A continuous polymerization process for nitrile rubber

Abstract

This invention discloses a continuous polymerization method for nitrile butadiene rubber. In the process of emulsion polymerization to synthesize acrylonitrile and butadiene copolymer, acrylonitrile and butadiene tend to undergo random alternating copolymerization through a continuous decreasing feeding method. This allows acrylonitrile to be uniformly incorporated into the butadiene-acrylonitrile copolymer (NBR) molecules. Compared with the existing NBR prepared by a one-time feeding method of acrylonitrile and butadiene, the NBR obtained by the technical solution of this invention exhibits excellent physical and mechanical properties, especially outstanding oil resistance.

Description

Technical Field

[0001] This invention relates to a method for synthesizing nitrile rubber, specifically a method for uniformly incorporating acrylonitrile into the molecular chain of butadiene-acrylonitrile copolymer by a continuous acrylonitrile feeding method, belonging to the field of nitrile rubber synthesis technology. Background Technology

[0002] Nitrile rubber is a copolymer of acrylonitrile and butadiene in an emulsion under the action of peroxide and other additives at low temperature. The mass fraction of acrylonitrile in commercially available nitrile rubber (such as NBR3365, NBR1052 and NBR3355 produced by Nandi Chemical Co., Ltd.) is usually 25% to 42%, and its vulcanizates are mainly used for oil-resistant seals.

[0003] In "Study on Acrylonitrile-Butadiene-Isoprene Ternary Emulsion Copolymerization", Gu Zhengwen, Dalian University of Technology, June 2011, the synthesis of acrylonitrile-butadiene-isoprene ternary emulsion copolymerization at low temperature was studied under the action of sodium dodecylbenzenesulfonate, potassium oleate, ferrous sulfate, disodium EDTA, and cumene peroxide. Chinese Patent (CN103665265A) discloses a method for preparing nitrile rubber, specifically describing a method for preparing nitrile rubber from butadiene and acrylonitrile via cold intermittent emulsion polymerization. The method is characterized by sequentially adding water, emulsifier, co-emulsifier, emulsion stabilizer, and a portion of the acrylonitrile monomer in the formulation to a polymerization reactor. When the temperature inside the polymerization reactor drops to 5-10°C, the oxidant, reducing agent, secondary reducing agent, and chelating agent of a redox initiator are added sequentially. Depending on the acrylonitrile content requirements of different specifications of nitrile rubber products, the remaining acrylonitrile monomers in the formulation are added. The polymerization reaction time is controlled between 8-12 hours, and the monomer conversion rate is controlled between 65%-80%. A terminator is added to terminate the emulsion polymerization reaction. The resulting nitrile rubber latex is degassed, coagulated, and dried with hot air to obtain the nitrile rubber product. Its technical indicators are: Mooney viscosity 30-95, acrylonitrile content 18-46% by total monomer mass, swelling degree 20-50%, and tensile strength 10-22 MPa. Chinese patent (CN103450397A) describes a method for preparing nitrile rubber (NBR), employing a two-stage material addition method. In this method, 85% of an aqueous solution of emulsifier, dispersant, electrolyte, chelating agent, reducing agent, activator, N-(p-anilinephenyl)unsaturated amide or imide, vinyl nitrile group, molecular weight regulator, and conjugated diene monomer are added to an initiator solution in two separate reactions. When the reaction conversion rate reaches 30-50%, the remaining emulsifier, dispersant, electrolyte, molecular weight regulator, and chelating agent are added to the reactor, achieving a conversion rate of 60-80%. The study ("Influence of Microstructure on the Physical Properties of Nitrile Rubber Vulcanizates," Rubber Industry, April 2013) investigated the influence of the microstructure of the rubber matrix and fillers on the physical properties of nitrile rubber (NBR) vulcanizates. However, none of the above techniques provide a microscopic description of the synthesized NBR molecular structure.

[0004] The results reported in (“Sequence Structure and Application Study of Nitrile Rubber”, Chen Haocheng, Qingdao University of Science and Technology, 2019, 6, 4) and (“220-MHz NBR Spectra of Butadiene and Acrylonitrile Alternating and Randon Copolymers”, Suzuki T, Polymer Journal, 1973, 4(6): 657-663.) show that the sequence distribution of the adjacent structural units of the two monomers in NBR molecules with medium and low bound acrylonitrile content is AAA, BAA, AAB and BAB, BBA and ABB, ABA. Existing NBR industrial technologies all employ a multi-reactor continuous feeding method, where butadiene and acrylonitrile are continuously added to the first reactor at once to initiate copolymerization. The mixed monomers remain in the polymerization environment for 6–10 hours. In a low-temperature emulsion polymerization environment, due to the lower polymerization concentration and higher reactivity of acrylonitrile compared to butadiene, as copolymerization proceeds, the amount of acrylonitrile bound in the middle and later stages of the polymerization reaction inevitably decreases, meaning that the chain segments in the middle and later stages are dominated by homopolymer chains of butadiene.

