Self-healing elastomer

Abstract

This invention discloses a self-healing elastomer, belonging to the field of new materials technology. The invention utilizes a one-pot method to prepare the elastomer using hydroxyl-terminated prepolymers, isocyanates, chain extenders, metal ions, and crosslinking agents. The elastomer contains a rich multi-dynamic network of H bonds, metal coordination bonds, and disulfide bonds, resulting in a self-healing elastomer. This invention reduces the difficulty of preparation and improves the excellent properties of polyurethane elastomers, such as heat resistance and solvent resistance, through crosslinking. Simultaneously, it can achieve rapid self-healing at a low temperature of -10℃ and exhibits good mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology and relates to a self-healing elastomer. Background Technology

[0002] Polyurethane elastomers, as widely used elastic materials, can be made as soft as rubber or as hard as engineering plastics by adjusting the ratio and composition of soft and hard segments. Therefore, polyurethane possesses flexible designability and shows application potential in multiple fields. In recent years, researchers have endowed polyurethane with novel functionalities, giving it good mechanical properties as well as good electrical or optical properties, thus enabling its use in wearable devices and other fields.

[0003] Ordinary polyurethane materials inevitably suffer damage during use, significantly reducing their lifespan and safety. Therefore, researchers have introduced dynamic networks into polyurethane elastomers to achieve self-healing properties. This allows the material to self-heal upon receiving micro-damage, preventing microcracks from propagating into permanent cracks and causing material failure, thus extending its lifespan and reducing maintenance costs. However, several challenges remain with self-healing polyurethanes. First, the actual synthesis process of polyurethane is complex and difficult. It is significantly affected by variations in material reactivity, reaction temperature, catalysts, and climate, making it difficult to achieve continuous and reproducible performance. Second, currently developed polyurethane elastomers have self-healing temperatures above room temperature. However, they inevitably need to be used in low-temperature environments such as winter, extremely low temperatures, and even space, thus the inability to achieve self-healing at low temperatures greatly limits the practical application of polyurethane materials. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention adopts the following technical solution:

[0005] The purpose of this invention is to provide a method for preparing a low-temperature self-healing bio-based crosslinked polyurethane elastomer, comprising the following steps:

[0006] (1) A hydroxyl-terminated bio-based unsaturated aliphatic prepolymer is obtained by reacting a bio-based diacid containing a double bond with a diol; the number average molecular weight of the hydroxyl-terminated bio-based unsaturated aliphatic prepolymer is 1100-6000.

[0007] (2) The obtained hydroxyl-terminated bio-based unsaturated aliphatic prepolymer was reacted with isocyanate and chain extender for a period of time, and then crosslinking agent, UPyMA and metal salt were added to continue the reaction. After the reaction was completed, it was dried.

[0008] In one embodiment of the present invention, the low-temperature self-healing bio-based crosslinked polyurethane elastomer is prepared by reacting a polyurethane prepolymer with a crosslinking agent, and its topological structure contains a multiple dynamic network composed of metal coordination bonds, hydrogen bonds, and disulfide bonds; the polyurethane prepolymer is obtained by reacting a hydroxyl-terminated prepolymer, isocyanate, chain extender, and metal ions.

[0009] In one embodiment of the present invention, the bio-based diol mentioned in step (1) is one or a combination of propylene glycol, butanediol, rubber seed oil-based diol, palm oil-based diol, sunflower seed oil-based diol, isosorbide, pentylene glycol, ethylene glycol, and dimerol.

[0010] In one embodiment of the present invention, the bio-based dicarboxylic acid in step (1) is any one or two of itaconic acid and fumaric acid, or any one or two of itaconic acid and fumaric acid combined with other dicarboxylic acids; the other dicarboxylic acids include sebacic acid, succinic acid, azelaic acid, dimeric fatty acid (DAA), and dodecyl dicarboxylic acid or a combination thereof.

[0011] In one embodiment of the present invention, the molar ratio of the bio-based dicarboxylic acid to the diol in step (1) is 1:(1.05-2).

[0012] In one embodiment of the present invention, step (1) further includes adding a polymerization inhibitor, wherein the polymerization inhibitor is any one of 4-methoxyphenol and hydroquinone. The amount of the polymerization inhibitor added relative to the total mass of the diacid and diol is 0.05-0.5 wt%.

[0013] In one embodiment of the present invention, the reaction temperature in step (1) is 120-180°C and the time is 2-8 hours.

