A slow-release polycarboxylate superplasticizer containing phosphate ester groups and its preparation method

Abstract

This invention relates to the field of concrete admixtures, and discloses a slow-release polycarboxylate superplasticizer containing phosphate ester groups and its preparation method. The superplasticizer is prepared by polymerization and post-modification of polyether macromonomers, unsaturated carboxylic acid monomers, slow-release functional monomers, and phosphorus-containing functional components. The molecule simultaneously contains carboxylic acid groups, polyether side chains, slow-release structural units, and phosphate ester groups. By introducing the synergistic effect of the slow-release structure and phosphate ester groups, the adsorption and dispersion capacity of the superplasticizer for cement particles and calcium ions is improved, giving it a high water reduction rate, good slump retention, low bleeding rate, and excellent mud content adaptability. The preparation method is simple, mild, and easily industrialized, and is suitable for ready-mixed concrete, high-performance concrete, and complex aggregate concrete systems.

Description

Technical Field

[0001] This invention belongs to the technical field of polycarboxylate superplasticizers, specifically a slow-release polycarboxylate superplasticizer containing phosphate ester groups and its preparation method. Background Technology

[0002] Polycarboxylate superplasticizers have become the most widely used high-performance superplasticizers in the concrete industry due to their significant advantages such as high water reduction rate, low dosage, and strong molecular structure designability. However, with the increasing complexity of engineering environments and fluctuations in the quality of building materials, conventional polycarboxylate superplasticizers are gradually showing obvious limitations in high-temperature construction, long-distance transportation, high stone powder and mud-containing aggregate systems, and adaptability to different cements. The main limitations are: the conventional single-tooth carboxyl anchoring method is easily affected by competitive adsorption of impurities such as clay in the aforementioned complex systems, making it difficult to balance the initial fluidity and later slump retention of the superplasticizer, resulting in significant time-varying performance and poor stability in field application.

[0003] To address the issue of slump loss in concrete over time, slow-release polycarboxylate superplasticizers have been proposed and applied in existing technologies. These superplasticizers typically introduce ester, amide, or other hydrolyzable groups into the polymer molecule structure, enabling it to gradually hydrolyze in alkaline cement pore liquid, thereby delaying the release of effective spatial dispersion sites and extending the retention time of fluidity.

[0004] Despite this, existing slow-release polycarboxylate superplasticizers still have the following significant shortcomings in practical engineering applications and industrial production: First, existing slow-release structures mostly rely on a single ester group or a single slow-release structural unit, resulting in a narrow release rate distribution. This single release rhythm makes it difficult to achieve an ideal balance between initial effectiveness and later dispersion compensation, especially under high-temperature conditions, easily leading to "pre-release surge" due to excessively rapid initial hydrolysis, or "insufficient tail release" due to the depletion of effective groups in the later stages. Second, existing slow-release systems are not ideally suited to cement with high tricalcium aluminate content, systems with fluctuating stone powder content, and systems containing mud aggregates, and lack stability in anti-mud and slump retention effects. Third, the industry has attempted to directly incorporate phosphorus-containing double-bonded monomers into the system for aqueous free radical copolymerization to improve anchoring force, but the chain transfer and local cross-linking side reactions easily triggered by phosphorus-containing monomers in the aqueous phase result in an extremely wide weight-average molecular weight distribution of the polymer, making it impossible to reproduce the product's application performance and posing a significant risk to industrial scale-up. Therefore, the industry urgently needs to develop a new type of polycarboxylate superplasticizer that combines multi-stage slow release, strong anchoring, and suitability for stable synthesis. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention provides a slow-release polycarboxylate superplasticizer containing phosphate ester groups and its preparation method. This invention primarily addresses the technical problem of uncontrolled release rhythm in existing slow-release systems due to reliance on a single slow-release structure.

[0006] According to one aspect of the present invention, a slow-release polycarboxylate superplasticizer containing phosphate ester groups is provided. The superplasticizer is a comb-shaped polycarboxylate copolymer, prepared by reacting the monomers under the action of an initiating system and then modifying them by anhydrous high-temperature esterification. Based on 100 parts by mass of the total effective raw material components involved in the preparation of the superplasticizer, it is composed of the following components:

[0007] Polyether macromonomer: 70-85 parts, which is a polyethylene glycol ether monomer containing unsaturated double bonds; its polymerization forms polyether side chain units that provide steric hindrance effects;

[0008] Unsaturated carboxylic acid monomers: 5 to 15 parts, which are carboxylic acid or carboxylate monomers containing unsaturated double bonds; their polymerization forms carboxylic acid or carboxylate main chain units used to provide basic anchoring and water reduction;

[0009] Slow-release monomer combination: 3 to 12 parts, including at least two hydrolyzable unsaturated monomers with different hydrolysis rates under alkaline conditions; their polymerization forms slow-release structural units with different delayed hydrolysis rates under alkaline conditions;

[0010] Phosphorus-containing functional components: 1 to 5 parts, which are phosphorus-containing reagents used for esterification modification; phosphate ester functional units used to introduce phosphate esters that enhance the adsorption and anchoring ability of cement particles and active mineral phase surfaces.

[0011] Preferably, the combination of sustained-release monomers is selected from at least two of hydrolyzable ester monomers and amide monomers;

[0012] The sustained-release structural unit formed by the polymerization of the sustained-release monomers includes at least two of the following structural units formed by the polymerization of corresponding chemical monomers: a fast-release unit formed by the polymerization of C1-C4 alkyl acrylate monomers or C1-C4 alkyl methacrylate monomers; a medium-release unit formed by the polymerization of methacrylate monomers containing C3-C8 branched alkyl groups; and a slow-release unit formed by the polymerization of dialkyl maleate monomers containing C4-C8 straight-chain alkyl groups or acrylamide monomers.

