Hyperbranched polycarboxylic acid concrete superplasticizer and preparation method thereof

Abstract

The application provides a hyperbranched polycarboxylic acid concrete superplasticizer, which comprises the following raw materials: monomer A, monomer B and monomer C, wherein the atom transfer radical polymerization reaction occurs among the monomer A, the monomer B and the monomer C, the molar amount of the monomer A and the monomer B satisfies B / A=(2.5-8):1, the molar amount of the monomer C satisfies C / (A+B)=(0.01-0.5):1 in relation to the total molar amount of the monomer A and the monomer B, and the monomer C contains two terminal olefin groups in the structure. The method has the advantages of good water solubility, no crosslinking polymer, controllable branched structure, mild preparation method, few synthesis steps, simple reaction device, multiple applicable solvents, convenient recovery, small environmental pollution, and the like. The polycarboxylic acid superplasticizer prepared by the method has the advantages of low mixing amount, high water-reducing rate, small slump loss, viscosity reduction, good clay adaptability, and the like.

Description

Technical Field

[0001] This invention relates to the field of concrete admixtures, specifically to a hyperbranched polycarboxylate superplasticizer for concrete and its preparation method. Background Technology

[0002] Polycarboxylate superplasticizers, as an important component in concrete, are increasingly becoming a research focus due to their high degree of molecular design freedom. While significant improvements have been made in comonomers and copolymerization techniques, they still cannot fully meet the current requirements of construction projects for high-performance cement dispersants, such as high water reduction rates, low viscosity, and strong clay adaptability. In particular, the high clay content of low-grade, inferior sand and gravel aggregates has become a significant obstacle to their application. The polyethoxylated side chains of ordinary comb-type polycarboxylate superplasticizers readily form hydrogen bonds with the silanol groups between clay mineral layers through water molecules as bridges. Furthermore, clay has a very large specific surface area, resulting in a higher adsorption rate of polycarboxylate superplasticizers compared to cement. Even trace amounts of clay in the aggregate can severely reduce the water-reducing performance of polycarboxylate superplasticizers. Therefore, developing a polycarboxylate superplasticizer that can inhibit the side effects of clay has become an urgent research requirement.

[0003] Developing novel structural polycarboxylic acid copolymers has become a direction for improving the performance of polycarboxylic acid superplasticizers. Researchers have found that the topological structure can not only increase the number of adsorption groups in the polymer molecular structure, but also has greater steric hindrance, which improves the dispersion effect on cement. At the same time, the novel topological structure also endows polycarboxylic acid superplasticizers with properties such as clay adaptability and lower viscosity.

[0004] Currently, there are few reports on methods for synthesizing hyperbranched polycarboxylate superplasticizers. Patent CN104371071 reports a method of introducing polymerizable monomers containing halogens (chlorine, bromine) and then synthesizing hyperbranched polycarboxylate superplasticizers via self-condensation vinyl polymerization. However, the halogen-containing polymerizable monomers used in this method are expensive, highly toxic, and the synthesis process is cumbersome and causes environmental pollution. Patent CN101580353 reports a method for preparing highly efficient hyperbranched polycarboxylate superplasticizers, which involves grafting hyperbranched polyamide structures onto both ends of the polymer backbone through a multi-step reaction. This method only introduces hyperbranched structures at the ends of the polymer chain, making it difficult to fully realize the advantages of hyperbranched structures. Furthermore, the synthesis steps are cumbersome, some raw materials are expensive, and the cost is high.

[0005] Patent CN106957398 reports a plasticizer with an eight-arm polyamide-amine dendritic macromolecule capped with unsaturated double bonds as its core, which can have water-reducing and slump-retaining effects. However, the process of first synthesizing amide-amine dendritic macromolecules and then pretreating them with carboxylic acid monomers containing unsaturated double bonds, followed by polymerizing the pretreated unsaturated dendritic macromolecules into polycarboxylic acid superplasticizers, is cumbersome and will inevitably increase the production cost of superplasticizers.

