Polyvinylidene chloride resin emulsion with excellent barrier property as well as preparation method and application thereof

Abstract

The invention provides a polyvinylidene chloride resin emulsion with excellent barrier property as well as a preparation method and application thereof. A barrier property accelerant is added in the preparation method, and the preparation method comprises the following steps: preparing a monomer pre-emulsion: mixing and stirring vinylidene chloride, a comonomer, an emulsifier and water to obtain the monomer pre-emulsion; seed emulsion polymerization: mixing a seed monomer, a seed emulsifier and water, adding an initiator, and reacting to obtain a seed emulsion; polymerizing polyvinylidene chloride emulsion: adding the monomer pre-emulsion into the seed emulsion, and adding an initiator; and after the monomer pre-emulsion is added, adding a barrier property accelerant, mixing and filtering to obtain a target product. The invention also provides a polyvinylidene chloride emulsion and an accelerant. A composite hard sheet prepared by coating a PVC hard sheet with the polyvinylidene chloride water-based emulsion has excellent barrier property and can be used in the fields of medicine, food packaging and the like.

Description

Technical Field

[0001] The present invention belongs to the field of polymer materials, and particularly relates to a polyvinylidene chloride resin emulsion with excellent barrier properties, a preparation method thereof, and an application thereof. Background Art

[0002] Polyvinylidene chloride (PVDC) is a polymer material with excellent barrier properties and is unique in the packaging and anti-corrosion industries. In the field of drug capsule packaging where high barrier properties are required, coating PVDC emulsion on materials such as PVC, PET, and PCT improves the defect of poor barrier properties of these materials, which leads to the oxidation and deterioration of drugs and extends the shelf life of drugs. Pharmaceutical packaging materials with better barrier properties have always been one of the important demands in the industry.

[0003] At present, one of the ways to improve the barrier properties of PVDC emulsion is by modifying it with comonomers or crosslinking aids. CN114829424A provides an aqueous latex of a vinylidene chloride copolymer. 2.0 - 5.5% of methacrylonitrile is added to the comonomer to improve the coating adhesion, and 0.5 - 1.4% of an ionic comonomer, 2 - acrylamido - 2 - methyl - 1 - propane sulfonic acid sodium salt, is added to improve the polymerization stability. Using vinylidene chloride, methyl methacrylate, and methacrylonitrile as the main polymerization monomers, a PVDC copolymer emulsion is prepared by the method of seed emulsion polymerization. After coating on the substrate, the oxygen barrier property is improved to a certain extent, but due to the addition of a certain amount of ionic comonomer, the water barrier property improvement is not obvious, and the application field is limited to a certain extent. CN102876149A provides a self - adhesive PVDC emulsion for coating and a preparation method thereof. The preparation method is as follows: vinylidene chloride monomer and other comonomers are polymerized by the method of seed emulsion polymerization to obtain a PVDC emulsion, then 0.5 - 5% of an amino - silane coupling agent, 3 - 5% of a slip agent, and 3 - 5% of an anti - sticking agent are added, and finally filtered and discharged. The disadvantages are that the process is complex, the operation is cumbersome, and the product has poor thermal stability and anti - yellowing ability, which is not suitable for large - scale production.

[0004] In summary, there is still an urgent need to solve the problem of insufficient comprehensive barrier properties of polyvinylidene chloride at present. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a preparation method of a polyvinylidene chloride emulsion with excellent barrier properties. The polyvinylidene chloride emulsion prepared by this method can obtain excellent barrier properties.

[0006] To achieve the above - mentioned invention purpose, the technical scheme adopted by the present invention is as follows:

[0007] A preparation method of a high - barrier polyvinylidene chloride emulsion, in which a barrier property promoter is added in the preparation method, and the preparation method includes the following steps:

[0008] S1: Prepare a monomer pre-emulsion: Mix vinylidene chloride, comonomer, emulsifier, and water and stir to obtain a monomer pre-emulsion;

[0009] S2: Seed emulsion polymerization: Mix seed monomer, seed emulsifier, and water, add an initiator, and react to obtain a seed emulsion;

[0010] S3: Polyvinylidene chloride emulsion polymerization: Add the monomer pre-emulsion to the seed emulsion and add an initiator;

[0011] S4: After the addition of the monomer pre-emulsion is completed, add a barrier promoter, mix, and filter to obtain the target product.

