A bio-based closed-loop recyclable thermoplastic elastomer and its preparation method

Abstract

This invention provides a novel closed-loop recyclable thermoplastic elastomer (TPE) and its preparation method. The method provided by this invention has the following advantages: 1) The raw materials used are non-toxic and harmless and are derived from biomass; the resulting triblock copolymer or star-shaped multi-arm block copolymer can be completely degraded under natural conditions; 2) The prepared TPE can be completely depolymerized and recycled to obtain monomers under mild conditions; the monomers can be repolymerized to obtain TPE with the same properties as the original material, achieving a closed loop; 3) The catalytic system used has high catalytic activity and high monomer conversion rate; 4) The prepared TPE material has good mechanical properties.

Description

Technical Field

[0001] This invention relates to the fields of polymer materials and chemical engineering. Specifically, this invention relates to a novel bio-based closed-loop recyclable thermoplastic elastomer and its preparation method. Background Technology

[0002] Thermoplastic elastomers (TPEs) combine the elasticity of cross-linked rubber with the thermal processing capabilities of thermoplastics. TPEs are widely used in coatings, automotive parts, footwear, medical devices, and pressure-sensitive adhesives. The most widely used commercial TPEs are styrene block copolymers, such as polystyrene-b-polybutadiene-b-polystyrene (SBS) and polystyrene-b-polyisoprene-b-polystyrene (SIS). While these styrene-based TPEs offer low cost and good performance, their main drawback is their reliance on finite fossil resources. Furthermore, due to their stable carbon-carbon backbone structure, these materials are not biodegradable at the end of their lifespan, leading to environmental pollution. With increasing concern about the environmental impact of finite petroleum resources and the large-scale production and improper disposal of petroleum-based polymers, the development of sustainable, biomass-derived TPEs holds great promise.

[0003] ABA triblock copolymers or (AB) are prepared by ring-opening polymerization (ROP) of cyclic lactones and lactide. xStar-shaped multi-arm block copolymers have become a research hotspot in the development of novel biodegradable TPEs (Accounts of Chemical Research 2014, 47(8), 2390-2396; Accounts of Chemical Research 2017, 50(7), 1762-1773). For example, Hillmyer and his team developed a series of biodegradable aliphatic polyester TPEs, in which polylactic acid (PLA) is often used as the hard segment (Biomacromolecules 2007, 8(11), 3634-3640; Biomacromolecules 2009, 10(10), 2904-2911; Macromolecules 2011, 44(1), 87-94). Although the above TPEs can be reused multiple times through physical recycling, chain breakage and oxidation during thermal reprocessing may lead to performance degradation, eventually causing the material to enter the "end-of-life" stage. Therefore, achieving chemical recycling of TPEs at this stage not only recovers the material value but also prevents them from entering the environment as waste after degradation. The development of closed-loop recyclable polymers has become a research frontier for next-generation polymers. These polymers can recover the original monomers through controlled depolymerization at the end of their service life, thereby establishing a closed-loop life cycle and theoretically achieving unlimited chemical recycling. Current research mainly focuses on preparing closed-loop recyclable homopolymers by designing new monomers, while research on chemically recyclable TPEs is relatively limited. For example, our group reported the chemical recycling of TPEs based on polylactic acid-b-poly(δ-caprolactone)-b-polylactic acid, which can recover δ-caprolactone and ethyl acetate with high yield and high purity (Angewandte Chemie International Edition. 2022, 61(16), e202201407). Recently, a PδVL-b-Pα-based TPE was reported. R Preparation and chemical recovery of TPE from VL-b-PδVL: Successful recovery of δ-valerolactone (δVL) and α-alkyl-substituted δ-valerolactone (αVL). RVL)(Nature Communications 2024, 15(1), 7904). Despite the examples mentioned above, there is still an urgent need to further explore high-performance chemically recyclable TPEs, especially those TPE materials that can be mass-produced from low-cost, readily available monomers. β-Methyl-δ-valerolactone is a biorenewable six-membered ring lactone monomer that can be efficiently synthesized through glucose fermentation or from the intermediate fermentation product 3-methyl-1,5-pentanediol via dehydrogenation. The expected cost is less than $2 per kilogram, making it ideal for large-scale applications. Poly(β-methyl-δ-valerolactone) has a low glass transition temperature and exhibits a rubbery state at room temperature, making it suitable for use as the soft segment of thermoplastic elastomers. Hillmyer et al. reported the synthesis of polylactic acid-b-poly(β-methyl-δ-valerolactone)-b-polylactic acid triblock copolymers. The resulting triblock copolymers exhibited the properties of thermoplastic elastomers and possessed high mechanical strength and elongation at break (Proceedings of the National Academy of Sciences of the United States of America, 2014, 111(23), 8357). δ-valerolactone is an important lactone compound that can be biosynthesized through microbial fermentation. δ-valerolactone is generated through the biotransformation of substrates (such as valeric acid) by engineered bacteria or natural microorganisms, offering advantages of environmental friendliness and renewability. Due to its good reactivity and biodegradability, δ-valerolactone is widely used in polymer synthesis, especially for preparing biodegradable polyester materials such as poly(δ-valerolactone). Poly(δ-valerolactone) is a semi-crystalline polyester that can be used as the hard segment of thermoplastic elastomers. By selecting a suitable catalytic system, the sequential ring-opening polymerization of β-methyl-δ-valerolactone and δ-valerolactone can be achieved to prepare structurally well-defined poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) triblock copolymers or poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) x Star-shaped multi-arm block copolymers. By adjusting the composition and ratio of the block copolymers, thermoplastic elastomers with excellent properties can be obtained. By selecting a suitable catalyst and depolymerization temperature, the block copolymers can be depolymerized to recover the original monomers. The recovered monomers can be separated or directly used to prepare TPEs with properties comparable to the original TPEs, thus establishing a closed-loop life cycle. However, recent literature reports that attempts to prepare TPE materials using the sequential ring-opening polymerization of β-methyl-δ-valerolactone and δ-valerolactone have failed due to an inappropriate ratio of β-methyl-δ-valerolactone to δ-valerolactone, resulting in polymers lacking mechanical properties.

