Sulfur-containing elastomer capable of being recycled in closed loop and preparation method and recycling method thereof

Abstract

The invention discloses a sulfur-containing elastomer capable of being recycled in a closed-loop manner, and a preparation method and a recycling method thereof, and belongs to the technical field of high polymer material synthesis. According to the method, monothiolactide and dithiolactide are adopted as raw materials, and the segmented copolymer type thermoplastic elastomer is prepared through a one-pot ring-opening copolymerization reaction. The elastomer can be depolymerized and recovered into an original monomer under the action of heating and a catalyst, so that a monomer-polymer-monomer closed-loop cycle is realized. The method disclosed by the invention is simple in preparation process, free of sequential feeding and high in production efficiency; the selected catalytic system is high in catalytic activity, the ring-opening copolymerization reaction of two monomers can be synchronously promoted under the same reaction condition, and a relatively high conversion rate is obtained; the obtained elastomer is excellent in mechanical property, can realize complete depolymerization and monomer recovery, is beneficial to resource recycling and same-level use, effectively relieves the problems of resource waste and environmental pollution caused by traditional thermoplastic elastomer wastes, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials and organic synthesis methodology. Specifically, it relates to a sulfur-containing closed-loop recyclable elastomer, its preparation method, and its recycling method. Background Technology

[0002] Thermoplastic elastomers (TPEs) are widely used in adhesives, clothing, electronics, medical devices, and automotive parts due to their combination of the high elasticity of rubber and the processability of thermoplastics. However, traditional TPE materials are mainly derived from fossil resources, such as widely used polystyrene elastomers and thermoplastic polyolefin elastomers. These typically have a stable carbon-carbon backbone structure, making them difficult to degrade and recycle after use, leading to serious environmental pollution and resource waste. AB-type or ABA-type block copolymers composed of aliphatic polyesters (where A is the hard segment, a crystalline or amorphous polymer with a melting temperature or glass transition temperature above room temperature; B is the soft segment, a flexible amorphous polymer with a glass transition temperature below room temperature) have become a research hotspot for environmentally friendly TPEs because polyesters are biodegradable and can be efficiently prepared through ring-opening polymerization of cyclic esters or lactone monomers. Although these TPE materials can be reused multiple times through physical recycling, their performance usually degrades significantly, requiring downgrading and ultimately reaching the "end-of-life" stage, resulting in resource waste. In the context of "green and low-carbon" and "circular economy", it is still of great significance to develop TPE materials with performance comparable to commercial elastomers and which can be recycled in a closed loop after use.

[0003] Closed-loop recycled polymers can depolymerize back to their original monomers after use, thus achieving resource recycling and same-level reuse, which is an effective way to fundamentally solve the problem of plastic pollution. Current research mainly focuses on designing and synthesizing new monomers and developing novel closed-loop recycled polymer materials, while research reports on closed-loop recycled elastomers are still limited. The literature *Advanced Functional Materials*, 2025, 35, 2422779 and Chinese invention patent 202411811316.9 report a method for preparing a closed-loop recycled thermoplastic elastomer using a one-pot sequential feeding method of β-methyl-δ-valerolactone and δ-valerolactone. The resulting elastomer material not only possesses excellent mechanical properties but also has a highly efficient closed-loop recycling capability. Chinese invention patent 202411811699.X reports a method for preparing a high-performance closed-loop recycled thermoplastic elastomer through the sequential ring-opening polymerization of β-methyl-δ-valerolactone and p-dioxanone. The resulting elastomer material can be completely depolymerized back to the lactone monomer in the presence of a catalyst. The paper *Nature Communications*, 2024, 15, 7904, reports the preparation of a ring-closed recyclable triblock thermoplastic elastomer using δ-valerolactone (δVL) and α-alkyl-substituted valerolactone as raw materials via sequential feeding. This elastomer exhibits excellent mechanical properties and ring-closed recycling performance. Despite these examples, the preparation process is cumbersome, typically requiring sequential feeding. Further development is needed to create ring-closed recyclable elastomer materials with high performance, simple preparation processes, low production costs, and ease of large-scale production. Summary of the Invention

[0004] This invention aims to address the resource waste and environmental pollution caused by waste from traditional thermoplastic elastomer materials, as well as the limited types of existing recyclable elastomers and the cumbersome preparation processes. Instead, it provides a sulfur-containing recyclable elastomer, its preparation method, and its recycling method.

