Covalent self-adaptive network cross-linking toughened polylactic acid polyurethane elastomer and preparation method thereof

Abstract

The invention belongs to the technical field of polylactic acid elastomers. The invention provides a covalent self-adaptive network cross-linked toughened polylactic acid polyurethane elastomer. The polylactic acid polyurethane elastomer is a cross-linked polyurethane elastomer of which the soft segment is dihydroxyl-terminated polylactic acid dihydric alcohol and the hard segment is a dynamic covalent bond-containing cross-linked polyurethane elastomer. The invention also provides a preparation method of the covalent self-adaptive network cross-linked and toughened polylactic acid polyurethane elastomer. The invention also provides application of the polylactic acid polyurethane elastomer in the fields of degradable medical implants and flexible electronics. The dynamic bond toughened cross-linked polylactic acid polyurethane is prepared from a low-molecular-weight polylactic acid dihydric alcohol derivative through a cross-linked structure in a manner of introducing a dynamic covalent bond, and has the advantages of intrinsic elasticity, high elongation at break, high toughness, biocompatibility, excellent self-healing property and recoverability.

Description

Technical Field

[0001] The invention belongs to the technical field of polylactic acid elastomers, and particularly relates to a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer and a preparation method thereof. Background Art

[0002] With the gradual depletion of oil resources and the increasing demand for environmental protection, research on alternatives to oil-based materials is becoming a focus. Natural bio-based resources represented by lactic acid, lignin, etc. have attracted much attention due to their renewable and environmentally friendly properties. Among them, polylactic acid (PLA), as a representative bio-based material, is gradually replacing some traditional plastics such as polyethylene with its advantages of high strength, heat resistance, degradability and biocompatibility. However, it is well known that its semi-crystalline nature leads to room temperature brittleness, low impact strength and low elongation at break, which seriously restricts its adaptability in multiple scenarios, especially in industrial and medical applications that require good deformation ability under high stress levels. Therefore, in order to further broaden the application scope of PLA, it needs to be appropriately physically or chemically modified to meet different usage requirements.

[0003] In the prior art, the plasticization and toughening modification of PLA mainly includes the methods of blending and copolymerization. Chinese patent CN108707322A uses bio-based difunctional plant oil-based derivatives to blend with diisocyanates and polylactic acid at high temperature to toughen and modify polylactic acid with flexible bio-based polyurethane. Although both have made great improvements to the toughness and tensile properties of polylactic acid, the high-temperature blending process involved carries the risk of high-temperature thermal degradation of polylactic acid, which may lead to unstable mechanical properties, and diisocyanates may also produce toxic volatiles under high-temperature processing. Therefore, the development of intrinsically elastic polylactic acid-based elastomers, the toughening of polylactic acid materials through strong chemical bonds at the molecular level, and the reaction is carried out within a relatively low temperature range (<150°C) to maintain the stability of polylactic acid performance.

[0004] Polyurethane (PU), with its adjustable ratio of soft and hard segments, allows for easy customization of its glass transition temperature and mechanical properties, making it an ideal chemical backbone for polylactic acid-based elastomers. Commercial thermosetting PU generally possesses a cross-linked network structure, resulting in high mechanical strength due to strong covalent crosslinking, but typically suffers from insufficient elongation at break and is not reshapeable. Thermoplastic PU, on the other hand, is typically a random entanglement of linear molecules. It exhibits poor resilience when subjected to external loads, is prone to chain slippage leading to permanent deformation, and exhibits relatively poor mechanical strength. Balancing high strength, resilience, and reshapeability has been a key challenge in the development of polyurethane to date. Summary of the Invention

[0005] The present invention aims to address the shortcomings of the existing technology and provide a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer and a method for preparing the same. The present invention innovatively introduces a cross-linked structure into the polylactic acid polyurethane system to provide high mechanical strength and good elasticity. Simultaneously, the introduction of dynamic covalent bonds constructs covalently adaptive networks (CANs)—polymer networks dominated by dynamic covalent bonds, with exchangeable chemical covalent bonds that can dissociate or reorganize upon heating. This strategy retains the high strength and toughness of traditional thermosetting polyurethanes while also enabling the reconfiguration and self-healing properties of thermoplastic polyurethanes. The prepared polylactic acid polyurethane elastomer exhibits ideal strength, elongation at break, and toughness, with no apparent strain yield in the tensile curve, and excellent self-healing and recyclability.

[0006] In order to solve the above problems, the present invention provides the following technical solutions: A covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer comprises a soft segment of dihydroxy-terminated polylactic acid diol and a hard segment of a cross-linked polyurethane elastomer containing dynamic covalent bonds.

[0007] In the polylactic acid polyurethane elastomer as described above, the dynamic covalent bond includes one or more of an oxime bond, a Diels-Alder bond, a borate bond, a disulfide bond, a diselenide bond, a hindered urea bond, an imine bond, and an acylhydrazone bond.

[0008] The polylactic acid polyurethane elastomer as described above, the polylactic acid diol structural formula is as shown in formula (I), Formula (I); Wherein, R represents a molecular structure having dithiol, dihydroxyl, and diamine groups; R' represents the carbon chain structure after the ring-opening copolymerization reaction between the first monomer and the second monomer, such as -O-CH2-(CH2)4-CO-, -O-CH2-(CH2)8-CO-, -O-CH2-(CH2) 10 -CO-, etc., m, n represent the number of structural units, m is 1~9, n is 1~9.

[0009] Based on the same inventive concept, the present invention provides a method for preparing a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer, comprising the following steps: (1) Preparation of polylactic acid diol: first, a first monomer, a second monomer, and a difunctional initiator are heated in an inert gas atmosphere for ring-opening polymerization under the catalysis of an appropriate amount of a first catalyst to prepare polylactic acid diol; (2) Preparation of polylactic acid polyurethane elastomer.

[0010] In the preparation method described above, the first monomer is lactide, and more preferably, the first monomer is L-lactide.

[0011] In the preparation method described above, the second monomer is selected from one or more of ε-caprolactone, δ-caprolactone, δ-valerolactone, γ-octalactone, and δ-decalactone. Further preferably, the second monomer comprises ε-caprolactone or δ-caprolactone. Most preferably, the second monomer is selected from ε-caprolactone.

[0012] Preferably, the difunctional initiator is selected from any one of the following (a)-(c): (a) The difunctional initiator is a diol. Specifically, the diol is selected from one or more of ethylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, or isosorbide. Preferably, the diol is selected from 1,4-butanediol. (b) the difunctional initiator is a diamine, specifically, the diamine is selected from one or more of ethylenediamine, 1,6-hexanediamine, p-phenylenediamine, and 4,4'-diaminodiphenylmethane; (c) The difunctional initiator is a dithiol initiator. Specifically, the dithiol initiator is selected from one or more of 1,2-ethanedithiol, 1,4-butanedithiol, 1,5-pentanedithiol, 1,6-hexanedithiol and 1,8-octanedithiol.