[0004] In view of this, the present invention provides a method for using a base or a base / urea binary catalytic system to achieve the sequential ring-opening polymerization of β-methyl-δ-valerolactone and δ-valerolactone, thereby preparing a well-defined poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) triblock copolymer or (poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone)) x A method for preparing star-shaped multi-arm block copolymers. The resulting poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) triblock copolymers or (poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone)) x Star-shaped multi-arm block copolymers possess the properties of thermoplastic elastomers. The method provided by this invention has the following advantages: 1) The raw materials used are non-toxic, harmless, and biomass-derived, and the resulting triblock copolymers or star-shaped multi-arm block copolymers can be completely degraded under natural conditions; 2) The prepared TPE can be completely depolymerized and recycled to obtain monomers under mild conditions, and the monomers can be repolymerized to obtain TPE with the same properties as the original material, achieving a closed-loop cycle of thermoplastic elastomers; 3) The catalytic system used has high catalytic activity, enabling the ring-opening polymerization of β-methyl-δ-valerolactone and δ-valerolactone under the same conditions, while achieving high conversion rates: β-methyl-δ-valerolactone conversion >85%, and δ-valerolactone conversion >95%; 4) The prepared poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) triblock copolymers or poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) x Star-shaped multi-arm block copolymers have good mechanical properties. Summary of the Invention

[0005] The purpose of this invention is to provide a novel bio-based, closed-loop recyclable thermoplastic elastomer and its preparation method.

[0006] The thermoplastic elastomer provided by this invention has an ABA-type triblock copolymer structure or (AB) x A star-shaped multi-arm block copolymer structure, wherein x ≥ 2; segment A has the structure shown in formula (I), and segment B has the structure shown in formula (II):

[0007]

[0008] Its characteristic is that 1 / 2 < n / m < 5 / 2, where m is a natural number greater than or equal to 300 and n is a natural number greater than or equal to 150.

[0009] The present invention also provides the above-mentioned ABA-type triblock copolymer or (AB) x A method for preparing star-shaped multi-arm block copolymers includes the following steps:

[0010] (1) Dissolve the initiator and catalyst in an organic solvent and stir at room temperature for 1 to 10 minutes;

[0011] (2) Add β-methyl-δ-valerolactone to the above mixed solution and react at -20 to 60°C for 0.1 to 8 hours;

[0012] (3) Add δ-valerolactone to the above reaction system and continue the reaction at -20 to 60°C for 0.1 to 8 hours. After purification, ABA-type triblock copolymer or (AB) is obtained. x Star-shaped multi-arm block copolymer.

