SEBS (styrene-ethylene-butylene-styrene) containing dynamic crosslinking bonds and preparation method thereof

Abstract

The invention provides SEBS (Styrene-Ethylene-Butylene-Styrene) containing dynamic crosslinking bonds and a preparation method thereof, and belongs to the technical field of high polymer materials. A polystyrene block in the SEBS containing the dynamic cross-linking bonds is bonded with polystyrene containing the dynamic cross-linking bonds at two ends; the preparation method comprises the following steps: firstly, carrying out Diels-Alder reaction on polystyrene of which the two ends contain furan groups and a maleimide compound of which the tail end contains hydroxyl to prepare polystyrene of which the two ends contain dynamic cross-linked bonds; secondly, introducing a chloromethyl group on a benzene ring of the SEBS polystyrene block; and finally, carrying out Williamson etherification reaction on the polystyrene containing the dynamic cross-linking bonds at the two ends and SEBS with chloromethyl groups on a benzene ring to prepare the SEBS containing the dynamic cross-linking bonds. The SEBS containing the dynamic crosslinking bond prepared by the invention has high tensile strength, and the processability of the SEBS material is maintained by reversible decrosslinking of the DA bond at high temperature. The SEBS containing the dynamic cross-linked bonds has a good application prospect in the fields of aerospace, medical instruments and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and relates to a SEBS containing dynamic crosslinking bonds and a preparation method thereof. The polystyrene block in the SEBS is bonded to the polystyrene containing dynamic crosslinking bonds at both ends. The dynamic crosslinking bonds are DA bonds formed by the Diels-Alder reaction of furan compounds and maleimide compounds. Background Art

[0002] SEBS is a new type of thermoplastic elastomer obtained by hydrogenating SBS (styrene-butadiene-styrene). Due to its excellent aging resistance, thermal stability, electrical insulation, and the advantage of being able to be processed without vulcanization, it is widely used in products such as wire and cable sheaths, injection syringes, runways, adhesives, etc., covering many fields such as aerospace, medical devices, civil use, and military. At the same time, it also has the dual characteristics of plastics and rubbers because SEBS is formed by the block polymerization of highly ordered polystyrene (PS) hard chain segments and disordered ethylene-butene (EB) soft chain segments. The PS segments, as the dispersed phase, are dispersed in the continuous phase formed by the EB segments, constituting a physical crosslinking network. When SEBS is heated and the temperature exceeds the glass transition temperature of polystyrene, the polystyrene phase softens and flows under shear, enabling processing. When the molded product cools, the polystyrene phase region hardens and has strength, and aggregates again as the dispersed phase acting as crosslinking points. However, compared with traditional thermosetting vulcanized rubber, the lack of a crosslinking structure causes problems such as low strength and poor resilience when SEBS is applied to scenarios with higher mechanical property requirements. Therefore, in practical applications, the SEBS system needs to be reinforced before use.

[0003] The literature (Journal of Applied Chemistry, 2023, 40(6): 833-844) used low number-average relative molecular mass homopolymer polystyrene and SEBS as raw materials to prepare SEBS materials with ionic bond crosslinking through chloromethylation, quaternization, and alkalization steps. Its mechanical properties and dimensional stability are significantly better than those of the original SEBS material. However, the above SEBS material contains crosslinkable ionic bonds, which do not have dynamic reversibility, and the bond energy of the ionic bonds is lower than that of chemical covalent bonds, resulting in limited improvement in the mechanical properties of the modified SEBS material.

[0004] Dynamic covalent chemical bonds provide a very effective method for preparing recyclable polymers. By introducing groups or structural units capable of forming dynamic covalent bonds in the molecular design of elastomers, dynamic elastomers based on covalent interactions can be obtained. The Diels-Alder reaction is one of the methods for generating dynamic covalent bonds, and the furan-maleimide system is more commonly used in polymer materials. The Diels-Alder reaction between furan and maleimide is a classic [4+2] cycloaddition reaction, which has the characteristics of high selectivity, high efficiency, mild reaction conditions, no need for a catalyst, and thermal reversibility. At the same time, the Diels-Alder reaction also has a rich stereochemical structure, with regio-selectivity, stereo-selectivity, and stereospecificity. It is very suitable for constructing reversible networks in thermoplastic polymers, and the reverse reaction of the Diels-Alder reaction occurs at about 120 °C, which is lower than the processing temperature of most polymers and will not affect the processing conditions of the polymers.

[0005] Patent CN116836432A discloses a method for preparing a high-performance recyclable styrenic elastomer film with a dynamic crosslinked network, which includes the following steps: (1) synthesis of a furyl styrenic elastomer; (2) uniformly mixing and dissolving the furyl styrenic elastomer synthesized in step (1), a maleimide curing agent, and a solvent in a container, and using the solution casting method to spread the mixture on a glass plate and place it in an oven at a temperature of 50-100 °C for 12-30 h to obtain a recyclable styrenic elastomer film with a dynamic crosslinked network. However, in the preparation of the above styrenic elastomer film with a dynamic crosslinked network, the furan group is on the unsaturated double bond of the soft segment in the styrenic elastomer, and the maleimide curing agent is a small molecule compound. The dynamic crosslinked bond formed by furan and maleimide crosslinks the soft segment in the styrenic elastomer, which weakens its elasticity to a certain extent. In addition, the maleimide curing agent is prone to small molecule migration and loss during repeated use, thus affecting its long-term use stability.

[0006] Patent CN201810357932 discloses a method for preparing a crosslinked elastomer using dynamic covalent bonds. First, an unsaturated elastomer is modified to contain hydroxyl functional groups, and then the hydroxyl groups in the unsaturated elastomer containing hydroxyl functional groups are modified to acetoacetyl groups. The acetoacetyl groups react with polyisocyanate to form dynamic amide bonds, thereby preparing a dynamically covalently crosslinked elastomer. The modification method is simple and efficient, without the need for a catalyst and without by-products. The prepared elastomer has excellent mechanical properties, good solvent resistance, and reprocessability. However, in the above elastomer material with a dynamic crosslinked network, the dynamic amide bond is bonded to the unsaturated double bond of the elastic segment, thereby achieving the crosslinking of the soft segment, which weakens its elasticity to a certain extent. The elastic segment in the elastomer material contains a large number of unsaturated double bonds, and the aging resistance of the material is worse than that of the elastomer material without unsaturated double bonds (such as SEBS material), affecting its use in the fields of aerospace, medical devices, etc.

