Preparation method of dynamic disulfide bond-based waterborne polyurethane heat-conducting self-repairing material

Abstract

This invention discloses a method for preparing a waterborne polyurethane thermally conductive self-healing material based on dynamic disulfide bonds. A two-step method introduces dynamic disulfide bonds into the polyurethane backbone, endowing the material with excellent self-healing properties. A pure polyurethane film with cut cracks can essentially heal completely after 1.5 hours at 40°C, achieving a tensile strength recovery rate of 99%. When the thermally conductive filler content is 10%, the thermal conductivity of the composite material can reach 1.74 W·m. ‑1 ·K ‑1 Cracks generated during film cutting can self-heal at 40℃ for 2 hours, with a tensile strength restoration rate of up to 86%. Furthermore, the thermal conductivity remains stable after crack healing, with a thermal conductivity of 1.69 W·m. ‑1 ·K ‑1 It can be widely used in protective materials, heat dissipation of electronic devices, etc.

Description

Technical Field

[0001] This invention belongs to the field of self-healing polymer heat dissipation materials technology, specifically relating to a preparation method of a waterborne polyurethane thermally conductive self-healing material based on dynamic disulfide bonds. Background Technology

[0002] Polyurethane coatings are a common type of coating, which can be divided into two-component and one-component polyurethane coatings. They generally possess good mechanical properties and high solids content, making them widely applicable in construction engineering, aerospace, and electronic devices. However, these coating materials often suffer mechanical damage such as scratches, peeling, or breakage during prolonged use due to mechanical impacts, friction, or abrasion. Therefore, researchers have been dedicated to developing self-healing functional coating materials, hoping that the coating can repair internal microcracks during use, thereby improving the stability and service life of the material. Intrinsic self-healing mainly utilizes the exchange of dynamic chemical bonds and supramolecular interactions between damaged interfaces within the polymer chain, which can lead to highly efficient repair performance. Currently, two types of dynamic chemical bonds have been studied and used in self-healing polyurethane coatings: one involves reversible non-covalent bonds, such as hydrogen bonds, host-guest interactions, metal ligand coordination, and π-π stacking; the other involves reversible covalent bonds, such as Diels-Alder (DA) bonds, disulfide bonds, boron-oxygen bonds, and imine bonds.

[0003] Chinese patent CN116284673A discloses a method for preparing and applying self-healing polyurethane. Under heating conditions, IPDI is added to PCL to prepare a prepolymer. 2,2'-dithiodiethanol, hydroxyethyl methacrylate, and hydroxylated eucommia gum are added to the prepolymer and stirred to obtain a self-healing polyurethane coating. When the 2,2'-dithiodiethanol content is at its highest, the tensile strength is 10.45 MPa, the elongation at break is 74.9%, and the apparent self-healing effect is good.

[0004] Chinese patent CN112226036A discloses a method for preparing a bio-based biodegradable crosslinked self-healing polyurethane. It is prepared in two steps using castor oil, isophorone diisocyanate (IPDI), and the aromatic disulfide 4,4'-diaminodiphenyl disulfide. The polyurethane has a maximum strength of 33.28 MPa, but its self-healing efficiency is only 85% after being treated at 60°C for 4 hours.

[0005] Current polyurethane coatings face a challenge in balancing mechanical properties and self-healing capabilities, making it difficult to simultaneously achieve high strength, high elongation at break, and high self-healing efficiency. Furthermore, with the development of high-power, high-frequency flexible electronic devices, timely and effective heat dissipation is crucial. Imparting good self-healing properties to thermally conductive materials allows for the timely repair of internal heat transfer path interruptions caused by mechanical damage during use, maintaining the material's long-lasting and efficient heat transfer capacity. Currently, research on waterborne polyurethane coatings possessing both self-healing and thermal conductivity is scarce. Summary of the Invention

[0006] Based on the problems existing in the prior art, the present invention provides a method for preparing a waterborne polyurethane thermally conductive self-healing material based on dynamic disulfide bonds. By introducing dynamic disulfide bonds with different structures into the waterborne polyurethane coating, the material is endowed with high mechanical strength and good self-healing effect. When it is further combined with thermally conductive fillers to form a thermally conductive coating, it can repair microcracks during heat transfer, optimize the material's heat dissipation capacity, and extend the material's service life.

