Polycarboxylate superplasticizer prepared from tea saponin-terminated unsaturated polyether monomer and preparation method thereof

Abstract

The invention discloses a polycarboxylate superplasticizer prepared from a tea saponin terminated unsaturated polyether monomer and a preparation method of the polycarboxylate superplasticizer, and the preparation method of the polycarboxylate superplasticizer comprises the following steps: firstly, activating carboxyl reaction sites in tea saponin molecules to prepare a tea saponin precursor; carrying out nucleophilic substitution reaction on the tea saponin precursor and an unsaturated polyether monomer to construct a tea saponin-terminated unsaturated polyether monomer; and finally, carrying out free radical copolymerization reaction on the tea saponin-terminated unsaturated polyether monomer and an acrylic monomer under the action of an initiator and a chain transfer agent to prepare the polycarboxylate superplasticizer with the tea saponin-terminated polyether side chain structure. The method disclosed by the invention is clear in process route, mild in reaction condition and easy in process control, the dispersing performance and the flow retention performance are remarkably improved, and the method has good engineering application value and popularization prospect.

Description

A polycarboxylate superplasticizer prepared from tea saponin-terminated unsaturated polyether monomers and its preparation method thereof. Technical Field

[0001] This invention belongs to the field of concrete admixture technology, specifically relating to a polycarboxylate superplasticizer prepared from tea saponin-terminated unsaturated polyether monomers and its preparation method. Background Technology

[0002] Concrete is one of the most widely used building materials in engineering construction, and its workability, mechanical properties, and durability have a significant impact on project quality. Polycarboxylate superplasticizers, as third-generation high-performance concrete admixtures, have been widely used in various concrete projects due to their high water reduction rate, good dispersibility, and highly designable molecular structure. With the development of engineering structures towards higher performance and greater complexity, higher requirements are being placed on polycarboxylate superplasticizers in terms of fluidity retention, adaptability, and stability.

[0003] Existing polycarboxylate superplasticizers typically use acrylic acid and its derivatives as the main chain monomers, with polyoxyethylene side chains introduced to improve their dispersion properties. However, these superplasticizers still suffer from limited adaptability to raw materials and insufficient slump retention in practical applications. To address these issues, researchers have attempted to introduce natural product structural units with hydrophobic or special functions into the molecular structure of polycarboxylate superplasticizers to enhance their adsorption and dispersion capabilities for cement particles. Tea saponin, a widely available natural triterpenoid compound, contains various oxygen-containing functional groups in its molecular structure, exhibiting certain surface activity and biomass properties, and has been explored for use in concrete admixtures in recent years.

[0004] Patent CN113336902B (publication date: September 3, 2021) reports a tea saponin-modified composite water-reducing agent and its preparation method. This invention uses tea saponin as a functional monomer and prepares a polycarboxylate water-reducing agent containing a tea saponin structure by conducting free radical polymerization of tea saponin with acrylic acid and its derivatives, polyoxyethylene macromonomers, etc., under the action of an initiator and a chain transfer agent. The advantage of this invention is that it utilizes the surface-active characteristics of tea saponin molecules to improve the dispersion performance of the water-reducing agent in cement systems and, to a certain extent, improves the fluidity and mechanical properties of concrete. However, in this invention, tea saponin, as a monomer, directly participates in the polymerization reaction. Its molecular structure contains multiple hydroxyl groups and active oxygen-containing functional groups, which easily lead to multi-site participation in the reaction during polymerization. This results in a relatively random polymer molecular structure and a wide molecular weight distribution, making it difficult to achieve precise control of the polycarboxylate water-reducing agent's molecular structure and also hindering the stability and repeatability of the water-reducing agent's performance.

[0005] Patent CN113354779B (publication date: September 7, 2021) reports an esterified tea saponin-modified composite water-reducing agent and its preparation method. This invention first esterifies tea saponin to improve its reactivity and compatibility. Then, the esterified tea saponin is used as a monomer or copolymer component to undergo free radical polymerization with acrylic acid and its derivatives, and polyoxyethylene macromonomers under the action of initiators and chain transfer agents to prepare a polycarboxylate-based water-reducing agent. The advantage of this invention is that by esterifying tea saponin, its reactivity in the polymerization system is improved to a certain extent, giving the water-reducing agent both water-reducing effect and mechanical properties. However, this invention still directly uses the modified tea saponin as a monomer in the free radical polymerization reaction without targeted control of the reaction sites of the tea saponin molecule. The problem of uncontrollable molecular structure due to the participation of multiple functional groups in the reaction remains, making it difficult to achieve functionalization and fine-tuning of the performance of the polycarboxylate water-reducing agent through molecular structure design.

