A butadiene-nitrile copolymer containing multiple polyacrylonitrile blocks and its preparation method

Abstract

This invention discloses a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks and its preparation method. In an emulsion polymerization solution system, at 20–40°C and a pressure of 0.3–0.5 MPa, a portion of acrylonitrile monomer is first added for a single-stage polymerization reaction for 3–4 hours, followed by the addition of butadiene monomer for a second-stage polymerization reaction for ≥2 hours, and then the remaining acrylonitrile monomer is added for a third-stage polymerization reaction for ≥3 hours. After coagulation, the butadiene-acrylonitrile copolymer is obtained. This butadiene-acrylonitrile copolymer has a molecular weight (Mn) of (8–12) × 10⁻⁶. 4 With a melt flow index (MFR) of (0.01~8) g / 10min, it has a large number of physical crosslinking points, exhibiting the behavior of a highly polar thermoplastic rubber. Blending and modifying it with existing thermoplastic elastomers can enhance the polarity of the blend and improve the affinity and adhesion between non-polar thermoplastic elastomers and other polar materials.

Description

Technical Field

[0001] This invention relates to a butadiene-nitrile copolymer and its preparation method, specifically to a butadiene-nitrile copolymer containing multiple polyacrylonitrile blocks, and also to a method for preparing butadiene-nitrile copolymer by emulsion polymerization, belonging to the field of butadiene-nitrile rubber synthesis technology. Background Technology

[0002] Commercially available nitrile rubber (such as NBR3365, NBR1052 and NBR3355 produced by Nan Di Chemical Co., Ltd.) typically has an acrylonitrile mass fraction of 25-42% and a Mooney viscosity of 30-90. It is formed by low-temperature initiation copolymerization of acrylonitrile and butadiene in an emulsion. In its NBR molecular structure, acrylonitrile and butadiene exhibit random alternating copolymerization. Its vulcanizates are mainly used for oil-resistant seals.

[0003] Chinese patent (CN103665265A) discloses a method for preparing nitrile rubber (NBR). Specifically, it describes a method for producing NBR from butadiene and acrylonitrile via cold batch emulsion polymerization. The method involves 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 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 NBR products, the remaining acrylonitrile monomers in the formulation are added. The polymerization reaction time is controlled between 8 and 12 hours, the monomer conversion rate is controlled between 65% and 80%, the Mooney viscosity is 30–95, the acrylonitrile content is 18–46% of the total monomer mass, the oil swelling resistance is 20–50%, and the tensile strength is 10–22 MPa. Currently, NBR is mainly used for vulcanized rubber products such as oil-resistant hoses and oil-resistant sealing rings. Chinese patent (CN103450397A) describes a method for preparing nitrile rubber, 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 in two separate steps, with the temperature controlled at 5–8°C. An initiator solution is then added to the reaction vessel. When the reaction conversion rate reaches 30–50%, the remaining emulsifier, dispersant, electrolyte, and chelating agent are added to the reactor. The remaining molecular weight regulator is then added to the polymerization reactor. The reaction is terminated when the conversion rate reaches 60–80%, with a reaction time of 7 hours. Chinese patent (CN104628955A) relates to a chemically modified nitrile rubber and its production method. It involves copolymerizing butadiene (64-65 parts by weight), acrylonitrile (20-21 parts by weight), butyl acrylate (0.30-0.31 parts by weight), sodium oleate (4.0-4.1 parts by weight), dodecyl mercaptan (0.18-0.19 parts by weight), and other additives at 35-45°C for a polymerization time of 15-22 hours. The synthesized raw rubber has a Mooney viscosity of over 120 but a tensile strength of only 14.5 MPa. Chinese Patent (CN110066481A) discloses an application of nitrile butadiene rubber, comprising 10-20 parts nitrile butadiene rubber; 12-20 parts chlorinated paraffin; 10-20 parts naphthenic oil; 6-12 parts carbon black N550; 30-40 parts polyvinyl chloride; 10-20 parts calcium carbonate; 3-10 parts foaming agent; 0.5-0.8 parts crosslinking agent DCP; 0.5-1 part foaming and crosslinking aid; and 0.2-0.5 parts stearic acid. A literature review (“Research on the Preparation Method of Rapidly Vulcanized Nitrile Butadiene Rubber”, Guangdong Chemical Industry, 2017, No. 10) discloses a method for preparing rapidly vulcanized nitrile butadiene rubber products by adding a vulcanization accelerator during the post-treatment stage of nitrile butadiene rubber, including the optimal method of accelerator addition and the effect of different accelerator dosages on the vulcanization performance of the product.In addition, the latest production and research status of NBR at home and abroad is reviewed in the literature ("Development status and application research progress of nitrile rubber", Elastomers, 2021, 31(1)). The main application fields of NBR are automobiles, sound insulation, damping, foaming, shock absorption and hydrogenated HNBR high oil-resistant products, etc.

