Composite polymerization-inhibiting regulated all-aqueous poly(vinyl butyral) solution and preparation method thereof

Abstract

The application relates to the technical field of high polymer material synthesis, and discloses a composite polymerization inhibition and regulation type full-water polyvinyl butyral solution and a preparation method thereof, which is prepared from raw materials such as polyvinyl alcohol, deionized water, a metal complex anchoring agent, an interface polymerization inhibitor, a grafting monomer, a chain transfer agent, an initiator and an acetalization reagent. The preparation method comprises the following steps: constructing redox active sites in polyvinyl alcohol segments by using the metal complex anchoring agent; constructing a water phase polymerization inhibition environment by using the interface polymerization inhibitor; synchronously adding the grafting monomer and the initiator to carry out grafting polymerization; and finally, preparing by a variable-temperature acetalization reaction. Through the synergistic effect of metal coordination orientation and interface polymerization inhibition effect, the application realizes the kinetic control of the grafting reaction, and effectively inhibits the homopolymerization of the grafting monomer. The introduced hydrophilic side chain is affected by electrostatic repulsion and a hydration layer, and under the condition of no organic solvent, the full-water polyvinyl butyral solution with high acetalization degree and uniform stability is prepared.

Description

Technical Field

[0001] This invention relates to the field of polymer material synthesis technology, and in particular to an all-aqueous polyvinyl butyral solution with composite polymerization inhibition control and its preparation method. Background Technology

[0002] Polyvinyl butyral (PVB) resin is widely used in safety glass interlayers, metal anti-corrosion coatings, and ink adhesives due to its excellent film-forming properties, adhesion, transparency, and impact resistance. Traditional PVB resin synthesis and applications mainly rely on alcohol, ester, or benzene-based organic solvent systems. With increasingly stringent environmental regulations and restrictions on volatile organic compound (VOC) emissions, developing all-waterborne PVB systems free of volatile organic solvents has become a key focus for the industry.

[0003] The main approaches to achieving water-based polyvinyl butyral include physical emulsification and chemical modification. Physical emulsification typically requires a large amount of emulsifier, resulting in emulsions with relatively large particle sizes. The water resistance and mechanical strength of the resulting film are often affected by residual emulsifier. Chemical modification primarily involves grafting ionic hydrophilic monomers onto the polyvinyl alcohol backbone, utilizing the electrostatic repulsion and hydration of the ionic groups to achieve the resin's water solubility. Among these methods, direct graft copolymerization in an aqueous phase followed by acetalization is an economical and environmentally friendly process for preparing fully water-based polyvinyl butyral.

[0004] However, grafting modification of polyvinyl alcohol (PVA) in an aqueous system faces challenges in controlling reaction kinetics. Because water, as a continuous phase, provides a homogeneous reaction medium, free radicals generated by the initiator diffuse randomly within the aqueous phase. When grafting monomers (such as vinyl monomers containing sulfonic acid groups) coexist with the initiator, the homopolymerization rate of the monomers in the aqueous bulk is often higher than their grafting rate onto the PVA molecular chain. This competitive reaction leads to a large amount of monomers being converted into free homopolymers, failing to effectively attach to the PVA backbone, thus significantly reducing grafting efficiency.

[0005] Insufficient grafting efficiency directly affects the subsequent acetalization process and product properties. Due to the lack of sufficiently dense hydrophilic ionic side chains supporting the polyvinyl alcohol backbone, when the acetalization reaction progresses to a certain extent, the introduced hydrophobic acetal groups lead to enhanced hydrophobic interactions between the molecular chains, resulting in macroscopic phase separation or precipitation, making it difficult to obtain a homogeneous solution with high acetal content. To maintain system stability, existing technologies often force the limitation of acetal content or the use of some organic solvents for solubilization, which sacrifices the material's water resistance and mechanical properties, deviating from the original design intent of all-aqueous materials. Therefore, how to effectively suppress monomer homopolymerization, improve grafting selectivity, and prepare a high-acetal-content and stable aqueous polyvinyl butyral solution in a pure aqueous system is a pressing technical problem that needs to be solved. Summary of the Invention

[0006] The technical problem solved by this invention is the low grafting efficiency, high homopolymer residue, and easy phase separation at high acetal degree in the existing waterborne polyvinyl butyral preparation process.

[0007] In a first aspect, the present invention provides a composite polymerization-inhibiting, all-aqueous polyvinyl butyral solution, made from raw materials comprising the following parts by weight:

[0008] 100 parts of polyvinyl alcohol;

[0009] 600-900 parts deionized water;

[0010] 0.005 to 0.02 parts of metal complexing anchoring agent;

[0011] 0.2 to 0.8 parts of interfacial polymerization inhibitor;

[0012] 15 to 35 parts of graft monomer;

[0013] Chain transfer agent 0.5 to 1.5 parts;

[0014] Initiator: 0.8 to 2.0 parts;

[0015] 40 to 70 parts of acetalizing reagent;

[0016] 15 to 25 parts of acidic pH adjuster;

[0017] And an alkaline pH adjuster, wherein the amount of alkaline pH adjuster used is the amount required to adjust the pH of the system to 7.0 to 8.0;

[0018] The metal complex anchoring agent is used to construct redox active sites in the polyvinyl alcohol chain segments, and the interfacial polymerization inhibitor is used to construct an aqueous polymerization inhibitory environment to suppress the homopolymerization of grafted monomers.

[0019] By adopting the above technical solution, this invention utilizes the synergistic effect of metal coordination guidance and interfacial polymerization inhibition to achieve kinetic control of graft polymerization. The specific mechanism is as follows:

[0020] In metal complex anchoring agents, transition metal ions utilize their empty orbitals to coordinate with the lone pair electrons of the hydroxyl oxygen atoms on the polyvinyl alcohol (PVA) molecular chain, forming a PVA-metal complex. This interaction confines the catalytically active center to the PVA polymer chain segment, rather than allowing it to be freely distributed in the aqueous phase, thus establishing the spatial basis for site-directed reactions.

