A polydimethyl diallyl ammonium chloride-based polymer and a method for preparing the same

Abstract

The application discloses a kind of polydimethyl diallyl ammonium chloride-based polymer and preparation method thereof, belong to polymer material technical field.The P (DMDAAC-NVP) of two monomers in aqueous solution is successfully synthesized by free radical polymerization way.The water absorption of P (DMDAAC-NVP) prepared in the application in air can reach 57%, and thermal decomposition temperature is as high as 406 DEG C.P (DMDAAC-NVP) of the application has high cationic degree, good water-soluble and thermal stability, and has wide application prospect in sewage treatment, daily cosmetics and papermaking industry.The application can also be controlled by monomer ratio, realize the accurate design of polymer molecular weight, charge density and solution behavior.

Description

Technical Field

[0001] This invention relates to a polydimethyldiallylammonium chloride-based polymer and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] Cationic polymers, as an important class of functional polymer materials, mainly fall into three categories: quaternary ammonium salt polymers, quaternary phosphate salt polymers, and quaternary sulfonium salt polymers. The latter two have been neglected due to difficulties in monomer manufacturing or the inability to synthesize stable polymers. The former, however, is highly valued by various countries due to its wide variety, excellent application effects, and broad applicability. These materials demonstrate significant application value in multiple industrial fields: in the textile industry, they are used as antistatic agents and softeners to improve fabric performance; in the paper industry, they are used to enhance filler retention and paper strength; in water treatment engineering, they play a highly efficient flocculation role; in the biopharmaceutical field, they serve as drug carriers and antibacterial agents; and in daily chemical products, they are used as shampoo conditioners. Currently, quaternary ammonium salt polymers have the most diverse product range and are the most extensively researched.

[0003] Quaternary ammonium salt polymers are generally polymerized from quaternary ammonium salt cationic monomers. A typical example of such cationic monomers is dimethyl diallyl ammonium chloride (DMDAAC). Among polymers obtained through homopolymerization or copolymerization, diallyl dimethyl ammonium chloride (DMDAAC) has been the most studied. DMDAAC can form cationic polymers through homopolymerization or copolymerization. These polymers retain some advantages of quaternary ammonium salt monomers, such as good water solubility, easily controllable relative molecular mass, low price, high and adjustable positive charge density on the macromolecular chain, adjustable relative molecular mass, stable and highly efficient non-toxic cationic structural units, etc., and are widely used in wastewater treatment, oilfield recovery, papermaking, textiles, and daily cosmetics.

[0004] DMDAAC is a highly water-soluble quaternary ammonium salt containing two unsaturated double bonds. It is a white or slightly yellow crystal with a melting point of 146℃~147℃. It is soluble in solvents such as water and ethanol, and is extremely hygroscopic in air, so its products are generally available in the form of aqueous solutions. DMDAAC contains two unique double bonds in its structure: allyl double bonds. These two double bonds open during reactions, undergoing free radical polymerization to form homopolymers or copolymers. Furthermore, during polymerization, DMDAAC readily forms intramolecular rings, existing in the polymer as five-membered rings.

[0005] Abdollahi et al. copolymerized acrylamide (AM) and DMDAAC in D2O at 50°C using potassium persulfate (KPS) as an initiator in the presence of 0.1 mol NaCl solution, and utilized... 1H-NMR spectroscopy was used to study the copolymerization kinetics. Guan Qingqing et al. prepared a cationic block copolymer of acrylamide (AM) and DMDAAC using UV-initiated polymerization. Vahid Vajihinejad et al. synthesized a P(DMDAAC-AM) copolymer using free radical polymerization and evaluated the effects of the copolymer's chemical composition and average molecular weight on the dehydration of mature fine tailings (MFTs) in oil sands using the Reactive Surface Methodology (RSM). Research on the synthesis of DMDAAC-based cationic polymers requires a greater focus on developing green and safe polymerization technologies. Furthermore, the industrial application of such copolymers strongly depends on their molecular weight, molecular weight distribution, and viscosity. Polymerization needs careful control and optimization from these perspectives. Using RAFT polymerization or synthesizing copolymers through crosslinking copolymerization or UV-initiated polymerization cannot achieve these goals. Summary of the Invention

[0006] This invention utilizes a free radical aqueous solution copolymerization of DMDAAC and NVP monomers to synthesize a cationic copolymer P (DADMAC-co-NVP). Solution polymerization offers advantages such as simple technology, low cost, and safe operation. Copolymerization of the two monomers can increase the molecular weight and effectively control the polymer's charge density and viscosity. Furthermore, this type of polymer also boasts advantages such as low cost, high efficiency, non-toxicity, environmental friendliness, stable cationic structure, and affordable price.