[0005] To address the aforementioned technical problems, the present invention adopts the following technical solution: The present invention aims to provide a sulfur-containing, ring-closed, recyclable elastomer, characterized in that it has an ABA-type triblock copolymer structure or an AB-type diblock copolymer structure, wherein segment A has the structure shown in Formula I, and segment B has the structure shown in Formula II. (I) (II) Wherein, R1 group is selected from any one of C5-C6 alicyclic hydrocarbon groups, phenyl, substituted or unsubstituted aryl, and isopropyl; R2 and R3 groups are selected from hydrogen and C1-C4 straight-chain or branched alicyclic hydrocarbon groups; m and n represent the number of repeating units in each part, where m is a natural number greater than 100 and less than 400, and n is a natural number greater than 50 and less than 250, and 1 / 10 < n / m < 1; it is prepared by the following steps: Step 1: Dissolve dithiolactone and monothiolactone in an organic solvent and stir until homogeneous at room temperature; Step 2: Dissolve the initiator and catalyst in an organic solvent and add them to the above mixed solution, and react at room temperature for 0.5 h to 12 h; Step 3: Quench the reaction, settle and centrifuge to obtain sulfur-containing recyclable elastomer; The dithiolactone structure is shown in Formula III below: (Ⅲ), The structural formula of monothiolactone is shown in Formula IV below: (Ⅳ).

[0006] Further specifying, in Formula III, the R1 group is selected from any one of C5-C6 alicyclic hydrocarbon groups, phenyl groups, substituted or unsubstituted aryl groups, and isopropyl groups; Further specifying, in Formula IV, the R2 and R3 groups are selected from hydrogen, and straight-chain or branched aliphatic hydrocarbon groups of C1-C4.

[0007] Further specifying, the dithiolactone is prepared according to the following steps: Amino acids were dissolved in water, and hydrobromic acid and sodium nitrite aqueous solution were added. The mixture was stirred at room temperature for 3 hours, extracted and concentrated with diethyl ether, and then sodium hydrosulfide aqueous solution was added. The mixture was reacted at 80°C for 6 hours, cooled, and acidified to obtain mercapto acids. Mercapto acids were dissolved in dichloromethane, and 4-(dimethylamino)pyridine and N,N'-dicyclohexylcarboimide were added. The mixture was stirred at room temperature for 3 hours, and purified to obtain dithiolactone. Further specifying, the monothiolactone is prepared according to the following steps: The acyl bromide reagent and mercapto acid were dissolved in acetonitrile, stirred evenly, and then triethylamine was added. The reaction was carried out at room temperature for 1 hour, then heated to 80°C, and acetonitrile solution containing triethylamine was added dropwise. The reaction was maintained at 80°C for 0.5 hours, quenched with acetic acid, and purified to obtain monothiolactone.

[0008] Further specifying, the initiator mentioned in step 2 is a monothiol or a dithiol.

[0009] To be further specified, the monothiol is selected from one of benzyl mercaptan, thiophenol, and propanethiol.

[0010] To further specify, the dithiol is selected from one of benzyl dithiol, ethylene dithiol, 1,2-propanedithiol, 1,4-butanedithiol, and 1,2-benzenedithiol.

[0011] Further specifying, the catalyst mentioned in step 2 is one of the following: organic base catalyst, alkali metal compound, alkali metal alkoxide, carbene reagent, guanidine reagent, amidine reagent, and phosphazene reagent. Specifically, it can be one of potassium hydride, sodium hydride, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,8-diazabicycloundec-7-ene (DBU), and 4-(dimethylamino)pyridine (DMAP).

[0012] Further specifying, the organic solvent mentioned in steps 1 and 2 is one of dichloromethane, tetrahydrofuran, acetonitrile, dimethyl sulfoxide, and ethyl acetate.

[0013] Further specified, the molar ratio of the monothiolactone to the dithiolactone is 10 / 1 to 1 / 1.

[0014] Further specified, the ratio of the total molar amount of monothiolactone and dithiolactone to the molar amount of initiator and catalyst is (800-300):1:(1-0.5).

[0015] Further specifying, the precipitation reagent mentioned in step 3 is one of methanol, ethanol, propanol, n-hexane, acetone, and petroleum ether.

[0016] Another object of the present invention is to provide a method for recycling the above-mentioned elastomer, which is carried out according to the following steps: Sodium thiophene and the elastomer are mixed and heated at 100℃~180℃ for 1h~10h. A mixture of monothiolactone and dithiolactone monomers is recovered by vacuum distillation. After separating the mixture, monothiolactone monomers and dithiolactone monomers are obtained, which can be used again in a one-step feeding, one-pot polymerization method to prepare a closed-loop recyclable elastomer material, achieving closed-loop recycling.

