CN109232818B

CN109232818B - Preparation method of pH response type comb-shaped polycarboxylic acid

Info

Publication number: CN109232818B
Application number: CN201810835164.4A
Authority: CN
Inventors: 刘晓; 许谦; 赖光洪; 管佳男; 王子明; 张琳
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2018-07-26
Filing date: 2018-07-26
Publication date: 2021-01-05
Anticipated expiration: 2038-07-26
Also published as: CN109232818A

Abstract

The invention relates to a preparation method of pH response type comb-shaped polycarboxylic acid. The method comprises the steps of preparing a polycarboxylic acid material by adopting raw materials such as acrylic ester, a pH response type monomer and the like through a method of self-polymerization, graft copolymerization and hydrolysis, wherein the acrylic ester is used as a reaction monomer, the polyacrylic ester with controllable molecular weight is generated through polymerization under the action of an initiator and a chain transfer agent, the polyacrylic ester is grafted and copolymerized with the pH response type monomer to obtain a graft copolymer which takes an acrylic ester polymer as a main chain and takes the pH response type polymer as a side chain, and finally the graft copolymer is hydrolyzed to prepare the polycarboxylic acid with a comb-shaped structure, wherein the main chain is polyacrylic acid and the side chain is the pH response type polymer. The method has mild conditions, saves energy and has high efficiency, introduces the pH response type polymer by a molecular structure design method, synthesizes the polycarboxylic acid with a special functional side chain, successfully realizes the pH response behavior, shows excellent characteristic of inhibiting the shrinkage of cement mortar, and has wide market prospect and popularization and application potential.

Description

Preparation method of pH response type comb-shaped polycarboxylic acid

Technical Field

The invention relates to the technical field of pH responsive polycarboxylic acid for cement concrete, in particular to a specific preparation method for synthesizing a comb-shaped polycarboxylic acid material by adopting acrylate monomers through self-polymerization, grafting of the acrylate monomers and hydrolysis.

Background

Concrete is one of the most widely used building materials in the field of construction engineering at present, and is an important structural engineering material, but the concrete is easy to shrink and deform under a low-water-content dry environment, so that cracking and other defects of hardened concrete are caused. The crack problem of large-scale foundation slab, building outer wall, underground structure, floor board, roof beam is comparatively common building engineering quality problem. The continuous development of green concrete and high-strength concrete makes the kind of concrete change day by day, however, the cracking problem is more and more emphasized by people in the industry, the damage caused by the cracking problem is difficult to estimate, and the cracking problem of concrete is a great problem in the field of concrete, so that the cracking problem of concrete in engineering is urgently needed to be inhibited. There are many reasons for generating cracks, and besides the influence of design and construction, temperature shrinkage, self-shrinkage, drying shrinkage and shaping shrinkage are common reasons for concrete cracking. Although the shrinkage amplitude of the concrete is not high, the damage caused by the concrete is extremely serious, the integral strength of the concrete can be reduced, and the attractiveness is influenced; the generated cracks can lead air and moisture to enter the concrete, so that the shrinkage cracking is accelerated, further sulfate corrosion, carbonization corrosion, steel bar rusting and the like occur, freeze-thaw circulation can occur in a cold area, the durability of the concrete is reduced, and the service life of a building is shortened.

In the field of polymer surface chemistry, self-assembly and hydrophilic-hydrophobic transition behavior of an environment-responsive multi-block copolymer in a specific environment have responsiveness and sensitivity to an external environment, and become one of research hotspots. The self-assembly of the polymer is a process that macromolecules spontaneously construct an aggregate with a special shape and structure under the mutual promotion of hydrogen bonds, Van der Waals force, electrostatic interaction and the like, and the combined action of blocks can enable the polymer to form molecular aggregates with various morphological structures, so that the self-assembly of the polymer has the potential of realizing hydrophilic and hydrophobic intelligent response characteristics. In recent years, a great deal of literature details about the self-assembly behavior of the amphiphilic block copolymer in a selective solvent and the corresponding hydrophilic-hydrophobic transformation behavior, and the amphiphilic block copolymer has wide application in aspects of sewage treatment, environmental purification, drug delivery and the like.

