A viscosity-reducing polycarboxylic water-reducing agent with branched side chains and a method for preparing the same

Abstract

The application discloses a viscosity-reducing polycarboxylic water reducing agent with branched side chains and a preparation method thereof.The water reducing agent is obtained by random copolymerization of a novel comb-shaped macromonomer C and unsaturated carboxylic monomer D at a mass ratio of 1:1-6;the novel comb-shaped macromonomer C is first copolymerized with carboxylic acid vinyl ester monomer A and methoxy-terminated polyoxyethylene ether monomer B to obtain a copolymer, then reactive hydroxyl groups are introduced at the end of the copolymer by using mercapto alcohol chain transfer agent, and finally, nucleophilic substitution reaction of the hydroxyl groups and halogenated olefins is carried out to obtain the product.The HLB value of the synthesized polycarboxylic water reducing agent is effectively reduced by introducing a hydrophobic ester bond structure into the side chain, which is beneficial to reducing the plastic viscosity of cement paste; and the multi-branched structure has a greater steric hindrance than the single side chain of the conventional polycarboxylic water reducing agent, thereby playing a role of strong dispersion and high water reduction.

Description

Technical Field

[0001] This invention belongs to the technical field of polycarboxylate superplasticizers for cement concrete, specifically relating to a viscosity-reducing polycarboxylate superplasticizer with branched side chains and its preparation method. Background Technology

[0002] In recent years, with the rapid development of the construction industry, modern buildings are trending towards high-rise, lightweight, and large-span structures. Therefore, high-performance concrete, with its advantages of high strength, good integrity, and light weight, is increasingly being used in some infrastructure projects. However, to achieve high or ultra-high strength, concrete must use a large amount of cementitious materials and a low water-cement ratio, along with some mineral admixtures, resulting in high viscosity and poor fluidity of fresh concrete. This problem poses significant difficulties for actual construction, especially for pumping ultra-high strength concrete, leading to frequent engineering accidents. Currently, there are two main technologies for reducing the viscosity of high-strength concrete: increasing the dosage of water-reducing agents and optimizing particle size distribution. The first technology has high construction costs, and the fresh concrete exhibits severe retardation, bleeding, and segregation, posing challenges to construction. While much research has been conducted on the second technology, it cannot completely solve the practical problems, as the good fluidity of fresh concrete is mainly due to the strong adsorption and dispersion capabilities of water-reducing agents. Therefore, developing a viscosity-reducing water-reducing agent is of great significance.

[0003] Polycarboxylate superplasticizers (PCEs) have become an indispensable component of concrete due to their excellent water reduction rate and highly designable molecular structure. The polymer molecules primarily reduce interparticle attraction and release water trapped within the aggregated cement particles by adsorbing onto the surface of cement particles, thus providing a steric hindrance effect. Numerous studies have focused on viscosity-reducing PCEs.

[0004] Patent CN110041468A discloses a method for synthesizing polycarboxylic acid water-reducing agent using styrene, maleic anhydride and polyethylene glycol monomethyl ether. The side chain of the water-reducing agent introduces benzene rings and acid anhydrides to adjust the hydrophilic and lipophilic values ​​of the polycarboxylic acid water-reducing agent, thereby reducing the viscosity of the slurry.

[0005] Patent CN109180876A describes the preparation of a slightly cross-linked, viscosity-reducing polycarboxylate superplasticizer by copolymerizing tricarboxylic acid phosphate monomers with unsaturated acids. This superplasticizer not only has viscosity-reducing properties but also water-reducing, slump-retaining, and anti-mud properties.

[0006] Patent CN109651566A uses block-modified unsaturated polyoxyethylene ether as raw material. The side chain of this block polyether contains hydrophobic groups, and the molecular structure has better flexibility. By adding different functional groups to optimize the structure, a high-performance viscosity-reducing water-reducing agent can be obtained.

[0007] Existing technologies typically involve copolymerization systems of three or more monomers, making it difficult to control the polymerization in practical applications. Summary of the Invention

[0008] This invention aims to overcome the technical problem of excessively high slurry viscosity and poor fluidity under low water-binder ratio, and provides a viscosity-reducing polycarboxylate superplasticizer with branched side chains based on a binary polymerization system and its preparation method.

[0009] This invention provides a viscosity-reducing polycarboxylate superplasticizer with branched side chains, wherein the superplasticizer is obtained by random copolymerization of a novel comb-shaped macromonomer C and an unsaturated carboxylic acid monomer D in a molar ratio of 1:1 to 6.