[0013] This invention uses lactide, a natural biomass-derived first monomer, as a raw material. After copolymerization with a second monomer to produce a low-molecular-weight, dihydroxy-terminated polylactic acid diol as the soft segment, dynamic reversible covalent bonds are introduced via a one-pot, two-step process to prepare a polylactic acid-polyurethane elastomer with a cross-linked network structure. Intermolecular hydrogen bonding within the hard domains promotes microphase separation, forming a physical entanglement network that serves as physical crosslinking points to toughen the material. Simultaneously, low-energy-barrier dynamic covalent bonds enable dynamic crosslinking regulation, allowing the material to dissipate more energy when subjected to external loads, endowing it with excellent toughness and self-healing properties, providing a new strategy for the development of sustainable materials.

[0014] The preparation method as described above is a preferred embodiment of the present invention. In the step (1), L-lactide, ε-caprolactone and 1,4-butanediol, as well as a stannous isooctoate catalyst, are placed in a Shlenk flask, and vacuum dehydration and nitrogen backfilling are repeated three times, followed by heating in an inert gas atmosphere for ring-opening polymerization to prepare polylactic acid diol. Under these conditions, vacuum dehydration can prevent the decrease in molecular weight caused by hydrolysis reaction.

[0015] In the preparation method described above, the reaction conditions for the ring-opening polymerization in step (1) are: the ring-opening polymerization is carried out at 50-150°C in an anhydrous and oxygen-free state for 12-48 hours; preferably, the reaction conditions for the ring-opening polymerization in step (1) are: the ring-opening polymerization is carried out at 120°C in an anhydrous and oxygen-free state for 24 hours. Under these conditions, the polymerization temperature is 120 o C can ensure sufficient reaction activity while avoiding unnecessary side reactions; the reaction time of 24 hours ensures that the reaction is close to equilibrium, avoiding low number average molecular weight Mn or excessive residual monomers due to insufficient reaction.

[0016] In the preparation method described above, the molecular weight of the polylactic acid diol prepared in step (1) is between 500 and 4000; preferably, the molecular weight of the polylactic acid diol prepared in step (1) is between 1000 and 2000. This molecular weight range provides a moderate length for the polyurethane soft segment and can form an effective microphase separation structure with the hard segment. A molecular weight that is too low, below 1000, will cause excessive aggregation of the hard segment, resulting in brittleness of the material; while a molecular weight that is too high, above 2000, will inhibit the self-assembly of the hard segment, weaken the physical crosslinking points, and reduce the strength and elasticity of the material.

[0017] In the preparation method described above, in step (1), the first catalyst is selected from one or more of 1,3-diphenylurea, potassium methoxide, dibutyltin dilaurate, stannous isooctanoate, stannous chloride, dibutyltin diacetate, tetrabutyl titanate, or 1,5,7-triazabicyclo[4.4.0]dec-5-ene. Preferably, the first catalyst is selected from stannous isooctanoate.

[0018] In the preparation method described above, in step (1), the amount of the first catalyst is 0.01% to 1% of the total mass of the monomers participating in the reaction; further preferably, in step (1), the amount of the first catalyst is 0.3% of the total mass of the monomers participating in the reaction; In the preparation method described above, in step (1), the molar ratio of the first monomer, the second monomer, and the difunctional initiator is (0.1-9):1:(0.02-2.5). Preferably, the molar ratio of the first monomer, the second monomer, and the difunctional initiator is (0.25-0.7):1:(0.05-0.1).

[0019] Optionally, in step (1), the molar ratio of the first monomer to the second monomer is 2:8, 3:7 or 4:6.

[0020] In some embodiments of the present invention, the preparation of the polylactic acid polyurethane elastomer in step (2) comprises the following steps: first, vacuum dehydrating the polylactic acid diol described in step (1), then adding diisocyanate and a second catalyst, and performing a prepolymerization reaction under the protection of an inert gas to obtain a prepolymer terminated with isocyanate groups at both ends, cooling the above prepolymer and vacuum degassing, adding a chain extender containing an oxime bond and a second catalyst to carry out a chain extension reaction, and then keeping the temperature overnight, and then adding an organic solvent to the chain extension reaction product of the previous step to prepare a polyurethane solution of a certain concentration, cooling to room temperature and pouring it into a polytetrafluoroethylene mold, vacuum degassing, and drying to obtain a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer.

[0021] Preferably, the preparation of the polylactic acid polyurethane elastomer in step (2) comprises the following steps: firstly heating the polylactic acid diol oil bath in step (1) to 120 o C, and vacuum for 3 h to remove residual moisture, then add excess diisocyanate and an appropriate amount of the second catalyst, and heat to 85 under the protection of inert gas. o C and prepolymerization was carried out under nitrogen protection for 2 h to obtain a prepolymer terminated with isocyanate groups at both ends. The prepolymer was cooled to 65 o C and vacuum degassing, add the chain extender containing oxime bond and the second catalyst to carry out chain extension reaction, and after reacting for 1 hour, transfer to 65 o C oven overnight, then add organic solvent to the chain extension reaction product of the previous step to prepare a polyurethane solution of a certain concentration, and after the solution is cooled to room temperature, pour it into a polytetrafluoroethylene mold, and after vacuum degassing, 60 o C blast drying oven for 48 hours to obtain a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer. o The vacuum dehydration step is to prevent the possible water from consuming the diisocyanate to be added next; the temperature is lowered to 65 before the prepolymerization reaction. o C can reduce the probability of diisocyanate being consumed by moisture in the air in an open system in the initial stage of the reaction, as well as the probability of diisocyanate self-polymerization, so that diisocyanate reacts with polylactic acid diol first; the prepolymerization reaction is maintained at 85 o C can ensure the stable reaction kinetics of diisocyanate; the temperature is lowered to 65 o C can promote the reaction of oxime bond of chain extenders containing oxime bond, such as dimethylglyoxime, with isocyanate bond to form oxime-carbamate bond, and weaken the dissociation reaction of oxime-carbamate bond. o The drying temperature of C can evaporate DMF at a moderate rate, so that there are almost no bubbles in the film caused by excessive evaporation of DMF.

[0022] In the preparation method described above, the diisocyanate is selected from one or more of isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane 4,4'-diisocyanate, 4,4'-methylenebis(phenyl isocyanate), and toluene diisocyanate. Preferably, the diisocyanate is selected from isophorone diisocyanate. The asymmetric structure of isophorone diisocyanate inhibits crystallization, preventing the material from becoming brittle due to crystallization. Furthermore, the absence of unsaturated bonds prevents yellowing of the material.

[0023] In the preparation method described above, the oxime-containing chain extender is selected from one or more of glyoxime, 1,4-benzoquinone dioxime, dimethylglyoxime, 2,4-pentanedione dioxime, and glutaraldehyde dioxime. Preferably, the oxime-containing chain extender is selected from dimethylglyoxime.

[0024] The preparation method as described above, the chain extension reaction temperature in step (2) is 40~100 o C, the reaction time is 0.5~3 h. Preferably, the chain extension reaction temperature in step (2) is 65 o C, reaction time is 1h.

[0025] In some other embodiments of the present invention, the preparation of the polylactic acid polyurethane elastomer in step (2) includes the following steps: first, vacuum dehydrating the polylactic acid diol described in step (1), then adding an excess of diisocyanate and an appropriate amount of a second catalyst, and performing a prepolymerization reaction under the protection of an inert gas to obtain a prepolymer terminated with isocyanate groups at both ends, cooling the above prepolymer and vacuum degassing, adding a furan structure-containing chain extender and a second catalyst to carry out a chain extension reaction, and then adding a solution of a bismaleimide structure-containing crosslinker dissolved in an organic solvent to carry out a crosslinking reaction, and then adding the organic solvent to the crosslinking reaction product of the previous step to prepare a polyurethane solution of a certain concentration, cooling to room temperature and pouring it into a polytetrafluoroethylene mold, vacuum degassing, and drying to obtain a covalently adaptive network cross-linked and toughened polylactic acid polyurethane elastomer.