[0007] In summary, a new crosslinking method can selectively construct a dynamic crosslinked network in the hard segment region while maintaining the plasticity of the elastomer. This dynamic crosslinking needs to act precisely between polymer molecular chains to ensure excellent compatibility, stability, and reversible performance. Summary of the Invention

[0008] Aiming at the problems existing in the prior art, the present invention provides an SEBS containing dynamic crosslinking bonds and a preparation method thereof, which can overcome the deficiencies of the existing SEBS material without reversible dynamic crosslinking bonds and low tensile strength. The present invention prepares an SEBS material containing dynamic crosslinking bonds through living anionic polymerization technology, end-capping reaction, Diels-Alder reaction, and Williamson etherification reaction. The polystyrene block in the SEBS is bonded to the polystyrene containing dynamic crosslinking bonds at both ends. The dynamic crosslinking bond (hereinafter referred to as the DA bond for short) is a DA bond formed by the reaction of a furan compound and a maleimide compound through the Diels-Alder reaction. The prepared SEBS containing dynamic crosslinking bonds has a high tensile strength, and the DA bond is reversibly de-crosslinked at high temperature to maintain the processability of the SEBS material. The SEBS containing dynamic crosslinking bonds has good application prospects in the fields of aerospace, medical devices, etc.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] The present invention provides a SEBS containing dynamic crosslinking bonds. The molecular structure of the SEBS containing dynamic crosslinking bonds is shown in (a). The SEBS is composed of a hydrogenated poly(ethylene-butene) soft segment, a polystyrene hard segment, and a polystyrene phase with dynamic crosslinking bonds at both ends. First, a chloromethyl group is introduced onto the benzene ring of the polystyrene block of SEBS through a chloromethylation reaction. Among them, the polystyrene with dynamic crosslinking bonds at both ends is synthesized by using an active anionic polymerization method to synthesize a dilithium initiator and initiate the polymerization of styrene, and then a capping agent is added to prepare a polystyrene with furan groups at both ends. Subsequently, a Diels-Alder reaction occurs with a maleimide compound containing a hydroxyl group at the end to obtain a polystyrene with DA bonds and hydroxyl groups at both ends. Finally, the polystyrene with DA bonds and hydroxyl groups at both ends and the SEBS with a chloromethyl group on the benzene ring are prepared into a SEBS containing dynamic crosslinking bonds through a Williamson etherification reaction.

[0011]

[0012] Wherein: x is an integer from 30 to 300; y is an integer from 10 to 220; m is an integer from 600 to 1200; n is an integer from 80 to 240; z is an integer from 15 to 80; R1 is -O-, -O-CH2-CH2-; R2 is -CH2-,

[0013] Furthermore, in the SEBS containing dynamic crosslinking bonds, based on 100% of the total mass, the mass percentage content of DA bonds is 1% - 25%, preferably 5% - 15%.

[0014] The present invention provides a preparation method of a SEBS containing dynamic crosslinking bonds, including the following steps:

[0015] Step 1, at room temperature, a polar activator and styrene are added to a reactor in a non-polar hydrocarbon solvent, stirring is turned on, and a dilithium initiator is added to start the polymerization of styrene. The dosage of the dilithium initiator is determined according to the number-average relative molecular mass of polystyrene. After the polymerization reaction is completed, a polystyrene solution with lithium (Li) at both active ends is obtained.

[0016] Step 2, the polystyrene solution with both active ends is capped with a capping agent and washed with ethanol to remove the unreacted capping agent, obtaining a polystyrene with furan groups at both ends; the capping agent is a compound containing furan groups.

[0017] Step 3, the polystyrene with furan groups at both ends is dissolved in a solvent and subjected to a Diels-Alder reaction with a compound containing a maleimide group to obtain a polystyrene with DA bonds and hydroxyl groups at both ends.

[0018] Step 4: Dissolve polystyrene with DA bonds and hydroxyl groups at both ends and SEBS with a chloromethyl group on the benzene ring in a polar solvent, carry out Williamson etherification reaction, and finally obtain SEBS containing dynamic cross-linking bonds.

[0019] Furthermore, the non-polar hydrocarbon solvents in Step 1 are selected from 1-3 combinations of pentane, hexane, heptane, octane, cyclohexane, benzene, toluene, ethylbenzene, and xylene; the polar activators are selected from 1-3 combinations of diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, triethylamine, N,N,N',N'-tetramethylethylenediamine, dipiperidinoethane, ethyl tetrahydrofurfuryl ether, and 2,2-bis(tetrahydrofuran)propane; the dilithium initiator is selected from one or more of 1,4-dilithio-2,3-dimethylbutane, 1,4-dilithiobutane, 1,4-dilithiohexane, 1,4-dilithiobenzene, or 2,6-dilithio-3-methylpyridine; the polymerization reaction temperature is controlled between 20-60 °C; the total polymerization reaction time is controlled between 10-40 minutes.

[0020] Furthermore, in Step 1, the molar ratio of the polar activator to the dilithium initiator is 1:1, and the addition amount of the dilithium initiator is jointly determined by the addition amount of styrene and the relative molecular mass of polystyrene.

[0021] Furthermore, the end-capping agents in Step 2 are selected from 1-3 combinations of 2-acetylfuran, 3-furaldehyde, 2-((oxiran-2-ylmethoxy)methyl)furan, 2-chloromethylfuran, and 2-furanacrylic acid; the molar ratio of the end-capping agent to Li in the double-active-end polystyrene is between 2 / 1-10 / 1; the end-capping reaction temperature is controlled between 20-100 °C; the total reaction time is controlled between 30-300 minutes.

