A cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer and its preparation method

Abstract

The present invention discloses a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer and a preparation method thereof. Under the condition of a catalyst, cellulose and lactide are reacted in solvent A to obtain modified cellulose; the modified cellulose is dissolved in solvent A and reacted with carbon disulfide and 2-bromoethanol to obtain a cellulose macromolecular chain transfer agent; under the conditions of solvent B and a catalyst, the cellulose macromolecular chain transfer agent and lactide monomer are subjected to a ring-opening reaction to obtain a cellulose-grafted polylactic acid polymer; under the conditions of solvent C and an initiator, the cellulose-grafted polylactic acid and isoprene monomer are subjected to a reversible addition-fragmentation chain transfer radical polymerization reaction to obtain a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer. The cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer in the present invention has excellent mechanical properties.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer materials, and particularly relates to a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer and a preparation method thereof. Background Art

[0002] Thermoplastic elastomers are a new type of polymer material between rubber and resin, having both the elasticity of rubber and the reprocessability of plastic. Thermoplastic elastomers have excellent physical and chemical properties and are easy to process, and have replaced some natural rubber, synthetic rubber and plastics, and are widely used in automotive parts, sports equipment, adhesives, construction industry, medicine and daily necessities, etc.

[0003] However, traditional thermoplastic elastomers are mainly synthesized from non-renewable petroleum resources. Due to the concern about the limitedness of petroleum resources, the development of thermoplastic elastomers also faces huge challenges and opportunities. In order to promote the sustainable and green development of polymer materials, the preparation of bio-based thermoplastic elastomers using bio-based monomers has received more and more attention from scientific researchers. Bio-based monomers are derived from natural organisms, are renewable and sustainable, and can well make up for the limitedness of petrochemical resources.

[0004] Cellulose, as the most abundant natural polymer compound in the world, can be derived from wood, cotton, straw, hemp, etc. Since each glucose unit of cellulose contains 3 hydrogen bonds, usually cellulose has strong polarity and intermolecular and intramolecular hydrogen bond interactions, making it very stable and insoluble in conventional solvents. Currently, the commonly used method is to chemically modify cellulose, and modifying the hydroxyl groups of cellulose into other groups can make it dissolve well in some conventional solvents. Since the cellulose chain is a rigid chain and has poor mechanical properties, and if you want to further obtain cellulose-based thermoplastic elastomers, it is necessary to combine other polymers on this basis to make it have good ductility and mechanical properties.

[0005] As disclosed in the patent with publication number CN103360550B, a cellulose-grafted polyisoprene copolymer and its preparation method are disclosed, which can be applied to the field of artificial skin. However, the grafted polyisoprene side chains undergo radical coupling termination and cannot achieve repeated processing like thermoplastic elastomers. In the patent with publication number CN111187385A, a cellulose-based bottlebrush thermoplastic elastomer and its preparation method are disclosed, which can prepare a cellulose-based thermoplastic elastomer with good tensile properties. However, the side-chain graft copolymer is not a bio-based polymer, and its maximum tensile strain is approximately 160%, and the maximum tensile stress is approximately 10 MPa. Another limiting aspect is that it modifies the terminal hydroxyl groups of cellulose into bromine groups, making it difficult to carry out ring-opening reactions of lactide (a bio-based cyclic monomer). Therefore, it is of great significance to design and optimize the microstructure of molecular chains, combine cellulose, a rich renewable natural resource, with some bio-based materials, and prepare sustainable cellulose-based thermoplastic elastomer materials with application value. Summary of the Invention

[0006] The purpose of the present invention is to provide a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer with good ductility and mechanical properties.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] A cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer has the following structural formula:

[0009]

[0010]

[0011] Among them, the degree of polymerization of cellulose is 200 ≤ n ≤ 800, the degree of polymerization of polylactic acid grafted by modification is 1 ≤ m ≤ 15, the degree of polymerization of polyisoprene is 1 ≤ l ≤ 300, x, y, and z are the percentages of 1,4-addition, 1,2-addition, and 3,4-addition polymerization of isoprene respectively, x + y + z = 1, and the degree of polymerization of polylactic acid is 1 ≤ h ≤ 300.

