High-water-reduction type polycarboxylate superplasticizer as well as preparation method and application thereof

Abstract

According to the high-water-reduction type polycarboxylic acid water reducing agent and the preparation method and application thereof, through introduction of sulfuric acid in the initial stage of reaction, excessive accumulation of acrylic acid is prevented, and the acid-ether ratio of an early product is reduced; meanwhile, water is added in the middle stage of the reaction, and an alkaline substance is used for adjusting the pH of the system to neutralize part of acrylic acid and increase the acid-ether ratio of middle-stage products; according to the preparation method, the acid-ether ratio of early-stage products in general polycarboxylic acid synthesis can be effectively reduced, the acid-ether ratio of middle-stage products can be increased, the water-reducing rate of polycarboxylic acid can be obviously increased, the water-reducing rate is increased by 10-20% compared with that of existing products, and the polycarboxylic acid water-reducing agent further has outstanding mud resistance, is high in adaptability to various admixtures and has wide market application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of concrete admixtures, and particularly relates to a high water-reducing polycarboxylate water reducer, a preparation method thereof and an application thereof. Background Art

[0002] Water reducers are a type of concrete admixture that is currently the most widely studied and applied. When the workability of concrete remains unchanged, adding water reducers can effectively save cement consumption, reduce water consumption, and improve the strength of concrete. As the latest generation of high-performance concrete water reducers, polycarboxylates have outstanding advantages such as low dosage, good slump retention, strong molecular structure controllability, and green and environmentally friendly production processes. Chemically speaking, polycarboxylate is a comb-shaped polymer, which consists of a main chain rich in carboxylic acid groups and polyether side chains. The carboxylic acid groups on the main chain can be adsorbed on the surface of positively charged cement or cement hydrates in a directional manner, while the polyether side chains stretch in the solution to form a hydration layer to provide steric repulsion to prevent cement agglomeration. Therefore, this structure endows polycarboxylate with a powerful ability to disperse cement particles.

[0003] The application proportion of industrial waste residues such as fly ash, mineral powder, and steel slag powder has been increasing year by year, further squeezing the water reduction rate of polycarboxylate water reducers, resulting in a significant increase in the dosage of polycarboxylate water reducers, which is extremely likely to cause concrete non-setting and insufficient strength. There is a need for high water-reducing polycarboxylate water reducers to reduce the dosage.

[0004] Two monomers, polyether and acrylic acid, are used in the synthesis of polycarboxylate water reducers. Researchers have found in long-term practice that the ratio of the two monomers directly affects the performance of polycarboxylate. Generally speaking, polycarboxylates with an acid-ether ratio (molar ratio of acrylic acid to polyether) of 3 to 4 have the best water-reducing performance. However, when synthesizing polycarboxylate, affected by the environment, the acid-ether ratio of each stage product is significantly different, and the water-reducing performance of each stage product also varies significantly. In the conventional polycarboxylate synthesis process, due to the huge difference in monomer activity, polyether is generally fed in a bottom feed manner, and acrylic acid is fed in a dropping manner. In the initial stage of polymerization, due to the existence of an induction period, there is an accumulation process of acrylic acid. After the reaction starts, due to the excessive accumulation of acrylic acid concentration, the acid-ether ratio of the initial product is higher than the optimal range. In the middle stage of the reaction, at this time, free radical polymerization enters the auto-acceleration period, and due to the consumption in the early stage, the acrylic acid concentration is prone to insufficient supply. Therefore, the acid-ether ratio of the middle stage product is easily lower than the optimal range. And the acid-ether ratio of the middle stage product cannot be simply improved by increasing the feeding speed of acrylic acid, because this will lead to too high an acrylic acid concentration, imbalance with the polyether concentration ratio, and easy self-polymerization, generating polyacrylic acid impurities without water-reducing ability, which is not worth the loss.