[0006] Patent CN102002134 reports a method of first synthesizing a star-shaped central structure with bromine at the end of a halide, and then preparing a hyperbranched polycarboxylic acid superplasticizer with carboxyl groups on the main chain by atom transfer radical polymerization. However, the star core structure synthesized in the first step has fixed the number of branching sites, and the branching rate cannot be further improved.

[0007] Patent CN104371078 reports a method that uses α-positions containing tertiary amines to generate free radicals, initiating free radical copolymerization of unsaturated macromonomers and monomers with adsorption properties. The unsaturated double bonds of the tertiary amine-containing unsaturated monomers also participate in the polymerization, thus forming a hyperbranched structure. This method suffers from poor control over the polymerization process, leading to excessive crosslinking, poor water solubility of the product, and decreased dispersion performance for cement particles.

[0008] Patent CN108586672 reports a polycarboxylate superplasticizer synthesized via free radical polymerization using hydroxymethylpropane triacrylate as a crosslinking point. This superplasticizer has a crosslinked structure and achieves slow-release and slump-retaining effects through hydrolysis in cement. While the crosslinked superplasticizer can achieve slow-release and slump-retaining effects, it delays the contact between some adsorbed groups and cement particles, leading to a decrease in initial water-reducing capacity.

[0009] Traditional free radical polymerization synthesizes highly branched polymers, but this method often leads to partial crosslinking in the early stages of polymerization due to its inherent limitations of slow initiation rates and rapid chain growth and termination reactions.

[0010] Developing a simple, low-cost, non-crosslinked hyperbranched polycarboxylate superplasticizer with excellent performance is of great significance. Summary of the Invention

[0011] The purpose of this invention is to address the limitations of existing polycarboxylate superplasticizers in dispersing cement, reducing viscosity, and adapting to clay. Furthermore, existing topological polycarboxylate superplasticizers suffer from complex synthesis steps, expensive raw materials, and easy cross-linking during polymerization, resulting in a lack of significant structural advantages. This invention provides a polycarboxylate superplasticizer with a hyperbranched structure that has a simple and controllable polymerization process and does not cross-link, along with its preparation method. The prepared product has advantages such as low dosage, high water reduction rate, minimal slump loss, and good clay adaptability.

[0012] A hyperbranched polycarboxylate superplasticizer for concrete comprises the following raw materials: monomer A, monomer B, and monomer C, wherein monomer A, monomer B, and monomer C undergo an atom transfer radical polymerization reaction. The molar amounts of monomer A and monomer B satisfy B / A = (2.5~8):1, and the molar amount of monomer C and the total molar amount of monomer A and monomer B satisfy C / (A+B) = (0.01~0.5):1.

[0013] Atom transfer radical polymerization of monomers A, B, and C synthesizes a polymer with a structure containing carboxyl groups, long polyether chains, and terminal double bonds of monomer C. The terminal double bonds of monomer C further react with monomers A, B, and unpolymerized monomer C, resulting in a hyperbranched polycarboxylic acid superplasticizer.

[0014] The above monomer A is represented by general formula (1) or general formula (2):

[0015] Wherein, R1 represents H or CH3; X represents O, CH2O, CH2CH2O; m represents the average number of moles of oxyethylene addition, where m is an integer from 5 to 200; n represents the average number of moles of oxypropylene addition, where n is an integer from 0 to 50. The order of connection of the repeating units of oxyethylene and oxypropylene is not limited here, and it can be a block or random polymer; monomer A mainly provides steric hindrance effect, thereby giving the hyperbranched copolymer excellent dispersion properties and slump retention properties.

[0016] The monomer B mentioned above is represented by general formula (3):

[0017] In this context, R2 represents H or COOM; R3 represents H or CH3; M represents H, Na, K, or NH4; the general formula of monomer B includes molecules with various chiral, cis-trans isomeric, and other conformational relationships, and monomer B mainly provides adsorption groups.

[0018] The aforementioned monomer C structure contains two terminal alkenyl groups.