[0012] As a further scheme of the present invention: A method for preparing a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer is to modify cellulose into a macromolecular reversible addition chain transfer agent with terminal hydroxyl groups, and obtain a copolymer through ring-opening reaction of lactide and reversible addition chain transfer radical polymerization of isoprene.

[0013] As a further scheme of the present invention: It includes the following steps:

[0014] Step 1: React cellulose and lactide in solvent A under the condition of a catalyst to obtain modified cellulose;

[0015] Step 2: Dissolve the modified cellulose in solvent A and react it with carbon disulfide and 2-bromoethanol to obtain a cellulose macromolecular chain transfer agent;

[0016] Step 3: Under the conditions of solvent B and a catalyst, carry out a ring-opening reaction on the cellulose macromolecular chain transfer agent and lactide monomer to obtain a cellulose-grafted polylactic acid polymer;

[0017] Step 4: Under the conditions of solvent C and an initiator, carry out a reversible addition-fragmentation chain transfer radical polymerization reaction on the cellulose-grafted polylactic acid and isoprene monomer to obtain a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer.

[0018] As a further scheme of the present invention: In Step 1, the cellulose is one or more of wood pulp cellulose, microcrystalline cellulose, rice pulp cellulose, cotton pulp cellulose, mulberry bark pulp cellulose or rice straw pulp cellulose;

[0019] The lactide is L-lactide;

[0020] The catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene;

[0021] The solvent A is dimethyl sulfoxide;

[0022] The reaction temperature for cellulose modification is 50 - 80 °C; the modification reaction time is 8 - 16 h;

[0023] The molar ratio of cellulose to lactide is 1:(27 - 45);

[0024] The molar ratio of cellulose to the catalyst is 1:(3 - 9).

[0025] As a further scheme of the present invention: In Step 2:

[0026] The molar ratio of the modified cellulose to carbon disulfide is 1:(6 - 12);

[0027] The molar ratio of the modified cellulose to 2-bromoethanol is 1:(3 - 9);

[0028] Among them, the reaction temperature is 40 - 50 °C, and the reaction time is 12 - 20 h.

[0029] As a further scheme of the present invention: In Step 3:

[0030] The solvent B is dichloromethane;

[0031] The catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene;

[0032] The molar ratio of the cellulose chain transfer agent to lactide is 1:(180 - 320);

[0033] The molar ratio of the cellulose chain transfer agent to the catalyst is 1:(3 - 4);

[0034] Among them, the ring-opening reaction temperature is 25 - 30 °C, and the ring-opening reaction time is 2.5 - 3.5 h.

[0035] As a further scheme of the present invention: In step four:

[0036] The solvent C is 1,4-dioxane;

[0037] The initiator is di-tert-butyl peroxide;

[0038] The molar ratio of the cellulose macromolecular chain transfer agent to the initiator is 1:(0.1 - 0.3);

[0039] The molar ratio of the cellulose-grafted poly(lactic acid) to isoprene is 1:(250 - 2000);

[0040] Among them, the temperature of the reversible addition-fragmentation chain transfer polymerization is 125 - 130 °C, and the reaction time of the reversible addition-fragmentation radical polymerization is 24 - 36 h.

[0041] The beneficial effects of the present invention:

[0042] The present invention provides a cellulose-grafted polyisoprene-block-poly(lactic acid) copolymer thermoplastic elastomer, which has a rigid cellulose as the main chain and grafted polyisoprene-block-poly(lactic acid) copolymer side chains. The hard segment-soft segment-hard segment structure makes the polymer have excellent mechanical properties. Cellulose is the most abundant natural polymer material, and lactide and isoprene can be prepared by biological methods. The obtained cellulose-grafted polyisoprene-block-poly(lactic acid) is a fully bio-based polymer material, which is environmentally friendly and conforms to the concept of sustainable development;

[0043] The present invention provides a preparation method of the above-mentioned cellulose-grafted polyisoprene-block-poly(lactic acid) copolymer thermoplastic elastomer, which combines rigid cellulose with soft rubber phase polyisoprene and hard phase poly(lactic acid).

