Preparation method of ester polycarboxylic acid water reducer

Abstract

The invention discloses a preparation method of an ester polycarboxylic acid water reducer, and belongs to the technical field of concrete admixtures. The preparation method of the ester polycarboxylic acid water reducing agent comprises the following steps: under an alkaline condition, carrying out free radical polymerization reaction on a polyether macromonomer and an unsaturated carboxylic acid monomer under the action of a chain transfer agent A, a chain transfer agent B and an initiator, continuously adding a catalyst, and carrying out dehydration esterification reaction under the action of the catalyst, so as to prepare the ester polycarboxylic acid water reducing agent, the polyether macromonomer is monohydroxy polyether of which the molecular weight is between 500 and 5000; the chain transfer agent A is one of acetone, isopropanol, sodium hydrogen sulfite, sodium hypophosphite, sodium formate and the like; the chain transfer agent B is one of mercaptoethanol, mercaptopropanol, mercaptoacetic acid, mercaptopropionic acid and the like; the catalyst is a phosphonic acid compound with hydroxyl or amino. The preparation method is simple in process and low in energy consumption, and the prepared ester polycarboxylic acid water reducer product is excellent in performance.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete admixtures, and particularly relates to a method for preparing an ester polycarboxylic acid water reducer. Background Art

[0002] Polycarboxylate water reducer is the third generation of high performance concrete water reducer and is also the most widely used water reducer in commercial concrete. Its molecular structure is comb-shaped, and both the adsorption group and the polyether side chain can be adjusted. It has the advantages of strong molecular structure designability, low dosage, high water reduction rate, good working performance, etc. It can significantly reduce the amount of cement in commercial concrete or improve the strength of concrete, and has an important impact on the green production of commercial concrete and the reduction of carbon emissions.

[0003] Polycarboxylate water reducers are divided into ether and ester polycarboxylate water reducers. Ethers occupy an absolute dominant position. Ester polycarboxylate water reducers are an important supplement to ether polycarboxylate water reducers. As a functional admixture, they have good application performance when used in combination with ether polycarboxylate water reducers or alone. With the application of low-grade raw materials such as machine-made sand and recycled aggregate in concrete, and the development of high-strength concrete with low water-cement ratio, the performance characteristics of ester polycarboxylate water reducers in terms of workability and early strength have been further studied and optimized.

[0004] At present, the main laboratory synthesis and industrial production method of ester polycarboxylic acid water reducers is the aqueous free radical polymerization method, which uses esterified macromonomers, acrylic monomers, functional monomers, etc. as raw materials and is synthesized by aqueous free radical polymerization (Research Progress in Synthesis Technology of Polycarboxylic Acid Water Reducers [J]. Materials Guide, 2019, 33(2), 558-568). The key point of this process route is to prepare esterified macromonomers with high esterification rate.

[0005] The preparation methods of esterification macromonomers include direct esterification, acyl chloride esterification, anhydride esterification, ester exchange (Preparation of high-performance esterification macromonomers [J], Guangzhou Chemical Industry, 2014, 42 (2), 1-3, 6), and carboxylic acid ester embedding method ethoxylation reaction method (Synthesis and characterization of methacrylate polyethylene glycol monomethyl ether ester macromonomer [J]. Polymer Materials Science and Engineering, 2011, 27 (11): 29-31, 35.). At present, the direct esterification method is mainly used in industrial applications. Methoxy polyether macromonomers or polyethylene glycol and unsaturated carboxylic acids are used as raw materials, strong acid catalysts are added, and water is continuously removed from the reaction system by cyclohexane or toluene under process conditions of 100-120°C and 15-30h. The reaction is completed when the esterification rate of the esterification macromonomer is ≥90%. After the reaction is completed, the water-carrying agent is removed by vacuum distillation. The difficulty of esterification of methoxy polyether macromonomers with number average molecular weight > 2000 and unsaturated carboxylic acids increases significantly, and the esterification rate rarely exceeds 90%, which has a certain adverse effect on the synthesis of downstream ester polycarboxylic acid water reducers.

