阅读说明：本技术 一种羧酸共聚物及其制备方法应用 (Carboxylic acid copolymer and preparation method and application thereof ) 是由 仝浩胜 何新耀 李玉博 于 2021-08-02 设计创作，主要内容包括：本发明属于混凝土外加剂制备技术领域,具体涉及一种羧酸共聚物及其制备方法应用。该羧酸共聚物为低聚合度共聚物,可单独或与减水剂配合使用；水泥加入水后会产生絮凝团结构,减水剂可以分散一部分絮凝团结构,但是仍然会残留部分絮凝团,加入减水剂和本发明的羧酸共聚物后,可以分散产生的絮凝团结构。本发明提供的羧酸共聚物与水分子的吸附力小,在水泥浆中的运动能力强,能够深入到水泥絮凝团结构的内部,吸附在水泥颗粒上,使水泥颗粒带上同种电荷,从而在电荷斥力的作用下分散开来,释放出絮凝团结构内部的水泥颗粒,从根本上解决水泥浆中的絮凝团结构问题,提高水泥水化率,增强水泥基材料的力学性能。(The invention belongs to the technical field of concrete admixture preparation, and particularly relates to a carboxylic acid copolymer and a preparation method and application thereof. The carboxylic acid copolymer is a copolymer with low polymerization degree, and can be used independently or in combination with a water reducing agent; after the water reducing agent and the carboxylic acid copolymer are added, the generated flocculation structure can be dispersed. The carboxylic acid copolymer provided by the invention has small adsorption force with water molecules and strong movement capability in cement slurry, can penetrate into the inside of a cement flocculation structure and be adsorbed on cement particles, so that the cement particles are charged with the same kind of charges, and are dispersed under the action of charge repulsion to release the cement particles in the flocculation structure, thereby fundamentally solving the flocculation structure problem in the cement slurry, improving the cement hydration rate and enhancing the mechanical property of a cement-based material.)

1. A carboxylic acid copolymer characterized by having the following structural formula,

wherein m is 0-8; n is 0 to 9; x is 0 to 10; y is 1 to 8; m, n and x cannot be 0 at the same time.

2. The carboxylic acid copolymer as claimed in claim 1, wherein the molecular weight of the carboxylic acid copolymer is 700-1600.

3. A process for preparing a carboxylic acid copolymer according to claim 1 or 2, wherein the carboxylic acid copolymer is obtained by radical polymerization of the reactive monomers under the action of an initiator.

4. The method according to claim 3, further comprising a step of adding a polymerization inhibitor during the radical polymerization;

the polymerization inhibitor is added at least 5 times, and the time interval between two adjacent times of adding the polymerization inhibitor is at most 30 min.

5. The production method according to claim 4, wherein the polymerization inhibitor is at least one of hydroquinone, p-benzoquinone, p-hydroxyanisole, 2, 6-di-tert-butyl-p-cresol, 2-tert-butylhydroquinone, 2, 5-di-tert-butylhydroquinone, and methylhydroquinone;

the adding amount of the polymerization inhibitor is 0.03-0.05% of the total molar amount of the monomers.

6. The production method according to any one of claims 3 to 5, wherein the reactive monomers include a first monomer and a second monomer;

the first monomer comprises-PO₃H₂And C ═ C;

the second monomer contains-COOH and C ═ C.

7. The method of claim 6, wherein the first monomer is at least one of isopropenylphosphonic acid, allylphosphonic acid, diethyl isopropenylphosphonate, and dimethyl isopropenylphosphonate; preferably, the first monomer is isopropenylphosphonic acid;

the second monomer is at least one of methacrylic acid, acrylic acid and isopentenoic acid.

8. The method according to claim 6 or 7, wherein the molar ratio of the first monomer, the isopentenoic acid, the methacrylic acid, and the acrylic acid in the reaction monomers is (1-8): (0-8): (0-9): (0-10);

preferably, the molar ratio of the first monomer, the isopentenoic acid, the methacrylic acid, and the acrylic acid is (3-5): (0-4): (0-5): (0-6); or the like, or, alternatively,

the molar ratio of the first monomer, the isopentenoic acid and the methacrylic acid is (2.8-3.1): (1.9-2.1): (0.9-1.1), preferably 3:2: 1.