[0013] In the above preparation method, the initiator is a diol or a polyol containing two or more hydroxyl groups. Specifically, the diol can be ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,4-butanediol, 1,4-cyclohexanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-benzenedimethanol, 1,3-benzenedimethanol, or 1,4-benzenedimethanol. The polyol containing two or more hydroxyl groups can be trimethylolpropane, pentaerythritol, or dipentaerythritol. When a diol is used as the initiator, an ABA-type triblock copolymer is prepared; when a polyol containing two or more hydroxyl groups is used as the initiator, (AB) is prepared. x Star-shaped multi-arm block copolymer.

[0014] In the above preparation method, the catalyst is an alkali or an alkali / urea binary catalyst;

[0015] The base may be an alkali metal, an alkali metal compound, or an organic base catalyst, specifically sodium, potassium, potassium hydride, sodium hydride, 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicycloundec-7-ene, N-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, hexa[tris(dimethylamine)phosphazene]tripolyphosphazene ({[(NMe2)3P=N]2P=N}3), phosphazene ligand P4-tert-butyl ([(NMe2)3P=N]3P=NtBu, tert-Bu-P4), phosphazene ligand P2-tert-butyl ( [(NMe2)3P=N](NMe2)2P=NtBu,tert-Bu-P2); the urea has one of the structures shown in formula (III) or formula (IV), where R1 and R2 are independently selected from alkyl or aryl groups, specifically methyl, ethyl, propyl, isopropyl, cyclohexyl, phenyl, 4-chlorophenyl, 4-methoxyphenyl, 4-trifluoromethylphenyl, 3,5-bis(trifluoromethyl)phenyl, 2,6-dimethylphenyl, 2,4-dimethoxyphenyl, 2,4,6-trimethoxyphenyl, and R3 can be ethylidene, propylidene, butylidene, hexylidene, or oxopentylene.

[0016]

[0017] According to an embodiment of the present invention, the urea has one of the following structures:

[0018]

[0019] The molar ratio of the catalyst to the initiator is 0.1 / 1 to 10 / 1; the molar ratio of the base to urea is 1 / 1 to 1 / 10.

[0020] In the above preparation method, the organic solvent in step (1) can be toluene, tetrahydrofuran, dichloromethane, acetonitrile, or N,N-dimethylformamide.

[0021] In the above preparation method, the molar concentration of β-methyl-δ-valerolactone in the system in step (2) is 4 to 9 mol / L; the molar ratio of β-methyl-δ-valerolactone to initiator is 200 / 1 to 3000 / 1.

[0022] In the above preparation method, the molar concentration of δ-valerolactone in the system is 0.1 to 11 mol / L; the molar ratio of β-methyl-δ-valerolactone to δ-valerolactone is 10 / 1 to 1 / 20.

[0023] The present invention also provides a recycling method for the above-mentioned thermoplastic elastomer: stannous octoate and the thermoplastic elastomer are mixed and heated at 100-200°C for 1-10 hours, and a mixture of β-methyl-δ-valerolactone and δ-valerolactone is recovered by vacuum distillation; the mixed monomers can be utilized by two methods: the first method is to separate the mixed monomers and then re-prepare the block polymer by sequential ring-opening polymerization; the second method is to directly utilize the mixed monomers for random copolymerization and then add δ-valerolactone to prepare the block copolymer. Attached Figure Description

[0024] Figure 1 The poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) prepared in Example 1 1 H NMR spectrum.

[0025] Figure 2 The poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) prepared in Example 1 13 C NMR spectrum.

[0026] Figure 3 The image shows the uniaxial tensile spectra of poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) prepared in Examples 1 to 3.

[0027] Figure 4 The GPC spectra of poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) prepared in Examples 3 to 5 are shown.

[0028] Figure 5 The image shows the uniaxial tensile spectra of poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) prepared in Examples 3 to 5.

[0029] Figure 6 The image shows the tensile cycling pattern of poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) prepared in Example 6.

[0030] Figure 7 The image shows the uniaxial tensile spectra of poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone) prepared in Examples 7 and 8.

[0031] Figure 8 The (poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone))3 three-arm block copolymer prepared in Example 9 1 H NMR spectrum.

[0032] Figure 9 The image shows the stretching cycle spectrum of the four-armed block copolymer ((poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone))4 prepared in Example 10. Detailed Implementation

[0033] The following embodiments illustrate the present invention in detail, but the present invention is not limited to these embodiments.