[0026] Preferably, the preparation of the polylactic acid polyurethane elastomer in step (2) comprises the following steps: firstly heating the polylactic acid diol oil bath in step (1) to 120 o C, and vacuum for 3 hours to remove residual moisture, then cool to 65 o C and stabilized, add excess diisocyanate and an appropriate amount of the second catalyst, and heat to 85 o C, a prepolymerization reaction is carried out under the protection of an inert gas to obtain a prepolymer terminated with isocyanate groups at both ends, the prepolymer is cooled to 65°C and vacuum degassed, a furan structure-containing chain extender and a second catalyst are added to carry out a chain extension reaction, and the prepolymer is heated to 65°C. oAfter 1.5 h of reaction, a crosslinking agent solution containing bismaleimide structure dissolved in an organic solvent was added to carry out a crosslinking reaction. Then, an organic solvent was added to the crosslinking reaction product of the previous step to prepare a polyurethane solution of a certain concentration. After cooling to room temperature, the solution was poured into a polytetrafluoroethylene mold. After vacuum degassing, the solution was placed at 60 o C blast drying oven for 48 h to obtain a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer. In the present invention, the temperature is lowered to 65 before the prepolymerization reaction. o C can reduce the probability of diisocyanate being consumed by moisture in the air in an open system in the initial stage of the reaction, as well as the probability of diisocyanate self-polymerization, so that diisocyanate reacts with polylactic acid diol first; the prepolymerization reaction is maintained at 85 o C can ensure the stable reaction kinetics of diisocyanate; the temperature is lowered to 65 o C can promote the reaction of the hydroxyl group of furan-containing chain extenders such as 2,5-furan dimethanol with the isocyanate bond to form a carbamate bond, and prevent the double bond oxidation caused by excessive temperature. Controlling the crosslinking stage at this temperature can promote the addition reaction of the furan group (conjugated diene) with the bismaleimide group (dienophile), crosslinking the two linear molecules. o At a drying temperature of 0.5°C, on the one hand, the effect of temperature on unsaturated bonds can be reduced, and on the other hand, DMF can be evaporated at a moderate rate, so that there are almost no bubbles in the film caused by excessive evaporation of DMF.

[0027] In the preparation method as described above, in step (2), the cross-linking agent containing a bismaleimide structure is selected from one or more of N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N'-m-phenylene bismaleimide, N,N'-(1,4-phenylene)bismaleimide, 1,2-bis(maleimide)ethane, 1,4-bis(maleimido)butane, and 1,6-dimaleimidohexane; preferably, the cross-linking agent containing a bismaleimide structure is selected from N,N'-(4,4'-methylenediphenyl)bismaleimide. Under these conditions, the furan group is introduced into the polyurethane hard segment as a conjugated diene, and reacts with the bismaleimide structure as a dienophile through a one-step synergistic [4+2] cycloaddition reaction to form a six-membered ring structure, cross-linking the two linear molecules, giving the linear polylactic acid polyurethane a cross-linked structure and dynamic properties, thereby improving the toughness and elasticity of the polylactic acid polyurethane.

[0028] In the preparation method as described above, in step (2), the second catalyst is selected from one or more of bis(dimethylaminoethyl)ether, pentamethyldiethylenetriamine, dibutyltin dilaurate, stannous isooctanoate, stannous chloride, dibutyltin diacetate or tetrabutyl titanate; preferably, the second catalyst is selected from stannous isooctanoate.

[0029] In the preparation method described above, in step (2), the polylactic acid diol is pre-dehydrated under vacuum conditions: during the vacuum dehydration process, the polylactic acid diol is heated to 80-120°C and dehydrated under vacuum for 1-6 hours. Preferably, in step (2), the polylactic acid diol is pre-dehydrated under vacuum conditions: during the vacuum dehydration process, the polylactic acid diol is heated to 120°C and dehydrated under vacuum for 3 hours.

[0030] In the preparation method as described above, in step (2), during the synthesis of the prepolymer, the reaction temperature is 60 to 100° C. Preferably, in step (2), during the synthesis of the prepolymer, the reaction temperature is 65 to 85° C.

[0031] In the preparation method as described above, in step (2), during the synthesis of the prepolymer, the molar ratio of diisocyanate to dihydroxy-terminated polylactic acid diol is (1-10):1. Preferably, in step (2), during the synthesis of the prepolymer, the molar ratio of diisocyanate to dihydroxy-terminated polylactic acid diol is (2-5):1. Within this range, the polylactic acid diol can be fully blocked by the isocyanate group, the molecular weight of the polyurethane can be maximized, and a moderate cross-linked structure can be formed. If the molar ratio of diisocyanate to dihydroxy-terminated polylactic acid diol is lower than 2:1, it cannot be completely blocked, resulting in a low molecular weight, which seriously affects the performance of the polylactic acid polyurethane; if the molar ratio of diisocyanate to dihydroxy-terminated polylactic acid diol is higher than 5:1, it may cause excessive cross-linking and reduce the elongation at break. There is also a biosafety risk.

[0032] In the preparation method described above, in step (2), the molar ratio of the furan-containing chain extender to the bismaleimide-containing cross-linker is 1:(0.1-1). Preferably, in step (2), the molar ratio of the furan-containing chain extender to the bismaleimide-containing cross-linker is 1:0.1.

[0033] In the present invention, the R value is the isocyanate index, which is defined as the ratio of the amount of NCO to OH substances involved in the polyurethane synthesis reaction. Preferably, in the present invention, the R value is 1 to 2.

[0034] In the preparation method described above, in step (2), the furan-containing chain extender is selected from one or more of 2,5-furan dimethanol, 3,4-bis(hydroxymethyl)furan, and 1-(furan-2-yl)-2,2-dimethylpropane-1,3-diol. Preferably, in step (2), the furan-containing chain extender is selected from 2,5-furan dimethanol.

[0035] The present invention also provides applications of the polylactic acid polyurethane elastomer described above or the polylactic acid polyurethane elastomer prepared by the above preparation method in the fields of degradable medical implants and flexible electronics, such as flexible motion sensor materials or electrocardiogram monitoring materials.

[0036] Compared with the existing technology, the effects and advantages of the present invention are: 1. The present invention uses a chemical copolymerization method to connect the diol derivatives of polylactic acid to the chemical skeleton of thermoplastic polyurethane through chemical bonding at a relatively low reaction temperature (60-85°C), thus avoiding the risks of poor compatibility between polylactic acid and flexible blends, thermal degradation of polylactic acid at high temperature (>150°C), and volatilization of toxic substances in traditional blending modification schemes.

[0037] 2. This invention prepares dynamically bond-toughened cross-linked polylactic acid polyurethane by crosslinking low-molecular-weight polylactic acid diol derivatives and introducing dynamic covalent bonds. These cross-linked polylactic acid polyurethanes exhibit intrinsic elasticity, high elongation at break, high toughness, biocompatibility, superior self-healing properties, and recyclability. By adjusting the type of chain extender and the ratio of other monomers, the polylactic acid polyurethane elastomers possess customizable mechanical properties.

