Long-hard-segment high-strength and high-toughness polyurethane based on bio-based isomer chain extender and preparation method of long-hard-segment high-strength and high-toughness polyurethane

Abstract

The invention discloses long-hard-segment high-strength and high-toughness polyurethane based on a bio-based isomer chain extender and a preparation method thereof.The polyurethane elastomer has the following structural formula, and the preparation method comprises the steps that 1, polycaprolactone and p-phenylene diisocyanate are subjected to a prepolymerization reaction to obtain PCL-PPDI; step 2, mixing and reacting isosorbide and / or 1, 4: 3, 6-didehydrated mannitol and dicyclohexylmethane diisocyanate in an organic solvent to obtain a long hard segment chain extender IS / IM / SM-HMDI (1, 4: 3, 6-didehydrated mannitol and dicyclohexylmethane diisocyanate); and step 3, dropwise adding the obtained long-hard-segment chain extender into the prepolymer PCL-PPDI to carry out chain extension reaction, and washing and drying to obtain the long-hard-segment high-strength and high-toughness polyurethane product based on the bio-based isomer chain extender. The polyurethane elastomer provided by the invention integrates high strength, high toughness, recoverability and good stability, and has wide application prospects in many fields.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of elastomers, in particular to a long hard segment high strength and toughness polyurethane based on bio-based isomeric chain extender and a preparation method thereof. BACKGROUND

[0002] The synthesis of traditional polyurethane materials relies on petroleum-based raw materials. With the increasing severity of global environmental problems and the deepening of the concept of sustainable development, the unsustainability of petroleum-based polyurethane has become increasingly prominent, restricting its development. In addition, petroleum-based polyurethane still faces problems such as insufficient biostability, degradation products that may cause inflammatory reactions or thrombosis when implanted for a long time, further limiting its application in the biomedical field. Therefore, developing high-strength and high-toughness bio-based polyurethane materials based on renewable resources has become an important direction of current research.

[0003] Under this background, bio-based polyurethane using renewable resources such as vegetable oil, lignin, and starch as raw materials has emerged. However, the polyurethane materials prepared from such chain extenders are usually cross-linked structures, which may make them difficult to be recycled by dissolution. Existing thermoplastic bio-based elastomers generally face the problem of insufficient mechanical properties, which makes the materials prone to irreversible deformation or even fracture when subjected to large stress. Their comprehensive mechanical properties still have a significant gap compared with petroleum-based high-performance elastomers. Bio-based high-strength and toughness elastomers, as an advanced polymer material that utilizes renewable biomass resources (such as vegetable oil, polysaccharides, lignin, etc.) to prepare high elasticity, high strength, good toughness, and recyclable materials, have important needs in wearable electronic devices, biomedical implants, green automotive parts, and many other fields.

[0004] CN118930800A discloses a bio-based polyurethane elastomer and its preparation method and degradation method: the bio-based polyurethane elastomer includes soft segments and hard segments, the mass ratio of the soft segments and the hard segments is 74-88:12-26, the soft segments are non-crystalline bio-based polyester diol structural units, and the hard segments are structural units composed of isocyanate and bio-based chain extender. The bio-based polyurethane elastomer provided by the invention not only has good comprehensive performance, but also has excellent degradable performance.

[0005] CN112979919A discloses a preparation method of a bio-based self-repairing polyurethane elastomer: a small molecule chain extender is obtained by using furfurylamine and vanillin as main raw materials, then a polyurethane prepolymer prepared from diphenylmethane diisocyanate and polypropylene glycol is subjected to chain extension reaction, and after vacuum degassing, the product is poured into a polytetrafluoroethylene mold for solidification, and finally the bio-based polyurethane elastomer with self-repairing function is obtained. The chain extender with imine dynamic covalent bond mentioned in the application is green and environmentally friendly, and the source is extensive. By molecular design, the chain extender is introduced into the polyurethane structure, which endows the elastomer with excellent self-repairing performance and mechanical properties, and the self-repairing efficiency at 60℃ can reach 87%, and the elongation at break is 220%.