[0010] The novel comb-shaped macromonomer C is first prepared by copolymerizing a carboxylic acid vinyl ester monomer A with a methoxy-terminated polyoxyethylene ether monomer B to obtain a copolymer. Then, a reactive hydroxyl group is introduced at the end of the copolymer using a mercapto alcohol chain transfer agent. Finally, the hydroxyl group undergoes a nucleophilic substitution reaction with a haloalkene to obtain the product.

[0011] The chemical structure of the ethylene carboxylate monomer A is represented by the following general formula (Ⅰ):

[0012] (I)

[0013] Wherein, R1 is -H, -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CH2CH2CH2CH3, -CH2CH2CH2CH2CH3 or -C6H5.

[0014] The polyoxyethylene ether monomer B is selected from 4. Any one of hydroxybutyl vinyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, allyl polyoxyethylene ether, and vinylphenol polyoxyethylene ether.

[0015] The haloalkene is selected from any one of allyl bromide, allyl chloride, bromostyrene, chlorostyrene, and methylallyl chloride.

[0016] The unsaturated carboxylic acid monomer D is preferably a mixture of any one or more of acrylic acid, methacrylic acid, itaconic acid, citraconic acid, and fumaric acid.

[0017] The preparation method of the viscosity-reducing polycarboxylate superplasticizer with branched side chains described in this invention comprises the following steps:

[0018] (1) Dissolve carboxylic acid vinyl ester monomer A and polyoxyethylene ether monomer B in an anhydrous solvent and add them to a reaction vessel and stir at a constant temperature. Then, add a mixed solution of initiator I and mercapto alcohol chain transfer agent I dropwise to the base solution of monomer A and monomer B. After the dropwise addition is complete, keep warm for 1-3 hours and quench free radicals in an ice-water bath to obtain a copolymer mixture for later use.

[0019] The stirring temperature is 50~100℃;

[0020] The dropping time for the mixed solution of initiator I and mercapto alcohol chain transfer agent I is 1-5 hours;

[0021] The monomers A and B are stirred evenly at a constant temperature.

[0022] (2) Add haloolefin, acid-binding agent, phase transfer catalyst and polymerization inhibitor to the copolymer mixture in step (1) in proportion, stir and heat at 50~180℃ and reflux for 1~6h, purify the product in precipitant, and dry to obtain a new comb-shaped macromonomer C;

[0023] (3) The novel comb-shaped macromonomer C obtained in step (2) is free radically polymerized with unsaturated carboxylic acid monomer D, deionized water, and chain transfer agent II under the action of initiator II to obtain the viscosity-reducing polycarboxylic acid water-reducing agent of the present invention.

[0024] The preferred molar ratio of the ethylene carboxylate monomer A to the polyoxyethylene ether monomer B in step (1) is n(A):n(B) = 1:1~5. When the proportion of monomer A is too high, the resulting copolymer is too hydrophobic, which is not conducive to the synthesis of the water-reducing agent in step (3) and also not conducive to the water-reducing performance of the product.

[0025] The anhydrous solvent in step (1) is an anhydrous aprotic organic solvent. The anhydrous organic solvent is selected from any one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, benzene, toluene, xylene, THF (tetrahydrofuran), and DMSO (dimethyl sulfoxide). The solvent is usually dehydrated by adding NaH to the solvent, heating and refluxing for 1-6 hours, and then distilling or distilling under reduced pressure. The amount of anhydrous solvent used must ensure that the mass concentration of the solute is 30-70%.

[0026] The mercapto alcohol chain transfer agent I in step (1) is selected from any one or more of mercaptoethanol, 2-mercaptopropanol, 3-mercaptopropanol, 2-mercaptobutanol and 3-mercaptobutanol, wherein the amount of mercapto alcohol chain transfer agent I is preferably 1 to 10% of the total molar amount of the reaction monomers in step (1).

[0027] In step (1), the initiator I is selected from any one or more of sodium persulfate, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, dimethyl azobisisobutyrate, azobisisobutyranidine hydrochloride, benzoyl peroxide, lauroyl peroxide, and cumene hydroperoxide, wherein the amount of initiator is preferably 0.5 to 5% of the total molar amount of the reaction monomers.

[0028] The copolymers obtained in step (1) are all oligomers with a weight-average molecular weight controlled between 1000 and 5000. The hydrophilicity and lipophilicity (HLB) of the polymer can be adjusted by changing the ratio of the two monomers.

