Bio-based polyurethane chain extender and method for preparing the same

Abstract

The application belongs to the polyurethane chain extension technical field, and particularly relates to a kind of generally applicable polyurethane chain extender and a preparation method thereof. First, 4-aminobutyric acid derivatives are used to prepare a series of chain extender precursors containing amide groups or urea groups with a series of diacyl chlorides and diisocyanates. The chain extender precursors continue to generate hydrazine-based polyurethane chain extenders containing amide groups or urea groups by reacting with hydrazine hydrate in alcohol solvents. The bio-based chain extender belongs to hydrazine compounds, is green in source and has low toxicity. Compared with conventional amine chain extenders, the solubility is lower and the reaction rate is relatively controllable. High-density hydrogen bonds can be introduced into the polyurethane main chain to further enhance the strength and toughness of the polyurethane material. The preparation method is templated, and the required chain extender structure can be customized according to the actual application requirements, enriches the application of polyurethane products, and meets the diversified needs of people for polyurethane materials.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polyurethane, and particularly relates to a kind of bio-based chain extender suitable for various polyurethanes and a preparation method thereof. BACKGROUND

[0002] Polyurethane is one of the most potential high molecular materials at present, and is called "the fifth plastic". Polyurethane material has the advantages of strong impact resistance, high elongation at break and good tear resistance, and is widely used in foams, coatings, adhesives and elastomers. However, most of the raw materials used to prepare polyurethane are derived from non-renewable petroleum resources, which greatly limits the sustainable development of polyurethane material industry in the future, and is very harmful to the environment. With the increasing depletion of petroleum resources and the gradual improvement of people's environmental awareness, it is imperative to seek bio-based substitutes for various petroleum-based raw materials of polyurethane.

[0003] Chain extender is an additive that can further react with the functional groups at the ends of linear polymer chains to further increase the molecular weight of the polymer, and is also a necessary link to improve the mechanical properties of polyurethane material. At present, although the polyurethane materials prepared by commonly used aliphatic alcohol chain extenders such as butanediol (BDO) have good weather resistance, they have low strength; aromatic chain extenders contain a large number of benzene rings, and the materials have high strength but are prone to yellowing. Most amine chain extenders can introduce urea groups into the polymer chain after reacting with -NCO, and the hydrogen bond action makes the prepared polyurethane material have high strength, but at the same time, the reaction speed is too fast, which limits its application in practice. 3,3'-dichloro-4,4'-diaminodiphenyl methane (MOCA) is the most widely used amine chain extender with steric effect, and its reaction speed is relatively controllable, but it has high benzene ring content, is prone to yellowing, and has high toxicity, which has carcinogenic effect on human body, so it is not an ideal polyurethane chain extender.

[0004] Patent CN201911319417.3 discloses an environmentally friendly polyurethane chain extender, its preparation method, and its application. The disclosed urethane-containing diol polyurethane chain extender does not contain aromatic groups, significantly reducing its toxicity. However, the polyurethane products prepared by this chain extender have low tensile strength, limiting its practical application. Patent CN202110917970.8 discloses a lignin-based polyurethane chain extender, its preparation method, and its application. The disclosed urethane-containing diol polyurethane chain extender is an environmentally friendly chain extender that can replace the currently used 3,3′-dichloro-4,4-diaminodiphenylmethane chain extender. The polyurethane materials prepared by this extender have improved strength compared to the former, but are still at a low level and cannot be applied to polyurethane materials requiring high tensile strength. Therefore, it is necessary to develop truly bio-based high-strength chain extenders that can replace MOCA in order to continuously improve the performance of polyurethane products, meet the requirements of polyurethane products such as certain working time, high strength, low toxicity, and exposing, and promote the diversification of polyurethane product applications. This is an urgent technical problem to be solved. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a type of bio-based polyurethane chain extender and its preparation method. This type of chain extender is a bio-based chain extender, possessing advantages such as green origin, high structural compatibility, long working time after mixing, and high strength.

[0006] In a first aspect, the present invention provides a class of bio-based polyurethane chain extenders, the structural formula of which is:

[0007]

[0008] Wherein, R is selected from furanyl, phenyl,

[0009] n is a natural number, with a value range of 4-10.