[0007] This invention provides a method for preparing a polydimethyldiallylammonium chloride-based polymer, the preparation method comprising the following steps: S1. Add dimethyl diallyl ammonium chloride to the reaction vessel; S2. Add N-vinylpyrrolidone to the initiator solution to prepare a mixed solution; S3. Introduce inert gas to purge the air from the reactor and raise the temperature to 75~90℃. Under this temperature condition, add the mixed solution from S2 dropwise into the reactor at a uniform rate and keep it at this temperature for 4~10 h. S4. After the reaction is complete, cool to room temperature and discharge to obtain a polymer solution.

[0008] In one embodiment of the present invention, the molar ratio of dimethyl diallyl ammonium chloride to N-vinylpyrrolidone is (1:9) to (9:1). Preferably, the molar ratio of dimethyl diallyl ammonium chloride to N-vinylpyrrolidone is (1:1) to (9:1).

[0009] Specifically, the molar ratio of dimethyl diallyl ammonium chloride to N-vinylpyrrolidone is 9:1, 8:2, 7:3, 6:4, or 1:1.

[0010] In one embodiment of the present invention, in S2, the initiator includes persulfate initiators and / or azo initiators.

[0011] Preferably, the azo initiator includes azobisisobutyramidine hydrochloride or azobisisobutyramidine zoline hydrochloride.

[0012] In one embodiment of the present invention, in step S2, the concentration of the initiator solution is 1% to 3%. Preferably, the concentration of the initiator solution is 1.5% to 2.5%.

[0013] Specifically, the concentration of the initiator solution is 1.6%, 1.8%, 2.0%, 2.2%, and 2.4%.

[0014] In one embodiment of the present invention, in S2, the initiator solution is prepared using water as a solvent.

[0015] In one embodiment of the present invention, in step S3, the inert gas includes at least one of nitrogen, helium, or argon.

[0016] In one embodiment of the present invention, in step S3, the dropping rate is 0.1 to 0.8 mL / min. Preferably, the dropping rate is 0.1 to 0.6 mL / min.

[0017] In one embodiment of the present invention, in step S3, the temperature is raised to 75-90°C. Preferably, the temperature is raised to 80-85°C.

[0018] Specifically, the temperature was raised to 80℃, 81℃, 82℃, 83℃, 84℃, and 85℃.

[0019] In one embodiment of the present invention, in step S3, the temperature is maintained for 4 to 10 hours. Preferably, the temperature is maintained for 6 to 10 hours.

[0020] Specifically, the insulation time is 6 h, 7 h, 8 h, 9 h, and 10 h.

[0021] In one embodiment of the present invention, the material is further purified and dried after discharge.

[0022] In one embodiment of the present invention, the purification method includes acetone precipitation.

[0023] In one embodiment of the present invention, the drying method includes freeze drying.

[0024] A second object of the present invention is to provide a polydimethyldiallylammonium chloride-based polymer prepared according to the above method.

[0025] A third objective of this invention is to provide the application of the polydimethyldiallylammonium chloride-based polymer prepared by the above method in the fields of wastewater treatment, daily cosmetics, papermaking, and pigments.

[0026] Specifically, in the field of wastewater treatment, it can be used as a flocculant, a heavy metal ion coagulant, a filter aid, and a dewatering agent. Specifically, in the field of daily cosmetics, it can be used as a moisturizer and spreader.

[0027] Specifically, in the papermaking industry, it can be used as a flocculant.

[0028] Specifically, in the field of pigments, it can be used as a decolorizing agent.

[0029] A fourth object of the present invention is to provide a product comprising a polydimethyldiallylammonium chloride polymer.

[0030] In one embodiment of the present invention, the product is a flocculant, a heavy metal ion co-coagulant, a filter aid, or a dehydrating agent.