[0007] This invention introduces dynamic disulfide bonds into the polyurethane backbone through a two-step method, endowing the material with excellent self-healing properties. Pure polyurethane films with cut cracks can essentially heal completely after 1.5 hours at 40°C, achieving a tensile strength recovery rate of 99%. When the thermally conductive filler content is 10%, the composite material's thermal conductivity can reach 1.74 W·m. -1 ·K -1 Cracks generated during film cutting can self-heal at 40℃ for 2 hours, with a tensile strength restoration rate of up to 86%. Furthermore, the thermal conductivity remains stable after crack healing, with a thermal conductivity of 1.69 W·m. -1 ·K -1 It can be widely used in protective materials, heat dissipation of electronic devices, etc.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention relates to a method for preparing a dynamic disulfide-bonded waterborne polyurethane thermally conductive self-healing material. First, diisocyanate and a hydrophilic compound are used as raw materials. After reacting with a diol, an isocyanate-terminated prepolymer is obtained. This prepolymer is then reacted with a disulfide compound to obtain a polyurethane prepolymer with disulfide bonds in its main chain. Next, a triethylamine neutralization reaction is performed, followed by high-speed shear emulsification with deionized water. Subsequently, an amine chain extender is reacted with the prepolymer to further extend the chain. Finally, after removing the solvent, the prepolymer is ultrasonically composited with a certain amount of thermally conductive filler to obtain the dynamic disulfide-bonded polyurethane thermally conductive self-healing material. The specific steps include the following:

[0010] Step 1: Preparation of prepolymer

[0011] At 50–100°C, 40–60 moles of diisocyanate and 10–30 moles of hydrophilic compound are sequentially added to 10–20 moles of diol and mixed thoroughly. A catalyst is then added, and the mixture is stirred at 50–80°C for 2–4 hours to obtain a polyurethane prepolymer.

[0012] Step 2: Preparation of self-healing polyurethane

[0013] The polyurethane prepolymer obtained in step 1 is cooled to 60°C, and 0-20 moles of disulfide chain extender are added. The mixture is stirred at 40-60°C for 4-8 hours. Solvent is added to control the viscosity of the reactants and prevent gelation. Triethylamine is then added to neutralize the reaction for 10-30 minutes. The mixture is then poured into a high-speed emulsifier and dispersed with deionized water for 10-15 minutes. Finally, 0-20 moles of the chain extender are added and the reaction is further carried out for 20-40 minutes.

[0014] In step 2, special attention must be paid to monitoring the residual amount of -NCO during the reaction with the disulfide chain extender, controlling it to 25-35% (molar ratio). A low residual isocyanate content indicates a high degree of prepolymerization, resulting in an excessively high viscosity of the prepolymer system, making it difficult to emulsify under high-speed shear and causing liquid-solid separation. Conversely, a high residual isocyanate content indicates insufficient prepolymerization, resulting in a low molecular weight prepolymer. This leads to poor emulsion stability after high-speed shear with deionized water, and the formation of a large amount of precipitation upon standing. Furthermore, special care must be taken when adding deionized water; the rate of addition must not be too rapid, otherwise, the isocyanate and water may react violently, resulting in explosive polymerization.

[0015] Step 3: Preparation of thermally conductive self-healing polyurethane material

[0016] A certain amount of thermally conductive filler and polyurethane emulsion are weighed and ultrasonically mixed evenly, and then coated and hot-pressed to obtain a thermally conductive self-healing polyurethane material.

[0017] In the preparation process of this invention, the ratio of polyurethane prepolymer is conventional. The main change is in the ratio of the raw materials of the two chain extenders, that is, the process of preparing polyurethane matrix with different disulfide bond contents.

[0018] Furthermore, in the preparation of the polyurethane prepolymer in step 1, the ratio of the total molar amount of hydroxyl groups to the total molar amount of isocyanate groups in the added raw materials is controlled to be 1:1.646.

[0019] Furthermore, in step 2, the total molar ratio of the post-chain extender and the disulfide chain extender to the total molar ratio of all raw materials remains constant at 20%. That is, when the post-chain extender is 0, the molar ratio of the disulfide chain extender is 20%; when the molar ratio of the post-chain extender is 20%, the amount of disulfide chain extender is 0, and neither is simultaneously zero. Observation of the scratch healing process under a polarizing microscope on polyurethane without added disulfide bonds reveals extremely slight signs of crack narrowing and shallowing. Figure 5(corresponding to the first sample WPU); and the stress-strain curves before and after healing can be used to determine ( Figure 6 (As shown in the first figure), the repair efficiency is weak, at only 45.8%. Its repair performance is mainly due to the asymmetric structure of IPDI, the flexible aliphatic segments of PPG, and the hydrogen bond interaction formed by isocyanate and isophorone diamine. These two factors synergistically endow the polyurethane film with a certain healing ability.