[0021] The initiator is a hydrophobic peroxide. In an aqueous system containing electrolytes, driven by salting-out effect and hydrophobic interactions, initiator molecules tend to accumulate from the bulk aqueous phase towards the relatively hydrophobic polyvinyl alcohol polymer coil microregions. When the initiator diffuses to segments anchored with metal ions, an in-situ redox reaction occurs (e.g., PVA-Cu). 2+ +TBHP→PVA-Cu 3+ +t-BuO·+OH - The resulting tert-butoxy radical has significant steric hindrance, reducing the probability of abstracting hydrogen atoms from the main chain. This allows it to efficiently initiate the formation of double bonds in nearby graft monomers while protecting the main chain from degradation and breakage.

[0022] The interfacial polymerization inhibitor is pre-dispersed in the aqueous phase, constructing a continuous phase polymerization barrier. Monomer radicals diffusing into the aqueous phase away from the polyvinyl alcohol (PVA) segments, or ungrafted growing chain radicals, are rapidly captured and quenched by the high concentration of the interfacial polymerization inhibitor, effectively suppressing the homopolymerization reaction of the grafted monomers. Within the microscopic regions of the PVA segments, due to the rapid generation rate of free radicals catalyzed by metal and the high local monomer concentration, the polymerization rate significantly exceeds the diffusion inhibition rate of the inhibitor, ensuring the efficient conduct of the grafting reaction.

[0023] The grafted side chains contain strongly hydrophilic groups and can be completely ionized across the entire pH range. In the subsequent acetalization reaction, although the hydrophilic hydroxyl groups on the polyvinyl alcohol backbone are largely replaced by hydrophobic acetal groups, the high density of ionic side chains provides sufficient electrostatic repulsion potential and a dense hydration layer to overcome the hydrophobic interactions between the backbones, allowing the product to maintain a stable molecular-level dispersion in water.

[0024] Preferably, the raw materials are in the following proportions by weight: 100 parts polyvinyl alcohol; 700-850 parts deionized water; 0.01-0.015 parts metal complex anchoring agent; 0.4-0.6 parts interfacial polymerization inhibitor; 20-30 parts grafted monomer; 0.8-1.2 parts chain transfer agent; 1.2-1.8 parts initiator; 50-60 parts acetalizing agent; and 18-22 parts acidic pH adjuster.

[0025] Preferably, the polyvinyl alcohol is a fully hydrolyzed polyvinyl alcohol with a degree of hydrolysis greater than 99.0 mole fraction and an average degree of polymerization of 1700-2400; the metal complex anchoring agent is selected from copper sulfate pentahydrate or manganese acetate tetrahydrate; the interfacial polymerization inhibitor is selected from sodium nitrite; and the acetalizing agent is selected from n-butyraldehyde.

[0026] Preferably, the grafting monomer is selected from 2-acrylamido-2-methylpropanesulfonic acid; the chain transfer agent is selected from sodium hypophosphite; the initiator is selected from tert-butyl hydroperoxide; the acidic pH adjuster is selected from hydrochloric acid; and the alkaline pH adjuster is selected from sodium hydroxide.

[0027] By employing the above technical solution, the structure of the grafted side chains can be precisely controlled by using 2-acrylamido-2-methylpropanesulfonic acid in conjunction with sodium hypophosphite. Sodium hypophosphite is added to the reaction system simultaneously with the monomer, acting as both a chain transfer agent and a reducing agent: on the one hand, it restricts side chain growth through chain transfer reactions, promoting the formation of short-chain, high-density grafted structures; on the other hand, it reduces the high-valence metal ions (such as Cu) generated during the reaction. 2+ ) Restore to the initial valence state (e.g., Cu) 2+ This enables in-situ regeneration and recycling of the catalyst, maintaining the stability of reaction kinetics.

[0028] Secondly, the present invention provides a method for preparing a composite polymerization-inhibited aqueous polyvinyl butyral solution, comprising the following steps:

[0029] Step S1: Dissolve polyvinyl alcohol in deionized water, add metal complexing anchoring agent and stir at a constant temperature to complete metal ion anchoring pre-complexation;

[0030] Step S2: Add an interfacial polymerization inhibitor to the solution obtained in step S1, stir and disperse to create a polymerization-inhibiting environment;

[0031] Step S3: Prepare drop solution A by mixing the grafting monomer and chain transfer agent, and prepare drop solution B by preparing the initiator; Under constant temperature conditions, drop solution A and drop solution B are simultaneously added to the system obtained in step S2 to carry out the grafting polymerization reaction.

[0032] Step S4: After the graft polymerization reaction is completed, lower the system temperature, add an acidic pH adjuster to adjust the pH value, add an acetalizing agent dropwise to carry out the acetalization reaction, and raise the temperature to mature after the dropwise addition is completed.

[0033] Step S5: After the acetalization reaction is complete, cool down, add an alkaline pH adjuster to neutralize the pH value of the system, and filter to obtain the final product.

[0034] By adopting the above technical solution, this invention establishes a step-by-step controlled reaction process, the specific process mechanism of which is as follows:

[0035] An independent metal ion anchoring pre-complexation step is set up in the early stage of the reaction to enable the metal ions to reach thermodynamic coordination equilibrium in the system, ensuring that the catalytic active center is fixed on the polyvinyl alcohol segment. This step avoids competitive side reactions between the metal ions and the subsequently added interfacial inhibitors or initiators in the aqueous phase, and establishes the basis for site-directed initiation of the reaction.

[0036] A two-component simultaneous dropping process was employed, in which the grafted monomer was prepared separately from the reducing chain transfer agent (dropping solution A) and the oxidizing initiator (dropping solution B) and added simultaneously. By controlling the dropping rate, the system was kept at a low monomer concentration, reducing the instantaneous monomer concentration in the aqueous bulk and thus suppressing the kinetic tendency of monomer homopolymerization. Simultaneously, the oxidant and reducing agent were added separately, limiting the redox reaction to mainly occur in the metal complexation site region, avoiding premature decomposition of the initiator due to premixing, and ensuring that the free radical generation rate matched the monomer grafting rate.

[0037] A variable temperature control strategy is employed during the acetalization stage. In the initial stage of the reaction, the reaction rate is reduced by lowering the temperature to avoid macroscopic phase separation caused by a rapid increase in the hydrophobicity of the molecular chains due to an excessively fast acetalization rate. The subsequent heating process increases the mobility of the polymer chain segments, promotes intramolecular and intermolecular structural rearrangement, and enables the acetal reaction to reach thermodynamic equilibrium, thereby forming a homogeneous and stable solution system.

