Z-type four-arm raft hyperdispersant, and preparation method and application thereof

Abstract

The application discloses a Z-type four-arm RAFT superdispersant and a preparation method and application thereof. The superdispersant is constructed by sequentially introducing monomers such as N-vinyl pyrrolidone, methoxy polyethylene glycol acrylate and butyl acrylate into a Z-type four-functional macromolecular RAFT reagent as a core through a RAFT controlled polymerization technology to form an amphiphilic block copolymer. In addition, monomers such as styrene, methyl methacrylate and acrylic acid can be selected and combined to optimize the performance of the dispersant. The four-arm superdispersant can be efficiently adsorbed on the surface of pigment particles due to the multi-anchor point structure, so that the grinding efficiency and dispersion stability are significantly improved; the hydrophilic polyethylene glycol segment inhibits particle agglomeration through a steric hindrance effect, and the hydrophobic block enhances the interfacial bonding force with the pigment. Further, the pigment after grinding is coated with styrene to form a dense polymer layer, so that the ink has excellent rheological properties and storage stability.

Description

Technical Field

[0001] This invention relates to the field of polymer materials and digital printing ink technology, and in particular to a Z-shaped four-armed RAFT superdispersant, its preparation method and application. Background Technology

[0002] In the field of digital printing inks, the dispersion stability of pigment particles is a core factor in ink performance. Pigments need to be uniformly dispersed with a nanometer-scale particle size of 50-200 nm to meet inkjet printing requirements. Key indicators include a particle size distribution range ≤1.5, a Zeta potential ≥40 mV, no sedimentation after aging at 60℃, and a viscosity of 25-35 mPa·s. Traditional dispersion technologies face challenges: nanoparticles are prone to agglomeration, and particle size is difficult to control (e.g., ceramic inks aim for <300 nm, but often exceed 500 nm); insufficient dispersant performance leads to particle aggregation, increased viscosity, and precipitation during storage; the hydrophilic-hydrophobic balance affects rheological properties, causing print line breaks or nozzle clogging. These challenges make dispersant molecule design a key bottleneck for performance breakthroughs.

[0003] RAFT polymerization, as an important branch of controlled radical polymerization, has become a core method for the precise design of polymeric dispersants since its commercialization in the early 21st century. Compared with traditional radical polymerization, RAFT achieves precise control over molecular weight, molecular weight distribution (PDI can be reduced to below 1.3), and block sequence through RAFT reagents. Narrow distribution characteristics enhance the dispersant's adsorption capacity and steric hindrance uniformity. In terms of block design, the performance of diblock dispersants, such as those in patent CN105418865, is significantly improved. RAFT polymerization has high monomer compatibility and can introduce functional groups to optimize interfacial interactions, thus becoming a mainstream technology for high-performance superdispersants.

[0004] Linear RAFT dispersants represent an early application of RAFT polymerization in the dispersant field. They feature a linear chain molecular structure, with anchoring groups binding to pigment particles and hydrophilic segments forming a steric hindrance layer. Patent CN105418865 discloses a PS-b-PAA diblock copolymer dispersant where the PS segment is hydrophobically anchored and the PAA segment is hydrophilically solvated, resulting in a PDI of 1.42, superior to traditional free radical polymerization products. However, this technology still has significant shortcomings: First, the arm segments have limited function and lack polarity-regulating segments, preventing the formation of multiple hydrogen bonds or dipole interactions with the pigment surface through polar groups, leading to limited interfacial binding energy. Second, molecular weight distribution control still needs optimization; while its PDI value of 1.15-1.25 is superior to linear structures, uneven adsorption due to differences in molecular chain length still occurs in the dispersion of high-pigment pigments (such as carbon black). Third, the process is complex, requiring step-by-step arm segment polymerization, resulting in a long production cycle. US Patent 9453127B2 (published in 2016) discloses a "method for preparing polymer-coated pigments" that employs a "grafting-to" strategy. It first synthesizes a dispersant and then grafts it onto the pigment surface via a chemical reaction. While this achieves the construction of the coating layer, it requires a separate coating reaction, increasing the number of process steps by more than 30%. Furthermore, the coating layer thickness is uneven, affecting the stability of the ink's rheological properties. These technological explorations indicate that while multi-arm structures can improve anchoring efficiency, there is still significant room for improvement in terms of functional integration and process simplification.

[0005] Z-type RAFT reagents have become a new direction for dispersant design due to their unique chain transfer activity and structural tunability. Their structure contains multiple thiocarbonyl sulfide (-SC(=S)-) groups, enabling multi-directional chain growth. Patent CN116444803A describes a bifunctional Z-type RAFT reagent prepared by alternating copolymerization of 2-vinylnaphthalene and maleic anhydride, possessing two chain transfer sites for the synthesis of two-armed block copolymers. However, the limited number of arms in the two-armed Z-type structure results in insufficient coverage and weak steric hindrance, leading to limited improvement in dispersion stability. In the research of four-armed RAFT dispersants, existing technologies such as patent CN106543321A employ RAFT polymerization, resulting in a wide molecular weight distribution, weak interfacial bonding, and insufficient long-term storage stability. These findings indicate that existing technologies face significant bottlenecks in terms of molecular weight control precision, synthesis efficiency, and functional synergy, making it difficult to meet the requirements of high-performance pigment inks.

[0006] The defects in molecular weight control and structural regularity of traditional RAFT dispersants affect the stability and reliability of their dispersion performance. Regarding molecular weight control, linear RAFT dispersants have a wide molecular weight distribution (e.g., the PS-b-PAA dispersant in patent CN105418865 has a PDI of 1.28), which can be effectively reduced by optimizing the multi-arm structure. This wide distribution leads to differences in adsorption between dispersant molecules: low molecular weight molecules have weak anchoring and are easily desorbed from the pigment surface during grinding or storage; high molecular weight molecules experience chain entanglement, resulting in abnormal viscosity. The problem with structural regularity is even more prominent. Traditional linear RAFT dispersants are prone to "gradient copolymerization" in the synthesis of multi-block copolymers. Taking a system with styrene (St) and acrylic acid (AA) monomers as an example, due to the difference in the polymerization rates of the two monomers (r_St=0.78, r_AA=0.15), the second block monomer still retains unreacted monomers in the later stages of polymerization, forming an impure block structure. This structural defect makes it difficult to precisely control the hydrophilic-hydrophobic balance of the dispersant, resulting in significant fluctuations in dispersion stability with temperature changes in pigment dispersion applications (particle size 120 nm at 25℃, 180 nm at 40℃). Furthermore, RAFT reagent microparticle stabilizers, such as those disclosed in patent CN102424703, have low anchoring efficiency, requiring the addition of surface modifiers, increasing cost and complexity. These shortcomings severely limit performance improvement.

