Polyurethane chain extender, polyurethane prepolymer, mechanochromic polyurethane adhesive and preparation method therefor

Abstract

Disclosed are a polyurethane chain extender, a polyurethane prepolymer, a mechanochromic polyurethane adhesive, and a preparation method therefor. The polyurethane chain extender has the following structure. The polyurethane prepolymer is prepared from raw materials of the following components: the polyurethane chain extender, polyether polyol and diisocyanate; the polyurethane chain extender is a diamine compound set forth in claim 1; a molar ratio of the polyurethane chain extender, the polyether polyol and the diisocyanate is 1:45-50:8-12. The mechanochromoic polyurethane adhesive comprises a component A and a component B, the component A being prepared from raw materials of the following components: hydroxyl resin, a catalyst, and an additive; the component B is prepared from raw materials of the following components: the polyurethane prepolymer, a latent curing agent, and a dehydrating agent. The polyurethane adhesive exhibits a significant color change when subjected to external tensile force, and has good bonding performance and mechanical properties.

Description

Polyurethane chain extender, polyurethane prepolymer, mechanochromic polyurethane adhesive and preparation method thereof Technical Field

[0001] The invention belongs to the technical field of adhesives, and in particular relates to a polyurethane chain extender, a polyurethane prepolymer, a mechanochromic polyurethane adhesive and a preparation method thereof. Background Art

[0002] Responsive polymers are polymers that respond to external environmental stimuli by producing significant physical or chemical changes, or even mutations. Responsive polymers are formed by introducing sensitive groups into the polymer. Currently, responsive polymers can be broadly categorized into photoresponsive polymers, electroresponsive polymers, thermoresponsive polymers, pH-responsive polymers, and force-responsive polymers, depending on the source of the external stimulus.

[0003] Mechano-responsive polymers incorporate force-sensitive groups covalently bonded to polymer chains. When the polymer chain is subjected to an external driving force, the force-sensitive groups undergo structural changes, resulting in changes in the polymer's physical or chemical properties. Mechanochromic materials offer intelligent early warning capabilities, providing warnings before cracks or breaks occur, and analyzing the material's stress response through color (or fluorescence) changes.

[0004] Polyurethane adhesives have a huge market potential due to their excellent bonding strength and wear resistance. If these adhesives can be developed with force-responsive properties, they could provide early warning before failure occurs, effectively mitigating potential hazards. The development of a polyurethane adhesive system with mechanochromic properties is crucial for improving the intelligent warning capabilities and high-end applications of polyurethane adhesives.

[0005] Summary of the Invention

[0006] Based on this, the object of the present invention is to provide a mechanochromic polyurethane adhesive.

[0007] In order to achieve the above-mentioned purpose of the invention, the present invention first provides a diamine compound with mechanochromic function, which can be used as a polyurethane chain extender for the preparation of polyurethane glue. The polyurethane glue prepared with the chain extender has mechanochromic function and excellent bonding strength and mechanical strength.

[0008] The polyurethane chain extender of the present invention includes the following technical solutions.

[0009] A diamine compound having the following structure:

[0010] The present invention also provides the use of the diamine compound as a polyurethane chain extender in the preparation of a polyurethane prepolymer or polyurethane glue having a mechanochromic function.

[0011] The present invention also provides a method for preparing the diamine compound, comprising the following steps:

[0012] Step 1: Under nitrogen or inert gas protection, p-cyanophenylhydrazine, 3-methyl-2-butanone and a catalyst react in acetic acid to obtain compound 1;

[0013] Step 2: Under nitrogen or inert gas protection, 2-bromoethanol and the product 1 react in a solvent to obtain compound 2;

[0014] Step 3: Under the protection of nitrogen or inert gas, the compound 2 reacts with 4-aminoethylbenzaldehyde in a solvent to obtain compound 3.

[0015] Step 4: Add compound 3 to an alkali-containing solvent for reaction, add the resulting reaction product to ethanol, add nickel dichloride, add NaBH4 in batches at 40° C.-50° C. with stirring, and react with stirring to obtain compound 4, i.e., the diamine compound;

[0016] The reaction formula is as follows:

[0017] In some embodiments, the molar ratio of p-cyanophenylhydrazine, 3-methyl-2-butanone and catalyst in step 1 is 1:1-1.3:0.002-0.008.