[0038] Preferably, in step S1, the dissolution temperature of the polyvinyl alcohol is 90℃~95℃, the temperature of the metal ion anchoring pre-complexation is 60℃~65℃, and the time is 30 minutes~45 minutes.

[0039] Preferably, in step S2, the stirring and dispersion time is 10 to 15 minutes, during which the pH value of the system is 6.0 to 7.0.

[0040] By adopting the above technical solution, the pH value of the system is controlled in the weakly acidic to neutral range before the grafting reaction, which can maintain the coordination stability of metal ions and polyvinyl alcohol hydroxyl groups and prevent metal ions from undergoing hydrolysis precipitation or changes in coordination structure.

[0041] Preferably, in step S3, the temperature of the graft polymerization reaction is controlled at 60℃~65℃; the synchronous addition time of the droplet A and the droplet B is controlled at 2.5 hours~3.0 hours, and the reaction is kept at the temperature for 45 minutes~60 minutes after the addition is completed.

[0042] Preferably, the specific operation of step S4 is as follows: cool the reaction solution to 40℃~45℃, add an acidic pH adjuster to adjust the pH to 1.0~2.0, add the acetalizing reagent dropwise at this temperature for 30 minutes~60 minutes; after the dropwise addition is completed, raise the temperature to 55℃~65℃ at a rate of 0.5℃~1.0℃ per minute, and keep it warm for 3 hours~5 hours.

[0043] By adopting the above technical solution, the temperature is reduced to 40℃~45℃ and a strongly acidic environment is controlled in the initial stage of acetalization, which slows down the diffusion and reaction rate of n-butyraldehyde in the aqueous phase, so that the acetalization reaction is carried out uniformly on the polymer chain; then the temperature is slowly raised to 55℃~65℃ for aging, which improves the acetalization degree of the final product and fixes the microphase structure of the product.

[0044] Preferably, in step S5, the pH of the final system is adjusted to 7.0-8.0, and the preparation process is carried out in an aqueous phase without the addition of organic solvents.

[0045] In summary, the present invention has at least one of the following beneficial technical effects:

[0046] 1. This invention utilizes the synergistic effect of metal ion anchoring and interfacial polymerization inhibition. A metal ion-induced initiator initiates an in-situ reaction within the micro-regions of the polyvinyl alcohol chain, while an aqueous polymerization inhibitor suppresses the accumulation of free radicals in the aqueous phase. This reaction mechanism effectively overcomes the tendency of water-soluble monomers to self-polymerize in the aqueous phase, significantly improves the grafting efficiency of monomers onto the main chain, greatly reduces the formation of free homopolymer byproducts, and ensures the uniformity of the graft copolymer structure.

[0047] 2. Compared to traditional redox systems that generate highly reactive hydroxyl radicals, this invention employs a sterically hindered organic peroxide combined with a metal catalytic system. Due to the steric hindrance effect and metal coordination directing effect, the initiator preferentially attacks the double bonds of the highly reactive monomer, greatly reducing the probability of abstracting hydrogen atoms from the polyvinyl alcohol backbone. This system effectively inhibits oxidative breakage and degradation of the backbone while efficiently initiating polymerization, thereby maintaining a high molecular weight in the product and ensuring the mechanical strength of the final material.

[0048] 3. The modified polyvinyl butyral prepared in this invention utilizes grafted hydrophilic side chains to impart excellent solubility and dispersion stability in the aqueous phase, achieving molecular-level dissolution. Simultaneously, during the drying and film-forming process, the self-assembly and microphase separation characteristics of the copolymer's amphiphilic molecular chains allow the hydrophobic framework to rearrange into a dense, continuous phase, effectively blocking the penetration of water molecules. This structural design resolves the technical contradiction of traditional waterborne resins simultaneously achieving high solution transmittance and high water resistance in the dry film.

[0049] 4. Benefiting from its well-organized grafted network structure and complete molecular chains, the all-aqueous solution of this invention exhibits significant pseudoplastic rheological characteristics. The viscosity of the system decreases at high shear rates, which is beneficial for coating leveling; at low shear rates or under static conditions, the viscosity recovers rapidly, effectively preventing sagging. These rheological properties significantly improve the process window for coating and the appearance quality of the coating film.

[0050] 5. This invention employs an all-aqueous system, completely eliminating the use of organic solvents and thus removing the risk of volatile organic compound (VOC) emissions at the source. Furthermore, through specific feeding process control, a one-pot continuous preparation of graft polymerization and acetalization reactions is achieved, eliminating the need for intermediate separation and purification steps. The process is simple, highly efficient, and meets the requirements of low-energy consumption and green manufacturing in industrial applications. Attached Figure Description

[0051] Figure 1 This is a comparison chart of the polymerization reaction efficiency of Examples 1-5 and Comparative Examples 1-2 of the present invention. (a) is a comparison chart of monomer conversion rate for each sample; (b) is a comparison chart of grafting rate for each sample.

[0052] Figure 2 The bar chart shows the variation of intrinsic viscosity of Examples 1-5 and Comparative Example 3 relative to the raw material PVA.

[0053] Figure 3 The following is a quantitative comparison of the physicochemical stability of the embodiments and some comparative examples of the present invention; wherein, (a) is a comparison of the transmittance of each sample at 600nm; and (b) is a comparison of the sedimentation rate of each sample under strong centrifugal force of 10000rpm.

[0054] Figure 4 This is a biaxial analysis of the water resistance and structural stability of the dry films in Examples 1-5 and Comparative Example 3 of the present invention. The left-axis bar chart represents the water absorption rate of each sample after immersion in water at 25°C for 24 hours; the right-axis line chart represents the mass loss rate of each sample during the immersion process.

[0055] Figure 5 The graphs show the steady-state rheological behavior of solutions in embodiments and some comparative examples of the present invention. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer.

