Polyester diol, its preparation method, polyurethane prepared from the polyester diol, and preparation method thereof

Abstract

The present invention relates to the field of thin films, in particular to polyester diols and their preparation methods, polyurethanes prepared from the polyester diols and their preparation methods. The polyester diols include at least one of Chemical Formulae 1-1 to 1-3. The polyester diols of the present invention have strict difunctionality, good molecular regularity, a molecular weight distribution PDI < 1.8, good controllability during esterification reactions, and the polyurethanes obtained after the esterification reactions have a uniform structure and excellent mechanical properties and environmental stability.

Description

Technical Field

[0001] The present invention relates to the fields of polymer materials and polymer chemistry, and particularly to polyester diols and their preparation methods, polyurethanes prepared from such polyester diols, and preparation methods thereof. Background Art

[0002] Due to their excellent mechanical properties, abrasion resistance, and chemical stability, polyurethane (PU) materials have been widely used in many fields such as elastomers, coatings, adhesives, and foam materials.

[0003] Through a large number of practices, the inventors found that the performance of PU depends to a large extent on the molecular structure of the polyester polyol used. When preparing polyester polyol molecules by traditional methods, a first polyol containing multiple functional groups is usually directly used for esterification reaction with a dicarboxylic acid. For example, the polyester polyol systems widely used in industry are polyester systems derived from polyols such as glycerol, sorbitol, and xylitol. The traditional methods mainly consider cost reduction and do not consider the control of the molecular structure of the obtained polyester polyol. Eventually, polyester polyols with highly branched structures, wide molecular weight distributions, and lack of linearity are obtained, which cannot meet the requirements of high-performance PU for the structural regularity of polyester diols. In addition, in addition to increasing the system complexity and affecting the regularity of polyester polyols, the branched structure also affects the microphase separation behavior and mechanical stability of the finally obtained PU, thereby restricting its application in the field of high-performance materials. Summary of the Invention

[0004] Based on this, the purpose of the present invention is to provide polyester diols and their preparation methods, polyurethanes prepared from such polyester diols, and preparation methods thereof. The polyester diols of the present invention have strict difunctionality, good molecular regularity, a polydispersity index (PDI) < 1.8, good controllability during esterification reaction, and the polyurethanes obtained after esterification have a uniform structure and excellent mechanical properties and environmental stability.

[0005] The technical solution of the present invention is achieved as follows:

[0006] A polyester diol, wherein the polyester diol comprises at least one of the following chemical formulas 1-1 to 1-3:

[0007] Formula 1-1

[0008] Formula 1-2

[0009] Formula 1-3

[0010] wherein R1 is a saturated or unsaturated hydrocarbon group with 7 to 17 carbon atoms; R2 is an alkyl group with 2 to 14 carbon atoms; and n is any integer between 2 and 8.

[0011] The polyester diol of the present invention has a strict bifunctionality, good molecular regularity, a molecular weight distribution PDI < 1.8, good controllability during the esterification reaction, and the resulting polyurethane has a uniform structure and excellent mechanical properties and environmental stability after the esterification reaction.

[0012] Further, n is 4. When n is 4, the prepared polyester diol has a suitable viscosity, is convenient for operation, and when preparing the polyester diol, the required reaction time is appropriate and it is easy to prepare.

[0013] The present invention also provides a method for preparing the polyester diol according to any one of the above, comprising the following steps: mixing a first polyol and a monocarboxylic acid in a molar ratio of 1:(1 to 4), adding a first catalyst, evacuating, reacting at a temperature of 180 to 240 °C for 3 to 16 h, then adding a dicarboxylic acid in a molar ratio of (0.9 to 1.1):1 to the first polyol, and continuing to react for 3 to 16 h to obtain the polyester diol;

[0014] The first polyol includes at least one of trimethylolpropane, trimethylolethane, pentaerythritol, and dipentaerythritol;

[0015] The monocarboxylic acid includes at least one of n-octanoic acid, isooctanoic acid, lauric acid, palmitoleic acid, linoleic acid, stearic acid, and vegetable oleic acid.

[0016] The inventors have found through a large amount of practice that the controllability of the molecular structure of polyester polyols is closely related to the type of hydroxyl groups (primary hydroxyl groups and secondary hydroxyl groups) of the precursor first polyol used, as well as the type and chain length of the acids used.

[0017] On the one hand, there is a large steric hindrance effect of the secondary hydroxyl group relative to the primary hydroxyl group, which limits the approach of the secondary hydroxyl group to the carboxylic acid functional group and affects the formation efficiency of the ester bond. Specifically, the esterification rate of the secondary hydroxyl group is about 20% - 30% of the esterification rate of the primary hydroxyl group. This will result in incomplete esterification and residue of the secondary hydroxyl group, and further lead to a more discrete molecular weight distribution of the polyester polyol, causing uncontrollable branching or crosslinking during the subsequent synthesis of PU. Moreover, the residue of the hydroxyl group will further affect the precise control of the NCO:OH molar ratio during the chain extension process, resulting in uneven chain length distribution, disturbing the microphase separation structure of the resulting PU, and further affecting the regular arrangement of the hard segments, reducing the mechanical properties, durability, and hydrolysis resistance of the PU. The mechanical properties of the PU material will rapidly decline due to the accelerated hydrolysis of the ester bond in a high-temperature and high-humidity environment, making it difficult to meet the requirements for long-term service.

[0018] On the other hand, during the chain extension process, the type and chain length of the acid also have an important impact on the performance of the final PU. For example, the hard segments formed by short-chain dibasic acids (such as succinic acid and glutaric acid) have stronger interactions, which can provide a higher hydrogen bond density and rigidity, significantly improving the tensile strength and wear resistance of the PU; while long-chain dibasic acids (such as sebacic acid and dodecanedioic acid) can introduce greater molecular flexibility, increasing the elongation at break of the PU and thus improving the flexibility.

