A method for preparing a recyclable high thermal conductivity vinyl resin adhesive

Abstract

This invention discloses a method for preparing a recyclable thermally conductive vinyl resin adhesive, comprising the following steps: (1) synthesis of furanyl hyperbranched polyethylene; (2) liquid-phase assisted exfoliation of h-BN using furanyl hyperbranched polyethylene to obtain non-covalently functionalized BNNSs powder free of free furanyl hyperbranched polyethylene; (3) uniformly mixing and dissolving furanyl hyperbranched polymer, maleimide curing agent, and organic solvent A in a container, and adding the BNNSs powder obtained in step (2), and ultrasonically treating the mixture to uniformly disperse BNNSs in the mixed solution to obtain an adhesive pre-curing solution; (4) open-air reaction of the obtained adhesive pre-curing solution to obtain a cross-linked and cured thermally conductive vinyl resin adhesive. This method allows the adhesive to possess high thermal conductivity while maintaining excellent bonding strength, and it can be recycled after curing.

Description

Technical Field

[0001] This invention discloses a method for preparing a recyclable, high thermal conductivity vinyl resin adhesive. Background Technology

[0002] As electronic devices become increasingly miniaturized, integrated, high-frequency, and high-power-density, the heat generated during operation is growing exponentially. The continuously generated heat accumulates unchecked, causing temperatures to rise in electronic devices. Consequently, the device's performance, reliability, and lifespan cannot be guaranteed. Currently, the common strategy is to use thermal interface materials (TMIs) to address this problem. TMIs achieve a tight connection between electronic components and heat sinks, promoting interfacial heat conduction and thus achieving efficient heat dissipation. Different types of TMIs have long been used in heat dissipation applications, including for electronic devices. Among them, thermally conductive adhesives have seen significant development and widespread application due to their excellent thermal conductivity and superior mechanical properties and dimensional stability after curing. Boron nitride nanosheets (BNNSs) are white crystalline materials with a graphene-like structure and extremely high thermal conductivity (approximately 2000 W / m²). -1 K -1 Its excellent electrical insulation properties and superior thermal stability make it a significant advantage as a filler in the preparation of thermally conductive composite adhesives.

[0003] While commercially available thermally conductive adhesives (TMIs) possess excellent bonding properties, enabling tight bonding between electronic components and heat dissipation devices and improving heat dissipation efficiency, they also pose a significant challenge to the effective separation of these components. Therefore, developing a recyclable thermally conductive adhesive is an effective way to address this issue. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a recyclable high thermal conductivity vinyl resin adhesive, which enables the adhesive to have a high thermal conductivity while maintaining excellent bonding strength, and can be recycled after curing.

[0005] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a recyclable thermally conductive vinyl resin adhesive includes the following steps:

[0007] (1) Synthesis of furanyl hyperbranched polyethylene: The copolymerization of ethylene and 2-(2-bromoisobutyryloxy)ethyl acrylate (BIEA) monomers was catalyzed by Pd-diimine catalyst through a "chain walking" mechanism to obtain the macromolecular initiator HBPE@Br containing terminal bromine; then, using HBPE@Br as initiator, furfuryl methacrylate (FMA) and styrene (St) as comonomers, pentamethyldiethylenetriamine (PMDETA) or 2,2'-bipyridine as ligands, and CuBr as catalyst, furanyl hyperbranched polyethylene HBPE@P(SrF) was synthesized by atom transfer radical polymerization (ATRP);

[0008] (2) Using the furanyl hyperbranched polyethylene HBPE@P(SrF) synthesized in step (1) to exfoliate h-BN with liquid phase assistance, the filter cake of BNNSs adsorbed with HBPE@P(SrF) was obtained by ultrasonication, centrifugation and vacuum filtration. The filter cake was then left to stand at room temperature until the solvent evaporated completely, and finally non-covalent functionalized BNNSs powder without free furanyl hyperbranched polyethylene was obtained.

[0009] (3) The furanyl hyperbranched polymer synthesized in step (1), maleimide curing agent and organic solvent A are uniformly mixed and dissolved in a container, and the BNNSs powder obtained in step (2) is added. The mixture is ultrasonically treated to make BNNSs uniformly dispersed in the mixed solution to obtain the adhesive pre-curing solution.

[0010] (4) The obtained adhesive pre-curing solution is placed in an oven at 25-80℃ for 3-5 days. During this process, the solvent gradually evaporates completely, and finally cross-linked and cured thermally conductive vinyl resin adhesive is obtained.

[0011] Preferably, the specific operation steps of step (1) are as follows:

[0012] (1-a) Under the protection of an ethylene atmosphere, 2-(2-bromoisobutyryloxy)ethyl acrylate (BIEA), Pd-diimine catalyst and anhydrous reagent B were added to the reaction vessel. The mixture was stirred thoroughly and the temperature was controlled at 15-35℃. The reaction was carried out for 12-24 h under an ethylene pressure of 0.01-0.1 MPa. After separation and purification, the macromolecular initiator HBPE@Br containing terminal bromine was obtained.

