Preparation method of chain extender containing imine bond and application of chain extender in thermosetting polyurethane

Abstract

The invention provides a preparation method of a chain extender containing an imine bond and application of the chain extender in thermosetting polyurethane, and the preparation method comprises the following steps: under anhydrous and anaerobic conditions, mixing a reagent A and a reagent B, adding a solvent, reacting at 25-40 DEG C for 4-6 hours, cooling to room temperature, and carrying out rotary evaporation to remove the solvent to obtain the chain extender, wherein the reagent A is a derivative of benzene, one substituent group is an aldehyde group, at least one of the other five substituent groups is a hydroxyl group or an aldehyde group, and the reagent B is an organic compound containing both amido and hydroxyl group or an organic compound containing both amido and hydroxyl group. When the chain extender is used for preparing thermosetting polyurethane, imine bonds and carbamate bonds can be introduced into one monomer at the same time, so that the thermosetting polyurethane can maintain original excellent mechanical properties, solvent resistance and thermal stability, and also has self-healing and recyclable capabilities; the compatibility is good, and the performance and the application range of the thermosetting polyurethane are widened.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane, and particularly relates to a preparation method of a chain extender containing an imine bond and application of the chain extender in thermosetting polyurethane. Background Art

[0002] Thermoplastic polyurethanes generally have a linear structure or a very low degree of crosslinking, allowing for reprocessing through hot pressing or solvent recovery. However, thermoplastic polyurethanes suffer from poor thermal stability, solvent resistance, and high-temperature resistance. Compared to thermoplastic polyurethanes, thermosetting polyurethanes possess an irreversible three-dimensional crosslinked network and a higher crosslink density. As a result, thermosetting polyurethanes exhibit excellent mechanical properties, outstanding thermal stability, and chemical resistance, leading to their widespread use in daily life, industrial production, aerospace, and other fields. However, during use, polyurethane materials can be subject to erosion from external factors such as force, light, heat, and chemicals, causing cracks to form within or on the surface of the material. This not only reduces the service life of thermosetting polyurethanes but also poses certain safety risks. Furthermore, processing and recycling are extremely difficult, which not only increases the economic burden but also contradicts the environmental protection concepts promoted in recent years.

[0003] In recent years, many researchers have introduced dynamic, reversible covalent or non-covalent bonds into the network structure to enable materials to self-repair when damaged, thereby extending their service life. Currently, imide bonds are commonly used for the self-repair of thermoplastic polyurethanes, and phenol-urethane bonds are commonly used for the self-repair of water-soluble polyurethanes. However, if the two dynamic bonds are directly applied to thermosetting polyurethanes, their self-repair performance is poor. When the two dynamic bonds are introduced into thermosetting polyurethanes through two monomers, due to the consideration of the ratio of soft and hard segments, if the addition amount is too large, the hard segment content is large, the molecular chain is difficult to migrate, and it is not conducive to self-healing. If the addition amount is too small, the dynamic bonds contained in the system are small, which is also not conducive to self-healing. Summary of the Invention

[0004] To address the shortcomings of the prior art, the present invention provides a method for preparing a chain extender containing an imine bond, and also provides the use of the chain extender in thermosetting polyurethanes. When used to prepare thermosetting polyurethanes, the chain extender can simultaneously introduce imine and urethane bonds into a single monomer, resulting in a polyurethane that not only maintains its original excellent mechanical properties but also exhibits excellent thermal stability and solvent resistance, as well as self-healing and recyclability.

[0005] A method for preparing a chain extender containing an imine bond, the preparation method comprising: mixing reagent A and reagent B under anhydrous and oxygen-free conditions, adding a solvent, reacting at 25-40° C. for 4-6 hours, cooling to room temperature, and removing the solvent by rotary evaporation to obtain the chain extender; Wherein, the structural formula of the reagent A is as follows: wherein at least one of R1-R5 is a hydroxyl group -OH or an aldehyde group -CHO; Reagent B is an organic compound containing both an amino group -NH2 and a hydroxyl group -OH or an organic compound containing both an amino group -NH2.

[0006] Preferably, the reagent B is any one of the following compounds: The solvent is tetrahydrofuran.

[0007] Preferably, the molar ratio of all aldehyde groups -CHO in the reagent A to the amine groups -NH2 in the reagent B is 1:0.9-1.1.