[0044] First, due to the strong polarity of cellulose, there are a large number of hydrogen bond interactions within and between molecular chains, making it insoluble in conventional solvents. In this invention, the synergistic effect of strongly polar dimethyl sulfoxide and catalyst 1,8-diazabicyclo[5.4.0]undec-7-ene is used to dissolve cellulose. Utilizing the characteristic of the ring-opening reaction of cellulose hydroxyl groups while retaining the terminal hydroxyl functional groups, this invention uses bio-based monomer lactide to modify cellulose, and at the same time makes the modified cellulose soluble in conventional solvents, facilitating subsequent polymerization reactions. Due to the steric hindrance effect of the cellulose chain, the degree of polymerization of polylactic acid grafted onto the modified cellulose is very low. By making the modified cellulose into a cellulose macromolecular chain transfer agent and retaining the terminal hydroxyl group, subsequent ring-opening reactions of lactide and reversible addition-fragmentation chain transfer radical polymerization of isoprene are carried out. Among them, reversible addition-fragmentation chain transfer radical polymerization uses transfer-to to graft a certain degree of polymerization of polylactic acid and polyisoprene onto cellulose, and at the same time controls the reaction time and temperature, regulating the conversion rate of isoprene monomer to about 10%, effectively avoiding the cross-linking phenomenon of the obtained product, and successfully synthesizing a cellulose-grafted polyisoprene-block-polylactic acid thermoplastic elastomer;

[0045] The test results show that the thermoplastic elastomer shown by the above structural formula prepared in this invention has excellent tensile properties, with an elongation at break of more than 190% and a strength of more than 8.1 MPa. Brief Description of the Drawings

[0046] The present invention will be further described below with reference to the accompanying drawings.

[0047] Figure 1 1H NMR spectrum of the modified cellulose, the product of Example 1 of the present invention;

[0048] Figure 2 1H NMR spectrum of the cellulose-grafted polylactic acid, the product of Example 3 of the present invention;

[0049] Figure 3 1H NMR spectrum of the product of Example 5 of the present invention;

[0050] Figure 4 Infrared spectra of cellulose and the product of Example 1 of the present invention;

[0051] Figure 5 Infrared spectra of the products of Examples 2, 3, and 5 of the present invention;

[0052] Figure 6 Atomic force microscopy test image of the product of Example 4 of the present invention;

[0053] Figure 7 Atomic force microscopy test image of the product of Example 5 of the present invention;

[0054] Figure 8 It is the atomic force microscope test chart of the product described in Example 6 of the present invention;

[0055] Figure 9 It is the tensile test chart of the product described in Example 3 of the present invention;

[0056] Figure 10 It is the tensile test chart of the products described in Example 4, Example 5, and Example 6 of the present invention. Detailed implementation manners

[0057] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0058] The reagents used in the following examples are all purchased from the market. The solvent needs to be dried and then distilled under reduced pressure before use. The isoprene needs to pass through an alkaline alumina column before use. The lactide needs to be purified 3 times before use.

[0059] Example 1

[0060] Preparation of modified cellulose

[0061] Under glove box conditions, take 0.162 g of dried microcrystalline cellulose and 25 mL of dimethyl sulfoxide, add them to a round-bottom flask, stir evenly at 50 °C, then add 448 μL of 1,8-diazabicyclo[5.4.0]undec-7-ene, and stir until the cellulose is completely dissolved to obtain a uniform and clear mixed solution. Add lactide, set the reaction temperature to 80 °C, and the reaction time to 12 h;

[0062] Finally, quench the reaction by adding 0.366 g of benzoic acid, slowly pour the reaction solution into methanol for precipitation and washing 3 times, and place the obtained white solid product in a vacuum oven at 40 °C for drying for 24 h to obtain modified cellulose.

