Synthesis method of low-temperature-resistant solution polymerized styrene-butadiene rubber
By preparing PS-b-PB diblock prepolymers through anionic polymerization and forming chelates with rare earth catalyst Nd(Oct)3 using β-diketone chain extender side groups, the problem of structural controllability and excellent performance in the synthesis of low-temperature solution-polymerized styrene-butadiene rubber was solved, realizing SSBR with low Tg and high cis structure, exhibiting excellent low-temperature resistance and processing stability.
Patent Information
- Application Number
- CN202511631738.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-10
- Publication Date
- 2026-01-02
AI Technical Summary
Existing low-temperature solution-polymerized styrene-butadiene rubber (SSBR) synthesis technologies struggle to balance structural controllability and superior performance, particularly in terms of low-temperature resistance, processing stability, and mechanical strength. The limitations of single catalytic systems, the limitations of functionalization modification directions, and the challenge of balancing low-temperature resistance with processing and mechanical properties have not been effectively addressed.
PS-b-PB diblock prepolymers were prepared by anionic polymerization and functionalized by β-diketone chain extension. Subsequently, the rare earth catalyst Nd(Oct)3 was used for in-situ chain extension to form β-diketone-Nd chelates. By anchoring the rare earth catalyst, high cis selectivity and block structure control were achieved. Combined with the high active center characteristics of the rare earth catalyst, the controllability and efficiency of chain growth were ensured.
It achieves low glass transition temperature (Tg < -80℃), good mechanical properties and easy processing of SSBR, significantly improves low temperature resistance and processing stability, solves the problem of balancing structural controllability and excellent performance in traditional technology, and has controllable molecular weight distribution with chain extension rate close to 100%.
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Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of butadiene rubber manufacturing, in particular to a synthesis method of low-temperature-resistant solution polymerized butadiene rubber. BACKGROUND
[0002] Low-temperature-resistant solution polymerized butadiene rubber (SSBR) is the core material of high-performance green tires and low-temperature sealing elements due to its excellent wet skid resistance and low rolling resistance. However, the current automobile industry has higher requirements for the low-temperature resistance (applicable below -40℃), processing stability and mechanical strength of SSBR. However, the existing synthesis technology has the core pain point that it is difficult to balance the "structure controllability" and "excellent performance", which is specifically as follows: 1. Performance limitations of single catalytic system The existing SSBR preparation relies on two types of catalytic systems, both of which have significant shortcomings: 1.1 Anionic polymerization system: structure controllable but poor low-temperature resistance The industrial mainstream anionic solution polymerization uses butyl lithium as an initiator and tetrahydrofuran (THF) as a regulator, which can precisely control the block ratio of styrene (St)-butadiene (Bd). However, Cui Yanjun et al. pointed out in "Synthetic Rubber Industry", Vol. 39, No. 3, 2016, "Synthesis and Properties of Low-Temperature-Resistant Solution Polymerized Butadiene Rubber", that THF is sensitive to temperature - the content of 1,2-structure of butadiene decreases by 20% when the temperature increases by 20℃, and only SSBR with 1,2-structure <57% can be prepared; more importantly, the cis-1,4 content of PB segment is usually <40%, resulting in a high glass transition temperature (Tg) of PB segment (Tg of commercially available SSBR is mostly >-40℃), which cannot meet the demand in severe cold regions. In addition, the use of THF in large quantities makes it difficult to recover, increasing the cost and affecting the stability of the system.
[0003] 1.2 Rare earth catalytic system: high cis-selectivity but difficult to control block structure Rare earth catalysis (such as Nd(Oct)3) can produce PB with cis-1,4 content >95% and Tg <-100℃, which has excellent low-temperature resistance. However, the active center of this system has low selectivity for monomers, which easily initiates the random copolymerization of St and Bd, making it difficult to precisely control the PS-b-PB block ratio. Directly using it to synthesize SSBR, styrene is easy to form random short chains, resulting in poor processing fluidity, and it is difficult to adjust the hardness and wear resistance through the PS segment, which cannot meet the demand of tires.
[0004] 2. Limitations of functional modification direction The existing functional modification focuses on the compatibility of fillers, which is inconsistent with the demand for "low-temperature resistance and high cis": 2.1 Functional target deviates from structure control Ansari et al. in 2024 Epoxy modified styrene butadiene rubber (SBR) in green tire application proposed that epoxy-modified ESBR can enhance compatibility with silica and improve wet traction, but did not regulate the cis structure of butadiene, and the Tg is still greater than -50°C, and the low temperature resistance is not improved; Qian Zhizhang reported in 2024 High-end low-temperature solution styrene-butadiene rubber research breakthrough that domestic double-end functional SSBR 3540F was put into production, but the product was characterized by "high styrene (25%) + low cis PB", which only optimized the wet skid resistance and did not solve the problem of extreme low temperature elasticity.
[0005] 2.2 Lack of efficient catalyst anchoring technology Existing SSBR chain extension is mostly "small molecule initiator + prepolymer" mode, with grafting rate <80% and molecular weight distribution >2.5. Cui Yankun et al. tried to improve the chain extension efficiency by adjusting the regulator, but the stability of anionic active center was limited, the PB cis content was difficult to break 50%, and the mechanical property improvement was insufficient. In addition, Hansen in 2021 Structural Studies of β-Diketones and Their Implications on Biological Effects confirmed that β-diketones can form stable chelates with metals, but this structure is only used in the field of drugs and has not been developed as a rubber catalyst anchoring unit, which cannot solve the problem of chain growth out of control caused by free rare earth catalysts.