With the gradual rise of molecular structure regulation and control technology in the field of polymer discipline, a theoretical basis is provided for designing and synthesizing macromonomer molecules with ideal structures. Comb polymers are becoming more and more popular with researchers because of their ability to fully exploit the respective performance advantages of the main and side chains of macromolecules. Therefore, pH response type monomers are introduced into the polycarboxylic acid macromolecule side chains to design and synthesize pH response type comb-shaped structure polycarboxylic acid, and excellent anchoring adsorption and hydrophilic-hydrophobic response behaviors are realized through the interaction of the main side chains. The polycarboxylic acid material with the structure not only has various performances of the traditional polycarboxylic acid material, but also has the characteristic advantage of pH response capability, and shows wide application value.

Patent CN 103803840B (published: 2016, 5, 4) reports the use of a hyperbranched polymer in cement concrete shrinkage reduction. The patent firstly synthesizes a hydroxyl-terminated hyperbranched polymer, and then introduces polyoxyethylene alkyl or polyethylene glycol chain segments into the tail end of the hyperbranched polymer, thereby synthesizing the hyperbranched concrete shrinkage-reducing agent. The hyperbranched concrete shrinkage reducing agent is applied to the field of concrete shrinkage reduction, has good shrinkage reducing effect, has small influence on the concrete strength, less doping amount, lower cost, simple and convenient synthesis and easy industrialization, and is a concrete shrinkage reducing agent with excellent performance. However, the raw materials used in the invention are polyoxyethylene alkyl or polyethylene glycol, belong to alkylene oxide derivatives, are limited by the raw materials as well as other shrinkage reducing agents, and can influence the production and application of products.

Patent CN 1648098A (published: 8/3/2005) reports a chemical admixture capable of inhibiting concrete shrinkage, which is compounded by a plurality of organic matters, including mono-alcohol, polyhydric alcohol and polyalcohol ether, and is colorless or light yellow liquid at normal temperature and easily soluble in water. The shrinkage reducing agent reported in the patent can not cause the mortar to be sticky when being mixed in cement mortar, can improve the fluidity of the mortar, but has low water reducing rate per se, and does not consider the water reducing effect generally; the shrinkage reducing agent has slightly improved working performance on mortar and concrete and slightly reduced other mechanical properties; when the shrinkage reducing agent is used in concrete, the mixing amount accounts for 0.5 to 2 percent of the total proportion; the shrinkage reducing agent can obviously reduce the drying shrinkage of mortar and concrete, reduce the autogenous volume shrinkage deformation of the concrete, and even change the shrinkage type of the concrete into the expansion type of the concrete. However, the reported shrinkage reducing agent does not have pH response characteristics, cannot realize the effects of reducing and cracking through the change of the pH value of the environment spontaneously, and cannot achieve the aim of realizing the functionalization of the polymer by a molecular structure design method.

Patent CN 106632925a (published: 5/10/2017) reports a preparation method of amphiphilic multiblock copolymer with pH sensitivity. A macromolecular chain transfer agent poly (tert-butyl acrylate) is synthesized by adopting a reversible addition-fragmentation chain transfer polymerization method, and then RAFT polymerization is carried out on the poly (tert-butyl acrylate), dimethylaminoethyl methacrylate and ethylene glycol methyl ether methacrylate again to obtain an amphiphilic multi-block copolymer P (tBA) -b-P (DMAEMA-co-PEGMA). In aqueous solution, the multi-block copolymer can self-assemble to form micelle and has pH sensitivity, and the critical value of pH response is 7. The invention has high polymerization yield, wide monomer application range, pH sensitivity of the obtained product and wide application prospect, and can be applied to the fields of chemical production such as dye adsorption and the like, environmental protection such as heavy metal pollution treatment and the like, and the field of biological medicines such as the controllable release of insoluble medicines and the like. The invention provides a preparation method of a pH-sensitive multi-block copolymer, which makes up the defects of the existing multi-block copolymer in the aspect of environmental response characteristics. However, the production process of the invention is complicated, the production cost is high, and the pH response characteristic is not applied to the field of improving the shrinkage performance of cement concrete.