[0019] The preparation method of the polyester diol of the present invention uses a first polyol with all primary hydroxyl groups as the raw material, effectively avoiding the problem of structural inhomogeneity caused by secondary hydroxyl groups. On this basis, a strategy of end-capping with a monobasic fatty acid is adopted. Specifically, the monobasic fatty acid is quantitatively reacted with the first polyol with all primary hydroxyl groups according to a stoichiometric ratio (molar ratio) of 1:(1~4±0.05), precisely end-capping a part of the hydroxyl groups of the all-primary hydroxyl polyol, so that the prepared polyester diol maintains a strict bifunctionality, effectively suppressing the branching tendency of the polyol in the esterification reaction, improving the linearity and predictability of the structure of the prepared polyester diol, and providing a more controllable precursor for the subsequent preparation of PU.

[0020] Furthermore, after adding the first catalyst and evacuating the air, when the acid value of the reaction system is lower than 3 mg KOH / g, the dibasic acid can be added to carry out further chain extension by esterification reaction; after adding the dibasic acid, when the acid value of the reaction system is lower than 3 mg KOH / g and the hydroxyl value of the reaction system reaches 30~80 mg KOH / g, the reaction can be regarded as complete and the reaction can be terminated. If the acid value is too high, the hydroxyl value is too low or the hydroxyl value is too high, it will all lead to poor mechanical properties of the polyurethane synthesized from the obtained polyester polyol.

[0021] Furthermore, the dibasic acid includes at least one of succinic acid, glutaric acid, adipic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid and tetradecanedioic acid. Preferred dibasic acids, since they are all straight-chain dibasic acids, can further improve the regularity of the molecules of the prepared polyester diol, making the PU prepared therefrom have more excellent mechanical properties and environmental stability.

[0022] Furthermore, the first catalyst includes at least one of tetrabutyl titanate, tetraisopropyl titanate, tetraoctyl titanate, titanate, tetrabutyl zirconate, tetraisopropyl zirconate, dibutyltin dilaurate and antimony zinc oxide.

[0023] The present invention also provides a polyurethane prepared from the polyester diol described in any one of the above. The PDI of the polyurethane of the present invention < 2.2, the molecular structure is regular, it has excellent mechanical properties, the strength retention rate exceeds 90% after being immersed in water at 70°C for 14 days, it has good hydrolysis resistance and good environmental stability.

[0024] The present invention also provides a preparation method of any of the above-mentioned polyurethanes, comprising the following steps:

[0025] Mix the polyester diol and the isocyanate uniformly, wherein the molar ratio of the hydroxyl group in the polyester diol to the NCO group in the isocyanate is 1:(2 - 2.02), and react at 50 - 90 °C for 1 - 3 h to obtain a polyurethane prepolymer;

[0026] Mix the polyurethane prepolymer and the second polyol uniformly, add a second catalyst, stir and mix uniformly, and react at 60 - 120 °C for 10 - 16 h to obtain the polyurethane;

[0027] The second polyol includes at least one of 1,4 - butanediol, ethylene glycol, diethylene glycol, 1,3 - propanediol, and 2 - methyl - 1,3 - propanediol;

[0028] The molar ratio of the polyurethane prepolymer to the second polyol is 1:(1 - 1.02).

[0029] When synthesizing the polyurethane prepolymer, if the reaction temperature is lower than 50 °C, the reaction is extremely slow, increasing the cost; if the reaction temperature is higher than 90 °C, explosive polymerization will occur; if the reaction time is shorter than 1 h, polymerization will not be sufficient; if the reaction time is longer than 3 h, the cost will increase. When synthesizing the polyurethane, if the reaction temperature is lower than 60 °C, the reaction is extremely slow, increasing the cost; if the reaction temperature is higher than 120 °C, the mechanical properties of the obtained product will deteriorate; if the reaction time is shorter than 10 h, the properties of the obtained product are poor; if the reaction time is longer than 16 h, the cost will increase. The second polyol in this application uses small - molecule polyols. The isocyanate in this application preferably uses Wanhua Chemical MDI100, which is commonly used in industry and has excellent mechanical properties.

[0030] Further, the addition amount of the second catalyst accounts for 0.001 - 0.1 wt% of the polyurethane prepolymer. If the addition amount of the second catalyst is less than 0.001 wt% of the polyurethane prepolymer, the reaction is too slow; if the addition amount of the second catalyst is greater than 0.1 wt% of the polyurethane prepolymer, the reaction is too fast, resulting in gelation.

[0031] Further, the second catalyst includes at least one of an organotin catalyst, an organic amine catalyst, an organic mercury catalyst, and an organic bismuth catalyst.

[0032] Further, the second catalyst includes at least one of dibutyltin dilaurate, dibutyltin dioctoate, organotin trichloride, triethylenediamine, dimethylaminoethanol, N - methylmorpholine, bis[2 - (dimethylamino)ethyl] ether, phenylmercury acetate, phenylmercury sulfate, bis(2 - ethylhexanoic acid) bismuth, tris(2 - ethylhexanoic acid) bismuth, and bismuth - zinc composite catalyst.

[0033] For better understanding and implementation, the present invention will be described in detail below with reference to the accompanying drawings. Description of the Drawings

[0034] Figure 1 Infrared characterization diagrams of the polyester diols of the examples and comparative examples of the present invention;

[0035] Figure 2 Infrared characterization diagrams of the polyurethanes of the examples and comparative examples of the present invention;

[0036] Figure 3 Stress-strain curves of the polyurethanes of Examples 1-5 and Comparative Examples 1-2 of the present invention;

[0037] Figure 4 Stress-strain curves of the polyurethane before and after hydrolysis in Example 1 of the present invention;

[0038] Figure 5 Stress-strain curves of the polyurethane before and after hydrolysis in Example 2 of the present invention;

[0039] Figure 6 Stress-strain curves of the polyurethane before and after hydrolysis in Example 3 of the present invention;

[0040] Figure 7 Stress-strain curves of the polyurethane before and after hydrolysis in Example 4 of the present invention;

[0041] Figure 8 Stress-strain curves of the polyurethane before and after hydrolysis in Example 5 of the present invention;

[0042] Figure 9 Stress-strain curves of the polyurethane before and after hydrolysis in Comparative Example 1 of the present invention. Detailed Embodiments

[0043] It should be clear that the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts belong to the scope of protection of the embodiments of the present application.

