A hyperbranched polycarboxylic acid water reducing agent and a preparation method thereof

Abstract

The application relates to the technical field of water-reducing agents, and particularly discloses a hyperbranched polycarboxylic acid water-reducing agent and a preparation method thereof. The hyperbranched polycarboxylic acid water-reducing agent is prepared by copolymerization of the following monomer raw materials: unsaturated carboxylic acid monomers, polyether macromonomers, functional monomers containing phosphate groups, monomers containing rigid benzene ring structures and hydrophobic association monomers containing long-chain alkyl groups; the preparation method comprises the following steps: dissolving the five kinds of monomers in water to prepare a mixed monomer solution; synchronously adding the mixed monomer solution and an oxidation-reduction initiator solution to the water which is heated to 30-60 DEG C; keeping the temperature at 55-65 DEG C for 1-2 hours; cooling to below 40 DEG C; adding a chain transfer agent with a mass fraction of 0.5%-1.5% of the total mass of the monomers; stirring for 0.5 hours; adjusting the pH to 6.0-7.0 by using alkali solution; and obtaining the product. The hyperbranched polycarboxylic acid water-reducing agent solves the stability contradiction problem that the slurry is easy to separate and bleed when the polycarboxylic acid water-reducing agent pursues high water-reducing rate.

Description

Technical Field

[0001] This application relates to the field of water-reducing agent technology, and more specifically, to a hyperbranched polycarboxylate water-reducing agent and its preparation method. Background Technology

[0002] With the increasing demand for high-strength, high-fluidity concrete in modern construction, polycarboxylate superplasticizers have become the mainstream choice due to their high water-reduction potential. In engineering projects, to reduce the water-cement ratio and increase concrete strength, it is necessary to optimize the molecular structure of the superplasticizer to achieve a high water reduction rate (typically requiring a water reduction rate ≥30%). However, under high water-reduction conditions, the proportion of free water in the cement paste increases, disrupting the lubrication balance between particles. On the one hand, excessive free water easily leads to aggregate settling and surface water rising, not only increasing the difficulty of fluidity control during construction but also causing hardened concrete to form internal pores and a layered structure, reducing compressive strength by 10%-20%. On the other hand, reducing the superplasticizer dosage to avoid segregation sacrifices the water-reduction effect, failing to meet the pumping and pouring requirements of high-fluidity concrete. This contradiction between "high water reduction and stable paste" has long constrained the application scope of polycarboxylate superplasticizers. Traditional polycarboxylate superplasticizers have a main molecular chain composed of flexible carbon chains. Under the alkaline environment of cement paste (pH≥12) and the adsorption pressure of particles, the main chain is prone to curling and shrinking, preventing the polyether side chains from continuously extending. The steric hindrance effect decays over time, resulting in significant slump loss. Existing improvement methods, such as introducing retarder components (e.g., sodium gluconate), can slow down the hydration process, but this reduces the early strength of concrete by 15%-25% on the first day. Increasing the side chain density to improve stability leads to increased paste viscosity, affecting pumpability. Furthermore, even if the fresh concrete meets performance standards, hardened concrete, lacking a stable microbubble system, is prone to cracking during freeze-thaw cycles in cold regions due to internal moisture freezing and expansion. After 200 freeze-thaw cycles, the mass loss rate often exceeds 5%, and insufficient freeze-thaw durability further limits the widespread application of polycarboxylate superplasticizers in major projects in frigid northern regions. Summary of the Invention

[0003] To address the instability issue of slurry segregation and bleeding that often occurs when pursuing high water reduction rates with polycarboxylate superplasticizers, this application provides a hyperbranched polycarboxylate superplasticizer and its preparation process.

[0004] The first part of this application provides a hyperbranched polycarboxylate superplasticizer using the following technical solution: A hyperbranched polycarboxylate superplasticizer is prepared by copolymerization of monomer raw materials comprising the following in molar amounts: 3-10 parts of unsaturated carboxylic acid monomers; 1-3 parts of polyether macromonomer; 5-20 parts of functional monomers containing phosphate groups; 0.5-5 parts of monomers containing rigid benzene ring structures; 0.1-2 parts of a hydrophobic associating monomer containing long-chain alkyl groups.

