A kind of thermoplastic polyurethane and its preparation method and application

Abstract

The present invention belongs to the technical field of polyurethane hot melt adhesives, and particularly relates to a thermoplastic polyurethane and its preparation method and application. The present invention provides a thermoplastic polyurethane, which introduces a 2-urea-4-pyrimidone group structure and a five-membered aromatic heterocyclic group structure into the molecular chain, which can improve the bonding strength of polyurethane as a hot melt adhesive and reduce the complexity of the operating conditions of the polyurethane hot melt adhesive. The 2-urea-4-pyrimidone group and the five-membered aromatic heterocyclic group act synergistically, so that the thermoplastic polyurethane hot melt adhesive can achieve high-strength bonding to a variety of substrates (metals, polycarbonates, epoxy resins, etc.) under mild operating conditions. In addition, the hot melt adhesive also has reusability and tolerance to extreme environments.

Description

Technical Field

[0001] The invention belongs to the technical field of polyurethane hot melt adhesives, and particularly relates to thermoplastic polyurethane and a preparation method and application thereof. Background Art

[0002] Polymer adhesives play an important role in both industrial production and daily life. Polyurethane hot melt adhesive can form non-covalent bonds or covalent bonds with the bonded substrates, and can form high bonding strength with a variety of substrates. Polyurethane hot melt adhesive also has the advantages of fast bonding speed, solvent-free, and environmental protection during use. Therefore, polyurethane hot melt adhesive is widely used in digital electronic parts, medical equipment, automotive industry, and aerospace fields.

[0003] Polyurethane hot melt adhesives are mainly divided into reactive polyurethane hot melt adhesives and thermoplastic polyurethane hot melt adhesives. Reactive polyurethane hot melt adhesives melt at high temperatures, react with moisture in the environment, form covalent bonds with the surface of the substrate, and play a bonding role after solidification. However, reactive polyurethane hot melt adhesives usually require higher operating temperatures, and the curing and bonding process takes a long time. After solidification, reactive polyurethane hot melt adhesives will form a permanent cross-linked network and cannot be reused. Thermoplastic polyurethane hot melt adhesives usually form non-covalent bonds, and their viscosity will decrease rapidly with increasing temperature. They will solidify quickly after cooling, and achieve bonding strength by forming non-covalent bonds with the substrate. Thermoplastic polyurethane hot melt adhesives have the characteristics of repeated use. However, thermoplastic polyurethane hot melt adhesives currently generally have the problems of low bonding strength and harsh operating conditions. The relevant technology discloses a thermoplastic polyurethane hot melt adhesive, which needs to be at a temperature of 130°C and the bonding surfaces must be bonded for 30 minutes to achieve the final bonding strength when used. The Chinese patent with publication number CN116285853A discloses a hyperbranched polyurethane hot melt adhesive containing 2-urea-4-pyrimidone groups as end capping. The hyperbranched structure can enhance the strength of the hot melt adhesive, and the 2-urea-4-pyrimidone groups with strong hydrogen bonding are beneficial to improving the bonding strength of the hot melt adhesive. However, the maximum bonding strength of the hot melt adhesive is only 6.8MPa, which cannot meet the application requirements of high bonding strength hot melt adhesives. Summary of the invention

[0004] In view of this, the object of the present invention is to provide a thermoplastic polyurethane and a preparation method and application thereof. The thermoplastic polyurethane provided by the present invention has the advantages of high bonding strength, simple operation, reusability and tolerance to extreme environments as a hot melt adhesive.

[0005] The present invention provides a thermoplastic polyurethane, wherein the thermoplastic polyurethane has a structure shown in Formula 1:

[0006]

[0007] In formula 1, n is a natural number ranging from 1 to 100;

[0008] R1 is an alkylene group, a cycloalkylene group or an aralkylene group;

[0009] R2 has the structure shown in Formula 2:

[0010]

[0011] In formula 2, m is a natural number of 1 to 6; R3 is an alkylene group, a cycloalkylene group or an aralkylene group; R4 is an alkyl group or hydrogen; R5 is an alkylene group, a cycloalkylene group or an aralkylene group; R6 is an alkyl group or hydrogen; X is oxygen or sulfur;

[0012] In formula 2, It represents the repeating unit of the reaction product obtained by the polycondensation reaction of polydiol and diisocyanate.

[0013] Preferably, the alkylene groups in R1, R3 and R5 independently include alkylene groups having 1 to 6 carbon atoms;

[0014] The cycloalkylene groups in R1, R3 and R5 independently include cycloalkylene groups having 5 to 10 carbon atoms;

[0015] The aralkylene groups in R1, R3 and R5 independently include aralkylene groups having 6 to 10 carbon atoms;

[0016] The alkyl groups in R4 and R6 independently include alkyl groups having 1 to 3 carbon atoms;

[0017] The polyglycol is one or more of polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, polyethylene glycol-propylene glycol, polyhexanediol adipate-1,6-diol, polyneopentyl glycol adipate diol and polybutanediol adipate-1,4-diol; the molecular weight of the polyglycol is 500-3000 Da;

[0018] The diisocyanate is one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate and 2,2,4-trimethylhexane diisocyanate.

[0019] The present invention also provides a method for preparing the thermoplastic polyurethane described in the above technical solution, comprising the following steps:

[0020] Mixing polyglycol, diisocyanate, a first solvent and a first organic metal catalyst to carry out polymerization reaction to obtain a prepolymer solution;

[0021] A chain extender is added into the prepolymer solution to carry out a chain extension reaction to obtain the thermoplastic polyurethane.

[0022] Preferably, the molar ratio of the polyglycol to diisocyanate is 0.33 to 0.67:1;

[0023] The polyglycol is one or more of polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, polyethylene glycol-propylene glycol, polyhexanediol adipate-1,6-diol, polyneopentyl glycol adipate diol and polybutanediol adipate-1,4-diol; the molecular weight of the polyglycol is 500-3000 Da;

[0024] The diisocyanate is one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate and 2,2,4-trimethylhexane diisocyanate.

[0025] Preferably, the molar ratio of the chain extender to the diisocyanate is 0.67 to 0.33:1;

[0026] The chain extender includes a diol containing a 2-ureido-4-pyrimidone group and a diol containing a five-membered aromatic heterocyclic group;

[0027] The molar ratio of the diol containing 2-urea-4-pyrimidone group to the diol containing five-membered aromatic heterocyclic group in the chain extender is 0.1:0.9 to 0.9:0.1.

[0028] Preferably, the diol containing a 2-urea-4-pyrimidinone group has a structure of Formula 3:

[0029]

[0030] In formula 3, R4 is an alkyl group or hydrogen, R5 is an alkylene group, a cycloalkylene group or an aralkylene group, and R6 is an alkyl group or hydrogen;

[0031] The diol containing a five-membered aromatic heterocyclic group has a structure of Formula 4:

[0032]

[0033] In formula 4, m is a natural number of 1 to 6, and X is oxygen or sulfur.

[0034] Preferably, the first organic metal catalyst comprises one or more of an organic tin metal catalyst and an organic bismuth metal catalyst;

[0035] The first solvent includes one or more of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

[0036] Preferably, the method for preparing the diol containing a 2-ureido-4-pyrimidone group comprises the following steps:

[0037] Mixing 2-amino-6-alkyl (H)-4-pyrimidinone, a second diisocyanate, a second organic metal catalyst and a second solvent, and performing a first addition reaction to obtain an isocyanate-2-urea-6-alkyl (H)-4-pyrimidinone;

[0038] The isocyanate-2-urea-6-alkyl (H)-4-pyrimidone, 2-amino-2-alkyl (H)-1,3-propanediol and a third solvent are mixed and subjected to a second addition reaction to obtain the diol containing a 2-urea-4-pyrimidone group.

