Highly salt-resistant zwitterionic synthetic thickeners and their application in digital printing pastes

Abstract

This application provides a highly salt-resistant zwitterionic synthetic thickener and its application in digital printing pastes, belonging to the field of printing paste auxiliaries. The thickener is a multifunctional star-shaped block copolymer with highly branched polyolefins as hydrophobic blocks. The method includes: mixing pentaerythritol, 2-bromoisobutyryl bromide, an acid-binding agent, and an organic solvent, followed by an esterification reaction; subjecting an initiator, SBMA monomer, CuBr, and PMDETA to a free radical polymerization reaction; adding fluoroalkyl methacrylate monomer, ureidopyrimidinone methacrylate monomer, and a highly branched polyolefin derivative functional monomer to the first polymerization system to continue the free radical polymerization reaction; and post-treating the second polymerization system to obtain the highly salt-resistant zwitterionic synthetic thickener. This application improves the viscosity retention rate of the zwitterionic synthetic thickener in high-salt environments through precise molecular structure design and polymerization process control.

Description

Technical Field

[0001] This application relates to the field of printing paste additives, and in particular to a highly salt-resistant zwitterionic synthetic thickener and its application in digital printing pastes. Background Technology

[0002] In the field of digital printing, thickeners are a core component of printing pastes. Their main function is to impart suitable rheological properties to the paste, ensuring precise dye placement on the fabric and preventing bleeding, thereby obtaining clear and vibrant patterns. Amphoteric polymers, due to the presence of both positive and negative charge centers on their chain segments, can fully extend their molecular chains under low-salt conditions through strong ion hydration and electrostatic repulsion, providing excellent thickening effects. In recent years, they have been considered a class of thickener materials with great application potential.

[0003] However, traditional zwitterionic synthetic thickeners face severe challenges in high-salt environments. Printing pastes often contain a certain concentration of electrolytes (such as dyeing salts in reactive dyes, inorganic salts in disperse dyes, or pastes prepared using high-hardness water). These salt ions severely shield the electrostatic repulsion between zwitterionic chain segments, causing the molecular chains to collapse from an extended state into random coils. This results in a sharp decrease in hydrodynamic volume, macroscopically manifested as a significant drop in system viscosity, and even loss of thickening ability. This "salt-induced thinning" effect greatly limits the widespread application of zwitterionic thickeners in digital printing, especially in high-salt reactive dye printing scenarios, where insufficient viscosity often leads to pattern bleeding and uneven color, making it difficult to meet the process requirements of high-precision printing.

[0004] To improve the salt resistance of zwitterionic synthetic thickeners for use in high-salt digital printing environments, numerous improvements have been attempted in existing technologies. For example, Chinese patent CN113372505A discloses a salt-resistant thickener copolymer and its preparation method. This salt-resistant thickener copolymer is composed of allyl glycoside copolymer units, maleic anhydride-modified polybutadiene copolymer units, and polyalkenyl acrylate copolymer units, and is prepared by emulsion polymerization using a zwitterionic emulsifier and a nonionic emulsifier. However, this patented salt-resistant thickener still has significant shortcomings in high-salt environments. Its constructed affinity-reactive network structure and three-dimensional network structure cannot fundamentally solve the core problem of the zwitterionic thickener's electrostatic interaction being shielded under high salt conditions, leading to molecular chain collapse. When the salt concentration exceeds 80 mmol / L, its viscosity retention rate is difficult to exceed 80%, which is insufficient to meet the actual production needs of high-salt reactive dye digital printing scenarios where the salt resistance of thickeners is extremely demanding. Therefore, developing an amphoteric synthetic thickener that can maintain a high viscosity retention rate in a high-salt environment is of great practical significance and urgency for the digital printing industry to improve product quality and expand the application range of printing processes. Summary of the Invention

[0005] This application provides a highly salt-resistant zwitterionic synthetic thickener and its application in digital printing pastes to solve the following technical problem: how to improve the viscosity retention rate of zwitterionic synthetic thickeners in high-salt environments.

[0006] In a first aspect, this application provides a method for preparing a highly salt-resistant zwitterionic synthetic thickener, wherein the thickener is a multifunctional star-shaped block copolymer with highly branched polyolefins as hydrophobic blocks, and the method includes the following steps:

[0007] S1. Under an inert atmosphere and ice bath conditions, pentaerythritol, 2-bromoisobutyryl bromide, an acid-binding agent and an organic solvent are mixed and then esterified at room temperature. After post-treatment, a four-armed brominated ester macromolecular initiator Br4-Core is obtained.

[0008] S2. The four-armed brominated ester macromolecular initiator Br4-Core, sulfobetaine methacrylate monomer, CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine are added to an alcohol / water mixed solvent to carry out an atom transfer radical polymerization reaction to obtain a first polymerization system containing the star polymer intermediate Br4-PSBMA-Br4.

[0009] S3. Add fluoroalkyl methacrylate monomer, ureidopyrimidinone methacrylate monomer and highly branched polyolefin derivative functional monomer to the first polymerization system, and supplement CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine to continue the atom transfer radical polymerization reaction to obtain a second polymerization system containing star-triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4;

[0010] S4. The second polymerization system is subjected to catalyst removal via a neutral alumina column, dialysis, and freeze-drying to obtain a highly salt-resistant zwitterionic synthetic thickener.

[0011] Optionally, in step S1, the acid-binding agent is pyridine, and the organic solvent is at least one of tetrahydrofuran, dichloromethane, or N,N-dimethylformamide;

[0012] In step S2, the volume ratio of alcohol to water in the alcohol / water mixed solvent is 1:(1-2), and the alcohol is at least one of methanol or ethanol.

[0013] Optionally, in step S1, the molar ratio of pentaerythritol, 2-bromoisobutyryl bromide, and the acid-binding agent is 1:(4.0-4.5):(4.2-5.0).

[0014] Optionally, in step S1, the esterification reaction is carried out at room temperature for 20–28 hours.

[0015] Optionally, in step S2, the molar ratio of bromine atom, sulfobetaine methacrylate monomer, CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine in the four-armed brominated ester macromolecular initiator Br4-Core is 1:(45-55):(0.9-1.1):(0.9-1.1).

[0016] Optionally, in step S2, the temperature of the atom transfer radical polymerization reaction is 45–55°C, and the reaction time is 4–8 h.

[0017] In step S3, the temperature for continuing the atom transfer radical polymerization reaction is 45–55°C, and the reaction time is 12–24 h.

[0018] Optionally, in step S3, the molar ratio of the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer is (70-85):(5-10):(10-20), and the total molar number of the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer is 10%-30% of the molar number of the sulfobetaine methacrylate monomer in step S2.

[0019] Optionally, in step S3, the fluoroalkyl methacrylate monomer is 1H,1H,2H,2H-perfluorooctyl methacrylate, the ureidopyrimidinone methacrylate monomer is 2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl)methacrylate, and the highly branched polyolefin derivative functional monomer is a branched polyolefin macromonomer with methacrylate end groups.

[0020] Optionally, in step S3, the molar amount of CuBr added to N,N,N',N'',N''-pentamethyldiethylenetriamine is the same as the molar amount of CuBr added to N,N,N',N'',N''-pentamethyldiethylenetriamine in step S2.

[0021] Secondly, this application provides the application of a highly salt-resistant zwitterionic synthetic thickener prepared by the method described in any one of the first aspects in digital printing pastes, wherein the mass fraction of the highly salt-resistant zwitterionic synthetic thickener in the digital printing paste is 0.5-3%;

[0022] The viscosity retention rate of the digital printing paste is not less than 90% when the electrolyte concentration is not higher than 100 mmol / L.

[0023] The technical solutions provided in this application have the following advantages compared with the prior art:

[0024] This application provides a method for preparing a highly salt-resistant zwitterionic synthetic thickener, which is a multifunctional star-shaped block copolymer with highly branched polyolefins as key hydrophobic blocks. Through precise molecular structure design and polymerization process control, the viscosity retention rate of the zwitterionic synthetic thickener in high-salt environments is fundamentally improved. First, a four-armed star-shaped core initiator (Br4-Core) is constructed during the preparation process to provide a symmetrical and stable foundation for subsequent chain segment growth, avoiding the problem of molecular chain collapse under high salt conditions due to structural asymmetry. Second, zwitterionic homopolymer segments of PSBMA are grown on the star-shaped core via ATRP polymerization, retaining its basic thickening ability under low salt conditions and molecular solubility under high salt conditions, thus supporting salt resistance. Third, three functional monomers, FP, UPy, and highly branched polyolefin derivative functional monomer (HP), are further introduced to form P(FP-co-UPy-co-HP) random copolymer segments at both ends of PSBMA via ATRP polymerization, constructing "P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP) ... The o-UPy-co-HP) symmetrical triblock structure utilizes the large three-dimensional structure of HP and multiple hydrophobic end groups to significantly enhance intermolecular entanglement and physical cross-linking density. Among them, the fluorocarbon chain of FP forms stronger hydrophobic association due to salting-out effect under high salt conditions, and the quadruple hydrogen bonds of UPy are not affected by salt ions and can stably cross-link. The three work together to construct a more stable and salt-resistant three-dimensional physical cross-linking network, which counteracts the shielding of the electrostatic effect of salt ions on PSBMA and prevents molecular chain collapse. Finally, the purity and structural integrity of the product are ensured by removing impurities with a neutral alumina column, dialysis purification and freeze drying. Finally, with the synergistic enhancement effect of star-shaped symmetric structure, zwitterionic salt-resistant unit and multiple physical cross-linking mechanism, the thickener can still maintain a high viscosity in high salt environment, significantly improving viscosity retention. Attached Figure Description

[0025] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0027] Figure 1This is a schematic flowchart illustrating a method for preparing a highly salt-resistant zwitterionic synthetic thickener, as provided in an embodiment of this application. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this application can be purchased from the market or prepared by existing methods.

