Preparation Method of a Polymer Emulsifier and Its Application in Coatings

Abstract

The present invention provides a preparation method of a polymer emulsifier and its application in coatings. The polymer emulsifier comprises the following raw materials in parts by weight: 2-8 parts of acrylic acid, 8-15 parts of hydrophobic monomers, 1-2 parts of reactive emulsifiers, 1-2 parts of functional monomers, 1-2 parts of nitrogen-containing RAFT chain transfer agents, 0.5-0.8 parts of initiators and 30-50 parts of solvents. The polymer emulsifier provided by the present invention can ensure that the prepared emulsion has a high solid content while reducing the emulsion viscosity, reducing the particle size of latex particles, and improving the flame retardant effect.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and particularly relates to a preparation method of a polymer emulsifier and its application in coatings. Background Art

[0002] When a polymer surfactant is applied to pore fluid polymerization, it is a polymer emulsifier. The polymer emulsifier consists of a hydrophobic segment and a hydrophilic segment, and has a relatively large molecular weight, generally greater than 3000. Although the ability of the polymer emulsifier to reduce the surface tension by surface activity is not as good as that of common small molecule surfactants, its emulsifying performance is very good. When used as an emulsifier, it has many unique advantages: good emulsifying performance and dispersing ability, and most polymer emulsifiers can stabilize the emulsion; it has good compatibility with latex particles and can improve the performance of emulsion products. The emulsion (such as acrylic emulsion) prepared by the polymer emulsifier has good water resistance and stain resistance, and the emulsion has the characteristics of narrow particle size distribution, good film-forming property, scrub resistance and high gloss, so it is more and more widely used in the fields of preparing coatings, adhesives and composite materials, etc.

[0003] In the field of coating applications, high solid content emulsions have the advantages of high equipment utilization rate, high production efficiency, low energy consumption, low transportation cost and fast drying, etc., but they also have high requirements for production processes and control. Due to the relatively high solid content of the emulsion and the relatively large particle size distribution, it is easy to have high viscosity, easy to generate gels, thereby reducing the heat dissipation efficiency and product fluidity; in addition, the emulsion prepared by the polymer emulsifier contains a large amount of flammable polymer materials, and the flame retardant performance is not good, which is easy to cause potential safety hazards.

[0004] Therefore, how to select appropriate components to modify the polymer emulsion so that the prepared emulsion and related products have good flame retardant performance, and at the same time reduce the latex particle size and lower the emulsion viscosity under the condition of relatively high solid content has become the key direction to be overcome. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the purpose of the present invention is to provide a preparation method of a polymer emulsifier and its application in coatings, aiming to solve the problems of large latex particle size and high viscosity that are prone to occur when the existing polymer emulsifiers are used for emulsion preparation, and poor flame retardant performance when applied to fields such as coatings.

[0006] The present invention designs the raw materials of the polymer emulsifier, introduces silicone acrylate as a hydrophobic monomer and phosphorus-containing acrylate as a functional monomer, and uses a reactive non-ionic emulsifier and a nitrogen-containing RAFT chain transfer agent to obtain a modified polymer emulsifier, which reduces the emulsion viscosity while ensuring that the emulsion prepared by the modified polymer emulsifier has a high solid content, reduces the latex particles with a small particle size, and realizes synergistic flame retardancy.

[0007] The technical solution of the present invention is as follows:

[0008] In the first aspect of the present invention, a preparation method of a polymer emulsifier is provided, which is prepared through the following steps:

[0009] Step S1: Prepare the raw materials of the polymer emulsifier according to the formula, and the formula includes the following raw materials in parts by weight: 2-8 parts of acrylic acid, 8-15 parts of hydrophobic monomers, 1-2 parts of reactive emulsifiers, 1-2 parts of functional monomers, 1-2 parts of nitrogen-containing RAFT chain transfer agents, 0.5-0.8 parts of initiators, and 30-50 parts of solvents.