[0012] During the use of the emulsion, it is coated on a hard or soft substrate to form a film. During the evaporation of water, the latex particles approach each other. As the water further evaporates, the interfacial parts of the particles fuse and penetrate each other to form a uniform film. The degree of fusion and penetration between the particle interfaces greatly affects the performance after film formation. Due to the existence of factors such as water and surface tension, during the film formation process of the latex particles, the degree of interfacial penetration between the particles is relatively low, forming weak points in performance, like lead balls connected by thin iron wires. Adding the polyurethane-type barrier promoter of the present invention, during the film formation process, the end group of the promoter molecule is NCO. As the water evaporates, the NCO concentration gradually increases, and at the same time, the acid that restricts the reaction of NCO gradually decreases. NCO begins to carry out a chain extension reaction with water, covering the latex particles like a net, greatly improving the crosslinking. At the same time, because the promoter contains a crystallizable soft segment, a dense network will be formed during the final film formation, which will also promote the improvement of the barrier property.

[0013] In one embodiment of the present invention, the comonomer in S1 is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, and methacrylonitrile.

[0014] In one embodiment of the present invention, the emulsifier in S1 is an anionic surfactant, preferably one or more of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecylbenzenesulfonate, sodium pentadecylbenzenesulfonate, and sodium dodecyl diphenyl ether disulfonate.

[0015] In one embodiment of the present invention, the addition ratio of vinylidene chloride, comonomer, water, and emulsifier in S1 is (60 - 65):(5 - 15):(25 - 30):(0.2 - 0.5).

[0016] In one embodiment of the present invention, the temperature in S1 is 0 - 5°C and the stirring time is 5 - 10 min.

[0017] In one embodiment of the present invention, the seed monomer in S2 is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, and methacrylonitrile.

[0018] In one embodiment of the present invention, the seed emulsifier in S2 is an anionic surfactant, preferably one or more of sodium dodecyl sulfate, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium pentadecyl benzene sulfonate, and sodium dodecyl diphenyl ether disulfonate.

[0019] In one embodiment of the present invention, the addition ratio of the seed monomer, seed emulsifier, and water in S2 is (2 - 6):(0.2 - 1):(90 - 95).

[0020] In one embodiment of the present invention, the initiator in S2 is a peroxide and / or an azo initiator, preferably one or more of sodium persulfate, potassium persulfate, ammonium persulfate, di-tert-butyl peroxide, azobisisobutyramidine hydrochloride, and 2,2'-azobis(2-methyl)propionamidine dihydrochloride; preferably, the addition amount of the initiator in S2 is 0.2 - 0.7% of the mass of the seed monomer.

[0021] In one embodiment of the present invention, the temperature in S2 is 75 - 80°C, and the stirring time is 10 - 30 min.

[0022] In one embodiment of the present invention, the addition ratio of the seed emulsion and the monomer pre-emulsion in S3 is 1:(10 - 12).

[0023] In one embodiment of the present invention, the initiator in S3 is a peroxide and / or an azo initiator, preferably one or more of sodium persulfate, potassium persulfate, ammonium persulfate, di-tert-butyl peroxide, azobisisobutyramidine hydrochloride, and 2,2'-azobis(2-methyl)propionamidine dihydrochloride; preferably, the addition amount of the initiator in S3 is 0.1 - 0.6% of the mass of the monomer pre-emulsion.

[0024] In one embodiment, the initiator in S3 is added dropwise, preferably with a dropwise addition time of 6 - 8 h.

[0025] In one embodiment of the present invention, the reaction temperature in S3 is 75 - 80°C.

[0026] In one embodiment of the present invention, the addition amount of the barrier promoter in S4 is 0.4 - 0.6% of the mass of the polyvinylidene chloride emulsion, preferably 0.45 - 0.55%.

[0027] In one embodiment of the present invention, the barrier promoter in S4 is the reaction product of hexamethylene diisocyanate (HDI), polyester diol, and polyethylene glycol monomethyl ether.

[0028] Exemplarily, the molecular structure of the barrier promoter is schematically shown as follows:

[0029]

[0030] Among them, the structure of R1 is schematically shown as:

[0031]

[0032] The structure of R2 is schematically shown as:

[0033]

[0034] Among them, the value of m is 19.3 - 20.0,

[0035] The structure of R3 is schematically shown as:

[0036]

[0037] Among them, the value of n is 11.

[0038] In one embodiment of the present invention, the mixing time in S4 is 20 - 25 min.