[0006] The tea saponin-modified polycarboxylate superplasticizers reported in the above patents can all improve the fluidity and dispersion properties of cement systems to a certain extent, demonstrating the application potential of introducing natural products into the molecular structure of polycarboxylate superplasticizers. However, from the perspective of molecular structure design and synthesis mechanism, the above technical solutions still have significant shortcomings: existing studies directly introduce tea saponin or its esterification products as monomers or copolymer components into free radical polymerization systems without targeted regulation of the multifunctional reaction sites in the tea saponin molecule. This makes it difficult to avoid the randomness of molecular structure caused by multiple sites participating in polymerization, and also fails to achieve refined design of the molecular structure of polycarboxylate superplasticizers. Research has found that by pretreating and functionalizing the reaction sites of natural product molecules to construct functional monomers with clear structural characteristics, and then introducing them into the polymerization system, it is helpful to achieve the designability and controllability of polymer molecular structures, thereby significantly improving their application effect and performance in cement systems.

[0007] To this end, the present invention employs activation treatment of the carboxyl groups on the surface of tea saponin molecules to prepare tea saponin precursors, and further constructs tea saponin-terminated unsaturated polyether monomers through nucleophilic substitution reactions. The unsaturated polyether monomers are then used in the preparation of polycarboxylate superplasticizers. This not only effectively avoids the problem of uncontrolled molecular structure caused by the direct participation of tea saponin multifunctional groups in polymerization reactions, but also achieves the goal of introducing the structure of natural products into polycarboxylate superplasticizer molecules in a controlled and functionalized manner. Summary of the Invention

[0008] To address the aforementioned problems, the present invention aims to provide a polycarboxylate superplasticizer prepared from tea saponin-terminated unsaturated polyether monomers and its preparation method. The method involves activating the carboxyl groups on tea saponin, followed by a nucleophilic substitution reaction with the unsaturated polyether monomer to obtain a tea saponin-terminated unsaturated polyether monomer. This monomer is then copolymerized with an acrylic monomer under the action of an initiator and a chain transfer agent via free radical polymerization to prepare a polycarboxylate superplasticizer with tea saponin-terminated polyether side chains.

[0009] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: In a first aspect, the present invention provides a polycarboxylate superplasticizer prepared from a tea saponin-terminated unsaturated polyether monomer, the chemical structural formula of which is shown below:

[0010] The structural formula for R is:

[0011] Where a, b, and n are integers, representing the number of repeating units in each part of the polymer, with a ranging from 3 to 10, b ranging from 5 to 20, and n ranging from 4 to 13.

[0012] In a second aspect, the present invention provides a method for preparing a polycarboxylate superplasticizer as described in the first aspect, comprising: activating the carboxyl group in a tea saponin molecule to form a reactive tea saponin precursor; subjecting the tea saponin precursor to a nucleophilic substitution reaction with an unsaturated polyether monomer to generate a tea saponin-terminated unsaturated polyether monomer; and using the tea saponin-terminated unsaturated polyether monomer as a side chain structural unit, subjecting it to a free radical copolymerization reaction with an acrylic monomer under the action of an initiator and a chain transfer agent to prepare a polycarboxylate superplasticizer having a tea saponin-terminated polyether side chain structure.