[0022] Furthermore, the solvents in Step 3 are selected from 1-3 combinations of dichloromethane, chloroform, acetonitrile, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, benzene, toluene, and xylene; the compounds containing maleimide groups are selected from 1-3 combinations of N-hydroxymaleimide, 4-maleimidophenol, and N-(2-hydroxyethyl)maleimide; the molar ratio of the maleimide group to the furan group in the polystyrene with furan groups at both ends is between 2 / 1-6 / 1; the reaction temperature is controlled between 20-90 °C; the total reaction time is controlled between 60-900 minutes.

[0023] Furthermore, the polar solvent in step 4 is selected from one to three combinations of acetonitrile, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, and 1,4-dioxane; the mass percentage of the chloromethyl group in the SEBS with a chloromethyl group on the benzene ring is 5% - 25%; the reaction temperature is controlled between 50 - 90 °C; the total reaction time is controlled between 30 - 480 minutes.

[0024] Advantages of the present invention:

[0025] Through living anionic polymerization technology, end-capping reaction, Diels-Alder reaction, and Williamson etherification reaction, the present invention prepares an SEBS material containing dynamic crosslinking bonds. The polystyrene block in SEBS is bonded to the polystyrene with dynamic crosslinking bonds at both ends. The dynamic crosslinking bond is a DA bond formed by the Diels-Alder reaction between a furan compound and a maleimide compound. The present invention can overcome the deficiencies of existing SEBS materials that do not contain reversible dynamic crosslinking bonds and have low tensile strength. The prepared SEBS containing dynamic crosslinking bonds has high tensile strength, and the DA bond can reversibly de-crosslink at high temperature to maintain the processability of the SEBS material. This SEBS containing dynamic crosslinking bonds has good application prospects in the fields of aerospace, medical devices, etc. Description of the drawings

[0026] Figure 1 1H-NMR spectrum of polystyrene with furan groups at both ends in Example 1 1 ;

[0027] Figure 2 1H-NMR spectrum of SEBS containing dynamic crosslinking bonds in Example 1 (in the figure, SEBS containing dynamic crosslinking bonds is simply referred to as DASEBS) 1 ;

[0028] Figure 3 FT-IR spectra of reactants and products in step 4 of Example 1 (in the figure, polystyrene with DA bonds and hydroxyl groups at both ends is simply referred to as HPS, and SEBS with a chloromethyl group on the benzene ring is simply referred to as CMSEBS)

[0029] Figure 4 Stress-strain curves of SEBS, SEBS containing dynamic crosslinking bonds in Example 1, and SEBS containing dynamic crosslinking bonds after the first processing in Performance Test 1 of Example 1 (simply referred to as Recycled DASEBS in the figure) Specific embodiments

[0030] In the experimental methods of the following examples, unless otherwise specified, they are all conventional methods, carried out according to the techniques or conditions described in the literature in this field or according to the product specifications. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0031] In the present invention, a nuclear magnetic resonance spectrometer ( 1 1H-NMR) and Fourier transform infrared spectroscopy (FT-IR) were used to analyze and test the types and contents of functional groups of polymers; a gel permeation chromatograph (GPC) was used to test the number-average relative molecular mass and molecular weight distribution of polymers; a universal material testing machine was used to test the mechanical properties of polymers.

[0032] Example 1

[0033] 1) 300 g of cyclohexane and 30 g of styrene were added to a 1-L three-necked glass flask. Stirring was started, and 10 mmol of 2,6-dilithium methylpyridine initiator and 10 mmol of N,N,N',N'-tetramethylethylenediamine were added to initiate the polymerization of styrene. The reaction was carried out at 25 °C for 0.5 h to obtain a polystyrene solution with double active ends. A small amount of the polymer was taken for GPC testing, and the number-average relative molecular mass was 2,670, and the molecular weight distribution index (PDI) was 1.09.

[0034] 2) 30.83 g of 2-((oxiran-2-ylmethoxy)methyl)furan (FGE) was added to the polystyrene solution with double active ends for end-capping reaction. After reacting at 65 °C for 2 h, it was washed 3 times with ethanol to remove the unreacted end-capping agent, and polystyrene containing furan groups at both ends was obtained. A small amount of the polymer was taken for 1 1H-NMR testing, and the results are shown in Figure 1 , and the end-capping efficiency was calculated to be 99%. After GPC testing, the number-average relative molecular mass of polystyrene containing furan groups at both ends was 2,985, and the molecular weight distribution index (PDI) was 1.10.

[0035] 3) Polystyrene containing furan groups at both ends (10 g, 3.33 mmol) was dissolved in 200 mL of N,N-dimethylformamide and subjected to a Diels-Alder reaction with 4-maleimidophenol (HPM) (1.89 g, 10.0 mmol). The reaction was carried out at 80 °C for 3 h to obtain polystyrene with DA bonds and hydroxyl groups at both ends. After 1 1H-NMR and FT-IR testing, the mass percentage content of DA bonds in polystyrene with DA bonds and hydroxyl groups at both ends was 11.75%.

[0036] 4) Dissolve polystyrene with DA bonds and hydroxyl groups at both ends (8.85 g, 2.95 mmol) and 1 g of SEBS with chloromethyl groups on the benzene ring (the mass percentage of chloromethyl groups is 10%) in 300 mL of N,N-dimethylformamide, and carry out Williamson etherification reaction. React at 60 °C for 5 hours. Finally, obtain SEBS containing dynamic crosslinking bonds. The mass percentage of DA bonds in the SEBS containing dynamic crosslinking bonds is 9.65%. Conduct NMR test on it, and the results are shown in Figure 2 ; Conduct FT-IR tests on the reactants and products, and the results are shown in Figure 3 , By comparing the infrared spectra of polystyrene with DA bonds and hydroxyl groups at both ends and SEBS with chloromethyl groups on the benzene ring, it can be seen that the strong stretching vibration absorption peak of -OH at 3482 cm -1 and the characteristic peak of C-Cl at 1265 cm -1 of the SEBS containing dynamic crosslinking bonds disappear, indicating that the hydroxyl group and chloromethyl group participate in the reaction and are consumed. In addition, the stretching vibration absorption peaks of the ether bond (aliphatic chain) C-O-C (benzene ring) appear at 1086 cm -1 and 1016 cm -1 , proving the formation of the ether bond; Make the SEBS containing dynamic crosslinking bonds into tensile splines, and use a universal material testing machine to conduct tensile tests on the SEBS containing dynamic crosslinking bonds. The results are shown in Table 1.