9. The method according to any one of claims 4 to 8, wherein the mass ratio of the initiator to the reactive monomer is (5 to 15): 100, respectively;

the initiator is a redox system initiator;

the oxidant in the initiator is persulfate or hydrogen peroxide; the reducing agent in the initiator is vitamin C or sodium bisulfite;

preferably, the method also comprises the step of adding a chain transfer agent in the polymerization reaction process;

the mass ratio of the chain transfer agent to the reaction monomer is (2-5): 100.

10. use of a carboxylic acid copolymer according to any of claims 1 to 2 or a carboxylic acid copolymer prepared by a process according to any of claims 3 to 9 in concrete.

Technical Field

The invention belongs to the technical field of concrete admixture preparation, and particularly relates to a carboxylic acid copolymer and a preparation method and application thereof.

Background

The cement-based material comprises cement concrete, cement mortar, cement grouting and other materials. The cement-based material has good plasticity after being stirred by adding water, has ultrahigh hardness after being solidified, and plays a great role in national production and life. As a developing country in China, the foundation construction projects such as the bridge, the airport wharf and the like are huge, and the dosage of cement-based materials is in the forefront of the world. The mechanical property of the cement-based material is an important factor for engineering design and construction. During the process of adding water into cement and stirring, the cement can spontaneously agglomerate due to the action of electrostatic attraction, particle thermal motion and van der Waals force to form a flocculation structure, so that a part of cement particles are wrapped and prevented from being hydrated when meeting water.

Generally speaking, only 60-70% of cement in cement paste without additives participates in the hydration process to finally form cement stones, after the high-performance water reducing agent is added, only 80-85% of cement in the cement paste participates in the hydration process, the rest cement is only used as filler to be wrapped in the cement stones, the value of the cement is not exerted, and the part of cement is wasted in a certain sense. The cement consumption is increased, the energy consumption is increased, and the development concept of energy conservation, emission reduction and environmental protection is not facilitated.

Many researchers have begun to research admixtures that can increase the hydration rate of cement and enhance the mechanical properties of cement-based materials. At present, some synergists (gel reducers) can disperse flocculation group structures of cement paste in the market, and the research on product components can discover that two products exist, namely, an alcohol amine compound product; and secondly, a compound product of lignin, a water reducing agent and inorganic salt. Both products can not realize further dispersion of the residual flocculation structure in the cement slurry doped with the polycarboxylic acid water reducing agent. The alcamines compound product improves the mechanical property of the cement-based material mainly by changing the crystal form of the cement hydration product crystal, does not assist the cement dispersion hydration effect, has poor compatibility with the water reducing agent, can cause the problems of poor fluidity, large slump loss and the like of the cement-based material, and is not beneficial to construction. The lignin product is one kind of water reducing agent, and the action of the lignin product is coincident with that of the water reducing agent, so that the water reducing agent is over-doped, and the bleeding segregation problem of cement-based materials is further caused.

Disclosure of Invention

Therefore, the invention provides a carboxylic acid copolymer and a preparation method and application thereof, aiming at overcoming the defects of cement flocculation, low hydration rate and the like in cement slurry in the prior art.

Therefore, the invention provides the following technical scheme.

The invention provides a carboxylic acid copolymer, which has the following structural formula,

wherein m is 0-8; n is 0 to 9; x is 0 to 10; y is 1 to 8; m, n and x cannot be 0 at the same time.

The molecular weight of the carboxylic acid copolymer is 700-1600.

The invention also provides a preparation method of the carboxylic acid copolymer, and the carboxylic acid copolymer is obtained by free radical polymerization of reaction monomers under the action of an initiator.

Further, a step of adding a polymerization inhibitor in the process of free radical polymerization reaction;

the polymerization inhibitor is added at least 5 times, and the time interval between two adjacent times of adding the polymerization inhibitor is at most 30 min.

Further, the polymerization inhibitor is at least one of hydroquinone, p-benzoquinone, p-hydroxyanisole, 2, 6-di-tert-butyl-p-cresol, 2-tert-butyl-hydroquinone, 2, 5-di-tert-butyl-hydroquinone and methyl hydroquinone;

the adding amount of the polymerization inhibitor is 0.03-0.05% of the total molar amount of the monomers. The reactive monomers include a first monomer and a second monomer;

the first monomer comprises-PO₃H₂And C ═ C;

the second monomer contains-COOH and C ═ C.