[0013] Furthermore, the preparation method of the polycarboxylate superplasticizer specifically includes the following steps: (1) Carboxyl group activation treatment on the surface of tea saponin: add tea saponin and water to the reactor to prepare a tea saponin solution, add alkaline solution to adjust the pH of the tea saponin solution to 3.5–6.5, preferably 4.0–6.0; then add appropriate amounts of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS), stir to dissolve, and carry out the stirring activation reaction at room temperature for 1–3 hours to complete the carboxyl group activation on the surface of tea saponin; (2) Preparation of tea saponin-terminated unsaturated polyether monomer: add the unsaturated polyether monomer to the reactor in step (1), heat in an oil bath, stir and raise the temperature to 40°C. After the reaction is completed, the product is purified by solvent washing 3-5 times and then vacuum dried to obtain tea saponin-terminated unsaturated polyether monomer; (3) Copolymerization: Add the product obtained in step (2) and water to a three-necked flask, stir and heat to 50-80℃ in an oil bath; Add solution A and solution B to the three-necked flask at a constant rate for 1-5 hours. Solution A is an aqueous solution of initiator and solution B is an aqueous solution of acrylic monomer and chain transfer agent; After the addition is completed, continue to stir the reaction at a constant temperature for 1-5 hours; After the reaction is completed, cool down to 25-40℃, neutralize with alkaline solution to pH 6-8 and add deionized water to obtain a tea saponin-terminated polycarboxylate superplasticizer solution with a solid content of 30%-40%.

[0014] Furthermore, in step (1), the mass ratio of tea saponin to water in the tea saponin solution is 5-50:100; the molar ratio of tea saponin:EDC·HCl:NHS is 1:1:0.5-2.5, preferably 1:1:1-2.

[0015] Furthermore, the alkaline solution mentioned in step (1) is an aqueous solution of any one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, and ammonia in any proportion; the alkaline solution mentioned in step (3) is an aqueous solution of any one or more of sodium hydroxide, potassium hydroxide, ethylenediamine, and triethanolamine in any proportion.

[0016] Furthermore, the unsaturated polyether monomer mentioned in step (2) is at least one of isopentenyl polyoxyethylene ether (TPEG), methyl allyl polyoxyethylene ether (HPEG), ethylene glycol monovinyl polyethylene glycol ether (EPEG), and allyl polyoxyethylene ether (APEG), with a number average molecular weight of 1000-5000, preferably 2000-4000, and the molar ratio of the unsaturated polyether monomer to tea saponin in step (1) is 1-3:1, preferably 1-2:1.

[0017] Furthermore, the solvent mentioned in step (2) is anhydrous methanol, anhydrous ethanol, acetone, toluene or chloroform, preferably anhydrous ethanol.

[0018] Furthermore, the initiator mentioned in step (3) is selected from persulfates, azo compounds or organic peroxides, preferably one or more of potassium persulfate, ammonium persulfate, sodium persulfate, azobisisobutyronitrile (AIBN) and benzoyl peroxide (BPO), and the molar ratio of the initiator to the product obtained in step (2) is 0.05-0.4:1.

[0019] Furthermore, the acrylic monomers mentioned in step (3) are selected from any one or more of acrylic acid, acrylamide, methacrylic acid, sodium propylene sulfonate, sodium methpropylene sulfonate, acrylonitrile, maleic anhydride, vinyl acetate, and methyl methacrylate, preferably acrylic acid and methacrylic acid, and the molar ratio of the acrylic monomers to the product obtained in step (2) (i.e., the tea saponin-terminated unsaturated polyether monomer) is 1-5:1.

[0020] Furthermore, the chain transfer agent mentioned in step (3) is a dithioester, mercaptoacetic acid, mercaptopropionic acid, sodium mercaptoacetate, n-dodecyl mercaptan, or dithiobenzoic acid. 2 Acrylonitrile isopropyl ester (CPDB), tert-butyl dithiobenzoate (CDB), or dithiobenzoic acid (2... ethoxycarbonyl)propionyl 2 The ester (EPDB) is preferably mercaptoacetic acid or mercaptopropionic acid, and the molar ratio of the chain transfer agent to the product obtained in step (2) (i.e., tea saponin-terminated unsaturated polyether monomer) is 0.05-0.7:1.

[0021] By adopting the above technical solution, the present invention has the following beneficial effects compared with the prior art: 1. It realizes the controlled utilization of the reaction sites of tea saponin and improves the controllability of molecular structure. The present invention activates the carboxyl reaction sites in the tea saponin molecule and constructs tea saponin-terminated unsaturated polyether monomers, thereby avoiding the multi-site reaction problem caused by the direct participation of the multifunctional groups of tea saponin in the free radical polymerization reaction, and effectively improves the controllability and stability of the molecular structure of polycarboxylate superplasticizer.

