A bio-based elastomer

Abstract

This invention discloses a bio-based elastomer, belonging to the field of new materials technology. The low-temperature self-healing bio-based polyurethane elastomer of this invention consists of soft segments and hard segments. The soft segments are composed of hydroxyl-terminated aliphatic prepolymers and semi-crystalline polymer polycaprolactone diol, while the hard segments include isocyanates and chain extenders. A bio-based polyester prepolymer with an amorphous structure and compliant long chains is prepared by multi-component copolymerization. Lowering its glass transition temperature yields a prepolymer with low-temperature resistance potential. Using the semi-crystalline polycaprolactone diol as part of the soft segments, a dynamic layered domain can be constructed through a crystal-locked dynamic network, serving as a rigid filler to reinforce the elastomer. Simultaneously, a rich network of hydrogen bonds, urethane esters, and disulfide bonds is introduced into the elastomer, endowing it with low-temperature self-healing properties, thus producing a polyester-type low-temperature self-healing bio-based elastomer constructed using a multi-dynamic network.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically relating to a bio-based elastomer. Background Technology

[0002] Elastomers are polymeric materials with low modulus and high elasticity, capable of rapidly returning to their original state after the release of external stress. Common elastomers include polyurethane elastomers and SBS elastomers, which are widely used in transportation, aerospace, and flexible wearable devices. With increasing application demands, the sustainability of these materials must be a focus. To date, almost all commercially available synthetic elastomers are derived from fossil resources. Therefore, with growing environmental awareness and the scarcity of petrochemical resources, the development of bio-based elastomers to replace elastomers made from non-renewable resources has attracted widespread attention.

[0003] Polyurethane elastomers, due to their microphase-separated structure composed of soft and hard segments, possess high mechanical strength, good resilience, and oil resistance, making them widely used in conveyor belts, coated products, and medical applications. However, fatigue damage is inevitable during use. Therefore, researchers have introduced dynamic networks into polyurethane to endow it with self-healing properties, significantly improving its service life. However, currently developed self-healing elastomers still have some problems: First, the commonly used soft segments of polyurethane are prone to crystallization, reducing their toughness and making them less resistant to low temperatures; second, the self-healing temperature of currently developed polyurethane elastomer materials is above room temperature, but they cannot be used in low-temperature environments such as winter, extremely low temperatures, or even space, thus the inability to achieve self-healing at low temperatures greatly limits the practical application of polyurethane materials.

[0004] Therefore, it is necessary to develop a new polyurethane elastomer to achieve the low-temperature self-healing properties of polyurethane and improve its low-temperature resistance and flexibility; and it is necessary to develop bio-based polyurethane elastomers using bio-based materials. Summary of the Invention

[0005] To address the problems existing in the prior art, the present invention adopts the following technical solution:

[0006] The purpose of this invention is to provide a low-temperature self-healing bio-based polyurethane elastomer, which is composed of soft segments and hard segments, and its topology contains a multiple dynamic network composed of hydrogen bonds, urethane esters and disulfide bonds; the soft segments are made of hydroxyl-terminated aliphatic prepolymers and semi-crystalline polymer polycaprolactone diol (PCL); the hard segments are made of isocyanate and chain extender.

[0007] In one embodiment of the present invention, the chain extender is U2-diol, or a combination of U2-diol and other chain extenders; other chain extenders include one or more of 4,4-diaminodiphenyl disulfide, diamine, bis(4-hydroxyphenyl) disulfide, and bis(2-hydroxyethyl) disulfide.

[0008] In one embodiment of the present invention, the molar percentage of U2-diol in the chain extender is 30%-100%, preferably 50%.

[0009] In one embodiment of the present invention, the number average molecular weight of the hydroxyl-terminated aliphatic prepolymer is 1000-15000.

[0010] In one embodiment of the present invention, the number-average molecular weight of the semi-crystalline polymer polycaprolactone diol (PCL) is 1000-12000.

[0011] In one embodiment of the present invention, the isocyanate is one or a combination of isoflurone isocyanate, hexamethylene diisocyanate, toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), dicyclohexylmethane diisocyanate (HMDI), and lysine diisocyanate (LDI).

[0012] The present invention also provides a method for preparing the above-mentioned low-temperature self-healing bio-based polyurethane elastomer, comprising the following steps:

[0013] (1) Add bio-based dicarboxylic acid, diol, polymerization inhibitor and catalyst into the reactor, the reaction temperature is 130-190℃, the esterification time is 1-8h, and then change the esterification system to a vacuum system, and react for 2-8h to obtain hydroxyl-terminated bio-based aliphatic prepolymer.