[0013] (1-b) Under a nitrogen atmosphere, HBPE@Br, styrene (St), furfuryl methacrylate (FMA), anhydrous toluene and ligands were injected into a reaction vessel and stirred thoroughly to form a homogeneous solution. The mixture was then subjected to a “liquid nitrogen freezing-vacuuming-thawing” cycle. After the cycle, the catalyst CuBr was added and the temperature was maintained at 80-100℃ for 5-12 h. After polymerization, furanyl hyperbranched polyethylene HBPE@P(SrF) was obtained by separation and purification.

[0014] As a further preferred option, in step (1-a), the anhydrous reagent B is selected from one of the following: anhydrous dichloromethane, chloroform, or chlorobenzene.

[0015] As a further preferred embodiment, in step (1-a), the Pd-diimine catalyst is selected from one of the following: acetonitrile-based Pd-diimine catalyst 1, and a six-membered ring Pd-diimine catalyst 2 containing a methyl ester group, the structural formulas of which are shown below:

[0016]

[0017] in,

[0018] Both of the above Pd-diimine catalysts can be synthesized in the laboratory with reference to the following literature:

[0019] [1] Johnson LK, Killian CM, Brookhart MJAm.Chem.Soc., 1995, 117, 6414; [2] Johnson LK, Mecking S., Brookhart MJAm.Chem.Soc., 1996, 118, 267.

[0020] As a further preferred embodiment, in step (1-a), the initial concentration of 2-(2-bromoisobutyryloxy)ethyl acrylate in the polymerization system is 0.1-1.0 mol / L; and the mass amount of the Pd-diimine catalyst is 3-34% of the mass amount of 2-(2-bromoisobutyryloxy)ethyl acrylate.

[0021] As a further preferred option, in step (1-a), the reaction temperature is 20-30℃, the ethylene pressure is 0.1MPa, and the reaction time is 20-24h.

[0022] As a further preferred embodiment, in step (1-a), the separation and purification method is carried out as follows: the reaction mixture solution is directly exposed to air, continuously stirred and purged with cold air to remove the solvent, thereby terminating the polymerization and obtaining a polymer containing impurities; an appropriate amount of THF is added to dissolve the above mixture, and small amounts of hydrochloric acid and hydrogen peroxide are added separately and stirred thoroughly for 1-5 hours to remove small amounts of Pd particles mixed in the product; then, the solvent is removed by purging with cold air again, and THF is added again to just completely dissolve the product until a polymer saturated solution is formed, and methanol is added dropwise to precipitate the product until the supernatant is clear and transparent (the volume of methanol added is 2-20 times the volume of THF); further, the upper layer solution is removed to obtain the precipitate, and THF is used to dissolve it again; this process (THF dissolution-methanol precipitation) is repeated 2-3 times to obtain the purified polymer, and finally, it is vacuum dried to obtain the final product HBPE@Br. As for step (1-b), the separation and purification method is largely the same as that of step (1-a) above. The difference is that HCl and H2O2 are not required to remove Pd black during the process, which will not be described in detail here.

[0023] As a further preferred embodiment, in step (1-b), the molar ratio of HBPE@Br, furfuryl methacrylate, styrene, ligand, and CuBr is 1:5-80:50-500:0.1-100:0.01-100, more preferably 1:5-15:150-250:1-5:0.5-2, wherein the molar amount of HBPE@Br is calculated based on the molar amount of Br contained therein. The volumetric amount of anhydrous toluene added is 0.05-0.2 L / mol, based on the total moles of the reactants.

[0024] As a further preferred embodiment, in step (1-b), the initial concentration of styrene in the reaction system is 2.0-20.0 mol / L.

[0025] As a further preferred option, in step (1-b), the reaction temperature is 90°C and the reaction time is 6 hours.

[0026] Preferably, in step (2), the preparation process of the BNNSs powder is as follows: First, furanyl hyperbranched polyethylene HBPE@P(SrF), h-BN powder and chloroform are respectively put into a glass container and sealed. Then, the mixture is placed in an ultrasonic bath for ultrasonic treatment to obtain BNNSs dispersion A mixed with large pieces of h-BN. After centrifugation at a certain speed, the BNNSs dispersion A is allowed to stand and the upper dispersion is collected to obtain BNNSs dispersion B containing excess HBPE@P(SrF). Finally, the obtained BNNSs dispersion B is vacuum filtered to remove free furanyl hyperbranched polyethylene to obtain BNNSs filter cake adsorbed with HBPE@P(SrF). The filter cake is allowed to stand at room temperature until the solvent evaporates completely to finally obtain non-covalent functionalized BNNSs powder without free furanyl hyperbranched polyethylene.

[0027] As a further preferred embodiment, in step (2), the ratio of h-BN powder to chloroform is 320-640 mg: 70-90 mL, and the mass ratio of furanyl hyperbranched polymer HBPE@P(SrF) to h-BN is 0.125-2:1, more preferably 0.125-0.6:1.