[0037] Example 2

[0038] 1) Add 300 g of benzene and 30 g of styrene into a 1-liter three-necked glass flask. Turn on the stirrer, add 6 mmol of 1,4-dilithium-2,3-dimethylbutane initiator and 6 mmol of diethyl ether, and start the polymerization of styrene. React at 25 °C for 30 min to obtain a polystyrene solution with double active ends; Take a small amount of the polymer for GPC test. The number-average relative molecular mass is 5130, and the molecular weight distribution index (PDI) is 1.08.

[0039] 2) Add 2.31 g of 2-((oxiran-2-ylmethoxy)methyl)furan (FGE) to the polystyrene solution with double active ends, and carry out end-capping reaction. After reacting at 65 °C for 2 hours, wash it 3 times with ethanol to remove the unreacted end-capping agent, and obtain polystyrene with furan groups at both ends; Through GPC test, the number-average relative molecular mass of the polystyrene with furan groups at both ends is 5440, and the molecular weight distribution index (PDI) is 1.09.

[0040] 3) Dissolve polystyrene with furan groups at both ends (10 g, 1.84 mmol) in 200 mL of dichloromethane, and carry out the Diels-Alder reaction with 4-maleimidophenyl (HPM) (1.34 g, 7.0 mmol) at 20 °C for 15 hours to obtain polystyrene with DA bonds and hydroxyl groups at both ends; after 1 H-NMR and FT-IR tests, the mass percentage content of DA bonds in polystyrene with DA bonds and hydroxyl groups at both ends is 3.47%.

[0041] 4) Dissolve polystyrene with DA bonds and hydroxyl groups at both ends (5.95 g, 1.00 mmol) and 1 g of SEBS with a chloromethyl group on the benzene ring (the mass percentage content of the chloromethyl group is 5%) in 300 mL of N,N-dimethylformamide, and carry out the Williamson etherification reaction at 90 °C for 0.5 hours to finally obtain SEBS with dynamic crosslinking bonds. The mass percentage content of DA bonds in SEBS with dynamic crosslinking bonds is 1.05%. Prepare a tensile spline from SEBS with dynamic crosslinking bonds, and use a universal material testing machine to carry out tensile tests on SEBS with dynamic crosslinking bonds. The results are shown in Table 1.

[0042] Example 3

[0043] 1) Add 300 g of benzene and 30 g of styrene to a 1-liter three-necked glass flask, turn on the stirrer, add 3.75 mmol of 1,4-dilithium-2,3-dimethylbutane, and start the polymerization of styrene. React at 20 °C for 40 min to obtain a polystyrene solution with two active ends; take a small amount of the polymer for GPC testing, the number-average relative molecular mass is 7970, and the molecular weight distribution index (PDI) is 1.07.

[0044] 2) Add 2.31 g of 2-((oxiran-2-ylmethoxy)methyl)furan (FGE) to the polystyrene solution with two active ends for end-capping reaction. After reacting at 65 °C for 2 hours, wash it 3 times with ethanol to remove the unreacted end-capping agent to obtain polystyrene with furan groups at both ends; after GPC testing, the number-average relative molecular mass of polystyrene with furan groups at both ends is 8290, and the molecular weight distribution index (PDI) is 1.08.

[0045] 3) Dissolve polystyrene with furan groups at both ends (10 g, 1.12 mmol) in 200 mL of dichloromethane, and carry out the Diels-Alder reaction with 4-maleimidophenyl (HPM) (1.34 g, 7 mmol) at 30 °C for 15 hours to obtain polystyrene with DA bonds and hydroxyl groups at both ends; after 1 H-NMR and FT-IR tests, the mass percentage content of DA bonds in polystyrene with DA bonds and hydroxyl groups at both ends is 5.37%.

[0046] 4) Dissolve polystyrene with DA bonds and hydroxyl groups at both ends (8.68 g, 1.01 mmol) and 1 g of SEBS containing chloromethyl groups on the benzene ring of the polystyrene block (mass percentage is 10%) in 300 mL of N,N-dimethylformamide, and carry out Williamson etherification reaction at 60 °C for 5 hours. Finally, SEBS containing dynamic crosslinking bonds is obtained. The mass percentage of DA bonds in the SEBS containing dynamic crosslinking bonds is 3.59%. Prepare a tensile spline from the SEBS containing dynamic crosslinking bonds, and use a universal material testing machine to conduct tensile tests on the SEBS containing dynamic crosslinking bonds. The results are shown in Table 1.

[0047] Example 4

[0048] 1) Add 300 g of toluene and 30 g of styrene into a 1-liter three-necked glass flask. Turn on the stirring, add 6 mmol of 1,4-dilithiobutane initiator and 6 mmol of tetrahydrofuran, and start the polymerization of styrene. React at 60 °C for 10 min to obtain a polystyrene solution with double active ends; take a small amount of the polymer for GPC testing. The number-average relative molecular mass is 4730, and the molecular weight distribution index (PDI) is 1.11.

[0049] 2) Add 1.85 g of 2-((oxiran-2-ylmethoxy)methyl)furan (FGE) into the polystyrene solution with double active ends for end-capping reaction. After reacting at 100 °C for 0.5 hour, wash it with ethanol 3 times to remove the unreacted end-capping agent, and obtain polystyrene with furan groups at both ends; through GPC testing, the number-average relative molecular mass of the polystyrene with furan groups at both ends is 5020, and the molecular weight distribution index (PDI) is 1.13.