[0017] The lactide monomer used in this invention is thermodynamically more favorable for cyclization and kinetically more favorable for ring-opening polymerization, thus successfully combining two seemingly contradictory properties into one monomer. This makes the lactide monomer both easy to synthesize and easy to polymerize, making it an ideal monomer for the synthesis of closed-loop recyclable polymers. Further research shows that monothiolactide monomers have high polymerization activity and fast polymerization rate, resulting in amorphous polymers with low glass transition temperatures (suitable as soft segments). In contrast, dithiolactide monomers with special side groups have relatively low polymerization activity and slow polymerization rate, resulting in polymers with good crystallinity and high glass transition temperatures (suitable as hard segments). The two lactide monomers have similar structures but significantly different polymerization rates, resulting in polymers with completely different crystallinity and significant differences in glass transition temperatures. Copolymerization of these two monomers provides a unique approach for the preparation of novel sulfur-containing, closed-loop recyclable elastomers. Compared with existing technologies, this invention has the following beneficial effects: This invention provides a novel sulfur-containing, closed-loop recyclable elastomer material and its preparation method. This material possesses excellent mechanical properties and can be efficiently depolymerized and recycled back to its original monomers after use, achieving a fully closed-loop cycle of "monomer-polymer-monomer." This fundamentally solves the resource waste and environmental pollution problems caused by traditional thermoplastic elastomer waste, aligning with the concepts of circular economy and sustainable development, and has broad application prospects.

[0018] The preparation method of this invention is based on the fact that monothiolactide monomers and dithiolactide monomers have similar structures but significantly different polymerization activities. Through a one-pot ring-opening copolymerization reaction with a single feed, a closed-ring recyclable elastomer material was successfully prepared. This method avoids the complex operation of sequential feeding required in existing technologies, simplifies the process, reduces production costs, and is suitable for large-scale production.

[0019] The catalytic system used has high catalytic activity and can simultaneously and efficiently catalyze the ring-opening copolymerization of two monomers under the same reaction conditions, and obtain a high monomer conversion rate.

[0020] Compared with traditional elastomers and their preparation processes, the present invention has the following main advantages: The preparation process is simple and the production efficiency is high. One-pot copolymerization does not require step-by-step feeding. The catalytic system has strong applicability and high activity, and can simultaneously achieve efficient copolymerization of different active monomers; The resulting elastomer material exhibits excellent mechanical properties and can be completely depolymerized and recycled back to the original monomer, achieving resource recycling and same-level reuse, effectively alleviating the environmental and resource pressures caused by elastomer waste.

[0021] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0022] Figure 1 A schematic diagram of the synthetic route for sulfur-containing closed-loop recyclable elastomers; Figure 2 This is the 1H NMR spectrum of the copolymer elastomer of Example 6 in this invention; Figure 3 This is a comparison of the hydrogen NMR spectra of the elastomer before and after depolymerization in Example 6 of this invention. Detailed Implementation

[0023] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0024] Example 1 Preparation of monothiolactone monomer M1 (in Formula IV, R2 is hydrogen and R3 is methyl): Bromoacetyl bromide (5.71 g, 28.3 mmol) and mercaptopropionic acid (3.0 g, 28.3 mmol) were dissolved in acetonitrile (100 mL), cooled to 0 °C, and a triethylamine / acetonitrile solution (2.86 g / 100 mL) was added dropwise, and the reaction was allowed to proceed at room temperature for 1 h. Then, 275 mL of an acetonitrile solution containing triethylamine (2.86 g, 28.3 mmol) was added dropwise through a feeding funnel at 80 °C, and the reaction was continued for 0.5 h. The reaction was then quenched with acetic acid (1 mL) and stirred for 10 min. The reaction mixture was concentrated and purified by column chromatography (dichloromethane / n-hexane = 1:3) to give a white solid M1 (2.27 g, 55% yield). 1 H NMR (500MHz, CDCl3): δ 4.92 (q, 2H), 4.23 (q, 1H), 1.60 (d, 3H).