[0010] Step S2: Add the raw materials into a reactor, stir and mix, introduce nitrogen, heat up and react, cool down after the reaction is completed, adjust the pH with ammonia water, and distill off the solvent to obtain the polymer emulsifier.

[0011] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the purpose and beneficial effects of the present invention can be better achieved.

[0012] As a preferred technical solution of the present invention, in step S1, the hydrophobic monomers include 4-7 parts of styrene and 4-8 parts of acrylate; the acrylate is a silicon-containing acrylate; the silicon-containing acrylate is selected from any one or a combination of at least two of silicon-containing acrylate I, silicon-containing acrylate II, silicon-containing acrylate III, and silicon-containing acrylate IV;

[0013] Among them, the structural formula of the silicon-containing acrylate I is:

[0014]

[0015] Among them, the structural formula of the silicon-containing acrylate II is:

[0016]

[0017] Among them, the structural formula of the silicon-containing acrylate III is:

[0018]

[0019] Among them, the structural formula of the silicon-containing acrylate IV is:

[0020] The surface energy of silicon elements in the silicon-containing acrylate monomer is relatively low, and it is easy to migrate to the surface of the overcoating film to form a silicon-containing protective layer, improving the thermal stability of the coating layer; combined with the nitrogen element in the nitrogen-containing RAFT chain transfer agent to produce flame-retardant nitrogen-containing compounds at high temperatures, diluting the concentration of combustion gases near the flame, realizing the synergistic flame retardancy of silicon and nitrogen.

[0021] It should be noted that in the present invention, there is no special limitation on the source of the silicone acrylate, which can be obtained by commercial purchase or prepared by oneself. There is no special limitation on the preparation method of the silicone acrylate in the present invention. Exemplarily, the preparation method in "CN108299493 A" can be referred to.

[0022] As a preferred technical solution of the present invention, the reactive emulsifier in step S1 is a reactive nonionic emulsifier; the reactive nonionic emulsifier is selected from any one or a combination of at least two of lauric acid polyoxyethylene ester, polyoxyethylene ether, and polyoxyethylene amide.

[0023] The reactive nonionic emulsifier can provide a stable steric hindrance effect to the latex particles, thereby slowing down the attack of cations on the double-layer structure of the latex particles, making the prepared latex particles have better stability, and avoiding agglomeration due to unstable latex particles, resulting in an increase in the particle size of the latex particles.

[0024] As a preferred technical solution of the present invention, the functional monomer-containing in step S1 is a phosphorus-containing acrylate; the phosphorus-containing acrylate is selected from any one or a combination of at least two of phosphorus-containing acrylate I, phosphorus-containing acrylate II, and phosphorus-containing acrylate III.

[0025] Among them, the structural formula of the phosphorus-containing acrylate I is:

[0026]

[0027] Among them, the structural formula of the phosphorus-containing acrylate II is:

[0028]

[0029] Among them, the structural formula of the phosphorus-containing acrylate III is:

[0030]

[0031] The phosphorus element in the phosphorus-containing acrylate monomer releases phosphorus-oxygen free radicals under high-temperature conditions, combines with the free radicals promoting combustion, thereby terminating the chain reaction of combustion; it cooperates with the nitrogen element in the nitrogen-containing RAFT chain transfer agent to form a hindered amine structure with a quenching effect, exerting a gas-phase dilution effect, and the two cooperate with each other in the gas phase to improve the flame retardant effect.

[0032] It should be noted that in the present invention, there is no special limitation on the source of the phosphorus-containing acrylate, which can be obtained by commercial purchase or prepared by oneself. There is no special limitation on the preparation method of the phosphorus-containing acrylate in the present invention. Exemplarily, the preparation method in "CN110121501A" can be referred to.

[0033] As a preferred technical solution of the present invention, the nitrogen-containing RAFT chain transfer agent in step S1 is selected from any one or a combination of at least two of nitrogen-containing RAFT chain transfer agent I, nitrogen-containing RAFT chain transfer agent II, and nitrogen-containing RAFT chain transfer agent III.