[0050] 3) Dissolve polystyrene with furan groups at both ends (10 g, 1.92 mmol) in 200 mL of tetrahydrofuran, and carry out Diels-Alder reaction with 4-maleimidophenol (4.35 g, 23.0 mmol) at 50 °C for 6 hours to obtain polystyrene with DA bonds and hydroxyl groups at both ends; through 1 ¹H-NMR and FT-IR testing, the mass percentage of DA bonds in the polystyrene with DA bonds and hydroxyl groups at both ends is 6.53%.

[0051] 4) Dissolve polystyrene with DA bonds and hydroxyl groups at both ends (10.29 g, 2.05 mmol) and 1 g of SEBS with a chloromethyl group on the benzene ring (the mass percentage of the chloromethyl group is 20%) in 300 mL of 1,4-dioxane, and carry out the Williamson etherification reaction at 80 °C for 2 hours. Finally, SEBS with dynamic cross-linking bonds is obtained. The mass percentage of DA bonds in SEBS with dynamic cross-linking bonds is 4.32%. Prepare a tensile spline from SEBS with dynamic cross-linking bonds, and use a universal material testing machine to conduct a tensile test on SEBS with dynamic cross-linking bonds. The results are shown in Table 1.

[0052] Example 5

[0053] 1) Add 300 g of xylene and 30 g of styrene to a 1-liter three-necked glass flask. Turn on the stirrer, add 7.5 mmol of 1,4-dilithium cyclohexane and 7.5 mmol of ethylene glycol dimethyl ether, and start the polymerization of styrene. React at 40 °C for 20 min to obtain a polystyrene solution with two active ends. Take a small amount of the polymer for GPC testing. The number-average relative molecular mass is 3710, and the molecular weight distribution index (PDI) is 1.11.

[0054] 2) Add 2.31 g of 2-((oxiran-2-ylmethoxy)methyl)furan (FGE) to the polystyrene solution with two active ends and carry out the end-capping reaction. After reacting at 70 °C for 2 hours, wash it 3 times with ethanol to remove the unreacted end-capping agent to obtain polystyrene with furan groups at both ends. After GPC testing, the number-average relative molecular mass of polystyrene with furan groups at both ends is 4020, and the molecular weight distribution index (PDI) is 1.13.

[0055] 3) Dissolve polystyrene with furan groups at both ends (10 g, 2.48 mmol) in 200 mL of dimethyl sulfoxide and carry out the Diels-Alder reaction with N-hydroxysuccinimide (0.56 g, 4.96 mmol) at 90 °C for 1 hour to obtain polystyrene with DA bonds and hydroxyl groups at both ends; by 1 ¹H-NMR and FT-IR tests, the mass percentage of DA bonds in polystyrene with DA bonds and hydroxyl groups at both ends is 7.85%.

[0056] 4) Dissolve polystyrene with DA bonds and hydroxyl groups at both ends (8.92 g, 2.05 mmol) and 1 g of SEBS with a chloromethyl group on the benzene ring (the mass percentage of the chloromethyl group is 20%) in 300 mL of dimethyl sulfoxide, and carry out the Williamson etherification reaction at 90 °C for 2 hours. Finally, SEBS containing dynamic cross-linking bonds is obtained. The mass percentage of DA bonds in the SEBS containing dynamic cross-linking bonds is 7.22%. Make the SEBS containing dynamic cross-linking bonds into tensile splines, and use a universal material testing machine to conduct tensile tests on the SEBS containing dynamic cross-linking bonds. The results are shown in Table 1.

[0057] Example 6

[0058] 1) Add 300 g of ethylbenzene and 30 g of styrene to a 1-liter three-necked glass flask. Turn on the stirrer, add 15 mmol of 1,4-dilithiobenzene and 15 mmol of triethylamine, and start the polymerization of styrene. React at 40 °C for 20 min to obtain a polystyrene solution with two active ends; take a small amount of the polymer for GPC testing. The number-average relative molecular mass is 1910, and the molecular weight distribution index (PDI) is 1.07.

[0059] 2) Add 6.60 g of 2-acetylfuran to the polystyrene solution with two active ends for end-capping reaction. After reacting at 50 °C for 3 hours, wash it 3 times with ethanol to remove the unreacted end-capping agent to obtain polystyrene with furan groups at both ends; after GPC testing, the number-average relative molecular mass of the polystyrene with furan groups at both ends is 2220, and the molecular weight distribution index (PDI) is 1.09.

[0060] 3) Dissolve polystyrene with furan groups at both ends (10 g, 4.50 mmol) in 200 mL of acetonitrile, and carry out the Diels-Alder reaction with N-hydroxysuccinimide (2.03 g, 18.00 mmol) at 40 °C for 8 hours to obtain polystyrene with DA bonds and hydroxyl groups at both ends; after 1 1H-NMR and FT-IR tests, the mass percentage of DA bonds in the polystyrene with DA bonds and hydroxyl groups at both ends is 13.12%.

[0061] 4) Dissolve polystyrene with DA bonds and hydroxyl groups at both ends (7.63 g, 3.05 mmol) and 1 g of SEBS with a chloromethyl group on the benzene ring (the mass percentage of the chloromethyl group is 15%) in 300 mL of acetonitrile, and carry out the Williamson etherification reaction at 50 °C for 6 hours. Finally, SEBS containing dynamic cross-linking bonds is obtained. The mass percentage of DA bonds in the SEBS containing dynamic cross-linking bonds is 11.74%. Make the SEBS containing dynamic cross-linking bonds into tensile splines, and use a universal material testing machine to conduct tensile tests on the SEBS containing dynamic cross-linking bonds. The results are shown in Table 1.

[0062] Example 7

[0063] 1) Add 300 g of pentane and 30 g of styrene into a 1 L three-necked glass flask. Turn on the stirring, add 20 mmol of 2,6-dilithium methylpyridine initiator and 20 mmol of dipiperidinoethane, and start the polymerization of styrene. React at 20 °C for 40 min to obtain a polystyrene solution with dual active ends. Take a small amount of the polymer for GPC testing. The number-average relative molecular mass is 1430, and the molecular weight distribution index (PDI) is 1.06.