[0039] Another object of the present invention is to provide a high-barrier polyvinylidene chloride emulsion.

[0040] A high-barrier polyvinylidene chloride emulsion, which is prepared by the above preparation method.

[0041] Another object of the present invention is to provide a method for preparing a barrier promoter.

[0042] A method for preparing a barrier promoter, the method comprising the following steps:

[0043] SS1: Reacting an isocyanate monomer and a polyester diol to obtain an NCO-terminated intermediate;

[0044] SS2: Adding polyethylene glycol monomethyl ether and a solvent and continuing the reaction to obtain a barrier promoter.

[0045] In one embodiment of the present invention, the isocyanate monomer in SS1 is hexamethylene diisocyanate.

[0046] In one embodiment of the present invention, the polyester diol in SS1 is polybutylene adipate; preferably, the hydroxyl value of the polyester diol is 55.0 - 57.0.

[0047] In one embodiment of the present invention, the ratio of the isocyanate monomer to the polyester diol in SS1 is 1:(5.5 - 6.5).

[0048] In one embodiment of the present invention, the reaction temperature in SS1 is 75 - 85°C.

[0049] In one embodiment of the present invention, the intermediate NCO in SS1 is 3.4% - 3.7%.

[0050] In one embodiment of the present invention, the mass ratio of methoxypolyethylene glycol and the SS1 component in SS2 is 1:(15 - 19).

[0051] In one embodiment of the present invention, the mass ratio of the solvent in SS2 and the component in SS1 is 1:(10 - 12); preferably, the solvent is one or more of acetone, methyl ethyl ketone, NMP, and NEP.

[0052] In one embodiment of the present invention, the reaction temperature in SS2 is 75 - 85°C, and the reaction time is 3 - 4 h.

[0053] In one embodiment of the present invention, the NCO of the barrier promoter in SS2 is 2.6% - 2.8%.

[0054] Another object of the present invention is to provide a barrier promoter.

[0055] A barrier promoter, which is the promoter used in the above preparation method, or the promoter contained in the above high-barrier polyvinylidene chloride emulsion, or the promoter prepared by the above method.

[0056] Another object of the present invention is to provide an application of a high-barrier polyvinylidene chloride emulsion.

[0057] An application of a high-barrier polyvinylidene chloride emulsion, the emulsion is the emulsion prepared by the above preparation method, or the above emulsion, and the emulsion is used in the fields of drug and food packaging, preferably used in the field of drug packaging.

[0058] The unit of the hydroxyl value of the substance in the present invention is mg KOH / g.

[0059] Compared with the prior art, the present invention has the following advantages:

[0060] The polyvinylidene chloride emulsion prepared by the present invention is added with a barrier promoter. On the premise that other properties do not change significantly, the barrier property is significantly improved and can be applied to the packaging fields of food, drugs, etc. Detailed Embodiments

[0061] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations to the present invention.

[0062] Vinylidene chloride: Shandong Xinglu Chemical Industry Co., Ltd., industrial product;

[0063] Methyl methacrylate: Wanhua Chemical Group Co., Ltd., industrial product;

[0064] Methyl acrylate: Wanhua Chemical Group Co., Ltd., industrial product;

[0065] Sodium dodecylbenzenesulfonate: Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0066] Ammonium persulfate: Shanghai Aladdin Biochemical Technology Co., Ltd.;

[0067] Preparation Example 1

[0068] Prepare barrier promoter 1.

[0069] The preparation method is as follows:

[0070] (1) After mixing 175 g of HDI and 1000 g of PBA2000 (polybutylene adipate diol) with a hydroxyl value of 55.0 evenly, react at 75 °C for 1 h, and measure the NCO to be 3.7%;

[0071] (2) Subsequently, add 78 g of MPEG520 (methoxypolyethylene glycol, molecular weight 520), and 98 g of acetone, react at 75 °C for 4 h, measure the NCO to be 2.8%, end the reaction, and cool for standby.

[0072] Preparation Example 2

[0073] Prepare barrier promoter 2.

[0074] The preparation method is as follows:

[0075] (1) After mixing 161 g of HDI and 1000 g of PBA2000 (polybutylene adipate diol) with a hydroxyl value of 57.0 evenly, react at 85 °C for 1 h, and measure the NCO to be 3.4%;

[0076] (2) Subsequently, add 61 g of MPEG520 (methoxypolyethylene glycol, molecular weight 520), and 116 g of acetone, react at 85 °C for 3 h, measure the NCO to be 2.6%, end the reaction, and cool for standby.