[0044] The terms used in the embodiments of the present application are only for the purpose of describing specific embodiments, and are not intended to limit the embodiments of the present application. The singular forms of "a", "the" and "said" used in the embodiments of the present application and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0045] When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims. In the description of the present application, it should be understood that the terms "first", "second", "third", etc. are only used to distinguish similar objects and do not have to be used to describe a specific order or sequence, nor can they be understood as indicating or implying relative importance. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0046] In addition, in the description of the present application, unless otherwise specified, "a plurality" means two or more. "And / or" describes the association relationship of associated objects and indicates that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0047] It should be understood that the embodiments of the present application are not limited to the precise structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the embodiments of the present application is only limited by the appended claims.

[0048] Please refer to Figure 1 , as an embodiment of the present invention, this embodiment provides a polyester diol, and the polyester diol includes at least one of the following chemical formulas 1-1 to 1-3:

[0049] Formula 1-1

[0050] Formula 1-2

[0051] Formula 1-3

[0052] Wherein R1 is a saturated or unsaturated hydrocarbon group with C7-C17; R2 is an alkyl group with C2-C14; n is any integer between 2 and 8.

[0053] Furthermore, the n is 4.

[0054] Furthermore, a first polyol and a monobasic fatty acid with a molar ratio of 1:(1 to 4) are mixed, a first catalyst is added, vacuum is pumped, and the reaction is carried out at a temperature of 180-240 °C for 3-16 h, and then a dibasic acid with a molar ratio of (0.9 to 1.1):1 to the first polyol is added, and the reaction is continued for 3-16 h to obtain the polyester diol;

[0055] The first polyol includes at least one of trimethylolpropane, trimethylolethane, pentaerythritol, and dipentaerythritol;

[0056] The monobasic fatty acid includes at least one of n-octanoic acid, isooctanoic acid, lauric acid, palmitoleic acid, linoleic acid, stearic acid, and vegetable oleic acid.

[0057] Further, after adding the first catalyst and evacuating the air, when the acid value of the reaction system is lower than 3 mg KOH / g, the dibasic acid can be added to carry out an esterification reaction for further chain extension; after adding the dibasic acid, when the acid value of the reaction system is lower than 3 mg KOH / g and the hydroxyl value of the reaction system reaches 30 - 80 mg KOH / g, the reaction can be regarded as complete and the reaction can be terminated.

[0058] Further, the dibasic acid includes at least one of succinic acid, glutaric acid, adipic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tridecanedicarboxylic acid, and tetradecanedicarboxylic acid.

[0059] Further, the first catalyst includes at least one of tetrabutyl titanate, tetraisopropyl titanate, tetraoctyl titanate, titanate, tetrabutyl zirconate, tetraisopropyl zirconate, dibutyltin dilaurate, and antimony zinc oxide.

[0060] The present invention also provides a polyurethane prepared from the polyester diol described in any one of the above.

[0061] The present invention also provides a preparation method of the polyurethane described in any one of the above, including the following steps:

[0062] Mix the polyester diol and the isocyanate evenly, wherein the molar ratio of the hydroxyl group in the polyester diol to the NCO group in the isocyanate is 1:(2 - 2.02), and react at 50 - 90 °C for 1 - 3 h to obtain a polyurethane prepolymer;

[0063] Mix the polyurethane prepolymer and the second polyol evenly, add a second catalyst, stir and mix evenly, and react at 60 - 120 °C for 10 - 16 h to obtain the polyurethane;

[0064] The second polyol includes at least one of 1,4 - butanediol (BDO), ethylene glycol (EG), diethylene glycol (DEG), 1,3 - propanediol (PDO), and 2 - methyl - 1,3 - propanediol (MPDO);

[0065] The molar ratio of the polyurethane prepolymer to the second polyol is 1:(1 - 1.02).

[0066] Further, the addition amount of the second catalyst accounts for 0.001 - 0.1 wt% of the polyurethane prepolymer.

[0067] Further, the second catalyst includes at least one of an organotin catalyst, an organic amine catalyst, an organomercury catalyst, and an organic bismuth catalyst.

[0068] The physical property indexes and their test methods of the embodiments or comparative examples of the present invention are specifically as follows:

[0069] The polyester diol and the polyurethane are specifically analyzed by a Fourier transform infrared spectrometer (ThermoNicolet 6500). The polyurethane film or the polyester diol is directly placed on the surface of the ZnSe crystal of the ATR-IR accessory, and the scanning range is 400~4000 cm -1 , the resolution is 4 cm -1 , and the number of scans is 32 times; before the test, measure the blank background to ensure that the baseline is smooth; place the sample on the detection table, after collecting the infrared spectrogram, analyze the position and intensity of the functional group absorption peak through software, and compare with the standard spectrogram to confirm the material structure characteristics.

[0070] The molecular weight and its distribution characteristics of the polyester diol and the polyurethane are determined by Waters 150CV gel permeation chromatography (GPC). Specifically, a GPC instrument equipped with a differential refractive index detector is used, the mobile phase is degassed dimethylformamide (DMF), and the standard sample is polystyrene particles with a known molecular weight. The experimental conditions include a flow rate of 0.5 mL / min and a column temperature of 40 °C. When preparing the sample, weigh about 5-10 mg of dry polyester diol / polyurethane, dissolve it in an appropriate amount of solvent, and control the concentration at 0.1%-1% w / w. After ensuring the stability of the system, perform the test, and finally calculate the molecular weight (Mw) and polydispersity index (PDI) through the calibration curve and data analysis software.

[0071] The test method for the mechanical properties of the sample is carried out according to the test method of the national standard GB / T 528-2009, and the tensile machine uses an Instron 5960 double-column bench-top tensile machine.

[0072] The test method for the hydrolysis resistance of the sample is to cut the polyurethane sample into dumbbell-shaped splines, soak them in hot water at 70 °C for two weeks and then take them out, and then test their mechanical properties such as tensile strength and elongation at break to evaluate the water resistance of the material.