[0004] In 2021, Li Wangming and Zhang Jianguo, from the R&D Center of the Synthetic Rubber Plant of Sinopec Baling Petrochemical Company, conducted emulsion copolymerization of acrylonitrile / butadiene (mass ratio) = (28-42) / (72-58). The results, obtained through NMR analysis, showed that the acrylonitrile bonded in the copolymer decreased with increasing monomer conversion, indicating a higher polymerization rate in the early stages of acrylonitrile polymerization compared to the later stages. (Chen Haocheng, Sequence Structure and Application Research of Nitrile Rubber. Qingdao University of Science and Technology, 2019, 6, 4) and ("Suzuki T. 220-MHz NBR Spectra of Butadiene and Acrylonitrile Alternating and Randon Copolymers", Polymer) This is consistent with the findings reported in Journal of 1973, 4(6):657-663.) that the sequence distribution of the two monomers in NBR molecules with medium and low acrylonitrile content is AAA, BAA, AAB and BAB, BBA and ABB, ABA.

[0005] In summary, the main characteristics of existing NBR technologies are a molecule containing 20-40% acrylonitrile by mass, a Mooney viscosity of 30-90, and a random alternating distribution of acrylonitrile and butadiene. Its application is in vulcanized rubber products. However, no polymers containing block or microblock polyacrylonitrile molecules linked to NBR have been reported in the literature. Summary of the Invention

[0006] The existing NBR raw rubber molecules contain short homopolymer (block) acrylonitrile chains with low physical crosslinking, which are random copolymers and exhibit non-Newtonian fluid behavior at low temperatures, thus lacking the behavior of thermoplastic elastomers.

[0007] The first objective of this invention is to provide a butadiene-acrylonitrile copolymer with acrylonitrile blocks at both ends and butadiene-acrylonitrile copolymer blocks containing acrylonitrile microblocks of varying lengths in the middle. This butadiene-acrylonitrile copolymer has a large number of physical crosslinking points and exhibits the behavior of a highly polar thermoplastic rubber. Blending and modifying it with existing thermoplastic elastomers can enhance the polarity of the blend and improve the affinity and adhesion between non-polar thermoplastic elastomers and other polar materials.

[0008] Another objective of this invention is to provide a method for preparing a nitrile butadiene copolymer containing multiple polyacrylonitrile blocks by emulsion polymerization, which is characterized by simple operation, low cost and ease of industrial production.

[0009] 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 in the content of this invention.

[0010] To achieve the above-mentioned technical objectives, the present invention provides a method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks. The method involves, in an emulsion polymerization solution system, at 20–40°C and a pressure of 0.3–0.5 MPa, first adding a portion of acrylonitrile monomer for a first-stage polymerization reaction for 3–4 hours, then adding butadiene monomer for a second-stage polymerization reaction for ≥2 hours, and then adding the remaining portion of acrylonitrile monomer for a third-stage polymerization reaction for ≥3 hours, followed by coagulation to obtain the copolymer.

[0011] As a preferred embodiment, the emulsion polymerization solution system contains water, emulsifier, dispersant, electrolyte, chain transfer agent, deoxidizer, oxidant, reducing agent, and activator.

[0012] As a preferred embodiment, the total mass ratio of water to acrylonitrile monomer and butadiene monomer is 150-250:100. More preferably, the total mass ratio of water to acrylonitrile monomer and butadiene monomer is 200:100.

[0013] As a preferred embodiment, the emulsifier is potassium hydrogenated rosin and potassium oleate; the amount of the emulsifier relative to the acrylonitrile monomer and butadiene monomer is 25-30 g / kg. More preferably, the emulsifier is composed of potassium hydrogenated rosin and potassium oleate in a mass ratio of 10-15:15-20.

[0014] As a preferred embodiment, the dispersant is sodium methylene dinaphthalene sulfonate, and the amount of the dispersant relative to the acrylonitrile monomer and butadiene monomer is 1.5 to 2.0 g / kg.

[0015] As a preferred embodiment, the electrolyte is at least one of sodium phosphate, potassium chloride, and sodium carbonate; the amount of the electrolyte relative to the acrylonitrile monomer and butadiene monomer is 4.0–5.0 g / kg.

[0016] As a preferred embodiment, the chain transfer agent is tert-dodecyl mercaptan; the amount of the chain transfer agent relative to the acrylonitrile monomer and butadiene monomer is 3-4 g / kg.