The first monomer is at least one of isopropenylphosphonic acid, allylphosphonic acid, diethyl isopropenylphosphonate and dimethyl isopropenylphosphonate; the first monomer is preferably isopropenylphosphonic acid;

the second monomer is at least one of methacrylic acid, acrylic acid and isopentenoic acid.

The molar ratio of the first monomer, the isopentenoic acid, the methacrylic acid and the acrylic acid in the reaction monomers is (1-8): (0-8): (0-9): (0-10).

Further, the molar ratio of the first monomer, the isopentenoic acid, the methacrylic acid and the acrylic acid is (3-5): (0-4): (0-5): (0-6).

Further, the molar ratio of the first monomer, the isopentenoic acid, and the methacrylic acid is (2.8-3.1): (1.9-2.1): (0.9-1.1), preferably 3:2: 1.

The mass ratio of the initiator to the reaction monomer is (5-15): 100, respectively;

the initiator is a redox system initiator;

the oxidant in the initiator is persulfate or hydrogen peroxide; the reducing agent in the initiator is vitamin C or sodium bisulfite;

preferably, the method also comprises the step of adding a chain transfer agent in the polymerization reaction process;

the mass ratio of the chain transfer agent to the reaction monomer is (2-5): 100.

in the preparation method, firstly, an oxidant in an initiator is prepared into a mixed solution A, then a reaction monomer is prepared into a mixed solution B, the mixed solution B is uniformly dripped into the mixed solution A, and a polymerization inhibitor is added in the process of dripping the mixed solution B into the mixed solution A from the beginning of dripping, wherein the adding frequency of the polymerization inhibitor is at least 5 times.

In addition, the invention also provides application of the carboxylic acid copolymer or the carboxylic acid copolymer prepared by the method in concrete.

The carboxylic acid copolymer provided by the invention can improve the hydration rate of cement by the cooperation of the carboxylic acid copolymer and the water reducing agent.

The technical scheme of the invention has the following advantages:

1. the carboxylic acid copolymer provided by the invention is a carboxylic acid copolymer with low polymerization degree, and the carboxylic acid copolymer is added into cement to be matched with a water reducing agent for use. After the water reducing agent and the carboxylic acid copolymer are added, the generated flocculation structure can be dispersed. The carboxylic acid copolymer provided by the invention has small adsorption force with water molecules and strong movement capability in cement paste, can penetrate into the inside of a cement flocculation structure and be adsorbed on cement particles, so that the cement particles are charged with the same kind of charges and are dispersed under the action of charge repulsion to release the cement particles in the flocculation structure, the flocculation structure problem in the cement paste is fundamentally solved, the cement hydration rate is improved, and the mechanical property of a cement-based material is enhanced, so that the problem that in the cement-cement system in the prior art, the cement particles are agglomerated under the actions of static electricity, particle thermal movement, van der Waals force and the like, and the internal particles cannot be subjected to hydration reaction to generate cement stones is solved.

The carboxylic acid copolymer provided by the invention contains carboxylic acid and phosphonic acid in the structure, so that the carboxylic acid copolymer and the water reducing agent have a good matching effect, and the cement hydration reaction is improved to the maximum extent. The phosphonic acid group is introduced into the copolymer, so that the copolymer has strong adsorption force with cement particles, the adsorption capability of the copolymer on the cement particles can be improved, and the adsorption of the copolymer and the cement particles is more stable. The carboxylic acid copolymer provided by the invention comprehensively considers factors such as polymerization activity of monomers, alkane chain length, active groups and the like, and finally obtains the carboxylic acid copolymer capable of improving cement hydration rate.

When the carboxylic acid copolymer is added into cement slurry doped with the water reducing agent, the performances of the cement-based material such as fluidity, slump and the like are not influenced.

2. The carboxylic acid copolymer provided by the invention is a polymer with low polymerization degree, has smaller molecular weight than a water reducing agent, has stronger motion capability in cement slurry due to the fact that one side of a molecular chain of the copolymer is a methyl hydrophobic group, and has weaker acting force with water molecules, so that the motion capability of the copolymer in the cement can be further improved, the copolymer extends into a flocculation group structure, cement particles in the flocculation group are taken out, and the problem of the flocculation group structure in the cement slurry is reduced.

3. According to the preparation method of the carboxylic acid copolymer, the carboxylic acid copolymer is obtained through free radical polymerization of the reaction monomer under the action of the initiator, and the prepared carboxylic acid copolymer can increase the reaction degree of cement doped with the water reducing agent, disperse the flocculation structure in the cement, improve the hydration rate of the cement and further improve the mechanical property of the cement.

