Gradient block polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention relates to a gradient block polycarboxylic acid water reducing agent and a preparation method thereof, the gradient block polycarboxylic acid water reducing agent is prepared by using acrylic acid, a functional anchoring monomer, a polyether macromonomer and a hydrophobic ester monomer as comonomers through a redox gradient polymerization method; wherein in the polymerization process, by controlling the ratio of the oxidizing agent to the reducing agent, the free radical generation rate in a polymerization reaction system is gradually reduced along with the reaction time, so that a chain segment structure with gradient distribution is formed, and the content of polar groups in the chain segment structure is gradually reduced along a polymer main chain from high to low. According to the preparation method, the free radical generation rate is regulated and controlled through an oxidation-reduction gradient polymerization process, ordered distribution of carboxylic acid groups, phosphonic acid groups and polyether chain segments on molecular chains is achieved, and a gradient structure with gradually decreased polarity is formed. Compared with a random copolymerization system, the gradient block polycarboxylate superplasticizer disclosed by the invention has better repeatability and distribution precision on the structural level.

Description

Technical Field

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

[0002] Current concrete viscosity-reducing and anti-mud admixtures are mostly based on polycarboxylate superplasticizers, improving fluidity and anti-mud properties by introducing highly polar groups (such as sulfonic acid groups and phosphonic acid groups) or sterically hindered polyether segments. Representative technologies include star-shaped polycarboxylate structures, amine-modified tannic acid polymers, or anti-mud systems compounded with cationic surfactants. These systems can alleviate adsorption failure caused by high-mud-content manufactured sand to some extent, but their molecular structures are mostly random copolymers or randomly distributed, making it difficult to achieve an ordered arrangement of functional segments on the molecular chain. Furthermore, while redox-initiated systems are used for mild polymerization reactions, they typically do not form true free radical gradient control, resulting in limited precision in structural regulation.

[0003] The main problem with existing anti-mud water-reducing agents lies in the random polar distribution of their molecular chains, which cannot simultaneously satisfy the requirements of highly selective adsorption of cement particles and repulsion of clay particles. In conventional free radical polymerization or constant-rate dropping polymerization, the differences in monomer reactivity cannot be fully reflected through time control, and the polar gradient of polymer chain segments is almost uncontrollable. As a result, slump loss and increased plasticizing viscosity still occur in mud-containing systems. In addition, although compounding sacrificial agents can improve flowability in the short term, the system has poor stability, high cost, and insufficient environmental friendliness.

[0004] The root cause lies in the fact that existing polymerization routes cannot establish a dynamic equilibrium between monomer reaction rates and free radical generation rates, resulting in a chaotic distribution of highly polar and hydrophobic monomers along the chain and a lack of a clear sequence gradient. Because cement and clay surfaces have different adsorption preferences for different polar functional groups, the heterogeneity of the molecular sequence leads to adsorption competition, causing functional mismatch of the water-reducing agent in the clay system. Simultaneously, the wide molecular weight distribution of polymers with random structures results in unstable rheological control properties, making it difficult to simultaneously achieve anti-mud properties and viscosity-reducing performance.

[0005] Attempts to construct gradient structures by simply changing the dropping rate, feeding sequence, or adding control agents often fail to precisely control the free radical concentration gradient. Furthermore, the polymerization system is susceptible to side reactions caused by temperature, pH, and redox ratio, resulting in non-reproducible structures. In addition, employing complex multi-reactor reaction routes significantly increases process difficulty and cost, hindering industrial scale-up.

[0006] Therefore, how to achieve a dynamic gradient in the rate of free radical generation through a controllable redox system in a single-reactor system, thereby forming block segments with varying polarity, is a key challenge that has not yet been effectively solved by existing technologies. Summary of the Invention

[0007] Therefore, it is necessary to provide a gradient block polycarboxylate superplasticizer and its preparation method, in order to solve the problems existing in the prior art.

[0008] To achieve the above objectives, the present invention provides a technical solution:

[0009] A gradient block polycarboxylate superplasticizer is prepared by a redox gradient polymerization method using unsaturated acid monomers, functional anchoring monomers, polyether macromonomers and hydrophobic ester monomers as comonomers.