[0007] Existing patents for dispersants suffer from insufficient functional synergy in their structural designs, making it difficult to achieve synergistic optimization of multiple action mechanisms involving hydrophobicity, hydrophilicity, and polarity. Linear dispersants, such as patent CN105418865, have a limited number of anchoring points, leading to easy desorption and pigment agglomeration, low grinding efficiency, and long grinding times. Multi-arm dispersants, such as patent CN112321879, have simple arm compositions, lack polarity-regulating segments, and have insufficient interfacial binding energy. Double-Z-type dispersants, such as patent CN116444803, exhibit weak steric hindrance, resulting in a thin adsorption layer and an inability to suppress van der Waals forces. Triblock dispersants, such as patent CN112321879, suffer from disordered polar monomer distribution due to their polymerization method, leading to poor dispersion stability and high sedimentation rates. These shortcomings indicate that existing dispersants cannot achieve the synergistic effect of hydrophobic anchoring, hydrophilic solvation, and polarity regulation, exhibiting significant limitations in their controllability.

[0008] The inherent defects of existing superdispersant technology have become a bottleneck in the high-performance pigment ink industry. According to an industry report released by TechHigh.com, pigment inks treated with existing dispersants show particle size increases exceeding 25% and color loss of 15-20% in accelerated aging tests, failing to meet requirements. Production efficiency is low: grinding time is long (e.g., grinding time for phthalocyanine blue pigment requires 5-6 hours), energy consumption increases by 40%, and the pass rate is only 85%. Environmentally, VOCs exceed 0.1%, failing to meet EU standards. In terms of application, nozzle clogging accounts for 35% of all failures, and increased particle size after long-term storage can lead to color deviations; for example, the color difference value (ΔE) of Hansa Yellow ink increased from 1.2 to 3.5 after 6 months of storage. The root cause of these problems lies in the inability of existing dispersants to simultaneously achieve precise molecular weight control, multi-block synergistic effects, and process integration, making it difficult to achieve breakthroughs in dispersion stability, production efficiency, and environmental performance of pigment inks. Therefore, developing new superdispersants with structural innovation and performance advantages has become an urgent need to solve industry pain points and promote the technological upgrade of high-performance pigment inks. To address the shortcomings of existing technologies, this invention aims to solve the following four core technical problems: First, by designing a four-armed Z-type RAFT reagent, precise control of the dispersant's molecular weight and improved structural regularity are achieved, reducing the PDI to below 1.2. Second, the synergistic effect of hydrophobic-hydrophilic-polar triblock polymerization enhances the pigment interfacial binding force and steric hindrance effect, increasing the adsorption layer thickness to over 15 nm. Third, the polymerization process is optimized to achieve efficient synthesis of the four-armed Z-type RAFT reagent, increasing the yield to over 85%. Fourth, an integrated control system for pigment grinding, coating, and ink formation is constructed, adaptable to various pigments, simultaneously achieving surface coating, resulting in ink with no sedimentation for 6 months and stable rheological properties. This patent provides a novel superdispersant with controllable structure, excellent performance, and efficient process, supporting the development of high-performance environmentally friendly pigment inks. Summary of the Invention

[0009] The technical problem to be solved by this invention is to provide a superdispersant prepared based on four-arm Z-type RAFT controlled polymerization technology, its synthesis method, and its application, so as to overcome the defects of traditional dispersants such as uncontrollable molecular weight, simple structure, and poor environmental compatibility, thereby adapting to different pigment systems and significantly improving the grinding efficiency and long-term stability of liquid dispersed dyes. The general structural formula of the superdispersant is as follows: Wherein: A is a hydrophobic acrylate monomer, selected from one of butyl acrylate (BA), ethyl acrylate (EA), and methyl methacrylate (MMA), which forms multiple anchoring points on the pigment surface through long alkyl chains to enhance interfacial bonding. B is a hydrophilic polyethylene glycol acrylate monomer, selected from one of methoxy polyethylene glycol acrylate (PEGA) and polyethylene glycol methacrylate (PEGMA). It provides steric hindrance through polyethylene glycol segments to inhibit particle aggregation. C is a polar vinyl monomer selected from N-vinylpyrrolidone (NVP), acrylic acid (AA), and dimethylaminoethyl methacrylate (DMAEMA). The polar group enhances the compatibility of the dispersant with the aqueous system. x, y, and z are integers of 5-10, 3-10, and 6-10, respectively. The molecular weight is precisely controlled to 11,000-29,000 Da using RAFT technology, and the polydispersity index is ≤1.2.

[0010] The superdispersant is constructed using RAFT controlled polymerization technology, with a Z-type tetrafunctional macromolecular RAFT reagent as the core, and sequentially introducing monomers such as N-vinylpyrrolidone (NVP), methoxy polyethylene glycol acrylate (PEGA), and butyl acrylate (BA) to form an amphiphilic block copolymer. In addition, monomers such as styrene (St), methyl methacrylate (MMA), and acrylic acid (AA) can be selected for combination screening to optimize the dispersant performance. This four-armed superdispersant, with its multi-anchoring structure, can efficiently adsorb onto the surface of pigment particles, significantly improving grinding efficiency and dispersion stability. Its hydrophilic polyethylene glycol segments inhibit particle aggregation through steric hindrance, while the hydrophobic blocks enhance the interfacial bonding with the pigment. Further surface coating of the ground pigment with styrene forms a dense polymer layer, giving the ink excellent rheological properties and storage stability. The resulting digital printing ink has uniform particle size, high color saturation, and shows no sedimentation even after long-term storage. The innovation of this invention lies in: 1) The introduction of a four-armed Z-type RAFT reagent greatly improves the controllability of the molecular weight and the regularity of the structure of the superdispersant; 2) The multi-block synergistic effect realizes the integrated control of pigment grinding-coating-inking; 3) The superdispersant can be adapted to a variety of pigment systems, providing a new strategy for the development of high-performance environmentally friendly inks.