[0018] In some embodiments, the catalyst in step 1 is concentrated sulfuric acid.

[0019] In some embodiments, the mass concentration of the concentrated sulfuric acid is 95-98%.

[0020] In some embodiments, the reaction temperature in step 1 is 35° C.-50° C., and the reaction time is 6 hours-10 hours.

[0021] In some embodiments, the molar ratio of 2-bromoethanol to compound 1 in step 2 is 1-1.3:1.

[0022] In some embodiments, the solvent in step 2 is acetonitrile.

[0023] In some embodiments, the reaction temperature in step 2 is 35° C.-50° C., and the reaction time is 15 hours-25 hours.

[0024] In some embodiments, the molar ratio of compound 2 to 4-aminoethylbenzaldehyde in step 3 is 1:1-1.3.

[0025] In some embodiments, the solvent in step 3 is ethanol.

[0026] In some embodiments, the reaction temperature in step 3 is 50° C.-60° C., and the reaction time is 10 hours-15 hours.

[0027] In some embodiments, the molar ratio of the compound 3 to the base in step 4 is 1:1.5-2.5.

[0028] In some embodiments, the molar ratio of the compound in step 4 to the nickel dichloride and NaBH4 is 1:0.015-0.025:0.005-0.015.

[0029] In some embodiments, the base in step 4 is sodium bicarbonate.

[0030] In some embodiments, the solvent in step 4 is water.

[0031] In some embodiments, the reaction time of compound 3 and base is 20 minutes to 40 minutes; and the stirring reaction time in step 4 is 3 hours to 5 hours.

[0032] The present invention also provides a polyurethane prepolymer having a mechanochromic function, which specifically includes the following technical solutions.

[0033] A polyurethane prepolymer is prepared from raw materials comprising the following components: a polyurethane chain extender, polyether polyol, and diisocyanate; the polyurethane chain extender is the above-mentioned diamine compound; and the mass ratio of the polyurethane chain extender, polyether polyol, and diisocyanate is 1:45-50:8-12.

[0034] In some embodiments, the mass ratio of the polyurethane chain extender, polyether polyol and diisocyanate is 1:48-52:9-11.

[0035] In some embodiments, the diisocyanate is selected from at least one of polymeric MDI, pure MDI, liquefied MDI and TDI.

[0036] In some embodiments, the diisocyanate is carbodiimide-modified MDI.

[0037] In some embodiments, the polyether polyol is selected from at least one of polyethylene glycol, polypropylene glycol and polyethylene oxide glycol.

[0038] In some embodiments, the molecular weight of the polyether polyol is 400-6000.

[0039] In some embodiments, the molecular weight of the polyether polyol is 1000-4000.

[0040] In some embodiments, the molecular weight of the polyether polyol is 1000-3000.

[0041] In some embodiments, the polyurethane prepolymer has a viscosity of 6000 cps-50000 cps at 25°C.

[0042] In some embodiments, the polyurethane prepolymer has a viscosity of 8000 cps-15000 cps at 25°C.

[0043] The present invention also provides a method for preparing the polyurethane prepolymer, which includes the following technical solutions.

[0044] A method for preparing the polyurethane prepolymer comprises the following steps:

[0045] The polyurethane chain extender, diisocyanate and polyether polyol are added to ethyl acetate, and stirred at 60-80° C. for 4-6 hours to obtain the product.

[0046] The present invention also provides a mechanochromic polyurethane adhesive, which includes the following technical solutions.

[0047] A mechanochromic polyurethane adhesive comprises a component A and a component B.

[0048] In parts by weight, the component A is prepared from the following raw materials: 100 parts of hydroxy resin, 0.5 to 2 parts of catalyst, and 0.5 to 2 parts of auxiliary agent;

[0049] In parts by weight, the B component is prepared from the following raw materials: 100 parts of the polyurethane prepolymer, 3 to 8 parts of the latent curing agent, and 0.5 to 2 parts of the water scavenger.

[0050] In some embodiments, the component A is prepared from the following raw materials, calculated in parts by weight: 100 parts of hydroxy resin; 0.8 to 1.5 parts of catalyst; 0.8 to 1.5 parts of auxiliary agent;

[0051] In parts by weight, the component B is prepared from the following raw materials: 100 parts of the polyurethane prepolymer, 4 to 6 parts of the latent curing agent, and 0.8 to 1.5 parts of the water scavenger.

