Modified styrene-butadiene latex as well as preparation method and application thereof

Abstract

The invention belongs to the field of building materials, and provides modified styrene-butadiene latex as well as a preparation method and application thereof. The preparation method of the modified styrene-butadiene latex comprises the following step: carrying out emulsion polymerization reaction on comonomers including a main monomer, a functional monomer I, a functional monomer II and a functional monomer III to form a modified styrene-butadiene copolymer. When the modified styrene-butadiene latex is applied to concrete, the workability of the concrete can be improved while the waterproof performance of the concrete is improved.

Description

Technical Field

[0001] This invention belongs to the field of building materials, specifically, it provides a modified styrene-butadiene latex, its preparation method, and its application. Background Technology

[0002] Concrete waterproofing agents are one of the core functional materials for improving the long-term durability and service safety of major infrastructure projects such as nuclear power plants, water conservancy dams, and underground utility tunnels. Among many modified materials, styrene-butadiene latex (SBR Latex) waterproofing agents are considered to have significant toughening, crack resistance, and waterproofing properties due to their unique mechanism of efficient film formation and physical filling of capillary pores and microcracks within concrete, and are therefore used in high-performance concrete engineering.

[0003] Despite the theoretical advantages of SBR latex, existing conventional technologies still suffer from a series of inherent defects in large-scale engineering applications, severely restricting its full performance and ease of construction. These defects manifest in three main ways: First, compatibility and stability failure under physical compounding: due to charge and spatial conformation mismatch, conventional SBR latex and polycarboxylate superplasticizer (PCE) undergo non-selective adsorption and deactivation, leading to flocculation and stratification of the system. Second, deterioration of workability due to insufficient hydrophilicity: the lack of hydrophilicity in polymer particles significantly increases internal friction and viscosity of the mixture, severely impairing pumpability and self-compacting performance. Third, while carboxyl-modified styrene-butadiene latex has been proposed to improve the hydrophilicity of SBR latex, its slump retention is insufficient. Methods such as carboxyl modification relying on initial electrostatic repulsion are quickly shielded from dispersion during the initial hydration stage, failing to provide long-term rheological control and making it difficult to meet the construction requirements of long-distance transportation and continuous pouring, resulting in poor workability. These defects collectively restrict the reliable and efficient application of SBR latex in high-end engineering projects. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, the present invention aims to provide a modified styrene-butadiene latex, its preparation method, and its application. When this modified styrene-butadiene latex is applied to concrete, it can improve the waterproofing performance of concrete while also enhancing its workability.

[0005] To achieve the above objectives, a first aspect of the present invention provides a method for preparing modified styrene-butadiene latex, the method comprising: subjecting a comonomer including a host monomer, functional monomer I, functional monomer II, and functional monomer III to an emulsion polymerization reaction in the presence of water, an emulsifier, an initiator, and optionally a chain transfer agent to form a modified styrene-butadiene copolymer; wherein the host monomer is composed of styrene and butadiene, the functional monomer I is an unsaturated carboxylic acid, the functional monomer II is a polyether macromonomer, and the functional monomer III has the structure shown in Formula 1: Formula 1, In Formula 1, R1 and R2 are each independently hydrogen or methyl (-CH3), R3 is hydrogen or hydroxyl (-OH), and m and n are each independently 0 or 1.

[0006] The aqueous dispersion obtained by the emulsion polymerization reaction of this invention is a modified styrene-butadiene latex, which contains a modified styrene-butadiene copolymer formed by copolymerization of styrene, butadiene, functional monomer I, functional monomer II, and functional monomer III. Specifically, the copolymerization of functional monomers I, II, and III with styrene and butadiene achieves structural modification and performance improvement of the styrene-butadiene latex at the molecular level. Functional monomer I (unsaturated carboxylic acid) introduces carboxyl groups (-COOH) into the polymer chain after copolymerization. These carboxyl groups can rapidly ionize in the alkaline environment of the initial stage of concrete mixing, making the latex particles negatively charged. This effectively disperses cement particles through electrostatic repulsion, thus providing excellent initial fluidity and dispersibility. Functional monomer II (polyether macromonomer) is grafted onto the polymer chain segment. Its hydrophilic polyether long chain forms a flexible hydration layer on the surface of the latex particles, generating a steric hindrance effect. This synergistic effect with the aforementioned electrostatic repulsion maintains the high fluidity and stability of the fresh concrete, exhibiting good spreadability and slump retention. Furthermore, functional monomer III (as shown in Formula 1) imparts a slow-release crosslinking function to the polymer chains after polymerization: its side chains are in a "dormant" state during the initial mixing stage, gradually hydrolyzing as the alkalinity of the cement hydration system increases, releasing active groups such as carboxyl groups. This process not only continuously provides dispersion and improves slump retention, but also enhances the crosslinking density of the polymer network after film formation, significantly improving the bonding strength of the waterproofing agent to the matrix, and improving the impermeability and waterproof durability of concrete. Therefore, by modifying the styrene-butadiene copolymer with the above three functional monomers, the prepared modified styrene-butadiene latex can maintain the excellent workability of concrete while achieving continuous dispersion and synergistic enhancement of the final hardened structure, thus balancing fluidity retention and long-term waterproof durability.

[0007] In some embodiments of the present invention, the unsaturated carboxylic acid is selected from at least one of acrylic acid, methacrylic acid, and itaconic acid. Preferably, the unsaturated carboxylic acid is methacrylic acid.

[0008] In some embodiments of the present invention, the polyether macromonomer is selected from at least one of methyl allyl monomethyl ether polyoxyethylene ether, 4-hydroxybutyl vinyl ether polyoxyethylene ether, ethylene glycol monovinyl polyoxypropylene ether, and isopentenyl polyethylene glycol ether.

[0009] In some embodiments of the present invention, the functional monomer III is selected from at least one of methyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

[0010] In some embodiments of the present invention, based on the total mass of the main monomers, styrene accounts for 25% to 50% of the mass and butadiene accounts for 50% to 75% of the mass.