[0039] Preferably, the 2-amino-6-alkyl (H)-4-pyrimidinone is 2-amino-6-1(H)-4-pyrimidinone, 2-amino-6-methyl-4-pyrimidinone, 2-amino-6-ethyl-4-pyrimidinone, 2-amino-6-propyl-4-pyrimidinone or 2-amino-6-isopropyl-4-pyrimidinone;

[0040] The second diisocyanate is hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate or 2,2,4-trimethylhexane diisocyanate;

[0041] The second organic metal catalyst is one or more of an organic tin metal catalyst and an organic bismuth metal catalyst;

[0042] The second solvent is tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide;

[0043] The third solvent is tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide;

[0044] The 2-amino-2-alkyl (H)-1,3-propanediol is 2-amino-2-1(H)-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol or 2-amino-2-ethyl-1,3-propanediol.

[0045] The present invention also provides the use of the thermoplastic polyurethane described in the above technical solution or the thermoplastic polyurethane prepared by the thermoplastic polyurethane preparation method in hot melt adhesive.

[0046] The present invention provides a thermoplastic polyurethane, wherein the thermoplastic polyurethane has a structure shown in Formula 1: In Formula 1, n is a natural number of 1 to 100; R1 is an alkylene group, a cycloalkylene group or an aralkylene group; and R2 has a structure shown in Formula 2:

[0047]

[0048] In Formula 2, m is a natural number of 1 to 6; R3 is an alkylene group, a cycloalkylene group or an aralkylene group; R4 is an alkyl group or hydrogen; R5 is an alkylene group, a cycloalkylene group or an aralkylene group; R6 is an alkyl group or hydrogen; X is oxygen or sulfur; In Formula 2, It represents the repeating unit of the reaction product obtained by the polycondensation reaction of polydiol and diisocyanate.

[0049] The present invention introduces a 2-urea-4-pyrimidone group structure (as shown in Formula 5) and a five-membered aromatic heterocyclic group structure (as shown in Formula 6) in the molecular chain. These two structures, as non-covalent interaction units, can improve the bonding strength of the polyurethane hot melt adhesive. The ether group / ester group, carbamate group, urea group, aromatic heterocyclic ring and pyrimidone group in the molecular chain can form a large number of hydrogen bonds. Hydrogen bonds, as thermally dynamic reversible non-covalent bonds, can achieve rapid dissociation and reconstruction with temperature changes. Therefore, the introduction of high-density strong hydrogen bond groups in the present invention is conducive to improving the bonding strength of the hot melt adhesive and reducing the complexity of the operating conditions of the polyurethane when in use. Among the many types of hydrogen bonds, urea hydrogen bonds have stronger interactions than other hydrogen bonds. The present invention adopts a 2-urea-4-pyrimidone structure containing a urea group, which can greatly enhance the hydrogen bond force in the polyurethane. In addition, the introduction of a five-membered aromatic ring heterocyclic structure can significantly improve the rigidity of the polyurethane hot melt adhesive polymer chain and can provide a certain bonding strength. The synergistic effect of the 2-urea-4-pyrimidone group and the five-membered aromatic heterocyclic group structure makes the thermoplastic polyurethane hot melt adhesive prepared by the present invention have the advantages of mild use conditions, high bonding strength to various substrates (metal, polycarbonate resin, epoxy resin, etc.), reusability and tolerance to extreme environments.

[0050] The results of the examples of the present invention show that the bonding strength of the polyurethane hot melt adhesive prepared by the present invention to the steel plate can reach 12.63 MPa, which is much higher than the bonding strength of the polyurethane hot melt adhesive disclosed in the prior art.

[0051] The present invention also provides a method for preparing the thermoplastic polyurethane described in the above technical solution, comprising the following steps: mixing polyglycol, diisocyanate, a first solvent and a first organic metal catalyst, performing a polymerization reaction, and obtaining a prepolymer solution; adding a chain extender to the prepolymer solution, performing a chain extension reaction, and obtaining the thermoplastic polyurethane. The preparation steps provided by the present invention are simple and easy to carry out industrial production.

[0052] The present invention also provides the use of the thermoplastic polyurethane or the thermoplastic polyurethane prepared by the preparation method in hot melt adhesive. The thermoplastic polyurethane provided by the present invention can achieve high-strength bonding to a variety of substrates (including metals, polycarbonate resins, epoxy resins, etc.) under mild operating conditions, and can be reused. The thermoplastic polyurethane hot melt adhesive provided by the present invention has excellent bonding effect in extreme environments. After the steel plate bonded by it is placed at an extremely low temperature of -196°C for 24 hours, the bonding strength can still be maintained above 8MPa after returning to room temperature, and it has tolerance to extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a graph of the lap shear strength of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 bonded to steel plates under different heating temperature conditions;

[0054] Figure 2 This is a graph of the lap shear strength of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 bonded to the steel plate under different heating time conditions;

[0055] Figure 3 This is a graph of the lap shear strength of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 after repeated recycling;

[0056] Figure 4 This is a physical picture of a steel plate bonded with thermoplastic polyurethane hot melt adhesive prepared in Example 6 and subjected to a load of 5 kg after being immersed in different liquids for 24 hours;

[0057] Figure 5 This is a graph of the lap shear strength of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 when placed in different temperature environments for different times;

[0058] Figure 6 This is a graph of the lap shear strength of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 when immersed in a -196°C liquid nitrogen environment for different times;

[0059] Figure 7 This is a real picture showing that the steel plate bonded with the thermoplastic polyurethane hot melt adhesive prepared in Example 6 can withstand a load of 5 kg after being immersed in a -196°C liquid nitrogen environment for 24 hours. DETAILED DESCRIPTION

[0060] The present invention provides a thermoplastic polyurethane, wherein the thermoplastic polyurethane has a structure shown in Formula 1:

[0061]

[0062] In formula 1, n is a natural number ranging from 1 to 100;

[0063] R1 is an alkylene group, a cycloalkylene group or an aralkylene group;

[0064] R2 has the structure shown in Formula 2:

[0065]

[0066] In formula 2, m is a natural number of 1 to 6; R3 is an alkylene group, a cycloalkylene group or an aralkylene group; R4 is an alkyl group or hydrogen; R5 is an alkylene group, a cycloalkylene group or an aralkylene group; R6 is an alkyl group or hydrogen; X is oxygen or sulfur;

[0067] In formula 2, It represents the repeating unit of the reaction product obtained by the polycondensation reaction of polydiol and diisocyanate.

[0068] In the present invention, unless otherwise specified, the raw materials used in the present invention are preferably commercially available products.

[0069] In the present invention, the molecular structure of the thermoplastic polyurethane preferably includes a main chain and a side chain.

[0070] In the present invention, the main chain preferably includes a five-membered aromatic heterocyclic group, and the five-membered aromatic heterocyclic group preferably has a structure shown in Formula 6:

[0071] In the present invention, m in Formula 6 is a natural number of 1 to 6, preferably a natural number of 1 to 5. In the present invention, X in Formula 6 is oxygen or sulfur.

[0072] In the present invention, the main chain Represents the repeating unit of the reaction product obtained after the polycondensation reaction of polyglycol and diisocyanate. In the present invention, the polyglycol is preferably one or more of polyethylene oxide glycol, polyoxypropylene glycol, polytetramethylene ether glycol, polyethylene oxide-propylene oxide glycol, polyadipate-1,6-hexanediol ester glycol, polyadipate-neopentyl glycol ester glycol and polyadipate-1,4-butanediol ester glycol. In the present invention, the molecular weight of the polyglycol is preferably 500 to 3000Da. In the present invention, the diisocyanate is preferably one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate and 2,2,4-trimethylhexane diisocyanate.