[0006] 3. Balancing problem of low temperature resistance, processing and mechanical properties Low temperature resistant SSBR needs "low Tg + good processability + excellent mechanical properties", but existing technologies are difficult to coordinate: reducing the content of St (such as <15%) can reduce Tg (such as Tg=-47°C of SSBR prepared by Cui Yankun team), but the processing fluidity is poor and the tear strength (32kN / m) is lower than that of commercial high St product (36kN / m); increasing the content of cis-1,4 leads to the contradiction between the insufficient capacity of anionic system and the block out of control of rare earth system, resulting in the decrease of wet skid resistance.
[0007] In summary, there are three major problems in existing technologies: ① It is difficult for a single catalyst system to balance "block controllability" and "high cis low temperature resistance"; ② Functionalization does not focus on cis regulation and catalyst anchoring, and the chain extension efficiency is low; ③ It is difficult to balance low temperature resistance, processing and mechanical properties. The development of "anion structure control + rare earth high cis" and the realization of catalyst anchoring by new ligand is the key to break through the bottleneck. SUMMARY
[0008] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for synthesizing low-temperature solution-polymerized styrene-butadiene rubber.
[0009] To achieve the above objectives, the present invention adopts the following technical solution: This invention first proposes a method for synthesizing low-temperature solution-polymerized styrene-butadiene rubber, comprising the following steps: S1. Synthesis of PS-b-PB diblock prepolymers and their chain-extended side-group functionalization Add cyclohexane and 100 parts of styrene monomer to the reactor, heat to 60°C, inject 5 parts of sec-butyllithium initiator solution, and react for 1-2 hours; After the styrene is completely converted, 400 parts of butadiene monomer are added to the reactor, and polymerization is continued at 60°C for 2 hours to generate styrene-block-butadiene-Li. sec-butyllithium is an anionic polymerization initiator, and its Li... + It forms a loose ion pair with the solvent cyclohexane. At 60°C, the C-Li bond of sec-butyllithium breaks, forming s-Bu. - The carbanion preferentially attacks the double bond of styrene, initiating styrene polymerization to form PS-Li, the active lithium polystyrene chain; after complete styrene conversion, butadiene monomer is added, and the active end of PS-Li (-PS)... - Li + It will continue to attack the double bonds of butadiene, initiating butadiene polymerization to generate styrene-block-butadiene-Li; After the butadiene is completely converted, 5-7 parts of β-diketone monomer are injected, and the reaction is continued at 60°C for 2 hours to ensure complete end-capping reaction, thus obtaining styrene-butadiene block prepolymer. The active end of styrene-block-butadiene-Li (-PS) - Li + () is a strong nucleophile that attacks the double bond in the β-diketone monomer, causing a nucleophilic addition reaction. This grafts the β-diketone monomer onto the chain extension side group of the PB chain, generating a styrene-butadiene block prepolymer (styrene-block-butadiene-acetoacetic acid methacrylate ethylene glycol ester-trimethylsilyl). TMS (trimethylsilyl) acts as a protecting group for the β-diketone structure, protecting the active hydrogen in the β-diketone through a "Si-O bond" to prevent premature deactivation.
[0010]
[0011] S2, Deprotection reaction 100 parts of styrene-butadiene block prepolymer were dissolved in anhydrous tetrahydrofuran to prepare a 5-10% (w / w) solution; 0.78-1.08 parts of tetrabutylammonium fluoride were added under stirring at room temperature, and the reaction was carried out for 6-12 hours; the reaction solution was poured into methanol to precipitate, filtered, washed with methanol, and dried under vacuum to obtain a β-diketone-styrene-butadiene block prepolymer with β-diketone extended side groups; F in tetrabutylammonium fluoride (TBAF) - It is a strong nucleophile, and the Si-F bond energy is extremely high. - It will preferentially attack the Si atoms in the β-diketone monomer, replace the TMS group, and generate volatile TMS-F; after the TMS is removed, the β-diketone structure is restored, and β-diketone-styrene-butadiene block prepolymer is obtained, that is, a block copolymer with β-diketone as the chain extension side group. S3, rare earth catalytic in-situ chain extension 100 parts of β-diketone-styrene-butadiene block prepolymer were dissolved in anhydrous cyclohexane, transferred to a polymerization reactor, heated to 60°C, and 10 parts of Nd(Oct)3 were added. The mixture was stirred for 1 hour. 40 parts of diisobutylaluminum hydride and 3 parts of tert-butyl hypochlorite were added sequentially as co-catalysts, and the mixture was stirred for 30 minutes. Butadiene monomer was added to the system, and the reaction was carried out at 60°C for 3-4 hours. After the reaction was completed, the reaction was terminated with ethanol containing 2,6-di-tert-butyl-p-cresol. The mixture was then coagulated, washed, and vacuum dried to obtain styrene-butadiene-Nd coordinated cis-butadiene composite rubber.