[0010] In this process, by controlling the ratio of oxidant to reducing agent during polymerization, the rate of free radical generation in the polymerization reaction system gradually decreases with reaction time, thereby forming a segmental structure with a gradient distribution. The content of polar groups in the segmental structure decreases from high to low along the polymer backbone.

[0011] Gradient polymerization dynamically controls the concentration of free radicals, enabling functional monomers to be arranged according to a preset sequence to form an ideal polar gradient distribution. This structural feature directly determines the performance of the final product.

[0012] Preferably, the unsaturated acid monomer includes acrylic acid.

[0013] Preferably, the polyether macromonomer is at least one of methyl allyl polyoxyethylene ether and isopentenyl polyoxyethylene ether, and the number average molecular weight of the polyether macromonomer is 1000-2400.

[0014] Preferably, the functional anchoring monomer includes at least one of 2-acrylamide-2-methylpropanesulfonic acid and vinylphosphonic acid.

[0015] Preferably, the hydrophobic ester monomer is at least one of isooctyl acrylate and isobutyl acrylate.

[0016] Specifically, the introduction of isooctyl acrylate has the following multiple effects:

[0017] 1. The hydrophobic segments and polyether segments form an appropriate hydrophilic-hydrophobic balance, which optimizes the conformation of the molecules in solution;

[0018] 2. The rigidity of the molecular chain is enhanced through hydrophobic interactions, thereby improving the steric hindrance effect;

[0019] 3. Appropriate hydrophobic properties promote the directional adsorption of polymers on the surface of cement particles.

[0020] Preferably, the oxidant includes at least one of hydrogen peroxide and ammonium persulfate.

[0021] Preferably, the reducing agent includes at least one of ferrous sulfate and ascorbic acid.

[0022] Preferably, the molar ratio of the oxidant to the reducing agent is 1:(3-6) to obtain a stable gradient.

[0023] Preferably, the raw materials for preparing the gradient block polycarboxylate superplasticizer, by weight, include:

[0024]

[0025] and

[0026] Water. This invention also provides a method for preparing a gradient block polycarboxylate superplasticizer, comprising the steps of:

[0027] At 40℃-50℃, unsaturated acid, functional anchoring monomer, reducing agent and water undergo first-stage polymerization to obtain a mixture;

[0028] Add hydrophobic ester monomers to the mixture, and add oxidant solution and solution A dropwise. After reacting for 4-6 hours, adjust the pH to 6-7 to obtain the gradient block polycarboxylate superplasticizer.

[0029] Solution A is a mixed solution of polyether macromonomer, hydrophobic ester monomer and water;

[0030] A redox gradient is created by slowly reducing the drop rate of the oxidant solution.

[0031] Excessively high reaction temperatures will lead to excessively fast polymerization rates, causing the formation of disordered chain segments.

[0032] Preferably, the gradient block polycarboxylate superplasticizer has a weight-average molecular weight of 30,000-60,000 and a dispersion coefficient of 1.2-1.5.

[0033] This water-reducing agent is applied to concrete at a dosage of 0.15–0.25 wt% of the cement mass. It is suitable for high-strength concrete systems with high mud content and manufactured sand.

[0034] The beneficial effects of this invention are:

[0035] 1. High controllability of molecular structure:

[0036] This invention regulates the free radical generation rate through a redox gradient polymerization process, achieving an ordered distribution of carboxylic acid groups, phosphonic acid groups, and polyether segments on the molecular chain, forming a gradient structure with decreasing polarity. Compared to random copolymerization systems, this design has better repeatability and distribution precision at the structural level.

[0037] 2. Significantly improves mud resistance:

[0038] The polar gradient block structure enables the polymer to exhibit selective adsorption behavior on the surface of cement and clay particles, effectively reducing the adsorption competition of clay on the main chain, thereby reducing the impact of clay particles on flowability.

[0039] 3. Rheological performance optimization:

[0040] Because the proportion and sequence of polyether blocks in the molecular chain are controlled, the polymer can form a stable swelling state in the solution, reducing the plastic viscosity of concrete and improving slump spread and flow retention.

[0041] 4. The system exhibits good stability:

[0042] The polymer products have a low dispersion coefficient (1.2–1.5), high solution stability, and are not prone to sedimentation or stratification, allowing for long-term storage.

