A liquid crystal epoxy monomer and a preparation method thereof, and an intrinsic high-thermal-conductivity remodelable liquid crystal epoxy resin and a preparation method thereof

Abstract

The application belongs to the technical field of epoxy resin materials, and particularly relates to a liquid crystal epoxy monomer and a preparation method thereof, an intrinsic high-thermal-conductivity remodelable liquid crystal epoxy resin and a preparation method thereof. The epoxy resin prepared from the liquid crystal epoxy monomer has excellent intrinsic thermal conductivity and remodelability.

Description

Technical Field

[0001] This invention belongs to the field of epoxy resin material technology, specifically relating to a liquid crystal epoxy monomer and its preparation method, and an intrinsically high thermal conductivity remodelable liquid crystal epoxy resin and its preparation method. Background Technology

[0002] Epoxy resins are considered excellent substrates and encapsulation materials for electronic devices due to their low curing shrinkage and excellent mechanical strength, insulation properties, and chemical resistance after curing. However, traditional epoxy resins form a disordered cross-linked network structure after curing, leading to severe phonon scattering. Their intrinsic thermal conductivity (λ) is typically only 0.2 W / (m·K), and their high rigidity and low elongation cannot meet the requirements of today's flexible electronic devices. Furthermore, the permanent three-dimensional cross-linked network formed after curing traditional epoxy resins cannot be reprocessed or recycled, resulting in resource waste and environmental burden. Against this backdrop, improving the intrinsic thermal conductivity of epoxy resins and modifying their traditional thermosetting properties to achieve recycling while maintaining their excellent thermal conductivity have become critical issues that urgently need to be addressed in the epoxy resin field. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a liquid crystal epoxy monomer and its preparation method, an intrinsically high thermal conductivity remodelable liquid crystal epoxy resin and its preparation method, wherein the epoxy resin prepared by the liquid crystal epoxy monomer provided by the present invention has excellent intrinsic thermal conductivity and remodelability.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] This invention provides a liquid crystal epoxy monomer having the structure shown in Formula 1:

[0006] Equation 1, where n = 1 or 2.

[0007] The present invention also provides a method for preparing the liquid crystal epoxy monomer described in the above technical solution, comprising the following steps:

[0008] p-Toluenesulfonyl chloride, an organic alcohol, an acid-binding agent, and a first organic solvent are mixed and subjected to a sulfonation reaction to obtain compound 1; the organic alcohol is diethylene glycol or tetraethylene glycol.

[0009] Compound 1, where n = 1 or 2;

[0010] Compound 1 was mixed with 4,4′-dihydroxybiphenyl, a first basic catalyst, and a second organic solvent to carry out a substitution reaction, yielding compound 2.

[0011] Compound 2, where n = 1 or 2;

[0012] Compound 2 was mixed with epichlorohydrin, a phase transfer catalyst, and a second basic catalyst to carry out a ring-opening-ring-closing reaction, yielding a liquid crystal epoxy monomer.

[0013] Preferably, the acid-binding agent includes one or more of triethylamine, pyridine, potassium hydroxide, and potassium carbonate.

[0014] Preferably, the sulfonation reaction is carried out at a temperature of 0-6°C for 12-24 hours.

[0015] Preferably, the first alkaline catalyst comprises one or more of potassium carbonate, cesium carbonate, and sodium hydride.

[0016] Preferably, the substitution reaction is carried out at a temperature of 70-130°C for a time of 40-60 hours.

[0017] Preferably, the phase transfer catalyst comprises one or more of tetrabutylammonium bromide, dodecyltrimethylammonium chloride, benzyltriethylammonium chloride, cyclodextrin, and pyridine.

[0018] Preferably, the ring-opening-ring-closing reaction includes a ring-opening reaction and a ring-closing reaction; the temperature of the ring-opening reaction is 100~130℃; the time of the ring-opening reaction is 1~5h; the temperature of the ring-closing reaction is 30~60℃; and the time of the ring-closing reaction is 0.5~4h.

[0019] This invention also provides an intrinsically high thermal conductivity remodelable liquid crystal epoxy resin, which is prepared by a disulfide bond-containing carboxylic acid curing agent and a liquid crystal epoxy monomer with the aid of an ester exchange catalyst; wherein the liquid crystal epoxy monomer is the liquid crystal epoxy monomer described in the above technical solution or the liquid crystal epoxy monomer prepared by the preparation method described in the above technical solution.

[0020] This invention also provides a method for preparing the intrinsically high thermal conductivity remodelable liquid crystal epoxy resin described in the above technical solution, comprising the following steps:

[0021] A carboxylic acid curing agent containing disulfide bonds and an ester exchange catalyst are added to a heated and molten liquid crystal epoxy monomer. The resulting molten mixture is then hot-pressed and cured to obtain an intrinsically high thermal conductivity remodelable liquid crystal epoxy resin.

[0022] This invention provides a liquid crystal epoxy monomer having the structure shown in Formula 1:

[0023] Equation 1, where n = 1 or 2.