[0008] Application of a chain extender containing an imine bond in thermosetting polyurethane, wherein the application is: (11) mixing the chain extender containing an imine bond and glyoxal bis(o-aminophenol), adding a solvent, and then adding isophorone diisocyanate and dibutyltin dilaurate, and reacting at 60-80° C. for 1-3 hours; (12) removing water from the polyether polyol or polyester polyol under reduced pressure, dissolving the polyether polyol in a solvent, and then adding the polyether polyol to the product of step (11) and continuing the reaction for 2-4 hours; (13) dissolving triethanolamine in a solvent, then adding it to the product of step (12), and continuing the reaction for 0.3-0.8 h; (14) drying to obtain self-repairing thermosetting polyurethane; Alternatively, the application is: (21) After removing water from the polyether polyol or polyester polyol under reduced pressure, isophorone diisocyanate and dibutyltin dilaurate are added to the solvent and reacted at 50-70°C for 1.5-3h; (22) dissolving 4,4'-diaminodiphenyl disulfide in a solvent, adding the mixture to the product of step (21), and continuing the reaction for 2-4 hours; (23) dissolving the chain extender containing an imine bond in a solvent, adding the resultant to the product of step (22), and continuing the reaction for 0.3-0.8 h; (24) drying to obtain self-repairing thermosetting polyurethane; The chain extender containing an imine bond is prepared by the preparation method of the present invention.

[0009] Preferably, the molar ratio of the hydroxyl group -OH on the chain extender containing an imine bond to isophorone diisocyanate is 1:(1.03-10.4).

[0010] Preferably, the molar ratio of isophorone diisocyanate to triethanolamine is (3.1-5.2):1; the molar ratio of glyoxal bis(o-aminophenol) acetal to isophorone diisocyanate is (0.02-0.35):1; and the molar ratio of 4,4'-diaminodiphenyl disulfide to isophorone diisocyanate is (0.05-0.33):1.

[0011] Preferably, the molar ratio of isophorone diisocyanate to polyether polyol or polyester polyol is (3.1-4.8):1.

[0012] Preferably, the added amount of dibutyltin dilaurate accounts for 8-15 wt% of the solid content.

[0013] Preferably, the polyether polyol is polytetrahydrofuran, polyethylene glycol or polypropylene glycol; the polyester polyol is polycaprolactone diol or polyethylene adipate diol.

[0014] Preferably, the solvent is tetrahydrofuran; and the drying condition is drying at 35-50° C. for 12-36 hours.

[0015] Advantages of the present invention: (1) The present invention prepares a chain extender containing an imine bond through a simple one-step process. When the chain extender is used to prepare thermosetting polyurethane, the imine bond and the urethane bond can be simultaneously introduced into a monomer, so that the thermosetting polyurethane can maintain the original excellent mechanical properties, solvent resistance and thermal stability while also having the ability to self-heal and be recyclable; (2) The chain extender containing an imine bond prepared by the present invention has good compatibility and can be used in combination with other chain extenders, such as a chain extender containing a disulfide bond, thereby broadening the performance and application range of thermosetting polyurethane and improving the stability of thermosetting polyurethane. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is the H NMR spectrum of chain extender C1; Figure 2 is the H NMR spectrum of chain extender C2; Figure 3 The stress-strain diagrams of Examples 1-5 and Comparative Examples 1-4 before and after repair; Figure 4 These are optical microscope images of Example 1 before and after restoration; Figure 5 The stress-strain diagrams of Examples 6-8 and Comparative Examples 5-8 before and after repair are shown; Figure 6 Optical microscope images of Example 6 before and after restoration; Figure 7 This is the stress-strain curve of the polyurethane acid after recycling three times in Example 1; Figure 8 This is the stress-strain curve of the polyurethane of Example 6 after hot pressing and recycling three times. DETAILED DESCRIPTION

[0017] Example 1 1. A method for preparing a chain extender containing an imine bond: Under anhydrous and oxygen-free conditions, 1.4 g of 2,5-dihydroxybenzaldehyde (10 mmol of aldehyde group) and 0.6 mL of ethanolamine (10 mmol of amino group) were mixed, 3 mL of tetrahydrofuran solvent was added, and the mixture was reacted at 30°C for 5 h. The mixture was cooled to room temperature and the solvent was removed by rotary evaporation to obtain a chain extender, which was designated as chain extender C1 and had the structural formula:

[0018] 2. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 72.5 mg of chain extender C1 (1.2 mmol hydroxyl group) and 110.3 mg of glyoxal bis(o-aminophenol) acetal (0.45 mmol) were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 10.9 wt% of the solid content in the system) were added, and the mixture was reacted at 70°C for 2 h; (2) 1 g of polytetrahydrofuran (1 mmol) was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0019] The reaction mechanism involved in Example 1 is as follows: It can be seen that the chain extender C1 contains a phenol-urethane bond and an imine bond after the reaction with isophorone diisocyanate, and the phenol-urethane bond and the imine bond are located on the same monomer.