[0011] The method for synthesizing the superdispersant includes the following steps: (1) Preparation of the four-armed Z-type RAFT reagent: K3PO4, CS2, and tetrahydrofuran were weighed and added to a flask. After low-temperature stirring and thorough mixing, pentaerythritol tetrakis(3-mercaptopropionic acid) was slowly added dropwise to the suspension. The mixture was stirred for 0.5 h, and then benzyl chloride was added. The mixture was stirred continuously for 24-48 h. After filtration to remove insoluble matter, the crude product was concentrated by rotary evaporation and then dried under vacuum to remove the solution. The product was then purified by silica gel column chromatography.

[0012] (2) Block polymerization of four-armed superdispersant: Under nitrogen protection, RAFT reagent, hydrophobic acrylate monomer (A), hydrophilic polyethylene glycol acrylate monomer (B) and polar vinyl monomer (C) are dissolved in 1,4-dioxane at a molar ratio of 1:20-40:12-40:24-40. Initiator 4-cyanopentanoic acid (ACVA, 1-4% of the total monomer mass) and pyridine are added, and the reaction is carried out at 70-80℃ for 4-6 hours.

[0013] (3) Purification and drying: The polymerization system was immersed in ice water to quench the reaction. Hexane (volume ratio of 1:5) was added to the quenched polymerization system to precipitate the product. After vacuum filtration, the product was dried at 45°C for 12 hours to obtain a yellow viscous four-armed Z-type superdispersant.

[0014] The synthetic route diagram of the above-mentioned hyperdispersant is as follows: in: A is a hydrophobic acrylate monomer, selected from one of butyl acrylate (BA), ethyl acrylate (EA), and methyl methacrylate (MMA); B is a hydrophilic polyethylene glycol acrylate monomer, selected from one of methoxy polyethylene glycol acrylate (PEGA) and polyethylene glycol methacrylate (PEGMA); C is a polar vinyl monomer selected from one of N-vinylpyrrolidone (NVP), acrylic acid (AA), and dimethylaminoethyl methacrylate (DMAEMA); x, y, and z are integers of 5-10, 3-10, and 6-10, respectively.

[0015] Preferably, in step (1), the molar ratio of pentaerythritol tetrakis(3-mercaptopropionic acid) to benzyl chloride is 1:4; the reaction temperature is 30°C; and the reaction time is 24 h.

[0016] Preferably, in step (2), the initiator is 4-cyanopentanoic acid (ACVA), and the amount added is 1% to 4% of the total mass of the monomer, more preferably 3%; the reaction temperature is 70-80℃, more preferably 80℃.

[0017] Preferably, the hydrophobic acrylate monomers, hydrophilic polyethylene glycol acrylate monomers, and polar vinyl monomers mentioned in step (2) are butyl acrylate (BA), methoxy polyethylene glycol acrylate (PEGA), and N-vinylpyrrolidone (NVP), respectively.

[0018] The application of the superdispersant in polymer-coated pigment inks includes the following steps: (1) Pigment pre-dispersion: Mix the pigment (such as Hansa Yellow, Phthalocyanine Blue, Naphthol Red) with the superdispersant at a mass ratio of 1:0.2-0.6, add deionized water with pH 8-9 (pigment concentration 10-20 wt%), and grind in a tissue grinder for 2-5 hours (speed 1500-2100 r / min) using zirconia beads (diameter 0.6-2.0 mm) to make the pigment particle size ≤200 nm.

[0019] (2) In-situ coating: Styrene monomer (20-40% of the dye liquor mass) and initiator azobisisobutyronitrile (AIBN, 1-3% of the monomer mass) are injected into the ground slurry and reacted at 65-75℃ for 4-6 hours to form a dense polymer coating layer on the pigment surface.

[0020] (3) Ink post-treatment: Adjust the pH of the system to 7-8, add dispersant glycerol (1-3% of total mass) and leveling agent 104e (0.5-1% of total mass), filter and obtain digital printing ink. The viscosity of the ink is 10-50 mPa·s (25℃), the absolute value of the Zeta potential is ≥40 mV, and the storage stability is ≥12 months without sedimentation.

[0021] Preferably, the grinding mill speed in step (1) is 1800 r / min.

[0022] Preferably, in step (2), the amount of styrene used is 40% of the mass of the dye solution; the reaction temperature is 68°C; and the reaction time is 5 h.

[0023] Compared with the prior art, the present invention has the following beneficial effects: I. Enhanced Adsorption through Multiple Anchoring Points: The four-arm Z-shaped structure connects four block copolymers through a pentaerythritol core, providing multiple anchoring points. This significantly improves the adsorption strength of pigments with high specific surface area (such as carbon black and phthalocyanine blue), resulting in a significant reduction in grinding time. II. Precise molecular weight control: RAFT technology achieves a narrow molecular weight distribution (PDI≤1.2), and the ratio of hydrophobic / hydrophilic segments can be dynamically adjusted (e.g., BA:PEGA:NVP=3:5:6), adapting to different polar pigment systems. III. Green process optimization: The n-hexane precipitation purification process is adopted to avoid the residue of traditional solvents (such as DMF and toluene), and VOC emissions are reduced by more than 50%. III. Superior ink performance: The "core-shell" structure formed by the participation of the super dispersant makes the pigment particle size uniform (≤200nm), the coating layer has high density, the ink viscosity is stable (±5% fluctuation), and there is no stratification during long-term storage; IV. Wide Applicability: By replacing monomers (such as EA instead of BA, PEGMA instead of PEGA), it can be adapted to pigments with different chemical structures such as Hansa Yellow and quinacridone, thus expanding the application scenarios. Attached Figure Description

[0024] Figure 1 This is a synthetic route diagram of the Z-type superdispersant used in the examples.

[0025] Figure 2 The Z-type superdispersant used in the examples 1 H-NMR spectrum.