[0077] The performance of the polyvinylidene chloride emulsion was tested according to the following analysis method:

[0078] (1) Particle size

[0079] The test method is as follows: Dilute the emulsion 1000 times with deionized water, and perform dynamic light scattering measurement using a Zetasizer Nano ZS (Malvern Instruments).

[0080] (2) Preparation of test samples

[0081] Coat the polyvinylidene chloride emulsion on the PVC hard sheet, and after coating, place it in an oven at 40 °C for 1 min. According to the dosage of 10 g / m 2 each time, coat continuously for 6 times, and the final coating amount is 60 g / m 2 .

[0082] Test Items Test Instruments Test Standards Index Range Water Vapor Transmission Rate Mocon 3 / 34, Mocon Inc., USA YBB00092003-2015 <![CDATA[≤0.4 g / (m 2 ·24 h)]]> Oxygen Transmission Rate Mocon 2 / 22, Mocon Inc., USA YBB00082003-2015 <![CDATA[≤2.0 cm 3 / (m 2 ·24 h·0.1 MPa)]]>

[0083] Example 1

[0084] Add 2080.3 g of vinylidene chloride, 170 g of vinyl acetate, 310 g of methyl methacrylate, 960 g of water, and 14.4 g of sodium dodecylbenzenesulfonate, and stir at 2 °C and 170 rpm for 10 min to obtain a monomer pre-emulsion.

[0085] Add 2.6 g of sodium dodecylbenzenesulfonate, 342 g of water, and 18 g of methyl methacrylate to a 5 L polymerization autoclave, stir at 150 rpm for 10 min, then heat up to 75 °C. After dissolving 0.3 g of ammonium persulfate in 18 g of water, add it to the autoclave. After 30 min, a seed emulsion is obtained.

[0086] Add the above monomer pre-emulsion to the seed emulsion in the polymerization kettle at a dropping rate of 8.4 g / min, and at the same time, drop an aqueous solution of ammonium persulfate with a mass fraction of 4.25% at 0.9 g / min. Set the reaction temperature at 75 °C, and end the dropping after 7 h. Cool down to below 30 °C, add 17.2 g of barrier promoter 1, stir for 20 min, and then filter through a 100-mesh filter to obtain a polyvinylidene chloride emulsion.

[0087] The product performance of the polyvinylidene chloride emulsion is shown in Table 1.

[0088] Example 2

[0089] Add 2311.4 g of vinylidene chloride, 88.4 g of ethyl acrylate, 143.2 g of acrylonitrile, 960 g of water, and 8 g of sodium dodecyl sulfate, and stir at 4 °C and 170 rpm for 6 min to obtain a monomer pre-emulsion.

[0090] Add 2.6 g of pentadecylbenzenesulfonate, 342 g of water, 10 g of methyl methacrylate, and 8 g of acrylonitrile to a 5 L polymerization autoclave, stir at 150 rpm for 10 min, then heat up to 80 °C. After dissolving 0.3 g of potassium persulfate in 18 g of water, add it to the autoclave. After 10 min, a seed emulsion is obtained.

[0091] The above monomer pre-emulsion was added to the seed emulsion in the polymerization kettle at a dropping rate of 8.4 g / min, and at the same time, an aqueous solution of potassium persulfate with a mass fraction of 4.25% was dropped at 0.9 g / min. The reaction temperature was set at 75 °C, and the dropping was completed after 7 h. The temperature was lowered to 30 °C, 21.3 g of barrier promoter 2 was added, and after stirring for 20 min, the polyvinylidene chloride emulsion was obtained by filtering through a 100-mesh filter screen.

[0092] The product properties of the polyvinylidene chloride emulsion are shown in Table 1.

[0093] Example 3

[0094] 2311.4 g of vinylidene chloride, 134.5 g of methyl acrylate, 244.6 g of methacrylonitrile, 1000 g of water, and 8 g of dodecyl diphenyl ether disulfonate were stirred at 2 °C and 170 rpm for 10 min to obtain a monomer pre-emulsion.