[0006] Wei Ruiping et al. (Preparation of MPEGMA, a polycarboxylic acid-based water-reducing agent active macromonomer under reduced pressure conditions [J]. Chemical Reaction Engineering and Technology, 2009, 25(5): 391-395.) conducted the esterification reaction of methacrylic acid and methoxy polyether macromonomer under reduced pressure conditions without using a water-carrying agent. The esterification rate reached 66.5% at -0.09 MPa, 80°C and 5 h. Since the boiling point of methacrylic acid is low under reduced pressure conditions, the esterification reaction temperature is not high, resulting in a low esterification rate. Yang Xiubao et al. (Study on the esterification reaction of PAA / MEPG catalyzed by p-toluenesulfonic acid [C]. New Progress in Research and Application of Chinese Chemical Admixtures and Mineral Admixtures, 2016 Cologne Cup Excellent Paper Collection, 2016: 71-74.) used polyacrylic acid and methoxy polyether macromonomer for dehydration esterification under reduced pressure conditions. At -0.1MPa, 120℃ and 6h, the esterification rate of methoxy polyether macromonomer reached about 95%, but it has the disadvantages of complex preparation process and high energy consumption.

[0007] In summary, the preparation process of ester polycarboxylic acid water-reducing agent is gradually developing towards a more environmentally friendly decompression dehydration process, especially the direct dehydration esterification process of polyacrylic acid and methoxy polyether macromonomer has a good industrialization prospect. However, the process of preparing low molecular weight polyacrylic acid (molecular weight ≤ 5000) is difficult to achieve. On the one hand, the molecular weight of polyacrylic acid is closely related to many factors such as monomer concentration, chain transfer agent dosage, initiator concentration, polymerization time and polymerization temperature, and is difficult to control; on the other hand, the concentration of the final prepared polymer is generally less than 50%, otherwise it is easy to cause the viscosity average molecular weight to be out of control. Summary of the invention

[0008] In order to solve the problems existing in the preparation process of the existing small molecule ester polycarboxylate water reducer, the present invention provides a preparation method of the ester polycarboxylate water reducer, the preparation method has simple process and low energy consumption, and the prepared ester polycarboxylate water reducer product has excellent performance.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A method for preparing an ester polycarboxylic acid water reducer comprises: under alkaline conditions, a polyether macromonomer and an unsaturated carboxylic acid monomer undergo a free radical polymerization reaction under the action of a chain transfer agent A, a chain transfer agent B and an initiator, and then a catalyst is added to undergo a dehydration esterification reaction under the action of the catalyst to obtain the ester polycarboxylic acid water reducer;

[0011] The polyether macromonomer is a monohydroxy polyether with a molecular weight between 500 and 5000;

[0012] The chain transfer agent A is one of acetone, isopropanol, sodium bisulfite, sodium hypophosphite, sodium formate, etc.;

[0013] The chain transfer agent B is one of mercaptoethanol, mercaptopropanol, thioglycolic acid, mercaptopropionic acid, etc.;

[0014] The catalyst is a phosphonic acid compound with a hydroxyl group or an amine group;

[0015] The mass ratio of the polyether macromonomer, the unsaturated carboxylic acid monomer, and the catalyst is 1: 0.05-0.15: 0.03-0.05; the molar ratio of the polyether macromonomer, the chain transfer agent A, and the chain transfer agent B is 1: 0.1-0.3: 0.02-0.1.

[0016] Furthermore, the polyether macromonomer structure is shown in the following formula (I):

[0017]

[0018] Wherein, R is an alkyl or aromatic group having 1-15 carbon atoms, which may be -CH3, -CH2CH3, -CH2-CH2-CH3, -CH(CH3)2, phenyl, cyclohexyl, isooctyl, etc.; AO is a mixture of ethylene oxide and propylene oxide, the molar ratio of propylene oxide to ethylene oxide is 0-10:10-115, and the molar amount of propylene oxide is not more than 0.1 times the molar amount of ethylene oxide; n is the average added mole number of AO, which is an integer of 10 to 125; (AO) n It is a homopolymer, random copolymer or block copolymer structure.

[0019] Furthermore, the unsaturated carboxylic acid monomer is one or a mixture of acrylic acid, methacrylic acid, itaconic acid, etc.