[0026] Figure 3 This is a comparison chart of the pigment dispersion performance of Z-type and R-type superdispersants.

[0027] Figure 4 Printing effect image of digital printing ink controlled by super-dispersant. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be specifically noted that the embodiments are only for the purpose of helping to understand the present invention, and do not limit the scope of the present invention. The technical features involved in the various embodiments can be combined with each other without conflict.

[0029] Example 1: Synthesis of a four-armed Z-type RAFT reagent This embodiment describes the synthesis of a four-armed Z-type RAFT reagent in tetrahydrofuran using pentaerythritol tetra(3-mercaptopropionic acid) and benzyl chloride as raw materials under K3PO4 catalysis.

[0030] Raw material specifications: Pentaerythritol tetrakis(3-mercaptopropionic acid) ester (PETMP): 98% purity, Sigma-Aldrich; K3PO4: Analytical grade, Sinopharm Group; Tetrahydrofuran (THF): Anhydrous grade, moisture <0.05%, Bailingwei; Carbon disulfide: analytical grade, Tianjin Damao Chemical Reagent Factory; Benzyl chloride: 99%, Aladdin Reagent Co., Ltd.; hexane and anhydrous NaSO4: analytical grade, Sinopharm Group; Silica gel: 200-300 mesh, Qingdao Ocean Chemical.

[0031] Equipment Model: 250mL four-necked flask (equipped with a mechanical stirrer, constant pressure dropping funnel, thermometer (accuracy ±0.5℃), and nitrogen delivery tube); Water bath (DC-0506, Ningbo Xinzhi); Rotary evaporator (RE-52AA, Shanghai Yarong, vacuum degree 0.08MPa); Vacuum drying oven (DZF-6050, Shanghai Yiheng).

[0032] The operation process is as follows Figure 1 As shown in (1), where x=5, y=3, z=6: Specific operating steps: (1) Solution preparation: Weigh 19.5g (91.2mmol) of K3PO4 and place it in a 250mL four-necked flask. Add 75mL of anhydrous tetrahydrofuran, turn on the mechanical stirrer (300rpm), and stir for 30 minutes until K3PO4 is completely dissolved to form a homogeneous suspension.

[0033] (2) Addition of raw materials: Place the four-necked flask containing the above homogeneous suspension in a water bath and cool it to 0-5℃. Add CS2 (14.0g, 184.5mmol) to the homogeneous suspension and slowly add 7.5g (15.4mmol) of pentaerythritol tetrakis(3-mercaptopropionic acid) dropwise with stirring for 30 minutes. Finally, add benzyl chloride (7.8g, 61.6mmol) and continue stirring for 24 hours.

[0034] (3) Post-treatment: Filter to remove K3PO4 solid and collect the filtrate. Add 500 mL of n-hexane for extraction, wash the organic phase three times with deionized water (500 mL each time), and dry with anhydrous NaSO4 for 2 hours. After filtration, remove the solvent by rotary evaporation (40℃, 0.08 MPa) to obtain a pale yellow crude product.

[0035] (4) Purification: silica gel column chromatography (200-300 mesh silica gel, eluent petroleum ether / ethyl acetate = 5:1), followed by rotary evaporation, and vacuum drying at 40°C for 24 hours to obtain a pale yellow viscous liquid product with a yield of 85%.

[0036] Product characterization: 1 H NMR, such as Figure 2 As shown; GPC: Mn=1151g / mol, PDI=1.08 (Waters 1515, THF mobile phase, polystyrene standard). Infrared spectrum: 2947 cm⁻¹ -1 (-CH2- stretchable), 1729cm -1 (-COO- Stretchable), 1688cm -1 (C=S characteristic peak), 1517 cm⁻¹ -1 (Vibration of the benzene ring skeleton).

[0037] Example 2: Optimized synthesis of a four-armed Z-type RAFT reagent (optimization of benzyl chloride excess ratio) Raw material adjustment: The molar ratio of benzyl chloride to pentaerythritol tetrakis(3-mercaptopropionic acid) was adjusted to 4.5:1, and other conditions were the same as in Example 1.

[0038] 8.77 g (69.3 mmol) of benzyl chloride and 7.5 g (15.4 mmol) of pentaerythritol tetrakis(3-mercaptopropionic acid) were used in a molar ratio of 4.5:1. The remaining steps remained unchanged.

[0039] Product characterization: 1 1H NMR: The thiol matrix sub-peak (δ 1.2-1.6 ppm) completely disappeared, indicating a 100% thiol conversion rate; GPC: Mn=1185g / mol, PDI=1.07; Yield: 88% (3% higher than Example 1).

[0040] Results analysis: An excess of benzyl chloride at a ratio of 4.5:1 ensures the complete reaction of the four thiol groups in pentaerythritol tetrakis(3-mercaptopropionic acid), reduces chain transfer site defects, and improves the structural symmetry of the RAFT reagent.

[0041] Example 3: Solvent ratio optimization of four-armed Z-type RAFT reagent (adjustment of tetrahydrofuran dosage) The concentration of the reaction system was reduced to 0.154 mol / L for pentaerythritol tetrakis(3-mercaptopropionic acid) ester (0.205 mol / L in Example 1), and other conditions were the same as in Example 1.

[0042] Solvent adjustment: 15.4 mmol of pentaerythritol tetrakis(3-mercaptopropionic acid) was dissolved in 100 mL of anhydrous tetrahydrofuran (75 mL in Example 1), 7.8 g (61.6 mmol) of benzyl chloride, and 19.5 g (91.2 mmol) of K3PO4. The remaining steps remained unchanged.

[0043] Product characterization: GPC: Mn=1160g / mol, PDI=1.06; Infrared spectrum: The characteristic peaks are consistent with those of Example 1, with no obvious impurity peaks.

[0044] Results analysis: Lowering the concentration reduces local side reactions, improves product purity, further reduces PDI, and increases structural regularity.

[0045] Example 4: Preparation of a four-arm Z-type superdispersant using butyl acrylate, methoxy polyethylene glycol acrylate, and N-vinylpyrrolidone as monomers Using the four-armed Z-type RAFT reagent from Example 1 as a chain transfer agent, NVP (polar segment), PEGA (hydrophilic segment), and BA (hydrophobic segment) were polymerized sequentially to synthesize a triblock superdispersant.