[0038] 3. The present invention overcomes the inherent brittleness and poor elongation of polylactic acid and the disadvantages of high processing temperature. The obtained elastomer has excellent mechanical properties at room temperature and an elongation at break of more than 1000%.

[0039] 4. The present invention reduces the interchain interaction by introducing dynamic covalent bonds, thereby obtaining a self-healing and recyclable thermoplastic cross-linked polyurethane elastomer, and the mechanical properties are almost unaffected after self-healing or recycling.

[0040] 5. The present invention has excellent elasticity and biocompatibility, and shows greater application prospects in flexible electronic fields such as flexible motion sensor materials and electrocardiogram monitoring materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 is the infrared spectrum of PLA diol prepared in Example 1 of the present invention; Figure 2 IR spectra of PLA diol, prepolymer, PU-DMG, and PU-BDO involved in Example 7 and Comparative Example 1 of the present invention; Figure 3 is a comparison of the XRD spectra of PU-DMG and PU-BDO involved in Example 7 and Comparative Example 1 of the present invention with the XRD spectrum of PLA; Figure 4 is the dynamic thermal analysis result of PU-DMG involved in Example 7 of the present invention; Figure 5 1 are uniaxial tensile stress-strain curves of PU-DMG and PU-BDO involved in Example 7 of the present invention and Comparative Example 1; Figure 6 is a stress-strain curve of a uniaxial cyclic tensile test of PU-DMG according to Example 7 of the present invention; Figure 7 is a stress-strain curve of a uniaxial cyclic tensile test of PU-BDO involved in Comparative Example 1 of the present invention; Figure 8 is a constant strain stress-strain curve of the uniaxial cyclic tensile test of PU-DMG involved in Example 7 of the present invention; Figure 9 is a constant strain stress-strain curve of the uniaxial cyclic tensile test of PU-BDO involved in Comparative Example 1 of the present invention; Figure 10 This is proof of the existence of the PU-DMG and PU-BDO cross-linked network involved in Example 7 and Comparative Example 1 of the present invention; Figure 11 1 is the uniaxial tensile stress-strain curve of the PU-DMG involved in Example 7 of the present invention after self-healing for different periods of time; Figure 12 1 is the uniaxial tensile stress-strain curve of PU-BDO involved in Comparative Example 1 of the present invention after undergoing 1.5 h of self-healing treatment; Figure 13 1 is the uniaxial tensile stress-strain curve of PU-DMG involved in Example 7 of the present invention after three solvent recovery; Figure 14 is a statistical graph of cell activity of PU-DMG involved in Example 7 of the present invention; Figure 15 is the uniaxial tensile stress-strain curve of the polyurethane elastomer involved in Comparative Examples 2-4 of the present invention; Figure 16 is the infrared spectrum of FPU-0.1 involved in Example 8 of the present invention; Figure 17 is the XRD spectrum of FPU-0.1 involved in Example 8 of the present invention; Figure 18 is the dynamic thermal analysis result of FPU-0.1 involved in Example 8 of the present invention; Figure 19 is the uniaxial tensile stress-strain curve of FPU-0.1 involved in Example 8 of the present invention; Figure 20 is a stress-strain curve of a uniaxial cyclic tensile test of FPU-0.1 involved in Example 8 of the present invention; Figure 21 uniaxial tensile stress-strain curves of FPU-0.1 involved in Example 8 of the present invention after self-healing for different periods of time; Figure 22 1 is a uniaxial tensile stress-strain curve of FPU-0.1 involved in Example 8 of the present invention after three solvent recovery; Figure 23 This is a statistical graph of cell activity of FPU-0.1 involved in Example 8 of the present invention; Figure 24 is the infrared spectrum of FPU-0.5 involved in Example 9 of the present invention; Figure 25 is the XRD spectrum of FPU-0.5 involved in Example 9 of the present invention; Figure 26 is the uniaxial tensile stress-strain curve of FPU-0.5 involved in Example 9 of the present invention; Figure 27 These are the uniaxial tensile stress-strain curves of Examples 8-11 of the present invention and FPU-0.1, FPU-0.5, FPU-0.05, FPU-0.3 and FPU-0 involved in Comparative Example 5. DETAILED DESCRIPTION

[0042] The following will be combined with the contents of the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] Unless otherwise defined, all technical and scientific terms used in this specification have the same meanings as those commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are intended solely for the purpose of describing specific embodiments and are not intended to limit the invention. The term "and / or" as used in this specification includes any and all combinations of one or more of the associated listed items.

[0044] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0045] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0046] Example 1 This embodiment provides a method for preparing dihydroxy-terminated polylactic acid diol, and the specific preparation steps are as follows: Weigh 3.18×10 -2mol of L-lactide, 0.13 mol of ε-caprolactone and 1.00×10 -2 mol of 1,4-butanediol, and 1.5×10 -4 mol of stannous isooctanoate catalyst, ε-caprolactone and L-lactide in a molar ratio of 8:2, the above raw materials were put into a Shlenk bottle, vacuum-dried and backfilled with nitrogen, repeated three times, and finally heated in an oil bath to 120 under nitrogen protection. o C, and reacted for 24 h to obtain polylactic acid diol with a number average molecular weight of 2000, namely PLA diol.

[0047] Example 2 This embodiment provides a method for preparing a dihydroxy-terminated polylactic acid diol, which differs from Example 1 in that the second monomer "ε-caprolactone" is replaced by "δ-caprolactone".

[0048] Example 3 This embodiment provides a method for preparing a dihydroxy-terminated polylactic acid diol, which differs from Example 1 in that the small molecule difunctional initiator "1,4-butanediol" is replaced by "isosorbide".

[0049] Example 4 This embodiment provides a method for preparing dihydroxy-terminated polylactic acid diol, which differs from Example 1 in that the molar ratio of ε-caprolactone to L-lactide is 7:3.

[0050] Example 5 This embodiment provides a method for preparing dihydroxy-terminated polylactic acid diol, which differs from Example 1 in that the molar ratio of ε-caprolactone to L-lactide is 6:4.

[0051] Example 6 This embodiment provides a method for preparing a dihydroxy-terminated polylactic acid diol, which differs from Example 1 in that the catalyst "stannous isooctanoate" is replaced by "stannous chloride".

[0052] Example 7 This embodiment provides a method for preparing a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer, and the specific preparation steps are as follows: (1) Weigh 20.00 g of PLA diol synthesized in Example 1; (2) Heat the PLA diol oil bath obtained in step (1) to 120 o C, and vacuum for 3 h to remove residual moisture, then cool to 65 o C and stabilized, add 3.30×10 -2 mol of isophorone diisocyanate and 1.28×10-4 mol of stannous isooctanoate catalyst and then heated to 85 o C and carry out prepolymerization under nitrogen protection for 2 h to obtain a prepolymer with isocyanate groups at both ends. o C and vacuum degassing, backfilling with nitrogen, repeat three times and then add 1.04×10 -2 mol of diacetyl oxime, and 1.37×10 -4 mol of stannous isooctanoate, and after 1 h of reaction, transfer to 65 o C oven overnight, the chain extension reaction product was added to anhydrous DMF to prepare a 40 wt% polyurethane solution, and after the solution cooled to room temperature, it was poured into a polytetrafluoroethylene mold, vacuum degassed, and placed at 60 o The product was dried in a forced air drying oven at C for 48 h, and was named PU-DMG; the R value was 1.61.

