High elongation self-healing polyurethane and method of making same

Abstract

The application discloses a high-elongation self-repairing polyurethane and a preparation method thereof, and comprises the following steps: in step 1, polyol and isocyanate are catalytically reacted in a solvent under an inert gas atmosphere to obtain a polyurethane prepolymer; and in step 2, an imine chain extender and a trihydroxy crosslinking agent are added into the reaction solution to obtain a self-repairing polyurethane through a chain extension reaction. In the application, the chain extender containing a dynamic reversible imine bond is used to chain extend the polyurethane prepolymer, and the trihydroxy crosslinking agent is used to construct a three-dimensional network structure, so that the crosslinking polyurethane containing the imine dynamic bond is prepared. Since the imine bond can be quickly exchanged at room temperature, and after the imine bond is broken, unlike traditional linear molecules, it is a branched molecule, the flow processing is better, the molecular chain collision probability is larger, the tensile elongation is better, and excellent self-repairing is exhibited at room temperature, so that the prepared crosslinking polyurethane has excellent self-repairing performance at room temperature.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high molecular materials, and in particular to a high-elongation self-repairing polyurethane and a preparation method thereof. BACKGROUND

[0002] Polyurethanes are widely used in coatings, adhesives, automobiles, and buildings, and many other fields. In these application scenarios, polyurethanes inevitably suffer mechanical, light, or thermal stimuli during use, resulting in micro-cracks or wounds, affecting their mechanical properties, and even leading to material failure. Therefore, the preparation of polyurethanes containing self-repairing functions has become a research hotspot. In the prior art, dynamic covalent bonds are usually introduced into polyurethanes to achieve self-healing effects, such as imine bonds, acylhydrazone bonds, disulfide bonds, borate bonds, D-A reactions, and the like. In addition, non-covalent bonds such as hydrogen bonds, ionic bonds, host-guest interactions, and metal ligands are also often introduced into polyurethanes. Under the stimulation of light, heat, microwaves, and the like, polyurethane segments flow, and cracks and damage are repaired.

[0003] CN115124688A discloses a polyurethane damping material containing dynamic disulfide bonds and imine bonds and a preparation method thereof. The damping material is prepared by reacting cystine, an alcohol compound, and thionyl chloride to introduce dynamic disulfide bonds and intramolecular hydrogen bonds into the system, then reacting with an aldehyde compound to synthesize a polyurethane chain extender containing both dynamic disulfide bonds and imine bonds, or synthesizing a polyurethane chain extender containing both dynamic disulfide bonds and imine bonds by reacting diamino diphenyl disulfide and an aldehyde compound in anhydrous ethanol, and finally reacting with a polyurethane prepolymer to obtain the polyurethane damping material containing dynamic disulfide bonds and imine bonds. The polyurethane damping material utilizes the dynamic and reversible characteristics of dynamic covalent bonds to increase energy dissipation, has a wide damping temperature range and high damping performance, and also has excellent mechanical properties and self-repairing performance, thus having a wide range of applications.

[0004] CN119661809A discloses a self-repairing, water-resistant polyurethane elastomer containing imine bonds and applied to a humidity sensor. However, these chain extenders all contain two imine bonds with high dynamic activity, and the simultaneous breaking of the two imine bonds will result in the loss of small molecules and affect the mechanical properties and self-repairing performance of the material, leading to material failure. CN116355173A discloses a self-repairing degradable bio-based polyurethane containing a single imine bond and having excellent repeatable performance. However, the self-repairing rate and effect, and the toughness are not as good as those of the chain extender system containing two imine bonds. Moreover, the synthesis and preparation of the chain extender containing a single imine bond are relatively complex and difficult to be practically applied. It can be seen that the coating needs to be separately heat-treated to achieve a good self-repairing effect.

[0005] However, the self-repairing polyurethane prepared at present has relatively high mechanical strength, and the repair temperature is relatively high, the mechanical strength is poor at low repair temperature, and the preparation is complex and difficult to be practically applied. SUMMARY

[0006] In view of the above technical defects, the imine-containing chain extender is synthesized, the polyurethane prepolymer is chain-extended by using the chain extender, and a three-dimensional network structure is constructed by using a trihydroxy crosslinking agent to prepare a crosslinked polyurethane containing an imine dynamic bond, so that the crosslinked polyurethane prepared has excellent self-repairing performance at room temperature.