[0005] By employing the above technical solution and through the synergistic copolymerization of these five monomers, a molecule with a unique "hyperbranched topology" was constructed. The unsaturated carboxylic acid monomer provides adsorption groups (-COOH), enabling the molecule to anchor onto the surface of cement particles; the polyether macromonomer provides long side chains that extend in water to form a strong steric hindrance effect, preventing cement particle flocculation—this is the core of achieving high water reduction; the functional monomer containing phosphate ester groups provides stronger anchoring ability and anti-mud properties; the monomer containing a rigid benzene ring is embedded in the main chain, enhancing the steric stability of the molecule and reducing chain coiling under high-pressure adsorption, thus ensuring the durability of the water reduction effect; and a small amount of hydrophobic associating monomers containing long-chain alkyl groups can form a weak, reversible cross-linked network in aqueous solution through hydrophobic interactions. This network effectively increases the viscosity of the cement paste, preventing particle segregation and bleeding due to excessive water under high water reduction conditions, thereby resolving the contradiction between high water reduction and paste stability.

[0006] Optionally, the unsaturated carboxylic acid monomer is at least one of acrylic acid and methacrylic acid; the polyether macromonomer is at least one of methyl allyl polyoxyethylene ether and isopentenyl alcohol polyoxyethylene ether, with a number average molecular weight of 1000-3000; and the hydrophobic associating monomer containing long-chain alkyl groups is at least one of octadecyl methacrylate, hexadecyl acrylate, and allyl octadecyl ether.

[0007] By employing the above technical solutions, acrylic acid or methacrylic acid, due to their high reactivity and suitable acidity, can efficiently provide carboxyl adsorption sites. Methallyl polyoxyethylene ether (HPEG) or isopentenyl polyoxyethylene ether (TPEG) are chosen as polyether macromonomers because they possess double-bonded functional groups, are easy to copolymerize, and their polyoxyethylene ether segments (PEG) are the best choice for generating steric hindrance effects. Limiting their molecular weight to 1000-3000 is to balance steric hindrance effects with molecular mobility: too low a molecular weight results in insufficient steric hindrance, while too high a molecular weight leads to excessive molecular chain entanglement, potentially affecting adsorption and dispersion efficiency. Octadecyl methacrylate and similar products are specified as hydrophobic associating monomers because their long-chain alkyl groups (C16-C18) have suitable hydrophobicity, enabling them to form a reversible associating network of moderate strength in water, effectively controlling slurry rheology without causing excessive flocculation or precipitation.

[0008] Optionally, the molar ratio of the functional monomer containing the phosphate ester group to the unsaturated carboxylic acid monomer is (3:1) to (5:1).

[0009] By employing the above technical solution, carboxylic acid groups (-COOH) exhibit strong adsorption of calcium ions on the surface of cement particles, while phosphate groups (-PO4) demonstrate a stronger and more stable chelating adsorption effect on the aluminum phase in cement particles. Especially in the presence of clay-containing aggregates, phosphate groups preferentially adsorb onto the clay surface, thereby counteracting the ineffective adsorption of the water-reducing agent by the clay and significantly improving the water-reducing agent's resistance to clay. Maintaining a high molar ratio of 3:1 to 5:1 aims to introduce sufficient strong anchoring points into the molecular structure, ensuring that the polymer molecules are firmly adsorbed on the surface of cement particles and are not easily desorbed. This provides stable support for the polyether side chains, fully utilizing their steric hindrance effect, which is crucial for achieving high water reduction rates and low water loss over time.

[0010] Optionally, the monomer containing the rigid benzene ring structure is one of benzyl methacrylate and vinyl benzoic acid.

[0011] By employing the above technical solution, the benzene ring, a large, rigid planar structure, can be chemically bonded to the polymer backbone or near-backbone positions, generating a significant "rigidity effect." This effect effectively resists the bending and coiling of the polymer backbone under solvation and pressure, ensuring that the polymer molecules adsorbed on the surface of cement particles maintain an extended conformation, thus making the steric hindrance effect provided by its polyether side chains more durable and stable. This directly translates into superior slump retention performance (i.e., reduced slump loss over time). The specified monomers all contain a polymerizable double bond and a benzene ring, and their chemical structure ensures that the benzene ring can be effectively fixed to the polymer backbone, thereby maximizing their rigidity-enhancing effect.

