Polyvinyl acetate aqueous dispersion with self-stabilizing structure and preparation method of polyvinyl acetate aqueous dispersion

Abstract

The invention provides a polyvinyl acetate aqueous dispersion with a self-stabilizing structure and a preparation method of the polyvinyl acetate aqueous dispersion. The polyvinyl acetate aqueous dispersion is prepared from a vinyl acetate monomer and at least one hydrophilic anchoring monomer through a free radical polymerization reaction, wherein the hydrophilic anchoring monomer is embedded into a polyvinyl acetate molecular chain in a polymerization process, so that an obtained polymer molecule forms a self-stabilization dispersion structure with a hydrophilic interface layer in a water phase. A hydrophilic anchoring structure unit is introduced into a polyvinyl acetate molecular chain to form a core-shell type particle structure with a core formed by a hydrophobic polyvinyl acetate chain segment and an outer layer interface formed by a hydrophilic anchoring monomer, so that polymer molecules can spontaneously form a stable dispersion structure in a water phase; the problem that polyvinyl acetate is easy to agglomerate in a water phase is solved from the molecular structure level, so that the polyvinyl acetate aqueous dispersion with uniform particle size and good storage stability is obtained under the condition that no or only a small amount of surfactant is needed.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a polyvinyl acetate aqueous dispersion with a self-stabilizing structure and its preparation method. Background Technology

[0002] Polyvinyl acetate (PVAc) is an important polymer material with advantages such as good film-forming properties, excellent adhesion, and low cost, and is widely used in adhesives, architectural coatings, and packaging materials. Due to the strong hydrophobicity of the PVAc backbone, its dispersion stability in aqueous phase is poor. Therefore, in industry, PVAc aqueous dispersions are usually prepared by emulsion polymerization.

[0003] In existing preparation processes, the stability of polyvinyl acetate aqueous dispersions mainly depends on the added surfactant system, especially anionic, nonionic, or a combination of both, which inhibit particle agglomeration by forming an adsorption layer on the polymer particle surface. For example, published literature commonly uses surfactants such as dodecyl sulfate and fatty alcohol polyoxyethylene ethers, and controls the particle size and storage stability of the dispersion by adjusting their dosage, ratio, and polymerization conditions.

[0004] However, the above technical approach has the following shortcomings: 1. The dispersion stability depends entirely on the added surfactant, which is a typical physical stabilization mechanism. Once the surfactant migrates, precipitates, or becomes ineffective, the dispersion is prone to sedimentation or aggregation. 2. The presence of surfactants can easily affect film-forming properties, water resistance, and the mechanical properties of the final product, and their use is limited in some application scenarios; 3. Existing technologies mainly focus on the selection of surfactant types and optimization of formulations, without fundamentally improving the impact of polymer molecular structure itself on the stability of the aqueous phase.

[0005] Therefore, there is an urgent need to provide a new process for preparing polyvinyl acetate aqueous dispersions, which can endow them with self-stabilizing ability in the aqueous phase at the level of polymer molecular structure, so as to overcome the shortcomings of existing technologies. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a polyvinyl acetate aqueous dispersion with a self-stabilizing structure. By introducing hydrophilic anchoring structural units into the polyvinyl acetate molecular chain, the polymer itself forms a stable dispersion structure in the aqueous phase. This allows for the production of a polyvinyl acetate aqueous dispersion with uniform particle size and good storage stability without or with only a small amount of surfactant. This addresses the problem in the prior art where the dispersion stability of polyvinyl acetate aqueous dispersions depends on the addition of external surfactants, and the presence of surfactants limits the final performance of the product. Furthermore, this invention also provides a method for preparing this polyvinyl acetate aqueous dispersion with a self-stabilizing structure.