[0031] [Beneficial Effects] P(DMDAAC-NVP) was successfully synthesized by free radical polymerization of two monomers in aqueous solution, and analyzed by FT-IR. 1 The successful polymerization was verified by ¹H-NMR characterization. The effect of monomer ratio on the polymerization reaction was investigated. As the DMDAAC content decreased, the molecular weight, viscosity, cationicity, and zeta potential all showed a decreasing trend. Different materials were prepared by adjusting the amount of initiator used in the system, and their zeta potentials were studied. It was found that the zeta potential was the highest and the colloidal stability was the best when the initiator content was 2%. P(DMDAAC-NVP) has a water absorption rate of up to 57% in air and a thermal decomposition temperature as high as 406℃. As a typical polyelectrolyte, P(DMDAAC-NVP) exhibits different viscosity behaviors in electrolyte solutions. In electrolyte solutions of the same concentration, the higher the polymer solution concentration, the higher the viscosity. In electrolyte solutions of the same concentration, when the polymer solution concentration is the same, the higher the electrolyte solution concentration, the lower the viscosity. In different types of electrolyte solutions, when the polymer solution concentration is the same, the higher the cationic valence state, the lower the viscosity. These research results also indicate that the precise design of polymer molecular weight, charge density, and solution behavior can be achieved by controlling the monomer ratio.

[0032] P(DMDAAC-NVP) combines high cationicity, good water solubility, and thermal stability, and has broad application prospects in wastewater treatment, daily cosmetics, and the paper industry. Attached Figure Description

[0033] Figure 1 DMDAAC aggregation method diagram; Figure 2 Infrared spectra of DMDAAC, NVP, and P(DMDAAC-NVP); Figure 3 1H NMR spectra of DMDAAC, NVP, and P(DMDAAC-NVP); Figure 4 The effect of different monomer ratios on the viscosity of the prepared polymer; Figure 5 The effect of different monomer ratios on the cationicity of the prepared polymer; Figure 6 The effect of different monomer ratios on the Zeta potential of the prepared polymer; Figure 7 The effect of different initiator ratios on the Zeta potential of the prepared polymer; Figure 8 TGA and DTG curves of P(DMDAAC-NVP); Figure 9 Water absorption curve of P(DMDAAC-NVP); Figure 10 Viscosity curves of dilute solutions of P(DMDAAC-NVP); (a) Effect of the same electrolyte solution on the viscosity of polymer solutions of different concentrations; (b) Effect of different concentrations of the same electrolyte solution on the viscosity of polymer solutions; (c) Effect of different electrolyte solutions on the viscosity of polymer solutions. Detailed Implementation

[0034] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0035] The raw materials involved in the following embodiments: Table 1 Experimental Reagents

[0036] The detection methods involved in the following embodiments: (1) Infrared spectroscopy (FT-IR): Infrared spectroscopy was performed using a Nicolet iS50 Fourier transform infrared spectrometer from Thermo Fisher Scientific. The purified sample was placed on the sample stage and scanned using a total reflectance infrared spectrometer.

[0037] (2) Nuclear magnetic resonance (NMR) 1 H-NMR: Weigh approximately 10 mg of the sample and dissolve it in 0.6 mL of deuterated reagent (D2O). Sonicate the solution until it is completely dissolved, and then perform structural analysis on the product using nuclear magnetic resonance spectroscopy.

[0038] (3) Relative molecular mass: tested by GPC. Weigh about 25 mg of the sample and dissolve it in 5 mL of pure water. Sonicate to dissolve it completely and filter it using a 22 μm aqueous phase needle filter.

[0039] (4) Cation degree test: Prepare a 0.1 g / mL aqueous solution of the test sample, add 2-3 drops of potassium chromate solution as an indicator, and titrate with 0.0206 mol / L silver nitrate solution. The titration endpoint is indicated by the appearance of a brick-red precipitate. A blank test is performed simultaneously. The formula for calculating the cation degree is as follows:

[0040] In the formula: D – degree of cationization (mmol / g) molar concentration (mol / L) of C-silver nitrate solution V0 – The volume (mL) of silver nitrate solution consumed during the titration of the blank solution. V1 – The volume (mL) of silver nitrate solution consumed during the titration of the sample solution. m – Mass of the sample taken (g) (5) Viscosity test: The apparent viscosity of the sample was determined using an NDJ-1B rotational viscometer.

