Micro-crosslinking viscosity reduction type polycarboxylate superplasticizer and preparation method thereof

Abstract

The preparation method comprises the following steps: halogenating the tail end of a first unsaturated polyether macromonomer, and then carrying out etherification reaction on the first unsaturated polyether macromonomer and low-molecular-weight partial alcoholysis-grade polyvinyl alcohol to obtain a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain; and carrying out free radical polymerization on the modified polyvinyl alcohol structure, maleic anhydride and a low-molecular-weight second unsaturated polyether macromonomer to prepare the micro-crosslinking viscosity reduction type polycarboxylic acid water reducer. The water reducing agent prepared by the method is high in molecular chain stretching degree, can be quickly adsorbed on cement particles, has excellent dispersion and dispersion maintaining capability, and can effectively reduce the viscosity of cement concrete system slurry.

Description

Technical Field

[0001] The invention relates to the technical field of polycarboxylate water reducers for cement concrete, and in particular to a slightly cross-linked viscosity-reducing polycarboxylate water reducer and a preparation method thereof. Background Art

[0002] As construction projects have higher requirements for concrete performance, traditional water reducers have certain limitations in improving concrete fluidity and reducing the water-cement ratio. Especially in the application of high-strength concrete, how to reduce the water-cement ratio while ensuring the workability and strength of concrete has become a key technical problem. Existing solutions mainly focus on increasing air content, increasing the amount of water reducer, and optimizing particle grading. Among them, although increasing air content has a viscosity-reducing effect to a certain extent, the amount is sensitive and difficult to control. Too much addition will have a counter-effect on the viscosity and strength of concrete. Increasing the amount of water reducer is prone to segregation and other problems. Optimizing particle grading has certain limitations in engineering applications due to the lack of high-quality materials and other problems.

[0003] In recent years, some scholars have also started from the structure, by reducing the molecular weight of the water reducer, introducing hydrophobic groups, or by reducing the length of the side chain to achieve the purpose of releasing more free water, thereby reducing the viscosity of the concrete. The patent with the publication number CN109749020A and the publication date of May 14, 2019, entitled "An early strength and viscosity reduction polycarboxylate water reducer containing alkyl groups and its preparation method" reports an early strength and viscosity reduction polycarboxylate water reducer by introducing a large number of hydrophobic alkyl groups in the side chain. This method reduces the combination of water reducer and water, quickly disperses, and releases more free water to achieve the purpose of viscosity reduction. The patent with the publication number of CN110172128A and the publication date of August 27, 2019, entitled "A brush-type polycarboxylic acid high-efficiency viscosity-reducing water-reducing agent and its preparation method", reports a brush-type polycarboxylic acid 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 due to the small molecular weight and high degree of freedom, it exhibits strong adsorption capacity, but the small molecular weight also limits its dispersion retention performance. The patent with the publication number of CN116102691A and the publication date of May 12, 2023, entitled "Viscosity-reducing water-reducing agent for high-strength concrete and its preparation method", reports a viscosity-reducing water-reducing agent for high-strength concrete and its preparation method. This method introduces ester hydrophobic monomers to make them less likely to entangle with each other, improve the fluidity of concrete, and have a good viscosity-reducing effect, but the introduction of too much ester monomers can easily cause a strong hydrophobic association effect, which plays a viscosity-increasing role. Summary of the invention

[0004] 1. Technical problems to be solved:

[0005] In view of the above technical problems, the present invention provides a micro-crosslinked viscosity-reducing polycarboxylic acid water-reducing agent and a preparation method thereof. Starting from the structure of the water-reducing agent, the adsorption capacity of the water-reducing agent is improved by introducing a multi-carboxyl adsorption group, and the solid-liquid interface energy of cement particles is reduced by introducing a short polyether side chain with a certain hydrophobic structure, thereby improving the dispersion and dispersion retention ability of the water-reducing agent in the cement particles. Moreover, by designing a certain micro-crosslinked structure, while ensuring the water-reducing and slump-retaining performance, the thickness of the water film layer on the surface of the cement particles is compressed as the thickness of the adsorption layer increases, thereby releasing more free water, improving the dispersion performance of the cement particles, and further reducing the viscosity of the cement concrete system.