[0052] In some embodiments, when used, the mixing mass ratio of the component A to the component B is 1-4:1.

[0053] In some embodiments, when used, the mixing mass ratio of the component A to the component B is 1-2:1.

[0054] In some embodiments, the mixed viscosity of the mechanochromic polyurethane adhesive before curing at 25° C. is 3,000 cps to 50,000 cps.

[0055] In some embodiments, the mixed viscosity of the mechanochromic polyurethane adhesive before curing at 25° C. is 3500 cps to 4500 cps.

[0056] In some embodiments, the hydroxyl resin is selected from at least one of plant-based polyols, polyether polyols, and polyester polyols.

[0057] In some embodiments, the hydroxy resin consists of castor oil, polyether polyol PPG-2000 and polyester polyol PDP-70.

[0058] In some embodiments, the hydroxy resin is composed of castor oil, polyether polyol PPG-2000 and polyester polyol PDP-70 in a mass ratio of 5-7:2-4:1.

[0059] In some embodiments, the catalyst is at least one of an organotin catalyst (such as stannous octoate, dibutyltin dilaurate, etc.) and a tertiary amine catalyst (such as triethylenediamine, triethanolamine).

[0060] In some embodiments, the auxiliary agent is one or more combinations of a thixotropic agent, a dust suppressant, a defoaming agent, an antioxidant, and a water scavenger.

[0061] In some embodiments, the auxiliary agent is BYK-A500 defoamer.

[0062] In some embodiments, the latent curing agent is an oxazolidine compound, which can be a monocyclic oxazolidine or a bicyclic oxazolidine.

[0063] In some embodiments, the water scavenger is toluenesulfonyl isocyanate (TI).

[0064] The present invention also provides a method for preparing the mechanochromic polyurethane adhesive, which includes the following technical solutions.

[0065] A method for preparing a mechanochromic polyurethane adhesive comprises the following steps:

[0066] Preparation of component A: Add the hydroxy resin into a reaction kettle, stir and disperse, remove water under vacuum at 100-120°C for 1-3 hours, cool to room temperature, add the catalyst and auxiliary agent, stir and disperse, and obtain the product;

[0067] Preparation of component B: Stir and disperse the polyurethane prepolymer, latent curing agent and water scavenger at room temperature, and vacuum degas.

[0068] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0069] The present invention uses p-cyanophenylhydrazine and 3-methyl-2-butanone as starting materials and prepares a bifunctional diamine compound through a multi-step chemical reaction. The compound contains an indoloxazoline group with a mechanochromic function and active groups - amino groups at both ends of the molecule. The compound can be used as a polyurethane chain extender for the preparation of polyurethane prepolymers and polyurethane adhesives with mechanochromic functions.

[0070] Furthermore, polyurethane prepolymers and polyurethane glues were prepared using the bifunctional diamine compounds of the present invention as polyurethane chain extenders. The molecular chains of these polyurethane prepolymers contain a large number of indoleoxazoline groups, which have mechanochromic properties compared to general polyurethane prepolymers or polyurethane glues. When subjected to external force, they will show a significant color change from yellow to orange-red, thereby improving the intelligent warning performance of the polyurethane glue and having potential application value in high-end industrial fields.

[0071] In addition, the polyurethane glue prepared using the bifunctional diamine compound of the present invention as a polyurethane chain extender has high tensile shear strength and colloid tensile strength, and has good bonding and mechanical properties, which is conducive to its application in multiple scenarios. DETAILED DESCRIPTION

[0072] The technical solutions of the present invention are further illustrated by specific examples below. Those skilled in the art should understand that the examples are only for helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0073] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as those commonly understood by those skilled in the art. The terms used in the specification of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0074] The terms "comprise," "comprising," and "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, apparatus, product, or device comprising a series of steps is not limited to the listed steps or modules but may optionally include steps not listed, or other steps inherent to the process, method, product, or device.

[0075] In this application, "plurality" refers to two or more. "And / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0076] The parts involved in the following examples are all parts by mass.

[0077] The room temperature or normal temperature mentioned in the following examples refers to 20°C-30°C.

[0078] The following are specific examples.

