A flexible temperature-sensitive polycaprolactone polyol, and a preparation method and use thereof

Abstract

The application discloses a flexible temperature-sensitive polycaprolactone polyol and a preparation method and application thereof, and is prepared from epsilon-caprolactone and pentyl lactone as raw materials and a starter; the number average molecular weight of the polycaprolactone polyol is 2950-3930. The polycaprolactone polyol has the characteristics of not being solidified at low temperature, the crystallization temperature of an adhesive can be controlled through formula design of the polyol, the adhesive can maintain good bonding capacity at normal temperature, and the bonding performance can be significantly reduced at high temperature, so that a bonded device is convenient to disassemble.

Description

Technical Field

[0001] This invention relates to the field of temperature-sensitive adhesives for electronic packaging, and particularly to a room-temperature liquid polycaprolactone polyol and a temperature-sensitive polyurethane adhesive for temporary fixing and rework of electronic devices, as well as its preparation method. Background Technology

[0002] With the widespread adoption of intelligent electronic products and the development of flexible electronics technology, many devices require temporary bonding during processing and disassembly after completion. Furthermore, consumable equipment needs to be disassembled and reassembled after use. Traditional thermosetting epoxy adhesives, with their high hardness and high modulus, are no longer suitable for this scenario. From the perspective of assembling and disassembling electronic components, adhesives need to maintain high bonding strength at room temperature, and after equipment maintenance, they should be able to lose their adhesive strength through hot air baking or microwave heating, facilitating the non-destructive separation of components.

[0003] The process of achieving these functions is often less than ideal. To meet the required performance, the selected polyester resin needs a lower glass transition temperature and a higher molecular weight. Usually, to lower the glass transition temperature, a large amount of long-chain polymer needs to be added during resin synthesis, making the synthesis process more complex and the formulation difficult to adjust.

[0004] Polycaprolactone polyol is a linear polymer with a straight chain that forms repeating units through ring-opening of ε-caprolactone by an initiator under certain temperature and catalyst conditions. It possesses good flexibility and features a regular molecular chain and easy crystallization. Due to its crystallization ability, it is typically a solid at room temperature and difficult to process. Therefore, through process design, other monomers are added to the ends of the molecular chain to disrupt its regular structure. This allows for control of molecular weight and molecular chain composition, altering the crystallization temperature and reducing viscosity, enabling it to be fluid at room temperature while maintaining a higher crystallization temperature in the bulk. Modification of polycaprolactone polyol can yield adhesives with controllable properties and good processability to meet the needs of flexible electronic devices.

[0005] This adhesive uses polycaprolactone polyols within a specific molecular weight range as the soft segment, leveraging their low-temperature non-solidification and controllable crystallization temperature to provide reliable adhesion during electronic component assembly. When device repair or disassembly is required, heating can significantly reduce the bond strength, achieving non-destructive separation, making it particularly suitable for rework processes of precision electronic components with high temperature sensitivity requirements. Specifically, it relates to a polycaprolactone polymer, an adhesive composition, and a method for preparing the same; the adhesive comprises a valerol-caprolactone copolymer, which is prepared by a ring-opening copolymerization reaction of ε-caprolactone monomer and valerol monomer, and the temperature-sensitive adhesive exhibits temperature-sensitive peelability. Summary of the Invention

[0006] To address the above problems, the present invention provides a flexible temperature-sensitive polycaprolactone polyol.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a flexible, temperature-sensitive polycaprolactone polyol includes the following steps: S11: By weight, mix 10 parts of initiator, 30-65 parts of caprolactone and 0.001-0.01 parts of catalyst, and heat to 130-170 °C for 60-180 min to pre-react and obtain the prepolymer; S12: Add 4-15 drops to the prepolymer, the dropping process is completed within 60-90 minutes, then keep it at the temperature for 2-4 hours, then keep the temperature constant, vacuum to remove impurities, cool down and discharge to obtain flexible temperature-sensitive polycaprolactone polyol.