The polymers for concrete described in most patents have been found to have good shrinkage-inhibiting and crack-resistant effects. However, the above design and synthesis methods all have certain disadvantages, researchers mostly focus on the idea of modifying the water reducing agent or blending alcohols to reduce the shrinkage and cracking phenomena of concrete, and rarely use polymers to perform hydrophilic and hydrophobic transformation in response to environmental changes, thereby realizing the hydrophobic effect of the material from inside to outside. The synthesis method of the active polymer such as the RAFT method and the like has the limitation of being applied to the field of concrete water reducing agents due to harsh reaction conditions and special catalytic systems, and the fact proves that the performance and the efficacy of the polymer can be obviously improved by designing and synthesizing a comb-shaped macromolecular structure and introducing a pH response type block side chain. Therefore, the synthesized pH response type polycarboxylic acid material is required to realize the innovation of a molecular structure, not only has the application performances of shrinkage reduction, crack resistance and the like according to the change of the pH environment of the cement concrete, but also can ensure convenient process operation, low preparation cost, simple and easily obtained reaction raw materials, is beneficial to industrial production and popularization and application, and has no report on the aspect at home and abroad.

Disclosure of Invention

The invention aims to provide a preparation process of pH response type comb-shaped structure polycarboxylic acid. The invention starts from the molecular structure design theory, introduces the pH response type polymer side chain innovatively, ensures the anchoring and adsorbing characteristics of the traditional polycarboxylic acid, increases the pH environment response characteristic, effectively improves the multiple working energy efficiency, and enriches the application of polymer structure-performance research in the field of polymers for concrete. Based on the pH response effect, the hydrophobicity of capillary tubes in the cement concrete can be regulated, the effect of inhibiting the shrinkage cracking of the cement concrete is further realized, and the intelligent response value and the wide development prospect which are more excellent than those of the traditional polycarboxylic acid shrinkage-reducing material are shown.

1. The invention provides a preparation method of a pH response type comb-shaped structure polycarboxylic acid material, which synthesizes the pH response type polycarboxylic acid material by a method of self-polymerization, grafting and hydrolysis, and comprises the following conditions and steps:

(1) self-polymerization reaction: firstly, adding an organic solvent, acrylic ester and a chain transfer agent into a reactor, stirring and heating to 50-120 ℃, then dropwise adding a mixed solution of an initiator and the organic solvent for 1-12 hours, and continuously reacting at a constant temperature of 50-120 ℃ for 1-6 hours after dropwise adding to obtain a self-polymerization product polyacrylate solution;

(2) graft copolymerization reaction: adjusting the temperature of the self-polymerization product obtained in the step (1) to 50-100 ℃, adding a molecular weight regulator, stirring for 15-40 minutes, uniformly mixing, dropwise adding a mixed solution of a pH response type monomer, an initiator and an organic solvent for 1-12 hours, continuously reacting at a constant temperature of 50-100 ℃ for 1-6 hours after dropwise adding, and then carrying out reduced pressure distillation to remove the organic solvent to obtain a graft copolymerization product;

(3) and (3) hydrolysis reaction: and (3) mixing the graft copolymerization product obtained in the step (2) with deionized water, stirring, heating to 30-80 ℃, adding inorganic base, hydrolyzing for 10-150 minutes, then carrying out reduced pressure distillation to remove the hydrosolvent and the byproduct, drying, and adding solvent water to obtain the pH response type polycarboxylic acid solution with the required concentration.