[0020] Furthermore, the molar amount of the disulfide chain extender added accounts for 15% of the total molar amount of diisocyanate, hydrophilic compound, diol, post-chain extender, and disulfide chain extender. At this ratio, the composite material exhibits the best healing performance.

[0021] The diisocyanate is one or a mixture of 1,6-hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), 4,4'-diphenylmethane diisocyanate (MDI), 4,4'-dicyclohexylmethane diisocyanate (HMDI), and toluene diisocyanate (TDI), preferably isophorone diisocyanate.

[0022] The hydrophilic compound is one or more of 2,2'-dimethylolpropionic acid (DMPA), 2,2'-dimethylolbutyric acid (DMBA), 1,4-butanediol, and ethylene glycol, preferably 2,2'-dimethylolpropionic acid.

[0023] The diol is one or a mixture of polycarbonate diol (PCDL), polycaprolactone (PCL), polypropylene glycol (PPG), and polytetrahydrofuran diol (PTMG), preferably polypropylene alcohol.

[0024] The catalyst is one or more of dibutyltin dilaurate, an organobismuth catalyst, and stannous octoate, preferably an organobismuth catalyst.

[0025] The disulfide chain extender is one or a mixture of 2-hydroxyethyl disulfide, 4,4'-diaminodiphenyl disulfide, 3,3'-disulfide diphenol, and dithioethylenediamine, preferably 4,4'-diaminodiphenyl disulfide and 2-hydroxyethyl disulfide.

[0026] The solvent is one or a mixture of acetone (Ac), toluene (Me), N,N'-dimethylformamide (DMF), and N,N'-dimethylacetamide (DMAc), preferably acetone. When adding solvent to control the viscosity of the reaction system, the volume of the added solvent is 10-30% of the total volume, and the solid content of the system is controlled at 30-35%.

[0027] The chain extender is one or more of isophorone diamine, ethylene glycol, and 1,4-butanediol, preferably isophorone diamine.

[0028] The curing process involves allowing the material to stand at room temperature for 12–24 hours, followed by further drying in a vacuum oven at 60–80°C for 6–10 hours until constant weight is achieved, resulting in a polyurethane self-healing material.

[0029] The thermally conductive filler is boron nitride with a size of 1 μm, and the addition mass is 5-20% (based on polyurethane emulsion).

[0030] When weighing and ultrasonically mixing the thermally conductive filler and polyurethane emulsion, the ultrasonic duration is 24 hours.

[0031] The hot pressing conditions are 100-120℃ for 10-30 minutes.

[0032] The beneficial effects of this invention are reflected in:

[0033] This invention synthesizes a thermally conductive polyurethane composite material with excellent self-healing properties based on a stepwise polymerization mechanism. On one hand, the disulfide containing a benzene ring structure can generate π-π interactions with the thermally conductive BN filler, improving the interfacial compatibility between the filler and the macromolecular chain, reducing interfacial thermal resistance, and forming a stable and continuous thermally conductive pathway. On the other hand, the introduction of 4,4'-diaminodiphenyl disulfide into the PU macromolecular chain can form urea bonds with isocyanates, exhibiting stronger hydrogen bonding interactions. The frequent exchange reactions of disulfide bonds in the main chain and hydrogen bonding interactions endow the BN / PU composite material with excellent self-healing effects and thermal conductivity stability. The thermal conductivity of the composite material before and after crack repair at 40℃ for 2 hours is 1.74 W·m. -1 ·K -1 and 1.69 W·m -1 ·K -1 Furthermore, the tensile repair rate of the composite material before and after healing can reach 86%. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the synthesis route of the dynamic disulfide bond waterborne polyurethane self-healing material of Embodiment 3 of the present invention;

[0035] Figure 2 This is a diagram of the dynamic disulfide bond self-healing mechanism obtained in Example 3 of the present invention;

[0036] Figure 3 The following are the FT-IR spectra of polyurethane samples from Example 3 and Comparative Examples 1 and 2 of this invention;

[0037] Figure 4 The UV-Vis absorption spectra of Example 3, Comparative Example 1, and Comparative Example 2 in water are shown below.

[0038] Figure 5 These are polarized light microscope images of the self-healing process in Embodiment 3 and Comparative Examples 1 and 2 of the present invention;

[0039] Figure 6 The stress-strain curves obtained from tensile tests before and after healing in Example 3 and Comparative Examples 1 and 2 of this invention are shown.