[0046] Raw material specifications: Four-armed Z-type RAFT reagent: Preparation in Example 1; BA: 99% purity, contains 200ppm MEHQ, Aladdin; PEGA: Mn=500g / mol, Aldrich; NVP: 99% purity, Sigma; ACVA: 98% purity, McLean; Pyridine: 99.8% purity, Maclean's; n-Hexane: Analytical grade, Sinopharm Group.

[0047] Equipment model: 500mL four-necked flask (with reflux condenser and nitrogen delivery tube); Oil bath (HH-S2).

[0048] The operation process is as follows Figure 1 As shown below, where x=5, y=3, z=6: Detailed operation steps: (1) Hydrophobic segment (BA) polymerization: Under nitrogen protection, 5.77 g (5 mmol) of RAFT reagent, 12.8 g (100 mmol) of BA (BA to RAFT molar ratio 20:1, x=5), 0.38 g of ACVA (ACVA is 1% of the monomer mass), 840 μL of pyridine, and 300 mL of 1,4-dioxane were added to a four-necked flask. After stirring evenly, nitrogen was purged for 30 minutes to remove oxygen, and the temperature was raised to 80 °C (oil bath) and reacted for 3 hours (stirring speed 300 rpm).

[0049] (2) Polymerization of hydrophilic segment (PEGA): Add 26.3 g of PEGA (60 mmol, PEGA to RAFT molar ratio 12:1, y=3), continue to purge with nitrogen, and react for 4 hours.

[0050] (3) Polar segment (NVP) polymerization: Add 13.3g of NVP (120mmol, NVP to RAFT molar ratio 24:1, z=6) and react for 5 hours.

[0051] (4) Post-treatment: The reaction system was quenched in ice water for 30 minutes, then 5 times the volume of n-hexane was added, and after shaking, the precipitate was formed. The excess n-hexane was discarded, and the mixture was vacuum dried at 45°C for 12 hours. The resulting yellow viscous four-armed Z-type superdispersant had a yield of 82%.

[0052] Product characterization: GPC: Mn=11270g / mol, PDI=1.04; 1 ¹H NMR (400MHz, CDCl₃): δ 0.8–1.0 (m, -CH₃, BA segment), 1.2–1.6 (m, -CH₂-, BA segment), 3.3–3.5 (s, -OCH₃, PEGA segment), 3.6–3.8 (m, -O-CH₂-CH₂-, PEGA segment), 3.9–4.1 (t, -COO-CH₂-, NVP segment), 6.0–6.2 (m, -CH=CH-, NVP segment); Infrared spectrum: 2880cm -1 (PEGA-CH2-stretching), 1725cm -1 (Ester group -COO-stretching), 1660cm -1 (NVP amide group -C=O stretching).

[0053] Example 5: Preparation of a superdispersant with methyl methacrylate as the hydrophobic monomer (alternative monomer example) MMA was used instead of BA as the hydrophobic segment monomer, and other conditions were the same as in Example 4.

[0054] Raw material adjustment: MMA 10g (100mmol, MMA to RAFT molar ratio 20:1), PEGA and NVP dosages are the same as in Example 4.

[0055] Product characterization: GPC: Mn=10539g / mol, PDI=1.08; 1 H NMR: δ 0.9-1.1 (s, -CH3, MMA α position), 1.8-2.0 (s, -CH3, MMA β position), 3.6-3.7 (s, -OCH3, MMA ester group), 3.3-3.5 (s, -OCH3, PEGA chain segment).

[0056] Example 6: Preparation of a superdispersant with acrylic acid as the polar monomer (alternative monomer example) AA was used instead of NVP as the polar segment monomer, and other conditions were the same as in Example 4.

[0057] Raw material adjustment: AA 8.65g (120mmol, AA to RAFT molar ratio 24:1), BA and PEGA dosages are the same as in Example 4.

[0058] Product characterization: GPC: Mn=10653g / mol, PDI=1.12; Infrared spectrum: 3433cm -1 (-COOH stretching vibration); Water contact angle: 65° (75° in Example 4), improved hydrophilicity.

[0059] Example 7: Preparation of Phthalocyanine Blue Pigment Ink Hansa Yellow pigment was dispersed using the superdispersant of Example 4, and ink was prepared using an integrated grinding-coating process.

[0060] Raw material specifications: Phthalocyanine Blue, particle size 1-3 μm, BASF; Four-armed Z-type superdispersant: Preparation in Example 4; Deionized water: pH 8-9; Styrene: 99% purity, Aladdin; AIBN: 98% purity, Sinopharm Group; Ink additives: Glycerin (Enage), 104e (Evonik).

[0061] Equipment models: horizontal sand mill (Netzsch LMZ, 0.3-0.5mm zirconia beads), ultrasonic disperser (SCIENTZ-IID), rotational viscometer (Brookfield DV3T), laser particle size analyzer (Malvin Mastersizer 3000).

[0062] (1) Pigment pre-dispersion: The pigment was mixed with the superdispersant at a mass ratio of 1:0.4 and added to a grinding jar. Deionized water with a pH of 8-9 (pigment concentration 10wt%) was added. The mixture was ground in a tissue homogenizer using zirconia beads (0.6 mm in diameter) for 2.5 hours (1800 r / min) at a grinding temperature <45℃. After grinding, the mixture was sonicated for 20 minutes to obtain the staining solution.

[0063] (2) In-situ coating: Styrene monomer (40% of the dye liquor mass) and initiator azobisisobutyronitrile (AIBN, 1% of the monomer mass) are injected into the ground slurry and reacted at 70°C for 5 hours to form a dense polymer coating layer on the pigment surface.

[0064] (3) Ink post-treatment: Adjust the pH of the system to 7-8, add dispersant glycerol (2% of total mass) and leveling agent 104e (1% of total mass), filter with a 0.22μm filter membrane to obtain phthalocyanine blue ink.

