CN109021180B - Low-sensitivity shrinkage-reducing polycarboxylate superplasticizer and preparation method thereof - Google Patents
Low-sensitivity shrinkage-reducing polycarboxylate superplasticizer and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a low-sensitivity shrinkage-reducing polycarboxylate superplasticizer and a preparation method thereof, wherein the molecular weight of an effective component is 10000-150000, and the structural formula of the effective component is as follows:
Description
Technical Field
The invention belongs to the technical field of building additives, and particularly relates to a low-sensitivity shrinkage type polycarboxylate superplasticizer and a preparation method thereof.
Background
Due to the characteristics of excellent water reducing performance and easy functional design, the polycarboxylic acid water reducing agent is a water reducing agent product with the largest dosage in China at present.
With the high-speed development of economy, real estate market and infrastructure construction in China are synchronously developed at a high speed, a large amount of cement and gravel are consumed by a large amount of engineering construction, the shortage of gravel resource supply is aggravated, natural sand and stone resources in many areas of China are increasingly deficient, the supply of gravel materials is insufficient, the problems that the gravel materials are extremely unstable and the gravel is high in mud content and unstable are caused, and when the polycarboxylic acid water reducing agent is applied to concrete produced by using the materials, the problems that the water reducing rate is insufficient, the slump loss is not good and the mud content is sensitive begin to occur. In addition, plastic shrinkage of concrete is one of the main causes of cracks in concrete, and it is desired to reduce the risk of plastic cracking of concrete by adding a polycarboxylic acid water reducing agent having a shrinkage reducing effect, and therefore, it is important to develop a polycarboxylic acid water reducing agent which is insensitive to the content of mud in the material, has a certain shrinkage reducing effect, and is excellent in the water reducing effect and slump retaining effect.
Disclosure of Invention
The invention aims to provide a low-sensitivity shrinkage-reducing polycarboxylate superplasticizer.
The invention also aims to provide a preparation method of the low-sensitivity shrinkage-reducing polycarboxylate superplasticizer.
The technical scheme of the invention is as follows:
the low-sensitivity shrinkage-reducing polycarboxylate superplasticizer comprises an effective component with the molecular weight of 10000-150000, wherein the structural formula of the effective component is as follows:
wherein a, b, d, e and n are integers, a is 1-30, b is 4-135, d is 1-75, e is 1-45, n is 26-90, R is1Is H or COOM, R2Is H or CH3，R3Is empty or C1-C4 alkyl, R4Is empty or C1-C4 alkyl, R5Is composed of
R6Is H or COOM, R7Is H or CH3，R8Is F or CF3M is H, Na, K or NH4；R3And R4The relationship with respect to the benzene ring is ortho, meta or para.
The preparation method of the low-sensitivity reduction type polycarboxylate superplasticizer comprises the following steps:
(1) esterification reaction: mixing methoxypolyethylene glycol with the molecular weight of 1200-4000 with a first compound, heating to 110-140 ℃ under the protection of nitrogen, adding a first catalyst, carrying out heat preservation reaction for 1.0-3.0 h, cooling to 70-90 ℃, adding unsaturated carboxylic acid or unsaturated carboxylic anhydride, a polymerization inhibitor and a second catalyst, continuing the heat preservation reaction for 1.0-3.0 h, removing water by vacuumizing or introducing nitrogen to carry out water, and cooling to room temperature after the reaction is finished to obtain a first mixture containing an esterification product and unreacted unsaturated carboxylic acid or unsaturated carboxylic anhydride; the structural formula of the first compound is
(2) monomer blending: mixing the first mixture prepared in the step (1) and fluorine-containing unsaturated carboxylic acid in a mass ratio of 200: 1-8, and adding water to dissolve the mixture to obtain a comonomer mixture solution; the fluorine-containing unsaturated carboxylic acid is 2- (trifluoromethyl) acrylic acid and/or 2-fluoroacrylic acid;
(3) and (3) copolymerization reaction: dripping the comonomer mixture solution, the initiator aqueous solution and the molecular weight regulator aqueous solution into water for reaction at the reaction temperature of 10-60 ℃ for 0.5-4.0 h, and preserving heat for 0-1.0 h after dripping to obtain a copolymerization product;
(4) and (3) neutralization reaction: and (4) adjusting the pH of the copolymerization product prepared in the step (3) to 5-7 by using alkali to obtain the low-sensitivity shrinkage type polycarboxylate superplasticizer.