[0073] Example 1

[0074] This example provides a polyester diol, and its preparation method includes the following steps:

[0075] Mix 202.79 g of vegetable oleic acid and 96.41 g of trimethylolpropane (TMP) evenly, add tetrabutyl titanate, evacuate, react at a temperature of 180 - 240 °C for 6 h, measure the acid value by acid value titration method, when the acid value is lower than 3 mgKOH / g, it is determined that the reaction has reached the end point; then add 114.42 g of sebacic acid, continue to evacuate, react for 6 h, measure the acid value by acid value titration method and the acid value < 3 mgKOH / g, measure the hydroxyl value by hydroxyl value titration method and the hydroxyl value is (45.6 ± 0.3) mgKOH / g, which is close to the theoretical hydroxyl value of 45.3 mgKOH / g, determine that the reaction has reached the end point and the structure of the obtained product conforms to the expectation, obtain polyester diol TPA - Polyol, its structure is shown in Formula 1 - 1, and carry out encapsulation. Among them, in this embodiment, n = 4, and in other embodiments, n can also be selected between 2 and 8.

[0076] Take an appropriate amount of the polyester diol TPA - Polyol prepared in this embodiment and characterize it by Fourier transform infrared spectrometer (FTIR). The characterization results are shown in Figure 1 . In the spectrum, the characteristic absorption peak of the carbonyl group (C=O) appears in the range of 1650 - 1780 cm -1 , indicating that the hydroxyl group in the raw material has undergone an esterification reaction with the carboxylic acid group. At the same time, a broad peak absorption is observed in the characteristic range of the terminal hydroxyl group at 3200 - 3600 cm -1 , further proving that hydroxyl functional groups are retained at both ends of the polyol molecule. This result confirms the completion of the esterification reaction and the characteristic structure of the polyol.

[0077] Test the aforementioned polyester diol TPA - Polyol by GPC. The test results are shown in Table 1.

[0078] This embodiment also provides a polyurethane, and its preparation method includes the following steps:

[0079] Take 4.8 g of the polyester diol TPA - Polyol prepared in this embodiment, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer and 0.32 g of BDO evenly, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high - speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 1.

[0080] Take an appropriate amount of the polyurethane sample 1 prepared in this embodiment and characterize it by Fourier transform infrared spectrometer (FTIR). The characterization results are shown in Figure 2 .

[0081] The polyurethane sample 1 described above was tested by gel permeation chromatography (GPC), and the film-forming properties and mechanical properties of the polyurethane sample 1 described above were tested. For the test results, please refer to Table 2, and for the stress-strain curve, please refer to Figure 3 .

[0082] The polyurethane sample 1 described above was tested for hydrolysis resistance. For the test results, please refer to Table 3, and for the stress-strain curves before and after hydrolysis, please refer to Figure 4 .

[0083] Example 2

[0084] This example provides a polyester diol, and its preparation method includes the following steps:

[0085] 103.61 g of n-octanoic acid and 96.41 g of trimethylolpropane (TMP) were mixed evenly, tetrabutyl titanate was added, the mixture was evacuated, and reacted at a temperature of 180 - 240 °C for 6 h. The acid value was measured by acid value titration method and found to be less than 3 mg KOH / g, determining that the reaction had reached the end point; then 114.42 g of sebacic acid was added, and the mixture was evacuated again and reacted for 6 h. The acid value was measured by acid value titration method and found to be < 3 mg KOH / g, and the hydroxyl value was measured by hydroxyl value titration method to be (60.8 ± 0.5) mg KOH / g, which is close to the theoretical hydroxyl value of 61.1 mg KOH / g, determining that the reaction had reached the end point and the structure of the obtained product met the expectations. The polyester diol TCA-Polyol was obtained, and its structure is shown in Formula 1-1, and it was encapsulated. Herein, n = 4 in this example, and in other examples, n can also be selected between 2 and 8.

[0086] An appropriate amount of the polyester diol TCA-Polyol prepared in this example was characterized by a Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 1 . In the spectrum, the characteristic absorption peak of the carbonyl group (C=O) appears in the range of 1650 - 1780 cm -1 , indicating that the esterification reaction has occurred between the hydroxyl group and the carboxylic acid group in the raw materials. At the same time, a broad peak absorption was observed in the characteristic range of the terminal hydroxyl group at 3200 - 3600 cm -1 , further proving that the hydroxyl functional groups are retained at both ends of the polyol molecule. This result confirmed the completion of the esterification reaction and the characteristic structure of the polyol.

[0087] The polyester diol TCA-Polyol described above was tested by GPC. For the test results, please refer to Table 1.

[0088] This example also provides a polyurethane, and its preparation method includes the following steps:

[0089] Take 3.8 g of the polyester diol TCA-Polyol prepared in this example, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer evenly with 0.32 g of BDO, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high-speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 2.

[0090] Take an appropriate amount of the polyurethane sample 2 prepared in this example and characterize it by Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 2 。

[0091] Test the aforementioned polyurethane sample 2 by gel permeation chromatography GPC, and test the film-forming properties and mechanical properties of the aforementioned polyurethane sample 2. For the test results, please refer to Table 2, and for the stress-strain curve, please refer to Figure 3 。

[0092] Conduct a hydrolysis resistance test on the aforementioned polyurethane sample 2. For the test results, please refer to Table 3, and for the stress-strain curves before and after hydrolysis, please refer to Figure 5 。

[0093] Example 3

[0094] This example provides a polyester diol, and its preparation method includes the following steps:

[0095] Mix 202.79 g of vegetable oleic acid and 96.41 g of trimethylolpropane TMP evenly, add tetrabutyl titanate, evacuate, react at a temperature of 180 - 240 °C for 6 h, and use the acid value titration method to measure that the acid value is lower than 3 mgKOH / g to determine that the reaction has reached the end point; then add 66.80 g of succinic acid, continue to evacuate, react for 6 h, use the acid value titration method to measure that the acid value < 3 mgKOH / g, use the hydroxyl value titration method to measure that the hydroxyl value is (52.0 ± 0.4) mgKOH / g, which is close to the theoretical hydroxyl value of 51.7 mgKOH / g, determine that the reaction has reached the end point and the structure of the obtained product meets the expectations, obtain the polyester diol TPS-Polyol, the structure of which is shown in Formula 1-1, and conduct encapsulation. Among them, n = 4 in this example, and in other examples, n can also be selected between 2 and 8.