[0014] (2) Add the semi-crystalline polymer polycaprolactone diol to the prepolymer, then place it under vacuum at a temperature of 90℃-120℃ to remove water, then adjust the reaction temperature to 50℃~80℃ and add isocyanate to react for 3~12h, then add chain extender to react for 6~12h, and dry.

[0015] In one embodiment of the present invention, the polymerization inhibitor mentioned in step (1) is any one of 4-methoxyphenol and hydroquinone, and the amount added is 0.05-0.5 wt%.

[0016] In one embodiment of the present invention, the catalyst in step (1) is tetrabutyl titanate, p-toluenesulfonic acid, antimony acetate, or dibutyltin laurate.

[0017] In one embodiment of the present invention, the amount of catalyst used in step (1) is 0.05-0.5 wt% of the total mass of the diol and dicarboxylic acid.

[0018] In one embodiment of the present invention, the molar ratio of diol to diacid in step (1) is 1.05 to 2:1.

[0019] 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.

[0020] In one embodiment of the present invention, the bio-based dicarboxylic acid in step (1) is one or a combination of itaconic acid, sebacic acid, succinic acid, azelaic acid, dimeric fatty acid (DAA), dodecyl dicarboxylic acid, and fumaric acid.

[0021] In one embodiment of the present invention, in step (2), the molar ratio of the soft segment to the isocyanate is 1:(1.2-5).

[0022] In one embodiment of the present invention, in step (2), the molar ratio of the semi-crystalline polymer polycaprolactone diol to the prepolymer is (1-5):3.

[0023] In one embodiment of the present invention, in step (2), the molar ratio of the chain extender to the prepolymer is 1:1.

[0024] In one embodiment of the present invention, the drying conditions in step (2) are drying at 60-90°C for 12-36 hours.

[0025] The present invention also provides the application of the above-mentioned low-temperature self-healing bio-based polyurethane elastomer in the fields of transportation, aerospace and flexible wearable devices.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] This invention provides a method for constructing a polyester-based low-temperature self-healing bio-based elastomer using a multi-dynamic network. Its key features include: utilizing multi-component copolymerization to obtain a bio-based polyester prepolymer with an amorphous structure and compliant long chains; lowering its glass transition temperature to obtain a prepolymer with low-temperature resistance potential; introducing a rich multi-dynamic network of hydrogen bonds, urethane esters, and disulfide bonds into the elastomer to endow it with low-temperature self-healing properties; and using semi-crystalline polycaprolactone diol (PCL) as part of the soft segment, which can construct dynamic layered domains through crystal-locked dynamic network construction, serving as a rigid filler to reinforce the elastomer and also effectively dissipating energy. Through topological design of the polyester-based polyurethane elastomer, its elongation at break and tensile strength can reach 1600% and 18 MPa, respectively. Furthermore, due to the presence of a multi-dynamic network and a glass transition temperature of -45°C, it possesses rapid self-healing capabilities at low temperatures; specifically, at 20°C, scratches disappear within 12 hours, demonstrating high self-healing efficiency. This has great application potential in fields such as flexible wearables.

[0028] Compared to existing self-healing polyurethane elastomers, the low-temperature self-healing bio-based elastomer of this invention exhibits low activation energy due to its lower glass transition temperature combined with abundant hydrogen bonds, urethane esters, and low-bond-energy disulfide bonds, thus enabling rapid self-healing at temperatures above -20°C. Furthermore, the use of bio-based prepolymers as soft segments modifies the polyurethane chain structure, imparting excellent toughness and low-temperature resistance. Finally, the use of PCL to construct dynamic layered domains further enhances the mechanical properties of the polyurethane elastomer. Detailed Implementation

[0029] 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.

[0030] The testing methods involved are:

[0031] Tensile properties (standard ASTM D638) of standard dumbbell-shaped specimens were tested using a universal testing machine (Instron 5967X, USA) at a crosshead rate of 10 mm / min to obtain tensile strength and elongation at break.

[0032] The molar amount of the prepolymer or PCL involved in this invention refers to the ratio of its mass to its number-average molecular weight.

[0033] Example 1

[0034] (1) Add 2.13 g (0.0167 mol) itaconic acid, 3.37 g (0.0167 mol) sebacic acid, 1.4 g (0.0183 mol) 1,3-propanediol, 1.67 g (0.0183 mol) 1,4-butanediol, 0.1 wt% hydroquinone, and 0.05 wt% tetrabutyl titanate 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 0.15 L / min, the magnetic stirring speed to 380 r / min, the reaction temperature to 170 °C, and the reaction time to 1.5 h. Then change the reaction system to a vacuum system and continue the reaction for 6 h to obtain a pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 3180 g / mol.