[0006] CN118440285A discloses a preparation method of a lignin-based flame-retardant and self-repairing polyurethane elastomer, CN114163598A discloses a bio-based polyol-derived self-repairing polyurethane and a preparation method thereof, and CN117866168A discloses a bio-based self-repairing high-strength and high-toughness polyurethane material and a preparation method thereof. The initial tensile strength of the above-mentioned polyurethane elastomers is below 30MPa. At present, a high-strength and high-toughness thermoplastic elastomer with excellent solvent recovery performance and good bio-based content has not been reported. SUMMARY

[0007] The present application aims at the poor mechanical properties of thermoplastic polyurethane elastomers based on bio-based chain extenders, and provides a polyurethane elastomer containing isosorbide and / or 1,4:3,6-dianhydromannitol long hard segment and poly-caprolactone (PCL) soft segment. The elastomer has excellent tensile recovery performance, tear resistance, puncture resistance, recyclability and high toughness. The bio-based long hard segment chain extender helps to improve the mechanical properties of bio-based polyurethane, and provides a new idea and method for preparing bio-based high-strength and high-toughness thermoplastic polyurethane elastomers.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is: A long hard segment high-strength and high-toughness polyurethane based on bio-based isomer chain extenders, the polyurethane elastomer has the following structural formula: Wherein, n is 2-45, m is 1-26, x is the repetition degree of hard segment, which is 1-5; the A structure is the residue of isosorbide or 1,4:3,6-dianhydromannitol; the molecular weight of the thermoplastic polyurethane elastomer is 2000-200000.

[0009] The polyurethane elastomer designed in the application contains both polycaprolactone soft segments and long hard segment structures, combines the flexibility, crystallinity of PCL chains and the mechanical strength of hard segments, and the PCL segments provide excellent ductility and low temperature performance through their inherent flexibility and crystallization tendency, and the length of the hard segment structure is optimized to ensure the formation of effective physical crosslinking points to provide strength support, while controlling the degree of phase separation to avoid excessive brittleness. The polyurethane elastomer still exhibits good comprehensive mechanical properties in complex environments.

[0010] The application also provides a preparation method of the long hard segment high strength and toughness polyurethane based on the bio-based isomer chain extender, comprising the following steps: Step 1, pre-polymerization of polycaprolactone represented by formula I and p-phenylene diisocyanate (PPDI) represented by formula II to obtain a product PCL-PPDI represented by formula III; Formula I Formula II Formula III Wherein n is 2-45; Step 2, mixing isosorbide (IS) and / or 1,4:3,6-dianhydro-D-mannitol (IM) represented by formula IV and dicyclohexyl methane diisocyanate represented by formula V in an organic solvent, and reacting under the action of a catalyst to obtain a long hard segment chain extender IS / IM / SM-HMDI represented by formula VI, and SM represents a mixture of IS and IM; Formula IV Formula V Formula VI Wherein, x is 1-5, and A structure is the residue of IS or IM; Step 3, adding the obtained long hard segment chain extender dropwise into the prepolymer PCL-PPDI for chain extension reaction, and after washing and drying, the bio-based high strength and toughness thermoplastic polyurethane elastomer product is obtained.

[0011] The preparation method of the long hard segment high strength and toughness polyurethane based on the bio-based isomer chain extender is characterized in that the molecular weight of the polycaprolactone is 248-5058 g / mol. The higher the molecular weight of the polycaprolactone indicates that the content of the soft segment in the structure is higher, and different molecular weights of the soft segment correspond to different flexible properties of the obtained polyurethane elastomer. Different lengths of the long hard segment chain extender also affect the mechanical properties of the obtained polyurethane elastomer, and too long hard segment leads to a decrease in material elasticity and brittleness.

[0012] Preferably, the molecular weight of the polycaprolactone is 800-2000 g / mol. The molar ratio of polycaprolactone to p-phenylene diisocyanate in step 1 is 1:2-3.

[0013] The temperature of the prepolymerization reaction in step 1 is 30-70℃, and the reaction time is 4-10h.

[0014] The molar ratio of isosorbide and / or 1,4:3,6-dianhydro-D-mannitol to dicyclohexylmethane diisocyanate in step 2 is 1.2-2.1:1.

[0015] The catalysts in steps 1 and 2 are independently selected from one of dibutyltin dilaurate, dibutyltin oxide, anhydrous stannous chloride, and dibutyltin dimethoxide, and the mass is 0.1-1% of the total mass of the reaction raw materials.