[0008] In a further improvement, the initiator is one of dimethylhexanediol, PPG-200, PPG-400, PPG-600, and PPG-1000; the catalyst is a tin-based catalyst or a titanium-based catalyst; the tin-based catalyst includes one or more of dibutyltin dilaurate, stannous octoate, and dibutyltin diacetate; the titanium-based catalyst includes one of tetrabenzyltitanium, tetrabutyl titanate, and tetrapropyl titanate.

[0009] In a further improvement, the ester monomer is a mixture of caprolactone and valproic acid; in the mixture, the mass ratio of caprolactone to caprolactone is 1:1 to 1:4; the amount of caprolactone used is 5.2%-11.3% of the total mass of all raw materials.

[0010] A use of a flexible thermosensitive polycaprolactone polyol, as described above, wherein the flexible thermosensitive polycaprolactone polyol is used as a raw material for preparing a flexible, peelable thermosensitive adhesive.

[0011] A further improvement is made to the preparation method of the flexible, peelable, temperature-sensitive adhesive as follows: S21: By weight, 20 parts of diisocyanate and 120-170 parts of flexible thermosensitive polycaprolactone polyol are mixed and heated to 80-110℃ and reacted for 2-6 hours to obtain a polyurethane prepolymer with -NCO end capping. S22: Cool the -NCO-terminated polyurethane prepolymer to 50-70℃, dilute with 18-45 parts of N-methylpyrrolidone (NMP), then add 3-10 parts of hydrophilic chain extender and 0.06-0.3 parts of catalyst II and mix evenly. Maintain the temperature at 60-90℃ and react for 2-8 hours to obtain the -NCO-terminated chain-extended polyurethane prepolymer. S23: Add 1-4 parts of triethylamine solution diluted with acetone to the chain-extended polyurethane prepolymer with -NCO end caps; maintain stirring speed at 400 rpm for 20 minutes, then change to 2000 rpm while adding 150-180 parts of deionized water, stir for 25 minutes, reduce stirring speed, then add 1-4 parts of chain extender 1,6-hexanediamine dropwise and stir for 30 minutes, remove acetone by vacuum to obtain a stable polyurethane emulsion, which is the flexible peelable temperature-sensitive adhesive.

[0012] Further improvements include a triethylamine solution in which the mass ratio of acetone to triethylamine is 2-5:2-5; and 1,6-hexanediamine is dissolved in N-methylpyrrolidone (NMP) in a mass ratio of 1.5-3:9-12.

[0013] In a further improvement, in step S21, the diisocyanate is an aromatic diisocyanate, such as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 4,4-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, terephthalic diisocyanate, isophthalimide diisocyanate, 3,3-dimethylbiphenyl-4,4-diisocyanate, or 3,3-dimethyl-4,4-diphenylmethane diisocyanate. The polyester polyol is at least one of the above-synthesized polycaprolactone polyol, polybutylene succinate diol, and polyhexylene adipate diol.

[0014] In a further improvement, the hydrophilic chain extender is selected from any one of dimethylolpropionic acid, dimethylolbutyric acid, and sodium 1,4-butanediol-2-sulfonate; the catalyst is any one of dibutyltin dilaurate, dibutyltin diacetate, stannous octoate, N-methylmorpholine, or triethylenediamine.

[0015] Advantages of this invention: 1. Modified polycaprolactone polyol has the characteristic of partial crystallization, which provides good adhesive strength for adhesives. At the same time, the crystallization is destroyed above a certain temperature, which reduces the adhesive strength. It will not delaminate, but it is easy to disassemble. After cooling down again, it can still provide a certain adhesive strength.

[0016] 2. The polyurethane resin is made from modified polycaprolactone polyol, which has good weather resistance, low-temperature adhesion and flexibility; it is also biodegradable, making the recycling process simpler and faster.

[0017] 3. The polycaprolactone polyol selected in this invention exhibits good room temperature processing performance after its end regular structure is disrupted. This eliminates the need to preheat the polyol in an oven before feeding, simplifying the polyurethane production process and reducing energy consumption in industrial production. Attached Figure Description

[0018] Figure 1 This is a comparison diagram of the flexible thermosensitive polycaprolactone polyol of Example 1 (left) and the polycaprolactone polyol of Comparative Example 1 (right).