[0022] 2. Introducing natural product structures in the form of end-capped side chains to construct well-defined polyether side chain structures. This invention introduces the tea saponin structure into the end of the polyether side chain in the form of end-capping, and embeds it into the polycarboxylic acid backbone through free radical copolymerization reaction to form a polycarboxylic acid water-reducing agent with tea saponin end-capped polyether side chain structure, thereby realizing the functionalization and orderly introduction of natural product structures into the polycarboxylic acid water-reducing agent molecule.

[0023] 3. It is beneficial to control the molecular weight and its distribution, and improve the stability and repeatability of the product. The present invention introduces the synergistic effect of initiator and chain transfer agent in the copolymerization process, which can effectively control the molecular weight and its molecular weight distribution of polycarboxylate superplasticizer, which is beneficial to obtaining superplasticizer products with stable structure and consistent performance, and improves the repeatability of its industrial application.

[0024] 4. The process route is clear and the conditions are mild, with good prospects for engineering applications. The reaction steps of the method of this invention are clear and the conditions are mild. The raw materials used are widely available, the process parameters are controllable, and it is easy to scale up. It is suitable for preparing polycarboxylate superplasticizers with excellent working performance and has good engineering promotion value.

[0025] 5. This invention expands the application of natural products in the field of concrete chemical admixtures. From the perspective of molecular structure design, this invention proposes a technical route that combines reaction site activation with end-capping monomer construction, providing a new technical path for the high-value utilization of natural products such as tea saponin in polycarboxylate superplasticizers, and enriching the theoretical and practical foundation for the structural design and performance regulation of polycarboxylate superplasticizers. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments. It should be particularly noted that the following embodiments are for illustrative purposes only and do not limit the scope of the invention. Similarly, the following embodiments are only some, not all, embodiments of the present invention, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] This invention provides a polycarboxylate superplasticizer prepared from tea saponin-terminated unsaturated polyether monomers, the chemical structural formula of which is shown in Formula A below:

[0028] In equation A, the structural formula of R is:

[0029] Where a, b, and n are integers representing the number of repeating units in each part of the polymer, with a ranging from 3 to 10, b from 5 to 20, and n from 4 to 13. The wavy line end of the R structure is connected to the carboxyl group (-COO-R) in formula A.

[0030] The preparation method of the above-mentioned polycarboxylate superplasticizer includes: activating the carboxyl group in the tea saponin molecule to form a tea saponin precursor with reactive activity; reacting the tea saponin precursor with an unsaturated polyether monomer in a nucleophilic substitution reaction to generate a tea saponin-terminated unsaturated polyether monomer; using the tea saponin-terminated unsaturated polyether monomer as a side chain structural unit, and reacting it with an acrylic monomer in the presence of an initiator and a chain transfer agent to prepare a polycarboxylate superplasticizer with a tea saponin-terminated polyether side chain structure; specifically including the following steps: (1) Activation treatment of carboxyl groups on the surface of tea saponin: adding tea saponin and water to the reactor to prepare a tea saponin solution, and adding an alkaline solution to adjust the pH of the tea saponin solution to 3. The concentration of the saponin solution is 0.5–6.5, preferably 4.0–6.0. ​​Then, appropriate amounts of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC·HCl) and N-hydroxysuccinimide (NHS) are added, stirred to dissolve, and the reaction is carried out at room temperature for 1–3 hours to activate the carboxyl groups on the surface of the saponin. The mass ratio of saponin to water in the saponin solution is 5–50:100; the molar ratio of saponin:EDC·HCl:NHS is 1:1:0.5–2.5, preferably 1:1:1–2; the alkaline solution is an aqueous solution of any one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, and ammonia in any proportion.

[0031] (2) Preparation of tea saponin-terminated unsaturated polyether monomer: The unsaturated polyether monomer is added to the reactor in step (1), heated in an oil bath, stirred and heated to 40°C, and reacted at a constant temperature for 3-7 hours. After the reaction is completed, the product is purified by solvent washing 3-5 times and then vacuum dried to obtain tea saponin-terminated unsaturated polyether monomer; wherein, the unsaturated polyether monomer is at least one of isopentenyl polyoxyethylene ether (TPEG), methyl allyl polyoxyethylene ether (HPEG), ethylene glycol monovinyl polyethylene glycol ether (EPEG), and allyl polyoxyethylene ether (APEG), and its number average molecular weight is 1000-5000, preferably 2000-4000, and the molar ratio of the unsaturated polyether monomer to tea saponin in step (1) is 1-3:1, preferably 1-2:1; the solvent is anhydrous methanol, anhydrous ethanol, acetone, toluene or chloroform, preferably anhydrous ethanol.