[0016] The reaction temperature in step 2 is 20-35℃, and the reaction time is 1.5-6h.

[0017] The chain extension reaction temperature in step 3 is 40-100℃, and the reaction time is 6-24h.

[0018] The chain extension agent used in step 2 of the present application is derived from renewable resources such as straw, gutter oil, etc. The thermoplastic polyurethane elastomer of the present application has a mechanical strength of 11 MPa to 49 MPa, and a toughness of 60-204 MJ / m 3 .

[0019] The long hard segment high strength and toughness polyurethane based on bio-based isomeric chain extender of the present application can still maintain excellent mechanical properties for a long time under extreme environments, including but not limited to strong acidic aqueous solution with pH=1, strong alkaline aqueous solution with pH=14, PBS solution, and various enzyme environments such as lipase, protease, and trypsin.

[0020] In some embodiments, the polyurethane elastomer exhibits excellent tensile recovery performance, tear resistance, and puncture resistance, such as in the single-edge notch experiment, the tear energy is as high as 165.6kJ / m 2 ; a 0.2mm thin film can withstand a downward puncture force of about 30N of a 500um diameter puncture needle.

[0021] In some embodiments, the polyurethane elastomer has excellent recyclability, and after three or more cycles of recycling using solvents including but not limited to tetrahydrofuran, dimethylformamide, and dimethyl sulfoxide, the mechanical properties remain good and are even improved under certain conditions.

[0022] In some embodiments, the polyurethane elastomer maintains integrity in quality and surface morphology in extreme environments, and the tensile properties remain good, with a tensile strength of greater than 30 MPa.

[0023] Compared with the prior art, the present application has the following beneficial effects: (1) The thermoplastic polyurethane elastomer provided by the present application promotes the formation of a dense hydrogen bond network between polymer segments by lengthening the chain length of the hard segment, thereby producing a strong microphase separation effect. At the same time, the steric hindrance effect of the hard segment and the rearrangement of the molecular chain inhibit the crystallization behavior of the soft segment to some extent, thereby improving the comprehensive performance of the polyurethane material using a bio-based diol as a chain extender.

[0024] (2) The thermoplastic polyurethane elastomer disclosed by the present application has excellent mechanical properties, and also has excellent tear resistance and puncture resistance, and the material can provide high load capacity even in the presence of damage.

[0025] (3) The thermoplastic polyurethane elastomer disclosed by the present application has a simple preparation process, uses a chain extender of bio-based origin, is green, environmentally friendly, sustainable, and easy to obtain raw materials, and has repeatability and reprocessing ability, in line with the concept of green and circular chemistry. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is the Fourier infrared spectrum of the polyurethane elastomer prepared in Examples 1-5.

[0027] Figure 2 is the stress-strain curve of the polyurethane elastomer prepared in Examples 1-5.

[0028] Figure 3 is a schematic diagram of a 0.2g polyurethane elastomer pulling up a 7kg dumbbell prepared in Example 1.

[0029] Figure 4 is the tear resistance energy calculated from the single-edge notched experiment of the polyurethane elastomer prepared in Examples 1-5.

[0030] Figure 5 is a test schematic diagram and process photo of the pants tear test of the polyurethane elastomer prepared in Example 1.

[0031] Figure 6 is a puncture test schematic diagram of the puncture needle puncture experiment of the polyurethane elastomer prepared in Example 1.

[0032] Figure 7 is a schematic diagram of the puncture test of the 0.5mm neutral pen on the PUIM-10 film of the polyurethane elastomer prepared in Example 1.

[0033] Figure 8Stress-strain curves of the polyurethane elastomer prepared in Example 1 in the original state and after three cycles of recovery.

[0034] Figure 9 Stress-strain curves of the polyurethane elastomer prepared in Example 1 after immersion in an aqueous solution with pH = 1 for different times. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below in conjunction with examples. It should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the present application. Those skilled in the art can make modifications or equivalent replacements without departing from the spirit and scope of the present application, which should be covered within the protection scope of the present application.

[0036] The raw materials used in the following specific embodiments are all purchased from the market.