[0057] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0058] Polyvinyl alcohol (PVA) was selected from fully hydrolyzed products with a degree of hydrolysis greater than 99.0% (mole fraction). Specifically, PVA-1799 had an average degree of polymerization of 1700±50, and PVA-2099 had an average degree of polymerization of 2000–2400, with CAS number 9002-89-5. 2-Acrylamido-2-methylpropanesulfonic acid was used as a grafting monomer with a purity greater than 98%, CAS number 15214-89-8. Tert-butyl hydroperoxide was used as an initiator in a 70% aqueous solution, CAS number 75-91-2. n-Butyraldehyde was used as an acetalizing agent with a purity greater than 99%, CAS number 123-72-8.

[0059] Sodium nitrite (CAS No. 7632-00-0), sodium hypophosphite monohydrate (CAS No. 10039-56-2), copper sulfate pentahydrate (CAS No. 7758-99-8), and manganese acetate tetrahydrate (CAS No. 6156-78-1) were all commercially available analytical grade reagents.

[0060] Hydrochloric acid, sodium hydroxide, and other pH adjusters, as well as deionized water, are all routine laboratory reagents.

[0061] Example 1:

[0062] This embodiment provides a method for preparing a composite polymerization-inhibiting, all-aqueous polyvinyl butyral solution, comprising the following steps:

[0063] (1) Add 750g of deionized water to a reactor equipped with an anchor stirrer, a reflux condenser and a thermometer, turn on the stirrer to 80rpm, add 100g of polyvinyl alcohol (PVA-1799), heat to 95℃ and keep warm for 60 minutes until completely dissolved; then cool down to 62℃, add 0.01g of copper sulfate pentahydrate, and stir at a constant temperature for 30 minutes to carry out metal ion anchoring pre-complexation;

[0064] (2) Add 0.5g of sodium nitrite to the above solution at once, stir for 10 minutes to make it evenly dispersed, and construct an interfacial polymerization-inhibiting environment. At this time, the pH value of the system is 6.5.

[0065] (3) Prepare drop solution A by dissolving 25g of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and 1g of sodium hypophosphite in 60g of deionized water, and prepare drop solution B by diluting 1.5g of tert-butyl hydrogen peroxide (70% aqueous solution) in 30g of deionized water; keep the reaction temperature at 62℃, and add drop solution A and drop solution B simultaneously through two metering pumps. The addition time is controlled at 3 hours, and the reaction is kept warm for 1 hour after the addition is completed.

[0066] (4) Cool the reaction solution to 42°C, add 20g hydrochloric acid (31% concentration) to adjust the pH to 1.5, and add 55g n-butyraldehyde evenly dropwise over 45 minutes; after the addition is complete, raise the temperature to 60°C at a rate of 0.5°C / min and keep the temperature for 4 hours.

[0067] (5) After the reaction is complete, cool down to 30°C, slowly add 15% sodium hydroxide solution to adjust the pH to 7.5, filter to remove trace impurities, and obtain an all-aqueous polyvinyl butyral solution.

[0068] Example 2:

[0069] This embodiment provides a method for preparing a composite polymerization-inhibiting, all-aqueous polyvinyl butyral solution, comprising the following steps:

[0070] (1) Add 850g of deionized water to the reactor, start stirring, add 100g of polyvinyl alcohol (PVA-2099), heat to 95℃ and keep warm for 90 minutes until completely dissolved; cool down to 65℃, add 0.015g of copper sulfate pentahydrate, and stir at a constant temperature for 40 minutes.

[0071] (2) Add 0.6g of sodium nitrite to the solution and stir for 15 minutes to construct an interfacial polymerization-inhibiting environment;

[0072] (3) Dissolve 30g AMPS and 1.2g sodium hypophosphite in 70g deionized water to prepare drop solution A, and dilute 1.8g tert-butyl hydrogen peroxide (70% aqueous solution) in 35g deionized water to prepare drop solution B; keep the reaction temperature at 65℃, and add drop solution A and drop solution B simultaneously for 3 hours, and keep warm for 1 hour after the reaction is completed;

[0073] (4) Cool down to 45°C, add 22g hydrochloric acid to adjust the pH to 1.2, and add 60g n-butyraldehyde dropwise over 60 minutes; after the addition is complete, slowly raise the temperature to 62°C and keep the reaction at this temperature for 4 hours.

[0074] (5) Cool to room temperature, neutralize with sodium hydroxide solution to pH 7.2, and filter to obtain the product.

[0075] Example 3:

[0076] This embodiment provides a method for preparing a composite polymerization-inhibiting, all-aqueous polyvinyl butyral solution, comprising the following steps:

[0077] (1) Add 700g of deionized water and 100g of polyvinyl alcohol (PVA-1799) to the reactor. After dissolving at 95°C, cool down to 60°C and add 0.01g of manganese acetate tetrahydrate to replace copper sulfate. Stir at a constant temperature for 30 minutes.

[0078] (2) Add 0.4g of sodium nitrite to the solution and stir for 10 minutes;

[0079] (3) Dissolve 20g AMPS and 0.8g sodium hypophosphite in 50g deionized water to prepare drop solution A, and dilute 1.2g tert-butyl hydrogen peroxide (70% aqueous solution) in 25g deionized water to prepare drop solution B; keep at 60℃, add the two solutions simultaneously for 2.5 hours, and keep warm for 45 minutes;

[0080] (4) Cool down to 40°C, add 18g hydrochloric acid to adjust the pH to 1.8, and add 50g n-butyraldehyde dropwise over 30 minutes; after the addition is complete, raise the temperature to 58°C and keep the reaction at that temperature for 3.5 hours.

[0081] (5) Cool down and neutralize to pH 7.0, then filter to obtain the product.

[0082] Example 4:

[0083] This embodiment provides a method for preparing a composite polymerization-inhibiting, all-aqueous polyvinyl butyral solution, comprising the following steps:

[0084] (1) Add 600g of deionized water and 100g of polyvinyl alcohol (PVA-1799) to the reactor. After dissolving, cool the mixture to 63°C and add 0.005g of copper sulfate pentahydrate. Stir for 30 minutes.