[0034] Among them, the structural formula of the nitrogen-containing RAFT chain transfer agent I is:

[0035]

[0036] Among them, the structural formula of the nitrogen-containing RAFT chain transfer agent II is:

[0037]

[0038] Among them, the structural formula of the nitrogen-containing RAFT chain transfer agent III is:

[0039]

[0040] The nitrogen-containing RAFT chain transfer agent has both the advantages of free radical polymerization and living controlled polymerization, and can prepare polymers with a well-defined structure, controllable molecular weight and narrow molecular weight distribution. By good control of the polymerization process, the regularity and uniformity of the molecular weight of the latex particles are improved, the molecular weight distribution of the latex particles is reduced, and the effect of reducing the emulsion viscosity is achieved. In addition, the nitrogen-containing RAFT chain transfer agent can cooperate with silicon-containing acrylate and phosphorus-containing acrylate to achieve the synergistic flame retardancy of phosphorus, silicon and nitrogen elements, and improve the limiting oxygen index.

[0041] It should be noted that in the present invention, there is no special limitation on the source of the nitrogen-containing RAFT chain transfer agent, which can be obtained by commercial purchase or prepared by itself. The present invention does not make any special limitation on the preparation method of the nitrogen-containing RAFT chain transfer agent. Exemplarily, it can be prepared by referring to the method in "Progress in Reversible Addition-Fragmentation Chain Transfer Polymerization and the Preparation of Chain Transfer Agents [J]. Guangzhou Chemical Industry, 2019, 47(13): 5, Deng Bo, Liao Wenping, Yang Ziteng, etc.".

[0042] Preferably, the initiator in step S1 is selected from any one or a combination of at least two of azobisisobutyronitrile, azodicyanovaleric acid, benzoyl peroxide, tert-butyl hydroperoxide, ammonium persulfate, and sodium persulfate.

[0043] Preferably, the solvent in step S1 is selected from any one or a combination of at least two of methanol, ethanol, propanol, butanol, isopropanol, and propylene glycol.

[0044] Preferably, the heating and temperature rising temperature in step S2 is 70-90 °C, the reaction time is 5-12 h, the temperature reduction temperature is 30-60 °C, and the pH adjustment range is 6-8.

[0045] In a second aspect, the present invention provides an application of the polymer emulsifier as described in the first aspect in a coating, which is characterized by including the following steps:

[0046] (1) Add 25 - 30 parts of the polymer emulsifier and 70 - 80 parts of deionized water to a reaction kettle, stir evenly and heat up to 85°C, add 0.3 - 0.5 parts of ammonium persulfate, 3 - 5 parts of deionized water, 3.5 - 4 parts of methyl methacrylate and 1 - 1.2 parts of butyl acrylate, and react for 45 min; heat up to 90°C, add 0.5 - 1 part of ammonium persulfate, 70 - 80 parts of deionized water, 55 - 60 parts of methyl methacrylate and 55 - 60 parts of butyl acrylate, keep the temperature constant and react for 5 h, continue to keep the temperature for 1 h after the reaction is completed, cool down to 70°C, add 0.2 - 0.3 parts of tert-butyl hydroperoxide, 3 - 5 parts of deionized water, 0.1 - 0.12 parts of sodium antiscorbutate and 3 - 5 parts of deionized water, cool down to 40°C, add ammonia water to adjust the pH = 8, add 0.2 - 0.3 parts of defoamer, and filter and discharge to obtain an emulsion.

[0047] (2) Apply the emulsion obtained in step (1) to the preparation of the coating.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] (1) By using a reactive non-ionic emulsifier in the present invention, a stable steric hindrance effect is given to the latex particles, avoiding agglomeration due to unstable latex particles, thereby reducing the particle size of the latex particles; by introducing a nitrogen-containing RAFT chain transfer agent, the regularity and uniformity of the latex particle molecular weight are improved, and the molecular weight distribution of the latex particles is reduced, achieving a reduction in the emulsion viscosity.

