Micro-crosslinking viscosity-reducing polycarboxylic water-reducing agent and preparation method thereof

Abstract

The application discloses a kind of micro-crosslinking viscosity-reducing polycarboxylate water-reducing agent and preparation method thereof, comprising: halogenation is carried out to the first unsaturated polyether macromonomer end, then it is reacted with low molecular weight partial alcoholysis grade polyvinyl alcohol to obtain modified polyvinyl alcohol structure containing unsaturated polyether macromonomer side chain;Modified polyvinyl alcohol structure is polymerized with maleic anhydride and low molecular weight second unsaturated polyether macromonomer to obtain micro-crosslinking viscosity-reducing polycarboxylate water-reducing agent.The water-reducing agent prepared by the method of the application has high molecular chain extension degree, can be quickly adsorbed on cement particles, not only has excellent dispersion and dispersion retention capacity, but also can effectively reduce the viscosity of cement concrete system slurry.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polycarboxylic water-reducing agent for cement concrete, and particularly relates to a micro-crosslinking viscosity-reducing polycarboxylic water-reducing agent and a preparation method thereof. BACKGROUND

[0002] With the improvement of the performance requirements of concrete in construction engineering, the traditional water-reducing agent has certain limitations in improving the fluidity of concrete and reducing the water-binder ratio. Especially in the application of high-strength concrete, how to reduce the water-binder ratio while ensuring the workability and strength of concrete has become a key technical problem. The existing solutions mainly focus on increasing the air content, increasing the water-reducing agent content and optimizing the particle size distribution. Among them, increasing the air content has a viscosity-reducing effect to a certain extent, but the content is sensitive and difficult to control, and too much content will have a negative effect on the viscosity and strength of concrete. Increasing the water-reducing agent content is prone to segregation and other problems, and optimizing the particle size distribution has certain limitations in engineering application due to the lack of high-quality materials.

[0003] In recent years, some scholars have also started from the structure, reduced the molecular weight of the water-reducing agent, introduced hydrophobic groups, or reduced the length of the side chain to release more free water, thereby reducing the viscosity of the concrete. Patent with publication number CN109749020A and publication date May 14, 2019, entitled "Early-strength viscosity-reducing polycarboxylic water-reducing agent containing alkyl groups and preparation method thereof" reports an early-strength viscosity-reducing polycarboxylic water-reducing agent by introducing a large number of hydrophobic alkyl groups into the side chain. This method reduces the combination of water-reducing agent and water, quickly disperses, and releases more free water to achieve the purpose of reducing viscosity. Patent with publication number CN110172128A and publication date August 27, 2019, entitled "Brush-type polycarboxylic high-efficiency viscosity-reducing water-reducing agent and preparation method thereof" reports a brush-type polycarboxylic water-reducing agent with good viscosity-reducing effect. The water-reducing agent prepared by this method has a smaller hydrodynamic volume due to the brush-type structure, and has a strong adsorption capacity due to the small molecular weight and high degree of freedom. However, the small molecular weight also limits its dispersion retention performance. Patent with publication number CN116102691A and publication date May 12, 2023, entitled "Viscosity-reducing water-reducing agent for high-strength concrete and preparation method thereof" reports a viscosity-reducing water-reducing agent for high-strength concrete and a preparation method thereof. This method introduces ester hydrophobic monomers, which are not easy to intertwine with each other, thereby improving the fluidity of concrete and having good viscosity-reducing effect. However, too much ester monomer will easily cause strong hydrophobic association effect and increase viscosity. SUMMARY

[0004] 1. The technical problem to be solved:

[0005] In view of the above technical problems, the present application provides a kind of micro-crosslinking viscosity-reducing polycarboxylate superplasticizer and its preparation method, from the structure of superplasticizer, by introducing multi-carboxyl adsorption group to improve the adsorption capacity of superplasticizer, by introducing short polyether side chain with certain hydrophobic structure, reduce the solid-liquid interface energy of cement particles, improve the dispersion and dispersion retention capacity of superplasticizer in cement particles, and by designing a certain micro-crosslinking structure, ensure the water-reducing and slump-retaining performance, while the thickness of the adsorption layer increases, the thickness of the water film layer on the surface of cement particles is compressed, more free water is released, the dispersion performance of cement particles is improved, and the viscosity of cement concrete system is further reduced

[0006] 2. Technical scheme:

[0007] A kind of micro-crosslinking viscosity-reducing polycarboxylate superplasticizer, characterized by the structure as follows:

[0008]

[0009] In the above formula, the polymerization degree m, n and r are each independently 1-100; the polymerization degree a and b are each independently 1-25; R1 and R2 are each one or a combination of two or more of -CH2-, -CH2CH2-, -OCH2CH2- or -OCH2CH2CH2CH2-; R3 and R4 are each one or a combination of two of H or -CH3; R5 is one or a combination of two or more of -CH3, -CH2CH3 or -CH2CH2CH3; and the wavy line is a low molecular weight partially alcoholized polyvinyl alcohol main chain structure.

[0010] A preparation method of a micro-crosslinking viscosity-reducing polycarboxylate superplasticizer, comprising the following steps:

[0011] Step one: terminal halogenation reaction of the first unsaturated polyether macromonomer and epoxy halopropane under the action of boron trifluoride ether, and then adding low molecular weight partially alcoholized polyvinyl alcohol into the solvent to generate modified polyvinyl alcohol structure containing unsaturated polyether macromonomer side chain through etherification reaction at 10-50 DEG C with acid binding agent;

[0012] Step two: the modified polyvinyl alcohol structure obtained in step one is subjected to oxidation-reduction free radical polymerization reaction at 10-50 DEG C with maleic anhydride and low molecular weight second unsaturated polyether macromonomer under the joint action of initiator, reducing agent and chain transfer agent to obtain the target micro-crosslinking viscosity-reducing polycarboxylate superplasticizer; wherein the molar ratio of the modified polyvinyl alcohol structure, maleic anhydride, low molecular weight second unsaturated polyether macromonomer, initiator, reducing agent and chain transfer agent is (0.01-0.05):(2-6):1:(0.02-0.2):(0.02-0.15):(0.02-0.15).

[0013] Further, in step one, the first unsaturated polyether macromonomer is any one or a combination of two or more of allyl polyoxyethylene ether, methallyl polyoxyethylene ether, prenyl polyoxyethylene ether, or vinyl polyoxyethylene ether, with a weight average molecular weight of 1000-3000 g / mol.

[0014] Further, in step one, the epoxy halopropane is any one or a combination of two or more of epoxy chloropropane, epoxy bromopropane, or epoxy fluoropropane.

[0015] Further, in step one, the low molecular weight partially alcoholized polyvinyl alcohol has a weight average molecular weight of 1000-5000 g / mol and an alcoholization degree of 70%-80%.

[0016] Further, in step one, the solvent is a mixed solvent of a main solvent and water; wherein the main solvent is any one or a combination of two or more of acetonitrile, acetone, dichloromethane, chloroform, dimethyl sulfoxide, N,N-dimethylformamide, or 1,2-dichloroethane, and the volume ratio of the main solvent to water is 1:(1-30); and the acid binding agent is any one or a combination of two or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, 4-dimethylaminopyridine, diethylamine, or triethylamine.

[0017] Further, the modified polyvinyl alcohol structure containing the unsaturated polyether macromonomer side chain generated in step one is as follows:

[0018]

[0019] In the above formula, the polymerization degree m is 1-100; R1 is any one or a combination of two or more of -CH2-, -CH2CH2-, -OCH2CH2-, or -OCH2CH2CH2CH2-; R3 is any one or a combination of two of H or -CH3; and the wavy line is the low molecular weight partially alcoholized polyvinyl alcohol backbone structure.