[0037] Example 1 (1) In a glove box filled with high-purity nitrogen, polycaprolactone (PCL), catalyst dibutyltin dilaurate and p-phenylene diisocyanate (PPDI) were accurately weighed and sequentially added to a dry three-necked reactor equipped with a mechanical stirrer. The three-necked reactor was sealed with vacuum grease and sealing film, and stirred at 60°C for 4h. When the viscosity of the reaction system no longer changed, the content of isocyanate groups (-NCO) in the prepolymer was determined by reverse titration with di-n-butylamine, and the -NCO content was 4.4%. The prepolymer was recorded as PCL-PPDI, wherein the molar ratio of PCL to PPDI was 1:2.1.

[0038] (2) According to the -NCO content of the prepolymer in the first step, excess chain extender 1,4:3,6-dianhydro-D-mannitol (IM), dicyclohexyl methane diisocyanate (HMDI) and catalyst dibutyltin dilaurate were accurately weighed in a flask in a glove box filled with high-purity nitrogen, and stirred at room temperature for 2h to form an -OH capped long hard segment chain extender, recorded as IM-HMDI. The molar ratio of IM to HMDI was 2.1:1, and the amount of catalyst was 1% of the total mass of the reaction raw materials.

[0039] (3) In a glove box filled with high purity nitrogen, a dry three-necked reactor was equipped with a mechanical stirrer, and PCL-PPDI and solvent were accurately added into the reactor, and stirred to dissolve at 70 °C. The obtained IM-HMDI was added dropwise into the PPDI-terminated PCL prepolymer for chain extension reaction, and the reactor was sealed with a sealing film again after the addition was completed. The reaction was carried out at 70 °C under constant mechanical stirring for 8 h. After the reaction was completed, the obtained product was slowly poured into excess deionized water for sedimentation and washing 3-5 times. The washed product was dried on a hot plate at 60 °C for 24 h, and then transferred to a vacuum oven at 60 °C for drying for 24 h until the weight was constant. Finally, a long hard segment high toughness polyurethane based on bio-based isomeric chain extender was obtained, which was recorded as PUIM-10. The number average molecular weight (Mn) of PUIM-10 was 1.8 x 10 4 g / mol, the weight average molecular weight (Mw) was 5.3 x 10 4 g / mol, and the dispersion index (PDI) was 2.9. The Fourier infrared spectrum of PUIM-10 is shown in Figure 1 .

[0040] Example 2 According to the preparation process of Example 1, the difference is only that the chain extender in step 2 is isosorbide, and the obtained polyurethane elastomer is recorded as PUIM-0, and the Mn is 1.2 x 10 4 g / mol, the Mw is 3.0 x 10 4 g / mol, and the PDI is 2.5. The Fourier infrared spectrum of PUIM-0 is shown in Figure 1 .

[0041] Example 3 According to the preparation process of Example 1, the difference is only that step 2 is a mixed chain extender of 1,4:3,6-dianhydro-D-mannitol and isosorbide, recorded as SM5-HMDI. The molar ratio of IM, IS and HMDI is 1.05:1.05:1, and the obtained polyurethane elastomer is recorded as PUIM-5, and the Mn is 2.2 x 10 4 g / mol, the Mw is 4.8 x 10 4 g / mol, and the PDI is 2.2. The Fourier infrared spectrum thereof is shown in Figure 1 .

[0042] Example 4 According to the preparation process of Example 1, the difference is only that step 2 is a mixed chain extender of 1,4:3,6-dianhydro-D-mannitol and isosorbide, recorded as SM1-HMDI. The molar ratio of IM, IS and HMDI is 1.89:0.21:1, and the obtained polyurethane elastomer is recorded as PUIM-1, and the Mn is 1.7 x 10 4 g / mol, the Mw is 3.6 x 104 g / mol, PDI was 2.2, and its Fourier infrared spectrum was shown in FIG. 1. Figure 1 .

[0043] Example 5 According to the preparation process of Example 1, the only difference was that step 2 was a mixed chain extender of 1,4:3,6-dianhydro-D-mannitol and isosorbide, denoted as SM9-HMDI. The molar ratio of IM, IS and HMDI was 0.21:1.89:1, and the obtained polyurethane elastomer was denoted as PUIM-9, whose Mn was 1.7 x 10 4 g / mol, Mw was 3.8 x 10 4 g / mol, PDI was 2.2, and its Fourier infrared spectrum was shown in FIG. 1. Figure 1 .