[0006] 2. Technical solution:

[0007] A slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent, characterized in that: its structure is as follows:

[0008]

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

[0010] A method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent comprises the following steps:

[0011] Step 1: subjecting the first unsaturated polyether macromonomer to a terminal halogenation reaction with an epoxyhalogenated propane under the action of boron trifluoride etherate, and then adding the first unsaturated polyether macromonomer and a low molecular weight partially alcoholysed polyvinyl alcohol to a solvent, and reacting the first unsaturated polyether macromonomer with an acid-binding agent at 10 to 50° C. to form an unsaturated polyether macromonomer side chain modified polyvinyl alcohol structure through an etherification reaction;

[0012] Step 2: The modified polyvinyl alcohol structure obtained in step 1 is subjected to an oxidation-reduction free radical polymerization reaction at 10-50° C. with 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 to obtain a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent; wherein the molar ratio of the modified polyvinyl alcohol structure, 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).

[0013] Furthermore, in step one, the first unsaturated polyether macromonomer is any one of allyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, isopentanol polyoxyethylene ether or vinyl polyoxyethylene ether, or a combination of two or more thereof, and has a weight average molecular weight of 1000 to 3000 g / mol.

[0014] Furthermore, in step 1, the epihalohydrin is any one of epichlorohydrin, epibromohydrin or epifluorohydrin, or a combination of two or more thereof.

[0015] Furthermore, in step 1, the weight average molecular weight of the low molecular weight partially alcoholysis grade polyvinyl alcohol is 1000 to 5000 g / mol, and the alcoholysis degree is 70% to 80%.

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

[0017] Furthermore, the structure of the modified polyvinyl alcohol containing unsaturated polyether macromonomer side chains generated in step 1 is as follows:

[0018]

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

[0020] Furthermore, in step 2, the low molecular weight second unsaturated polyether macromonomer has a molecular weight of 500 to 1000 g / mol and a structure of:

[0021]

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

[0023] Furthermore, in step 2, the initiator is any one of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, azobisisobutyronitrile or azobisisoheptanenitrile, or a combination of two or more thereof; the reducing agent is any one of vitamin C, sodium sulfite, sodium bisulfite, sodium pyrosulfite or sodium hypophosphite, or a combination of two or more thereof; the chain transfer agent is any one of thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptoethanol, dodecanethiol or sodium methyl methacrylate sulfonate, or a combination of two or more thereof.

[0024] 3. Beneficial effects:

[0025] (1) The polycarboxylate water reducer prepared by the present invention uses polyvinyl alcohol with a small molecular weight and a low alcoholysis degree as a raw material, and introduces a short polyether side chain with a certain hydrophobic structure, thereby increasing the degree of freedom of the water reducer molecule and reducing the generation of bound water, thereby reducing the solid-liquid interface energy of cement particles and improving the dispersion and dispersion retention ability of the water reducer on cement particles.

[0026] (2) The polycarboxylate water reducer prepared by the present invention increases the adsorption group density of the water reducer by introducing polycarboxyl maleic anhydride, increases the adsorption rate of the water reducer, quickly disperses cement particles, and reduces the viscosity of the cement concrete system.

[0027] (3) The polycarboxylate water reducer prepared by the present invention has a certain micro-crosslinking structure, which improves the adsorption stability of the water reducer on cement particles, ensures the water reduction and slump retention performance, and compresses the thickness of the water film layer on the surface of the cement particles as the thickness of the adsorption layer increases, releases more free water, improves the dispersion performance of cement particles, and further reduces the viscosity of the cement concrete system.

[0028] (4) The polycarboxylic acid water reducer is prepared by this method, and its raw material source is abundant, the synthesis method is simple, and it is easy to industrialize. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below with reference to specific embodiments.

[0030] In the following specific examples, the water reducing agent structure 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 terminal halogenation reaction under the action of boron trifluoride etherate (0.1 mol), and then it is reacted with polyvinyl alcohol (0.02 mol, Mw=1500 g / mol, alcoholysis degree 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 a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent.

[0035] The generated water reducing agent has the structural formula of: the polymerization degrees m, n, r, a and b are 44, 4, 1, 2 and 11 respectively, R2 is -CH2CH2-; R4 is H; 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 terminal halogenation reaction under the action of boron trifluoride etherate (0.1 mol), and then it is reacted with polyvinyl alcohol (0.03 mol, Mw=2000 g / mol, alcoholysis degree 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 a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent.