[0024] Beneficial effects:

[0025] The liquid crystal epoxy monomer provided by this invention is a small molecule composed of rigid liquid crystal units bridged by flexible alkoxy chains. The structural unit contains biphenyl groups (rigid liquid crystal units) and flexible alkoxy chains (obtained from diethylene glycol or tetraethylene glycol), giving the epoxy monomer thermotropic liquid crystal properties. The stacking of rigid biphenyl groups, combined with the intermolecular π-π stacking structure, suppresses the random orientation of molecular chains and promotes the formation of ordered domains in a layered structure. Furthermore, the superior flexibility of the molecular chains ensures excellent kinetic crystallization ability and the thermodynamic stability of the ordered domains. During heat transfer, the liquid crystal epoxy resin obtained by curing this structure exhibits efficient phonon conduction along the molecular chains aligned in the ordered domains, thereby significantly improving the thermal conductivity of the epoxy resin bulk. The results of the embodiments show that the intrinsically high thermal conductivity liquid crystal resin provided by this invention has an in-plane λ of 1.95 W / (m·K), which is far higher than that of traditional epoxy resins. Attached Figure Description

[0026] Figure 1 The 1H NMR spectrum of the liquid crystal epoxy monomer LCE1 prepared in Example 1;

[0027] Figure 2 The 1H NMR spectrum of the liquid crystal epoxy monomer LCE2 prepared in Example 2;

[0028] Figure 3 Fourier transform infrared spectra of the liquid crystal epoxy monomers LCE1 and LCE2 prepared in Examples 1 and 2;

[0029] Figure 4 Differential scanning calorimetry curves of the heating and cooling cycle of the liquid crystal epoxy monomer LCE1 prepared in Example 1;

[0030] Figure 5 Differential scanning calorimetry curves of the heating and cooling cycle of the liquid crystal epoxy monomer LCE2 prepared in Example 2;

[0031] Figure 6 A polarizing microscope image of the heating and cooling cycle of the liquid crystal epoxy monomer LCE1 prepared in Example 1;

[0032] Figure 7 A polarizing microscope image of the heating and cooling cycle of the liquid crystal epoxy monomer LCE2 prepared in Example 2;

[0033] Figure 8 Differential scanning calorimetry (DSC) curves of the heating process of liquid crystal epoxy resins LCER1 and LCER2 prepared in Examples 1 and 2.

[0034] Figure 9 X-ray diffraction patterns of liquid crystal epoxy resins LCER1 and LCER2 prepared in Examples 1 and 2;

[0035] Figure 10 Small-angle X-ray scattering spectra of liquid crystal epoxy resins LCER1 and LCER2 prepared in Examples 1 and 2;

[0036] Figure 11 Infrared thermal images of liquid crystal epoxy resins LCER1 and LCER2 prepared in Examples 1 and 2.

[0037] Figure 12 Thermal conductivity diagrams for the three remodelings of liquid crystal epoxy resins LCER1 and LCER2 prepared in Examples 1 and 2.

[0038] Figure 13 Stress-strain curves of liquid crystal epoxy resins LCER1 and LCER2 prepared in Examples 1 and 2 are shown.

[0039] Figure 14 Tensile strength diagrams of the three remodelings of liquid crystal epoxy resins LCER1 and LCER2 prepared in Examples 1 and 2. Detailed Implementation

[0040] This invention provides a liquid crystal epoxy monomer having the structure shown in Formula 1:

[0041] Equation 1, where n = 1 or 2.

[0042] Unless otherwise specified, the present invention does not have special requirements on the source of raw materials used, and commercially available products well known to those skilled in the art can be used.

[0043] As one embodiment, the structural formula of the liquid crystal epoxy monomer is as follows: or .

[0044] In this invention, the liquid crystal epoxy monomer is an epoxy monomer with diethylene glycol or tetraethylene glycol as flexible chain segments bridging biphenyl liquid crystal units. The liquid crystal epoxy monomer provided by this invention contains biphenyl groups (rigid liquid crystal units) and alkoxy chains (flexible chains), giving the epoxy monomer thermotropic liquid crystal properties. The stacking of rigid biphenyl groups, combined with the intermolecular π-π stacking structure, suppresses the random orientation of molecular chains and promotes the formation of ordered domains in the layered structure. According to the embodiments, the liquid crystal epoxy resin prepared using the liquid crystal epoxy monomer of this invention not only has good in-plane thermal conductivity but also can be remolded and reprocessed while maintaining good remolding efficiency.

[0045] The present invention also provides a method for preparing the liquid crystal epoxy monomer described in the above technical solution, comprising the following steps:

[0046] p-Toluenesulfonyl chloride, an organic alcohol, an acid-binding agent, and a first organic solvent are mixed and subjected to a sulfonation reaction to obtain compound 1; the organic alcohol is diethylene glycol or tetraethylene glycol.

[0047] Compound 1, where n = 1 or 2;

[0048] Compound 1 was mixed with 4,4′-dihydroxybiphenyl, a first basic catalyst, and a second organic solvent to carry out a substitution reaction, yielding compound 2.

[0049] Compound 2, where n = 1 or 2;

[0050] Compound 2 was mixed with epichlorohydrin, a phase transfer catalyst, and a second basic catalyst to carry out a ring-opening-ring-closing reaction, yielding a liquid crystal epoxy monomer.

[0051] In this invention, p-toluenesulfonyl chloride, diethylene glycol, an acid-binding agent, and a first organic solvent are mixed and subjected to a sulfonation reaction to obtain compound 1;

[0052] Compound 1, where n = 1 or 2.

[0053] In one embodiment, the acid-binding agent includes one or more of triethylamine, pyridine, potassium hydroxide, and potassium carbonate, with triethylamine being a specific example; the first organic solvent includes one or more of dichloromethane, tetrahydrofuran, and acetone, with dichloromethane being a specific example.