The invention also comprises a step of adding a polymerization inhibitor in the process of free radical polymerization reaction, and the polymerization inhibitor consumes free radicals generated in the reaction to prevent the molecular weight from increasing, so that the low-polymerization-degree polymer can be obtained. The molecular weight of the polymer can be controlled to be 700-1600 by simultaneously using the chain transfer agent and the polymerization inhibitor in the preparation process and controlling the adding mode of the polymerization inhibitor, and after the carboxylic acid copolymer is added, the problem of flocculation of cement paste can be obviously improved, and the strength of cement is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

FIG. 1 is a figure of the appearance of cement under an electron microscope after a water reducing agent is added in a test example of the invention;

FIG. 2 is a graphical representation of the appearance of the cement under an electron microscope after the water reducing agent and the carboxylic acid copolymer of example 1 are added simultaneously in the test examples of the present invention;

FIG. 3 is a graph showing the molecular weight distribution of a carboxylic acid copolymer of example 1 of the present invention;

FIG. 4 is a graph showing the molecular weight distribution of the carboxylic acid copolymer of example 7 of the present invention.

Detailed Description

The following examples are provided to further understand the present invention, not to limit the scope of the present invention, but to provide the best mode, not to limit the content and the protection scope of the present invention, and any product similar or similar to the present invention, which is obtained by combining the present invention with other prior art features, falls within the protection scope of the present invention.

The examples do not show the specific experimental steps or conditions, and can be performed according to the conventional experimental steps described in the literature in the field. The reagents or instruments used are not indicated by manufacturers, and are all conventional reagent products which can be obtained commercially.

Example 1

This example provides a method for preparing a carboxylic acid copolymer comprising the steps of,

adding 30kg of deionized water and 6kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 35.74kg of acrylic acid and 30.25kg of isopropenylphosphonic acid into 60kg of deionized water, stirring to uniformly mix, then adding 2kg of mercaptopropionic acid, stirring to dissolve, finally adding 1kg of vitamin C, and stirring to dissolve to form a mixed solution B; and (2) after the temperature of the mixed solution A reaches 20 +/-2 ℃, uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding a hydroquinone polymerization inhibitor (28.64g) accounting for 0.035% of the total molar weight of the monomers when the mixed solution B is dropwise added into the mixed solution A for 30min, 60min, 90min, 120min and 150min respectively, beginning timing when the mixed solution B starts to be dropwise added into the mixed solution A, and reacting for 2h at 35 +/-5 ℃ after the dropwise addition is finished to obtain the carboxylic acid copolymer.

Example 2

This example provides a method for preparing a carboxylic acid copolymer comprising the steps of,

adding 30kg of deionized water and 5kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 35.12kg of methacrylic acid and 24.88kg of isopropenylphosphonic acid into 60kg of deionized water, stirring to uniformly mix, then adding 2kg of mercaptopropionic acid, stirring to dissolve, finally adding 0.85kg of vitamin C, and stirring to dissolve to form a mixed solution B; and (2) after the temperature of the mixed solution A reaches 20 +/-2 ℃, uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding hydroquinone polymerization inhibitor (23.56g) with the total molar weight of the monomers of 0.035% into the mixed solution A respectively at the dropwise adding time of 30min, 60min, 90min, 120min and 150min in the process of dropwise adding the mixed solution B into the mixed solution A, beginning timing when the mixed solution B starts to be dropwise added into the mixed solution A, and reacting for 2h at 35 +/-5 ℃ after the dropwise adding is finished to obtain the carboxylic acid copolymer.

Example 3

This example provides a method for preparing a carboxylic acid copolymer comprising the steps of,

adding 30kg of deionized water and 4.6kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 37.14kg of isopentene acid and 22.86kg of isopropenylphosphonic acid into 60kg of deionized water, stirring to uniformly mix, then adding 2kg of mercaptopropionic acid, stirring to dissolve, finally adding 0.78kg of vitamin C, and stirring to dissolve to form a mixed solution B; controlling the temperature of the mixed solution A to be 20 +/-2 ℃, then uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding a p-benzoquinone polymerization inhibitor (21.50g) with the total molar weight of monomers of 0.035% into the mixed solution B respectively at the dropwise adding time of 30min, 60min, 90min, 120min and 150min in the process of dropwise adding the mixed solution B into the mixed solution A, starting timing when the mixed solution B starts to be dropwise added into the mixed solution A, controlling the temperature of a reaction material to be 35 +/-5 ℃ after the dropwise adding is finished, and reacting for 2h to obtain the carboxylic acid copolymer.