[0028] As a further preferred option, in step (2), the ultrasonic pool power is 100-320W, the cumulative ultrasonic time is 8-72h, and the ultrasonic temperature is 15-35℃, so as to obtain BNNSs dispersion A.

[0029] As a further preferred option, in step (2), the BNNSs dispersion A is centrifuged at room temperature, with a centrifugation speed of 1000-5000 rpm and a centrifugation time of 20-60 min; after centrifugation, the dispersion is allowed to stand for 30-60 min, and the upper dispersion is collected to obtain BNNSs dispersion B.

[0030] As a further preferred option, in step (2), the BNNSs dispersion B is vacuum filtered using a microporous filter membrane. The average pore size of the microporous filter membrane is 0.1-0.2 μm, and the material is one of PA6, PTFE, PVDF, or Al2O3. The filter membrane with deposited BNNSs is placed in chloroform at room temperature and then dispersed again by ultrasound for 0.5-24 h with an ultrasonic power of 40-100 W. This vacuum filtration-ultrasonic redispersion can be performed multiple times as needed. Finally, the BNNSs filter cake is removed from the filter membrane and allowed to stand at room temperature until the solvent evaporates completely, ultimately obtaining BNNSs powder without free furanyl hyperbranched polyethylene.

[0031] Preferably, in step (3), the added maleimide curing agent is 4,4'-methylene bis(N-phenylmaleimide) (BMI), and its addition amount is 0.5%-3% of the mass of the added furanyl hyperbranched polyethylene, most preferably 0.9-1%.

[0032] Preferably, in step (3), the added organic solvent A is selected from one of the following chemically pure or analytically pure solvents: dichloromethane, chloroform, toluene, xylene, o-dichlorobenzene, and more preferably dichloromethane or chloroform.

[0033] Preferably, in step (3), the solid content of the added furanyl hyperbranched polyethylene in organic solvent A is 50-500 mg / mL, and most preferably 90 mg / mL.

[0034] Preferably, in step (3), the mass fraction of BNNSs is preferably 10%-40%, and most preferably 20%, based on the mass of polymer HBPE@P(SrF) as 100%.

[0035] Preferably, in step (3), the ultrasonic power is 40-100W and the ultrasonic treatment time is 7-24h.

[0036] Preferably, in step (4), the obtained pre-cured adhesive solution is placed in an oven at 30°C for 5 days to react.

[0037] The thermally conductive vinyl resin adhesive prepared by this invention can be recycled. The recycling method is as follows: the thermally conductive vinyl resin adhesive to be recycled is heat-treated at 125-160℃ for 5-60 minutes to obtain a dissociated adhesive sample; organic solvent A is added to the dissociated adhesive sample, and ultrasonication is performed for 12-24 hours to redissolve the polymer and curing agent, and BNNSs are uniformly dispersed in the solvent again to obtain a pre-cured solution; the pre-cured solution is operated according to the process in step (4) to obtain the thermally conductive vinyl resin adhesive again.

[0038] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0039] 1. This invention utilizes a Pd-diimine catalyst to catalyze the copolymerization of ethylene and other olefin monomers via a "chain-walking" mechanism, combined with atom transfer radical polymerization (ATRP) technology, to prepare long-chain star-shaped hyperbranched copolymers. Their unique topological structure allows them to simultaneously possess the characteristics of hyperbranched polymers (lower solution / melt viscosity, strong solubility) and linear polymers (high mechanical strength). Furthermore, this invention introduces furan groups into hyperbranched polyethylene, achieving dynamic and reversible covalent bond modification. This invention introduces the Diels-Alder reaction into thermally conductive adhesives through crosslinking of HBPE@P(SrF) and maleimide-based curing agents. This introduction of reversible covalent bonds, while retaining the characteristics of traditional thermosetting materials, can also activate chemical bonds through thermal stimulation, achieving a transformation from thermosetting to thermoplastic materials, thus enabling material separation and recycling, and endowing the adhesives and their bonded components with the ability to be reused.

[0040] 2. This invention utilizes HBPE@P(SrF)-assisted liquid-phase exfoliation of h-BN to prepare low-defect oligolayer BNNSs under mild conditions. Simultaneously, based on the π-π interaction between furanyl hyperbranched polyethylene and BNNSs, non-covalent modification of BNNSs is further achieved. Using this BNNSs as a filler, an HBPE@P(SrF)-based composite adhesive is prepared. The interfacial compatibility between the nanosheets and the matrix is ​​significantly improved, effectively promoting the uniform dispersion of the filler in the matrix, greatly reducing the interfacial thermal resistance of the composite adhesive, and effectively improving the thermal conductivity and heat transfer capacity of the composite adhesive, while also possessing good bonding strength. Attached Figure Description

[0041] Figure 1 This is a flowchart of the preparation of non-covalent functionalized BNNSs using HBPE@P(SrF) liquid-phase ultrasonication according to the present invention;

[0042] Figure 2 This is a flowchart illustrating the preparation and reuse of the HBPE@P(SrF) / BNNSs thermally conductive composite adhesive of the present invention.