[0011] In some embodiments of the present invention, the amount of functional monomer I is 2 to 10 parts by weight relative to 100 parts by weight of the main monomer, the amount of functional monomer II is 15 to 25 parts by weight, and the amount of functional monomer III is 1 to 8 parts by weight.

[0012] In some embodiments of the present invention, the temperature of the emulsion polymerization reaction is 50~90°C and the reaction time is 2~10h.

[0013] In some embodiments of the present invention, the amount of water used is such that the solid content of the prepared modified styrene-butadiene latex is 40% to 55%.

[0014] In some embodiments of the present invention, the initiator is a redox initiator, wherein the oxidant is selected from at least one of benzoyl peroxide, hydrogen peroxide, tert-butyl hydroperoxide, ammonium persulfate, sodium persulfate and potassium persulfate; and the reducing agent is selected from at least one of ferrous sulfate, sodium formaldehyde sulfoxylate and ascorbic acid, and the mass ratio of oxidant to reducing agent is 1:(0.2~2).

[0015] In some embodiments of the present invention, the initiator is used in an amount of 0.1% to 2% of the total mass of the comonomer.

[0016] In some embodiments of the present invention, the emulsifier is selected from sodium dodecyl sulfate and / or sodium dodecylbenzenesulfonate.

[0017] In some embodiments of the present invention, the emulsifier is used in an amount of 0.5% to 5% of the total mass of the comonomer.

[0018] In some embodiments of the present invention, the chain transfer agent is selected from at least one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, isooctylthiol, sodium formate, and sodium hypophosphite.

[0019] In some embodiments of the present invention, the chain transfer agent is used in an amount of 0.1% to 1% of the total mass of the comonomer.

[0020] In some embodiments of the present invention, the preparation method is a seed emulsion polymerization method, and includes the following steps: 1) Styrene, some functional monomer I, emulsifier and water are mixed and pre-emulsified to obtain a pre-emulsion; 2) Under the protection of an inert gas, the pre-emulsion, butadiene and part of the initiator are mixed evenly in a reactor, the pressure inside the reactor is maintained at 0.4~0.6MPa, and the reaction is kept at the first temperature T1 for 0.5~1.5h. Then, the aqueous solution of the remaining functional monomer I is added dropwise, and the dropwise addition time is controlled to be 2~4h. 3) Add the remaining initiators to the system obtained in step 2), heat the system to the second temperature T2, and then add the aqueous solution of functional monomer II, the aqueous solution of functional monomer III and the aqueous solution of chain transfer agent dropwise, controlling the dropwise addition time to 2~4h; 4) After the addition is complete, continue the reaction at the second temperature T2 for 0.5~2 hours; among which, The first temperature T1 is 60~75℃, and the second temperature T2 and the first temperature T1 satisfy the following relationship: 5℃≤T2-T1≤20℃; 5) Add alkali solution to adjust the pH of the reaction system obtained in step 4) to 6-8.

[0021] A second aspect of the present invention provides a modified styrene-butadiene latex prepared by the preparation method described in the first aspect of the present invention.

[0022] A third aspect of the present invention provides the application of the modified styrene-butadiene latex described in the second aspect of the present invention in building materials.

[0023] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0024] The embodiments of this application are described in detail below. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0025] The "scope" disclosed in this application is defined in the form of a lower limit and / or an upper limit, whereby a given scope is defined by selecting a lower limit and / or an upper limit. This type of scope may or may not include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form an undefined scope, and any lower limit can be combined with other lower limits to form an undefined scope, similarly, any upper limit can be combined with any other upper limit to form an undefined scope. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value, or with other lower or upper limits, to form an undefined scope.

[0026] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0027] In a first aspect, the present invention provides a method for preparing modified styrene-butadiene latex, the method comprising: subjecting a comonomer including a host monomer, functional monomer I, functional monomer II and functional monomer III to an emulsion polymerization reaction in the presence of water, an emulsifier, an initiator and optionally a chain transfer agent to form a modified styrene-butadiene copolymer.

[0028] In this invention, the main monomers are composed of styrene (St) and butadiene (BD), which copolymerize to form the main chain backbone of the polymer and determine the basic mechanical properties of the latex. According to some embodiments, based on the total mass of the main monomers, the mass percentage of styrene can be 25% to 50%, for example, 25%, 30%, 32%, 35%, 40%, 45%, 50%, etc.; the mass percentage of butadiene can be 50% to 75%, for example, 50%, 55%, 60%, 65%, 68%, 70%, 75%, etc.

[0029] In this invention, the functional monomer I is an unsaturated carboxylic acid, which introduces carboxyl groups into the copolymer molecular chain through a copolymerization reaction, thereby providing basic adsorption sites and active sites for chemical reactions with cement hydration products. The unsaturated carboxylic acid is typically selected from monocarboxylic acids or dicarboxylic acids containing double bonds. According to some embodiments, the unsaturated carboxylic acid is selected from at least one of acrylic acid (AA), methacrylic acid (MAA), and itaconic acid (IA).

[0030] In some embodiments, for 100 parts by weight of the main monomer, the amount of the functional monomer I is 2 to 10 parts by weight, such as 3 parts by weight, 4 parts by weight, 5 parts by weight, 5.5 parts by weight, 5.8 parts by weight, 6 parts by weight, 6.5 parts by weight, 8 parts by weight, 10 parts by weight, etc.

[0031] In this invention, the functional monomer II is a polyether macromonomer, used to provide steric stabilization for the polymer. The polyether side chains formed after copolymerization can constitute an effective steric hindrance layer on the surface of latex particles, achieving dispersion stability. According to some embodiments, the polyether macromonomer is selected from at least one of methyl allyl monomethyl ether polyoxyethylene ether (HPEG), 4-hydroxybutyl vinyl ether polyoxyethylene ether (VPEG), ethylene glycol monovinyl polyoxypropylene ether (EPEG), and isopentenyl polyethylene glycol ether (TPEG).