[0019] Preferably, the monomer C is represented by general formula (C1), general formula (C2), general formula (C3), general formula (C4), general formula (C5), general formula (C6), or general formula (C7):

[0020] Monomer C primarily provides branching points for the hyperbranched structure of the polymer, thereby regulating the branching rate of the hyperbranched copolymer and providing greater steric hindrance. The amount of monomer C is extremely important to this invention. The molar amount of monomer C and the total molar amount of monomers A and B satisfy the following formula: C / (A+B)=(0.01~0.5):1. If the amount of monomer C is too small, there will be too few branching sites, and it will not be able to provide a sufficiently large steric hindrance effect; if the amount of monomer C is too large, it will cause the branching rate of the product to increase sharply, resulting in polymer chain segments that are too short, which is not conducive to the rapid adsorption of the product with cement particles to achieve a dispersion effect.

[0021] The weight-average molecular weight of the above-mentioned hyperbranched polycarboxylate superplasticizers for concrete is 20,000 to 60,000.

[0022] The monomer A mentioned above is selected from at least one of isopentenyl polyoxyethylene, allyl polyoxyethylene, vinyl polyoxyethylene, isobutylene polyoxyethylene, isopentenyl poly(oxyvinyl-oxypropylene), and ω-methoxy polyoxyethylene methacrylate with a molecular weight of (300-5000).

[0023] The monomer B mentioned above is selected from at least one of acrylic acid, methacrylic acid, maleic acid, or their corresponding sodium, potassium, or ammonium salts.

[0024] The preparation method of the hyperbranched polycarboxylate superplasticizer for concrete according to any one of claims 1-4 includes the following steps: (1) After uniformly dispersing monomer A, monomer B, monomer C, initiator, catalyst and solvent, N2 is introduced to remove oxygen from the mixture while N2 is used as a protective gas, and the mixture is placed under light source conditions for 5h to 15h to obtain a hyperbranched polymer solution; (2) The solvent is removed by vacuum distillation, and then the pH of the solution is adjusted to neutral to obtain a uniform and transparent aqueous solution of hyperbranched polycarboxylate superplasticizer for concrete.

[0025] In step (1) above, the total mass of monomers A, B, and C is controlled to account for 35-60% of the total mass of all materials, where all materials refer to monomers A, B, C, initiator, catalyst, and solvent.

[0026] In step (1) above, the initiator is any one of ethyl α-bromophenylacetate, methyl 2-bromopropionate, or ethyl 2-bromo-2-methylpropionate; the amount of the initiator used is 1 / 200 to 1 / 50 of the total molar amount of monomer A, monomer B, and monomer C.

[0027] In step (1) above, the catalyst is either graphite-like carbon nitride (g-C3N4) or triarylhexafluorophosphate thioonium salt; the amount of the catalyst used is 1 / 100 to 1 / 20 of the total mass of monomers B and C.

[0028] In step (1) above, the solvent is at least one of dimethyl sulfoxide, dichloromethane, tetrahydrofuran, ethyl acetate, acetonitrile, 1,4-dioxane, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, toluene, and water.

[0029] In step (1) above, the light source has a wavelength of 350-480nm.

[0030] After the polymerization reaction in step (2) above is completed, dilute sodium hydroxide solution is added to the reactants to adjust the pH to 6.0-7.0 in order to improve the storage stability of the product.

[0031] The hyperbranched polycarboxylate superplasticizer for concrete described in this invention can also be used in combination with at least one superplasticizer selected from known prior art lignin sulfonate superplasticizers, naphthalene sulfonate / formaldehyde condensate superplasticizers, phenol / p-aminobenzenesulfonic acid / formaldehyde condensate superplasticizers, melamine sulfonate / formaldehyde condensate superplasticizers, polycarboxylate superplasticizers, etc. In addition to the known concrete superplasticizers mentioned above, air-entraining agents, early-strength agents, thickeners, and defoamers can also be added.