[0020] Furthermore, the initiator is one of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide and the like. Increasing the concentration of the initiator helps to reduce the molecular weight of the polymer to a certain extent. Preferably, the molar amount of the initiator in the present invention is 3%-8% of the molar amount of the unsaturated carboxylic acid monomer.

[0021] Furthermore, the catalyst is one or more of hydroxyethylidene diphosphonic acid (HEDP), 2-hydroxyphosphonoacetic acid (HPAA), aminotrimethylphosphonic acid (ATMP), ethylenediaminetetramethylenephosphonic acid (EDTMPS), hexamethylenediaminetetramethylenephosphonic acid (HDTMPS), etc., used in combination in any proportion. In addition to being able to catalyze the esterification reaction, the hydroxyl and amine groups in the molecular structure can undergo an esterification reaction with the carboxylic acid group of the low molecular weight polycarboxylic acid and be grafted onto the main chain of the ester polycarboxylic acid water reducer, and the performance of the water reducer is significantly improved through the hybridization of the carboxyl and phosphate groups.

[0022] The preparation method of the ester polycarboxylate water reducer specifically comprises the following steps:

[0023] (2) Controllable preparation of low molecular weight polycarboxylic acid: using polyether macromonomer and chain transfer agent A as primer, unsaturated carboxylic acid monomer and liquid alkali as dropwise C material, chain transfer agent B as dropwise D material, and initiator as dropwise E material; dropping C material, D material and E material into the primer at the same time, and obtaining a polyether solution of low molecular weight polycarboxylic acid after the dropping is completed;

[0024] (2) Preparation of ester polycarboxylic acid water reducer: Add a catalyst to the polyether solution of low molecular weight polycarboxylic acid in step (1), and the low molecular weight polycarboxylic acid in the polyether solution reacts with the polyether macromonomer to undergo esterification reaction. Distill off water in the reaction system under reduced pressure. After the reaction is completed, dilute with water and add liquid alkali to neutralize the mixture to obtain an ester polycarboxylic acid water reducer.

[0025] Furthermore, the liquid alkali in step (1) is industrial liquid alkali, which is used to neutralize the unsaturated carboxylic acid monomers and reduce the reaction activity of the unsaturated carboxylic acid monomers. The molar amount of the liquid alkali is 10%-30% of the molar amount of the unsaturated carboxylic acid monomers.

[0026] Furthermore, in the step (1), material C is an aqueous solution prepared from an unsaturated carboxylic acid monomer and liquid alkali, material D is an aqueous solution prepared from a chain transfer agent B, and material E is an aqueous solution prepared from an initiator; and material C, material D, and material E are controlled to be added dropwise at the same time, and the addition time is 1.0-3.0 hours.

[0027] The reaction temperature for synthesizing the low molecular weight polyacrylic acid in step (1) is 50-80° C., and the reaction pressure is normal pressure under a nitrogen protective atmosphere.

[0028] The number average molecular weight of the low molecular weight polycarboxylic acid in step (1) is between 500 and 5000.

[0029] The reaction temperature of the low molecular weight polycarboxylic acid and the polyether macromonomer in step (2) is 120-150° C., and the reaction time is 5.0-10.0 h.

[0030] After the reaction of the low molecular weight polycarboxylic acid and the polyether macromonomer in step (2) is completed, the temperature must first be lowered to between 60-70° C., and then diluted with water and neutralized with liquid alkali.

[0031] Furthermore, the ester polycarboxylic acid water-reducing agent obtained in step (2) is a brown solution with a solid content of 30%-50%.

[0032] The ester polycarboxylic acid water-reducing agent in step (2) of the present invention has a number average molecular weight between 10,000 and 50,000, a molecular weight distribution between 1.5 and 2.5, and an esterification rate of the polyether macromonomer between 95% and 98% calculated according to the area percentage of the peak tested by GPC.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) The present invention uses polyether macromonomers instead of water as the reaction solvent for unsaturated carboxylic acid monomers, thereby increasing the solution concentration of low molecular weight polycarboxylic acids, avoiding excessive decompression and dehydration time and energy consumption in the subsequent dehydration process, and significantly shortening the production process. Furthermore, the "one-pot process" for the preparation of ester polycarboxylic acid water reducers is realized, where low molecular weight polycarboxylic acids are synthesized in a polyether macromonomer solution, and then a catalyst is added to continue the esterification reaction to obtain an ester polycarboxylic acid water reducer.