[0012] The chain-extended side group of the β-diketone-styrene-butadiene block prepolymer has a β-diketone structure, and the lone pair electrons of the carbonyl oxygen can form a coordinate bond with the empty orbital of the metal ion. As a "chelating ligand," the β-diketone can form a stable six-membered ring chelate with the metal ion; Li + With a +1 valence and a small ionic radius, although it is a hard acid, its low charge results in a relatively weak coordination with the β-diketone oxygen of the hard base, leading to limited stability of the resulting complex; Nd 3+ As a +3 rare earth ion, Nd(Oct)3 has a large ionic radius, high charge, and abundant valence shell orbitals, resulting in a significantly stronger coordination effect with β-diketone oxygen. When Nd(Oct)3 comes into contact with β-diketone-styrene-butadiene block prepolymer, Nd... 3+ It will preferentially accept the lone pair electrons of the β-diketone oxygen through its empty orbital, forming an Nd-β-diketone chelate. At this time, the Li, which was originally weakly coordinated with the β-diketone, will be released. + Due to its inferior thermodynamic stability, it was used by Nd 3+ "Substitution" refers to the removal of the polymer chain extender side group;
[0013] The β-diketone chain extender side group of the β-diketone-styrene-butadiene block prepolymer interacts with Nd through lone pair electrons. 3+ The formation of stable Nd-β-diketone chelates anchors the rare earth catalyst to the polymer chain-extending side groups, preventing uncontrolled chain growth caused by catalyst detachment. Diisobutylaluminum hydride acts as an alkylaluminum co-catalyst, and its Al-H bonds can bind Nd... 3+ Reduced to a more reactive lower valence state, such as Nd 2+ Simultaneously, it provides Al-alkyl groups to form Nd-alkyl active intermediates; tert-butyl chloride (tert-butyl hypochlorite) acts as a chlorinating agent, via Cl... - Coordination with Nd significantly enhances the catalytic activity of Nd-alkyl intermediates by adjusting the coordination number and electronic environment of Nd; butadiene monomers interact with Nd through the π electrons of their double bonds. 2+ Coordination forms a monomer-catalyst complex; subsequently, the coordinated double bond inserts into the Nd-R bond to achieve chain growth, extending the PB segment on the chain extension side group of the β-diketone-styrene-butadiene block prepolymer to generate a block copolymer with high PB content. The chain-extended side group of the β-diketone-styrene-butadiene block prepolymer contains a β-diketone structure, and its two carbonyl oxygen atoms interact with Nd(Oct)3 through lone pair electrons. 3+ A stable six-membered ring chelate is formed, anchoring the rare earth catalyst to the chain extension side group site of the prepolymer. This avoids random polymerization caused by catalyst detachment and ensures that subsequent reactions occur only at the chain extension side group of the prepolymer, demonstrating in-situ growth characteristics. The butadiene monomer interacts with Nd through the π electrons of its conjugated double bond. 2+ The active center coordinates to form a butadiene-Nd complex, redistributing and activating the double bond electron cloud density. Subsequently, the activated butadiene inserts into the Nd-R bond via a cis-1,4 addition reaction, where R is either the original PB chain or an alkyl group. Specifically, the first carbon of the butadiene combines with Nd, and the fourth carbon forms a new CC bond with the terminal carbon of the R group, allowing the butadiene unit to be incorporated into the chain with a "-CH2-CH=CH-CH2-" structure. The insertion reaction repeats, continuously extending the chain-extending side groups of the original PB chain segment to form a longer PB chain segment. The molar ratio of butadiene to β-diketone-styrene-butadiene block prepolymer is 600-700:1, which means that each initial block chain can be spliced with 600-700 butadiene units, significantly increasing the proportion of PB soft segments, significantly reducing the overall Tg of the rubber, and greatly enhancing its low-temperature resistance. S4, Rubber Preparation Preheat the internal mixer to 180°C, add styrene-butadiene-Nd coordinated cis-butadiene composite rubber, and plasticize for 1-2 minutes. Add inorganic fillers and zinc oxide treated with coupling agent, and mix for 5-10 minutes. At 40-60°C, mix with sulfur and other additives for 2-3 minutes, discharge the rubber, and vulcanize to obtain low-temperature solution-polymerized styrene-butadiene rubber.
[0014] Preferably, in S1, the molar ratio of sec-butyllithium, styrene, butadiene, and β-diketone monomers is 1:20:80:1-1.4; in the styrene-butadiene block prepolymer, the total mass of styrene, butadiene, and β-diketone monomers accounts for 15% of the total mass of the styrene-butadiene block prepolymer.
[0015] Preferably, the preparation process of the β-diketone monomer in S1 specifically includes the following steps: Add ethylene glycol acetoacetate and anhydrous triethylamine to the reactor, add anhydrous tetrahydrofuran as a solvent, start stirring to dissolve, and control the reaction temperature at 0-5℃; prepare trimethylchlorosilane, i.e., TMS, into a 30% tetrahydrofuran solution and add it to the reactor; remove the ice-water bath and allow the reaction mixture to naturally warm to room temperature, and stir the reaction under nitrogen protection for 6-12 hours; Anhydrous triethylamine abstracts the active hydrogen atom from the β-diketone in ethylene glycol acetoacetate methacrylate, forming a carbanion intermediate; the carbanion attacks the Si atom in TMS, replacing the Cl atom. - The TMS-protected β-diketone structure is generated, while triethylamine reacts with HCl to generate triethylamine hydrochloride, which is then removed by washing. After the reaction was completed, the product was washed, extracted, and separated to obtain a crude product. After high-vacuum distillation, the β-diketone monomer was obtained.
[0016]
[0017] Preferably, in the preparation of the β-diketone monomer, the molar ratio of ethylene glycol acetoacetate methacrylate, trimethylchlorosilane, and anhydrous triethylamine is 1:1.1:1.1.
[0018] Preferably, in S2, the molar ratio of β-diketone monomer to added tetrabutylammonium fluoride in the styrene-butadiene block prepolymer is 1:1.05.