[0032] In this invention, the number-average molecular weight of the polyether macromonomer is preferably 2000-4500, such as 2400, 3000, 3500, 4000, 4500, etc. As some examples, the polyether macromonomer can be HPEG-2400, HPEG-3000, VPEG-2400, VPEG-3000, VPEG-3500, TPEG-2400, TPEG-3000, TPEG-4000, etc. Furthermore, the polyether macromonomer of this invention can be commercially available, for example, selected from the OXAC-608A, OXAC-609E, OXAC-609H, OXAC-604, OXAC-605 series polyether products of Jiangsu Aoke Chemical Co., Ltd.

[0033] In some embodiments, the amount of functional monomer II is 15 to 25 parts by weight relative to 100 parts by weight of the main monomer, for example, 16 parts by weight, 16.2 parts by weight, 18.5 parts by weight, 18.9 parts by weight, 19.2 parts by weight, 20.2 parts by weight, 21.2 parts by weight, 22.9 parts by weight, 23.5 parts by weight, 24.3 parts by weight, 25.0 parts by weight, etc.

[0034] In this invention, the functional monomer III has the structure shown in Formula 1: Formula 1, In this context, R1 and R2 are each independently hydrogen or methyl (-CH3), R3 is hydrogen or hydroxyl (-OH), and m and n are each independently 0 or 1.

[0035] The functional monomer III is a slow-release crosslinking monomer, specifically (meth)acrylate (R3 is hydrogen) or (meth)acrylate hydroxyl ester (R3 is -OH). Through copolymerization with other monomers, hydrolyzable ester structural units are introduced into the polymer chain. The ester groups can undergo slow hydrolysis in the alkaline environment of concrete, releasing active groups that can slowly crosslink with cement hydration products or latex particles, thereby effectively controlling the rheological properties of the paste and extending the slump retention time.

[0036] In some embodiments, the structure of the functional monomer III is selected from any one of Formulas 1-1 to 1-3:

[0037] As some preferred examples, the functional monomer III is selected from at least one of methyl methacrylate (MMA), hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), hydroxyethyl methacrylate (HEMA), and hydroxypropyl methacrylate (2HPMA).

[0038] In some embodiments, the amount of functional monomer II relative to 100 parts by weight of the main monomer is 1 to 8 parts by weight, for example 2.05 parts by weight, 3.70 parts by weight, 3.75 parts by weight, 3.80 parts by weight, 4.05 parts by weight, 4.5 parts by weight, 4.85 parts by weight, 5.0 parts by weight, 5.12 parts by weight, 5.25 parts by weight, 6.05 parts by weight, 7.20 parts by weight, etc.

[0039] In this invention, the emulsifier may be an anionic emulsifier, preferably sodium dodecyl sulfate (SDS) and / or sodium dodecylbenzene sulfonate (SDBS). The amount of the emulsifier can be selected according to the total amount of comonomers. According to some embodiments, the mass amount of the emulsifier can be 0.5% to 5% of the total mass of the comonomers, for example, 0.5%, 0.8%, 0.9%, 1.1%, 1.2%, 1.3%, 1.4%, 1.8%, 2.0%, 3.0%, 5.0%, etc.

[0040] In this invention, the initiator can be selected from various water-soluble initiators, such as one or more of redox initiators, persulfate initiators, and peroxide initiators, with redox initiators being preferred.

[0041] The redox initiator includes an oxidant and a reducing agent. Preferably, the oxidant is selected from one or more of benzoyl peroxide, hydrogen peroxide, tert-butyl hydroperoxide, ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent is selected from one or more of ferrous sulfate, sodium formaldehyde sulfoxylate, and ascorbic acid.

[0042] In some embodiments, the mass ratio of oxidant to initiator in the redox initiator is 1:(0.2~2), for example 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:1, 1:2, etc.

[0043] In this invention, the amount of initiator can be selected according to the total amount of comonomer. According to some embodiments, the mass amount of the initiator is 0.1% to 2% of the total mass of the comonomer, for example, 0.2%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.2%, 1.3%, 1.5%, 1.8%, etc.

[0044] In this invention, the chain transfer agent may be selected from at least one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, isooctyl mercaptan, sodium formate, and sodium hypophosphite. The mass amount of the chain transfer agent may be 0.1% to 1% of the total mass of the comonomer, for example, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, etc.

[0045] In this invention, the temperature of the emulsion polymerization reaction can be 50~90℃, for example, 50℃, 55℃, 60℃, 70℃, 75℃, 80℃, 90℃, etc. In some embodiments, the temperature of the polymerization reaction can be controlled within any temperature range of the above range, for example, controlled between 60~70℃, between 70~75℃, between 75~85℃, etc.

[0046] In this invention, the emulsion polymerization time can be determined based on the conversion rate of the comonomer, preferably controlling the conversion rate to be not less than 95%. As some examples, the emulsion polymerization time can be 2 to 10 hours, such as 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, etc.

[0047] In this invention, after the emulsion polymerization reaction is completed, whether or not pH adjustment is performed can be determined based on the type of monomer used (especially the content of acidic functional monomers). Preferably, an alkali is added to adjust the pH of the product to a neutral range (e.g., 6-8) to improve the storage stability of the latex. The alkali may include, but is not limited to, sodium hydroxide and potassium hydroxide. Preferably, the alkali is added in the form of an alkaline solution.