[0073] In the present invention, the side chain preferably contains a 2-urea-4-pyrimidinone group, and the 2-urea-4-pyrimidinone group preferably has a structure shown in Formula 5:

[0074] In the present invention, R4 in Formula 5 is an alkyl group or hydrogen. In the present invention, R5 in Formula 5 is an alkylene group, a cycloalkylene group or an aralkylene group, preferably an alkylene group or an aralkylene group. In the present invention, R6 in Formula 5 is an alkyl group or hydrogen.

[0075] In the present invention, the alkylene group in R1, R3 and R5 preferably independently includes an alkylene group having 1 to 6 carbon atoms. In the present invention, the cycloalkylene group in R1, R3 and R5 preferably independently includes a cycloalkylene group having 5 to 10 carbon atoms, more preferably a cycloalkylene group having 6 to 10 carbon atoms. In the present invention, the aralkylene group in R1, R3 and R5 preferably independently includes an aralkylene group having 6 to 10 carbon atoms. In the present invention, the alkylene group in R4 and R6 preferably independently includes an alkylene group having 1 to 3 carbon atoms.

[0076] The present invention also provides a method for preparing the thermoplastic polyurethane described in the above technical solution, comprising the following steps:

[0077] Mixing polyglycol, diisocyanate, a first solvent and a first organic metal catalyst to carry out polymerization reaction to obtain a prepolymer solution;

[0078] A chain extender is added into the prepolymer solution to carry out a chain extension reaction to obtain the thermoplastic polyurethane.

[0079] The present invention mixes polydiol, diisocyanate, a first solvent and a first organic metal catalyst, and performs polymerization reaction to obtain a prepolymer solution.

[0080] In the present invention, the polyglycol is preferably one or more of polyethylene oxide glycol, polyoxypropylene glycol, polytetramethylene ether glycol, polyethylene oxide-propylene oxide glycol, polyadipate-1,6-hexanediol ester glycol, polyadipate-neopentyl glycol ester glycol and polyadipate-1,4-butylene glycol ester glycol, more preferably polytetramethylene ether glycol or polyadipate-1,4-butylene glycol ester glycol. In the present invention, the molecular weight of the polyglycol is preferably 500-3000Da, more preferably 500-2000Da, and further preferably 1000-2000Da. The present invention uses polyglycol as a raw material, which can regulate the polyurethane soft segment structure, thereby improving the thermal stability and low temperature resistance of the polyurethane hot melt adhesive.

[0081] In the present invention, the diisocyanate is preferably one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate and 2,2,4-trimethylhexane diisocyanate, more preferably isophorone diisocyanate, hexamethylene diisocyanate or diphenylmethane diisocyanate. The present invention uses isophorone diisocyanate, hexamethylene diisocyanate or diphenylmethane diisocyanate, which has the advantages of high reactivity, easy regulation of polyurethane hard segment structure, and improved weather resistance and bonding strength of polyurethane hot melt adhesive.

[0082] In the present invention, the molar ratio of the polyglycol to the diisocyanate is preferably 0.33 to 0.67:1, more preferably 0.33 to 0.5:1.

[0083] In the present invention, the first organic metal catalyst preferably includes one or more of an organic tin metal catalyst and an organic bismuth metal catalyst, and is more preferably an organic bismuth metal catalyst. In a specific embodiment of the present invention, the organic bismuth metal catalyst is preferably MC-710, produced by Beijing Baiyuan Chemical. The organic bismuth metal catalyst used in the present invention has the advantages of high catalytic activity and few side reactions.

[0084] In the present invention, the first solvent preferably includes one or more of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide, and more preferably N,N-dimethylacetamide.

[0085] In the present invention, the polymerization reaction is preferably carried out under a nitrogen protective atmosphere. In the present invention, the temperature of the polymerization reaction is preferably 40 to 90° C., more preferably 70° C. In the present invention, the time of the polymerization reaction is preferably 0.5 to 8 hours, more preferably 2 hours. In the present invention, the polymerization reaction is preferably carried out in a three-necked flask. In the present invention, in the polymerization reaction, the mass of the first organic metal catalyst is preferably 0.01 to 0.1% of the mass of the diisocyanate, more preferably 0.03 to 0.1%.

[0086] After obtaining the prepolymer solution, the present invention adds a chain extender into the prepolymer solution to carry out a chain extension reaction to obtain the thermoplastic polyurethane.

[0087] In the present invention, the chain extender preferably includes a diol containing a 2-urea-4-pyrimidinone group and a diol containing a five-membered aromatic heterocyclic group. In the present invention, the diol containing a 2-urea-4-pyrimidinone group preferably has a structure shown in Formula 3: In the present invention, R4 in Formula 3 is preferably an alkyl group or hydrogen, R5 is preferably an alkylene group, a cycloalkylene group or an aralkylene group, and R6 is preferably an alkyl group or hydrogen. The present invention uses a diol containing a 2-ureido-4-pyrimidone group, which can provide a high-density strong hydrogen bonding group, which is beneficial to improving the bonding strength of the polyurethane hot melt adhesive.

[0088] In the present invention, the method for preparing the diol containing a 2-urea-4-pyrimidone group preferably comprises the following steps:

[0089] Mixing 2-amino-6-alkyl (H)-4-pyrimidinone, a second diisocyanate, a second organic metal catalyst and a second solvent, and performing a first addition reaction to obtain an isocyanate-2-urea-6-alkyl (H)-4-pyrimidinone;

[0090] The isocyanate-2-urea-6-alkyl (H)-4-pyrimidone, 2-amino-2-alkyl (H)-1,3-propanediol and a third solvent are mixed and subjected to a second addition reaction to obtain the diol containing a 2-urea-4-pyrimidone group.

[0091] The invention mixes 2-amino-6-alkyl (H)-4-pyrimidone, a second diisocyanate, a second organic metal catalyst and a second solvent, and performs a first addition reaction to obtain isocyanate-2-urea-6-alkyl (H)-4-pyrimidone.

[0092] In the present invention, the 2-amino-6-alkyl (H) -4-pyrimidone is preferably 2-amino-6-1 (H) -4-pyrimidone, 2-amino-6-methyl-4-pyrimidone, 2-amino-6-ethyl-4-pyrimidone, 2-amino-6-propyl-4-pyrimidone or 2-amino-6-isopropyl-4-pyrimidone. In the present invention, the second diisocyanate is preferably hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate or 2,2,4-trimethylhexane diisocyanate, more preferably diphenylmethane diisocyanate or hexamethylene diisocyanate. In the present invention, the second organic metal catalyst is preferably one or more of an organic tin metal catalyst and an organic bismuth metal catalyst, more preferably an organic bismuth metal catalyst. In the present invention, the second solvent is preferably tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide, more preferably dimethyl sulfoxide. In the present invention, the amount of the second solvent added is preferably 1 to 15 times the sum of the mass of the 2-amino-6-alkyl (H)-4-pyrimidone and the diisocyanate, more preferably 1 to 8 times.

[0093] In the present invention, the first addition reaction is preferably carried out in a three-necked flask. In the present invention, the first addition reaction is preferably carried out under a nitrogen protective atmosphere. In the present invention, the first addition reaction is preferably carried out under the condition of magnetic stirring. In the present invention, the temperature of the first addition reaction is preferably 30 to 150° C., more preferably 100° C. In the present invention, the time of the first addition reaction is preferably 5 to 15 hours, more preferably 10 hours. In the present invention, in the first addition reaction, the mass of the second organic metal catalyst is preferably 0.01 to 0.2% of the mass of the 2-amino-6-alkyl (H)-4-pyrimidinone.