[0019] Preferably, in S3, the mass ratio of β-diketone-styrene-butadiene block prepolymer, Nd(Oct)3, diisobutylaluminum hydride, and tert-butyl hypochlorite is 100:10:40:3; and the molar ratio of the added butadiene monomer to the β-diketone-styrene-butadiene block prepolymer is 600-700:1.
[0020] Preferably, in step S4, the amount of silica used is 60-80% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber, and the amount of carbon black used is 0-20% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The amount of sulfur used is 1.5-2.0% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber; The amount of zinc oxide used is 2-4% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber; The accelerator is a sulfenamide-based vulcanization accelerator, and its dosage is 0.8-1.5% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The activator is stearic acid activator, and the dosage is 0.2-0.5% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber; The scorching inhibitor is N-cyclohexylthiophthalimide, and its dosage is 0.1-0.3% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The plasticizer is a bio-based oil plasticizer, and its dosage is 2-4% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The dispersant is a polymeric dispersant, and the amount used is 2-3% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber.
[0021] Compared with the prior art, the beneficial effects of the present invention are: The β-diketone chain-extended side group generated by the deprotection reaction in this invention has bidentate ligand properties and can react with Nd in the rare earth catalyst Nd(Oct)3. 3+ Stable six-membered ring chelates are formed; in this coordination mode, bidentate coordination restricts Nd 3+ The free rotation of the β-diketone prevents it from contacting impurities and becoming inactive, thus extending the lifetime of the active center. Simultaneously, the conjugated structure of the β-diketone enhances the Nd... 3+ The σ-π bond polarization ability of butadiene monomers is improved, reducing the activation energy of monomer insertion. Comparative experiments show that in the system using β-diketone chain extender side groups, the monomer conversion rate in the rare earth catalytic chain extension stage can reach over 98%.
[0022] Unlike traditional small-molecule initiator-prepolymer chain extension systems, this invention anchors rare-earth active centers to the prepolymer chain extension side groups through β-diketone-Nd chelation, forming a "macromolecule rare-earth catalyst." This design solves the problems of "poor compatibility between initiator and prepolymer and low grafting rate" in traditional systems. Each prepolymer molecular chain has a rare-earth active center loaded on its chain extension side group, and the grafting rate of the chain extension reaction is close to 100%. The single active center characteristic allows the molecular weight distribution of the chain extension product to be controlled within 1.5-2.0, which is significantly better than traditional free radical chain extension. Traditional SSBR preparation routes mostly involve single catalytic systems. All-anionic polymerization can precisely control the PS-b-PB block structure, but its polymerization selectivity for butadiene is limited. The content of cis-1,4 structure in the PB segment is usually <40%, and the lower the content of cis-1,4 structure, the higher the glass transition temperature (Tg) of the PB segment and the worse the low-temperature resistance. On the other hand, all-rare earth catalysis has extremely high cis selectivity for butadiene polymerization, with cis-1,4 content usually >95%, which can prepare high cis PB, but it is prone to random copolymerization and it is difficult to precisely control the PS-b-PB block structure. This invention first prepares a "PS-b-PB" diblock prepolymer using anionic polymerization (sec-butyllithium). The PS segment provides processability and hardness, while the PB segment provides basic elasticity, and the segment length and ratio are controllable. Then, rare earth catalysis is used for chain extension. Taking advantage of the high cis selectivity of neodymium, a high cis PB segment is extended on the chain extension side group of the prepolymer, further reducing the overall Tg and enhancing low-temperature resistance. This combination of "anionic controlled structure + superior rare earth performance" solves the pain point of "difficulty in balancing structural control and low-temperature resistance" in traditional single catalytic systems. It is a non-obvious design and has inventiveness.
[0023] The core requirements for low-temperature resistant SSBR are low Tg, good mechanical properties, and easy processing. This solution uses a dual PB design of "prepolymer PB segment + rare earth chain extended PB segment" with a high cis structure to reduce the overall Tg to below -80℃, which is far superior to traditional lithium-based SSBR. The introduction of PS segment not only improves processability, but also balances low-temperature resistance and tensile strength by adjusting the PS / PB ratio. Attached Figure Description
[0024] Figure 1 The infrared spectrum of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber produced by this invention is shown. Detailed Implementation
[0025] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.