[0012] Secondly, this application provides a method for preparing a hyperbranched polycarboxylate superplasticizer, as follows: A method for preparing a hyperbranched polycarboxylate superplasticizer includes the following steps: The unsaturated carboxylic acid monomer, polyether macromonomer, functional monomer containing phosphate ester group, monomer containing rigid benzene ring structure and hydrophobic associative monomer containing long chain alkyl group in the proportions described in claim 1 are dissolved in water to form a mixed monomer solution. Add some bottom water to the reactor and heat it to 30-60℃; Simultaneously, the mixed monomer solution and redox initiator solution are added dropwise to the reactor, wherein the amount of redox initiator is 0.5%-2.5% of the total mass of the monomer, and the dropwise addition is completed within 2-4 hours. After the addition is complete, keep it at 55-65℃ for 1-2 hours to mature; After cooling to below 40°C, add 0.5%-1.5% of chain transfer agent relative to the total mass of monomers, and stir the reaction for 0.5 hours; The pH value is adjusted to 6.0-7.0 with an alkaline solution to obtain the hyperbranched polycarboxylate superplasticizer.

[0013] By adopting the above technical solution, aqueous solution polymerization is environmentally friendly and low-cost. Simultaneous dropwise addition of the monomer mixture and initiator solution, rather than a single addition, controls the reaction rate and exothermic response, preventing explosive polymerization and ensuring uniform and sufficient monomer participation in the reaction. This results in polymer products with more uniform molecular weight distribution and more controllable structure. The redox initiation system allows for reaction initiation at lower temperatures (30-60℃), saving energy and reducing chain breakage and side reactions that may occur at high temperatures. The heat preservation and curing step ensures complete reaction and improves monomer conversion rate. Adding a chain transfer agent is a crucial step in controlling polymer molecular weight and branching degree. By actively terminating certain growing chains, it prevents unlimited molecular weight increase, thereby regulating the dispersion performance and viscosity of the final product. Adjusting the pH to near neutral ensures product stability during storage and use and conforms to application practices in the concrete industry.

[0014] Optionally, the redox initiator is a hydrogen peroxide-ascorbic acid system.

[0015] By employing the above technical solution, hydrogen peroxide (oxidant) and ascorbic acid (reducing agent) can rapidly undergo a redox reaction at low temperatures, generating a large number of free radicals, thereby efficiently initiating the polymerization of olefin monomers. This ensures high reaction rates and high conversion rates even at lower temperatures, avoids molecular chain structure defects caused by high temperatures, helps to form the designed hyperbranched topology, and simultaneously achieves energy conservation and consumption reduction in the production process.

[0016] Optionally, the temperature of the reaction system is controlled at 45℃±2℃ during the dropwise addition process.

[0017] By employing the above-mentioned technical solutions, excessively low temperatures result in slow initiation rates and excessively long reaction cycles; excessively high temperatures lead to rapid initiator decomposition, causing a sudden surge in free radical concentration, resulting in violent reactions, excessively wide molecular weight distribution, and even gelation. Precise temperature control within this narrow range optimizes the matching between the free radical generation rate and the monomer consumption rate, ensuring a stable and uniform polymerization reaction. This is a key process guarantee for obtaining products with regular molecular structures, consistent properties, and high reproducibility.

[0018] Optionally, the chain transfer agent is one of mercaptoethanol, mercaptopropionic acid, and dodecanethiol.

[0019] By employing the above-described technical solution, mercaptoethanol and mercaptopropionic acid, being highly water-soluble chain transfer agents, are well-suited for aqueous polymerization systems. They effectively terminate growing polymer chains through hydrogen transfer reactions of the thiol (-SH) group, while simultaneously generating new free radicals to continue initiating the reaction. This allows for precise control of the polymer molecular weight and prevents the formation of excessively large molecules. Although dodecanethiol has slightly lower water solubility, its long-chain alkyl hydrophobic tails may be partially encapsulated within the final polymer micelles, subtly affecting product performance. Limiting the use of these efficient and commonly used chain transfer agents ensures that those skilled in the art can reliably reproduce the method and achieve effective control over the product molecular weight.

[0020] Optionally, after the pH adjustment step, 0.1%-0.5% of a nanoporous stabilizer based on the mass of the finished water-reducing agent is added and stirred. The nanoporous stabilizer is a modified siloxane.