[0034] Unless otherwise specified, all materials and reagents used in the following implementation examples are commercially available.

[0035] Comparative Example 1

[0036] 0.05 mmol, 6.9 mg) of 1,4-benzyl diethanol, 0.05 mmol, 18.4 mg) of phosphazene ligand P2-tert-butyl catalyst, and 0.05 mmol, 29.2 mg) of 1,1'-(propylidene)bis(3-(3,5-bis(trifluoromethyl)phenyl)urea) were dissolved in 0.91 mL of tetrahydrofuran and stirred at room temperature for 10 min. 10 mmol, 1.09 mL of β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 20 min. Then, 10 mmol, 0.87 mL of δ-valerolactone was mixed with 1.13 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 10 min, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane and poured into 100 mL of methanol. Centrifugation was performed to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 200, n = 200, n / m = 1. GPC measurements showed a molecular weight of 36.9 kg / mol and a molecular weight distribution of 1.38. The relatively small m value indicates a low molecular weight and no mechanical properties.

[0037] Comparative Example 2

[0038] 0.05 mmol, 6.9 mg) of 1,4-benzyl diethanol, 0.05 mmol, 18.4 mg) of phosphazene ligand P2-tert-butyl catalyst, and 0.05 mmol, 29.2 mg) of 1,1'-(propylidene)bis(3-(3,5-bis(trifluoromethyl)phenyl)urea) were dissolved in 2.72 mL of tetrahydrofuran and stirred at room temperature for 10 min. 30 mmol, 3.28 mL of β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 20 min. Then, 10 mmol, 0.87 mL of δ-valerolactone was mixed with 1.13 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 10 min, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane and poured into 100 mL of methanol. Centrifugation was performed to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 600, n = 200, n / m = 1 / 3. GPC analysis revealed a number-average molecular weight of 88.2 kg / mol and a molecular weight distribution of 1.35. The ratio of added β-methyl-δ-valerolactone to δ-valerolactone was unsuitable, resulting in a low hard segment content (n / m = 1 / 2). The obtained polymer was a transparent, viscous state with no mechanical properties.

[0039] Example 1

[0040] 0.05 mmol, 6.9 mg) of 1,4-benzyldiethanol and 0.05 mmol, 6.9 mg) of 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst were dissolved in 1.36 mL of tetrahydrofuran and stirred at room temperature for 10 min. 15 mmol, 1.64 mL of β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 30 min. Then, 30 mmol, 2.6 mL of δ-valerolactone was mixed with 3.4 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 2 h, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 300, n = 600, n / m = 2. 1 H NMR spectrum as shown Figure 1 As shown, 13 The C NMR spectrum is as follows Figure 2 As shown. GPC measurements revealed a number-average molecular weight of 102.5 kg / mol and a molecular weight distribution of 1.15. Tensile mechanical property tests showed an elongation at break of 2007% and a tensile strength of approximately 48.2 MPa. The tensile spectra are shown below. Figure 3 As shown, after being stretched to 100% of its original length and cyclically repeated 10 times, its elastic recovery rate was measured to be approximately 96%, and the residual strain was approximately 3%.

[0041] Example 2

[0042] (0.05 mmol, 6.9 mg) 1,4-benzyldiethanol and (0.05 mmol, 6.9 mg) 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst were dissolved in 1.36 mL of tetrahydrofuran and stirred at room temperature for 10 min. (15 mmol, 1.64 mL) β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 30 min. Then, (22.5 mmol, 1.96 mL) δ-valerolactone was mixed with 2.54 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 1 h, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 300, n = 450, n / m = 3 / 2. GPC analysis revealed a number-average molecular weight of 92.4 kg / mol and a molecular weight distribution of 1.12. Tensile mechanical property testing showed the polymer had an elongation at break of 1986% and a tensile strength of approximately 39.4 MPa. The tensile spectra are shown below. Figure 3 As shown, after being stretched to 100% of its original length and cyclically repeated 10 times, its elastic recovery rate was measured to be approximately 96%, and the residual strain was approximately 4%.