[0019] Figure 2 This is the GPC diagram of the flexible thermosensitive polycaprolactone polyol from Example 1.

[0020] Figure 3 This is the GPC diagram of the flexible thermosensitive polycaprolactone polyol of Example 2. Detailed Implementation

[0021] The technical solution of the present invention will be specifically described below through specific embodiments and in conjunction with the accompanying drawings.

[0022] Example 1 Example 1 1. Preparation of flexible thermosensitive polycaprolactone polyol (S1) Under dry nitrogen protection, 10 parts by weight of initiator PPG-400, 60 parts by weight of caprolactone and 0.01 parts by weight of catalyst dibutyltin diacetate were added to a reactor equipped with a stirrer, thermometer and reflux condenser. The stirring was started, the temperature was raised to 60°C, and the reactor was dehydrated under vacuum for 3 hours. The temperature was then raised to 140°C and reacted for 210 minutes.

[0023] After the reaction was complete, the temperature was raised to 160°C, and the ester monomer mixture was added dropwise. This ester monomer mixture was prepared by pre-mixing 2 parts caprolactone and 4 parts valproic acid (caprolactone to valproic acid blend ratio of 1:2, with valproic acid accounting for 5.2% of the total weight). The dropwise addition was completed within 75 minutes, maintaining the reaction temperature at 160°C throughout the process. After the addition was complete, the reaction was continued at this temperature for another 105 minutes.

[0024] After the reaction is complete, the temperature is kept constant, and the mixture is evacuated for 30 minutes to remove impurities. The mixture is then cooled to room temperature and discharged to obtain flexible temperature-sensitive polycaprolactone polyol.

[0025] The resulting product is a white, semi-transparent, viscous liquid. Figure 1 The sample on the left, analyzed by gel permeation chromatography (GPC), has the following detailed data, as shown in Table 1: number-average molecular weight (Mn) of 3484 and molecular weight distribution (PDI) of 1.19. No lumpy precipitate was observed after standing at the lowest temperature of 22℃ for 72 hours, and the product remained translucent and fluid. The viscosity of this product at 20℃ was 1725 mPa·s, the acid value was 0.12 mg KOH / g, the hydroxyl value was 37.7 mg KOH / g, and the functionality was 2.

[0026] Table 1. GPC molecular weight distribution of flexible temperature-sensitive polycaprolactone polyol in Example 1 2. Preparation of temperature-sensitive polyurethane adhesive (S2) (1) Prepolymerization reaction (S21) 130 parts of the polycaprolactone polyol prepared above were added to a reaction vessel, heated to 110°C, and vacuum dehydrated for 2 hours to reduce the moisture content to below 0.03%. The temperature was then lowered to 60°C, 20 parts of diisocyanate (IPDI) were added, and the temperature was raised to 85°C. The reaction was carried out for 3 hours to obtain a polyurethane prepolymer with -NCO end caps.

[0027] (2) Chain extension and neutralization (S22-S23) The prepolymer was cooled to 50°C and diluted with 25 parts NMP to reduce the viscosity of the system. 6 parts dimethylolpropionic acid (DMPA) and 0.08 parts dibutyltin dilaurate catalyst were added and mixed thoroughly. The reaction was maintained at 80°C for 3 hours to obtain a chain-extended polyurethane prepolymer with -NCO end-capping.

[0028] The temperature was lowered to 60°C, and 2.5 parts of triethylamine (diluted with 3 parts acetone) were added to the system. The mixture was stirred at medium speed for 25 minutes to neutralize the mixture. Then, the stirring speed was increased to high speed, and 180 parts of deionized water were added at a uniform rate. The mixture was stirred for 25 minutes, and the stirring speed was reduced. Then, 1.5 parts of hexamethylenediamine (prepared as a 10-part NMP solution) was added dropwise as a chain extender, and the mixture was stirred for 30 minutes. The acetone was removed under vacuum to obtain a stable polyurethane emulsion, which is the temperature-sensitive polyurethane adhesive.