[0010] Furthermore, the phenyl group is linked at the para or meta position.

[0011] Furthermore, the furanyl group is linked at position -2,5-.

[0012] Secondly, the present invention provides a method for preparing a type of bio-based polyurethane chain extender. First, a chain extender precursor containing amide groups or urea groups is prepared by using a 4-aminobutyric acid derivative and diacyl chloride or diisocyanate. Then, the chain extender precursor is reacted with hydrazine hydrate in an alcohol solvent to generate a hydrazine-based bio-based polyurethane chain extender containing amide groups or urea groups.

[0013] Furthermore, the preparation method of the bio-based polyurethane chain extender includes the following steps:

[0014] S1. Add 4-aminobutyric acid methyl ester hydrochloride, acid-binding agent and solvent to the reactor, slowly add diacyl chloride or diisocyanate solution between -10 and 10℃, and reflux the reaction between 25 and 60℃ to generate the corresponding dicarboxylic acid dimethyl ester.

[0015] S2. Add the dimethyl dicarboxylic acid, hydrazine hydrate, and alcohol solvent prepared in step S1 to the reactor and reflux at 70-100℃ to generate the corresponding dihydrazide. After separation and purification, the polyurethane chain extender is obtained.

[0016] Furthermore, the diacyl chloride is selected from at least one of succinyl chloride, glutaryl chloride, adipyl chloride, heptayl chloride, octyl chloride, azelaic chloride, sebacyl chloride, 2,5-furandicarboxyl chloride, terephthaloyl chloride, and isophthaloyl chloride.

[0017] Further, the molar ratio of 4-aminobutyrate methyl hydrochloride, diacyl chloride, and acid-binding agent in step S1 is 2:(0.8-1.2):(3.6-4.4).

[0018] Furthermore, the diisocyanate is selected from at least one of isoflurone diisocyanate and 1,3-bis(1-isocyanate-1-methylethyl)benzene.

[0019] Further, the molar ratio of 4-aminobutyric acid methyl ester hydrochloride, diisocyanate, and acid-binding agent in step S1 is 2:(0.8-1.2):2.

[0020] Furthermore, the molar ratio of dimethyl dicarboxylic acid and hydrazine hydrate in step S2 is 1:(2.5-10).

[0021] Furthermore, the acid-binding agent mentioned in step S1 is selected from at least one of triethylamine and pyridine.

[0022] Further, the solvent in step S1 is selected from at least one of dichloromethane, chloroform, tetrahydrofuran, acetonitrile, acetone, methyl tert-butyl ether, and 1,4-dioxane, preferably dichloromethane or tetrahydrofuran.

[0023] Further, the alcohol solvent mentioned in step S2 is selected from at least one of methanol, ethanol, isopropanol, n-butanol, and tert-butanol, preferably methanol or ethanol.

[0024] Beneficial effects:

[0025] (1) The polyurethane chain extender provided by the present invention is derived from 4-aminobutyric acid, which is an amino acid that is widely present in vertebrates, plants and microorganisms. It is a bio-based chain extender with green source and low toxicity.

[0026] (2) The bio-based polyurethane chain extender provided by the present invention belongs to the acylhydrazine compound, which has lower solubility than conventional amine chain extenders, and the reaction rate is relatively controllable. The viscosity in the polymerization device will not increase suddenly.

[0027] (3) The bio-based polyurethane chain extender provided by the present invention can introduce high-density hydrogen bonds into the polyurethane main chain, further enhancing the strength and toughness of polyurethane materials;

[0028] (4) The preparation method of bio-based polyurethane chain extender provided by the present invention is templated, and the required chain extender structure can be customized according to actual application needs. It is simple to prepare and easy to realize large-scale industrial production, and has good implementation value and market prospects. Attached Figure Description

[0029] Figure 1 The synthetic route diagrams for the bio-based polyurethane chain extenders in Examples 1-6 are shown.