[0053] Example 8 This embodiment provides a method for preparing a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer, and the specific preparation steps are as follows: (1) Weigh 20.00 g of PLA diol synthesized in Example 1; (2) Heat the PLA diol oil bath obtained in step (1) to 120 o C, and vacuum for 3 hours to remove residual moisture, then cool to 65 o C and stabilized, add 3.50×10 -2 mol of isophorone diisocyanate and 1.28×10 -4 mol of stannous isooctanoate catalyst and then heated to 85 o C, and carry out prepolymerization under nitrogen protection for 2 h to obtain a prepolymer with isocyanate groups at both ends. o C and vacuum degassing, backfilling with nitrogen, repeat three times and then add 2.33×10 -2 mol 2,5-furan dimethanol, and 1.28×10 -4 mol stannous isooctanoate, at 65 o After the reaction of C for 1.5 h, 2.33×10 -3 mol N,N'-(4,4'-methylenediphenyl)bismaleimide in DMF solution, after cross-linking reaction at the same temperature for 2 h, the cross-linking reaction product was added into anhydrous DMF to prepare a 40 wt% polyurethane solution. After the solution cooled to room temperature, it was poured into a polytetrafluoroethylene mold, vacuum degassed, and placed at 60 oThe product was dried in a forced air drying oven at C for 48 h to obtain a product, which was named FPU-0.1, wherein 0.1 represents the molar ratio of N,N'-(4,4'-methylenediphenyl)bismaleimide to 2,5-furan dimethanol being 0.1:1.

[0054] Example 9 This embodiment provides a method for preparing a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer. The only difference from Example 8 is that the molar ratio of the cross-linking agent to the chain extender is changed to 0.5:1. The cross-linking degree of the polyurethane is regulated by changing the feed ratio.

[0055] The specific preparation steps are as follows: (1) Weigh 20.00 g of PLA diol synthesized in Example 1; (2) Heat the PLA diol oil bath obtained in step (1) to 120 o C, and vacuum for 3 h to remove residual moisture, then cool to 65 o C and stabilized, add 3.50×10 -2 mol of isophorone diisocyanate and 1.28×10 -4 mol of stannous isooctanoate catalyst and then heated to 85 o C, and carry out prepolymerization under nitrogen protection for 2 h to obtain a prepolymer with isocyanate groups at both ends. o C and vacuum degassing, backfilling with nitrogen, repeat three times and then add 2.33×10 -2 mol 2,5-furan dimethanol, and 1.28×10 -4 mol stannous isooctanoate, at 65 o C was reacted for 1.5 h, and 1.17×10 -2 mol N,N'-(4,4'-methylenediphenyl)bismaleimide solution was prepared and cross-linked at the same temperature for 2 h. The cross-linked reaction product was added to anhydrous DMF to prepare a 40 wt% polyurethane solution. After the solution was cooled to room temperature, it was poured into a polytetrafluoroethylene mold and placed at 60 o The product was dried in a forced air drying oven at C for 48 h and named FPU-0.5, where 0.5 represents the molar ratio of N,N'-(4,4'-methylenediphenyl)bismaleimide to 2,5-furan dimethanol being 0.5:1.

[0056] Example 10 This embodiment provides a method for preparing a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer. The only difference from Example 8 is that the molar ratio of the cross-linking agent to the chain extender is changed to 0.05:1. The cross-linking degree of the polyurethane is regulated by changing the feed ratio.

[0057] The specific preparation steps are as follows: (1) Weigh 20.00 g of PLA diol synthesized in Example 1; (2) Heat the PLA diol oil bath obtained in step (1) to 120 o C, and vacuum for 3 h to remove residual moisture, then cool to 65 o C and stabilized, add 3.50×10 -2 mol of isophorone diisocyanate and 1.28×10 -4 mol of stannous isooctanoate catalyst and then heated to 85 o C, and carry out prepolymerization under nitrogen protection for 2 h to obtain a prepolymer with isocyanate groups at both ends. o C and vacuum degassing, backfilling with nitrogen, repeat three times and then add 2.33×10 -2 mol 2,5-furan dimethanol, and 1.28×10 -4 mol stannous isooctanoate, at 65 o C was reacted for 1.5 h, and 1.17×10 -3 mol N,N'-(4,4'-methylenediphenyl)bismaleimide solution was prepared by cross-linking reaction at the same temperature for 2 h, and then the cross-linking reaction product was added into anhydrous DMF to prepare a 40 wt% polyurethane solution. After the solution was cooled to room temperature, it was poured into a polytetrafluoroethylene mold and placed in a 60 o The product was dried in a forced air drying oven at C for 48 h and named FPU-0.05, where 0.05 represents the molar ratio of N,N'-(4,4'-methylenediphenyl)bismaleimide to 2,5-furan dimethanol being 0.05:1.

[0058] Example 11 This embodiment provides a method for preparing a covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer. The only difference from Example 8 is that the molar ratio of the cross-linking agent to the chain extender is changed to 0.3:1. The cross-linking degree of the polyurethane is regulated by changing the feed ratio.

[0059] The specific preparation steps are as follows: (1) Weigh 20.00 g of PLA diol synthesized in Example 1; (2) Heat the PLA diol oil bath obtained in step (1) to 120 o C, and vacuum for 3 h to remove residual moisture, then cool to 65 o C and stabilized, add 3.50×10 -2 mol of isophorone diisocyanate and 1.28×10 -4 mol of stannous isooctanoate catalyst and then heated to 85 o C, and carry out prepolymerization under nitrogen protection for 2 h to obtain a prepolymer with isocyanate groups at both ends. o C and vacuum degassing, backfilling with nitrogen, repeat three times and then add 2.33×10 -2 mol 2,5-furan dimethanol, and 1.28×10 -4 mol stannous isooctanoate, at 65 o C was reacted for 1.5 h, and 7.00×10 -3 mol N,N'-(4,4'-methylenediphenyl)bismaleimide solution was prepared by cross-linking reaction at the same temperature for 2 h, and then the cross-linking reaction product was added into anhydrous DMF to prepare a 40 wt% polyurethane solution. After the solution was cooled to room temperature, it was poured into a polytetrafluoroethylene mold and placed in a 60 o The product was dried in a forced air drying oven at C for 48 h and named FPU-0.3, where 0.3 represents the molar ratio of N,N'-(4,4'-methylenediphenyl)bismaleimide to 2,5-furan dimethanol being 0.3:1.

[0060] Comparative Example 1 This comparative example provides a method for preparing a polylactic acid polyurethane elastomer. The difference between this comparative example and Example 7 is that the chain extender "dimethylglyoxime" is replaced by "1,4-butanediol" without dynamic bonds.