[0013] C1-C4, C3-C8, and C4-C8 represent 1-4 carbon atoms, 3-8 carbon atoms, and 4-8 carbon atoms, respectively; that is, C1-C4 alkyl acrylate monomers, which are alkyl acrylate monomers containing 1-4 carbon atoms;

[0014] To address the parabolic release rate defect of a single ester group, this invention innovatively introduces a multi-stage sustained-release mechanism based on "steric hindrance kinetics." In alkaline pore liquids, the nucleophilic attack of hydroxide ions on the carbonyl carbon atom is the essence of triggering the hydrolysis of the sustained-release group. This invention cleverly utilizes the chemical principle that "large-volume side groups hinder nucleophilic attack":

[0015] Fast-release unit: Low-carbon alkyl esters (such as methyl acrylate) have a wide space around the ester group, OH - The ions are easily accessible and undergo nucleophilic addition, with extremely low hydrolysis activation energy. Within 30 minutes of mixing and adding water, it can rapidly break bonds and release free carboxyl groups, quickly compensating for the dispersion points lost due to the rapid hydration of tricalcium aluminate cement;

[0016] Medium-speed release unit: Monomers containing branched alkyl groups (such as tert-butyl methacrylate), whose large branches form a tight steric barrier to the ester carbonyl group in space like a "shield", greatly increasing the thermodynamic energy barrier of the hydrolysis transition state, forcing its hydrolysis half-life to be delayed to a critical window period of 30 to 120 minutes (i.e., the conventional transportation and pumping stage) for smooth bond breaking.

[0017] Slow-release unit: Contains C4-C8 straight-chain alkyl dialkyl maleate monomers or high-bond-energy acrylamide monomers. The long straight chains not only possess a strong physical steric shading effect, but the amide bond itself, due to the lone pair electrons of the nitrogen atom forming p-π conjugation with the carbonyl group, further significantly increases the chemical bond energy that must be overcome for hydrolysis. This extremely inert structure only slowly activates after prolonged strong alkali immersion for 120 minutes, specifically designed to cope with extreme and harsh conditions such as ultra-long-distance pumping and high-temperature waiting.

[0018] Preferably, the phosphorus-containing functional component is a phosphorus-containing reagent used for esterification modification, selected from at least one of polyphosphoric acid, orthophosphoric acid, phosphorous acid, and phosphorus pentoxide.

[0019] Conventional polycarboxylate superplasticizers rely solely on the "monodentate complexation" between free carboxyl groups and calcium ions. This adsorption force is easily stripped away by the stronger van der Waals forces and interlayer electrostatic attraction of clay (such as montmorillonite crystal layers). This invention introduces phosphate groups through esterification modification. The electron-rich phosphorus-oxygen double bonds and the phosphate anions generated by the ionization of multiple hydroxyl groups can form stable and irreversible "multidentate cyclic chelate structures" with calcium ions on the surface of cement particles and active mineral phases. According to the principles of coordination chemistry thermodynamics, the binding constant of multidentate chelation exhibits a geometric progression greater than that of monodentate coordination. Therefore, the polymer chain grafted with phosphate groups achieves an absolute "targeted site-grabbing advantage" in thermodynamic adsorption competition, directly cutting off the interlayer intercalation path of clay impurities from the underlying logic, thus endowing the product with excellent anti-mud adaptability.

[0020] Preferably, the polyether macromonomer is selected from at least one of methacryl alcohol polyoxyethylene ether, isopentenol polyoxyethylene ether, and isobutylenol polyoxyethylene ether;

[0021] The unsaturated carboxylic acid monomer is selected from one or more of acrylic acid, methacrylic acid, maleic acid, fumaric acid and their salts.

[0022] The selection of polyether macromonomers is limited to methacryl alcohol polyoxyethylene ether, isopentenyl alcohol polyoxyethylene ether, etc. These specific macromonomers have different reactivity of the end double bonds, and the degree of polymerization of polyethylene glycol branches can be adjusted, which can provide the copolymer macromolecules with side chain distributions of varying lengths and densities, thereby forming a more elastic and thicker three-dimensional steric hindrance layer on the surface of cement particles.

[0023] The selection of unsaturated carboxylic acid monomers was limited to acrylic acid, methacrylic acid, and maleic acid. Among them, acrylic acid monomers have high polymerization reactivity and can quickly provide initial monocarboxyl adsorption sites; while maleic acid, as a dicarboxylic acid, can form high-density negatively charged regions (dicarboxyl structures) locally in the molecular chain. The synergistic copolymerization of different acidic monomers precisely adjusted the charge density and segment rigidity of the main chain, ensuring that the copolymer possesses optimal molecular conformation and charge repulsion when providing initial water-reducing effects.

[0024] When the phosphorus-containing functional component is a phosphorus-containing reagent used for esterification modification, it is selected from at least one of polyphosphoric acid, orthophosphoric acid, phosphorous acid, and phosphorus pentoxide.

[0025] Therefore, this approach more preferably employs post-modification (such as using polyphosphoric acid or orthophosphoric acid). This path follows the process logic of "first constructing the host polymer, then introducing phosphate ester groups." First, free radical copolymerization of the polyether side chains and the sustained-release backbone is completed in a clean system free from phosphorus interference, ensuring an extremely concentrated molecular weight distribution of the copolymer backbone and minimizing residual monomers. Subsequently, the strongly anchored phosphate ester groups are precisely covalently grafted onto the terminal hydroxyl groups of the polyether side chains through an esterification reaction. This mechanism effectively avoids interference from functional components in the host polymerization process, fundamentally solving the engineering defects of traditional sustained-release systems, such as molecular structure variations and significant fluctuations in product application performance after industrial scale-up.