[0043] 5. Strong process adaptability:

[0044] The redox system has mild reaction conditions and can be directly applied to existing polycarboxylate superplasticizer production lines. The process of this invention can be directly implemented in existing polycarboxylate superplasticizer reactors, has scale-up stability and batch reproducibility, requires no additional equipment modification, and has good industrial feasibility. Detailed Implementation

[0045] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0046] In the embodiments, unless otherwise specified, the experimental methods used are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0047] Example 1

[0048] It uses a 500mL four-necked glass reactor, equipped with a constant temperature water bath, stirrer, dropping funnel and nitrogen protection system.

[0049] The main raw materials include: acrylic acid (AA, analytical grade), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), vinylphosphonic acid (VPA), methyl allyl polyoxyethylene ether (MPEG, Mn=2000), isooctyl acrylate (IA), ferrous sulfate (FeSO4·7H2O), hydrogen peroxide (H2O2, 30wt.%) and 30wt.% ammonia.

[0050] The system uses monomer raw materials with a purity of ≥99% and maintains an oxygen-free state throughout the entire process.

[0051] The specific reaction steps are as follows:

[0052] Add 150g of deionized water to the reactor, purge with nitrogen for 30 minutes to remove oxygen, and adjust the system temperature to 45℃.

[0053] Dissolve 10g of acrylic acid, 3g of AMPS, and 2g of vinylphosphonic acid in 30g of water to prepare a monomer solution, and simultaneously dissolve 0.2g of FeSO4 in 10g of water to prepare a reducing agent solution.

[0054] Add monomer solution and reducing agent solution to the reaction vessel, and start adding 30wt% H2O2 solution dropwise (initial rate 0.05mL / min). Maintain the reaction for 1h to form anchored chain segments rich in polar groups.

[0055] Adjust the temperature to 50℃ and begin adding the product dropwise in two separate streams:

[0056] One stream is a mixed solution of MPEG40 g and IA6 g, which is dripped over 60 minutes.

[0057] Another approach is to use an oxidant solution, namely a 30 wt.% H2O2 solution, with the dropping rate gradually decreasing from 0.3 mL / min to 0.05 mL / min. By dynamically increasing the oxidant concentration, the rate of free radical generation is controlled, causing the content of polar functional groups on the polymer chain to decrease along the reaction time direction.

[0058] After the addition is complete, continue the reaction for 3 hours to ensure complete monomer conversion.

[0059] After the reaction is complete and cooled to room temperature, the pH is adjusted to 6.8 with 25 wt.% ammonia water. After filtration to remove impurities, a light yellow transparent liquid is obtained, which is the gradient block polycarboxylate superplasticizer.

[0060] Nitrogen deoxygenation should be continuously introduced until the end of polymerization to avoid side reactions that could lead to abnormal molecular weight. Temperature fluctuations should be controlled within ±2℃. The drop rate should change uniformly to prevent sudden changes in free radicals. The polymer should be stored in the form of mother liquor, and high-temperature drying is not recommended.

[0061] The steps in other embodiments are the same as in Embodiment 1, with the differences shown in Table 1.

[0062] Table 1 Conditions in each embodiment

[0063]

[0064] In order to objectively evaluate the beneficial effects of the present invention, we designed the following comparative examples and compared them based on the method of controlling variables.

[0065] Comparative Example 1 (constant rate of addition)

[0066] The formulation is exactly the same as in Example 1, but the oxidant (H2O2) is added at a constant rate (0.15 mL / min).

[0067] Comparative Example 2 (without hydrophobic monomers)

[0068] Compared to Example 1, which removed isooctyl acrylate from the formulation and increased the mass of the polyether macromonomer accordingly, Comparative Example 3 (commercial water-reducing agent control) was used.

[0069] Point-S polycarboxylate superplasticizer, produced by Kezhijie New Materials Group Co., Ltd., is based on random copolymer and has a solid content of 20%.

[0070] Examples 1-3 and Comparative Examples 1-3 were tested using the same verification method. The verification method mainly referred to the Chinese national standards GB / T 50080-2016 "Standard for Test Methods of Performance of Concrete Mixtures" and GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete". The test conditions were uniformly set as follows: C50 concrete mix proportion (cement content 500 kg / m³). 3 The water-cement ratio was 0.3, the mud content of the manufactured sand was 3%, and the water-reducing agent dosage was 0.48% of the cementitious material mass. The verification results are shown in Table 2.