[0030] Figure 2 This is a synthetic route diagram of the bio-based polyurethane chain extender in Example 7;

[0031] Figure 3 The dihydrazide compound containing the hexamethylenediamide structure in Example 2 1 H-NMR;

[0032] Figure 4 The diacylhydrazine compound containing the furan dicarboxamide structure in Example 5 1 H-NMR. Detailed Implementation

[0033] To better understand the above-mentioned objectives, features, and advantages of the present invention, the solutions of the present invention will be further described below. It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other.

[0034] Many specific details are set forth in the following description in order to provide a full understanding of the invention, but the invention may also be practiced in other ways different from those described herein; obviously, the embodiments in the specification are only some embodiments of the invention, and not all embodiments.

[0035] The preferred embodiments of the present invention will now be described in detail with reference to specific examples. It should be understood that the following examples are given for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and substitutions to the present invention without departing from its spirit and essence.

[0036] Test instrument models: The nuclear magnetic resonance spectrometer used was a Vaian DLG400 (Varian, USA), and the universal tensile testing machine used was an Instron 5567A.

[0037] Example 1 (Preparation of chain extender: dihydrazide compound containing succinamide structure, n=4)

[0038] (1) Preparation of chain extender precursor: 12.29 g of methyl 4-aminobutyrate hydrochloride, 16.19 g of triethylamine, and 150 ml of anhydrous dichloromethane were placed in a reaction flask. 6.20 g of succinyl chloride was dissolved in 50 ml of anhydrous dichloromethane and added dropwise to the reaction system at 0 °C. After the addition was completed, the temperature was raised to 45 °C and the reaction was carried out for 8 h. After the reaction was completed, the mixture was washed three times with water, the solvent was removed by rotary evaporation, and the mixture was recrystallized with ethanol to obtain a dimethyl ester compound containing a succinamide structure with a yield of 82.3%. The synthetic route is shown in [reference needed]. Figure 1 .

[0039] (2) Preparation of chain extender: 6.33 g of dimethyl ester compound containing succinamide structure, 5 g of hydrazine hydrate and 40 mL of ethanol were placed in a reaction flask and refluxed at 80 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with ethanol. After drying, 6.04 g of white powder, i.e., polyurethane chain extender, was obtained with a yield of 95.4%. The synthetic route is shown in [reference needed]. Figure 2 .

[0040] Example 2 (Preparation of chain extender: a dihydrazide compound containing an adipamide structure, n=6)

[0041] (1) Preparation of chain extender precursor: 12.29 g of methyl 4-aminobutyrate hydrochloride, 16.19 g of triethylamine, and 150 ml of anhydrous dichloromethane were placed in a reaction flask. 7.32 g of adipic acid chloride was dissolved in 50 ml of anhydrous dichloromethane and added dropwise to the reaction system at 0 °C. After the addition was completed, the temperature was raised to 45 °C and the reaction was carried out for 8 h. After the reaction was completed, the mixture was washed three times with water, the solvent was removed by rotary evaporation, and the mixture was recrystallized with ethanol to obtain a dimethyl ester compound containing an adipamide structure with a yield of 84.2%. The synthetic route is shown in [reference needed]. Figure 1 .

[0042] (2) Preparation of chain extender: 6.89 g of a dimethyl ester compound containing an adipamide structure, 5 g of hydrazine hydrate, and 50 mL of ethanol were placed in a reaction flask and refluxed at 80 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with ethanol. After drying, 6.65 g of white powder, i.e., polyurethane chain extender, was obtained with a yield of 96.5%. The synthetic route is shown in [reference needed]. Figure 2 .

[0043] Example 3 (Preparation of chain extender: dihydrazide compound containing octadiamide structure, n=8)

[0044] (1) Preparation of chain extender precursor: 12.29 g of methyl 4-aminobutyrate hydrochloride, 16.19 g of triethylamine, and 150 ml of anhydrous dichloromethane were placed in a reaction flask. 8.44 g of octanoyl chloride was dissolved in 50 ml of anhydrous dichloromethane and added dropwise to the reaction system at 0 °C. After the addition was completed, the temperature was raised to 45 °C and the reaction was carried out for 8 h. After the reaction was completed, the mixture was washed three times with water, the solvent was removed by rotary evaporation, and the mixture was recrystallized with ethanol to obtain a dimethyl ester compound containing an octanoyl diamide structure with a yield of 81.5%. The synthetic route is shown in [reference needed]. Figure 1 .