Example 4

This example provides a method for preparing a carboxylic acid copolymer comprising the steps of,

adding 30kg of deionized water and 5kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 16.81kg of acrylic acid, 19.36kg of isopentene acid and 23.83kg of isopropenylphosphonic acid into 60kg of deionized water, stirring to uniformly mix, then adding 2kg of mercaptopropionic acid, stirring to dissolve, finally adding 0.78kg of vitamin C, and stirring to dissolve to form a mixed solution B; controlling the temperature of the mixed solution A to be 20 +/-2 ℃, then uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding hydroquinone polymerization inhibitor (34.22g) with the total monomer molar amount of 0.05% into the mixed solution B at the dropwise adding time of 30min, 60min, 90min, 120min and 150min respectively in the process of dropwise adding the mixed solution B into the mixed solution A, beginning timing when the mixed solution B starts to be dropwise added into the mixed solution A, controlling the temperature of a reaction material to be 35 +/-5 ℃ after the dropwise adding is finished, and reacting for 2h to obtain the carboxylic acid copolymer.

Example 5

This example provides a method for preparing a carboxylic acid copolymer comprising the steps of,

adding 30kg of deionized water and 6kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 35.74kg of acrylic acid and 48.12kg of diethyl isopropenylphosphonate into 60kg of deionized water, stirring to uniformly mix, then adding 2kg of mercaptopropionic acid, stirring to dissolve, finally adding 1kg of vitamin C, and stirring to dissolve to form a mixed solution B; controlling the temperature of the mixed solution A to be 20 +/-2 ℃, then uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding hydroquinone polymerization inhibitor (28.64g) with the total molar weight of monomers of 0.035% into the mixed solution B respectively at the dropwise adding time of 30min, 60min, 90min, 120min and 150min in the process of dropwise adding the mixed solution B into the mixed solution A, starting timing when the mixed solution B starts to be dropwise added into the mixed solution A, controlling the temperature of a reaction material to be 35 +/-5 ℃ after the dropwise adding is finished, and reacting for 2h to obtain the carboxylic acid copolymer.

Example 6

This example provides a method for preparing a carboxylic acid copolymer comprising the steps of,

adding 30kg of deionized water and 6kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 20kg of isopentenoic acid, 8.6kg of methacrylic acid and 36.6kg of isopropenylphosphonic acid into 60kg of deionized water, stirring to uniformly mix, then adding 2.6kg of mercaptopropionic acid, stirring to dissolve, finally adding 1kg of vitamin C, and stirring to dissolve to form a mixed solution B; and (2) after the temperature of the mixed solution A reaches 20 +/-2 ℃, uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding hydroquinone polymerization inhibitor (23.10g) accounting for 0.05 percent of the total molar amount of monomers respectively at the dropwise adding time of 30min, 60min, 90min, 120min and 150min in the process of dropwise adding the mixed solution B into the mixed solution A, beginning timing when the mixed solution B starts to be dropwise added into the mixed solution A, and reacting for 2h at 35 +/-5 ℃ after the dropwise adding is finished to obtain the carboxylic acid copolymer.

Example 7

This example provides a method for preparing a carboxylic acid copolymer comprising the steps of,

adding 30kg of deionized water and 6kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 35.74kg of acrylic acid and 30.25kg of isopropenylphosphonic acid into 60kg of deionized water, stirring to uniformly mix, then adding 2kg of mercaptopropionic acid, stirring to dissolve, finally adding 1kg of vitamin C, and stirring to dissolve to form a mixed solution B; and (3) when the temperature of the mixed solution A reaches 20 +/-2 ℃, uniformly dropwise adding the mixed solution B into the mixed solution A for 3 hours, and after dropwise adding is finished, reacting for 2 hours at 35 +/-5 ℃ to obtain the carboxylic acid copolymer.