[0021] By employing the above technical solution, the nanoporous stabilizer, through its arrangement at the gas-liquid interface, reduces surface tension and forms a robust interfacial film, stabilizing the microbubbles introduced into the concrete and preventing them from merging, growing larger, or rupturing during mixing and transportation. Ultimately, this results in a fine, uniform, and closed microbubble system (pore size D50 ≤ 25 μm) within the concrete. These microbubbles improve the lubricity of fresh concrete like ball bearings, and more importantly, significantly enhance the freeze-thaw resistance of hardened concrete.

[0022] In summary, this application has the following beneficial effects: 1. Because this application achieves a high water reduction rate of ≥30% to reduce the water-cement ratio of concrete by synergistically combining unsaturated carboxylic acid monomers, polyether macromonomers and hydrophobic associative monomers containing long-chain alkyl groups, it effectively controls the viscosity of cement paste, avoids aggregate segregation and surface bleeding, and makes the internal structure of hardened concrete uniform, meeting the requirements of high-flow concrete pumping and high strength.

[0023] 2. In this application, functional monomers containing phosphate ester groups and monomers containing rigid benzene ring structures are preferred. Even if the mud content of the aggregate reaches 3%-8%, the effective amount of water-reducing agent can still be reduced to less than 15%, without the need to increase the dosage. At the same time, the slump loss rate of fresh concrete is ≤25% within 1-2 hours, which meets the time window requirements for long-distance transportation of more than 10km in urban subway projects.

[0024] 3. The method of this application, with the help of redox initiation system and chain transfer agent, avoids early strength loss caused by the introduction of retarding components, and improves freeze-thaw resistance through nanoporous stabilizer, thus solving the problem of freeze resistance in bridge and tunnel engineering in cold northern regions and broadening the application boundaries of polycarboxylate superplasticizer. Detailed Implementation

[0025] The following detailed description of this application is provided in conjunction with the embodiments. It should be noted that: unless otherwise specified, the conditions in the following embodiments are performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the raw materials used in the following embodiments are all from commercially available sources. Example

[0026] Example 1 A preparation process for a hyperbranched polycarboxylate superplasticizer: Prepare the following raw materials (based on the production of 1 ton of water-reducing agent with a solid content of 40%): Unsaturated carboxylic acid monomer: acrylic acid (AA), 24 kg (equivalent to ~3 parts); Polyether macromonomer: methyl allyl polyoxyethylene ether (HPEG, Mn=2400), 240kg (corresponding to 1 part); Functional monomers containing phosphate groups: methacryloyloxyethyl phosphate (PMEA), 110 kg (equivalent to 5 parts); Monomer containing a rigid benzene ring structure: benzyl methacrylate (BzMA), 17.5 kg (corresponding to 0.5 parts); Hydrophobic associative monomer containing long-chain alkyl groups: octadecyl methacrylate (SMA), 3.4 kg (0.1 parts).

[0027] Other additives: 7.5 kg of hydrogen peroxide (H2O2, 30% aqueous solution), 1.5 kg of ascorbic acid (Vc), 4.8 kg of mercaptoethanol (ME), 150 kg of 30% sodium hydroxide aqueous solution (for neutralization), and 1600 kg of deionized water.

[0028] In a 10-cubic-meter preparation vessel, approximately 1000 kg of deionized water was added. HPEG, PMEA, BzMA, and SMA were added sequentially with stirring, followed by AA. The mixture was stirred until all monomers were completely dissolved, forming a mixed monomer solution. In another container, H2O2 solution and vitamin C solution were dissolved separately for later use.

[0029] In a 5-cubic-meter reactor, approximately 600 kg of water was added, stirring was started, and the temperature was raised to 45°C. The prepared mixed monomer solution and two initiator solutions (H₂O₂ solution and Vc solution) were then simultaneously added dropwise to the reactor using a metering pump. The dropping rate was controlled to ensure that all solutions were added at a uniform rate over 3 hours. During the dropping process, the reaction temperature was strictly controlled at 45°C ± 2°C using jacket cooling.

[0030] After the addition is complete, steam is introduced to heat the material in the reactor to 60°C, and the reaction is continued at this temperature with stirring for 1.5 hours. The steam is then turned off, and cooling water is introduced to cool the reaction solution to 35°C. 9.5 kg of mercaptoethanol (ME) is added, and stirring is continued for 0.5 hours.

[0031] Approximately 220 kg of a 30% sodium hydroxide aqueous solution was slowly added dropwise to the reaction solution, and the final pH value was controlled to 6.5 using an online pH monitor. Finally, the remaining deionized water was added to adjust the solid content of the final product to 40%. After cooling to room temperature and passing laboratory testing, the product was filtered and discharged to obtain the hyperbranched polycarboxylate superplasticizer.