[0007] To achieve the above and other related objectives, the present invention provides the following technical solutions: In a first aspect, the present invention provides a polyvinyl acetate aqueous dispersion having a self-stabilizing structure, the polyvinyl acetate aqueous dispersion being prepared by free radical polymerization of a vinyl acetate monomer and at least one hydrophilic anchoring monomer; In this process, the hydrophilic anchoring monomer is embedded into the polyvinyl acetate molecular chain, causing the resulting polymer molecules to form a self-stabilizing dispersion structure with a hydrophilic interface layer in the aqueous phase. This self-stabilizing dispersion structure is a core-shell microparticle structure with hydrophobic polyvinyl acetate segments forming the core and hydrophilic anchoring monomers forming the outer interface. This self-stabilizing structural feature allows the polyvinyl acetate aqueous dispersion to maintain a stable dispersion state under conditions containing no surfactant or only a small amount of surfactant.

[0008] Furthermore, the hydrophilic anchoring monomer is selected from one or more of the following: vinyl monomers containing hydroxyl groups, vinyl monomers containing carboxyl groups or hydrolyzable ester groups, and vinyl monomers containing amide groups.

[0009] Furthermore, the hydroxyl-containing vinyl monomer is selected from at least one of hydroxyethyl methacrylate (HEMA), hydroxyethyl acrylate (HEA), hydroxypropyl acrylate (HPA), hydroxypropyl methacrylate (HPMA), and vinyl alcohol monomers; preferably hydroxyethyl methacrylate (HEMA) or hydroxypropyl methacrylate (HPMA). These monomers provide hydrophilic anchoring sites for hydroxyl groups in the polymer chain, enhancing the interaction between the polymer and the aqueous phase through hydrogen bonding.

[0010] The vinyl monomer containing a carboxyl group or a hydrolyzable ester group is selected from at least one of acrylic acid (AA), methacrylic acid (MAA), maleic acid (maleic acid), methyl acrylate (MA), ethyl acrylate (EA), and methyl methacrylate (MMA); preferably acrylic acid (AA) or methacrylic acid (MAA). These monomers can form carboxyl or potential carboxyl structures in the aqueous phase, enhancing dispersion stability through electrochemical interactions and hydrogen bonding.

[0011] The amide-containing vinyl monomer is selected from at least one of acrylamide (AM), methacrylamide (MAM), N-hydroxymethylacrylamide (NMA), N,N-dimethylacrylamide (DMAM), and vinylpyrrolidone (NVP); preferably acrylamide (AM) or vinylpyrrolidone (NVP). This type of monomer introduces a highly polar amide group into the polymer chain, significantly improving aqueous phase stability through multi-point hydrogen bonding.

[0012] Furthermore, the amount of the hydrophilic anchoring monomer added is 0.5% to 10% of the molar amount of vinyl acetate monomer.

[0013] Furthermore, the polyvinyl acetate aqueous dispersion contains less than 0.5% surfactant by mass, or contains no surfactant.

[0014] Furthermore, the average particle size of the polyvinyl acetate aqueous dispersion is 100~400 nm, and the solid content is 20%~35%.

[0015] A second aspect of the present invention provides a method for preparing a polyvinyl acetate aqueous dispersion having a self-stabilizing structure, comprising the following steps: Vinyl acetate monomer and hydrophilic anchoring monomer are added to an aqueous system, and an initiator is added under stirring conditions to carry out a free radical polymerization reaction, so that the hydrophilic anchoring monomer is embedded in the polyvinyl acetate molecular chain. After the reaction is completed, a polyvinyl acetate aqueous dispersion with a self-stabilizing structure is obtained.

[0016] Furthermore, the free radical polymerization reaction is carried out at a temperature of 60-80°C for 1-5 hours.

[0017] Furthermore, the initiator is selected from at least one of persulfate initiators and water-soluble azo initiators.

[0018] The persulfate initiator is selected from at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; The water-soluble azo initiator is selected from at least one of 2,2'-azo(2-methylpropylamidine) dihydrochloride (AIBA) and 2,2′-azobis(2-methylpropionamide) dihydrochloride (VA-044).

[0019] Furthermore, the aqueous system contains a small amount of surfactant or contains no surfactant, wherein the surfactant is selected from anionic surfactants and / or nonionic surfactants.