[0020] Example 2 The chain extender C1 in Example 1 was used to prepare thermosetting polyurethane as follows: (1) 36.25 mg of chain extender C1 (0.6 mmol hydroxyl group) and 144.16 mg of glyoxal bis(o-aminophenol) acetal (0.6 mmol) were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 11 wt% of the solid content in the system) were added, and the mixture was reacted at 70°C for 2 h; (2) 1 g of polytetrahydrofuran was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0021] Example 3 The chain extender C1 in Example 1 was used to prepare thermosetting polyurethane as follows: (1) Take 18.13 mg of chain extender C1 (0.3 mmol hydroxyl group) and 216.23 mg of glyoxal bis(o-aminophenol) acetal (0.9 mmol), add 5 mL of tetrahydrofuran solvent, then add 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 10.3 wt% of the solid content in the system), and react at 70 ° C for 2 h; (2) 1 g of polytetrahydrofuran (1 mmol) was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0022] Example 4 The chain extender C1 in Example 1 was used to prepare thermosetting polyurethane as follows: (1) 108.75 mg of chain extender C1 (1.8 mmol hydroxyl group) and 36.039 mg of glyoxal bis(o-aminophenol) acetal (0.15 mmol) were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 11 wt% of the solid content in the system) were added, and the mixture was reacted at 70°C for 2 h; (2) 1 g of polytetrahydrofuran (1 mmol) was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0023] Example 5 The chain extender C1 in Example 1 was used to prepare thermosetting polyurethane as follows: (1) 117.81 mg of chain extender C1 (1.95 mmol hydroxyl group) and 18.02 mg of glyoxal bis(o-aminophenol) acetal (0.075 mmol) were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 11.2 wt% of the solid content in the system) were added, and the mixture was reacted at 70°C for 2 h; (2) 1 g of polytetrahydrofuran (1 mmol) was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0024] Example 6 1. A method for preparing a chain extender containing an imine bond: Under anhydrous and oxygen-free conditions, 661.8 mg of 1,3,5-benzenetricarboxaldehyde (12 mmol of aldehyde group) and 0.78 mL of ethanolamine (13 mmol of amino group) were mixed, 3 mL of tetrahydrofuran solvent was added, and the mixture was reacted at 30°C for 5 h. The mixture was cooled to room temperature and the solvent was removed by rotary evaporation to obtain a chain extender, designated as chain extender C2, with the following structural formula:

[0025] 2. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 1.4 g of polytetrahydrofuran (0.7 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (8 wt% of the solid content in the system) were added to 3 mL of tetrahydrofuran and reacted at 60°C for 2 h. (2) 223.5 mg of 4,4'-diaminodiphenyl disulfide (0.9 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (1), and the reaction was continued for 3 h; (3) 305.44 mg of chain extender C2 (2.7 mmol hydroxyl group) was dissolved in 10 mL of tetrahydrofuran and added to the product of step (2), and the reaction was continued for 0.5 h; (4) Drying at 40° C. for 24 hours to obtain the polyurethane.

[0026] The reaction mechanism involved in Example 6 is as follows: It can be seen that the chain extender C2 contains a urethane bond and an imine bond after the reaction with isophorone diisocyanate, and the urethane bond and the imine bond are located on the same monomer.

[0027] Example 7 The chain extender C2 in Example 6 was used to prepare thermosetting polyurethane as follows: (1) 1.5 g of polytetrahydrofuran (0.75 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 7.9 wt% of the solid content in the system) were added to 3 mL of tetrahydrofuran and reacted at 60°C for 2 h. (2) 248.3 mg of 4,4'-diaminodiphenyl disulfide (1 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (1), and the reaction was continued for 3 h; (3) 271.506 mg of chain extender C2 (2.4 mmol hydroxyl group) was dissolved in 10 mL of tetrahydrofuran and added to the product of step (2), and the reaction was continued for 0.5 h; (4) Drying at 40° C. for 24 hours to obtain the polyurethane.

[0028] Example 8 The chain extender C2 in Example 6 was used to prepare thermosetting polyurethane as follows: (1) 1.3 g of polytetrahydrofuran (0.65 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 8.5 wt% of the solid content in the system) were added to 3 mL of tetrahydrofuran and reacted at 60°C for 2 h; (2) 198.64 mg of 4,4'-diaminodiphenyl disulfide (0.8 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (1), and the reaction was continued for 3 h; (3) 339.382 mg of chain extender C2 (3 mmol hydroxyl group) was dissolved in 10 mL tetrahydrofuran and added to the product of step (2), and the reaction was continued for 0.5 h; (4) Drying at 40° C. for 24 hours to obtain the polyurethane.

[0029] Example 9 1. A method for preparing a chain extender containing an imine bond: Under anhydrous and oxygen-free conditions, 1.38 g of 3,5-dihydroxybenzaldehyde (10 mol of aldehyde group) and 0.78 mL of 1-amino-2-propanol (10 mmol of amine group) were mixed, and tetrahydrofuran (3 mL) was added as a solvent. The mixture was reacted at 30°C for 5 h, cooled to room temperature, and the solvent was removed by rotary evaporation to obtain a chain extender, which was recorded as chain extender C3.