[0095] 2.6 g of sodium dodecyl sulfate, 342 g of water, 12 g of methyl acrylate, and 6 g of acrylic acid were added to a 5 L polymerization autoclave, stirred at 150 rpm for 10 min, then heated to 75 °C. After 0.3 g of 2,2'-azobis(2-methyl)propionamidine dihydrochloride was dissolved in 18 g of water, it was added to the autoclave, and the seed emulsion was obtained after 30 min.

[0096] The above monomer pre-emulsion was added to the seed emulsion in the polymerization kettle at a dropping rate of 8.8 g / min, and at the same time, an aqueous solution of 2,2'-azobis(2-methyl)propionamidine dihydrochloride with a mass fraction of 4.25% was dropped at 0.9 g / min. The reaction temperature was set at 75 °C, and the dropping was completed after 7 h. The temperature was lowered to 30 °C, 26.7 g of barrier promoter 1 was added, and after stirring for 20 min, the polyvinylidene chloride emulsion was obtained by filtration.

[0097] The product properties of the polyvinylidene chloride emulsion are shown in Table 1.

[0098] Comparative Example 1

[0099] Compared with Example 3, the difference is that no barrier promoter is added after cooling.

[0100] 2311.4 g of vinylidene chloride, 134.5 g of methyl acrylate, 244.6 g of methacrylonitrile, 1000 g of water, and 8 g of dodecyl diphenyl ether disulfonate were stirred at 2 °C and 170 rpm for 10 min to obtain a monomer pre-emulsion.

[0101] Add 2.6 g of sodium dodecyl sulfate, 342 g of water, 12 g of methyl acrylate, and 6 g of acrylic acid to a 5 L polymerization autoclave. After stirring at 150 rpm for 10 min, heat up to 75 °C. Dissolve 0.3 g of 2,2'-azobis(2-methyl)propionamidine dihydrochloride in 18 g of water and then add it to the autoclave. After 30 min, a seed emulsion is obtained.

[0102] Add the above monomer pre-emulsion to the seed emulsion in the polymerization autoclave at a dropping rate of 8.8 g / min. At the same time, dropwise add an aqueous solution of 2,2'-azobis(2-methyl)propionamidine dihydrochloride with a mass fraction of 4.25% at a rate of 0.9 g / min. Set the reaction temperature at 75 °C and finish dropping after 7 h. Cool down to 30 °C, add 26.7 g of barrier promoter 1, stir for 20 min, and then filter to obtain a polyvinylidene chloride emulsion.

[0103] The product properties of the polyvinylidene chloride emulsion are shown in Table 1.

[0104] Table 1 Performance tests of polyvinylidene chloride emulsions in each example and comparative example

[0105]

[0106] As can be seen from Table 1, in Comparative Example 1, no barrier promoter was added. During the film-forming process of the emulsion, as the water volatilized, the penetration and diffusion effect between the latex particle interfaces was poor, and effective connections could not be formed between the particles, resulting in high oxygen and water vapor transmission rates. In Examples 1-3, a barrier promoter was added. During the water volatilization process, the end group of the promoter molecule was NCO. As the water volatilized, the NCO concentration gradually increased, and at the same time, the acid that restricted the NCO reaction gradually decreased. NCO began to carry out a chain extension reaction with water, covering the latex particles like a net, greatly improving the crosslinking. At the same time, since the promoter contains a crystallizable soft segment, a dense network will be formed during the final film formation, which will also promote the improvement of the barrier property.

[0107] Those skilled in the art can understand that under the teaching of this specification, some modifications or adjustments can be made to the present invention. These modifications or adjustments should also be within the scope defined by the claims of the present invention.

Claims

1. A preparation method of a high-barrier polyvinylidene chloride emulsion, characterized in that, A barrier property promoter is added in the preparation method, and the preparation method comprises the following steps: S1: Prepare a monomer pre-emulsion: Mix vinylidene chloride, comonomer, emulsifier and water and stir to obtain a monomer pre-emulsion; S2: Seed emulsion polymerization: Mix seed monomer, seed emulsifier and water, add an initiator, and react to obtain a seed emulsion; S3: Polyvinylidene chloride emulsion polymerization: Add the monomer pre-emulsion to the seed emulsion, and add an initiator; S4: After the addition of the monomer pre-emulsion is completed, add a barrier property promoter, mix, and filter to obtain the target product.