[0035] (2) According to the characteristics of the chain transfer agent, the present invention uses the processes of chain transfer agent A priming and chain transfer agent B dripping to control the polymerization molecular weight of the unsaturated carboxylic acid monomer. Furthermore, the unsaturated carboxylic acid monomer is neutralized to further adjust the polymerization activity of the unsaturated carboxylic acid monomer to ensure the preparation of low molecular weight polycarboxylic acid. The "double-regulated chain transfer" technology used in the present invention overcomes the difficulty of controlling the molecular weight in the conventional synthesis of low molecular weight polycarboxylic acid, and at the same time, the unsaturated carboxylic acid monomer is neutralized to achieve stable control of the low molecular weight polycarboxylic acid.

[0036] (3) The present invention uses a phosphonic acid-based medium-strong acid with a hydroxyl group or an amine group as a catalyst. While ensuring the esterification conversion rate of low molecular weight polyacrylic acid and polyether macromonomer, the hydroxyl group and the amine group in the phosphonic acid-based medium-strong acid can undergo esterification or amidation reaction with the carboxylic acid group and be grafted onto the main chain of the ester polycarboxylic acid water reducer, thereby achieving hybridization of the adsorption group and improving the material adaptability of the ester polycarboxylic acid of the present invention. The retarding effect of the phosphonic acid group or the phosphite group is utilized to achieve the effect of retarding setting and preventing collapse, and at the same time has a viscosity reduction effect, which can significantly improve the workability of concrete and further improve the comprehensive performance of the ester polycarboxylic acid water reducer. DETAILED DESCRIPTION

[0037] The present invention is described in detail below by examples, which are merely illustrative and do not limit the scope of application of the present invention. According to the disclosure herein, those skilled in the art can change the reagents, catalysts and reaction process conditions within the scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

[0038] In the embodiments of the present invention, the number average molecular weight of the low molecular weight polycarboxylic acid is tested by the end group titration method reported in the reference literature (Study on the Preparation Process of Low Molecular Weight Polyacrylic Acid [J], 2008, 7 (1): 58-61). The molecular weight and molecular weight distribution of the ester polycarboxylic acid water reducer are determined by gel permeation chromatography of Wyatt Technology Corporation. (Mobile phase: 0.1 mol / L NaNO3 aqueous solution; mobile phase speed: 1 ml / min; injection volume: 20 μl; sample preparation concentration: 0.5% (sample g / mobile phase g); detector: Shodex RI-71 differential refractive index detector; standard: polyethylene glycol GPC standard (Sigma-Aldrich, molecular weight 1010000, 478000, 263000, 118000, 44700, 18600, 6690, 1960, 628, 232).

[0039] The synthesis method in the embodiment is divided into two parts, firstly the synthesis of low molecular weight polyacrylic acid, and then the synthesis of ester polycarboxylic acid water reducer. The parts mentioned in the embodiment are specifically parts by mass, and the addition amounts of other materials are converted to parts by mass.

[0040] The polyether macromonomers used in the examples are all commercially available products produced by Jiangsu Subote New Materials Co., Ltd. The structural formula and number average molecular weight of the polyether macromonomers are shown in Table 1.

[0041] Table 1 Polyether macromonomer structure and molecular weight

[0042]

[0043]

[0044] Example 1

[0045] Weigh 100 parts of PEG-1 polyether macromonomer and 1.12 parts of chain transfer agent acetone, add them to the reaction device, start stirring to mix and dissolve thoroughly. Weigh 5.0 parts of acrylic acid, add 0.93 parts of liquid alkali, dilute with water to a solid content of 70%, record as dropwise addition of C material; weigh 0.11 parts of chain transfer mercaptoethanol, dilute with water to a solid content of 70%, record as dropwise addition of D material; weigh 0.48 parts of initiator ammonium persulfate, dilute with water to a solid content of 70%, record as dropwise addition of E material. Set the reaction temperature to 50°C, and add C material, D material, and E material dropwise for 3.0 hours under a nitrogen atmosphere. After the dropwise addition is completed, a low molecular weight polycarboxylic acid is obtained, named LPAA-1, and the titrated number average molecular weight is 4972.