[0085] (2) Add 0.2g of sodium nitrite to the solution and stir for 10 minutes;

[0086] (3) Dissolve 15g AMPS and 0.5g sodium hypophosphite in 50g deionized water to prepare drop solution A, and dilute 0.8g tert-butyl hydrogen peroxide (70% aqueous solution) in 20g deionized water to prepare drop solution B; keep at 63℃, add drop solution simultaneously for 3 hours, and keep warm for 1 hour;

[0087] (4) Cool down to 42°C, add 15g hydrochloric acid to adjust the pH to 2.0, and add 40g n-butyraldehyde dropwise over 40 minutes; after the addition is complete, raise the temperature to 55°C and keep the reaction at that temperature for 3 hours.

[0088] (5) Cool down and neutralize to pH 7.8, then filter to obtain the product.

[0089] Example 5:

[0090] This embodiment provides a method for preparing a composite polymerization-inhibiting, all-aqueous polyvinyl butyral solution, comprising the following steps:

[0091] (1) Add 900g of deionized water and 100g of polyvinyl alcohol (PVA-1799) to the reactor. After dissolving, cool the mixture to 60°C and add 0.02g of copper sulfate pentahydrate. Stir for 45 minutes.

[0092] (2) Add 0.8g of sodium nitrite to the solution and stir for 15 minutes;

[0093] (3) Dissolve 35g AMPS and 1.5g sodium hypophosphite in 80g deionized water to prepare drop solution A, and dilute 2g tert-butyl hydrogen peroxide (70% aqueous solution) in 40g deionized water to prepare drop solution B; keep at 60℃, add drop solution simultaneously for 3 hours, and keep warm for 1 hour;

[0094] (4) Cool down to 40°C, add 25g hydrochloric acid to adjust the pH to 1.0, and add 70g n-butyraldehyde dropwise over 60 minutes; after the addition is complete, raise the temperature to 65°C and keep the reaction at that temperature for 5 hours.

[0095] (5) Cool down and neutralize to pH 8.0, then filter to obtain the product.

[0096] Comparative Example 1:

[0097] Compared with Example 1, the difference is that copper sulfate pentahydrate was not added in step (1), while the amount of other raw materials and the operation steps are the same.

[0098] Comparative Example 2:

[0099] Compared with Example 1, the difference is that sodium nitrite was not added in step (2), while the amount of other raw materials and the operation steps are the same.

[0100] Comparative Example 3:

[0101] Compared with Example 1, the difference is that the initiator is replaced with an equimolar amount of hydrogen peroxide (H2O2), while the amounts of other raw materials and operating steps are the same.

[0102] Comparative Example 4:

[0103] Compared with Example 1, the difference is that all sodium hypophosphite is added to the substrate (PVA solution in step 1) beforehand, instead of being dissolved in the drop solution A and added dropwise with the monomer. The amounts of other raw materials and the operation steps are the same.

[0104] Comparative Example 5:

[0105] Compared with Example 1, the difference is that AMPS monomer was not added in step (3), but the acetalization reaction in step (4) was carried out directly. The amount of other raw materials and the operation steps are the same.

[0106] Test Example 1:

[0107] The experimental steps are as follows:

[0108] (1) Take 50g of the emulsion sample after the reaction is completed, add excess ethanol / acetone mixed solvent (volume ratio 3:1) to demulsify and precipitate, let stand for 2 hours, filter, and collect filtrate A and solid precipitate B.

[0109] (2) The filtrate A and the washing liquid were combined, and the content of unreacted AMPS monomers remaining in the solution was determined by potassium bromate-potassium bromide titration. Under acidic conditions, the residual monomers reacted with the bromine generated in situ, and the excess bromine was reduced with potassium iodide to precipitate iodine. Finally, the monomer conversion rate was calculated by titration with sodium thiosulfate standard solution.

[0110] (3) Place the solid precipitate B in a vacuum oven and dry it at 50°C to constant weight, then grind it into powder.

[0111] (4) Weigh 2g of the dried powder and place it in a Soxhlet extractor. Use 80% (volume) ethanol aqueous solution as solvent and heat under reflux for 24 hours. During this process, the ungrafted AMPS homopolymer (PAMPS) and its salts are readily soluble in the solvent and are eluted; at the same time, the free polyvinyl butyral (PVB) backbone that has not undergone the grafting reaction is also eluted due to its good solubility in hot ethanol. The successfully grafted PVA-g-PAMPS copolymer, due to its combination of hydrophilic side chains and hydrophobic backbone, forms a tight amphiphilic physical entanglement network in the solvent, is insoluble in the mixed solvent, and is thus retained in the filter paper tube.

[0112] (5) After extraction, remove the residue from the filter paper tube, vacuum dry it again to constant weight, and weigh it. Calculate the grafting rate based on the mass difference before and after extraction. The calculation formula is: Grafting rate = (Mass of residue after extraction / Total mass of polymer before extraction) × 100%.

[0113] The experimental results are shown in Table 1.

[0114] Table 1. Monomer conversion rate and grafting rate test data for each example and comparative example:

[0115]

[0116] According to Table 1 and Figure 1 Data analysis showed that the monomer conversion rates in Examples 1-5 remained above 90%, and the grafting rates were consistently high, ranging from 78% to 85%. This indicates that the reaction system constructed in this invention can efficiently initiate the polymerization of AMPS monomers and directionally graft them onto the PVA backbone.

[0117] Comparative Example 1 (without metal catalyst) showed that although the monomer conversion rate reached 88.7%, the grafting rate was only 14.2%. This confirms the crucial role of the metal complex targeted anchoring mechanism. In the absence of metal ion anchoring, the initiator cannot undergo efficient site-directed redox reactions within the microregions of the PVA chain. Although sodium nitrite inhibitor was present in the system, with the continuous addition of the initiator, the concentration of free radicals generated by thermal decomposition in the aqueous bulk gradually accumulated, eventually exceeding the inhibition threshold of the inhibitor and initiating the disordered homopolymerization reaction of AMPS monomers. Since these free radicals were not generated in situ on the PVA backbone, the main product was a free PAMPS homopolymer, rather than a PVA-g-PAMPS graft copolymer, resulting in an extremely low grafting rate.

[0118] Comparative Example 2 (with sodium nitrite inhibitor removed) showed a monomer conversion rate as high as 96.2%, but a grafting rate of only 32.8%, which verifies the necessity of the spatially selective polymerization inhibition mechanism. In the absence of an aqueous phase inhibitor, thermally initiated free radicals or escaped free radicals in the aqueous phase cause explosive disordered homopolymerization of AMPS monomers, competitively consuming a large amount of monomers and significantly reducing the effective grafting ratio of monomers on the PVA backbone surface.