[0079] Example 1: Preparation of polyurethane chain extender

[0080] Its synthetic route is as follows:

[0081] Step 1: p-Cyanophenylhydrazine, 3-methyl-2-butanone and 98% concentrated sulfuric acid are added to an acetic acid solvent (100 times the molar amount of p-cyanophenylhydrazine) in a molar ratio of 1:1.1:0.005, and reacted for 8 hours under nitrogen protection at a temperature of 40-45°C. Dichloromethane (50 times the molar amount of p-cyanophenylhydrazine) is added to the reaction solution to dissolve it, and the dissolved mixture is then washed with a sodium carbonate aqueous solution. The organic layer is then dried over anhydrous sodium sulfate and distilled under reduced pressure to obtain product 1.

[0082] Step 2: Under nitrogen protection and a temperature of 40-45°C, 2-bromoethanol and product 1 are reacted in acetonitrile (100 times the molar amount of product 1) at a molar ratio of 1.1:1 for 20 hours. The reaction solution is washed with an aqueous sodium bicarbonate solution, and the organic layer is dried over anhydrous sodium sulfate and distilled under reduced pressure to obtain ethanolyl quaternary ammonium bromide (product 2).

[0083] Step 3: Under nitrogen protection and a temperature of 55°C, product 2 and 4-aminoethylbenzaldehyde are reacted in a molar ratio of 1:1.1 in ethanol (100 times the molar amount of product 2) for 12 hours. The reaction solution is washed with ethyl acetate, and the upper liquid is taken and distilled under reduced pressure to obtain product 3.

[0084] Step 4: Add product 3 to a 0.1 mol / L sodium bicarbonate aqueous solution and stir for 30 minutes until the solution turns brownish yellow. Extract the reaction solution with ethyl acetate and then distill under reduced pressure. Add the resulting product to ethanol (add 1 mol of product 3 to 400 mL of ethanol), add nickel dichloride (the amount added is 2% of the molar amount of product 3), add NaBH4 (the amount added is 1% of the molar amount of product 3) in batches at 45°C and under vigorous stirring, and then stir and react for 4 hours. Remove ethanol by distillation under reduced pressure and then extract with ether. The resulting organic layer is washed with alkaline water and saturated brine, dried over anhydrous sodium sulfate, and distilled under reduced pressure to remove ether to obtain product 4, i.e., the polyurethane chain extender.

[0085] H NMR spectrum of product 4 1 HNMR (400 MHz, CDCl3), (TMS, ppm): δ = 1.38-1.40 (hydrogen on the methyl group); 2.80-3.00 (hydrogen on the two methylene groups between the benzene ring and the amino group); 3.50-3.60 (hydrogen on the methylene group on the nitrogen oxide five-membered ring and hydrogen on the nitrogen of the anilino group); 5.0-5.20 (hydrogen on the nitrogen attached to the amino group); 6.20-7.55 (hydrogen on the benzene ring and hydrogen on the double bond carbon between the nitrogen oxide five-membered ring and the benzene ring).

[0086] Example 2: Preparation of polyurethane prepolymer 1

[0087] The polyurethane chain extender prepared in Example 1 (1 part), carbodiimide-modified MDI (Wanhua Chemical 100-LL, 50 parts), and polyether polyol PPG-1000 (10 parts) were added to ethyl acetate and stirred at 70°C for 5 hours. The mixture was then distilled under reduced pressure to obtain a yellow polyurethane prepolymer having a viscosity of 9200 cps at 25°C.

[0088] Example 3: Preparation of polyurethane prepolymer 2

[0089] The polyurethane chain extender prepared in Example 1 (1 part), carbodiimide-modified MDI (Wanhua Chemical 100-LL, 50 parts), and polyether polyol DL-3000D (Bluestar Dongda, 10 parts) were added to ethyl acetate and stirred at 70°C for 5 hours. A yellow polyurethane prepolymer was then obtained by vacuum distillation with a viscosity of 11,000 at 25°C.

[0090] Example 4: Preparation of mechanochromic polyurethane adhesive

[0091] The preparation process of component A is as follows:

[0092] 100 parts of a hydroxyl resin (specifically, 60 parts of castor oil, 30 parts of polyether polyol PPG-2000, and 10 parts of polyester polyol (Stepan PDP-70)) were added to a reaction kettle and stirred at room temperature for 20 minutes. The mixture was then vacuumed at 110°C (vacuum level: -0.08 MPa) to remove water for 2 hours. The mixture was cooled to room temperature, and 1 part of dibutyltin dilaurate and 1 part of BYK-A500 defoamer were added. The mixture was then stirred and dispersed at room temperature to obtain the product.