[0050] (2) Through the component design in the present invention, phosphorus, silicon, and nitrogen are introduced to synergistically flame retard; among them, the synergistic effect of phosphorus and silicon elements is to avoid the oxidation of the carbon layer on the material surface by forming a phosphorus-containing carbon layer and a silicon-containing protective layer, and the synergistic effect of silicon and nitrogen elements is to play a flame retardant effect in the condensed phase and gas phase by generating a non-combustible nitrogen-containing gas. Through the synergy of phosphorus - silicon - nitrogen, high-efficiency flame retardation is achieved. Specific embodiments

[0051] To facilitate the understanding of the present invention, the following examples are listed. Those skilled in the art should understand that the examples are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

[0052] The sources of some components in the examples and comparative examples are as follows:

[0053] Acrylic acid: The CAS number of acrylic acid is 79 - 10 - 7;

[0054] Hydrophobic monomers: The CAS number of styrene is 100-42-5, the CAS number of butyl acrylate is 141-32-2, and the CAS number of methyl methacrylate is 80-62-6;

[0055] Reactive emulsifiers: The CAS number of polyoxyethylene ether is 9004-95-9, and the CAS number of sodium allyloxyhydroxypropyl sulfonate is 52556-42-0;

[0056] Functional monomers: The CAS number of 2-hydroxyethyl methacrylate is 868-77-9;

[0057] Initiators: The CAS number of azobisisobutyronitrile is 78-67-1;

[0058] Solvents: The CAS number of isopropyl alcohol is 67-63-0.

[0059] Example 1

[0060] This example provides a preparation method of a polymer emulsifier a. The preparation of this polymer emulsifier: Weigh 2.4 parts of acrylic acid, 5 parts of styrene, 6 parts of silicone-containing acrylate I, 1.8 parts of polyoxyethylene ether, 1.5 parts of phosphorus-containing acrylate II, 1.5 parts of nitrogen-containing RAFT chain transfer agent III, 0.6 part of azobisisobutyronitrile and 45 parts of isopropyl alcohol into a reaction flask, stir and mix, pass nitrogen, heat up to 75 °C and react for 9 h, cool down to 45 °C, add ammonia water to neutralize to pH = 7.5, and distill out the solvent to obtain the polymer emulsifier.

[0061] Example 2

[0062] This example provides a preparation method of a polymer emulsifier b. The preparation of this polymer emulsifier: Weigh 2 parts of acrylic acid, 4 parts of styrene, 4 parts of silicone-containing acrylate III, 1 part of polyoxyethylene ether, 1 part of phosphorus-containing acrylate I, 1 part of nitrogen-containing RAFT chain transfer agent II, 0.5 part of azobisisobutyronitrile and 30 parts of isopropyl alcohol into a reaction flask, stir and mix, pass nitrogen, heat up to 50 °C and react for 5 h, cool down to 30 °C, add ammonia water to neutralize to pH = 6, and distill out the solvent to obtain the polymer emulsifier.

[0063] Example 3

[0064] This example provides a preparation method of a polymer emulsifier c. The preparation of this polymer emulsifier: Weigh 8 parts of acrylic acid, 7 parts of styrene, 8 parts of silicon-containing acrylate IV, 2 parts of polyoxyethylene ether, 2 parts of phosphorus-containing acrylate III, 2 parts of nitrogen-containing RAFT chain transfer agent I, 0.8 part of azobisisobutyronitrile and 50 parts of isopropanol and add them to a reaction flask, stir and mix, pass nitrogen, heat up to 90 °C and react for 12 h, cool down to 8 °C, add ammonia water to neutralize to pH = 8, and distill out the solvent to obtain the polymer emulsifier.

[0065] Example 4

[0066] This example provides a preparation method of a polymer emulsifier d. The difference between the preparation of this polymer emulsifier and that of Example 1 is that 6 parts of silicon-containing acrylate I are replaced by 3 parts of butyl acrylate and 3 parts of methyl methacrylate.