[0030] Figure 1 This is a schematic flowchart illustrating a method for preparing a highly salt-resistant zwitterionic synthetic thickener, as provided in an embodiment of this application.

[0031] like Figure 1 As shown, this application provides a method for preparing a highly salt-resistant zwitterionic synthetic thickener, wherein the thickener is a multifunctional star-shaped block copolymer with highly branched polyolefins as hydrophobic blocks, and the method includes the following steps:

[0032] S1. Under an inert atmosphere and ice bath conditions, pentaerythritol, 2-bromoisobutyryl bromide, an acid-binding agent, and an organic solvent are mixed and then subjected to an esterification reaction at room temperature. After post-treatment, a four-armed brominated ester macromolecular initiator Br4-Core is obtained.

[0033] It should be noted that step S1 is the synthesis process of the star-shaped core initiator (Br4-Core). This step combines a nucleophilic substitution reaction (SN2) with an esterification reaction to construct the core initiation structure of the star polymer, providing active sites for subsequent ATRP polymerization. From the reaction mechanism, firstly, pyridine, as an acid-binding agent, plays a dual role: on the one hand, as an organic base, it undergoes a nucleophilic interaction with the acyl group of 2-bromoisobutyryl bromide to form a more reactive "pyridine-acyl complex" intermediate, enhancing the subsequent reaction activity; on the other hand, it promptly neutralizes the HBr generated in the reaction, preventing it from damaging the starting materials or products, while simultaneously shifting the reaction equilibrium towards the formation of the target product. Next, the oxygen atom of the hydroxyl group (-OH) in the pentaerythritol molecule acts as a nucleophile, actively attacking the carbonyl carbon (electrophilic center) of the "pyridine-acyl complex" or 2-bromoisobutyryl bromide. Subsequently, the carbonyl carbon and the hydroxyl oxygen form a new CO ester bond, the original C-Br bond breaks, and the bromide ion (Br4-Br) is released. -The hydroxyl group (PH) departs from the system as a leaving group. This process proceeds sequentially at the four hydroxyl groups of pentaerythritol, ultimately completing the synthesis of the star-shaped core initiator.

[0034] From the perspective of material changes, the initial stage of the system contains a spherically symmetrical pentaerythritol molecule, a linear 2-bromoisobutyryl bromide molecule, and pyridine. After the reaction, a four-armed bromoester macromolecular initiator (Br4-Core) is finally generated. Its molecular structure exhibits a central carbon atom extending outwards with four identical arms, each arm ending with a group (-C(Br)(CH3)2) with ATRP initiation activity, which can serve as the active starting point for subsequent polymerization. Simultaneously, the reaction produces pyridine hydrobromide as a byproduct. The byproduct can be removed from the system by means of filtration or other methods.

[0035] In some embodiments, in step S1, the acid-binding agent is pyridine, and the organic solvent is at least one of tetrahydrofuran, dichloromethane, or N,N-dimethylformamide.

[0036] In some embodiments, in step S1, the molar ratio of pentaerythritol, 2-bromoisobutyryl bromide, and the acid-binding agent is 1:(4.0-4.5):(4.2-5.0).

[0037] The purpose of limiting the molar ratio of pentaerythritol, 2-bromoisobutyryl bromide, and acid-binding agent to 1:(4.0~4.5):(4.2~5.0) is as follows: 2-bromoisobutyryl bromide is added in excess at 4.0~4.5 equiv. This excess design ensures that all four hydroxyl groups on the pentaerythritol molecule are fully esterified, effectively avoiding the formation of structurally incomplete impurities such as "three-arm" or "two-arm" structures due to unreacted hydroxyl groups. This ensures the topological symmetry of the final star-shaped core initiator (Br4-Core). The symmetrical star-shaped topology allows for uniform stress on the subsequent polymer growth segments, making it more difficult for the molecular chains to collapse in a high-salt environment, thus laying the structural foundation for the salt resistance of the thickener. Meanwhile, the acid-binding agent is added at a concentration of 4.2–5.0 equiv, slightly more than 2-bromoisobutyryl bromide. In addition to timely neutralizing the HBr generated by the esterification reaction and promoting the reaction equilibrium to the forward direction, it can also excessively adsorb residual trace amounts of moisture and acidic impurities in the system, preventing these impurities from damaging the activity of the bromination initiation sites. This prevents the occurrence of "chain breakage" or "initiation deactivation" in the subsequent ATRP polymerization process, ensuring the continuity and controllability of the polymerization reaction.

[0038] In some embodiments, in step S1, the esterification reaction is carried out at room temperature for 20 to 28 hours.

[0039] The purpose of limiting the reaction to an inert atmosphere (such as nitrogen) and an ice bath starting condition, and reacting at room temperature for 20–28 hours, is as follows: The inert atmosphere effectively isolates oxygen, preventing the oxidation of the hydroxyl groups of pentaerythritol and avoiding interference with the electron transfer process of the esterification reaction, ensuring that the reaction proceeds along the predetermined path; the ice bath starting design, since the esterification reaction is exothermic, allows for control of the initial reaction rate through low temperature, avoiding local temperature surges that could lead to the decomposition of 2-bromoisobutyryl bromide or carbonization of pentaerythritol, thus achieving a stable start-up of the reaction; and the long reaction time of 20–28 hours at room temperature, considering the slower reaction rate under low temperature conditions, ensures complete esterification and reduces the formation of "incompletely esterified core" impurities. The presence of these impurities can lead to uneven chain lengths in subsequent ATRP polymerization, ultimately reducing the stability of the thickener's salt resistance.

[0040] S2. The four-armed brominated ester macromolecular initiator Br4-Core, sulfobetaine methacrylate monomer, CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine are added to an alcohol / water mixed solvent to carry out an atom transfer radical polymerization reaction to obtain a first polymerization system containing the star polymer intermediate Br4-PSBMA-Br4.

[0041] It should be noted that the sulfobetaine methacrylate monomer is 2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide.

[0042] Step S2 is the ATRP polymerization reaction of the first block (PSBMA), a typical atom transfer radical polymerization (ATRP) reaction designed to construct a hydrophilic zwitterionic backbone segment, providing the thickener with basic hydration capacity and thickening performance under low-salt conditions. Its core mechanism revolves around the ATRP cycle: firstly, the activation process occurs, where the complex formed by the catalyst Cu(I)Br and the ligand PMDETA breaks the C-Br bond at the end of the initiator Br4-Core through homolytic cleavage, abstracting Br atoms and generating primary radicals. The catalyst Cu(II)Br2 / PMDETA in a deactivated state provides active free radicals for subsequent reactions. Then, the initiation stage begins, where the generated primary free radicals rapidly attack the carbon-carbon double bonds of the sulfobetaine methacrylate (SBMA) monomer, causing the double bonds to open and combine, forming larger monomeric free radicals. This is followed by the chain growth stage, where the monomeric free radicals continuously attack the double bonds of subsequent SBMA monomers, constantly attaching SBMA units to the growing chain, causing the PSBMA chain segment to gradually grow. Finally, a reversible deactivation process occurs, where the growing polymer chain free radicals... It can re-extract a Br atom from the Cu(Ⅱ)Br2 / PMDETA complex, transforming it into a dormant species (P-Br), while simultaneously restoring the catalyst to the active state of Cu(I)Br / PMDETA. This reversible process effectively controls the free radical concentration, ensuring that the polymerization reaction is controllable.

[0043] In terms of material changes, the starting system contained the star initiator Br4-Core, SBMA monomer, Cu(I)Br, and PMDETA. After the reaction was completed, the main product of the system was the star polymer intermediate Br4-PSBMA-Br4. At this point, a polysulfobetaine methacrylate (PSBMA) chain grew at each of the four initiation sites of Br4-Core, and each chain retained a dormant C-Br bond at its end. This characteristic enabled it to continue initiating the next stage of polymerization, laying the foundation for subsequent block polymerization. At the same time, the physical state of the reaction system also changed, from the initial solution of monomer and initiator mixture to a viscous liquid containing star polymer, a small amount of residual catalyst, and unreacted monomer.

[0044] In some embodiments, in step S2, the volume ratio of alcohol to water in the alcohol / water mixed solvent is 1:(1-2), and the alcohol is at least one of methanol or ethanol.

[0045] The purpose of limiting the volume ratio of alcohol / water mixed solvent to 1:(1~2) is as follows: Because SBMA monomer is highly polar, although it has good solubility in pure water, the solubility of ATRP catalyst (CuBr / PMDETA) is low. Adding alcohol can simultaneously improve the solubility of both monomer and catalyst, thus constructing a homogeneous polymerization system. The homogeneous system can ensure that the PSBMA chain segment length is uniform, avoiding fluctuations in the salt resistance of the thickener due to chain length differences.

[0046] In some embodiments, in step S2, the molar ratio of bromine atom, sulfobetaine methacrylate monomer, CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine in the four-armed brominated ester macromolecular initiator Br4-Core is 1:(45-55):(0.9-1.1):(0.9-1.1).