[0045] (2) Preparation of chain extender: 7.45 g of dimethyl ester compound containing octadiamide structure, 5 g of hydrazine hydrate and 80 mL of ethanol were placed in a reaction flask and refluxed at 80 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with ethanol. After drying, 7.14 g of white powder, i.e., polyurethane chain extender, was obtained with a yield of 95.8%. The synthetic route is shown in [reference needed]. Figure 1 .

[0046] Example 4 (Preparation of chain extender: dihydrazide compound containing sebacamide structure, n=10)

[0047] (1) Preparation of chain extender precursor: 12.29 g of methyl 4-aminobutyrate hydrochloride, 16.19 g of triethylamine, and 150 ml of anhydrous dichloromethane were placed in a reaction flask. 9.56 g of sebacyl chloride was dissolved in 50 ml of anhydrous dichloromethane and added dropwise to the reaction system at 0 °C. After the addition was complete, the temperature was raised to 45 °C and the reaction was carried out for 8 h. After the reaction was completed, the mixture was washed three times with water, the solvent was removed by rotary evaporation, and the mixture was recrystallized with ethanol to obtain a dimethyl ester compound containing a sebacylamide structure with a yield of 85.3%. The synthetic route is shown in [reference needed]. Figure 1 .

[0048] (2) Preparation of chain extender: 8.01 g of a dimethyl ester compound containing a sebacamide structure, 5 g of hydrazine hydrate, and 100 mL of ethanol were placed in a reaction flask and refluxed at 80 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with ethanol. After drying, 7.84 g of white powder, i.e., polyurethane chain extender, was obtained with a yield of 97.8%. The synthetic route is shown in [reference needed]. Figure 1 .

[0049] Example 5 (Preparation of chain extender: a dihydrazide compound containing a furanyl dicarboxamide structure, R = 2,5-substituted furanyl group)

[0050] (1) Preparation of chain extender precursor: 12.29 g of methyl 4-aminobutyrate hydrochloride, 16.19 g of triethylamine, and 150 ml of anhydrous dichloromethane were placed in a reaction flask. 7.72 g of 2,5-furandicarboxyl chloride was dissolved in 50 ml of anhydrous dichloromethane and added dropwise to the reaction system at 0 °C. After the addition was completed, the temperature was raised to 45 °C and the reaction was carried out for 8 h. After the reaction was completed, the mixture was washed three times with water, the solvent was removed by rotary evaporation, and the mixture was recrystallized from tetrahydrofuran to obtain a dimethyl ester compound containing a furandicarboxamide structure with a yield of 75.3%. The synthetic route is shown in [reference needed]. Figure 1 .

[0051] (2) Preparation of chain extender: 7.08 g of a dimethyl ester compound containing a furan dicarboxamide structure, 5 g of hydrazine hydrate, and 40 mL of ethanol were placed in a reaction flask and refluxed at 80 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, and a solid precipitated out. The solid was filtered, the filter cake was washed with cold ethanol, and dried to obtain 6.88 g of white powder, which is the polyurethane chain extender, with a yield of 97.2%. The synthetic route is shown in [reference needed]. Figure 1 .

[0052] Example 6 (Preparation of chain extender: a dihydrazide compound containing a terephthalamide structure, R = 1,4-substituted phenyl)

[0053] (1) Preparation of chain extender precursor: 12.29 g of methyl 4-aminobutyrate hydrochloride, 16.19 g of triethylamine, and 150 ml of anhydrous dichloromethane were placed in a reaction flask. 8.12 g of terephthaloyl chloride was dissolved in 50 ml of anhydrous dichloromethane and added dropwise to the reaction system at 0 °C. After the addition was completed, the temperature was raised to 45 °C and the reaction was carried out for 8 h. After the reaction was completed, the mixture was washed three times with water, the solvent was removed by rotary evaporation, and the mixture was recrystallized with ethanol to obtain a dimethyl ester compound containing a terephthalamide structure with a yield of 85.6%. The synthetic route is shown in [reference needed]. Figure 1 .