[0048] In this invention, the modified styrene-butadiene latex is preferably prepared using a seed emulsion polymerization method to impart a core-shell structure to the latex particles. As some preferred embodiments, the steps for preparing the modified styrene-butadiene latex using the seed emulsion polymerization method include: 1) Styrene, some functional monomer I, emulsifier and water are mixed and pre-emulsified to obtain a pre-emulsion; 2) Under the protection of an inert gas, the pre-emulsion, butadiene, and part of the initiator are mixed evenly in a reactor, the pressure inside the reactor is maintained at 0.4~0.6MPa, and the reaction is stirred at a first temperature T1 (T1 is 60~75℃, for example 60℃, 70℃ or 75℃) for 0.5~1.5h, and then the aqueous solution of the remaining functional monomer I is added dropwise. 3) Add the remaining initiator to the system obtained in step 2), heat the system to the second temperature T2 (5℃≤T2-T1≤20℃), and then add dropwise the aqueous solution of functional monomer II, the aqueous solution of functional monomer III, and the aqueous solution of chain transfer agent; 4) After the addition is complete, continue the reaction at the second temperature T2; 5) Add alkali solution to adjust the pH of the reaction system obtained in step 4) to 6-8.

[0049] In step 1), pre-emulsification is preferably carried out using a high-speed disperser, which uses high-speed shear force to disperse the system uniformly, aiming to form a stable pre-emulsion that is not prone to stratification. The amount of functional monomer I used is 10% to 40% based on its total amount, for example, 10%, 20%, 30%, 40%, etc.

[0050] In step 2), an inert gas (such as nitrogen or argon) can be used to replace the air in the reactor and establish a pressurized reaction atmosphere to ensure that butadiene remains in a liquid state. When using a redox initiation system, it is preferable to add its oxidant component as part of the initiator at this stage. The reaction can be carried out under stirring, specifically including the following operations: 2-1) Seed polymerization: Styrene and butadiene are copolymerized, and the monomer conversion rate is 50%~70% by controlling the reaction time (e.g. 0.5h, 1h or 1.5h), thus initially forming the core of latex particles; 2-2) Addition of functional monomer I: Slowly add the remaining aqueous solution of functional monomer I to the system, allowing it to accumulate on the particle surface. The addition time is typically 2-4 hours (e.g., 2 hours, 2.5 hours, 3 hours, or 4 hours) to ensure that the monomer is converted as completely as possible to form a carboxyl-modified copolymer. After the addition is complete, the reactor can be depressurized.

[0051] Step 3) is the shell formation and functionalization stage of latex particles. In this stage, functional monomer II preferentially distributes on the surface of the latex particles through copolymerization, forming a shell layer grafted with sterically hindered long side chains, thereby endowing the latex with efficient dispersion ability. Simultaneously, functional monomer III participates in copolymerization and is introduced into the shell layer to provide sustained-release crosslinking functionality. Furthermore, the addition of a chain transfer agent can regulate the polymer molecular weight, prevent gel formation, and improve latex stability. This step can be carried out under normal pressure.

[0052] When a redox initiation system is selected, the remaining initiators added in this stage are preferably a combination of oxidant and reductant. The oxidant in this combination may be the same as or different from the oxidant used in step 2).

[0053] In step 3), by controlling the dropping time of the three aqueous solutions, the conversion rate of the reactant monomer is preferably not less than 90%. The dropping time is usually controlled between 2 and 4 hours, for example, 2.5 hours, 3 hours, 4 hours, etc.

[0054] In step 4), in order to further improve the monomer conversion rate (usually not less than 95%), the reaction is kept at a constant temperature after the addition is completed. The holding time is usually controlled to be 0.5~2h, for example 0.5h, 1h or 2h.

[0055] In step 5), adding alkali solution can improve the storage stability of latex. Optionally, in step 5), other additives such as defoamers and preservatives may be added as needed to control foaming or prevent spoilage. The types and amounts of the additives are well known in the art and will not be described in detail here.

[0056] In this invention, the amount of water used can be selected according to the desired solid content of the modified styrene-butadiene latex. According to some embodiments, the amount of water used results in a solid content of 40% to 55% for the modified styrene-butadiene latex, such as 45%, 49.5%, 50%, 52%, etc.

[0057] Secondly, this invention provides a modified styrene-butadiene latex prepared by the method described in the first aspect. Compared to traditional styrene-butadiene latex, this invention effectively and synergistically improves the waterproofness and workability of the latex by simultaneously introducing polyether side chains and structural units provided by functional monomer III onto its polymer molecular chain. Specifically, the polyether side chains significantly enhance the initial dispersibility and storage stability of the latex (aqueous dispersion) through steric hindrance; while the structural units provided by functional monomer III can undergo slow-release crosslinking under alkaline conditions, endowing the system with a "delayed activation" rheological regulation capability. This allows building materials such as concrete to maintain excellent workability during construction while extending slump retention time and improving the final waterproofing effect.

[0058] Thirdly, the present invention provides the application of the modified styrene-butadiene latex described in the second aspect of the present invention in building materials. The building materials may be, for example, concrete or mortar. When the modified styrene-butadiene latex is applied as a waterproofing agent to concrete or mortar, its "delayed activation" rheological modulation capability can effectively extend the slump retention time of the system and enhance the waterproof performance of the final hardened body.

[0059] The following describes embodiments of the present invention. These embodiments are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0060] In the following examples and comparative examples, the alkaline solution used is an aqueous sodium hydroxide solution with a NaOH mass concentration of 32%. Unless otherwise stated, all parts are parts by weight.

[0061] Example 1 Mix 20 parts water, 1.5 parts sodium dodecyl sulfate, 30 parts styrene and 1 part MAA, heat to 40°C and pre-emulsify using a high-speed disperser to form a pre-emulsion.

[0062] The pre-emulsion was transferred to a reactor, and nitrogen was introduced to purge oxygen three times. After the final purging, the nitrogen atmosphere was maintained, and the pressure inside the reactor was increased to 0.45 MPa. Then, 70 parts of butadiene (pre-pressurized to 0.5 MPa to maintain a liquid state) were injected into the reactor and stirred until homogeneous at room temperature. 0.4 parts of potassium persulfate were added, and the temperature was raised to 60°C to initiate the reaction. The reaction was maintained at this temperature with stirring for 1 hour. Then, a solution prepared from 4 parts of MAA and 30 parts of water was added dropwise over 3 hours. After the addition was completed, the pressure was released to atmospheric pressure.