[0017] As a preferred embodiment, the deoxidizer is sodium dithionite; the amount of the deoxidizer relative to the acrylonitrile monomer and butadiene monomer is 0.2-0.3 g / kg.

[0018] As a preferred embodiment, the oxidant is at least one of highly active para-monane peroxide and pinane peroxide; the amount of the oxidant relative to the acrylonitrile monomer and butadiene monomer is 1.2 to 1.5 g / kg.

[0019] As a preferred embodiment, the reducing agent is sodium formaldehyde sulfoxylate; the amount of the reducing agent relative to the acrylonitrile monomer and butadiene monomer is 1.0 to 1.3 g / kg.

[0020] As a preferred embodiment, the activator is EDTA-sodium iron; the amount of the activator relative to the acrylonitrile monomer and butadiene monomer is 0.4-0.5 g / kg.

[0021] As a preferred embodiment, the flocculation is performed using an aqueous solution with a pH of 3-4 and a mass percentage concentration of 0.20-0.25% for dicyandiamine-formaldehyde condensate.

[0022] As a preferred embodiment, the acrylonitrile monomer accounts for 30-50% of the total mass of acrylonitrile monomer during the polymerization process.

[0023] As a preferred embodiment, the acrylonitrile monomer accounts for 50-70% of the total mass of acrylonitrile monomer in the three-stage polymerization process.

[0024] As a preferred embodiment, the total mass ratio of butadiene monomer to acrylonitrile monomer in the two-stage polymerization process is (40-50) / (50-60).

[0025] As a preferred embodiment, the acrylonitrile monomer conversion rate during the first-stage polymerization is ≥70%. An acrylonitrile monomer conversion rate of ≥70% ensures that a small amount of residual acrylonitrile monomer enters the second-stage polymerization.

[0026] As a preferred embodiment, the butadiene monomer conversion rate during the two-stage polymerization process is >80%. A butadiene monomer conversion rate of >80% ensures that a small amount of residual butadiene monomer enters the three-stage polymerization.

[0027] As a preferred embodiment, the total conversion rate of acrylonitrile monomer and butadiene monomer in the three-stage polymerization process is ≥97%.

[0028] As a preferred method, the polymerization temperature is 20–30°C, and the total polymerization time is 8–10 hours. Under these preferred polymerization conditions, the total monomer conversion rate can be guaranteed to be >97%. It is worth noting that increasing the polymerization temperature is beneficial to improving the polymerization rate. However, excessively high polymerization temperatures can lead to excessive gelation of the monomers during polymerization, while excessively long polymerization times increase the monomer conversion rate, but in the later stages of polymerization, the probability of residual monomers undergoing chain growth decreases, resulting in a decrease in overall polymerization efficiency.

[0029] As a preferred embodiment, the nitrile butadiene copolymer of the present invention is branched; the molecular weight distribution index is 2.5 to 3.5.

[0030] The preparation method of the butadiene-acrylonitrile copolymer of the present invention is as follows: A measured amount of deionized water, emulsifier, dispersant, electrolyte, molecular weight regulator, deoxidizer, oxidant, reducing agent, and activator are sequentially added to a polymerization reactor and stirred. The solution temperature is maintained at 20–30°C. Then, a measured amount of acrylonitrile monomer is added to the polymerization reactor for homopolymerization for 3–4 hours. Next, a measured amount of butadiene is added to the polymerization emulsion for copolymerization for 2–4 hours. Then, the remaining measured amount of acrylonitrile is added to the polymerization reactor for copolymerization for 3–4 hours. Finally, the polymerization emulsion is discharged, and a measured amount of antioxidant is added and stirred evenly. The prepared emulsion is then poured into a coagulant and coagulated at 50–70°C to obtain a milky white granular raw rubber. Finally, the granular raw rubber is vacuum dehydrated at 75°C to obtain a pale yellow polymer raw rubber with a volatile content of no more than 0.5% by mass.

[0031] The present invention also provides a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks, which is obtained by the preparation method described above.

[0032] As a preferred embodiment, the number-average molecular weight of the nitrile butadiene copolymer is 8 × 10⁻⁶. 4 ~12×10 4 The melt index is 0.01 g / 10 min to 8 g / 10 min. Note: Because the nitrile copolymer of this invention contains a small amount of gel and ultra-large molecules, when determining its molecular weight using gel permeation chromatography (GPC), the polymer needs to be dissolved in toluene first. During the filtration process, some large molecules and gel will be removed, affecting the accuracy of the polymer molecular weight. At the same time, it will still clog the GPC column. Therefore, it is more practical to use the melt index, which is commonly used in thermoplastic elastics, to characterize the molecular weight of the polymer in this invention.