[0067] Example 5

[0068] This example provides a preparation method of a polymer emulsifier e. The difference between the preparation of this polymer emulsifier and that of Example 1 is that 1.8 parts of polyoxyethylene ether are replaced by 1.8 parts of allyloxyhydroxypropyl sulfonate.

[0069] Example 6

[0070] This example provides a preparation method of a polymer emulsifier f. The difference between the preparation of this polymer emulsifier and that of Example 1 is that 1.5 parts of phosphorus-containing acrylate II are replaced by 1.5 parts of 2-hydroxyethyl methacrylate.

[0071] Example 7

[0072] This example provides a preparation method of a polymer emulsifier g. The difference between the preparation of this polymer emulsifier and that of Example 1 is that Example 7 does not contain 1.5 parts of nitrogen-containing RAFT chain transfer agent III.

[0073] Comparative Example 1

[0074] This comparative example provides a preparation method of a polymer emulsifier h. The preparation of this polymer emulsifier: Weigh 2.4 parts of acrylic acid, 5 parts of styrene, 3 parts of butyl acrylate, 3 parts of methyl methacrylate, 1.8 parts of allyloxyhydroxypropyl sulfonate, 1.5 parts of 2-hydroxyethyl methacrylate, 0.6 part of azobisisobutyronitrile and 45 parts of isopropanol and add them to a reaction flask, stir and mix, pass nitrogen, heat up to 75 °C and react for 9 h, cool down to 45 °C, add ammonia water to neutralize to pH = 7.5, and distill out the solvent to obtain the polymer emulsifier.

[0075] Comparative Example 2

[0076] This comparative example provides a method for preparing a polymer emulsifier i. The difference in the preparation of this polymer emulsifier from Comparative Example 1 is that 3 parts of butyl acrylate and 3 parts of methyl methacrylate are replaced by 6 parts of silicone-containing acrylate Ⅰ.

[0077] Comparative Example 3

[0078] This comparative example provides a method for preparing a polymer emulsifier j. The difference in the preparation of this polymer emulsifier from Comparative Example 1 is that 1.8 parts of allyloxyhydroxypropyl sulfonate are replaced by 1.8 parts of polyoxyethylene ether.

[0079] Comparative Example 4

[0080] This comparative example provides a method for preparing a polymer emulsifier k. The difference in the preparation of this polymer emulsifier from Comparative Example 1 is that 1.5 parts of hydroxyethyl methacrylate are replaced by 1.5 parts of phosphorus-containing acrylate II.

[0081] Application Example

[0082] The above polymer emulsifiers a - k are respectively used to prepare emulsions. The preparation process of the emulsions is as follows: Add 30 parts of the polymer emulsifier and 70 parts of deionized water to the reaction kettle, stir evenly and heat up to 85°C, add 0.3 parts of ammonium persulfate, 3 parts of deionized water, 3.5 parts of methyl methacrylate and 1.2 parts of butyl acrylate, and react for 45 min; Heat up to 90°C, add 0.5 parts of ammonium persulfate, 70 parts of deionized water, 60 parts of methyl methacrylate and 55 parts of butyl acrylate, and react at a constant temperature for 5 h. After the reaction is completed, keep the temperature for 1 h, cool down to 70°C, add 0.3 parts of tert-butyl hydroperoxide, 3 parts of deionized water, 0.12 parts of sodium antiscorbutic and 3 parts of deionized water, cool down to 40°C, add ammonia water to adjust the pH = 8, add 0.3 parts of defoamer, and filter and discharge to obtain the emulsion.