[0094] After the first addition reaction is completed, the present invention preferably further comprises cooling the reaction liquid to room temperature and filtering to obtain a crude product. In the present invention, the obtained crude product is preferably washed and dried in sequence to obtain a white powder, i.e., isocyanate-2-urea-6-alkyl (H)-4-pyrimidone. In the present invention, the washing reagent is preferably n-hexane, and the number of washings is preferably ≥2 times. In the present invention, the drying is preferably carried out in an oven, and the drying temperature is preferably 40 to 80°C, more preferably 60°C; the drying time is preferably 12 to 48h, more preferably 24h.

[0095] After obtaining the isocyanate-2-urea-6-alkyl (H)-4-pyrimidone, the present invention mixes the isocyanate-2-urea-6-alkyl (H)-4-pyrimidone, 2-amino-2-alkyl (H)-1,3-propanediol and a third solvent to perform a second addition reaction to obtain a diol containing a 2-urea-4-pyrimidone group.

[0096] In the present invention, the 2-amino-2-alkyl (H)-1,3-propanediol is preferably 2-amino-2-1 (H)-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol or 2-amino-2-ethyl-1,3-propanediol, more preferably 2-amino-2-1 (H)-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol. In the present invention, the third solvent is preferably tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide, more preferably dimethyl sulfoxide. In the present invention, the amount of the third solvent added is preferably 5 to 15 times the sum of the mass of the isocyanate-2-urea-6-alkyl (H)-4-pyrimidone and the 2-amino-2-alkyl (H)-1,3-propanediol, more preferably 8 to 15 times. In the present invention, the molar ratio of the isocyanate-2-ureido-6-alkyl (H)-4-pyrimidone to the 2-amino-2-alkyl (H)-1,3-propanediol is preferably 1:1 to 1.5.

[0097] In the present invention, the second addition reaction is preferably carried out in a three-necked flask. In the present invention, the second addition reaction is preferably carried out under a nitrogen atmosphere. In the present invention, the second addition reaction is preferably carried out under magnetic stirring. In the present invention, the temperature of the second addition reaction is preferably 30 to 80° C., more preferably 50° C. In the present invention, the time of the second addition reaction is preferably 5 to 15 hours, more preferably 10 hours.

[0098] After the second addition reaction is completed, the present invention preferably filters the reaction liquid while hot to remove insoluble matter. In the present invention, it is preferred to add a precipitant to the filtered reaction liquid, precipitate and filter to obtain a white precipitate, and dry the white precipitate to obtain the diol containing 2-urea-4-pyrimidone group. In the present invention, the precipitant is preferably one or more of petroleum ether, n-hexane, cyclohexane, ethyl acetate, acetone, ether and acetonitrile. In the present invention, the filtration is performed according to a conventional filtration method. In the present invention, the drying temperature is preferably 40 to 80°C, more preferably 50°C; the drying time is preferably 12 to 48h, more preferably 24h; the drying is preferably carried out in an oven.

[0099] In the present invention, the diol containing a five-membered aromatic heterocyclic group preferably has a structure shown in Formula 4:

[0100]

[0101] In the present invention, m in Formula 4 is preferably a natural number of 1 to 6. In the present invention, X in Formula 4 is preferably oxygen or sulfur. In the present invention, when X in Formula 4 is oxygen, the five-membered aromatic heterocyclic ring is a furan ring; when X in Formula 4 is sulfur, the five-membered aromatic heterocyclic ring is a thiophene ring. In a specific embodiment of the present invention, the chain extender of the diol containing a five-membered aromatic heterocyclic group preferably includes furan dimethanol. The present invention uses a diol containing a five-membered aromatic heterocyclic group as a chain extender, which has the advantages of increasing the rigidity of the polymer chain and increasing the bonding strength.

[0102] In the present invention, the molar ratio of the chain extender to the diisocyanate is preferably 0.67 to 0.33: 1, more preferably 0.5 to 0.33: 1. In the present invention, the molar ratio of the diol containing a 2-ureido-4-pyrimidone group to the diol containing a five-membered aromatic heterocyclic group in the chain extender is preferably 0.1: 0.9 to 0.9: 0.1, more preferably 0.1: 0.9 to 0.8: 0.2.

[0103] In the present invention, the chain extension reaction is preferably carried out under a nitrogen protective atmosphere. In the present invention, the temperature of the chain extension reaction is preferably 40 to 90° C., more preferably 70° C. In the present invention, the time of the chain extension reaction is preferably 3 to 32 hours, more preferably 20 hours. In the present invention, the chain extension reaction is preferably carried out in a three-necked flask. In the present invention, the solid content of the thermoplastic polyurethane in the reaction liquid obtained after the chain extension reaction is preferably 15 to 40wt%.

[0104] After the chain extension reaction, the present invention preferably further comprises drying the obtained polymer solution, and after removing the solvent, the thermoplastic polyurethane is obtained. In the present invention, the drying method is preferably vacuum drying, and the vacuum drying is preferably carried out in a vacuum oven. In the present invention, the temperature of the vacuum drying is preferably 40 to 90° C., more preferably 60° C., and the time is preferably 24 to 48 hours, more preferably 30 hours.

[0105] The present invention also provides the use of the thermoplastic polyurethane described in the above technical solution or the thermoplastic polyurethane prepared by the thermoplastic polyurethane preparation method described in the above technical solution in hot melt adhesive.

[0106] The technical solution of the present invention is further described below through specific implementation methods. Those skilled in the art should understand that the embodiments are only used to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0107] Example 1

[0108] Add 20.0g of polytetramethylene ether glycol (PTMEG1000, molecular weight 1000Da, BASF Chemical), 6.67g of isophorone diisocyanate, 69.56g of N,N-dimethylacetamide and 4.0mg of bismuth catalyst (MC-710, Beijing Baiyuan Chemical) to a dry three-necked flask, stir evenly, and polymerize for 2h under nitrogen protection at 70℃ to obtain a prepolymer solution. Then add 2.53g of diol chain extender A containing 2-urea-4-pyrimidone group and 0.61g of diol chain extender furan dimethanol containing furan ring group (Shanghai Bid Pharmaceutical) to the above prepolymer solution, stir evenly, and carry out chain extension reaction for 20h under nitrogen protection at 70℃ to obtain a polymer solution. The obtained polymer solution was dried in a vacuum oven at 60℃ for 30h to remove the solvent, and a thermoplastic polyurethane hot melt adhesive was obtained.

[0109] The thermoplastic polyurethane prepared in Example 1 has a structure of Formula 7:

[0110]

[0111] In Formula 7, R1 is trimethylcyclohexyl, n=14; R2 has the structure of Formula 8:

[0112]

[0113] In formula 8, It represents the repeating unit of the reaction product obtained by the condensation reaction of polytetramethylene ether glycol (molecular weight 1000Da) and isophorone diisocyanate; m=1, R3 is trimethylcyclohexyl, R4 is methyl, R5 is diphenylmethane, R6 is methyl, and X is oxygen.

[0114] The preparation method of the diol chain extender A containing a 2-urea-4-pyrimidone group described in Example 1 comprises the following steps:

[0115] (1) 5.02 g of 2-amino-6-methyl-4-pyrimidinone, 200.0 g of diphenylmethane diisocyanate, 307.5 g of dimethyl sulfoxide and 5.0 mg of bismuth catalyst were fully mixed in a dry three-necked flask, and a first addition reaction was carried out under a nitrogen atmosphere and magnetic stirring. The temperature of the first addition reaction was 100° C. and the reaction time was 10 h. After the first addition reaction was completed, the reaction liquid was cooled to room temperature, filtered to obtain a crude product, and the crude product was washed twice with 100 mL of n-hexane, and further vacuum dried at 60° C. for 24 h to obtain 13.50 g of white powder isocyanate-benzylphenyl-2-ureido-6-methyl-4-pyrimidinone.

