Amphiphilic disulfides, process for their preparation and use in the post-treatment of polymeric emulsions

Abstract

The application discloses a kind of amphiphilic disulfides and its preparation method and application, belong to emulsion polymerization technical field, the disulfide has the following structure general formula (I), (I) formula: R1 It is C1-C6 straight chain or branched alkyl group;R2 It is C2-C6 straight chain or branched alkyl group:M1 It is alkali metal ion or NH4 + , M2 It is alkali metal ion.The disulfide and oxidizing agent constitute redox system for the post-processing of polymerization emulsion can efficiently target removal residual monomer and free radical in emulsion, keep excellent emulsion stability, and do not release formaldehyde.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of emulsion polymerization, and in particular, the present application relates to an amphiphilic disulfide, a preparation method thereof and application thereof in post-treatment of polymerized emulsion. BACKGROUND

[0002] Emulsion polymerization is a common polymerization method and is widely used in polymerization processes of various monomers. However, after the emulsion polymerization reaction is terminated, free radicals and residual monomers are often left in the system, which can adversely affect the performance of subsequent products, such as causing the stability of the product to decrease, the risk of toxicity (such as VOC release) and the deterioration of subsequent processing performance. Therefore, post-treatment is required after emulsion polymerization.

[0003] One of the post-treatment methods for emulsion polymerization in the prior art is to terminate residual free radicals by an oxidation-reduction system. Common reducing agents include ascorbic acid, sodium bisulfite, formaldehyde sodium sulfite (sodium formaldehyde sulfoxylate), commercially available FF6M, etc. However, these traditional reducing agents have a limited removal efficiency, can easily cause latex coagulation, have a high residue rate, and even introduce toxic byproducts such as formaldehyde, etc.

[0004] Therefore, there is an urgent need in the art to develop a new reducing agent for post-treatment after emulsion polymerization to improve the removal efficiency of residual monomers and residual free radicals and maintain the stability of the emulsion. SUMMARY

[0005] In view of the above problems existing in the prior art, the present application provides an amphiphilic disulfide and application thereof in post-treatment of polymerized emulsion.

[0006] In a first aspect of the present application, an amphiphilic disulfide is provided, which has the following general structure (I),

[0007] (I)

[0008] In the formula, R1 is a C1-C6 linear or branched alkyl group; R2 is a C2-C6 linear or branched alkyl group; M1 is an alkali metal ion or NH4

[0009] M2 is an alkali metal ion. +

[0010] In some embodiments of the first aspect of the present application, R1 is a C1-C4 linear or branched alkyl group; R2 is a C2-C4 linear or branched alkyl group.

[0011] In some embodiments of the first aspect of the present application, R1 is a C1-C4 linear or branched alkyl group; R2 is a C2-C4 linear or branched alkyl group.

[0012] ​In some embodiments of the first aspect of the application, R1 is -CH2-, -CH2CH2-, -CH2CH2CH2-, or -CH(CH3)-; R2 is -CH2CH2-, -CH2CH2CH2-, or -CH2CH2CH2CH2-.

[0013] In some embodiments of the first aspect of the application, M1 is Na + , K + , or NH4 + ; M2 is Na + , or K + .

[0014] In some embodiments of the first aspect of the application, the amphiphilic disulfide has the following structural formula:

[0015]

[0016]

[0017]

[0018] or

[0019] .

[0020] In the second aspect of the application, a method for preparing the amphiphilic disulfide according to the first aspect of the application is provided, which comprises the following steps:

[0021] under inert atmosphere and alkaline conditions, a first mercapto compound with a structure of HS-R1-COOM1 is subjected to oxidative coupling reaction with a second mercapto compound with a structure of HS-R2-SO3M2, to obtain a target product with a general structure of (I),

[0022] (I)

[0023] wherein:

[0024] R1 is a C1-C6 linear or branched alkyl group; R2 is a C2-C6 linear or branched alkyl group:

[0025] M1 is an alkali metal ion or NH4 + , and M2 is an alkali metal ion.

[0026] In some embodiments of the second aspect of the application, the reaction temperature of the oxidative coupling reaction is 0-5°C.

[0027] In some embodiments of the second aspect of the application, R1 is C1-C4 linear or branched alkyl; R2 is C2-C4 linear or branched alkyl.

[0028] In some embodiments of the second aspect of the application, R1 is -CH2-, -CH2CH2-, -CH2CH2CH2- or -CH(CH3)-; R2 is -CH2CH2-, -CH2CH2CH2- or -CH2CH2CH2CH2-; M1 is Na + , K + or NH4 + ; M2 is Na + or K + .

[0029] In a third aspect of the application, there is provided use of the amphiphilic disulfide according to the first aspect of the application in post-treatment of a polymer emulsion.

[0030] In a fourth aspect of the application, there is provided a post-treatment method of a polymer emulsion, the post-treatment method comprising the following steps:

[0031] providing a polymer emulsion to be treated, the polymer emulsion to be treated comprising a dispersion medium, polymer particles, an emulsifier and residual monomers;

[0032] adding a redox system comprising an oxidizing agent and the amphiphilic disulfide according to the first aspect of the application as a reducing agent to the polymer emulsion to be treated to react, the temperature of the reaction system being 40-65°C.

[0033] In some embodiments of the fourth aspect of the application, the temperature of the reaction system is 55-65°C.

[0034] In some embodiments of the fourth aspect of the application, the pH of the reaction system is controlled to be 7.0-8.0.

[0035] In some embodiments of the fourth aspect of the application, the oxidizing agent is selected from one or more of the following compounds: tert-butyl hydroperoxide, hydrogen peroxide, cumene hydroperoxide, ammonium persulfate.

[0036] In some embodiments of the fourth aspect of the application, the oxidizing agent is tert-butyl hydroperoxide, the addition amount of the amphiphilic disulfide is 1.5-2.2 times the total molar amount of the residual monomers; and the molar ratio of the amphiphilic disulfide to the oxidizing agent is (1.1-1.3):1.