[0046] Similarly, the following low molecular weight polycarboxylic acids LPAA-2 to LPAA-7 were prepared according to the same method, and the raw material proportions are shown in Table 2.

[0047] Table 2 Raw material ratio of low molecular weight polycarboxylic acid

[0048]

[0049]

[0050] The reaction process parameters and titration number average molecular weight test results of low molecular weight polycarboxylic acids LPAA-2 to LPAA-7 are shown in Table 3.

[0051] Table 3 Process parameters and titration number average molecular weight of low molecular weight polycarboxylic acid

[0052]

[0053] Example 2

[0054] Weigh 3.0 parts of catalyst hydroxyethylidene diphosphonic acid (HEDP) and add it to LPAA-1 prepared in Example 1. Control the reaction temperature to 120°C, dehydrate under reduced pressure at -0.1MPa, and the reaction time is 10.0h. After the reaction is completed, cool to 60-70°C, then dilute with water and neutralize with liquid alkali to obtain a brown solution with a solid content of 40% and pH = 7, which is the finished product of ester polycarboxylic acid water reducer, named PCE-1. After GPC test, the number average molecular weight (Mn) = 11052, PDI = 1.58, and the PEG-1 monomer esterification rate is 98% according to the peak area percentage.

[0055] Similarly, the following ester polycarboxylate water reducers PCE-2 to PCE-7 were prepared according to the same method. The raw material ratios and process parameters are shown in Table 4.

[0056] Table 4 Raw material ratio and process parameters

[0057]

[0058]

[0059] The GPC test results of ester polycarboxylate water reducers PCE-2 to PCE-7 are shown in Table 5.

[0060] Table 5 GPC test of ester polycarboxylate water reducer

[0061]

[0062] Comparative Example 1

[0063] In this comparative example, only chain transfer agent A was used in the preparation of low molecular weight polycarboxylic acid, and chain transfer agent B was not added. The molecular weight of the prepared low molecular weight polycarboxylic acid exceeded the requirement. In this comparative example, organic phosphonic acid was not used as a catalyst in the preparation of ester polycarboxylic acid water reducer, and the molecular weight and molecular weight distribution of the water reducer exceeded the requirement. The specific preparation is as follows:

[0064] Weigh 100 parts of PEG-6 polyether macromonomer and 30.0 parts of chain transfer agent isopropanol, add them to the reaction device, start stirring to mix and dissolve thoroughly. Weigh 10.0 parts of acrylic acid, add water to dilute to 50% solid content, record as dropwise addition of C material; weigh 0.63 parts of initiator ammonium persulfate, add water to dilute to 50% solid content, record as dropwise addition of E material. Set the reaction temperature to 60°C, and add C material and E material dropwise for 5.0 hours under a nitrogen atmosphere. After the dropwise addition is completed, a low molecular weight polycarboxylic acid is obtained, named LPAA-8, and the titrated number average molecular weight is 8105.

[0065] Weigh 4.0 parts of concentrated sulfuric acid (mass fraction 98%) as a catalyst, add it to the prepared LPAA-8, control the reaction temperature to 130°C, dehydrate under reduced pressure at -0.1MPa, and the reaction time is 6.0h. After the reaction is completed, cool to 60-70°C, then dilute with water and neutralize with liquid alkali to obtain a brown solution with a solid content of 40% and pH = 7, which is the finished product of the ester polycarboxylic acid water reducer, named PCE-8. After GPC testing, the number average molecular weight (Mn) = 73547, PDI = 3.52, and the PEG-1 monomer esterification rate is 90.3% according to the peak area percentage.