The organic solvent used in the self-polymerization reaction in the step (1) is tetrahydrofuran, N-dimethylformamide, aniline, sulfolane or dimethyl sulfoxide, and the mass ratio of the dosage to the acrylate is 1-12: 1; the acrylate is methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate or amyl acrylate; the chain transfer agent is isopropanol, isooctyl 3-mercaptopropionate, 2-mercaptoethanol or 3-mercaptopropanol, and the molar ratio of the dosage to the acrylate is 0.05-0.6: 1; the initiator is azobisisobutyronitrile, azobisisoheptonitrile, dibenzoyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate or di-tert-butyl peroxide, and the molar ratio of the dosage to the acrylate is 0.05-0.2: 1; in the mixed solution of the initiator and the organic solvent, the organic solvent is tetrahydrofuran, N-dimethylformamide, aniline, sulfolane or dimethyl sulfoxide, and the mass fraction of the initiator in the mixed solution is 5-50%.

The molecular weight regulator used in the graft copolymerization reaction in the step (2) is n-dodecyl mercaptan, tert-dodecyl mercaptan, thioglycolic acid or 3-mercaptopropionic acid, and the molar ratio of the dosage to the pH response type monomer is 0.05-0.3: 1; the pH response type monomer is dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-vinylpyridine, 4-vinylpyridine or N, N-diethyl-2-acrylamide, and the molar ratio of the used amount to the acrylate in the step (1) is 2-10: 1; the initiator is azobisisobutyronitrile, azobisisoheptonitrile, dibenzoyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate or di-tert-butyl peroxide, and the molar ratio of the dosage to the pH response type monomer is 0.05-0.2: 1; in the mixed solution of the initiator and the organic solvent, the organic solvent is tetrahydrofuran, N-dimethylformamide, aniline, sulfolane or dimethyl sulfoxide, and the mass fraction of the initiator in the mixed solution is 5-50%.

The molar ratio of the usage amount of deionized water used in the hydrolysis reaction in the step (3) to the acrylate in the step (1) is 1-10: 1; the inorganic alkali is sodium hydroxide or potassium hydroxide, and the molar ratio of the amount of the inorganic alkali to the deionized water is 0.001-0.02: 1.

The pH response type comb-structure polycarboxylic acid is characterized in that the structural expression is as follows:

wherein R is₁Is dimethylaminoethyl ester, diethylaminoethyl ester, 2-pyridyl, 4-pyridyl or N, N-diethyl-2-amido; r₂Is hydrogen radical or methyl;

wherein a, b are positive integers representing the number of individual repeat units randomly distributed in the polymerization, a: b is in the range of 0.1 to 10: 1;

wherein n is a positive integer representing the number of side chain repeat units, and n is in the range of 5 to 120.

The synthesized pH response type polycarboxylic acid material has a typical comb-shaped structure, a polyacrylic acid main chain of the synthesized pH response type polycarboxylic acid material is adsorbed on cement particles, and a pH response type polymer side chain of the synthesized pH response type polycarboxylic acid material shows excellent hydrophilic-hydrophobic conversion characteristics through response to an environmental pH value, so that the contact angle of a capillary meniscus in cement concrete can be increased, the capillary pressure is reduced, and the effect of inhibiting the shrinkage cracking of the cement concrete is further realized.

Compared with the prior art, the method of the invention has the following beneficial effects:

1. the invention starts from the theory of molecular structure design, and forms the pH responsive polycarboxylic acid material with the comb structure which takes polyacrylic acid as a main chain and takes a pH responsive polymer block as a side chain after acrylic ester monomer self-polymerization, graft copolymerization and hydrolysis reaction, the structure of the invention is similar to the traditional pH responsive polycarboxylic acid water reducing agent, the invention is another innovation and breakthrough in the polymer field for cement concrete, and the invention widens the thought and direction for the subsequent deep development of new polycarboxylic acid materials.

2. The synthesized pH response type polycarboxylic acid material has a typical comb-shaped structure, a polycarboxylic acid main chain is adsorbed on cement particles, the pH response type polymer block structure serving as a side chain plays an excellent environment response hydrophilic-hydrophobic conversion role, and the comb-shaped structure has good effects on preventing cement concrete from cracking and improving the stability of hardened concrete. The product is a pH response type polycarboxylic acid material with a comb-shaped structure and has unique advantages, and the product shows good application prospect and market competitiveness.