[0037] Compared with the prior art, the application has the following beneficial effects:

[0038] The amphiphilic disulfide provided by the present application has both hydrophilicity and lipophilicity. When the amphiphilic disulfide is used as a reducing agent and an oxidizing agent to form a redox system for post-treatment of a polymerized emulsion, the lipophilic group makes the reducing agent be distributed at the interface of colloidal particles, and the residual monomers in the colloidal particles are efficiently targeted and enriched. The polymerization rate is fast, the content of residual monomers in the emulsion can be quickly reduced, and the removal efficiency is significantly higher than that of a traditional reducing agent. The post-treated emulsion has excellent stability, the emulsion PDI is less than or equal to 0.04, and there is no flocculation. In addition, the post-treated emulsion also has good storage stability, which shows that the free radicals in the emulsion have been removed.

[0039] In addition, the amphiphilic disulfide of the present application does not contain a formaldehyde group, and does not release formaldehyde when used for post-treatment of a polymerized emulsion, thereby eliminating safety risks and environmental pollution. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 The nuclear magnetic resonance hydrogen spectrum of the amphiphilic disulfide (product 1) prepared according to Example 1 of the present application is shown in Figure 1. 1 H NMR).

[0041] Figure 2 The nuclear magnetic resonance hydrogen spectrum of the amphiphilic disulfide (product 2) prepared according to Example 2 of the present application is shown in Figure 2. 1 H NMR).

[0042] Figure 3 The nuclear magnetic resonance hydrogen spectrum of the amphiphilic disulfide (product 3) prepared according to Example 3 of the present application is shown in Figure 3. 1 H NMR).

[0043] Figure 4 The nuclear magnetic resonance hydrogen spectrum of the amphiphilic disulfide (product 4) prepared according to Example 4 of the present application is shown in Figure 4. 1 H NMR).

[0044] Figure 5 The nuclear magnetic resonance hydrogen spectrum of the amphiphilic disulfide (product 5) prepared according to Example 5 of the present application is shown in Figure 5. 1 H NMR).

[0045] Figure 6 The gas chromatogram of the emulsion sample 1 in Example 6 is shown in Figure 6.

[0046] Figure 7 The gas chromatogram of the emulsion sample 2 in Example 6 is shown in Figure 7.

[0047] Figure 8 The gas chromatogram of the emulsion sample 3 in Example 6 is shown in Figure 8.

[0048] Figure 9is the gas chromatogram of emulsion sample 4 in Example 6.

[0049] Figure 10 is the gas chromatogram of emulsion sample 5 in Example 6.

[0050] Figure 11 is the gas chromatogram of emulsion sample 6 in Example 6.

[0051] Figure 12 is the gas chromatogram of emulsion sample 7 in Example 6.

[0052] Figure 13 is the gas chromatogram of emulsion sample 8 in Example 6.

[0053] Figure 14 is the gas chromatogram of emulsion sample 9 in Example 6.

[0054] Figure 15 is the gas chromatogram of emulsion sample 0 in Example 6.

[0055] Figure 16 is the standard curve of internal standard method gas chromatography used in Example 6.

[0056] Figure 17 is the post-processing polymerization rate curve diagram of emulsion samples 1 to 9 in Example 6.

[0057] Figure 18 is the appearance photo of the emulsion film formed by emulsion samples 1 to 9 in Example 6. DETAILED DESCRIPTION

[0058] The various aspects of the present application will be described in detail hereinafter with reference to the specific embodiments, which are only used to illustrate the present application and do not constitute limitations to the scope and substance of the present application.

[0059] The present application provides a new reducing agent for post-processing of polymerization emulsion, which is an amphiphilic disulfide having the structure shown in general formula (I). As can be seen from the structure, the disulfide reducing agent has both hydrophilic groups (sulfonic acid group -SO3M1, carboxyl group -COOM2) and lipophilic groups (alkyl chain). When the reducing agent is used in the post-processing of polymerization emulsion together with an oxidizing agent (such as TBHP) to form a redox system, the lipophilic groups make the reducing agent directional distribution at the interface of the colloidal particles, and the residual monomers are enriched in the interface layer of the colloidal particles. The high activity free radicals generated by the reaction of the reducing agent and the oxidizing agent can be generated in situ in the area with the highest monomer concentration, and the local high concentration greatly accelerates the generation of free radicals and the polymerization rate of monomers, thereby significantly improving the post-processing efficiency and efficiently reducing the residual monomers to below the target value.

[0060] The amphiphilic disulfide of the present application can be prepared by the following synthetic route:

[0061]

[0062] wherein:

[0063] R1 is a C1-C6 linear or branched alkyl group; R2 is a C2-C6 linear or branched alkyl group:

[0064] M1 is an alkali metal ion or NH4 + M2 is an alkali metal ion.

[0065] In the above synthetic route, the reaction raw materials are selected from a first mercapto compound having the structure HS-CH(R1)-COOM 1 and a second mercapto compound having the structure HS-(CH2) n -SO3M 2 The two mercapto compounds undergo oxidative coupling reaction under inert atmosphere and alkaline aqueous solution conditions, and the oxidizing agent can be iodine (I2). The oxidative coupling reaction temperature is 0-5°C. After the reaction is completed, the excess iodine can be quenched by a reducing agent, and the target product, i.e. the amphiphilic disulfide of the present application, can be obtained by concentration, desalting and recrystallization purification.

[0066] The amphiphilic disulfide of the present application can be used as a reducing agent to form a redox system with an oxidizing agent for post-treatment of a polymerized emulsion. The post-treatment of a polymerized emulsion refers to a step performed after the main polymerization reaction of the emulsion is completed. By adding the redox system, free radicals are generated at a relatively low temperature (e.g. 40-70°C) to make the residual monomers continue to polymerize, thereby reducing the residual monomer content in the emulsion to a low level.