[0061] The specific preparation steps are as follows: (1) Weigh 20.00 g of PLA diol synthesized in Example 1; (2) Heat the PLA diol oil bath obtained in step (1) to 120 o C, and vacuum for 3 h to remove residual moisture, then cool to 65 o C and stabilized, add 3.30×10 -2 mol of isophorone diisocyanate and 1.28×10 -4 mol of stannous isooctanoate catalyst and then heated to 85 oC and carry out prepolymerization under nitrogen protection for 2 h to obtain a prepolymer with isocyanate groups at both ends. o C and vacuum degassing, backfilling with nitrogen, repeat three times and then add 1.04×10 -2 mol of 1,4-butanediol, and 1.4×10 -4 mol of stannous isooctanoate, and after 1 h of reaction, transfer to 85 o The chain extension reaction product was added to anhydrous DMF to prepare a 40 wt% polyurethane solution. After the solution cooled to room temperature, it was poured into a polytetrafluoroethylene mold and placed in a 60 o The product was dried in a forced air drying oven at C for 48 h, and was named PU-BDO; the R value was 1.61.

[0062] Comparative Example 2 This comparative example provides a method for preparing a polylactic acid polyurethane elastomer. The difference between this comparative example and comparative example 1 is that the R value is 1.05, so there is almost no chemical crosslinking.

[0063] The specific preparation steps are as follows: (1) Weigh 20.00 g of PLA diol synthesized in Example 1; (2) Heat the PLA diol oil bath obtained in step (1) to 120 o C, and vacuum for 3 h to remove residual moisture, then cool to 65 o C and stabilized, add 3.50×10 -2 mol of isophorone diisocyanate and 1.28×10 -4 mol of stannous isooctanoate catalyst and then heated to 85 o C and carry out prepolymerization under nitrogen protection for 2 h to obtain a prepolymer with isocyanate groups at both ends. o C and vacuum degassing, backfilling with nitrogen, repeat three times and then add 2.33×10 -2 mol of 1,4-butanediol, and 3.69×10 -4 mol of stannous isooctanoate, and after 1 h of reaction, transfer to 85 o C oven overnight, then add anhydrous DMF to prepare a 40 wt% polyurethane solution, and after the solution cools to room temperature, pour it into a polytetrafluoroethylene mold, and place it in a 60 o The product was dried in a forced air drying oven at C for 48 h, and was named LPU-BDO; the R value was 1.05.

[0064] Comparative Example 3 This comparative example provides a method for preparing a polylactic acid polyurethane elastomer. The difference between this comparative example and comparative example 2 is that the molar ratio of ε-caprolactone and L-lactide in the PLA diol is 7:3.

[0065] The specific preparation steps are as follows: (1) Synthesize 20.00 g of PLA diol using the same method as Example 4; (2) The subsequent steps are the same as step (2) of Comparative Example 2.

[0066] Comparative Example 4 This comparative example provides a method for preparing a polylactic acid polyurethane elastomer. The difference between this comparative example and comparative example 2 is that the molar ratio of ε-caprolactone and L-propylene glycol in the PLA diol is 6:4.

[0067] The specific preparation steps are as follows: (1) Synthesize 20.00 g of PLA diol using the same method as in Example 5; (2) The subsequent steps are the same as step (2) of Comparative Example 2.

[0068] Comparative Example 5 This comparative example provides a method for preparing a polylactic acid polyurethane elastomer. The difference between this comparative example and Example 8 is that no cross-linking agent is added, so there is almost no chemical cross-linking structure.

[0069] The specific preparation steps are as follows: (1) Weigh 20.00 g of PLA diol synthesized in Example 1; (2) Heat the PLA diol oil bath obtained in step (1) to 120 o C, and vacuum for 3 hours to remove residual moisture, then cool to 65 o C and stabilized, add 3.50×10 -2 mol of isophorone diisocyanate and 1.28×10 -4 mol of stannous isooctanoate catalyst and then heated to 85 o C, and carry out prepolymerization under nitrogen protection for 2 h to obtain a prepolymer with isocyanate groups at both ends. o C and vacuum degassing, backfilling with nitrogen, repeat three times and then add 2.33×10 -2 mol 2,5-furan dimethanol, and 1.28×10 -4 mol stannous isooctanoate, react for 1 hour and transfer to 65 oC oven overnight, then add anhydrous DMF to prepare a 40 wt% polyurethane solution, and after the solution cools to room temperature, pour it into a polytetrafluoroethylene mold, and place it in a 60 o The product was dried in a forced air drying oven at C for 48 h, and was named FPU-0; the R value was 1.05.

[0070] The test method and results are as follows: The embodiments and comparative examples of the present invention were tested by the following test method: the polyurethanes of the embodiments and comparative examples were dissolved in DMF to prepare a polyurethane solution with a concentration of 40 wt %. o C. Dry in a forced air drying oven and / or vacuum drying oven for 48 h.

[0071] The tensile properties and toughness were tested according to GB / T 528-2009. The specimen was dumbbell-shaped (narrow width 2.0 ± 0.1 mm) and the tensile rate was 50 mm min. -1 .

[0072] Dissipated energy and hysteresis rate were tested according to GB / T 33609-2017, and cyclic stretching (rate 50 mm min -1 ).

[0073] The self-healing efficiency is measured by testing the elongation at break of standard specimens before and after healing according to GB / T 528-2009. The self-healing efficiency (η) is defined as the ratio of the elongation at break of the self-healed specimen (ε) to the elongation at break of the original specimen (ε0).

[0074] In vitro biosafety testing was performed using relative cell viability as an indicator. Polyurethane samples (100 mg) were first rinsed twice in phosphate buffer, then sterilized by ultraviolet irradiation for 1 h, and then immersed in 1 mL of PBS buffer to obtain a concentration of 100 mg mL -1 The immersion solution was mixed with 1000, 975, 950, 925, and 900 μL of Dulbecco's Modified Eagle Medium (DMEM) to obtain final concentrations of 0, 2.5, 5, 7.5, and 10 mg mL -1 Then L929 cells were seeded into 96-well plates at a density of 5000 cells / well, 100 μL of cell suspension was added to each well, and the cells were placed in DMEM medium containing 10% fetal bovine serum and incubated at 37 oC, 5% CO2 in a culture environment for 12 hours. After the incubation period, the cells were washed three times with PBS buffer, and 10 μL of CCK-8 solution was added to each well. The cells were incubated under the same conditions for another 4 hours. Finally, the absorbance of each well was measured at a wavelength of 450 nm using a microplate reader. The culture medium without polyurethane soaking solution was used as a blank control group. The final cell activity was calculated according to the following formula:

[0075] Among them A s , A b , A c are the absorbance values ​​of the experimental group, blank group and control group, respectively.

[0076] Figure 1 This is the infrared spectrum of PLA diol prepared in Example 1 of the present invention. It can be seen from the figure that the OH vibration absorption band appears at 3515 cm -1 Nearby, COC stretching at 1098 cm -1 There is a peak at 2866~2948 cm -1 There is a double absorption peak near 1733 cm, corresponding to the symmetric and asymmetric stretching of aliphatic CH2 and CH3. −1 The peak nearby corresponds to C=O. These data provide evidence for the successful synthesis of PLA diol.

[0077] Figure 2 The infrared spectra of PLA diol, prepolymer, PU-DMG, and PU-BDO involved in Example 7 and Comparative Example 1 of the present invention are shown. In the infrared spectrum corresponding to the prepolymer, the N=C=O signal appears at 2260 cm −1 The NH absorption peak appears at 3370 cm −1 The results show that the prepolymer was successfully synthesized. In the spectra corresponding to PU-DMG and PU-BDO, the peak at 2260 cm -1 There is no obvious N=C=O peak at 3374 cm-1, indicating that the isocyanate group has completely reacted. -1 and 1735 cm -1 The peak at 3372 cm corresponds to the NH and C=O bonds in the oxime urethane unit; in the spectrum corresponding to PU-BDO, the peak at 3372 cm -1 and 1733 cm -1 The peaks at correspond to the NH and C=O bonds in the urethane unit. The above results confirm the synthesis of PU-DMG and PU-BDO.