[0029] The amount of haloolefin used in step (2) is 0.5 to 15% of the mass of the copolymer mixture from step (1) added in step (2).

[0030] The phase transfer catalyst in step (2) is selected from any one of hexadecyltrimethylammonium bromide, tetrabutylammonium chloride, tetramethylammonium chloride, tetramethylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium iodide, and benzyltributylammonium bromide, and the molar mass of the phase transfer catalyst is 0.5 to 5 mol of the haloolefin.

[0031] The acid-binding agent in step (2) is an alkaline organic or inorganic substance, preferably a mixture of any one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, NaHCO3, sodium acetate, pyridine, and triethylamine. When using the acid-binding agent, the molar ratio of the raw material haloolefin to the acid-binding agent is 1:1 to 10. The acid-binding agent absorbs the acid and weakly basic substances generated in the reaction to prevent them from affecting the reaction or the reaction equilibrium.

[0032] The polymerization inhibitor in step (2) is selected from any one of phenothiazine, 2,2,6,6-tetramethylpiperidine oxide, hydroquinone, and diphenylamine sulfide, and the amount used is 0.2% to 0.5% of the total mass of the copolymer mixture and halogenated olefins added in step (2).

[0033] The purification method described in step (2) involves concentrating the crude product mixture by distillation or vacuum distillation to remove most of the solvent or low-boiling-point reactants, and then adding precipitants such as icy acetone, petroleum ether, diethyl ether, cyclohexane, n-hexane, and dioxane. The ratio of the amount of precipitant to the mass of the concentrated crude product is 5 to 20. The above precipitation steps are repeated at least twice, and the novel comb-shaped macromonomer C is obtained after vacuum drying.

[0034] In step (2), the weight-average molecular weight of the novel comb-shaped macromonomer C is controlled between 2000 and 8000. If the double bond concentration is too high, the double bond concentration will be too low, affecting the polymerization activity. If the double bond concentration is too low, it will not play a strong dispersing role.

[0035] Step (3) The polymerization method is aqueous redox free radical polymerization, the polymerization mass concentration range is 20%~80%, and the polymerization temperature is 15-50℃.

[0036] Initiator II in step (3) consists of an oxidant and a reducing agent. Specifically, in step (3), a mixed solution of deionized water, unsaturated carboxylic acid monomer D, chain transfer agent II and reducing agent is added dropwise to the base solution of the novel comb-shaped macromonomer C obtained in step (2) and the oxidant. The dropwise addition time is 1-6 hours, and the heat preservation time is 1-6 hours.

[0037] Initiator II in step (3) consists of an oxidant and a reducing agent. The preferred oxidant is selected from any one or more of hydrogen peroxide, potassium permanganate, tertiary alkyl hydrogen peroxide, ditertiary alkyl peroxide, diacyl peroxide, tertiary alkyl peroxide ester, dicarbonate peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate. The preferred reducing agent is selected from any one or more of ascorbic acid, sodium formaldehyde sulfoxylate, and sodium dithionite. The amount of reducing agent is 0.1-3 wt% of the total mass of the reactants, and the amount of oxidant is 0.1-5 wt% of the total mass of the reactants. The molar ratio of oxidant to reducing agent is usually 2-8:1.

[0038] The chain transfer agent II mentioned in step (3) is selected from any one of mercaptoethanol, mercaptopropionic acid, mercaptoacetic acid, thioglycerol, thiohydroxyacetic acid, thiomalic acid, 2-mercaptoethanesulfonic acid, butanethiol, octylthiol, decanethiol, and laurylthiol; the amount used is 0.5-8 wt% of the total mass of the reactants.

[0039] Specifically, the present invention preferably provides a viscosity-reducing polycarboxylate superplasticizer with a weight-average molecular weight range of 10,000 to 50,000.

[0040] The beneficial effects of this invention are as follows:

[0041] (1) The introduction of hydrophobic ester bond structure into the side chain effectively reduces the HLB value of the synthesized polycarboxylate superplasticizer and reduces the water association ability of the polyether long chain, which will make the superplasticizer have a lower surface tension in the cement paste. The conformation of the superplasticizer changes and the thickness of its adsorption layer increases, which is beneficial to reduce the plastic viscosity of the cement paste.

[0042] (2) As the ester bond gradually hydrolyzes in the alkaline environment, the polyhydroxyl groups of the side chain are released, which form a large number of hydrogen bonds with free water, thus improving the extension of the side chain; and the multi-branched structure has a greater steric hindrance than the single side chain of conventional polycarboxylate superplasticizer, thereby playing a role in strong dispersion and high water reduction. Detailed Implementation

[0043] The technical solution of the present invention will be further described in detail below through embodiments. The amounts described in each embodiment and comparative example are by weight.