[0014] In one embodiment of the present invention, the isocyanate in step (2) is one or a combination of isoflurone isocyanate, hexamethylene diisocyanate, toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), and lysine diisocyanate (LDI).

[0015] In one embodiment of the present invention, the molar ratio of isocyanate to hydroxyl-terminated bio-based unsaturated aliphatic prepolymer in step (2) is (2-3):1.

[0016] In one embodiment of the present invention, the chain extender in step (2) is one or a combination of 4,4-diaminodiphenyl disulfide, diamine, bis(4-hydroxyphenyl) disulfide, bis(2-hydroxyethyl) disulfide, and dimethylglyoxime.

[0017] In one embodiment of the present invention, the molar ratio of the chain extender to the isocyanate in step (2) is (1-4):1.

[0018] In one embodiment of the present invention, the pre-reaction in step (2) further includes the addition of a ligand, wherein the ligand is dimethylglyoxime. The molar ratio of the ligand to the isocyanate is (1-4):1.

[0019] In one embodiment of the present invention, the temperature of the pre-reaction in step (2) is 40℃-90℃ and the time is 2-12h.

[0020] In one embodiment of the present invention, the temperature for the continued reaction in step (2) is 40℃-90℃ and the time is 3-12h.

[0021] In one embodiment of the present invention, the metal salt in step (2) is one or a combination of zinc chloride and copper chloride.

[0022] In one embodiment of the present invention, the molar ratio of the ligand to the metal salt in step (2) is 0-30:1; more preferably 0.5-30:1.

[0023] In one embodiment of the present invention, the crosslinking agent in step (2) is a mercapto crosslinking agent, including one or more of 3,6-dioxa-1,8-octanedithiol (difunctional), trimethylolpropane tris(3-mercaptopropionate) (trifunctional), and pentaerythritol tetra-3-mercaptopropionate (tetrafunctional).

[0024] In one embodiment of the present invention, the molar ratio of the crosslinking agent in step (2) to the total amount of double bonds in the hydroxyl-terminated bio-based unsaturated aliphatic prepolymer and UPyMA is (0.4-0.8):1. Preferably, it is 0.4-0.6:1.

[0025] In one embodiment of the present invention, the mass fraction of UPyMA in step (2) relative to the hydroxyl-terminated bio-based unsaturated aliphatic prepolymer is 0-20%. More preferably, it is 5-20%.

[0026] In one embodiment of the present invention, an initiator may be added to the continued reaction in step (2). The initiator is divided into a photoinitiator and a thermal initiator. The photoinitiator is 1173, benzoin dimethyl ether, and I907, and the thermal initiator is azobisisobutyronitrile, diethylazo, and tetramethylazo.

[0027] In one embodiment of the present invention, the drying conditions in step (2) are drying at 50-120°C for 12-36 hours.

[0028] This invention provides a low-temperature self-healing bio-based crosslinked polyurethane elastomer prepared based on the above method.

[0029] The present invention also provides the application of the above-mentioned low-temperature self-healing bio-based crosslinked polyurethane elastomer in self-powered triboelectric generators and wearable devices.

[0030] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0031] This invention provides a low-temperature self-healing bio-based crosslinked polyurethane elastomer and its preparation method. Its key feature is the one-pot preparation of the elastomer using hydroxyl-terminated prepolymers, isocyanates, chain extenders, metal ions, and crosslinking agents, resulting in a multi-layered dynamic network rich in H bonds, metal coordination bonds, and disulfide bonds. This simplifies the preparation method of polyurethane elastomers, reduces the preparation difficulty, and improves the excellent properties of polyurethane elastomers such as heat resistance and solvent resistance through crosslinking. Bio-based diacids and diols are used to reduce the content of toxic isocyanates, thus obtaining a bio-based polyurethane elastomer. More importantly, this invention utilizes the selection of crosslinking agents with different functionalities and the control of the crosslinking agent content to regulate the mechanical properties of the polyurethane elastomer.

[0032] The low-temperature self-healing bio-based crosslinked polyurethane elastomer of the present invention can achieve rapid self-healing at a low temperature of -10℃ and has good mechanical properties. Detailed Implementation

[0033] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0034] Example 1

[0035] (1) 7.8 g (0.060 mol) itaconic acid, 8.09 g (0.040 mol) sebacic acid, 4.18 g (0.055 mol) 1,3-propanediol, 4.95 g (0.055 mol) 1,4-butanediol, and 0.05 wt% 4-methoxyphenol were added to a 100 mL three-necked flask. Water generated during the reaction was collected using a water separator and condenser. The nitrogen flow rate was set to 0.2 L / min, the magnetic stirring speed was set to 320 r / min, the reaction temperature was 160 °C, and the reaction time was 4 h. A pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 1760 g / mol was obtained. (The molar weight of the prepolymer is the ratio of mass to number average molecular weight.)