[0078] Figure 3 The XRD spectra of PU-DMG and PU-BDO involved in Example 7 and Comparative Example 1 of the present invention and the XRD spectrum of polylactic acid are shown in FIG. o / min scanning rate test, we can see that the o PU is in an amorphous state within the 2θ range, which provides a guarantee for high stretchability; while polylactic acid shows a clear crystallization peak, so it is a brittle plastic at room temperature.

[0079] Figure 4 The dynamic thermal analysis results of PU-DMG in Example 7 of the present invention are as follows: o The high glass transition temperature (Tg) of C and the Tg of PU-DMG which is far below room temperature make it show better flexibility in conventional environment and are more conducive to processing.

[0080] Figure 5 Figures 2 and 3 show the uniaxial tensile stress-strain curves of PU-DMG and PU-BDO according to Example 7 and Comparative Example 1 of the present invention. Uniaxial tensile tests were performed at room temperature. The figure shows that neither PU-DMG nor PU-BDO exhibited significant yielding behavior, exhibiting significant elastic behavior. PU-DMG exhibited a tensile strength of 38.72 ± 0.55 MPa, an elongation at break of 1102.68 ± 36.27%, and a toughness of 162.44 ± 8.98 MJ m - ³, while the PU-BDO of Comparative Example 1 has a tensile strength of 38.41 ± 1.40 MPa, an elongation at break of 1100.02 ± 91.10%, and a toughness of 147.32 ± 31.95 MJ m - ³, proving that the introduction of weak dynamic interactions not only does not weaken the mechanical properties, but enhances the toughness of the material.

[0081] Figure 6 1 is the stress-strain curve of the uniaxial different strain cyclic tensile test of PU-DMG involved in Example 7 of the present invention.

[0082] Figure 7 1 is a stress-strain curve of the uniaxial different strain cyclic tensile test of PU-BDO involved in Comparative Example 1 of the present invention. Figure 6 and Figure 7 In the case of a cycle with no pause between cycles, it is clearly observed that the dissipated energy increases with the strain, which is attributed to the presence of a large number of hydrogen bonds within the molecules. Figure 6As shown, compared to Comparative Example 1, PU-DMG exhibits significantly larger hysteresis loops in each cycle. This is due to the additional dynamic covalent interaction of the oxime carbamate, which allows the sample to dissipate more energy during stretching, playing a significant role in improving the toughness of PU-DMG. Furthermore, the small residual strain of PU-DMG is clearly noticeable, demonstrating its good resilience.

[0083] Figure 8 1 is a stress-strain curve of the uniaxial fixed strain cyclic tensile test of PU-DMG involved in Example 7 of the present invention.

[0084] Figure 9 1 is a stress-strain curve of the uniaxial fixed strain cyclic tensile test of PU-BDO involved in Comparative Example 1 of the present invention. Figure 8 and Figure 9 In the embodiment, the stretching cycle was repeated 20 times at 200% strain, and the 21st stretching cycle was performed after a 30-minute rest. D 298.48 kJm - ³, the hysteresis rate is 57.38%, compared with the dissipation energy W of PU-BDO in comparative example 1 D 144.16 kJ m - The hysteresis rate was significantly improved by 40.00%, which can dissipate stress more effectively and improve toughness. In addition, the dissipation energy of PU-DMG recovered to 276.88 kJ m after the 21st cycle. - ³, recovered 92.76%, while PU-BDO only recovered 91.71%, confirming the superior recovery ability of PU-DMG.

[0085] Figure 10 This demonstrates the crosslinking properties of PU-DMG and PU-BDO in Example 7 and Comparative Example 1. After immersion in a hot organic solvent for one hour, PU-BDO swells but does not dissolve due to its high R value, resulting in irreversible crosslinking. However, PU-DMG, due to its reversible dynamic covalent bonds, readily dissolves despite its crosslinking. The organic solvents, from left to right, are ethanol, N,N-dimethylformamide, dimethylacetamide, tetrahydrofuran, and dimethyl sulfoxide.

[0086] Figure 11 The uniaxial tensile stress-strain curves of the PU-DMG involved in Example 7 of the present invention after self-healing at different times are shown. Specifically, the polyurethane tensile splines cut horizontally from the middle are neatly connected and placed at 90 o The samples were placed in a C forced air drying oven and subjected to uniaxial tensile tests after self-healing for 0.5h, 1h, and 1.5h, respectively. The healing efficiency was as high as 97.71% after 1.5h of healing.

[0087] Figure 12 This is the uniaxial tensile stress-strain curve of PU-BDO according to Comparative Example 1 of the present invention after 1.5 hours of self-healing treatment. The inset is a magnified image of the stress-strain curve at the initial stage, indicating that the lack of dynamic covalent bonds severely reduces the self-healing efficiency of PU-BDO to only 0.59%.

[0088] Figure 13 This is the uniaxial tensile stress-strain curve of the PU-DMG involved in Example 7 of the present invention after three DMF solvent recovery, showing excellent recyclability. There is almost no obvious difference in mechanical properties after three recovery.

[0089] Figure 14 This is a statistical diagram of the cell activity of PU-DMG involved in Example 7 of the present invention. It can be seen that PU-DMG has very considerable biocompatibility.

[0090] Figure 15 The uniaxial tensile stress-strain curves of the polyurethane elastomers described in Comparative Examples 2-4 of the present invention show that as the L-lactide content increases, the modulus and breaking stress of the material gradually increase, while the elongation at break gradually decreases. Therefore, considering all factors, a molar ratio of ε-caprolactone to L-lactide of 8:2 is preferred for synthesizing PLA diol.

[0091] Figure 16 The infrared spectrum of FPU-0.1 involved in Example 8 of the present invention is shown at 2260 cm -1 There is no obvious N=C=O peak at 1705~1725 cm -1 The peak at 3360–3370 cm corresponds to the C=O bond in the urethane unit. -1 The peak at corresponds to NH, indicating the formation of carbamate or urea groups and confirming the synthesis of FPU-0.1.

[0092] Figure 17 is the XRD spectrum of FPU-0.1 involved in Example 8 of the present invention, with 5 o / min scanning rate test, we can see that the o The 2θ range of the nanostructured carbon nanotubes is in an amorphous state, which provides a guarantee for high stretchability.

[0093] Figure 18 This is the dynamic thermal analysis result of FPU-0.1 involved in Example 8 of the present invention, which also shows a Tg below room temperature.

[0094] Figure 19This is the uniaxial tensile stress-strain curve of FPU-0.1 involved in Example 8 of the present invention, and the uniaxial tensile test was performed at room temperature. From the figure, it can be seen that FPU-0.1 has no obvious yield phenomenon.