[0007] To achieve the above object, the technical scheme adopted by the present application is:

[0008] A preparation method of high-strength self-repairing polyurethane, comprising the following steps:

[0009] Step 1: under an inert gas atmosphere, polyurethane prepolymer is prepared by catalytic reaction of polyol and isocyanate in a solvent;

[0010] Step 2: imine chain extender and trihydroxy crosslinking agent are added to the reaction solution, and self-repairing polyurethane is obtained through chain extension reaction;

[0011] The structure of the imine chain extender is as follows:

[0012] .

[0013] In the present application, the polyurethane prepolymer is chain-extended by using a chain extender containing a dynamic and reversible imine bond, and a three-dimensional network structure is constructed by using a trihydroxy crosslinking agent to prepare a crosslinked polyurethane containing an imine dynamic bond. The double benzene ring structure contained in the chain extender can more effectively improve the strength of the product. After the prepared sample is cut, the tensile strength reaches 98% of that of the uncut sample after repair at 30 DEG C for 6 hours, and excellent self-repairing ability is exhibited. Since the imine bond can be rapidly exchanged at room temperature, and after the imine bond is broken, unlike traditional linear molecules, it is a branched molecule, which is more excellent in flow processing, and the collision probability of the molecular chain is larger, so that the tensile elongation is more excellent, and excellent self-repairing is exhibited at room temperature, so that the prepared crosslinked polyurethane has excellent self-repairing performance at room temperature.

[0014] The preparation of the imine chain extender comprises the following steps: anhydrous sodium sulfate and p-aminophenol are added to a p-hydroxybenzaldehyde solution, after reaction, the filtrate is filtered, and the precipitate obtained after removal of the solvent is dried to obtain the imine chain extender.

[0015]

[0016] The molar ratio of the p-hydroxybenzaldehyde to anhydrous sodium sulfate is 1:0.1-0.12;

[0017] The molar ratio of the p-hydroxybenzaldehyde to 4-aminophenol is 1:0.8-1.2;

[0018] The reaction temperature is 30-50℃, and the reaction time is 3-8h. The preparation conditions of the chain extender are mild, and the process is simple, which creates favorable conditions for industrialization.

[0019] The polyol includes at least one of polytetrahydrofuran diol, polycaprolactone diol, and polybutylene adipate;

[0020] The isocyanate includes one of isophorone diisocyanate, 4,4-diisocyanate dicyclohexyl methane, and diphenyl methane diisocyanate;

[0021] The catalyst used in step 1 includes one or more of dibutyltin dilaurate, bismuth neodecanoate, and stannous octoate; the mass of the catalyst is 20-500ppm of the polyol;

[0022] The solvent used in step 1 includes one or more of toluene, ethylbenzene, and xylene.

[0023] The molar ratio of the polyol to the isocyanate in step 1 is 1:1.95-1:2.05, the reaction temperature of the polyol and the isocyanate is 30-60℃, and the reaction time is 3-5h. Preferably, the polyol is dehydrated in advance before use.

[0024] The trihydroxy crosslinking agent includes one or more of glycerol and triethanolamine;

[0025] The molar ratio of the total hydroxyl groups of the imine chain extender and the trihydroxy crosslinking agent to the isocyanate groups in the polyurethane prepolymer is 1.0:1-1.3:1.

[0026] The molar ratio of the imine chain extender to the trihydroxy crosslinking agent is 4:1-1:1;

[0027] The chain extension reaction of step 2 is carried out under an inert gas atmosphere, the reaction temperature is 30-80℃, and the reaction time is 2-10h.

[0028] The present application also provides a polyurethane prepared according to the preparation method, which has the advantages of simple preparation method, mild reaction conditions, and the product obtained can realize self-repairing at room temperature without additional conditions. In addition, the polyurethane of the present application also has excellent repeated processability, and the polyurethane material obtained by repeated processing after damage basically maintains consistent mechanical strength, and the toughness is also improved.

[0029] Compared with the prior art, the present application has the following beneficial effects:

[0030] (1) The polyurethane material with excellent self-repairing performance and tensile toughness is obtained by using the chain extender containing benzene ring and imine bond and the trihydroxy crosslinking agent to chain extend the polyurethane prepolymer, and the self-repairing effect can be realized at room temperature.

[0031] (2) The polyurethane has excellent repeated processability, and the polyurethane material obtained by repeated processing after damage basically maintains consistent mechanical strength, and the toughness is improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The nuclear magnetic spectrum of the imine chain extender obtained in Preparation Example 1.

