Covalent self-adapting polyurethane elastomers containing a schiff base based bio-based chain extender and preparation thereof
By preparing a bio-based chain extender containing Schiff base and compounding it with betulin, a covalently adaptive polyurethane elastomer was prepared. This solved the problems of non-remodeling and non-degradability of the bio-based cross-linked structure, and achieved self-healing and shape memory functions. The raw material is renewable biomass resources.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NINGBO INST OF MATERIALS TECH & ENG CHINESE ACAD OF SCI
- Filing Date
- 2023-11-14
- Publication Date
- 2026-06-30
Smart Images
Figure CN117645553B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of bio-based polymer materials technology, specifically to a bio-based chain extender containing a Schiff base and the covalently adaptive polyurethane elastomer prepared therefrom. Background Technology
[0002] Polyurethane (PU) is a general-purpose polymer compound, typically synthesized from isocyanates and polyols / polyamines. The properties of the synthesized polyurethane are affected by variations in raw materials, additives, chain extenders, and processing conditions. Polyurethane has a wide range of applications, including home furnishings, construction, daily necessities, transportation, and home appliances. Polyurethane products come in various forms, including foams, elastomers, fibers, and adhesives. Among these, polyurethane elastomers possess excellent elasticity, toughness, and good oil resistance, abrasion resistance, low-temperature resistance, and aging resistance, making them one of the most important categories of synthetic polyurethane materials.
[0003] Currently, developing green, environmentally friendly, and biodegradable bio-based polyurethane elastomers using biomass resources instead of petroleum-based resources has become mainstream. However, some cross-linked polyurethane elastomers suffer from drawbacks such as non-remodeling, non-degradability, and limited functionalization. Therefore, introducing reversible covalent bonds into polyurethane materials endows them with properties such as remodeling, self-healing, shape memory, and degradation. Under certain external conditions (heat, catalysts, pH, etc.), the reversible covalent bonds introduced into the material can achieve dynamic separation and recombination between molecules, and have been widely used in cross-linked polymer systems. Currently, there are many widely used dynamic covalent reactions, among which the imine bond, also known as a Schiff base, has received considerable attention.
[0004] Chinese patent document CN112979919A discloses a bio-based self-healing polyurethane elastomer. This invention uses furfurylamine and vanillin as main raw materials to obtain a small molecule chain extender, which is then reacted with a polyurethane prepolymer to obtain a bio-based polyurethane elastomer with self-healing function. Chinese patent document CN114561145A discloses a self-healing waterborne polyurethane coating containing imine bonds. This invention first reacts compounds containing -CHO, -OH and -NH2 to generate a chain extender containing imine bonds, reacts it with a polymer polyol and a diisocyanate, then uses an anionic monomer to extend the chain, and finally neutralizes it with acetic acid to form a salt and emulsifies it to obtain a self-healing waterborne polyurethane coating. The self-healing waterborne polyurethane coating prepared has a self-healing rate of up to 99.2%.
[0005] In order to reduce the use of petroleum-based resources, it is necessary to utilize biomass resources to prepare a polyurethane elastomer with self-healing properties, shape memory, biodegradability, and good processability. Summary of the Invention
[0006] This invention provides a bio-based chain extender containing a Schiff base, obtained by the condensation reaction of vanillin and 1,5-pentanediamine. When combined with betulin as a chain extender, it can be used to prepare covalently adaptive polyurethane elastomers with a series of functions such as good processability, good degradation, self-healing, and editable shape memory.
[0007] The specific technical solution adopted is as follows:
[0008] A bio-based chain extender containing a Schiff base, with the structural formula shown in formula (Ⅰ):
[0009]
[0010] The aforementioned bio-based chain extender containing Schiff base is obtained by an aldehyde-amine condensation reaction of vanillin and 1,5-pentanediamine.
[0011] Specifically, the preparation method of the bio-based chain extender containing Schiff base is as follows: two parts of vanillin are completely dissolved in dichloromethane by molar ratio, and one part of 1,5-pentanediamine is slowly injected into the reaction system at 40°C using a syringe pump; then the temperature is raised to 60°C, and the reaction is refluxed for 8 hours. After the reaction is completed, the mixture is cooled to room temperature, filtered, purified, and dried to obtain the bio-based chain extender containing Schiff base.
[0012] Vanillin, derived from renewable lignin, is a bio-based monomer; 1,5-pentanediamine is a linear aliphatic diamine that can be obtained from xylose, glucose, hemicellulose, etc., through fermentation or bioengineering. Bio-based chain extenders containing Schiff bases are obtained using aldehyde-amine condensation reactions. When these are compounded with betulin as chain extenders, covalently adaptive polyurethane elastomers with remodeling, biodegradability, and self-healing properties can be obtained.