[0063] Example 2

[0064] Preparation of cellulose macromolecular chain transfer agent

[0065] Take 2.4 g of dried modified cellulose in a round-bottom flask, add 20 mL of dimethyl sulfoxide, and stir to dissolve at 40 °C. Take 0.304 g of triethylamine and 0.375 g of 2-bromoethanol in a vial, add 5 mL of dimethyl sulfoxide and stir for 10 min, then add 0.457 g of carbon disulfide, stir for 10 min and then dropwise add it to the above-mentioned round-bottom flask;

[0066] After the reaction solution was stirred at 40 °C for 12 h, it was slowly poured into methanol for precipitation and washing three times to obtain a pale yellow cellulose macromolecular chain transfer agent product. The product was placed in a vacuum drying oven and dried at 40 °C for 24 h.

[0067] Example 3

[0068] Preparation of Cellulose Grafted with Poly(lactic acid)

[0069] Under glove box conditions, 0.5 g of cellulose macromolecular chain transfer agent and 14.4 g of lactide were dissolved in 80 mL of dichloromethane. 75 μL of 1,8-diazabicyclo[5.4.0]undec-7-ene was added to initiate the ring-opening reaction of lactide. The reaction was carried out at room temperature for 2.5 h.

[0070] Finally, 61 mg of benzoic acid was added to quench the reaction. The reaction solution was slowly poured into methanol for precipitation and washing three times to obtain a white product, cellulose grafted with poly(lactic acid). The product was placed in a vacuum drying oven and dried at 40 °C for 24 h.

[0071] Example 4

[0072] Preparation of Cellulose Grafted with Poly(isoprene)-block-Poly(lactic acid) 1

[0073] 2.8 g of cellulose grafted with poly(lactic acid) and 8 mL of isoprene monomer were taken and completely dissolved in 40 mL of 1,4-dioxane in a specific flask. 2 μL of initiator di-tert-butyl peroxide was added. The reaction flask was degassed by three freeze-thaw cycles and then sealed, and placed in an oil bath at 125 °C for reaction for 24 h. After the reaction was completed, the solution was poured into methanol for precipitation and washing three times. The obtained white solid was the product. The product was placed in a vacuum drying oven and dried at 40 °C for 24 h to obtain cellulose grafted with poly(isoprene)-block-poly(lactic acid) 1.

[0074] Example 5

[0075] Preparation of Cellulose Grafted with Poly(isoprene)-block-Poly(lactic acid) 2

[0076] 2.8 g of cellulose grafted with poly(lactic acid) and 16 mL of isoprene monomer were taken and completely dissolved in 40 mL of 1,4-dioxane in a specific flask. 2 μL of initiator di-tert-butyl peroxide was added. The reaction flask was degassed by three freeze-thaw cycles and then sealed, and placed in an oil bath at 125 °C for reaction for 24 h. After the reaction was completed, the solution was poured into methanol for precipitation and washing three times. The obtained white solid was the product. The product was placed in a vacuum drying oven and dried at 40 °C for 24 h to obtain cellulose grafted with poly(isoprene)-block-poly(lactic acid) 2.

[0077] Example 6

[0078] Preparation of Cellulose Grafted with Poly(isoprene)-block-Poly(lactic acid) 3

[0079] Take 2.8 g of cellulose-grafted polylactic acid and 25 mL of isoprene monomer, add 40 mL of 1,4-dioxane and dissolve completely in a specific flask, and then add 2 μL of initiator di-tert-butyl peroxide. After the reaction flask is degassed through 3 freeze-thaw cycles, it is sealed and placed in an oil bath at 125 °C for reaction for 24 h. After the reaction is completed, the solution is poured into methanol for precipitation and washing 3 times. The obtained white solid is the product, and the product is placed in a vacuum drying oven and dried at 40 °C for 24 h to obtain cellulose-grafted polyisoprene-block-polylactic acid 3.

[0080] Experimental data and analysis:

[0081] Figure 1 It is the 1H NMR spectrum of the product described in Example 1. In the figure, a and b respectively represent the chemical shifts of the hydrogen atoms on -CH and -CH3 within the molecular chain of polylactic acid, and c and d respectively represent the chemical shifts of the hydrogen atoms on -CH and -CH3 at the end of the polylactic acid molecular chain, which strongly proves the correct synthesis of the product.