[0054] In one embodiment, the molar ratio of p-toluenesulfonyl chloride to organic alcohol is 2:0.8~0.9, more preferably 2:0.8 or 2:0.9; the molar ratio of p-toluenesulfonyl chloride to acid-binding agent is 1:0.8~1.2, another embodiment is 1:1.0~1.2, and in a specific embodiment it is 1:1 or 1:1.1; the volume ratio of p-toluenesulfonyl chloride to the first organic solvent is 66mmol:50~100mL, and in a specific embodiment it is 66mmol:70mL.

[0055] In one embodiment, the mixing of p-toluenesulfonyl chloride, organic alcohol, acid-binding agent, and first organic solvent includes the following steps: mixing p-toluenesulfonyl chloride and the first organic solvent to obtain a p-toluenesulfonyl chloride solution; and sequentially adding the organic alcohol and acid-binding agent to the p-toluenesulfonyl chloride solution. In one embodiment, the mixing of p-toluenesulfonyl chloride and the first organic solvent is carried out under stirring conditions; the stirring is magnetic stirring; the present invention does not have a particular limitation on the stirring rate and time, as long as the components are mixed evenly. In one embodiment, the organic alcohol and acid-binding agent are added dropwise; the present invention does not have a particular limitation on the dropping rate and time, and dropping rates and times well known to those skilled in the art can be used.

[0056] In this invention, the temperature of the sulfonation reaction is 0~6℃, and in a specific embodiment it is 0~3℃; the sulfonation reaction is carried out under ice-water bath conditions; the time of the sulfonation reaction is 12~24h, and in a specific embodiment it is 12~18h; the time of the sulfonation reaction begins from the time the raw material is added dropwise.

[0057] As one embodiment, after the sulfonation reaction is completed, the process further includes: washing, first drying, rotary evaporation, recrystallization and second drying of the reaction solution obtained from the sulfonation reaction in sequence to obtain compound 1.

[0058] In one embodiment, the washing is performed sequentially with a saturated sodium bicarbonate aqueous solution and a distilled aqueous solution; the washing equipment is a separatory funnel; the number of washing cycles for the saturated sodium bicarbonate aqueous solution and distilled water is 2 to 4 times, and in a specific embodiment, it is 3 times.

[0059] After washing, the present invention performs a first drying on the material obtained after washing; the first drying is carried out using a desiccant; the desiccant is anhydrous magnesium sulfate. The present invention does not specifically limit the parameters of the rotary evaporation, as long as the first organic solvent can be removed.

[0060] In one embodiment, the solvent used for recrystallization is ethanol; the recrystallization temperature is 65~75℃, specifically 70℃ in this embodiment; the second drying temperature is 30~60℃, specifically 60℃ in this embodiment, and the time is 12~18h, specifically 12h in this embodiment; the second drying method is vacuum drying; the vacuum drying is carried out in a vacuum drying oven; the vacuum degree of the vacuum drying is -0.08~-0.1MPa, specifically -0.1MPa in this embodiment.

[0061] In this invention, the principle of the sulfonation reaction is as shown in Formula 2:

[0062] Equation 2.

[0063] After obtaining compound 1, the present invention mixes compound 1 with 4,4′-dihydroxybiphenyl, a first basic catalyst and a second organic solvent to carry out a substitution reaction to obtain compound 2;

[0064] Compound 2, where n = 1 or 2.

[0065] In one embodiment, the first alkaline catalyst includes one or more of potassium carbonate, cesium carbonate, and sodium hydride, with potassium carbonate being a specific example; the second organic solvent includes tetrahydrofuran and acetone.

[0066] In one embodiment, the molar ratio of compound 1 to 4,4′-dihydroxybiphenyl is 1:1.8~2.3, another embodiment is 1:2~2.3, and in specific embodiments it is 1:2 or 1:2.1; the amount of the first alkaline catalyst is 3~5 times the amount of 4,4′-dihydroxybiphenyl, and in specific embodiments it is 5 times; when the first alkaline catalyst includes potassium carbonate, the molar ratio of compound 1 to potassium carbonate is 1:3~10, and in specific embodiments it is 1:3 or 1:10; the ratio of compound 1 to the second organic solvent is 30mmol:80~120mL, and in specific embodiments it is 30mmol:100mL.

[0067] The present invention comprises the following steps of mixing compound 1 with 4,4'-dihydroxybiphenyl, a first basic catalyst, and a second organic solvent: dissolving compound 1 and 4,4'-dihydroxybiphenyl in a second organic solvent; adding a first basic catalyst to the resulting mixture; and mixing compound 1, 4,4'-dihydroxybiphenyl, and the second organic solvent under stirring conditions; wherein the stirring is magnetic stirring.

[0068] In one embodiment, the temperature of the substitution reaction is 70~130℃, specifically 80~90℃, and the time is 40~60h, specifically 48h; the substitution reaction is carried out under reflux conditions.