[0096] Take an appropriate amount of the polyester diol TPS-Polyol prepared in this example and characterize it by Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 1 。In the spectrum, the characteristic absorption peak of the carbonyl group (C=O) appears at 1650 - 1780 cm -1Within the range, it indicates that the esterification reaction has occurred between the hydroxyl groups and carboxylic acid groups in the raw materials. Meanwhile, broad peak absorption is observed in the characteristic range of terminal hydroxyl groups at 3200 - 3600 cm -1 and a wide peak absorption is observed in the characteristic range, further proving that hydroxyl functional groups are retained at both ends of the polyol molecule. This result confirms the completion of the esterification reaction and the characteristic structure of the polyol.

[0097] The aforementioned polyester diol TPS-Polyol was tested by GPC. The test results are shown in Table 1.

[0098] This example also provides a polyurethane, and its preparation method includes the following steps:

[0099] Take 4.2 g of the polyester diol TPS-Polyol prepared in this example, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer evenly with 0.32 g of BDO, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high-speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 3.

[0100] Take an appropriate amount of the polyurethane sample 3 prepared in this example and characterize it by Fourier transform infrared spectrometer (FTIR). The characterization results are shown in Figure 2 .

[0101] The aforementioned polyurethane sample 3 was tested by gel permeation chromatography GPC, and the film-forming performance and mechanical properties of the aforementioned polyurethane sample 3 were tested. The test results are shown in Table 2, and the stress-strain curve is shown in Figure 3 .

[0102] The aforementioned polyurethane sample 3 was subjected to hydrolysis resistance test. The test results are shown in Table 3, and the stress-strain curves before and after hydrolysis are shown in Figure 6 .

[0103] Example 4

[0104] This example provides a polyester diol, and its preparation method includes the following steps:

[0105] Mix 405.58 g of vegetable oleic acid and 97.73 g of pentaerythritol evenly, add tetrabutyl titanate, evacuate, react at a temperature of 180 - 240 °C for 6 h, measure the acid value by acid value titration method, when the acid value is lower than 3 mgKOH / g, it is determined that the reaction has reached the end point; then add 114.42 g of sebacic acid, continue to evacuate, react for 6 h, measure the acid value by acid value titration method and the acid value < 3 mgKOH / g, measure the hydroxyl value by hydroxyl value titration method and the hydroxyl value is (30.1 ± 0.4) mgKOH / g, which is close to the theoretical hydroxyl value of 29.8 mgKOH / g, determine that the reaction has reached the end point and the structure of the obtained product meets the expectation, obtain polyester diol PPA - Polyol, the structure is shown in Formula 1 - 2, and carry out encapsulation. Among them, in this embodiment, n = 4, and in other embodiments, n can also be selected between 2 and 8.

[0106] Take an appropriate amount of the polyester diol PPA - Polyol prepared in this embodiment and characterize it by Fourier transform infrared spectrometer (FTIR), and the characterization results are shown in Figure 1 . In the spectrum, the characteristic absorption peak of the carbonyl group (C=O) appears in the range of 1650 - 1780 cm -1 , indicating that the hydroxyl group in the raw material has undergone an esterification reaction with the carboxylic acid group. At the same time, a broad peak absorption is observed in the characteristic range of the terminal hydroxyl group at 3200 - 3600 cm -1 , further proving that hydroxyl functional groups are retained at both ends of the polyol molecule. This result confirms the completion of the esterification reaction and the characteristic structure of the polyol.

[0107] Test the above - mentioned polyester diol PPA - Polyol by GPC, and the test results are shown in Table 1.

[0108] This embodiment also provides a polyurethane, and its preparation method includes the following steps:

[0109] Take 8.2 g of the polyester diol PPA - Polyol prepared in this embodiment, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer and 0.32 g of BDO evenly, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high - speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 4.

[0110] Take an appropriate amount of the polyurethane sample 4 prepared in this embodiment and characterize it by Fourier transform infrared spectrometer (FTIR), and the characterization results are shown in Figure 2 .

[0111] The foregoing polyurethane sample 4 was tested by gel permeation chromatography (GPC), and the film-forming properties and mechanical properties of the foregoing polyurethane sample 4 were tested. For the test results, please refer to Table 2, and for the stress-strain curve, please refer to Figure 3 .

[0112] The foregoing polyurethane sample 4 was tested for hydrolysis resistance. For the test results, please refer to Table 3, and for the stress-strain curves before and after hydrolysis, please refer to Figure 7 .

[0113] Example 5

[0114] This example provides a polyester diol, and its preparation method includes the following steps:

[0115] 811.16 g of vegetable oleic acid and 182.72 g of dipentaerythritol were mixed evenly, tetrabutyl titanate was added, and the mixture was evacuated. The reaction was carried out at a temperature of 180 - 240 °C for 6 h. The acid value was measured by acid value titration method and found to be less than 3 mg KOH / g, determining that the reaction had reached the end point; then 114.42 g of sebacic acid was added, and the evacuation was continued for 6 h. The acid value was measured by acid value titration method and found to be < 3 mg KOH / g, and the hydroxyl value was measured by hydroxyl value titration method to be (16.1 ± 0.2) mg KOH / g, which was close to the theoretical hydroxyl value of 16.4 mg KOH / g, determining that the reaction had reached the end point and the structure of the obtained product met the expectation. The polyester diol DpPA-Polyol was obtained, and its structure is shown in Formula 1-3 and was encapsulated. Herein, n = 4 in this example, and in other examples, n can also be selected between 2 and 8.

[0116] An appropriate amount of the polyester diol DpPA-Polyol prepared in this example was characterized by a Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 1 . In the spectrum, the characteristic absorption peak of the carbonyl group (C=O) appeared in the range of 1650 - 1780 cm -1 , indicating that the esterification reaction had occurred between the hydroxyl group and the carboxylic acid group in the raw materials. At the same time, a broad peak absorption was observed in the characteristic range of the terminal hydroxyl group at 3200 - 3600 cm -1 , further proving that the hydroxyl functional groups were retained at both ends of the polyol molecule. This result confirmed the completion of the esterification reaction and the characteristic structure of the polyol.

[0117] The foregoing polyester diol DpPA-Polyol was tested by GPC. For the test results, please refer to Table 1.