[0032] Example 2 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 lies in the raw material formulation: Unsaturated carboxylic acid monomer: acrylic acid (AA), 48 kg (6 parts); Polyether macromonomer: HPEG (Mn=2400), 480kg (equivalent to 2 parts); Phosphate-containing functional monomer: PMEA, 330kg (equivalent to 15 parts); Contains rigid benzene ring monomer: BzMA, 70kg (equivalent to 2 parts); Contains long-chain alkyl hydrophobic monomer: SMA, 17kg (corresponding to 0.5 parts).

[0033] Other additives: 15kg H2O2 (30%), 3kg Vc, 9.5kg ME, 220kg 30% NaOH, 1300kg deionized water.

[0034] Example 3 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 lies in the raw material formulation: Unsaturated carboxylic acid monomer: acrylic acid (AA), 80 kg (equivalent to 10 parts); Polyether macromonomer: HPEG (Mn=2400), 720kg (equivalent to 3 parts); Phosphate-containing functional monomer: PMEA, 440kg (equivalent to 20 parts); Contains rigid benzene ring monomer: BzMA, 175kg (equivalent to 5 parts); Contains long-chain alkyl hydrophobic monomer: SMA, 68kg (equivalent to 2 parts).

[0035] Other additives: 22 kg H2O2 (30%), 4.4 kg Vc, 20 kg mercaptopropionic acid (M=92) (adjusted due to molecular weight and upper limit of usage), 280 kg 30% NaOH, and 900 kg deionized water (the amount of water is reduced due to the increase in the total amount of monomers).

[0036] Example 4 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the molar ratio of the functional monomer containing phosphate ester groups to the unsaturated carboxylic acid monomer is 4:1.

[0037] Example 5 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the molar ratio of the functional monomer containing phosphate ester groups to the unsaturated carboxylic acid monomer is 5:1.

[0038] Example 6 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the saturated carboxylic acid monomer is methacrylic acid.

[0039] Example 7 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the polyether macromonomer is isopentenyl alcohol polyoxyethylene ether.

[0040] Example 8 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the hydrophobic associating monomer containing long-chain alkyl groups is hexadecyl acrylate.

[0041] Example 9 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the hydrophobic associating monomer containing long-chain alkyl groups is allyl octadecyl ether.

[0042] Example 10 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the hydrophobic associating monomer containing long-chain alkyl groups is a mixture of octadecyl methacrylate, hexadecyl acrylate, and allyl octadecyl ether in a molar ratio of 1:1:1.

[0043] Example 11 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the monomer containing a rigid benzene ring structure is vinyl benzoic acid.

[0044] Example 12 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the temperature of the reaction system is controlled at 35℃±2℃ during the dropwise addition process.

[0045] Example 13 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the temperature of the reaction system is controlled at 55℃±2℃ during the dropwise addition process.

[0046] Example 14 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the chain transfer agent is mercaptopropionic acid.

[0047] Example 15 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the chain transfer agent is dodecanethiol.

[0048] Example 16 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that the oxidant is replaced with an equal amount of ammonium persulfate (APS), and the reducing agent is replaced with an equal amount of sodium bisulfite (SBS).

[0049] Example 17 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that after the pH adjustment step, a nanoporous stabilizer accounting for 0.1% of the mass of the finished superplasticizer is added and stirred. The nanoporous stabilizer is a polyether-modified polysiloxane.

[0050] Example 18 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that after the pH adjustment step, a nanoporous stabilizer accounting for 0.3% of the mass of the finished superplasticizer is added and stirred. The nanoporous stabilizer is a polyether-modified polysiloxane.

[0051] Example 19 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that after the pH adjustment step, a nanoporous stabilizer accounting for 0.5% of the mass of the finished superplasticizer is added and stirred. The nanoporous stabilizer is a polyether-modified polysiloxane.

[0052] Comparative Example 1 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that no functional monomers containing phosphate ester groups are added.

[0053] Comparative Example 2 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that no monomer containing a rigid benzene ring structure is added.

[0054] Comparative Example 3 A preparation process for a hyperbranched polycarboxylate superplasticizer: The difference from Example 1 is that no hydrophobic associating monomer containing long-chain alkyl groups is added.