[0026] The purity and manufacturers of the various drugs used in the experiment are shown in Table 1. Table 1. Raw Material Drug Information
[0027] Example 1: S1, Synthetic styrene-butadiene block prepolymer Add cyclohexane and styrene monomer to the reactor, heat to 60°C, inject sec-butyllithium initiator solution, and react for 1-2 hours; After styrene is completely converted, butadiene monomer is added to the reactor, and polymerization is continued at 60°C for 2 hours to generate styrene-block-butadiene-Li; After complete conversion of butadiene, β-diketone monomer is injected, and the reaction is continued at 60°C for 2 hours to ensure complete end-capping reaction, thus obtaining styrene-butadiene block prepolymer. S2, Deprotection reaction Styrene-butadiene block prepolymer was dissolved in anhydrous tetrahydrofuran to prepare a 5-10% (w / w) solution; tetrabutylammonium fluoride was added under stirring at room temperature and the reaction was carried out for 6-12 h; the reaction solution was poured into methanol to precipitate, filtered, washed with methanol, and dried under vacuum to obtain β-diketone-styrene-butadiene block prepolymer with β-diketone extended side groups; S3, rare earth catalytic in-situ chain extension β-Diketone-styrene-butadiene block prepolymer was dissolved in anhydrous cyclohexane, transferred to a polymerization reactor, heated to 60°C, and Nd(Oct)3 was added. The mixture was stirred for 1 hour. Then, the co-catalyst diisobutylaluminum hydride and the chlorinating agent tert-butyl hypochlorite were added sequentially, and the mixture was stirred for 30 minutes. Butadiene monomer was added to the system, and the reaction was carried out at 60°C for 3-4 hours. After the reaction was completed, the reaction was terminated with ethanol containing 2,6-di-tert-butyl-p-cresol. The mixture was then coagulated, washed, and vacuum dried to obtain styrene-butadiene-Nd coordinated cis-butadiene composite rubber. Styrene-butadiene-Nd coordinated cis-butadiene composite rubber was dissolved in n-hexane and then subjected to infrared spectroscopy. The results are as follows. Figure 1 As shown; 3500–3200cm -1 The absence of a significant broad peak in the OH stretching vibration region indicates that the carbonyl oxygen of the β-diketone chain-extended side group has reacted with Nd. 3+ Coordination, not existing in the form of free hydroxyl groups, verifies the structural design of the "β-diketone-Nd chelate anchored rare earth catalyst"; 3000 cm -1 The nearby aromatic ring CH and 2900cm -1 The coexistence of nearby saturated CH peaks directly proves that the styrene-butadiene block prepolymer was successfully prepared during the anionic polymerization stage; 720 cm⁻¹ -1 Broad peak and 960cm -1 The absence of peaks confirms that the rare-earth catalytic chain extension stage generates highly cis-1,4-structured PB segments, explaining the source of the rubber's low-temperature resistance (Tg < -80℃); 1000cm -1 No Si-O peak, 3500 cm⁻¹ -1 The absence of a free OH peak confirms that the S2 deprotection reaction was complete, and that the β-diketone reacted with Nd... 3+The formation of stable chelates achieves "anchoring" of the rare earth catalyst, avoiding random polymerization caused by free catalysis. Infrared spectroscopy verifies the process route of "anionic polymerization to prepare styrene-butadiene block prepolymer → deprotection to generate β-diketone side groups → rare earth catalytic in-situ chain extension of high cis PB" at the functional group level. Key evidence includes: the CH vibration of the aromatic ring in the PS segment, the characteristic fingerprint peak of high cis PB, the absence of absorption in fully deprotected Si-O, and the interaction between β-diketone and Nd. 3+ The coordinated OH groups exhibit no absorption. These characteristics are highly consistent with the molecular structure and reaction mechanism described in the invention.
[0028] S4, Rubber Preparation Preheat the internal mixer to 180℃, add styrene-butadiene-Nd coordinated cis-butadiene composite rubber, and plasticize for 1-2 minutes. Add silica, carbon black, and zinc oxide treated with coupling agent, and mix for 5-10 minutes. At 40-60℃, mix with sulfur, accelerator, activator, anti-scorching agent, plasticizer, and dispersant for 2-3 minutes. Discharge the rubber and vulcanize to obtain low-temperature solution-polymerized styrene-butadiene rubber.
[0029] The preparation process of the β-diketone monomer in S1 specifically includes the following steps: Add ethylene glycol acetoacetate and anhydrous triethylamine to the reaction vessel, add anhydrous tetrahydrofuran as a solvent, start stirring to dissolve, and control the reaction temperature at 0-5℃; prepare trimethylchlorosilane into a 30% tetrahydrofuran solution and add it to the reaction vessel; remove the ice-water bath, allow the reaction mixture to naturally warm to room temperature, and stir the reaction for 12 hours under nitrogen protection; After the reaction was completed, the product was washed, extracted, and separated to obtain a crude product. After high-vacuum distillation, the β-diketone monomer was obtained.
[0030] In S1, the molar ratio of sec-butyllithium, styrene, butadiene, and β-diketone monomers is 1:20:80:1-1.4; in the styrene-butadiene block prepolymer, the total mass of styrene, butadiene, and β-diketone monomers accounts for 15% of the total mass of the styrene-butadiene block prepolymer.
[0031] In the preparation of the β-diketone monomer, the molar ratio of ethylene glycol acetoacetate methacrylate, trimethylchlorosilane, and anhydrous triethylamine is 1:1.1:1.1.
[0032] In S2, the molar ratio of β-diketone monomer to added tetrabutylammonium fluoride in the styrene-butadiene block prepolymer is 1:1.05.
[0033] In S3, the mass ratio of β-diketone-styrene-butadiene block prepolymer, Nd(Oct)3, diisobutylaluminum hydride, and tert-butyl hypochlorite is 100:10:40:3; the molar ratio of the added butadiene monomer to the β-diketone-styrene-butadiene block prepolymer is 700:1.
[0034] In step S4, the amount of silica used is 60-80% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber, and the amount of carbon black used is 0-20% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The amount of sulfur used is 1.5-2.0% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber; The amount of zinc oxide used is 2-4% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber; The dosage of sulfonamide vulcanization accelerator is 0.8% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber; the dosage of stearic acid activator is 0.5% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber; the dosage of N-cyclohexylthiophthalimide scorch inhibitor is 0.1% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber; the dosage of bio-based oil plasticizer is 4% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber; and the dosage of polymeric dispersant is 2% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber.
[0035] Example 2 The preparation method and raw materials are the same as in Example 1, but... In S1, the molar ratio of sec-butyllithium, styrene, butadiene, and β-diketone monomer is 1:20:80:1.2; In S3, the mass ratio of β-diketone-styrene-butadiene block prepolymer, Nd(Oct)3, diisobutylaluminum hydride, and tert-butyl hypochlorite is 100:10:40:3; the molar ratio of the added butadiene monomer to the β-diketone-styrene-butadiene block prepolymer is 650:1.