[0118] This example also provides a polyurethane, and its preparation method includes the following steps:

[0119] Take 14.4 g of the polyester diol DpPA-Polyol prepared in this example, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer evenly with 0.32 g of BDO, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high-speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 5.

[0120] Take an appropriate amount of the polyurethane sample 5 prepared in this example and characterize it by Fourier transform infrared spectrometer (FTIR). The characterization results are shown in Figure 2 .

[0121] Test the aforementioned polyurethane sample 5 by gel permeation chromatography (GPC), and test the film-forming performance and mechanical properties of the aforementioned polyurethane sample 5. The test results are shown in Table 2, and the stress-strain curve is shown in Figure 3 .

[0122] Conduct a hydrolysis resistance test on the aforementioned polyurethane sample 5. The test results are shown in Table 3, and the stress-strain curves before and after hydrolysis are shown in Figure 8 .

[0123] Comparative Example 1

[0124] This comparative example provides a polyester diol, and its preparation method includes the following steps:

[0125] Mix 202.79 g of vegetable oleic acid and 66.11 g of glycerol evenly, add tetrabutyl titanate, evacuate, react at a temperature of 180 - 240 °C for 6 h, measure the acid value by acid value titration method, and when the acid value is lower than 3 mgKOH / g, it is determined that the reaction has reached the end point; then add 114.42 g of sebacic acid, continue to evacuate, react for 6 h, measure the acid value by acid value titration method and the acid value < 3 mgKOH / g, measure the hydroxyl value by hydroxyl value titration method and the hydroxyl value is (49.9 ± 0.9) mgKOH / g, which is close to the theoretical hydroxyl value of 48.7 mgKOH / g, determine that the reaction has reached the end point and the structure of the obtained product meets the expectation, obtain polyester diol GMP-Polyol, and conduct encapsulation. Among them, n = 4 in this comparative example, and in other examples, n can also be selected between 2 and 8.

[0126] Take an appropriate amount of the polyester diol GMP-Polyol prepared in this comparative example and characterize it by Fourier transform infrared spectrometer (FTIR). The characterization results are shown in Figure 1 , and the characteristic structure of the polyol is confirmed.

[0127] Test the aforementioned polyester diol GMP-Polyol by GPC. The test results are shown in Table 1.

[0128] This comparative example also provides a polyurethane, and its preparation method includes the following steps:

[0129] Take 4.4 g of the polyester diol GMP-Polyol prepared in this comparative example, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer evenly with 0.32 g of BDO, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high-speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 6.

[0130] Take an appropriate amount of the polyurethane sample 6 prepared in this comparative example, and characterize it by a Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 2 .

[0131] Test the aforementioned polyurethane sample 6 by gel permeation chromatography (GPC), and test the film-forming properties and mechanical properties of the aforementioned polyurethane sample 6. For the test results, please refer to Table 2, and for the stress-strain curve, please refer to Figure 3 .

[0132] Conduct a hydrolysis resistance test on the aforementioned polyurethane sample 6. For the test results, please refer to Table 3, and for the stress-strain curves before and after hydrolysis, please refer to Figure 9 .

[0133] Comparative Example 2

[0134] This comparative example provides a polyester diol, and its preparation method includes the following steps:

[0135] Mix 202.79 g of vegetable oleic acid and 43.83 g of erythritol evenly, add tetrabutyl titanate, evacuate, react at a temperature of 180 - 240 °C for 6 h, use the acid value titration method to measure that the acid value is lower than 3 mgKOH / g, and determine that the reaction has reached the end point; then add 57.21 g of sebacic acid, continue to evacuate, react for 6 h, use the acid value titration method to measure that the acid value < 3 mgKOH / g, use the hydroxyl value titration method to measure that the hydroxyl value is (31.1 ± 1.1) mgKOH / g, which is close to the theoretical hydroxyl value of 30.4 mgKOH / g, determine that the reaction has reached the end point and the structure of the obtained product meets the expectations, obtain polyester diol EMP-Polyol, and conduct encapsulation. Among them, n = 4 in this comparative example, and in other embodiments, n can also be selected between 2 and 8.

[0136] Take an appropriate amount of the polyester diol EMP-Polyol prepared in this comparative example, and characterize it by a Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 1 , and this result confirms the characteristic structure of the polyol.

[0137] The above-mentioned polyester diol EMP-Polyol was tested by GPC. For the test results, please refer to Table 1.

[0138] This comparative example also provides a polyurethane, and its preparation method includes the following steps:

[0139] Take 7 g of the polyester diol EMP-Polyol prepared in this comparative example, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer evenly with 0.32 g of BDO, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high-speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 7.

[0140] Take an appropriate amount of polyurethane sample 7 prepared in this comparative example and characterize it by Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 2 .

[0141] The above-mentioned polyurethane sample 7 was tested by gel permeation chromatography GPC, and the film-forming performance and mechanical properties of the above-mentioned polyurethane sample 7 were tested. For the test results, please refer to Table 2, and for the stress-strain curve, please refer to Figure 3 .

[0142] The above-mentioned polyurethane sample 7 was subjected to a hydrolysis resistance test. For the test results, please refer to Table 3. Polyurethane sample 7 did not form a film after being immersed in water at 70 °C for two weeks.

[0143] Comparative Example 3

[0144] This comparative example provides a polyester diol, and its preparation method includes the following steps:

[0145] Mix 608.37 g of vegetable oleic acid and 109.19 g of xylitol evenly, add tetrabutyl titanate, evacuate, react at a temperature of 180 - 240 °C for 6 h, and use the acid value titration method to measure that the acid value is lower than 3 mgKOH / g to determine that the reaction has reached the end point; then add 114.42 g of sebacic acid, continue to evacuate, react for 6 h, use the acid value titration method to measure that the acid value < 3 mgKOH / g, use the hydroxyl value titration method to measure that the hydroxyl value is (21.5 ± 0.4) mgKOH / g, which is close to the theoretical hydroxyl value of 22.1 mgKOH / g, determine that the reaction has reached the end point and the structure of the obtained product meets the expectation, obtain polyester diol XMP-Polyol, and carry out encapsulation. Among them, n = 4 in this comparative example, and in other embodiments, n can also be selected between 2 and 8.

[0146] Take an appropriate amount of the polyester diol XMP-Polyol prepared in this comparative example and characterize it by a Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 1 , which confirms the characteristic structure of the polyol.