2. The preparation method according to claim 1, characterized in that, In S1, the comonomer is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, and methacrylonitrile; And / or, in S1, the emulsifier is an anionic surfactant, preferably one or more of sodium lauryl sulfate, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium pentadecyl benzene sulfonate, and sodium dodecyl diphenyl ether disulfonate; And / or, in S1, the addition ratio of vinylidene chloride, comonomer, water, and emulsifier is (60-65):(5-15):(25-30):(0.2-0.5); And / or, in S1, the temperature is 0-5°C, and the stirring time is 5-10 min.

3. The preparation method according to claim 1, characterized in that, In S2, the seed monomer is one or more of methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, vinyl acetate, acrylic acid, methacrylic acid, acrylonitrile, and methacrylonitrile; And / or, in S2, the seed emulsifier is an anionic surfactant, preferably one or more of sodium lauryl sulfate, sodium dodecyl sulfonate, sodium dodecyl benzene sulfonate, sodium pentadecyl benzene sulfonate, and sodium dodecyl diphenyl ether disulfonate; And / or, in S2, the addition ratio of seed monomer, seed emulsifier, and water is (2-6):(0.2-1):(90-95); And / or, in S2, the initiator is a peroxide and / or an azo initiator, preferably one or more of sodium persulfate, potassium persulfate, ammonium persulfate, di-tert-butyl peroxide, azodiisobimidazoline, and 2,2'-azobis(2-methyl)propionamidine dihydrochloride; Preferably, the addition amount of the initiator in S2 is 0.2-0.7% of the mass of the seed monomer; And / or, in S2, the temperature is 75-80°C, and the stirring time is 10-30 min.

4. The preparation method according to claim 1, characterized in that, In S3, the addition ratio of the seed emulsion to the monomer pre-emulsion is 1:(10-12); And / or, in S3, the initiator is a peroxide and / or an azo initiator, preferably one or more of sodium persulfate, potassium persulfate, ammonium persulfate, di-tert-butyl peroxide, azodiisobimidazoline, and 2,2'-azobis(2-methyl)propionamidine dihydrochloride; Preferably, the addition amount of the initiator in S3 is 0.1-0.6% of the mass of the monomer pre-emulsion; And / or, in S3, the reaction temperature is 75-80°C.

5. The preparation method according to claim 1, characterized in that, In S4, the addition amount of the barrier property promoter is 0.4-0.6% of the mass of the polyvinylidene chloride emulsion, preferably 0.45-0.55%; And / or, the barrier promoter in S4 is the reaction product of hexamethylene diisocyanate (HDI), polyester diol, and methoxypolyethylene glycol; And / or, the mixing time in S4 is 20 - 25 min.

6. A high-barrier polyvinylidene chloride emulsion, wherein the emulsion is prepared by the preparation method described in any one of claims 1 - 5.

7. A method for preparing a barrier promoter, characterized in that, The method comprises the following steps: SS1: Mix and react an isocyanate monomer and a polyester diol to obtain an NCO-terminated intermediate; SS2: Add methoxypolyethylene glycol and a solvent and continue the reaction to obtain a barrier promoter.

8. The preparation method according to claim 7, characterized in that, The isocyanate monomer in SS1 is hexamethylene diisocyanate; And / or, the polyester diol in SS1 is polybutylene adipate; Preferably, the hydroxyl value of the polyester diol is 55.0 - 57.0; And / or, the ratio of the isocyanate monomer to the polyester diol in SS1 is 1:(5.5 - 6.5); And / or, the reaction temperature in SS1 is 75 - 85 °C; And / or, the NCO of the intermediate in SS1 is 3.4% - 3.7%; And / or, the mass ratio of methoxypolyethylene glycol in SS2 to the components in SS1 is 1:(15 - 19); And / or, the mass ratio of the solvent in SS2 to the components in SS1 is 1:(10 - 12); And / or, the reaction temperature in SS2 is 75 - 85 °C, and the reaction time is 3 - 4 h; And / or, the NCO of the barrier promoter in SS2 is 2.6% - 2.8%.

9. A barrier promoter, wherein the barrier promoter is the promoter used in the preparation method described in any one of claims 1 - 5, or the promoter contained in the high-barrier polyvinylidene chloride emulsion described in claim 6, or the promoter prepared by the method described in claim 7 or 8.

10. An application of a high-barrier polyvinylidene chloride emulsion, wherein the emulsion is the emulsion prepared by the preparation method described in any one of claims 1 - 5, or the emulsion described in claim 6, and the emulsion is used in the fields of pharmaceutical and food packaging, preferably in the field of pharmaceutical packaging.

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