[0013] The present invention also provides the application of the aforementioned bio-based chain extender containing Schiff base in the preparation of polyurethane elastomers.
[0014] This invention also provides a method for preparing a covalently adaptive polyurethane elastomer, comprising the following steps:
[0015] (1) Under a nitrogen atmosphere, vegetable oil and diisocyanate were reacted in an organic solvent to obtain a polyurethane prepolymer solution;
[0016] (2) The polyurethane prepolymer solution, chain extender solution and catalyst are mixed and reacted to obtain the covalent adaptive polyurethane elastomer;
[0017] The solute in the chain extender solution is the bio-based chain extender containing Schiff base, or a mixture of the bio-based chain extender containing Schiff base and betulin, and the solvent in the chain extender solution is tetrahydrofuran, butanone, or toluene.
[0018] Preferably, when the solute in the chain extender solution is a mixture of the Schiff base-containing bio-based chain extender and betulin, the hydroxyl ratio of the Schiff base-containing bio-based chain extender to betulin is 7:3 to 3:7. Polyurethane elastomers prepared using betulin alone as a chain extender have relatively poor properties, require improved reprocessing performance, and have limited functionalization. When the Schiff base-containing bio-based chain extender is used to replace part of the betulin, not only are the mechanical properties of the polyurethane elastomer improved, but it also endows the polyurethane elastomer with functional applications such as self-healing, biodegradability, and shape memory.
[0019] Preferably, the vegetable oil is castor oil or modified soybean oil, both with a hydroxyl functionality greater than 2.0; these two vegetable oils have simple structures, are inexpensive, and contain relatively long fatty acid chains and a high degree of hydroxyl functionality.
[0020] Preferably, the diisocyanate is selected from 1,5-pentanediisocyanate (PDI) or toluene diisocyanate (TDI); the selection of 1,5-pentanediisocyanate can increase the biomass content of the covalently adaptive polyurethane elastomer; toluene diisocyanate has better activity and can form a better crosslinking network with the hydroxyl groups of the chain extender.
[0021] Preferably, in step (1), the organic solvent is tetrahydrofuran or methyl ethyl ketone. Methyl ethyl ketone and tetrahydrofuran have lower boiling points, which is beneficial for the post-processing.
[0022] Preferably, in step (1), the reaction conditions are 60-80℃ for 0.5h-3h.
[0023] The catalysts mentioned include, but are not limited to, organotin catalysts and tertiary amine catalysts.
[0024] Preferably, in step (2), the reaction conditions are 60-90℃ for 0.5h-12h.
[0025] Preferably, the ratio of hydroxyl groups in the solutes of the polyurethane prepolymer solution and the chain extender solution is 1:1.
[0026] Specifically, in the process of preparing the covalent adaptive polyurethane elastomer, castor oil or modified soybean oil, betulin and solvents all need to be dehydrated before the reaction.
[0027] This invention also provides a method for preparing the aforementioned covalently adaptive polyurethane elastomer, resulting in a covalently adaptive polyurethane elastomer. The hard segment of the covalently adaptive polyurethane elastomer comprises a dynamic imine structure, betulin, and isocyanate structure, while the soft segment comprises a vegetable oil structure. Adjusting the ratio of the Schiff base-containing bio-based chain extender to the hydroxyl groups of betulin can regulate the dynamic exchange properties and mechanical properties of the covalently adaptive polyurethane elastomer.
[0028] The covalent adaptive polyurethane elastomer described above has self-healing and rapid degradation capabilities, with a tensile strength of 2.68–18.9 MPa and an elongation at break of 246%–279%.
[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0030] (1) This invention uses vanillin and 1,5-pentanediamine to synthesize a bio-based chain extender containing Schiff base, and then combines it with betulin as a mixed chain extender to successfully prepare a series of covalent adaptive polyurethane elastomers. Most of the raw materials are renewable, green and sustainable biomass resources, reducing the use of petroleum-based resources.
[0031] (2) In the covalent adaptive polyurethane elastomer of the present invention, dynamic imine bonds are introduced into the network structure. The dynamic imine bonds enable the cross-linked polyurethane network to have a series of functions such as processability, self-healing, degradability and editable shape memory. Attached Figure Description
[0032] Figure 1 Synthetic routes for bio-based chain extenders containing Schiff bases and their 1H NMR spectra.