[0044] Performance test and result analysis The products prepared in the examples were characterized and tested for performance, and the test process was as follows: 1. Fourier infrared spectrum The infrared spectrum of the sample was tested using an infrared spectrometer of model Nicolet IS 50 of Thermo Scientific Company of the United States, using attenuated total reflection. No stretching vibration peak of -NCO was observed at 2230 cm -1 , which indicated that the diisocyanate had been completely reacted. In the wavelength interval of 1740-1690 cm -1 , a clear stretching vibration peak was observed, which belonged to the vibration peak of ester carbonyl (C=O). The absorption peak in the wavelength interval of 3400-3320 cm -1 belonged to the stretching vibration peak of -NH group, indicating that the reaction between -NCO and -OH had occurred, and the urethane bond (-NH-COO-) was successfully generated, the characteristic peak appeared, indicating the successful synthesis of the target polyurethane elastomer.

[0045] 2. Mechanical property test The sample film was cut into dumbbell-shaped sample pieces with a size of 20 mm x 2.0 mm x 0.5 mm. The two ends of the sample piece were fixed on the metal clamps of the testing machine, and the tensile test was carried out at a stretching rate of 50 mm / min. The stress-strain curve of the polyurethane elastomer was shown in FIG. 2, and PUIM-10 showed the highest tensile strength, reaching 48.5 MPa, and the elongation at break was 1250%, as shown in FIG. 3, PUIM-10 exhibited significant performance advantages. Figure 2 Figure 3

[0046] 3. Measurement of fracture energy (1) Single-edge notch test​​ The tear resistance of each sample was evaluated by a single edge notched experiment and the fracture energy was calculated. The sample film was cut into a rectangular specimen with a size of 20 mm x 5.0 mm x 0.5 mm. The notched specimen was cut with a sharp blade or scissors to make an initial notch with a width of 1 mm in the middle of the specimen to simulate the defects or damages that might exist in the material during actual use. Both the notched and unnotched specimens were fixed at both ends of the metal clamp and the tensile test was performed at a stretching speed of 50 mm / min until the sample was pulled apart. The fracture energy was calculated according to the following formula: wherein G is the fracture energy, c is the notch length (1 mm), W is the strain energy calculated by integrating the stress-strain curve of the unnotched sample, and λ c is the elongation at break of the notched sample.

[0047] (2) Pants tear experiment The tear resistance of the elastomer was further evaluated by a pants tear experiment. The sample film was cut into a specimen with a size of 40 mm x 20 mm x 0.5 mm and a length of 20 mm was cut as an initial notch. The specimen was fixed at both ends of the metal clamp and the tear test was performed at a tear rate of 50 mm / min at room temperature until the specimen was completely torn open. The fracture energy of the sample was calculated as follows: wherein G is the fracture energy, F is the force required for tearing, L is the displacement, t is the thickness of the specimen, and L bulk is the tear length.

[0048] The single edge notched experiment was performed as Figure 4 , and the tear energy of PUIM-10 was 165.5 kJ / m 2 , which was highly consistent with the results of the pants tear experiment in Figure 5 , further proving the excellent tear resistance of PUIM-10. The long hard segment structure enhances the interaction between the molecular chains and the energy dissipation mechanism of the material under high strain. When the specimen is subjected to a large strain, the transverse notch is obviously blunted, effectively inhibiting the propagation of the crack, 4. Puncture resistance test The puncture resistance of the sample was tested by a material testing machine (CAAKER, China). The film sample with a thickness of 0.2 mm was fixed between two circular metal pieces to ensure that the film was flat and wrinkle-free. The puncture needle was vertically fixed above the film and moved downward until the film was pierced.

[0049] As shown in Figure 6 , the puncture force of the PUIM-10 film was the largest, reaching 33.9 N, and the maximum displacement was 40.6 mm. AsFigure 7 As shown, under the action of artificial force, the PUIM-10 film was punctured using a 0.5 mm neutral pen, the PUIM-10 film was not punctured, and the punctured film still maintained a colorless and transparent state, without obvious cracks or damage, with excellent puncture resistance and structural stability, and was able to resist the impact of certain external environments.