[0033] The molecular chain segment composition of the nitrile butadiene copolymer involved in this invention is as follows:

[0034] A I -B m1 Ann -B m2 A nn-1 …B mm-1 A n2 -B mm A n1 -B mm-1 A n2 ...B m2 A nn-1 -B m1 A nn -A II

[0035] Formula 1

[0036] Where "A" represents the polyacrylonitrile block, "B" represents the polybutadiene block, I, II, n1, n2...nn-1, nn represent the degree of polymerization of A, and m1, m2...mm-1, mm represent the degree of polymerization of B. All degrees of polymerization are positive integers ≥ 0; and I and II are significantly greater than n1, n2...nn-1, and nn. I and A II B represents the homopolymer polyacrylonitrile blocks with relatively large molecular weights at both ends of the nitrile-butadiene copolymer. m1 A nn -B m2 A nn-1 …B mm-1 A n2 -B mm A n1 -B mm-1 A n2 ...B m2 A nn-1 -B m1 A nn This represents the random copolymerization block of acrylonitrile and butadiene. Due to the different reactivity ratios of butadiene and acrylonitrile and their different initial concentrations in the emulsion polymerization solution system, the random copolymerization of the two exhibits a gradual trend, with the degree of polymerization m1 to mm increasing sequentially and the degree of polymerization n1 to nn increasing sequentially, and 0≤m1<3, mm≥3, 3≥n1≥0, nn>3.

[0037] The butadiene-nitrile copolymer involved in this invention contains A I and A II B is a homopolymer of polyacrylonitrile, consisting of two homopolymer blocks at both ends of the butadiene-acrylonitrile copolymer. m1 A nn -B m2 A nn-1 …B mm-1 A n2 -B mm A n1 -B mm-1 A n2 ...B m2 A nn-1-B m1 A nn This represents a random copolymer block of acrylonitrile and butadiene. The random copolymer block contains many tiny polyacrylonitrile and polybutadiene blocks. The lengths of these tiny blocks exhibit a gradual change, such as the length of the tiny polybutadiene block increasing from B... m1 To B mm The length gradually increases, with Bmm representing the butadiene homopolymer block with a relatively high degree of polymerization, while the length of the tiny polyacrylonitrile blocks increases from A... n1 To A nn Gradually getting longer, A n1 The butadiene-acrylonitrile copolymer consists of polyacrylonitrile blocks with relatively low polymerization degree at both ends, which are equivalent to hard segments. The random copolymer blocks of acrylonitrile and butadiene in the middle are equivalent to soft segments due to the incorporation of polybutadiene blocks. Therefore, the entire butadiene-acrylonitrile copolymer exhibits thermoplastic elastomer behavior.

[0038] The butadiene-nitrile copolymer involved in this invention contains A n1 In the block, A is 5-15% of the total A content, more preferably 5-10%.

[0039] The raw rubber of the butadiene-acrylonitrile copolymer provided by the present invention exhibits no cold flow phenomenon at room temperature. That is, when the polymer is stored at room temperature, it does not flow under the action of gravity (gravity), and it is granular without sticking together or clumping.

[0040] The butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks provided by this invention is prepared by three-stage polymerization:

[0041] The emulsion polymerization solution system used consists of deionized water, emulsifier, dispersant, electrolyte, molecular weight regulator, deoxidizer, oxidant, reducing agent and activator;

[0042] The polymerization reaction conditions are: a temperature of 30–40℃ and a polymerization pressure of 0.3–0.5 MPa. The polymerization raw materials are added in three stages, as detailed below:

[0043] One-stage polymerization: Add 30-50% of acrylonitrile monomer (A) to homopolymerize for 3-4 hours; only a portion of the acrylonitrile undergoes homopolymerization in this process, and the conversion rate of A is preferably controlled at ≥70%, and the number average molecular weight Mn of the polyacrylonitrile block is >12000 (this block is insoluble in solvents such as tetrahydrofuran).

[0044] Two-stage polymerization: Add a set amount of butadiene (B) and carry out the polymerization reaction for no less than 2 hours; this process includes the molecular chain growth of B with the polyacrylonitrile (PA) segments already generated in the first stage polymerization and the copolymerization of unreacted A with B, and the conversion rate of B is preferably controlled to be >80%; among them, the combination of A and B remaining in the polymerization environment, A is distributed in the copolymer molecules in a decreasing gradient to form soft segments.