[0020] Further, in step two, the low molecular weight second unsaturated polyether macromonomer has a molecular weight of 500-1000 g / mol and a structure as follows:

[0021]

[0022] In the above formula, the polymerization degrees a and b are each independently 1-25; R2 is any one or a combination of two or more of -CH2-, -CH2CH2-, -OCH2CH2-, or -OCH2CH2CH2CH2-; R4 is any one or a combination of two of H or -CH3; and R5 is any one or a combination of two or more of -CH3, -CH2CH3, or -CH2CH2CH3.

[0023] Further, in step two, the initiator is any one or a combination of two or more of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, azobisisobutyronitrile or azobisisoheptyl nitrile; the reducing agent is any one or a combination of two or more of vitamin C, sodium sulfite, sodium bisulfite, sodium metabisulfite or sodium hypophosphite; and the chain transfer agent is any one or a combination of two or more of mercaptoacetic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptoethanol, dodecanethiol or sodium methallyl sulfonate.

[0024] 3. Beneficial effects:

[0025] (1) The polycarboxylic acid water reducing agent prepared by the method has a lower molecular weight and a lower alcoholysis degree, and has a short polyether side chain with a certain hydrophobic structure, thereby improving the freedom of the water reducing agent molecules, reducing the generation of bound water, reducing the solid-liquid interface energy of cement particles, and improving the dispersion and dispersion retention capacity of the water reducing agent on the cement particles.

[0026] (2) The polycarboxylic acid water reducing agent prepared by the method has a high adsorption group density and a high adsorption speed, and can quickly disperse the cement particles and reduce the viscosity of the cement concrete system.

[0027] (3) The polycarboxylic acid water reducing agent prepared by the method has a certain micro-crosslinking structure, which improves the stability of the water reducing agent on the cement particles, ensures the water reducing and slump retaining properties, and reduces the thickness of the water film layer on the surface of the cement particles with the increase of the thickness of the adsorption layer, thereby releasing more free water, improving the dispersion performance of the cement particles, and further reducing the viscosity of the cement concrete system.

[0028] (4) The polycarboxylic acid water reducing agent prepared by the method has a rich raw material source, a simple synthesis method, and is easy to industrialize. DETAILED DESCRIPTION

[0029] The application will be specifically described below with reference to specific examples.

[0030] In the following specific examples, the structure of the water reducing agent is as follows:

[0031]

[0032] Example 1

[0033] Step S01: Methyl allyl polyoxyethylene ether (0.05 mol, Mw = 2000 g / mol) and epichlorohydrin (0.06 mol) are subjected to a terminal halogenation reaction in the presence of boron trifluoride etherate (0.1 mol), and then reacted with polyvinyl alcohol (0.02 mol, Mw = 1500 g / mol, degree of alcoholysis 70%) in acetonitrile / water (120 mL, volume ratio of 1:20) at 35° C. with diethylamine (0.1 mol) to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain through an etherification reaction;

[0034] Step S02: The modified polyvinyl alcohol structure (0.02 mol) obtained in step S01 is reacted with maleic anhydride (4 mol) and a low molecular weight second unsaturated polyether macromonomer (1 mol, Mw = 800 g / mol) in the presence of ammonium persulfate (0.08 mol), sodium bisulfite (0.11 mol) and 3-mercaptopropionic acid (0.1 mol) at 35° C. to undergo an oxidation-reduction free radical polymerization reaction to obtain the target slightly cross-linked viscosity-reducing polycarboxylate water reducer.

[0035] The structural formula of the water-reducing agent generated is as follows: the polymerization degrees m, n, r, a and b are 44, 4, 1, 2 and 11 respectively; R2 is -CH2CH2-; R4 is H; and R5 is -CH3.