[0026] Preferably, the water-reducing agent is coated with an inorganic silicon shell, and the water-reducing agent, as the core, together with the inorganic silicon shell forms a two-stage slow-release system.

[0027] This scheme constructs a dual time-delay barrier of macroscopic physics and microscopic chemistry. During extremely high temperatures or long-distance transport, the outermost dense physical shell (inorganic silicon shell) first acts as a physical barrier, completely blocking contact between the highly alkaline pore liquid and the internal macromolecules, forcibly "freezing" all chemical hydrolysis reactions of the core polymer chains. Only with the mechanical shearing and grinding force of the concrete mixer drum, and the slow microporous dissolution of the inorganic silicon shell framework by the highly alkaline liquid, does the physical shell gradually disintegrate. At this point, the released water-reducing agent macromolecules "break out of the shell" and initiate their own "fast, medium, and slow" chemical steric hindrance relay hydrolysis. This cross-scale composite response mechanism of "physical shell breaking followed by chemical bond breaking" completely breaks the slump retention time limit of traditional single-phase polymer admixtures.

[0028] Specific working principle: First stage: Synergistic mechanism of multi-tooth strong anchoring and three-dimensional spatial dispersion (initial mixing stage);

[0029] In the initial stage of concrete mixing, the water-reducing agent macromolecules respond rapidly. First, the main chain formed by the copolymerization of unsaturated carboxylic acid monomers rapidly ionizes into free carboxyl groups in an alkaline environment, generating initial electrostatic repulsion. More importantly, the phosphate ester functional units grafted by anhydrous high-temperature dehydration in this invention simultaneously play a decisive "targeted anti-mud" intervention role. Its electron-rich phosphorus-oxygen double bond and polyhydroxy structure can form a stable and irreversible "multidentate ring chelate" structure with calcium ions on the surface of cement particles and active mineral phases. The thermodynamic binding constant of this multidentate coordination is geometrically greater than that of conventional carboxyl group monodentate complexation, giving the water-reducing agent molecule an extremely good site-grabbing advantage, enabling it to be preferentially and extremely firmly adsorbed on the effective working surface without being interfered with by the interlayer charge of clay minerals (such as montmorillonite) in inferior aggregates such as high mud and high powder.

[0030] Supported by this strong anchoring base, the long-chain polyethylene glycol side chains formed by copolymerization of polyether macromonomers can fully extend in the aqueous solution, constructing a highly elastic and thick three-dimensional hydration film on the particle surface. The efficient synergy of multi-toothed strong chelation, electrostatic repulsion, and strong steric hindrance instantly disintegrates the initial flocculation structure of cement, releasing the trapped free water, thus achieving good initial water reduction and molding workability even in extremely complex and inferior material systems.

[0031] Second stage: Continuous consumption of hydration and delayed compensation mechanism of free carboxyl groups (mid-to-late stage of hydration).

[0032] As the cement hydration process continues, the newly generated hydration products will quickly cover and devour the water-reducing agent molecules that were initially anchored, leading to the gradual loss of the spatial steric hindrance established in the early stage and causing the concrete fluidity to decrease (i.e., the slump loss over time).

[0033] To address this continuous dynamic depletion, the slow-release structural units embedded within the copolymer macromolecular backbone begin to play a crucial role in relay compensation. The underlying mechanism lies in the irreversible delayed bond-breaking hydrolysis of the hydrolyzable groups (ester or amide groups) in the slow-release units under the nucleophilic attack of hydroxide ions in the strongly alkaline cement pore liquid (pH>12), continuously exposing new free carboxyl groups. These continuously released new free carboxyl groups can replenish the supply in a timely manner and re-adsorb onto the surface of newly formed hydration products, reconstructing the steric hindrance layer and thus offsetting the depletion caused by hydration.

[0034] The third stage: a multi-stage relay release mechanism dominated by spatial steric dynamics (full-cycle collapse preservation).

[0035] In order to fundamentally avoid the engineering risks of initial "release rush (leading to water separation)" or later "insufficient tail release (leading to sudden bottoming out)" that are easily caused by conventional single fixed hydrolysis rate ester groups, the copolymer macromolecule of the present invention is ingeniously polymerized with at least two hydrolyzable unsaturated monomers with significant differences in steric energy barriers, and cleverly utilizes the principle of "steric kinetics" to artificially create a thermodynamic time difference for chemical bond breaking.

[0036] Under the nucleophilic attack of alkaline pore liquid, groups with different physical shielding effects take turns in a precise time dimension: the fast release unit with low steric hindrance experiences minimal resistance and hydrolyzes rapidly within the initial mixing phase to 30 minutes, filling the early rapid consumption gap; the medium-speed release unit with branched structure significantly increases the hydrolysis transition state energy barrier due to the "physical shield" effect of its large branches, allowing it to smoothly break bonds within the conventional transport and pumping window of 30–120 minutes; while the slow release unit with large-volume aromatic ring side groups or high bond energies requires a longer period of strong base activation and only begins to release significantly after 120 minutes, dedicated to ensuring the ultra-long collapse retention requirements under extreme working conditions.

[0037] This time-based relay effect, utilizing the steric hindrance effect of microscopic molecular side groups, effectively flattens the traditional steep, concentrated release curve into a broad, gentle "multi-stage release spectrum." Supported by the strong, multi-toothed phosphate ester base for mud-resistant anchoring, it fundamentally achieves long-term, intelligent, and stable multi-stage dynamic slump retention of water-reducing agents on complex cement pastes.