[0040] Figure 7 This is a comparison of the thermal conductivity of the composite coating before and after healing in Example 3 of the present invention and Comparative Examples 1 and 2.

[0041] Figure 8 The stress-strain curves obtained from tensile tests of the composite coatings in Example 3 and Comparative Examples 1 and 2 of this invention are shown below.

[0042] Figure 9 The stress-strain curves are obtained from tensile tests of the composite coating before and after healing in Example 3 and Comparative Examples 1 and 2 of this invention. Detailed Implementation

[0043] The technical solution of the present invention will be further described in detail below through specific embodiments. These embodiments are implemented on the premise of the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0044] In the following embodiments, the mechanical property testing method is as follows: The waterborne polyurethane film prepared in the mold is cut into 1cm thick samples, and then cut into dumbbell-shaped strips using a standard cutter, conforming to the national standard GB / T6344-2008 Sample Type 1A. The tensile rate is 100mm / min. The self-healing efficiency testing method is as follows: A crack is made in the standard dumbbell-shaped sample with a sharp knife, and the sample is heat-treated at 40℃ for 2 hours on a heating table. The tensile strength of the repaired sample is then retested; wherein, the repair efficiency η is defined as the ratio of the repaired sample strength to the original sample tensile strength.

[0045] Example 1:

[0046] This embodiment prepares the polyurethane self-healing coating material and the thermally conductive composite coating according to the following steps:

[0047] 1. Preparation of prepolymer

[0048] 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid was dried in an oven at 70 °C for 6 h. 30 g (15.0 mmol, PPG molecular weight 2000) of polypropylene glycol was vacuum dehydrated in a rotary evaporator at 90 °C and a vacuum degree of 200 mbar for 4 h. After cooling to room temperature, the polypropylene glycol was transferred to a dry 250 mL three-necked flask. 15 g (67.5 mmol) of isophorone diisocyanate and 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid were added sequentially. 50 mL of acetone was added to adjust the viscosity and 2-3 drops (about 0.0763 g) of organic bismuth catalyst were added. The mixture was reacted at 80 °C for 3 h under electric mechanical stirring to obtain a polyurethane prepolymer.

[0049] 2. Preparation of self-healing polyurethane

[0050] When the polyurethane prepolymer was cooled to 60°C, 1.6761 g (6.75 mmol) of 4,4'-diaminodiphenyl disulfide was added and reacted for 6 h. After the reaction was completed, 45 mL of acetone was added to reduce the viscosity of the reaction. Then, the mixture was cooled to 25°C, and 2.63 mL of triethylamine was added to neutralize it for 30 min. The mixture was then transferred to a stirred tank and 100 mL of deionized water was added. The mixture was emulsified at 1000 rpm for 15 min using high-speed shearing. The speed was reduced to 625 rpm and 3.3633 g (19.75 mmol) of isophorone diamine was added dropwise for post-chain extension for 30–60 min. Then, acetone was removed using a rotary evaporator at a vacuum of 200–325 mbr and a temperature of 50°C to obtain a polyurethane solution. Finally, 15 mL of the aqueous polyurethane emulsion was poured into a mold and cured at room temperature for 24 h. Finally, the mixture was placed in a vacuum oven at 40°C for further drying for 12 h. The resulting material was designated as SWPU5.

[0051]

[0052]

[0053] Example 2:

[0054] 1. Preparation of prepolymer

[0055] 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid was dried in an oven at 70 °C for 6 h. 30 g (15.0 mmol) of polypropylene glycol was vacuum dehydrated in a rotary evaporator at 90 °C and a vacuum degree of 200 mbar for 4 h. After cooling to room temperature, the polypropylene glycol was transferred to a dry 250 mL three-necked flask. 15 g (67.5 mmol) of isophorone diisocyanate and 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid were added sequentially. 50 mL of acetone was added to adjust the viscosity and 2-3 drops (about 0.0763 g) of organic bismuth catalyst were added. The mixture was reacted at 80 °C for 3 h under electric mechanical stirring to obtain a polyurethane prepolymer.