[0005] Currently, in order to improve the oil resistance of nitrile rubber, increasing the molecular weight of acrylonitrile during NBR preparation and hydrogenating it to prepare H-NBR are two effective methods. However, these methods result in varying degrees of loss or unsatisfactory performance in terms of the rubber's processing properties and overall physical properties.

[0006] In summary, the main characteristics of existing NBR technologies are that the mass fraction of acrylonitrile in the molecule is 20-40%, and the Mooney viscosity is 30-90. The distribution of the two monomers in the molecule is difficult to accurately describe using existing equipment for molecular chain segment analysis, as the monomer sequence distribution and conformation are challenging to determine. Although acrylonitrile and butadiene generally exhibit random copolymerization in existing NBR synthesis, research has found that if acrylonitrile and butadiene are added to the polymerization environment simultaneously for copolymerization, indirect analysis of the molecular chain structure reveals that acrylonitrile exhibits a decreasing distribution in the polymer molecular chain segments. This means that the terminal segments of the nitrile rubber molecular chain are mainly homopolymers of butadiene, and since polybutadiene blocks are not oil-resistant, this affects the overall oil resistance of the nitrile rubber. Summary of the Invention

[0007] The existing NBR (Non-Butadiene-Acrylonitrile Rubber) molecules exhibit a decreasing distribution of acrylonitrile within the chain segments, resulting in vulcanizates suitable only for mid-range oil-resistant products, with oil resistance inferior to hydrogenated nitrile butadiene rubber, chlorohydrin rubber, and fluororubber. The purpose of this invention is to provide a method for preparing nitrile butadiene rubber that achieves a relatively uniform and alternating distribution of acrylonitrile within the butadiene-acrylonitrile copolymer molecular chain segments. This method avoids the presence of partial homopolymer butadiene "back-end" segments in existing butadiene-acrylonitrile copolymer molecules, which negatively impacts their oil resistance. Furthermore, this method aims to ensure that the physical properties of the vulcanizate meet the national standards set by the People's Republic of China, and to satisfy the needs of mid- to high-end or even higher-grade oil-resistant seals, molded rubber parts, gaskets, fillers, O-rings, high-elasticity parts, rubber rollers, and other industries. Moreover, this method is simple to operate, low-cost, and efficient, making it suitable for industrial production.

[0008] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0009] To achieve the above-mentioned technical objectives, the present invention provides a continuous polymerization method for nitrile rubber, the method comprising a single-reactor polymerization method or a multi-reactor polymerization method;

[0010] The single-reactor polymerization method is as follows: the emulsion system is cooled to below 6°C, butadiene monomer and 40-60 mol% of acrylonitrile monomer are added to the emulsion system, and after induction for 18-25 min and copolymerization reaction for 2-3 h, the remaining acrylonitrile monomer is added to the emulsion system in batches in a gradient decreasing manner to carry out copolymerization reaction. After all the acrylonitrile monomer has been added, the copolymerization reaction is carried out until the total monomer conversion rate reaches more than 85%, and then the copolymerization reaction is terminated.

[0011] The multi-reactor polymerization method is as follows: After cooling the emulsion system to below 6°C, it is uniformly transported to the first reactor of the series polymerization reactors. At the same time, butadiene monomer and 40-60 mol% of acrylonitrile monomer are continuously and uniformly added to the first reactor. The mixture undergoes blending, emulsification, induction, and copolymerization reactions in the first reactor for 2-3 hours. Then, it is sequentially transported to the subsequent reactors for copolymerization reactions. At the same time, the remaining acrylonitrile monomer is added to the subsequent reactors in a gradient decreasing manner. When the total monomer conversion rate in the last reactor reaches more than 85%, the material is discharged and the copolymerization is terminated.