[0036] (2) Weigh 10 mmol of prepolymer according to the number average molecular weight and add it to a 100 ml three-necked flask. Then remove water at 100 °C under vacuum for 2 h. Then cool down to 70 °C and add 20 mmol of isoflurane isocyanate (molar ratio of prepolymer to isocyanate is 1:2), 3 drops of catalyst dibutyltin laurylate, bis(4-hydroxyphenyl) disulfide (molar ratio of isocyanate to isocyanate is 2:1), and dimethylglyoxime (molar ratio of isocyanate to isocyanate is 2:1) under nitrogen atmosphere. After reacting for 6 h, add trimethylolpropane tris(3-mercaptopropionate) (0.4 times the molar content of double bonds in bio-based unsaturated aliphatic prepolymer) and continue to react for 6 h. Pour into a mold and dry at 70 °C to obtain a cross-linked polyurethane elastomer with low-temperature self-healing properties.

[0037] Example 2

[0038] (1) Add 7.8 g (0.060 mol) itaconic acid, 8.09 g (0.040 mol) sebacic acid, 4.18 g (0.055 mol) 1,3-propanediol, 4.95 g (0.055 mol) 1,4-butanediol and 0.05 wt% 4-methoxyphenol to a 100 mL three-necked flask. Collect the water generated by the reaction using a water separator and a condenser. Set the nitrogen flow rate to 0.2 L / min, the magnetic stirring speed to 320 r / min, the reaction temperature to 170 °C, and the reaction time to 4 h to obtain a pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 2160 g / mol.

[0039] (2) Weigh 10 mmol of prepolymer according to the number average molecular weight and add it to a 100 ml three-necked flask. Then remove water at 100 °C under vacuum for 2 h. Then cool down to 70 °C and add 20 mmol of isoflurane isocyanate (molar ratio of prepolymer to isocyanate is 1:2), 3 drops of catalyst dibutyltin laurylate, bis(4-hydroxyphenyl) disulfide (molar ratio of isocyanate to dimethylglyoxime to dimethylglyoxime to dimethylglyoxime to dimethylglyoxime) under nitrogen atmosphere and react for 6 h. Then add trimethylolpropane tris(3-mercaptopropionate) (0.4 times the molar content of double bonds in bio-based unsaturated aliphatic prepolymer) and copper chloride (addition amount is 1 / 30 of the molar amount of dimethylglyoxime) and continue to react for 6 h. Then pour into a mold and dry at 70 °C to obtain cross-linked polyurethane elastomer with low temperature self-healing properties.

[0040] Example 3

[0041] (1) Add 7.8 g (0.060 mol) itaconic acid, 8.09 g (0.040 mol) sebacic acid, 4.18 g (0.055 mol) 1,3-propanediol, 4.95 g (0.055 mol) 1,4-butanediol and 0.05 wt% 4-methoxyphenol to a 100 mL three-necked flask. Collect the water generated by the reaction using a water separator and a condenser. Set the nitrogen flow rate to 0.2 L / min, the magnetic stirring speed to 320 r / min, the reaction temperature to 180 °C, and the reaction time to 4 h to obtain a pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 2860 g / mol.

[0042] (2) Weigh 10 mmol of prepolymer according to the number average molecular weight and add it to a 100 ml three-necked flask. Then remove water at 100 °C under vacuum for 2 h. Then cool down to 70 °C and add 20 mmol of isoflurane isocyanate (molar ratio of prepolymer to isocyanate is 1:2), 3 drops of catalyst dibutyltin laurylate, bis(4-hydroxyphenyl) disulfide (molar ratio of isocyanate to isocyanate is 2:1), dimethylglyoxime (molar ratio of isocyanate to dimethylglyoxime is 2:1) under nitrogen atmosphere. After reacting for 6 h, add trimethylolpropane tris(3-mercaptopropionate) (mercaptogroup content is 0.4 times that of double bonds (double bonds in prepolymer + double bonds in UPyMA)), 5% wt (5% of the mass of unsaturated aliphatic prepolymer) of UPyMA and copper chloride (addition amount is 1 / 30 of the molar amount of dimethylglyoxime). Continue to react for 6 h and pour into a mold and dry at 70 °C to obtain cross-linked polyurethane elastomer with low-temperature self-healing properties.