[0033] Figure 2 This is a synthesis route diagram for the covalent adaptive polyurethane elastomers described in Examples 3 and 4.
[0034] Figure 3 The stress-strain curves are shown for the polyurethane elastomers prepared in Examples 2-6 and Comparative Example 1.
[0035] Figure 4 The Fourier transform infrared spectra of the polyurethane elastomers prepared in Examples 2-6 and Comparative Example 1 are shown.
[0036] Figure 5 The image shows the stress-strain curves of the covalent adaptive polyurethane elastomer prepared in Example 3 after reshaping and self-healing.
[0037] Figure 6 The results show the self-healing performance test results of the covalent adaptive polyurethane elastomer prepared in Example 3.
[0038] Figure 7 The results are the shape memory performance test results of the covalent adaptive polyurethane elastomer prepared in Example 3. Detailed Implementation
[0039] The present invention will be further illustrated below with reference to the embodiments and accompanying drawings. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.
[0040] The betulin used in the following examples and comparative examples was purchased from Shaanxi Lvshengyuan Biological Products Manufacturing Co., Ltd., with a purity of 98%; 1,5-pentanediisocyanate was purchased from Wanhua Chemical Group Co., Ltd., with a purity of 99%; and 1,5-pentanediamine was purchased from Shanghai Guotai Biotechnology Co., Ltd., with a purity of 96%. The solid raw materials were dried in a vacuum oven at 80°C for 12 hours before use, and the solvent was dried by passing it through an activated molecular sieve.
[0041] In the examples and comparative examples, the polyurethane elastomers prepared were laminated into sheets, and then their performance was tested. The mechanical property testing method was as follows: a German ZWICK tensile testing machine was used to analyze the mechanical properties of the samples. Tensile clamps and rubber grips were selected. The sample dimensions were 20.0 mm (length) × 2.0 mm (width) × 0.5 mm (thickness), and the loading speed was 10.00 mm / min. For accuracy, each sample was measured three times, and the average value was taken.
[0042] Example 1: Synthesis of a bio-based chain extender containing a Schiff base
[0043] Two parts of vanillin were completely dissolved in dichloromethane by molar ratio. One part of 1,5-pentanediamine was slowly injected into the reaction system at 40°C using a syringe pump. The temperature was then raised to 60°C and the reaction was refluxed for 8 hours. After the reaction was completed, the mixture was cooled to room temperature, filtered and purified to obtain a yellow solid, which was then dried in a vacuum oven at 70°C for 24 hours. The resulting yellow product is the bio-based chain extender containing Schiff bases.
[0044] The synthetic route of the bio-based chain extender containing Schiff base and its 1H NMR spectrum are shown below. Figure 1 As shown, this demonstrates the successful execution of the aldehyde-amine condensation reaction and the successful preparation of the bio-based chain extender containing the Schiff base.
[0045] Example 2
[0046] Ten parts of the bio-based chain extender containing Schiff base (3.7 g, molecular weight 370) synthesized in Example 1 and 0 parts of betulin (the ratio of the hydroxyl groups of the bio-based chain extender containing Schiff base to betulin was 10:0) were dissolved in 22 mL of tetrahydrofuran solution and stirred thoroughly to obtain a saturated solution of the chain extender.
[0047] Two parts of dried castor oil (6.91 g, molecular weight 933, functionality f = 2.7) and four parts of biomass-derived 1,5-pentanediisocyanate (3.08 g, molecular weight 154) were weighed and mixed. Then, 15 mL of methyl ethyl ketone solution was added and the mixture was stirred at 60 °C for 40 minutes under a nitrogen atmosphere to obtain a polyurethane prepolymer solution.
[0048] The polyurethane prepolymer solution was then mixed with the chain extender solution and 50 μL of catalyst DBTDL (di-n-butyltin dilaurate), and reacted at 60°C for 30 minutes. The reacted solution was poured onto a polytetrafluoroethylene mold and placed in a vacuum drying oven for curing to obtain the covalent adaptive polyurethane elastomer.
[0049] Covalent adaptive polyurethane elastomer was cut into dumbbell-shaped tensile specimens and tested on a universal tensile testing machine. The tensile property curves are shown in the figure below. Figure 3 As shown, the elastomer has a modulus of 50.4 MPa, a tensile strength of 9.5 MPa, an elongation at break of 250%, and a breaking energy of 13.2 MJ / m. 3 .