[0056] 2. Preparation of self-healing polyurethane

[0057] When the polyurethane prepolymer was cooled to 60°C, 3.3522 g (13.5 mmol) of 4,4'-diaminodiphenyl disulfide was added and reacted for 6 h. After the reaction was completed, 45 mL of acetone was added to reduce the viscosity of the reaction. Then, the mixture was cooled to 25°C, and 2.63 mL of triethylamine was added for neutralization for 30 min. The mixture was then transferred to a stirring tank, and 100 mL of deionized water was added. The mixture was emulsified at 1000 rpm for 15 min using high-speed shearing. The stirring speed was reduced to 625 rpm, and 2.2138 g (13.0 mmol) of isophorone diamine was added dropwise for post-chain extension for 30–60 min. Then, acetone was removed using a rotary evaporator at a vacuum of 200–325 mbr and a temperature of 50°C to obtain a polyurethane solution. Finally, 15 mL of the aqueous polyurethane emulsion was poured into a mold and cured at room temperature for 24 h. Finally, the mixture was placed in a vacuum oven at 40°C for further drying for 12 h. The resulting material was designated SWPU10.

[0058]

[0059]

[0060] Example 3:

[0061] 1. Preparation of prepolymer

[0062] 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid was dried in an oven at 70 °C for 6 h. 30 g (15.0 mmol) of polypropylene glycol was vacuum dehydrated in a rotary evaporator at 90 °C and a vacuum degree of 200 mbar for 4 h. After cooling to room temperature, the polypropylene glycol was transferred to a dry 250 mL three-necked flask. 15 g (67.5 mmol) of isophorone diisocyanate and 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid were added sequentially. 50 mL of acetone was added to adjust the viscosity and 2-3 drops (about 0.0763 g) of organic bismuth catalyst were added. The mixture was reacted at 80 °C for 3 h under electric mechanical stirring to obtain a polyurethane prepolymer.

[0063] 2. Preparation of self-healing polyurethane

[0064] When the polyurethane prepolymer was cooled to 60°C, 5.0283 g (20.25 mmol) of 4,4'-diaminodiphenyl disulfide was added and reacted for 6 h. After the reaction was completed, 45 mL of acetone was added to reduce the viscosity of the reaction. Then, the mixture was cooled to 25°C, and 2.63 mL of triethylamine was added for neutralization for 30 min. The mixture was then transferred to a stirred tank and 100 mL of deionized water was added. The mixture was emulsified at 1000 rpm for 15 min using high-speed shearing. The speed was reduced to 625 rpm and 1.0643 g (6.25 mmol) of isophorone diamine was added dropwise for post-chain extension for 30–60 min. Then, acetone was removed using a rotary evaporator at a vacuum of 200–325 mbr and a temperature of 50°C to obtain a polyurethane solution. Finally, 15 mL of the aqueous polyurethane emulsion was poured into a mold and cured at room temperature for 24 h. Finally, the mixture was placed in a vacuum oven at 40°C for further drying for 12 h. The resulting material was designated SWPU15.

[0065] Take 9.0g of polyurethane emulsion (SWPU15), add 1.0gh-BN, ultrasonically treat for 24h, pour into a mold and cure at room temperature for 24h, and finally hot press at 110℃ for 15min. The resulting composite material is denoted as BN / SWPU15.

[0066]

[0067]

[0068]

[0069] Example 4:

[0070] 1. Preparation of prepolymer

[0071] 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid was dried in an oven at 70 °C for 6 h. 30 g (15.0 mmol) of polypropylene glycol was vacuum dehydrated in a rotary evaporator at 90 °C with a vacuum degree of 200 mbar for 4 h. After cooling to room temperature, the polypropylene glycol was transferred to a dry 250 mL three-necked flask, and 15 g (67.5 mmol) of isophorone diisocyanate and 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid were added sequentially. 50 mL of acetone was added to adjust the viscosity, and 2-3 drops (about 0.0763 g) of organic bismuth catalyst were added. The mixture was reacted at 80 °C for 3 h under electric mechanical stirring to obtain a polyurethane prepolymer.

[0072] 2. Preparation of self-healing polyurethane

[0073] When the polyurethane prepolymer was cooled to 60°C, 6.5802 g (26.5 mmol) of 4,4'-diaminodiphenyl disulfide was added and reacted for 6 h. After the reaction was completed, 45 mL of acetone was added to reduce the viscosity of the reaction. Then, the mixture was cooled to 25°C, and 2.63 mL of triethylamine was added to neutralize it for 30 min. The mixture was then transferred to a stirring tank and 100 mL of deionized water was added. The mixture was emulsified at 1000 rpm for 15 min. Finally, acetone was removed using a rotary evaporator at a vacuum of 200–325 mbr and a temperature of 50°C to obtain an aqueous polyurethane solution. 15 mL of the aqueous polyurethane emulsion was poured into a mold and cured at room temperature for 24 h. Finally, the mixture was placed in a vacuum oven at 40°C for 12 h to dry further. The resulting material was designated SWPU20.