[0012] The key to this invention lies in the strict control of the addition method of acrylonitrile to achieve uniform integration of acrylonitrile into the butadiene-acrylonitrile copolymer molecular chain. Extensive experiments have demonstrated that during the copolymerization of acrylonitrile and butadiene at low temperatures, the reactivity ratio of acrylonitrile is higher than that of butadiene. In the early stage of polymerization, acrylonitrile monomers of 40-60 mol% are copolymerized with butadiene. Utilizing the advantage of a significantly higher butadiene concentration and the controlled low-temperature environment, butadiene and acrylonitrile undergo random polymerization at similar reactivity rates. In the later stages of polymerization, the temperature is slightly increased, but as the concentration of butadiene gradually decreases, the polymerization rate also shows a gradient decrease, similar to a linear function curve with a negative slope. By continuously adding acrylonitrile monomers, especially by continuously adding acrylonitrile monomers in a gradient decreasing manner, it is ensured that butadiene and acrylonitrile in the polymerization system undergo random copolymerization at similar polymerization rates. This ensures that acrylonitrile is evenly distributed throughout the butadiene-acrylonitrile copolymer molecular chain and avoids the appearance of butadiene blocks with high repeating units (greater than 3).

[0013] As a preferred embodiment, the emulsion system comprises components including deionized deoxygenated water, potassium organic carboxylate, dispersant, composite electrolyte, deoxidizer, reducing agent, molecular weight regulator, activator, and oxidant.

[0014] As a preferred embodiment, the dissolved oxygen content of the deionized deoxygenated water is <0.05 mg / L, and the total content of calcium ions, magnesium ions and iron ions is <1.0 mg / L; the amount of deionized deoxygenated water added relative to butadiene monomer and acrylonitrile monomer is 2-3 kg / kg.

[0015] As a preferred embodiment, the organic carboxylic acid potassium salt comprises potassium oleate and potassium disproportionate rosin; the amount of potassium oleate added relative to the butadiene monomer and acrylonitrile monomer is 10-20 g / kg; the amount of potassium disproportionate rosin added relative to the butadiene monomer and acrylonitrile monomer is 10-25 g / kg. In this invention, potassium oleate and potassium disproportionate rosin are added in solution form; potassium oleate is preferably added in an aqueous solution with a concentration of 10-16% by weight, and potassium disproportionate rosin is preferably added in an aqueous solution with a concentration of 20-25% by weight.

[0016] As a preferred embodiment, the dispersant is sodium methylene dinaphthalene sulfonate, and the amount of the dispersant added relative to the butadiene monomer and acrylonitrile monomer is 2.0–3.5 g / kg. Sodium methylene dinaphthalene sulfonate is preferably added as an aqueous solution with a concentration of 12–15% by weight.

[0017] As a preferred embodiment, the composite electrolyte is composed of sodium carbonate and potassium phosphate; the amount of sodium carbonate added relative to the butadiene monomer and acrylonitrile monomer is 1.0–3.0 g / kg; the amount of potassium phosphate added relative to the butadiene monomer and acrylonitrile monomer is 1.0–3.0 g / kg. Preferably, sodium carbonate and potassium phosphate are added as aqueous solutions with a mass concentration of 9–10%.

[0018] As a preferred embodiment, the deoxidizer is sodium dithionite; the amount of the deoxidizer added relative to the butadiene monomer and acrylonitrile monomer is 0.01–0.1 g / kg. Sodium dithionite is preferably added in the form of an aqueous solution with a concentration of 1.0–1.5% by weight.

[0019] As a preferred embodiment, the reducing agent is sodium formaldehyde sulfoxylate (Rhodium monoxide); the amount of the reducing agent added relative to the butadiene monomer and acrylonitrile monomer is 0.5–1.5 g / kg. Sodium formaldehyde sulfoxylate is preferably added in the form of a 6.5% by weight aqueous solution.

[0020] As a preferred embodiment, the activator is composed of sodium iron EDTA and sodium EDTA tetraacetate; the amount of sodium iron EDTA added relative to the butadiene monomer and acrylonitrile monomer is 0.5–1.5 mmol / kg, wherein the sodium iron EDTA is measured in molar amounts of iron; the amount of sodium EDTA tetraacetate added relative to the butadiene monomer and acrylonitrile monomer is 0.2–0.8 mmol / kg. The activator is generally added in solution form. For example, sodium iron EDTA and sodium EDTA tetraacetate are prepared into a mixed aqueous solution containing 0.05 mol / L sodium iron EDTA and 0.025 mol / L sodium EDTA tetraacetate. The most preferred molar ratio of iron to sodium EDTA tetraacetate in the sodium iron EDTA is 1 / 2.

[0021] As a preferred embodiment, the molecular weight regulator is tert-dodecyl mercaptan; the amount of the molecular weight regulator added relative to the butadiene monomer and acrylonitrile monomer is 5-10 g / kg.