[0005] High water-reducing polycarboxylic acids have always been a research hotspot in the industry, and related patents have emerged in an endless stream. Patent CN107722194B uses a technical solution that concentrates the adsorption groups on the side chain to increase the water reduction rate of existing polycarboxylic acid products by more than 30%; Patent CN115819685A modifies the polyether monomer through a carboxyl-terminated polyether side chain. Due to the carboxyl groups in both the polyether side chain and the adsorption chain, under the influence of the repulsive effect, the extension of the polyether side chain in the system is effectively enhanced, which can improve the local curling of the long chain and other situations, and increase the steric hindrance effect to increase water reduction; Patent CN109970921B introduces a benzene ring and a carboxyl structure at the end of the branched chain of the polycarboxylic acid water reducer molecule, enhancing the steric hindrance effect of the polycarboxylic acid water reducer molecule, and the prepared polycarboxylic acid water reducer has a higher water reduction rate. Summary of the Invention

[0006] In view of the problems in the prior art such as too high acid-ether ratio of early products and too low acid-ether ratio of intermediate products in the synthesis process of polycarboxylic acids, this application provides a high water-reducing polycarboxylic acid water reducer, its preparation method and application. By introducing sulfuric acid in the initial stage of the reaction, the excessive accumulation of acrylic acid is prevented, and the acid-ether ratio of early products is reduced; at the same time, water is added in the middle stage of the reaction and the pH of the system is adjusted with an alkaline substance to neutralize part of the acrylic acid and increase the acid-ether ratio of intermediate products. Through the preparation method of this application, the acid-ether ratio of early products in the synthesis of general polycarboxylic acids can be effectively reduced, the acid-ether ratio of intermediate products can be increased, the water reduction rate of polycarboxylic acids can be significantly improved, the water reduction rate is increased by 10-20% compared with existing products, and it also has relatively prominent anti-sludge performance and strong adaptability to various admixtures, with broad market application prospects.

[0007] A preparation method of a high water-reducing polycarboxylic acid water reducer, comprising the following steps:

[0008] (1) After adding sulfuric acid and an initiator to the polyether monomer, immediately start dropping the acrylic acid monomer and the chain transfer agent. After the dropping reaction for 0.1-1 h, add water to stop the reaction and dilute the reaction system at the same time;

[0009] (2) Add an oxidant to the reaction solution in step (1), prepare a solution of the acrylic acid monomer, a reducing agent, and a chain transfer agent and slowly drop it into the reaction system. During the dropping process, use an alkaline substance to control the pH of the reaction process to be maintained between 5.5 and 6.5. After the dropping is completed, keep the reaction at a certain temperature for 1-2 h to make the monomers react completely, and then the product can be discharged;

[0010] The mass ratio of the polyether monomer, acrylic acid monomer, sulfuric acid, initiator, and chain transfer agent in the above step (1) is 100:(2-7):(0.3-0.5):(0.1-2):(0.8-3);

[0011] In step (2), the mass ratio of the acrylic monomer, the oxidant, the reductant, the chain transfer agent, and the polyether monomer in step (1) is (3-7):(0.5-2):(0.4-1):(0.2-1.2):100.

[0012] The structural formula of the above polyether monomer is shown in the following general formula (I):

[0013] R1 is -H or -CH3, R2 is -OCH2CH2-, -OCH2CH2CH2CH2-, -CH2-, -CH2CH2-; n is an integer from 45 to 90, indicating that the weight-average molecular weight of the polyether monomer is 2000 to 4000.

[0014] The above initiator is selected from any one or a combination of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide.

[0015] The above chain transfer agent is selected from any one or a combination of mercaptoacetic acid, mercaptopropionic acid, mercaptoethanol. And the types of chain transfer agents used in steps (1) and (2) are the same.

[0016] The above oxidant is selected from any one or a combination of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate; the above reductant is selected from any one or a combination of L-ascorbic acid, sodium formaldehyde sulfoxylate, sodium sulfite, sodium bisulfite, ferrous sulfate.

[0017] The above basic substance is selected from any one or a combination of sodium hydroxide, potassium hydroxide, pyridine, ethylenediamine, triethylamine, diethylenetriamine, sodium acetate.

[0018] In the above step (1), the reaction temperature is 60-90°C. The reaction temperature melts the polyether monomer and then the sulfuric acid and the initiator are added; no water is added during the reaction process in step (1), which belongs to bulk polymerization. After the reaction ends, the amount of water added should make the concentration of the reaction system 50-60%; the dropping reaction time in step (1) is determined by the conversion rate of the polyether. When the conversion rate of the polyether reaches 20-30%, water is added to stop the reaction. Due to the differences in the polyether monomer, the initiator, and the temperature, the dropping times to reach the target polyether conversion rate are also different, and the range is 0.1-1h.

[0019] In the above step (1), other organic or inorganic liquid strong acids can be used to replace sulfuric acid, and the effects are similar. However, these alternative acids are not suitable for the synthesis of polycarboxylic acids because of their strong oxidizing properties or high costs.