[0069] In one embodiment, after the substitution reaction, the process further includes: sequentially subjecting the solution after the substitution reaction to a first filtration, a first wash, a second filtration, a second wash, a third filtration, rotary evaporation, a third wash, a fourth filtration, and drying to obtain compound 2. In this invention, the first, second, third, and fourth filtrations do not have specific limitations on the vacuum level or filter paper; they only need to be able to separate the solid and liquid components of the solution after the substitution reaction. The first wash involves washing the solid separated product obtained from the first filtration with a second organic solvent, followed by a second filtration. The temperature of the first wash is 70-90°C, specifically 80°C in this embodiment, and the time is 0.8-1.2 hours, specifically 1 hour in this embodiment. The second wash involves washing the solid separated product obtained from the second filtration with a second organic solvent, followed by a third filtration. The temperature of the second wash is 70-90°C, specifically 80°C in this embodiment, and the time is 0.8-1.2 hours, specifically 1 hour in this embodiment. This invention does not specifically limit the parameters of the rotary evaporation, as long as the organic solvent can be removed; the third washing involves sequentially washing with saturated sodium bicarbonate solution, distilled water, ethanol, and dichloromethane, and this invention does not limit the number of washing cycles; the drying temperature is 55~65℃, specifically 60℃ in this embodiment, and the time is 12~24h, specifically 12~18h in this embodiment; the drying method is vacuum drying; the equipment used for vacuum drying is a vacuum drying oven; the vacuum degree of the vacuum drying oven is -0.08~-0.1MPa, specifically -0.1MPa in this embodiment.

[0070] In this invention, the principle of the substitution reaction is as shown in Formula 3:

[0071] Formula 3.

[0072] After obtaining compound 2, the present invention mixes compound 2 with epichlorohydrin, a phase transfer catalyst and a second basic catalyst to carry out a ring-opening-ring-closing reaction to obtain a liquid crystal epoxy monomer.

[0073] In one embodiment, the epichlorohydrin undergoes a ring-opening reaction with compound 2, and is also used as a solvent in the reaction.

[0074] In one embodiment, the molar ratio of compound 2 to epichlorohydrin is 1:10 to 20, and in a specific embodiment it is 1:10.

[0075] In one embodiment, the second alkaline catalyst is a sodium hydroxide solution; the mass concentration of the sodium hydroxide aqueous solution is 13-18%, and in a specific embodiment it is 14-16%; the phase transfer catalyst includes one or more of tetrabutylammonium bromide, dodecyltrimethylammonium chloride, benzyltriethylammonium chloride, cyclodextrin and pyridine, and in a specific embodiment it is benzyltriethylammonium chloride.

[0076] In one embodiment, the molar ratio of compound 2 to sodium hydroxide in the sodium hydroxide aqueous solution is 1:2 to 2.2, and in a specific embodiment it is 1:2; the molar ratio of compound 2 to the phase transfer catalyst is 1:0.02 to 0.04, and in a specific embodiment it is 1:0.03.

[0077] In this invention, benzyltriethylammonium chloride is used as a phase transfer catalyst to promote the reaction of compound 2 with epichlorohydrin.

[0078] In one embodiment, the compound 2 is mixed with epichlorohydrin, the second phase transfer catalyst and the basic catalyst by mixing the compound 2 with epichlorohydrin and the phase transfer catalyst, refluxing, and then adding the second basic catalyst to the reaction system; the refluxing temperature is 110~130℃, 120℃ in a specific embodiment, and the time is 30~50min, 40min in a specific embodiment.

[0079] In one embodiment, the sodium hydroxide aqueous solution is added dropwise; the present invention does not impose any special limitations on the rate and time of the dropwise addition, and dropwise rates and times known to those skilled in the art can be used.

[0080] In one embodiment, the ring-opening-ring-closing reaction includes a ring-opening reaction and a ring-closing reaction; the temperature of the ring-opening reaction is 100~130℃, specifically 120℃ in this embodiment; the time of the ring-opening reaction is 1~5h, specifically 2~4h in this embodiment; the temperature of the ring-closing reaction is 30~60℃, specifically 40℃ in this embodiment; the time of the ring-closing reaction is 0.5~4h, specifically 0.8~1.2h in this embodiment.

[0081] In this invention, the ring-opening reaction is a ring-opening reaction of the epoxy group, and the ring-closing reaction is a ring-closing reaction of the epioxyethyne group. Hydroxyl groups typically undergo a nucleophilic ring-opening reaction with epichlorohydrin, where the hydroxyl group acts as a nucleophile, attacking the epoxy group and causing the epoxy ring to cleave, forming a new carbon-oxygen bond.

[0082] In one embodiment, after the epoxy ring-opening-ring-closing reaction, the method further includes: sequentially subjecting the product obtained from the epoxy ring-opening-ring-closing reaction to rotary evaporation, washing, and drying; the rotary evaporation temperature is 65~75℃, specifically 75℃ in this embodiment; the rotary evaporation speed is 80~100 rpm, specifically 90 rpm in this embodiment. In this invention, the purpose of the rotary evaporation is to remove epichlorohydrin.

[0083] In one embodiment, the washing solvent used is ethanol and distilled water; the ethanol washing is performed 4 to 6 times, specifically 3 to 5 times in this embodiment; the distilled water washing is performed 4 to 6 times, specifically 3 to 5 times in this embodiment.

[0084] In one embodiment, the drying is vacuum drying; the equipment used for vacuum drying is a vacuum drying oven; the drying temperature is 55~65℃, specifically 60℃ in this embodiment, and the drying time is 8~15h, specifically 12h in this embodiment; the vacuum degree of the vacuum drying oven is -0.08~-0.1MPa, specifically -0.1MPa in this embodiment.

[0085] In this invention, the principle of the epoxy ring-opening-ring-closing reaction is shown in Equation 4:

[0086] Formula 4.

[0087] This invention also provides an intrinsically high thermal conductivity remodelable liquid crystal epoxy resin, which is prepared by a disulfide bond-containing carboxylic acid curing agent and a liquid crystal epoxy monomer with the aid of an ester exchange catalyst; wherein the liquid crystal epoxy monomer is the liquid crystal epoxy monomer described in the above technical solution or the liquid crystal epoxy monomer prepared by the preparation method described in the above technical solution.