[0032] The present invention has the following advantages over the prior art:

[0033] 1. The method of the present invention has the advantages of good water solubility and controllable crosslinking degree compared with the reported hyperbranched polycarboxylate concrete superplasticizers;

[0034] 2. Compared with the reported synthesis of polycarboxylic acid superplasticizers by atom transfer radical polymerization, the method of the present invention has the advantages of not requiring catalysts or ligands, using light-controlled "start-stop" of the atom transfer radical polymerization process, which improves the flexibility of operation; mild conditions, fewer synthesis steps, simple reaction equipment, applicable to a wide variety of solvents, convenient recovery, and less environmental pollution.

[0035] 3. The polycarboxylate superplasticizer prepared by the method of the present invention has the advantages of low dosage, high water reduction rate, small slump loss, viscosity reduction and good clay adaptability as a concrete admixture. Detailed Implementation

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0037] In this embodiment of the invention, the molecular weight of all polymers was determined using an Agilent GPC1260, and the experimental conditions were as follows: Gel permeation chromatography column: TSKguard Column PWXL + TSKgel G3000PWXL + mixed bed column TSKgel . GMPWXL three-column tandem; mobile phase: 0.1M NaNO3 solution; mobile phase rate: 1 ml / min; injection: 20 μL 0.5% aqueous solution; detector: Agilent differential refractive index detector; standard: polyethylene glycol GPC standard (Sigma-Aldrich, molecular weight 1,010,000, 478,000, 263,000, 118,000, 44,700, 18,600, 6,690, 1,960, 628, 232).

[0038] Example 1

[0039] 1.22 g C1 (n = 1), 44.5 g isopentenyl polyoxyethylene (Mn = 600 g / mol), 20.9 g sodium acrylate, 0.4 g g-C3N4, 1.2 g α-bromophenylethyl acetate, and 57.5 g tetrahydrofuran were mixed and dispersed evenly. N2 was introduced to remove O2 from the solution and act as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 7 h to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight average molecular weight was 22655 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral to obtain a uniform and transparent aqueous solution of hyperbranched polycarboxylate concrete superplasticizer.

[0040] Example 2

[0041] 0.61g C2, 55.63g allyl polyoxyethylene (Mn = 1200g / mol), 17.4g sodium acrylate, 0.4g g-C3N4, 0.64g α-bromophenylethyl acetate, and 50.99g dichloromethane were mixed and dispersed evenly. N2 was then introduced to remove O2 from the solution, which also served as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 12 hours to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight-average molecular weight was determined to be 39353 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral, yielding a hyperbranched polycarboxylate superplasticizer for concrete.

[0042] Example 3

[0043] 1.67g C3 (n=2), 44.5g isobutylene-based polyoxyethylene (Mn=2400g / mol), 12g sodium acrylate, 0.37g g-C3N4, 0.45g ethyl 2-bromo-2-methylpropionate, and 50.99g toluene were mixed and dispersed evenly. N2 was introduced to remove O2 from the solution and act as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 9 hours to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight average molecular weight was 40185 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral to obtain a uniform and transparent aqueous solution of hyperbranched polycarboxylate concrete superplasticizer.

[0044] Example 4

[0045] 2.0 g C4 (n=1), 47.5 g isopentenyl poly(oxyvinyl-oxypropylene) (Mn=2400 g / mol), 12.6 g sodium acrylate, 0.3 g g-C3N4, 0.27 g α-bromophenylethyl acetate, and 60.1 g ethanol were mixed and dispersed evenly. N2 was then introduced to remove O2 from the solution, which was used as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 12 h to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight-average molecular weight was 45567 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral, resulting in a uniform and transparent aqueous solution of hyperbranched polycarboxylate-based concrete superplasticizer.

[0046] Example 5

[0047] 1.6 g of C4 (n=5), 89 g of isobutylene-based polyoxyethylene (Mn=2400 g / mol), 19 g of sodium acrylate, 0.5 g of g-C3N4, 0.23 g of methyl 2-bromopropionate, and 102 g of ethanol were mixed and dispersed evenly. N2 was then introduced to remove O2 from the solution, which was used as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 10 h to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight-average molecular weight was determined to be 53757 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral, resulting in a uniform and transparent aqueous solution of hyperbranched polycarboxylate-based concrete superplasticizer.