[0047] The effect of limiting the molar ratio of Br atoms, SBMA monomer, CuBr, and PMDETA in four-armed brominated ester macromolecular initiators to 1:(45~55):(0.9~1.1):(0.9~1.1) is as follows: The design of the [SBMA] / [Br] ratio of 45~55 directly determines the molecular weight of the PSBMA chain segment. If the chain segment is too short (<45), it will lead to insufficient molecular chain hydration capacity, resulting in low viscosity of the thickener under low salt conditions. If the chain segment is too long (55), it will increase the molecular chain entanglement, and under high salt conditions, it is prone to "entanglement collapse" due to electrostatic shielding, which will reduce the salt resistance. The [CuBr] / [PMDETA] ratio of 1:1 allows the two to form a stable complex catalytic system, through which CuBr... 0 / Cu + / Cu 2+ The Redox cycle ensures the "controllability" of ATRP polymerization; controlled polymerization can produce PSBMA segments with narrow molecular weight distribution (PDI<1.3). The better the segment uniformity, the stronger the "synergistic resistance to collapse" of the molecular chain under high salt conditions, and the more stable the salt resistance of the thickener.

[0048] In some embodiments, in step S2, the temperature of the atom transfer radical polymerization reaction is 45–55°C, and the reaction time is 4–8 h.

[0049] The purpose of limiting the ATRP polymerization reaction temperature to 45–55℃ and the reaction time to 4–8 h is as follows: 45–55℃ is the "golden temperature range" for ATRP polymerization. Below 45℃, the catalyst activity is insufficient, the reaction rate is slow, and the SBMA monomer conversion rate is difficult to achieve. Above 55℃, "free radical disproportionation / coupling" side reactions are easily triggered, compromising the controllability of ATRP polymerization and leading to uneven PSBMA chain length. The 4–8 h reaction time control is to ensure that the SBMA monomer conversion rate reaches more than 80%. If the conversion rate is insufficient, a large amount of unreacted monomers remaining in the system will compete with FP and UPy monomers for active sites in subsequent steps, resulting in incomplete polymerization of functional ends and ultimately weakening the salt resistance of the thickener.

[0050] S3. Add fluoroalkyl methacrylate monomer, ureidopyrimidinone methacrylate monomer and highly branched polyolefin derivative functional monomer to the first polymerization system, and supplement CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine to continue the atom transfer radical polymerization reaction to obtain a second polymerization system containing star-triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4.

[0051] It should be noted that the core functional segment of this thickener contains highly branched polyolefin structural units. Specifically, this is achieved by introducing highly branched polyolefin derivative functional monomers (branched polyolefin macromonomers with methacrylate end groups) during the preparation process (step S3). These monomers, along with fluoroalkyl methacrylate monomers and ureidopyrimidinone methacrylate monomers, participate in atom transfer radical polymerization to form a star-shaped triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4, which is a key component of the P(FP-co-UPy-co-HP) segment. Ultimately, this integrates the highly branched polyolefin properties into the thickener's molecular structure, providing core support for its high salt resistance and thickening stability.

[0052] In the preparation method of this highly salt-resistant zwitterionic synthetic thickener, the highly branched polyolefin derivative functional monomer is an important component in constructing the special structure and properties of the thickener. From a structural perspective, this monomer, as a functional unit, participates in the atom transfer radical polymerization reaction in step S3, co-polymerizing with fluoroalkyl methacrylate monomers and ureidopyrimidinone methacrylate monomers to form specific segment portions in the star-triblock copolymer, namely the P(FP-co-UPy-co-HP) segment, thereby endowing the final product with a star-triblock overall molecular structure. Its highly branched structural characteristics can increase the steric hindrance and entanglement of polymer molecular chains, providing a structural basis for the thickening performance of the thickener. At the same time, in terms of performance realization, the hydrophobicity and branched structure of the highly branched polyolefin derivative can synergistically work with the segments formed by other monomers to enhance the stability of the thickener in a high-salt environment. The branched structure reduces the interference of salt ions on the intermolecular interactions of polymer molecules. At the same time, its unique spatial configuration helps maintain the viscosity of the system. Together with zwitterionic groups and other components, it enhances the high salt resistance of the thickener, enabling it to maintain good thickening effect in salt-containing systems. In addition, the chemical structure of this monomer allows it to adapt to the reaction conditions of atom transfer radical polymerization and is compatible with initiators, other monomers and catalytic systems in the system, ensuring the smooth progress of the polymerization reaction and ultimately forming a structurally stable and high-performance target thickener.

[0053] The meanings of the components in the star-shaped triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4 are as follows:

[0054] The "Br4" on the far left represents the core initiation structure of the star polymer. "Br" refers to bromine atoms, and "4" indicates that there are four bromine-containing active initiation sites on the core, corresponding to the "arm initiation ends" of the four-arm star topology. These bromine atoms are derived from the previously synthesized four-arm bromoester macromolecular initiator (Br4-Core), which is the active starting point for subsequent atom transfer radical polymerization (ATRP), ensuring that the four polymer arms can grow synchronously and uniformly from the core.

[0055] The overall structure within the brackets “[]” represents the “single-arm chain segment composition” of the star polymer. The “4” in the lower right corner outside the brackets echoes the “Br4” on the left, indicating that the star copolymer contains 4 identical arms that together form a four-arm star topology around the central core, which is different from linear, three-arm or multi-arm (4) polymer structures. This four-arm symmetrical design can improve the hydrodynamic volume and salt resistance of the molecular chain.

[0056] The “P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)” inside a single arm is a typical triblock structure. The “-b-” is the characteristic linking symbol of the block copolymer, representing the orderly connection of different homopolymer / copolymer segments through chemical bonds, forming a symmetrical triblock sequence of “end segment-middle segment-end segment”. That is, two identical end segments (FP-co-UPy-co-HP) are connected to the two ends of the middle segment (PSBMA).

[0057] Specifically, "FP-co-UPy-co-HP" represents an end-functional copolymer segment: "P" is an abbreviation for polymer, indicating that this part is a polymeric segment; the "co" in "FP-co-UPy" is an abbreviation for copolymerization, indicating that this segment is formed by random copolymerization of three monomers, "FP", "UPy", and "HP", rather than a homopolymer of a single monomer; among them, "FP" corresponds to the fluoroalkyl methacrylate (such as perfluorooctyl methacrylate) monomer unit, which imparts hydrophobic properties and salt-enhanced association energy to the segment. The key functional groups are: "UPy" corresponds to the ureidinone methacrylate monomer unit, which contains ureidinone groups that can form quadruple hydrogen bonds, providing stable non-covalent crosslinking sites for the chain segments; "HP" corresponds to the highly branched polyolefin derivative functional monomer, whose highly branched polyolefin segments have strong hydrophobicity and are expected to enhance the salt resistance and thickening ability of thickeners through physical crosslinking; at the same time, the star-triblock structure combined with highly branched segments can more effectively control hydrodynamic volume and solution rheological behavior; in addition, branched polyolefin segments may produce synergistic effects with other components (such as fluoroalkyl chains) to further optimize performance.

[0058] "PSBMA" represents the intermediate zwitterionic homopolymer segment: "P" also indicates a polymer, and "SBMA" is an abbreviation for sulfobetaine methacrylate, indicating that this segment is formed by homopolymerization of a single SBMA monomer; the SBMA monomer unit contains -N + (CH3)3 and -SO3 - The positive and negative charge groups give the PSBMA chain segment strong ionic hydration ability and electrostatic interaction. It is not only the hydrophilic backbone that provides basic viscosity in low-salt environments, but also the core structure that maintains molecular solubility and supports the function of end group segments in high-salt environments.

[0059] In summary, the entire structural expression fully presents the copolymer’s “four-arm star topology + symmetrical triblock segments + functionalized monomer units” characteristics. The core initiation site (Br4) determines the topological starting point, the four-arm structure ([]4) determines the spatial morphology, and the triblock sequence P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP) determines the functional partitions. All parts work together to form a salt-resistant polymer structure that combines hydrophilic thickening, hydrogen bonding crosslinking and hydrophobic association capabilities.

[0060] Step S3 is the ATRP polymerization reaction of the second block P(FP-co-UPy-co-HP). This step combines atom transfer radical polymerization (ATRP) with random copolymerization, introducing functional blocks at both ends of the hydrophilic backbone, which is a key step in endowing the thickener with excellent salt resistance. Its reaction mechanism is completely consistent with the ATRP cycle in step S2. The core is to use the dormant C-Br bond at the end of the Br4-PSBMA-Br4 chain as a new initiation center, and restart the ATRP process under the action of supplementary catalysts (Cu(I)Br and PMDETA). Since three monomers, fluoroalkyl methacrylate (FP), ureidopyrimidinone methacrylate (UPy) and highly branched polyolefin derivative functional monomer, are added simultaneously to the reaction system, these three monomers will randomly add to the growing polymer chain under the action of growing free radicals to form P(FP-co-UPy-co-HP) random copolymer segments, and finally complete the construction of the triblock structure.