[0067] The oxidizing agent used in the redox system with the amphiphilic disulfide of the present application for post-treatment of a polymerized emulsion can be an oxidizing agent commonly used in the art, for example, can be selected from one or more of the following compounds: tert-butyl hydroperoxide, hydrogen peroxide, cumene hydroperoxide, ammonium persulfate.

[0068] In the redox system used for post-treatment of a polymerized emulsion, the molar ratio of the oxidizing agent to the reducing agent (the amphiphilic disulfide of the present application) is (1.1-1.3):1. The oxidizing agent and the reducing agent are respectively prepared into their own aqueous solutions, and the oxidizing agent solution and the reducing agent solution are simultaneously added dropwise into the polymerized emulsion for reaction and incubation to make the reaction sufficient to remove the residual monomers in the emulsion. In the post-treatment, the temperature of the emulsion system is 40-70°C, preferably 55-65°C; the emulsion system is kept weakly alkaline, for example, the pH value is 7.0-8.0.

[0069] In the post-treatment of the polymer emulsion according to the present application, the amount of the oxidant and the reducing agent in the redox system can be determined according to the content of the residual monomers in the emulsion to be treated, for example, the amount of the oxidant can be 1.0-1.5 times of the total moles of the residual monomers. In addition, the amount of the oxidant and the reducing agent can also be determined according to the total mass of the monomers in the emulsion, for example, the amount of the oxidant can be 0.01-0.5 wt% of the total mass of the monomers, and the amount of the reducing agent can be 0.01-0.5 wt% of the total mass of the mixed monomers.

[0070] The "polymer emulsion to be treated" according to the present application refers to the original emulsion obtained after the main polymerization reaction, wherein the content of the residual monomers exceeds the desired level. In other words, the polymer emulsion to be treated according to the present application refers to the polymer emulsion that needs to be treated by the post-treatment step to reduce the amount of the residual monomers to the desired level. In the specific embodiments of the present application, the polymer emulsion to be treated is exemplified by the aqueous acrylate copolymer emulsion, wherein the total content of the residual monomers in the polymer emulsion to be treated exceeds 1900 ppm, and after the post-treatment using the redox system composed of the amphiphilic disulfide and the oxidant, the total content of the residual monomers in the emulsion can be less than 120 ppm.

[0071] The amphiphilic disulfide according to the present application can also be used in other various emulsion systems that need to reduce the content of the residual monomers.

[0072] In order to evaluate the effect of the application and the post-treatment of the amphiphilic disulfide according to the present application, the polymer emulsion to be treated can be directly obtained from the prior art or synthesized according to the teachings of the prior art. For example, for the aqueous acrylate copolymer emulsion, the following components can be included:

[0073] a) dispersion medium: deionized water accounts for 40-70 wt% based on the total mass of the emulsion;

[0074] b) copolymer colloidal particles: formed by in-situ polymerization of the mixed monomers in the dispersion medium, the mixed monomers account for 30-60 wt% of the total mass of the emulsion, and the mixed monomers include:

[0075] i. 40-99.5 wt% of (meth)acrylate main monomers;

[0076] ii. 0.5-5 wt% of functional monomers containing carboxyl, hydroxyl or amide groups;

[0077] c) free radical providing initiator: water-soluble initiator and / or redox system initiator, accounting for 0.1-2.0% of the total mass of the mixed monomers;

[0078] d) emulsifier: 0.1-5.0% of one or more emulsifiers based on the total mass of the mixed monomers; the emulsifier comprises a conventional emulsifier and a reactive emulsifier.

[0079] In the post-treated polymer emulsion system of the present application, the (meth)acrylate main monomer forming the emulsion can be selected from one or more of methyl acrylate, ethyl acrylate, n-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, n-butyl methacrylate, styrene, isobornyl methacrylate. The functional monomer is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, maleic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, acrylamide, methacrylamide. The functional monomer is selected from one or more of acrylic acid, methacrylic acid, itaconic acid, maleic acid, hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, acrylamide, methacrylamide. The emulsifier is selected from an anionic emulsifier, a non-ionic emulsifier or a complex system thereof; preferably, the anionic emulsifier is selected from one or more of alkyl sulfate, alkyl ether sulfate, alkyl sulfonate, alkyl aryl sulfonate; the non-ionic emulsifier is selected from one or more of alkyl phenol polyoxyethylene ether, fatty alcohol polyoxyethylene ether, polyoxyethylene-polyoxypropylene block copolymer.

[0080] The initiator for providing free radicals in the polymer emulsion is a water-soluble persulfate salt, preferably ammonium persulfate, potassium persulfate or sodium persulfate.

[0081] The amphiphilic disulfide and the preparation method thereof and the application thereof in the post-treatment of polymer emulsion of the present application are further described in detail below by way of illustration.

[0082] Example 1

[0083] The synthesis route of the amphiphilic disulfide of the present example is as follows:

[0084]

[0085] Sodium mercaptoacetate (HS-CH2-COONa, 0.1 mol, 11.4 g) and sodium 2-mercaptoethanesulfonate (HS-CH2-CH2-SO3Na, 0.1 mol, 16.4 g) were dissolved in 200 mL of 1% aqueous NaHCO3solution. The system was cooled to 0-5°C using an ice bath, and iodine in ethanol (0.05 mol, 12.7 g of I2in 50 mL of ethanol) was slowly added dropwise over 2 hours under nitrogen protection. After the dropwise addition was completed, the reaction was continued for 1.5 hours, and 10% aqueous Na2S2O3solution (15 mL) was added to quench the reaction to colorless. The reaction solution was concentrated to 1 / 3 of the original volume by rotary evaporation, and 200 mL of anhydrous ethanol was added to precipitate inorganic salts (Nal, NaHCO3, etc.), which were filtered and the filter cake was washed with 50 mL of ethanol. The combined filtrate was concentrated to dryness to obtain the crude product. The crude product was recrystallized from 30 mL of a water-acetone mixture (V 水 :V 丙酮 = 1:4), and the target product selectively precipitated to obtain white solid product 1, sodium 2-((2-sulfonatoethyl)disulfanyl)acetate (yield 88%, HPLC purity ≥ 98%). The structure of product 1 was confirmed by 1 H NMR characterization as sodium 2-((2-sulfonatoethyl)disulfanyl)acetate, and the specific characterization results are as follows:

[0086] 1 H NMR (600 MHz, CDCl3) δ 3.36 (dt, J = 236.4, 0.0, 0.0 Hz, 2H), 3.24(t, J = 4.9 Hz, 2H), 3.03 (td, J = 4.9, 3.8 Hz, 2H). The corresponding 1 H NMR spectrum is shown in Figure 1 .

