of the comonomers.

22. The method of making according to any one of claims 1-4, wherein, The chain transfer agent is selected from at least one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, sodium formate and sodium hypophosphite.

23. The method of making according to any one of claims 1-4, wherein, The mass amount of the chain transfer agent is 0.1%-2% of the total mass of the comonomers.

24. The method of any one of claims 1-4, wherein, The preparation method comprises the following steps: (1) uniformly mixing the unsaturated polyether macromonomer, unsaturated esterification product, viscosity regulator, part of the initiator and water, and dropping into the mixture an aqueous solution of the mixed unsaturated monomer I and unsaturated carboxylic acid ester monomer, an aqueous solution of the remaining initiator and an aqueous solution of the chain transfer agent; or uniformly mixing the unsaturated polyether macromonomer, unsaturated esterification product, viscosity regulator, chain transfer agent, part of the initiator and water, and dropping into the mixture an aqueous solution of the mixed unsaturated monomer I and unsaturated carboxylic acid ester monomer and an aqueous solution of the remaining initiator; wherein, the dropping time is controlled to be 0.5-3h, and the temperature of the reaction system during the dropping process is 10-60℃; (2) after the dropping is completed, continuing the reaction at 10-60℃ for 0.5-1h.

25. A polycarboxylic acid slump retaining agent prepared by the preparation method of any one of claims 1-24.

26. Use of the polycarboxylic acid slump retaining agent of claim 25 in building materials.

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