[0043] Figure 3 It is the hyperbranched polymer HBPE@Br and HBPE@P(SrF) prepared in Example 1 of this invention. 1 H NMR spectrum;

[0044] Figure 4 These are TEM images of BNNSs prepared in Example 1 of this invention at different magnifications: (a) 50 nm; (b) 10 nm;

[0045] Figure 5 This is a thermogravimetric curve of h-BN used in the embodiments of the present invention and BNNSs prepared in Example 1;

[0046] Figure 6 This is the overlap shear test curve of the HBPE@P(SrF) based adhesive prepared by the present invention under different BNNSs filling ratios;

[0047] Figure 7 This is a bar chart showing the thermal conductivity of HBPE@P(SrF)-based thermally conductive discs prepared under different filler filling ratios according to the present invention.

[0048] Figure 8 This is a temperature rise graph of HBPE@P(SrF) based thermally conductive discs prepared under different BNNSs filling ratios according to the present invention.

[0049] Figure 9 This is a SEM image of the cross-section of the HBPE@P(SrF)-based thermally conductive disc prepared under different BNNSs filling ratios according to the present invention;

[0050] Figure 10 This is a schematic diagram (a) of the recycling process of HBPE@P(SrF)cured / BNNSs-20wt% prepared by the present invention, and the stress-strain curves (b) of HBPE@P(SrF)cured / BNNSs-20wt% before and after recycling.

[0051] Figure 11 This is a graph showing the temperature change of HBPE@P(SrF)cured / BNNSs-20wt% before and after the reuse of this invention. Detailed Implementation

[0052] The present invention will be further described in detail below with reference to specific embodiments and accompanying drawings, but the implementation of the present invention is not limited thereto.

[0053] Example 1

[0054] 1. Sample preparation

[0055] (1) The sample preparation for Example 1 was carried out according to the following steps:

[0056] Step 1: Under an ethylene atmosphere, 1.8 g of BIEA monomer, 200 mg of acetonitrile-based Pd-diimine catalyst 1, and 20 mL of anhydrous dichloromethane were added to a sealed 250 mL Schlenk flask. The temperature was set to 25 °C, and the mixture was stirred thoroughly to ensure complete dissolution of the monomer and catalyst. Polymerization was then carried out under light-shielded conditions at an ethylene pressure of 0.1 MPa for 24 h. After polymerization, the reaction mixture was placed in an open container and purged with cold air to remove the solvent. The polymer was then dissolved in 20 mL of THF, and 36-38% HCl and 30% H2O2 (6-10 drops each) were added, followed by thorough stirring for 3 h to dissolve the Pd particles. Next, the solvent was removed again by cold air purging, and 15 mL of THF was added. Methanol was then added dropwise (total 50 mL) to slowly precipitate the polymer from the solution. The supernatant was removed, and the purification process was repeated twice to obtain a macromolecular initiator containing a small amount of solvent. Finally, the obtained initiator was treated in a vacuum oven at 60°C for 48 hours to obtain the target product HBPE@Br.

[0057] Step 2: Under nitrogen atmosphere, 0.8 g (0.52 mmol Br) of the macromolecular initiator HBPE@Br synthesized in Step 1 was dissolved in 12 mL of anhydrous toluene and injected into a 100 mL Schlenk flask. Then, the monomers St (98.8 mmol), FMA (5.2 mmol), and ligand PMDETA (1.04 mmol) were added and thoroughly stirred to form a stable and homogeneous solution. Further, the mixed solution was subjected to a liquid nitrogen freezing-vacuuming-thawing cycle three times to remove oxygen from the solution. Subsequently, 0.52 mmol CuBr was added under nitrogen protection, and the reaction was continued at a constant temperature of 90 °C for 6 h. After polymerization, the solvent was dried with cold air and dissolved in 15 mL of THF. Methanol (45 mL in total) was added dropwise to precipitate the polymer. Once no more precipitate appeared, the supernatant was removed. The purification process was repeated twice, and the residual solvent in the polymer was removed by a vacuum oven at 30°C for 48 hours, finally yielding the target product HBPE@P(SrF).

[0058] Step 3: Take 80 mg of HBPE@P(SrF) synthesized in Step 2, 640 mg of h-BN powder, and 80 mL of chloroform and put them into a 100 mL cylindrical glass bottle. Seal the bottle with PTFE tape and sealing film. Further, control the temperature of the ultrasonic bath at 25-35℃ using circulating cooling water, and ultrasonically treat the mixture at a power of 240 W for a total of 48 hours. After ultrasonication, centrifuge the resulting mixture (3000 rpm, 45 min) to remove large, unpeeled h-BN fragments. Let the centrifuged mixture stand for 30 min and collect the supernatant dispersion. Then, remove the free polymer from the dispersion by vacuum filtration using a PTFE membrane with an average pore size of 200 nm. After filtration, the filter membrane was placed in 20 mL of chloroform for ultrasonic redispersion (100 W, 3 h). The ultrasonic redispersion was repeated twice during the washing process and the filtration was repeated three times. The BNNSs filter cake was then removed from the PTFE filter membrane and allowed to stand at room temperature for 30 min until the solvent evaporated completely, finally yielding BNNSs powder free of free polymer.