[0119] In summary, only by simultaneously introducing metal ion anchoring and interfacial polymerization inhibition can we achieve a high grafting rate while ensuring high conversion and thus guaranteeing the uniformity of the product structure.

[0120] Test Example 2:

[0121] The experimental steps are as follows:

[0122] (1) The final product solutions prepared in Examples 1-5 and Comparative Example 3 were poured into excess acetone and precipitated under high-speed stirring. The precipitated solid polymer was collected by filtration and then washed three times with anhydrous ethanol to remove residual small molecule monomers and impurities. The washed polymer was placed in a vacuum drying oven and dried at 45°C for 24 hours to constant weight to obtain the dry powder sample to be tested.

[0123] (2) Weigh 0.5 g of each group of dried polymer samples and 0.5 g of PVA as a control, and dissolve them in 100 mL of deionized water to prepare a test solution with a concentration of 0.5 g / dL. Place the solution in a constant temperature shaker and stir at 30 °C for 4 hours to ensure complete dissolution. Let it stand to remove bubbles before use.

[0124] (3) The measurements were performed using an Ubbelohde viscometer (capillary inner diameter 0.55 mm) in a constant temperature water bath at 30.0 ± 0.1 °C. First, the eluent time t0 of the pure solvent (deionized water) was measured, and then the eluent time t of each sample solution was measured sequentially. Each sample was measured three times, and the average value with an error not exceeding 0.2 seconds was taken as the valid data.

[0125] (4) According to the formula Calculate the relative viscosity, then use the single-point method formula. Calculate the intrinsic viscosity, where C is the solution concentration. Finally, use the formula... Calculate the viscosity retention rate.

[0126] The experimental results are shown in Table 2.

[0127] Table 2. Test data of intrinsic viscosity and viscosity retention rate for each embodiment and comparative example:

[0128]

[0129] According to Table 2 and Figure 2 Data analysis showed that the intrinsic viscosity of Examples 1-5 ranged from 0.675 to 0.731 dL / g, with viscosity retention rates all above 93%. Example 4 even showed a slight increase in viscosity (101.0%). This result demonstrates that the TBHP initiation system used in this invention effectively protects the PVA main chain structure while achieving monomer grafting.

[0130] The high retention rates of the examples are attributed to the hydrophobic properties of TBHP and its anchoring effect on metal ions. TBHP molecules preferentially enter the hydrophobic microregions inside the PVA coils and undergo in-situ redox reactions at the metal ion sites. The generated tert-butoxy radicals (t-BuO·) have a large steric hindrance effect and mainly tend to initiate AMPS monomers with higher double bond reactivity, rather than abstracting hydrogen atoms from the PVA main chain, thus avoiding random breakage of the PVA main chain. The viscosity of Example 4 increased slightly, presumably due to the additional hydrodynamic volume introduced by the grafted PAMPS side chains and the minimal main chain breakage.

[0131] Conversely, the intrinsic viscosity of Comparative Example 3 (initiated using H2O2) dropped sharply to 0.314 dL / g, with a viscosity retention of only 43.4%. This confirms that under conditions of no metal anchoring and the use of a strongly hydrophilic initiator, the highly reactive hydroxyl radicals (·OH) generated by the decomposition of H2O2 in the aqueous phase indiscriminately attacked the PVA backbone, leading to severe β-fracture degradation. This drastic decrease in molecular weight directly results in a loss of mechanical strength and a significant reduction in water resistance of the final film material.

[0132] Test Example 3:

[0133] The experimental steps are as follows:

[0134] (1) Transmittance determination (T%): The final products prepared in Examples 1-5 and Comparative Examples 1-5 were precisely diluted with deionized water to a solid content of 10 wt%. Using deionized water as a blank reference, the transmittance of the solution was measured at a wavelength of 600 nm using a UV-Vis spectrophotometer. Each group of samples was measured in parallel three times, and the average value was taken.

[0135] (2) Determination of sedimentation rate: Weigh approximately 40g of the original solution m0 from each group into centrifuge tubes and weigh the total mass W1 of the centrifuge tubes and samples. Centrifuge at 10,000 rpm for 30 minutes using a high-speed centrifuge. After centrifugation, discard the supernatant and retain the sediment at the bottom (if any). Place the centrifuge tubes and sediment in an 80℃ vacuum oven to dry to constant weight and weigh the mass W2. The mass of the empty centrifuge tube is known to be W. tube .

[0136] Calculation formula: Settlement ratio = [(W2−W tube [(m0 × solid content)] × 100%. This index is used to quantitatively characterize whether there is microphase separation or insoluble gel in the system.

[0137] (3) Thermal aging viscosity change rate: The initial viscosity η0 of each sample was measured. The samples were sealed and placed in a 50℃ constant temperature oven for 168 hours (7 days). After being taken out and cooled to room temperature, the aged viscosity η was measured. aged .

[0138] Calculation formula: Viscosity change rate = [(η aged -η0) / η0]×100%.

[0139] The experimental results are shown in Table 3.

[0140] Table 3 Comparison of optical performance and stability data of each embodiment and comparative example:

[0141]

[0142] According to Table 3 and Figure 3 Data analysis showed that Examples 1-5 exhibited excellent overall performance, with transmittance consistently above 95% and extremely low centrifugal sedimentation rate (<0.1wt%). This data demonstrates the effectiveness of the polyelectrolyte support mechanism. The grafted, highly hydrophilic PAMPS side chains fully extend in water, forming an ion hydration layer that effectively shields the hydrophobic interactions of the PVB backbone. This allows the polymer chains to achieve molecular-level dissolution at the microscale, rather than simple colloidal dispersion, thus exhibiting extremely high transmittance and extremely low sedimentation rate.

[0143] In contrast, the comparative data reveals the differences in microstructure caused by various fabrication defects:

[0144] Comparative Example 1 (without metal catalysis): the transmittance was only 12.4%, and the sedimentation rate was as high as 85.4%. This indicates that most of the products in the system are ungrafted hydrophobic PVB, which cannot exist stably in water and undergo macroscopic phase separation under centrifugal force.