[0061] From a material perspective, the starting materials are the star-shaped polymer intermediate Br4-PSBMA-Br4, FP monomers, UPy monomers, HP monomers, and a supplementary catalyst. After the reaction, the target product, a star-shaped triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4, is finally generated. This product exhibits a four-armed star topology, with each arm being a symmetrical triblock structure: the middle segment is a hydrophilic PSBMA homopolymer segment (B segment), mainly responsible for providing hydration capacity and thickening basis under low-salt conditions; the two ends are hydrophobic / hydrogen-bonding functional P(FP-co-UPy-co-HP) random copolymer segments (A and A' segments), where the hydrophobic effect of FP and the hydrogen bonding effect of UPy play a key role in high-salt conditions, jointly maintaining the viscosity of the system. This molecular design allows functional groups (FP, UPy, and HP) to be precisely positioned at both ends of the molecular arm, greatly increasing the probability that they will recognize each other, meet, and form a physical cross-linked network in solution, thus providing structural protection for the thickener's excellent salt resistance.

[0062] In some embodiments, in step S3, the molar ratio of the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer is (70-85):(5-10):(10-20), and the total molar number of the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer is 10%-30% of the molar number of the sulfobetaine methacrylate monomer in step S2.

[0063] The molar ratio of the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer is (70-85):(5-10):(10-20), and the total molar number of the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer is 10%-30% of the molar number of the sulfobetaine methacrylate monomer in step S2. The design of this ratio aims to achieve a synergistic balance among "hydrophobic association strength", "dynamic hydrogen bond crosslinking" and "three-dimensional entanglement": if the FP ratio is too high (>85), it will lead to excessively strong hydrophobic association, especially in low-salt environments, which will easily form an overly dense association structure, affecting the solubility and leveling properties of the thickener; if the UPy ratio is too high (>10), the hydrogen bond crosslinking points will be too dense, which will limit the network dynamics, leading to a decrease in the elasticity of the material under high salt conditions and easy cracking; while the addition of HP significantly enhances the stability of the hydrophobic microregions and introduces the topological entanglement effect, but its dosage must be strictly controlled. If it is too high (>20), it will lead to excessive rigidity of the molecular chain, affecting the dynamic reconstruction ability of the thickening network. The total amount of the three components is controlled at 10% to 30% of SBMA, based on the consideration of "balance between functional modification and hydrophilicity". When the amount is less than 10%, there are insufficient physical cross-linking points, and it is difficult to resist chain collapse caused by electrostatic shielding under high salt conditions. When the amount is more than 30%, too many hydrophobic and hydrogen-bonded groups will destroy the hydration of PSBMA chain segments, resulting in a significant decrease in the solubility of the thickener, or even phase separation in water, and complete loss of thickening ability.

[0064] In some embodiments, in step S3, the fluoroalkyl methacrylate monomer is 1H,1H,2H,2H-perfluorooctyl methacrylate, the ureidopyrimidinone methacrylate monomer is 2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl)methacrylate, and the highly branched polyolefin derivative functional monomer is a branched polyolefin macromonomer with methacrylate end groups.

[0065] In some embodiments, in step S3, the molar amount of CuBr added to N,N,N',N'',N''-pentamethyldiethylenetriamine is the same as the molar amount of CuBr added to N,N,N',N'',N''-pentamethyldiethylenetriamine in step S2.

[0066] In some embodiments, in step S3, the temperature for continuing the atom transfer radical polymerization reaction is 45–55°C, and the reaction time is 12–24 h.

[0067] The purpose of supplementing the polymerization process with the same amount of CuBr and PMDETA as initially added in step S2, and controlling the reaction temperature at 45–55°C and the reaction time at 12–24 h, is as follows: Supplementing with an equal amount of catalyst aims to maintain a sufficient catalytic concentration in the system. Since the Br active sites at the ends of the PSBMA segments are partially deactivated or encapsulated after the first polymerization step, supplementing with catalyst effectively restores and maintains the catalytic activity of the system. This ensures that FP, UPy, and HP monomers can be efficiently and quantitatively grafted to both ends of the PSBMA segments, avoiding structural defects such as "single-end grafting" or "ungrafted" structures, and guaranteeing the integrity of the final star-triblock structure and the accuracy of the molecular design. The reaction temperature of 45–55°C, consistent with step S2, helps maintain the thermodynamic equilibrium and kinetic controllability of the ATRP reaction, preventing temperature fluctuations from causing a broadening of the molecular weight distribution or deviations from the designed segment structure. The longer reaction time of 12 to 24 hours is due to the significant differences in steric hindrance and diffusion rate between FP, UPy, and HP monomers and SBMA (the fluorocarbon chain, UPy ring structure, and HP's large three-dimensional structure all increase steric hindrance and mass transfer difficulties). Their polymerization rate is relatively slow, and the reaction time needs to be extended to ensure that the conversion rate of all types of functional monomers reaches more than 90%. If the functional monomers are not completely polymerized, the density of terminal functional groups in the thickener will be insufficient, and a complete, uniform, and strong physical cross-linking network cannot be formed under high salt conditions, resulting in a significant decrease in salt resistance.

[0068] S4. The second polymerization system is subjected to catalyst removal via a neutral alumina column, dialysis, and freeze-drying to obtain a highly salt-resistant zwitterionic synthetic thickener.

[0069] It should be noted that step S4 is a post-processing step. This step removes impurities from the system through a series of physical and chemical processes to obtain a high-purity target product while protecting the integrity of the polymer structure. The specific process and its function are as follows: First, neutral alumina column treatment is performed. The alumina surface is alkaline, which can efficiently remove residual catalyst Cu(II)Br2 / PMDETA complexes from the system through strong adsorption, preventing the catalyst from interfering with subsequent thickening performance. Simultaneously, the alkaline surface can promote the hydrolysis or elimination reaction of unstable C-Br bonds at the polymer ends, converting them into more stable ends (such as -OH or olefin end groups), improving the product's storage and usage stability. Next, dialysis is performed. Using the semi-permeable membrane sieving function of a dialysis bag (MWCO3500-5000), residual small molecule impurities in the system are separated and removed, including trace amounts of salt, unreacted FP and UPy monomers, further improving product purity and preventing impurities from affecting the rheological properties and salt resistance of the thickener. Finally, freeze-drying is used to sublimate the water in the sample directly from the solid to the gaseous state under low temperature and vacuum conditions, avoiding damage to the polymer structure (especially the hydrogen bond network of the UPy group) caused by high temperature drying, and finally obtaining a dry white flocculent or powdery target product.

[0070] In terms of material transformation, the starting system is a complex mixture containing catalyst, unreacted monomer, by-products and target polymer. After post-processing, a high-purity, highly salt-resistant zwitterionic synthetic thickener is finally obtained. Its structure is complete and its performance is stable, which can meet the application needs in fields such as digital printing paste.

[0071] Based on a general inventive concept, this application provides the application of a highly salt-resistant zwitterionic synthetic thickener prepared by any of the above methods in digital printing pastes, wherein the mass fraction of the highly salt-resistant zwitterionic synthetic thickener in the digital printing paste is 0.5-3%;

[0072] The viscosity retention rate of the digital printing paste is not less than 90% when the electrolyte concentration is not higher than 100 mmol / L.

[0073] The thickening mechanism of traditional polyzwitterionic electrolytes (such as PSBMA) relies on the strong electrostatic repulsion and ion hydration generated by the positive and negative charged groups on their chains, which causes the molecular chains to be highly extended in water, resulting in high viscosity. However, in a high-salt environment, the added salt ions shield these electrostatic effects, causing the molecular chains to collapse and the viscosity to drop sharply.

[0074] This application constructs a four-fold synergistic network of "electrostatic-hydrogen bonding-hydrophobic association-topological entanglement" through precise molecular structure design and mechanism regulation, achieving synergistic and relay effects under different salt concentrations. This fundamentally overcomes the bottleneck of high-salt failure in traditional PSBMA thickeners. The specific improvement path is as follows:

[0075] In low-salt environments (0–50 mmol / L), the system is dominated by electrostatic interactions of the PSBMA segments, with hydrogen bonding, hydrophobic association, and topological entanglement providing auxiliary enhancements, thus laying the foundation for its salt tolerance. The -N atoms on the PSBMA segments... + (CH3)3 and -SO 3- The strong electrostatic repulsion between positively and negatively charged groups propels the molecular chains to a high degree of extension. Simultaneously, ion hydration causes the chain segments to bind a large number of water molecules, forming a large hydrodynamic volume and directly providing the initial high viscosity. At this point, although the quadruple hydrogen bonds of the UPy group, the hydrophobic association of the FP group, and the three-dimensional entanglement of the HP group are weakened by environmental conditions (the hydrogen bond network of water molecules inhibits hydrophobic aggregation, and the electrostatic repulsion masks the hydrogen bond effect), they can still form weak physical cross-linking points. These cross-linking points can reduce the random entanglement of the molecular chains, optimize the rheological properties of the system (such as increasing the low shear viscosity to prevent ink bleeding), and more importantly, reserve the structural basis for the switching of action under high salt conditions, avoiding the direct collapse of the molecular chains when the salt concentration increases later.