[0059] 2. Characterization and Testing

[0060] (1) Proton nuclear magnetic resonance spectrum 1 H NMR)

[0061] HBPE@Br and furanyl hyperbranched polyethylene HBPE@P(SrF) 1 H NMR was measured using a 500MHz AVANCE III nuclear magnetic resonance spectrometer (Bruker, Switzerland), with deuterated chloroform as the solvent and a test temperature of 25°C.

[0062] (2) TEM test

[0063] High-resolution TEM images of BNNSs were obtained using a Tecnai G2 S-Twin electron microscope (FEI, Switzerland). Before testing, a small amount of low-concentration BNNSs dispersion was dropped onto a non-porous carbon support membrane and dried with an infrared lamp to obtain the test sample.

[0064] 3. Test Result Analysis

[0065] Figure 3 For HBPE@Br and HBPE@P(SrF) 1 The H NMR spectrum shows that furfuryl methacrylate and styrene have been successfully grafted onto hyperbranched polyethylene, with grafting rates of styrene and furfuryl methacrylate of 79.6 mol% and 0.6 mol%, respectively. Figure 4TEM images of boron nitride nanosheets show that oligolayer low-defect two-dimensional nanosheets were successfully obtained by exfoliation using furanyl hyperbranched polyethylene as an additive, with lateral dimensions ranging from 100 to 250 nm. Figure 5 As shown, TG tests were performed on unpeeled h-BN powder and ultrasonically peeled and washed BNNSs. It was found that the weight of h-BN did not change significantly with increasing temperature, while for BNNSs, the mass had decreased by 33.9% when the temperature was raised to 550℃. This indicates that 33.9% of furanyl hyperbranched polyethylene was adsorbed on the surface of BNNSs.

[0066] Example 2, Comparative Examples 1-4

[0067] 1. Sample preparation

[0068] (1) Example 2 provides a method for preparing a thermally conductive adhesive with furanyl hyperbranched polyethylene as the matrix and boron nitride nanosheets as the filler. The specific steps are as follows:

[0069] Step 1: Take 170.8 mg of the polymer HBPE@P(SrF) synthesized in Example 1, 1.6 mg of BMI, and 27.2 mg of BNNSs obtained in Example 1 (containing 9.2 mg of HBPE@P(SrF)) into a glass bottle, add 2 mL of dichloromethane, and place in an ultrasonic bath (100 W, 8 h) to redisperse the BNNSs uniformly in the solution, thus obtaining a pre-cured adhesive solution. The total amount of HBPE@P(SrF) is maintained at 180 mg, the concentration is 90 mg / mL, and the mass of pure BNNSs is 10% of the mass of HBPE@P(SrF).

[0070] Step 2: The pre-cured solution obtained above is drip-coated onto the surface of a glass slide using a solution casting method, and then overlapped with another glass slide to form a sandwich structure with an adhesive layer in the middle, with an overlap area of ​​20mm × 25.6mm. Further, the overlapped sample is placed in an oven at 30℃ for 5 days to cure, obtaining a composite adhesive sample for subsequent shear performance testing.

[0071] (2) Comparison Example 1

[0072] Comparative Example 1 provides a method for preparing an adhesive based on pure HBPE@P(SrF), the specific steps of which are as follows:

[0073] Step 1: Weigh 180mg HBPE@P(SrF) and 1.6mg BMI into a glass bottle, add 2mL of dichloromethane solvent, and sonicate at room temperature for 1h to obtain a pre-cured solution of pure adhesive.

[0074] Step 2: The operation steps are the same as those in Step 2 of Example 2, and will not be repeated here.

[0075] (3) Comparative Example 2

[0076] The preparation process is the same as in Example 2, except that the mass of pure BNNSs is 20% of the mass of HBPE@P(SrF).

[0077] (3) Comparison Example 3

[0078] The preparation process is the same as in Example 2, except that the mass of pure BNNSs is 30% of the mass of HBPE@P(SrF).

[0079] (4) Comparison Example 4

[0080] The preparation process is the same as in Example 2, except that the mass of pure BNNSs is 40% of the mass of HBPE@P(SrF).

[0081] 1. Characterization and Testing

[0082] (1) Thermogravimetric analysis (TGA)

[0083] The thermogravimetric curves of h-BN and BNNSs were obtained using an SDT Q600 thermal analyzer (TA Instruments, USA). The sample amount was approximately 5 mg. Test conditions: Under a nitrogen atmosphere, the sample was heated from 25 °C to 100 °C at a heating rate of 20 °C / min, held at that temperature for 10 min, and then heated again to 800 °C at the same heating rate.