[0035] (2) Weigh 3 mmol of the prepolymer and 3 mmol of PCL together and add them to a 100 ml three-necked flask according to the number average molecular weight of the prepolymer. Then remove water at 100 °C under vacuum for 2 h. Then cool down to 50 °C and add 12 mmol of isoflurane isocyanate (molar ratio of soft segment to isocyanate is 1:2) under nitrogen atmosphere and react for 12 h. Then add the measured chain extender bis(4-hydroxyphenyl) disulfide and U2-diol (1:1, the molar ratio of total chain extender to prepolymer is 1:1) and continue to react for 12 h. Then pour into a mold and dry at 70 °C for 24 h to obtain a low-temperature self-healing bio-based polyurethane elastomer.

[0036] Comparative Example 1

[0037] The soft segment contains no PCL, chain extenders, sulfur, or U2-diol.

[0038] (1) Add 2.13 g (0.0167 mol) itaconic acid, 3.37 g (0.0167 mol) sebacic acid, 1.4 g (0.0183 mol) 1,3-propanediol, 1.67 g (0.0183 mol) 1,4-butanediol, 0.1 wt% hydroquinone, and 0.05 wt% tetrabutyl titanate 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 0.15 L / min, the magnetic stirring speed to 380 r / min, the reaction temperature to 170 °C, and the reaction time to 1.5 h. Then change the reaction system to a vacuum system and continue the reaction for 6 h to obtain a pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 3180 g / mol.

[0039] (2) Weigh 3 mmol of the prepolymer according to its 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 50 °C and add 6 mmol of isoflurane isocyanate (molar ratio of soft segment to isocyanate is 1:2) under nitrogen atmosphere and react for 12 h. Then add the measured chain extender butanediol (molar ratio of chain extender to prepolymer is 1:1) and continue to react for 12 h. Then pour it into a mold and dry at 70 °C for 24 h to obtain a low-temperature self-healing bio-based polyurethane elastomer.

[0040] Comparative Example 2

[0041] The soft segment contains no PCL, and the chain extender contains sulfur but no U2-diol.

[0042] (1) Add 2.13 g (0.0167 mol) itaconic acid, 3.37 g (0.0167 mol) sebacic acid, 1.4 g (0.0183 mol) 1,3-propanediol, 1.67 g (0.0183 mol) 1,4-butanediol, 0.1 wt% hydroquinone, and 0.05 wt% tetrabutyl titanate 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 0.15 L / min, the magnetic stirring speed to 380 r / min, the reaction temperature to 170 °C, and the reaction time to 1.5 h. Then change the reaction system to a vacuum system and continue the reaction for 6 h to obtain a pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 3180 g / mol.

[0043] (2) Weigh 3 mmol of the prepolymer according to its 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 50 °C and add 6 mmol of isoflurane isocyanate (molar ratio of soft segment to isocyanate is 1:2) under nitrogen atmosphere and react for 12 h. Then add the measured chain extender butanediol and bis(2-hydroxyethyl) disulfide (molar ratio of chain extender to prepolymer is 1:1) and continue to react for 12 h. Then pour it into a mold and dry at 70 °C for 24 h to obtain a low-temperature self-healing bio-based polyurethane elastomer.

[0044] Comparative Example 3

[0045] The soft segment contains no PCL, and the chain extender contains sulfur but no U2-diol.

[0046] (1) Add 2.13 g (0.0167 mol) itaconic acid, 3.37 g (0.0167 mol) sebacic acid, 1.4 g (0.0183 mol) 1,3-propanediol, 1.67 g (0.0183 mol) 1,4-butanediol, 0.05 wt% 4-methoxyphenol and 0.05 wt% tetrabutyl titanate 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 0.15 L / min, the magnetic stirring speed to 380 r / min, the reaction temperature to 170 °C, and the reaction time to 2 h. Then change the reaction system to a vacuum system and continue the reaction for 6 h to obtain a pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 3180 g / mol.

[0047] (2) Weigh 3 mmol of the prepolymer according to its number average molecular weight and add it to a 100 ml three-necked flask. Then remove water at 120 °C under vacuum for 2 h. Then cool down to 70 °C and add 6 mmol of dicyclohexylmethane diisocyanate (molar ratio of prepolymer to isocyanate is 1:2) under nitrogen atmosphere and react for 3 h. Then add the measured chain extender 4,4-diaminodiphenyl disulfide and dimethylglyoxime (1:1, molar ratio of chain extender to prepolymer is 1:1) and continue to react for 12 h. Then pour it into a mold and dry at 70 °C for 24 h to obtain a low-temperature self-healing bio-based polyurethane elastomer.