[0066] Comparative Example 2

[0067] In this comparative example, only chain transfer agent B was used when preparing low molecular weight polycarboxylic acid, without adding chain transfer agent A, and without polyether macromonomer as primer, the molecular weight of the prepared low molecular weight polycarboxylic acid exceeded the requirement; in this comparative example, organic phosphonic acid was not used as a catalyst when preparing ester polycarboxylic acid water reducer, and the water reducer adopted conventional water esterification process, and the esterification rate did not meet the requirements of the invention content. The specific preparation is as follows:

[0068] Weigh 100 parts of water, add it to the reaction device, start stirring to mix and dissolve thoroughly. Weigh 20.0 parts of acrylic acid, dilute it with water to a solid content of 50%, add 7.41 parts of liquid alkali, record it as dropwise addition of C material; weigh 0.11 parts of chain transfer mercaptoethanol, dilute it with water to a solid content of 50%, record it as dropwise addition of D material; weigh 1.57 parts of initiator hydrogen peroxide (mass fraction of 28.0%), dilute it with water to a solid content of 50%, record it as dropwise addition of E material. Set the reaction temperature to 90°C, and add C material, D material, and E material for 2.0 hours under a nitrogen atmosphere. After the addition is completed, a low molecular weight polycarboxylic acid is obtained, named LPAA-9, and the titration number average molecular weight is 7512.

[0069] Weigh 6.0 parts of catalyst p-toluenesulfonic acid, 40.0 parts of water-carrying toluene, and 133 parts of PEG-7 polyether macromonomer to the prepared LPAA-9, control the reaction temperature to be 120°C, and the reaction time to be 20.0h. After the reaction is completed, the water-carrying toluene is distilled out under reduced pressure, then cooled to 60-70°C, then diluted with water and neutralized with liquid alkali to obtain a brown solution with a solid content of 40% and pH = 7, which is the finished product of the ester polycarboxylic acid water-reducing agent, named PCE-9, tested by GPC, the number average molecular weight (Mn) = 37568, PDI = 2.94, and the PEG-7 monomer esterification rate is 83.8% according to the peak area percentage.

[0070] Application Example 1

[0071] The cement paste fluidity test was carried out in accordance with GB / T8077-2012 standard, using 300g of base cement and 87g of water, and the cement paste fluidity was measured on a flat glass. The viscosity of the initial cement paste was measured in accordance with GB / T10274-2008 "Viscosity Measurement Method". The admixture dosage was fixed at 0.14% of the cement dosage, and the paste test results are shown in Table 6.

[0072] Table 6 Cement paste fluidity test results

[0073]

[0074]

[0075] The test results of the pure slurry in the table show that the ester polycarboxylate water-reducing agent prepared by the preparation method of the present invention is superior to Comparative Example 1 and Comparative Example 2 in terms of initial water reduction and slump retention, indicating that the present invention adopts the "double-regulated chain transfer" technology to better control the molecular weight of the product, and obtains beneficial components with a higher conversion rate, so that the performance is further improved. Furthermore, the cement paste viscosity of the ester polycarboxylate water-reducing agent of the present invention is lower, and has a significant effect of reducing the viscosity of the pure cement slurry. It shows that the retarding effect of the phosphonic acid group or the phosphinate group in the present invention, the retarding effect of the retarding effect of the slump retention, and the viscosity are also reduced, further improving the performance of the ester polycarboxylate water-reducing agent.

[0076] Application Example 2

[0077] The test methods for air content and water reduction rate refer to the relevant provisions of GB8076-2008 "Concrete Admixtures". The slump of fresh concrete with the water reducer of the present invention and the change of slump over time after 60 minutes are measured with reference to the relevant methods of JC473-2001 "Concrete Pumping Agents", and the slump bucket emptying time of fresh concrete is measured to measure the viscosity of the concrete. The admixture dosage is fixed at 0.16% of the cement dosage, and the concrete test results are shown in Table 7.

[0078] Table 7 Concrete test results

[0079]

[0080] The concrete test results in the table show that the ester polycarboxylate water-reducing agent prepared by the preparation method of the present invention is superior to comparative example 1 and comparative example 2 in terms of concrete expansion and slump, indicating that the ester polycarboxylate water-reducing agent of the present invention has good water reduction and slump retention performance. Furthermore, from the perspective of the initial slump bucket inversion time of the slump bucket, the ester polycarboxylate water-reducing agent of the present invention has a shorter inversion slump bucket time, and has a better effect of improving the workability of concrete, which is consistent with the trend of reducing the viscosity of cement paste shown in the slurry test.