[0074]

[0075] Comparative Example 1:

[0076] 1. Preparation of prepolymer

[0077] 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid was dried in an oven at 70 °C for 6 h. 30 g (15.0 mmol) of polypropylene glycol was vacuum dehydrated in a rotary evaporator at 90 °C with a vacuum degree of 200 mbar for 4 h. After cooling to room temperature, the polypropylene glycol was transferred to a dry 250 mL three-necked flask, and 15 g (67.5 mmol) of isophorone diisocyanate and 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid were added sequentially. 50 mL of acetone was added to adjust the viscosity, and 2-3 drops (about 0.0763 g) of organic bismuth catalyst were added. The mixture was reacted at 80 °C for 3 h under electric mechanical stirring to obtain a polyurethane prepolymer.

[0078] 2. Preparation of self-healing polyurethane

[0079] When the polyurethane prepolymer was cooled to 60°C, 4.5128 g (26.5 mmol) of isophorone diamine was added and reacted for 6 h. After the reaction was completed, 45 mL of acetone was added to reduce the viscosity of the reaction. Then, the mixture was cooled to 25°C, and 2.63 mL of triethylamine was added to neutralize it for 30 min. The mixture was then transferred to a stirring tank and 100 mL of deionized water was added. The mixture was then emulsified at 1000 rpm for 15 min using a high-speed shearing method. Finally, the acetone was removed using a rotary evaporator at a vacuum of 200–325 mbr and a temperature of 50°C to obtain a polyurethane solution. 15 mL of the aqueous polyurethane emulsion was then poured into a mold and cured at room temperature for 24 h. Finally, the mixture was placed in a vacuum oven at 40°C for further drying for 12 h. The resulting material was denoted as WPU.

[0080] Take 9.0g of (WPU) polyurethane emulsion, add 1.0gh-BN, ultrasonically treat for 24h, pour into a mold and cure at room temperature for 24h, and finally hot press at 110℃ for 15min. The resulting composite material is denoted as BN / WPU.

[0081]

[0082] Comparative Example 2:

[0083] 1. Preparation of prepolymer

[0084] 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid was dried in an oven at 70 °C for 6 h. 30 g (15.0 mmol) of polypropylene glycol was vacuum dehydrated in a rotary evaporator at 90 °C with a vacuum degree of 200 mbar for 4 h. After cooling to room temperature, the polypropylene glycol was transferred to a dry 250 mL three-necked flask, and 15 g (67.5 mmol) of isophorone diisocyanate and 3.5 g (26.0 mmol) of 2,2-hydroxymethylpropionic acid were added sequentially. 50 mL of acetone was added to adjust the viscosity, and 2-3 drops (about 0.0763 g) of organic bismuth catalyst were added. The mixture was reacted at 80 °C for 3 h under electric mechanical stirring to obtain a polyurethane prepolymer.

[0085] 2. Preparation of self-healing polyurethane

[0086] When the polyurethane prepolymer was cooled to 60°C, 3.124 g (20.25 mmol) of 2-hydroxyethyl disulfide was added and reacted for 6 h. After the reaction was completed, 45 mL of acetone was added to reduce the viscosity of the reaction. Then, the mixture was cooled to 25°C, and 2.63 mL of triethylamine was added for neutralization for 30 min. The mixture was then transferred to a stirring tank, and 100 mL of deionized water was added. The mixture was emulsified at 1000 rpm for 15 min using high-speed shearing. The stirring speed was reduced to 625 rpm, and 1.0643 g (6.25 mmol) of isophorone diamine was added dropwise for post-chain extension for 30–60 min. Finally, acetone was removed using a rotary evaporator at a vacuum of 200–325 mbr and a temperature of 50°C to obtain an aqueous polyurethane solution. Finally, 10 mL of the polyurethane emulsion was taken, a certain amount of BN was added, and the mixture was ultrasonically treated for 24 h. The mixture was then poured into a mold and cured at room temperature for 24 h to form the final product. Finally, the mixture was hot-pressed at 110°C for 15 min. The resulting material is designated as EWPU15.

[0087] Take 9.0g of (EWPU15) polyurethane emulsion, add 1.0g of h-BN, ultrasonically treat for 24h, pour into a mold and cure at room temperature for 24h, and finally hot press at 110℃ for 15min. The resulting composite material is denoted as BN / EWPU15.