[0076] When the environmental salt concentration rises to 50–100 mmol / L (high-salt environment), traditional PSBMA thickeners will fail due to electrostatic shielding effects. However, this application achieves precise relay of salt resistance performance through "triple salt-resistant module activation + star-shaped topology assistance." On one hand, salt ions (Na+)... + / Cl - The charged groups of PSBMA are encapsulated through electrostatic shielding: Na + Neutralize-SO 3- The negative charge, Cl - Neutralization-N + The positive charge of (CH3)3 significantly weakens the electrostatic repulsion, causing the molecular chains to tend to collapse. On the other hand, the "triple salt-resistant module" in the system is simultaneously activated: the quadruple hydrogen bonds of the UPy group are unaffected by salt ions and can stably crosslink at different molecular chain ends (e.g., the combination of UPy A chain and UPy B chain), forming "molecular anchors" that hold back the collapsing PSBMA chain segments, preventing excessive chain curling; the fluorocarbon chains of the FP group, due to the salting-out effect, are pushed and aggregated by the repulsive force of water molecules to form "hydrophobic microregions"; HP, with its large three-dimensional branched structure and multiple hydrophobic end groups, further enhances the stability of the hydrophobic microregions and introduces a strong topological entanglement effect. These microregions, as strong physical crosslinking points, together with the UPy hydrogen bonds and HP entanglement network, construct a more robust three-dimensional physical crosslinking network. Meanwhile, the four-armed star topology plays a key auxiliary role: the hydrophobic Br4-Core core and the FP hydrophobic microregions synergistically associate, further enhancing the stability of the three-dimensional network; and the high branching degree of the star structure makes the hydrodynamic volume of the molecular chain more than 30% larger than that of the linear structure, so even if partial collapse occurs, it can still maintain a high viscosity and avoid a sharp drop in the viscosity of the system.

[0077] This "intelligent relay of a four-way network" mechanism ultimately achieves a significant improvement in salt resistance: at a salt concentration of 100 mmol / L (equivalent to 1 / 3 of seawater salinity), the viscosity retention rate of the thickener in this application can be further increased to ≥95%, while the viscosity of traditional PSBMA thickeners will decrease by more than 80% under the same conditions (from 10000 mPa˙s to <2000 mPa˙s). When applied to digital printing pastes (addition amount 0.5-3%), it can also adapt to the process requirements of high-salt dye systems: during the printing process (high shear), the physical cross-linking network is temporarily destroyed, and the viscosity drops to 50-100 mPa˙s, ensuring smooth ink jetting without clogging; during the post-printing resting stage (low shear), the network quickly recovers, and the viscosity rises back to 5000-8000 mPa˙s, effectively preventing pattern bleeding, balancing fluid stability and printing clarity, and completely solving the performance defects of traditional thickeners in high-salt application scenarios.

[0078] In summary, the highly salt-resistant zwitterionic synthetic thickener provided in this application has the following advantages:

[0079] (1) Advantages of molecular design: Precise topology and functional partitioning lay the foundation for salt tolerance. This application adopts a precise molecular topology design of "four-arm star-symmetric triblock". The core advantage is to achieve the directional distribution and synergistic effect of functional groups. With the four-arm bromide ester macromolecular initiator (Br4-Core) as the star core, it ensures that the four polymer arms grow synchronously and uniformly to form a symmetric topological structure. Compared with linear or asymmetric multi-arm structures, this design increases the hydrodynamic volume of the molecular chain by more than 30%, and is more difficult to collapse as a whole under high salt conditions. The "P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)" symmetric triblock sequence of each arm combines hydrophilic thickening (PSBMA), hydrogen bonding (UPy), hydrophobic association (FP) and topological entanglement (HP). With precise functional partitioning, the middle PSBMA segment ensures low-salt thickening and high-salt solubility, while the two P(FP-co-UPy-co-HP) segments at both ends serve as the core functional modules for salt resistance, avoiding "ineffective aggregation" or "dissolution imbalance" caused by disordered distribution of functional groups, thus achieving "functional complementarity and synergistic salt resistance" at the molecular structure level.

[0080] (2) Advantages of the preparation process: Atom transfer radical polymerization (ATRP) is used throughout the process. Through the redox cycle of the CuBr / PMDETA catalytic system, the molecular weight and distribution of each block are precisely controlled (PDI<1.3). Compared with traditional free radical polymerization, the fluctuation of salt resistance caused by uneven chain length can be avoided, and the viscosity retention rate of each batch of products under high salt conditions can be ensured. Moreover, the dormant C-Br bond at the chain end is used to realize the "one-pot" block polymerization, which eliminates the need to separate intermediates, simplifies the process and reduces product loss. Meanwhile, the core parameters of each step are optimized. For example, in S1, the molar ratio of pentaerythritol: 2-bromoisobutyryl bromide: acid binder = 1:(4.0~4.5):(4.2~5.0) ensures complete esterification of the star-shaped core without "residual arm" impurities; in S2, the ratio of [SBMA] / [Br] = 45~55 balances the hydration capacity and anti-entanglement properties of PSBMA segments; in S3, FP:UPy:HP = (70~85):(5~10):(10~20) and the total amount is 10%~30% of SBMA, precisely controlling the synergistic balance of hydrophobicity, hydrogen bonding and entanglement. These parameter designs avoid "overdoing it" and ensure that the polymerization process is controllable and the product performance is stable. In addition, the post-processing flow of "neutral alumina column catalyst removal - dialysis impurity removal - freeze drying" is adopted. The neutral alumina column can efficiently remove copper salts without destroying the molecular structure, and freeze drying avoids the destruction of UPy quadruple hydrogen bonds by high temperature. Compared with high temperature drying or organic solvent precipitation, this process can achieve a product purity of over 95% while preserving the integrity of the key salt-resistant structures (hydrogen bond network, hydrophobic microregions and topological entanglement structure).

[0081] (3) Performance advantages: The core performance advantage of this application lies in the construction of a smart relay network with four functions of "electrostatic-hydrogen bond-hydrophobic association-topological entanglement", which completely solves the defect of "high salt will inevitably lose thickening" of traditional PSBMA thickener. In low-salt environments (0–50 mmol / L), the electrostatic repulsion and ion hydration of the PSBMA segment dominate, providing initial high viscosity. At the same time, UPy / FP / HP form weak physical cross-linking points, optimizing rheological properties (improving low-shear viscosity and preventing ink bleeding), reserving a structural basis for switching to high-salt conditions. Meanwhile, in high-salt environments (50–100 mmol / L), when salt ions shield electrostatic effects, the quadruple hydrogen bonds of UPy (unaffected by salt) immediately form "molecular anchors" to hold back the collapsing chain segments. The fluorocarbon chains of FP are strengthened by the salting-out effect, enhancing hydrophobic association. HP further enhances the network resilience and stability through its three-dimensional entanglement structure, forming a more robust three-dimensional physical cross-linking network. With the structural support of the star-shaped topology, the viscosity retention rate is significantly improved to ≥95% at a salt concentration of 100 mmol / L (equivalent to 1 / 3 of seawater salinity), while the viscosity of traditional PSBMA decreases by more than 80% under the same conditions (from 10000 mPa·s to <2000 mPa·s), achieving a qualitative breakthrough in salt resistance.

[0082] (4) Application advantages: The thickener of this application has significant advantages in the field of digital printing paste, and is perfectly suited to the process requirements of high-salt dye systems (such as reactive dyes). Only 0.5-3% needs to be added to the digital printing paste to achieve the required viscosity. Compared with traditional thickeners (addition amount of 5-8%), the amount used is reduced, which reduces the cost of the paste and the burden of subsequent cleaning. At the same time, the high shear (during printing) physical cross-linking network is temporarily destroyed, and the viscosity drops to 50-100 mPa·s, ensuring smooth ink spraying and no nozzle clogging. The low shear (post-printing) network can recover more quickly due to the topological entanglement effect introduced by HP, and the viscosity rises back to 5000-8000 mPa·s, effectively preventing pattern bleeding and taking into account both "smooth spraying" and "printing clarity". In addition, the strong ionic hydration layer of the PSBMA segment can stably disperse dye molecules, avoid "color spots" and "color differences" caused by dye aggregation under high salt conditions, and ensure the color fastness (≥4 grade) and color uniformity of printed products.

[0083] The present application is further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the application. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to industry standards. If there is no corresponding industry standard, then common international standards, conventional conditions, or conditions recommended by the manufacturer are followed.

[0084] Example 1

[0085] This embodiment provides a method for preparing a highly salt-resistant zwitterionic synthetic thickener, comprising the following steps:

[0086] S11. Under nitrogen (inert atmosphere) and ice bath conditions, pentaerythritol (CAS No.: 115-77-5), 2-bromoisobutyryl bromide (CAS No.: 20769-85-1), and the acid-binding agent pyridine (CAS No.: 110-86-1) were added to the organic solvent tetrahydrofuran (CAS No.: 109-99-9) and mixed, wherein the molar ratio of pentaerythritol, 2-bromoisobutyryl bromide, and pyridine was 1:4.25:4.6; then the system was heated to room temperature and esterification reaction was carried out for 24 h. After the reaction was completed, the byproduct pyridine hydrobromide was removed by filtration to obtain the four-armed bromoester macromolecular initiator Br4-Core;

[0087] S12. A four-armed brominated ester macromolecular initiator Br4-Core, sulfobetaine methacrylate monomer (SBMA, CAS No.: 3637-26-1, specification: 98%, source leaf S70859), CuBr (CAS No.: 7787-70-4), and N,N,N',N'',N''-pentamethyldiethylenetriamine (CAS No.: 3030-47-5) were added to an alcohol / water mixed solvent. The molar ratio of bromine atoms in Br4-Core, sulfobetaine methacrylate monomer, CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine was 1:50:1:1, and the volume ratio of methanol (CAS No.: 67-56-1) to water in the alcohol / water mixed solvent was 1:1.5. Atom transfer radical polymerization was carried out at 45-55℃ for 6 hours to obtain a first polymerization system containing the star polymer intermediate Br4-PSBMA-Br4.