[0116] (2) 7.51 g of isocyanate-benzylphenyl-2-ureido-6-methyl-4-pyrimidone, 3.02 g of 2-amino-2-methyl-1,3-propanediol and 100 g of dimethyl sulfoxide were added to a three-necked flask. Under nitrogen protection and magnetic stirring, the temperature was raised to 50° C. to carry out a second addition reaction for 10 h. After the second addition reaction was completed, the reaction liquid was filtered while hot, and the filtrate was precipitated in anhydrous ether to obtain a white solid. The product was filtered and further dried in a vacuum drying oven at 50° C. for 24 h to obtain 6.72 g of a diol chain extender A containing a 2-ureido-4-pyrimidone group, whose structure is shown in Formula 9:

[0117]

[0118] In formula 9, R4 is a methyl group, R5 is a diphenylmethane group, and R6 is a methyl group.

[0119] H NMR spectrum of diol chain extender A containing 2-ureido-4-pyrimidone group: 1H NMR (400MHz, DMSO-d6): δ11.48(s,1H),9.67(s,1H),7.45(s,1H),7.40(d,4H),6.96(d,4H),6.16(t,J=5.5Hz,1H),5.77(s,1H), 5.63(s,1H),5.10(t,J=5.5Hz,2H),3.83(s,2H),3.41(dd,J=10.6,5.3Hz,2H),2.94(q,J=6.5Hz,2H),2.10(s,3H),1.08(s,3H).

[0120] Example 2

[0121] The difference from Example 1 is that 2.02 g of diol chain extender B containing 2-ureido-4-pyrimidone group is used instead of diol chain extender A.

[0122] The thermoplastic polyurethane prepared in Example 2 has a structure of Formula 10:

[0123]

[0124] In formula 10, R1 is trimethylcyclohexyl, n=13, and R2 has the structure of formula 11:

[0125]

[0126] In formula 11, It represents the repeating unit of the reaction product obtained by the condensation reaction of polytetramethylene ether glycol (molecular weight 1000Da) and isophorone diisocyanate; m=1, R3 is trimethylcyclohexyl, R4 is methyl, R5 is hexamethylene, R6 is methyl, and X is oxygen.

[0127] The preparation method of the diol chain extender B containing a 2-urea-4-pyrimidone group described in Example 2 comprises the following steps:

[0128] (1) 4.96 g of 2-amino-6-methyl-4-pyrimidinone, 50.2 g of hexamethylene diisocyanate, 110.0 g of dimethyl sulfoxide and 5.0 mg of bismuth catalyst were fully mixed in a dry three-necked flask, and a first addition reaction was carried out under a nitrogen atmosphere and magnetic stirring. The temperature of the first addition reaction was 100° C. and the reaction time was 10 h. After the first addition reaction was completed, the reaction liquid was cooled to room temperature and filtered to obtain a crude product. The crude product was washed twice with 100 mL of n-hexane and further dried in vacuum at 60° C. for 24 h to obtain 10.67 g of white powder isocyanate-hexamethylene-2-urea-6-methyl-4-pyrimidinone.

[0129] (2) 6.02 g of isocyanate-hexamethylene-2-urea-6-methyl-4-pyrimidinone, 3.03 g of 2-amino-2-methyl-1,3-propanediol and 100 g of dimethyl sulfoxide were added to a three-necked flask, and the temperature was raised to 50° C. under nitrogen protection and magnetic stirring to carry out a second addition reaction for 10 h. After the second addition reaction was completed, the reaction liquid was filtered while hot, and the filtrate was precipitated in anhydrous ether to obtain a white solid. The product was filtered and further dried in a vacuum drying oven at 50° C. for 24 h to obtain 5.53 g of a diol group chain extender B containing a 2-urea-4-pyrimidinone group, whose structure is shown in Formula 12:

[0130]

[0131] In formula 12, R4 is a methyl group, R5 is a hexamethylene group, and R6 is a methyl group.

[0132] H NMR spectrum of diol chain extender B containing 2-ureido-4-pyrimidone group: 1 H NMR (400MHz, DMSO-d6): δ11.48(s,1H),9.67(s,1H),7.40(s,1H),6.16(t,J=5.5Hz,1H),5.77(s,1H),5.63(s,1H),5.10(t,J=5.5Hz,2H),3.41( dd,J=10.6,5.3Hz,2H),3.32(dd,J=10.5,5.2Hz,2H),3.13(q,J=6.6Hz,2H),2.94(q,J=6.5Hz,2H),2.10(s,3H),1.49-1.24(m,8H),1.08(s,3H).

[0133] Example 3

[0134] 20.00g of polytetramethylene ether glycol (PTMEG1000, molecular weight 1000Da, BASF Chemical), 8.89g of isophorone diisocyanate, 79.78g of N,N-dimethylacetamide and 5.0mg of bismuth catalyst (MC-710, Beijing Baiyuan Chemical) were added to a dry three-necked flask, stirred evenly, and polymerized for 2h under nitrogen protection at 70°C to obtain a prepolymer solution. Then 3.98g of diol chain extender B containing 2-urea-4-pyrimidone group and 1.28g of diol chain extender furan dimethanol containing furan ring group (Shanghai Bid Pharmaceutical) were added to the above prepolymer solution, stirred evenly, and chain extension reaction was carried out for 20h under nitrogen protection at 70°C to obtain a polymer solution.

[0135] The obtained polymer solution was dried in a vacuum oven at 60° C. for 30 h to remove the solvent, thereby obtaining a thermoplastic polyurethane hot melt adhesive.

[0136] The thermoplastic polyurethane prepared in Example 3 has the following structure:

[0137]

[0138] In Formula 13, R1 is trimethylcyclohexyl, n=14; R2 has the structure of Formula 14:

[0139]

[0140] In formula 14, It represents the repeating unit of the reaction product obtained by the condensation reaction of polytetramethylene ether glycol (molecular weight 1000Da) and isophorone diisocyanate; m=1, R3 is trimethylcyclohexyl, R4 is methyl, R5 is hexamethylene; R6 is methyl, and X is oxygen.

[0141] The preparation method of the diol chain extender B containing 2-ureido-4-pyrimidone group in Example 3 is the same as that in Example 2.

[0142] Example 4

[0143] The difference from Example 3 is that poly(1,4-butylene adipate) glycol (XCP-1044, molecular weight 1000Da, Asahikawa Chemical) is used instead of polytetramethylene ether glycol to obtain a thermoplastic polyurethane hot melt adhesive.

[0144] The thermoplastic polyurethane prepared in Example 4 has the structure of Formula 15:

[0145]

[0146] In Formula 15, R1 is trimethylcyclohexyl, n=13; R2 has the structure of Formula 16:

[0147]

[0148] In formula 16, It represents the repeating unit of the reaction product obtained by the condensation reaction of polybutylene adipate diol (molecular weight 1000Da) and isophorone diisocyanate; m=1, R3 is trimethylcyclohexyl, R4 is methyl, R5 is hexamethylene, R6 is methyl, and X is oxygen.

[0149] The preparation method of the diol chain extender B containing 2-urea-4-pyrimidone group in Example 4 is the same as that in Example 2.

[0150] Example 5

[0151] The difference from Example 3 is that 10.03 g of diphenylmethane diisocyanate is used instead of isophorone diisocyanate, the mass of N,N-dimethylacetamide is 82.41 g, and a thermoplastic polyurethane hot melt adhesive is obtained.

[0152] The thermoplastic polyurethane prepared in Example 5 has the structure of Formula 17:

[0153]

[0154] In Formula 17, R1 is diphenylmethane, n=13; R2 has the structure of Formula 18:

[0155]

[0156] In formula 18, It represents the repeating unit of the reaction product obtained by the condensation reaction of polytetramethylene ether glycol (molecular weight 1000Da) and diphenylmethane diisocyanate; m=1, R3 is diphenylmethane, R4 is methyl, R5 is hexamethylene, R6 is methyl, and X is oxygen.