[0043] Example 3

[0044] 0.05 mmol, 6.9 mg) of 1,4-benzyldiethanol and 0.05 mmol, 6.9 mg) of 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst were dissolved in 1.36 mL of tetrahydrofuran and stirred at room temperature for 10 min. 15 mmol, 1.64 mL of β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 30 min. Then, 15 mmol, 1.3 mL of δ-valerolactone was mixed with 1.7 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 1 h, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 300, n = 300, n / m = 1. GPC analysis revealed a number-average molecular weight of 85.0 kg / mol and a molecular weight distribution of 1.10. The GPC spectrum is shown below. Figure 4 As shown. The tensile mechanical property test showed that the polymer's elongation at break was 1667%, and its tensile strength was approximately 10.8 MPa. The tensile spectrum is shown below. Figure 3 As shown, after being stretched to 100% of its original length and cyclically repeated 10 times, its elastic recovery rate was measured to be approximately 92%, and the residual strain was approximately 6%.

[0045] Example 4

[0046] 0.05 mmol, 6.9 mg) of 1,4-benzyldiethanol and 0.05 mmol, 6.9 mg) of 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst were dissolved in 1.81 mL of tetrahydrofuran and stirred at room temperature for 10 min. 20 mmol, 2.19 mL of β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 45 min. Then, 20 mmol, 1.74 mL of δ-valerolactone was mixed with 2.26 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 1.5 h, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 400, n = 400, n / m = 1. GPC analysis revealed a number-average molecular weight of 103.3 kg / mol and a molecular weight distribution of 1.11. The GPC spectrum is shown below. Figure 4 As shown. The tensile mechanical property test showed that the polymer's elongation at break was 2044%, and its tensile strength was approximately 15.4 MPa. The tensile spectrum is shown below. Figure 5 As shown, after being stretched to 100% of its original length and cyclically repeated 10 times, its elastic recovery rate was measured to be approximately 94%, and the residual strain was approximately 5%.

[0047] Example 5

[0048] (0.05 mmol, 6.9 mg) 1,4-benzyldiethanol and (0.05 mmol, 6.9 mg) 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst were dissolved in 2.27 mL of tetrahydrofuran and stirred at room temperature for 10 min. (25 mmol, 2.73 mL) β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 1 h. Then, (25 mmol, 2.18 mL) δ-valerolactone was mixed with 2.82 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 2 h, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 500, n = 500, n / m = 1. GPC analysis revealed a number-average molecular weight of 118.1 kg / mol and a molecular weight distribution of 1.10. The GPC spectrum is shown below. Figure 4 As shown. The tensile mechanical property test showed that the polymer's elongation at break was 2136%, and its tensile strength was approximately 23.7 MPa. The tensile spectrum is shown below. Figure 5As shown, after being stretched to 100% of its original length and cyclically repeated 10 times, its elastic recovery rate was measured to be approximately 95%, and the residual strain was approximately 4%.

[0049] Example 6

[0050] Ethylene glycol (0.05 mmol, 2.8 μL), phosphazene ligand P2-tert-butyl catalyst (0.05 mmol, 34.8 mg), and 1-(3,5-bis(trifluoromethyl)phenyl)-3-phenylurea were dissolved in 0.86 mL of tetrahydrofuran and stirred at room temperature for 10 min. Then, β-methyl-δ-valerolactone (15 mmol, 1.64 mL) was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 20 min. Next, δ-valerolactone (15 mmol, 1.3 mL) was mixed with 1.2 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 10 min, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 300, n = 300, n / m = 1. GPC analysis revealed a number-average molecular weight of 52.9 kg / mol and a molecular weight distribution of 1.75. Tensile mechanical property testing showed the polymer had an elongation at break of 1208% and a tensile strength of approximately 5.1 MPa. After stretching to 100% of its original length and cycling 10 times, the elastic recovery rate was approximately 84%, and the residual strain was approximately 10%. The tensile cycle spectrum is shown below. Figure 6 As shown.

[0051] Example 7

[0052] 1,2-Propanediol (0.05 mmol, 3.7 μL), phosphazene ligand P4-tert-butyl catalyst (0.05 mmol, 31.7 mg), and 1,1'-(oxobis(ethylene))bis(3-(3,5-di(trifluoromethyl)phenyl)urea) were dissolved in 1.81 mL of tetrahydrofuran and stirred at room temperature for 20 min. Then, 20 mmol, 2.19 mL of β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 30 min. Next, 20 mmol, 1.73 mL of δ-valerolactone was mixed with 2.27 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 10 min, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 400, n = 400, n / m = 1. GPC analysis revealed a number-average molecular weight of 66.8 kg / mol and a molecular weight distribution of 1.78. Tensile mechanical property testing showed an elongation at break of 1134% and a tensile strength of approximately 14.7 MPa. The tensile spectra are shown below. Figure 7 As shown, after being stretched to 100% of its original length and cyclically repeated 10 times, its elastic recovery rate was measured to be approximately 87%, and the residual strain was approximately 9%.