[0045] Three-stage polymerization: The remaining 50-70% of the total set amount of A is added to the polymerization environment for copolymerization. The polymerization reaction time is not less than 3 hours, and the total monomer conversion rate is not less than 97%. This process includes the chain growth reaction of A with the chain segments generated in the second stage, as well as the copolymerization reaction of B that was not completely reacted in the second stage with A. During this process, the amount of B remaining is relatively small. It changes dynamically with the difference in monomer concentration and the rate of competition between A and B in the polymerization environment. The B bound in the chain growth of the copolymerization reaction is distributed in the polymer molecule in a decreasing sequence.

[0046] Compared with existing technologies, the beneficial effects of the technical solution of this invention are as follows:

[0047] Addressing the shortcomings of existing NBR raw rubber molecules, such as short homopolymer (block) acrylonitrile chains and low physical crosslinking density, making them unsuitable for use as thermoplastic elastomers, this invention unexpectedly reveals that the polymer prepared by the three-stage feeding method exhibits a resinous state in the first stage, while the polymer after three-stage polymerization displays thermoplastic elastomer behavior. This indicates that the third polymer chain also exhibits a rigid polymer chain, meaning that the polyacrylonitrile chain segments with a high mass fraction also show physical crosslinking characteristics. The polymer described in this invention has a melt flow index (MFR) that can be controlled at (1-8) g / 10min at 200℃; its hot melt sheet rubber has the following characteristics: 300% tensile stress > 1.3 MPa, tensile strength > 15.0 MPa, elongation at break > 900%, permanent deformation < 28%, hardness (Shao A) 60-70, and glass transition temperature < -19℃, fully embodying the characteristics of thermoplastic rubber (TPR).

[0048] The process and method for synthesizing the butadiene-acrylonitrile copolymer (TPR) of this invention are simple, efficient, and the raw materials are readily available and low in cost.

[0049] The nitrile butadiene copolymer (A-TPR) of this invention belongs to a strongly polar thermoplastic elastomer with high molecular cohesion and good affinity and compatibility with strongly polar, water-insoluble inorganic salts such as white carbon black, calcium carbonate, and barium sulfate (powder). It also acts as a modifier for weakly polar styrene-butadiene thermoplastic elastomers (TPE) and their hydrides (SEBS), as well as polar polyvinyl acetate elastomers, enhancing their affinity with other polar materials. Furthermore, it can be used as a modifier for asphalt composite materials for concrete and stone pavements, as well as for oil-resistant products, adhesives, damping agents, and foaming materials. Attached Figure Description

[0050] Figure 1 The infrared spectrum of the butadiene-nitrile polymer prepared in Example 1 is shown.

[0051] Figure 2 The preparation of nitrile butadiene polymer (A-TPR, designation NBR50-78) for Example 1 1 H-NMR spectrum.

[0052] Figure 3 The liquid chromatography (GPC) chromatogram of the butadiene-nitrile polymer (A-TPR, calibration number NBR50-78) prepared in Example 1 is shown.

[0053] Figure 4 DSC analysis of the butadiene-nitrile polymer prepared in Example 1. Detailed Implementation

[0054] In the following examples, the molecular weight distribution index of A-TPR was determined by gel permeation chromatography (GPC); the glass transition temperature (Tg) of the polymer was determined by differential thermal analysis (DSC); the microstructure of the polymer was determined by H-NMR spectroscopy; and the microstructure of the polymer was determined by a NEXUS-870 Fourier transform infrared spectrometer.

[0055] The tensile stress-strain properties of the vulcanizate were determined using an INSTRON tensile testing machine according to the method in GB / T528-2009.