[0036] Example 2

[0037] Step S01: isopentanol polyoxyethylene ether (0.06 mol, Mw = 1500 g / mol) and epichlorohydrin (0.07 mol) are subjected to a terminal halogenation reaction in the presence of boron trifluoride etherate (0.1 mol), and then reacted with polyvinyl alcohol (0.03 mol, Mw = 2000 g / mol, degree of alcoholysis 75%) in chloroform / water (120 mL, volume ratio of 1:25) at 25° C. with triethylamine (0.1 mol) to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain through an etherification reaction;

[0038] Step S02: The modified polyvinyl alcohol structure (0.03 mol) obtained in step S01 is reacted with maleic anhydride (5 mol) and a low molecular weight second unsaturated polyether macromonomer (1 mol, Mw = 500 g / mol) in the presence of potassium persulfate (0.07 mol), vitamin C (0.08 mol) and dodecanethiol (0.07 mol) at 35° C. to undergo an oxidation-reduction free radical polymerization reaction to obtain the target slightly cross-linked viscosity-reducing polycarboxylate water reducer.

[0039] The structural formula of the water-reducing agent generated is as follows: the polymerization degrees m, n, r, a and b are 32, 5, 1, 1 and 6 respectively; R2 is -CH2-; R4 is -CH3; and R5 is -CH2CH3.

[0040] Example 3

[0041] Step S01: the terminal halogenation reaction of allyl polyoxyethylene ether (0.08 mol, Mw = 2200 g / mol) with epichlorohydrin (0.09 mol) under the action of boron trifluoride ether (0.1 mol), and then etherification reaction with polyvinyl alcohol (0.03 mol, Mw = 4000 g / mol, alcoholysis degree 70%) in acetone / water (100 mL, volume ratio 1:20) at 30°C with sodium hydroxide (0.1 mol) to generate a modified polyvinyl alcohol structure containing unsaturated polyether macromonomer side chains;

[0042] Step S02: oxidative-reductive radical polymerization reaction of the modified polyvinyl alcohol structure (0.03 mol) obtained in step S01 with maleic anhydride (3 mol) and low molecular weight second unsaturated polyether macromonomer (1 mol, Mw = 1000 g / mol) under the joint action of hydrogen peroxide (0.1 mol), sodium metabisulfite (0.13 mol) and 2-mercapto propionic acid (0.1 mol) at 35°C to obtain the target micro-crosslinking viscosity-reducing polycarboxylic acid water reducer.

[0043] The structure of the water reducing agent generated is: the polymerization degrees m, n, r, a and b are 49, 3, 1, 2 and 10 respectively, R2 is -OCH2CH2-, R4 is H, and R5 is -CH2CH2CH3.

[0044] Example 4

[0045] Step S01: terminal halogenation reaction of vinyl polyoxyethylene ether (0.08 mol, Mw = 1200 g / mol) with epoxy bromopropane (0.09 mol) under the action of boron trifluoride ether (0.1 mol), and then etherification reaction with polyvinyl alcohol (0.05 mol, Mw = 2000 g / mol, alcoholysis degree 70%) in dimethyl sulfoxide / water (150 mL, volume ratio 1:15) at 20°C with sodium carbonate (0.1 mol) to generate a modified polyvinyl alcohol structure containing unsaturated polyether macromonomer side chains;

[0046] Step S02: oxidative-reductive radical polymerization reaction of the modified polyvinyl alcohol structure (0.05 mol) obtained in step S01 with maleic anhydride (5 mol) and low molecular weight second unsaturated polyether macromonomer (1 mol, Mw = 800 g / mol) under the joint action of ammonium persulfate (0.09 mol), vitamin C (0.13 mol) and sodium methallyl sulfonate (0.12 mol) at 30°C to obtain the target micro-crosslinking viscosity-reducing polycarboxylic acid water reducer.

[0047] The structure of the water reducing agent generated is: the polymerization degrees m, n, r, a and b are 26, 5, 1, 1 and 11 respectively, R2 is -OCH2CH2CH2CH2-, R4 is -CH3, and R5 is -CH3.