[0087] Example 2

[0088] The synthesis route of the amphiphilic disulfide of this example is as follows:

[0089]

[0090] Sodium mercaptoacetate (HS-CH2-COONa, 0.1 mol, 11.4 g) and sodium 4-mercaptobutanesulfonate (HS-CH2-CH2-CH2-CH2-SO3Na, 0.1 mol, 19.2 g) were dissolved in 200 mL of 1% NaHCO3 aqueous solution. The system was cooled to 0-5°C using an ice bath, and iodine in ethanol (0.05 mol, 12.7 g of I2 dissolved in 50 mL of ethanol) was slowly added dropwise over 2 hours under nitrogen protection. After the dropwise addition was completed, the reaction was continued for 1.5 hours, and 10% Na2S2O3 aqueous solution (15 mL) was added to quench the reaction to colorless. The reaction solution was concentrated to 1 / 3 of the original volume by rotary evaporation, and 200 mL of anhydrous ethanol was added to precipitate inorganic salts (Nal, NaHCO3, etc.), which were filtered and the filter cake was washed with 50 mL of ethanol. The combined filtrate was concentrated to dryness to obtain a crude product. The crude product was recrystallized from 30 mL of a water-acetone mixed solvent (V 水 :V 丙酮 = 1:4), and the target product selectively precipitated to obtain white solid product 2, which was sodium 2-((4-sulfobutyl)disulfanyl)acetate (yield 85%, HPLC purity ≥ 98%). The structure of product 2 was confirmed by 1 H NMR characterization as sodium 2-((4-sulfobutyl)disulfanyl)acetate, and the specific characterization results are as follows:

[0091] 1 H NMR (600 MHz, CDCl3) δ 3.34 (s, 2H), 3.00 (t, J = 6.1 Hz, 2H), 2.57(t, J = 6.3 Hz, 2H), 1.87 – 1.77 (m, 2H), 1.74 – 1.64 (m, 2H). The corresponding 1 H NMR spectrum is shown in Figure 2 .

[0092] Example 3

[0093] The synthesis route of the amphiphilic disulfide of this example is as follows:

[0094]

[0095] Potassium mercaptoacetate (HS-CH2-COOK, 0.1 mol, 13.0 g) and sodium 2-mercaptoethanesulfonate (HS-CH2-CH2-SO3Na, 0.1 mol, 16.4 g) were dissolved in 200 mL of 1% aqueous NaHCO3solution. The system was cooled to 0-5°C using an ice bath, and iodine in ethanol (0.05 mol, 12.7 g of I2in 50 mL of ethanol) was slowly added dropwise over 2 hours under nitrogen protection. After the dropwise addition was completed, the reaction was continued for 1.5 hours, and 10% aqueous Na2S2O3solution (15 mL) was added to quench the reaction to colorless. The reaction solution was concentrated to 1 / 3 of the original volume by rotary evaporation, and 200 mL of anhydrous ethanol was added to precipitate inorganic salts (Nal, NaHCO3, etc.), which were filtered and the filter cake was washed with 50 mL of ethanol. The combined filtrate was concentrated to dryness to obtain the crude product. The crude product was recrystallized from 30 mL of a water-acetone mixture (V 水 :V 丙酮 = 1:4), and the target product selectively precipitated to obtain white solid product 3, which was 2-[(2-sulfonatoethyl)dithio]acetic acid potassium sodium salt (yield 87%, HPLC purity ≥ 98%). The structure of product 3 was confirmed by 1 H NMR characterization as 2-[(2-sulfonatoethyl)dithio]acetic acid potassium sodium salt, and the specific characterization results are as follows:

[0096] 1 H NMR (600 MHz, CDCl 3) δ 3.36 (s, 2H), 3.24 (t, J = 4.9 Hz, 2H), 3.03(t, J = 4.9 Hz, 2H). The corresponding 1 H NMR spectrum is shown in Figure 3 .

[0097] Example 4

[0098] The synthesis route of the amphipathic disulfide of this example is as follows:

[0099]

[0100] Ammonium mercaptoacetate (HS-CH2-COONH 4,0.1 mol (10.9 g) of sodium 2-mercaptoethanesulfonate (HS-CH2-CH2-SO3Na, 0.1 mol, 16.4 g) was dissolved in 200 mL of 1% NaHCO3 aqueous solution. The system was cooled to 0-5°C using an ice bath, and under nitrogen protection, an ethanol solution of iodine (0.05 mol, 12.7 g of I2 dissolved in 50 mL of ethanol) was slowly added dropwise over 2 hours. After the addition was complete, the reaction was continued at this temperature for 1.5 hours, and then quenched with 10% Na2S2O3 aqueous solution (15 mL) until colorless. The reaction solution was concentrated to 1 / 3 of its original volume by rotary evaporation, and 200 mL of anhydrous ethanol was added to precipitate inorganic salts (NaI, NaHCO3, etc.). The mixture was filtered, and the filter cake was washed with 50 mL of ethanol. The filtrates were combined and concentrated to dryness to obtain the crude product. The crude product was then dissolved in 30 mL of a water-acetone mixture (V... 水 :V 丙酮 Recrystallization at a ratio of 1:4 yielded the target product, which selectively precipitated to obtain a white solid product 4, sodium 2-[(2-sulfonicoethyl)dithioalkyl]acetate (yield 86%, HPLC purity ≥ 98%). The structure of product 4 was determined by... 1 ¹H NMR characterization confirmed it to be sodium salt of 2-[(2-sulfonylethyl)dithioalkyl]acetate, and the specific characterization results are as follows:

[0101] 1 ¹H NMR (600 MHz, CDCl₃) δ 3.56 (s, 2H), 3.24 (t, J = 4.9 Hz, 2H), 3.03 (t, J = 4.9 Hz, 2H). Correspondingly... 1 H NMR spectrum as shown Figure 4 As shown.