[0082] Figure 2 It is the 1H NMR spectrum of the product described in Example 3. In the figure, a and b are respectively the chemical shifts of the hydrogen atoms on -CH and -CH3 within the polylactic acid molecular chain. By comparison Figure 1 It can be found that the corresponding peaks of the hydrogen atoms on -CH and -CH3 at the end of the polylactic acid molecular chain disappear, indicating that the polylactic acid chain has a relatively high degree of polymerization, thus proving the successful grafting of the long polylactic acid chain.

[0083] Figure 3 It is the 1H NMR spectrum of the product described in Example 5. In the figure, the methyl hydrogens of the cis-1,4 and trans-1,4 structures of polyisoprene are at chemical shifts of 1.58 and 1.68 ppm, and the secondary methyl hydrogens are at a chemical shift of about 5.13 ppm. The olefinic hydrogens of the 3,4 addition of polyisoprene are at chemical shifts of 4.60 - 4.78 ppm, while the olefinic hydrogens of the 1,2 addition of polyisoprene are at chemical shifts of 4.80 - 4.95 and 5.70 - 5.80 ppm, which strongly proves the successful grafting of polyisoprene.

[0084] Figure 4 It is the infrared spectrum of cellulose and the product described in Example 1. In the infrared spectrum corresponding to Example 1 in the figure, an ester group peak appears at 1750 cm -1 which represents the ester group in the polylactic acid on the modified cellulose, thus effectively proving the successful synthesis of the modified cellulose.

[0085] Figure 5 It is the infrared spectra of the products described in Example 2, Example 3, and Example 5. An absorption peak at 1642 cm appears in the infrared spectrum corresponding to Example 5 -1The absorption peak represents the stretching vibration of the carbon-carbon double bond in polyisoprene. 2991 cm -1 The absorption peak at the position represents the out-of-plane stretching vibration of the methyl group in polyisoprene, and the absorption peaks at 2941 and 2877 cm -1 The absorption peak at the position represents the in-plane stretching vibration of the methylene group in polyisoprene. This strongly proves the successful grafting of polyisoprene, thus proving the successful synthesis of cellulose-grafted polyisoprene-block polylactic acid.

[0086] Figure 6 It is an atomic force microscope test diagram of the product described in Example 4. In the figure, the microphase separation structure is a spherical structure, where the bright area corresponds to the high-modulus polylactic acid hard-phase microdomain, and the dark area corresponds to the low-modulus polyisoprene soft-phase microdomain.

[0087] Figure 7 It is an atomic force microscope test diagram of the product described in Example 5. In the figure, the microphase separation structure is a spherical structure, where the bright area corresponds to the high-modulus polylactic acid hard-phase microdomain, and the dark area corresponds to the low-modulus polyisoprene soft-phase microdomain.

[0088] Figure 8 It is an atomic force microscope test diagram of the product described in Example 6. In the figure, the microphase separation structure is a spherical structure, where the bright area corresponds to the high-modulus polylactic acid hard-phase microdomain, and the dark area corresponds to the low-modulus polyisoprene soft-phase microdomain.

[0089] Figure 9 It is a tensile test diagram of the product described in Example 3. The product described in Example 3 was cut into dumbbell-shaped specimens with a thickness of about 0.3 mm, a width of 2 mm, and a length of 35 mm for tensile testing. The results are as Figure 9 shown. The breaking strength of the product obtained in Example 3 is 44.2 MPa, the Young's modulus is 1818 MPa, and the elongation at break is 6.2%.

[0090] Figure 10 It is a tensile test diagram of the products described in Example 4, Example 5, and Example 6. The products described in Example 4, Example 5, and Example 6 were cut into dumbbell-shaped specimens with a thickness of about 0.3 mm, a width of 2 mm, and a length of 35 mm for tensile testing. The results are as Figure 10 shown. The breaking strength of the product obtained in Example 4 is 26.5 MPa, the Young's modulus is 791 MPa, and the elongation at break is 192.0%. The breaking strength of the product obtained in Example 5 is 16.1 MPa, the Young's modulus is 480 MPa, and the elongation at break is 216.5%. The breaking strength of the product obtained in Example 6 is 8.1 MPa, the Young's modulus is 89 MPa, and the elongation at break is 246.3%. This indicates that the materials obtained by the present invention have excellent ductility and mechanical properties.