[0088] The intrinsically high thermal conductivity remodelable liquid crystal epoxy resin prepared by this invention contains abundant ester bonds and disulfide bonds.

[0089] In one embodiment, the molar ratio of the liquid crystal epoxy monomer to the carboxylic acid curing agent containing disulfide bonds is 0.8~1.3:1~1.2, and in a specific embodiment it is 0.9~1.0:1; the amount of the transesterification catalyst is 4~6 mol% of the amount of the carboxylic acid curing agent containing disulfide bonds, and in a specific embodiment it is 5 mol.

[0090] As one embodiment, the carboxylic acid curing agent containing disulfide bonds includes one or more of 4,4′-dithiodibutyric acid, 3,3′-dithiodipropionic acid, and 4,4′-dicarboxylic acid diphenyl disulfide, with 4,4′-dithiodibutyric acid being a specific example. When the carboxylic acid curing agent containing disulfide bonds is two or more of the above-mentioned specific selections, the present invention does not impose any special limitation on the proportion of the specific substances, and they can be mixed in any proportion.

[0091] In one embodiment, the transesterification catalyst includes one or more of 1,5,7-triazabicyclo[4.4.0]dec-5-ene, zinc acetoacetate, and zinc naphthenate, with 1,5,7-triazabicyclo[4.4.0]dec-5-ene being a specific example.

[0092] This invention also provides a method for preparing the intrinsically high thermal conductivity remodelable liquid crystal epoxy resin described in the above technical solution, comprising the following steps:

[0093] A carboxylic acid curing agent containing disulfide bonds and an ester exchange catalyst are added to a heated and molten liquid crystal epoxy monomer. The resulting molten mixture is then hot-pressed and cured to obtain an intrinsically high thermal conductivity remodelable liquid crystal epoxy resin.

[0094] As one implementation method, adding a carboxylic acid curing agent containing disulfide bonds and an ester exchange catalyst to the heated and molten liquid crystal epoxy monomer is as follows: the liquid crystal epoxy monomer is added to a polytetrafluoroethylene beaker and heated to melt, then the carboxylic acid curing agent containing disulfide bonds is added to it, and after stirring evenly, the ester exchange catalyst is added.

[0095] In one embodiment, the temperature of the hot-press curing is 150~200℃, and in a specific embodiment it is 165~185℃; the pressure of the hot-press curing is 7~11MPa, and in a specific embodiment it is 8~10MPa; the heat preservation and pressure holding time of the hot-press curing is 2~6h, and in a specific embodiment it is 4~5h.

[0096] As one implementation method, the specific steps of the hot-press curing are as follows: the molten mixture is quickly transferred between two templates covered with a polyimide film, and hot-pressed and cured using a flat vulcanizing machine. The resulting cured product is then naturally cooled to room temperature and demolded.

[0097] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, but they should not be construed as limiting the scope of protection of the present invention.

[0098] Example 1

[0099] 12.6 g (66 mmol) of p-toluenesulfonyl chloride was dissolved in 70 mL of dichloromethane and cooled to 0 °C in an ice-water bath. Then, 2.8 mL (30 mmol) of diethylene glycol and 9.1 mL (66 mmol) of triethylamine were slowly added dropwise. The resulting mixture was reacted with stirring for 18 h. The organic phase was then washed three times each with saturated sodium bicarbonate aqueous solution and distilled water, dried over anhydrous magnesium sulfate, and the dichloromethane was removed by rotary evaporation to obtain a transparent liquid product. Finally, recrystallization from ethanol at 70 °C yielded a white needle-like crystalline product, which was dried at 60 °C under a vacuum of -0.1 MPa for 12 h to obtain compound 1.

[0100] 12.4 g (30 mmol) of compound 1 and 11.2 g (60 mmol) of 4,4′-dihydroxybiphenyl were dissolved in 100 mL of tetrahydrofuran and stirred until homogeneous. Then, 41.4 g (300 mmol) of potassium carbonate was added to the mixture, and the mixture was refluxed at 80 °C for 48 h. After the reaction, the mixture was filtered while hot. The residue was washed twice with hot tetrahydrofuran at 80 °C and separated by vacuum filtration. The filtrate was rotary evaporated to remove tetrahydrofuran. The organic phase was washed successively with saturated sodium bicarbonate solution, distilled water, hot ethanol and dichloromethane to obtain a white solid. The product was dried at 60 °C and a vacuum of -0.1 MPa for 12 h to obtain compound 2.

[0101] 8.8 g (20 mmol) of compound 2 was dissolved in 15.6 mL (200 mmol) of epichlorohydrin, and then 0.14 g of benzyltriethylammonium chloride was added. The molar ratio of compound 2 to phase transfer catalyst was 1:0.03. The mixture was refluxed at 120 °C for 40 min, and 10.6 g of 15 wt% sodium hydroxide aqueous solution was slowly added dropwise. The molar ratio of compound 2 to sodium hydroxide was 1:2. The mixture was reacted at 120 °C for 3 h, and then at 40 °C for 1 h. The solvent was removed by rotary evaporation at 75 °C and 90 rpm. The white solid was washed three times with ethanol and distilled water, and dried in a vacuum oven at 60 °C and -0.1 MPa for 12 h to obtain the liquid crystal epoxy monomer LCE1.

[0102] The molecular structure of the liquid crystal epoxy monomer LCE1 is shown in Formula 5:

[0103] Formula 5.