3. Compared with the traditional polycarboxylic acid material, the synthesis method of the product has the advantages that the raw materials required by the reaction are more common and easily available, the price is low, the whole reaction process is simple and controllable, the used steps of self-polymerization, graft copolymerization and hydrolysis are common operation processes, special operation and expensive reagents are not needed, the preparation is independent of the preparation of the alkylene oxide compound and derivatives thereof, no special requirements are required on synthesis equipment and experimental environment, and the industrial production is easy to realize.

4. The preparation process of the product has the advantages of low energy consumption, safety, environmental protection, mild conditions, cleanness, no pollution, no toxicity, no harm and simple and easy synthetic method. The organic solvent after the self-polymerization reaction is not required to be removed, the subsequent graft copolymerization reaction can be directly carried out, and the organic solvent removed after the graft polymerization can be recycled after being condensed and recovered, so that the waste of raw materials is greatly reduced, and the production cost is reduced. Meanwhile, the applicable molecular weight range of the used acrylate and the pH response type monomer is wide, the diversity of raw materials is enriched, and the product competitiveness and the development prospect are improved.

5. The pH response type polycarboxylic acid synthesized by the invention has good shrinkage reducing and crack resisting effects on cement concrete materials, can show good shrinkage inhibiting capability under a low mixing amount, and shows consistent regularity under different ages. In addition, the product is a clear and homogeneous solution in appearance, has a stable system state, and does not delaminate after standing at high concentration. The synthesis method has the advantages of simplicity and directness, and the synthesized product has excellent performance indexes, is beneficial to market promotion and has good economic benefit and application prospect.

Drawings

Fig. 1 is an infrared spectrum of pH-responsive comb-structured polycarboxylic acid at pH 11 in example 1.

FIG. 2 is a graph showing the particle size of pH-responsive comb-structured polycarboxylic acid in example 1 as a function of pH. The pH values were 7, 8, 9, 10, 11, 12, 13, 14, respectively.

FIG. 3 is a graph showing transmittance of pH-responsive comb-structured polycarboxylic acid according to pH in example 1. The pH values were 7, 8, 9, 10, 11, 12, 13, 14, respectively.

Detailed Description

The present invention will be described in further detail with reference to examples, but the practice of the present invention is not limited thereto.

Example 1

Firstly, adding 90g of N, N-dimethylformamide, 30g of ethyl acrylate and 32.75g of 3-isooctyl mercaptopropionate into a reactor, stirring and heating to 60 ℃, then dropwise adding a mixed solution of 5.96g of azodiisoheptanonitrile and 8.94g of N, N-dimethylformamide for 10 hours, and continuing to react at the constant temperature of 60 ℃ for 5 hours after the dropwise addition is finished to obtain a self-polymerization product of a polyethylacrylate solution; adjusting the temperature of the obtained self-polymerization product to 60 ℃, adding 24.29g of tert-dodecyl mercaptan, stirring for 35 minutes until the self-polymerization product is uniformly mixed, dropwise adding a mixed solution of 377.31g of dimethylaminoethyl methacrylate, 29.80g of azobisisoheptonitrile and 44.71g of N, N-dimethylformamide for 10 hours, continuing reacting at the constant temperature of 60 ℃ for 5 hours after the dropwise adding is finished, and then carrying out reduced pressure distillation to remove the N, N-dimethylformamide to obtain a graft copolymerization product; 407.31g of graft copolymerization product is mixed with 43.20g of deionized water, stirred and heated to 40 ℃, 0.40g of potassium hydroxide is added, hydrolysis is carried out for 120 minutes, then reduced pressure distillation is carried out to remove hydrosolvent and by-product, 271.54g of solvent water is added after drying, and pH response type polycarboxylic acid solution with the concentration of 60 percent by mass is obtained.