[0025] Preparation of dithiolactone M2 (in Formula III, R1 is cyclohexyl): L-cyclohexylglycine (32.1 g, 200.0 mmol) was dissolved in water (200 mL), and HBr aqueous solution (250 mL, 48%) and 250 mL of aqueous solution containing sodium nitrite (21.0 g, 300 mmol) were added. The mixture was stirred at room temperature for 3 h. Extraction was performed with diethyl ether (300 mL), and the solution was dried over anhydrous sodium sulfate and concentrated to obtain 2-bromocyclohexyl acid. At 0 °C, the aqueous solution of 2-bromocyclohexyl acid was slowly added to an aqueous solution containing sodium hydrosulfide hydrate (2.1 eq), and the mixture was heated at 80 °C for 6 h. The solution was cooled to 0°C and acidified with 30% H₂SO₄. It was then extracted with diethyl ether, concentrated, and purified by column chromatography (dichloromethane / methanol = 100 / 1) to give a pale yellow oily substance, 2-mercapto-2-cyclohexyl acid (31.3 g, 88% yield). The 2-mercapto-2-cyclohexyl acid (31.3 g, 179.6 mmol) was then dissolved in dichloromethane (5 L), and DMAP (5 g, 40.9 mmol) and N,N′-dicyclohexylcarbodiimide (38.5 g, 184.2 mmol) were added. The reaction was carried out at room temperature for 3 hours. The reaction was quenched with acetic acid (15 ml), filtered, and the filtrate was concentrated and purified by column chromatography (n-hexane / dichloromethane = 2 / 1) to give a white solid M₂ (24.1 g, 85% yield). 1 H NMR (500MHz, CDCl3): δ 4.13 (d, 2H), 2.18 (m, 2H), 1.72-1.91 (m, 8H), 1.63-1.72 (d, 2H), 1.08-1.40 (m, 10H).

[0026] Preparation of a closed-loop recyclable elastomer: Weigh (0.5 mmol, 73 mg) M1 and (0.25 mmol, 78 mg) M2 into a dried polymerization tube (M1 / M2 = 2:1), dissolve in 0.25 ml of dichloromethane, then add (0.0025 mmol, 0.311 mg) benzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). Maintain a nitrogen atmosphere and react at room temperature for 30 min. Quench the reaction with a trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), precipitate in methanol, centrifuge, and dry to obtain a diblock copolymer, namely poly(cyclohexyl dithioester)-b-poly(methyl monothioglycolate) elastomer. GPC analysis showed a number-average molecular weight of 35.8 kg / mol, and mechanical property testing revealed an elongation at break of approximately 232% and a tensile strength of approximately 10.2 MPa.

[0027] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 5 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 150 °C for 5 h to obtain 436 mg of a monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 33.5 kg / mol, an elongation at break of 221%, and a tensile strength of 9.8 MPa.

[0028] Example 2 The monothiolactone monomer M1 and dithiolactone M2 used in this embodiment were prepared using the method of Example 1.

[0029] Preparation of a closed-loop recyclable elastomer: (0.5 mmol, 73 mg) M1 and (0.5 mmol, 156 mg) M2 were weighed and placed in a dried polymerization tube (M1 / M2 = 1:1). 0.25 ml of dichloromethane was added to dissolve them, followed by (0.0025 mmol, 0.311 mg) benzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). The reaction was carried out under a nitrogen atmosphere at room temperature for 5 h. The reaction was quenched by adding a trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), and the elastomer was settled in methanol. After centrifugation and drying, a diblock copolymer, poly(cyclohexyl dithioester)-b-poly(methyl monothioglycolate), was obtained. GPC analysis showed a number-average molecular weight of 47.1 kg / mol, and mechanical property tests showed an elongation at break of approximately 296% and a tensile strength of approximately 13.8 MPa.

[0030] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 10 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 180 °C for 6 h to obtain 446 mg of monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was prepared again with a number average molecular weight of 45.5 kg / mol, an elongation at break of 301%, and a tensile strength of 13.1 MPa.

[0031] Example 3 The monothiolactone monomer M1 and dithiolactone M2 used in this embodiment were prepared using the method of Example 1.

[0032] Preparation of a closed-loop recyclable elastomer: (0.5 mmol, 73 mg) M1 and (0.5 mmol, 156 mg) M2 were weighed and placed in a dried polymerization tube (M1 / M2 = 1:1). 0.5 ml of dichloromethane was added to dissolve them, followed by (0.0025 mmol, 0.311 mg) benzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). The reaction was carried out under a nitrogen atmosphere at room temperature for 12 h. The reaction was quenched by adding a trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml). The elastomer precipitated in methanol, centrifuged, and dried to obtain a diblock copolymer, namely poly(cyclohexyl dithioester)-b-poly(methyl monothioglycolate) elastomer. GPC analysis showed a number-average molecular weight of 42.8 kg / mol, and mechanical property tests showed an elongation at break of approximately 363% and a tensile strength of approximately 12.6 MPa.