Comparative example 1

This comparative example provides a method for preparing a copolymer using 2-acrylamido-2-methylpropanesulfonic acid instead of methacrylic acid in example 2, comprising the following steps,

adding 15kg of deionized water and 3.31kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 22.83kg of 2-acrylamide-2-methylpropanesulfonic acid and 15.86kg of isopropenylphosphonic acid into 60kg of deionized water, stirring to uniformly mix the materials, then adding 1.12kg of mercaptopropionic acid, stirring to dissolve the mercaptopropionic acid, finally adding 0.55kg of vitamin C, and stirring to dissolve the vitamin C to form a mixed solution B; and when the temperature of the mixed solution A reaches 20 +/-2 ℃, uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding hydroquinone polymerization inhibitor with the total molar weight of the monomers of 0.035% respectively at the dropwise adding time of 30min, 60min, 90min, 120min and 150min in the process of dropwise adding the mixed solution B into the mixed solution A, starting timing when the mixed solution B starts to be dropwise added into the mixed solution A, and reacting for 2h at the temperature of 40 +/-5 ℃ after the dropwise adding is finished to obtain the carboxylic acid copolymer.

Comparative example 2

This comparative example provides a method for preparing a carboxylic acid copolymer using acrylonitrile instead of methacrylic acid in example 2, comprising the steps of,

adding 15kg of deionized water and 3.34kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 12.72kg of acrylonitrile and 36.6kg of isopropenylphosphonic acid into 60kg of deionized water, stirring to uniformly mix, then adding 1.98kg of mercaptopropionic acid, stirring to dissolve, finally adding 0.56kg of vitamin C, and stirring to dissolve to form a mixed solution B; and when the temperature of the mixed solution A reaches 20 +/-2 ℃, uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding hydroquinone polymerization inhibitor with the total molar weight of the monomers of 0.035% respectively at the dropwise adding time of 30min, 60min, 90min, 120min and 150min in the process of dropwise adding the mixed solution B into the mixed solution A, starting timing when the mixed solution B starts to be dropwise added into the mixed solution A, and reacting for 2h at the temperature of 40 +/-5 ℃ after the dropwise adding is finished to obtain the carboxylic acid copolymer.

Comparative example 3

This comparative example provides a process for the preparation of a copolymer using 2-acrylamido-2-methylpropanesulfonic acid instead of the isopropenylphosphonic acid of example 2, comprising the following steps,

adding 30kg of deionized water and 5kg of ammonium persulfate into a reaction kettle, and stirring to dissolve the deionized water and the ammonium persulfate to form a mixed solution A; adding 45.66kg of 2-acrylamide-2-methylpropanesulfonic acid and 22.36kg of methacrylic acid into 60kg of deionized water, stirring to uniformly mix, then adding 2kg of mercaptopropionic acid, stirring to dissolve, finally adding 0.85kg of vitamin C, and stirring to dissolve to form a mixed solution B; and when the temperature of the mixed solution A reaches 20 +/-2 ℃, uniformly dropwise adding the mixed solution B into the mixed solution A for 3h, adding hydroquinone polymerization inhibitor with the total molar weight of the monomers of 0.035% respectively at the dropwise adding time of 30min, 60min, 90min, 120min and 150min in the process of dropwise adding the mixed solution B into the mixed solution A, starting timing when the mixed solution B starts to be dropwise added into the mixed solution A, and reacting for 2h at the temperature of 40 +/-5 ℃ after the dropwise adding is finished to obtain the carboxylic acid copolymer.

Test examples

The present test example provides the performance tests and test results of the carboxylic acid copolymers prepared in examples 1-7 and comparative examples 1-3, the test methods are as follows, and the test results are shown in Table 2.

The carboxylic acid copolymer prepared in each example and each comparative example is doped into a cement mortar mixture, the cement mortar adopts the proportion in the table 1, the mortar test cement adopts reference cement, the sand adopts standard sand, the copolymer with the designed doping amount is added into an experimental group, and the same amount of clear water is added into a blank group; wherein the water reducing agent is optimized PG-102.

TABLE 1 proportioning of the raw materials in the cement mortar

Material(s)	Cement/g	Sand/g	Water reducing agent/g	Water/g	Carboxylic acid copolymer/g
						Blank space	650	1350	4.0	240.1	\
Test of	650	1350	4.0	240	0.1

The cement mortar was stirred according to the protocol in table 1, the fluidity of the mortar was measured and then filled into molds. The test block was placed in a standard curing room for curing and the flexural and compressive strengths after 3d, 7d and 28d were recorded and the results are shown in Table 2.