Example 2

Firstly, adding 30g of tetrahydrofuran, 30g of methyl acrylate and 12.54g of isopropanol into a reactor, stirring and heating to 50 ℃, then dropwise adding a mixed solution of 2.86g of azobisisobutyronitrile and 2.86g of tetrahydrofuran for 12 hours, and continuously reacting at the constant temperature of 50 ℃ for 6 hours after dropwise adding to obtain a self-polymerization product, namely a polymethyl acrylate solution; regulating the temperature of the obtained self-polymerization product to 50 ℃, adding 35.22g of n-dodecyl mercaptan, stirring for 40 minutes until the mixture is uniformly mixed, dropwise adding a mixed solution of 498.27g of dimethylaminoethyl acrylate, 28.57g of azobisisobutyronitrile and 28.57g of tetrahydrofuran for 12 hours, continuing to react at the constant temperature of 50 ℃ for 6 hours after the dropwise adding is finished, and then carrying out reduced pressure distillation to remove the tetrahydrofuran to obtain a graft copolymerization product; 528.27g of graft copolymerization product is mixed with 62.64g of deionized water, stirred and heated to 30 ℃, 0.14g of sodium hydroxide is added, hydrolysis is carried out for 150 minutes, then reduced pressure distillation is carried out to remove hydrosolvent and by-product, 352.18g of solvent water is added after drying, and pH response type polycarboxylic acid solution with the concentration of 60 percent by mass is obtained.

Example 3

Firstly, adding 270g of dimethyl sulfoxide, 30g of amyl acrylate and 1.27g of isopropanol into a reactor, stirring and heating to 70 ℃, then dropwise adding a mixed solution of 6.56g of tert-butyl peroxybenzoate and 59.02g of dimethyl sulfoxide for 8 hours, and continuing to react at constant temperature of 70 ℃ for 4 hours after dropwise adding is finished to obtain a self-polymerization product of a amyl polyacrylate solution; regulating the temperature of the obtained self-polymerization product to 80 ℃, adding 32.03g of n-dodecyl mercaptan, stirring for 25 minutes until the n-dodecyl mercaptan and the n-dodecyl mercaptan are uniformly mixed, then dropwise adding a mixed solution of 66.55g of 4-vinyl pyridine, 19.67g of tert-butyl peroxybenzoate and 177.04g of dimethyl sulfoxide for 6 hours, continuing to react at the constant temperature of 80 ℃ for 3 hours after the dropwise adding is finished, and then carrying out reduced pressure distillation to remove the dimethyl sulfoxide to obtain a graft copolymerization product; mixing 96.55g of graft copolymerization product with deionized water, stirring, heating to 60 ℃, adding 0.38g of sodium hydroxide, hydrolyzing for 60 minutes, then carrying out reduced pressure distillation to remove a water solvent and a byproduct, drying, and adding 144.83g of solvent water to obtain a pH response type polycarboxylic acid solution with the mass percentage concentration of 40%.

Example 4

Firstly, 210g of sulfolane, 30g of butyl acrylate and 6.47g of 3-mercaptopropanol are added into a reactor, stirred and heated to 110 ℃, then a mixed solution of 2.53g of tert-butyl hydroperoxide and 10.13g of sulfolane is dripped for 3 hours, and after the dripping is finished, the reaction is continued for 2 hours at a constant temperature of 110 ℃ to obtain a self-polymerization product of a polybutyl acrylate solution; adjusting the temperature of the obtained self-polymerization product to 90 ℃, adding 24.85g of 3-mercaptopropionic acid, stirring for 20 minutes until the self-polymerization product is uniformly mixed, dropwise adding a mixed solution of 123.07g of 2-vinylpyridine, 12.66g of tert-butyl hydroperoxide and 50.63g of sulfolane for 3 hours, continuing to react at the constant temperature of 90 ℃ for 2 hours after the dropwise adding is finished, and then carrying out reduced pressure distillation to remove the sulfolane to obtain a graft copolymerization product; 153.07g of graft copolymerization product is mixed with 21.07g of deionized water, stirred and heated to 70 ℃, 0.66g of potassium hydroxide is added, hydrolysis is carried out for 30 minutes, then reduced pressure distillation is carried out to remove hydrosolvent and by-product, and 153.07g of solvent water is added after drying, thus obtaining 50% mass percent concentration pH response type polycarboxylic acid solution.