[0033] Closed-loop cycle: Take 500 mg of copolymer elastomer, add 5 mg of sodium thiophene, and distill under reduced pressure at 160 °C for 5 h to obtain 428 mg of monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 40.6 kg / mol, an elongation at break of 353%, and a tensile strength of 11.6 MPa.

[0034] Example 4 The monothiolactone monomer M1 and dithiolactone M2 used in this embodiment were prepared using the method of Example 1.

[0035] Preparation of a closed-loop recyclable elastomer: Weigh (0.5 mmol, 73 mg) M1 and (0.25 mmol, 78 mg) M2 into a dried polymerization tube (M1 / M2 = 2:1), dissolve in 0.5 ml of dichloromethane, then add (0.00125 mmol, 0.213 mg) dibenzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). Maintain a nitrogen atmosphere and react at room temperature for 8 h. Quench the reaction with a trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), precipitate in methanol, centrifuge, and dry to obtain a diblock copolymer, namely poly(cyclohexyl dithioester)-b-poly(methyl monothioglycolate) elastomer. GPC analysis showed a number-average molecular weight of 59.9 kg / mol, and mechanical property tests showed an elongation at break of approximately 357% and a tensile strength of approximately 16.3 MPa.

[0036] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 5 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 170 °C for 6.5 h to obtain 411 mg of a monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 55.1 kg / mol, an elongation at break of 372%, and a tensile strength of 15.3 MPa.

[0037] Example 5 The monothiolactone monomer M1 and dithiolactone M2 used in this embodiment were prepared using the method of Example 1.

[0038] Preparation of a closed-loop recyclable elastomer: Weigh (0.5 mmol, 73 mg) M1 and (0.125 mmol, 39 mg) M2 into a dried polymerization tube (M1 / M2 = 4:1), dissolve in 0.25 ml of dichloromethane, then add (0.000625 mmol, 0.107 mg) dibenzyl mercaptan and (0.00125 mmol, 0.191 mg) 1,8-diazabicycloundec-7-ene (DBU). Maintain a nitrogen atmosphere and react at room temperature for 6 h. Quench the reaction with trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), precipitate in methanol, centrifuge and dry to obtain a triblock copolymer, namely poly(cyclohexyl disulfide)-b-poly(methyl monothioglycolic acid)-b-poly(cyclohexyl disulfide) elastomer. The number-average molecular weight measured by GPC was 65.8 kg / mol, and the mechanical property test showed that its elongation at break was approximately 586% and its tensile strength was approximately 21.6 MPa.

[0039] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 6 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 150 °C for 5 h to obtain 422 mg of monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 66.5 kg / mol, an elongation at break of 553%, and a tensile strength of 19.7 MPa.

[0040] Example 6 The monothiolactone monomer M1 and dithiolactone M2 used in this embodiment were prepared using the method of Example 1.

[0041] Preparation of a closed-loop recyclable elastomer: Weigh (0.5 mmol, 73 mg) M1 and (0.5 mmol, 156 mg) M2 into a dried polymerization tube (M1 / M2 = 1:1), dissolve in 0.25 ml of dichloromethane, then add (0.00125 mmol, 0.213 mg) dibenzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). Maintain a nitrogen atmosphere and react at room temperature for 10 h. Quench the reaction with trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), precipitate in methanol, centrifuge and dry to obtain a triblock copolymer, namely poly(cyclohexyl dithioester)-b-poly(methyl monothioglycolate)-b-poly(cyclohexyl dithioester) elastomer. The number-average molecular weight measured by GPC was 110.8 kg / mol, and the mechanical property test showed that its elongation at break was approximately 903% and its tensile strength was approximately 29.5 MPa.

[0042] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 10 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 150 °C for 10 h to obtain 405 mg of monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 100.5 kg / mol, an elongation at break of 856%, and a tensile strength of 28.4 MPa.

[0043] Example 7 The dithiolated ester M2 used in this embodiment was prepared using the method described in Example 1.