[0020] The anionic surfactant is selected from at least one of sodium dodecyl sulfonate, sodium benzene sulfonate, sodium laurate, sodium sorbate, and sodium alkyl sulfonate. The nonionic surfactant is selected from at least one of octylphenol polyoxyethylene ether, Tween, nonylphenol polyoxyethylene ether, and fatty alcohol polyoxyethylene ether.

[0021] When a small amount of surfactant is added to the aqueous system, the surfactant accounts for 0 to 0.5% of the total mass of the polyvinyl acetate aqueous dispersion; preferably 0.05 to 0.25%.

[0022] A third aspect of the present invention provides the use of a polyvinyl acetate aqueous dispersion having a self-stabilizing structure in adhesives, coatings, paper sizing or functional coating materials.

[0023] As described above, the polyvinyl acetate aqueous dispersion with a self-stabilizing structure and its preparation method of the present invention have the following beneficial effects: This invention introduces hydrophilic anchoring structural units into the polyvinyl acetate (PVC) molecular chain, forming a core-shell microparticle structure with hydrophobic PVC segments forming the core and hydrophilic anchoring monomers forming the outer interface. This allows the polymer molecules to spontaneously form a stable dispersion structure in the aqueous phase, solving the problem of PVC's tendency to aggregate in aqueous phase at the molecular structure level. It also changes the traditional approach of relying on added surfactants for stability, thus reducing or eliminating the need for surfactants. The resulting PVC aqueous dispersion is less prone to sedimentation or stratification during storage, exhibiting excellent long-term stability. Simultaneously, it reduces or avoids the adverse effects of surfactants on film-forming properties and the final product performance, making it suitable for continuous industrial production and various applications. Detailed Implementation

[0024] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0025] A self-stabilizing polyvinyl acetate aqueous dispersion, wherein the polyvinyl acetate aqueous dispersion is prepared by free radical polymerization of a vinyl acetate monomer and at least one hydrophilic anchoring monomer; In this process, the hydrophilic anchoring monomer is embedded into the polyvinyl acetate molecular chain, forming a core-shell microparticle structure with hydrophobic polyvinyl acetate segments forming the core and the hydrophilic anchoring monomer forming the outer interface. This results in a self-stabilizing dispersion structure with a hydrophilic interface layer in the aqueous phase. This self-stabilizing structural feature allows the polyvinyl acetate aqueous dispersion to maintain a stable dispersion state even when it contains no surfactant or only a small amount of surfactant. The mass fraction of surfactant is less than 0.5%, or there is no surfactant present.

[0026] The hydrophilic anchoring monomer is selected from one or more of hydroxyl-containing vinyl monomers, carboxyl-containing or hydrolyzable ester-containing vinyl monomers, and amide-containing vinyl monomers; the hydroxyl-containing vinyl monomer is selected from at least one of hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and vinyl alcohol monomers; the carboxyl-containing or hydrolyzable ester-containing vinyl monomer is selected from at least one of acrylic acid, methacrylic acid, maleic acid, methyl acrylate, ethyl acrylate, and methyl methacrylate; the amide-containing vinyl monomer is selected from at least one of acrylamide, methacrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, and vinylpyrrolidone. The amount of the hydrophilic anchoring monomer added is 0.5% to 10% of the molar amount of vinyl acetate monomer.

[0027] The method for preparing the polyvinyl acetate aqueous dispersion includes the following steps: adding vinyl acetate monomer and hydrophilic anchoring monomer to an aqueous system; adding an initiator under stirring conditions to carry out a free radical polymerization reaction; the reaction temperature of the free radical polymerization reaction is 60-80℃, and the reaction time is 1-5h, so that the hydrophilic anchoring monomer is embedded in the polyvinyl acetate molecular chain; after the reaction, a polyvinyl acetate aqueous dispersion with a self-stabilizing structure is obtained. The average particle size of the obtained polyvinyl acetate aqueous dispersion is 100-400 nm, and the solid content is 20%-35%.

[0028] The initiator is selected from at least one of persulfate initiators and water-soluble azo initiators; the persulfate initiator is selected from at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; the water-soluble azo initiator is selected from at least one of 2,2'-azo(2-methylpropylamidine) dihydrochloride and 2,2′-azobis(2-methylpropionamide) disalt.