[0088] S13. Add to the first polymerization system a fluoroalkyl methacrylate monomer (1H,1H,2H,2H-perfluorooctyl methacrylate, CAS No.: 2144-53-8, Bailingwei 579376-25G), a ureidopyrimidinone methacrylate monomer (2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl) methacrylate), and a highly branched polyolefin derivative functional monomer (branched polyolefin macromonomers with methacrylate end groups), wherein the fluoroalkyl methacrylate monomer and the ureidopyrimidinone methacrylate monomer... The molar ratio of the functional monomers of the highly branched polyolefin derivative is 70:5:10, and the total molar amount of the three is 10% of the molar amount of sulfobetaine methacrylate monomer in step S12; at the same time, CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine are added in the same molar amount as added in step S12, and the atom transfer radical polymerization reaction is continued at 45-55°C for 18 hours to obtain a second polymerization system containing star-shaped triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4;

[0089] The preparation method of the 2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl)methacrylate is as follows: 2-amino-6-methyl-4(1H)-pyrimidinone (UPy-NH2, CAS No.: 4611-97-8) is dissolved in anhydrous and deoxygenated N,N-dimethylformamide (DMF) and placed in a three-necked flask equipped with a magnetic stirrer, a thermometer and a constant pressure dropping funnel. Under nitrogen protection, a slightly excess of triethylamine was added to the system as an acid-binding agent, and the system temperature was lowered to 0–5 °C (ice-water bath). A calculated amount of 3-isocyanate propyl methacrylate (CAS No.: 30674-80-7) was weighed and dissolved in an appropriate amount of anhydrous DMF, and the solution was transferred to a constant-pressure dropping funnel. Under ice-water bath and vigorous stirring, the DMF solution of 3-isocyanate propyl methacrylate was slowly added dropwise to the DMF solution of 2-amino-6-methyl-4(1H)-pyrimidinone. The dropping rate was controlled to maintain the reaction system temperature below 10 °C. After the addition was complete, the ice-water bath was removed, and the reaction mixture was slowly raised to room temperature, and the reaction was continued to be stirred at this temperature for 24 h. The reaction progress was monitored by thin-layer chromatography (TLC) or Fourier transform infrared spectroscopy (FTIR) (monitoring the isocyanate groups (-NCO) in the system at 2270 cm⁻¹). -1 (Whether the characteristic absorption peaks in the vicinity have completely disappeared); after the reaction is completed, the reaction mixture is poured into a large amount of ice-cold diethyl ether to precipitate. Filter and collect the solid product; purify the crude product by column chromatography (using silica gel as the support and dichloromethane / methanol mixed solvent as the eluent) to obtain a high-purity white or off-white solid product; place the purified product in a vacuum drying oven and dry it thoroughly at 45℃ for 24h to obtain the final target monomer 2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl)methacrylate;

[0090] The preparation method of the branched polyolefin macromonomer with methacrylate end groups is as follows: Hydroxylated branched polyolefin (commercial model: POLYTAIL H, CAS: 68954-10-9) is dissolved in anhydrous and deoxygenated tetrahydrofuran (THF) and placed in a three-necked flask equipped with a magnetic stirrer, thermometer, and constant-pressure dropping funnel. Under nitrogen protection, a slightly excess of triethylamine is added to the system as an acid-binding agent, and the system temperature is lowered to 5°C (ice-water bath). A calculated amount of methacryloyl chloride (CAS: 920-46-7) is weighed and dissolved in an appropriate amount of anhydrous THF, and the solution is transferred to a constant-pressure dropping funnel. Under ice-water bath and vigorous stirring, the THF solution of methacryloyl chloride is slowly added dropwise to the THF solution of hydroxylated branched polyolefin, controlling the dropping rate to maintain the reaction system temperature below 10°C. After the addition is complete, the ice-water bath is removed, and the reaction mixture is slowly raised to room temperature, and the reaction is continued to be stirred at this temperature for 18 hours. The reaction process was monitored by Fourier transform infrared spectroscopy (FTIR) (monitoring the hydroxyl group (-OH) in the system at 3400 cm⁻¹). -1 The weakening of the characteristic absorption peak and the presence of the carbonyl group (C=O) in the methacryloyl group at 1720 cm⁻¹ -1 (Enhancement of nearby characteristic absorption peaks); After the reaction, the reaction mixture was filtered to remove triethylamine hydrochloride, and the filtrate was precipitated in ice-cold diethyl ether. The solid product was collected by filtration and washed repeatedly with cold diethyl ether. The crude product was washed with n-hexane for 24 h using a Soxhlet extractor to completely remove unreacted small molecule impurities, and then dried under vacuum at 40 °C for 48 h to obtain the final target product—a branched polyolefin macromonomer with methacrylate end groups.

[0091] S14. The second polymerization system is adsorbed through a neutral alumina column to remove the catalyst CuBr2 / PMDETA complex. Then, it is dialyzed for 48 hours with a dialysis bag with a molecular weight cutoff of 3500-5000 to remove small molecule impurities. Finally, the dialyzed system is placed in a freeze dryer for freeze drying to obtain a highly salt-resistant zwitterionic synthetic thickener.

[0092] Example 2

[0093] This embodiment provides a method for preparing a highly salt-resistant zwitterionic synthetic thickener, comprising the following steps:

[0094] S21. Under nitrogen (inert atmosphere) and ice bath conditions, pentaerythritol, 2-bromoisobutyryl bromide, and the acid-binding agent pyridine were added to the organic solvent dichloromethane and mixed, wherein the molar ratio of pentaerythritol, 2-bromoisobutyryl bromide, and pyridine was 1:4.0:4.2; then the system was heated to room temperature and the esterification reaction was carried out for 20 h. After the reaction was completed, the byproduct pyridine hydrobromide was removed by filtration to obtain the four-armed bromoester macromolecular initiator Br4-Core;

[0095] S22. A four-armed brominated ester macromolecular initiator Br4-Core, sulfobetaine methacrylate monomer (SBMA, specification: 98%), CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine were added to an alcohol / water mixed solvent. The molar ratio of bromine atoms in Br4-Core, sulfobetaine methacrylate monomer, CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine was 1:45:0.9:0.9, and the volume ratio of ethanol to water in the alcohol / water mixed solvent was 1:1. Atom transfer radical polymerization was carried out at 45–55 °C for 4 h to obtain a first polymerization system containing the star polymer intermediate Br4-PSBMA-Br4.

[0096] S23. Add fluoroalkyl methacrylate monomer (1H,1H,2H,2H-perfluorooctyl methacrylate), ureidopyrimidinone methacrylate monomer (2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl) methacrylate), and highly branched polyolefin derivative functional monomer (branched polyolefin macromonomer with methacrylate end groups) to the first polymerization system, wherein the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer... The molar ratio of the monomers is 70:5:20, and the total molar amount of the three is 20% of the molar amount of sulfobetaine methacrylate monomer in step S22; at the same time, CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine are added in the same molar amount as added in step S22, and the atom transfer radical polymerization reaction is continued at 45-55℃ for 12h to obtain a second polymerization system containing star-shaped triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4;

[0097] S24. The second polymerization system is adsorbed through a neutral alumina column to remove the catalyst CuBr2 / PMDETA complex. Then, it is dialyzed for 48 hours with a dialysis bag with a molecular weight cutoff of 3500-5000 to remove small molecule impurities. Finally, the dialyzed system is placed in a freeze dryer for freeze drying to obtain a highly salt-resistant zwitterionic synthetic thickener.

[0098] Example 3

[0099] This embodiment provides a method for preparing a highly salt-resistant zwitterionic synthetic thickener, comprising the following steps:

[0100] S31. Under nitrogen (inert atmosphere) and ice bath conditions, pentaerythritol, 2-bromoisobutyryl bromide and pyridine, an acid-binding agent, were added to the organic solvent N,N-dimethylformamide and mixed, wherein the molar ratio of pentaerythritol, 2-bromoisobutyryl bromide and pyridine was 1:4.5:5.0; then the system was heated to room temperature and esterification reaction was carried out for 28 h. After the reaction was completed, the byproduct pyridine hydrobromide was removed by filtration to obtain the four-armed brominated ester macromolecular initiator Br4-Core;

[0101] S32. A four-armed brominated ester macromolecular initiator Br4-Core, sulfobetaine methacrylate monomer (SBMA, specification: 98%), CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine were added to an alcohol / water mixed solvent. The molar ratio of bromine atoms in Br4-Core, sulfobetaine methacrylate monomer, CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine was 1:55:1.1:1.1, and the volume ratio of methanol to water in the alcohol / water mixed solvent was 1:2. Atom transfer radical polymerization was carried out at 45–55 °C for 8 h to obtain a first polymerization system containing the star polymer intermediate Br4-PSBMA-Br4.

[0102] S33. Add fluoroalkyl methacrylate monomer (1H,1H,2H,2H-perfluorooctyl methacrylate), ureidopyrimidinone methacrylate monomer (2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl) methacrylate), and highly branched polyolefin derivative functional monomer (branched polyolefin macromonomer with methacrylate end groups) to the first polymerization system, wherein the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer... The molar ratio of the monomers is 80:7:15, and the total molar amount of the three is 25% of the molar amount of sulfobetaine methacrylate monomer in step S32; at the same time, CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine are added in the same molar amount as added in step S32, and the atom transfer radical polymerization reaction is continued at 45-55℃ for 24h to obtain a second polymerization system containing star-shaped triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4;

[0103] S34. The second polymerization system was subjected to adsorption of the catalyst CuBr2 / PMDETA complex through a neutral alumina column. Then, it was dialyzed for 48 hours with a dialysis bag with a molecular weight cutoff of 3500-5000 to remove small molecule impurities. Finally, the dialyzed system was placed in a freeze dryer for freeze drying to obtain a highly salt-resistant zwitterionic synthetic thickener.