[0157] The preparation method of the diol chain extender B containing 2-ureido-4-pyrimidone group in Example 5 is the same as that in Example 2.

[0158] Example 6

[0159] The difference from Example 3 is that the amount of diol chain extender B containing a 2-ureido-4-pyrimidone group is 6.38 g, the amount of furandimethanol containing a furan ring group is 0.52 g, and the mass of N,N-dimethylacetamide is 83.51 g, thereby obtaining a thermoplastic polyurethane hot melt adhesive.

[0160] The thermoplastic polyurethane prepared in Example 6 has the structure of Formula 19:

[0161]

[0162] In Formula 19, R1 is trimethylcyclohexyl, n=14; R2 has the structure of Formula 20:

[0163]

[0164] In formula 20, It represents the repeating unit of the reaction product obtained by the condensation reaction of polytetramethylene ether glycol (molecular weight 1000Da) and isophorone diisocyanate; m=1, R3 is trimethylcyclohexyl, R4 is methyl, R5 is hexamethylene, R6 is methyl, and X is oxygen.

[0165] The preparation method of the diol chain extender B containing 2-ureido-4-pyrimidone group in Example 6 is the same as that in Example 2.

[0166] Example 7

[0167] The difference from Example 6 is that 40.00 g of polytetramethylene ether glycol (PTMEG2000, molecular weight 2000 Da, BASF Chemical) is used instead of polytetramethylene ether glycol (molecular weight 1000 Da), the mass of N,N-dimethylacetamide is 130.32 g, and a thermoplastic polyurethane hot melt adhesive is obtained.

[0168] The thermoplastic polyurethane prepared in Example 7 has the following structure:

[0169]

[0170] In formula 21, R1 is trimethylcyclohexyl, n=13; R2 has the structure of formula 22:

[0171]

[0172] In formula 22, It represents the repeating unit of the reaction product obtained by the condensation reaction of polytetramethylene ether glycol (molecular weight 2000Da) and isophorone diisocyanate; m=1, R3 is trimethylcyclohexyl, R4 is methyl, R5 is hexamethylene, R6 is methyl, and X is oxygen.

[0173] The preparation method of the diol chain extender B containing 2-ureido-4-pyrimidone group in Example 7 is the same as that in Example 2.

[0174] Example 8

[0175] The difference from Example 6 is that 0.58 g of thiophene-2,5-diyldimethanol (Jilin Zhongkeshen) which is a diol chain extender containing thiophene groups is used instead of furandimethanol which is a diol chain extender containing furan ring groups to obtain a thermoplastic polyurethane hot melt adhesive.

[0176] The thermoplastic polyurethane prepared in Example 8 has the structure of Formula 25:

[0177]

[0178] In Formula 25, R1 is trimethylcyclohexyl, n=13; R2 has the structure of Formula 26:

[0179]

[0180] In formula 26, It represents the repeating unit of the reaction product obtained by the condensation reaction of polytetramethylene ether glycol (molecular weight 1000Da) and isophorone diisocyanate; m=1, R3 is trimethylcyclohexyl, R4 is methyl, R5 is hexamethylene; R6 is methyl, and X is sulfur.

[0181] The preparation method of the diol chain extender B containing 2-ureido-4-pyrimidone group in Example 8 is the same as that in Example 2.

[0182] Comparative Example 1

[0183] The difference from Example 3 is that 1.80 g of 1,4-butanediol (Tianjin Bohai Chemical Reagent Company) is used instead of the diol chain extender B containing a 2-ureido-4-pyrimidone group and the diol chain extender furandimethanol containing a furan ring group to obtain a thermoplastic polyurethane hot melt adhesive.

[0184] The thermoplastic polyurethane prepared in the comparative example has the structure of Formula 27:

[0185]

[0186] In Formula 27, R1 is trimethylcyclohexyl, n=15; R2 has the structure of Formula 28:

[0187]

[0188] In formula 28, It represents the repeating unit of the reaction product obtained by the condensation reaction of polytetramethylene ether glycol (molecular weight 1000Da) and isophorone diisocyanate; R3 is trimethylcyclohexane and R7 is n-butyl.

[0189] The properties of the polyurethane hot melt adhesives prepared in Examples 1 to 8 and Comparative Example 1 were tested. The weight average molecular weight and molecular weight dispersity index of the polyurethane were detected by gel permeation chromatography (Waters 600E), wherein the reference sample was polystyrene and the mobile phase was N,N-dimethylformamide. The test results are shown in Table 1.

[0190] A universal tensile testing machine (Shanghai Sonton, WDW-5) was used to test the mechanical properties of thermoplastic polyurethane, including tensile strength and elongation at break. The test results are shown in Table 1.

[0191] The thermal decomposition temperature of polyurethane was measured by a thermogravimetric analyzer (TG209, NETZSCH, Germany). The test results are shown in Table 1.

[0192] Table 1 Test results of thermoplastic polyurethane hot melt adhesives prepared in Examples 1 to 8 and Comparative Example 1

[0193]

[0194] It can be seen from Table 1 that the molecular weight of the thermoplastic polyurethane prepared in Examples 1 to 8 of the present invention is 3.1×10 4 ~4.3×10 4Da range, the molecular weight dispersity index is in the range of 1.73 to 1.92, and the molecular weight distribution is relatively narrow; Examples 1 to 8 of the present invention use chain extenders containing 2-urea-4-pyrimidone group structure and five-membered aromatic heterocyclic group structure to synthesize polyurethane hot melt adhesive, while Comparative Example 1 uses ordinary chain extender 1,4-butanediol to synthesize polyurethane hot melt adhesive. The tensile strength and elongation at break of the polyurethane hot melt adhesive obtained in Examples 1 to 8 of the present application are higher than those in Comparative Example 1, indicating that the present invention uses 2-urea-4-pyrimidone group structure and five-membered aromatic heterocyclic group structure as chain extenders to improve the mechanical properties of polyurethane hot melt adhesive, and the excellent mechanical strength helps the polyurethane hot melt adhesive to exert higher bonding performance. In addition, the thermal decomposition temperature of the polyurethane hot melt adhesive obtained in Examples 1 to 8 is also higher than the thermal decomposition temperature of the polyurethane hot melt adhesive obtained in Comparative Example 1, indicating that the polyurethane hot melt adhesive containing 2-urea-4-pyrimidone group structure and five-membered aromatic heterocyclic group structure in the present invention has higher thermal stability.

[0195] Test Example 1

[0196] The polyurethane hot melt adhesive prepared in Examples 1 to 8 and Comparative Example 1 was used to bond different substrates, including steel, copper, aluminum, epoxy resin and polycarbonate resin, and the size of the substrate was 80 mm × 25 mm × 1.5 mm. After the polyurethane hot melt adhesive was cured, a shear strength test was performed, and the specific operation included: cutting the obtained polyurethane film into a rectangle of 25 mm × 12.5 mm × 200 μm and placing it on two substrates of the same size, heating it at 120°C for 10 min, taking out the sample and cooling it at room temperature for 15 min to obtain a test sample. Then a universal tensile testing machine (Shanghai Sonton, WDW-5) was used to test the lap shear strength of the substrate bonded by the polyurethane hot melt adhesive, and the test results are shown in Table 2.

[0197] Table 2 Adhesiveness of thermoplastic polyurethane hot melt adhesives prepared in Examples 1 to 8 and Comparative Example 1

[0198]

[0199] It can be seen from Table 2 that the bonding strengths of the thermoplastic polyurethane hot melt adhesives obtained in Examples 1 to 8 to different substrates are higher than the bonding strength of the thermoplastic polyurethane hot melt adhesive obtained in Comparative Example 1, and the thermoplastic polyurethane hot melt adhesive obtained in Example 6 has the best comprehensive bonding performance, and the bonding strength to the steel plate can reach 12.63 MPa.