[0063] Subsequently, 0.1 parts of ammonium persulfate and 0.3 parts of ferrous sulfate were added to the reactor. The temperature was raised to 80°C and stirred continuously. Simultaneously, an aqueous solution of HPEG-3000 (21.25 parts HPEG-3000, 40 parts water), an aqueous solution of HEA (3.75 parts HEA, 20 parts water), and an aqueous solution of isooctyl mercaptan (0.3 parts isooctyl mercaptan, 25 parts water) were added dropwise over a period of 3 hours. After the addition was complete, the reaction was continued at 80°C with stirring for 1 hour to obtain an emulsion-type modified butadiene-styrene copolymer with a solid content of approximately 50%. The mixture was cooled to room temperature, and the pH of the system was adjusted to 7.5 with alkali solution to obtain modified styrene-butadiene latex, denoted as A1.

[0064] Example 2 Mix 21 parts water, 1.8 parts sodium dodecyl sulfate, 40 parts styrene and 1.2 parts MAA, heat to 35°C and pre-emulsify using a high-speed disperser to form a pre-emulsion.

[0065] The pre-emulsion was transferred to a reactor, and nitrogen was introduced to purge oxygen from the system three times. After the final purging, the nitrogen atmosphere was maintained, and the pressure inside the reactor was increased to 0.40 MPa. Then, 60 parts of butadiene (pre-pressurized to 0.45 MPa to maintain a liquid state) were injected into the reactor and stirred until homogeneous at room temperature. 0.5 parts of potassium persulfate were added, and the temperature was raised to 65°C to initiate the reaction. The reaction was maintained at this temperature with stirring for 1 hour. Then, a solution prepared from 4.6 parts of MAA and 29 parts of water was added dropwise over 2.5 hours. After the addition was completed, the pressure was released to atmospheric pressure.

[0066] Subsequently, 0.2 parts of tert-butyl hydroperoxide and 0.26 parts of ascorbic acid were added to the reactor. The temperature was raised to 70°C and stirred continuously. Simultaneously, an aqueous solution of HPEG-2400 (22.9 parts HPEG-2400, 40 parts water), an aqueous solution of 2HPMA (4.85 parts 2HPMA, 20 parts water), and an aqueous solution of mercaptoethanol (0.3 parts mercaptoethanol, 25 parts water) were added dropwise over a period of 3 hours. After the addition was complete, the reaction was continued at 70°C with stirring for 1 hour to obtain an emulsion-type modified butadiene-styrene copolymer with a solid content of approximately 50%. The mixture was cooled to room temperature, and the pH of the system was adjusted to 7.5 with alkali solution to obtain modified styrene-butadiene latex, denoted as A2.

[0067] Example 3 Mix 25 parts water, 2.0 parts sodium dodecyl sulfate, 50 parts styrene and 2 parts MAA, heat to 45°C and pre-emulsify using a high-speed disperser to form a pre-emulsion.

[0068] The pre-emulsion was transferred to a reactor, and nitrogen was introduced three times to purge oxygen from the system. After the final purging, the nitrogen atmosphere was maintained, and the pressure inside the reactor was increased to 0.45 MPa. Then, 50 parts of butadiene (pre-pressurized to 0.5 MPa to maintain a liquid state) were injected into the reactor and stirred until homogeneous at room temperature. 0.6 parts of potassium persulfate were added, and the temperature was raised to 70°C to initiate the reaction. The reaction was maintained at this temperature with stirring for 1 hour. Then, an aqueous solution prepared from 4.5 parts of MAA and 25 parts of water was added dropwise over a period of 2.0 hours. After the addition was completed, the pressure was released to atmospheric pressure.

[0069] Subsequently, 0.3 parts of hydrogen peroxide (H2O2, added as 30wt% hydrogen peroxide solution) and 0.35 parts of ferrous sulfate were added to the reactor. The temperature was raised to 75°C and stirred continuously. Simultaneously, an aqueous solution of TPEG-2400 (16.2 parts TPEG-2400, 40 parts water), an aqueous solution of HEA (3.80 parts HEA, 20 parts water), and an aqueous solution of mercaptoacetic acid (0.5 parts mercaptoacetic acid, 21 parts water) were added dropwise over a period of 3 hours. After the addition was complete, the reaction was continued at 75°C with stirring for 1 hour to obtain an emulsion-type modified butadiene-styrene copolymer with a solid content of approximately 50%. The mixture was cooled to room temperature, and the pH of the system was adjusted to 7.5 with alkali solution to obtain modified styrene-butadiene latex, denoted as A3.

[0070] Example 4 Mix 20 parts water, 1.5 parts sodium dodecyl sulfate, 30 parts styrene and 1 part AA, heat to 40°C and pre-emulsify using a high-speed disperser to form a pre-emulsion.

[0071] The pre-emulsion was transferred to a reactor, and nitrogen was introduced three times to purge oxygen from the system. After the final purging, the nitrogen atmosphere was maintained, and the pressure inside the reactor was increased to 0.45 MPa. Then, 70 parts of butadiene (pre-pressurized to 0.5 MPa to maintain a liquid state) were injected into the reactor and stirred until homogeneous at room temperature. 0.4 parts of potassium persulfate were added, and the temperature was raised to 60°C to initiate the reaction. The reaction was maintained at this temperature with stirring for 1 hour. Then, a solution prepared from 4 parts of AA and 30 parts of water was added dropwise over 3 hours. After the addition was completed, the pressure was released to atmospheric pressure.