[0038] In another aspect, the present invention provides a method for preparing a slow-release polycarboxylate superplasticizer containing phosphate ester groups, comprising the following steps:

[0039] S1. Preparation of the base liquid: Polyether macromonomer and deionized water are added to the reactor, heated and dissolved under stirring, and oxidant of the redox initiation system is added to obtain the base liquid;

[0040] S2. Solution preparation: Combine unsaturated carboxylic acid monomers and sustained-release monomers to prepare monomer solution A; prepare the reducing agent and molecular weight regulator of the redox initiation system to prepare initiation solution B; prepare the phosphorus-containing reagent for esterification modification as modification solution C;

[0041] S3, Main copolymerization reaction: Under stirring conditions, monomer solution A and initiator solution B are added dropwise to the base solution to carry out free radical copolymerization reaction. After the addition is completed, the reaction is kept at the temperature to obtain an aqueous solution of the main polymer.

[0042] S4. Dehydration and post-modification with phosphorus: The free water in the system is removed by vacuum distillation of the aqueous solution of the main polymer. Then, the modification solution C is added and the bulk melt esterification reaction is carried out under anhydrous high temperature to dehydrate and covalently graft the phosphate ester groups onto the terminal hydroxyl groups of the polyether side chain.

[0043] S5. Dissolution, neutralization and post-treatment: After the reaction is completed, the temperature is lowered, deionized water is added to dissolve the product, and a neutralizing agent is added to adjust the pH value to 6-8, thus obtaining a slow-release polycarboxylate superplasticizer containing phosphate ester groups.

[0044] In traditional phosphorus copolymerization processes, phosphorus-containing unsaturated monomers directly participate in free radical polymerization. Because phosphate groups readily initiate chain transfer reactions, and the reactivity ratios of different monomers vary significantly, the kinetics of the polymerization reaction are difficult to control precisely, easily generating byproducts with extremely wide molecular weights and uncontrollable crosslinking degrees.

[0045] In the method of this invention, step S3 first involves the free radical copolymerization of a combination of polyether macromonomers, unsaturated carboxylic acid monomers, and multi-level slow-release monomers in a clean aqueous system free from phosphorus interference. This ensures that the water-reducing agent molecular backbone (providing steric hindrance) and the slow-release structure (providing slump retention) can stably combine according to the designed polymerization ratio, forming a main polymer with an extremely narrow molecular weight distribution. Subsequently, in step S4, with the main backbone already stably formed, a modifying liquid C is precisely added to initiate an esterification reaction, directionally covalently grafting strongly anchored phosphate ester groups onto the terminal hydroxyl groups of the polyether side chains. This stepwise synthesis method fundamentally eliminates the negative interference of phosphorus-containing groups on the growth of free radical chains, significantly improving the consistency of molecular structure and the reproducibility of product application performance in industrial-scale production.

[0046] Preferably, in step S1, the dissolution temperature is controlled at 20 to 60°C; in step S3, the dripping time is 2 to 4 hours, the temperature of the free radical copolymerization reaction is controlled at 25 to 50°C, and the reaction is continued at the temperature for 0.5 to 2 hours after the dripping is completed; in step S4, the temperature of the bulk melt esterification reaction is controlled at 100 to 140°C.

[0047] The 2-4 hour dropping time forces the system into a starved polymerization mode. The extremely low instantaneous monomer concentration compels monomers with large differences in polymerization rates to achieve uniform random copolymerization, preventing highly reactive monomers from self-polymerizing to form block structures and ensuring that the single molecular chain has the functions of water reduction, slump retention, and anchoring. At the same time, the mild reaction range of 25-50℃ precisely matches the initiation half-life of the redox system, effectively avoiding the sharp reduction in molecular weight and exothermic runaway caused by high-temperature explosive polymerization, and ensuring a stable balance between chain initiation and chain growth.

[0048] Preferably, in step S2, the molecular weight regulator is selected from at least one of thiocarboxylic acids, thiohydric alcohols, or phosphites;

[0049] In step S3, monomer solution A and initiator solution B are added to the base solution by simultaneous dropwise addition.

[0050] The selected mercaptocarboxylic acids or alcohols act as molecular weight regulators, providing active hydrogen atoms to trigger a chain transfer mechanism, actively terminating overgrown active chains and re-initiating polymerization. This mechanism precisely limits the limiting chain length, avoiding bridging and flocculation defects caused by excessively large molecular weights, and locking the weight-average molecular weight within the optimal range for steric hindrance. Furthermore, the simultaneous addition of monomers and the initiating solution allows for flexible control of the polymer monomer sequence (e.g., synthesizing gradient copolymers), thereby precisely characterizing multi-stage sustained-release profiles.

[0051] Preferably, in step S5, the neutralizing agent is selected from one or more of sodium hydroxide, potassium hydroxide, and organic amines.

[0052] By adjusting the pH of the system to 6–8 using a neutralizing agent, the unionized carboxyl groups on the coiled backbone are converted into negatively charged carboxylates. The electrostatic repulsion of like charges forces the polymer molecular chains to extend in the aqueous phase, exhibiting an optimal sterically hindered active conformation. Simultaneously, this neutralization process eliminates residual acidity in the system, effectively inhibiting premature hydrolysis of the slow-release ester groups during storage, thus endowing the product with long-term stable storage quality.

[0053] Preferably, after step S5, a composite coating step is further included, using a reverse emulsion coating process, in which the aqueous solution of the obtained water-reducing agent is dispersed as an aqueous phase in an oil phase containing an emulsifier to form reverse emulsion microdroplets, followed by the addition of an inorganic silicon precursor, and the slow droplet addition of an aqueous solution of an alkaline catalyst to the reverse emulsion system, in-situ polymerization or sol-gel reaction occurs at the water-oil phase interface of the microdroplets to generate an inorganic silicon shell that encapsulates the core.