[0044] Preparation of monothiolactone monomer M3 (in Formula IV, R2 is methyl and R3 is methyl): Bromopropionyl bromide (6.11 g, 28.3 mmol) and mercaptopropionic acid (3.0 g, 28.3 mmol) were dissolved in acetonitrile (100 mL), cooled to 0 °C, and a triethylamine / acetonitrile solution (2.86 g / 100 mL) was added dropwise, and the reaction was allowed to proceed at room temperature for 1 h. Then, 275 mL of an acetonitrile solution containing triethylamine (2.86 g, 28.3 mmol) was added dropwise through a feeding funnel at 80 °C, and the reaction was continued for 0.5 h. The reaction was then quenched with acetic acid (1 mL) and stirred for 10 min. The reaction mixture was concentrated and purified by column chromatography (dichloromethane / n-hexane = 1:3) to give a white solid M1 (2.76 g, 61% yield). 1 H NMR (500MHz, CDCl3): δ 4.90-5.11 (q, 1H), 4.25-4.37 (q, 1H), 1.47-1.66 (d, 6H).

[0045] Preparation of a closed-loop recyclable elastomer: Weigh (0.5 mmol, 80 mg) M3 and (0.25 mmol, 78 mg) M2 into a dried polymerization tube (M3 / M2 = 2:1), dissolve in 0.25 ml of dichloromethane, then add (0.00125 mmol, 0.213 mg) dibenzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). Maintain a nitrogen atmosphere and react at room temperature for 6 h. Quench the reaction with trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), precipitate in methanol, centrifuge and dry to obtain a triblock copolymer, namely poly(cyclohexyl disulfide)-b-poly(methyl monothioglycolic acid)-b-poly(cyclohexyl disulfide) elastomer. The number-average molecular weight measured by GPC was 53.6 kg / mol, and the mechanical property test showed that its elongation at break was approximately 532% and its tensile strength was approximately 19.6 MPa.

[0046] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 10 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 120 °C for 6 h to obtain 388 mg of a monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 60.5 kg / mol, an elongation at break of 512%, and a tensile strength of 19.2 MPa.

[0047] Example 8 The monothiolated lactone monomer M3 used in this embodiment was prepared using the method described in Example 7.

[0048] Preparation of dithiolactone M4 (in Formula III, R1 is cyclopentyl): L-cyclopentylglycine (29.2 g, 200.0 mmol) was dissolved in water (200 mL), and HBr aqueous solution (250 mL, 48%) and 250 mL of aqueous solution containing sodium nitrite (21.0 g, 300 mmol) were added. The mixture was stirred at room temperature for 3 h. Extraction was performed with diethyl ether (300 mL), and the solution was dried over anhydrous sodium sulfate and concentrated to obtain 2-bromocyclopentyl acid. At 0 °C, the aqueous solution of 2-bromocyclopentyl acid was slowly added to an aqueous solution containing sodium hydrosulfide hydrate (2.1 eq), and the mixture was heated at 90 °C for 6 h. The solution was cooled to 0°C and acidified with 30% H₂SO₄. It was then extracted with diethyl ether, concentrated, and purified by column chromatography (dichloromethane / methanol = 100 / 1) to give a pale yellow oily substance, 2-mercapto-2-cyclopentyl acid (27.8 g, 85% yield). The 2-mercapto-2-cyclopentyl acid (27.8 g, 173.4 mmol) was dissolved in dichloromethane (5 L), and DMAP (5 g, 40.9 mmol) and N,N′-dicyclohexylcarbodiimide (37.5 g, 182.4 mmol) were added. The reaction was carried out at room temperature for 4 hours. The reaction was quenched with acetic acid (15 ml), filtered, and the filtrate was concentrated and purified by column chromatography (n-hexane / dichloromethane = 4 / 1) to give a white solid M₂ (21.3 g, 82% yield). 1 H NMR (500MHz, CDCl3): δ 4.02 (d, 2H), 2.16 (m, 2H), 1.70-1.90 (m, 8H), 1.64-1.71 (d, 2H), 1.06-1.36 (m, 8H).

[0049] Preparation of a closed-loop recyclable elastomer: Weigh (0.5 mmol, 80 mg) M3 and (0.25 mmol, 72 mg) M4 into a dried polymerization tube (M4 / M2 = 2:1), add 0.25 ml of dichloromethane to dissolve, then add (0.00125 mmol, 0.213 mg) dibenzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). Maintain a nitrogen atmosphere and react at room temperature for 20 h. Quench the reaction with trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), precipitate in methanol, centrifuge and dry to obtain a triblock copolymer, namely poly(cyclohexyl disulfide)-b-poly(methyl monothioglycolic acid)-b-poly(cyclohexyl disulfide) elastomer. The number-average molecular weight measured by GPC was 76.8 kg / mol, and the mechanical property test showed that its elongation at break was approximately 632% and its tensile strength was approximately 22.7 MPa.