[0029] The aqueous phase system contains a small amount of surfactant or contains no surfactant. When a small amount of surfactant is added to the aqueous phase system, the surfactant accounts for 0 to 0.5% of the total mass of the polyvinyl acetate aqueous dispersion; preferably 0.05 to 0.25%.

[0030] Example 1 This embodiment provides a polyvinyl acetate aqueous dispersion with a self-stabilizing structure, which is prepared by free radical polymerization of vinyl acetate monomer and a hydroxyl-containing vinyl hydrophilic anchoring monomer. The preparation method specifically includes the following steps: 200g of deionized water and 0.4g of nonionic surfactant (fatty alcohol polyoxyethylene ether) were added to the reactor and dissolved completely. The system was then heated to 70°C. Under stirring, 80g of vinyl acetate monomer and 2g of hydroxyl-containing vinyl hydrophilic anchoring monomer (hydroxyethyl methacrylate) were added dropwise. The reaction temperature was maintained, and 0.6g of ammonium persulfate was added as an initiator. The reaction was carried out at this temperature for 4 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain a milky white, homogeneous aqueous dispersion of polyvinyl acetate.

[0031] The polyvinyl acetate aqueous dispersion prepared in Example 1 was tested, and the results are as follows: Average particle size: approximately 180 nm; Particle size distribution index (PDI): 0.21; Solid content: Approximately 30%; After standing at room temperature (25℃) for 60 days, the system remained homogeneous with no obvious sedimentation or stratification. Centrifugal stability test (3000 rpm, 30 min): No obvious flocculation or deposition was observed in the system; Thermal cycling stability test (-5℃~40℃, 3 cycles): No significant change in the appearance of the dispersion.

[0032] The test results show that by introducing hydroxyl-containing hydrophilic anchoring structural units into the polyvinyl acetate molecular chain, a stable self-dispersing system can be formed in the aqueous phase.

[0033] Example 2 This embodiment provides a self-stabilizing polyvinyl acetate aqueous dispersion and its preparation method. The only difference from Example 1 is that no surfactant is added to the reaction system. After the reaction, a polyvinyl acetate aqueous dispersion that can remain stable without surfactant is obtained.

[0034] The polyvinyl acetate aqueous dispersion prepared in Example 2 was tested, and the results are as follows: Average particle size: approximately 260 nm; Particle size distribution index (PDI): 0.28; Solid content: Approximately 25%; After standing at room temperature (25℃) for 60 days, the system showed no obvious sedimentation or stratification. Centrifugal stability test (3000 rpm, 30 min): The system remained generally dispersed, with only slight increase in particle size. Thermal cycling stability test (-5℃~40℃, 3 cycles): No demulsification occurred in the system.

[0035] The test results show that even without the addition of any surfactant, the present invention can still maintain the stable dispersion of polyvinyl acetate in the aqueous phase through the hydrophilic anchoring structure embedded in the molecular chain, thus verifying the effectiveness of the self-stabilizing structure.

[0036] Example 3 This embodiment provides a polyvinyl acetate aqueous dispersion with a self-stabilizing structure, which is prepared by free radical polymerization of vinyl acetate monomer and an amide-containing vinyl hydrophilic anchoring monomer. The preparation method specifically includes the following steps: 210g of deionized water and 0.45g of nonionic surfactant (fatty alcohol polyoxyethylene ether) were added to the reactor. After complete dissolution, the system was heated to 75°C. Under stirring, 78g of vinyl acetate monomer and 3g of amide-containing vinyl hydrophilic anchoring monomer (vinylpyrrolidone) were added dropwise. The reaction temperature was maintained, and 0.65g of potassium persulfate was added as an initiator. The free radical polymerization reaction was carried out at this temperature for 3 hours. After the reaction was completed, the mixture was cooled to obtain a homogeneous and stable aqueous dispersion of polyvinyl acetate.