[0048] Example 6

[0049] 1.1 g of C6 (n=1), 89 g of isopentenyl polyoxyethylene (Mn=3000 g / mol), 16 g of sodium acrylate, 0.42 g of triarylhexafluorophosphate sulfonium salt, 0.5 g of α-bromophenylethyl acetate, and 105 g of water were mixed and dispersed evenly. N2 was then introduced to remove O2 from the solution, which was used as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 15 h to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight-average molecular weight was determined to be 38846 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral, resulting in a uniform and transparent aqueous solution of hyperbranched polycarboxylate-based concrete superplasticizer.

[0050] Example 7

[0051] 2.9g C7, 45.5g vinyl polyoxyethylene (Mn = 2400g / mol), 8g sodium acrylate, 0.28g triarylhexafluorophosphate sulfonium salt, 0.37g α-bromophenylethyl acetate, and 70g ethanol were mixed and dispersed evenly. N2 was then introduced to remove O2 from the solution, which served as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 15 hours to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight-average molecular weight was determined to be 44552 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral, resulting in a uniform and transparent aqueous solution of hyperbranched polycarboxylate-based concrete superplasticizer.

[0052] Comparative Example 1

[0053] In a three-necked round-bottom flask equipped with a thermometer and stirrer, 45.5 g of vinyl polyoxyethylene (Mn = 2400 g / mol) and 30 g of ethanol were mixed and placed in a constant temperature bath. After heating to 65 °C and stirring for 15 min, 2.9 g of C7, 8 g of sodium acrylate and 20 g of distilled water were added dropwise over 3 hours. Then, 1.42 g of ammonium persulfate and 20 g of distilled water were added dropwise over 3.5 hours. After the addition was complete, the temperature was raised to 70 °C and maintained at this temperature for 2 hours. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain a hyperbranched polymer. The weight-average molecular weight was 44,000 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral, resulting in a uniform and transparent aqueous solution of hyperbranched polycarboxylate-based concrete superplasticizer.

[0054] Comparative Example 2

[0055] The most common commercially available polycarboxylate superplasticizer is PCA(I) polycarboxylate superplasticizer produced by Jiangsu Subote New Material Co., Ltd.

[0056] Comparative Example 3

[0057] 0.1 g C4 (n=1), 47.5 g isopentenyl poly(oxyvinyl-oxypropylene) (Mn=2400 g / mol), 12.6 g sodium acrylate, 0.3 g g-C3N4, 0.27 g ethyl α-bromophenylacetate, and 60.1 g ethanol were mixed and dispersed evenly. N2 was then introduced to remove O2 from the solution, which was used as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 12 h to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight-average molecular weight was determined to be 58567 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral, resulting in a uniform and transparent aqueous solution of hyperbranched polycarboxylate-based concrete superplasticizer.

[0058] Comparative Example 4

[0059] 20g of C4 (n=1), 47.5g of isopentenyl poly(oxyvinyl-oxypropylene) (Mn=2400g / mol), 12.6g of sodium acrylate, 0.3g of g-C3N4, 0.27g of α-bromophenylethyl acetate, and 60.1g of ethanol were mixed and dispersed evenly. N2 was then introduced to remove O2 from the solution, which was used as a protective gas. Atom transfer radical polymerization was carried out under light irradiation for 12 hours to obtain a hyperbranched polymer solution. The solvent and unreacted small molecule compounds were removed by vacuum distillation to obtain the hyperbranched polymer. The weight-average molecular weight was determined to be 17757 by aqueous phase GPC analysis. The solution was diluted with water to adjust the pH to neutral, resulting in a uniform and transparent aqueous solution of hyperbranched polycarboxylate-based concrete superplasticizer.

[0060] Test Example 1: To evaluate the dispersion and dispersion retention properties of the hyperbranched polycarboxylate superplasticizer for concrete prepared in this invention, the flowability of cement paste was tested according to GB / T 8077-2012 standard. 300g of cement and 87g of water were added, and the mixture was stirred immediately (slow stirring for 120s, pause for 15s, then rapid stirring for 120s). The flowability of the cement paste was then measured on a flat glass plate, and the flowability was also tested after 30 minutes. The experimental results are shown in Table 1.