[0054] A secondary encapsulation process based on macroscopic physical morphology was determined. A synthesized water-reducing agent was used as the core material, and an inorganic silicon shell was constructed using interface engineering techniques (such as emulsification, in-situ polymerization, or sol-gel). Micro- and nano-scale supramolecular assembly provided a robust physical barrier for the active polymer core, constructing a complete secondary sustained-release composite system. This fundamentally met the extreme collapse-preserving requirements for long-distance transport in extreme high-temperature environments or large-scale engineering projects.

[0055] To ensure the stable implementation of the reverse emulsion sol-gel process, preferably, in the reverse emulsion coating process, the oil phase is selected from at least one of non-polar solvents such as cyclohexane, liquid paraffin, or white oil; the emulsifier is selected from nonionic emulsifiers such as sorbitan monooleate, and its amount is 1% to 5% of the oil phase mass; the inorganic silicon precursor is selected from tetraethyl orthosilicate or methyl orthosilicate; and the alkaline catalyst is selected from ammonia or sodium hydroxide solution.

[0056] The beneficial effects of this invention are as follows:

[0057] 1. This invention breaks through the industry's heavy reliance on single ester group slow-release technology. By compounding at least two polymeric monomers with significant differences in steric hindrance energy barriers, a time difference in hydrolysis kinetics is successfully constructed within a single polymer chain. The fast, medium, and slow release units exhibit a good relay bond-breaking behavior in alkaline solutions, enabling the copolymer to continuously expose new active anchoring sites at 30 min, 120 min, and longer time points. This microscopic molecular design forcibly flattens and broadens the traditional "steep single-peak release" that easily leads to hydrolysis and segregation into a "smooth multi-level release spectrum across the entire frequency band," achieving long-term working performance of "zero peaks and zero gaps" for over 120 minutes.

[0058] 2. Compared to conventional polycarboxylic acids that rely solely on the weak electrostatic anchoring of monodentate carboxyl groups, this invention, through the post-modification and directional introduction of phosphate ester functional units, can form a highly energetic "multidentate cyclic chelate" structure with calcium ions on the surface of cement minerals and admixtures. This powerful coordination with overwhelming thermodynamic advantages endows the molecules of this invention with extremely strong site-grabbing immunity, unaffected by the interlayer charge of montmorillonite in high-mud-content manufactured sand. Even in harsh construction site environments with significant fluctuations in stone powder or soil, it can still preferentially seize effective adsorption sites, significantly broadening the application boundaries of water-reducing agents in engineering materials.

[0059] 3. This invention first utilizes a pure aqueous phase to starve copolymerize and lock in a narrowly distributed main chain backbone with a good comb-like conformation; then, using reverse thinking, it utilizes depressurized dehydration to forcibly overcome the thermodynamic equilibrium limitation that aqueous phase cannot dehydrate and esterify, achieving site-specific grafting of phosphate ester groups in a high-temperature melt. This process effectively avoids the toxicity of phosphorus-containing groups to free radical chain growth, ensuring not only an extremely high functional group grafting conversion rate, but also highly uniform microscopic molecular structure between batches of products (extremely low PDI fluctuation), fundamentally removing the core technological barrier to the large-scale, stable industrial production of phosphorus-containing high-performance water-reducing agents.

[0060] 4. This invention further innovates the in-situ coating technology of inorganic silicon shell at the reverse emulsion interface, which effectively links the macroscopic hard physical shielding layer of silica with the microscopic multi-level chemical hydrolysis mechanism of polymers in a spatiotemporal sequence. This dual insurance mechanism of "physical shell breaking and unsealing + chemical relay hydrolysis" provides a reliable rheological performance guarantee solution that far exceeds the limits of existing single-phase admixtures for extreme engineering scenarios with extremely long material waiting periods, such as continuous pouring of ultra-large volumes in summer, high-temperature long-term construction of cross-sea bridges, and long-distance intercity transportation of commercial concrete. Detailed Implementation

[0061] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0062] Example 1:

[0063] Based on a total mass of 400.0g of all effective raw material components involved in the preparation of this water-reducing agent: the polyether macromonomer is 312.0g of isopentenyl alcohol polyoxyethylene ether; the unsaturated carboxylic acid monomers can be selected from the following combinations: ① 24.0g of acrylic acid and 16.0g of maleic acid; ② 16.0g of fumaric acid and 16.0g of acrylic acid; the slow-release monomer combination is 10.0g of methyl acrylate (low steric hindrance fast release unit), 6.0g of isobutyl methacrylate (branched steric hindrance medium-speed release unit), and 20.0g of dibutyl maleate (long chain large volume steric hindrance slow release unit); the phosphorus-containing reagent is 12.0g of polyphosphoric acid or 16.0g of phosphorous acid.

[0064] Preparation of the base solution: Add 312.0 g of isopentenyl alcohol polyoxyethylene ether and 220.0 g of deionized water to a four-necked flask. Turn on the mechanical stir and heat the mixture in a water bath to 40°C. After dissolving, add 3.2 g of hydrogen peroxide aqueous solution (as the oxidant in the redox system) and stir until homogeneous to obtain the base solution.

[0065] Solution preparation: Combine unsaturated carboxylic acid monomers and sustained-release monomers with 40.0g of deionized water to prepare monomer solution A; prepare initiation solution B with 2.4g of ascorbic acid (as a reducing agent), 1.6g of mercaptoacetic acid and 36.0g of deionized water; prepare 12.0g of polyphosphoric acid (pure reagent) or 16.0g of phosphorous acid as modification solution C.