[0104] Example 2

[0105] 12.7 g (66 mmol) of p-toluenesulfonyl chloride was dissolved in 70 mL of dichloromethane and cooled to 0 °C in an ice-water bath. Then, 5.0 mL (30 mmol) of tetraethylene glycol and 9.1 mL (66 mmol) of triethylamine were slowly added dropwise. The resulting mixture was reacted with stirring for 18 h. The organic phase was then washed three times with saturated sodium bicarbonate aqueous solution and distilled water, dried over anhydrous magnesium sulfate, and the dichloromethane was removed by rotary evaporation to obtain a transparent liquid product. Finally, recrystallization from ethanol at 70 °C yielded a white needle-like crystalline product, which was dried at 60 °C under a vacuum of -0.1 MPa for 12 h to give compound 1.

[0106] 15.0 g (30 mmol) of compound 1 and 11.3 g (60 mmol) of 4,4′-dihydroxybiphenyl were dissolved in 100 mL of tetrahydrofuran and stirred until homogeneous. Then, 41.4 g (300 mmol) of potassium carbonate was added to the mixture, and the mixture was refluxed at 80 °C for 48 h. After the reaction, the mixture was filtered while hot. The residue was washed twice with hot tetrahydrofuran at 80 °C and separated by vacuum filtration. The filtrate was rotary evaporated to remove tetrahydrofuran. The organic phase was washed successively with saturated sodium bicarbonate solution, distilled water, hot ethanol and dichloromethane to obtain a white solid. The product was dried at 60 °C and a vacuum of -0.1 MPa for 12 h to obtain compound 2.

[0107] 10.4 g (20 mmol) of compound 2 was dissolved in 15.6 mL (200 mmol) of epichlorohydrin, and then 0.14 g of benzyltriethylammonium chloride was added. The molar ratio of compound 2 to phase transfer catalyst was 1:0.03. The mixture was refluxed at 120 °C for 40 min, and 10.6 g of 15 wt% NaOH aqueous solution was slowly added dropwise. The molar ratio of compound 2 to sodium hydroxide was 1:2. The mixture was reacted at 120 °C for 3 h, and then at 40 °C for 1 h. The solvent was removed by rotary evaporation at 75 °C and 90 rpm. The white solid was washed three times with ethanol and distilled water, and dried in a vacuum oven at 60 °C and -0.1 MPa for 12 h to obtain the liquid crystal epoxy monomer LCE2.

[0108] The molecular structure of the liquid crystal epoxy monomer LCE2 is shown in Formula 6:

[0109] Formula 6.

[0110] Application Example 1

[0111] The liquid crystal epoxy resin LCE1 was prepared by adding 5.54 g (10 mmol) of LCE1 prepared in Example 1 and 2.38 g (10 mmol) of 4,4′-dithiodibutyric acid to a polytetrafluoroethylene beaker and heating it to a molten state and mixing it evenly. Then, 0.07 g (0.5 mmol) of 1,5,7-triazabicyclo[4.4.0]dec-5-ene was added. After cooling slightly, the mixture was quickly transferred between two templates covered with a polyimide film. The mixture was hot-pressed for 4 hours at 185°C and 8 MPa using a flat vulcanizing machine. After the reaction was completed, the cured material was naturally cooled to room temperature and demolded to obtain the liquid crystal epoxy resin LCE1.

[0112] Application Example 2

[0113] The liquid crystal epoxy resin LCE2 was prepared by adding 6.42 g (10 mmol) of LCE2 prepared in Example 2 and 2.38 g (10 mmol) of 4,4′-dithiodibutyric acid to a polytetrafluoroethylene beaker and heating it to a molten state and mixing it evenly. Then, 0.07 g (0.5 mmol) of 1,5,7-triazabicyclo[4.4.0]dec-5-ene was added. After slightly cooling, the mixture was quickly transferred between two templates covered with a polyimide film. The mixture was hot-pressed for 4 hours at 165°C and 8 MPa using a flat vulcanizing machine. After the reaction was completed, the cured material was naturally cooled to room temperature and demolded to obtain the liquid crystal epoxy resin LCE2.

[0114] Performance testing

[0115] 1. The liquid crystal epoxy monomers prepared in Examples 1 and 2 were subjected to proton nuclear magnetic resonance (NMR) spectroscopy. The results are shown in the figures below. Figures 1-2 It can be seen that the peaks with chemical shifts of 7.47 ppm and 6.99 ppm belong to the characteristic peaks of protons on the benzene ring of the biphenyl structure; the peaks with chemical shifts of 4.24 ppm, 4.00 ppm, 3.38 ppm, 2.93 ppm, and 2.79 ppm belong to the characteristic peaks of protons on the epoxy groups. Meanwhile, Figure 1 The chemical shifts at 4.21 ppm and 3.97 ppm are attributed to hydrogen atoms on the LCE1 flexible chain; Figure 2 The chemical shifts at 4.14 ppm, 3.87 ppm, 3.73 ppm and 3.71 ppm are attributed to hydrogen atoms on the LCE2 flexible chain.