[0065] Ink performance test: Particle size: 148.6 nm (Malvern Mastersizer 3000, diluted 100 times, sonicated for 2 minutes); Viscosity: 28 mPa·s (25℃, shear rate 100 s⁻¹)-1 , Brookfield DV3T, spindle S62); Zeta potential: -48mV (Malvern Zetasizer Nano ZS); Accelerated aging at 60℃: After 3 months, the nanometer diameter was 159.3 nm (change rate 7.2%), with no sedimentation. Color performance: K / S=18.3, ΔE=0.2 (X-Rite Ci7860 spectrophotometer, printed on pure cotton fabric).

[0066] Example 8: Effect of dispersant dosage on ink performance (Application parameter optimization example) The effect of adjusting the mass ratio of pigment to superdispersant on grinding efficiency and stability was investigated, using Hansa Yellow as the subject, with other conditions the same as in Example 7.

[0067] Experimental Design: Experimental group 1:1:0.2 (pigment 1g, superdispersant 0.2g); Experimental group 2: 1:0.6 (pigment 1g, superdispersant 0.6g); Control group: Example 7 (1:0.4).

[0068] Performance test results: Experimental group 1: Grinding time 5 hours (low efficiency), particle size 178.2nm; aging at 60℃ for 3 months, change rate 25.3%, slight sedimentation; Experimental group 2: Grinding time 2 hours (high efficiency), particle size 143.8nm, but viscosity 38mPa·s (exceeding the nozzle range of 25-35mPa·s). Control group: Grinding for 2.5 hours, particle size 148.6 nm, viscosity 28 mPa·s, aging change rate 7.2%, which is the optimal dosage.

[0069] Summary of Particle Size and Distribution Test Methods and Examples Test method: Malvern Mastersizer 3000 laser particle size analyzer, based on Mie scattering theory. 1 mL of sample was diluted 100 times with deionized water and sonicated for 2 minutes (300W). Test conditions: refractive index 1.52, absorptivity 0.1, stirring speed 2000 rpm, each sample was measured 3 times and the average was taken.

[0070] Summary of Example Data: Results analysis: The ink particle size of this invention is ≤178.2nm, which meets the requirements of digital printing. The multi-anchoring point structure of the four-arm super-dispersant makes the pigment dispersion more uniform. Insufficient dispersant dosage leads to increased particle size and wider distribution, while excessive dispersant dosage leads to excessively high viscosity, making it unsuitable for inkjet printing.

[0071] Example 9: Evaluation of Printing Effects of Different Pigment Inks Phthalocyanine blue, Hansa yellow, and naphthol red were selected as dispersants, and the corresponding digital printing inks were prepared according to the "grinding and refining—in-situ coating—ink post-treatment" process described in Example 7. The mass ratio of pigment to Z-shaped four-arm RAFT superdispersant was maintained at 1:0.4, and other process parameters remained consistent. The resulting inks were used for fabric inkjet printing tests, and the printing effect was as follows: Figure 4 As shown in the figure, all inks of different colors exhibit good imaging uniformity and color saturation, and no obvious streaks, ink splatter, or broken lines caused by clogging are observed. This indicates that the super-dispersant of the present invention has good compatibility and robustness in application to different types of pigment systems.

[0072] Summary of Dispersion Stability Test Methods and Examples Test method: Stability analysis of LUMiSizer: Using a LUMiSizer 611 analyzer, 2 mL of sample was injected into a centrifuge tube and centrifuged at 25°C and 4000 rpm for 12 hours. The change in transmittance was monitored to calculate the particle size growth rate. Accelerated aging test: The ink was sealed in a 50mL brown bottle and stored in a 60℃ oven for 3 months. Samples were taken monthly to measure the particle size and the rate of change was calculated.

[0073] Summary of Example Data: Results analysis: The growth rate of the ink LUMiSizer of this invention is <4.8%, and the aging change rate is <7.2%, which is better than the system with insufficient dispersant (25.3%). The excellent stability is attributed to the adsorption of multiple anchoring points on the four arms (not easy to desorb) and the styrene coating layer (strong steric hindrance).

[0074] Summary of Rheological Performance Testing Methods and Examples Test method: Brookfield DV3T rotational viscometer, Spindle S62, shear rate tested at 25°C for 10-1000 s. -1 The viscosity was measured to evaluate the shear-thinning behavior.

[0075] Summary of Example Data: Results Analysis: The ink of this invention has low shear (10s) -1Viscosity 25-36 mPa·s (anti-settling), high shear (1000s) -1 The pressure is 5-8 mPa·s (to ensure smooth spraying), and the shear thinning index is 0.20-0.22, which meets the requirements. Excessive dispersant causes n to increase to 0.27, weakening the shear thinning. Summary of color performance and storage stability test methods and example data. Test method: Comparative Example 1: Performance Comparison with Linear RAFT Dispersant Comparative approach: Phthalocyanine blue ink was prepared using the linear PS-b-PAA dispersant (PDI=1.42) of patent CN105418865, following the process in Example 7, with a dispersant ratio of 1:0.4.

[0076] Experimental steps: Synthesis of linear dispersant (benzyl dithiobenzoate as RAFT reagent, polystyrene and acrylic acid), pigment grinding and coating as in Example 7.

[0077] Performance test results: Particle size: 185.6 nm; Aging at 60℃ for 3 months: Particle size change rate 35%, significant sedimentation; Color performance: K / S=18.2, ΔE=2.8 (exceeding the acceptable value of 2.0).

[0078] Comparative analysis: Linear dispersants have a single anchoring point (only the terminal carboxyl group), resulting in weak adsorption strength, leading to low grinding efficiency and poor stability. The four-arm structure of this invention, through multi-anchoring point adsorption (increasing interfacial binding energy by 2-3 times), exhibits significantly superior performance compared to linear dispersants.

[0079] Comparative Example 2: Performance Comparison with Existing Four-Arm RAFT Dispersants Comparative scheme: Phthalocyanine blue ink was prepared using the four-arm dispersant (PDI>1.5) of patent CN106543321A according to the process of Example 7, with a dispersant dosage of 1:0.4.

[0080] Experimental steps: The four-arm dispersant of patent CN106543321A, pigment grinding and coating are the same as in Example 7.