[0033] Figure 2 The infrared spectrum of the imine chain extender obtained in Preparation Example 1.

[0034] Figure 3 The infrared spectrum of the polyurethane synthesized in Example 1 and Comparative Example 1.

[0035] Figure 4 The stress-strain curve of the polyurethane sample of the example and the comparative example.

[0036] Figure 5 The self-repairing control diagram of the polyurethane sample of Example 1 and Comparative Example 1.

[0037] Figure 6 The stress-strain curve of Comparative Example 1 at room temperature for different repair times.

[0038] Figure 7 The stress-strain curve of Example 1 at room temperature for different repair times.

[0039] Figure 8 The repeated processing control diagram of the polyurethane sample of Example 1 and Comparative Example 1.

[0040] Figure 9 The stress-strain curve of the polyurethane sample of Example 1 after repeated processing for multiple times. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below in combination 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 modify or replace equivalently on the basis of understanding the technical scheme of the present application, without departing from the spirit and scope of the technical scheme of the present application, which should be covered within the protection scope of the present application.

[0042] The raw materials used in the following specific embodiments are purchased from the market.

[0043] Preparation Example 1

[0044] Para-hydroxybenzaldehyde (12.21 g) was added to a 100 mL three-necked flask, and then 40 mL of anhydrous ethanol was added to dissolve it. After warming to 40 °C, anhydrous sodium sulfate (1.42 g) was added, followed by para-4-aminophenol (10.91 g), and the solution turned a beautiful golden yellow. After continuing the reaction for 5 h, the solution was filtered to separate the inorganic salt. The solution was distilled under reduced pressure to remove most of the anhydrous ethanol, and then vacuum dried at 60 °C for 12 h to obtain the imine chain extender as a yellow solid, with a calculated yield of 90%.

[0045] The infrared test was performed on a Thermo Nicolet 6700 infrared spectrometer. The sample to be tested was applied to a KBr sheet and dried under an infrared lamp, and then tested. The test temperature was room temperature (25 °C), the scanning range was 4000-500 cm -1 , the scanning frequency was 32 s -1 , and the resolution was 4 cm -1 .

[0046] Nuclear magnetic resonance (1H-NMR Agilent 600MHz DD2) was used to analyze the structure of the product. The substance to be analyzed was dissolved in deuterated dimethyl sulfoxide (DMSO-D6) at room temperature, and then tested.

[0047] As shown in Figure 1 , it can be seen from the nuclear magnetic resonance that there is a peak of hydrogen on the imine bond (-CH=N-) at 8.44 ppm, a doublet of hydrogen on the benzene ring of the original para-hydroxybenzaldehyde close to the aldehyde group at 7.72-7.76 ppm, a peak of hydrogen on the benzene ring close to the N atom at 7.10-7.12 ppm, a peak of hydrogen on the benzene ring of the original para-hydroxybenzaldehyde close to the hydroxyl group at 6.83-6.87 ppm, and a peak of hydrogen on the benzene ring of the original para-hydroxybenzaldehyde close to the hydroxyl group at 6.76-6.79 ppm.

[0048] As shown in Figure 2 , the characteristic absorption peak of the aldehyde group of para-hydroxybenzaldehyde at 1700 cm -1 disappeared completely, the benzene ring C=C absorption peaks appeared at 1517 cm -1 , 1580 cm -1 , and 1496 cm -1 , a new imine bond (-CH=N-) absorption peak appeared at 1602 cm -1 , and absorption peaks appeared at 3370 cm -1 and 734 cm -1The characteristic absorption peak of -OH appeared, indicating that the imine chain extender was successfully synthesized, and its -OH could react with isocyanate (-NCO) to chain extend, and the imine bond could provide self-repairing performance for the prepared polyurethane.

[0049] As shown in Table 1, the reaction conditions and the amount of anhydrous sodium sulfate were changed to obtain Preparation Examples 1-5, and the yield was calculated.