[0200] Test Example 2

[0201] A plurality of substrate steels with a size of 80 mm × 25 mm × 1.5 mm were prepared, and the polyurethane film obtained in Example 6 was cut into a rectangle of 25 mm × 12.5 mm × 200 μm and placed on two substrate steels of the same size. The heating temperatures for heating and melting the polyurethane film were 80° C., 100° C., 120° C. and 140° C., respectively. After the heating time was 10 min, the bonded test samples were cooled at room temperature for 15 min to obtain test samples under different heating temperature conditions. The lap shear strength of the test samples was tested using a universal tensile testing machine (Shanghai Sonton, WDW-5). The test results are shown in Tables 3 and 4. Figure 1 shown.

[0202] Table 3 Lap shear strength of test example 2 under different heating temperature conditions

[0203] Heating temperature, °C Lap shear strength, MPa 80 2.10 100 5.60 120 12.63 140 12.58

[0204] Figure 1 The lap shear strength diagram of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 bonded to the steel plate under different heating temperature conditions. Figure 1 It can be seen from Table 3 that the thermoplastic polyurethane hot melt adhesive prepared in Example 6 has the highest lap shear strength when the adhesive heating temperature is 120°C.

[0205] Test Example 3

[0206] The difference from Test Example 2 is that the heating temperature is 120° C., and the heating time is 5 min, 10 min, 15 min and 20 min, respectively, to obtain test samples under different heating time conditions.

[0207] The lap shear strength of the test samples was tested using a universal tensile testing machine. The test results are shown in Table 4 and Figure 2 shown.

[0208] Table 4 Lap shear strength of test example 3 under different heating time conditions

[0209] Heating time, min Lap shear strength, MPa 5 5.44 10 12.63 15 12.58 20 12.75

[0210] Figure 2 The lap shear strength diagram of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 bonded to the steel plate under different heating time conditions. Figure 2 It can be seen from Table 4 that the thermoplastic polyurethane hot melt adhesive prepared in Example 6 can achieve a bonding strength of 12.63 MPa when the heating time for application is 10 min. Too long a heating time means a long operation time. The thermoplastic polyurethane hot melt adhesive prepared by the present invention can achieve excellent bonding effect after applying for 10 min. Compared with the harsh application conditions of the existing hot melt adhesive, the application conditions of the thermoplastic polyurethane hot melt adhesive obtained by the present invention are milder and the use conditions are more convenient.

[0211] Test Example 4

[0212] Prepare several pieces of substrate steel with a size of 80mm×25mm×1.5mm, cut the polyurethane film obtained in Example 6 into a rectangle of 25mm×12.5mm×200μm, and place it on two pieces of substrate steel of the same size. The heating temperature of the melted polyurethane film is 120℃, and the heating time is 10min. The bonded test sample is cooled at room temperature for 15min to obtain the test sample. The lap shear strength of the test sample is tested using a universal tensile testing machine. The test sample after the lap shear strength test is heated to 120℃ again for 10min, and then bonded again and cooled. The lap shear strength of the sample is tested again. This is repeated many times to verify the bonding properties of the thermoplastic polyurethane hot melt adhesive after repeated recycling. The test results are shown in Table 5 and Figure 3 shown.

[0213] Table 5 Lap shear strength after repeated use of test example 4

[0214] Repeated use times, times Lap shear strength, MPa 1 12.63 2 12.11 3 11.90 4 11.27 5 11.07

[0215] Figure 3 This is a graph showing the lap shear strength of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 after repeated use. Figure 3 It can be seen from Table 5 that the thermoplastic polyurethane hot melt adhesive obtained in Example 6 has good recyclability. After being used continuously for 5 times, it can still maintain 88% of the lap shear strength when it was used for the first time, indicating that the polyurethane hot melt adhesive prepared in the present invention has good repeated recyclability.

[0216] Test Example 5

[0217] Prepare multiple pieces of substrate steel with a size of 80mm×25mm×1.5mm, cut the polyurethane film obtained in Example 6 into a rectangle of 25mm×12.5mm×200μm, and place it on two pieces of substrate steel of the same size. The heating temperature for melting the polyurethane film is 120℃, and the heating time is 10min. The bonded test sample is cooled at room temperature for 15min to obtain the test sample. The obtained test sample is soaked in different liquids for 24h, taken out and wiped dry, and then the lap shear strength of the test sample is tested using a universal tensile testing machine. The different liquids include tap water, artificial seawater, pH=1 hydrochloric acid solution, pH=14 sodium hydroxide solution, and silicone oil to verify the adhesion of the thermoplastic polyurethane hot melt adhesive in different liquid environments. The test results are shown in Table 6 and Figure 4 shown.

[0218] Table 6 Lap shear strength of test example 5 in different liquid environments

[0219] Liquid type Lap shear strength, MPa water 11.72 Artificial seawater 11.08 pH=1 hydrochloric acid solution 8.85 pH = 14 sodium hydroxide solution 9.17 Silicone oil 10.10

[0220] Figure 4 The steel plates bonded with thermoplastic polyurethane hot melt adhesive prepared in Example 6 were immersed in different liquids for 24 hours and then subjected to a load of 5 kg. Figure 4 It can be seen from Table 6 that the steel plate bonded by the thermoplastic polyurethane hot melt adhesive obtained in Example 6 can still withstand a load of 5 kg after being immersed in different liquids for 24 hours, indicating that the thermoplastic polyurethane hot melt adhesive prepared by the present invention has good tolerance in different liquid environments, and the steel plate bonded by the thermoplastic polyurethane hot melt adhesive obtained in Example 6 can still achieve a bonding strength of more than 8 MPa after being immersed in different liquids for 24 hours, indicating that the polyurethane hot melt adhesive prepared by the present invention has the potential to be used in different liquid environments.

[0221] Test Example 6

[0222] Prepare several pieces of substrate steel with a size of 80mm×25mm×1.5mm, cut the polyurethane film obtained in Example 6 into a rectangle of 25mm×12.5mm×200μm, and place it on two substrate steels of the same size. The heating temperature for melting the polyurethane film is 120°C, and the heating time is 10min. Cool the bonded test samples at room temperature for 15min to obtain test samples.

[0223] The obtained test samples were placed in -30°C, 25°C and 60°C environments, and the lap shear strength of the test samples after being placed in different temperature environments for 1 day, 7 days, 14 days and 21 days was tested respectively to verify the lap shear strength of the thermoplastic polyurethane hot melt adhesive placed in different temperature environments for different times. The test results are shown in Tables 7 and Figure 5 shown.

[0224] Table 7 Lap shear strength of test example 6 placed in different temperature environments for different times

[0225]

[0226] Figure 5 The lap shear strength diagram of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 placed in different temperature environments for different time periods. Figure 5It can be seen from Table 7 that the steel plates bonded by the thermoplastic polyurethane hot melt adhesive prepared in Example 6 were placed in temperature environments of -30°C, 25°C and 60°C for 1 day, 7 days, 14 days and 21 days respectively, and then the lap shear strength of the test samples was tested after returning to room temperature, indicating that the thermoplastic polyurethane hot melt adhesive obtained in the present invention has good temperature tolerance. The steel plates bonded by the thermoplastic polyurethane hot melt adhesive obtained in Example 6 were placed in extreme ambient temperatures of -30°C and 60°C, and the lap shear strength after 21 days was not less than 88% of the maximum lap shear strength, which fully proves that the polyurethane hot melt adhesive prepared in the present invention has good tolerance to different ambient temperatures.