[0050] Example 3
[0051] The difference between this invention and Example 2 is that the solute in the chain extender solution is 7 parts of the Schiff base-containing bio-based chain extender (2.59g, molecular weight 370) synthesized in Example 1 and 3 parts of betulin (the ratio of the hydroxyl groups of the Schiff base-containing bio-based chain extender to betulin is 7:3), and the covalent adaptive polyurethane elastomer is prepared.
[0052] Covalent adaptive polyurethane elastomer was cut into dumbbell-shaped tensile specimens and tested on a universal tensile testing machine. The tensile property curves are shown in the figure below. Figure 3 As shown, the elastomer has a modulus of 38.2 MPa, a tensile strength of 7.5 MPa, an elongation at break of 246%, and a breaking energy of 10.7 MJ / m. 3 .
[0053] Example 4
[0054] The difference between this invention and Example 2 is that the solute in the chain extender solution is 3 parts of a Schiff base-containing bio-based chain extender (1.85g, molecular weight 370) synthesized in Example 1 and 7 parts of betulin (the ratio of the hydroxyl groups of the Schiff base-containing bio-based chain extender to betulin is 3:7), and the covalent adaptive polyurethane elastomer is prepared.
[0055] Covalent adaptive polyurethane elastomer was cut into dumbbell-shaped tensile specimens and tested on a universal tensile testing machine. The tensile property curves are shown in the figure below. Figure 3As shown, the elastomer has a modulus of 29.8 MPa, a tensile strength of 4.4 MPa, an elongation at break of 279%, and a breaking energy of 6.8 MJ / m. 3 .
[0056] Example 5
[0057] The only difference between this invention and Example 3 is that toluene diisocyanate (3.48g, molecular weight 174) is used instead of 1,5-pentanediisocyanate to prepare the covalent adaptive polyurethane elastomer.
[0058] Covalent adaptive polyurethane elastomer was cut into dumbbell-shaped tensile specimens and tested on a universal tensile testing machine. The tensile property curves are shown in the figure below. Figure 3 As shown, the elastomer has a tensile strength of 18.9 MPa, an elongation at break of 240%, and a breaking energy of 24.2 MJ / m. 3 .
[0059] Compared with Example 3, the overall performance of the covalently adaptive polyurethane elastomer is improved due to the increase in the content of benzene rings in the polyurethane network.
[0060] Example 6
[0061] The only difference between this invention and Example 4 is that toluene diisocyanate (3.48g, molecular weight 174) is used instead of 1,5-pentanediisocyanate to prepare the covalent adaptive polyurethane elastomer.
[0062] Covalent adaptive polyurethane elastomer was cut into dumbbell-shaped tensile specimens and tested on a universal tensile testing machine. The tensile property curves are shown in the figure below. Figure 3 As shown, the elastomer has a tensile strength of 2.68 MPa, an elongation at break of 260%, and a breaking energy of 4.76 MJ / m. 3 .
[0063] Compared to Example 5, the mechanical properties of the covalently adaptive polyurethane elastomer are reduced due to the increased content of betulin, which has lower hydroxyl activity, in the polyurethane network.
[0064] Comparative Example 1
[0065] The only difference between this comparative example and Example 2 is that the solute in the chain extender solution is 0 parts of a bio-based chain extender containing a Schiff base and 10 parts of betulin (4.43 g, molecular weight 442.72) (the ratio of the hydroxyl groups of the bio-based chain extender containing a Schiff base to betulin is 0:10), that is, no dynamic imine bonds are introduced, and a polyurethane elastomer is prepared.
[0066] Polyurethane elastomer was cut into dumbbell-shaped tensile test strips and tested on a universal tensile testing machine. The tensile performance curve is shown in the figure below. Figure 3 As shown, this polyurethane elastomer has a modulus of 41 MPa, a tensile strength of 1.74 MPa, an elongation at break of 414%, and a breaking energy of 4.87 MJ / m. 3 .
[0067] Comparative Example 2
[0068] The only difference between this comparative example and Comparative Example 1 is that toluene diisocyanate (3.48 g, molecular weight 174) was used instead of 1,5-pentanediisocyanate to prepare the polyurethane elastomer.
[0069] Polyurethane elastomer was cut into dumbbell-shaped tensile specimens and tested on a universal tensile testing machine. The polyurethane elastomer exhibited a tensile strength of 26.9 MPa, an elongation at break of 110%, and a breaking energy of 20.8 MJ / m. 3 .