[0029] Example 2 1. Preparation of flexible thermosensitive polycaprolactone polyol (S1) Under the protection of dry nitrogen, 10 parts by weight of initiator PPG-600, 40 parts by weight of caprolactone and 0.008 parts by weight of catalyst stannous octoate were added to a reactor equipped with a stirrer, thermometer and reflux condenser. Stirring was started, the temperature was raised to 55°C, and vacuum dehydration was carried out for 3 hours. The temperature was then raised to 150°C and reacted for 180 minutes until the viscosity was constant.

[0030] After the reaction was completed, a mixture of ester monomers was added dropwise. This mixture was prepared by pre-mixing 3 parts caprolactone and 7 parts valproic acid (caprolactone to valproic acid blend ratio of 3:7), with valproic acid accounting for 11.6%. The dropwise addition was completed within 90 minutes, maintaining the reaction temperature at 155°C during the process. After the addition was complete, the reaction was continued at this temperature for 180 minutes. After the reaction was finished, the temperature was raised to 160°C, and a vacuum was applied for 30 minutes to remove impurities. The mixture was then cooled to room temperature and discharged to obtain flexible, temperature-sensitive polycaprolactone polyol.

[0031] The obtained product is a white, semi-transparent, viscous liquid. GPC analysis showed a number-average molecular weight (Mn) of 3241 (detailed data are shown in Table 2), and a molecular weight distribution (PDI) of 1.22. No lumpy precipitate was observed after standing at a minimum temperature of 18℃ for 72 hours, and the product remained semi-transparent and fluid. The viscosity of the product at 20℃ was 1633 mPa·s, the acid value was 0.17 mg KOH / g, the hydroxyl value was 36.9 mg KOH / g, and the functionality was 2.

[0032] Table 2. GPC molecular weight distribution of flexible thermosensitive polycaprolactone polyol in Example 2 2. Preparation of temperature-sensitive polyurethane adhesive (S2) (1) Prepolymerization reaction (S21) 150 parts of the polycaprolactone polyol prepared above were added to a reaction vessel, heated to 110°C, and vacuum dehydrated for 2 hours to reduce the moisture content to below 0.03%. The temperature was then lowered to 70°C, and 20 parts of 4,4-diphenylmethane diisocyanate (MDI) were added. The reaction was carried out for 3.5 hours to obtain a polyurethane prepolymer with -NCO end caps.

[0033] (2) Chain extension and neutralization (S22-S23) The prepolymer system was cooled to 50°C, diluted with 35 parts NMP, and then 8 parts dimethylolbutyric acid (DMBA) and 0.4 parts N-methylmorpholine catalyst were added. The temperature was maintained at 85°C for 3.5 hours.

[0034] Cool to 55°C, add 3.5 parts triethylamine (4 parts acetone for dilution) to the system, stir at medium speed for 20 minutes, then switch to high speed while adding 220 parts deionized water, stir for 25 minutes, reduce the stirring speed, and then add 2.5 parts hexamethylenediamine (prepared as a 12-part NMP solution) dropwise, stir for 30 minutes, remove acetone under vacuum, and obtain a stable milky white polyurethane emulsion, which is the temperature-sensitive polyurethane adhesive.

[0035] Comparative Example 1 1. Preparation of polycaprolactone polyol (S1) The difference between this comparative example and Example 1 is that the amount of valproic acid added is greater than 12%.

[0036] Under dry nitrogen protection, 10 parts of initiator PPG-200, 104 parts of caprolactone, and 0.01 parts of catalyst dibutyltin dilaurate were added sequentially to the reactor. Stirring was started and the temperature was raised to 60°C, followed by vacuum dehydration for 3 hours. Then, the temperature was raised to 160°C, and the pre-reaction was carried out for 180 minutes. After the reaction was completed, a mixture of ester monomers (12 parts of caprolactone and 24 parts of valproic acid, with a total mixing ratio of 1:2, and valproic acid accounting for 16% of the total mass) was added dropwise over 75 minutes, followed by holding at this temperature for 105 minutes. After the reaction was completed, vacuum was applied to remove impurities, and the mixture was cooled and discharged.