In a preferred embodiment of the present invention, in the step (1), the mole ratio of the methoxypolyethylene glycol, the first compound and the unsaturated carboxylic acid or unsaturated carboxylic acid anhydride is 1: 2 to 4: 5 to 10.
Further preferably, the amount of the first catalyst is 0.3-3.0% of the total mass of the methoxypolyethylene glycol and the first compound; the amount of the polymerization inhibitor is 0.2-3.0% of unsaturated carboxylic acid or unsaturated carboxylic anhydride; the dosage of the second catalyst is 0.2-2.0% of the mass of the unsaturated carboxylic acid or the unsaturated carboxylic anhydride.
In a preferred embodiment of the present invention, the total amount of water used in the steps (2) and (3) is such that the mass concentration of the copolymerization product is 20 to 70%.
Further preferably, the amount of the initiator is 0.5 to 3.0% of the total mass of the solutes in the comonomer mixture solution, and the amount of the molecular weight regulator is 0.2 to 2.0% of the total mass of the solutes in the comonomer mixture solution.
In a preferred embodiment of the invention, the initiator is a water-soluble redox initiator system or a water-soluble azo initiator.
In a preferred embodiment of the present invention, the molecular weight regulator is at least one of thioglycolic acid, mercaptopropionic acid, mercaptoethanol, isopropanol, sodium hypophosphite and trisodium phosphate.
The invention has the beneficial effects that:
1. according to the low-sensitivity shrinkage-reducing polycarboxylate water reducer disclosed by the invention, the rigid benzene ring structure is introduced at the joint of the branched chain and the main chain, so that the low-sensitivity shrinkage-reducing polycarboxylate water reducer is more extended in conformation in a solution, larger in molecular size and not easy to be adsorbed to interlayers by clay with a layered structure to weaken the water reducing performance of the low-sensitivity shrinkage-reducing polycarboxylate water reducer, and the obtained low-sensitivity shrinkage-reducing polycarboxylate water reducer has the characteristic of low sensitivity to mud content.
2. The low-sensitivity shrinkage-reducing polycarboxylate superplasticizer has a high water reducing effect because the side group with a benzene ring structure is introduced into the main chain and the steric hindrance is high.
3. The low-sensitivity shrinkage-reducing polycarboxylate superplasticizer has an ester-based structure which can explain the release of carboxylic acid groups with water-reducing effect under the concrete alkaline condition, so that the low-sensitivity shrinkage-reducing polycarboxylate superplasticizer has an outstanding slump-retaining effect.
4. Because the molecular structure of the low-sensitivity shrinkage-reducing polycarboxylate water reducer is introduced with the fluorocarbon structure, when the low-sensitivity shrinkage-reducing polycarboxylate water reducer is applied to concrete, compared with the conventional carbon-carbon structure, the low-sensitivity shrinkage-reducing polycarboxylate water reducer has a more obvious effect of reducing the surface tension of a solution, so that the low-sensitivity shrinkage-reducing polycarboxylate water reducer has an obvious effect of reducing the shrinkage of the concrete.
Detailed Description
The technical solution of the present invention is further illustrated and described by the following detailed description.
The molecular weight of the effective component of the low-sensitivity shrinkage-reducing polycarboxylate superplasticizer prepared in the following example is 10000-150000, and the structural formula of the effective component is as follows:
wherein a, b, d, e and n are integers, a is 1-30, b is 4-135, d is 1-75, e is 1-45, n is 26-90, R is1Is H or COOM, R2Is H or CH3，R3Is empty or C1-C4 alkyl, R4Is empty or C1-C4 alkyl, R5Is composed of
R6Is H or COOM, R7Is H or CH3，R8Is F or CF3M is H, Na, K or NH4；R3And R4The relationship with respect to the benzene ring is ortho, meta or para.