[0022] As a preferred embodiment, the oxidant is p-menthol peroxide; the amount of the oxidant added relative to the butadiene monomer and acrylonitrile monomer is 0.5–2.0 g / kg.

[0023] As a preferred option, the mass ratio of acrylonitrile monomer to butadiene is (20-40) / (80-60).

[0024] As a preferred option, in the single-reactor polymerization method, the copolymerization reaction temperature is controlled at 4–8℃, the total copolymerization reaction time is controlled at 6–10h, and the copolymerization reaction pressure is controlled at 0.2–0.4MPa.

[0025] As a preferred option, in the multi-reactor polymerization method, the copolymerization reaction temperature is controlled at 5-8℃, the total copolymerization reaction time is controlled at 7-10h, and the copolymerization reaction pressure is controlled at 0.2-0.4MPa.

[0026] As a preferred option, in the single-reactor polymerization method, the process of continuously adding acrylonitrile monomer in a gradient decreasing manner is as follows: the remaining acrylonitrile monomer is added in 3 batches, the first batch being 20-30 mol% of the total acrylonitrile monomer, the second batch being 10-15 mol% of the total acrylonitrile monomer, and the third batch being the remaining acrylonitrile monomer, with a total addition time of 2-3 hours.

[0027] As a preferred embodiment, in the multi-reactor polymerization method, the process of continuously adding the remaining acrylonitrile monomer in a gradient decreasing manner is as follows: first, 20-30 mol% of the total acrylonitrile monomer is added to the second reactor, and the mixture reacts in the second reactor for 1.5-2 hours; then, 10-15 mol% of the total acrylonitrile monomer is added to the third reactor, and the mixture reacts in the third reactor for 1.5-2 hours; finally, the remaining acrylonitrile monomer is added to the fourth reactor, and the mixture reacts in the fourth reactor for no less than 2 hours.

[0028] The preferred single-reactor polymerization method of this invention is as follows: First, deionized water, potassium organic carboxylate, dispersant, composite electrolyte, deoxidizer, reducing agent, activator, molecular weight regulator, and oxidant are added to the polymerization reactor to form an emulsion system. Then, the emulsion is cooled to below 6°C. Under stirring, all the set amount of butadiene and 40-60% of the total set amount of acrylonitrile are added to the polymerization reactor. After induction for 18-25 minutes, the copolymerization reaction will cause a temperature rise. After the copolymerization reaction has been going on for 2-3 hours, the remaining acrylonitrile can be continuously added to the polymerization reactor. The best method for adding the remaining acrylonitrile is to gradually reduce the flow rate. The continuous feeding time is 2-3 hours. Then, the copolymerization reaction is continued for no less than 2 hours. When the monomer conversion rate is not less than 85% and the Mooney viscosity reaches the set requirements, the product can be discharged and the copolymerization emulsion can be terminated.

[0029] The preferred multi-reactor continuous polymerization method of this invention is as follows: First, a mixed emulsion (mother liquor) consisting of deionized water cooled to below 6°C, potassium organic carboxylate, dispersant, composite electrolyte, deoxidizer, reducing agent, activator, molecular weight regulator, and oxidant is uniformly fed into the inlet of the first reactor of a series of polymerization reactors at a set constant flow rate. Simultaneously, butadiene monomer and 40-60 mol% of the total set amount of acrylonitrile monomer are continuously and uniformly added to the bottom of the first reactor, and the copolymerization reaction is carried out for 2-3 hours. Then, 20-30 mol% of the total set amount of acrylonitrile monomer is added to the inlet of the second reactor, and the reaction is carried out for 1.5-2 hours. Next, 10-15 mol% of the total set amount of acrylonitrile is added to the inlet of the third reactor, and the reaction is carried out for 1.5-2 hours. Finally, the remaining total set amount of acrylonitrile is added to the inlet of the fourth reactor, and the reaction is carried out for at least 2 hours. Once the monomer conversion rate of the final reactor is measured to be no less than 85% and the Mooney viscosity reaches the set requirements, the material can be discharged and the copolymerization emulsion terminated.

[0030] In the multi-reactor continuous polymerization method of the present invention, the preferred polymerization reactor height-to-diameter ratio H / D = (6~10) / 1, and the total residence time of butadiene in the polymerization reactor is not less than 9h.