[0055] 1. Flowability of neat pulp and loss over time Test method: Weigh 300g of reference cement, add 105g of water (water-cement ratio 0.35) and the water-reducing agent to be tested (constituent solids content 0.2%), and mix according to the standard procedure. Pour the mixed cement paste into a truncated cone mold, lift it up, and measure the maximum diameter of the cement paste on the glass plate and the diameter in the vertical direction. Take the average value as the initial fluidity. Measure the fluidity after 30min and 60min, and calculate the fluidity loss over time.

[0056] 2. Concrete water reduction rate Test method: Prepare reference concrete and test concrete. The slump of the reference concrete is controlled at (80±10) mm, and the unit water consumption W0 is recorded. Under the same cement content, sand ratio and slump conditions, the test concrete contains 0.2% water-reducing agent, and the unit water consumption W1 is recorded. The water reduction rate WR is calculated as follows: WR=[(W0-W1) / W0]×100%.

[0057] 3. Concrete slump and loss over time Test method: The initial slump Sl0 of the concrete being tested is measured upon discharge from the mixer. The concrete is then left to stand in a non-absorbent, sealed container, and stirred again after 1 hour and 2 hours. The slump Sl1 and Sl2 are then measured. The slump loss rate is calculated.

[0058] 4. Compressive strength ratio Test method: Mold and cure reference concrete and test concrete specimens (100mm×100mm×100mm), and test their compressive strength at 7 days and 28 days, respectively. Calculate the ratio of the compressive strength of the test concrete to that of the reference concrete at each age.

[0059] 5. Mud Resistance Test Method: An internal admixture method was used, replacing cement with a certain proportion of clay (5% montmorillonite in this application) to prepare mud-containing mortar. The flowability of the water-reducing agent in the reference mortar and the mud-containing mortar were tested separately. The flowability ratio was calculated; the higher the ratio, the better the mud resistance.

[0060] 6. Bubble structure and antifreeze parameters Test methods: The air bubble spacing coefficient and average air bubble diameter were measured using a hardened concrete pore structure analyzer. The relative dynamic modulus of elasticity retention after 300 freeze-thaw cycles was determined using the rapid freezing method to evaluate the freeze-thaw durability.

[0061] Table 1 Detection Data

[0062] Combining Example 1 and Comparative Example 1 with Table 1, it can be seen that Comparative Example 1, lacking the addition of functional monomers containing phosphate groups, exhibits only 65% ​​resistance to mud, a 60-minute neat cement paste flowability of only 205 mm, a 2-hour concrete slump loss rate of 18.00%, and a relative dynamic elastic modulus of only 70% after 300 freeze-thaw cycles. This indicates that functional monomers containing phosphate groups can significantly improve resistance to mud by preferentially adsorbing clay to offset ineffective adsorption. Simultaneously, their strong chelating and anchoring effect on the aluminum phase of cement particles reduces molecular desorption, lowers time-related losses, and optimizes the bubble structure to enhance freeze-thaw resistance. This confirms the core role of this monomer in addressing insufficient resistance to mud and time-related losses.

[0063] Combining Example 1 and Comparative Example 2 with Table 1, it can be seen that Comparative Example 2, without the addition of monomers containing rigid benzene ring structures, had a 60-minute slurry flowability of 235 mm and a 2-hour concrete slump loss rate of 14.00%. This is because the rigid benzene ring structure can resist the coiling of the polymer backbone under alkaline environment and adsorption pressure through the "rigidity effect," allowing the polyether side chains to continue to extend to maintain the steric hindrance effect. Without it, the molecular conformational stability decreases, and the dispersion performance decays more rapidly over time. This fully demonstrates that monomers containing rigid benzene ring structures are key to ensuring the durability of water-reducing effects.

[0064] Combining Example 1 and Comparative Example 3 with Table 1, it can be seen that Comparative Example 3, due to the absence of hydrophobic associating monomers containing long-chain alkyl groups, although achieving an initial water reduction rate of 40% and an initial concrete slump of 240 mm, exhibited a 2-hour slump loss rate as high as 25.00%, a 7-day compressive strength ratio of only 135%, a bubble spacing coefficient of 350 μm, and a relative dynamic elastic modulus of 65% after 300 freeze-thaw cycles. This indicates that the reversible cross-linked network formed by the hydrophobic associating monomer can effectively regulate the slurry viscosity, balancing high water reduction rate and slurry stability. Its absence easily leads to segregation and bleeding, resulting in decreased strength and deterioration of the bubble structure, highlighting its irreplaceable role in resolving the contradiction between "high water reduction and stable slurry."