Example 1
(1) Esterification reaction: mixing 120.00g of methoxypolyethylene glycol with the molecular weight of 1200 and 27.00g of p-hydroxybenzoic acid, heating to 110 ℃ under the protection of nitrogen, adding 1.60g of p-toluenesulfonic acid, carrying out heat preservation reaction for 1.0h, cooling to 70 ℃, adding 60.00g of acrylic acid, 1.25g of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-1-oxygen radical and 0.50g of a second catalyst, carrying out heat preservation reaction for 2.0h, removing water by a vacuumizing and water-carrying method during the heat preservation reaction, and cooling to room temperature after the reaction is finished to obtain a first mixture containing an esterified product and unreacted acrylic acid;
(2) monomer blending: mixing 200.00g of the first mixture obtained in step (1) with 2.00g of 2- (trifluoromethyl) acrylic acid, and adding 100.00g of water to dissolve it, to obtain a comonomer mixture solution;
(3) and (3) copolymerization reaction: dripping the comonomer mixture solution, a hydrogen peroxide aqueous solution (wherein 0.90g of hydrogen peroxide and 20.00g of water), an ascorbic acid aqueous solution (wherein 0.30g of water and 20.00g of water) and a thioglycolic acid aqueous solution (wherein 0.70g of thioglycolic acid and 20.00g of water) into 140.00g of water for reaction at the reaction temperature of 55 ℃ for 2.5h, and preserving heat for 0.5h after dripping to obtain a copolymerization product;
(4) and (3) neutralization reaction: and (4) adjusting the pH of the copolymerization product prepared in the step (3) to 5-7 by using alkali to obtain the low-sensitivity shrinkage type polycarboxylate superplasticizer PCE-1.
Example 2
(1) Esterification reaction: mixing 200.00g of methoxy polyethylene glycol with molecular weight of 2000 and 35.00g of p-hydroxymethyl benzoic acid, heating to 120 ℃ under the protection of nitrogen, adding 2.80g of benzenesulfonic acid, carrying out heat preservation reaction for 1.5h, cooling to 80 ℃, adding 60.00g of methacrylic acid, 0.90g of 2, 2-bis (4-tert-octylphenyl) -1-picrazino radical and 0.8g of second catalyst, carrying out heat preservation reaction for 3.0h, removing water by introducing nitrogen during the heat preservation reaction, and cooling to room temperature after the reaction is finished to obtain a first mixture containing an esterified product and unreacted methacrylic acid;
(2) monomer blending: mixing 200.00g of the first mixture obtained in step (1) with 3.00g of 2-fluoroacrylic acid, and adding 100.00g of water to dissolve it, to obtain a comonomer mixture solution;
(3) and (3) copolymerization reaction: dropping the comonomer mixture solution, azobisisobutylamidine hydrochloride aqueous solution (wherein the weight of the azobisisobutylamidine hydrochloride is 2.20g and the weight of the water is 30.00g) and sodium hypophosphite aqueous solution (wherein the weight of the sodium hypophosphite is 1.80g and the weight of the water is 30.00g) into 40.00g of water for reaction, wherein the reaction temperature is 45 ℃, the dropping time is 2.0h, and after the dropping is finished, preserving the heat for 0.5h to obtain a copolymerization product;
(4) and (3) neutralization reaction: and (3) adjusting the pH of the copolymerization product prepared in the step (4) to 5-7 by using alkali to obtain the low-sensitivity shrinkage type polycarboxylate superplasticizer PCE-2.
Example 3
(1) Esterification reaction: 240.00g of methoxypolyethylene glycol with the molecular weight of 2400 and 40.00g of p-hydroxyphenylsulfonic acid are mixed, the mixture is heated to 125 ℃ under the protection of nitrogen, 6.80g of p-toluenesulfonic acid is added, the mixture is subjected to heat preservation reaction for 2.0h, the temperature is reduced to 75 ℃, 35.00g of maleic acid, 25.00g of acrylic acid, 0.60g of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-1-oxygen radical and 1.00g of a second catalyst are added, the mixture is subjected to heat preservation reaction for 1.5h, a vacuumizing and water carrying method is used for removing water during the heat preservation reaction, and the mixture is cooled to room temperature after the reaction is finished to obtain a first mixture containing an esterification product, unreacted maleic acid and unreacted acrylic acid;
(2) monomer blending: mixing 200.00g of the first mixture obtained in step (1) with 4.00g of 2- (trifluoromethyl) acrylic acid, and adding 100.00g of water to dissolve it, to obtain a comonomer mixture solution;
(3) and (3) copolymerization reaction: dripping the comonomer mixture solution, an azodicyano valeric acid aqueous solution (wherein 2.20g of azodicyano valeric acid and 30.00g of water) and a trisodium phosphate aqueous solution (wherein 3.20g of trisodium phosphate and 30.00g of water) into 140.00g of water for reaction at the reaction temperature of 50 ℃ for 1.5h, and preserving heat for 1.0h after dripping to obtain a copolymerization product;
(4) and (3) neutralization reaction: and (3) adjusting the pH of the copolymerization product prepared in the step (4) to 5-7 by using alkali to obtain the low-sensitivity shrinkage type polycarboxylate superplasticizer PCE-3.