[0043] Comparative Example 1

[0044] (1) Add 7.8 g (0.060 mol) itaconic acid, 8.09 g (0.040 mol) sebacic acid, 4.18 g (0.055 mol) 1,3-propanediol, 4.95 g (0.055 mol) 1,4-butanediol and 0.05 wt% 4-methoxyphenol to a 100 mL three-necked flask. Collect the water generated by the reaction using a water separator and a condenser. Set the nitrogen flow rate to 0.2 L / min, the magnetic stirring speed to 320 r / min, the reaction temperature to 180 °C, and the reaction time to 4 h to obtain a pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 2860 g / mol.

[0045] (2) Weigh 10 mmol of prepolymer according to the number average molecular weight and add it to a 100 ml three-necked flask. Then remove water at 100 °C under vacuum for 2 h. After cooling to 70 °C, add 20 mmol of isoflurane isocyanate (molar ratio of prepolymer to isocyanate is 1:2), 3 drops of catalyst dibutyltin laurylate, bis(4-hydroxyphenyl) disulfide (molar ratio of isocyanate to isocyanate is 2:1), and butanediol (molar ratio of isocyanate to isocyanate is 2:1) under nitrogen atmosphere. React for 6 h and continue to react for 6 h. Then pour into a mold and dry at 70 °C to obtain polyurethane elastomer.

[0046] Table 1 Performance Test Results

[0047]

[0048] As shown in Table 1, the low-temperature self-healing bio-based crosslinked polyurethane elastomer of the present invention exhibits a low glass transition temperature under the regulation of hydroxyl-terminated bio-based unsaturated aliphatic prepolymers, providing the necessary conditions for achieving low-temperature self-healing. The elastomer obtained in the embodiments of the present invention incorporates abundant hydrogen bonds, disulfide bonds, and metal coordination bonds, enabling self-healing at -10°C. Furthermore, as the prepolymer preparation temperature increases, its molecular weight gradually increases, leading to a gradual improvement in the mechanical properties of the polyurethane. In contrast, Comparative Example 1 only achieves self-healing at 30°C; below 30°C, it cannot effectively self-heal.

[0049] Example 4

[0050] Referring to Example 3, without adding UPyMA or replacing UPyMA with other crosslinking agents containing double bonds, while keeping everything else unchanged, the corresponding polyurethane elastomer was obtained.

[0051] The properties of the polyurethane elastomers obtained from the tests are shown in Table 2.

[0052] Table 2

[0053]

[0054]

[0055] Example 5

[0056] Referring to Example 3, the type and content of the crosslinking agent were adjusted while other aspects remained unchanged to obtain the corresponding elastomer film. The results are shown in Table 3.

[0057] Table 3

[0058]

[0059] The aforementioned crosslinking agent functionality refers to the number of thiol functional groups in the crosslinking agent.

[0060] As shown in Table 3, the tensile strength of the low-temperature self-healing bio-based crosslinked polyurethane elastomer of this invention gradually increases with the increase of crosslinking agent functionality, but the elongation at break shows a decreasing trend. Similarly, the elastomer exhibits the same trend when the sulfhydryl group content increases. Analysis suggests that as the crosslinking agent functionality and content increase, the crosslinking density increases, and the Tg slightly decreases. The low-temperature self-healing efficiency can be controlled by controlling the crosslinking density and the dynamic network. In some cases (e.g., when the functionality is 4 and the molar ratio is 0.6 or 0.8), self-healing can only be achieved at 10 or 15°C; effective self-healing is not possible below 10 or 15°C.

[0061] Example 6

[0062] Referring to Example 3, the types and contents of metal ions were adjusted while other aspects remained unchanged to obtain the corresponding elastomer films. The results are shown in Table 4.

[0063] Table 4

[0064]

[0065]

[0066] As shown in Table 4, the tensile strength of the low-temperature self-healing bio-based crosslinked polyurethane elastomer of the present invention tends to increase after the introduction of metal coordination bonds. The metal coordination bonds form a weak crosslinked network in the system, which to a certain extent inhibits the movement of molecular chains during the stretching process, thus reducing the elongation at break.

[0067] Example 7

[0068] Referring to Example 3, the mass fraction of UPyMA relative to the unsaturated aliphatic prepolymer was adjusted, while other parameters remained unchanged, to prepare the corresponding elastomer film. The results are shown in Table 5.