[0041] (6) Zeta potential analysis: Zeta potential was tested using a Brookhaven 90plus PALS Zeta potential and nanoparticle size analyzer. The sample was dispersed in pure water until it became a clear and transparent liquid. The electrode was placed in a cuvette containing the liquid to be tested, and the test was performed after ensuring that there were no air bubbles.

[0042] Example 1 Synthesis of polydimethyldiallylammonium chloride-based polymer In this embodiment, the molar ratio of DMDAAC to NVP is controlled at 9:1, AIBA is used as the initiator, and the reaction temperature is controlled at 85°C. The polymerization reaction yields P(DMDAAC-NVP), and the synthetic route is shown below. Figure 1 As shown, the details are as follows: 1. Polymer Synthesis S1. Add 92.9037g of a 60% (w / w) aqueous solution of dimethyl diallyl ammonium chloride (DMDAAC) to the reactor as the reaction substrate; S2. Add 52.8385 g of deionized water and 0.6 g of initiator AIBA to a beaker and sonicate to dissolve them completely. Then, add 4.2578 g of N-vinylpyrrolidone (NVP) to the solution and sonicate to mix evenly to obtain a mixed solution.

[0043] S3. Purge the reaction vessel from S1 with nitrogen gas for 15 min to remove air from the vessel, raise the temperature to 85 ℃ and maintain the temperature stable; use a peristaltic pump to add the mixed solution prepared in S2 dropwise to the reaction vessel at a uniform rate, and control the addition to be completed within 2 h (control the flow rate to be 0.5~0.6 mL / min); after the addition is completed, continue to keep it at 85 ℃ for 6 h; S4. After cooling to room temperature, the crude product is obtained and discharged.

[0044] 2. Purification of crude product Prepare a 0.1 g / mL aqueous solution from part of the crude product in step 1, add it dropwise to acetone to precipitate, let it stand for a period of time, pour off the supernatant, centrifuge, transfer the precipitate to a container, freeze dry the sample for later testing.

[0045] 3. Testing and Characterization Infrared characterization of the monomers and their polymers was performed using infrared spectroscopy. The infrared spectra are shown below. Figure 2 As shown, it can be seen that at 3387 cm -1 and 3384 cm -1 The appearance of the H-OH stretching vibration peak of water at 2994 cm⁻¹ is due to the sample's high water absorption rate. -1 and 2995 cm -1 Absorption peaks for the stretching vibrations of methyl and methylene groups appear at 1668 cm⁻¹. -1 and 1670 cm -1 The absorption peak at 1479 cm⁻¹ represents the C=O concentration in the polymer. -1 and 1484 cm -1 The absorption peak at 1640 cm⁻¹ represents the stretching vibration of a five-membered nitrogen heterocycle. -1 The peak at point C=C double bond disappears, indicating that the monomer has undergone polymerization.

[0046] The 1H NMR spectrum of P (DMDAAC-NVP) is as follows: Figure 3 As shown. By Figure 3 (a) It can be seen that the peak at δ=5.5~6 belongs to the hydrogen protons (c, d) on the carbon-carbon double bond. Figure 3 In (b), the peaks at δ=4.5 and 6.5~7 belong to the hydrogen protons (d and e) on the carbon-carbon double bond. Figure 3 In (c), the characteristic peaks from the carbon-carbon double bond disappear, and methylene and methine peaks (a, b, h) appear at δ=1.0~2.0 and 3.8 after the carbon-carbon double bond is opened. These results indicate that the reaction proceeded successfully.

[0047] Example 2: This example examines the thermal stability, hygroscopic capacity, and performance in different electrolyte aqueous solutions of the P(DMDAAC-NVP) polymer sample synthesized in Example 1. 1. Polymer thermogravimetric analysis The thermal decomposition process of the P(DMDAAC-NVP) polymer sample synthesized in Example 1 was analyzed using a thermogravimetric analyzer. The TGA and DTG curves are shown below. Figure 8 .

[0048] (1) Test method: Thermogravimetric analysis (TGA): The thermal stability of the polymer was tested using a Mettler Toledo thermogravimetric analyzer. 9 mg of the sample was weighed and heated from 50 °C to 600 °C at a rate of 10 °C / min under a nitrogen atmosphere (50 ml / min).