Example 4
(1) Esterification reaction: mixing 300.00g of methoxypolyethylene glycol with the molecular weight of 3000 and 45.00g of p-hydroxyphenylacetic acid, heating to 130 ℃ under the protection of nitrogen, adding 6.00g of ethylsulfonic acid, keeping the temperature for reaction for 2.5h, cooling to 85 ℃, adding 30.00g of maleic anhydride, 30.00g of acrylic acid, 0.90g of 2, 2-bis (4-tert-octylphenyl) -1-picrazino radical and 0.70g of a second catalyst, keeping the temperature for reaction for 2.5h, introducing nitrogen to carry out water carrying, and cooling to room temperature after the reaction is finished to obtain a first mixture containing an esterification product, unreacted maleic anhydride and unreacted acrylic acid with water removed;
(2) monomer blending: mixing 200.00g of the first mixture obtained in step (1), 2.00g of 2- (trifluoromethyl) acrylic acid and 2.00g of 2-fluoroacrylic acid, and adding 100.00g of water to dissolve them, to obtain a comonomer mixture solution;
(3) and (3) copolymerization reaction: dripping the comonomer mixture solution, a hydrogen peroxide aqueous solution (wherein, 2.00g of hydrogen peroxide and 20.00g of water), a trisodium phosphate aqueous solution (wherein, 1.00g of trisodium phosphate and 20.00g of water) and an ascorbic acid aqueous solution (wherein, 0.20 g of ascorbic acid and 20.00g of water) into 240.00g of water for reaction, wherein the reaction temperature is 35 ℃, the dripping time is 2.0h, and preserving heat for 1.0h after dripping is finished to obtain a copolymerization product;
(4) and (3) neutralization reaction: and (3) adjusting the pH of the copolymerization product prepared in the step (4) to 5-7 by using alkali to obtain the low-sensitivity shrinkage type polycarboxylate superplasticizer PCE-4.
Example 5
(1) Esterification reaction: 400.00g of methoxypolyethylene glycol with the molecular weight of 4000 and 50.00g of p-hydroxymethylbenzenesulfonic acid are mixed, the mixture is heated to 140 ℃ under the protection of nitrogen, 9.00g of concentrated sulfuric acid is added, the mixture is subjected to heat preservation reaction for 3.0h, the temperature is reduced to 90 ℃, 60.00g of acrylic acid, 0.90g of 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-1-oxygen free radical and 1.10g of a second catalyst are added, the mixture is subjected to heat preservation reaction for 1.0h, water is removed by a vacuumizing and water-carrying method during the heat preservation reaction, and the temperature is reduced to room temperature after the reaction is finished to obtain a first mixture containing an esterified product and unreacted acrylic;
(2) monomer blending: mixing 200.00g of the first mixture obtained in step (1) with 6.00g of 2- (trifluoromethyl) acrylic acid, and adding 100.00g of water to dissolve it, to obtain a comonomer mixture solution;
(3) and (3) copolymerization reaction: dripping the comonomer mixture solution and an azodicyano valeric acid aqueous solution (wherein, the azodicyano valeric acid is 3.80g, the water is 30.00g) and a sodium hypophosphite aqueous solution (wherein, the sodium hypophosphite is 2.20g, the water is 30.00g) into 40.00g of water for reaction, wherein the reaction temperature is 40 ℃, the dripping time is 3.0h, and after the dripping is finished, preserving the heat for 0.5h to obtain a copolymerization product;
(4) and (3) neutralization reaction: and (3) adjusting the pH of the copolymerization product prepared in the step (4) to 5-7 by using alkali to obtain the low-sensitivity shrinkage type polycarboxylate superplasticizer PCE-5.
According to GB/T8076-2008, when the low-sensitivity shrinkage-reducing polycarboxylate water reducing agents prepared in the embodiments 1 to 5 are tested, when the folding-fixing content is 0.20% (relative to the cement dosage), the water reducing rate is higher than 40%, the 28d compressive strength ratio is larger than 150%, and the 28d shrinkage ratio is smaller than 90%.
Adopting Fufu P.O 42.5.5 common Portland cement, and the concrete mixing ratio is as follows: cement 300kg/m3100kg/m of fly ash3100kg/m of mineral powder3690kg/m of sand31050kg/m of stones3160kg/m of water3And 4.0% of bentonite (relative to the amount of cement) was added, and a performance test was conducted on the low-sensitivity shrinkage-reducing polycarboxylate water reducer obtained in examples 1 to 5 and a commercially available high water-reducing polycarboxylate water reducer (PCE) in accordance with a set admixture of 0.16%. Test coagulationThe initial slump and the expansion degree of the soil, the slump and the expansion degree of 2h and the test results of different additives are shown in the table 1.