[0050] Table 1 Reaction temperature, amount of anhydrous sodium sulfate added, and yield of imine chain extender in Preparation Examples 1-5

[0051]

[0052] Example 1

[0053] Step 1, a three-necked flask containing polytetrahydrofuran diol (PTMEG, Mn≈1000 g / mol, 10 g) was dehydrated at 100℃ under reduced pressure for 1 h. Then, under the protection of high-purity nitrogen, the temperature was lowered to 70℃. Isophorone diisocyanate (4.45 g) and 30 mL of anhydrous toluene were added according to a -NCO / -OH molar ratio of 2 / 1, and 20 ppm of the catalyst dibutyltin dilaurate (DBTDL) was added. After reacting for 3 h under the protection of high-purity nitrogen, the flask was cooled to 40℃, and the product was treated to obtain a prepolymer;

[0054] Step 2, the content of -NCO in the product of Step 1 was titrated, and according to the -NCO content, the imine chain extender was added in a molar ratio of 1:1 with the crosslinking agent triethanolamine (the total hydroxyl molar amount of the chain extender and the crosslinking agent was equal to the -NCO molar amount of the prepolymer), and the reaction was continued. After the reaction mixture gelled, stirring was stopped, and the reaction was continued at 50℃ for 6 h to complete the reaction. Finally, the product was vacuum dried at 80℃ for 12 h to obtain an imine dynamic crosslinking polyurethane (CPU-I). Different polyurethanes were obtained according to the raw material usage ratio of Table 2.

[0055] Table 2 Molar ratio of raw materials for preparing self-repairing polyurethane in Examples 1-5

[0056]

[0057] Comparative Example 1

[0058] Step 1, a three-necked flask containing polytetrahydrofuran (PTMEG, Mn≈1000 g / mol, 10 g) was dehydrated at 100 ℃ under reduced pressure for 1 h. Then the temperature was lowered to 70 ℃ under high purity nitrogen protection. Isophorone diisocyanate (4.45 g) and 30 mL of anhydrous toluene were added according to the -NCO / -OH molar ratio of 2 / 1, and 20 ppm of catalyst dibutyltin dilaurate (DBTDL) was added. After reaction under high purity nitrogen protection for 3 h, the flask was cooled to 40 ℃;

[0059] Step 2, the -NCO content of the product of step 1 was titrated, and according to the -NCO content, a metered amount of butanediol (BDO) was added with a crosslinking agent triethanolamine molar ratio of 1:1 (the total hydroxyl molar amount of the chain extender and crosslinking agent was equal to the -NCO molar amount of the prepolymer), and the reaction was continued. After the reaction mixture gelled, stirring was stopped, and the reaction was continued at 50 ℃ for 6 h to complete the reaction. Finally, the product was vacuum dried at 80 ℃ for 12 h to obtain a conventional crosslinked polyurethane (CPU-B).

[0060] As shown in Figure 3 CPU-I and CPU-B crosslinked polyurethanes generated by adding crosslinking agents and imine chain extenders or BDO, the characteristic absorption peak of -NCO at 2258 cm -1 disappeared completely, and a new benzene ring absorption peak appeared at 1517 cm -1 and an imine bond (-CH=N-) absorption peak appeared at 1602 cm -1 in the infrared spectrum of CPU-I, indicating that the imine dynamic crosslinked polyurethane has been successfully synthesized.

[0061] The stress-strain curve and mechanical data of Examples 1-4 and Comparative Example 1 are shown in Table 3 and Figure 4 As shown in Table 3 and

[0062] As can be seen from Examples 1 and Comparative Example 1, the polyurethane prepared by using a chain extender containing an imine bond in the chain extension reaction has a fast-exchanging imine bond, resulting in lower strength than ordinary polyurethane; however, due to the presence of fast-exchanging dynamic bonds, chain segment rearrangement also occurs during stretching, resulting in higher elongation at break for the dynamic crosslinked polymer, especially at lower stretching rates, the elongation at break is longer.

[0063] Table 3 Mechanical properties of samples of Examples 1-4 and Comparative Example 1

[0064]

[0065] The crosslinked polyurethane was cut with a blade to show clear blade marks, as shown in Figure 5 The scratch self-repairing experiment was carried out on a polarizing microscope with a cold and hot stage (ECLIPSE E600W POL). The sample was placed in air with a temperature of 30 °C, and the magnification was 100 times. The scratch repair condition was observed. Example 1 could be repaired to no trace, while Comparative Example 1 could not be repaired.

[0066] Further, the repair effect of the crosslinked polyurethane was quantitatively characterized by a cutting-repairing experiment. The synthesized crosslinked polyurethane of Example 1 and Comparative Example 1 was cut into two halves with a blade, and then the sample was tightly contacted again. After repairing at 30 °C for a specific time, stress-strain test was carried out, and the results are shown in Figure 6 and Figure 7 The repair rate is defined as the ratio of the tensile strength of the repaired sample to the tensile strength of the uncut sample.