[0049] (2) Results and Analysis: The TGA and DTG curves show that the polymer experienced its first significant weight loss at 64℃, primarily due to the polymer solid readily absorbing moisture from the air, which evaporates upon heating, resulting in weight loss of approximately 14.77%. Further temperature increases led to a second significant weight loss peak at 210℃, mainly due to the demethylation of quaternary ammonium groups within the polymer, with a weight loss of approximately 7.62%. Subsequently, at 406℃, the polymer sample exhibited a third significant weight loss, indicating the polymer began rapid decomposition. At this point, the polymer backbone began to break down, and organic matter began to carbonize. Decomposition essentially ended at 600℃.

[0050] The DTG curve is the first derivative of the TGA curve, and the temperature corresponding to its peak value represents the temperature at which the maximum thermal decomposition rate (T) is reached. max ). Figure 8 The data shows a sharp and symmetrical peak at approximately 455°C, indicating that the main decomposition process of the polymer is relatively concentrated, and its maximum decomposition rate temperature is 455°C.

[0051] The polymer prepared by this invention exhibits excellent thermal stability. It has a high initial decomposition temperature (approximately 406°C) and a maximum decomposition rate temperature reaching 455°C, indicating that the polymer can maintain structural stability at high temperatures, thus broadening its potential in applications requiring heat resistance.

[0052] 2. Polymer water absorption analysis Because the P(DMDAAC-NVP) synthesized in Example 1 is highly hygroscopic in air, the water absorption of the polymer in air was investigated, and the results are as follows: Figure 9 .

[0053] (1) Test method: First, the P(DMDAAC-NVP) polymer sample synthesized in Example 1 was dried to constant weight in a vacuum oven at 60°C, and this initial weight (W0) was recorded. Then, the dried sample was placed in a constant temperature and humidity environment (temperature 25°C, relative humidity 80%), and removed and weighed rapidly every five hours, recording this current weight (W0). t The water absorption rate of the polymer at time t is calculated using the following formula: Water absorption rate (%) = [ (W t - W0) / W0] × 100% The water absorption rate data at different time points were plotted as curves to analyze its hygroscopic kinetic characteristics.

[0054] (2) Results and Analysis: The trend shown in the graph indicates that the water absorption rate exhibits a clear three-stage characteristic: Initial stage (0-10 h): The water absorption rate rapidly increases from about 27% to 40%, which is due to the strong hydration of hydrophilic groups such as quaternary ammonium groups and amide groups in the polymer, resulting in sufficient water absorption power; Mid-term (10-40 h): The growth rate slows down, and the water absorption rate gradually increases from 40% to about 56% as the hydrophilic groups gradually become saturated, increasing the polymer's resistance to water adsorption. Later stage (40-60 h): The water absorption rate stabilized at 56%-57%, indicating that the polymer water absorption reached a dynamic equilibrium and the binding of hydrophilic groups with water molecules reached a saturated state.

[0055] The results show that the polymer prepared in this invention has significant hygroscopic properties. Its hygroscopic kinetics are characterized by rapid initial water absorption response and the ability to quickly reach and maintain a stable hygroscopic equilibrium in the later stages.

[0056] 3. Analysis of the properties of polymer dilute solutions The P(DMDAAC-NVP) synthesized in Example 1 is a relatively typical water-soluble polyelectrolyte. Polyelectrolytes exhibit different viscosity behaviors in dilute solutions, so the properties of the polymer in dilute solutions were investigated, and the results are as follows: Figure 10 As shown: (1) Test method: The viscosity of dilute solutions of the polymer prepared in this invention under different solvent environments was measured using an NDJ-1B rotational viscometer at 25°C. Specifically, the investigation was conducted through experiments in the following three dimensions: (a) A series of polymer solutions with different concentrations (0.1 g / mL, 0.2 g / mL, 0.3 g / mL, 0.4 g / mL, 0.5 g / mL) were prepared (using 0.1 M NaCl aqueous solution as solvent) to study the effect of polymer concentration on viscosity.

[0057] (b) Prepare a polymer solution of 0.1 g / mL and dissolve it in NaCl aqueous solutions of different concentrations (0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M) to study the effect of the concentration of the added electrolyte on the viscosity.

[0058] (c) Prepare a 0.1 g / mL polymer solution and dissolve it in different 0.1 M electrolyte solutions (H2O, NaCl, CaCl2, FeCl3) to study the effect of electrolyte cation valence state on viscosity.