[0084] (2) Overlap shear performance test

[0085] The lap shear properties were tested using an Instron 5966 high and low temperature double column tester (Instron Corporation, USA), with a tensile rate of 5 mm / min.

[0086] 2. Comparison and Analysis of Test Results

[0087] The results of tensile tests on HBPE@P(SrF) / BNNSs adhesive samples with different composite ratios are as follows: Figure 6 As shown, the shear strength of the composite adhesive gradually decreases with increasing filler mass fraction, but the effect on shear strength is not significant when the filler content is 10wt% and 20wt%. However, when the filler content reaches 30wt%, its performance drops sharply. When the filler mass fraction reaches 40wt%, its bond strength can still be maintained at around 0.89MPa, as shown in the table below.

[0088] Table 1

[0089]

[0090] Example 3, Comparative Examples 5-8

[0091] 1. Sample preparation

[0092] (1) Example 3 provides a method for preparing thermally conductive discs using boron nitride nanosheets as fillers:

[0093] Step 1: The specific steps are the same as Step 1 in Example 2, and will not be repeated here.

[0094] Step 2: Take the pre-cured solution prepared in Step 1 above and degas it under vacuum for 20 minutes at room temperature. Then add the solution into a PTFE mold with a diameter of 12.7 mm and a depth of 1 mm (pre-sprayed with release agent). After the solvent has completely evaporated, demold the mold in advance and place the resulting sample in a 30℃ oven to cure for 5 days, finally obtaining a cured thermally conductive disc.

[0095] (2) Comparison Example 5

[0096] Comparative Example 5 provides a method for preparing a thermally conductive disc from pure HBPE@P(SrF), the preparation method of which is as follows:

[0097] Step 1: Obtain the pre-cured solution of the adhesive by referring to the process configuration in Comparative Example 1.

[0098] Step 2: Obtain a thermally conductive disc of pure polymer, referring to step 2 in Example 3.

[0099] (3) Comparison Example 6

[0100] The preparation steps are the same as in Example 3, except that the mass of pure BNNSs is 20% of the mass of HBPE@P(SrF).

[0101] (4) Comparison Example 7

[0102] The preparation steps are the same as in Example 3, except that the mass of pure BNNSs is 30% of the mass of HBPE@P(SrF).

[0103] (5) Comparison Example 8

[0104] The preparation steps are the same as in Example 3, except that the mass of pure BNNSs is 40% of the mass of HBPE@P(SrF).

[0105] 2. Characterization and Testing

[0106] (1) Thermal conductivity

[0107] The thermal diffusivity (α) was measured using an LFA467 laser thermal conductivity meter (Netzsch GmbH, Germany).

[0108] Specific heat capacity (C) p The data were characterized by a DSC214 differential scanning calorimeter (Netzsch GmbH, Germany).

[0109] The density (ρ) of composite discs with different BNNSs mass fractions was read by a ME204 electronic densitometer (METTLERTOLEDO, Netherlands).

[0110] The thermal conductivity (λ) is given by the formula λ = α × ρ × C p Calculated.

[0111] (2) Heat transfer test

[0112] Temperature changes on the surface of the disc were captured using a C300 infrared thermal imager (Hangzhou Alpha Co., Ltd., China). Before testing, the heating stage was first heated to 80°C and kept stable. Then, the heat-conducting disc was quickly placed on the heating stage, and the sample was photographed at regular intervals.

[0113] (3) SEM characterization

[0114] SEM images of the cross-sections of thermally conductive discs with different BNNSs mass fractions were obtained using a regulus 8100 field emission scanning electron microscope (Hitachi, Japan). Before testing, the samples were fixed on the sample stage with the cross-section facing upwards using conductive adhesive, and the cross-sections were then sputter-coated with gold.

[0115] 3. Comparison and Analysis of Test Results

[0116] To investigate the effect of BNNSs filling ratio on the thermal conductivity and heat transfer capacity of adhesives, the thermal conductivity and heat transfer rate of adhesives with different BNNSs composite mass fractions were tested. Figure 7 It can be seen that the thermal conductivity of the pure polymer is around 0.204 W / mK. With the increase of the BNNSs composite mass fraction, the thermal conductivity also increases stepwise, reaching approximately 3.275 W / mK when the content is 40 wt%. Specific values ​​are shown in Table 2 below. This also corresponds to the heat transfer rate of the sample. Figure 8 As the filler content increases, the heat transfer rate and steady-state temperature of the composite adhesive gradually increase. On the other hand, cross-sectional SEM analysis of the samples... Figure 9 Characterization showed that as the filler composite ratio increased, the density of BNNSs in the adhesive matrix gradually increased. However, even at high filler ratios, no nanosheet agglomeration was observed, indicating that BNNSs and the matrix have good interfacial compatibility, which greatly reduces the interfacial thermal resistance of the composite adhesive and effectively improves the thermal conductivity and heat transfer capacity of the composite adhesive.