[0102] Example 5

[0103] The synthetic route for the amphiphilic disulfide in this embodiment is as follows:

[0104]

[0105] Sodium 2-mercapto-propionate (HS-CH(CH3)-COONa, 0.1 mol, 12.8 g) and sodium 2-mercapto-ethanesulfonate (HS-CH2-CH2-SO3Na, 0.1 mol, 16.4 g) were dissolved in 200 mL of 1% NaHCO3 aqueous solution. The system was cooled to 0-5°C using an ice bath, and iodine in ethanol (0.05 mol, 12.7 g of I2 dissolved in 50 mL of ethanol) was slowly added dropwise over 2 hours under nitrogen protection. After the dropwise addition was completed, the reaction was continued for 1.5 hours, and 10% Na2S2O3 aqueous solution (15 mL) was added to quench the reaction to colorless. The reaction solution was concentrated to 1 / 3 of the original volume by rotary evaporation, and 200 mL of anhydrous ethanol was added to precipitate inorganic salts (Nal, NaHCO3, etc.), which were filtered and washed with 50 mL of ethanol. The filtrate was combined and concentrated to dryness to obtain a crude product. The crude product was recrystallized using 30 mL of a water-acetone mixed solvent (V 水 :V 丙酮 =1:4), and the target product selectively precipitated to obtain white solid product 5, sodium 2-[(2-sulfonatoethyl)dithio]propanoate (yield 85%, HPLC purity ≥ 98%). The structure of product 5 was confirmed by 1 H NMR characterization as sodium 2-[(2-sulfonatoethyl)dithio]propanoate, and the specific characterization results are as follows:

[0106] 1 H NMR (600 MHz, CDCl3) δ 3.56 (q, J = 6.9 Hz, 1H), 3.25 (t, J = 4.8Hz, 2H), 3.04 (t, J = 4.9 Hz, 2H), 1.57 (d, J = 6.9 Hz, 3H). The corresponding 1 H NMR spectrum is shown in Figure 5 .

[0107] Example 6

[0108] In order to evaluate the application performance of the amphiphilic disulfides of Examples 1 to 5 for post-emulsion polymerization treatment, this example takes an acrylate-styrene copolymer emulsion as an example to compare the application performance of the amphiphilic disulfides prepared in Examples 1 to 5 with that of traditional reducing agents.

[0109] The acrylate-styrene copolymer emulsion used in this example can be directly obtained from the prior art or synthesized according to the prior art, for example, prepared according to the following steps:

[0110] 1. Preparation of acrylate-styrene copolymer emulsion

[0111] 1.1 Preparation of primer solution:

[0112] Into a 500 mL glass reactor equipped with a mechanical stirrer, thermometer, reflux condenser and nitrogen inlet, the following components were added in sequence:

[0113] Butyl acrylate: 75 g

[0114] Styrene: 25 g

[0115] Deionized water: 125 g

[0116] Ammonium persulfate: 1.5 g

[0117] Stirring was started at room temperature at 300 rpm, and the mixture was mixed well to form a primer. Nitrogen was introduced to replace the air in the reactor for about 20 minutes.

[0118] 1.2 Preparation of pre-emulsion:

[0119] In another conical flask, the following components were mixed:

[0120] Butyl acrylate: 100 g

[0121] Styrene: 50 g

[0122] Acrylic acid: 4.33 g

[0123] Deionized water: 250 g

[0124] Emulsifier SR-10: 1.42 g

[0125] Emulsifier AEO-7: 4.92 g:

[0126] A uniform and stable pre-emulsion was prepared by emulsifying with a German IKA digital disperser T25 at a speed of 10000 rpm for 10 minutes.

[0127] 1.3 Emulsion polymerization reaction

[0128] The reaction kettle system was heated to 85±2°C. Stirring was continued at a speed of 400 rpm and nitrogen was introduced for protection. After the primer showed a clear blue light, the pre-emulsion was started to be added dropwise, with a control dropwise time of 2 hours, and the reaction temperature was maintained at 85±2°C.

[0129] 1.4 Incubation and maturation

[0130] After the pre-emulsion was added, the reaction system was heated to 90±2°C and incubated for 1 hour to obtain a treated emulsion for post-treatment experiments.

[0131] The emulsion system includes:

[0132] Polymer particles: butyl acrylate-styrene-acrylic acid copolymer (P(BA-St-AA)) particles; particle size: 228 nm, PDI = 0.03, usually between tens to hundreds of nanometers, presenting a clear blue light (Tyndall effect);

[0133] Dispersing medium: deionized water;

[0134] Emulsifier: anionic emulsifier SR-10; non-ionic emulsifier AEO-7;

[0135] Residual monomers: including un-polymerized butyl acrylate (BA), styrene (St), the total content of residual monomers is 2165 ppm, of which BA 947 ppm, St 1218 ppm, distributed in the interior of the polymer particles and the aqueous phase.