[0070] Sample Analysis
[0071] The Fourier transform infrared spectra of the polyurethane elastomers prepared in Examples 2-6 and Comparative Example 1 were tested, and the results are as follows: Figure 4 As shown; Fourier transform infrared measurements were performed on an Agilent Technologies Nicolet 6700FT-IR spectrometer, with a spectral recording range of 400-4000 cm⁻¹. -1 32 scans were performed at a resolution of 4.0 cm. -1 .
[0072] from Figure 4 It can be seen that the infrared spectra of the synthesized polyurethane elastomers all show similar absorption peaks. At 2930 cm⁻¹... -1 and 2870cm -1 The strong absorption peaks are due to the stretching vibrations of -CH2 and -CH3; in the range of 1640-1720 cm⁻¹. -1 The absorption peak at 3200-3600 cm⁻¹ is the absorption peak of the carbon group in the carbamate; -1 The broader peak values are due to the asymmetric stretching vibrations of -NH- and -OH; additionally, at 2250 cm⁻¹... -1 The -NCO absorption peak disappeared, indicating the successful synthesis of the polyurethane elastomer.
[0073] from Figure 5 As can be seen, after secondary reshaping of the covalent adaptive polyurethane elastomer of Example 3, its tensile strength recovered to 76.9% of the initial value, and its elongation at break recovered to 95.5% of the initial value. It exhibits good reshaping and reprocessing properties.
[0074] The healing process of scratches on the covalent adaptive polyurethane elastomer of Example 3 at 80°C was observed using a microscope, and the results are as follows: Figure 6 As shown in the figure, after 20 minutes at 80°C, the approximately 60μm wide scratch on the film of this elastomer is significantly reduced, and after 40 minutes the scratch almost disappears, demonstrating good self-healing properties.
[0075] from Figure 7 As can be seen, in Example 3, the covalent adaptive polyurethane elastomer sample, after being held at 60°C for 2 minutes, was formed into a "spiral state" by external force. After cooling to room temperature, the external force was removed, resulting in a temporary "spiral" shape. When the ambient temperature rose again to 60°C (above Tg), the sample returned to its initial shape from the temporary "spiral" shape. The sample was bent into an "M" shape by external force at 120°C and held for 20 minutes. This temperature is higher than the topological freezing transition temperature Tg of the imine bond. v This causes a rearrangement of the polyurethane network structure. Therefore, after cooling to room temperature and removing the external force, the sample is fixed in a permanent "M" shape. The temperature is then raised to 60°C and bent into an "N" shape. After cooling to room temperature, the sample is fixed in a temporary "N" shape. It is noteworthy that when the temperature is raised to 60°C again, the sample reverts from an "N" shape to an "M" shape, instead of the initial rectangular shape. Only when the temperature is raised above the topological freeze transition temperature does the Example 3 spline return to its initial state. These morphological changes demonstrate that the Example 3 spline possesses good triple shape memory.
[0076] The embodiments described above provide a detailed explanation of the technical solutions of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, or similar substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing a covalently adaptive polyurethane elastomer, characterized in that, Includes the following steps: (1) Under a nitrogen atmosphere, vegetable oil and diisocyanate were reacted in an organic solvent to obtain a polyurethane prepolymer solution; (2) The polyurethane prepolymer solution, chain extender solution and catalyst are mixed and reacted to obtain the covalent adaptive polyurethane elastomer; The solute in the chain extender solution is a mixture of a bio-based chain extender containing a Schiff base and betulin, wherein the hydroxyl ratio of the bio-based chain extender containing a Schiff base to betulin is 7:3 to 3:7; the solvent of the chain extender solution is tetrahydrofuran, butanone, or toluene. Bio-based chain extenders containing Schiff bases are obtained by the aldehyde-amine condensation reaction of vanillin and 1,5-pentanediamine, and their structural formula is shown in formula (I):
2. The method for preparing the covalent adaptive polyurethane elastomer according to claim 1, characterized in that, The vegetable oil is castor oil or modified soybean oil; the diisocyanate is selected from 1,5-pentanediisocyanate or toluenediisocyanate.
3. The method for preparing the covalent adaptive polyurethane elastomer according to claim 1, characterized in that, In step (1), the reaction conditions are 60-80℃ for 0.5h-3h.
4. The method for preparing the covalent adaptive polyurethane elastomer according to claim 1, characterized in that, In step (2), the reaction conditions are 60-90℃ for 0.5h-12h.
5. The covalently adaptive polyurethane elastomer prepared by the method for preparing covalently adaptive polyurethane elastomers according to any one of claims 1-4, characterized in that, The covalent adaptive polyurethane elastomer has a tensile strength of 2.68–18.9 MPa and an elongation at break of 246%–279%.