[0069] Table 5

[0070]

[0071] As shown in Table 5, the low-temperature self-healing bio-based crosslinked polyurethane elastomer of this invention introduces multiple hydrogen bonds into the dynamic network of the elastomer through UPyMA. With increasing UPyMA content, the tensile strength of the elastomer significantly increases, while the elongation at break does not decrease significantly. This is because the H bonds act as physical crosslinking points, improving mechanical strength; and the H bonds possess dynamic reversibility, acting as sacrificial bonds under external forces, dissipating a large amount of energy through preferential fracture and reversible fracture-reconstruction, ensuring that the decrease in elongation at break is not significant. It is particularly noteworthy that the double bonds on UPyMA can be co-cured with the main chain through a thiol crosslinking agent to reinforce the elastomer.

Claims

1. A method for preparing a low-temperature self-healing bio-based crosslinked polyurethane elastomer, characterized in that, Includes the following steps: (1) A hydroxyl-terminated bio-based unsaturated aliphatic prepolymer is obtained by reacting a bio-based dicarboxylic acid containing a double bond and a bio-based diol; the number average molecular weight of the hydroxyl-terminated bio-based unsaturated aliphatic prepolymer is 1100-6000. (2) The obtained hydroxyl-terminated bio-based unsaturated aliphatic prepolymer was reacted with isocyanate and chain extender for a period of time, and then crosslinking agent, UPyMA and metal salt were added to continue the reaction. After the reaction was completed, the product was dried. The pre-reaction further includes the addition of a ligand, wherein the ligand is dimethylglyoxime; The chain extender is one or a combination of 4,4-diaminodiphenyl disulfide, bis(4-hydroxyphenyl) disulfide, and bis(2-hydroxyethyl) disulfide; When the crosslinking agent is one or more of 3,6-dioxa-1,8-octanedithiol and trimethylolpropane tris(3-mercaptopropionate), the molar ratio of the crosslinking agent to the total amount of double bonds in the hydroxyl-terminated bio-based unsaturated aliphatic prepolymer and UPyMA is (0.4-0.8):1; When the crosslinking agent is pentaerythritol tetra-3-mercaptopropionate, the molar ratio of the crosslinking agent to the total amount of double bonds in the hydroxyl-terminated bio-based unsaturated aliphatic prepolymer and UPyMA is 0.4:

1.

2. The method according to claim 1, characterized in that, The bio-based diol mentioned in step (1) is one or a combination of propylene glycol, butylene glycol, rubber seed oil-based diol, palm oil-based diol, sunflower seed oil-based diol, isosorbide, pentylene glycol, ethylene glycol, and dimerol; the bio-based dicarboxylic acid containing double bonds is any one or two of itaconic acid and fumaric acid, or any one or two of itaconic acid and fumaric acid combined with other dicarboxylic acids; the other dicarboxylic acids include one or a combination of sebacic acid, succinic acid, azelaic acid, dimer fatty acids, and dodecyl dicarboxylic acids; the molar ratio of bio-based dicarboxylic acid to bio-based diol is 1:(1.05~2).

3. The method according to claim 1, characterized in that, Step (1) further includes adding a polymerization inhibitor, which is either 4-methoxyphenol or hydroquinone; the amount of polymerization inhibitor added relative to the total mass of bio-based dicarboxylic acid and bio-based diol is 0.05-0.5 wt.

4. The method according to claim 1, characterized in that, The isocyanate mentioned in step (2) is one or a combination of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, and lysine diisocyanate.

5. The method according to claim 1, characterized in that, The molar ratio of isocyanate to hydroxyl-terminated bio-based unsaturated aliphatic prepolymer in step (2) is (2-3):

1.

6. The method according to claim 1, characterized in that, In step (2), the molar ratio of the chain extender to the isocyanate is (1-4):1; the molar ratio of the ligand to the isocyanate is (1-4):1; and the molar ratio of the ligand to the metal salt is 0.5-30:

1.

7. The method according to claim 1, characterized in that, The metal salt mentioned in step (2) is one or a combination of zinc chloride and copper chloride.

8. The method according to any one of claims 1-7, characterized in that, In step (2), the mass fraction of UPyMA relative to the hydroxyl-terminated bio-based unsaturated aliphatic prepolymer is 5-20%.

9. A low-temperature self-healing bio-based crosslinked polyurethane elastomer prepared by the method according to any one of claims 1-8.

10. The application of the low-temperature self-healing bio-based crosslinked polyurethane elastomer according to claim 9 in self-powered triboelectric generators and wearable devices.

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