[0104] Example 4

[0105] This embodiment provides a method for preparing a highly salt-resistant zwitterionic synthetic thickener, comprising the following steps:

[0106] S41. Under nitrogen (inert atmosphere) and ice bath conditions, pentaerythritol, 2-bromoisobutyryl bromide, and the acid-binding agent pyridine were added to a mixed solvent of tetrahydrofuran and dichloromethane (volume ratio 1:1), wherein the molar ratio of pentaerythritol, 2-bromoisobutyryl bromide, and pyridine was 1:4.3:4.8; the system was then heated to room temperature and esterified for 26 hours. After the reaction was completed, the byproduct pyridine hydrobromide was removed by filtration to obtain the four-armed bromoester macromolecular initiator Br4-Core.

[0107] S42. A four-armed brominated ester macromolecular initiator Br4-Core, sulfobetaine methacrylate monomer (SBMA, specification: 98%), CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine were added to an alcohol / water mixed solvent. The molar ratio of bromine atoms in Br4-Core, sulfobetaine methacrylate monomer, CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine was 1:48:1.0:1.0, and the volume ratio of ethanol to water in the alcohol / water mixed solvent was 1:1.8. Atom transfer radical polymerization was carried out at 45–55 °C for 7 h to obtain a first polymerization system containing the star polymer intermediate Br4-PSBMA-Br4.

[0108] S43. Add fluoroalkyl methacrylate monomer (1H,1H,2H,2H-perfluorooctyl methacrylate), ureidopyrimidinone methacrylate monomer (2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl) methacrylate), and highly branched polyolefin derivative functional monomer (branched polyolefin macromonomer with methacrylate end groups) to the first polymerization system, wherein the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer... The molar ratio of the monomers is 85:10:15, and the total molar amount of the three is 30% of the molar amount of sulfobetaine methacrylate monomer in step S42; at the same time, CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine are added in the same molar amount as added in step S42, and the atom transfer radical polymerization reaction is continued at 45-55℃ for 20h to obtain a second polymerization system containing star-shaped triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4;

[0109] S44. The second polymerization system was subjected to adsorption of the catalyst CuBr2 / PMDETA complex through a neutral alumina column. Then, it was dialyzed for 48 hours with a dialysis bag with a molecular weight cutoff of 3500-5000 to remove small molecule impurities. Finally, the dialyzed system was placed in a freeze dryer for freeze drying to obtain a highly salt-resistant zwitterionic synthetic thickener.

[0110] Comparative Example 1

[0111] This comparative example is modified from the one disclosed in Example 1 as follows:

[0112] In step S11, instead of using the four-armed brominated ester macromolecular initiator Br4-Core, a linear brominated initiator (ethyl 2-bromoisobutyrate) was used. In step S12, the linear brominated initiator was used instead of Br4-Core for atom transfer radical polymerization, and finally a linear polyzwitterionic thickener P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP) was prepared, instead of a star-triblock structure.

[0113] Comparative Example 2

[0114] This comparative example is modified from the one disclosed in Example 1 as follows:

[0115] In step S13, no ureidopyrimidinone methacrylate monomer or highly branched polyolefin derivative functional monomer was added; only fluoroalkyl methacrylate monomer was added, meaning the functional monomer was only fluoroalkyl methacrylate. The final star-shaped triblock copolymer structure was Br4-[P(FP)-b-PSBMA-bP(FP)]4, lacking UPy and HP functional units.

[0116] Comparative Example 3

[0117] This comparative example is modified from the one disclosed in Example 1 as follows:

[0118] In step S13, no fluoroalkyl methacrylate monomers or highly branched polyolefin derivative functional monomers were added; only ureidopyrimidinone methacrylate monomers were added, meaning the functional monomer was only ureidopyrimidinone methacrylate. The final star-shaped triblock copolymer structure was Br4-[P(UPy)-b-PSBMA-bP(UPy)]4, lacking FP and HP functional units.

[0119] The monomer conversion rate, molecular weight and distribution of block copolymers in the polymerization products, and the content of homopolymers in the products of the highly salt-resistant zwitterionic synthetic thickeners of Examples 1-4 and Comparative Examples 1-3 were determined. The results are shown in Table 1. The determination methods are as follows:

[0120] (1) Monomer conversion rate: calculated by monitoring the decrease in the peak area of ​​characteristic monomers in the reaction system by gas chromatography (GC).

[0121] (2) Number average molecular weight (Mn): Determined by gel permeation chromatography (GPC) with polystyrene as standard and an aqueous solution of DMF containing LiBr (for zwitterionic polymers) as the mobile phase.

[0122] (3) Molecular weight distribution (Dispersity): also known as polydispersity index (PDI), which is given directly from the GPC test results.

[0123] (4) Homopolymer content: The peak shape of the GPC chromatogram is analyzed and the preparative GPC or gradient precipitation method is used for separation and weighing.

[0124] Table 1. Polymerization properties and product structural parameters of highly salt-resistant zwitterionic thickeners

[0125]

[0126] As shown in Table 1, the conversion rates of SBMA monomers in all systems exceeded 95%, and the conversion rates of FP and UPy functional monomers (except for Comparative Example 1) also exceeded 90%. This indicates that the atom transfer radical polymerization (ATRP) system has high reactivity towards each monomer, and the selected reaction conditions (such as the type of initiator, the ratio of the catalytic system, and the solvent environment) can efficiently promote the polymerization reaction and achieve full conversion of each monomer, thus providing a guarantee for the structural construction of the target thickener.

[0127] From the perspective of topological influence, Comparative Example 1 (linear structure) differs significantly from the Example 2 (star structure): Comparative Example 1's number-average molecular weight (9.1 × 10⁻⁶) is significantly different. 4 The concentration (g / mol) was significantly lower than that of the examples (33.0–40.5 × 10⁻⁶ g / mol). 4 The results (g / mol) directly confirm that the four-armed star initiator Br4-Core can effectively achieve simultaneous growth of the four arms of the chain segment, significantly increasing the molecular weight of the product. Its molecular weight distribution (1.45) is wider than that of the example (1.18-1.22), and the homopolymer content (8.10%) is much higher than that of the example (1.44%-1.85%). Moreover, the conversion rates of FP and UPy (88.7% and 85.7%) are lower than those of the example. This result indicates that the star structure is more conducive to suppressing the termination side reactions (such as bimolecular termination and chain transfer) during the polymerization process and maintaining the activity of the chain ends. At the same time, the star topology can reduce the viscosity of the reaction system and promote the diffusion and reaction contact of functional monomers (FP, UPy) in the solution. In contrast, the linear structure is prone to increased viscosity in the later stage of the reaction and the active ends being buried by the polymer chain, resulting in a decrease in the controllability of polymerization and thus an increase in the amount of homopolymer generated.

[0128] Regarding the synergistic effect of functional monomers, the number-average molecular weights of Comparative Example 2 (containing only FP functional monomers) and Comparative Example 3 (containing only UPy functional monomers) were 36.0 × 10⁻⁶. 4 37.2×10 4 The g / mol and molecular weight distributions (1.21, 1.23) are similar to those of the examples, indicating that the polymerization process of the single functional monomer system still has good controllability; however, the homopolymer content of the two (2.45%, 2.52%) is slightly higher than that of most examples. It is speculated that the single functional monomer causes an imbalance in the compatibility of monomers in the system or changes in the local reaction microenvironment (such as polarity, solubility), triggering a small amount of additional chain termination reaction. The synergistic introduction of FP and UPy can optimize the system microenvironment and further reduce the amount of homopolymer generated.

[0129] The application performance and effects of the highly salt-tolerant zwitterionic synthetic thickeners from Examples 1 to 4 and Comparative Examples 1 to 3 were determined, and the results are shown in Tables 2 and 3. The determination was performed according to the following methods:

[0130] The basic conditions for testing are as follows:

[0131] Test fabric: Commercially available rayon woven fabric was selected as the printing carrier fabric.

[0132] Printing formulation (mass fraction): 1% highly salt-resistant zwitterionic synthetic thickener (Examples 1-4 and Comparative Examples 1-3), 2% baking soda, 1% anti-dyeing salt, 10% urea, 5% reactive dye, and 81% water.

[0133] Printing process flow: Printing → Drying → Steaming (105℃, keep warm for 8 min) → Cold water washing → Warm water washing (80℃) → Soap washing (95℃, add 2g / L Yacos SWconc. soaping agent) → Warm water washing → Cold water washing → Cold water washing → Drying, to complete the post-printing treatment.

[0134] The specific performance testing methods are as follows:

[0135] (1) Thickening ability (viscosity η) (水) (Measurement)

[0136] Sample preparation: Prepare 200g of thickener white paste with a mass concentration of 3% (containing only thickener and water, without other printing components).

[0137] Instruments and measurement parameters: Brookfield RVDV-II+Pro viscometer with #6 rotor was used, the rotation speed was set to 20 rpm, and the test temperature was controlled at 25℃.

[0138] Measurement procedure: Immerse the viscometer rotor into the white slurry to the specified depth. After the instrument reading stabilizes, record the viscosity value at this point, denoted as η(water), which characterizes the basic thickening ability of the thickener.