[0031] In the preparation of (nitrile butadiene rubber) NBR of this invention, the amount of acrylonitrile relative to butadiene is relatively small. Extensive experimental results show that during the copolymerization of acrylonitrile and butadiene, as the monomers undergo further conversion, the amount of acrylonitrile bound in the copolymer decreases progressively, meaning the polymerization rate of acrylonitrile is higher in the initial stage than in the later stage. During the copolymerization of acrylonitrile and butadiene, after the polymerization induction period, the copolymerization reaction is dominant. The butadiene concentration in the system exhibits a gradient decrease, similar to a linear function with a negative slope, in the initial, middle, and later stages of the copolymerization reaction. Therefore, adding the remaining acrylonitrile in a gradient manner best conforms to the kinetics of alternating copolymerization.

[0032] The NBR molecular chain prepared by this invention has the molecular structure of (Formula 1).

[0033] AAABAA…BBA…BBAABBBA…BBBAB…ABBA

[0034] Formula 1

[0035] In Formula 1, A is an acrylonitrile unit and B is a butadiene unit.

[0036] In the butadiene-acrylonitrile rubber of the present invention, the number of repeating units of A and B in the front, middle and rear segments of the entire polymer molecular chain is between 1 and 3, indicating that the copolymerization mode of butadiene and acrylonitrile is closest to alternating copolymerization, and acrylonitrile is uniformly inserted into the butadiene-acrylonitrile copolymer, avoiding the appearance of butadiene homopolymer blocks with a high number of repeating units in the butadiene-acrylonitrile rubber.

[0037] The NBR raw rubber prepared by this invention has a molecular weight distribution index of 3.5-4.5, a Mooney viscosity of 30-70, a bound acrylonitrile mass fraction of 20-40%, and a vinyl mass fraction of 10-13% in the butadiene segment.

[0038] The vulcanizate made from NBR prepared in this invention has the following properties: 300% tensile stress ≥ 9.5 MPa, tensile strength ≥ 25.0 MPa, permanent deformation < 12%, swelling rate in octane ≤ 0.5%, and swelling degree ≤ 32%.

[0039] Compared with existing technologies, the beneficial technical effects of the present invention are as follows:

[0040] Compared to existing NBR molecules where the acrylonitrile is distributed in decreasing order within the polymer chain, with the middle and terminal segments primarily composed of butadiene homopolymer segments, the NBR molecules of this invention exhibit a largely random alternating distribution of acrylonitrile. The mass content of the acrylonitrile in the raw rubber can be arbitrarily adjusted between 20% and 40% without limitation. The prepared NBR raw rubber has a wide molecular weight distribution, demonstrating excellent processing performance. The physical properties of the vulcanized rubber are no less than those of the national standard (GB / T 36089-2018) formulated by the People's Republic of China, such as 300% tensile stress ≥9.5MPa, tensile strength ≥25.0MPa, permanent deformation <12%, swelling rate in octane ≤0.5%, and swelling degree ≤32%. In particular, its oil resistance is unparalleled by existing NBRs and is comparable to chlorohydrin rubber, meeting the needs of mid- to high-end oil-resistant sealing molding rubber parts, high-elasticity parts, and rubber rollers. Attached Figure Description

[0041] Figure 1 The NBR 1H NMR spectrum prepared in Example 1.

[0042] Figure 2 The dynamic viscoelastic spectra of NBR prepared in Examples 1, 2, and 3; from Figure 2 As can be seen from the results, the dynamic viscoelastic spectrum curves of the NBR vulcanizates prepared in Examples 1 to 3 did not show an upward trend between 40 and 80°C, but were generally smooth downwards. This indicates that there are no high acrylonitrile homopolymer segments in the three vulcanizates, that is, acrylonitrile and butadiene exhibit random alternating copolymerization during the copolymerization process.

[0043] Figure 3 The continuous polymerization apparatus for preparing NBR is described in Example 3. Detailed Implementation

[0044] In the following examples, the molecular weight distribution index of the polymer was determined by gel permeation chromatography (GPC); the Mooney viscosity of the polymer was determined by a Mooney viscometer; the block distribution of centrally bound acrylonitrile in the polybutadiene segment of the polymer was characterized by a dynamic viscoelastic spectrometer; the microstructure of the polymer was quantitatively determined by ¹H NMR spectroscopy; the physical properties of the vulcanized rubber were determined by an INSTRON tensile testing machine; and the mixing, vulcanization, and oil resistance properties of the raw rubber were performed in accordance with the national standard GB / T-34685-2017.