[0059] (2) Results and Analysis: Depend on Figure 10 As can be seen from a, in electrolyte solutions of the same concentration, when the polymer solution concentration is different, at lower polymer concentrations, as a water-soluble polyelectrolyte, the molecular chains contain positively charged groups and are in an extended state due to electrostatic repulsion in the solution. In the low concentration stage, the distance between molecular chains is large and there is little entanglement, and the viscosity is mainly determined by the hydrodynamic volume of a single molecular chain; as the concentration increases, the positive charge density in the solution increases, the electrostatic repulsion increases, the degree of molecular chain expansion increases, the chain segment packing density increases sharply, and the frictional resistance in the solution increases significantly.

[0060] Depend on Figure 10 As can be seen from b, when the polymer solution concentration is the same in different concentrations of the same electrolyte solution, the polymer molecular chain carries cationic groups. When a low molecular weight electrolyte solution is added to the polymer solution, on the one hand, the anions on the polymer molecular chain are suppressed from diffusing outward, and the electric field of the cation is weakened by the anions it carries. On the other hand, a large number of external anions are dispersed around the polymer chain, which cancels out the original cationic electric field. The repulsive effect within the molecular chain decreases, the molecular chain gradually curls up, and the size shrinks, so the polymer viscosity decreases.

[0061] Depend on Figure 10 From c, we can see that in different types of electrolyte solutions, when the polymer solution concentration is the same, the Cl in the solution... - The concentration increases with increasing cation valence state; electrolyte solutions with higher cation valence states have a greater impact on polymer viscosity. In solutions with higher cation valence states, Cl... - The greater the polarization ability, the greater the cancellation effect of the cationic electric field, which in turn leads to a weaker mutual repulsion of the cationic electric fields on the polymer molecular chain, and the more the macromolecules curl up, thus reducing the viscosity.

[0062] In summary, the polymer P (DMDAAC-NVP) prepared in this invention exhibits significant polyelectrolyte properties in dilute solutions. Its solution viscosity is highly sensitive to the polymer's own concentration, the concentration of the added electrolyte, and the valence state of the electrolyte ions. This indicates that the molecular structure of polymer P (DMDAAC-NVP) contains a large number of cationic groups; it also shows that by controlling the ionic environment of the solution, its molecular conformation and solution rheology can be effectively controlled, making it applicable to various scenarios (such as thickening, flocculation, drag reduction, etc.).

[0063] Example 3: Effect of monomer ratio on polymerization reaction Referring to Example 1, the ratio of n(DMDAAC):n(NVP) was adjusted to 8:2, 7:3, 6:4, 1:1, 4:6, 3:7, 2:8, and 1:9, while keeping other conditions unchanged, to synthesize P(DMDAAC-NVP). The specific results are as follows: 1. Effect of monomer ratio on polymer molecular weight The molecular weights of P(DMDAAC-NVP) prepared with different monomer ratios are shown in Table 3.

[0064] Table 3. Molecular weights of polymers prepared with different monomer ratios

[0065] As the DMDAAC ratio decreases, the NVP ratio increases. In the reaction, the DMDAAC reactivity ratio is less than 1, indicating a tendency towards copolymerization; the NVP reactivity ratio is greater than 1, indicating a tendency towards self-polymerization. When the DMDAAC ratio is high, the polymer is more likely to polymerize into long-chain random copolymers. The chain transfer constant of NVP is higher than that of DMDAAC, and its side-chain pyrrolidone structure may promote chain transfer through hydrogen bonding or polar interactions, leading to a decrease in molecular weight. The molecular weight distribution (Mw / Mn) exhibits a "wide then narrow" characteristic: at low NVP ratios (e.g., 9:1), excess DMDAAC induces frequent chain transfers, generating short chain segments, resulting in a wider distribution (Mw / Mn≈3.27); while at a 1:1 ratio, NVP self-polymerization dominates segment formation, resulting in a more uniform copolymer structure, and the distribution narrows significantly to 1.34. This indicates that the molecular weight and segment uniformity of the polymer can be precisely controlled by adjusting the NVP ratio. For example, a high DMDAAC ratio (9:1 or 8:2) is suitable for preparing high molecular weight products, while a 1:1 ratio is suitable for obtaining materials with a narrow distribution.