[0037] The obtained product was a completely transparent viscous liquid. Gel permeation chromatography (GPC) determined its number-average molecular weight (Mn) to be 3122 and its molecular weight distribution (PDI) to be 1.28. No lumpy precipitate was observed after standing at a minimum temperature of 12°C for 72 hours, and the product remained translucent and fluid. The product had a viscosity of 1035 mPa·s at 20°C, an acid value of 0.15 mg KOH / g, a hydroxyl value of 36.7 mg KOH / g, and a functionality of 2.

[0038] 2. Preparation of polyurethane adhesive (S2) (1) Prepolymerization reaction (S21) 130 parts of the polycaprolactone polyol prepared above were added to a reaction vessel, heated to 115°C, and vacuum dehydrated for 1.5 hours until the moisture content was reduced to below 0.03%. The temperature was then lowered to 65°C, and 20 parts of 4,4-diphenylmethane diisocyanate (MDI) were added. The temperature was then raised to 85°C, and the reaction was carried out for 3 hours to obtain a polyurethane prepolymer with -NCO end caps.

[0039] (2) Chain extension and neutralization (S22-S23) The prepolymer was cooled to 60°C and diluted with 35 parts NMP to reduce the viscosity of the system. 6 parts dimethylolpropionic acid (DMPA) and 0.1 parts dibutyltin dilaurate catalyst were added, and the reaction was maintained at 80°C for 3 hours to obtain a chain-extended polyurethane prepolymer with -NCO end-capping.

[0040] The temperature was lowered to 60°C, and 2.5 parts of triethylamine diluted with 4 parts acetone were added to the system. The mixture was stirred at medium speed for 20 minutes for neutralization. Then, the stirring speed was increased to high speed, and 180 parts of deionized water were added at a uniform rate. Stirring at high speed continued for 30 minutes for emulsification. After emulsification, the stirring speed was reduced, and 1.5 parts of hexamethylenediamine (prepared as a 10-part NMP solution) as a chain extender were added dropwise. The mixture was stirred for 30 minutes. Acetone was removed under vacuum to obtain a stable polyurethane emulsion, which is the temperature-sensitive polyurethane adhesive.

[0041] Comparative Example 2 1. Preparation of polycaprolactone polyol (S1) The difference between this comparative example and Example 1 is that all monomers were added at once in a one-step process without pre-reaction or dropwise addition.

[0042] Under dry nitrogen protection, 10 parts of initiator PPG-400, 62 parts of caprolactone, 4 parts of valproic acid (i.e., valproic acid, accounting for 5.2% of the total weight, was added to the reactor along with caprolactone in one batch), and 0.005 parts of catalyst dibutyltin dilaurate were added sequentially. Stirring was started, and the temperature was directly raised to 160℃, reacting for 390 minutes. After the reaction was completed, impurities were removed by vacuuming, and the mixture was cooled and discharged.

[0043] The obtained product was a completely transparent viscous liquid. Gel permeation chromatography (GPC) determined its number-average molecular weight (Mn) to be 3340 and its molecular weight distribution (PDI) to be 1.33. No lumpy precipitate was observed after standing at a minimum temperature of 8°C for 72 hours, and the product remained completely transparent and fluid. The product had a viscosity of 822 mPa·s at 20°C, an acid value of 0.17 mg KOH / g, a hydroxyl value of 35.8 mg KOH / g, and a functionality of 2.

[0044] 2. Preparation of polyurethane adhesive (S2) (1) Prepolymerization reaction (S21) 150 parts of the polycaprolactone polyol prepared above were added to a reaction vessel, heated to 110°C, and vacuum dehydrated for 2 hours to reduce the moisture content to below 0.03%. The temperature was then lowered to 70°C, and 20 parts of 4,4-diphenylmethane diisocyanate (MDI) were added. The reaction was carried out for 3.5 hours to obtain a polyurethane prepolymer with -NCO end caps.