[0032] (3) Copolymerization: Add the product obtained in step (2) and water to a three-necked flask, stir and heat in an oil bath to 50-80℃; add solution A and solution B dropwise to the three-necked flask at a constant rate over 1-5 hours, where solution A is an aqueous solution of initiator and solution B is an aqueous solution of acrylic monomer and chain transfer agent; continue stirring at a constant temperature for 1-5 hours after the dropwise addition is completed; after the reaction is completed, cool down to 25-40℃, neutralize with alkaline solution to pH 6-8 and add deionized water to obtain a polycarboxylate superplasticizer solution with tea saponin end-capped with a solid content of 30%-40%; wherein, the initiator is selected from persulfates, azo compounds or organic peroxides, preferably potassium persulfate, ammonium persulfate, sodium persulfate, azobisisobutyrate. The initiator is selected from any one or more of nitrile butadiene butadiene (AIBN) and benzoyl peroxide (BPO), and the molar ratio of the initiator to the product obtained in step (2) (i.e., tea saponin-terminated unsaturated polyether monomer) is 0.05-0.4:1; the acrylic monomer is selected from any one or more of acrylic acid, acrylamide, methacrylic acid, sodium propylene sulfonate, sodium methpropylene sulfonate, acrylonitrile, maleic anhydride, vinyl acetate, and methyl methacrylate, preferably acrylic acid and methacrylic acid, and the molar ratio of the acrylic monomer to the product obtained in step (2) (i.e., tea saponin-terminated unsaturated polyether monomer) is 1-5:1; the chain transfer agent is dithioester, mercaptoacetic acid, mercaptopropionic acid, sodium mercaptoacetate, n-dodecyl mercaptan, or dithiobenzoic acid. 2 Acrylonitrile isopropyl ester (CPDB), tert-butyl dithiobenzoate (CDB), or dithiobenzoic acid (2... ethoxycarbonyl)propionyl 2 The ester (EPDB) is preferably mercaptoacetic acid or mercaptopropionic acid, and the molar ratio of the chain transfer agent to the product obtained in step (2) is 0.05-0.7:1; the alkaline solution is an aqueous solution of any one or more of sodium hydroxide, potassium hydroxide, ethylenediamine, and triethanolamine in any proportion.

[0033] Example 1: 10.0 g of tea saponin was weighed and added to 100 g of deionized water. The solution was dissolved by stirring at room temperature to prepare a tea saponin solution. The pH of the solution was adjusted to 4.5 using sodium hydroxide solution. Subsequently, 1.6 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 0.96 g of N-hydroxysuccinimide were added sequentially to the system. The reaction was continued to be stirred at room temperature for 2 hours to complete the activation of the carboxyl reaction site in the tea saponin molecule, yielding the tea saponin precursor reaction solution.

[0034] 30 g of methyl allyl polyoxyethylene ether (HPEG, number average molecular weight approximately 2400) was added to the resulting reaction solution. The system was heated in an oil bath under nitrogen protection to 40 °C and stirred continuously for 5 h to allow the activated tea saponin precursor to undergo a nucleophilic substitution reaction with the unsaturated polyether monomer. After the reaction, the resulting product was washed and purified three times with anhydrous ethanol, and then dried under vacuum at 40 °C to obtain the tea saponin-terminated unsaturated polyether monomer.

[0035] The obtained tea saponin-terminated unsaturated polyether monomer was added to a three-necked flask, along with 25 g of deionized water. The mixture was heated to 65°C with stirring. Solutions A and B were prepared: Solution A was an aqueous solution of 0.6 g ammonium persulfate and 5 g deionized water, and Solution B was an aqueous solution of 2.4 g acrylic acid, 0.16 g mercaptoacetic acid, and 5 g deionized water. Solutions A and B were simultaneously added dropwise to the reaction system at a constant rate over 3 hours. After the addition was complete, the reaction was continued with stirring at a constant temperature for 2 hours. After the reaction was complete, the system was cooled to 35°C, and the pH was adjusted to 7.0 using a 30% sodium hydroxide solution. Finally, 28.6 g of deionized water was added to obtain a polycarboxylate superplasticizer solution with a solid content of 30-40% and a tea saponin-terminated polyether side chain structure.