[0117] Table 2

[0118]

[0119] Examples 4-5, Comparative Example 2, Comparative Example 6

[0120] 1. Sample preparation

[0121] Based on the above tests on the shear strength and heat transfer performance of the composite adhesive, it can be found that when the BNNSs filling amount is 20wt%, its shear strength and heat transfer capacity reach a relative balance, that is, it simultaneously possesses high shear strength and heat transfer rate. Therefore, at this filling ratio, the recycling effect of the adhesive will be investigated.

[0122] (1) Example 4 provides a method for preparing a recyclable composite adhesive:

[0123] Step 1: Collect 217.5 mg of the cured BNNSs adhesive sample (containing a total polymer content of 180 mg) from Comparative Example 2 with a filler content of 20 wt%, and heat-treat it at 160 °C for 5 min. After the sample cools to room temperature, add 2 mL of dichloromethane and seal. Place it in an ultrasonic bath and sonicate for 8 h until a uniform and stable dispersion is formed.

[0124] Step 2: The preparation method is the same as step 2 in Example 2, and will not be repeated here.

[0125] (2) Example 5 provides a method for preparing a reusable composite thermally conductive disc:

[0126] Step 1: The process is the same as step 1 in Example 4, and will not be repeated here.

[0127] Step 2: The preparation method is the same as step 2 in Example 3, and will not be repeated here.

[0128] 2. Characterization and Testing

[0129] Shear strength and heat transfer rate were tested in Examples 4-5.

[0130] The testing method is the same as in Examples 2 and 3.

[0131] 3. Comparison and Analysis of Test Results

[0132] like Figure 10 As shown in (a), the adhesive containing 20 wt% BNNSs, after pyrolysis and ultrasonic treatment, reformed into a homogeneous dispersion in dichloromethane. Tensile specimens were prepared using this dispersion for testing, as shown in... Figure 10(b) It can be observed that the recycled composite adhesive still retains approximately 60% of its initial shear strength. Furthermore, characterization by infrared thermography shows no significant difference in heating rate between the recycled sample and the initially cured sample, although the steady-state temperature is somewhat lower. In conclusion, this thermally conductive composite adhesive possesses excellent recyclability.

Claims

1. A method for preparing a recyclable thermally conductive vinyl resin adhesive, characterized in that: The preparation method includes the following steps: (1) Synthesis of furanyl hyperbranched polyethylene: The copolymerization of ethylene and 2-(2-bromoisobutyryloxy)ethyl acrylate monomers was catalyzed by Pd-diimine catalyst through the "chain walking" mechanism to obtain the macromolecular initiator HBPE@Br containing terminal bromine; then, using HBPE@Br as initiator, furfuryl methacrylate and styrene as comonomers, pentamethyldiethylenetriamine or 2,2'-bipyridine as ligands, and CuBr as catalyst, furanyl hyperbranched polyethylene HBPE@P(SrF) was synthesized by atom transfer radical polymerization. (2) Using the furanyl hyperbranched polyethylene HBPE@P(SrF) synthesized in step (1) to exfoliate h-BN with liquid phase assistance, the filter cake of BNNSs adsorbed with HBPE@P(SrF) was obtained by ultrasonication, centrifugation and vacuum filtration. The filter cake was then left to stand at room temperature until the solvent evaporated completely, and finally non-covalent functionalized BNNSs powder without free furanyl hyperbranched polyethylene was obtained. (3) The furanyl hyperbranched polymer synthesized in step (1), maleimide curing agent and organic solvent A are uniformly mixed and dissolved in a container, and the BNNSs powder obtained in step (2) is added. The resulting mixture is ultrasonically treated so that BNNSs is uniformly dispersed in the mixed solution to obtain the adhesive pre-curing solution. (4) Place the obtained pre-cured adhesive solution in an open container at 25°C. Reaction 3 in an 80℃ oven Over 5 days, the solvent gradually evaporates completely, eventually yielding a cross-linked and cured thermally conductive vinyl resin adhesive.

2. The preparation method according to claim 1, characterized in that: The specific operation steps of step (1) are as follows: (1-a) Under the protection of an ethylene atmosphere, ethyl acrylate (2-bromoisobutyryloxy) acrylate, Pd-diimine catalyst, and anhydrous reagent B are added to the reaction vessel, and the mixture is stirred thoroughly while the temperature is controlled at 15°C. At 35 ℃, with an ethylene pressure of 0.01 Reaction 12 under 0.1 MPa conditions After 24 h, the macromolecular initiator HBPE@Br containing terminal bromine was obtained after separation and purification. (1-b) Under a nitrogen atmosphere, HBPE@Br, styrene, furfuryl methacrylate, anhydrous toluene, and ligands were injected into a reaction vessel and stirred thoroughly to form a homogeneous solution. The solution was then subjected to a "liquid nitrogen freezing-vacuuming-thawing" cycle. After the cycle, the catalyst CuBr was added, and the temperature was maintained at 80°C. Reaction at 100℃ for 5 minutes After 12 h of polymerization, furanyl hyperbranched polyethylene HBPE@P(SrF) was obtained by separation and purification.