[0066] 2. Effect of monomer ratio on polymer viscosity The viscosity of P(DMDAAC-NVP) prepared with different monomer ratios is as follows: Figure 4 As shown, when the proportion of DMDAAC is high, its polymerization activity is high, the resistance to chain growth is low, the molecular weight is large, the entanglement and internal friction between molecular chains increase, and the viscosity is high; as the proportion of DMDAAC decreases, the polymer charge density decreases, the electrostatic repulsion decreases, the degree of polymer chain expansion decreases, and the viscosity begins to decrease.

[0067] 3. Polymer cationicity analysis The effect of monomer ratio on the cationicity of P(DMDAAC-NVP) is as follows: Figure 5As shown in the figure, the significant relationship between the polymer cationicity and the monomer molar ratio is evident: when the ratio of DMDAAC to NVP decreases from 9:1 to 1:9, the cationic capacity continuously decreases from approximately 3.1 mmol / g to 0.4 mmol / g, exhibiting a nearly linear negative correlation. Specifically: in the high DMDAAC ratio stage (9:1~6:4), the cationic capacity rapidly decreases from 3.1 mmol / g to 2.1 mmol / g (a decrease of 32%), with an average capacity reduction of approximately 0.4 mmol / g for every 10% decrease in the DMDAAC ratio within this range; in the low DMDAAC ratio stage (5:5~1:9), the capacity further decreases to 0.4 mmol / g, with a slower but clear trend. After the NVP ratio exceeds 50%, the rate of capacity decrease significantly decreases (only 0.2~0.3 mmol / g is reduced for every 10% decrease in the ratio). DMDAAC, as a cationic monomer, has its quaternary ammonium salt groups on its molecular chain directly determining its cationic density. NVPs do not contain ionic groups, and their segments physically separate DMDAAC units, reducing the steric accessibility of cationic groups. When the NVP ratio exceeds a critical threshold (approximately 1:1), this dilution effect intensifies, leading to a significant decrease in the density of cationic groups.

[0068] 4. Effect of different monomer ratios on zeta potential The effect of monomer ratio on the cationicity of P(DMDAAC-NVP) is as follows: Figure 6 As shown. DMDAAC is a cationic monomer containing positively charged quaternary ammonium salt groups in its molecule, while NVP is a nonionic monomer. During copolymerization, a decrease in the molar ratio of DMDAAC means a reduction in the number of cationic groups in the polymer chain, which directly leads to a decrease in the positive charge density on the polymer surface. When the proportion of DMDAAC decreases, the total positive charge of the polymer chain decreases, thereby lowering the Zeta potential. During free radical polymerization, the two monomers tend to form random copolymers. The reduction in DMDAAC content makes the distribution of cationic groups in each polymer segment more sparse, further diluting the surface charge density.

[0069] Example 4: Effect of reaction temperature on polymerization reaction Referring to Example 1, the reaction temperature was adjusted to 75℃, 80℃, and 90℃, while other conditions remained unchanged, to synthesize P(DMDAAC-NVP). The specific results are as follows: Table 4 Effect of reaction temperature on the synthesis of P(DMDAAC-NVP)

[0070] Example 5: Effect of initiator concentration on polymerization reaction Referring to Example 1, the initiator concentration was adjusted to 1.6%, 1.8%, 2.0%, 2.2%, and 2.4%, while other conditions remained unchanged, to synthesize P(DMDAAC-NVP). Specific results are as follows: Table 5 Effect of initiator concentration on the synthesis of P(DMDAAC-NVP)

[0071] At low initiator concentrations, the free radical generation rate is low, and chain growth dominates, resulting in longer polymer chains. Longer chains are more easily extended, exposing more cationic groups and increasing the surface positive charge density, leading to an increase in the Zeta potential. At an optimal initiator concentration, chain length and charge exposure are balanced, resulting in the highest Zeta potential. High initiator concentrations cause a surge in free radical density, accelerating the chain termination rate and generating a large number of short-chain polymers. These short chains cannot extend sufficiently, cationic groups are encapsulated, the effective charge density decreases, and the Zeta potential also decreases. Figure 7 ).

[0072] Comparative Example 1 Referring to Example 1, the initiator AIBA in S2 was changed to APS, while other conditions remained unchanged, to synthesize P(DMDAAC-NVP). The specific results are as follows: When APS is used as an initiator, polymerization cannot occur, thus preventing the synthesis of P(DMDAAC-NVP).