[0088]

[0089]

[0090]

[0091] Figure 1 This is a schematic diagram of the synthesis reaction process of the dynamic disulfide bond waterborne polyurethane self-healing material in Example 3 of the present invention;

[0092] Figure 2 This is a diagram of the dynamic disulfide bond self-healing mechanism obtained in Example 3 of the present invention;

[0093] Figure 3 The FT-IR spectra of Example 3 and Comparative Examples 1 and 2 of this invention are shown; at 3328 cm⁻¹ -1 The characteristic peak of -OH appeared, and the absorption peak of SS in the introduced disulfide 4,4'-diaminodiphenyl disulfide appeared at 638 cm⁻¹. -1 However, the absorption intensity is weak, and because the disulfide structure contains a benzene ring, the spectrum is at 1638 cm⁻¹. -1 Skeletal vibrations of the benzene ring were observed, at 2931 and 2825 cm⁻¹. -1 The presence of CH stretching vibrations in -CH3 and -CH2 indicates that disulfide bonds have been successfully introduced into the polyurethane system.

[0094] Figure 4 The images show the UV-Vis absorption spectra of Example 3, Comparative Examples 1 and 2 in water. The figures show that the polyurethane emulsion without disulfide bonds exhibits an absorption peak at 200.1 nm, caused by the n-π* transition of C=O in the urethane backbone of the polyurethane. However, the SWPU15 emulsion with added disulfide bonds shows a new absorption peak at 262.9 nm. This is because the added disulfide structure contains a benzene ring structure with delocalized π, which may lead to π-π* transitions, indirectly indicating the introduction of disulfide bonds into the polyurethane molecular chain. The SWPU15 emulsion with added disulfide bonds shows a slight red shift and increased intensity, which may be due to the influence of 2-hydroxyethyl disulfide on the n-π* transition.

[0095] Figure 5 The images show the self-healing process of Example 3, Comparative Examples 1 and 2 of this invention under polarized light microscopy. It can be seen that the scratches on the polyurethane film without disulfide bonds did not show significant healing within 1.5 hours at 40°C. However, the polyurethane film incorporating 4,4'-diaminodiphenyl disulfide completely healed the scratches within 1 hour at a healing temperature of 40°C, and the cracks disappeared after another 30 minutes of healing. The polyurethane film incorporating 2-hydroxyethyl disulfide showed significantly narrower and shallower scratches after 1.5 hours at a healing temperature of 40°C, but the marks still remained.

[0096] Figure 6The tensile tests conducted before and after healing in Example 3 and Comparative Examples 1 and 2 of this invention show that the tensile strength of WPU before healing was 12.6 MPa, and the elongation at break was 1055%. After healing at 40℃ for 2 hours, the tensile strength only reached 5.78 MPa, indicating a weak healing effect. In contrast, the tensile strength of EWPU15 sample before healing was 15.68 MPa, and the tensile strength after healing was 11.86 MPa, with a healing rate of 75.6%. Compared with EWPU15 sample, SWPU15 sample had a tensile strength of 14.43 MPa before healing and a tensile strength of 14.27 MPa after healing, with a healing efficiency of 99%, demonstrating the best healing effect.

[0097] Figure 7 The thermal conductivity of Example 3 and Comparative Examples 1 and 2 before and after healing is shown in the figures. It can be seen that the thermal conductivity of the pure polyurethane sample is 0.23 W·m. -1 ·K -1 After adding thermally conductive fillers, the thermal conductivity of SWPU15 and EWPU15 samples were 1.74 and 1.72 W·m, respectively. -1 ·K -1 The thermal conductivity of the sample was measured again after scratch healing experiment, and was 1.69 and 1.28 W·m. -1 ·K -1 As can be seen, compared with BN / EWPU15, the BN / SWPU15 sample still has better heat transfer capacity after healing. This is not only because SWPU15 has a better healing effect under the same conditions, but also because the SWPU15 structure contains benzene rings, which have π-π interactions with BN filler, thus forming a stable and continuous heat conduction path, which is beneficial to the material's long-term heat dissipation.

[0098] Figure 8 The stress-strain curves obtained from tensile tests in Example 3 and Comparative Examples 1 and 2 of this invention are shown. It can be seen that after adding the thermally conductive filler, the tensile strengths of BN / WPU, BN / SWPU15, and BN / EWPU15 are 2.98, 3.73, and 3.38 MPa, respectively. Among them, BN / SWPU15 has the highest tensile strength. This is due to the presence of a benzene ring structure in the introduced 4,4'-diaminodiphenyl disulfide, which allows for π-π interactions with the BN filler, achieving a reinforcing effect. This further illustrates that the disulfide structure of 4,4'-diaminodiphenyl disulfide provides dual reinforcement for both thermal conductivity and self-healing.