[0050] 5. Recyclability test The prepared elastomer film sample was cut and then dissolved in a THF solution, and poured into a tetrafluoro mold to prepare a new film. This process was repeated 3 times, and the tensile properties of the film prepared each time were tested. As shown in Figure 8 As shown, the tensile strength of PUIM-10 slightly increased after the first recycling, and the tensile strength of the third recycled sample changed little compared with the original sample, indicating that after multiple dissolving and reprocessing, the internal structure of the material tended to be stable and no longer changed significantly.

[0051] 6. Extreme environmental stability test All sample films were cut into dumbbell-shaped samples (20 mm x 2.0 mm x 0.5 mm) and placed in PBS solutions containing lipase (pH = 7.3-7.4), and aqueous solutions of pH = 1 and pH = 14, and placed in a 37 °C constant temperature shaker. The films were taken out at regular intervals, rinsed and dried, and the tensile properties of the samples were tested.

[0052] The stress-strain curve of the PUIM-10 sample after immersion in a strong acid solution of pH = 1 is shown in Figure 9 As shown, the tensile strength remained above 30 MPa after 30 days of immersion, and the film had good resistance to extreme environments.

Claims

1. A long hard segment, high strength and toughness polyurethane based on a bio-based isomeric chain extender, characterized in that, The thermoplastic polyurethane elastomer has the following structural formula: Wherein, n is 2-45, m is 1-26, x is the repeating degree of hard segment, which is 1-5; A structure is the residue of isosorbide or 1,4:3,6-dianhydro-D-mannitol; the molecular weight of the thermoplastic polyurethane elastomer is 2000-200000.

2. The process for the preparation of long hard segment high tenacity polyurethane based on bio-based isomeric chain extender as claimed in claim 1, wherein, The method comprises the steps of: Step 1, pre-polymerization of polycaprolactone shown in formula I and p-phenylene diisocyanate shown in formula II under the action of a catalyst to obtain a pre-polymer PCL-PPDI shown in formula III; Formula I Formula II Formula III Wherein, n is 2-45; Step 2, mixing isosorbide and / or 1,4:3,6-dianhydro-D-mannitol shown in formula IV and dicyclohexylmethane diisocyanate shown in formula V in an organic solvent, and reacting under the action of a catalyst to obtain a long hard segment chain extender shown in formula VI; Formula IV Formula V Formula VI Wherein, x is 1-5, and A structure is the residue of isosorbide or 1,4:3,6-dianhydro-D-mannitol; Step 3, dropwise adding the long hard segment chain extender obtained in step 2 into the pre-polymer PCL-PPDI for chain extension reaction, and after washing and drying, the bio-based high-strength and tough thermoplastic polyurethane elastomer is obtained.

3. The process for the preparation of long hard segment high tenacity polyurethane based on bio-based isomeric chain extender as claimed in claim 2, wherein, The molecular weight of the polycaprolactone is 248-5058 g / mol.

4. The process for the preparation of long hard segment high tenacity polyurethane based on bio-based isomeric chain extender as claimed in claim 2, wherein, The molar ratio of polycaprolactone to p-phenylene diisocyanate in step 1 is 1:2-3.

5. The method of making long hard segment, high tenacity polyurethane based on bio-based isomeric chain extender of claim 2, characterized in that, The temperature of the pre-polymerization in step 1 is 30-70℃, and the reaction time is 4-10h.

6. The method of making long hard segment, high tenacity polyurethane based on bio-based isomeric chain extender of claim 2, characterized in that, The molar ratio of isosorbide and / or 1,4:3,6-dianhydro-D-mannitol to dicyclohexylmethane diisocyanate in step 2 is 1.2-2.1:

1.

7. The method of making long hard segment, high tenacity polyurethane based on bio-based isomeric chain extender of claim 2, characterized in that, The catalyst used in the reaction is independently selected from one of dibutyltin dilaurate, dibutyltin oxide, anhydrous stannous chloride and dibutyltin dimethoxide, and the mass is 0.1-1% of the total mass of the reaction raw materials.

8. The method of making long hard segment, high tenacity polyurethane based on bio-based isomeric chain extender of claim 2, characterized in that, The reaction temperature in step 2 is 20-35℃, and the reaction time is 1.5-6h.

9. The method of making long hard segment, high strength and toughness polyurethane based on bio-based isomeric chain extender of claim 2, characterized in that, The chain extension reaction temperature in step 3 is 40-100℃, and the reaction time is 6-24h.

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