[0044] Synthesis Example 1

[0045] (1) Mix 10 parts of vinyl acetate monomer A with 120 parts of 4-hydroxybutylvinyl polyoxyethylene ether (methoxy-terminated). M w =1000) was dissolved in 150 parts of N,N-dimethylformamide and stirred thoroughly at 70°C; 0.2 parts of azobisisobutyronitrile (AIBN) and 1 part of mercaptoethanol were dissolved in 50 parts of N,N-dimethylformamide and added dropwise to the vinyl acetate and polyether solution over 4 hours. After the addition was completed, the mixture was kept warm for 1 hour and free radicals were quenched in an ice-water bath to obtain the copolymer mixture;

[0046] (2) Take 240 parts of copolymer mixture, 24 parts of allyl bromide, 64 parts of sodium hydroxide, 1.2 parts of hexadecyltrimethylammonium bromide, and 0.4 parts of phenothiazine and heat to 150°C. o After refluxing C for 1 hour, the product was removed by vacuum distillation to remove most of the solvent and then precipitated in 500 parts of ice acetone. The precipitate was collected and dried under vacuum overnight to obtain the novel comb-shaped macromonomer C.

[0047] (3) A mixture of 50 parts of novel comb-shaped macromonomer C, 7.5 parts of acrylic acid, 50 parts of deionized water, and 0.6 parts of mercaptoethanol was prepared under the action of 0.4 parts of ascorbic acid and 1.5 parts of hydrogen peroxide (30 wt%) for 15 minutes. o After adding C dropwise for 1 hour and maintaining the temperature for 1 hour, the polymer was obtained as a viscosity-reducing polycarboxylate superplasticizer LV-PCE-1.

[0048] Synthesis Example 2

[0049] (1) Mix 10 parts of vinyl formate monomer A with 350 parts of isopentenyl polyoxyethylene ether (methoxy-terminated). M w =500) dissolved in 150 parts of N,N-dimethylacetamide, placed at 90°C o Stirring at temperature C until fully mixed; dissolve 2 parts of dimethyl azobisisobutyrate and 2 parts of 2-mercaptopropanol in 50 parts of N,N-dimethylacetamide, and continuously add dropwise to vinyl formate and polyether solution for 1 hour; after the addition is completed, keep warm for 1 hour, and quench free radicals in an ice-water bath to obtain copolymer mixture;

[0050] (2) Take 160 parts of copolymer mixture, 1.6 parts of allyl chloride, 2.4 parts of potassium hydroxide, 0.4 parts of tetrabutylammonium chloride, and 0.8 parts of 2,2,6,6-tetramethylpiperidine oxide, and heat to 100°C. o After refluxing C for 2 hours, the product was removed by vacuum distillation to remove most of the solvent and then precipitated in 500 parts of ice-cold petroleum ether. The precipitate was collected and dried under vacuum overnight to obtain the novel comb-shaped macromonomer C.

[0051] (3) A mixture of 50 parts of novel comb-shaped macromonomer C, 4.5 parts of methacrylic acid, 50 parts of deionized water, and 0.3 parts of mercaptopropionic acid, reacted with 0.3 parts of sodium formaldehyde sulfoxylate and 2.5 parts of ammonium persulfate at a concentration of 45%. o After adding C dropwise for 2 hours and maintaining the temperature for 2 hours, polymerization was carried out to obtain the viscosity-reducing polycarboxylate superplasticizer LV-PCE-2.

[0052] Synthesis Example 3

[0053] (1) Mix 10 parts of vinyl propionate monomer A with 200 parts of methyl allyl polyoxyethylene ether (methoxy-terminated). M w =2000) dissolved in 150 parts toluene, placed at 100 o Stirring at temperature C until fully mixed; dissolve 2.4 parts sodium persulfate and 1.5 parts 3-mercaptopropanol in 50 parts toluene, and continuously add dropwise to the vinyl propionate and polyether solution for 5 hours. After the addition is complete, keep warm for 3 hours, and quench free radicals in an ice-water bath to obtain the copolymer mixture.

[0054] (2) Take 200 parts of copolymer mixture, 30 parts of bromostyrene, 200 parts of potassium carbonate, 0.8 parts of tetramethylammonium chloride, and 0.8 parts of hydroquinone, and heat to 170°C. o After refluxing C for 3 hours, the product was removed by vacuum distillation to remove most of the solvent and then precipitated in 500 parts of ice-cold diethyl ether. The precipitate was collected and dried under vacuum overnight to obtain the novel comb-shaped macromonomer C.