[0030] 2. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 72.5 mg of chain extender C3 (1.64 mmol hydroxyl group) and 110.3 mg of glyoxal bis(o-aminophenol) acetal (0.46 mmol) were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 9 wt% of the solid content in the system) were added, and the mixture was reacted at 70°C for 2 h; (2) 1 g of polyethylene glycol (1 mmol) was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0031] Example 10 1. A method for preparing a chain extender containing an imine bond: Under anhydrous and oxygen-free conditions, 661.8 mg of 1,3,5-benzenetricarboxaldehyde (13 mmol of aldehyde group) and 1.02 mL of 1-amino-2-propanol (13 mmol of amine group) were mixed, 3 mL of tetrahydrofuran solvent was added, and the mixture was reacted at 30°C for 5 h. The mixture was cooled to room temperature and the solvent was removed by rotary evaporation to obtain a chain extender, which was recorded as chain extender C4.

[0032] 2. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 1.4 g of polytetrahydrofuran (0.7 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 10 wt% of the solid content in the system) were added to 3 mL of tetrahydrofuran and reacted at 60°C for 2 h; (2) 223.5 mg of 4,4'-diaminodiphenyl disulfide (0.9 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (21), and the reaction was continued for 3 h; (3) 339.4 mg of chain extender C4 (3 mmol hydroxyl group) was dissolved in 10 mL tetrahydrofuran and added to the product of step (22), and the reaction was continued for 0.5 h; (4) Drying at 40° C. for 24 hours to obtain the polyurethane.

[0033] Example 11 1. A method for preparing a chain extender containing an imine bond: Under anhydrous and oxygen-free conditions, 1.38 g of 2,3-dihydroxybenzaldehyde (10 mmol of aldehyde group) and 375.5 uL of 1,3-propylenediamine (9 mmol of amino group) were mixed, 3 mL of tetrahydrofuran solvent was added, and the mixture was reacted at 25°C for 6 h. The mixture was cooled to room temperature and the solvent was removed by rotary evaporation to obtain a chain extender, which was recorded as chain extender C5.

[0034] 2. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 102.4 mg of chain extender C5 (1.8 mmol hydroxyl group) and 37.24 mg of glyoxal bis(o-aminophenol) acetal (0.155 mmol) were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 11.2 wt% of the solid content in the system) were added, and the mixture was reacted at 60°C for 3 h; (2) 1 g (1 mmol) of polytetrahydrofuran was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 2 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.3 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 35° C. for 36 hours to obtain the thermosetting polyurethane.

[0035] Example 12 1. A method for preparing a chain extender containing an imine bond: Under anhydrous and oxygen-free conditions, 1.38 g of 2,3-dihydroxybenzaldehyde (10 mol of aldehyde group) and 841 uL of 3-amino-1-propanol (11 mol of amine group) were mixed, 3 mL of tetrahydrofuran solvent was added, and the mixture was reacted at 40°C for 4 h. The mixture was cooled to room temperature and the solvent was removed by rotary evaporation to obtain a chain extender, which was recorded as chain extender C6.

[0036] 2. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 86.2 mg of chain extender C6 (1.2 mmol hydroxyl group) and 110.3 mg of glyoxal bis(o-aminophenol) acetal were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 10.5 wt% of the solid content in the system) were added, and the mixture was reacted at 80°C for 1 h; (2) 1 g of polytetrahydrofuran (1 mmol) was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 4 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.8 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 35° C. for 36 hours to obtain the thermosetting polyurethane.

[0037] Example 13 The chain extender C2 in Example 6 was used to prepare thermosetting polyurethane as follows: (1) 1 g of polycaprolactone diol (1 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 9.8 wt% of the solid content in the system) and 3 mL of tetrahydrofuran were added and reacted at 50°C for 3 h. (2) 223.5 mg of 4,4'-diaminodiphenyl disulfide (0.9 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (1), and the reaction was continued for 2 h; (3) 305.4 mg of chain extender C2 (2.7 mmol hydroxyl group) was dissolved in 10 mL tetrahydrofuran and added to the product of step (2), and the reaction was continued for 0.3 h; (4) Drying at 35° C. for 36 hours to obtain the polyurethane.

[0038] Example 14 The chain extender C2 in Example 6 was used to prepare thermosetting polyurethane as follows: (1) 1 g of polyethylene adipate glycol (1 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 9.7 wt% of the solid content in the system) and 3 mL of tetrahydrofuran were added and reacted at 70°C for 1.5 h. (2) 223.5 mg of 4,4'-diaminodiphenyl disulfide (0.9 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (1), and the reaction was continued for 4 h; (3) 305.4 mg of chain extender C2 (2.7 mmol hydroxyl group) was dissolved in 10 mL tetrahydrofuran and added to the product of step (2), and the reaction was continued for 0.8 h; (4) Drying at 50° C. for 12 h to obtain the polyurethane.