[0136] 2. Post-treatment

[0137] The following uses the amphiphilic disulfide of Examples 1 to 5 and the reducing agent commonly used in the art (commercially available reducing agents Bruggolite® FF6M, L-ascorbic acid (vitamin C), sodium bisulfite (NaHSO3), sodium sulfite, respectively) to post-treat the emulsion to be treated. The specific steps are as follows:

[0138] 2.1 Preparation of emulsion sample to be treated

[0139] Cool the emulsion to be treated obtained in step 1.4 above to below 60°C, adjust the pH of the system to 7.5±0.2 with saturated sodium bicarbonate solution, then divide it into 10 parts (each part has a mass of about 45 g), and label them as emulsion samples to be treated 1 to 9 and emulsion sample 0 (blank control) respectively, and place them in 10 independent constant temperature reaction flasks at 60±2°C.

[0140] 2.2 Oxidation-reduction system treatment:

[0141] The emulsion samples to be treated 1 to 9 are synchronously added with the following oxidation-reduction system under the conditions of 60±2°C and pH 7.5±0.2.

[0142] Reducing agent solution B: the molar ratio of the specific reducing agent to the total residual monomers of the base emulsion is 1.8:1.

[0143] Oxidizing agent solution A: tert-butyl hydroperoxide (TBHP), the molar ratio of the oxidizing agent (TBHP) to the reducing agent is 1:1.2.

[0144] The emulsion sample 0 to be treated is used as a blank control and is not treated with an oxidation-reduction system, i.e. no solution A and B is added, but is kept at the same temperature for the same time to obtain emulsion sample 0 for comparison of the post-treatment effect.

[0145] The emulsion sample 0 to be treated was used as a blank control, and no redox system treatment was performed, i.e. no addition of the above-mentioned solution A and B, but the same temperature was maintained for the same time, to obtain the emulsion sample 0 for comparison of the post-treatment effect.

[0146] The specific substances in solution B added to the emulsion samples 1 to 9 to be treated were as follows:

[0147] Sample 1 : product 1 prepared in Example 1, i.e. sodium 2-((2-sulfonatoethyl)disulfanyl)acetate;

[0148] Sample 2: product 2 prepared in Example 2, i.e. sodium 2-((4-sulfonatobutyl)disulfanyl)acetate;

[0149] Sample 3: product 3 prepared in Example 3, i.e. sodium potassium 2-[(2-sulfonatoethyl)disulfanyl]acetate;

[0150] Sample 4: product 4 prepared in Example 4, i.e. sodium ammonium 2-[(2-sulfonatoethyl)disulfanyl]acetate;

[0151] Sample 5: product 5 prepared in Example 5, i.e. sodium 2-[(2-sulfonatoethyl)disulfanyl]propanoate;

[0152] Sample 6: commercially available reducing agent Bruggolite® FF6M;

[0153] Sample 7: L-ascorbic acid (vitamin C);

[0154] Sample 8: sodium bisulfite (NaHSO3);

[0155] Sample 9: sodium thiosulfate.

[0156] Dropwise addition: two independent high-precision syringe pumps were used to add solution A and solution B to each emulsion sample to be treated at a constant rate, and the total dropwise addition time of the two solutions was controlled to be 30 minutes, to ensure that the oxidizing agent solution and the reducing agent solution were added synchronously and mixed thoroughly.

[0157] 2.3 Post-heat preservation:

[0158] After the dropwise addition of solution A and solution B was completed, the system of the emulsion samples 1 to 9 was maintained at 60±2°C and pH 7.5±0.2 for continued reaction for 4 hours. The emulsion sample 0 to be treated (blank control) was also maintained for 4 hours.

[0159] 2.4 Termination and discharge:

[0160] After the end of the heat preservation, each emulsion sample was naturally cooled or water-bathed to room temperature (about 25°C) respectively. Each emulsion sample was filtered using 100 mesh nylon filter cloth to remove possible gel or impurities, and the final emulsion product was obtained (labeled as emulsion sample 0 to emulsion sample 9).

[0161] 3. Effect test

[0162] In order to evaluate the application performance of the amphiphilic disulfides prepared in Examples 1-5 in the post-treatment of the polymerization emulsion, the following tests and comparisons were carried out on emulsion samples 0-9, including: determination of residual monomer content in the emulsion, emulsion particle size and distribution determination, polymerization rate test, formaldehyde content test, slagging rate test, latex film appearance test, and emulsion stability test after post-treatment.

[0163] 3.1 Determination of residual monomer content in the emulsion

[0164] For emulsion samples 1-5 obtained after post-treatment using the amphiphilic disulfides prepared in Examples 1-5 and emulsion samples 6-9 obtained after post-treatment using traditional reducing agents in Example 6, the residual monomer content in the emulsion was quantitatively analyzed by internal standard gas chromatography, and the specific operation steps were as follows: a certain amount of internal standard cyclohexanone (CPMK) solution was added to the emulsion sample through a headspace sampler, and a capillary column (5% phenyl-95% dimethyl polysiloxane as stationary phase) was used for separation, and a hydrogen flame ionization detector (FID) was used for quantitative analysis, and the residual monomer mass percentage was calculated by internal standard method. The gas chromatograms of emulsion samples 1-9 are shown in Figures 6 to 14 , respectively. The gas chromatogram of emulsion sample 0 (blank control) is shown in Figure 15 . The standard curve of residual monomer by gas chromatography is shown in Figure 16 .

[0165] The residual monomer content of styrene (BA) and butyl acrylate (St) in each emulsion sample was calculated according to the gas chromatography Figures 9 to 15 , and is shown in Tables 1-10, respectively, wherein:

[0166] Table 1 is the residual monomer content of emulsion sample 1 calculated based on the gas chromatogram Figure 6 .

[0167]

[0168] Table 2 is the residual monomer content of emulsion sample 2 calculated based on the gas chromatogram Figure 7 .