[0081] Performance test results: Grinding efficiency: requires 5 hours (2.5 hours in this invention), efficiency is 50% lower; Particle size: 172.6 nm; Aging at 60℃ for 3 months: Particle size change rate 28%, stratification occurs.

[0082] Comparative analysis: Existing four-arm RAFT dispersants have a wide molecular weight distribution (PDI>1.5) and uneven adsorption of dispersant molecules, resulting in low grinding efficiency and poor stability. The RAFT technology of this invention achieves PDI≤1.12, high structural regularity, and significant performance advantages.

[0083] Comparative Example 3: Performance Comparison with R-type RAFT Dispersant The "Z-type four-arm RAFT superdispersant" described in this invention refers to a multifunctional core connected to the Z group of the RAFT group, with the RAFT end group located "inner / near the core side" of the arm chain; the "R-type four-arm RAFT superdispersant" refers to a multifunctional core connected to the R (leaving group) of the RAFT group, with the RAFT end group located "outer / near the end side" of the arm chain. The two types differ in their RAFT end group connection methods, while the other monomer types and polymerization conditions remain consistent to eliminate the influence of compositional differences.

[0084] Comparative approach: In this embodiment, phthalocyanine blue ink was prepared by replacing the Z-type four-arm RAFT dispersant of the present invention with an R-type RAFT dispersant, according to the process of Example 7. The effect of different RAFT reagent topologies on dispersion performance was investigated. The amount of dispersant was kept the same as in Example 7 (pigment to dispersant mass ratio 1:0.4).

[0085] The method for synthesizing the R-type RAFT dispersant includes the following steps: (1) Under nitrogen protection, carbon disulfide (27.4 g, 0.36 mol), chloroform (107.5 g, 0.90 mol), acetone (52.3 g, 0.90 mol), tetrabutylammonium hydrosulfate (2.41 g, 7.1 mmol), and mineral oil solvent mineralspirits (120 mL) were added sequentially to the reactor, stirred and mixed, and the system temperature was controlled to be ≤25 ℃ by cooling. Under stirring and cooling conditions, 50% (mass fraction) sodium hydroxide aqueous solution (201.6 g, 2.52 mol) was added dropwise to the system obtained in step (1) over about 90 min, and the reaction temperature was controlled to be <25 ℃ throughout the dropwise addition. After the dropwise addition was completed, the reaction was stirred overnight (8–16 h) under nitrogen protection. After the reaction was completed, deionized water (900 mL) was added to the system to dissolve the inorganic salt and promote phase separation; then concentrated hydrochloric acid (120 mL) was added to the aqueous phase for acidification to precipitate the product. After stirring for 30 min, the solid was separated by filtration, washed with deionized water until the washings were nearly neutral, and dried to obtain the crude product. The crude product obtained in step (4) was purified by recrystallization using an acetone / water mixed solvent (60% acetone aqueous solution), filtered and dried to obtain yellow crystalline R-type RAFT reagent BDAAT.

[0086] (2) N-vinylpyrrolidone (NVP, 1.34 g, 12 mmol), methoxy polyethylene glycol acrylate (PEGA, 2.88 g, 6 mmol), and butyl acrylate (BA, 1.28 g, 10 mmol) were added sequentially to a reaction flask containing deoxygenated R-type RAFT reagent BDAAT (0.282 g, 1 mmol), initiator ACVA (0.056 g, 0.1 mmol), and 1,4-dioxane (36.66 g). The reaction was carried out in an oil bath at 80 °C for 3-5 h per stage under nitrogen protection. After the reaction was completed, the mixture was quenched in an ice-water bath and dried under vacuum at room temperature for 48 h to remove the solvent, thus obtaining the R-type RAFT dispersant.

[0087] Phthalocyanine blue ink preparation process: Following the process of Example 7, phthalocyanine blue pigment (PB15:3) was used as the dispersion target, and the dispersant dosage was 1:0.4 (10g pigment, 4g R-type RAFT superdispersant). The grinding parameters, in-situ coating conditions, and ink post-treatment steps were the same as in Example 7.

[0088] Performance test results: Particle size: 178.7 nm; GPC: Z type: 105.5 (PDI=1.3); R type (PDI=3.3) Aging at 60℃ for 3 months: Particle size change rate 33%, significant sedimentation; like Figure 3 As shown, the upper part displays the particle size distribution curves of the pigment dispersion system measured using a laser particle size analyzer. The comparison reveals that the particle size distribution peaks of the pigment dispersion system prepared using the Z-type four-arm RAFT superdispersant shift towards smaller particle sizes and have narrower peaks, indicating higher efficiency in refining pigment particles and a more concentrated particle size distribution. In contrast, the R-type RAFT dispersant system exhibits a larger particle size distribution and a wider distribution, showing a more pronounced tendency for agglomeration / reflocculation. This result is consistent with the average particle size data measured in this comparative example: the Z-type system has a particle size of 148.6 nm, while the R-type system has a particle size of 178.7 nm.

[0089] at the same time, Figure 3 The lower part shows the transmission electron microscopy (TEM) characterization results (scale bar 500 nm). It can be seen that the R-type system particles exhibit obvious flocculent agglomeration and continuous structure, while the Z-type system particles have clearer outlines and more uniform dispersion. This indicates that the Z-type four-arm structure can form a more stable multi-point anchoring adsorption layer and steric hindrance layer on the pigment surface, which supports its better dispersion stability and anti-settling ability from the microscopic morphology.

[0090] Comparative analysis: In this comparative scheme, only the dispersant was replaced from the Z-type four-arm RAFT superdispersant to the R-type dispersant synthesized from the R-type RAFT reagent BDAAT. The other monomer types, dispersant dosage (pigment:dispersant = 1:0.4), grinding parameters, in-situ coating conditions and ink post-processing steps were kept the same. Therefore, the performance difference between the two can be attributed to the RAFT end-group connection method and the resulting topological differences.