[0036] In Example 2, 40.0 g of tea saponin was weighed and added to 100 g of deionized water. The solution was stirred and dissolved at room temperature to prepare a tea saponin solution. The pH of the solution was adjusted to 5.5 using sodium hydroxide solution. Subsequently, 6.4 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 3.84 g of N-hydroxysuccinimide were added sequentially to the system. The reaction was continuously stirred at room temperature for 2 hours to complete the activation of the carboxyl reaction site in the tea saponin molecule, yielding the tea saponin precursor reaction solution.

[0037] 120 g of isopentenyl polyoxyethylene ether (TPEG, number average molecular weight approximately 3000) was added to the resulting reaction solution. The system was heated in an oil bath under nitrogen protection to 40 °C and stirred continuously for 5 h to allow the activated tea saponin precursor to undergo a nucleophilic substitution reaction with the unsaturated polyether monomer. After the reaction, the resulting product was washed and purified three times with anhydrous ethanol, and then dried under vacuum at 40 °C to obtain the tea saponin-terminated unsaturated polyether monomer.

[0038] The obtained tea saponin-terminated unsaturated polyether monomer was added to a three-necked flask, along with 60 g of deionized water. The mixture was heated to 65°C with stirring. Solutions A and B were prepared: Solution A was an aqueous solution of 2.4 g ammonium persulfate and 10 g deionized water, and Solution B was an aqueous solution of 9.6 g acrylic acid, 0.64 g mercaptoacetic acid, and 10 g deionized water. Solutions A and B were simultaneously added dropwise to the reaction system at a constant rate over 3 hours. After the addition was complete, the reaction was continued with constant temperature stirring for 2 hours. After the reaction was complete, the system was cooled to 35°C, and the pH was adjusted to 6.0 using a 30% sodium hydroxide solution. Finally, 222.9 g of deionized water was added to obtain a polycarboxylate superplasticizer solution with a solid content of 30-40% and a tea saponin-terminated polyether side chain structure.

[0039] In Example 3, 20.0 g of tea saponin was weighed and added to 100 g of deionized water. The solution was dissolved by stirring at room temperature to prepare a tea saponin solution. The pH of the solution was adjusted to 6.5 using sodium hydroxide solution. Subsequently, 3.2 g of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.92 g of N-hydroxysuccinimide were added sequentially to the system. The reaction was continued to be stirred at room temperature for 2 hours to complete the activation of the carboxyl reaction site in the tea saponin molecule, yielding the tea saponin precursor reaction solution.

[0040] 60 g of ethylene glycol monovinyl polyethylene glycol ether (EPEG, number average molecular weight approximately 4000) was added to the resulting reaction solution. The system was heated in an oil bath under nitrogen protection to 40°C and stirred continuously for 5 h to allow the activated tea saponin precursor to undergo a nucleophilic substitution reaction with the unsaturated polyether monomer. After the reaction, the resulting product was washed and purified three times with anhydrous ethanol, and then dried under vacuum at 40°C to obtain the tea saponin-terminated unsaturated polyether monomer.

[0041] The obtained tea saponin-terminated unsaturated polyether monomer was added to a three-necked flask, along with 40 g of deionized water. The mixture was heated to 65°C with stirring. Solutions A and B were prepared: Solution A was an aqueous solution of 1.2 g potassium persulfate and 8 g deionized water, and Solution B was an aqueous solution of 4.8 g acrylic acid, 0.32 g mercaptopropionic acid, and 8 g deionized water. Solutions A and B were simultaneously added dropwise to the reaction system at a constant rate over 3 hours. After the addition was complete, the reaction was continued with constant temperature stirring for 2 hours. After the reaction was complete, the system was cooled to 35°C, and the pH was adjusted to 7.0 using a 30% sodium hydroxide solution. Finally, 110 g of deionized water was added to obtain a polycarboxylate superplasticizer solution with a solid content of 30-40% and a tea saponin-terminated polyether side chain structure.

[0042] Comparative Example 1 uses a commercially available polycarboxylate superplasticizer as Comparative Example 1.

[0043] Comparative Example 2 used commercially available sodium lignosulfonate water-reducing agent as Comparative Example 2.