[0055] (3) A mixture of 50 parts of novel comb-shaped macromonomer C, 2 parts of acrylic acid, 50 parts of deionized water, and 4 parts of mercaptoacetic acid, under the action of 0.5 parts of sodium dithionite and 2 parts of potassium persulfate, at 35°C o After adding C dropwise for 6 hours and maintaining the temperature for 6 hours, polymerization was carried out to obtain the viscosity-reducing polycarboxylate superplasticizer LV-PCE-3.

[0056] Synthesis Example 4

[0057] (1) Mix 10 parts of vinyl butyrate monomer A with 150 parts of allyl polyoxyethylene ether (methoxy-terminated). M w =500) Dissolve in 100 parts DMSO, and place at 70 o Stirring at temperature C until fully mixed; dissolve 2.5 parts benzoyl peroxide and 1.1 parts 2-mercaptobutanol in 50 parts DMSO, and continuously add dropwise to the solution of vinyl butyrate and polyether over 4 hours. After the addition is complete, keep warm for 3 hours, and quench free radicals in an ice-water bath to obtain the copolymer mixture.

[0058] (2) Take 200 parts of copolymer mixture, 10 parts of chlorostyrene, 36 parts of triethylamine, 0.4 parts of tetramethylammonium bromide, and 0.4 parts of diphenylamine sulfide, and heat to 90°C. oAfter refluxing C for 6 hours, the product was removed by vacuum distillation to remove most of the solvent and then precipitated in 500 parts of ice-cold hexane. The precipitate was collected and dried under vacuum overnight to obtain a novel comb-shaped macromonomer C.

[0059] (3) The viscosity-reducing polycarboxylate superplasticizer consists of 50 parts of a novel comb-shaped macromonomer C, 2 parts of citralic acid, 50 parts of deionized water, and 2.5 parts of butanethiol, mixed with 0.2 parts of ascorbic acid and 2.5 parts of potassium permanganate. o After adding C dropwise for 4 hours and maintaining the temperature for 3 hours, LV-PCE-4 was obtained by polymerization.

[0060] Synthesis Example 5

[0061] (1) Mix 10 parts of vinyl isobutyrate monomer A with 140 parts of vinylphenol polyoxyethylene ether (methoxy-terminated). M w =800) dissolved in 150 parts tetrahydrofuran, placed at 50 o Stirring at temperature C until fully mixed; dissolve 1.5 parts of azobisisobutylamidine hydrochloride and 0.3 parts of 3-mercaptobutanol in 50 parts of tetrahydrofuran, and continuously add dropwise to the vinyl isobutyrate and polyether solution for 2 hours. After the addition is completed, keep warm for 3 hours, and quench free radicals in an ice-water bath to obtain the copolymer mixture.

[0062] (2) Take 240 parts of copolymer mixture, 1.2 parts of methyl allyl chloride, 1.2 parts of pyridine, 0.2 parts of tetrabutylammonium bromide, and 0.8 parts of phenothiazine, and heat to 50°C. o After refluxing C for 5 hours, the product was removed by vacuum distillation to remove most of the solvent and then precipitated in 500 parts of cyclohexane. The precipitate was collected and dried under vacuum overnight to obtain the novel comb-shaped macromonomer C.

[0063] (3) A mixture of 50 parts of novel comb-shaped macromonomer C, 4 parts of itaconic acid, 50 parts of deionized water, and 1 part of octylthiol, reacted with 0.25 parts of ascorbic acid and 0.5 parts of hydrogen peroxide (30 wt%). o After adding C dropwise for 1 hour and maintaining the temperature for 1 hour, polymerization was carried out to obtain the viscosity-reducing polycarboxylate superplasticizer LV-PCE-5.

[0064] Synthesis Implementation 6

[0065] (1) Mix 10 parts of vinyl benzoate monomer A with 135 parts of methyl allyl polyoxyethylene ether (methoxy-terminated). M w =2000) dissolved in 200 parts xylene, placed at 60 o Stirring at temperature C until fully mixed; dissolve 1.6 parts lauroyl peroxide and 0.2 parts mercaptoethanol in 100 parts xylene, and add dropwise to the vinyl formate and polyether solution over 2 hours. After the addition is complete, keep warm for 1 hour, and quench free radicals in an ice-water bath to obtain the copolymer mixture.