[0064] 2) Add 11.52 g of 3-furaldehyde into the polystyrene solution with dual active ends for end-capping reaction. After reacting at 20 °C for 5 hours, wash it 3 times with ethanol to remove the unreacted end-capping agent, and obtain polystyrene with furan groups at both ends. After GPC testing, the number-average relative molecular mass of the polystyrene with furan groups at both ends is 1720, and the molecular weight distribution index (PDI) is 1.07.

[0065] 3) Dissolve polystyrene with furan groups at both ends (10 g, 5.81 mmol) in 200 mL of benzene, and carry out the Diels-Alder reaction with 4-maleimidophenol (6.58 g, 34.86 mmol). React at 50 °C for 5 hours to obtain polystyrene with DA bonds and hydroxyl groups at both ends. After 1 1H-NMR and FT-IR testing, the mass percentage content of DA bonds in the polystyrene with DA bonds and hydroxyl groups at both ends is 17.12%.

[0066] 4) Dissolve polystyrene with DA bonds and hydroxyl groups at both ends (6.10 g, 3.05 mmol) and 1 g of SEBS with a chloromethyl group on the benzene ring (the mass percentage content of the chloromethyl group is 15%) in 300 mL of acetonitrile, and carry out the Williamson etherification reaction. React at 50 °C for 6 hours to finally obtain SEBS containing dynamic crosslinking bonds. The mass percentage content of DA bonds in the SEBS containing dynamic crosslinking bonds is 15.37%. Make the SEBS containing dynamic crosslinking bonds into tensile splines, and use a universal material testing machine to conduct tensile testing on the SEBS containing dynamic crosslinking bonds. The results are shown in Table 1.

[0067] Example 8

[0068] 1) Add 300 g of pentane and 30 g of styrene into a 1 L three-necked glass flask. Turn on the stirring, add 20 mmol of 2,6-dilithium methylpyridine initiator and 20 mmol of ethyl tetrahydrofurfuryl ether, and start the polymerization of styrene. React at 20 °C for 40 min to obtain a polystyrene solution with dual active ends. Take a small amount of the polymer for GPC testing. The number-average relative molecular mass is 1370, and the molecular weight distribution index (PDI) is 1.07.

[0069] 2) 11.52 g of 3-furaldehyde was added to the solution of polystyrene with two active ends for end-capping reaction. After reacting at 50 °C for 3 hours, it was washed 3 times with ethanol to remove the unreacted end-capping agent, and polystyrene with furan groups at both ends was obtained. By GPC measurement, the number-average relative molecular mass of polystyrene with furan groups at both ends was 1680, and the molecular weight distribution index (PDI) was 1.09.

[0070] 3) Polystyrene with furan groups at both ends (10 g, 5.95 mmol) was dissolved in 200 mL of tetrahydrofuran and subjected to Diels-Alder reaction with 4-maleimidophenol (8.78 g, 46.48 mmol). After reacting at 40 °C for 8 hours, polystyrene with DA bonds and hydroxyl groups at both ends was obtained. By 1 1H-NMR and FT-IR measurements, the mass percentage content of DA bonds in polystyrene with DA bonds and hydroxyl groups at both ends was 24.05%.

[0071] 4) Polystyrene with DA bonds and hydroxyl groups at both ends (8.01 g, 4.05 mmol) and 1 g of SEBS with chloromethyl groups on the benzene ring (the mass percentage content of chloromethyl groups was 20%) were dissolved in 300 mL of tetrahydrofuran for Williamson etherification reaction. After reacting at 50 °C for 6 hours, SEBS with dynamic cross-linking bonds was finally obtained. The mass percentage content of DA bonds in SEBS with dynamic cross-linking bonds was 20.46%. SEBS with dynamic cross-linking bonds was made into tensile splines, and a universal material testing machine was used to conduct tensile tests on SEBS with dynamic cross-linking bonds. The results are shown in Table 1.

[0072] Example 9

[0073] 1) 300 g of heptane and 30 g of styrene were added to a 1-L three-necked glass flask. After stirring was turned on, 20 mmol of 2,6-dilithiummethylpyridine initiator and 20 mmol of 2,2-bis(tetrahydrofuran)propane were added to initiate the polymerization of styrene. After reacting at 20 °C for 40 min, a solution of polystyrene with two active ends was obtained. A small amount of the polymer was taken for GPC measurement, and the number-average relative molecular mass was 1430, and the molecular weight distribution index (PDI) was 1.05.

[0074] 2) 15.36 g of 3-furaldehyde was added to the solution of polystyrene with two active ends for end-capping reaction. After reacting at 50 °C for 3 hours, it was washed 3 times with ethanol to remove the unreacted end-capping agent, and polystyrene with furan groups at both ends was obtained. By GPC measurement, the number-average relative molecular mass of polystyrene with furan groups at both ends was 1750, and the molecular weight distribution index (PDI) was 1.07.

[0075] 3) Dissolve polystyrene with furan groups at both ends (10 g, 5.71 mmol) in 200 mL of tetrahydrofuran, and carry out the Diels - Alder reaction with 4 - maleimidophenol (8.63 g, 45.68 mmol). React at 40 °C for 10 hours to obtain polystyrene with DA bonds and hydroxyl groups at both ends; through 1 1H - NMR and FT - IR tests, the mass percentage content of DA bonds in polystyrene with DA bonds and hydroxyl groups at both ends is 30.51%.

[0076] 4) Dissolve polystyrene with DA bonds and hydroxyl groups at both ends (10.61 g, 5.05 mmol) and 1 g of SEBS with chloromethyl groups on the benzene ring (the mass percentage content of chloromethyl groups is 25%) in 300 mL of tetrahydrofuran, and carry out the Williamson etherification reaction. React at 50 °C for 6 hours to finally obtain SEBS containing dynamic cross - link bonds. The mass percentage content of DA bonds in SEBS containing dynamic cross - link bonds is 24.93%. Make the SEBS containing dynamic cross - link bonds into tensile splines, and use a universal material testing machine to conduct tensile tests on the SEBS containing dynamic cross - link bonds. The results are shown in Table 1.