[0039] The generated water reducer has a structural formula in which 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: Allyl polyoxyethylene ether (0.08 mol, Mw=2200 g / mol) and epichlorohydrin (0.09 mol) are subjected to terminal halogenation reaction under the action of boron trifluoride etherate (0.1 mol), and then it is reacted with polyvinyl alcohol (0.03 mol, Mw=4000 g / mol, alcoholysis degree 70%) in acetone / water (100 mL, volume ratio of 1:20) at 30° C. with sodium hydroxide (0.1 mol) to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain through an etherification reaction;

[0042] Step S02: The modified polyvinyl alcohol structure (0.03 mol) obtained in step S01 is reacted with maleic anhydride (3 mol) and a low molecular weight second unsaturated polyether macromonomer (1 mol, Mw=1000 g / mol) in the presence of hydrogen peroxide (0.1 mol), sodium pyrosulfite (0.13 mol) and 2-mercaptopropionic acid (0.1 mol) at 35° C. to undergo an oxidation-reduction free radical polymerization reaction to obtain a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent.

[0043] The generated water reducer has a structural formula in which 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: vinyl polyoxyethylene ether (0.08 mol, Mw=1200 g / mol) and epibromopropane (0.09 mol) are subjected to terminal halogenation reaction under the action of boron trifluoride etherate (0.1 mol), and then reacted with polyvinyl alcohol (0.05 mol, Mw=2000 g / mol, alcoholysis degree 70%) in dimethyl sulfoxide / water (150 mL, volume ratio of 1:15) at 20° C. with sodium carbonate (0.1 mol) to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain through an etherification reaction;

[0046] Step S02: The modified polyvinyl alcohol structure (0.05 mol) obtained in step S01 is reacted with maleic anhydride (5 mol) and a low molecular weight second unsaturated polyether macromonomer (1 mol, Mw=800 g / mol) in the presence of ammonium persulfate (0.09 mol), vitamin C (0.13 mol) and sodium methyl methacrylate sulfonate (0.12 mol) at 30° C. to undergo an oxidation-reduction free radical polymerization reaction to obtain a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent.

[0047] In the structural formula of the water-reducing agent generated, 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: methyl allyl polyoxyethylene ether (0.03 mol, Mw=3000 g / mol) and epichlorohydrin (0.04 mol) are subjected to terminal halogenation reaction under the action of boron trifluoride etherate (0.1 mol), and then reacted with polyvinyl alcohol (0.02 mol, Mw=3000 g / mol, alcoholysis degree 70%) in N, N-dimethylformamide / water (160 mL, volume ratio of 1:30) at 35° C. with potassium hydroxide (0.1 mol) to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain through an etherification reaction;

[0050] Step S02: The modified polyvinyl alcohol structure (0.02 mol) obtained in step S01 is reacted with maleic anhydride (6 mol) and a low molecular weight second unsaturated polyether macromonomer (1 mol, Mw=600 g / mol) in the presence of azobisisobutyronitrile (0.16 mol), sodium bisulfite (0.14 mol) and 3-mercaptopropionic acid (0.13 mol) at 25° C. to undergo an oxidation-reduction free radical polymerization reaction to obtain a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent.

[0051] The structural formula of the water-reducing agent generated is as follows: 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: isopentanol polyoxyethylene ether (0.07 mol, Mw=2600 g / mol) and epifluoropropane (0.08 mol) are subjected to terminal halogenation reaction under the action of boron trifluoride etherate (0.1 mol), and then reacted with polyvinyl alcohol (0.04 mol, Mw=3000 g / mol, alcoholysis degree 70%) in acetonitrile / water (140 mL, volume ratio of 1:15) at 30° C. with potassium carbonate (0.1 mol) to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain through an etherification reaction;

[0054] Step S02: The modified polyvinyl alcohol structure (0.04 mol) obtained in step S01 is reacted 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 undergo an oxidation-reduction free radical polymerization reaction to obtain a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent.