[0056] Example 1

[0057] Add 1.7 liters of deoxygenated deionized water to a 5-liter polymerization reactor. Then, add to the polymerization sight glass 90 mL of 15.0 wt% potassium oleate solution, 40 mL of 25.0 wt% potassium disproportionated rosin solution, 20 mL of 2.0 wt% sodium iron EDTA solution, 17 mL of 10.5 wt% sodium methylene dinaphthalene sulfonate aqueous solution, 20 mL of 5 wt% sodium carbonate, 35 mL of sodium phosphate, and 20 mL of 10.0 wt% potassium chloride aqueous solution, 6 mL of 5 wt% sodium dithionite aqueous solution, and 6.5 wt% sodium formaldehyde sulfoxylate. 18 mL of aqueous solution, 1.5 g of para-menine peroxide, and 3.5 g of tert-dodecyl mercaptan were added to the polymerization reactor under nitrogen pressure. Stirring was started, and hot water was introduced to heat the material to 20-30°C. Then, 250 g of acrylonitrile was added to the polymerization reactor under nitrogen pressure and reacted at 20-30°C for 3.5 h. The polymer emulsion sample was taken and the polymer was precipitated with anhydrous ethanol. After filtration and drying, the conversion rate of the polymer monomers was 76.4%, and the number average molecular weight of the polymer was Mn = 12500. The molecular structure of the polymer is shown in the infrared spectrum (1) labeled "A". n"; At this point, add 805 mL (500 g) of butadiene to the polymerization reactor, maintain the pressure inside the reactor at 0.3-0.5 MPa for 4 hours, take out a small amount of polymer emulsion, and process the sample in the same way as "An". The polyacrylonitrile-butadiene copolymer sample is shown in the infrared spectrum (1) of the calibration "A". n -B m The monomer conversion rate was 84.6%. Finally, 250g of the remaining acrylonitrile from the third stage design was added for copolymerization for 4 hours. At this point, the monomer conversion rate was measured to be 97.8%. After the polymerization reaction showed no further temperature change, the reaction was considered complete. The material was then discharged, and 3.0g of antioxidant 1076 was added to the latex solution. After mixing thoroughly, the latex was slowly added in batches to a solution containing 40g of dicyandiamine-formaldehyde condensate, 25g of concentrated sulfuric acid, and 20 liters of water at 50-60℃ for coagulation. The mixture was stirred, and the remaining unreacted acrylonitrile monomer dissolved in the aqueous phase. After 10 minutes, milky white granular micelles were obtained, which were then dried to obtain a pale yellow A-TPR (infrared spectrum shown in [reference needed]). Figure 1 The calibration number NBR50-78 in the text, its NBR50-78 infrared spectrum, 1 The H-NMR spectrum, liquid chromatography (GPC), and DSC analysis are shown below. Figure 1 , Figure 2 , Figure 3 , Figure 4 The melt flow index (MFR) of NBR50-78 is 1.83 g / 10 min.

[0058] Figure 1 Note: 2237cm -1 A moderate-intensity acrylonitrile "nitrile group" absorption peak appears at 918 cm⁻¹. -1 The corresponding absorption peak is at 969 cm⁻¹, representing the 1,2-structure absorption peak. -1 The absorption peak for the trans-1,4 structure is observed; however, no absorption peaks for the 1,2- or 1,4- structure are found in polymer "An," indicating that polymer "An" is a homopolymer. This contrasts with the butadiene-acrylonitrile copolymer, which exhibits a peak at 1705 cm⁻¹. -1 1224cm -1 591cm -1 Deformation and vibration peaks were generated in multiple locations.

[0059] Figure 2 Note: Chemical shift A (2.5-2.7) is the integral of the hydrogen proton structural unit of acrylonitrile, A (5.0) is the 1,2-addition, and A (5.4-5.6) is the proton integral value of the 1,4-addition. The measured mass fraction of bound acrylonitrile is 49.85%, and the mass fraction of vinyl groups in the polybutadiene segment is 9.52%.

[0060] Figure 3 Note: The molecular weight distribution of A-TPR is a broad single-peak distribution, Mn = 11.3 × 10⁻⁶.4 M w / M n =3.2.

[0061] Figure 4 Note: A-TPR (NBR50-78) glass transition temperature Tg = -24.68℃.

[0062] Example 2

[0063] Without making significant adjustments to the relevant conditions in Example 1, and controlling the amount of additives used within the limits of the present invention, only the amount of tert-dodecyl mercaptan added is 4g.

[0064] The results showed that the number-average molecular weight of the first polymer was Mn1 = 13280, the yield of A-TPR after aggregation was 97.3%, and Mn = 9.6 × 10⁻⁶. 4 M w / M n =3.5, vinyl unit mass fraction 10.8%, bound acrylonitrile mass fraction 49.6%, glass transition temperature -25.4℃, MFR = 4.67 g / 10 min.

[0065] Example 3

[0066] Keeping the basic conditions in Example 1 unchanged, only the amount of tert-dodecyl mercaptan added was 3.8g and p-menthane peroxide was 1.3g; 270g of acrylonitrile was added in the first stage, and the polymerization time was 4h; 460g of butadiene was added in the second stage, and the polymerization time was 3.5h; 270g of acrylonitrile was added in the third stage, and the polymerization time was 3h.

[0067] The results showed that the number-average molecular weight of the first polymer was Mn1 = 15520, the yield of A-TPR after aggregation was 98.1%, and Mn = 9.2 × 10⁻⁶. 4 M w / M n =3.7, vinyl unit mass fraction 9.64%, bound acrylonitrile mass fraction 53.6%, glass transition temperature -22.6℃, MFR = 5.31 g / 10 min.