[0039] Comparative Example 1 A method for preparing thermosetting polyurethane comprises the following steps: (1) Mix 93 μL of 1,4-butanediol (2.1 mmol of hydroxyl group), add 5 mL of tetrahydrofuran solvent, then add 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 11.5 wt% of the solid content in the system), and react at 60 ° C for 3 h; (2) 1 g of polytetrahydrofuran (1 mmol) was decompressed at 120° C. for 3 h to remove moisture, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 2 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 35° C. for 36 hours to obtain the thermosetting polyurethane.

[0040] Compared with Example 1, the thermosetting polyurethane prepared in Comparative Example 1 does not contain dynamic bonds (imide bonds and phenol-urethane bonds).

[0041] Comparative Example 2 1. A method for preparing a chain extender containing an imine bond: Under anhydrous and oxygen-free conditions, 670.65 mg of terephthalaldehyde (10 mmol of aldehyde group) and 0.6 mL of ethanolamine (10 mmol of amino group) were mixed, and tetrahydrofuran (3 mL) was added as a solvent. The mixture was reacted at 40°C for 4 h, cooled to room temperature, and the solvent was removed by rotary evaporation to obtain a chain extender, which was recorded as chain extender C7.

[0042] 2. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 110.7 mg of chain extender C7 (1.2 mmol hydroxyl group) and 110.3 mg of dialdehyde bis(o-aminophenol) acetal (0.45 mmol) were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 9.4 wt% of the solid content in the system) were added, and the mixture was reacted at 70°C for 2 h; (2) 1 g of polytetrahydrofuran (1 mmol) was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0043] Compared with Example 1, the thermosetting polyurethane prepared in Comparative Example 2 also contains dynamic bonds, imine bonds and phenol-carbamate bonds, but the imine bonds and phenol-carbamate bonds are located on two monomers, not on the same monomer, because the chain extender C7 only contains imine bonds and aliphatic hydroxyl groups, but does not contain phenolic hydroxyl groups. The imine bonds in the prepared polyurethane are provided by the chain extender C7. Glyoxal bis(o-aminophenol) acetal contains phenolic hydroxyl groups and reacts with isophorone diisocyanate to form a phenol-carbamate bond, so the imine bonds and phenol-carbamate bonds are not on the same monomer.

[0044] Comparative Example 3 1. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) Take 110.3 mg of glyoxal bis(o-aminophenol)acetal, add 5 mL of tetrahydrofuran solvent, then add 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 11 wt% of the solid content in the system), and react at 70 ° C for 2 h; (2) 1 g of polytetrahydrofuran was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 132 μL (1 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0045] Compared with Example 1, the thermosetting polyurethane prepared in Comparative Example 3 contains only one dynamic bond, that is, only a phenol-urethane bond, and no imine bond.

[0046] Comparative Example 4 The chain extender C7 in Comparative Example 2 was used to prepare thermosetting polyurethane as follows: (1) 110.7 mg of chain extender C7 (1.2 mmol hydroxyl group) and 40 μL of 1,4-butanediol (0.45 mol) were mixed, 5 mL of tetrahydrofuran solvent was added, and then 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 9.4 wt% of the solid content in the system) were added, and the mixture was reacted at 60 °C for 3 h; (2) 1 g of polytetrahydrofuran (1 mmol) was removed from the water by decompression at 120° C. for 3 h, dissolved in 3 mL of tetrahydrofuran, and then added to the product of step (1), and the reaction was continued for 3 h; (3) Dissolve 79.216 μL (0.6 mmol) of triethanolamine in 2 mL of tetrahydrofuran, then add it to the product of step (2) and continue the reaction for 0.5 h; (4) Finally, the product is slowly poured into a polytetrafluoroethylene mold and dried at 40° C. for 24 hours to obtain the thermosetting polyurethane.

[0047] Compared with Example 1, the thermosetting polyurethane prepared in Comparative Example 4 contains only one dynamic bond, that is, only an imine bond, and does not contain a phenol-urethane bond.

[0048] Comparative Example 5 1. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 1.4 g of polytetrahydrofuran (0.7 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (8 wt% of the solid content in the system) were added to 3 mL of tetrahydrofuran and reacted at 60°C for 2 h. (2) 80 μL of 1,4-butanediol (0.9 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (1), and the reaction was continued for 3 h; (3) 119 μL triethanolamine (0.9 mmol) was dissolved in 10 mL tetrahydrofuran and added to the product of step (2), and the reaction was continued for 0.5 h; (4) Drying at 40° C. for 24 hours to obtain the polyurethane.

[0049] Compared with Example 6, the thermosetting polyurethane prepared in Comparative Example 5 does not contain dynamic bonds (imide bonds, urethane bonds and disulfide bonds).