Example 5

Firstly, adding 360g of tetrahydrofuran, 30g of methyl acrylate and 3.81g of 3-isooctyl mercaptopropionate into a reactor, stirring and heating to 120 ℃, then dropwise adding a mixed solution of 10.19g of di-tert-butyl peroxide and 193.65g of tetrahydrofuran for 1 hour, and continuing to react at constant temperature of 120 ℃ for 1 hour after dropwise adding is finished to obtain a self-polymerization product, namely a polymethyl acrylate solution; adjusting the temperature of the obtained self-polymerization product to 100 ℃, adding 42.32g of tert-dodecyl mercaptan, stirring for 15 minutes until the self-polymerization product is uniformly mixed, dropwise adding a mixed solution of 88.65g of N, N-diethyl-2-acrylamide, 20.39g of di-tert-butyl peroxide and 387.31g of tetrahydrofuran for 1 hour, continuing to react at the constant temperature of 100 ℃ for 1 hour after the dropwise adding is finished, and then carrying out reduced pressure distillation to remove tetrahydrofuran to obtain a graft copolymerization product; 118.65g of graft copolymerization product is mixed with 6.27g of deionized water, stirred and heated to 80 ℃, 0.39g of potassium hydroxide is added, hydrolysis is carried out for 10 minutes, then reduced pressure distillation is carried out to remove hydrosolvent and by-product, and 177.97g of solvent water is added after drying, thus obtaining pH response type polycarboxylic acid solution with 40 percent of mass percentage concentration.

Example 6

Firstly, adding 150g of aniline, 30g of propyl acrylate and 8.21g of 2-mercaptoethanol into a reactor, stirring and heating to 90 ℃, then dropwise adding a mixed solution of 6.37g of dibenzoyl peroxide and 14.85g of aniline for 6 hours, and continuously reacting at the constant temperature of 90 ℃ for 3 hours after dropwise adding is finished to obtain a self-polymerization product of a polypropylene acrylate solution; adjusting the temperature of the obtained self-polymerization product to 70 ℃, adding 25.42g of thioglycolic acid, stirring for 30 minutes until the self-polymerization product is uniformly mixed, dropwise adding a mixed solution of 340.80g of diethylaminoethyl methacrylate, 44.56g of dibenzoyl peroxide and 103.98g of aniline for 8 hours, continuing to react at the constant temperature of 70 ℃ for 4 hours after the dropwise adding is finished, and then carrying out reduced pressure distillation to remove aniline to obtain a graft copolymerization product; 370.80g of graft copolymerization product is mixed with 33.11g of deionized water, stirred and heated to 50 ℃, 0.37g of sodium hydroxide is added, hydrolysis is carried out for 90 minutes, then reduced pressure distillation is carried out to remove hydrosolvent and by-product, and 370.80g of solvent water is added after drying, thus obtaining 50% mass percent concentration pH response type polycarboxylic acid solution.

Shrinkage reducing effect of cement mortar

The material mixing proportion of the cement mortar is as follows: 647kg/m³1293kg/m of cement³Sand with a particle size of 0-2mm and 453kg/m³Water, water reducing agent (folding and fixing amount) with the cement amount of 0.75 percent is added, and the folding and fixing amount of the pH response type polycarboxylic acid solution synthesized by the invention is 0.3 percent of the cement amount. The comparative example used was cement mortar to which no pH-responsive polycarboxylic acid was added, and the proportions of the remaining components were unchanged. The results of the mortar shrinkage tests are shown in Table 1. TABLE 1