[0050] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 5 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 120 °C for 6 h to obtain 423 mg of a monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 76.5 kg / mol, an elongation at break of 626%, and a tensile strength of 21.6 MPa.

[0051] Example 9 The dithiolated ester M2 used in this embodiment was prepared using the method described in Example 1.

[0052] Preparation of monothiolactone monomer M5 (in Formula IV, R2 is hydrogen and R3 is ethyl): Bromoacetyl bromide (5.71 g, 28.3 mmol) and mercaptobutyric acid (3.4 g, 28.3 mmol) were dissolved in acetonitrile (100 mL), cooled to 0 °C, and a triethylamine / acetonitrile solution (2.86 g / 100 mL) was added dropwise, and the reaction was allowed to proceed at room temperature for 1 h. Then, 275 mL of an acetonitrile solution containing triethylamine (2.86 g, 28.3 mmol) was added dropwise through a feeding funnel at 80 °C, and the reaction was continued for 0.5 h. The reaction was then quenched with acetic acid (1 mL) and stirred for 10 min. The reaction mixture was concentrated and purified by column chromatography (dichloromethane / n-hexane = 1:4) to give a white solid M1 (3.22 g, 65% yield). 1 H NMR (500 MHz, CDCl3): δ 4.87 (q, 2H), 4.01 (t, 1H), 2.14 (m, 2H), 1.13 (t, 3H).

[0053] Preparation of a closed-loop recyclable elastomer: Weigh (0.5 mmol, 80 mg) M5 and (0.5 mmol, 156 mg) M2 into a dried polymerization tube (M5 / M2 = 1:1), dissolve in 0.25 ml of dichloromethane, then add (0.00125 mmol, 0.213 mg) dibenzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). Maintain a nitrogen atmosphere and react at room temperature for 12 h. Quench the reaction with trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), precipitate in methanol, centrifuge and dry to obtain a triblock copolymer, namely poly(cyclohexyl disulfide)-b-poly(methyl monothioglycolic acid)-b-poly(cyclohexyl disulfide) elastomer. The number-average molecular weight measured by GPC was 90.4 kg / mol, and the mechanical property test showed that its elongation at break was approximately 681% and its tensile strength was approximately 25.4 MPa.

[0054] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 10 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 150 °C for 10 h to obtain 403 mg of monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 85.3 kg / mol, an elongation at break of 664%, and a tensile strength of 24.9 MPa.

[0055] Example 10 The monothiolated lactone monomer M3 used in this embodiment was prepared using the method of Example 7; The dithiolated lactone M2 used was prepared using the method described in Example 1.

[0056] Preparation of a closed-loop recyclable elastomer: Weigh (0.5 mmol, 80 mg) M3 and (0.25 mmol, 78 mg) M2 into a dried polymerization tube (M3 / M2 = 1:1), dissolve in 0.25 ml of dichloromethane, then add (0.00125 mmol, 0.213 mg) dibenzyl mercaptan and (0.0025 mmol, 0.381 mg) 1,8-diazabicycloundec-7-ene (DBU). Maintain a nitrogen atmosphere and react at room temperature for 6 h. Quench the reaction with trifluoroacetic acid / dichloromethane solution (1 ml / 10 ml), precipitate in methanol, centrifuge and dry to obtain a triblock copolymer, namely poly(cyclohexyl disulfide)-b-poly(methyl monothioglycolic acid)-b-poly(cyclohexyl disulfide) elastomer. The number-average molecular weight measured by GPC was 95.6 kg / mol, and the mechanical property test showed that its elongation at break was approximately 756% and its tensile strength was approximately 26.8 MPa.

[0057] Closed-loop cycle: 500 mg of copolymer elastomer was taken and 10 mg of sodium thiophene was added. The mixture was distilled under reduced pressure at 150 °C for 9 h to obtain 396 mg of a monomer mixture of monothiolactide and dithiolactide. After separation, purification and repolymerization, the elastomer material was re-prepared with a number average molecular weight of 92.5 kg / mol, an elongation at break of 724%, and a tensile strength of 25.6 MPa.