[0037] The polyvinyl acetate aqueous dispersion prepared in Example 3 was tested, and the results are as follows: Average particle size: approximately 220 nm; Particle size distribution index (PDI): 0.24; Solid content: approximately 27%; After standing at room temperature (25℃) for 60 days, the system showed no obvious sedimentation and remained stable with slight opalescence. Centrifugal stability test (3000 rpm, 30 min): The system remained dispersed with no obvious particle aggregation; Thermal cycling stability test (-5℃~40℃, 3 cycles): No demulsification or significant particle size increase was observed.

[0038] The test results show that the introduction of hydrophilic anchoring monomers containing amide groups can further enhance the interaction between polymer molecules and the aqueous phase, and improve the storage stability of the dispersion.

[0039] Example 4 This embodiment provides a polyvinyl acetate aqueous dispersion with a self-stabilizing structure, which is prepared by free radical polymerization of vinyl acetate monomer and a carboxyl-containing vinyl hydrophilic anchoring monomer. The preparation method specifically includes the following steps: 220g of deionized water and 0.3g of nonionic surfactant (fatty alcohol polyoxyethylene ether) were added to the reactor. After complete dissolution, the system was heated to 72°C. Under stirring, 75g of vinyl acetate monomer and 3g of carboxyl-containing vinyl hydrophilic anchoring monomer (methacrylic acid) were added dropwise. While maintaining the reaction temperature, 0.6g of ammonium persulfate was added as an initiator, and the free radical polymerization reaction was carried out at this temperature for 3.5h. After the reaction was completed, the mixture was cooled to obtain a homogeneous and stable aqueous dispersion of polyvinyl acetate.

[0040] The polyvinyl acetate aqueous dispersion prepared in Example 4 was tested, and the results are as follows: Average particle size: approximately 160 nm; Particle size distribution index (PDI): 0.18; Solid content: approximately 32%; After standing at room temperature (25℃) for 60 days, there was no obvious sedimentation or stratification. Centrifugation stability test (3000 rpm, 30 min): No obvious aggregation or precipitation was observed; Thermal cycling stability test (-5℃~40℃, 3 cycles): No demulsification or significant particle size increase was observed.

[0041] The test results show that by introducing carboxyl-containing hydrophilic anchoring structural units into the polyvinyl acetate molecular chain, a stable self-dispersing structure can be formed in the aqueous phase, which significantly improves the storage stability of the dispersion system.

[0042] Example 5 This embodiment provides a polyvinyl acetate aqueous dispersion with a self-stabilizing structure, which is prepared by free radical polymerization of vinyl acetate monomer, hydroxyl-containing vinyl hydrophilic anchoring monomer, and amide-containing vinyl hydrophilic anchoring monomer. The preparation method specifically includes the following steps: 240 g of deionized water was added to the reactor. Under stirring, 70 g of vinyl acetate monomer, 1.5 g of a hydroxyl-containing vinyl hydrophilic anchoring monomer (hydroxypropyl methacrylate), and 2.5 g of an amide-containing vinyl hydrophilic anchoring monomer (acrylamide) were added dropwise. The system was heated to 65 °C, and 0.5 g of a water-soluble azo initiator (VA-044) was added. Free radical polymerization was carried out at this temperature for 4 hours. After the reaction was completed and cooled, a polyvinyl acetate aqueous dispersion with further enhanced self-stabilizing ability was obtained.

[0043] The polyvinyl acetate aqueous dispersion prepared in Example 5 was tested, and the results are as follows: Average particle size: approximately 210 nm; Particle size distribution index (PDI): 0.22; Solid content: Approximately 28%; After standing at room temperature (25℃) for 90 days, the system remained homogeneous with no visible sedimentation. Thermal cycling stability test (-5℃~40℃, 5 cycles): The system did not show demulsification or significant particle size increase.

[0044] The test results show that the polyvinyl acetate aqueous dispersion obtained by synergistic introduction of composite hydrophilic anchoring monomers still maintains good dispersion stability under different environmental conditions, further verifying the universality of the self-stabilizing structure design of the present invention.