[0116] 2. Fourier transform infrared spectroscopy was performed on the liquid crystal epoxy monomers prepared in Examples 1 and 2. The results are shown in the figure. Figure 3 It can be seen that LCE1 and LCE2 are at 3340cm. -1 There is no hydroxyl peak at 912 cm⁻¹, but at 912 cm⁻¹... -1 The appearance of stretching vibration peaks of epoxy groups at the 2870–3100 cm⁻¹ indicates that the terminal hydroxyl group successfully formed epoxy groups with epichlorohydrin. LCE1 and LCE2 show peaks in the 2870–3100 cm⁻¹ range. -1 Both LCE1 and LCE2 exhibited stretching vibration peaks of the methylene group, with the signal from LCE2 being stronger than that from LCE1. This is because the flexible chain is longer, resulting in an increased number of methylene groups. This confirms that the molecular structures of LCE1 and LCE2 are consistent with their design.

[0117] 3. Differential scanning calorimetry was performed on the liquid crystal epoxy monomers prepared in Examples 1 and 2. The results are shown in the figures below. Figures 4-5 .from Figure 4As can be seen, LCE1 exhibits three endothermic peaks at 168℃, 190℃, and 210℃. The first endothermic peak corresponds to the transition from crystal to smectic liquid crystal phase, the second to the transition from smectic to nematic liquid crystal phase, and the third to the transition from nematic liquid crystal phase to liquid state. During the cooling process, LCE1 shows two exothermic peaks at 192℃ and 158℃, corresponding to the transitions from liquid to liquid crystal phase and from liquid crystal phase to crystal, respectively. This indicates that LCE1 is a bidirectional thermotropic liquid crystal, with a heating range of 168~210℃. Figure 5 It can be seen that LCE2 only showed one endothermic peak and one exothermic peak (158℃ and 148℃) during the heating and cooling process, respectively, which correspond to the melting and crystallization processes, indicating that LCE2 is a crystalline small molecule.

[0118] 4. Polarizing microscope images of the heating and cooling processes of the liquid crystal epoxy monomers prepared in Examples 1 and 2 are shown in the following figures. Figures 6-7 As shown. Figure 6 As shown in the polarized light microscope images of LCE1 at different temperatures during the heating process, LCE1 remained in a crystalline state before reaching 150℃. When the temperature rose to 180℃, the crystals of LCE1 gradually disappeared, and it exhibited a flowing state, indicating the appearance of a liquid crystal phase. With further increases in temperature, the birefringence decreased until it disappeared completely, reaching an isotropic liquid state at 220℃. Polarized light microscope images at different temperatures during the cooling process show that LCE1 began to exhibit birefringence at 210℃, and when the temperature dropped to 190℃, the field of view was filled with bright birefringence. With further decreases in temperature, the crystallization became more complete, and the field of view darkened. Figure 7 It can be seen that LCE2 remained in a crystalline state before reaching 158℃. When the temperature was slightly increased to 162℃, the crystals of LCE2 rapidly disappeared, transforming into an isotropic liquid. During the cooling process, LCE2 began to crystallize at 160℃, and the crystals quickly filled the entire field of view. This indicates that LCE2 does not have a liquid crystal phase and is a crystalline small molecule. This is because when the flexible chain segments are too long, the proportion of flexibility increases significantly, and the overall flexibility of the molecule is too high. The π-π interactions between rigid units are weakened, making it impossible to maintain the orientational order required for a liquid crystal phase. The molecules tend to form a lower-energy crystal structure through closer stacking.

[0119] As can be seen from the above embodiments, the present invention provides liquid crystal epoxy monomers LCE1 and LCE2 having the structures shown in Formulas 5 and 6. Because the liquid crystal epoxy monomers possess highly rigid diphenyl groups and have a highly ordered main chain, they easily form local crystalline structures. The cured liquid crystal epoxy resin has a locally ordered network structure, exhibiting both microscopic anisotropy and macroscopic isotropy.

[0120] 5. Figure 8 The image shows the temperature rise differential scanning calorimetry (DSC) curves of the liquid crystal epoxy resins obtained in Examples 1 and 2. Figure 8 It can be seen that the glass transition temperatures of the liquid crystal epoxy resins obtained in Application Examples 1 and 2 are 139.2℃ and 78.0℃, respectively; meanwhile, the liquid crystal epoxy resin described in Application Example 1 has an isotropic transition temperature of 175.3℃.

[0121] 6. Figure 9 The X-ray diffraction curves of the liquid crystal epoxy resins obtained in Examples 1 and 2 show that LCE1 from Example 1 exhibits six sharp diffraction peaks at 2θ = 19.9°, 21.1°, 23.8°, 8.7°, 32.0°, and 45.6°, while LCE2 from Example 2 only exhibits three sharp diffraction peaks at 2θ = 19.6°, 22.1°, and 27.7°. The interplanar spacings of LCE1, calculated using Bragg's formula, are 0.446 nm, 0.421 nm, 0.373 nm, 0.311 nm, 0.279 nm, and 0.198 nm; while those of LCE2 are 0.452 nm, 0.402 nm, and 0.322 nm. The relatively smaller interplanar spacings indicate that LCE1 has a more dense crystal structure.

[0122] 7. Figure 10 The small-angle X-ray scattering (SAXS) curves of the liquid crystal epoxy resins obtained using Examples 1 and 2 show that LCE R1 exhibits high SXS at q = 0.061 Å. -1 0.18Å -1 and 0.34Å -1 Three scattering peaks appeared, with a ratio of approximately 1:3:6 between their positions, while LCE R2 only showed up at q = 0.27 Å. -1 A scattering peak appeared. This indicates that the electron cloud density is not uniform in the network systems of the two LCERs, resulting in strong scattering peaks in both. Specifically, the proportional scattering peaks of LCER1 indicate that it formed a layered structure during the curing process. The thickness of the main scattering peak of LCER1 was calculated using L=2π / q, yielding a layer thickness of 10.3 nm. LCER2, however, does not possess a layered structure; its ordered domains are uniformly dispersed within the network structure, with a distance of 2.3 nm between ordered periods.