Polymer and method of making same	The blending amount is%	1d[mm/m]	7d[mm/m]	14d[mm/m]	28d[mm/m]
						Example 1	0.3	-0.03	-0.20	-0.37	-0.51
Example 2	0.3	-0.13	-0.42	-0.56	-0.70
						Example 3	0.3	-0.06	-0.35	-0.40	-0.62
Example 4	0.3	-0.05	-0.23	-0.39	-0.60
						Example 5	0.3	-0.10	-0.41	-0.52	-0.66
Example 6	0.3	-0.07	-0.37	-0.43	-0.64
						Comparative example	0	-0.16	-0.45	-0.69	-1.00

As can be seen from Table 1, the pH-responsive polycarboxylic acid synthesized by the embodiment of the invention has good shrinkage reduction effect on cement mortar, and the shrinkage reduction principle is based on the action of the pH-responsive polymer block on the macromolecular side chain, which is one of the most remarkable characteristics different from other concrete shrinkage reducers. From the perspective of shrinkage performance, the polymer synthesized by the embodiment of the invention can effectively reduce the drying shrinkage of concrete, and the shrinkage of 1d, 7d, 14d and 28d is better than that of the comparative example.

Claims

1. A preparation method of a pH response type comb-shaped structure polycarboxylic acid material is characterized in that the polycarboxylic acid material is synthesized by a method of self-polymerization, grafting and hydrolysis, and the specific conditions and steps are as follows:

(3) and (3) hydrolysis reaction: mixing the graft copolymerization product in the step (2) with deionized water, stirring, heating to 30-80 ℃, adding inorganic base, hydrolyzing for 10-150 minutes, then carrying out reduced pressure distillation to remove a water solvent and a byproduct, drying, and adding solvent water to obtain a pH response type polycarboxylic acid solution with the required concentration;

wherein the organic solvent used in the self-polymerization reaction in the step (1) is tetrahydrofuran, N-dimethylformamide, aniline, sulfolane or dimethyl sulfoxide, and the mass ratio of the dosage to the acrylate is 1-12: 1; the acrylate in the step (1) is methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate or amyl acrylate; the chain transfer agent in the step (1) is isopropanol, isooctyl 3-mercaptopropionate, 2-mercaptoethanol or 3-mercaptopropanol, and the molar ratio of the dosage to the acrylate is 0.05-0.6: 1; the initiator in the step (1) is azobisisobutyronitrile, azobisisoheptonitrile, dibenzoyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate or di-tert-butyl peroxide, and the molar ratio of the dosage to the acrylate is 0.05-0.2: 1; in the mixed solution of the initiator and the organic solvent in the step (1), the organic solvent is tetrahydrofuran, N-dimethylformamide, aniline, sulfolane or dimethyl sulfoxide, and the mass fraction of the initiator in the mixed solution is 5-50%;

the molecular weight regulator used in the graft copolymerization reaction in the step (2) is n-dodecyl mercaptan, tert-dodecyl mercaptan, thioglycolic acid or 3-mercaptopropionic acid, and the molar ratio of the dosage to the pH response type monomer is 0.05-0.3: 1; the pH response type monomer in the step (2) is dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, 2-vinylpyridine or 4-vinylpyridine, and the molar ratio of the dosage to the acrylate in the step (1) is 2-10: 1; the initiator in the step (2) is azobisisobutyronitrile, azobisisoheptonitrile, dibenzoyl peroxide, tert-butyl hydroperoxide, tert-butyl peroxybenzoate or di-tert-butyl peroxide, and the molar ratio of the dosage to the pH response type monomer is 0.05-0.2: 1; in the mixed solution of the initiator and the organic solvent in the step (2), the organic solvent is tetrahydrofuran, N-dimethylformamide, aniline, sulfolane or dimethyl sulfoxide, and the mass fraction of the initiator in the mixed solution is 5-50%;

the molar ratio of the use amount of deionized water used in the hydrolysis reaction in the step (3) to the acrylic ester in the step (1) is 1-10: 1; the inorganic alkali in the step (3) is sodium hydroxide or potassium hydroxide, and the molar ratio of the usage amount to the deionized water is 0.001-0.02: 1.