[0058] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A sulfur-containing, closed-loop recyclable elastomer, characterized in that, It has an ABA-type triblock copolymer structure or an AB-type diblock copolymer structure, wherein segment A has the structure shown in Formula I, and segment B has the structure shown in Formula II: (Ⅰ) (Ⅱ) Wherein, R1 group is selected from any one of C5-C6 alicyclic hydrocarbon group, phenyl, substituted or unsubstituted aryl, and isopropyl; R2 and R3 groups are selected from hydrogen and C1-C4 straight-chain or branched alicyclic hydrocarbon group; m and n represent the number of repeating units in each part, m is a natural number greater than 100 and less than 400, n is a natural number greater than 50 and less than 250, and 1 / 10 < n / m < 1.

2. The method for preparing the sulfur-containing closed-loop recyclable elastomer as described in claim 1, characterized in that, Includes the following steps: Step 1: Dissolve dithiolactone and monothiolactone in an organic solvent and stir until homogeneous at room temperature; Step 2: Dissolve the initiator and catalyst in an organic solvent and add them to the above mixed solution, and react at room temperature for 0.5 h to 12 h; Step 3: Quench the reaction, settle and centrifuge to obtain sulfur-containing recyclable elastomer; The dithiolactone structure is shown in Formula III below: (Ⅲ)， The structural formula of monothiolactone is shown in Formula IV below: (Ⅳ)。 In Formula III, the R1 group is selected from any one of C5-C6 alicyclic hydrocarbon groups, phenyl groups, substituted or unsubstituted aryl groups, and isopropyl groups. In Formula IV, the R2 and R3 groups are selected from hydrogen, or from a straight-chain or branched aliphatic hydrocarbon group of C1-C4.

3. The method according to claim 2, characterized in that, In step 1, the dithiolactone is prepared according to the following steps: Amino acids were dissolved in water, and hydrobromic acid and sodium nitrite aqueous solution were added. The mixture was stirred at room temperature for 3 hours, extracted and concentrated with diethyl ether, and then sodium hydrosulfide aqueous solution was added. The mixture was reacted at 80°C for 6 hours, cooled, and acidified to obtain mercapto acids. Mercapto acids were dissolved in dichloromethane, and 4-(dimethylamino)pyridine and N,N'-dicyclohexylcarboimide were added. The mixture was stirred at room temperature for 3 hours, and purified to obtain dithiolactone. Monothiolated lactones are prepared according to the following steps: The acyl bromide reagent and mercapto acid were dissolved in acetonitrile, stirred evenly, and then triethylamine was added. The reaction was carried out at room temperature for 1 hour, then heated to 80°C, and acetonitrile solution containing triethylamine was added dropwise. The reaction was maintained at 80°C for 0.5 hours, quenched with acetic acid, and purified to obtain monothiolactone.

4. The method according to claim 2, characterized in that, The initiator mentioned in step 2 is a monothiol or a dithiol; the monothiol is selected from benzyl mercaptan, thiophene, and propanethiol; the dithiol is selected from benzyl dithiol, ethylene dithiol, 1,2-propanedithiol, 1,4-butanedithiol, and 1,2-benzenedithiol.

5. The method according to claim 2, characterized in that, The catalyst mentioned in step 2 is one of the following: organic base catalyst, alkali metal compound, alkali metal alkoxide, carbene reagent, guanidine reagent, amidine reagent, and phosphazene reagent.

6. The method according to claim 2, characterized in that, The organic solvent mentioned in steps 1 and 2 is one of dichloromethane, tetrahydrofuran, acetonitrile, dimethyl sulfoxide, and ethyl acetate.

7. The method according to claim 2, characterized in that, The molar ratio of monothiolactone to dithiolactone is 10 / 1 to 1 / 1.

8. The method according to claim 2, characterized in that, The ratio of the total molar amount of monothiolactone and dithiolactone to the molar amount of initiator and catalyst is 800 / 1 / 1 to 300 / 1 / 0.

5.

9. The method according to claim 2, characterized in that, The precipitation reagent mentioned in step 3 is one of methanol, ethanol, propanol, n-hexane, acetone, and petroleum ether.

10. A method for recycling a closed-loop recyclable elastomer prepared according to claim 1 or any one of claims 2-9, characterized in that: Sodium thiophene and the elastomer are mixed and heated at 100℃~180℃ for 1~10h. After separation by vacuum distillation, monothiolactone and dithiolactone are obtained. These can be used again by polymerization to prepare a closed-loop recyclable elastomer material, thus achieving closed-loop recycling.

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