[0073] Comparative Example 2 Referring to Example 1, the order of feeding was adjusted while other conditions remained unchanged to synthesize P(DMDAAC-NVP). Details are as follows: S1. In the reaction vessel, add 52.8385 g of deionized water and 0.6 g of initiator AIBA, and sonicate to dissolve it completely. S2. Subsequently, 4.2578 g of NVP was dissolved in 92.9037 g of DMDAAC with a mass percentage concentration of 60%, and the mixture was homogeneous to obtain a mixed solution.

[0074] S3. Purge nitrogen gas into the reaction vessel in S1 for 15 min to remove air from the vessel, raise the temperature to 85 ℃ and maintain the temperature stable; use a peristaltic pump to add the mixed solution prepared in S2 dropwise into the reaction vessel at a uniform rate, and control the addition to be completed within 2 h (control the flow rate to be 0.5~0.6 mL / min); after the addition is completed, continue to keep it at 85 ℃ for 6 h; S4. After cooling to room temperature, the crude product is obtained and discharged.

[0075] The results showed that its molecular weight and viscosity were not as good as those of Example 1.

[0076] Comparative Example 3 Referring to Example 1, P(DMDAAC-NVP) was synthesized using a one-pot method. Details are as follows: S1. In the reactor, add 52.8385 g of deionized water and 0.6 g of initiator AIBA, and sonicate to dissolve it completely; then add 4.2578 g of NVP and 92.9037 g of DMDAAC with a mass percentage concentration of 60%, and mix well. S2. Purge nitrogen into the reactor in S1 for 15 min to remove air from the reactor, raise the temperature to 85 ℃ and maintain the temperature for 6 h. S3. After cooling to room temperature, the crude product is obtained and discharged.

[0077] The results showed that the yield of the main polymerization product P (DMDAAC-NVP) was low, and homopolymers of the monomers appeared in the product.

[0078] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing a polydimethyldiallylammonium chloride-based polymer, characterized in that, The preparation method steps are as follows: S1. Add dimethyl diallyl ammonium chloride to the reaction vessel; S2. Add N-vinylpyrrolidone to the initiator solution to prepare a mixed solution; S3. Introduce inert gas to purge the air from the reactor and raise the temperature to 75~90℃. Under this temperature condition, add the mixed solution from S2 dropwise into the reactor at a uniform rate and keep it at this temperature for 4~10 h. S4. After the reaction is complete, cool to room temperature and discharge to obtain a polymer solution; The molar ratio of dimethyl diallyl ammonium chloride to N-vinylpyrrolidone is (1:9) to (9:1).

2. The preparation method according to claim 1, characterized in that, In S2, the initiator includes persulfate initiators and / or azo initiators; Preferably, the azo initiator includes azobisisobutyramidine hydrochloride or azobisisobutyramidine zoline hydrochloride.

3. The preparation method according to claim 1, characterized in that, In S2, the concentration of the initiator solution is 1% to 3%; Preferably, the concentration of the initiator solution is 1.5% to 2.5%.

4. The preparation method according to claim 1, characterized in that, In S3, the inert gas includes at least one of nitrogen, helium, or argon; preferably, the inert gas is nitrogen.

5. The preparation method according to claim 1, characterized in that, In S3, the dropping rate is 0.1~0.8 mL / min; Preferably, the dropping rate is 0.1~0.6 mL / min.

6. The preparation method according to claim 1, characterized in that, In S3, the temperature is raised to 80~85℃ and held for 6~10 hours.

7. The preparation method according to claim 1, characterized in that, After discharge, the material undergoes further purification and drying. Preferably, the purification method includes acetone precipitation; Preferably, the drying method includes freeze drying.

8. The polydimethyldiallylammonium chloride-based polymer prepared by any one of the methods described in claims 1 to 7.

9. The application of the polydimethyldiallylammonium chloride-based polymer prepared by any of the methods of claims 1 to 7 in the fields of wastewater treatment, daily cosmetics, papermaking, and pigments.

10. The application according to claim 9, characterized in that, In the field of wastewater treatment, it can be used as a flocculant, heavy metal ion co-coagulant, filter aid, and dewatering agent; In the field of daily cosmetics, it can be used as a moisturizer and spreader; In the papermaking industry, it can be used as a flocculant; In the pigment industry, it can be used as a decolorizing agent.

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