[0066] (2) Take 280 parts of copolymer mixture, 14 parts of allyl bromide, 56 parts of sodium acetate, 0.5 parts of benzyltributylammonium bromide, and 1.2 parts of 2,2,6,6-tetramethylpiperidine oxide and heat to 120°C. o After refluxing C for 5 hours, the product was removed by vacuum distillation to remove most of the solvent and then precipitated in 500 parts of icy dioxane. The precipitate was collected and dried under vacuum overnight to obtain a novel comb-shaped macromonomer C.

[0067] (3) A mixture of 50 parts of novel comb-shaped macromonomer C, 3 parts of methacrylic acid, 50 parts of deionized water, and 3 parts of lauryl thiol, reacted with 0.15 parts of formaldehyde sodium bisulfite and 0.5 parts of hydrogen peroxide (30 wt%). o After adding C dropwise for 3 hours and maintaining the temperature for 3 hours, polymerization was carried out to obtain the viscosity-reducing polycarboxylate superplasticizer LV-PCE-6.

[0068] Comparative Example 1

[0069] 10 parts of vinyl acetate monomer A were mixed with 120 parts of 4-hydroxybutyl vinyl polyoxyethylene ether (methoxy-terminated). M w =1000) dissolved in 150 parts of N,N-dimethylformamide, placed at 70°C o Stirring at temperature C until fully mixed; dissolve 0.2 parts of azobisisobutyronitrile (AIBN) and 1 part of mercaptoethanol in 50 parts of N,N-dimethylformamide, and continuously add dropwise to the vinyl acetate and polyether solution for 4 hours. After the addition is completed, keep warm for 1 hour, and quench free radicals in an ice-water bath to obtain copolymer mixture REF-1.

[0070] Comparative Example 2

[0071] 50 parts 4-hydroxybutylvinyl polyoxyethylene ether, 7.5 parts acrylic acid, 50 parts deionized water, 0.6 parts mercaptoethanol, in the presence of 0.4 parts ascorbic acid and 1.5 parts hydrogen peroxide (30 wt%), 15 o C was added dropwise for 1 hour, and the mixture was kept at this temperature for 1 hour to polymerize and obtain REF-2.

[0072] Application Example 1

[0073] The fluidity of the cement paste was tested according to GB / T 8077—2012 "Test Method for Homogeneity of Concrete Admixtures", with a water-cement ratio of 0.29 and Helin cement used. As shown in Table 1, the viscosity-reducing polycarboxylate superplasticizer described in this invention, at a dosage of 0.12%, has an advantage over the control sample at a dosage of 0.13%, exhibiting better water reduction and slump retention.

[0074] Table 1 Results of Pulping

[0075]

[0076] Application Example 2

[0077] The mortar flowability was determined according to a standard mix ratio of m(cement):m(standard sand):m(water) = 700:1350:175. A V-funnel test was used to evaluate the workability of the mortar, controlling the initial flowability at 280 mm ± 5. The apparent viscosity was measured using a Model R / S SST200 rheometer manufactured by Brookfield Instruments, USA. The data in Table 2 show that, compared to REF-1 and REF-2, LV-PCE-1~6 exhibit better overall performance, with a shorter V-funnel time and a significant decrease in apparent viscosity. This indicates that the water-reducing agent sample can significantly reduce the viscosity of cement mixtures.

[0078] Table 2 Mortar Results

[0079]

[0080] Application Example 3

[0081] Concrete was prepared according to the C30 concrete mix design according to GB / T 8077—2012 "Test Method for Homogeneity of Concrete Admixtures". The air content of the concrete was controlled at 2.5-3.0%, and the spread of the concrete was controlled at 550-620 mm. Referring to the "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" (GB / T50080-2016), the viscosity of the concrete was tested using the inverted slump cone method. The shorter the time it takes for the concrete to flow out of the inverted slump cone, the lower the viscosity of the concrete. Table 4 of the experimental results shows that the viscosity-reducing polycarboxylate provided by this invention has better water reduction and slump retention than the standard comparison sample REF-2. Furthermore, at similar spread and flowability, the emptying time of its inverted slump cone is significantly reduced by half compared to the comparison sample, proving that its viscosity-reducing effect is significant.

[0082] Table 3. C30 Concrete Mix Proportions (kg)

[0083]

[0084] Table 4 Results of C30 Concrete

[0085]

[0086] Application Example 4

[0087] Concrete was prepared according to the mix proportions of GB / T 8077—2012 "Test Method for Homogeneity of Concrete Admixtures", and the specific mix proportions are shown in the table below.