The fluidity test method comprises the following steps: weighing materials according to the mass of each material in the table 1, adding the materials into a stirring pot, automatically stirring by using a mortar stirrer, wiping a glass plate and a test mold once by using wet cleaning cloth which can not be twisted out in the stirring process, covering the cleaning cloth, finishing stirring, taking the cleaning cloth away, pouring mortar into the test mold, slightly raising the opening of the test mold, scraping redundant slurry by using a spatula, vertically lifting the test mold upwards without exceeding 15s in the whole process, allowing the slurry to flow freely, scraping the mortar adhered to the wall of the test mold onto the glass plate, selecting the maximum diameter and the diameter in the vertical direction after the mortar stops flowing, and averaging to obtain the mortar flow degree.

The test method of the flexural strength and the compressive strength refers to GB/T17671-1999, which is as follows:

the method for testing the flexural strength comprises the following steps: after the test block is aged, taking out the test block from the curing box half an hour in advance, wiping off surface moisture, covering the test block with wet cleaning cloth, and after the test block is aged, flatly placing the test block in a clamp, and paying attention to the fact that the upper surface and the lower surface cannot be pressed and the side surface is pressed; setting the load speed of the pressure tester to 50N/s +/-10N/s, uniformly and vertically loading the load on the prism until the prism is broken, and automatically displaying the anti-breaking strength value by the tester.

The test method of the compressive strength comprises the following steps: and flatly placing the broken test block into a clamp, wherein the difference between the center of the test block and the pressed center of a press plate of the press is within +/-0.5 mm, and l0mm is arranged on the part of the test block exposed out of the press plate. The loading was carried out uniformly throughout the loading process at a rate of 2400N/s + -200N/s until failure. The instrument will automatically display the compressive strength value.

TABLE 2 fluidity and strength of cement mortar

As can be seen from the experimental results shown in Table 2, the carboxylic acid copolymer of the present invention, when added to cement and used in combination with a water reducing agent, can provide cement with better compressive strength and flexural strength, and for the present field, the effect of significantly increasing the strength is brought about by the increase of the hydration rate of cement when the ratio of cement to sand to water is fixed.

It can also be seen from the results of table 2 that when the carboxylic acid copolymer contains isopropenylphosphonic acid, isopentenylic acid and methacrylic acid in a specific ratio at the same time, the resulting carboxylic acid copolymer brings about the most advantageous technical effects when used in cement.

FIG. 1 shows the appearance of a cement paste obtained by adding a water reducing agent but not adding the carboxylic acid copolymer of the present invention under an electron microscope, FIG. 2 shows the appearance of a cement paste obtained by adding the water reducing agent and the carboxylic acid copolymer of the present invention in example 1 under an electron microscope, and it can be known from comparing FIG. 1 with FIG. 2 that the significant flocculation phenomenon can be reduced by adding the carboxylic acid copolymer of the present invention.

This test example also provides the results of measuring the molecular weight of the carboxylic acid copolymers obtained in examples 1 and 7, and the molecular weight distribution was measured by Gel Permeation Chromatography (GPC).

The molecular weight distribution of the carboxylic acid copolymer of example 1 is shown in table 3 and fig. 3; the molecular weight distribution of the carboxylic acid copolymer of example 7 is shown in table 4 and fig. 4.

TABLE 3 molecular weight distribution of the carboxylic acid copolymer obtained in example 1

	Number average molecular weight (Mn)	Weight average molecular weight (Mw)	Mw/Mn	％
					Total of	1	1286	1199.71383	100.0000
1	1466	1474	1.00544	56.7431
					2	1152	1156	1.00332	37.3083
3	827	830	1.00371	2.2326
					4	0	0	1.13437	3.7160

TABLE 4 molecular weight distribution of the carboxylic acid copolymer obtained in example 7

	Number average molecular weight (Mn)	Weight average molecular weight (Mw)	Mw/Mn	％
					Total of	1	4776	3257.62874	100.0000
1	4989	5832	1.16890	75.5945
					2	1794	1812	1.01036	19.6248
3	798	823	1.03065	1.4043
					4	0	8	158.23252	3.3765

The test results of example 1 and example 7 show that the molecular weight of the polymer can be controlled well by adding the polymerization inhibitor in the present invention, and that the strength of cement can be improved when the carboxylic acid copolymer is used for cement.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.