[0061] Table 1

[0062]

[0063] With the water-cement ratio kept constant, the dosage refers to the proportion of superplasticizer to cement. The dosage of hyperbranched polycarboxylate superplasticizer is 0.12%, and the dosage of comparative examples (Comparative Example 1: polycarboxylate superplasticizer obtained by free radical polymerization; Comparative Example 2: commercially available polycarboxylate superplasticizer PCA(I); Comparative Example 3: polycarboxylate superplasticizer synthesized with monomer C content below the required range; Comparative Example 4: polycarboxylate superplasticizer synthesized with monomer C content above the required range) is 0.15%. The cement with samples from Examples 1 to 7 exhibits better initial fluidity and mid-to-late stage fluidity retention than the comparative examples. Furthermore, the cement with sample from Example 7 exhibits better initial fluidity than the partially cross-linked sample from Comparative Example 1 obtained through free radical polymerization. Comparative Examples 3 and 4, obtained with monomer C content that is too low or too high, show significantly worse initial fluidity and mid-to-late stage fluidity retention compared to Example 4. These results demonstrate that the hyperbranched polycarboxylate superplasticizer-dispersed cement synthesized using this method has the characteristics of low dosage and high water reduction rate.

[0064] Test Example 2: To evaluate the clay adaptability of the hyperbranched polycarboxylate superplasticizer for concrete prepared in this invention, the flowability of cement paste was tested in the examples and comparative examples according to GB / T 8077-2012 standard (the difference being the addition of a small amount of montmorillonite). The mixture consisted of 300g cement, 3g montmorillonite, and 87g water. The mixture was stirred immediately (slow stirring for 120s, paused for 15s, then rapid stirring for 120s). The flowability of the cement paste was then measured on a flat glass plate after the experiment, and the flowability was also tested after 30 minutes and 60 minutes. The experimental results are shown in Table 2.

[0065] Table 2

[0066]

[0067]

[0068] The results show that by adding 1% montmorillonite, increasing the dosage of samples in Examples 1-7 from 0.12% to 0.13% achieves cement slurry fluidity similar to that without montmorillonite; while the dosage of traditional comb-type polycarboxylate superplasticizer needs to be increased from 0.15% to 0.19% to reach the previous level. Therefore, the hyperbranched polycarboxylate superplasticizer for concrete prepared by this method exhibits better clay adaptability than traditional comb-type polycarboxylate superplasticizers.

[0069] Test Example 3: The hyperbranched polycarboxylate superplasticizers of concrete from Examples 1-7 and the comparative sample were added to concrete as admixtures. The concrete mix proportions are shown in Table 3 below:

[0070] Table 3

[0071]

[0072] The specific testing method is as follows:

[0073] Concrete slump and viscosity test methods: The consistency test method was conducted according to GB / 50080-2002 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The test included the time Ts for the concrete to flow out of the slump bucket, the time T50 for the concrete to reach 500 mm of spread, and the slump and spread of the concrete. The experimental data obtained through the above test methods are shown in Table 4.

[0074] Table 4

[0075]

[0076]

[0077] As shown in the table above, after adding the hyperbranched polycarboxylate superplasticizers from Examples 1-7, the fluidity of the concrete was significantly enhanced compared to the comparative example, and the slump loss was also less. This indicates that the hyperbranched polycarboxylate superplasticizer has a good viscosity-reducing effect when applied to high-strength concrete. In summary, the hyperbranched polycarboxylate superplasticizer and its preparation method according to the embodiments of this application have a good viscosity-reducing effect when applied to high-strength concrete.