[0083] The properties of the emulsions (such as in the Application Example) prepared from the polymer emulsifiers provided in the above examples and comparative examples are tested. The test methods are as follows:

[0084] Solid content: Test according to the requirements of "GB / T 2793-1995 Determination of non-volatile content of adhesives";

[0085] Average particle size: Test according to the requirements of "GB / T 11175-2021 Test methods for synthetic resin emulsions";

[0086] Viscosity: Test according to the requirements of "GB / T 2794-2022 Determination of viscosity of adhesives";

[0087] Limiting Oxygen Index (LOI): The emulsion was evenly coated in a polytetrafluoroethylene mold, first dried naturally to form a film, and then dried in an electric heating blast drying oven at 70 °C until constant weight to prepare a resin sample bar with a length of 140 mm, a width of 52 mm, and a thickness of 2 mm. The sample was ignited by the top surface ignition method, and the LOI of the sample was tested using a British FTT0077 oxygen index meter.

[0088] The above performance test data are shown in Table 1.

[0089] Table 1 Performance Test Results

[0090]

[0091]

[0092] As can be seen from the above, in the present invention, by designing the raw materials of the polymer emulsifier, introducing silicone acrylate as a hydrophobic monomer and phosphorus-containing acrylate as a functional monomer, using a reactive non-ionic emulsifier and a nitrogen-containing RAFT chain transfer agent, a modified polymer emulsifier is obtained, and the solid content of the emulsion and related products (Examples 1 to 3) prepared therefrom is 57.38 to 57.55 wt%, the average particle size is 120.4 to 123.1 nm, the viscosity is 40 to 41 mPa·s, and the limiting oxygen index (LOI) is 23.1 to 23.6.

[0093] Compared with Example 1, if silicone acrylate is not used, the limiting oxygen index decreases (Example 4); compared with Example 1, if polyoxyethylene ether is not used, the average particle size increases (Example 5); compared with Example 1, if phosphorus-containing acrylate is not used, the limiting oxygen index decreases (Example 6); compared with Example 1, if the nitrogen-containing RAFT chain transfer agent is not used, the viscosity increases and the limiting oxygen index decreases at the same time (Example 7).

[0094] Comparative Example 1 did not adopt the technical innovation points of the present invention, so the performance was poor. In the case of a solid content of 57.45 wt%, the average particle size was 184.3, the viscosity was 72 mPa·s, and the limiting oxygen index (LOI) was 18.2. Compared with Comparative Example 1, if silicone acrylate was adopted, the limiting oxygen index increased (Comparative Example 2); compared with Comparative Example 1, if polyoxyethylene ether was adopted, the average particle size decreased (Comparative Example 3); compared with Comparative Example 1, if phosphorus-containing acrylate was adopted, the limiting oxygen index increased (Comparative Example 4).

[0095] In summary, by designing the raw materials of the polymer emulsifier, introducing silicone acrylate as the hydrophobic monomer and phosphorus-containing acrylate as the functional monomer, and using a reactive nonionic emulsifier and a nitrogen-containing RAFT chain transfer agent, a modified polymer emulsifier is obtained, which can reduce the emulsion viscosity while ensuring that the emulsion prepared from the modified polymer emulsifier has a high solid content, reduce the particle size of latex particles, and achieve synergistic flame retardancy.