[0048] Comparative Example 4

[0049] Adding PCL to soft segments and chain extenders containing sulfur but not U2-diol:

[0050] (1) Add 2.13 g (0.0167 mol) itaconic acid, 3.37 g (0.0167 mol) sebacic acid, 1.4 g (0.0183 mol) 1,3-propanediol, 1.67 g (0.0183 mol) 1,4-butanediol, 0.05 wt% hydroquinone, and 0.05 wt% p-toluenesulfonic acid 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 0.15 L / min, the magnetic stirring speed to 380 r / min, the reaction temperature to 170 °C, and the reaction time to 2 h. Then change the reaction system to a vacuum system and continue the reaction for 6 h to obtain a pale yellow hydroxyl-terminated bio-based unsaturated aliphatic prepolymer with a number average molecular weight of 3180 g / mol.

[0051] (2) Weigh 3 mmol and 2 mmol of PCL according to the number average molecular weight of the prepolymer and add them to a 100 ml three-necked flask. Then remove water at 100 °C and vacuum for 2 h. Then cool down to 50 °C and add a measured amount of diphenylmethane diisocyanate (molar ratio of soft segment to isocyanate is 1:2) under nitrogen atmosphere and react for 12 h. Then add a measured amount of chain extender bis(4-hydroxyphenyl) disulfide and diamine (1:1, molar ratio of chain extender to prepolymer is 1:1) and continue to react for 12 h. Then pour into a mold and dry at 70 °C for 24 h to obtain a low-temperature self-healing bio-based polyurethane elastomer.

[0052] The test results of the elastomers obtained in Example 1 and Comparative Examples 1-4 are shown in Table 1.

[0053] Table 1 Performance Test Results

[0054]

[0055]

[0056] As shown in Table 1, the low-temperature self-healing bio-based polyurethane elastomer of the present invention, due to its abundant hydrogen bonds, urethane esters, and low-bond-energy disulfide bonds forming a multi-layered dynamic network, combined with the low glass transition temperature imparted by the amorphous prepolymer, can achieve self-healing at a low temperature of -15°C. Furthermore, the introduction of dynamic layered domains can act as rigid nanofillers to reinforce the elastomer, increasing the tensile strength from 9.3 MPa to 19.3 MPa. Additionally, the dynamic layered domains can effectively dissipate energy, imparting high toughness to the elastomer and significantly improving damage tolerance. In contrast, Comparative Example 1 could not obtain an effectively self-healing elastomer, while Comparative Examples 2, 3, and 4 could only obtain elastomers that could self-heal at approximately 30°C, 25°C, and 10°C, respectively, and none of them could achieve sub-zero low-temperature self-healing.

[0057] Comparative Example 5

[0058] Referring to Example 1, without adding U2-diol or replacing U2-diol with an equimolar amount of other diol chain extenders, while keeping everything else unchanged, the corresponding polyurethane elastomer was prepared.

[0059] The properties and structure of the polyurethane elastomers obtained from the tests are shown in Table 2.

[0060] Table 2

[0061]

[0062] It is evident that different diol chain extenders have a significant impact on the self-healing properties of the resulting polyurethane elastomers. Without using U2-diol, or by replacing it with other diol-structured chain extenders, only elastomers capable of self-healing at around 10°C can be obtained; none can achieve sub-zero low-temperature self-healing.

[0063] Example 2

[0064] Referring to Example 1, the PCL content was adjusted while other parameters remained unchanged to obtain the corresponding elastomer film. The results are shown in Table 3.

[0065] Table 3

[0066]

[0067]

[0068] As shown in Table 3, the tensile strength of the low-temperature self-healing bio-based polyurethane elastomer of the present invention increases from 14.2 MPa to 24.5 MPa as the PCL content gradually increases. The dynamic locking of hydrogen bonds in the PCL crystallization segment forms dynamic stratified domains, which can not only serve as rigid fillers to reinforce the elastomer, but also effectively dissipate energy through deformation and dissociation, significantly improving the damage resistance of the elastomer.

[0069] Example 3

[0070] Referring to Example 1, keeping the molar ratio of total chain extender to prepolymer at 1:1, the molar ratio of sulfur-containing chain extender to U2-diol in the chain extender was adjusted, while other parameters remained unchanged, to obtain the corresponding elastomer film. The results are shown in Table 4.