[0066] Main copolymerization: While maintaining the bottom solution temperature at 40±1℃, monomer solution A (takes 3.0 hours) and initiator solution B (takes 3.5 hours) were added dropwise at a uniform rate. A forced starvation dropwise addition mode was used to promote random copolymerization of the monomers. After the addition was completed, the reaction was continued at the temperature for 1.0 hour to obtain an aqueous solution of the main polymer with a regular weight-average molecular weight distribution and an extremely narrow polydispersity index.

[0067] Dehydration and post-modification with phosphorus: The flask was connected to a vacuum distillation apparatus, and the temperature was gradually increased to 95°C under a vacuum of -0.09 MPa to break the thermodynamic hydrolysis equilibrium and completely remove the free water in the system, resulting in a viscous, anhydrous molten polymer. After the vacuum was released, the temperature was raised to 110°C, and modified solution C (12.0 g of polyphosphoric acid) was slowly added dropwise. The mixture was kept at 110°C in an anhydrous bulk state for 2.0 hours for high-temperature dehydration and esterification. The thermodynamic driving force of high-temperature evaporation of the byproduct water was used to efficiently covalently graft the phosphate ester groups onto the terminal hydroxyl groups of the polyether side chain, avoiding the defect of reacting with the carboxyl groups of the main chain to form unstable mixed anhydrides.

[0068] Dissolution, neutralization, and post-treatment: After the reaction is complete, cool to 60°C and slowly add deionized water to re-dissolve; after naturally cooling to below 30°C, add sodium hydroxide aqueous solution or triethanolamine (as an organic amine neutralizing agent) dropwise to neutralize to pH 7.0, and adjust the total solid content to 40.0% to obtain the finished water-reducing agent.

[0069] Example 2:

[0070] Based on a total raw material composition of 400.0g: 280.0g of methacrylic acid polyoxyethylene ether and 40.0g of isobutylene alcohol polyoxyethylene ether; 18.0g of acrylic acid and 14.0g of methacrylic acid; 8.0g of ethyl acrylate, 12.0g of tert-butyl methacrylate (medium-speed release due to large branched umbrella-shaped steric hindrance) and 12.0g of acrylamide (slow release due to high conjugation activation energy); and 16.0g of orthophosphoric acid or 16.0g of phosphorus pentoxide for the phosphorus-containing modified solution C.

[0071] The base solution was prepared at 35°C with polyether macromonomer, 210.0 g of deionized water, and 3.0 g of hydrogen peroxide. Monomer solution A had 38.0 g of water added. Initiator solution B contained 2.2 g of ascorbic acid, 1.4 g of mercaptoethanol, and 34.0 g of water.

[0072] Liquid A (3.5 h) and liquid B (3.5 h) were added simultaneously at 38 to 42 °C, and the temperature was maintained for 1.0 h to complete the construction of a good steric framework.

[0073] Subsequently, vacuum distillation was initiated to completely remove the water from the system. The temperature was then raised to 120°C, and 16.0 g of orthophosphoric acid was slowly added dropwise. A high-temperature dehydration esterification reaction was carried out in an anhydrous molten state for 2.5 h. After cooling and reconstitution, the solution was neutralized with potassium hydroxide to a pH of 6.8, and the solids content was adjusted to 40.0%.

[0074] Example 3:

[0075] An inorganic silicon shell was constructed following the principle of in-situ shell formation at the inverse colloidal interface. 100.0 parts by weight of the water-reducing agent aqueous solution (40% solid content) prepared in Example 1 was used as the core material of the aqueous phase; 200.0 parts by weight of cyclohexane and 5.0 parts by weight of the nonionic emulsifier sorbitan monooleate were mixed to form a continuous oil phase. Under high-speed shear mechanical stirring (4000 rpm), the aqueous phase was slowly added dropwise to the dispersed oil phase to form a highly homogeneous and stable water-in-oil inverse microemulsion system.

[0076] Subsequently, 8.0 parts by mass of tetraethyl orthosilicate, serving as an inorganic silicon precursor, were slowly added dropwise, along with 1.5 parts by mass of a 25% ammonia solution as an alkaline catalyst, adjusting the pH of the system's microenvironment to 9.0–10.0. The reaction system temperature was controlled at 35°C. Due to the interfacial confinement effect, the oil-soluble silicon source spontaneously migrated to the water-oil interface of the micro-droplets, where it encountered water under alkaline conditions and underwent a continuous sol-gel reaction. After 3.0 hours, it in-situ encapsulated and cross-linked to form a dense inorganic silica shell. After demulsification, separation, and washing, a secondary slow-release composite powder with dual time-delay characteristics of "physical shell breaking + multi-stage chemical hydrolysis" was obtained.

[0077] Comparative Example 1:

[0078] The difference from Example 1 is that no phosphorus-containing functional components are added, and the post-modification phosphorus introduction in step S4 is not performed. The other monomer types, amounts, and polymerization processes are the same as in Example 1.

[0079] Comparative Example 2:

[0080] The difference from Example 1 is that the sustained-release monomer combination is changed to use only 36.0g of methyl acrylate, without adding isobutyl methacrylate and dibutyl maleate, that is, without constructing multi-stage sustained-release units with different hydrolysis rates. The other monomer types, amounts and process conditions are the same as in Example 1.

[0081] Comparative Example 3:

[0082] The difference from Example 1 is that 12.0g of polyphosphoric acid is replaced with 12.0g of ethylene glycol monomethacrylate and directly added to monomer liquid A to participate in free radical copolymerization. The post-modification phosphorus introduction in step S4 is cancelled, and the remaining process conditions are the same as in Example 1.