[0088] Table 5. C80 Concrete Mix Proportions (kg)

[0089]

[0090] Intensity, evacuation time, and T50

[0091] Table 6 Results of C80 High-Strength Concrete

[0092]

[0093] Table 6 shows that the results for C80 high-strength concrete are basically consistent with those for C30. Its air content is relatively low. Under similar slump and spread conditions, the evacuation time of the viscosity-reducing polycarboxylate inverted cylinder provided by this invention is shorter, and the time required for T50 is also nearly half that of the comparative samples REF-1 and REF-2. The strength at 3d, 7d, and 28d indicates that even if it can reduce the viscosity of fresh concrete, it does not affect the development of the later strength of the concrete.

Claims

1. A viscosity-reducing polycarboxylate superplasticizer with branched side chains, characterized in that, The water-reducing agent is obtained by random copolymerization of a novel comb-shaped macromonomer C and an unsaturated carboxylic acid monomer D in a molar ratio of 1:1~6. The novel comb-shaped macromonomer C is first prepared by copolymerizing a carboxylic acid vinyl ester monomer A with a methoxyl-terminated polyoxyethylene ether monomer B to obtain a copolymer. Then, a reactive hydroxyl group is introduced at the end of the copolymer using a mercapto alcohol chain transfer agent. Finally, the hydroxyl group undergoes a nucleophilic substitution reaction with a haloalkene to obtain the product. The chemical structure of the ethylene carboxylate monomer A is represented by the following general formula (Ⅰ): （Ⅰ） Wherein, R1 is -H, -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH3)2, -CH2CH2CH2CH3, -CH2CH2CH2CH2CH3 or -C6H5.

2. The viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 1, characterized in that, The methoxy-terminated polyoxyethylene ether monomer B is selected from any one of methoxy-terminated 4-hydroxybutyl vinyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, allyl polyoxyethylene ether, and vinylphenol polyoxyethylene ether. The molar range of the vinyl carboxylate monomer A and the methoxyl-terminated polyoxyethylene ether monomer B is n(A):n(B) = 1:1~5.

3. The viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 1, characterized in that, The haloalkene is selected from any one of allyl bromide, allyl chloride, bromostyrene, chlorostyrene, and methylallyl chloride.

4. The viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 1, characterized in that, The unsaturated carboxylic acid monomer D is selected from any one or more of acrylic acid, methacrylic acid, itaconic acid, citraconic acid, and fumaric acid.

5. A method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to any one of claims 1 to 4, characterized in that, The specific steps are as follows: (1) Dissolve carboxylic acid vinyl ester monomer A and methoxy-terminated polyoxyethylene ether monomer B in an anhydrous solvent and add them to a reaction vessel and stir at a constant temperature. Then, add a mixed solution of initiator I and mercapto alcohol chain transfer agent I dropwise to the base solution of monomer A and monomer B. After the dropwise addition is complete, keep warm for 1-3 hours and quench free radicals in an ice-water bath to obtain a copolymer mixture for later use. The amount of anhydrous solvent used ensures that the mass concentration of the solute in step (1) is between 30% and 70%. (2) Add haloolefin, acid-binding agent, phase transfer catalyst and polymerization inhibitor to the copolymer mixture in step (1) in proportion, stir and heat at 50~180℃ and reflux for 1~6h, purify the product in precipitant, and dry to obtain a new comb-shaped macromonomer C; The amount of the haloolefin used is 0.5-15% of the mass of the copolymer mixture; (3) The novel comb-shaped macromonomer C obtained in step (2) is free radical polymerized with unsaturated carboxylic acid monomer D, deionized water, and chain transfer agent II under the action of initiator II to obtain the viscosity-reducing polycarboxylic acid water-reducing agent.

6. The method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 5, characterized in that, The stirring temperature in step (1) is 50~100℃, and the dropping time of the mixed solution of initiator I and mercapto alcohol chain transfer agent I is 1~5h; Step (3) The polymerization method is aqueous redox free radical polymerization, the polymerization mass concentration range is 20%~80%, and the polymerization temperature is 15-50℃.

7. A method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 5 or 6, characterized in that, The amount of mercapto alcohol chain transfer agent I used in step (1) is 1-10% of the total molar amount of the monomers reacted in step (1); The amount of initiator I is 0.5-5% of the total molar amount of the monomers in step (1); The copolymers obtained in step (1) are all oligomers with a weight-average molecular weight controlled between 1000 and 5000.