[0091] The above has described in detail an embodiment of the present invention, but the above content is only a preferred embodiment of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made in accordance with the scope of application of the present invention shall still fall within the scope covered by the patent of the present invention.

Claims

1. A cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer, characterized in that : Its structural formula is as follows: ； ； Among them, the degree of polymerization of cellulose is 200 ≤ n ≤ 800, the degree of polymerization of polylactic acid grafted by modification is 1 ≤ m ≤ 15, the degree of polymerization of polyisoprene is 1 ≤ l ≤ 300, x, y, and z are the percentages of 1,4-addition, 1,2-addition, and 3,4-addition polymerization of isoprene respectively, x + y + z = 1, and the degree of polymerization of polylactic acid is 1 ≤ h ≤ 300.

2. A method for preparing a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer as described in claim 1, characterized in that, Modify cellulose into a macromolecular reversible addition chain transfer agent with terminal hydroxyl groups, and obtain a copolymer through the ring-opening reaction of lactide and the reversible addition chain transfer radical polymerization of isoprene.

3. A method for preparing a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer according to claim 2, characterized in that, It includes the following steps: Step 1: Under the condition of a catalyst, react cellulose and lactide in solvent A to obtain modified cellulose; Step 2: Dissolve the modified cellulose in solvent A, and react it with carbon disulfide and 2-bromoethanol to obtain a cellulose macromolecular chain transfer agent; Step 3: Under the conditions of solvent B and a catalyst, carry out a ring-opening reaction on the cellulose macromolecular chain transfer agent and lactide monomer to obtain a cellulose-grafted polylactic acid polymer; Step 4: Under the conditions of solvent C and an initiator, carry out a reversible addition chain transfer radical polymerization reaction on the cellulose-grafted polylactic acid and isoprene monomer to obtain a cellulose-grafted polyisoprene block polylactic acid copolymer thermoplastic elastomer.

4. A method for preparing a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer according to claim 3, characterized in that, In Step 1, the cellulose is one or more of wood pulp cellulose, microcrystalline cellulose, rice pulp cellulose, cotton pulp cellulose, mulberry bark pulp cellulose, or rice straw pulp cellulose; The lactide is L-lactide; The catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene; The solvent A is dimethyl sulfoxide; The reaction temperature for cellulose modification is 50 - 80 °C; the modification reaction time is 8 - 16 h; The molar ratio of cellulose to lactide is 1:27 - 45; The molar ratio of cellulose to the catalyst is 1:3 - 9.

5. A method for preparing a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer according to claim 3, characterized in that, In Step 2: The molar ratio of the modified cellulose to carbon disulfide is 1:6 - 12; The molar ratio of the modified cellulose to 2-bromoethanol is 1:3 - 9; Among them, the reaction temperature is 40 - 50 °C, and the reaction time is 12 - 20 h.

6. A method for preparing a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer according to claim 3, characterized in that, In Step 3: The solvent B is dichloromethane; The catalyst is 1,8-diazabicyclo[5.4.0]undec-7-ene; The molar ratio of the cellulose chain transfer agent to lactide is 1:180 - 320; The molar ratio of the cellulose chain transfer agent to the catalyst is 1:3 - 4; Among them, the ring-opening reaction temperature is 25 - 30 °C, and the ring-opening reaction time is 2.5 - 3.5 h.

7. A method for preparing a cellulose-grafted polyisoprene-block-polylactic acid copolymer thermoplastic elastomer according to claim 3, characterized in that, In Step 4: The solvent C is 1,4-dioxane; The initiator is di-tert-butyl peroxide; The molar ratio of the cellulose macromolecular chain transfer agent to the initiator is 1:0.1 - 0.3; The molar ratio of the cellulose-grafted polylactic acid to isoprene is 1:250 - 2000; Among them, the reaction temperature for the reversible addition chain transfer polymerization reaction is 125 - 130 °C, and the reaction time for the reversible addition chain transfer radical polymerization reaction is 24 - 36 h.

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