[0044] Comparative Test 1. Cement Paste Flowability: To investigate the effect of the polycarboxylate superplasticizer solution synthesized in this invention on the flowability of different cements, the flowability of cement paste in each example and comparative example with different cement types was measured at the same dosage. The test was conducted according to GB / T8077-2012 "Test Method for Homogeneity of Concrete Admixtures", with a water-cement ratio of 0.29 and a reduced-solids dosage of 0.3%. The test results are shown in Table 1.

[0045] Table 1. Results of Cement Paste Flowability Test

[0046] As can be seen from the data in Table 1, under the same water-cement ratio and admixture dosage, the polycarboxylate superplasticizers prepared in Examples 1-3 all exhibited better fluidity control effects than Comparative Examples 1-2 in the cement paste system. Compared with the comparative examples, the superplasticizer prepared by the present invention, while maintaining a high initial fluidity of the cement paste, also maintained good fluidity of the paste at 1h and 2h, demonstrating superior dispersion ability and slump retention performance. 2. Comparison of cement paste fluidity at different dosages: Under different dosages (0.15%-0.25%), the dispersion and slump retention performance of the cement paste compared with the comparative examples at the same water-cement ratio were compared. The test was conducted according to GB / T8077-2012 "Test Method for Homogeneity of Concrete Admixtures", using reference cement with a water-cement ratio of 0.29. The test results are shown in Table 2.

[0047] Table 2 Results of the flow properties of cement paste under different admixture dosages

[0048] As can be seen from the data in Table 2, the polycarboxylate superplasticizer solution synthesized by the method of the present invention has good pulp flowability and pulp flowability retention results at different dosages or even lower dosages, and the effect is better than that of the selected comparative sample.

[0049] 3. Concrete slump and spread were tested according to GB50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". Performance results are shown in Table 3. The water-reducing agent dosage was 0.8 wt% of the total concrete volume. Concrete mix proportion (kg·m³) -3 The ratio of cement: fly ash: mineral powder: sand: gravel: water is 340:82:67:657:1059:153.

[0050] Table 3 Results of Concrete Flowability

[0051] As can be seen from Table 3, the polycarboxylate superplasticizer solution synthesized by the method of the present invention exhibits excellent slump and spread in concrete systems, and in particular, it exhibits even better slump retention.

[0052] In summary, this invention uses tea saponin, unsaturated polyether monomers, and acrylic monomers as the main reactants to prepare a polycarboxylate superplasticizer through reaction site activation, end-capping monomer construction, and free radical copolymerization. Specifically, the carboxyl reaction sites in the tea saponin molecule are first activated to prepare a tea saponin precursor. Then, the tea saponin precursor undergoes a nucleophilic substitution reaction with the unsaturated polyether monomer to construct a tea saponin-end-capped unsaturated polyether monomer. Finally, the tea saponin-end-capped unsaturated polyether monomer is copolymerized with an acrylic monomer under the action of an initiator and a chain transfer agent via free radical copolymerization to obtain a polycarboxylate superplasticizer with a tea saponin-end-capped polyether side chain structure. The method of this invention has a clear process route, mild reaction conditions, and is easy to control. By introducing the tea saponin structure into the polycarboxylate superplasticizer molecule in a controlled reaction site and end-capped side chain form, the refined design of the polycarboxylate superplasticizer molecular structure is successfully achieved, significantly improving its dispersion and flow retention properties, and demonstrating good engineering application value and promising prospects for promotion.

[0053] The above description is only a part of the embodiments of the present invention and does not limit the scope of protection of the present invention. Any equivalent device or equivalent process transformation made based on the content of the present invention specification, or direct or indirect application in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A polycarboxylate superplasticizer prepared from tea saponin-terminated unsaturated polyether monomers, characterized in that, Its chemical structural formula is shown below: The structural formula for R is: Where a, b, and n are integers, representing the number of repeating units in each part of the polymer, with a ranging from 3 to 10, b ranging from 5 to 20, and n ranging from 4 to 13.