[0227] Test Example 7

[0228] Prepare several pieces of substrate steel with a size of 80mm×25mm×1.5mm, cut the polyurethane film obtained in Example 6 into a rectangle of 25mm×12.5mm×200μm, and place it on two substrate steels of the same size. The heating temperature for melting the polyurethane film is 120°C, and the heating time is 10min. Cool the bonded test samples at room temperature for 15min to obtain test samples.

[0229] The obtained test samples were placed in a liquid nitrogen environment at -196°C, and the lap shear strength of the test samples after being placed in the liquid nitrogen environment at -196°C for 12 hours and 24 hours was tested respectively to verify the lap shear strength of the thermoplastic polyurethane hot melt adhesive in an extreme environment. The test results are shown in Table 8. Figure 6 and Figure 7 shown.

[0230] Table 8 Lap shear strength of test example 7 immersed in -196℃ liquid nitrogen environment for different time periods

[0231] Time, h Lap shear strength, MPa 0 12.63 12 9.02 24 8.06

[0232] Figure 6 This is a graph of the lap shear strength of the thermoplastic polyurethane hot melt adhesive prepared in Example 6 when immersed in a -196°C liquid nitrogen environment for different times. Figure 7 This is a photo of the steel plate bonded with the thermoplastic polyurethane hot melt adhesive prepared in Example 6 being able to withstand a load of 5 kg after being immersed in a -196°C liquid nitrogen environment for 24 hours. Figure 6 , Figure 7It can be seen from Table 8 that the steel plates bonded by the thermoplastic polyurethane hot melt adhesive prepared in Example 6 were taken out after being immersed in a liquid nitrogen environment at -196°C for different periods of time, and then restored to room temperature to test the lap shear strength graph, which proves that the thermoplastic polyurethane hot melt adhesive obtained in the present invention has good extreme low temperature tolerance. The lap shear strength of the steel plates bonded by the thermoplastic polyurethane hot melt adhesive obtained in the present invention after being placed in a liquid nitrogen environment at -196°C for 24 hours can be maintained above 8MPa, which fully proves that the polyurethane hot melt adhesive prepared in the present invention has the potential to be used at extremely low temperatures.

[0233] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A thermoplastic polyurethane used as a hot melt adhesive, characterized in that: The thermoplastic polyurethane has a structure shown in Formula 1: In formula 1, n is a natural number ranging from 1 to 100; R1 is an alkylene group, a cycloalkylene group or an aralkylene group; R2 has the structure shown in Formula 2: In formula 2, m is a natural number of 1 to 6; R3 is an alkylene group, a cycloalkylene group or an aralkylene group; R4 is an alkyl group or hydrogen; R5 is an alkylene group, a cycloalkylene group or an aralkylene group; R6 is an alkyl group or hydrogen; X is oxygen or sulfur; In formula 2, It represents the repeating unit of the reaction product obtained by the polycondensation reaction of polydiol and diisocyanate; The polyglycol is one or more of polyethylene oxide glycol, polypropylene oxide glycol, polytetramethylene ether glycol, polyethylene oxide-propylene oxide glycol, polyhexanediol adipate-1,6-diol, polyneopentyl adipate glycol and polybutanediol adipate-1,4-diol; the molecular weight of the polyglycol is 500-3000 Da.

2. The thermoplastic polyurethane according to claim 1, characterized in that The alkylene groups in R1, R3 and R5 independently include alkylene groups having 1 to 6 carbon atoms; The cycloalkylene groups in R1, R3 and R5 independently include cycloalkylene groups having 5 to 10 carbon atoms; The aralkylene groups in R1, R3 and R5 independently include aralkylene groups having 6 to 10 carbon atoms; The alkyl groups in R4 and R6 independently include alkyl groups having 1 to 3 carbon atoms; The diisocyanate is one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate and 2,2,4-trimethylhexane diisocyanate.

3. The method for preparing thermoplastic polyurethane according to claim 1 or 2, characterized in that: The following steps are involved: Mixing polyglycol, diisocyanate, a first solvent and a first organic metal catalyst to carry out polymerization reaction to obtain a prepolymer solution; A chain extender is added into the prepolymer solution to carry out a chain extension reaction to obtain the thermoplastic polyurethane.

4. The preparation method according to claim 3, characterized in that: The molar ratio of the polyglycol to the diisocyanate is 0.33 to 0.67:1; The polyglycol is one or more of polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol, polyethylene glycol-propylene glycol, polyhexanediol adipate-1,6-diol, polyneopentyl glycol adipate diol and polybutanediol adipate-1,4-diol; the molecular weight of the polyglycol is 500-3000 Da; The diisocyanate is one or more of hexamethylene diisocyanate, isophorone diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate and 2,2,4-trimethylhexane diisocyanate.

5. The preparation method according to claim 3, characterized in that: The molar ratio of the chain extender to the diisocyanate is 0.67 to 0.33:1; The chain extender includes a diol containing a 2-ureido-4-pyrimidone group and a diol containing a five-membered aromatic heterocyclic group; The molar ratio of the diol containing 2-urea-4-pyrimidone group to the diol containing five-membered aromatic heterocyclic group in the chain extender is 0.1:0.9 to 0.9:0.

1.

6. The preparation method according to claim 5, characterized in that: The diol containing 2-urea-4-pyrimidinone group has the structure of formula 3: In formula 3, R4 is an alkyl group or hydrogen, R5 is an alkylene group, a cycloalkylene group or an aralkylene group, and R6 is an alkyl group or hydrogen; The diol containing a five-membered aromatic heterocyclic group has a structure of Formula 4: In formula 4, m is a natural number of 1 to 6, and X is oxygen or sulfur.

7. The preparation method according to claim 3, characterized in that: The first organic metal catalyst comprises one or more of an organic tin metal catalyst and an organic bismuth metal catalyst; The first solvent includes one or more of tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

8. The preparation method according to any one of claims 5 to 6, characterized in that: The method for preparing the diol containing a 2-urea-4-pyrimidone group comprises the following steps: Mixing 2-amino-6-alkyl (H)-4-pyrimidinone, a second diisocyanate, a second organic metal catalyst and a second solvent, and performing a first addition reaction to obtain an isocyanate-2-urea-6-alkyl (H)-4-pyrimidinone; The isocyanate-2-urea-6-alkyl (H)-4-pyrimidone, 2-amino-2-alkyl (H)-1,3-propanediol and a third solvent are mixed and subjected to a second addition reaction to obtain the diol containing a 2-urea-4-pyrimidone group.

9. The preparation method according to claim 8, characterized in that: The 2-amino-6-alkyl (H)-4-pyrimidone is 2-amino-6-1 (H)-4-pyrimidone, 2-amino-6-methyl-4-pyrimidone, 2-amino-6-ethyl-4-pyrimidone, 2-amino-6-propyl-4-pyrimidone or 2-amino-6-isopropyl-4-pyrimidone; The second diisocyanate is hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, toluene diisocyanate, p-phenylene diisocyanate, ethylphenyl diisocyanate, methylcyclohexyl diisocyanate or 2,2,4-trimethylhexane diisocyanate; The second organic metal catalyst is one or more of an organic tin metal catalyst and an organic bismuth metal catalyst; The second solvent is tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide; The third solvent is tetrahydrofuran, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone or dimethyl sulfoxide; The 2-amino-2-alkyl (H)-1,3-propanediol is 2-amino-2-1(H)-1,3-propanediol, 2-amino-2-methyl-1,3-propanediol or 2-amino-2-ethyl-1,3-propanediol.

10. Use of the thermoplastic polyurethane according to claim 1 or 2 or the thermoplastic polyurethane prepared by the preparation method according to any one of claims 3 to 9 in hot melt adhesives.

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