[0147] Test the aforementioned polyester diol XMP-Polyol by GPC. For the test results, please refer to Table 1.

[0148] This comparative example also provides a polyurethane, and its preparation method includes the following steps:

[0149] Take 9.8 g of the polyester diol XMP-Polyol prepared in this comparative example, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer and 0.32 g of BDO evenly, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high-speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 8.

[0150] Take an appropriate amount of the polyurethane sample 8 prepared in this comparative example and characterize it by a Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 2 .

[0151] Test the aforementioned polyurethane sample 8 by gel permeation chromatography GPC, and test the film-forming performance and mechanical properties of the aforementioned polyurethane sample 8. For the test results, please refer to Table 2.

[0152] Comparative Example 4

[0153] This comparative example provides a polyester diol, and its preparation method includes the following steps:

[0154] Mix 811.16 g of vegetable oleic acid and 130.78 g of sorbitol evenly, add tetrabutyl titanate, evacuate, react at a temperature of 180 - 240 °C for 6 h, measure the acid value by acid value titration method and the acid value is lower than 3 mgKOH / g to determine that the reaction has reached the end point; then add 114.42 g of sebacic acid, continue to evacuate, react for 6 h, measure the acid value by acid value titration method and the acid value < 3 mgKOH / g, measure the hydroxyl value by hydroxyl value titration method and the hydroxyl value is (16.7 ± 0.6) mgKOH / g, which is close to the theoretical hydroxyl value of 17.3 mgKOH / g to determine that the reaction has reached the end point and the structure of the obtained product meets the expectation, obtain the polyester diol SMP-Polyol, and carry out encapsulation. Among them, n = 4 in this comparative example, and in other embodiments, n can also be selected between 2 and 8.

[0155] Take an appropriate amount of the polyester diol SMP-Polyol prepared in this comparative example and characterize it by a Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 1 , and this result confirms the characteristic structure of the polyol.

[0156] Test the aforementioned polyester diol SMP-Polyol by GPC. For the test results, please refer to Table 1.

[0157] This comparative example also provides a polyurethane, and its preparation method includes the following steps:

[0158] Take 12.4 g of the polyester diol SMP-Polyol prepared in this comparative example, mix it evenly with 1.4 g of isocyanate MDI100, react at 80 °C for 2 h to obtain a polyurethane prepolymer, then mix the obtained polyurethane prepolymer evenly with 0.32 g of BDO, add an organotin catalyst accounting for 0.06 wt% of the polyurethane prepolymer, blend in a high-speed mixer, pour it into a mold, and cure for 10 - 16 h to obtain polyurethane sample 9.

[0159] Take an appropriate amount of the polyurethane sample 9 prepared in this comparative example and characterize it by a Fourier transform infrared spectrometer (FTIR). For the characterization results, please refer to Figure 2 .

[0160] Test the aforementioned polyurethane sample 9 by gel permeation chromatography GPC, and test the film-forming performance and mechanical properties of the aforementioned polyurethane sample 9. For the test results, please refer to Table 2.

[0161] Table 1 GPC test results of the polyester polyols in Examples 1 - 5 and Comparative Examples 1 - 4

[0162]

[0163] Table 2 GPC test, film-forming performance test and mechanical property test results of Samples 1 - 9

[0164]

[0165] Table 3 Hydrolysis resistance test results of Samples 1 - 7 (immersed in water at 70 °C for two weeks)

[0166]

[0167] Combined with the molecular weight data in Table 1 and Figure 1 the FTIR data analysis of Figure 2 , the successful synthesis of 9 kinds of polyester diols can be verified; combined with the molecular weight data in Table 2 and

[0168] The present invention reasonably selects the combination of end-capping monobasic acid and chain-extending dibasic acid, effectively regulating the rigid-flexible balance of the PU material. The PDI of the polyester diols in Examples 1 to 5 is <1.8, improving the controllability of the prepared polyurethane structure and the stability of microphase separation. The polyurethane prepared with the polyester diols in Examples 1 to 5 of the present invention has a PDI <2.2, with regular molecules, excellent reaction controllability, good processing applicability, a breaking stress of at least 3.2 MPa, a relative increase of more than 60% compared to the secondary hydroxyl group system, a breaking elongation of at least 229.4%, and a toughness of at least 3.5 MJ / m 3 , and after the hydrolysis resistance test, the mechanical properties of the polyurethane can decrease by no more than 10% after being immersed in water at 70 °C for 14 days.

[0169] The polyester diols in Comparative Examples 1 to 4 are all prepared from polyols containing secondary hydroxyl groups, and their PDI ≥ 2.25, which is generally greater than the PDI of the polyester diols in the examples of the present application. The polyurethane prepared with the polyester diols in Comparative Examples 1 to 4 has a PDI > 4 and poor film-forming properties. Only the polyurethanes prepared with the polyester diols in Comparative Examples 1 to 2 can form films, but their breaking stress, breaking elongation, and toughness are generally inferior to those of the polyurethanes in the examples of the present application. And after the hydrolysis resistance test, only the polyurethane in Comparative Example 1 can form a film, but its mechanical properties decrease by more than 50%, making it difficult to meet the requirements for long-term service.

[0170] It can be seen that the PDI of the PU prepared from the polyester diol synthesized from all primary hydroxyl group polyols is significantly lower than that of the PU synthesized from the polyol system containing secondary hydroxyl groups.

[0171] By comparing polyurethane samples 1 to 3 and 6, it can be known that under the condition of the same hydroxyl functionality, the polyester diol formed by end-capping with monobasic fatty acid and combined with chain-extending dibasic acid, the content of primary hydroxyl groups in the precursor polyol small molecules directly determines the molecular structure and mechanical properties of the final PU. With the increase in the content of primary hydroxyl groups, the polymer regularity of the obtained PU is enhanced, and the mechanical properties are significantly improved. The steric hindrance effect of secondary hydroxyl groups makes its esterification activity much lower than that of primary hydroxyl groups (about 20% - 30% of it), resulting in incomplete esterification reaction and the formation of unreacted hydroxyl residues. These residual hydroxyl groups will cause uncontrollable branching or cross-linking during the PU synthesis process, increasing the PDI of the PU > 4, thereby destroying the microphase separation structure of the PU, making the hard segment arrangement disordered, and finally reducing the mechanical properties of the PU.