[0145] Comparative Example 2 (without polymerization inhibitor): The light transmittance was extremely low (3.1%), but the sedimentation rate (1.25%) was much lower than that of Comparative Example 1. This indicates that the system is mainly composed of a large number of PAMPS homopolymer latex particles and some grafted materials. Although the suspension stability is acceptable, the light transmittance is extremely poor due to the light scattering effect of the latex particles, which cannot meet the requirements of high transparency applications.

[0146] Comparative Example 4 (bottom-feed process): The sedimentation rate reached 8.7%, and the viscosity increased dramatically by 125.4% after thermal aging. This confirms that the bottom-feed process caused local cross-linking, generating a large number of microgels. These microgels are difficult to distinguish with the naked eye under normal conditions, but they will settle under a strong centrifugal field, and will further cross-link and aggregate during thermal aging, causing the system to lose its fluidity.

[0147] In summary, only by relying on the specific synthesis process of this invention can both high transmittance and high stability be achieved simultaneously.

[0148] Test Example 4:

[0149] The experimental steps are as follows:

[0150] (1) A clean glass plate with a size of 10cm×10cm was selected as the substrate. The polymer solutions of Examples 1 to 5 and Comparative Example 3 were first diluted with deionized water to a solid content of 10wt%, and then poured onto the glass plate. The wet film thickness was controlled to be 500μm using an automatic coating machine. The coated glass plate was placed in a clean room to dry naturally for 24 hours, and then transferred to a vacuum oven to dry further at 60°C for 48 hours to completely remove residual moisture and volatile solvents. A transparent dry film with a thickness of about 50μm was carefully peeled off.

[0151] (2) Cut the prepared dry film into 3cm×3cm square samples, place them in a desiccator to cool to room temperature, and then use an analytical balance to accurately weigh their initial mass, which is recorded as W0.

[0152] (3) Immerse the sample completely in a beaker containing 25°C deionized water and seal it for 24 hours. Take out the soaked sample, use a dust-free filter paper to quickly absorb the free water adhering to the surface, and immediately weigh its wet weight, which is recorded as W1.

[0153] (4) Observe the appearance changes of the sample after soaking and record whether whitening, swelling deformation or cracking and dissolution occur. Then place the wet sample in an 80℃ oven to dry to constant weight, weigh the dried sample and record the mass as W2 (to correct for errors caused by the dissolution and loss of some polymer).

[0154] (5) Calculate the water absorption rate and solubility loss rate according to the formula:

[0155] Water absorption rate = [(W1−W2) / W2]×100%;

[0156] Dissolution rate = [(W0−W2) / W0]×100%.

[0157] The experimental results are shown in Table 4.

[0158] Table 4. Dry film water resistance test data for each embodiment and comparative example:

[0159]

[0160] According to Table 4 and Figure 4 Data analysis showed that the dry films of Examples 1-5 exhibited excellent water resistance, with water absorption rates controlled within a low range of 15.3% to 21.2%, and extremely low solubility loss (<1.5%). This result verifies the film-forming mechanism of the amphiphilic structural rearrangement of the present invention.

[0161] Although the polymers in the examples exhibit good solubility in aqueous solutions, during the drying film-forming process, microphase separation and self-assembly of the polymer segments occur as the solvent evaporates. The hydrophilic PAMPS groups grafted onto the side chains tend to aggregate to form physical crosslinking points (ionic clusters), while the high acetal degree PVB hydrophobic segments on the main chain tightly pack together to form a continuous phase. This dense hydrophobic network effectively blocks the penetration of water molecules, resulting in a dry film that macroscopically exhibits significant hydrophobicity and water-resistant whitening properties, achieving a balance between water-soluble preparation and water-resistant film formation.

[0162] In contrast, Comparative Example 3 (H2O2-initiated) exhibited a water absorption rate as high as 145.6% and a solubility loss rate of 38.4%, displaying a severely whitish and sticky appearance. This is due to severe chain scission caused by H2O2 initiation, as shown in Test Example 2, resulting in an excessively low polymer molecular weight and an inability to form effective physical entanglement between molecular chains. The short-chain molecules create a loose film structure with a large free volume, allowing water molecules to easily penetrate and disrupt the weak intermolecular forces, leading to film swelling and even partial re-dissolution. This further demonstrates the necessity of maintaining a high molecular weight to preserve the inherent hydrophobic properties of PVB materials.

[0163] Test Example 5:

[0164] The experimental steps are as follows:

[0165] (1) Sample preparation: The final products of Examples 1, 5, 2, 3 and 4 were selected. Each sample was precisely diluted with deionized water to a homogeneous solution / dispersion with a solid content of 8.0 wt%.

[0166] (2) Test conditions: A rotational rheometer equipped with a cone plate clamp (40 mm in diameter, 1° cone angle) was used. The test temperature was set to 25.0 ± 0.1℃.

[0167] (3) Steady-state shear scan: at 0.1s -1 up to 100s -1 Logarithmic scans were performed within the range of shear rates to record the curves of apparent viscosity (η) of each sample as a function of shear rate.

[0168] (4) Data recording: Focus on recording the low shear rate of 0.1s. -1 The zero-shear viscosity η0 characterizes the molecular chain entanglement ability under static conditions and the high shear rate of 100 s⁻¹. -1 The viscosity at a given level characterizes the processing fluidity.

[0169] The experimental results are shown in Table 5.

[0170] Table 5. Test data of rheological parameters for each sample:

[0171]

[0172] Table 5 and Figure 5 The rheological characteristics reveal the influence of different synthesis processes on the polymer microstructure and solution state.

[0173] Examples 1 and 5 exhibit typical characteristics of polymeric polyelectrolyte solutions, namely significant shear-thinning behavior. At low shear rates, the system maintains a high zero-shear viscosity, attributed to the full extension of the grafted PAMPS side chains in the aqueous phase, leading to the formation of a broad physical entanglement network in the main chain. As the shear rate increases, the molecular chains align along the flow direction, the entanglement dissolves, and the viscosity decreases. This rheological property not only confirms the product's high molecular weight and good linear structure but also benefits practical coating processes, exhibiting good flowability during high-shear coating and rapidly recovering viscosity during post-coating rest (low shear), preventing coating sagging.