[0055] The generated water reducer has a structural formula in which 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: methyl allyl polyoxyethylene ether (0.02 mol, Mw=3000 g / mol) and epibromopropane (0.03 mol) are subjected to terminal halogenation reaction under the action of boron trifluoride etherate (0.1 mol), and then the methyl allyl polyoxyethylene ether (0.01 mol, Mw=2500 g / mol, alcoholysis degree 80%) is reacted with polyvinyl alcohol (0.01 mol, Mw=2500 g / mol, alcoholysis degree 80%) in N, N-dimethylformamide / water (150 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;

[0058] Step S02: The modified polyvinyl alcohol structure (0.01 mol) obtained in step S01 is reacted 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 undergo an oxidation-reduction free radical polymerization reaction to obtain a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent.

[0059] The generated water reducer has a structural formula in which 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: vinyl polyoxyethylene ether (0.04 mol, Mw=2200 g / mol) and epichlorohydrin (0.05 mol) are subjected to terminal halogenation reaction under the action of boron trifluoride etherate (0.1 mol), and then it is reacted with polyvinyl alcohol (0.02 mol, Mw=2000 g / mol, alcoholysis degree 70%) in chloroform / water (180 mL, volume ratio of 1:30) at 35° C. with sodium hydroxide (0.1 mol) to generate a modified polyvinyl alcohol structure containing an unsaturated polyether macromonomer side chain through an etherification reaction;

[0062] Step S02: The modified polyvinyl alcohol structure (0.02 mol) obtained in step S01 is reacted with maleic anhydride (2 mol) and a low molecular weight second unsaturated polyether macromonomer (1 mol, Mw=1000 g / mol) in the presence of ammonium persulfate (0.11 mol), vitamin C (0.1 mol) and 3-mercaptopropionic acid (0.1 mol) at 15° C. to undergo an oxidation-reduction free radical polymerization reaction to obtain a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent.

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

[0064] Comparative Example 1

[0065] The difference from Example 1 is that step S01 is not performed, the first unsaturated polyether macromonomer, maleic anhydride and the second unsaturated macromonomer are directly subjected to free radical polymerization, and the micro-crosslinking structure is not prepared.

[0066] Comparative Example 2

[0067] Ordinary high performance polycarboxylate water reducer ART-JR1.

[0068] Comparative Example 3

[0069] HPWR-S water reducer is commercially available and complies with GB 8076-2008 "Concrete Admixtures" standard.

[0070] Test Case

[0071] 1. Cement paste Marsh time test

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

[0073] The results show that when the water-binder ratio is 0.29 and the fluidity of the cement paste reaches (200±5) mm, (240±5) mm, and (280±5) mm, respectively, the average Marsh time of Examples 1 to 8 relative to Comparative Examples 1 to 3 is reduced by 54.9 s, 53.3 s, and 49.9 s, respectively. When the water-binder ratio is 0.20 and the fluidity of the cement paste reaches (200±5) mm, (240±5) mm, and (280±5) mm, respectively, the average Marsh time of Examples 1 to 8 relative to Comparative Examples 1 to 3 is reduced by 59.0 s, 58.3 s, and 58.1 s, respectively. This shows that the examples prepared by the present invention 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] With reference to GB 8076-2008 Concrete Admixtures, the initial slump / expansion of concrete, the loss of slump / expansion after 1h, the collapse time, and the strength of concrete specimens were measured for the samples obtained in Examples 1 to 8 and Comparative Examples 1 to 3. The amount of water reducer was controlled so that the initial expansion of concrete was 600±10. The concrete mix proportions are 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 to 3, the dosage required for Examples 1 to 8 to achieve the same expansion is lower, and the collapse time is shorter, indicating that Examples 1 to 8 have better dispersion, dispersion retention and viscosity reduction capabilities in the cement concrete system. Comparing Example 1 with Comparative Example 1, it is shown that the micro-crosslinked structure of the present invention has a promoting effect on the dispersion effect of cement particles and reducing the viscosity of cement paste. In addition, Examples 1 to 8 also have an overall improvement effect on strength compared with Comparative Examples 1 to 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 invention has been disclosed as above in terms of preferred embodiments, they are not intended to limit the present invention. Anyone skilled in the art can make various changes or modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims of this application.