[0045] Example 1

[0046] Add 1.80 L of deionized water (dissolved oxygen content <0.05 mg / L, total calcium, magnesium, and iron ion content <1.0 mg / L) to a 5 L polymerization reactor under nitrogen protection. Then, add the following solutions to the polymerization reactor's feeding sight glass: 70 mL of 15.0 wt% potassium oleate solution, 60 mL of 25.0 wt% potassium disproportionated rosin solution, 16 mL of a mixed aqueous solution containing 0.05 mol / L EDTA iron sodium salt and 0.025 mol / L EDTA tetraacetic acid sodium salt, 18 mL of 13.2 wt% sodium methylene dinaphthalene sulfonate aqueous solution, and 10 wt%... 13 mL each of sodium carbonate and sodium phosphate solutions, 5 mL of 1.5 wt% sodium dithionite aqueous solution, 15 mL of 6.5 wt% sodium formaldehyde sulfoxylate aqueous solution, 1.2 mL of PMHP, and 5.8 mL of tert-dodecyl mercaptan were added. The above materials were then pressurized into the polymerization reactor under nitrogen, and stirring was started for emulsification. The emulsion was cooled to below 5°C, and then 860 mL (534 g) of butadiene and 105 g of acrylonitrile were added to the polymerization reactor under nitrogen. The polymerization temperature was controlled to not exceed 7°C. After reacting for 2.5 h, a sample was taken, and the mass fraction of acrylonitrile bound in the copolymer molecules was measured to be 26.6%. Acrylonitrile was then added dropwise to the polymerization reactor continuously in three time intervals.

[0047] After the first stage was added dropwise at a flow rate of 0.83 g / min for 60 min, a sample was taken and the mass fraction of acrylonitrile bound in the copolymer molecule was measured to be 27.4%.

[0048] After the second stage was added dropwise at a flow rate of 0.58 g / min for 60 min, a sample was taken and the mass fraction of acrylonitrile bound in the copolymer molecule was measured to be 28.1%.

[0049] After the third stage was added dropwise at a flow rate of 0.33 g / min for 60 min, a sample was taken and the mass fraction of acrylonitrile bound in the copolymer molecule was measured to be 28.4%.

[0050] The reaction was then continued with stirring for another 2.5 hours. A sample was taken and the Mooney viscosity of the polymer raw rubber was measured to be 47.8, the mass fraction of bound acrylonitrile was 28.1%, and the vinyl unit content was 11.7%. At this point, the material was discharged, and 0.6 g of sodium dithiocarbamate and 2.5 g of antioxidant 1520 were added to the latex solution. After mixing thoroughly, the latex was coagulated with a dilute sulfuric acid solution of dicyandiamine-formaldehyde condensate, washed with water, and dried to obtain the final product. The total monomer conversion rate was measured to be 86.4%, and the molecular weight distribution index of the raw rubber was 3.9.

[0051] Example 2

[0052] The water and additives in Example 1 were not significantly adjusted, and the feeding method remained unchanged. After the emulsion cooled to below 5°C, 860 mL (534 g) of butadiene and 135 g of acrylonitrile were added to the polymerization reactor with nitrogen gas. The reaction was carried out at below 7°C for 2.5 h. The mass fraction of acrylonitrile bound in the copolymer molecules was measured to be 26.6%.

[0053] Then, after adding the copolymer dropwise at a flow rate of 1.10 g / min for 60 min, a sample was taken and the mass fraction of acrylonitrile bound in the copolymer molecule was measured to be 32.4%.

[0054] After adding the copolymer dropwise at a flow rate of 0.68 g / min for 60 min, the mass fraction of acrylonitrile bound in the copolymer molecule was measured to be 32.7%.

[0055] After the third dropping stage, the copolymer was added at a flow rate of 0.42 g / min for 58 min. A sample was taken and the mass fraction of acrylonitrile bound in the copolymer molecule was measured to be 32.9%. The reaction was then stirred for another 3 h. A sample was taken and the Mooney viscosity of the raw polymer was measured to be 46.2, the mass fraction of acrylonitrile bound was 33.2%, and the vinyl unit content was 12.3%. The latex was unloaded and processed according to the post-processing method in Example 1. The conversion rate of total monomers was measured to be 87.3%, and the molecular weight distribution index of raw rubber was 4.2.

[0056] Example 3

[0057] The polymerization unit consists of five reactors connected in series, namely a first reactor with a height H = 1240 mm and a diameter D = 200 mm (H / D = 6.2) and four second reactors, each with a height h = 1100 mm and a diameter d = 150 mm (h / d = 7.3). (See attached diagram) Figure 3In the process described in Example 2, water and additives are first mixed and stirred to form a polymerization mother emulsion without significant adjustments to the ratio. Then, the mother emulsion, butadiene, and acrylonitrile are simultaneously and continuously added to the bottom inlet of the first tower reactor in the series-connected reaction device at flow rates of 74.0 mL / min, 26.8 mL / min, and 7.0 mL / min, respectively. The polymerization emulsion is stirred while maintaining the polymerization temperature of the mixed emulsion at 5–8 °C and the pressure at 0.2–0.3 MPa until the system is full and the process is stable.