8. A method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 5 or 6, characterized in that, The molar mass of the phase transfer catalyst in step (2) is 0.5 to 5 mol% of the haloolefin; The acid-binding agent is an alkaline organic or inorganic substance, and the molar ratio of the raw material haloolefin to the acid-binding agent is 1:1 to 10. The amount of the polymerization inhibitor is 0.2% to 0.5% of the total mass of the copolymer mixture and halogenated olefins added in step (2); In step (2), the weight-average molecular weight of the novel comb-shaped macromonomer C is controlled at 2000~8000.

9. A method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 5 or 6, characterized in that, The initiator II mentioned in step (3) consists of an oxidant and a reducing agent. The amount of reducing agent is 0.1-3 wt% of the total mass of the reactants in step (3), and the amount of oxidant is 0.1-5 wt% of the total mass of the reactants. The molar ratio of oxidant to reducing agent is 2-8:

1. The amount of chain transfer agent II is 0.5-8 wt% of the total mass of the reactants; The weight-average molecular weight range of the viscosity-reducing polycarboxylate superplasticizer is controlled between 10,000 and 50,000.

10. The method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 7, characterized in that, The anhydrous solvent in step (1) is an anhydrous aprotic organic solvent, which is selected from any one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide, benzene, toluene, xylene, THF (tetrahydrofuran), and DMSO (dimethyl sulfoxide); The mercaptool chain transfer agent I is selected from any one or more of mercaptoethanol, 2-mercaptopropanol, 3-mercaptopropanol, 2-mercaptobutanol, and 3-mercaptobutanol; The initiator I is selected from any one or more of sodium persulfate, potassium persulfate, ammonium persulfate, azobisisobutyronitrile, dimethyl azobisisobutyrate, azobisisobutyronitrile hydrochloride, benzoyl peroxide, lauroyl peroxide, and cumene hydroperoxide.

11. The method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 8, characterized in that, The phase transfer catalyst in step (2) is selected from any one of hexadecyltrimethylammonium bromide, tetrabutylammonium chloride, tetramethylammonium chloride, tetramethylammonium bromide, tetrabutylammonium bromide, tetrabutylammonium iodide, and benzyltributylammonium bromide; The acid-binding agent is selected from any one or more of sodium hydroxide, potassium hydroxide, potassium carbonate, sodium carbonate, NaHCO3, sodium acetate, pyridine, and triethylamine; The polymerization inhibitor is selected from any one of phenothiazine, 2,2,6,6-tetramethylpiperidine oxide, hydroquinone, and diphenylamine sulfide.

12. The method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 9, characterized in that, Initiator II in step (3) is composed of an oxidant and a reducing agent. The oxidant is selected from any one or more of hydrogen peroxide, potassium permanganate, tertiary alkyl hydrogen peroxide, ditertiary alkyl peroxide, diacyl peroxide, tertiary alkyl peroxide ester, dicarbonate peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate. The reducing agent is selected from any one or more of ascorbic acid, sodium formaldehyde sulfoxylate, and sodium dithionite. The chain transfer agent II is selected from any one of mercaptoethanol, mercaptopropionic acid, mercaptoacetic acid, thioglycerol, thiohydroxyacetic acid, thiomalic acid, 2-mercaptoethanesulfonic acid, butanethiol, octylthiol, decanethiol, and laurylthiol.

13. The method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 10, characterized in that, The method for removing water from the anhydrous solvent in step (1) is to add NaH to an aprotic organic solvent, heat under reflux for 1-6 hours, and then distill or distill under reduced pressure.

14. A method for preparing a viscosity-reducing polycarboxylate superplasticizer with branched side chains according to claim 5 or 6, characterized in that, The purification method described in step (2) is to concentrate the crude product mixture by distillation or vacuum distillation to remove most of the solvent or low-boiling-point reactants, and then add precipitants such as icy acetone, petroleum ether, diethyl ether, cyclohexane, n-hexane, and dioxane. The ratio of the amount of precipitant to the mass of the concentrated crude product is 5 to 20. The above precipitation steps are repeated at least twice. After vacuum drying, a novel comb-shaped macromonomer C is obtained. In step (3), a mixed solution of deionized water, unsaturated carboxylic acid monomer D, chain transfer agent II and reducing agent is added dropwise to the base solution of the novel comb-shaped macromonomer C and oxidant obtained in step (2). The dropwise addition time is 1-6 hours, and the heat preservation time is 1-6 hours.

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