[0048] Example 5

[0049] Step S01: terminal halogenation reaction of methyl allyl polyoxyethylene ether (0.03 mol, Mw = 3000 g / mol) with epichlorohydrin (0.04 mol) under the action of boron trifluoride etherate (0.1 mol), and then etherification reaction with polyvinyl alcohol (0.02 mol, Mw = 3000 g / mol, alcoholysis degree 70%) in N, N-dimethylformamide / water (160 mL, volume ratio 1:30) at 35°C with potassium hydroxide (0.1 mol) to generate a modified polyvinyl alcohol structure containing unsaturated polyether macromonomer side chains;

[0050] Step S02: oxidative-reductive radical polymerization reaction of the modified polyvinyl alcohol structure (0.02 mol) obtained in step S01 with maleic anhydride (6 mol) and a low molecular weight second unsaturated polyether macromonomer (1 mol, Mw = 600 g / mol) under the joint action of azobisisobutyronitrile (0.16 mol), sodium bisulfite (0.14 mol) and 3-mercaptopropionic acid (0.13 mol) at 25°C to obtain the target micro-crosslinking viscosity reducing polycarboxylic acid water reducing agent.

[0051] The structure of the water reducing agent generated is: the polymerization degrees m, n, r, a and b are 66, 6, 1, 1 and 9 respectively, R2 is -CH2-, R4 is H, and R5 is -CH3.

[0052] Example 6

[0053] Step S01: terminal halogenation reaction of isopentenyl polyoxyethylene ether (0.07 mol, Mw = 2600 g / mol) with epifluorohydrin (0.08 mol) under the action of boron trifluoride etherate (0.1 mol), and then etherification reaction with polyvinyl alcohol (0.04 mol, Mw = 3000 g / mol, alcoholysis degree 70%) in acetonitrile / water (140 mL, volume ratio 1:15) at 30°C with potassium carbonate (0.1 mol) to generate a modified polyvinyl alcohol structure containing unsaturated polyether macromonomer side chains;

[0054] Step S02: oxidative-reductive radical polymerization of the modified polyvinyl alcohol structure (0.04 mol) obtained in step S01 with maleic anhydride (4 mol) and a low-molecular-weight second unsaturated polyether macromonomer (1 mol, Mw = 500 g / mol) in the presence of ammonium persulfate (0.06 mol), sodium pyrosulfite (0.12 mol) and mercaptoethanol (0.07 mol) at 45°C to obtain the target micro-crosslinking viscosity-reducing polycarboxylic acid water reducer.

[0055] The structure of the water reducer generated thereby is as follows: the polymerization degrees m, n, r, a and b are 57, 4, 1, 1 and 4 respectively, R2 is -OCH2CH2-, R4 is -CH3, and R5 is -CH2CH2CH3.

[0056] Example 7

[0057] Step S01: terminal halogenation of methylallyl polyoxyethylene ether (0.02 mol, Mw = 3000 g / mol) with epibromohydrin (0.03 mol) in the presence of boron trifluoride diethyl ether (0.1 mol), followed by etherification of the product with polyvinyl alcohol (0.01 mol, Mw = 2500 g / mol, alcoholysis degree 80%) in N,N-dimethylformamide / water (150 mL, volume ratio 1:20) at 35°C using diethylamine (0.1 mol) to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain;

[0058] Step S02: oxidative-reductive radical polymerization of the modified polyvinyl alcohol structure (0.01 mol) obtained in step S01 with maleic anhydride (5 mol) and a low-molecular-weight second unsaturated polyether macromonomer (1 mol, Mw = 800 g / mol) in the presence of sodium persulfate (0.1 mol), sodium hypophosphite (0.1 mol) and 3-mercaptopropionic acid (0.12 mol) at 25°C to obtain the target micro-crosslinking viscosity-reducing polycarboxylic acid water reducer.

[0059] The structure of the water reducer generated thereby is as follows: the polymerization degrees m, n, r, a and b are 66, 5, 1, 2 and 9 respectively, R2 is -CH2CH2-, R4 is H, and R5 is -CH2CH3.