[0045] (2) Chain extension and neutralization (S22-S23) The prepolymer system was cooled to 50°C, diluted with 35 parts NMP, and then 8 parts dimethylolbutyric acid (DMBA) and 0.4 parts N-methylmorpholine catalyst were added. The temperature was maintained at 85°C for 3.5 hours.

[0046] Cool to 55°C, add 3.5 parts triethylamine (4 parts acetone for dilution) to the system, stir at medium speed for 20 minutes, then switch to high speed while adding 220 parts deionized water, stir for 25 minutes, reduce the stirring speed, and then add 2.5 parts hexamethylenediamine (prepared as a 12-part NMP solution) dropwise, stir for 30 minutes, remove acetone under vacuum to obtain a stable milky white polyurethane emulsion, add water to adjust the solid content to 36%, which is the temperature-sensitive polyurethane adhesive.

[0047] Room temperature peel strength test: Cut 25mm × 100mm strips from a 0.2mm thick aluminum sheet, apply the obtained temperature-sensitive water-based polyurethane adhesive, ensuring even application and no adhesive buildup. After standing at room temperature for 10 minutes, place in an 80°C oven for 5 minutes, then bond while hot, apply 0.2MPa pressure for 10 seconds, and test the T-type peel strength at room temperature after 24 hours of room temperature adjustment. The experiment was conducted under constant temperature and humidity conditions (23±2℃, 50±5%). Specific data are as follows.

[0048] High-temperature peel strength test: After the above-mentioned bonding strips were conditioned to room temperature for 24 hours, they were placed in an 80°C oven for 10 minutes, and the T-type hot peel strength was tested while they were hot.

[0049] The relevant test data for each embodiment are shown in Table 3.

[0050] Table 3 Test data of adhesives in each embodiment Results analysis: According to the data in the table, both Examples 1 and 2 exhibit high peel strength and good adhesion at room temperature. After high-temperature treatment, peeling while hot results in significantly lower peel strength. However, due to the strong hydrogen bonding of the polar groups, a certain degree of adhesion is still maintained, and no automatic debonding occurs. It is evident that the obtained centrally regular polyol can significantly improve the peel strength at room temperature through partial crystallization. The resulting temperature-sensitive waterborne polyurethane adhesive can achieve good adhesion to electronic devices, and when heated to above 80°C, it facilitates the non-destructive disassembly of electronic devices.

[0051] Compared with Example 1, the initiator in Comparative Example 1 has a lower impact on material properties. However, the addition of valerol in the first step effectively disrupts the crystallinity of the entire polyol, resulting in a decrease in polymer chain segment regularity and a further decrease in the minimum crystallization temperature. At the same time, due to the significant disruption of crystallinity, the peel strength decreases significantly.

[0052] Compared with Examples 1 and 2, Comparative Example 2 uses a one-step polymerization method. The initiator and the two monomers compete for the reaction indiscriminately, which cannot guarantee that the core of the initiator is grafted with a regular caprolactone chain. This results in insufficient uniformity of copolymer chain distribution, which in turn further reduces the low-temperature crystallization performance, and further reduces the peel strength at room temperature and the peel strength after heating.

[0053] The above is only one specific implementation method of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantial modifications made to the present invention using this concept shall be considered as infringing the protection scope of the present invention.

Claims

1. A method for preparing a flexible, temperature-sensitive polycaprolactone polyol, characterized in that, Includes the following steps: S11: By weight, mix 10 parts of initiator, 30-65 parts of caprolactone and 0.001-0.01 parts of catalyst, and heat to 130-170 °C for 60-180 min to pre-react and obtain the prepolymer; S12: Add 4-15 drops to the prepolymer, the dropping process is completed within 60-90 minutes, then keep it at the temperature for 2-4 hours, then keep the temperature constant, vacuum to remove impurities, cool down and discharge to obtain flexible temperature-sensitive polycaprolactone polyol.