[0072] Subsequently, 0.1 parts of ammonium persulfate and 0.3 parts of ferrous sulfate were added to the reactor. The temperature was raised to 80°C and stirred continuously. Simultaneously, an aqueous solution of HPEG-3000 (21.25 parts HPEG-3000, 40 parts water), an aqueous solution of HEA (3.75 parts HEA, 20 parts water), and an aqueous solution of isooctyl mercaptan (0.3 parts isooctyl mercaptan, 25 parts water) were added dropwise over a period of 3 hours. After the addition was complete, the reaction was continued at 80°C with stirring for 1 hour to obtain an emulsion-type modified butadiene-styrene copolymer with a solid content of approximately 50%. The mixture was cooled to room temperature, and the pH of the system was adjusted to 7.5 with alkali solution to obtain modified styrene-butadiene latex, denoted as A4.

[0073] Example 5 Mix 20 parts water, 1.5 parts sodium dodecyl sulfate, 30 parts styrene and 2 parts MAA, heat to 40°C and pre-emulsify using a high-speed disperser to form a pre-emulsion.

[0074] The pre-emulsion was transferred to a reactor, and nitrogen was introduced to purge oxygen three times. After the final purging, the nitrogen atmosphere was maintained, and the pressure inside the reactor was increased to 0.45 MPa. Then, 70 parts of butadiene (pre-pressurized to 0.5 MPa to maintain a liquid state) were injected into the reactor and stirred until homogeneous at room temperature. 0.4 parts of potassium persulfate were added, and the temperature was raised to 60°C to initiate the reaction. The reaction was maintained at this temperature with stirring for 1 hour. Then, a solution prepared from 4 parts of MAA and 30 parts of water was added dropwise over 3 hours. After the addition was completed, the pressure was released to atmospheric pressure.

[0075] Subsequently, 0.1 parts of ammonium persulfate and 0.3 parts of ferrous sulfate were added to the reactor. The temperature was raised to 70°C and stirred. Simultaneously, an aqueous solution of VPEG-3500 (18.25 parts VPEG-3500, 35 parts water), an aqueous solution of MMA (5.25 parts MMA, 20 parts water), and an aqueous solution of mercaptoacetic acid (0.3 parts mercaptoacetic acid, 25 parts water) were added dropwise over a period of 3 hours. After the addition was complete, the reaction was continued at 70°C with stirring for 1 hour to obtain an emulsion-type modified butadiene-styrene copolymer with a solid content of approximately 50%. The mixture was cooled to room temperature, and the pH of the system was adjusted to 7.5 with alkali solution to obtain modified styrene-butadiene latex, denoted as A5.

[0076] Comparative Example 1 (1) Preparation of styrene-butadiene latex Mix 55 parts water, 1.2 parts sodium dodecyl sulfate, 30 parts styrene and 1 part MAA, heat to 40°C and pre-emulsify using a high-speed disperser to form a pre-emulsion.

[0077] The pre-emulsion was transferred to a reactor, and nitrogen was introduced three times to purge oxygen from the system. After the final purging, the nitrogen atmosphere was maintained, and the pressure inside the reactor was increased to 0.45 MPa. Then, 70 parts of butadiene (pre-pressurized to 0.5 MPa to maintain a liquid state) were injected into the reactor and stirred until homogeneous at room temperature. 0.5 parts of potassium persulfate were added, and the temperature was raised to 60°C to initiate the reaction. The reaction was maintained at this temperature and stirred for 1 hour. Then, a solution prepared from 4 parts of MAA and 52 parts of water was added dropwise over 3 hours. After the dropwise addition was completed, the temperature was raised to 80°C and the reaction was stirred for another 1 hour. After the reaction was completed, an emulsion-type methacrylic acid-butadiene-styrene copolymer with a solid content of approximately 50% was obtained. Finally, the pressure was released to atmospheric pressure, cooled to room temperature, and the pH of the system was adjusted to 7.5 with an alkaline solution to obtain conventional styrene-butadiene latex.

[0078] (2) Preparation of compound styrene-butadiene latex The traditional styrene-butadiene latex prepared in step (1) was mixed with a polycarboxylate superplasticizer (commercially available, purchased from Kezhijie Company, brand name Point-440S) at a mass ratio of 19:8 and stirred evenly to obtain a compound styrene-butadiene latex, denoted as D1.

[0079] Comparative Example 2 Mix 38 parts water, 1.5 parts sodium dodecyl sulfate, 30 parts styrene and 1 part MAA, heat to 40°C and pre-emulsify using a high-speed disperser to form a pre-emulsion.

[0080] The pre-emulsion was transferred to a reactor, and nitrogen was introduced to purge oxygen three times. After the final purging, the nitrogen atmosphere was maintained, and the pressure inside the reactor was increased to 0.45 MPa. Then, 70 parts of butadiene (pre-pressurized to 0.5 MPa to maintain a liquid state) were injected into the reactor and stirred until homogeneous at room temperature. 0.4 parts of potassium persulfate were added, and the temperature was raised to 60°C to initiate the reaction. The reaction was maintained at this temperature with stirring for 1 hour. Then, an aqueous solution prepared from 4 parts of MAA and 30 parts of water was added dropwise over 3 hours. After the addition was completed, the pressure was released to atmospheric pressure.

[0081] Subsequently, 0.1 parts of ammonium persulfate and 0.3 parts of ferrous sulfate were added to the reactor, the temperature was raised to 80°C and stirred, and an aqueous solution of HEA (3.75 parts HEA, 20 parts water) and an aqueous solution of isooctyl mercaptan (0.3 parts isooctyl mercaptan, 25 parts water) were added dropwise simultaneously over a period of 3 hours. After the addition was complete, the reaction was continued at 80°C with stirring for 1 hour to obtain a modified butadiene-styrene copolymer with a solid content of approximately 50%. The mixture was cooled to room temperature, and the pH of the system was adjusted to 7.5 with an alkaline solution to obtain a modified styrene-butadiene latex, denoted as D2.

[0082] Comparative Example 3 Mix 36 parts water, 1.5 parts sodium dodecyl sulfate, 30 parts styrene and 1 part MAA, heat to 40°C and pre-emulsify using a high-speed disperser to form a pre-emulsion.