[0053] Example 8

[0054] (0.05 mmol, 3.7 μL) 1,4-Butanediol, (0.05 mmol, 59.9 mg) hexa[tris(dimethylamine)phosphazene]tripolyphosphazene, and (0.05 mmol, 22.4 mg) 1,1'-(propane-1,3-diyl)bis(3-(3,5-bis(trifluoromethyl)phenyl)urea) were dissolved in 2.27 mL of tetrahydrofuran and stirred at room temperature for 30 min. (25 mmol, 2.73 mL) β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 40 min. Then, (25 mmol, 2.17 mL) δ-valerolactone was reacted with 2.83 mL of tetrahydrofuran. The mixture was added to the above system and reacted at 25°C under nitrogen protection for 10 min. The reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane and poured into 100 mL of methanol. The precipitate was separated by centrifugation to obtain the polymer. NMR characterization showed the polymer to be a triblock copolymer, namely poly(δ-valerolactone)-b-poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone), m = 500, n = 500, n / m = 1. GPC analysis showed a number-average molecular weight of 80.5 kg / mol and a molecular weight distribution of 1.81. Tensile mechanical property testing showed the polymer had an elongation at break of 1145% and a tensile strength of approximately 21 MPa. The tensile spectra are shown below. Figure 7 As shown, after being stretched to 100% of its original length and cyclically repeated 10 times, its elastic recovery rate was measured to be approximately 92%, and the residual strain was approximately 6%.

[0055] Example 9

[0056] (0.05 mmol, 6.8 mg) trimethylolpropane and (0.05 mmol, 6.9 mg) 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst were dissolved in 2.72 mL of tetrahydrofuran and stirred at room temperature for 10 min. (30 mmol, 3.28 mL) β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 30 min. Then, (30 mmol, 2.6 mL) δ-valerolactone was mixed with 3.4 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 1 h, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a three-armed star-shaped block copolymer, namely (poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone))3, m = 600, n = 600, n / m = 1. 1 H NMR spectrum as shown Figure 8As shown. GPC measured the number-average molecular weight to be 126.9 kg / mol, with a molecular weight distribution of 1.21. Tensile mechanical property tests showed the polymer's elongation at break to be 1988%, and its tensile strength to be approximately 26.8 MPa. After being stretched to 100% of its original length and cyclically repeated 10 times, its elastic recovery rate was measured to be approximately 92%, and the residual strain to be approximately 4%.

[0057] Example 10

[0058] (0.05 mmol, 6.8 mg) pentaerythritol and (0.05 mmol, 6.9 mg) 1,5,7-triazabicyclo[4.4.0]dec-5-ene catalyst were dissolved in 2.72 mL of tetrahydrofuran and stirred at room temperature for 10 min. (30 mmol, 3.28 mL) β-methyl-δ-valerolactone was added to the reaction tube, and the reaction was carried out at 25 °C under nitrogen protection for 30 min. Then, (30 mmol, 2.6 mL) δ-valerolactone was mixed with 3.4 mL of tetrahydrofuran and added to the above system. The reaction was carried out at 25 °C under nitrogen protection for 1 h, and the reaction was terminated by adding 1 mL of acetic acid. The reaction mixture was dissolved in 10 mL of dichloromethane, poured into 100 mL of methanol, and centrifuged to separate the precipitate, yielding the polymer. NMR characterization showed the polymer to be a four-armed star-shaped block copolymer, namely (poly(β-methyl-δ-valerolactone)-b-poly(δ-valerolactone))4, m = 600, n = 600, n / m = 1. GPC analysis showed a number-average molecular weight of 130.1 kg / mol and a molecular weight distribution of 1.20. Tensile mechanical property testing revealed an elongation at break of 1763% and a tensile strength of approximately 23.5 MPa. After stretching to 100% of its original length and cycling 10 times, the elastic recovery rate was approximately 93%, and the residual strain was approximately 5%. The tensile cycle spectrum is shown below. Figure 9 As shown.