[0139] (2) Salt resistance stability (viscosity retention rate determination)

[0140] Sample preparation: Add 3.0g Na2SO4 (simulating the dyeing salt environment in reactive printing paste, with an electrolyte concentration higher than 100mmol / L) to 200g of 3% thickener white paste used in the "thickening ability test" and stir evenly.

[0141] Viscosity Measurement: Using the same instruments, rotor, and temperature conditions as in the "Thickening Ability Measurement," the viscosity of the white paste after adding Na2SO4 was measured and denoted as η. (盐) .

[0142] Calculation method: Salt tolerance is characterized by viscosity retention rate, calculated using the formula "Viscosity retention rate = η". (盐) / η (水) According to the calculation of "×100%", the higher the viscosity retention rate, the better the viscosity stability of the thickener in a high-salt environment.

[0143] (3) Rheological compatibility (determination of printing viscosity index PVI value)

[0144] Sample preparation: Same as "Thickening ability test", prepare 200g of thickener white paste with a mass concentration of 3%.

[0145] Instruments and parameters: The apparent viscosity of the white paste was measured using a viscometer at two shear rates of 6 rpm and 60 rpm (the two shear rates differed by a factor of 10), and the test temperature was 25℃.

[0146] Calculation method: The printing viscosity index (PVI) is calculated according to the formula "PVI value = η(60) / η(6)", where η(60) is the apparent viscosity at a shear rate of 60 rpm and η(6) is the apparent viscosity at a shear rate of 6 rpm. The PVI value reflects the viscosity change characteristics of the thickener under different shear conditions and is suitable for printing and setting requirements.

[0147] (4) Printing color effect (determination of apparent printing depth K / S value)

[0148] Sample preparation: According to the above printing formula and process, the printing and post-treatment (drying, steaming, washing, soaping, etc.) are completed on the rayon woven fabric to obtain the printed finished fabric.

[0149] Instruments and Operation: Using a Datacolor400 colorimeter, under specified measurement conditions (such as standard light source D65, 10° viewing angle), the apparent color gain on the surface of the printed fabric is measured and recorded as the K / S value.

[0150] Results characterization: The larger the K / S value, the more dye the fabric adsorbs, the higher the apparent color yield of the printed color, and the richer and brighter the color.

[0151] (5) Desizing performance (desizing rate determination)

[0152] Sample weighing: Weigh the mass of the dried rayon woven fabric before printing (recorded as W0), the mass of the dried fabric after printing without desizing (recorded as W1), and the mass of the dried fabric after desizing through the above printing process (water washing, soap washing) (recorded as W2).

[0153] Calculation method: The desizing rate is calculated according to the formula "Desizing rate = (W1-W2) / (W1-W0)×100%". The higher the desizing rate, the more thoroughly the thickener paste remaining after printing is removed, and the better the fabric's hand feel and wearing performance.

[0154] Table 2 Viscosity properties of highly salt-resistant zwitterionic synthetic thickeners

[0155]

[0156] Table 3. Printing effect of highly salt-resistant zwitterionic synthetic thickeners

[0157]

[0158] As shown in Tables 2 and 3, the thickening ability η of the highly salt-tolerant zwitterionic synthetic thickeners from Examples 1 to 4 is... (水) Its salt tolerance is 48,500–55,000 cps, and its salt resistance η is... (盐) The viscosity ranges from 44,500 to 51,300 cps, with a viscosity retention rate of 91.8% to 93.3%. The viscosity of its printing working paste ranges from 4,900 to 5,600 cps, with a rheological compatibility (PVI) value of 0.25 to 0.27, a printing color yield (K / S) value of 17.7 to 18.1, and a desizing rate of 97.9% to 98.5%.

[0159] In Comparative Example 1, a linear initiator was used instead of a star-shaped topological initiator, which resulted in the loss of the inherent large hydrodynamic volume and multi-site initiation advantage of star molecules, leading to a severe deficiency in thickening ability (η). (水) With a viscosity of only 19,500 cps, and the complete shielding of the electrostatic repulsion of the linear zwitterionic chains in a high-salt environment, the molecular chains collapse violently and cannot maintain viscosity (viscosity retention rate of only 50.3%), ultimately resulting in uncontrolled viscosity of the working paste (1,800 cps), severe printing bleeding, and low color yield (K / S value of 15.3).

[0160] In Comparative Example 2, no ureidopyrimidinone (UPy) methacrylate monomer and highly branched polyolefin derivative functional monomer were introduced. It relied solely on the hydrophobic association of the fluorocarbon chain (FP). Although the association was enhanced due to the "salting-out effect" in a high-salt environment, it was still insufficient to completely resist the shielding effect of salt ions on the zwitterionic backbone. As a result, its salt resistance stability (viscosity retention rate of 76.0%) and printing clarity (slight bleeding) were significantly lower than those of the Example.

[0161] In Comparative Example 3, no fluoroalkyl (FP) methacrylate monomers or highly branched polyolefin derivative functional monomers were introduced. It relied solely on the quadruple hydrogen bonding of UPy. Although this bonding is not sensitive to salt, it lacks the synergistic enhancement of hydrophobic association and cannot form a sufficiently dense physical crosslinking network to completely resist the collapse of the zwitterionic backbone. As a result, its salt resistance stability (viscosity retention rate of 67.6%) and working slurry viscosity (3500 cps) were the worst among all functionalized groups, and significant bleeding occurred in the printing.

[0162] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0163] Furthermore, in the description of this application, the terms "comprising," "including," etc., mean "including but not limited to." In this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0164] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing a highly salt-resistant zwitterionic synthetic thickener, characterized in that, The thickener is a multifunctional star-shaped block copolymer with highly branched polyolefins as hydrophobic blocks, and the method includes the following steps: S1. Under an inert atmosphere and ice bath conditions, pentaerythritol, 2-bromoisobutyryl bromide, an acid-binding agent and an organic solvent are mixed and then esterified at room temperature. After post-treatment, a four-armed brominated ester macromolecular initiator Br4-Core is obtained. S2. The four-armed brominated ester macromolecular initiator Br4-Core, sulfobetaine methacrylate monomer, CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine are added to an alcohol / water mixed solvent to carry out an atom transfer radical polymerization reaction to obtain a first polymerization system containing the star polymer intermediate Br4-PSBMA-Br4. S3. Add fluoroalkyl methacrylate monomer, ureidopyrimidinone methacrylate monomer and highly branched polyolefin derivative functional monomer to the first polymerization system, and supplement CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine to continue the atom transfer radical polymerization reaction to obtain a second polymerization system containing star-triblock copolymer Br4-[P(FP-co-UPy-co-HP)-b-PSBMA-bP(FP-co-UPy-co-HP)]4; S4. The second polymerization system is subjected to catalyst removal by neutral alumina column, dialysis and freeze-drying to obtain a highly salt-resistant zwitterionic synthetic thickener; The molar ratio of pentaerythritol, 2-bromoisobutyryl bromide, and the acid-binding agent is 1:(4.0-4.5):(4.2-5.0). The esterification reaction is carried out at room temperature for 20–28 hours. The molar ratio of bromine atom, sulfobetaine methacrylate monomer, CuBr, and N,N,N',N'',N''-pentamethyldiethylenetriamine in the four-armed brominated ester macromolecular initiator Br4-Core is 1:(45-55):(0.9-1.1):(0.9-1.1). The atom transfer radical polymerization reaction is carried out at a temperature of 45–55°C for a reaction time of 4–8 h. The atom transfer radical polymerization reaction is continued at a temperature of 45–55°C for a reaction time of 12–24 h. The molar ratio of the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer is (70-85):(5-10):(10-20), and the total molar number of the fluoroalkyl methacrylate monomer, the ureidopyrimidinone methacrylate monomer, and the highly branched polyolefin derivative functional monomer is 10%-30% of the molar number of the sulfobetaine methacrylate monomer. The highly branched polyolefin derivative functional monomer is a branched polyolefin macromonomer with methacrylate end groups.

2. The method for preparing the highly salt-tolerant zwitterionic synthetic thickener according to claim 1, characterized in that, In step S1, the acid-binding agent is pyridine, and the organic solvent is at least one of tetrahydrofuran, dichloromethane, or N,N-dimethylformamide. In step S2, the volume ratio of alcohol to water in the alcohol / water mixed solvent is 1:(1-2), and the alcohol is at least one of methanol or ethanol.

3. The method for preparing the highly salt-tolerant zwitterionic synthetic thickener according to claim 1, characterized in that, In step S3, the fluoroalkyl methacrylate monomer is 1H,1H,2H,2H-perfluorooctyl methacrylate, and the ureidopyrimidinone methacrylate monomer is 2-(3-({[6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl]amino}formamido)propyl)methacrylate.

4. The method for preparing the highly salt-tolerant zwitterionic synthetic thickener according to claim 1, characterized in that, In step S3, the molar amounts of CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine added are the same as the molar amounts of CuBr and N,N,N',N'',N''-pentamethyldiethylenetriamine added in step S2.

5. The application of a highly salt-resistant zwitterionic synthetic thickener prepared by the method according to any one of claims 1 to 4 in digital printing paste, characterized in that, The mass fraction of the highly salt-resistant zwitterionic synthetic thickener in the digital printing paste is 0.5%–3%. The viscosity retention rate of the digital printing paste is not less than 90% when the electrolyte concentration is not higher than 100 mmol / L.

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