[0020] In step (2) above, the reaction temperature is 15 to 50 °C. The dropping time of the solution prepared from acrylic monomers, reducing agents, and chain transfer agents is 1 to 5 h. The alkaline substance in step (2) can be added in a base or dropped, as long as the pH value of the reaction system is controlled within 5.5 to 6.5.

[0021] The weight average molecular weight of the above high water-reducing polycarboxylate superplasticizer is 20,000 to 80,000.

[0022] When the above high water-reducing polycarboxylate superplasticizer is applied to a cement concrete system, the dosage of the superplasticizer is 0.05% to 0.3% of the total mass of the binder. The dosage is the pure solid dosage, and the percentage is the mass percentage. If the dosage is too low, its performance will deteriorate. If the dosage is too high, it will cause economic waste and the performance will not be improved.

[0023] The high water-reducing polycarboxylate superplasticizer of the present invention can be used in combination with other commercially available superplasticizers, such as lignosulfonate superplasticizers, naphthalene sulfonate superplasticizers, polycarboxylate superplasticizers, etc., and can also be used after adding air-entraining agents, retarders, early strength agents, expansive agents, thickening agents, shrinkage reducing agents, and defoamers.

[0024] Except for sulfuric acid and alkaline substances, other raw materials in the present invention are common raw materials used in polycarboxylate synthesis. However, through process innovation in the present invention, the acid-ether ratio of the synthesized product is more consistent with the optimal range (3 to 4), and the water reduction rate of the product is greater. The principle of the new process is: (1) In the initial stage of the reaction, by introducing sulfuric acid, the activity of the monomers is increased, the induction period is greatly shortened, and the excessive accumulation of acrylic acid is prevented. At the same time, by using bulk polymerization, the activity gap between polyether and acrylic monomers can be reduced, so that the acid-ether ratio of the early product decreases and enters the optimal range; (2) In the middle stage of the reaction (conversion rate greater than 20 to 30%), water is added at this time, and the pH of the reaction system is adjusted to 5.5 to 6.5 with an alkaline substance to partially neutralize acrylic acid. At this time, the activity gap between polyether and acrylic monomers becomes larger again, and the acid-ether ratio of the middle-stage product increases and also enters the optimal range. The superplasticizer obtained by this polymerization method has the following advantages:

[0025] (1) Excellent water reduction ability, and the water reduction rate is increased by 10 to 20% compared with the conventional polycarboxylate water reduction ability;

[0026] (2) It has outstanding anti-sludge performance and can effectively open the initial fluidity of high-sludge-content concrete;

[0027] (3) It has strong adaptability to various admixtures, has a low dosage in the application of high-proportion admixture concrete, and can be used as a binder-reducing agent to reduce the cost of enterprises;

[0028] (4) The production process is simple. By using the one-pot method, it is simple and efficient, and can be continuously produced in the same reaction kettle. It has high reaction efficiency and short reaction time, which is basically the same as the production conditions of conventional polycarboxylate water reducers. There is no need to improve the equipment, and it is easy to achieve large-scale industrial production. Detailed implementation manners

[0029] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] The polyether monomers (double bond retention value > 98%) used in the embodiments of the present invention are produced by Nanjing Bote New Materials Co., Ltd., and other raw materials are all purchased from TCI Chemical Reagent Co., Ltd.

[0031] The polyether monomers used in the embodiments of the present invention are respectively methallyl polyoxyethylene ether (HPEG), isopentenyl polyoxyethylene ether (TPEG), 4-hydroxybutyl vinyl polyoxyethylene ether (VPEG), and diethylene glycol mono vinyl ether polyoxyethylene ether (EPEG). The numbers following the English abbreviations of the polyethers in the embodiments represent the weight average molecular weight. For example, TPEG-2400 represents isopentenyl polyoxyethylene ether with a weight average molecular weight of 2400.