[0083] Comparative Example 4:

[0084] The difference from Example 1 is that no slow-release monomer combination or phosphorus-containing functional components are added. Only 348.0g of isopentenyl polyoxyethylene ether, 36.0g of acrylic acid and 16.0g of maleic acid are used for conventional free radical copolymerization. The remaining polymerization and neutralization steps are the same as in Example 1.

[0085] Test example:

[0086] The water-reducing agents prepared in Examples 1-3 and Comparative Examples 1-4 were used for performance testing of C40 concrete. The cementitious material was a composite system of cement, fly ash, and mineral powder, with a total cementitious material content of 480 kg / m³, a sand ratio of 44%, and a water-reducing agent dosage of 0.18% of the total cementitious material content. The water reduction rate, initial slump, 60-minute slump, 120-minute slump, and bleeding rate were measured. The mud resistance test used manufactured sand with 3% sodium bentonite admixture, and the 120-minute slump was measured at 35°C.

[0087] The test results for the above test items are shown in the table below. The table below shows the performance test results of the water-reducing agents prepared in Examples 1-3 and Comparative Examples 1-4;

[0088]

[0089] By comparing the data in the cross-reference table, the necessary causal relationship between the technical features, underlying mechanisms, and unexpected effects of this invention can be clearly demonstrated, fully proving that this application possesses extremely prominent substantive features and significant progress:

[0090] Confirmation of the advantages of the multi-toothed chelating mechanism in resisting mud: A horizontal comparison between Example 1 and Comparative Example 1 shows that Comparative Example 1, which did not introduce a multi-toothed chelating group of phosphate ester, faced an extreme environment of 35°C and mud (strong van der Waals forces and charge adsorption of montmorillonite). Its traditional single-toothed anchoring force was quickly destroyed by the ineffective adsorption of impurities, resulting in a significant decrease in slump to 122 mm after 120 minutes of mud content. However, Example 1, due to the introduction of a phosphate ester system with strong chelating bond energy, stably occupied the effective adsorption sites at the cement interface from a thermodynamic perspective. Even under harsh conditions with high mud content, its slump could still maintain an excellent level of 196 mm in the later stages.

[0091] Verification of the advantages of multi-level steric hindrance slow-release and stable yield: Comparing Example 1 and Comparative Example 2, it can be seen that Comparative Example 2, which only uses a single low-activation-energy ester group, exhibits very typical defects of "pre-release surge" and "insufficient tail release"—the initial slump is extremely high (244 mm), but this leads to poor water retention (bleeding rate of 0.7%); and because the effective group is exhausted by rapid hydrolysis in the early stage, there is a lack of follow-up replenishment, and the slump rapidly decays to 142 mm at 120 min. Example 1, thanks to the stable follow-up hydrolysis set by the fast, medium, and slow multi-level steric hindrance kinetics, effectively smoothed out the violent yield curve, achieving extremely low bleeding (0.4%) and stable high slump retention (221 mm) throughout the entire cycle.

[0092] The advantages of the "dehydration and decoupling" synthesis process are most clearly demonstrated by comparing Example 1 and Comparative Example 3. Comparative Example 3 employs the conventional and obvious "direct aqueous copolymerization of phosphorus-containing monomers" route. Although the final system also contains phosphorus and slow-release monomers, the phosphorus-containing double bonds act as strong chain transfer agents in the aqueous polymerization, interfering with the controllable growth of the steric hindrance layer of the macromolecular skeleton, resulting in the destruction of the polymer molecular conformation. This caused its initial water reduction rate to drop below 30%, and all slump retention indicators were significantly inferior. This horizontal comparison irrefutably confirms, with experimental data, that the unconventional process of "aqueous phase construction of a good skeleton + depressurized dehydration to break the equilibrium + high-temperature bulk melt esterification grafting" pioneered in this application has achieved an extremely significant and unexpected leap in product performance.

[0093] Verification of the ultimate performance of the dual-time-dependent cross-scale barrier: Example 3, through in-situ encapsulation of a physical silica shell with a reverse emulsion, provides a long-lasting protective coating to the internal multi-level chemical slow-release system. Despite a slightly lower initial slump (236 mm) due to the physical coating, its slump retention performance under extremely harsh conditions (35°C, high temperature, and muddy system) for 120 minutes actually surpassed the initial performance (205 mm), with the bleeding rate reduced to the limit of 0.3%. This fully demonstrates the ultimate rheological control capabilities of this "physical-chemical combination" in addressing the long-distance transportation challenges of world-class ultra-long-span bridges.

[0094] Those skilled in the art should understand that the present invention has listed the preparation scheme and performance under the optimal ratio in Examples 1-3. However, when the polyether macromonomer, unsaturated carboxylic acid monomer, slow-release monomer combination and phosphorus-containing functional component are formulated within the endpoint range defined in claim 1 (such as when the polyether macromonomer is 70 parts by mass or 85 parts by mass), the multi-stage slow release and multi-toothed chelation effect described in the present invention can still be achieved, with only the conventional expected fluctuations in the specific values ​​of each performance.

[0095] The embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments described above. The specific embodiments described above are merely illustrative and not restrictive. Those skilled in the art can make many other forms under the guidance of the present invention without departing from the spirit and scope of the claims. All of these forms are within the protection scope of the present invention.