[0174] Conversely, Comparative Example 3 exhibits extremely low viscosity that hardly changes with shear rate, displaying characteristics similar to a Newtonian fluid. This directly reflects the severe oxidative degradation caused by the H2O2-initiated system, which leads to the breakage of the polymer backbone into short chain segments, preventing the formation of effective intermolecular entanglement and resulting in the loss of the rheological properties and film strength expected of polymer materials.

[0175] Comparative Example 4 exhibits abnormally high viscosity in the low-shear region. This is not due to benign chain entanglement, but rather to the structural resistance caused by microgel particles generated from local cross-linking induced by the bottom-feeding process. This heterogeneous structure easily leads to defects such as orange peel or graininess on the coating surface during coating. The lower viscosity of Comparative Example 2 indicates that, in the absence of a polymerization inhibitor, the system mainly consists of coiled PVB particles and PAMPS homopolymers, failing to form a through-cell polymer network. Its small hydrodynamic volume prevents it from demonstrating the thickening effect of the graft copolymer.

[0176] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fully aqueous polyvinyl butyral solution with composite polymerization inhibition regulation, characterized in that, Made from the following ingredients in parts by weight: 100 parts of polyvinyl alcohol; 600-900 parts deionized water; 0.005 to 0.02 parts of metal complexing anchoring agent; 0.2 to 0.8 parts of interfacial polymerization inhibitor; 15 to 35 parts of graft monomer; Chain transfer agent 0.5 to 1.5 parts; Initiator: 0.8 to 2.0 parts; 40 to 70 parts of acetalizing reagent; 15 to 25 parts of acidic pH adjuster; And an alkaline pH adjuster, wherein the amount of alkaline pH adjuster used is the amount required to adjust the pH of the system to 7.0 to 8.0; The metal complex anchoring agent is used to construct redox active sites in the polyvinyl alcohol chain segment, and the interfacial polymerization inhibitor is used to construct an aqueous polymerization inhibitory environment to inhibit the homopolymerization of grafted monomers. The polyvinyl alcohol is a fully hydrolyzed polyvinyl alcohol with a degree of hydrolysis greater than 99.0 mole fraction and an average degree of polymerization of 1700-2400; the metal complex anchoring agent is selected from copper sulfate pentahydrate or manganese acetate tetrahydrate; the interfacial polymerization inhibitor is selected from sodium nitrite; and the acetalizing agent is selected from n-butyraldehyde. The grafting monomer is selected from 2-acrylamido-2-methylpropanesulfonic acid; the chain transfer agent is selected from sodium hypophosphite; the initiator is selected from tert-butyl hydroperoxide; the acidic pH adjuster is selected from hydrochloric acid; and the alkaline pH adjuster is selected from sodium hydroxide. The preparation method of the composite polymerization-inhibiting and controlled all-aqueous polyvinyl butyral solution includes the following steps: S1. Dissolve polyvinyl alcohol in deionized water, add metal complexing anchoring agent and stir at a constant temperature to complete the metal ion anchoring pre-complexation. S2. Add an interfacial polymerization inhibitor to the solution obtained in S1, stir and disperse to create a polymerization-inhibiting environment; S3. Prepare dropwise solution A by mixing the grafting monomer and chain transfer agent, and prepare dropwise solution B by mixing the initiator; under constant temperature conditions, simultaneously add dropwise solution A and dropwise solution B to the system obtained in S2 to carry out the grafting polymerization reaction. S4. After the graft polymerization reaction is completed, lower the system temperature, add an acidic pH adjuster to adjust the pH value, add an acetalizing agent dropwise to carry out the acetalization reaction, and raise the temperature to mature after the dropwise addition is completed. S5. After the acetalization reaction is complete, cool down, add an alkaline pH adjuster to neutralize the pH value of the system, and filter to obtain the final product.

2. The all-aqueous polyvinyl butyral solution with composite polymerization inhibition control according to claim 1, characterized in that, The weight parts of the raw materials are: 100 parts of polyvinyl alcohol; 700-850 parts deionized water; 0.01 to 0.015 parts of metal complex anchoring agent; 0.4 to 0.6 parts of interfacial polymerization inhibitor; 20 to 30 parts of graft monomer; Chain transfer agent 0.8 to 1.2 parts; Initiator: 1.2 to 1.8 parts; 50 to 60 parts of acetalizing reagent; 18 to 22 parts of acidic pH adjuster.

3. The all-aqueous polyvinyl butyral solution with composite polymerization inhibition control according to claim 1, characterized in that, In step S1, the dissolution temperature of the polyvinyl alcohol is 90℃~95℃, the temperature of the metal ion anchoring pre-complexation is 60℃~65℃, and the time is 30 minutes~45 minutes.

4. The all-aqueous polyvinyl butyral solution with composite polymerization inhibition control according to claim 1, characterized in that, In step S2, the stirring and dispersion time is 10 to 15 minutes, during which the pH value of the system is 6.0 to 7.

0.

5. The all-aqueous polyvinyl butyral solution with composite polymerization inhibition control according to claim 1, characterized in that, In step S3, the temperature of the graft polymerization reaction is controlled at 60℃~65℃; the simultaneous addition time of the drop solution A and the drop solution B is controlled at 2.5 hours~3.0 hours, and the reaction is kept at the temperature for 45 minutes~60 minutes after the addition is completed.

6. The all-aqueous polyvinyl butyral solution with composite polymerization inhibition control according to claim 1, characterized in that, The specific steps for S4 are as follows: Cool the reaction solution to 40℃~45℃, add an acidic pH adjuster to adjust the pH to 1.0~2.0, and add the acetalizing reagent dropwise at this temperature over a period of 30 minutes to 60 minutes; After the addition is complete, the temperature is increased to 55℃ to 65℃ at a rate of 0.5℃ to 1.0℃ per minute, and then kept warm for 3 to 5 hours.

7. The all-aqueous polyvinyl butyral solution with composite polymerization inhibition control according to claim 1, characterized in that, In step S5, the pH of the final system is adjusted to 7.0–8.0, and the preparation process is carried out in an aqueous phase without the addition of organic solvents.

Images