[0071] Table 4

[0072]

[0073] As shown in Table 4, the tensile strength of the low-temperature self-healing bio-based polyurethane elastomer of the present invention increases from 17.1 MPa to 21.8 MPa with increasing U2-diol content, while the elongation at break gradually decreases. This is because U2-diol contains a large number of H bonds, forming non-covalent crosslinks, and they aggregate to form a microcrystalline structure, thereby increasing the tensile strength of the elastomer. Furthermore, elastomers without U2-diol cannot achieve low-temperature self-healing. This is because hydrogen bonds, as a dynamic and reversible non-covalent interaction, play a crucial role in the self-healing properties of elastomers due to their dynamic characteristics. When the elastomer is damaged, the hydrogen bonds break, and new hydrogen bonds are formed when the crack is re-exposed. Combined with the low Tg of the elastomer of the present invention, low-temperature self-healing can be achieved.

[0074] The embodiments provided above are not intended to limit the scope of the invention, nor are the described steps intended to limit the order of execution. Any obvious modifications made to the invention by those skilled in the art based on existing common knowledge also fall within the scope of protection defined by the claims.

Claims

1. A low temperature self-healing bio-based polyurethane elastomer, characterized in that, Composed of soft segments and hard segments, its topological structure contains a multiple dynamic network composed of hydrogen bonds, urethane esters, and disulfide bonds; the soft segments are made from hydroxyl-terminated bio-based aliphatic prepolymers and semi-crystalline polymer polycaprolactone diol; the hard segments are made from isocyanates and chain extenders. The chain extender is a combination of U2-diol and other chain extenders; the other chain extenders include one or more of 4,4'-diaminodiphenyl disulfide, bis(4-hydroxyphenyl) disulfide, and bis(2-hydroxyethyl) disulfide.

2. The cryogenic self-healing bio-based polyurethane elastomer according to claim 1, characterized in that, The number-average molecular weight of the hydroxyl-terminated bio-based aliphatic prepolymer is 1000-15000; the number-average molecular weight of the semi-crystalline polymer polycaprolactone diol is 1000-12000.

3. The cryogenic self-healing bio-based polyurethane elastomer according to claim 1, wherein, The isocyanate is one or a combination of isophorone diisocyanate, hexamethylene diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, and lysine diisocyanate.

4. A method of preparing a low temperature self-healing bio-based polyurethane elastomer according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Add bio-based dicarboxylic acid, bio-based diol, polymerization inhibitor and catalyst into the reactor, the reaction temperature is 130~190℃, the esterification time is 1~8h, and then change the esterification system to a vacuum system, and react for 2~8h to obtain hydroxyl-terminated bio-based aliphatic prepolymer. (2) Add semi-crystalline polymer polycaprolactone diol to hydroxyl-terminated bio-based aliphatic prepolymer, then place it under vacuum at 90℃-120℃ to remove water, then adjust the reaction temperature to 50℃~80℃ and add isocyanate to react for 3~12h, then add chain extender to react for 6~12h, and dry.

5. The method according to claim 4, characterized in that, In step (1), the polymerization inhibitor is any one of 4-methoxyphenol and hydroquinone, and the amount added is 0.05-0.5 wt%; the catalyst is tetrabutyl titanate, p-toluenesulfonic acid, antimony acetate, or dibutyltin laurate; the amount of catalyst used is 0.05-0.5 wt% of the total mass of diol and diacid.

6. The method according to claim 4, characterized in that, In step (1), the molar ratio of diol to diacid is 1.05~2:1; the bio-based diol 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; the bio-based diacid is one or a combination of itaconic acid, sebacic acid, succinic acid, azelaic acid, dimer fatty acid, dodecyl diacid, and fumaric acid.

7. The method according to claim 4, characterized in that, In step (2), the molar ratio of the soft segment to the isocyanate is 1:(1.2~5); the molar ratio of the semi-crystalline polymer polycaprolactone diol to the hydroxyl-terminated bio-based aliphatic prepolymer is (1-5):3; and the molar ratio of the chain extender to the hydroxyl-terminated bio-based aliphatic prepolymer is 1:

1.

8. The method according to any one of claims 4-7, characterized in that, The drying conditions in step (2) are drying at 60~90℃ for 12~36h.

9. The application of the low-temperature self-healing bio-based polyurethane elastomer according to any one of claims 1-3 in the fields of transportation, aerospace and flexible wearable devices.

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