3. The preparation method according to claim 2, characterized in that: In step (1-a), the initial concentration of 2-(2-bromoisobutyryloxy)ethyl acrylate in the polymerization system is 0.1%. 1.0 mol / L; the mass amount of the Pd-diimine catalyst is 3-34% of the mass amount of 2-(2-bromoisobutyryloxy)ethyl acrylate.

4. The preparation method according to claim 2, characterized in that: In step (1-b), the molar ratio of HBPE@Br, furfuryl methacrylate, styrene, ligand, and CuBr is 1:

5. 80:50 500:0.1 100:0.01 100, where the molar amount of HBPE@Br is expressed as the molar amount of Br contained therein.

5. The preparation method according to claim 4, characterized in that: In step (1-b), the molar ratio of HBPE@Br, furfuryl methacrylate, styrene, ligand, and CuBr is 1:

5. 15:150 250:1 5:0.5 2.

6. The preparation method according to claim 1, characterized in that: In step (2), the preparation process of the BNNSs powder is as follows: First, furanyl hyperbranched polyethylene HBPE@P(SrF), h-BN powder and chloroform are respectively put into a glass container and sealed. Then, the above mixture is placed in an ultrasonic bath for ultrasonic treatment to obtain BNNSs dispersion A mixed with large pieces of h-BN. After centrifugation at a certain speed, BNNSs dispersion A is allowed to stand and the upper dispersion is collected to obtain BNNSs dispersion B containing excess HBPE@P(SrF). Finally, the obtained BNNSs dispersion B is vacuum filtered to remove free furanyl hyperbranched polyethylene to obtain BNNSs filter cake adsorbed with HBPE@P(SrF). The filter cake is allowed to stand at room temperature until the solvent evaporates completely to finally obtain non-covalent functionalized BNNSs powder without free furanyl hyperbranched polyethylene.

7. The preparation method according to claim 6, characterized in that: In step (2), the ratio of h-BN powder to chloroform is 320. 640 mg: 70 90 mL of furanyl hyperbranched polymer HBPE@P(SrF) was added at a mass ratio of 0.125 to h-BN. twenty one.

8. The preparation method according to claim 7, characterized in that: In step (2), the mass ratio of the furanyl hyperbranched polymer HBPE@P(SrF) to h-BN is 0.

125. 0.6: 1。 9. The preparation method according to any one of claims 6-8, characterized in that: In step (2), the ultrasonic pool power is 100. 320 W, cumulative ultrasound time 8 72 h, ultrasonic temperature at 15 BNNSs dispersion A was obtained at 35 °C; BNNSs dispersion A was centrifuged at room temperature at a speed of 1000 rpm. 5000 rpm, centrifugation time controlled at 20 minutes 60 min; after centrifugation, let the dispersion stand for another 30 min. The mixture was heated for 60 min, and the upper dispersion was collected to obtain BNNSs dispersion B. BNNSs dispersion B was then vacuum filtered using a microporous membrane with an average pore size of 0.1 mm. The membrane, with a thickness of 0.2 μm, is made of one of PA6, PTFE, PVDF, or Al2O3. At room temperature, the filter membrane deposited with BNNSs is placed in chloroform and then dispersed again by ultrasonication for 0.5 μm. 24 hours, ultrasonic power of 40 100 W; This vacuum filtration-ultrasonic redispersion can be performed multiple times as needed. Finally, the BNNSs filter cake is removed from the filter membrane and left to stand at room temperature until the solvent evaporates completely, thus obtaining BNNSs powder without free furanyl hyperbranched polyethylene.

10. The preparation method according to claim 1, characterized in that: In step (3), the added maleimide curing agent is 4,4'-methylenebis(N-phenylmaleimide), and its addition amount is 0.5% of the mass of the added furanyl hyperbranched polyethylene. 3%.

11. The preparation method according to claim 1, characterized in that: In step (3), the added maleimide curing agent is 4,4'-methylenebis(N-phenylmaleimide), and its addition amount is 0.9-1% of the mass of the added furanyl hyperbranched polyethylene.

12. The preparation method according to claim 1, characterized in that: In step (3), with the mass of polymer HBPE@P(SrF) as 100%, the mass fraction of BNNSs is 10%. 40%.

13. The preparation method according to claim 1, characterized in that: In step (3), the mass fraction of BNNSs is 20%, with the mass of polymer HBPE@P(SrF) being 100%.

14. The preparation method according to claim 1, characterized in that: In step (4), the obtained pre-cured adhesive solution is placed in an open oven at 30 °C for 5 days to react.

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