[0065] As can be seen from Examples 1-3 and Table 1, the three examples correspond to the lower, middle, and upper limits of the monomer molar amounts in claim 1, respectively, and all exhibit excellent performance: initial pulp fluidity of 265-285 mm, water reduction rate of 33%-38%, 2-hour slump loss rate of 4.80%-11.40%, and mud resistance of 89%-92%. Example 2, with its superior monomer ratio, demonstrates the best water reduction rate and slump retention. This indicates that within the monomer molar range defined in claim 1, the five monomers can stably and synergistically form a hyperbranched structure, and different ratios can all meet the requirements of high water reduction, low loss, and strong mud resistance, verifying the rationality and applicability of this molar range.

[0066] Combining Examples 1 and 4-5 with Table 1, it can be seen that in Examples 4-5, when the molar ratio of functional monomers containing phosphate groups to unsaturated carboxylic acid monomers was controlled at 4:1-5:1, the anti-mud properties reached 94% and 96%, respectively; the 60-minute neat cement paste fluidity was 260-265 mm; and the 2-hour slump loss rate was 7.00%-7.50%. This is because within this ratio range, the number of phosphate groups is sufficient, which can preferentially occupy clay adsorption sites to enhance anti-mud properties and form sufficient strong anchoring points on the surface of cement particles, reducing molecular desorption and thus reducing time-related losses. This proves that a molar ratio of 3:1-5:1 is the key range for achieving high anti-mud properties and low time-related losses.

[0067] Combining Examples 1, 6-11, and Table 1, it can be seen that the performance of Example 6 (replacing the unsaturated carboxylic acid with methacrylic acid), Example 7 (replacing the polyether with isopentenyl alcohol polyoxyethylene ether), Examples 8-10 (replacing / combining hydrophobic associating monomers), and Example 11 (replacing the rigid benzene ring monomer with vinylbenzoic acid) is basically the same as that of Example 1: initial pulp fluidity 280-284 mm, water reduction rate 36%-37%, 2-hour slump loss rate 6.60%-7.80%, and mud resistance 90%-92%. This indicates that the monomer types defined in claims 2 and 4 all possess good copolymerization activity, can stably construct hyperbranched structures, and there is no significant performance degradation after different monomer replacements. This ensures product performance stability, broadens the range of raw material selection, and improves process flexibility.

[0068] Combining Examples 1 and 12-13 with Table 1, it can be seen that Examples 12-13, controlling the dropping temperature at 35℃±2℃ and 55℃±2℃, all achieved good performance: initial slurry flowability of 278-281mm, water reduction rate of 36%-37%, and 2-hour slump loss rate of 8.00%-8.50%. While the 2-hour loss rate was slightly higher at 45℃±2℃, it was still superior to the traditional process overall. The reaction was more stable at 35℃±2℃ and 55℃±2℃, with slightly lower losses over time. This indicates that the dropping temperature range of 30-60℃ can effectively control the free radical generation rate, avoid explosive polymerization or insufficient initiation, and ensure a regular molecular structure. Furthermore, 45℃±2℃ is the optimal range, further verifying the rationality of the process parameters.

[0069] Combining Examples 1 and 14-15 with Table 1, it can be seen that Examples 14-15, using mercaptopropionic acid and dodecanethiol as chain transfer agents respectively, exhibited initial slurry flowability of 280-283 mm, 60-minute flowability of 263-267 mm, and 2-hour slump loss of 7.00%-7.80%, which are comparable to the performance of Example 1. This indicates that all three chain transfer agents can precisely control the polymer molecular weight and branching degree through mercapto hydrogen transfer, avoiding excessively short or overly entangled molecular chains, ensuring dispersion efficiency and viscosity control capability, thus proving that the chain transfer agents defined in claim 8 possess high efficiency and versatility.

[0070] Combining Examples 1 and 16 with Table 1, it can be seen that Example 16, using the ammonium persulfate-sodium bisulfite initiation system, achieved an initial slurry flowability of 279 mm, a 60-minute flowability of 261 mm, a 2-hour slump loss of 8.80%, and a water reduction rate of 36%. Although slightly inferior to the hydrogen peroxide-ascorbic acid system, it still meets engineering requirements. This indicates that the hydrogen peroxide-ascorbic acid system has higher initiation efficiency at low temperatures, reducing high-temperature side reactions to ensure the integrity of the hyperbranched structure and achieving energy saving and consumption reduction. Other redox systems can also be considered as alternatives, further demonstrating the flexibility of the preparation method.