[0078] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A hyperbranched polycarboxylate superplasticizer for concrete, characterized in that, Including the following raw materials: Monomers A, B, and C are involved in an atom transfer radical polymerization reaction; the molar amounts of monomers A and B satisfy B / A = (2.5~8):1, and the molar amount of monomer C and the total molar amount of monomers A and B satisfy C / (A+B) = (0.01~0.5):

1. The monomer A is represented by general formula (1) or general formula (2): ， Wherein, R1 represents H or CH3; X represents O, CH2O, CH2CH2O; m represents the average number of moles of oxyethylene addition, where m is an integer from 5 to 200; n represents the average number of moles of oxypropylene addition, where n is an integer from 0 to 50. The order of connection of the repeating units of oxyethylene and oxypropylene is not limited here, and it can be a block or random polymer. The monomer B is represented by general formula (3): （3）， Wherein, R2 represents H or COOM; R3 represents H or CH3; M represents H, Na, K or NH4; The monomer C is represented by general formula (C1), general formula (C2), general formula (C3), general formula (C4), general formula (C5), general formula (C6), or general formula (C7): ； Atom transfer radical polymerization of monomers A, B, and C synthesizes a polymer with a structure containing carboxyl groups, long polyether chains, and terminal double bonds of monomer C. The terminal double bonds of monomer C further react with monomers A, B, and unpolymerized monomer C, resulting in a polycarboxylic acid superplasticizer with a hyperbranched structure. The "start-stop" process of controllable atom transfer radical polymerization is controlled by light. The wavelength of the light source is 350~480nm.

2. The hyperbranched polycarboxylate superplasticizer for concrete according to claim 1, characterized in that: The weight-average molecular weight of the hyperbranched polycarboxylate superplasticizer for concrete is 20,000 to 60,000.

3. The hyperbranched polycarboxylate superplasticizer for concrete according to claim 1, characterized in that: The monomer A is selected from at least one of isopentenyl polyoxyethylene, allyl polyoxyethylene, vinyl polyoxyethylene, isobutyleneyl polyoxyethylene, isopentenyl poly(oxyvinyl-oxypropylene), and ω-methoxy polyoxyethylene methacrylate.

4. The hyperbranched polycarboxylate superplasticizer for concrete according to claim 1, characterized in that: The monomer B is selected from at least one of acrylic acid, methacrylic acid, maleic acid, or their corresponding sodium, potassium, or ammonium salts.

5. The method for preparing the hyperbranched polycarboxylate-based concrete superplasticizer according to any one of claims 1-4, characterized in that, Includes the following steps: (1) After mixing and dispersing monomers A, B, C, initiator, catalyst and solvent evenly, N2 is introduced to remove oxygen from the mixture. At the same time, N2 is used as a protective gas. The mixture is placed under light source conditions and reacted for 5h~15h to obtain hyperbranched polymer solution; (2) The organic solvent is removed by vacuum distillation, and then water is added to dilute and adjust the pH of the solution to neutral to obtain hyperbranched polycarboxylic acid concrete superplasticizer.

6. The preparation method of the hyperbranched polycarboxylate superplasticizer for concrete according to claim 5, characterized in that: In step (1), the total mass of monomers A, B, and C is controlled to account for 35-60% of the total mass of all materials, where all materials refer to monomers A, B, and C, initiator, catalyst, and solvent.

7. The method for preparing hyperbranched polycarboxylate superplasticizer for concrete according to claim 5, characterized in that: In step (1), the initiator is any one of ethyl α-bromophenylacetate, methyl 2-bromopropionate, and ethyl 2-bromo-2-methylpropionate; the amount of the initiator is 1 / 200 to 1 / 50 of the total molar amount of monomer A, monomer B, and monomer C.

8. The method for preparing hyperbranched polycarboxylate superplasticizer for concrete according to claim 5, characterized in that: In step (1), the catalyst is either graphitic carbon nitride (g-C3N4) or triarylhexafluorophosphate thioonium salt; the amount of catalyst used is 1 / 100 to 1 / 20 of the total mass of monomers B and C.

9. The method for preparing hyperbranched polycarboxylate superplasticizer for concrete according to claim 5, characterized in that: The solvent in step (1) is at least one of dimethyl sulfoxide, dichloromethane, tetrahydrofuran, ethyl acetate, acetonitrile, 1,4-dioxane, ethanol, N,N-dimethylformamide, N,N-dimethylacetamide, toluene, and water.

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