Claims

1. A bio-based, closed-loop recyclable thermoplastic elastomer, characterized in that, It has an ABA-type triblock copolymer structure or (AB) x A star-shaped multi-arm block copolymer structure, wherein x ≥ 2; segment A has the structure shown in formula (I), and segment B has the structure shown in formula (II): Where 1 / 2 < n / m < 5 / 2, m is a natural number greater than or equal to 300, and n is a natural number greater than or equal to 150.

2. The method for preparing the thermoplastic elastomer according to claim 1, comprising the following steps: (1) Dissolve the initiator and catalyst in an organic solvent and stir at room temperature for 1 to 10 minutes; (2) Add β-methyl-δ-valerolactone to the above mixed solution and react at -20 to 60°C for 0.1 to 8 hours; (3) Add δ-valerol to the above reaction system and continue the reaction at -20 to 60°C for 0.1 to 8 hours. After purification, a thermoplastic elastomer is obtained. It is characterized in that The catalyst is an alkali or an alkali / urea binary catalyst.

3. The method according to claim 2, characterized in that: The initiator is a diol or a polyol containing two or more hydroxyl groups; the diol is selected from ethylene glycol, 1,2-propanediol, 1,2-butanediol, 1,4-butanediol, 1,4-cyclohexanediol, 2-butyl-2-ethyl-1,3-propanediol, 1,2-benzenedimethanol, 1,3-benzenedimethanol, and 1,4-benzenedimethanol; the polyol containing two or more hydroxyl groups is selected from trimethylolpropane, pentaerythritol, and dipentaerythritol.

4. The method according to claim 2, characterized in that: The base is an alkali metal, an alkali metal compound, or an organic base; the alkali metal is selected from sodium or potassium; the alkali metal compound is selected from potassium hydride or sodium hydride; the organic base is selected from 1,5,7-triazabicyclo[4.4.0]dec-5-ene, 1,8-diazabicycloundec-7-ene, N-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, hexa[tris(dimethylamine)phosphazene]tripolyphosphazene ({[(NMe2)3P=N]2P=N}3), phosphazene ligand P4-tert-butyl ([(NMe2)3P=N]3P=NtBu, tert-Bu-P4), phosphazene ligand P2-tert-butyl ([(NMe2)3P=N](NMe2)2P=NtBu, tert-Bu-P2).

5. The method according to claim 2, characterized in that, The urea has one of the structures shown in formula (III) or formula (IV): R1 and R2 are independently selected from methyl, ethyl, propyl, isopropyl, cyclohexyl, phenyl, 4-chlorophenyl, 4-methoxyphenyl, 4-trifluoromethylphenyl, 3,5-bis(trifluoromethyl)phenyl, 2,6-dimethylphenyl, 2,4-dimethoxyphenyl, and 2,4,6-trimethoxyphenyl; R3 is one of ethylidene, propylidene, butylidene, hexylidene, and oxopentylene.

6. The method according to claim 2, characterized in that, The urea has one of the following structures:

7. The method according to claim 2, characterized in that: The molar ratio of the catalyst to the initiator is 0.1 / 1 to 10 / 1; the molar ratio of the base to urea is 1 / 1 to 1 / 10; the organic solvent in step (1) is toluene, tetrahydrofuran, dichloromethane, acetonitrile, or N,N-dimethylformamide; the molar concentration of β-methyl-δ-valerolactone in the system in step (2) is 4 to 9 mol / L; the molar ratio of β-methyl-δ-valerolactone to the initiator is 200 / 1 to 3000 / 1; the molar concentration of δ-valerolactone in the system in step (3) is 0.1 to 11 mol / L; the molar ratio of β-methyl-δ-valerolactone to δ-valerolactone is 10 / 1 to 1 / 20.

8. The method for recycling thermoplastic elastomers according to claim 1, characterized in that: Stannous octoate and a thermoplastic elastomer are mixed and heated at 100–200 °C for 1–10 h. The mixture of β-methyl-δ-valerolactone and δ-valerolactone is recovered by vacuum distillation. This mixed monomer can be utilized in two ways: the first method is to separate the mixed monomer and then re-prepare the thermoplastic elastomer by sequential ring-opening polymerization; the second method is to directly use the mixed monomer for random copolymerization and then add δ-valerolactone to prepare the thermoplastic elastomer.

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