[0169]

[0170] Table 3 is the residual monomer content of emulsion sample 3 calculated based on the gas chromatogram Figure 8The residual monomer content of emulsion sample 3 was calculated based on the gas chromatogram of

[0171]

[0172] Table 4 is based on the gas chromatogram of Figure 9 The residual monomer content of emulsion sample 4 was calculated based on the gas chromatogram of

[0173]

[0174] Table 5 is based on the gas chromatogram of Figure 10 The residual monomer content of emulsion sample 5 was calculated based on the gas chromatogram of

[0175]

[0176] Table 6 is based on the gas chromatogram of Figure 11 The residual monomer content of emulsion sample 6 was calculated based on the gas chromatogram of

[0177]

[0178] Table 7 is based on the gas chromatogram of Figure 12 The residual monomer content of emulsion sample 7 was calculated based on the gas chromatogram of

[0179]

[0180] Table 8 is based on the gas chromatogram of Figure 13 The residual monomer content of emulsion sample 8 was calculated based on the gas chromatogram of

[0181]

[0182] Table 9 is based on the gas chromatogram of Figure 14 The residual monomer content of emulsion sample 9 was calculated based on the gas chromatogram of

[0183]

[0184] Table 10 is based on the gas chromatogram of Figure 15 The residual monomer content of emulsion sample 0 was calculated based on the gas chromatogram of

[0185]

[0186] The total residual monomer content in each emulsion sample is shown in Table 11.

[0187] 3.2 Emulsion particle size and distribution determination

[0188] The emulsion particle size and distribution of emulsion samples 1 to 10 obtained after the above post-processing were determined by dynamic light scattering method. Specifically, the emulsion was diluted to a solid content of 0.1%-0.5%, placed in a constant temperature condition of 25°C, a laser light source with a wavelength of 633 nm was used, the scattering angle was 90°, and the Z-average particle size and polydispersity index (PDI) were calculated by cumulative analysis method. The test results of the particle size and distribution of each emulsion are shown in Table 11.

[0189] 3.3 Polymerization rate test

[0190] From the start of the post-processing, 1 mL of emulsion was extracted every 15 minutes after the end of the dropwise addition of solutions A and B, and immediately quenched in an ice water bath. The sample was thermostatted to 25±0.5°C, and the Brix% value was determined using a digital refractometer (ATAGO PAL-1), repeated 3 times to take the average value. When the Brix% value fluctuated by ≤0.1% for three consecutive samplings, the time at which the reaction endpoint was recorded. The Brix% value is positively correlated with the solid content, R²≥0.99, and can represent a monomer conversion rate of ≥99.5%. The test results of the polymerization rate are shown in Table 11. Figure 17 and Table 11.

[0191] 3.4 Formaldehyde content test

[0192] The free formaldehyde content in the emulsion of emulsion samples 1 to 9 obtained after post-processing and blank control emulsion sample 0 was determined according to GB18583-2008 standard, and the test results are shown in Table 11.

[0193] 3.5 Residue yield test

[0194] The residue yield test was performed on emulsion samples 1 to 9 obtained after post-processing and blank control emulsion sample 0. The specific test steps are as follows: the emulsion was filtered using a 100 mesh filter screen, and all the filter residue was transferred to a weighing dish that had been weighed. The weighing dish was placed in a 105±2°C oven for drying for 2 hours, and then taken out and cooled to room temperature in a desiccator. The weight was accurately weighed, and the drying-cooling-weighing steps were repeated until the difference between the two consecutive weighings was ≤0.0005 g, and the constant weight was recorded. The filter residue rate was calculated according to the following formula:

[0195] Filter residue rate (%) = (constant weight of filter residue after drying / total weight of solid contained in emulsion sample) × 100%

[0196] The test results of the residue yield are shown in Table 11.

[0197] 3.6 Appearance of rubber film:

[0198] For emulsion samples 1 to 9 and blank control emulsion sample 0 obtained after post-treatment, 10 mL of each emulsion was cast into a polytetrafluoroethylene culture dish to form a film, and then baked at 50°C for 2 hours and at 110°C for 1 hour. After cooling to room temperature, the appearance of the latex film was observed and photographed. Figure 18 The color of the latex film is shown in Table 11.

[0199] Table 11 Test data results of emulsion samples 0 to 9 in Example 6

[0200]

[0201] 3.7 Storage stability test of emulsion after post-treatment

[0202] (1) Sample preparation:

[0203] For emulsion samples 1 to 9 and blank control emulsion sample 0 obtained after post-treatment in Example 6, 35 g of each emulsion sample was sealed in a glass sample bottle. All the samples were placed in a constant temperature oven at 50°C for accelerated storage aging test. Samples were taken at 0 days (i.e. at the time of post-treatment completion), 3 days, and 7 days, and the total residual monomer content of each sample at different time points was determined by gas chromatography internal standard method. The change in total residual monomer content of each emulsion during storage is shown in Table 12.

[0204] Table 12 Total residual monomer content and its change amount (ppm) of emulsion samples during storage

[0205]

[0206] As can be seen from Table 12, the emulsion samples 1 to 5 treated with the amphiphilic disulfide of the present application have only a slight fluctuation in residual monomer content after 7 days of accelerated aging, with a very small change amount (the maximum change amount is -6 ppm), which indicates that the free radicals in the emulsion system after post-treatment have been removed and the polymerization reaction has terminated, and the product has very high storage stability.

[0207] In contrast, the emulsion samples 6 to 9 treated with traditional reducing agents have a significant decrease in residual monomer content within 7 days (the maximum change amount is -117 ppm), indicating that there are still active free radicals in the system and they continue to consume monomers during storage. This continuous reaction can lead to unstable emulsion performance and high VOC release risk.

[0208] The sharp decrease in monomer content of the blank control sample further verifies the effectiveness of the test method.

[0209] Monitoring the storage stability of residual monomers shows that post-treatment of emulsions with the amphiphilic disulfide provided by this invention can effectively remove residual free radicals in the emulsion system, and its effect is better than that of traditional reducing agents.