[0060] Example 8

[0061] Step S01: end halogenation reaction of vinyl polyoxyethylene ether (0.04 mol, Mw = 2200 g / mol) with epichlorohydrin (0.05 mol) under the action of boron trifluoride ether (0.1 mol), and then etherification reaction with polyvinyl alcohol (0.02 mol, Mw = 2000 g / mol, alcoholysis degree 70%) in chloroform / water (180 mL, volume ratio 1:30) at 35°C with sodium hydroxide (0.1 mol) to form a modified polyvinyl alcohol structure containing unsaturated polyether macromonomer side chains;

[0062] Step S02: oxidative-reductive radical polymerization of the modified polyvinyl alcohol structure (0.02 mol) obtained in step S01 with maleic anhydride (2 mol) and a low molecular weight second unsaturated polyether macromonomer (1 mol, Mw = 1000 g / mol) under the action of ammonium persulfate (0.11 mol), vitamin C (0.1 mol) and 3-mercaptopropionic acid (0.1 mol) at 15°C to obtain the target micro-crosslinked viscosity-reducing polycarboxylic acid water reducing agent.

[0063] The structure of the water reducing agent generated is: the polymerization degrees m, n, r, a and b are 48, 2, 1, 3 and 4 respectively, R2 is -CH2-; R4 is -CH3; and R5 is -CH3.

[0064] Comparative Example 1

[0065] The difference from Example 1 is that step S01 is not performed, and the first unsaturated polyether macromonomer, maleic anhydride and the second unsaturated macromonomer are directly subjected to radical polymerization, without preparing a micro-crosslinked structure.

[0066] Comparative Example 2

[0067] Common high-performance polycarboxylic acid water reducing agent ART-JR1.

[0068] Comparative Example 3

[0069] Commercially available HPWR-S type water reducing agent meeting the standard of GB 8076-2008 "Concrete Admixture".

[0070] Test Example

[0071] 1. Marsh time test of cement paste

[0072] The water-binder ratio is set to 0.29 and 0.20, respectively, and the cement paste fluidity is adjusted to (200±5) mm, (240±5) mm and (280±5) mm by adjusting the dosage of the water reducing agent. 300 g of paste is weighed and poured into a funnel, and the flow time is recorded as the Marsh time of the cement paste.

[0073] The results show that when the water-binder ratio is 0.29, the cement paste fluidity reaches (200±5) mm, (240±5) mm, (280±5) mm respectively, the Marsh time of examples 1-8 relative to comparative examples 1-3 is reduced by 54.9s, 53.3s and 49.9s on average respectively. When the water-binder ratio is 0.20, the cement paste fluidity reaches (200±5) mm, (240±5) mm, (280±5) mm respectively, the Marsh time of examples 1-8 relative to comparative examples 1-3 is reduced by 59.0s, 58.3s and 58.1s on average respectively. This shows that the prepared examples of the application can effectively reduce the viscosity of the cement paste.

[0074] Table 1 Marsh time of cement paste of different samples

[0075]

[0076]

[0077] 2. Concrete performance test

[0078] According to GB 8076-2008 "Concrete Admixture", the initial slump / spread of concrete, the 1h time loss of slump / spread, the slump reversal time, and the strength of concrete test of the samples of examples 1 to 8 and comparative examples 1 to 3 were determined, the water reducing agent content was controlled to make the initial spread of concrete 600±10, the concrete mix ratio is shown in Table 2, and the concrete test results are shown in Table 3.

[0079] From the results, it can be seen that compared with comparative examples 1-3, the dosage required by examples 1-8 to achieve the same spread is lower, and the slump reversal time is shorter, indicating that examples 1-8 have better dispersion, dispersion retention and viscosity reduction ability in the cement concrete system. Comparing example 1 with comparative example 1 shows that the micro-crosslinking structure of the application has a promoting effect on the dispersion effect of cement particles and the reduction of cement paste viscosity. In addition, examples 1-8 also have an overall strength improvement effect relative to comparative examples 1-3.