[0077] Comparative Example 1

[0078] Use 1.0 phr of dicumyl peroxide as a cross - linker to chemically cross - link 100 phr of SEBS, and add 0.5 phr of antioxidant. Melt the SEBS in a mixer (temperature: 180 °C, rotation speed: 60 rpm), add dicumyl peroxide and mix for 5 - 10 minutes until uniform. Place the mixed material in a flat vulcanizing machine (temperature: 180 °C, pressure: 10 MPa, time: 10 minutes), and press it into tensile splines. The mechanical properties of the polymer are shown in Table 1.

[0079] Table 1

[0080] Number Content of DA key / % Tensile strength / MPa Elongation at break / % Example 1 9.65 55.34 620.4 Example 2 1.05 34.23 821.6 Example 3 3.59 38.74 748.5 Example 4 4.32 41.81 714.8 Example 5 7.22 50.69 675.2 Example 6 11.74 58.36 572.5 Example 7 15.37 62.73 517.1 Example 8 20.46 65.97 490.3 Example 9 24.93 67.13 464.9 Comparative example 1 / 40.78 425.8

[0081] The mechanical properties of SEBS usually show the mutual restriction between tensile strength and elongation at break. As shown in Table 1, in Examples 1 - 9, with the increase in the content of DA bonds, the tensile strength of the obtained SEBS materials shows a regular increase, while the elongation at break decreases accordingly. It is worth noting that the dynamic cross - link system of the present invention exhibits unique performance advantages: while the tensile strength is significantly improved, the decrease in the elongation at break is significantly less than that of the chemical cross - link system in Comparative Example 1.

[0082] Comparative Example 1 used a SEBS material crosslinked by conventional peroxide chemistry. Its tensile strength was similar to that of Example 4, but the elongation at break decreased significantly. This difference was due to the different crosslinking methods: the crosslinking reaction in Comparative Example 1 acted on both the hydrogenated poly(ethylene-butene) soft segment and the polystyrene hard segment simultaneously, resulting in the rigidification of the entire molecular network, severely restricting the movement ability of the molecular chains, and thus making the material brittle and the elongation at break drop significantly.

[0083] In contrast, the dynamic crosslinking system of the present invention precisely controls the crosslinking sites of the DA bonds, enabling them to selectively act on the polystyrene hard segment region while maintaining the freedom of movement of the molecular chains in the soft segment region. This selective crosslinking strategy maximally retains its extensibility (the elongation at break does not drop significantly) while ensuring that the material obtains sufficient strength. Experimental data fully demonstrate that the dynamic reversible crosslinking network of the present invention is significantly superior to the traditional irreversible chemical crosslinking system in terms of mechanical properties.

[0084] Verification of the reversibility of the dynamic reversible crosslinking network of SEBS containing dynamic crosslinking bonds:

[0085] Verification object: The product obtained by tensile testing the SEBS containing dynamic crosslinking bonds obtained in Example 1 using a flat vulcanizing machine, which is defined as the test product here.

[0086] Performance test 1 of the test product: First, cut the test product into pieces and add them to the mold, preheat at 190 °C for 10 min, and hot press at a pressure of 10 MPa for 10 min to form, then keep the pressure and naturally cool to room temperature to obtain the SEBS containing dynamic crosslinking bonds after the first processing. Make it into a tensile spline, and use a universal material testing machine to conduct a tensile test on the SEBS containing dynamic crosslinking bonds after the first processing. The mechanical properties are shown in Table 2.

[0087] Performance test 2 of Example 1: The SEBS containing dynamic crosslinking bonds after the first processing in Performance test 1 was processed again using the same processing method as in Performance test 1 to obtain the SEBS containing dynamic crosslinking bonds after the second processing. Make it into a tensile spline, and use a universal material testing machine to conduct a tensile test on the SEBS containing dynamic crosslinking bonds after the second processing. The mechanical properties are shown in Table 2.

[0088] Table 2

[0089] Number Young's modulus / MPa Tensile strength / MPa Elongation at break / % Example 1 42.57 55.34 620.4 Performance test 1 41.68 53.59 672.4 Performance test 2 40.55 49.97 754.5

[0090] The SEBS sample with dynamic cross - link bonds that had undergone tensile testing in Example 1 was crushed, then placed in a mold, preheated at 190 °C for 10 minutes, and hot - pressed at 10 MPa for 10 minutes. During this hot - pressing process, the dynamic DA bonds reversibly dissociated under the action of heat stimulation, causing the cross - linked network structure in the material to temporarily unravel, and the polymer to return to a linear structure, thus enabling thermoplastic processing. After molding, the pressure was maintained and it was naturally cooled to room temperature. During the cooling process, the dynamic DA bonds reformed and the material restored its original cross - linked network structure. This process fully demonstrates that the SEBS with dynamic cross - link bonds of the present invention has the unique property of "plasticizable upon heating (decross - linking) - strengthened upon cooling (re - cross - linking)".

[0091] As shown in Table 2, the results of the mechanical property tests of the samples after two recycling processes indicate that: the tensile strength decreased slightly compared to Example 1, but the decrease was within 5%, which is within an acceptable range. This phenomenon is attributed to the fact that a small amount of DA bonds did not fully recover during the processing, resulting in a slight decrease in the cross - link density. The elongation at break increased compared to Example 1, with an increase of approximately 8 - 15%. This is because the fracture - recombination characteristic of the dynamic cross - link bonds causes the material to form a looser network structure after processing, enhancing the movement ability of the molecular chain segments.

[0092] The above experimental results fully prove that the SEBS material with dynamic cross - link bonds of the present invention has excellent recyclability. After secondary processing, the material can still maintain more than 90% of its original mechanical properties, and at the same time, the elongation at break is improved, demonstrating extremely high value for recycling. This characteristic makes the material have important application prospects in the field of sustainable development.