[0210] Example 7

[0211] Preparation of the base emulsion: A scaled-up acrylate-styrene copolymer base emulsion (pH=7.5±0.2) was prepared according to steps 1.1 to 1.4 in Example 6. The total residual monomer content in the emulsion was 2165 ppm, including BA 947 ppm and St1 218 ppm. The emulsion was divided into 10 equal portions, each approximately 60 g, and labeled as Sample A to Sample J.

[0212] Samples A to J underwent post-processing using the amphiphilic disulfide (SDSA) from Example 1 as a reducing agent to form a redox system with the oxidant (TBHP). The molar ratio of oxidant (TBHP) to reducing agent was fixed at 1:1.2. The amount of reducing agent SDSA and the system temperature were varied to test the effects of reducing agent dosage and post-processing reaction temperature on the removal of residual monomers. Specific changes are shown in Table 12. Other post-processing steps and conditions were the same as steps 2.1 to 2.4 in Example 6. The final emulsion test method was the same as in Example 6, and the test results are shown in Table 13.

[0213] Sample A: No reducing agent was added, and the sample was kept at 60°C for 30 minutes, followed by 4 hours, as a blank control.

[0214] Sample BD: The amount of SDSA was fixed at 1.5 times the total molar amount of residual monomers in the base emulsion, and the reaction was carried out at 50℃, 60℃, and 70℃ respectively.

[0215] Sample EG:SDSA was used at a fixed amount of 1.8 times the total molar amount of the residual monomer, and the reaction was carried out at 50℃, 60℃, and 70℃ respectively.

[0216] Sample HJ: The amount of SDSA used was fixed at 2.2 times the total molar amount of the residual monomer, and the reaction was carried out at 50℃, 60℃, and 70℃ respectively.

[0217] Table 13: Results of Optimization Experiments on Post-Treatment Process Conditions of Emulsion Using SDSA Reducing Agent

[0218]

[0219] From the data in Table 13, under the condition that the molar ratio of oxidant (TBHP) to reducing agent is 1:1.2, and the molar ratio of SDSA to total residual monomers of the base emulsion is in the range of 1.5:1 to 2.2:1, the reaction at 60℃ can obtain low residual monomer content (<220 ppm) and good emulsion stability. When the molar ratio is lower than this range, the reaction efficiency is too low to effectively reduce the residual monomer content; when the reaction temperature is too high, the system will produce gel and the stability will decrease due to side reactions, and even the residual monomer content will increase. In combination of reaction efficiency and product stability, the molar ratio of SDSA to total residual monomers of the base emulsion is 1.8:1, and the reaction temperature is 60℃, which are the preferred conditions (sample F, 98 ppm).

[0220] The present application shows through systematic experiments that when using the reducing agent SDSA for post-treatment, the molar ratio of oxidant (TBHP) to reducing agent is 1:1.2, the molar ratio of SDSA to total residual monomers of the base emulsion is (1.5-2.2):1, and the reaction temperature is 50-70℃, the total residual monomer content in the emulsion can be stably and efficiently reduced to below 220 ppm, and the stability of the emulsion system can be fully maintained.

[0221] The above has specifically described the present application in combination with specific examples, which are only exemplary and cannot limit the protection scope of the present application. Those skilled in the art can make various modifications, changes or replacements to the present application without departing from the essence and scope of the present application. Therefore, various equivalent changes made in accordance with the present application still belong to the scope covered by the present application.

Claims

1. An amphiphilic disulfide having the general structure (I) ###0001### wherein: R1 is -CH2-, -CH2CH2-, -CH2CH2CH2-, or -CH(CH3)-; R2 is -CH2CH2-, -CH2CH2CH2-, or -CH2CH2CH2CH2-. （I） 2. The amphiphilic disulfide of claim 1 having the structure: ###0002### 3. A method of preparing the amphiphilic disulfide of claim 1, the method comprising the steps of: oxidatively coupling a first mercaptan compound having the structure HS-R1-COOM1 with a second mercaptan compound having the structure HS-R2-SO3M2 under inert atmosphere and basic conditions to obtain the target product having the general structure (I), ###0003### wherein: R1 is -CH2-, -CH2CH2-, -CH2CH2CH2-, or -CH(CH3)-; R2 is -CH2CH2-, -CH2CH2CH2-, or -CH2CH2CH2CH2-; and the oxidative coupling reaction is carried out at a temperature of 0-5°C.

5. Use of the amphiphilic disulfide of claim 1 in the post-treatment of a polymer emulsion. M1 is Na + , K + , or NH4 + ; M2 is Na + , or K + . The post-treatment method comprises the steps of: providing a polymer emulsion to be treated, the polymer emulsion to be treated comprising a dispersion medium, polymer particles, an emulsifier, and residual monomers; and adding a redox system comprising the amphiphilic disulfide of claim 1 or 2 as a reducing agent and an oxidizing agent to the polymer emulsion to be treated, and allowing the redox system to react at a temperature of 40-65°C. or 。 The temperature of the reaction system is 55-65°C. The pH of the reaction system is controlled to be 7.0-8.

0. （I） The oxidizing agent is selected from one or more of the following compounds: tert-butyl hydroperoxide, hydrogen peroxide, cumene hydroperoxide, and ammonium persulfate. The oxidizing agent is tert-butyl hydroperoxide, the amphiphilic disulfide is added in an amount of 1.5-2.2 times the total moles of residual monomers, and the molar ratio of the amphiphilic disulfide to the oxidizing agent is (1.1-1.3):

1. ​ M1is Na + , K + or NH4 + ; M2 is Na + or K + .

4. The production method according to claim 3, wherein ​ ​ 6. A method for post-treatment of a polymer emulsion, characterized by ​ ​ ​ 7. The post-treatment method of claim 6, wherein, ​ 8. The post-processing method of claim 6, wherein, ​ 9. The post-treatment method of claim 7 or 8, wherein, ​ 10. The post-treatment method of claim 9, wherein, ​

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