[0095] Figure 20 This is the stress-strain curve from the uniaxial cyclic tensile test of FPU-0.1, according to Example 8 of the present invention. Loading-unloading cyclic tensile testing was performed at strains ranging from 100% to 500%. Without pausing between cycles, a hysteresis loop is clearly observed, with its area increasing with strain, indicating increasing dissipated energy. This is attributed to the abundant hydrogen bonding and Diels-Alder dynamic covalent interactions within FPU-0.1, which play a significant role in enhancing its toughness. Furthermore, the low residual strain maintained throughout the cyclic test demonstrates the polymer's good resilience.

[0096] Figure 21 The uniaxial tensile stress-strain curves of FPU-0.1 involved in the embodiment of the present invention after self-healing for different time periods are shown. Specifically, the polyurethane tensile splines cut horizontally from the middle are neatly connected and placed at 90 o The samples were placed in a C forced air drying oven and subjected to uniaxial tensile tests after self-healing for 0.5 h, 1 h, and 1.5 h, respectively. The healing efficiency was as high as 94.15% after 1.5 h of healing.

[0097] Figure 22 This is the uniaxial strain-stress curve of FPU-0.1 involved in Example 8 of the present invention after three DMF recycling. Almost no obvious mechanical difference can be seen after three recycling.

[0098] Figure 23 This is a statistical diagram of the cell activity of FPU-0.1 involved in Example 8 of the present invention. It can be seen that FPU-0.1 has very considerable biocompatibility.

[0099] Figure 24 The infrared spectrum of FPU-0.5 involved in Example 9 of the present invention is shown at 2260 cm -1 There is no obvious N=C=O peak at 1705~1725 cm -1 The peak at 3360–3370 cm corresponds to the C=O bond in the urethane unit. -1 The peak at corresponds to NH, indicating the formation of carbamate or urea groups and confirming the synthesis of FPU-0.5.

[0100] Figure 25 is the XRD spectrum of FPU-0.5 involved in Example 9 of the present invention, with 5 o / min scanning rate test, we can see that the o The 2θ range of the nanostructured carbon nanotubes is in an amorphous state, which provides a guarantee for high stretchability.

[0101] Figure 26 This is the uniaxial tensile stress-strain curve for FPU-0.5, according to Example 9 of the present invention. Uniaxial tensile testing was performed at room temperature. The figure shows no apparent yielding in FPU-0.5. Increasing crosslinking significantly increases the initial modulus and tensile strength of the polyurethane, but significantly reduces its elongation at break. This is because more crosslinks limit chain deformation and recombination, resulting in a more stable crosslinked network. Consequently, higher strength but lower elongation at break are achieved.

[0102] Figure 27 The uniaxial tensile stress-strain curves of Examples 8-11 of the present invention and FPU-0.1, FPU-0.5, FPU-0.05, FPU-0.3, and FPU-0 involved in Comparative Example 5 show a trend that the mechanical properties change significantly with the increase (or decrease) of the crosslinking degree.

[0103] It should be noted that the specific embodiments are only representative examples of the present invention. Obviously, the technical solutions of the present invention are not limited to the above embodiments and may be subject to many variations. Those skilled in the art who are clear about the disclosure of the present invention or who can unambiguously derive the invention from the written description of the document should be considered to be within the scope of protection of this patent.

Claims

1. A covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer, characterized in that: The polylactic acid polyurethane elastomer comprises: a soft segment of polylactic acid diol terminated with dihydroxyl groups, and a hard segment of a cross-linked polyurethane elastomer containing dynamic covalent bonds.

2. The polylactic acid polyurethane elastomer according to claim 1, characterized in that The dynamic covalent bond includes one or more of an oxime bond, a Diels-Alder bond, a borate bond, a disulfide bond, a diselenide bond, a hindered urea bond, an imine bond, and an acylhydrazone bond.

3. The method for preparing the covalently adaptive network cross-linked toughened polylactic acid polyurethane elastomer according to claim 1, characterized in that: The following steps are involved: (1) Preparation of polylactic acid diol: first, a first monomer, a second monomer, and a difunctional initiator are heated in an inert gas atmosphere for ring-opening polymerization under the catalysis of an appropriate amount of a first catalyst to prepare polylactic acid diol; (2) Preparation of polylactic acid polyurethane elastomer.

4. The preparation method according to claim 3, characterized in that The first catalyst is selected from one or more of 1,3-diphenylurea, potassium methoxide, dibutyltin dilaurate, stannous isooctanoate, stannous chloride, dibutyltin diacetate, tetrabutyl titanate or 1,5,7-triazabicyclo[4.4.0]dec-5-ene.

5. The preparation method according to claim 3, characterized in that The preparation of the polylactic acid polyurethane elastomer in step (2) comprises the following steps: first, vacuum dehydrating the polylactic acid diol described in step (1), then adding diisocyanate and a second catalyst, and performing a prepolymerization reaction under the protection of an inert gas to obtain a prepolymer terminated with isocyanate groups at both ends; cooling the prepolymer and vacuum degassing it, then adding a chain extender containing an oxime bond and a second catalyst to carry out a chain extension reaction; then keeping the temperature overnight; and then adding an organic solvent to the chain extension reaction product of the previous step to prepare a polyurethane solution of a certain concentration; cooling it to room temperature and pouring it into a polytetrafluoroethylene mold; vacuum degassing it, and drying it to obtain a covalently adaptive network cross-linked and toughened polylactic acid polyurethane elastomer.

6. The preparation method according to claim 5, characterized in that The chain extender containing an oxime bond is selected from one or more of glyoxime, 1,4-benzoquinone dioxime, dimethylglyoxime, 2,4-pentanedione dioxime and glutaraldehyde dioxime.

7. The preparation method according to claim 3, characterized in that The preparation of the polylactic acid polyurethane elastomer in the step (2) comprises the following steps: first, vacuum dehydrating the polylactic acid diol described in step (1), then adding diisocyanate and a second catalyst, and performing a prepolymerization reaction under the protection of an inert gas to obtain a prepolymer terminated with isocyanate groups at both ends; cooling the prepolymer and vacuum degassing it, then adding a furan structure-containing chain extender and a second catalyst to carry out a chain extension reaction; then adding a solution containing a bismaleimide structure cross-linking agent dissolved in an organic solvent to carry out a cross-linking reaction; then adding the organic solvent to the cross-linking reaction product of the previous step to prepare a polyurethane solution of a certain concentration; cooling it to room temperature and then pouring it into a polytetrafluoroethylene mold; after vacuum degassing, drying it to obtain a covalently adaptive network cross-linked and toughened polylactic acid polyurethane elastomer.

8. The preparation method according to claim 7, characterized in that The furan structure-containing chain extender is selected from one or more of 2,5-furan dimethanol, 3,4-bis(hydroxymethyl)furan, and 1-(furan-2-yl)-2,2-dimethylpropane-1,3-diol.

9. The preparation method according to claim 7, characterized in that The bismaleimide structure-containing crosslinking agent is selected from one or more of N,N'-(4,4'-methylenediphenyl)bismaleimide, N,N'-m-phenylenebismaleimide, N,N'-(1,4-phenylene)bismaleimide, 1,2-bis(maleimide)ethane, 1,4-bis(maleimido)butane, and 1,6-bismaleimidohexane.

10. Use of the polylactic acid polyurethane elastomer according to any one of claims 1 to 2 or the polylactic acid polyurethane elastomer prepared by the preparation method according to any one of claims 3 to 9 in the fields of degradable medical implants and flexible electronics.

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