Claims

1. A slow-release polycarboxylate water reducer containing phosphate groups, characterized by: The water-reducing agent is a comb-shaped polycarboxylic acid copolymer, which is prepared by reacting the polymer monomers under the action of an initiation system and then modifying them by anhydrous high-temperature esterification. Based on a total mass of 100 parts by mass of all effective raw material components involved in the preparation of this water-reducing agent, it includes the following components: Polyether macromonomers: 70-85 parts, which are polyethylene glycol ether monomers containing unsaturated double bonds; Its polymerization forms polyether side chain units that provide steric hindrance effects; Unsaturated carboxylic acid monomers: 5 to 15 parts, which are carboxylic acid or carboxylate monomers containing unsaturated double bonds; their polymerization forms carboxylic acid or carboxylate main chain units used to provide basic anchoring and water reduction; Slow-release monomer combination: 3 to 12 parts, including at least two hydrolyzable unsaturated monomers with different hydrolysis rates under alkaline conditions; The polymerization forms sustained-release structural units with different delayed hydrolysis rates under alkaline conditions; the sustained-release structural units formed by the polymerization of the sustained-release monomers include at least two of the following chemical monomers: fast-release units formed by polymerization of C1-C4 alkyl acrylate monomers or C1-C4 alkyl methacrylate monomers; medium-release units formed by polymerization of methacrylate monomers containing C3-C8 branched alkyl groups; and slow-release units formed by polymerization of dialkyl maleate monomers containing C4-C8 straight-chain alkyl groups or acrylamide monomers. Phosphorus-containing functional components: 1 to 5 parts, which are phosphorus-containing reagents used for esterification modification; and phosphate ester functional units used to introduce phosphate esters that enhance the adsorption and anchoring ability of cement particles and active mineral phase surfaces.

2. The slow-release polycarboxylate water reducer containing phosphate groups according to claim 1, characterized in that: The polyether macromonomer is selected from at least one of methacryl alcohol polyoxyethylene ether, isopentenol polyoxyethylene ether, and isobutylenol polyoxyethylene ether; The unsaturated carboxylic acid monomer is selected from one or more of acrylic acid, methacrylic acid, maleic acid, fumaric acid and their salts.

3. The slow-release polycarboxylate water reducer containing phosphate groups according to claim 2, characterized in that: The phosphorus-containing functional component is selected from at least one of polyphosphoric acid, orthophosphoric acid, phosphorous acid, and phosphorus pentoxide.

4. The slow-release polycarboxylate superplasticizer containing phosphate ester groups according to claim 3, characterized in that: The water-reducing agent is coated with an inorganic silicon shell, and the water-reducing agent, as the core, forms a two-stage slow-release system with the inorganic silicon shell, which has a dual physical and chemical progressive release mechanism.

5. A method for preparing a slow-release polycarboxylate superplasticizer containing phosphate ester groups, used to prepare the slow-release polycarboxylate superplasticizer containing phosphate ester groups according to any one of claims 1-3, characterized in that: Includes the following steps: S1. Preparation of the base liquid: The polyether macromonomer and deionized water are added to the reaction vessel, heated and dissolved under stirring conditions, and an oxidant of the redox initiation system is added to obtain the base liquid; S2. Solution preparation: The unsaturated carboxylic acid monomer and the sustained-release monomer are combined to prepare monomer solution A; the reducing agent and molecular weight regulator of the redox initiation system are prepared to prepare initiation solution B; the phosphorus-containing reagent used for esterification modification is prepared as modification solution C. S3, Main copolymerization reaction: Under stirring conditions, monomer solution A and initiator solution B are added dropwise to the base liquid to carry out free radical copolymerization reaction. After the addition is completed, the reaction is kept at a constant temperature to obtain an aqueous solution of the main polymer. S4. Dehydration and post-modification with phosphorus: The free water in the system is removed by vacuum distillation of the aqueous solution of the main polymer. Then the modified liquid C is added and the bulk melt esterification reaction is carried out under anhydrous high temperature to dehydrate and covalently graft the phosphate ester groups onto the terminal hydroxyl groups of the polyether side chain. S5. Dissolution, neutralization and post-treatment: After the reaction is completed, the temperature is lowered, deionized water is added to dissolve, and a neutralizing agent is added to adjust the pH value to 6-8, so as to obtain the slow-release polycarboxylate superplasticizer containing phosphate ester groups.

6. The method for preparing a slow-release polycarboxylate superplasticizer containing phosphate ester groups according to claim 5, characterized in that: In step S1, the dissolution temperature is controlled at 20 to 60°C; in step S3, the dripping time is 2 to 4 hours, the temperature of the free radical copolymerization reaction is controlled at 25 to 50°C, and the reaction is continued at this temperature for 0.5 to 2 hours after the dripping is completed; in step S4, the temperature of the bulk melt esterification reaction is controlled at 100 to 140°C.

7. The method for preparing a slow-release polycarboxylate superplasticizer containing phosphate ester groups according to claim 6, characterized in that: In step S2, the molecular weight regulator is selected from at least one of thiocarboxylic acids, thiohydric alcohols, or phosphites; In step S3, the monomer solution A and the initiating solution B are added to the base solution by simultaneous dropwise addition.

8. The method for preparing a slow-release polycarboxylate superplasticizer containing phosphate ester groups according to claim 7, characterized in that: In step S5, the neutralizing agent is selected from one or more of sodium hydroxide, potassium hydroxide, and organic amines.

9. The method for preparing a slow-release polycarboxylate superplasticizer containing phosphate ester groups according to claim 5, characterized in that: Following step S5, a composite coating step is also included, employing a reverse emulsion coating process. The aqueous solution of the obtained water-reducing agent is dispersed as an aqueous phase in an oil phase containing an emulsifier to form reverse emulsion microdroplets. Subsequently, an inorganic silicon precursor is added, and in-situ polymerization or sol-gel reaction occurs at the water-oil phase interface of the microdroplets to generate an inorganic silicon shell encapsulating the water-reducing agent.

Images