2. The method for preparing flexible thermosensitive polycaprolactone polyol as described in claim 1, characterized in that, The initiator is one of dimethylhexanediol, PPG-200, PPG-400, PPG-600, and PPG-1000; the catalyst is a tin-based catalyst or a titanium-based catalyst; the tin-based catalyst includes one or more of dibutyltin dilaurate, stannous octoate, and dibutyltin diacetate; the titanium-based catalyst includes one of tetrabenzyltitanium, tetrabutyl titanate, and tetrapropyl titanate.

3. The method for preparing flexible thermosensitive polycaprolactone polyol as described in claim 1, characterized in that, The ester monomers are a mixture of caprolactone and valproic acid; in the mixture, the mass ratio of caprolactone to caprolactone is 1:1 to 1:4; the amount of caprolactone used is 5.2% to 11.3% of the total mass of all raw materials.

4. The use of a flexible temperature-sensitive polycaprolactone polyol, wherein the flexible temperature-sensitive polycaprolactone polyol is as described in claim 1, characterized in that, The flexible thermosensitive polycaprolactone polyol is used as a raw material for preparing flexible, peelable thermosensitive adhesives.

5. The use of the flexible temperature-sensitive polycaprolactone polyol as described in claim 4, characterized in that, The preparation method of the flexible, peelable, temperature-sensitive adhesive is as follows: S21: By weight, 20 parts of diisocyanate and 120-170 parts of flexible thermosensitive polycaprolactone polyol are mixed and heated to 80-110℃ and reacted for 2-6 hours to obtain a polyurethane prepolymer with -NCO end capping. S22: Cool the -NCO-terminated polyurethane prepolymer to 50-70℃, dilute with 18-45 parts of N-methylpyrrolidone (NMP), then add 3-10 parts of hydrophilic chain extender and 0.06-0.3 parts of catalyst II and mix evenly. Maintain the temperature at 60-90℃ and react for 2-8 hours to obtain the -NCO-terminated chain-extended polyurethane prepolymer. S23: Add 1-4 parts of triethylamine solution diluted with acetone to the chain-extended polyurethane prepolymer with -NCO end caps; maintain stirring speed at 400 rpm for 20 minutes, then change to 2000 rpm while adding 150-180 parts of deionized water, stir for 25 minutes, reduce stirring speed, then add 1-4 parts of chain extender 1,6-hexanediamine dropwise and stir for 30 minutes, remove acetone by vacuum to obtain a stable polyurethane emulsion, which is the flexible peelable temperature-sensitive adhesive.

6. The use of the flexible temperature-sensitive polycaprolactone polyol as described in claim 5, characterized in that, In the triethylamine solution, the mass ratio of acetone to triethylamine is 2-5:2-5; 1,6-hexanediamine is dissolved by N-methylpyrrolidone (NMP), and the mass ratio of 1,6-hexanediamine to NMP is 1.5-3:9-12.

7. The use of the flexible temperature-sensitive polycaprolactone polyol as described in claim 5, characterized in that, In step S21, the diisocyanate is an aromatic diisocyanate, such as toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 4,4-diphenylmethane diisocyanate, 1,5-naphthalene diisocyanate, terephthalic diisocyanate, isophthalimide diisocyanate, 3,3-dimethylbiphenyl-4,4-diisocyanate, or 3,3-dimethyl-4,4-diphenylmethane diisocyanate. The polyester polyol is at least one of the above-synthesized polycaprolactone polyol, polybutylene succinate diol, and polyhexylene adipate diol.

8. The use of the flexible temperature-sensitive polycaprolactone polyol as described in claim 5, characterized in that, The hydrophilic chain extender is selected from any one of dimethylolpropionic acid, dimethylolbutyric acid, and sodium 1,4-butanediol-2-sulfonate; the catalyst is any one of dibutyltin dilaurate, dibutyltin diacetate, stannous octoate, N-methylmorpholine, or triethylenediamine.

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