[0058] A sample was taken at the inlet of the second column in the polymerization apparatus (Note: the residence time of the monomer in the polymerization environment is 3h at this time), and the mass fraction of acrylonitrile bound in the copolymer molecule was measured to be 38.6%. At the same time, acrylonitrile was continuously added to the inlet of the second column using a metering pump at a rate of 6.25mL / min.

[0059] Similarly, a sample was taken at the inlet of the third column, and the mass fraction of acrylonitrile bound in the copolymer molecules was measured to be 39.3%. At the same time, acrylonitrile was continuously added to the inlet of the third column at a rate of 4.17 mL / min.

[0060] A sample was taken at the inlet of the fourth column, and the mass fraction of acrylonitrile bound in the copolymer molecule was found to be 39.8%. Acrylonitrile was then continuously added to the inlet of the fourth column at a rate of 2.08 mL / min.

[0061] All the starting materials and the additional acrylonitrile added three times were then continuously polymerized in two subsequent vertical polymerization reactors for about 3 hours. Finally, the material was discharged and the latex was treated according to the post-treatment method in Example 1. The Mooney viscosity of the raw rubber of the copolymer was measured to be 58.6, the conversion rate of total monomers was 86.2%, the mass fraction of bound acrylonitrile was 40.3%, the vinyl unit content was 11.7%, and the molecular weight distribution index of raw rubber was 4.5.

[0062] Comparative Example 1

[0063] The basic conditions in Example 2 were kept unchanged, except that 860 mL of butadiene and 270 g of acrylonitrile were added to the polymerization reactor at one time to carry out the polymerization reaction. The polymerization reaction temperature was 5-8 °C, and the characteristics of the polymer were measured at different time periods. The results are shown in Table 1.

[0064] Table 1

[0065]

[0066] As shown in Table 1, when the mass ratio of A to B is 33 / 66, the amount of acrylonitrile bound in the polymer molecules decreases as the polymerization reaction progresses. That is, in the early stage of polymerization, the acrylonitrile has a higher polymerization rate than butadiene. Small polyacrylonitrile homopolymers are produced in the early stage of polymerization, while small polybutadiene homopolymers are produced in the later stage of polymerization. The NMR analysis results show that the amount of acrylonitrile bound in the polymer molecules shows a decreasing distribution.

[0067] Example 4

[0068] The NBR prepared in Examples 1, 2, and 3, and Comparative Example 1, as well as commercially available NBR1052 and chloroprene rubber T3108XL manufactured by ZEON Corporation of Japan, were used to prepare test samples according to the relevant items in GB / T34685-2017 and tested. The dynamic viscoelastic spectra of the vulcanizates in Examples 1, 2, and 3 are shown below. Figure 2 The physical properties of the vulcanized rubber are shown in Table 2.

[0069] Table 2

[0070]

[0071] As can be seen from Table 2, the overall physical properties and oil resistance of the NBR of the present invention are comparable to those of chlorinated rubber.