[0045] In summary, this invention introduces hydrophilic anchoring structural units into the polyvinyl acetate (PVC) molecular chain, forming a core-shell microparticle structure with hydrophobic PVC segments forming the core and hydrophilic anchoring monomers forming the outer interface. This allows the polymer molecules to spontaneously form a stable dispersion structure in the aqueous phase, solving the problem of PVC's tendency to aggregate in aqueous phase at the molecular structure level. Therefore, a PVC aqueous dispersion with uniform particle size and good storage stability can be obtained with little or no surfactant. Thus, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial application value.

[0046] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A polyvinyl acetate aqueous dispersion with a self-stabilizing structure, characterized in that, The polyvinyl acetate aqueous dispersion is prepared by free radical polymerization of vinyl acetate monomer and at least one hydrophilic anchoring monomer. In this process, the hydrophilic anchoring monomer is embedded in the polyvinyl acetate molecular chain, so that the resulting polymer molecules form a self-stabilizing dispersion structure with a hydrophilic interface layer in the aqueous phase.

2. The polyvinyl acetate aqueous dispersion with a self-stabilizing structure according to claim 1, characterized in that, The hydrophilic anchoring monomer is selected from one or more of the following: vinyl monomers containing hydroxyl groups, vinyl monomers containing carboxyl groups or hydrolyzable ester groups, and vinyl monomers containing amide groups.

3. The polyvinyl acetate aqueous dispersion with a self-stabilizing structure according to claim 2, characterized in that, The hydroxyl-containing vinyl monomer is selected from at least one of hydroxyethyl methacrylate, hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and vinyl alcohol monomers; the carboxyl-containing or hydrolyzable ester-containing vinyl monomer is selected from at least one of acrylic acid, methacrylic acid, maleic acid, methyl acrylate, ethyl acrylate, and methyl methacrylate; the amide-containing vinyl monomer is selected from at least one of acrylamide, methacrylamide, N-hydroxymethylacrylamide, N,N-dimethylacrylamide, and vinylpyrrolidone.

4. The polyvinyl acetate aqueous dispersion with a self-stabilizing structure according to claim 1, characterized in that, The amount of the hydrophilic anchoring monomer added is 0.5% to 10% of the molar amount of vinyl acetate monomer.

5. The polyvinyl acetate aqueous dispersion with a self-stabilizing structure according to claim 1, characterized in that, The polyvinyl acetate aqueous dispersion contains less than 0.5% surfactant by mass, or contains no surfactant.

6. The polyvinyl acetate aqueous dispersion with a self-stabilizing structure according to claim 1, characterized in that, The average particle size of the polyvinyl acetate aqueous dispersion is 100~400 nm, and the solid content is 20%~35%.

7. A method for preparing a polyvinyl acetate aqueous dispersion with a self-stabilizing structure, characterized in that, The process includes the following steps: adding vinyl acetate monomer and hydrophilic anchoring monomer to an aqueous system, adding an initiator under stirring conditions to carry out a free radical polymerization reaction, so that the hydrophilic anchoring monomer is embedded in the polyvinyl acetate molecular chain, and after the reaction is completed, a polyvinyl acetate aqueous dispersion with a self-stabilizing structure is obtained.

8. The preparation method according to claim 7, characterized in that, The free radical polymerization reaction is carried out at a temperature of 60-80°C for 1-5 hours.

9. The preparation method according to claim 7, characterized in that, The initiator is selected from at least one of persulfate initiators and water-soluble azo initiators; the persulfate initiator is selected from at least one of ammonium persulfate, potassium persulfate, and sodium persulfate; the water-soluble azo initiator is selected from at least one of 2,2'-azo(2-methylpropylamidine) dihydrochloride and 2,2′-azobis(2-methylpropionamide) disalt.

10. The preparation method according to claim 7, characterized in that, The aqueous phase system contains a small amount of surfactant or contains no surfactant, wherein the surfactant is selected from anionic surfactants and / or nonionic surfactants; when a small amount of surfactant is added to the aqueous phase system, the surfactant accounts for 0.05 to 0.25% of the total mass of the polyvinyl acetate aqueous dispersion.