[0050] Comparative Example 6 1. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 1.4 g of polytetrahydrofuran (0.7 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 8.7 wt% of the solid content in the system) were added to 3 mL of tetrahydrofuran and reacted at 60°C for 2 h. (2) 223.5 mg of 4,4'-diaminodiphenyl disulfide (0.9 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (21), and the reaction was continued for 3 h; (3) 118.8 μL triethanolamine (2.7 mmol hydroxyl group) was dissolved in 3 mL tetrahydrofuran and added to the product of step (22), and the reaction was continued for 0.5 h; (4) Drying at 40° C. for 24 hours to obtain the polyurethane.

[0051] 6, in Comparative Example 6, the chain extender C2 is not added, and triethanolamine is used instead of C2 as a trifunctional chain extender to synthesize the thermosetting polyurethane. The synthesized thermosetting polyurethane contains only one dynamic bond, disulfide bond.

[0052] Comparative Example 7 1. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 1.4 g of polytetrahydrofuran (0.7 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol) and 200 μL of dibutyltin dilaurate (accounting for 9 wt% of the solid content in the system) were added to 3 mL of tetrahydrofuran and reacted at 60°C for 2 h; (2) 305.44 mg of chain extender C2 (2.7 mmol hydroxyl group) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (1), and the reaction was continued for 3 h; (3) 79.5 μL 1,4-butanediol (0.9 mmol) was dissolved in 2 mL tetrahydrofuran and added to the product of step (2), and the reaction was continued for 0.5 h; (4) Drying at 40° C. for 24 hours to obtain the polyurethane.

[0053] Compared with Example 6, in Comparative Example 7, 4,4'-diaminodiphenyl disulfide was not added, and 1,4-butanediol was used instead of 4,4'-diaminodiphenyl disulfide as a difunctional chain extender. The synthesized thermosetting polyurethane contained only one dynamic bond, namely, an imine bond.

[0054] Comparative Example 8 1. A method for preparing a chain extender containing an imine bond, comprising: mixing 1.23 g of 2,4-diaminobenzaldehyde (9 mmol of aldehyde group) and 334 μL of ethylenediamine (10 mmol of amine group) under anhydrous and oxygen-free conditions, adding tetrahydrofuran (3 mL) as a solvent, reacting at 40° C. for 4 h, cooling to room temperature, and removing the solvent by rotary evaporation to obtain a chain extender, designated as chain extender C8, having the structural formula:

[0055] 2. A method for preparing a thermosetting polyurethane, comprising the following steps: (1) 1.4 g of polytetrahydrofuran (0.7 mmol) was decompressed at 120°C for 3 h to remove moisture, and 653 μL of isophorone diisocyanate (3.1 mmol), 200 μL of dibutyltin dilaurate (8 wt% of the solid content), and 3 mL of tetrahydrofuran were added and reacted at 60°C for 2 h. (2) 111.75 mg of 4,4'-diaminodiphenyl disulfide (0.45 mmol) was dissolved in 2 mL of tetrahydrofuran and added to the product of step (1), and the reaction was continued for 2 h; (3) Dissolve 40 μL of 1,4-butanediol (0.45 mmol) in 5 mL of tetrahydrofuran, add it to the product of step (2), and continue the reaction for 1 h; (4) 218.63 mg of chain extender C8 (2.7 mmol of amine group) was dissolved in 10 mL of tetrahydrofuran and added to the product of step (3), and the reaction was continued for 0.5 h; (5) Drying at 40° C. for 24 hours to obtain the polyurethane.

[0056] Compared with Example 6, the polyurethane prepared in Comparative Example 8 also contains dynamic bond imine bonds and carbamate bonds, but the imine bonds and carbamate bonds are located on different monomers. The carbamate bond is generated by the reaction of 1,4-butanediol and isophorone diisocyanate. The imine bond in the polyurethane is provided by the chain extender C8, so the imine bond and the carbamate bond are not on the same monomer.