[0083] The pre-emulsion was transferred to a reactor, and nitrogen was introduced to purge oxygen three times. After the final purging, the nitrogen atmosphere was maintained, and the pressure inside the reactor was increased to 0.45 MPa. Then, 70 parts of butadiene (pre-pressurized to 0.5 MPa to maintain a liquid state) were injected into the reactor and stirred until homogeneous at room temperature. 0.4 parts of potassium persulfate were added, and the temperature was raised to 60°C to initiate the reaction. The reaction was maintained at this temperature with stirring for 1 hour. Then, an aqueous solution prepared from 4 parts of MAA and 30 parts of water was added dropwise over 3 hours. After the addition was completed, the pressure was released to atmospheric pressure.

[0084] Subsequently, 0.1 parts of ammonium persulfate and 0.3 parts of ferrous sulfate were added to the reactor. The temperature was raised to 80°C and stirred continuously. Simultaneously, an aqueous solution of HPEG-3000 (21.25 parts HPEG-3000, 40 parts water) and an aqueous solution of isooctyl mercaptan (0.3 parts isooctyl mercaptan, 25 parts water) were added dropwise over a period of 3 hours. After the addition was complete, the reaction was continued at 80°C with stirring for 1 hour to obtain an emulsion-type modified butadiene-styrene copolymer with a solid content of approximately 50%. The mixture was cooled to room temperature, and finally, the pH of the system was adjusted to 7.5 with an alkaline solution to obtain modified styrene-butadiene latex, denoted as D3.

[0085] Test case The following test examples illustrate the performance of the waterproofing agents A1-A5 and D1-D3 prepared in Examples 1-5 and Comparative Examples 1-3.

[0086] 1. Test Basis and Sample Preparation Test Standards: This test example is conducted in accordance with the relevant provisions of GB 8076-2008 Concrete Admixtures, JC 474-2008 Mortar and Concrete Waterproofing Agents, GB / T 50080-2016 Standard for Test Methods of Performance of Ordinary Concrete Mixtures, and GB / T 50082-2009 Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete.

[0087] Materials and mix proportions: Ordinary Portland cement (P·O 42.5), 5-20mm continuously graded crushed stone, and medium sand with a fineness modulus of 2.6-2.9 are used. The design mix proportions for C30 strength grade benchmark concrete (per cubic meter): cement 380kg, water 175kg, sand 780kg, aggregate 1085kg, water-cement ratio 0.46.

[0088] In the tested concrete, the waterproofing agent to be tested was added externally at an equal amount of 5% of the mass of the cementitious material, with a dosage of 19 kg / m³; and 2.1% of the mass of the cementitious material was added to the commercially available polycarboxylate superplasticizer (Point-440S), with a dosage of 8 kg / m³.

[0089] Mixing and testing environment: Concrete mixing was carried out in accordance with GB / T 50080-2016, using a forced mixer. First, sand, stone, and cement were dry-mixed for 30 seconds, then the pre-mixed mixing water, waterproofing agent, and water-reducing agent were added, and mixing continued for 120 seconds. The test was conducted in a constant temperature and humidity environment of (20±2)℃ and 60% relative humidity.

[0090] 2. Performance Testing Methods 1) Performance test of fresh concrete: According to GB / T 50080-2016, test the initial slump and spread of concrete, as well as the slump and spread after standing for 1 hour.

[0091] 2) Performance testing of hardened concrete 28-day water absorption ratio: According to JC 474-2008, 100 mm × 100 mm × 100 mm specimens were molded and cured to a standard age of 28 days. The specimens were dried at 75~80℃ to constant weight and then weighed, with the mass recorded as M1. The dried specimens were placed in a water tank with the molded side down, supported at the bottom by Ø10 mm steel bars, and filled with clean water to 35 mm above the specimen height. The water tank was covered and left to stand for (48±0.5) h in an environment of (20±3)℃ and relative humidity above 80%. After removing the specimens and wiping off the surface water, they were weighed immediately, and the mass recorded as M2. The water absorption is calculated as M2-M1, and the water absorption ratio is the percentage of the water absorption of the tested concrete to that of the reference concrete.

[0092] Permeability grade: Referring to GB / T 50082-2009, the molded specimens were left to stand in a standard curing room for 24 hours before demolding and continued curing for 28 days. After the surface dried, the specimens were sealed with sealant and placed in a permeameter. The water pressure was started at 0.2 MPa and maintained at a constant pressure for 2 hours, then increased to 0.3 MPa, and thereafter increased by 0.1 MPa every hour. When three out of six specimens showed signs of seepage at their end faces, the test was stopped and the water pressure value was recorded. If no water permeation was observed after pressurizing to 1.5 MPa and maintaining the pressure for 1 hour, the pressure was stopped. The permeability pressure was taken as the maximum water pressure value when four out of six specimens in each group did not show signs of seepage, and the permeability grade (P) of the concrete was evaluated based on this value.

[0093] The test results are shown in Table 1.

[0094] Table 1

[0095] According to the data in Table 1, compared with Comparative Examples 1-3, Examples 1-5 showed better overall performance: not only was the initial fluidity high and the loss over time small, but it also had lower water absorption and higher impermeability.

[0096] Comparative Example 1, which uses traditional styrene-butadiene latex and a water-reducing agent for physical blending, exhibits low initial spread (455 mm) and slump (170 mm). Furthermore, after 1 hour, the spread loss reaches 75 mm and the slump loss reaches 70 mm, resulting in a waterproofing grade of only P6. This indicates that physical mixing methods are significantly inadequate in improving initial fluidity, maintaining workability, and achieving the final waterproofing effect.