[0099] Figure 9The stress-strain curves obtained from tensile tests before and after healing of the composite coatings in Example 3 and Comparative Examples 1 and 2 of this invention are shown. It can be seen that the healing rate of BN / WPU without disulfide bonds at 60℃ for 2 hours is only 73.2%. This is mainly due to the asymmetric structure of IPDI and the hydrogen bond interactions on the main chain, which endow the composite coating with a certain self-healing ability. In contrast, the tensile healing rate of BN / SWPU15 containing disulfide bonds at 40℃ for 2 hours can reach 86%, which is lower than the pure sample. This is mainly because the introduction of BN hinders the movement of polyurethane chain segments. Secondly, the repair rate of BN / EWPU15 at 40℃ for 2 hours reaches 66.2%. It can be seen that the healing conditions of the composite coating after the addition of disulfide bonds become relatively mild, and the healing temperature decreases.

[0100]

[0101] Note: For tensile testing, the healing conditions for the pure sample, BN / SWPU15, and BN / EWPU15 composite material are 40℃ for 2 hours, while the healing condition for BN / WPU is 60℃ for 2 hours. This is because crack repair is not visible in BN / WPU at 40℃, so the temperature is increased to 60℃. This is noted to distinguish them.

[0102] The above are merely exemplary embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a waterborne polyurethane thermally conductive self-healing material based on dynamic disulfide bonds, characterized in that: First, diisocyanate and hydrophilic compounds are used as raw materials. After reacting with diol, an isocyanate-terminated prepolymer is obtained. Then, it is reacted with a disulfide chain extender to obtain a polyurethane prepolymer with disulfide bonds in the main chain. Then, through a triethylamine neutralization reaction, deionized water is added for high-speed shear emulsification. Subsequently, a post-chain extender is reacted with it to further extend the chain. Finally, after removing the solvent, it is ultrasonically composited with a certain amount of thermally conductive filler to obtain a dynamic disulfide bond polyurethane thermally conductive self-healing material. Includes the following steps: Step 1: Preparation of prepolymer At 50-100℃, 40-60 moles of diisocyanate and 10-30 moles of hydrophilic compound are added sequentially to 10-20 moles of diol and mixed evenly. A catalyst is added, and the mixture is stirred at 50-80℃ for 2-4 hours to obtain a polyurethane prepolymer. Step 2: Preparation of self-healing polyurethane The polyurethane prepolymer obtained in step 1 is cooled to 60°C, disulfide chain extender is added, and the mixture is stirred at 40-60°C for 4-8 hours. Solvent is added to control the viscosity of the reactants and prevent gelation. Triethylamine is then added to neutralize the reaction for 10-30 minutes. The mixture is then poured into a high-speed emulsifier and deionized water is added for dispersion for 10-15 minutes. After that, a post-chain extender is added and the reaction is further carried out for 20-40 minutes. Step 3: Preparation of thermally conductive self-healing polyurethane material A certain amount of thermally conductive filler and polyurethane emulsion are weighed and ultrasonically mixed evenly, and then coated and hot-pressed to obtain a thermally conductive self-healing polyurethane material. The disulfide chain extender is 4,4'-diaminodiphenyl disulfide, and the post-chain extender is isophorone diamine; In step 2, the total molar amount of the post-chain extender and the disulfide chain extender accounts for 20% of the total molar amount of all raw materials, of which the molar amount of the added disulfide chain extender accounts for 15% of the total molar amount of diisocyanate, hydrophilic compound, diol, post-chain extender and disulfide chain extender; The thermally conductive filler is boron nitride, and its addition mass is 5-30% based on polyurethane emulsion.

2. The preparation method according to claim 1, characterized in that: The diisocyanate is one or a mixture of 1,6-hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, and toluene diisocyanate. The hydrophilic compound is one or more of 2,2'-dimethylolpropionic acid and 2,2'-dimethylolbutyric acid; The diol is one or a mixture of polycarbonate diol, polycaprolactone, polypropylene glycol, and polytetrahydrofuran diol; The catalyst is one or more of dibutyltin dilaurate, organic bismuth catalyst, and stannous octoate, or a mixture thereof.

3. The preparation method according to claim 2, characterized in that: In the preparation of polyurethane prepolymer in step 1, the ratio of the total molar amount of hydroxyl groups to the total molar amount of isocyanate in the added raw materials is controlled to be 1:1.

646.

4. The preparation method according to claim 1, characterized in that: The hot pressing conditions are 100~120℃ for 10~30min.

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