[0096] The applicant declares that the detailed process flow of the present invention is illustrated by the above embodiments, but the present invention is not limited to the above detailed process flow, that is, it does not mean that the present invention must rely on the above detailed process flow to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent replacement of each raw material of the product of the present invention, the addition of auxiliary components, the selection of specific methods, etc. all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of a polymer emulsifier, characterized in that, It is prepared through the following steps: Step S1: Prepare the raw materials of the polymer emulsifier according to the formula. The formula includes the following raw materials in parts by weight: 2-8 parts of acrylic acid, 8-15 parts of hydrophobic monomers, 1-2 parts of emulsifier 1, 1-2 parts of functional monomers, 1-2 parts of nitrogen-containing RAFT chain transfer agent, 0.5-0.8 parts of initiator, and 30-50 parts of solvent; wherein, emulsifier 1 is any one or a combination of at least two of lauric acid polyoxyethylene ester, polyoxyethylene ether, and polyoxyethylene amide; Step S2: Add the above raw materials into a reactor, stir and mix, introduce nitrogen, heat up and react, cool down after the reaction is completed, adjust the pH with ammonia water, and distill out the solvent to obtain the polymer emulsifier; The hydrophobic monomers in Step S1 include 4-7 parts of styrene and 4-8 parts of acrylate; The acrylate is a silicone-containing acrylate; The silicone-containing acrylate is selected from any one or a combination of at least two of silicone-containing acrylate I, silicone-containing acrylate II, silicone-containing acrylate III, and silicone-containing acrylate IV; Among them, the structural formula of the silicone-containing acrylate I is: ； Among them, the structural formula of the silicone-containing acrylate II is: ； Among them, the structural formula of the silicone-containing acrylate III is: ； Among them, the structural formula of the silicone-containing acrylate IV is: ； The functional monomer in Step S1 is a phosphorus-containing acrylate; The phosphorus-containing acrylate is selected from any one or a combination of at least two of phosphorus-containing acrylate I, phosphorus-containing acrylate II, and phosphorus-containing acrylate III; Among them, the structural formula of the phosphorus-containing acrylate I is: ； Among them, the structural formula of the phosphorus-containing acrylate II is: ； Among them, the structural formula of the phosphorus-containing acrylate III is: 。 2. The preparation method of a polymer emulsifier according to claim 1, characterized in that, The nitrogen-containing RAFT chain transfer agent in Step S1 is selected from any one or a combination of at least two of nitrogen-containing RAFT chain transfer agent I, nitrogen-containing RAFT chain transfer agent II, and nitrogen-containing RAFT chain transfer agent III; Among them, the structural formula of the nitrogen-containing RAFT chain transfer agent I is: ； Among them, the structural formula of the nitrogen-containing RAFT chain transfer agent II is: ； Among them, the structural formula of the nitrogen-containing RAFT chain transfer agent III is: 。 3. The preparation method of a polymer emulsifier according to claim 1, characterized in that, The initiator in Step S1 is selected from any one or a combination of at least two of azobisisobutyronitrile, azodicyanovaleric acid, benzoyl peroxide, tert-butyl hydroperoxide, ammonium persulfate, and sodium persulfate.

4. The preparation method of a polymer emulsifier according to claim 1, characterized in that, The solvent in Step S1 is selected from any one or a combination of at least two of methanol, ethanol, propanol, butanol, isopropanol, and propylene glycol.

5. The preparation method of a polymer emulsifier according to claim 1, characterized in that, The heating temperature in Step S2 is 70-90°C, the reaction time is 5-12 h, the cooling temperature is 30-60°C, and the pH adjustment range is 6-8.

6. Use of the polymer emulsifier prepared by the method according to any one of claims 1-5 in a coating, characterized in that, It includes the following processes: (1) Add 25 - 30 parts of high - molecular emulsifier and 70 - 80 parts of deionized water into the reaction kettle, stir evenly and heat up to 85°C. Then add 0.3 - 0.5 parts of ammonium persulfate, 3 - 5 parts of deionized water, 3.5 - 4 parts of methyl methacrylate and 1 - 1.2 parts of butyl acrylate, and react for 45 minutes. Heat up to 90°C, add a mixture consisting of 0.5 - 1 part of ammonium persulfate, 70 - 80 parts of deionized water, 55 - 60 parts of methyl methacrylate and 55 - 60 parts of butyl acrylate, and keep the temperature constant for reaction for 5 hours. After the reaction is completed, keep the temperature for 1 hour, cool down to 70°C, add 0.2 - 0.3 parts of tert - butyl hydroperoxide, 3 - 5 parts of deionized water, 0.1 - 0.12 parts of sodium antiscorbutate and 3 - 5 parts of deionized water, cool down to 40°C, add ammonia water to adjust the pH = 8, add 0.2 - 0.3 parts of defoamer, and filter and discharge to obtain the emulsion. (2) Apply the emulsion obtained in step (1) to the preparation of coatings.

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