[0071] Table 2 Verification Results

[0072]

[0073] As shown in Table 2, with the 28-day compressive strength of Comparative Example 3 as the benchmark (100%), all Examples 1-3 of the present invention showed significant performance improvement, with strength ratios reaching 112%-116%.

[0074] The comparison results between Comparative Example 1 (constant rate dropping) and Example 1 show that, although the same raw material formulation is used, the strength ratio of the constant rate dropping product is 105%, which is significantly lower than the 112% of the gradient polymerization product in Example 2. This indicates that the gradient dropping process of the oxidant is the core technical feature for achieving precise molecular chain construction.

[0075] The strength ratio of Comparative Example 2 (without hydrophobic monomer) was 108%, which was better than that of Comparative Example 3, but significantly lower than that of Example 1 (112%). This fully demonstrates that the hydrophobic monomer plays an irreplaceable role in the system.

[0076] Example 3 exhibited the best performance (116%), which indicates that by optimizing the redox gradient parameters, the regularity of the molecular structure can be further enhanced, thereby achieving a better enhancement effect.

[0077] It should be noted that the specific parameters or reagents in the above embodiments are specific or preferred embodiments under the concept of the present invention, and not limitations thereof; those skilled in the art can make adaptive adjustments within the concept and protection scope of the present invention.

Claims

1. A gradient block polycarboxylate superplasticizer, characterized by, The gradient block polycarboxylic acid water reducer is prepared by an oxidation-reduction gradient polymerization method using unsaturated acid monomers, functional anchor monomers, polyether macromonomers and hydrophobic ester monomers as comonomers. During the polymerization, the ratio of the oxidant to the reducing agent is controlled to gradually reduce the free radical generation rate in the polymerization system with the reaction time, thereby forming a chain segment structure with a gradient distribution, and the content of the polar group in the chain segment structure gradually decreases from high to low along the polymer main chain. 2.The gradient block polycarboxylate superplasticizer of claim 1, characterized in that, The polyether macromonomer is at least one of a methyl allyl polyoxyethylene ether and an iso-pentenyl polyoxyethylene ether, and the number average molecular weight of the polyether macromonomer is 1000-2400. 3.The gradient block polycarboxylate superplasticizer of claim 1, characterized in that, The functional anchor monomer includes at least one of 2-acrylamide-2-methylpropane sulfonic acid and vinyl phosphonic acid. 4.The gradient block polycarboxylate superplasticizer of claim 1, wherein, The hydrophobic ester monomer is at least one of isooctyl acrylate and isobutyl acrylate. 5.The gradient block polycarboxylate superplasticizer of claim 1, wherein, The oxidant includes at least one of hydrogen peroxide and ammonium persulfate. 6.The gradient block polycarboxylate superplasticizer of claim 1, The reducing agent includes at least one of ferrous sulfate and ascorbic acid. 7.The gradient block polycarboxylate superplasticizer of claim 1, The molar ratio of the oxidant to the reducing agent is 1:(3-6). 8.The gradient block polycarboxylate superplasticizer of claim 1, The preparation raw materials of the gradient block polycarboxylic acid water reducer include, in parts by weight:

9. A method for preparing the gradient block polycarboxylate superplasticizer according to any one of claims 1 to 8, characterized in that, The method includes the steps of: At 40-50°C, the unsaturated acid monomer, the functional anchor monomer, the reducing agent and water are subjected to first-stage polymerization to obtain a mixture; The hydrophobic ester monomer is added to the mixture, and an oxidant solution and A liquid are added dropwise, and after 4-6h of reaction, the pH is adjusted to 6-7, thereby obtaining the gradient block polycarboxylic acid water reducer; The A liquid is a mixed solution of the polyether macromonomer, the hydrophobic ester monomer and water; The dropping speed of the oxidant solution is slowly reduced to form an oxidation-reduction gradient.

10. The method of claim 9, wherein, The weight average molecular weight of the gradient block polycarboxylic acid water reducer is 30,000-60,000, and the dispersion coefficient of the gradient block polycarboxylic acid water reducer is 1.2-1.5.

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