[0091] (1) In Z-type four-arm RAFT superdispersants, the RAFT groups are connected to the multifunctional core through the Z groups, and the active center is located on the inner side of the arm chain. During chain growth, each arm extends synchronously on the same core, making it easier to maintain the reversible addition-fracture equilibrium, thereby obtaining higher chain length consistency and more controllable polymerization behavior. In contrast, R-type dispersants use BDAAT as the RAFT reagent, and the RAFT end group is located on the end side of the chain. Under multi-stage polymerization and high temperature conditions, side reactions such as chain transfer / termination coupling are more likely to occur, resulting in a significant widening of the molecular weight distribution. This difference is reflected in the GPC of the coated shell polymer: the PDI of the Z-type coated system is 1.3, while the PDI of the R-type coated system is 3.3, indicating that the shell / free polymer chain length distribution in the R-type system is more discrete and the structural consistency is worse.

[0092] (2) The superdispersant needs to maintain a stable adsorption layer under conditions of shear, temperature rise and fluctuation of medium composition throughout the process of "grinding and refining → in-situ coating and polymerization → ink storage". The Z-type four-arm structure has the configurational advantage of multiple arms contacting the pigment surface at the same time. The single molecule can form multi-point anchoring, with higher equivalent adsorption energy and lower desorption probability, thus more effectively inhibiting reflocculation and maintaining particle size stability during grinding and coating. The R-type single-chain structure is more dependent on configuration and local action sites. It is more likely to undergo local desorption under thermal / shear disturbance, causing short-term exposure of particle surface and inducing reagglomeration.

[0093] (3) The Z-type system has higher structural consistency (smaller PDI after coating) and more stable anchoring, which is more conducive to the controlled growth of the shell on the particle surface and the formation of a continuous and dense steric barrier. The PDI of the R-type system increases significantly after coating (3.3), which means that there are a large number of short chain and long chain components at the same time. Short chains may lead to insufficient local coating, while long chains may cause local thickening or cross-particle bridging, thereby reducing the uniformity and long-term stability of the coating layer.

[0094] (4) Under the same process conditions, the phthalocyanine blue ink prepared by the Z-type system has a particle size of 148.6 nm, while the particle size of the R-type system is 178.7 nm. After accelerated aging at 60 °C for 3 months, the particle size change rate of the R-type system reached 33% and significant sedimentation occurred, indicating that its dispersion-coating structure underwent significant instability under thermal aging. In contrast, the Z-type system, due to its multi-point anchoring and more uniform shell / steric barrier, is better able to maintain particle size stability and suppress sedimentation, demonstrating superior storage stability and application robustness.

[0095] The preferred embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the specific embodiments described above. Devices and structures not described in detail should be understood as being implemented in a conventional manner in the art. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention using the methods and techniques disclosed above, or modify them into equivalent embodiments with equivalent changes, without departing from the scope of the present invention. This does not affect the essential content of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the present invention's technical solutions still fall within the protection scope of the present invention.

Claims

1. A Z-type four-arm RAFT superdispersant, characterized in that, Its general structural formula is: in: A is a hydrophobic acrylate monomer; B is a hydrophilic polyethylene glycol acrylate monomer; C is a polar vinyl monomer; x is an integer between 5 and 10, y is an integer between 3 and 10, and z is an integer between 6 and 10.

2. The Z-type four-arm RAFT superdispersant as described in claim 1, characterized in that, The hydrophobic acrylate monomer is selected from one of butyl acrylate, ethyl acrylate, and methyl methacrylate; The hydrophilic polyethylene glycol acrylate monomer is selected from one of methoxy polyethylene glycol acrylate and polyethylene glycol methacrylate; The polar vinyl monomer is selected from one of N-vinylpyrrolidone, acrylic acid, and dimethylaminoethyl methacrylate.

3. The Z-type four-arm RAFT superdispersant as described in claim 2, characterized in that, The hydrophobic acrylate monomer is butyl acrylate; The hydrophilic polyethylene glycol acrylate monomer is methoxy polyethylene glycol acrylate; The polar vinyl monomer is N-vinylpyrrolidone.

4. A method for preparing a Z-type four-arm RAFT superdispersant as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Weigh K3PO4, dissolve it in tetrahydrofuran, and add it to the reactor and stir. After mixing evenly, add pentaerythritol tetra(3-mercaptopropionic acid) and carbon disulfide to the suspension, stir, then add benzyl chloride and continue stirring. After post-treatment, the four-armed Z-type RAFT reagent is obtained. (2) Under nitrogen protection, first add polar vinyl monomer C to the four-armed Z-type RAFT reagent to carry out the first step reaction, then add hydrophilic polyethylene glycol acrylate monomer B to carry out the second step reaction, and finally add hydrophobic acrylate monomer A to carry out the third step reaction to form a polymerization system. (3) The polymerization system was immersed in ice water and exposed to air for free radical quenching. Hexane was added to cause precipitation in the polymerization system. The resulting product was dried to obtain Z-type four-arm RAFT superdispersant.

5. The preparation method according to claim 4, characterized in that, In step (1), the structural formula of the four-armed Z-type RAFT reagent is: 。 6. The preparation method according to claim 4, characterized in that, In step (2), the molar ratio of the hydrophobic acrylate monomer A to the four-armed Z-type RAFT reagent is 20:1 to 40:1; The molar ratio of the hydrophilic polyethylene glycol acrylate monomer B to the four-armed Z-type RAFT reagent is 12:1 to 40:1; The molar ratio of the polar vinyl monomer C to the four-armed Z-type RAFT reagent is 24:1 to 40:

1.

7. The application of the Z-type four-arm RAFT superdispersant as described in any one of claims 1-3 in the preparation of polymer-coated pigment inks.

8. The application as described in claim 7, characterized in that, include: (a) Mix the pigment with Z-type four-arm RAFT superdispersant, add deionized water, grind, and finally sonicate to obtain the dye solution; (b) Styrene monomer and initiator azobisisobutyronitrile are injected into the dye bath to react and form a polymerization system. The pH of the polymerization system is adjusted to 7-8, and digital printing ink auxiliaries are added. After filtration, digital printing ink is obtained.

9. The application as described in claim 8, characterized in that, In step (a), the pigment is Hansa Yellow, Phthalocyanine Blue, or Naphthol Red; Mix the pigment with Z-type four-arm RAFT superdispersant at a mass ratio of 1:0.2-0.6; Grind for 2-5 hours.

10. The application as described in claim 8, characterized in that, In step (b), the reaction is carried out at 60-70℃ for 4-6 hours.

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