[0032] The corresponding codes of the raw materials used in the embodiments and comparative examples of the present invention are shown in Table 1 below:

[0033] Raw material Code name Raw material Code name Azobisisobutyronitrile AIBN Mercaptopropionic acid MPA Azodiisovaleronitrile V-65 L-Ascorbic acid VC Dimethyl 2,2'-azobis(2-methylpropionate) V-601 Sodium formaldehyde sulfoxylate SFS Benzoyl peroxide BPO Ethylenediamine EA Mercaptoacetic acid MEA Diethylenetriamine DEA Mercaptoethanol ME Sodium acetate SA

[0034] In each embodiment and comparative example of the present application, the number average molecular weight of the polymer is measured by a gel permeation chromatograph of Wyatt technology corporation. (Gel column: two Shodex SB806 + 803 chromatographic columns in series; eluent: 0.1M NaNO3 solution; mobile phase velocity: 1.0 ml / min; detector: Shodex RI-7 differential refractive index detector; molecular weight standard: polyethylene glycol GPC standard sample (Sigma-Aldrich, molecular weights 1010000, 478000, 263000, 118000, 44700, 18600, 6690, 1960, 628, 232).

[0035] Example 1

[0036] The preparation steps of the high water-reducing polycarboxylate water reducer are as follows:

[0037] (1) Add 100 parts of VPEG-4000 into a four-necked flask equipped with a thermometer, mechanical stirrer, and N2 purge tube. Subsequently, heat it up to 90 °C to melt the polyether. After adding 0.420 parts of sulfuric acid and 0.604 parts of initiator AIBN and stirring evenly, start to dropwise add a mixed solution composed of 6.532 parts of acrylic acid and 2.119 parts of chain transfer agent ME. The dropping time is 0.1 h. Immediately after the dropping is completed, add 108.4 parts of water to terminate the reaction. The conversion rate of the product measured by GPC is 26.3%.

[0038] (2) Lower the temperature of the above reactants to 15 °C, add 0.632 parts of oxidant hydrogen peroxide. Prepare a solution by mixing 3.979 parts of acrylic acid, 0.873 parts of reducing agent VC, 0.577 parts of chain transfer agent ME, and 7.5 parts of water, and slowly drop it into the reaction system. The dropping time is 1 h. During the preparation and dropping process, use NaOH to control the pH of the reaction process to be maintained between 5.5 and 6.5 (a total of 1.394 parts of NaOH is used). After the dropping is completed, keep the reaction at a constant temperature for 1 h to ensure that the monomers react completely. Then discharge the material to obtain the water reducer sample of Example 1. The conversion rate of the final product measured by GPC is 93.9%, the molecular weight is 61313, and the solid content measured by an oven is 49.1%.

[0039] The synthesis methods of Examples 2 to 10 are the same as that of Example 1, and the specific reaction conditions are listed in the following table. Table 2 shows the types and dosages of raw materials in step (1), Table 3 shows the types and dosages of raw materials in step (2), and Table 4 shows the specific reaction conditions and product characterization data.

[0040] Table 2

[0041]

[0042] Table 3

[0043]

[0044]

[0045] Table 4

[0046]

[0047] Comparative Example 1

[0048] Add 100 parts of HPEG-2400, 0.142 parts of hydrogen peroxide and 100 parts of water into a flask equipped with a stirrer and a thermometer. Then stir and heat up to 45°C. At this temperature, dropwise add a mixed solution composed of 12 parts of acrylic acid, 0.25 parts of mercaptopropionic acid, 0.183 parts of L-ascorbic acid and 12.5 parts of water. The dropping time is 3 h. After the dropping is completed, keep warm for 1 h. Then add 4.1 g of sodium hydroxide. This is a common polycarboxylate water reducer prepared by a conventional method in the laboratory. The measured solid content is 50.1, the molecular weight measured by GPC is 31692, and the conversion rate is 94.8%.

[0049] Comparative Example 2

[0050] A commercially available high-performance polycarboxylate water reducer was purchased from an admixture company in South China. The measured solid content is 34.8, the molecular weight measured by GPC is 40615, and the conversion rate is 93.7%.

[0051] The actual acid-ether ratio of the polymer was determined by nuclear magnetic resonance method (NMR). The test instrument was a Bruker AvanceIII 400MHz NMR spectrometer. D2O was used as the solvent, and the ratio of the characteristic peak areas was taken to calculate the acid-ether ratio. During the test, when the conversion rates reached C1 (20 - 30%) and C2 (60 - 70%), a small amount of the sample was taken out and quickly put into an ice-water bath to terminate the reaction. Then the sample was put into a dialysis bag (with a cut-off molecular weight of 7000) and dialyzed in deionized water for 7 days to remove unreacted monomers. The obtained sample was freeze-dried at low temperature to remove water, and then NMR test was carried out. The test value of the sample taken out at the conversion rate C1 is the average acid-ether ratio of the product between the conversion rates of 0 - C1 (this data represents the acid-ether ratio of the early-stage product). The test value of the sample taken out at the conversion rate C2 needs to be calculated by removing the data of the product between the conversion rates of 0 - C1 and converted to the average acid-ether ratio of the product between the conversion rates of C1 - C2 (this data represents the acid-ether ratio of the mid-stage product). The test results are shown in Table 5.