Claims

1. A slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent, characterized in that: Its structure is as follows: In the above formula, the polymerization degrees m, n and r are each independently 1 to 100; the polymerization degrees a and b are each independently 1 to 25; R1 and R2 are both -CH2-, -CH2CH2-, -OCH2CH2- or -OCH2CH2CH2CH2-, or a combination of two or more; R3 and R4 are both H or -CH3, or a combination of two or more; R5 is -CH3, -CH2CH3 or -CH2CH2CH3, or a combination of two or more; the wavy line is the main chain structure of a low molecular weight partially alcoholysed grade polyvinyl alcohol.

2. A method for preparing a slightly cross-linked viscosity-reducing polycarboxylic acid water reducer, used for preparing the water reducer as claimed in claim 1, characterized in that: The following steps are involved: Step 1: subjecting the first unsaturated polyether macromonomer to a terminal halogenation reaction with an epoxyhalogenated propane under the action of boron trifluoride etherate, and then adding the first unsaturated polyether macromonomer and a low molecular weight partially alcoholysed polyvinyl alcohol to a solvent, and reacting the first unsaturated polyether macromonomer with an acid-binding agent at 10 to 50° C. to form an unsaturated polyether macromonomer side chain modified polyvinyl alcohol structure through an etherification reaction; Step 2: The modified polyvinyl alcohol structure obtained in step 1 is subjected to an oxidation-reduction free radical polymerization reaction at 10-50° C. with 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 to obtain a target slightly cross-linked viscosity-reducing polycarboxylic acid water-reducing agent; wherein the molar ratio of the modified polyvinyl alcohol structure, 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).

3. The method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent according to claim 2, characterized in that: In step 1, the first unsaturated polyether macromonomer is any one of allyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, isopentanol polyoxyethylene ether or vinyl polyoxyethylene ether, or a combination of two or more thereof, and has a weight average molecular weight of 1000 to 3000 g / mol.

4. The method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent according to claim 2, characterized in that: In step 1, the epihalohydrin is any one of epichlorohydrin, epibromohydrin or epifluorohydrin, or a combination of two or more thereof.

5. The method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent according to claim 2, characterized in that: In step 1, the weight average molecular weight of the low molecular weight partially alcoholysis grade polyvinyl alcohol is 1000-5000 g / mol, and the alcoholysis degree is 70%-80%.

6. The method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent according to claim 2, characterized in that: In step 1, the solvent is a mixed solvent of a main solvent and water; wherein the main solvent is any one of acetonitrile, acetone, dichloromethane, chloroform, dimethyl sulfoxide, N,N-dimethylformamide or 1,2-dichloroethane, or a combination of two or more thereof, and the volume ratio of the main solvent to water is 1:(1-30); the acid binding agent is any one of sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, 4-dimethylaminopyridine, diethylamine or triethylamine, or a combination of two or more thereof.

7. The method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent according to claim 2, characterized in that: The structure of the modified polyvinyl alcohol containing unsaturated polyether macromonomer side chains generated in step 1 is as follows: In the above formula, the degree of polymerization m is 1 to 100; R1 is one or a combination of two or more of -CH2-, -CH2CH2-, -OCH2CH2- or -OCH2CH2CH2CH2-; R3 is one or a combination of two of H or -CH3; the wavy line is the main chain structure of low molecular weight partially alcoholysed grade polyvinyl alcohol.

8. The method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent according to claim 2, characterized in that: In step 2, the low molecular weight second unsaturated polyether macromonomer has a molecular weight of 500 to 1000 g / mol and a structure of: In the above formula, the polymerization degrees a and b are each independently 1 to 25; R2 is one or a combination of two or more of -CH2-, -CH2CH2-, -OCH2CH2- or -OCH2CH2CH2CH2-; R4 is one or a combination of two or more of H or -CH3; R5 is one or a combination of two or more of -CH3, -CH2CH3 or -CH2CH2CH3.

9. The method for preparing a slightly cross-linked viscosity-reducing polycarboxylate water-reducing agent according to claim 2, characterized in that: In step 2, the initiator is any one of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, azobisisobutyronitrile or azobisisoheptanenitrile, or a combination of two or more; the reducing agent is any one of vitamin C, sodium sulfite, sodium bisulfite, sodium pyrosulfite or sodium hypophosphite, or a combination of two or more; the chain transfer agent is any one of thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, mercaptoethanol, dodecanethiol or sodium methyl methacrylate sulfonate, or a combination of two or more.

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