[0172] Through further comparison of polyurethane samples 1 and 2, it can be seen that as the alkyl chain segment of the end-capping monocarboxylic acid shortens, the breaking stress of the prepared PU increases. This is attributed to the higher regularity of the short-chain alkyl end-capping structure, which makes the arrangement of the hard segment microdomains in PU more orderly, thereby enhancing the hydrogen bond interaction and increasing the breaking stress of PU. However, while the alkyl chain segment of the end-capping monocarboxylic acid shortens, the breaking strain of PU decreases because the long-chain alkyl end-capping provides greater molecular flexibility, making PU more easily deformed during the stretching process.

[0173] Through further comparison of polyurethane samples 1 and 3, it can be seen that the shorter the chain segment of the dicarboxylic acid used in the polyester chain extension process, the higher the breaking stress of the final PU. This is because the shorter dicarboxylic acid chain segment will shorten the ester bond spacing, increase the hard segment density, enhance the rigidity, thereby improving the tensile strength of PU, but at the same time reduce the flexibility of PU, resulting in a decrease in its breaking strain.

[0174] Through further comparison of polyurethane samples 4 and 7, it can be seen that when the number of hydroxyl groups in the polyol small molecule is the same, when all hydroxyl groups are primary hydroxyl groups (sample 4), its mechanical properties are significantly better than those of sample 7 with some secondary hydroxyl groups.

[0175] Through further comparison of polyurethane samples 5 and 9, it can be seen that when dipentaerythritol and sorbitol, both with 6 hydroxyl groups, are used as precursors to prepare polyester diols and their PU products respectively, the sorbitol system (sample 9) cannot form a film, while the dipentaerythritol system (sample 5) still has good mechanical properties. This further verifies the decisive role of the primary hydroxyl group content of the precursor polyol small molecule for preparing polyester diols in the structural regularity and mechanical properties of the finally prepared TPU.

[0176] In summary, the content of primary hydroxyl groups in the polyester diol precursor directly determines the structure and mechanical properties of PU. As the content of primary hydroxyl groups increases, the obtained PU has higher molecular regularity and more excellent mechanical properties. In addition, the structures of the end-capping monocarboxylic acid and dicarboxylic acid also significantly affect the properties of PU. Short-chain end-capping enhances rigidity, while long-chain end-capping improves flexibility; short-chain dicarboxylic acid increases the tensile strength, while long-chain dicarboxylic acid increases the breaking strain. The above research results provide a new strategy for the molecular design of high-performance PU materials.

[0177] The above-described embodiments merely represent several implementation manners of the present invention. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and the present invention also intends to include these changes and modifications.

Claims

1. A polyurethane prepared from polyester diol, characterized in that, The PDI of the polyester diol is < 1.8, and the polyester diol includes at least one of the following chemical formulas 1-1 to 1-3: Formula 1-1 Formula 1-2 Formula 1-3 Wherein, R1 is a saturated or unsaturated hydrocarbon group with 7 to 17 carbon atoms; R2 is an alkylene group with 2 to 14 carbon atoms; n is any integer between 2 and 8; The preparation method of the polyester diol includes the following steps: mixing a fully primary hydroxyl group-containing first polyol and a monocarboxylic acid in a molar ratio of 1:(1 to 4), adding a first catalyst, evacuating the air, reacting at a temperature of 180 to 240 °C for 3 to 16 h, then adding a dicarboxylic acid with a molar ratio of (0.9 to 1.1):1 to the fully primary hydroxyl group-containing first polyol, and continuing the reaction for 3 to 16 h. When the acid value of the reaction system is lower than 3 mg KOH / g and the hydroxyl value of the reaction system reaches 30 to 80 mg KOH / g, the reaction is terminated to obtain the polyester diol; The fully primary hydroxyl group-containing first polyol includes at least one of trimethylolpropane, pentaerythritol, and dipentaerythritol; The first catalyst includes at least one of titanate, tetrabutyl zirconate, tetraisopropyl zirconate, dibutyltin dilaurate, and antimony zinc oxide; 2. The polyurethane according to claim 1, characterized in that, The n is 4; 3. The polyurethane according to claim 1, characterized in that, The monocarboxylic acid includes at least one of n-octanoic acid, isooctanoic acid, lauric acid, palmitoleic acid, linoleic acid, stearic acid, and vegetable oleic acid; 4. The polyurethane according to claim 1, characterized in that, After adding the first catalyst and evacuating the air, when the acid value of the reaction system is lower than 3 mg KOH / g, the dicarboxylic acid can be added; 5. The polyurethane according to claim 1, characterized in that, The dicarboxylic acid includes at least one of succinic acid, glutaric acid, adipic acid, sebacic acid, undecanedicarboxylic acid, dodecanedicarboxylic acid, tridecanedicarboxylic acid, and tetradecanedicarboxylic acid; 6. A method for preparing a polyurethane according to any one of claims 1 to 5, characterized in that, It includes the following steps: Mix the polyester diol and the isocyanate evenly, wherein the molar ratio of the hydroxyl group in the polyester diol to the NCO group in the isocyanate is 1:(2 to 2.02), and react at 50 to 90 °C for 1 to 3 h to obtain a polyurethane prepolymer; Mix the polyurethane prepolymer and a second polyol evenly, add a second catalyst, stir and mix evenly, and react at 60 to 120 °C for 10 to 16 h to obtain the polyurethane; The second polyol includes at least one of 1,4-butanediol, ethylene glycol, diethylene glycol, 1,3-propanediol, and 2-methyl-1,3-propanediol; The molar ratio of the polyurethane prepolymer to the second polyol is 1:(1 to 1.02); 7. The preparation method of the polyurethane according to claim 6, characterized in that, The addition amount of the second catalyst accounts for 0.001 to 0.1 wt% of the polyurethane prepolymer; 8. A method for preparing a polyurethane as described in claim 6, characterized in that, The second catalyst includes at least one of an organotin catalyst, an organic amine catalyst, an organic mercury catalyst, and an organic bismuth catalyst.

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