2. A method for preparing the polycarboxylate superplasticizer as described in claim 1, characterized in that, include: The carboxyl group in the tea saponin molecule is activated to form a reactive tea saponin precursor. A tea saponin precursor is subjected to a nucleophilic substitution reaction with an unsaturated polyether monomer to generate a tea saponin-terminated unsaturated polyether monomer. Using the tea saponin-terminated unsaturated polyether monomer as a side chain structural unit, it is subjected to a free radical copolymerization reaction with an acrylic monomer under the action of an initiator and a chain transfer agent to prepare a polycarboxylate superplasticizer with a tea saponin-terminated polyether side chain structure.

3. The preparation method according to claim 2, characterized in that, Specifically, the steps are as follows: (1) Activation treatment of carboxyl groups on the surface of tea saponin: Add tea saponin and water to the reactor to prepare a tea saponin solution. Add alkaline solution to adjust the pH of the tea saponin solution to 3.5–6.

5. Then add appropriate amounts of EDC·HCl and NHS, stir to dissolve, and carry out the activation reaction at room temperature for 1–3 hours to complete the activation of carboxyl groups on the surface of tea saponin; (2) Preparation of tea saponin-terminated unsaturated polyether monomer: Add the unsaturated polyether monomer to the reactor in step (1), heat in an oil bath, stir and raise the temperature to 40°C, and keep the temperature constant for 3–7 hours. After the reaction is completed, the obtained product is purified by solvent washing 3–5 times. (2) Dry in the air to obtain tea saponin-terminated unsaturated polyether monomer; (3) Copolymerization: Add the product obtained in step (2) and water to a three-necked flask, stir and heat in an oil bath to 50-80℃; Add solution A and solution B to the three-necked flask at a constant rate for 1-5 hours. Solution A is an aqueous solution of initiator and solution B is an aqueous solution of acrylic monomer and chain transfer agent; After the addition is completed, continue to stir at a constant temperature for 1-5 hours; After the reaction is completed, cool down to 25-40℃, neutralize with alkaline solution to pH 6-8 and add deionized water to obtain a tea saponin-terminated polycarboxylate superplasticizer solution with a solid content of 30%-40%.

4. The preparation method according to claim 3, characterized in that, In step (1), the mass ratio of tea saponin to water in the tea saponin solution is 5-50:100; the molar ratio of tea saponin:EDC·HCl:NHS is 1:1:0.5-2.

5.

5. The preparation method according to claim 3, characterized in that, The alkaline solution mentioned in step (1) is an aqueous solution of any one or more of sodium carbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide, and ammonia in any proportion; the alkaline solution mentioned in step (3) is an aqueous solution of any one or more of sodium hydroxide, potassium hydroxide, ethylenediamine, and triethanolamine in any proportion.

6. The preparation method according to claim 3, characterized in that, The unsaturated polyether monomer mentioned in step (2) is at least one of isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, ethylene glycol monovinyl polyethylene glycol ether, and allyl polyoxyethylene ether, with a number average molecular weight of 1000-5000, and the molar ratio of the unsaturated polyether monomer to tea saponin in step (1) is 1-3:

1.

7. The preparation method according to claim 3, characterized in that, The solvent mentioned in step (2) is anhydrous methanol, anhydrous ethanol, acetone, toluene or chloroform.

8. The preparation method according to claim 3, characterized in that, The initiator mentioned in step (3) is selected from any one or more of potassium persulfate, ammonium persulfate, sodium persulfate, azobisisobutyronitrile, and benzoyl peroxide, and the molar ratio of the initiator to the product obtained in step (2) is 0.05-0.4:

1.

9. The preparation method according to claim 3, characterized in that, The acrylic monomers mentioned in step (3) are selected from any one or more of acrylic acid, acrylamide, methacrylic acid, sodium propylene sulfonate, sodium methpropylene sulfonate, acrylonitrile, maleic anhydride, vinyl acetate, and methyl methacrylate, and the molar ratio of the acrylic monomers to the product obtained in step (2) is 1-5:

1.

10. The preparation method according to claim 3, characterized in that, The chain transfer agent mentioned in step (3) is a dithioester, mercaptoacetic acid, mercaptopropionic acid, sodium mercaptoacetate, n-dodecyl mercaptan, and dithiobenzoic acid. 2 Acrylonitrile isopropyl ester, tert-butyl dithiobenzoate or dithiobenzoic acid (2 ethoxycarbonyl)propionyl 2 The ester, wherein the molar ratio of the chain transfer agent to the product obtained in step (2) is 0.05-0.7:1.

Images