TABLE 1 results of different admixtures
As can be seen from Table 1, for the material doped with bentonite, the synthesized examples of the invention have larger water reducing rate and better slump keeping performance compared with the commercial polycarboxylic acid water reducing agent (PCE) with high water reducing rate, so that the low-sensitivity shrinkage-reducing polycarboxylic acid water reducing agent prepared by the invention has lower sensitivity to the material with high mud content.
It is obvious to those skilled in the art that the technical solution of the present invention can still obtain the same or similar technical effects as the above embodiments when changed within the following scope, and still fall into the protection scope of the present invention:
the low-sensitivity shrinkage-reducing polycarboxylate superplasticizer comprises an effective component with the molecular weight of 10000-150000, wherein the structural formula of the effective component is as follows:
wherein a, b, d, e and n are integers, a is 1-30, b is 4-135, d is 1-75, e is 1-45, n is 26-90, R is1Is H or COOM, R2Is H or CH3，R3Is empty or C1-C4 alkyl, R4Is empty or C1-C4 alkyl, R5Is composed of
R6Is H or COOM, R7Is H or CH3，R8Is F or CF3M is H, Na, K or NH4；R3And R4The relationship with respect to the benzene ring is ortho, meta or para.
The preparation method of the low-sensitivity reduction type polycarboxylate superplasticizer comprises the following steps:
(1) esterification reaction: mixing methoxypolyethylene glycol with the molecular weight of 1200-4000 with a first compound, heating to 110-140 ℃ under the protection of nitrogen, adding a first catalyst, carrying out heat preservation reaction for 1.0-3.0 h, cooling to 70-90 ℃, adding unsaturated carboxylic acid or unsaturated carboxylic anhydride, a polymerization inhibitor and a second catalyst, continuing the heat preservation reaction for 1.0-3.0 h, removing water by vacuumizing or introducing nitrogen to carry out water, and cooling to room temperature after the reaction is finished to obtain a first mixture containing an esterification product and unreacted unsaturated carboxylic acid or unsaturated carboxylic anhydride; the structural formula of the first compound is as follows
(2) monomer blending: mixing the first mixture prepared in the step (1) and fluorine-containing unsaturated carboxylic acid in a mass ratio of 200: 1-8, and adding water to dissolve the mixture to obtain a comonomer mixture solution; the fluorine-containing unsaturated carboxylic acid is 2- (trifluoromethyl) acrylic acid and/or 2-fluoroacrylic acid;
(3) and (3) copolymerization reaction: dripping the comonomer mixture solution, the initiator aqueous solution and the molecular weight regulator aqueous solution into water for reaction at the reaction temperature of 10-60 ℃ for 0.5-4.0 h, and preserving heat for 0-1.0 h after dripping to obtain a copolymerization product;
(4) and (3) neutralization reaction: and (4) adjusting the pH of the copolymerization product prepared in the step (3) to 5-7 by using alkali to obtain the low-sensitivity shrinkage type polycarboxylate superplasticizer.
In the step (1), the molar ratio of the methoxypolyethylene glycol, the first compound and the unsaturated carboxylic acid or unsaturated carboxylic acid anhydride is 1: 2-4: 5-10. The dosage of the first catalyst is 0.3-3.0% of the total mass of the methoxy polyethylene glycol and the first compound; the amount of the polymerization inhibitor is 0.2-3.0% of unsaturated carboxylic acid or unsaturated carboxylic anhydride; the dosage of the second catalyst is 0.2-2.0% of the mass of the unsaturated carboxylic acid or the unsaturated carboxylic anhydride.
The total amount of water used in the step (2) and the step (3) enables the mass concentration of the copolymerization product to be 20-70%. The amount of the initiator is 0.5-3.0% of the total mass of the solute in the comonomer mixture solution, and the amount of the molecular weight regulator is 0.2-2.0% of the total mass of the solute in the comonomer mixture solution.
The initiator is a water-soluble redox initiation system or a water-soluble azo initiator. The molecular weight regulator is at least one of thioglycolic acid, mercaptopropionic acid, mercaptoethanol, isopropanol, sodium hypophosphite and trisodium phosphate.
The above description is only a preferred embodiment of the present invention, and therefore should not be taken as limiting the scope of the invention, which is defined by the appended claims.