[0067] As can be seen from Figure 6 Comparative Example 1 has almost no self-repairing performance, only 21.6% of the repair rate, and almost no change with time, indicating that Comparative Example 1 is only slightly bonded together due to the excellent bonding performance of polyurethane, and cannot be self-repaired. As can be seen from Figure 7 Example 1 has very high repair efficiency, and can reach 44.9% of the repair rate after 0.5 h of repair, and 97.9% of the repair rate after 6 h of repair, basically realizing self-repairing. This result more powerfully indicates that the introduction of imine dynamic bond can make the crosslinked polyurethane have very excellent self-repairing performance.

[0068] To further test the repeatable processing performance, as shown in Figure 8 The sample after tensile test was cut into small pieces at room temperature with scissors, and then the small pieces were put into a stainless steel mold and pressed at 2 MPa and 90 °C for 20 min, and then cooled to room temperature to obtain a repeatable processing sample. As can be seen from the figure, Example 1 can be repeatedly processed, and Comparative Example 1 cannot be repeatedly processed. The sample obtained by repeated processing was also subjected to mechanical property test, and the results are shown in Figure 9 and Table 4.

[0069] Table 4 Mechanical properties of polyurethane sample of Example 1 after repeated processing

[0070]

[0071] From Table 4 and Figure 9It can be seen that the Young's modulus and the breaking strength of Example 1 decrease after one time of repeated processing, and the breaking elongation is obviously improved. This is because during the hot pressing process, the polymer molecules can exchange sufficiently, and the internal stress can be relaxed as much as possible, so that the yield strength decreases, the breaking elongation increases, and the toughness of the material is better. After repeated processing, the breaking elongation and the breaking strength change little.

Claims

1. A process for the preparation of a high elongation self-repairing polyurethane, characterized in that, The preparation method comprises the steps of: Step 1, under an inert gas atmosphere, a polyol and an isocyanate are catalytically reacted in a solvent to obtain a polyurethane prepolymer; the polyol is polytetrahydrofuran diol; Step 2, an imine chain extender and a trihydroxy crosslinking agent are added to the reaction solution, and a self-repairing polyurethane is obtained through a chain extension reaction; the trihydroxy crosslinking agent is triethanolamine; The molar ratio of the imine chain extender and the crosslinking agent is 1.5:1-1:1; The imine chain extender has the following structure:

2. The process for the preparation of high elongation self-repairing polyurethane according to claim 1, characterized in that, The preparation of the imine chain extender comprises the steps of adding anhydrous sodium sulfate and p-aminophenol to a p-hydroxybenzaldehyde solution, filtering after reaction, and drying the precipitate obtained after removing the solvent from the filtrate to obtain the imine chain extender.

3. The process for the preparation of high elongation self-repairing polyurethane according to claim 2, characterized in that, The molar ratio of the p-hydroxybenzaldehyde to the anhydrous sodium sulfate is 1:0.1-0.12; The molar ratio of the p-hydroxybenzaldehyde to the 4-aminophenol is 1:0.8-1.2; The reaction temperature is 30-50℃, and the reaction time is 3-8h.

4. The process for the preparation of high elongation self-healing polyurethane as claimed in claim 1, wherein, The isocyanate comprises one of isophorone diisocyanate, 4,4-diisocyanate dicyclohexyl methane, and diphenyl methane diisocyanate; The catalyst used in step 1 comprises one or more of dibutyltin dilaurate, bismuth neodecanoate, and stannous octoate; the mass of the catalyst is 20-500ppm of the polyol; The solvent used in step 1 comprises one or more of toluene, ethylbenzene, and xylene.

5. The process for the preparation of high elongation self-healing polyurethane as claimed in claim 1, wherein, The molar ratio of the polyol to the isocyanate in step 1 is 1:1.95-1:2.05, the reaction temperature of the polyol and the isocyanate is 30-60℃, and the reaction time is 3-5h.

6. The process for the preparation of high elongation self-repairing polyurethane according to claim 1, characterized in that, The total molar amount of the hydroxyl groups of the imine chain extender and the trihydroxy crosslinking agent to the molar amount of the isocyanate groups in the polyurethane prepolymer is 1.0:1-1.3:

1.

7. The process for the preparation of high elongation self-repairing polyurethane as claimed in claim 1, wherein, The chain extension reaction of step 2 is carried out under an inert gas atmosphere, the reaction temperature is 30-80℃, and the reaction time is 2-10h.

8. A polyurethane prepared by the preparation method according to any one of claims 1-7.

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