[0097] Furthermore, compared to Example 1, Comparative Example 2, which did not incorporate polyether macromonomers that provide polyether side chains, exhibited the lowest initial spread (440 mm) and slump (160 mm) among all samples. This demonstrates that the polyether side chains introduced by the polyether macromonomers play a crucial role in significantly improving the initial dispersibility and flowability of the concrete system. Comparative Example 3, which did not incorporate functional monomer III that provides slow-release crosslinking units, showed a spread loss as high as 110 mm and a slump loss of 70 mm after 1 hour. This indicates that the "delayed activation" rheological modulation function achieved by functional monomer III through slow-release crosslinking is essential for maintaining the workability of concrete during construction.

[0098] Furthermore, comparing Example 1 with Example 4, it can be seen that Example 1 uses methacrylic acid (MAA) in copolymerization, while Example 4 uses acrylic acid (AA). The former performs better in terms of water absorption ratio and impermeability grade. This indicates that compared with AA, MAA is more beneficial in reducing the water absorption of concrete and improving its impermeability.

[0099] In summary, this invention effectively and synergistically improves the application performance of concrete by simultaneously introducing functional monomers II and III into the styrene-butadiene latex molecular chain for copolymerization modification. Functional monomer II (polyether macromonomer) primarily contributes to the steric hindrance effect, significantly enhancing the initial fluidity and dispersion stability of the system; while functional monomer III (slow-release crosslinking monomer), through a delayed crosslinking mechanism, dominates the long-term maintenance of workability and the formation of the final dense polymer-cement composite structure. The two synergistically bond at the molecular level through chemical bonding, thereby achieving excellent waterproofing and impermeability while maintaining high initial fluidity and low loss over time.

[0100] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A method for preparing modified styrene-butadiene latex, characterized in that, include: In the presence of water, emulsifier, initiator, and optionally chain transfer agent, comonomers including the host monomer, functional monomer I, functional monomer II, and functional monomer III undergo emulsion polymerization to form a modified styrene-butadiene copolymer; wherein, The main monomer is composed of styrene and butadiene. The functional monomer I is an unsaturated carboxylic acid. The functional monomer II is a polyether macromonomer. The functional unit III has the structure shown in Formula 1: Formula 1, In Formula 1, R1 and R2 are each independently hydrogen or methyl, R3 is hydrogen or hydroxyl, and m and n are each independently 0 or 1.

2. The preparation method according to claim 1, characterized in that, The unsaturated carboxylic acid is selected from at least one of acrylic acid, methacrylic acid and itaconic acid, preferably methacrylic acid.

3. The preparation method according to claim 1 or 2, characterized in that, The polyether macromonomer is selected from at least one of methyl allyl monomethyl ether polyoxyethylene ether, 4-hydroxybutyl vinyl ether polyoxyethylene ether, ethylene glycol monovinyl polyoxypropylene ether and isopentenyl polyethylene glycol ether. Preferably, the functional monomer III is selected from at least one of methyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, and hydroxypropyl methacrylate.

4. The preparation method according to any one of claims 1-3, characterized in that, Based on the total mass of the main monomers, styrene accounts for 25% to 50% of the mass, and butadiene accounts for 50% to 75% of the mass; Preferably, relative to 100 parts by weight of the main monomer, the amount of functional monomer I is 2 to 10 parts by weight, the amount of functional monomer II is 15 to 25 parts by weight, and the amount of functional monomer III is 1 to 8 parts by weight.

5. The preparation method according to any one of claims 1-4, characterized in that, The emulsion polymerization reaction is carried out at a temperature of 50~90℃ for 2~10h. Preferably, the amount of water used is such that the solid content of the prepared modified styrene-butadiene latex is 40% to 55%.

6. The preparation method according to any one of claims 1-5, characterized in that, The initiator is a redox initiator, and the oxidant in the redox initiator is selected from at least one of benzoyl peroxide, hydrogen peroxide, tert-butyl hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate; the reducing agent in the redox initiator is selected from at least one of ferrous sulfate, sodium formaldehyde sulfoxylate, and ascorbic acid, and the mass ratio of the oxidant to the reducing agent is 1:(0.2~2). Preferably, the initiator is used in an amount of 0.1% to 2% of the total mass of the comonomer.

7. The preparation method according to any one of claims 1-6, characterized in that, The emulsifier is selected from sodium dodecyl sulfate and / or sodium dodecylbenzene sulfonate; Preferably, the emulsifier is used in an amount of 0.5% to 5% of the total mass of the comonomer; Preferably, the chain transfer agent is selected from at least one of mercaptopropionic acid, mercaptoacetic acid, mercaptoethanol, isooctyl mercaptan, sodium formate, and sodium hypophosphite; Preferably, the chain transfer agent is used in an amount of 0.1% to 1% of the total mass of the comonomer.

8. The preparation method according to any one of claims 1-7, characterized in that, The preparation method is a seed emulsion polymerization method, and includes the following steps: 1) Styrene, some functional monomer I, emulsifier and water are mixed and pre-emulsified to obtain a pre-emulsion; 2) Under the protection of an inert gas, the pre-emulsion, butadiene and part of the initiator are mixed evenly in a reactor, the pressure inside the reactor is maintained at 0.4~0.6MPa, and the reaction is kept at the first temperature T1 for 0.5~1.5h. Then, the aqueous solution of the remaining functional monomer I is added dropwise, and the dropwise addition time is controlled to be 2~4h. 3) Add the remaining initiators to the system obtained in step 2), heat the system to the second temperature T2, and then add the aqueous solution of functional monomer II, the aqueous solution of functional monomer III and the aqueous solution of chain transfer agent dropwise, controlling the dropwise addition time to 2~4h; 4) After the addition is complete, continue the reaction at the second temperature T2 for 0.5~2 hours; among which, The first temperature T1 is 60~75℃, and the second temperature T2 and the first temperature T1 satisfy the following relationship: 5℃≤T2-T1≤20℃; 5) Add alkali solution to adjust the pH of the reaction system obtained in step 4) to 6-8.

9. A modified styrene-butadiene latex is prepared by the preparation method according to any one of claims 1-8.

10. The application of the modified styrene-butadiene latex according to claim 9 in building materials.

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