Claims

1. A continuous polymerization method for nitrile rubber, characterized in that: This includes using single-reactor polymerization or multi-reactor polymerization methods; The single-reactor polymerization method is as follows: the emulsion system is cooled to below 6°C, butadiene monomer and 40-60 mol% of acrylonitrile monomer are added to the emulsion system, and after induction for 18-25 min and copolymerization reaction for 2-3 h, the remaining acrylonitrile monomer is added to the emulsion system in batches in a gradient decreasing manner to carry out copolymerization reaction. After all the acrylonitrile monomer has been added, the copolymerization reaction is carried out until the total monomer conversion rate reaches more than 85%, and then the copolymerization reaction is terminated. The multi-reactor polymerization method is as follows: After cooling the emulsion system to below 6°C, it is uniformly transported to the first reactor of the series polymerization reactors. At the same time, butadiene monomer and 40-60 mol% of acrylonitrile monomer are continuously and uniformly added to the first reactor. The mixture undergoes blending, emulsification, induction, and copolymerization reactions in the first reactor for 2-3 hours. Then, it is sequentially transported to the subsequent reactors for copolymerization reactions. At the same time, the remaining acrylonitrile monomer is continuously added to the subsequent reactors in a gradient decreasing manner. When the total monomer conversion rate in the last reactor reaches more than 85%, the material is discharged and the copolymerization is terminated. The mass ratio of acrylonitrile monomer to butadiene is (20~40) / (80~60); In the single-reactor polymerization method, the process of continuously adding acrylonitrile monomer in a gradient decreasing manner is as follows: the remaining acrylonitrile monomer is added in 3 batches. The first batch is 20-30 mol% of the total acrylonitrile monomer, the second batch is 10-15 mol% of the total acrylonitrile monomer, and the third batch is the remaining acrylonitrile monomer. The total time for adding acrylonitrile monomer is 2-3 hours. In the multi-reactor polymerization method, the process of continuously adding the remaining acrylonitrile monomer in a gradient decreasing manner is as follows: First, 20-30 mol% of the total acrylonitrile monomer is added to the second reactor, and the mixture reacts in the second reactor for 1.5-2 hours; then, 10-15 mol% of the total acrylonitrile monomer is added to the third reactor, and the mixture reacts in the third reactor for 1.5-2 hours; finally, the remaining acrylonitrile monomer is added to the fourth reactor, and the mixture reacts in the fourth reactor for no less than 2 hours.

2. The continuous polymerization method for nitrile rubber according to claim 1, characterized in that: The emulsion system comprises components including deionized deoxygenated water, organic carboxylic acid potassium salt, dispersant, composite electrolyte, deoxygenator, reducing agent, molecular weight regulator, activator and oxidant.

3. The continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The dissolved oxygen content of the deionized deoxygenated water is <0.05 mg / L, and the total content of calcium ions, magnesium ions and iron ions is <1.0 mg / L; the amount of deionized deoxygenated water added relative to butadiene monomer and acrylonitrile monomer is 2~3 kg / kg.

4. The continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The organic carboxylic acid potassium salt includes potassium oleate and potassium hydrogenated disproportionate rosin; the amount of potassium oleate added relative to butadiene monomer and acrylonitrile monomer is 10~20 g / kg; the amount of potassium hydrogenated disproportionate rosin added relative to butadiene monomer and acrylonitrile monomer is 10~25 g / kg.

5. A continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The dispersant is sodium methylene dinaphthalene sulfonate, and the amount of the dispersant added relative to the butadiene monomer and acrylonitrile monomer is 2.0~3.5 g / kg.

6. The continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The composite electrolyte is composed of sodium carbonate and potassium phosphate; the amount of sodium carbonate added relative to butadiene monomer and acrylonitrile monomer is 1.0~3.0 g / kg; the amount of potassium phosphate added relative to butadiene monomer and acrylonitrile monomer is 1.0~3.0 g / kg.

7. The continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The deoxidizing agent is sodium dithionite; the amount of the deoxidizing agent added relative to butadiene monomer and acrylonitrile monomer is 0.01~0.1g / kg.

8. The continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The reducing agent is sodium formaldehyde sulfoxylate; the amount of the reducing agent added relative to butadiene monomer and acrylonitrile monomer is 0.5~1.5 g / kg.

9. A continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The molecular weight regulator is tert-dodecyl mercaptan; the amount of the molecular weight regulator added relative to the butadiene monomer and acrylonitrile monomer is 5~10 g / kg.

10. The continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The activator is composed of sodium iron EDTA and sodium tetraacetate EDTA; the amount of sodium iron EDTA added relative to butadiene monomer and acrylonitrile monomer is 0.5~1.5 mmol / kg, wherein the sodium iron EDTA is measured in molar amounts of iron. The amount of sodium EDTA tetraacetate added relative to butadiene monomer and acrylonitrile monomer is 0.2~0.8 mmol / kg.

11. The continuous polymerization method for nitrile rubber according to claim 2, characterized in that: The oxidant is methylhydrogen peroxide; the amount of oxidant added relative to butadiene monomer and acrylonitrile monomer is 0.5~2.0 g / kg.

12. The continuous polymerization method for nitrile rubber according to claim 1, characterized in that: In the single-reactor polymerization method, the copolymerization reaction temperature is controlled at 4~8℃, the total copolymerization reaction time is controlled at 6~10h, and the copolymerization reaction pressure is controlled at 0.2~0.4MPa; In the multi-reactor polymerization method, the copolymerization reaction temperature is controlled at 5~8℃, the total copolymerization reaction time is controlled at 7~10h, and the copolymerization reaction pressure is controlled at 0.2~0.4MPa.

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