[0080] Table 2 Concrete mix ratio (kg / m 3 )

[0081] cement fly ash sand stone water 450 70 760 980 160

[0082] Table 3 Concrete performance test results of different samples

[0083]

[0084]

[0085] Although the present application has been disclosed in its preferred embodiments with reference to the accompanying drawings, it is not intended to limit the present application thereto, and various changes or modifications can be made thereto by those skilled in the art without departing from the spirit and scope of the present application, and the scope of protection of the present application should be defined by the scope of protection of the claims.

Claims

1.A method for preparing a micro-crosslinking viscosity-reducing polycarboxylate superplasticizer, comprising the following steps: Step 1: carrying out a terminal halogenation reaction on a first unsaturated polyether macromonomer and an epoxy halopropane in the presence of boron trifluoride etherate, and then adding a low-molecular-weight partially alcoholized polyvinyl alcohol into a solvent to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain through an etherification reaction with an acid-binding agent at 10-50 ℃; Step 2: carrying out an oxidation-reduction radical polymerization reaction on the modified polyvinyl alcohol structure obtained in Step 1, maleic anhydride and a low-molecular-weight second unsaturated polyether macromonomer in the presence of an initiator, a reducing agent and a chain transfer agent at 10-50 ℃ to obtain a target micro-crosslinking viscosity-reducing polycarboxylate superplasticizer; wherein the molar ratio of the modified polyvinyl alcohol structure, the maleic anhydride, the low-molecular-weight second unsaturated polyether macromonomer, the initiator, the reducing agent and the chain transfer agent is (0.01-0.05) :(2-6) :1:(0.02-0.2):(0.02-0.15):(0.02-0.15) ; in Step 1, the low-molecular-weight partially alcoholized polyvinyl alcohol has a weight-average molecular weight of 1000-5000 g / mol and an alcoholization degree of 70%-80%; in Step 2, the low-molecular-weight second unsaturated polyether macromonomer has a molecular weight of 500-1000 g / mol; in Step 1, the first unsaturated polyether macromonomer is any one or a combination of two or more of allyl polyoxyethylene ether, methylallyl polyoxyethylene ether, iso-pentenyl alcohol polyoxyethylene ether and vinyl polyoxyethylene ether, and has a weight-average molecular weight of 1000-3000 g / mol; in Step 1, the epoxy halopropane is any one or a combination of two of epoxy chloropropane and epoxy bromopropane; in Step 1, the solvent is a mixed solvent of a main solvent and water; wherein the main solvent is any one or a combination of two or more of acetonitrile, acetone, dichloromethane, chloroform, dimethyl sulfoxide, N, N-dimethylformamide and 1, 2-dichloroethane, and the volume ratio of the main solvent to water is 1:(1-30); and the acid-binding agent is any one or a combination of two or more of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, 4-dimethylamino pyridine, diethylamine and triethylamine; in Step 2, the initiator is any one or a combination of two or more of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, azobis isobutyronitrile and azobis isoheptyl nitrile; the reducing agent is any one or a combination of two or more of vitamin C, sodium sulfite, sodium hydrogen sulfite, sodium pyrosulfite and sodium hypophosphite; and the chain transfer agent is any one or a combination of two or more of mercaptoacetic acid, 2-mercapto propionic acid, 3-mercapto propionic acid, mercaptoethanol, dodecanethiol and sodium methylallyl sulfonate. 5.A micro-crosslinking viscosity-reducing polycarboxylate superplasticizer prepared by the method according to any one of claims 1-4. ​ ​ ​ ​ 2. The method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent according to claim 1, wherein: ​ 3. The preparation method of the micro-cross-linked viscosity-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: ​ 4. The preparation method of the micro-cross-linked viscosity-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: ​ ​

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