Claims (8)
1. A low-sensitivity shrinkage-reducing polycarboxylate superplasticizer is characterized in that: the molecular weight of the effective component is 10000-150000, and the structural formula of the effective component is as follows:
wherein a, b, d, e and n are integers, a is 1-30, b is 4-135, d is 1-75, e is 1-45, n is 26-90, R is1Is H or COOM, R2Is H or CH3，R3Is empty or C1-C4 alkyl, R4Is empty or C1-C4 alkyl, R5Is composed of
R6Is H or COOM, R7Is H or CH3，R8Is F or CF3M is H, Na, K or NH4；R3And R4The relationship with respect to the benzene ring is ortho, meta or para.
2. The preparation method of the low-sensitivity shrinkage-reducing polycarboxylate superplasticizer according to claim 1, which is characterized by comprising the following steps: the method comprises the following steps:
(1) esterification reaction: mixing methoxypolyethylene glycol with the molecular weight of 1200-4000 with a first compound, heating to 110-140 ℃ under the protection of nitrogen, adding a first catalyst, carrying out heat preservation reaction for 1.0-3.0 h, cooling to 70-90 ℃, adding unsaturated carboxylic acid or unsaturated carboxylic anhydride, a polymerization inhibitor and a second catalyst, continuing the heat preservation reaction for 1.0-3.0 h, removing water by vacuumizing or introducing nitrogen to carry out water, and cooling to room temperature after the reaction is finished to obtain a first mixture containing an esterification product and unreacted unsaturated carboxylic acid or unsaturated carboxylic anhydride; the structural formula of the first compound is
The first catalyst is at least one of concentrated sulfuric acid, benzenesulfonic acid, p-toluenesulfonic acid and ethylsulfonic acid, the unsaturated carboxylic acid or unsaturated carboxylic anhydride is at least one of acrylic acid, methacrylic acid, maleic acid and maleic anhydride, the polymerization inhibitor is 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine-1-oxygen radical and/or 2, 2-di (4-tert-octylphenyl) -1-picrazino radical, and the second catalyst is formed by combining mellitic acid and p-toluenesulfonic acid according to the mass ratio of 0.8-1.2: 0.8-1.2;
(2) monomer blending: mixing the first mixture prepared in the step (1) and fluorine-containing unsaturated carboxylic acid in a mass ratio of 200: 1-8, and adding water to dissolve the mixture to obtain a comonomer mixture solution; the fluorine-containing unsaturated carboxylic acid is 2- (trifluoromethyl) acrylic acid and/or 2-fluoroacrylic acid;
(3) and (3) copolymerization reaction: dripping the comonomer mixture solution, the initiator aqueous solution and the molecular weight regulator aqueous solution into water for reaction at the reaction temperature of 10-60 ℃ for 0.5-4.0 h, and preserving heat for 0-1.0 h after dripping to obtain a copolymerization product;
(4) and (3) neutralization reaction: and (4) adjusting the pH of the copolymerization product prepared in the step (3) to 5-7 by using alkali to obtain the low-sensitivity shrinkage type polycarboxylate superplasticizer.
3. The method of claim 2, wherein: in the step (1), the molar ratio of the methoxypolyethylene glycol, the first compound and the unsaturated carboxylic acid or unsaturated carboxylic acid anhydride is 1: 2-4: 5-10.
4. The method of claim 3, wherein: the dosage of the first catalyst is 0.3-3.0% of the total mass of the methoxy polyethylene glycol and the first compound; the using amount of the polymerization inhibitor is 0.2-3.0% of the mass of the unsaturated carboxylic acid or the unsaturated carboxylic anhydride; the dosage of the second catalyst is 0.2-2.0% of the mass of the unsaturated carboxylic acid or the unsaturated carboxylic anhydride.
5. The method of claim 2, wherein: the total amount of water used in the step (2) and the step (3) enables the mass concentration of the copolymerization product to be 20-70%.
6. The method of claim 5, wherein: the amount of the initiator is 0.5-3.0% of the total mass of the solute in the comonomer mixture solution, and the amount of the molecular weight regulator is 0.2-2.0% of the total mass of the solute in the comonomer mixture solution.
7. The method according to any one of claims 2 to 6, wherein: the initiator is a water-soluble redox initiation system or a water-soluble azo initiator.
8. The method according to any one of claims 2 to 6, wherein: the molecular weight regulator is at least one of thioglycolic acid, mercaptopropionic acid, mercaptoethanol, isopropanol, sodium hypophosphite and trisodium phosphate.
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