[0036] In step S4, the inorganic fillers are silica and carbon black, with silica accounting for 70% of the mass of the styrene-butadiene-Nd-coordinated butadiene composite rubber and carbon black accounting for 10% of the mass of the styrene-butadiene-Nd-coordinated butadiene composite rubber; sulfur accounting for 1.75% of the mass of the styrene-butadiene-Nd-coordinated butadiene composite rubber; and zinc oxide accounting for 3% of the mass of the styrene-butadiene-Nd-coordinated butadiene composite rubber. The dosage of sulfonamide vulcanization accelerator is 1.15% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber; the dosage of stearic acid activator is 0.35% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber; the dosage of N-cyclohexylthiophthalimide scorch inhibitor is 0.2% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber; the dosage of bio-based oil plasticizer is 3% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber; and the dosage of polymeric dispersant is 2.5% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber.
[0037] Example 3 The preparation method and raw materials are the same as in Example 1, but... In S1, the molar ratio of sec-butyllithium, styrene, butadiene, and β-diketone monomer is 1:20:80:1.4; In S3, the mass ratio of β-diketone-styrene-butadiene block prepolymer, Nd(Oct)3, diisobutylaluminum hydride, and tert-butyl hypochlorite is 100:10:40:3; the molar ratio of the added butadiene monomer to the β-diketone-styrene-butadiene block prepolymer is 600:1.
[0038] In step S4, the inorganic filler is only silica, and the amount of silica used is 80% of the mass of styrene-butadiene-Nd coordinated butadiene composite rubber; the amount of sulfur used is 2.0% of the mass of styrene-butadiene-Nd coordinated butadiene composite rubber; and the amount of zinc oxide used is 2% of the mass of styrene-butadiene-Nd coordinated butadiene composite rubber. The following dosages are used: sulfenamide vulcanization accelerator (1.5% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber); stearic acid activator (0.2% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber); N-cyclohexylthiophthalimide scorch inhibitor (0.3% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber); bio-based oil plasticizer (2% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber); and polymeric dispersant (3% of the mass of styrene-butadiene-Nd-coordinated butadiene composite rubber).
[0039] Based on this, the following design was also created: Comparative Example 1: Same formulation and experimental method as Example 2, but without using β-diketone monomers to chelate Nd ions; Comparative Example 2: The formulation and experimental methods were the same as in Example 2, but the same molar amount of organic lithium catalyst was used; Comparative Example 3: The formulation and experimental method are the same as those in Example 2, but in S1, the molar ratio of sec-butyllithium, styrene, butadiene, and β-diketone monomer is 1:20:80:0.5; Comparative Example 4: The formulation and experimental methods are the same as those in Example 2, but in S1, the molar ratio of sec-butyllithium, styrene, butadiene, and β-diketone monomer is 1:20:80:3; Comparative Example 5: The formulation and experimental methods were the same as in Example 2, but the molar ratio of the added butadiene monomer to the β-diketone-styrene-butadiene block prepolymer was 1000:1; Comparative Example 6: The formulation and experimental methods were the same as in Example 2, except that the molar ratio of the added butadiene monomer to the β-diketone-styrene-butadiene block prepolymer was 200:1.
[0040] The product underwent performance tests according to ASTM D412, ASTM D624, and ASTM D2084, including stress-strain properties, tear strength, glass transition temperature (Tg), and vulcanization characteristics. The test data for each performance item are summarized in Table 3. Table 2. Test data of various properties of low-temperature solution-polymerized styrene-butadiene rubber
[0041] Data analysis shows that: Comparative Example 1 used the same formulation and experimental methods as Example 2, but did not use β-diketone monomers for chain-extending side-group functionalization, thus lacking the chelation effect between the β-diketone chain-extending side-groups and rare earth metal Nd ions. In Example 2, the β-diketone chain-extending side-groups (β-diketone-styrene-butadiene block prepolymer) generated after the hydrolysis of the β-diketone monomer formed a stable chelate structure with Nd(Oct)3, which served as an active center to efficiently initiate in-situ chain extension of the butadiene monomer. This increased the polymer chain length and optimized the molecular weight distribution, thereby improving the chain flexibility and regularity. In contrast, Comparative Example 1 lacked chelation, resulting in an insufficient chain extension reaction, shorter and disordered molecular chains, leading to a significant increase in the glass transition temperature (Tg), indicating poor chain segment mobility and deteriorated low-temperature performance. The tensile strength, elongation at break, and tear strength of Comparative Example 1 were all low because of insufficient chain extension, reduced effective crosslinking points, and decreased stress transfer efficiency. Meanwhile, the vulcanization characteristics showed that the scorch time (t10) and positive vulcanization time (t90) were prolonged, and the torque difference (MH-ML) was reduced, indicating that the crosslinking density was low, the vulcanization network was not well formed, and the mechanical properties were further weakened.