[0052] Table 5

[0053]

[0054] From the analysis of the data in Table 5, it can be seen that the acid-ether ratio of the pre-stage product in Comparative Example 1 is 6.78, and that of the mid-stage product is 2.77, both of which are not within the range of 4-5 in the optimal period, which is the drawback of the conventional method for synthesizing polycarboxylic acids. In Examples 1-12, the acid-ether ratio of the pre-stage product is between 3.4 and 4.4, and that of the mid-stage product is between 3 and 3.9, which is very close to the optimal acid-ether ratio range. The above results show that the high water-reducing polycarboxylate superplasticizer described in the present invention has obvious differences in the acid-ether ratio composition of its stage products compared with the conventional polycarboxylate superplasticizer, providing a theoretical basis for further improving the performance of polycarboxylic acids. The actual acid-ether ratios of the pre-stage and mid-stage products of the samples in Examples 1-12 and Comparative Example 1 were used to verify the effect of the method described in the present invention for controlling the stage reaction.

[0055] In the following test examples, the cement used is Conch PⅡ 42.5, the mineral powder is S95 type mineral powder produced by Jiangnan Grinding Co., Ltd., the fly ash is Class I fly ash produced by Jiangsu Huanneng Electric Power Company, the sand is Yongqiang machine-made sand, and the gravel is basalt with a continuous particle size of 5-20 mm.

[0056] Test Example 1: Determination of mortar fluidity

[0057] According to the regulations in GB / T8077-2012 "Test Methods for the Homogeneity of Concrete Admixtures", the water reduction rate of the high water-reducing polycarboxylate superplasticizer synthesized in the examples of the present invention was determined to evaluate the true water reduction performance of the samples. In the test, the cement dosage was 450 g and the sand was 1350 g. The results are shown in Table 5. The solid content of the superplasticizer in Test 1 was 0.15%, and in Test 2 was 0.20%. The results are shown in Table 6.

[0058] Table 6

[0059]

[0060]

[0061] From the data in Table 6, it can be seen that in Test 1, the water reduction rate of the comparative example was 25-26%, and that of the example was 28-31%. The water reduction rate of the example was about 15% higher than that of the comparative example. The results of Test 2 were similar. The water reduction rate of the comparative example was 35-37%, and that of the example was 40-45%. The water reduction rate of the example was about 17% higher than that of the comparative example. The above results show that the high water-reducing polycarboxylate superplasticizer described in the present invention has more excellent water reduction performance compared with the conventional polycarboxylate superplasticizer.

[0062] Test Example 2: Anti-clay performance test

[0063] Montmorillonite is a typical clay that widely exists in some poor-quality materials and can greatly weaken the dispersion performance of polycarboxylic acid. Therefore, in this experiment, the method of adding montmorillonite to cement was used to mimic the mud content in the actual application environment to test the tolerance of the high water-reducing polycarboxylic acid water reducer in the examples to the mud content. Test method: The total of cement and montmorillonite is 300 g, the water-cement ratio is fixed at 0.29, and the dosage of the water reducer is adjusted so that the fluidity of the sample reaches 280 ± 5 mm without montmorillonite to clearly show the anti-mud effect of the sample. The results are shown in Table 7.

[0064] Table 7

[0065]

[0066]

[0067] Note: a = (fluidity without montmorillonite - fluidity with 1% montmorillonite) / fluidity without montmorillonite.

[0068] The data in Table 7 show that when no montmorillonite is added, the fluidity of both the examples and the comparative examples is about 280 mm. After adding 0.4% montmorillonite, the net paste fluidity of both the examples and the comparative examples decreases. The fluidity of the examples decreases to about 240 mm, and that of the comparative examples decreases to 180 mm. After adding 0.8% montmorillonite, the fluidity of the examples decreases to about 200 mm, and the comparative examples lose fluidity. This clearly shows that the high water-reducing polycarboxylic acid water reducer described in the present invention has excellent anti-mud performance.