[0071] Combining Examples 1 and 17-19 with Table 1, it can be seen that in Examples 17-19, adding 0.1%-0.5% of modified siloxane nanoporous stabilizer reduced the bubble spacing coefficient to 135-185 μm, and the relative dynamic elastic modulus after 300 freeze-thaw cycles reached 92%-98%, with 0.3% showing the best effect. This is because the nanoporous stabilizer can form a robust interfacial film at the gas-liquid interface, stabilizing small, closed microbubbles, thus improving both the lubricity of fresh concrete and the freeze-thaw resistance of hardened concrete. This proves that the stabilizer and its addition range can effectively solve the freeze-thaw resistance problem in extremely cold regions, broadening the application boundaries of the product.

[0072] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A hyperbranched polycarboxylate superplasticizer, characterized in that, It is prepared by copolymerization of monomeric raw materials comprising the following in molar amounts: 3-10 parts of unsaturated carboxylic acid monomers; 1-3 parts of polyether macromonomer; 5-20 parts of functional monomers containing phosphate groups; 0.5-5 parts of monomers containing rigid benzene ring structures; 0.1-2 parts of a hydrophobic associating monomer containing long-chain alkyl groups.

2. The hyperbranched polycarboxylate superplasticizer according to claim 1, characterized in that, The unsaturated carboxylic acid monomer is at least one of acrylic acid and methacrylic acid; the polyether macromonomer is at least one of methyl allyl polyoxyethylene ether and isopentenyl alcohol polyoxyethylene ether, with a number average molecular weight of 1000-3000; the hydrophobic associating monomer containing long-chain alkyl groups is at least one of octadecyl methacrylate, hexadecyl acrylate, and allyl octadecyl ether.

3. The hyperbranched polycarboxylate superplasticizer according to claim 1, characterized in that, The molar ratio of the functional monomer containing the phosphate ester group to the unsaturated carboxylic acid monomer is (3:1) to (5:1).

4. The hyperbranched polycarboxylate superplasticizer according to claim 1, characterized in that, The monomer containing the rigid benzene ring structure is one of benzyl methacrylate and vinyl benzoic acid.

5. A method for preparing a hyperbranched polycarboxylate superplasticizer as described in any one of claims 1-4, characterized in that, Includes the following steps: The unsaturated carboxylic acid monomer, polyether macromonomer, functional monomer containing phosphate ester group, monomer containing rigid benzene ring structure and hydrophobic associative monomer containing long chain alkyl group in the proportions described in claim 1 are dissolved in water to form a mixed monomer solution. Add some bottom water to the reactor and heat it to 30-60℃; Simultaneously, the mixed monomer solution and redox initiator solution are added dropwise to the reactor, wherein the amount of redox initiator is 0.5%-2.5% of the total mass of the monomer, and the dropwise addition is completed within 2-4 hours. After the addition is complete, keep it at 55-65℃ for 1-2 hours to mature; After cooling to below 40°C, add 0.5%-1.5% of chain transfer agent relative to the total mass of monomers, and stir the reaction for 0.5 hours; The pH value is adjusted to 6.0-7.0 with an alkaline solution to obtain the hyperbranched polycarboxylate superplasticizer.

6. The method for preparing the hyperbranched polycarboxylate superplasticizer according to claim 5, characterized in that, The redox initiator is a hydrogen peroxide-ascorbic acid system.

7. The method for preparing the hyperbranched polycarboxylate superplasticizer according to claim 5, characterized in that, The temperature of the reaction system during the dropwise addition process is controlled at 45℃±2℃.

8. The method for preparing the hyperbranched polycarboxylate superplasticizer according to claim 5, characterized in that, The chain transfer agent is one of mercaptoethanol, mercaptopropionic acid, and dodecanethiol.

9. The method for preparing the hyperbranched polycarboxylate superplasticizer according to claim 5, characterized in that, After the pH adjustment step, add 0.1%-0.5% of a nanoporous stabilizer by mass of the finished water-reducing agent and stir to mix. The nanoporous stabilizer is a modified siloxane.

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