[0068] Example 4

[0069] Keeping the basic conditions in Example 3 unchanged, only the amount of tert-dodecyl mercaptan added was 4.5g; 300g of acrylonitrile was added in the first stage, and the polymerization time was 3.5h; 430g of butadiene was added in the second stage, and the polymerization time was 3h; 270g of acrylonitrile was added in the third stage, and the polymerization time was 3.5h.

[0070] The results showed that the number-average molecular weight of the first polymer was Mn1 = 16420, the yield of A-TPR after aggregation was 97.8%, and Mn = 8.7 × 10⁻⁶. 4 M w / M n =3.2, vinyl unit mass fraction 9.94%, bound acrylonitrile mass fraction 56.8%, glass transition temperature -21.5℃, MFR = 6.32 g / 10 min.

[0071] Example 5

[0072] Keeping the basic conditions in Example 3 unchanged, only the amount of tert-dodecyl mercaptan added was 4.8g; 300g of acrylonitrile was added in the first stage, and the polymerization time was 3h; 400g of butadiene was added in the second stage, and the polymerization time was 3h; 300g of acrylonitrile was added in the third stage, and the polymerization time was 4h.

[0073] The results showed that the number-average molecular weight of the first-stage polymer was Mn1 = 17820, the A-TPR yield was 97.3%, and Mn = 8.2 × 10⁻⁶. 4 M w / M n =3.8, vinyl unit mass fraction 9.42%, bound acrylonitrile mass fraction 58.7%, glass transition temperature -20.3℃, MFR = 7.64 g / 10 min.

[0074] Comparative Example 1

[0075] Keeping the basic conditions in Example 1 unchanged, the only difference was that acrylonitrile and butadiene were added to the polymerization reactor at once. After 8 hours of polymerization, the monomer conversion rate was measured to be 97.4%, the mass fraction of acrylonitrile bound in the polymer was 58.16%, the mass fraction of vinyl units was 10.25%, and the Mooney viscosity was 53.7.

[0076] Comparative Example 2

[0077] The basic conditions in Example 1 were kept unchanged, except that 228g of acrylonitrile and 860mL of butadiene (A / B mass ratio = 30 / 70) were added to the polymerization reactor at one time to carry out the polymerization reaction. The polymerization temperature was 5-8℃, and the characteristics of the polymerization reaction and the generated polymer were measured at different time periods. The results are shown in Table 1.

[0078] Table 1

[0079]

[0080]

[0081] As shown in Table 1, when the A / B mass ratio is 30 / 70, 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 polymerization rate is higher than that of butadiene, resulting in small acrylonitrile homopolymer blocks. In the later stage of polymerization, more small butadiene homopolymer blocks are produced. The NMR analysis results show that the amount of acrylonitrile bound in the polymer molecules exhibits a decreasing distribution, which is consistent with the relevant results of the literature "Sequence Structure and Application Research of Nitrile Rubber". However, the prepared polymer NBR still exhibits the behavior of vulcanized rubber.

[0082] Comparative Example 3

[0083] The basic conditions in Example 1 were kept unchanged, except that 258 g of acrylonitrile and 860 mL of butadiene (A / B mass ratio = 33 / 67) were added to the polymerization reactor at once and the polymerization reaction was carried out for 8 hours. The results showed a monomer conversion rate of 97.7%, a polymer with a bound acrylonitrile mass fraction of 33.44%, a vinyl unit mass fraction of 12.32%, and a Mooney viscosity of 47. The polymer exhibited the behavior of NBR raw rubber, and its infrared spectrum is shown below. Figure 1 The "calibration of NBR33-47" in the document.

[0084] Physical properties of the compression adhesives in the examples and comparative examples

[0085] The samples prepared in Examples 1-5 and Comparative Examples 1-3, as well as the elastomer SBS-805, were placed on a two-roll mill and hot-melted at 160°C. Then, they were hot-melted and pressed into sheets at 150°C and cooled and shaped at room temperature. The physical properties of the pressed rubber are shown in Table 2.

[0086] Table 2

[0087]

[0088]

[0089] Note: SBS-805 is a styrene-butadiene thermoplastic elastomer produced by the Synthetic Rubber Division of Sinopec Baling Petrochemical Company. Table 2 shows that the polymers prepared in Examples 1, 2, 3, 4, and 5 exhibit the behavior of thermoplastic elastomers, while the polymers prepared in the comparative examples exhibit the behavior of random copolymer nitrile butadiene rubber (NBR).