[0054] (2) Preparation of chain extender: 7.29 g of dimethyl ester compound containing terephthalamide structure, 5 g of hydrazine hydrate and 100 mL of ethanol were placed in a reaction flask and refluxed at 80 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, and a solid precipitated out. The filter cake was washed three times with ethanol and dried to obtain 7.19 g of white powder, which is the polyurethane chain extender, with a yield of 98.6%. The synthetic route is shown in [reference needed]. Figure 1 .

[0055] Example 7 (Preparation of chain extender: a dihydrazide compound containing isoflurone diurea group, R = 1-substituted-3-(substituted methyl)-3,5,5-trimethylcyclohexyl)

[0056] (1) Preparation of chain extender precursor: 12.29 g of methyl 4-aminobutyrate hydrochloride, 8.1 g of triethylamine, and 100 ml of anhydrous dichloromethane were placed in a reaction flask. 8.89 g of isophorone diisocyanate was dissolved in 50 ml of anhydrous dichloromethane and added dropwise to the reaction system at room temperature. After the addition was completed, the reaction was continued for 8 h. After the reaction was completed, the mixture was washed three times with water, the solvent was removed by rotary evaporation, and the mixture was recrystallized with ethanol. The yield was 84.7%. The synthetic route is shown in [reference needed]. Figure 1 .

[0057] (2) Preparation of chain extender: 9.14 g of a dimethyl ester compound containing an isophorone diurea group, 5 g of hydrazine hydrate, and 100 mL of ethanol were placed in a reaction flask and refluxed at 80 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature, rotary evaporated, and then vacuum dried to obtain a solid. Recrystallization from tetrahydrofuran yielded 8.56 g of a white powder, which is the polyurethane chain extender, with a yield of 93.7%. The synthetic route is shown in [reference needed]. ​ .

[0058] Example 8 (Preparation of polyurethane; chain extender: bio-based chain extender containing dihydrazide compounds with furanyl dicarboxamide structure)

[0059] The reaction was carried out in a three-necked reaction flask equipped with a mechanical stirrer and nitrogen inlet / outlet. Polytetrahydrofuran (PTMG, weight average molecular weight 1000, 5.6 g, 0.0056 mol) was added to the reactor, the oil bath temperature was raised to 100°C, and a vacuum was applied for 3 hours (<100 Pa) to dehydrate it. Then, isophorone diisocyanate (IPDI, 1.78 g, 0.008 mol), dibutyltin dilaurate (0.0074 g, 0.1% of the total mass of PTMG and IPDI), and 3 mL of DMF were added. The temperature was lowered to 70°C, and the reaction was carried out for 4 hours to obtain the prepolymer. Then, the bio-based chain extender containing a furan-dicarboxamide structure, a dihydrazide compound (0.85 g, 0.0024 mol) prepared in Example 5, was dissolved in 50 mL of DMF and mixed thoroughly with the prepolymer. The reaction was continued at 50°C for 3 hours. The polymer solution was cast into uniform sheets 2-3 mm thick. The synthesized polymer was then dried in a 50°C hot air circulating oven for 24 hours, followed by further drying in a 50°C vacuum oven for 24 hours to remove the solvent. The prepared polyurethane material was mechanically tested and found to have a tensile strength of 42.78 MPa and an elongation at break of 1675.23%.

[0060] Example 9 (Preparation of polyurethane; chain extender: diacylhydrazide compound containing succinamide structure (n=4))

[0061] (1) Preparation of the prepolymer: The reaction was carried out in a three-necked reaction flask equipped with a mechanical stirrer and nitrogen inlet and outlet. Polytetrahydrofuran ether diol (PTMG, weight average molecular weight 1000, 5.6 g, 0.0056 mol) was added to the reactor, the oil bath temperature was raised to 100℃, and the mixture was evacuated for 3 h (<100 Pa) to remove water. Then, isophorone diisocyanate (IPDI, 1.78 g, 0.008 mol), dibutyltin dilaurate (0.0074 g, 0.1% of the total mass of PTMG and IPDI) and 3 ml DMF were added, the temperature was lowered to 70℃, and the reaction was carried out for 4 h to obtain the prepolymer.