[0093] The preparation process of component B is as follows:

[0094] Take 100 parts of the polyurethane prepolymer 1 prepared in Example 2, 5 parts of oxazolidine (CAS No. 504-76-7), and 1 part of the polyurethane dewatering agent TI (methylbenzenesulfonyl isocyanate), stir and disperse at room temperature for 30 minutes, and then degas in vacuum (vacuum degree of -0.08 MPa). The viscosity of the obtained component B at 25°C is 6800 cps.

[0095] Example 5: Preparation of mechanochromic polyurethane adhesive

[0096] The preparation process of component A is as follows:

[0097] 100 parts of a hydroxyl resin (specifically, 60 parts of castor oil, 30 parts of polyether polyol PPG-2000, and 10 parts of polyester polyol (Stepan PDP-70)) were added to a reaction kettle and stirred at room temperature for 20 minutes. The mixture was then vacuumed at 110°C (vacuum level: -0.08 MPa) to remove water for 2 hours. The mixture was cooled to room temperature, and 1 part of dibutyltin dilaurate and 1 part of BYK-A500 defoamer were added. The mixture was then stirred and dispersed at room temperature to obtain the product.

[0098] The preparation process of component B is as follows:

[0099] Take 100 parts of the polyurethane prepolymer 2 prepared in Example 3, 5 parts of oxazolidine (CAS No. 504-76-7), and 1 part of the polyurethane dewatering agent TI (methylbenzenesulfonyl isocyanate), stir and disperse at room temperature for 30 minutes, and then degas in vacuum (vacuum degree of -0.08 MPa). The viscosity of the obtained component B at 25°C is 9700 cps.

[0100] Comparative Example 1: Preparation of two-component polyurethane adhesive

[0101] The preparation process of component A is as follows:

[0102] 100 parts of a hydroxyl resin (specifically, 60 parts of castor oil, 30 parts of polyether polyol PPG-2000, and 10 parts of polyester polyol (Stepan PDP-70)) were added to a reaction kettle and stirred at room temperature for 20 minutes. The mixture was then vacuumed at 110°C (vacuum level: -0.08 MPa) to remove water for 2 hours. The mixture was cooled to room temperature, and 1 part of dibutyltin dilaurate and 1 part of BYK-A500 defoamer were added. The mixture was then stirred and dispersed at room temperature to obtain the product.

[0103] The preparation process of component B is as follows:

[0104] Take 100 parts of carbodiimide-modified MDI (Wanhua Chemical 100-LL), 5 parts of oxazolidine (CAS No. 504-76-7), and 1 part of polyurethane dewatering agent TI, stir and disperse at room temperature for 30 minutes, and then degas in vacuum (vacuum degree is -0.08 MPa). The viscosity of the obtained component B at 25°C is 3100 cps.

[0105] Comparative Example 2: Preparation of two-component polyurethane adhesive

[0106] The preparation process of component A is as follows:

[0107] 100 parts of a hydroxyl resin (specifically, 60 parts of castor oil, 30 parts of polyether polyol PPG-2000, and 10 parts of polyester polyol (Stepan PDP-70)) were added to a reaction kettle and stirred at room temperature for 20 minutes. The mixture was then vacuumed at 110°C (vacuum level: -0.08 MPa) to remove water for 2 hours. The mixture was cooled to room temperature, and 1 part of dibutyltin dilaurate and 1 part of BYK-A500 defoamer were added. The mixture was then stirred and dispersed at room temperature to obtain the product.

[0108] The preparation process of component B is as follows:

[0109] Take 100 parts of polyurethane prepolymer 3, 5 parts of oxazolidine (CAS No. 504-76-7), and 1 part of polyurethane dewatering agent TI, stir and disperse at room temperature for 30 minutes, and then degas in vacuum (vacuum degree is -0.08 MPa). The viscosity of the obtained component B at 25°C is 6500 cps.

[0110] Wherein, the preparation method of polyurethane prepolymer 3 is as follows:

[0111] A polyurethane chain extender, 1,4-butanediol (1 part), carbodiimide-modified MDI (Wanhua Chemical 100-LL, 50 parts), and polyether polyol PPG-1000 (10 parts) were added to ethyl acetate and stirred at 70°C for 5 hours. A yellow polyurethane prepolymer with a viscosity of 12,000 cps at 25°C was then obtained by vacuum distillation.