Claims

1. A method for preparing an ester polycarboxylate water reducer, characterized in that: Under alkaline conditions, a free radical polymerization reaction occurs with polyether macromonomers and unsaturated carboxylic acid monomers under the action of chain transfer agent A, chain transfer agent B and initiator, and a catalyst is continuously added to cause a dehydration esterification reaction under the action of the catalyst to obtain an ester polycarboxylic acid water reducer; The polyether macromonomer is a monohydroxy polyether with a molecular weight between 500 and 5000; The chain transfer agent A is one of acetone, isopropanol, sodium bisulfite, sodium hypophosphite, and sodium formate; The chain transfer agent B is one of mercaptoethanol, mercaptopropanol, thioglycolic acid, and mercaptopropionic acid; The catalyst is a phosphonic acid compound with a hydroxyl group or an amine group; The mass ratio of the polyether macromonomer, the unsaturated carboxylic acid monomer, and the catalyst is 1: 0.05-0.15: 0.03-0.05; the molar ratio of the polyether macromonomer, the chain transfer agent A, and the chain transfer agent B is 1: 0.1-0.3: 0.02-0.

1.

2. The method for preparing the ester polycarboxylate water reducer according to claim 1, characterized in that: The polyether macromonomer structure is shown in the following formula (I): Wherein, R is an alkyl or aromatic group having 1-15 carbon atoms; AO is a mixture of oxyethylene and oxypropylene, the molar ratio of oxypropylene to oxyethylene is 0-10:10-115, and the molar amount of oxypropylene is not more than 0.1 times the molar amount of oxyethylene; n is the average added mole number of AO, which is an integer of 10 to 125; (AO) n It is a homopolymer, random copolymer or block copolymer structure.

3. The method for preparing the ester polycarboxylate water reducer according to claim 1, characterized in that: The unsaturated carboxylic acid monomer is one of acrylic acid, methacrylic acid and itaconic acid or a mixture of several of them.

4. The method for preparing the ester polycarboxylate water reducer according to claim 1, characterized in that: The initiator is one of ammonium persulfate, sodium persulfate, potassium persulfate and hydrogen peroxide.

5. The method for preparing the ester polycarboxylate water-reducing agent according to claim 1 or 4, characterized in that: The molar amount of the initiator is 3%-8% of the molar amount of the unsaturated carboxylic acid monomer.

6. The method for preparing the ester polycarboxylate water reducer according to claim 1, characterized in that: The catalyst is one or more of hydroxyethylidene diphosphonic acid, 2-hydroxyphosphonoacetic acid, aminotri(methylene)phosphonic acid, ethylenediaminetetra(methylene)phosphonic acid and hexamethylenediaminetetra(methylene)phosphonic acid in any proportion.

7. The method for preparing the ester polycarboxylate water reducer according to claim 1, characterized in that: The specific steps include: (1) Controllable preparation of low molecular weight polycarboxylic acid: polyether macromonomer and chain transfer agent A are used as primer, unsaturated carboxylic acid monomer and liquid alkali are used as dropwise C material, chain transfer agent B is used as dropwise D material, and initiator is used as dropwise E material; dropwise C material, D material and E material are added to the primer at the same time, and a polyether solution of low molecular weight polycarboxylic acid is obtained after the dropwise addition is completed; (2) Preparation of ester polycarboxylic acid water reducer: Add a catalyst to the polyether solution of low molecular weight polycarboxylic acid in step (1), and the low molecular weight polycarboxylic acid in the polyether solution reacts with the polyether macromonomer to undergo esterification reaction. Distill off water in the reaction system under reduced pressure. After the reaction is completed, dilute with water and add liquid alkali to neutralize the mixture to obtain an ester polycarboxylic acid water reducer.

8. The method for preparing the ester polycarboxylate water-reducing agent according to claim 7, characterized in that: The reaction temperature for synthesizing the low molecular weight polyacrylic acid in step (1) is 50-80°C.

9. The method for preparing the ester polycarboxylate water reducer according to claim 7, characterized in that: The reaction pressure in step (1) is normal pressure under a nitrogen protective atmosphere.

10. The method for preparing the ester polycarboxylate water reducer according to claim 7, characterized in that: The reaction temperature of the low molecular weight polycarboxylic acid and the polyether macromonomer in step (2) is 120-150° C., and the reaction time is 5.0-10.0 h.

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