[0062] (2) Chain extension and curing: A bio-based chain extender, a dihydrazide compound containing a succinamide structure (0.76 g, 0.0024 mol), was dissolved in 50 mL of DMF and mixed thoroughly with the prepolymer. The reaction was continued at 50 °C for 3 h. The polymer solution was cast into uniform sheets 2-3 mm thick. The synthesized polymer was then dried in a 50 °C hot air circulating oven for 24 h, followed by further drying in a 50 °C vacuum oven for 24 h to remove the solvent. The prepared polyurethane material was mechanically tested and found to have a tensile strength of 33.77 MPa and an elongation at break of 1455.72%.

[0063] Example 10 (Preparation of polyurethane; chain extender: dihydrazide compound containing terephthalamide structure (R = 1,4-substituted phenyl))

[0064] (1) Preparation of the prepolymer: The reaction was carried out in a three-necked reaction flask equipped with a mechanical stirrer and nitrogen inlet and outlet. Polytetrahydrofuran ether diol (PTMG, weight average molecular weight 1000, 5.6 g, 0.0056 mol) was added to the reactor, the oil bath temperature was raised to 100℃, and the mixture was evacuated for 3 h (<100 Pa) to remove water. Then, isophorone diisocyanate (IPDI, 1.78 g, 0.008 mol), dibutyltin dilaurate (0.0074 g, 0.1% of the total mass of PTMG and IPDI) and 3 ml DMF were added, the temperature was lowered to 70℃, and the reaction was carried out for 4 h to obtain the prepolymer.

[0065] (2) Chain extension and curing: The bio-based chain extender, a dihydrazide compound containing a terephthalamide structure (0.88 g, 0.0024 mol), was dissolved in 50 mL of DMF and mixed thoroughly with the prepolymer. The reaction was continued at 50 °C for 3 h. The polymer solution was cast into uniform sheets 2-3 mm thick. The synthesized polymer was then dried in a 50 °C hot air circulating oven for 24 h, and further dried in a 50 °C vacuum oven for 24 h to remove the solvent. The prepared polyurethane material was mechanically tested and showed a tensile strength of 38.25 MPa and an elongation at break of 1723.52%.

[0066] Example 11 (Preparation of polyurethane; chain extender: a dihydrazide compound containing isoflurone diurea group (R = 1-substituted-3-(substituted methyl)-3,5,5-trimethylcyclohexyl))

[0067] (1) Preparation of the prepolymer: The reaction was carried out in a three-necked reaction flask equipped with a mechanical stirrer and nitrogen inlet and outlet. Polytetrahydrofuran ether diol (PTMG, weight average molecular weight 1000, 5.6 g, 0.0056 mol) was added to the reactor, the oil bath temperature was raised to 100℃, and the mixture was evacuated for 3 h (<100 Pa) to remove water. Then, isophorone diisocyanate (IPDI, 1.78 g, 0.008 mol), dibutyltin dilaurate (0.0074 g, 0.1% of the total mass of PTMG and IPDI) and 3 ml DMF were added, the temperature was lowered to 70℃, and the reaction was carried out for 4 h to obtain the prepolymer.

[0068] (2) Chain extension and curing: A bio-based chain extender containing a dihydrazide compound with an isoflurane diurea group (1.10 g, 0.0024 mol) was dissolved in 50 mL of DMF and mixed thoroughly with the prepolymer. The reaction was continued at 50 °C for 3 h. The polymer solution was cast into uniform sheets 2-3 mm thick. The synthesized polymer was then dried in a 50 °C hot air circulating oven for 24 h, and further dried in a 50 °C vacuum oven for 24 h to remove the solvent. The prepared polyurethane material was mechanically tested and showed a tensile strength of 36.43 MPa and an elongation at break of 1240.45%.