[0069] Test Example 3: Dispersion ability test

[0070] The application effect of the high water-reducing polycarboxylic acid water reducer described in the present invention in concrete with a large amount of mineral admixtures was evaluated through a concrete fluidity test. Concrete mass mix ratio: cement 185, mineral powder 45, fly ash 75, manufactured sand 945, crushed stone 1000, water 160, sodium gluconate 0.04%. The test results are shown in Table 8.

[0071] Table 8

[0072]

[0073]

[0074] From the concrete test results in Table 8, it can be seen that to achieve a similar slump, the dosage of the examples is about 15-20% lower than that of the comparative examples with a lower dosage. This once again demonstrates the fact that the water reduction of the example samples is relatively large. Additionally, in this test, when the proportion of mineral admixture is as high as 38.3%, the dosage of the example samples is relatively low, and the concrete strength can still reach above 37 Mpa at 28 days, which is 1-3 Mpa higher than that of the comparative examples. This shows that the high water-reducing polycarboxylate water reducer described in the present invention is very suitable for use in concrete with a relatively large proportion of mineral admixture, and well meets the actual needs of current users.

[0075] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of a high water-reducing polycarboxylate water reducer, characterized in that, It includes the following steps: (1) After putting sulfuric acid and an initiator into the polyether monomer, immediately start dropping acrylic monomer and a chain transfer agent. After the dropping reaction for 0.1 - 1 h, add water to terminate the reaction; (2) Add an oxidizing agent to the reaction solution in step (1). Prepare a solution of acrylic monomer, a reducing agent, and a chain transfer agent and slowly drop it into the reaction system. During the dropping process, use an alkaline substance to control the pH of the reaction process to be maintained between 5.5 and 6.

5. After the dropping is completed, keep the reaction at a certain temperature for 1 - 2 h, and then the product can be discharged. In step (1), the mass ratio of the polyether monomer, acrylic monomer, sulfuric acid, initiator, and chain transfer agent is 100:(2 - 7):(0.3 - 0.5):(0.1 - 2):(0.8 - 3); In step (2), the mass ratio of the acrylic monomer, oxidizing agent, reducing agent, chain transfer agent, and the polyether monomer in step (1) is (3 - 7):(0.5 - 2):(0.4 - 1):(0.2 - 1.2):

100.

2. The preparation method of a high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The structural formula of the polyether monomer is shown as the following general formula (I): R1 is -H or -CH3, R2 is -OCH2CH2-, -OCH2CH2CH2CH2-, -CH2-, -CH2CH2-; n is an integer from 45 to 90.

3. The preparation method of a high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The initiator is selected from any one or a combination of azobisisobutyronitrile, azobisisoheptonitrile, dimethyl 2,2'-azobis(2-methylpropionate), benzoyl peroxide; the chain transfer agent is selected from any one or a combination of mercaptoacetic acid, mercaptopropionic acid, mercaptoethanol.

4. The preparation method of a high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The oxidizing agent is selected from any one or a combination of hydrogen peroxide, ammonium persulfate, sodium persulfate, potassium persulfate; the reducing agent is selected from any one or a combination of L-ascorbic acid, sodium formaldehyde sulfoxylate, sodium sulfite, sodium bisulfite, ferrous sulfate.

5. The preparation method of a high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: The alkaline substance is selected from any one or a combination of sodium hydroxide, potassium hydroxide, pyridine, ethylenediamine, triethylamine, diethylenetriamine, sodium acetate.

6. The preparation method of a high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: In step (1), the reaction temperature is 60 - 90 °C; the amount of water added to terminate the reaction in step (1) makes the concentration of the reaction system 50 - 60%.

7. The preparation method of a high water-reducing polycarboxylate water reducer according to claim 1, characterized in that: In step (2), the reaction temperature is 15 - 50 °C; the dropping time of the solution prepared from acrylic monomer, reducing agent, and chain transfer agent is 1 - 5 h.

8. A high water-reducing polycarboxylate water reducer obtained by the preparation method according to any one of claims 1 - 7.

9. A high water-reducing polycarboxylate water reducer according to claim 8, characterized in that: The high water-reducing polycarboxylate water reducer has a weight-average molecular weight of 20,000 - 80,000.

10. The application method of a high water-reducing polycarboxylate water reducer according to claim 8, characterized in that: When the water reducer is applied to a cement concrete system, the dosage of the water reducer is 0.05% - 0.3% of the total mass of the binder.

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