[0057] Performance testing 1. H NMR spectroscopy The chain extenders C1 and C2 provided in Example 1 and Example 6 were subjected to hydrogen nuclear magnetic resonance spectroscopy, respectively. Deuterated dimethyl sulfoxide was used as solvent to dissolve them in a nuclear magnetic resonance tube and the nuclear magnetic resonance spectroscopy was performed at room temperature using a JNM-ECZ400R / SI nuclear magnetic spectrometer produced by Bruker. The results were as follows: Figure 1 and Figure 2 ; Depend on Figure 1 It can be seen that the peaks at chemical shifts of 6.71, 6.75, and 6.80 correspond to the three protons e, g, and h on the benzene ring of chain extender C1, the peak at chemical shift of 3.62 corresponds to the two protons on the methylene b and c in chain extender C1, the peak at chemical shift of 8.40 corresponds to the proton on the imine bond d, and the peaks at chemical shifts of 4.73, 8.94, and 12.6 correspond to the active hydrogens on the hydroxyl groups a, f, and i, respectively. The area of each peak is proportional to the number of hydrogen atoms in the structural formula of chain extender C1, indicating that chain extender C1 was successfully prepared. Depend on Figure 2 It can be seen that the peak at the chemical shift of 8.19 corresponds to the proton on the benzene ring a of the chain extender C2, the peak at the chemical shift of 3.67 corresponds to the two protons on the methylene c and d in the chain extender C2, the peak at the chemical shift of 8.42 corresponds to the proton on the imine bond b, and the peak at the chemical shift of 4.66 corresponds to the active hydrogen on the hydroxyl group e. The area of each peak is proportional to the number of hydrogen atoms in the structural formula of the chain extender C2, indicating that the chain extender C2 was successfully prepared.

[0058] 2. Mechanical properties testing Mechanical properties were tested using an electronic universal testing machine, with tensile testing performed at a rate of 50 mm / min. The results are shown in Tables 1 and 2. Table 1 shows the mechanical tensile testing of Examples 1-5 and Comparative Examples 1-4, while Table 2 shows the mechanical tensile testing of Examples 6-8 and Comparative Examples 5-8. The mechanical tensile testing of the polyurethanes shows that the mechanical properties of the Examples are superior to those of the Comparative Examples.

[0059] Table 1 Mechanical properties test of Examples 1-5 and Comparative Examples 1-4 Table 2 Mechanical properties test of Examples 6-8 and Comparative Examples 5-8 3. Self-repair performance testing The mechanical properties of the polyurethane samples of Examples 1-5 and Comparative Examples 1-4 were tested. The polyurethane samples were then simply cut in the middle and the two parts were reassembled along the cross section. The samples were repaired at the same time and temperature (100°C for 12 hours). They were then tested on an electronic universal testing machine at a rate of 50 mm / min to test their mechanical properties. Figure 3 ; At the same time, use an optical microscope to observe the situation of the sample of Example 1 before and after self-repair and take pictures to record, see Figure 4 ;in, Figure 3 The stress-strain diagrams of Examples 1-5 and Comparative Examples 1-4 before and after repair are shown. η in the figure represents the repair efficiency (in %). It can be seen that Example 1 has the highest stress repair efficiency. When the two sheared polyurethane segments are reconnected and placed in a 100°C oven, the polymer segments move, and the hydrogen bonds, phenol-urethane bonds, and imine bonds that were broken at the cross section are re-bonded, thus achieving a self-repairing effect. Figure 4 These are optical microscope images of Example 1 before and after repair. It can be seen that there is an obvious scratch before repair, but after repair, the scratch disappears and the film surface becomes smooth again. The mechanical properties of the polyurethane samples of Examples 6-8 and Comparative Examples 5-8 were tested. A mark was then made on a complete polyurethane film with a knife. The scratched polyurethane film was repaired at 120°C for 12 hours and then tested on an electronic universal testing machine. The film was stretched at a rate of 50 mm / min to test its mechanical properties. Figure 5 At the same time, the sample of Example 6 and the sample scratches were observed under an optical microscope before and after repair at 120 ° C for 12h and photographed and recorded. Figure 6 ; Figure 5 The stress-strain diagrams of Examples 6-8 and Comparative Examples 5-8 before and after self-repair under thermal repair conditions are shown in FIG. , where η in the figure is the repair efficiency in %. It can be seen that Example 6 has the highest recovery efficiency. When the scratched polyurethane film is placed on a glass slide and heated, the polymer chain segments move, and the hydrogen bonds, imine bonds, and carbamate bonds that were broken at the cross section are re-bonded, and the broken disulfide bonds are exchanged to form complete disulfide bonds again, thereby allowing the polyurethane in Example 6 to basically restore the mechanical properties of the original material.

[0060] Figure 6 These are optical microscope images of Example 6 before and after thermal repair. It can be seen that heating can restore the scratches to a smooth surface.

[0061] 4. Recyclability test Acid recovery: Cut the polyurethane film into small pieces and dissolve them in an acidic solution consisting of 5 mL of tetrahydrofuran and 50 μL of 12 mol / L concentrated hydrochloric acid. After the polyurethane fragments are completely dissolved to form a uniform solution, gently pour it into a polytetrafluoroethylene mold, and then move the mold into a 50°C oven to allow the solvent to fully evaporate within 24 hours. Subsequently, remove the recycled polyurethane film from the mold for tensile performance evaluation of mechanical properties, see Figure 7 ; Figure 7 The stress-strain curve of the polyurethane acid after recycling 3 times in Example 1 is shown in FIG. Figure 7 It can be seen that after one acid recovery, the tensile strength of the polyurethane in Example 1 is 9.61 MPa and the elongation at break is 565%. After three acid recovery, the tensile strength is 7.97 MPa and the elongation at break is 527%. It can still maintain strong mechanical strength and elongation at break, indicating that it can be recycled and reused multiple times. Hot pressing recycling: The shredded polyurethane is hot pressed at 159°C and 1 MPa for 1 hour to obtain a re-molded polyurethane film.