[0042] Comparative Example 2 used the same molar amount of an organolithium catalyst instead of a rare earth catalyst for chain extension, with other conditions identical to Example 2. However, this substitution affected the microstructure of the polymer chain and the catalytic efficiency. The rare earth catalyst Nd(Oct)3 can induce butadiene polymerization to form a high cis-1,4 structure (cis content typically >95%). This structure exhibits good chain segment flexibility, and the molecular chain is easily oriented and crystallized, thereby significantly reducing Tg (-86.2℃) and improving elasticity. In contrast, the organolithium catalyst used in Comparative Example 2 typically produces a mixed microstructure, with cis, trans, and 1,2- structures coexisting. The lower cis content leads to increased chain segment rigidity, higher Tg, and poorer low-temperature performance. Rare earth catalysts possess higher single-point activity characteristics, enabling precise chelation with β-diketone chain-extending side groups to achieve controllable chain extension and form linear long-chain structures, which is beneficial for stress dispersion and energy dissipation. In contrast, the organolithium catalyst in Comparative Example 2 may initiate random polymerization, resulting in poor chain growth control and a wide molecular weight distribution, leading to lower tensile and tear strength. During vulcanization, Comparative Example 2 exhibits longer t10 and t90 and smaller MH-ML values, indicating a slower crosslinking reaction, which may be related to irregular chain structure and insufficient active sites.
[0043] In Comparative Example 3, the amount of β-diketone monomer used was insufficient, less than that of the initiator sec-butyllithium. This meant that only about 50% of the active polymer chains (PS-b-PB-Li) were successfully end-capped, introducing β-diketone functional groups. In the S3 rare-earth catalytic chain extension step, only these functionalized chains could chelate with Nd ions, serving as active centers to continue initiating butadiene polymerization and achieving significant chain growth. The remaining approximately 50% of the chains lacked functional groups and could not participate in the chain extension reaction, resulting in lower molecular weights. This led to a wider molecular weight distribution in the polymer system, with a large number of "short chains." The proportion of cis-1,4 structure in Comparative Example 3 was significantly lower than in Example 2. This is because the number of active centers in the rare earth catalyst was insufficient. Some butadiene monomers may have been polymerized by residual or other non-specific active sites in the system. The stereoselectivity of these active sites was not as good as that of the Nd / β-diketone chelate centers, resulting in a decrease in the regularity of the microstructure of the polymerization product. Due to the presence of a large number of short chains, molecular chain movement was hindered, chain segment flexibility deteriorated, leading to a shift in glass transition temperature to higher temperatures and a deterioration in low-temperature performance. Short chains could not effectively bear and transfer stress, and the resulting sulfurized network had many defects and uneven crosslinking density, resulting in poor strength. The low elongation at break also reflected the material's high brittleness and insufficient toughness.
[0044] In Comparative Example 4, an excess of β-diketone monomer was used. Although theoretically all active chains could be functionalized, the excess β-diketone monomer might still exist in the system after the end-capping reaction. In the subsequent S3 step, these free β-diketone monomers would also chelate with the valuable Nd(Oct)3 catalyst, diluting the concentration of catalytic active centers that should be concentrated at the polymer chain ends. The chelates formed by the free β-diketones and Nd, independent of the chain ends, could also initiate butadiene polymerization, generating new, independent polybutadiene homopolymer chains instead of the expected "PS-PB-PB" block structure. This resulted in a product that was a mixture of the target block copolymer and the polybutadiene homopolymer. The presence of the homopolymer disrupted the microphase separation structure with PS microdomains as physical crosslinking points, weakening the reinforcing effect of the material. In terms of macroscopic performance, the presence of a large number of compliant polybutadiene homopolymer chains in the system endows the material with good low-temperature flexibility and high elongation. However, the effective chain-extended network is "diluted" by the homopolymer, and the physical cross-linking network is weakened, resulting in stress concentration and the strength cannot reach the optimal level. Excessive oxygen-containing functional groups (β-diketones) interfere with the microenvironment of the active center of rare earth catalysts, slightly reducing their stereoregularity control ability.
[0045] In Comparative Example 5, excessive chain extension resulted in excessively long polybutadiene soft segments, disrupting the effective physical cross-linking network. The extended side groups of each macromolecular chain produced very long polybutadiene segments, making polybutadiene the dominant continuous phase in the final product. The PS hard segment microregions, on the other hand, were diluted, becoming very far apart. The role of the PS microregions as physical cross-linking points was severely weakened because the molecular chains connecting two physical cross-linking points were too long, reducing the effective cross-linking density. The excessively long, highly cis polybutadiene soft segments endowed the molecular chains with extremely high flexibility and mobility, resulting in the lowest Tg. Simultaneously, due to the sparse physical cross-linking points, the molecular chains easily slipped and stretched during stretching, exhibiting high elastic deformation similar to pure rubber, thus resulting in the highest elongation at break. Maintaining strength requires not only flexible chain segments but also a stable network to transfer and disperse stress. The weakening of the physical cross-linking network in Comparative Example 5 led to ineffective stress transfer, making the material prone to plastic flow and failure under significant external forces, resulting in insufficient strength.
[0046] Comparative Example 6 shows insufficient chain extension, resulting in excessively short polybutadiene soft segments and inadequate "soft-hard" microphase separation. Each macromolecular chain only grew relatively short polybutadiene segments. This leads to a small volume fraction of the polybutadiene phase ("soft segments") and an excessively high relative proportion of the polystyrene (PS) phase ("hard segments"). Within the material, the physical crosslinking points of the PS segments are too close together and have an excessively high density, severely restricting the chain movement of the polybutadiene soft segments. Due to the severely restricted soft segment mobility, higher temperatures are required for the segments to transition from freezing to movement, causing a significant shift in the glass transition temperature towards higher temperatures and extremely poor low-temperature performance. The short soft segments cannot effectively extend and orient to disperse stress, making the material brittle and hard with very low tensile and tear strengths.