Claims

1. A method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks, characterized in that: In an emulsion polymerization solution system, at 20~40℃ and a pressure of 0.3~0.5MPa, a portion of acrylonitrile monomer is first added to carry out a first-stage polymerization reaction for 3~4 hours, then butadiene monomer is added to carry out a second-stage polymerization reaction for 2~4 hours, and then the remaining portion of acrylonitrile monomer is added to carry out a third-stage polymerization reaction for 3~4 hours. After coagulation, the product is obtained. In the aforementioned polymerization process, acrylonitrile monomer accounts for 30-50% of the total mass of acrylonitrile monomer; In the three-stage polymerization process, acrylonitrile monomer accounts for 50-70% of the total mass of acrylonitrile monomer; The total mass ratio of butadiene monomer added during the two-stage polymerization process to acrylonitrile monomer added during the one-stage and three-stage polymerization processes is (40~50) / (50~60). The molecular chain segment composition of the butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks is distributed as follows: A I -B m1 A nn -B m2 A nn-1 …B mm-1 A n2 -B mm A n1 -B mm-1 A n2 ...B m2 A nn-1 -B m1 A nn -A II Where A represents the polyacrylonitrile block, B represents the polybutadiene block, I, II, n1, n2...nn-1, nn represent the degree of polymerization of A, and m1, m2...mm-1, mm represent the degree of polymerization of B; and I and II are much greater than n1, n2...nn-1 and nn, A I and A II B represents the homopolymer polyacrylonitrile blocks with relatively large molecular weights at both ends of the nitrile-butadiene copolymer. m1 A nn -B m2 A nn-1 …B mm-1 A n2 -B mm A n1 -B mm-1 A n2 ...B m2 A nn-1 -B m1 A nn This represents a random copolymer block of acrylonitrile and butadiene, with the degree of polymerization increasing sequentially from m1 to mm and from n1 to nn, and 0≤m1<3, mm≥3, 3≥n1≥0, and nn>3.

2. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 1, characterized in that: The emulsion polymerization solution system contains water, emulsifier, dispersant, electrolyte, chain transfer agent, deoxidizer, oxidant, reducing agent and activator.

3. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The total mass ratio of water to acrylonitrile monomer and butadiene monomer is 150~250:

100.

4. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The emulsifier is potassium hydrogenated rosin and potassium oleate; the amount of the emulsifier relative to the acrylonitrile monomer and butadiene monomer is 25~30g / kg.

5. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The dispersant is sodium methylene dinaphthalene sulfonate, and the amount of the dispersant relative to the acrylonitrile monomer and butadiene monomer is 1.5~2.0 g / kg.

6. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The electrolyte is at least one of sodium phosphate, potassium chloride, and sodium carbonate; the amount of the electrolyte relative to the acrylonitrile monomer and butadiene monomer is 4.0~5.0 g / kg.

7. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The chain transfer agent is tert-dodecyl mercaptan; the amount of the chain transfer agent relative to the acrylonitrile monomer and butadiene monomer is 3~4 g / kg.

8. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The deoxidizing agent is sodium dithionite; the amount of the deoxidizing agent relative to acrylonitrile monomer and butadiene monomer is 0.2~0.3 g / kg.

9. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The oxidant is at least one of p-menthol peroxide and pinane peroxide; the amount of the oxidant relative to the acrylonitrile monomer and butadiene monomer is 1.2~1.5 g / kg.

10. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The reducing agent is sodium formaldehyde sulfoxylate; the amount of the reducing agent relative to acrylonitrile monomer and butadiene monomer is 1.0~1.3 g / kg.

11. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 2, characterized in that: The activator is EDTA-sodium iron; the amount of the activator relative to the acrylonitrile monomer and butadiene monomer is 0.4~0.5 g / kg.

12. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 1, characterized in that: The coagulation process uses an aqueous solution with a pH of 3-4 and a mass percentage concentration of 0.20-0.25% for dicyandiamine-formaldehyde condensate.

13. The method for preparing a butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks according to claim 1, characterized in that: The acrylonitrile monomer conversion rate during the polymerization process is ≥70%; The butadiene monomer conversion rate during the two-stage polymerization process is >80%; The total conversion rate of acrylonitrile monomer and butadiene monomer in the three-stage polymerization process is ≥97%.

14. A butadiene-acrylonitrile copolymer containing multiple polyacrylonitrile blocks, characterized in that: It is obtained by the preparation method according to any one of claims 1 to 13.

15. A butadiene-acrylonitrile copolymer containing a plurality of polyacrylonitrile blocks according to claim 14, characterized in that: The number-average molecular weight of the nitrile copolymer is 8 × 10⁻⁶. 4 ~12×10 4 .

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