[0062] Figure 8 The stress-strain curves of the polyurethane from Example 6 after three hot-press recycling cycles are shown below. After one hot-press recycling cycle, the tensile strength of the polyurethane from Example 6 was 29.08 MPa, and the elongation at break was 631%. After three hot-press recycling cycles, the tensile strength was 21.08 MPa, and the elongation at break was 896%. These strong mechanical strength and elongation at break were maintained, indicating that the polyurethane can be recycled and reused multiple times.

Claims

1. A method for preparing a chain extender containing an imine bond, characterized in that: The preparation method comprises: mixing reagent A and reagent B under anhydrous and oxygen-free conditions, adding a solvent, reacting at 25-40° C. for 4-6 hours, cooling to room temperature, and removing the solvent by rotary evaporation to obtain a chain extender; Wherein, the structural formula of the reagent A is as follows: wherein at least one of R1-R5 is a hydroxyl group -OH or an aldehyde group -CHO; Reagent B is an organic compound containing both an amino group -NH2 and a hydroxyl group -OH or an organic compound containing both an amino group -NH2.

2. The method for preparing a chain extender containing an imine bond according to claim 1, wherein: The reagent B is any one of the following compounds: The solvent is tetrahydrofuran.

3. The method for preparing a chain extender containing an imine bond according to claim 1 or 2, characterized in that: The molar ratio of the aldehyde group -CHO in reagent A to the amine group -NH2 in reagent B is 1:0.9-1.

1.

4. Use of a chain extender containing an imine bond in thermosetting polyurethane, characterized in that: The applications are: (11) mixing the chain extender containing an imine bond and glyoxal bis(o-aminophenol), adding a solvent, and then adding isophorone diisocyanate and dibutyltin dilaurate, and reacting at 60-80° C. for 1-3 hours; (12) removing water from the polyether polyol or polyester polyol under reduced pressure, dissolving the polyether polyol in a solvent, and then adding the polyether polyol to the product of step (11) and continuing the reaction for 2-4 hours; (13) dissolving triethanolamine in a solvent, then adding it to the product of step (12), and continuing the reaction for 0.3-0.8 h; (14) drying to obtain self-repairing thermosetting polyurethane; Alternatively, the application is: (21) After removing water from the polyether polyol or polyester polyol under reduced pressure, isophorone diisocyanate and dibutyltin dilaurate are added to the solvent and reacted at 50-70°C for 1.5-3h; (22) dissolving 4,4'-diaminodiphenyl disulfide in a solvent, adding the mixture to the product of step (21), and continuing the reaction for 2-4 hours; (23) dissolving the chain extender containing an imine bond in a solvent, adding the resultant to the product of step (22), and continuing the reaction for 0.3-0.8 h; (24) drying to obtain self-repairing thermosetting polyurethane; The chain extender containing an imine bond is prepared by the preparation method according to claim 1.

5. Use of the chain extender containing an imine bond in thermosetting polyurethane according to claim 4, characterized in that: The molar ratio of the hydroxyl group -OH on the chain extender containing an imine bond to isophorone diisocyanate is 1:(1.03-10.4).

6. Use of the chain extender containing an imine bond in thermosetting polyurethane according to claim 5, characterized in that: The molar ratio of isophorone diisocyanate to triethanolamine is (3.1-5.2):1; the molar ratio of glyoxal bis(o-aminophenol) acetal to isophorone diisocyanate is 0.02-0.35:1; and the molar ratio of 4,4'-diaminodiphenyl disulfide to isophorone diisocyanate is 0.05-0.33:

1.

7. Use of the chain extender containing an imine bond in thermosetting polyurethane according to claim 6, characterized in that: The molar ratio of isophorone diisocyanate to polyether polyol or polyester polyol is 3.1-4.8:

1.

8. Use of the chain extender containing an imine bond in thermosetting polyurethane according to claim 7, characterized in that: The amount of dibutyltin dilaurate added is 8-15 wt % of the solid content in the reaction system.

9. Use of the chain extender containing an imine bond in thermosetting polyurethane according to claim 4, characterized in that: The polyether polyol is polytetrahydrofuran, polyethylene glycol or polypropylene glycol; the polyester polyol is polycaprolactone diol or polyethylene adipate diol.

10. Use of the chain extender containing an imine bond in thermosetting polyurethane according to claim 4, characterized in that: The solvent is tetrahydrofuran; the drying condition is drying at 35-50° C. for 12-36 hours.

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