[0093] The above - described embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can be made, and these all fall within the protection scope of the present invention.

Claims

1. A SEBS containing dynamic crosslinking bonds, characterized in that, The polystyrene block in the SEBS containing dynamic crosslinking bonds is bonded to the polystyrene with dynamic crosslinking bonds at both ends. The dynamic crosslinking bonds are formed by the Diels-Alder reaction of furan compounds and maleimide compounds. Hereinafter, the dynamic crosslinking bonds will be simply referred to as DA bonds. The molecular structure of the SEBS containing dynamic crosslinking bonds is shown as follows: Wherein: x is an integer in the range of 30 - 300; y is an integer in the range of 10 - 220; m is an integer in the range of 600 - 1200; n is an integer in the range of 80 - 240; z is an integer in the range of 15 - 80; R1 is - O -, R2 is 2. The SEBS containing dynamic crosslinking bonds according to claim 1, wherein In the SEBS containing dynamic crosslinking bonds, based on 100% of the total mass, the mass percentage content of DA bonds is 1% - 25%.

3. A preparation method of an SEBS containing dynamic crosslinking bonds as described in claim 1 or 2, characterized in that, The preparation method is as follows: First, the polystyrene with furan groups at both ends reacts with the maleimide compound with a hydroxyl group at the end through the Diels-Alder reaction to obtain the polystyrene with dynamic crosslinking bonds at both ends. Among them, the polystyrene with furan groups at both ends is synthesized by an active anionic polymerization method using a dilithium initiator to initiate the polymerization of styrene, and then a capping agent is added. Second, a chloromethyl group is introduced onto the benzene ring of the SEBS polystyrene block. Finally, the polystyrene with dynamic crosslinking bonds at both ends and the SEBS with a chloromethyl group on the benzene ring are prepared into the SEBS containing dynamic crosslinking bonds through the Williamson etherification reaction.

4. The preparation method of an SEBS containing dynamic crosslinking bonds according to claim 3, characterized in that, It includes the following steps: Step 1, add a polar activator and styrene into a reactor in a non-polar hydrocarbon solvent, turn on the stirring, add a dilithium initiator to initiate the polymerization of styrene, and obtain a polystyrene solution with two active lithium ends after the polymerization reaction. Among them, the polymerization reaction temperature is 20 - 60 °C, and the time is 10 - 40 minutes; Step 2, the polystyrene solution with two active ends is subjected to a capping reaction with a capping agent, and washed with ethanol to remove the unreacted capping agent to obtain the polystyrene with furan groups at both ends. The capping agent is a compound containing a furan group. Among them, the temperature of the capping reaction is 20 - 100 °C, and the time is 30 - 300 minutes; Step 3, dissolve the polystyrene with furan groups at both ends in a solvent, and perform the Diels-Alder reaction with the compound containing a maleimide group to obtain the polystyrene with dynamic crosslinking bonds at both ends. Among them, the reaction temperature is between 20 - 90 °C, and the time is 60 - 900 minutes; Step 4, dissolve the polystyrene with dynamic crosslinking bonds at both ends and the SEBS with a chloromethyl group on the benzene ring in a polar solvent, perform the Williamson etherification reaction, and finally obtain the SEBS containing dynamic crosslinking bonds. Among them, the reaction temperature is between 50 - 90 °C, and the time is 30 - 480 minutes.

5. The preparation method of a SEBS containing dynamic crosslinking bonds according to claim 4, characterized in that, In the above Step 1: The non-polar hydrocarbon solvent is selected from 1 - 3 combinations of pentane, hexane, heptane, octane, cyclohexane, benzene, toluene, ethylbenzene, and xylene; The polar activator is selected from 1 - 3 combinations of diethyl ether, tetrahydrofuran, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, triethylamine, N,N,N',N'-tetramethylethylenediamine, dipiperidinoethane, ethyl tetrahydrofurfuryl ether, and 2,2-bis(tetrahydrofuran)propane; The dilithium initiator is selected from one or more of 1,4-dilithio-2,3-dimethylbutane, 1,4-dilithiobutane, 1,4-dilithio-cyclohexane, 1,4-dilithiobenzene or 2,6-dilithio-picoline.

6. The preparation method of an SEBS containing dynamic crosslinking bonds according to claim 4, characterized in that, In the step 1, the molar ratio of the polar activator to the dilithium initiator is 1:1, and the addition amount of the dilithium initiator is jointly determined by the addition amount of styrene and the relative molecular mass of polystyrene.

7. The preparation method of an SEBS containing dynamic crosslinking bonds according to claim 4, characterized in that, In the step 2, the capping agent is selected from 1-3 combinations of 2-acetylfuran, 3-furaldehyde, 2-((oxiran-2-ylmethoxy)methyl)furan, 2-chloromethylfuran, 2-furanacrylic acid; the molar ratio of the capping agent to Li in the double-active-end polystyrene is between 2 / 1 and 10 / 1.

8. The preparation method of a SEBS containing dynamic crosslinking bonds according to claim 4, characterized in that, In the step 2, the solvent in the step 3 is selected from 1-3 combinations of dichloromethane, chloroform, acetonitrile, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, benzene, toluene, xylene; the compound containing a maleimide group in the step 3 is selected from 1-3 combinations of N-hydroxymaleimide, 4-maleimidophenol, N-(2-hydroxyethyl)maleimide; the polar solvent in the step 4 is selected from 1-3 combinations of acetonitrile, tetrahydrofuran, N,N-dimethylformamide, dimethyl sulfoxide, 1,4-dioxane.

9. The preparation method of a SEBS containing dynamic crosslinking bonds according to claim 4, characterized in that, In the step 2, in the step 3, the molar ratio of the maleimide group to the furan group in the polystyrene with double-terminal furanyl groups is between 2 / 1 and 6 / 1.

10. The preparation method of an SEBS containing dynamic crosslinking bonds according to claim 4, wherein, In the step 2, in the step 4, the mass percentage content of the chloromethyl group in the SEBS with a chloromethyl group on the benzene ring is 5%-25%.

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