[0047] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A method for synthesizing low-temperature solution-polymerizable styrene-butadiene rubber, characterized in that, Includes the following steps: S1, Synthetic styrene-butadiene block prepolymer Add cyclohexane and 100 parts of styrene monomer to the reactor, heat to 60°C, inject 5 parts of sec-butyllithium initiator solution, and react for 1-2 hours; After the styrene is completely converted, 400 parts of butadiene monomer are added to the reactor, and polymerization is continued at 60°C for 2 hours to generate styrene-block-butadiene-Li. After the butadiene is completely converted, 5-7 parts of β-diketone monomer are injected, and the reaction is continued at 60°C for 2 hours to ensure complete end-capping reaction, thus obtaining styrene-butadiene block prepolymer. S2, Deprotection reaction 100 parts of styrene-butadiene block prepolymer were dissolved in anhydrous tetrahydrofuran to prepare a 5-10% (w / w) solution; 0.78-1.08 parts of tetrabutylammonium fluoride were added under stirring at room temperature, and the reaction was carried out for 6-12 hours; the reaction solution was poured into methanol to precipitate, filtered, washed with methanol, and dried under vacuum to obtain a β-diketone-styrene-butadiene block prepolymer with β-diketone extended side groups; S3, rare earth catalytic in-situ chain extension 100 parts of β-diketone-styrene-butadiene block prepolymer were dissolved in anhydrous cyclohexane, transferred to a polymerization reactor, heated to 60°C, and 10 parts of Nd(Oct)3 were added. The mixture was stirred for 1 hour. 40 parts of diisobutylaluminum hydride and 3 parts of tert-butyl hypochlorite were added sequentially as co-catalysts, and the mixture was stirred for 30 minutes. Butadiene monomer was added to the system, and the reaction was carried out at 60°C for 3-4 hours. After the reaction was completed, the reaction was terminated with ethanol containing 2,6-di-tert-butyl-p-cresol. The mixture was then coagulated, washed, and vacuum dried to obtain styrene-butadiene-Nd coordinated cis-butadiene composite rubber. S4, Rubber Preparation Preheat the internal mixer to 180℃, add styrene-butadiene-Nd coordinated cis-butadiene composite rubber, and plasticize for 1-2 minutes. Add silica, carbon black, and zinc oxide treated with coupling agent, and mix for 5-10 minutes. At 40-60℃, mix with sulfur, accelerator, activator, anti-scorching agent, plasticizer, and dispersant for 2-3 minutes. Discharge the rubber and vulcanize to obtain low-temperature solution-polymerized styrene-butadiene rubber.
2. The method for synthesizing low-temperature solution-polymerized styrene-butadiene rubber according to claim 1, characterized in that, In S1, the molar ratio of sec-butyllithium, styrene, butadiene, and β-diketone monomers is 1:20:80:1-1.4; in the styrene-butadiene block prepolymer, the total mass of styrene, butadiene, and β-diketone monomers accounts for 15% of the total mass of the styrene-butadiene block prepolymer.
3. The method for synthesizing low-temperature solution-polymerized styrene-butadiene rubber according to claim 1, characterized in that, The preparation process of the β-diketone monomer in S1 specifically includes the following steps: Add ethylene glycol acetoacetate and anhydrous triethylamine to the reactor, add anhydrous tetrahydrofuran as a solvent, start stirring to dissolve, and control the reaction temperature at 0-5℃; prepare trimethylchlorosilane into a 30% tetrahydrofuran solution and add it to the reactor; remove the ice-water bath and allow the reaction mixture to naturally warm to room temperature, and stir the reaction under nitrogen protection for 6-12 hours; After the reaction was completed, the product was washed, extracted, and separated to obtain a crude product. After vacuum distillation, the β-diketone monomer was obtained.
4. The method for synthesizing low-temperature solution-polymerized styrene-butadiene rubber according to claim 3, characterized in that, In the preparation of the β-diketone monomer, the molar ratio of ethylene glycol acetoacetate methacrylate, trimethylchlorosilane, and anhydrous triethylamine is 1:1.1:1.
1.
5. The method for synthesizing low-temperature solution-polymerizable styrene-butadiene rubber according to claim 1, characterized in that, In S2, the molar ratio of β-diketone monomer to added tetrabutylammonium fluoride in the styrene-butadiene block prepolymer is 1:1.
05.
6. The method for synthesizing low-temperature solution-polymerized styrene-butadiene rubber according to claim 1, characterized in that, In S3, the mass ratio of β-diketone-styrene-butadiene block prepolymer, Nd(Oct)3, diisobutylaluminum hydride, and tert-butyl hypochlorite is 100:10:40:3; the molar ratio of the added butadiene monomer to the β-diketone-styrene-butadiene block prepolymer is 600-700:
1.
7. The method for synthesizing low-temperature solution-polymerized styrene-butadiene rubber according to claim 1, characterized in that, In step S4, the amount of silica used is 60-80% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber, and the amount of carbon black used is 0-20% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The amount of sulfur used is 1.5-2.0% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber; The amount of zinc oxide used is 2-4% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber; The accelerator is a sulfenamide-based vulcanization accelerator, and its dosage is 0.8-1.5% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The activator is stearic acid activator, and the dosage is 0.2-0.5% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber; The scorching inhibitor is N-cyclohexylthiophthalimide, and its dosage is 0.1-0.3% of the mass of styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The plasticizer is a bio-based oil plasticizer, and its dosage is 2-4% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber. The dispersant is a polymeric dispersant, and the amount used is 2-3% of the mass of the styrene-butadiene-Nd coordinated cis-butadiene composite rubber.