[0069] Comparative Example 1 (Preparation of Polyurethane)

[0070] The reaction was carried out in a three-necked flask equipped with a mechanical stirrer and nitrogen inlet / outlet. Polytetrahydrofuran (PTMG, weight average molecular weight 1000, 5.6 g, 0.0056 mol) was added to the reactor, the oil bath temperature was raised to 100°C, and a vacuum was applied for 3 hours (<100 Pa) to dehydrate it. Then, isophorone diisocyanate (IPDI, 1.78 g, 0.008 mol), dibutyltin dilaurate (0.0074 g, 0.1% of the total mass of PTMG and IPDI), and 3 mL of DMF were added. The temperature was lowered to 70°C, and the reaction was carried out for 4 hours to obtain the prepolymer. Then, the chain extender MOCA (0.64 g, 0.0024 mol) was dissolved in 50 mL of DMF and mixed thoroughly with the prepolymer. The reaction was continued at 50°C for 3 hours. The polymer solution was cast into uniform sheets 2-3 mm thick. The synthesized polymer was then dried in a 50°C hot air circulating oven for 24 hours, followed by further drying in a 50°C vacuum oven for 24 hours to remove the solvent. The prepared polyurethane material was mechanically tested and found to have a tensile strength of 32.4 MPa and an elongation at break of 503.45%.

[0071] As can be seen from Example 8 and Comparative Example 1 above, the dihydrazide compound containing a furan dicarboxamide structure prepared in Example 5, as a bio-based chain extender, can not only replace the traditional amine chain extender MOCA in terms of biofriendliness, but also improve the mechanical properties of polyurethane elastomers prepared by chain extension with dihydrazide compounds containing furan dicarboxamide structures compared with polyurethane elastomers prepared by MOCA, especially with a significant increase in toughness. At the same time, the bio-based polyurethane chain extender of this embodiment can be prepared by a template, and the required chain extender structure can be customized according to actual application needs. Moreover, the preparation is simple, requires no catalyst, and is easy to realize large-scale industrial production, showing good application prospects and promotion value.

[0072] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A type of bio-based polyurethane chain extender, characterized in that, The chain extender has the following structural formula: ; Wherein, R is selected from furanyl, phenyl, , , ; n is a natural number, with a value range of 4-10.

2. A method for preparing the bio-based polyurethane chain extender as described in claim 1, characterized in that, Includes the following steps: S1. Preparation of precursor: 4-aminobutyric acid methyl ester hydrochloride, acid-binding agent and solvent are added to the reactor, and diacyl chloride or diisocyanate solution is added dropwise at -10-10℃. The mixture is refluxed at 25-60℃ to generate the corresponding dicarboxylic acid dimethyl ester. The corresponding dimethyl carboxylic acid ester structural formula is: S2. Preparation of chain extender: The corresponding dimethyl dicarboxylic acid, hydrazine hydrate, and alcohol solvent prepared in step S1 are added to the reactor and refluxed at 70-100℃ to generate the corresponding dihydrazide. After separation and purification, the bio-based polyurethane chain extender is obtained. The corresponding dihydrazide structural formula is: The diacyl chloride is selected from at least one of succinyl chloride, glutaryl chloride, adipicoyl chloride, heptacyanoyl chloride, octyl chloride, azeloyl chloride, sebacyl chloride, 2,5-furandicarboxyl chloride, terephthaloyl chloride, and isophthaloyl chloride; the diisocyanate is selected from at least one of isoflurane diisocyanate and 1,3-bis(1-isocyanate-1-methylethyl)benzene.

3. The preparation method according to claim 2, characterized in that, The molar ratio of 4-aminobutyric acid methyl ester hydrochloride, diacyl chloride, and acid-binding agent in step S1 is 2:(0.8-1.2):(3.6-4.4).

4. The preparation method according to claim 2, characterized in that, The molar ratio of 4-aminobutyric acid methyl ester hydrochloride, diisocyanate, and acid-binding agent in step S1 is 2:(0.8-1.2):

2.

5. The preparation method according to claim 2, characterized in that, The molar ratio of the corresponding dimethyl carboxylic acid and hydrazine hydrate in step S2 is 1:(2.5-10).

6. The preparation method according to claim 2, characterized in that, The acid-binding agent mentioned in step S1 is selected from at least one of triethylamine and pyridine.

7. The preparation method according to claim 2, characterized in that, The solvent in step S1 is selected from at least one of dichloromethane, chloroform, tetrahydrofuran, acetonitrile, acetone, methyl tert-butyl ether, and 1,4-dioxane.

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