[0112] Example 6 Viscosity Test

[0113] The polyurethane adhesives prepared in Examples 4-5 and Comparative Examples 1-2 were subjected to viscosity tests according to the standard "GB / T 2794-2013 Adhesives - Determination of Viscosity - Single Cylinder Viscometer Method", and the test results are shown in Table 1.

[0114] Table 1

[0115] The mixed viscosity is the viscosity of component A and component B after mixing in a mass ratio of 100:65.

[0116] Example 7 Performance Test

[0117] The polyurethane adhesives prepared in the above examples and comparative examples (components A and B were mixed in a mass ratio of 100:65, and sample preparation was performed according to the standard) were tested for performance according to the adhesion testing standards: GB7124-2008 Adhesives - Determination of Tensile Shear Strength (Rigid Material to Rigid Material) and GB / T1040.2-2006 Colloid Tensile Testing Standard: Determination of Tensile Properties of Plastics - Part 2: Tests for Molded and Extruded Plastics. The adhesive and mechanical strength of the adhesives were evaluated using the results of shear tensile tests on 3003 aluminum / 3003 aluminum specimens and dumbbell-shaped test pieces. The test results are shown in Table 2 below.

[0118] Table 2

[0119] The colloid color changes before and after stretching in Examples 4 and 5, as well as Comparative Examples 1-2, indicate that the polyurethane adhesives using chain extenders containing mechanochromic groups exhibit a significant color change after external stretching. However, the polyurethane adhesives in Comparative Examples 1-2, which do not use the chain extenders of the present invention, do not exhibit a color change due to the absence of mechanochromic groups in their molecular chains. This is because the indoloxazoline groups undergo a molecular configuration change under external stretching, leading to a gradual transition from ring closure to ring opening. The molecular structure after ring opening has a longer conjugated structure, resulting in a gradual deepening of the colloid's color from pale yellow to orange-red.

[0120] The above test results also show that the tensile shear strength and colloid tensile strength of the colloid using polyurethane prepolymer are greater than those of the polyurethane glue without prepolymer (Comparative Example 1). This is because the molecular weight of the prepolymer itself is much higher than that of liquefied MDI (carbodiimide-modified MDI) after the prepolymerization reaction. The molecular weight and crosslink density of the adhesive layer formed after the colloid cure are both higher than those of the colloid without prepolymerization. Therefore, the bonding strength and tensile strength are greater, and the elongation at break is also greater. Although Comparative Example 2 also uses a prepolymer, its chain extender is 1,4-butanediol. As a result, the tensile shear strength, colloid tensile strength, and elongation at break of the polyurethane glue prepared therein are also lower than those of the polyurethane glue prepared in the Examples. This demonstrates that using the diamine compound prepared by the present invention as a chain extender not only imparts mechanochromic properties to the resulting polyurethane glue, but also effectively improves its bonding strength and mechanical strength.

[0121] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0122] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A diamine compound, characterized in that, It has the following structure:

2. A method for preparing the diamine compound according to claim 1, characterized in that, It includes the following steps: Step 1: Under the protection of nitrogen or inert gas, react p-cyanophenylhydrazine, 3-methyl-2-butanone and a catalyst in acetic acid to obtain Compound 1; Step 2: Under the protection of nitrogen or inert gas, react 2-bromoethanol and the product 1 in a solvent to obtain Compound 2; Step 3: Under the protection of nitrogen or inert gas, react the Compound 2 with 4-aminoethylbenzaldehyde in a solvent to obtain Compound 3. Step 4: Add Compound 3 to a solvent containing a base for reaction, add the obtained reaction product to ethanol, add nickel dichloride, and add NaBH4 in batches under the conditions of 40°C - 50°C and stirring, and stir for reaction to obtain Compound 4, that is, the diamine compound; The reaction formula is as follows:

3. The preparation method of the diamine compound according to claim 2, characterized in that, The molar ratio of the p-cyanophenylhydrazine, 3-methyl-2-butanone and the catalyst in Step 1 is 1:1 - 1.3:0.002 - 0.008; and / or, The catalyst in Step 1 is concentrated sulfuric acid; and / or, The temperature of the reaction in Step 1 is 35°C - 50°C, and the reaction time is 6 hours - 10 hours; and / or, The molar ratio of the 2-bromoethanol and Compound 1 in Step 2 is 1 - 1.3:1; and / or, The solvent in Step 2 is acetonitrile; and / or, The temperature of the reaction in Step 2 is 35°C - 50°C, and the reaction time is 15 hours - 25 hours; and / or, The molar ratio of the Compound 2 and 4-aminoethylbenzaldehyde in Step 3 is 1:1 - 1.3; and / or, The solvent in Step 3 is ethanol; and / or, The temperature of the reaction in Step 3 is 50°C - 60°C, and the reaction time is 10 hours - 15 hours; and / or, The molar ratio of the Compound 3 and the base in Step 4 is 1:1.5 - 2.5; and / or, The molar ratio of the Compound 3, nickel dichloride and NaBH4 in Step 4 is 1:0.015 - 0.025:0.005 - 0.015; and / or, The solvent in Step 4 is water; and / or, The base in Step 4 is sodium bicarbonate; and / or, The reaction time of Compound 3 and the base is 20 minutes - 40 minutes; the stirring reaction time in Step 4 is 3 hours - 5 hours.

4. Use of the diamine compound according to claim 1 as a polyurethane chain extender in the preparation of a polyurethane prepolymer or polyurethane adhesive having a force-induced color change function.

5. A polyurethane prepolymer, characterized in that, It is prepared from raw materials including the following components: a polyurethane chain extender, a polyether polyol, a diisocyanate; the polyurethane chain extender is the diamine compound according to claim 1; the mass ratio of the polyurethane chain extender, the polyether polyol and the diisocyanate is 1:45 - 50:8 - 12.

6. The polyurethane prepolymer according to claim 5, characterized in that, The mass ratio of the polyurethane chain extender, the polyether polyol and the diisocyanate is 1:48 - 52:9 - 11; and / or, The diisocyanate is selected from at least one of polymeric MDI, pure MDI, liquefied MDI and TDI; and / or, The polyether polyol is selected from at least one of polyethylene glycol, polypropylene glycol and polyethylene oxide glycol; and / or, The molecular weight of the polyether polyol is 400 - 6000; and / or, The viscosity of the polyurethane prepolymer at 25 °C is 6000 cps - 50000 cps.

7. A method for preparing the polyurethane prepolymer according to claim 5 or 6, characterized in that, It includes the following steps: Add the polyurethane chain extender, diisocyanate, and polyether polyol into ethyl acetate, and stir at 60 °C - 80 °C for 4 hours - 6 hours to obtain the product.

8. A force-induced color-changing polyurethane adhesive, characterized in that, It includes component A and component B. Calculated by weight, component A is prepared from raw materials including the following components: Hydroxy resin 100 parts Catalyst 0.5 - 2 parts Auxiliary agent 0.5 - 2 parts; Calculated by weight, component B is prepared from raw materials including the following components: The polyurethane prepolymer described in claim 5 or 6 100 parts Latent curing agent 3 - 8 parts Water scavenger 0.5 - 2 parts.

9. The force-induced color-changing polyurethane glue according to claim 8, wherein, During use, the mixing mass ratio of component A and component B is 1 - 4:1; and / or, The mixing viscosity of the force - induced color - changing polyurethane adhesive before curing at 25 °C is 3000 cps - 50000 cps; and / or, The hydroxy resin is selected from at least one of vegetable polyols, polyether polyols, and polyester polyols; and / or, The catalyst is at least one of organotin catalysts and tertiary amine catalysts; and / or, The auxiliary agent is one or a combination of a thixotropic agent, a dust - proof agent, an antifoaming agent, an antioxidant, and a water scavenger; and / or, The latent curing agent is an oxazolidine compound; and / or, The water scavenger is p - toluenesulfonyl isocyanate.

10. A method for preparing the color-changing polyurethane adhesive according to claim 8 or 9, characterized in that, It includes the following steps: Preparation of component A: Add the hydroxy resin into a reaction kettle, stir and disperse, evacuate water at 100 °C - 120 °C for 1 - 3 hours, cool to room temperature, add the catalyst and the auxiliary agent, and stir and disperse to obtain the product; Preparation of component B: Stir and disperse the polyurethane prepolymer, latent curing agent, and water scavenger at room temperature, and carry out vacuum degassing to obtain the product.

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