[0123] 8. The thermal conductivity of the liquid crystal epoxy resins obtained in Application Examples 1 and 2 was tested using a Hot Disk thermal conductivity meter. The in-plane λ of LCER1 was 1.95 W / (m·K), which was higher than that of LCER2 (1.47 W / (m·K). This is because the rigid biphenyl units stacked together suppressed the random orientation of the molecular chains and promoted the formation of ordered domains in the layered structure. Furthermore, phonons were efficiently conducted along the molecular chains aligned in the ordered domains, effectively suppressing phonon scattering and thus significantly improving the thermal conductivity of LCER1. The flexible chains not only modulated the liquid crystal properties of the liquid crystal epoxy molecules but also acted as thermal bridges between two liquid crystal units. The shorter the bridge, the higher the phonon transmission efficiency. However, excessively long flexible chains could lead to ineffective molecular stacking, which was not conducive to the ordered arrangement of liquid crystal units and the close packing of liquid crystal domains, thereby increasing phonon scattering. Therefore, the thermal conductivity of LCER1 was better than that of LCER2.

[0124] 9. Figure 11 The images show infrared thermal images of the liquid crystal epoxy resins LCER1 and LCER2 obtained in Examples 1 and 2. It can be seen that, with the same heating time, LCER1 has the highest surface temperature, indicating that its heat diffusion rate is the fastest, reaching 65°C after 24 seconds, further demonstrating its optimal thermal conductivity.

[0125] 10. Figure 12 The thermal conductivity of LCE R1 and LCE R2 after three remodeling cycles is shown. It can be seen that λ retains a good rate after the third reprocessing, reaching 88% and 95% of the original, respectively. LCE R2 exhibits a higher thermal conductivity retention rate after remodeling than LCE R1. This is because the layered structure of LCE R1 is damaged to some extent after repeated exposure to temperature and pressure; while LCE R2, lacking a layered structure, is minimally affected by the reprocessing process due to its relatively uniform network, and thus maintains the highest degree of thermal conductivity path retention.

[0126] 11. Figure 13 The stress-strain curves of the liquid crystal epoxy resins LCE1 and LCE2 obtained in Examples 1 and 2 are shown. It can be seen that as the flexible chain segments increase, the tensile strength of LCE decreases, while the elongation at break increases. Specifically, the tensile strength of LCE1 is 27.1 MPa, higher than that of LCE2 (18.9 MPa). This is because the flexible chains of LCE1 are shorter, with fewer internal molecular chain folds, while the molecular chains of LCE2 are more easily stretched under external force. The lower proportion of rigid structures in the cured network of LCE2 results in weaker intermolecular forces than LCE1, thus exhibiting lower tensile strength and higher elongation at break than LCE1.

[0127] 12. Figure 14The diagram shows the tensile strength of LCER1 and LCER2 after three reprocessing cycles. It can be seen that after three reprocessing cycles, the tensile strengths of LCER1 and LCER2 are 24.1 MPa and 17.4 MPa, respectively, reaching 89% and 92% of their original strengths, both exhibiting high tensile strength retention rates.

[0128] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention and not all embodiments. People can obtain other embodiments based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. An intrinsically high thermal conductivity remodelable liquid crystal epoxy resin, characterized in that, It is prepared by using a carboxylic acid curing agent containing disulfide bonds and a liquid crystal epoxy monomer with the assistance of an ester exchange catalyst; The liquid crystal epoxy monomer has the structure shown in Formula 1: Equation 1, where n = 1 or 2; The carboxylic acid curing agent containing disulfide bonds includes one or more of 4,4′-dithiodibutyric acid, 3,3′-dithiodipropionic acid, and 4,4′-dicarboxylic acid diphenyl disulfide. The molar ratio of the liquid crystal epoxy monomer to the carboxylic acid curing agent containing disulfide bonds is 0.8~1.3:1~1.

2.

2. The intrinsically high thermal conductivity remodelable liquid crystal epoxy resin according to claim 1, characterized in that, The preparation method of the liquid crystal epoxy monomer includes the following steps: p-Toluenesulfonyl chloride, an organic alcohol, an acid-binding agent, and a first organic solvent are mixed and subjected to a sulfonation reaction to obtain compound 1; the organic alcohol is diethylene glycol or tetraethylene glycol. Compound 1, where n = 1 or 2; Compound 1 was mixed with 4,4′-dihydroxybiphenyl, a first basic catalyst, and a second organic solvent to carry out a substitution reaction, yielding compound 2. Compound 2, where n = 1 or 2; Compound 2 was mixed with epichlorohydrin, a phase transfer catalyst, and a second basic catalyst to carry out a ring-opening-ring-closing reaction, yielding a liquid crystal epoxy monomer.

3. The intrinsically high thermal conductivity remodelable liquid crystal epoxy resin according to claim 2, characterized in that, The acid-binding agent includes one or more of triethylamine, pyridine, potassium hydroxide, and potassium carbonate.

4. The intrinsically high thermal conductivity remodelable liquid crystal epoxy resin according to claim 2 or 3, characterized in that, The sulfonation reaction is carried out at a temperature of 0-6°C for 12-24 hours.

5. The intrinsically high thermal conductivity remodelable liquid crystal epoxy resin according to claim 2, characterized in that, The first alkaline catalyst includes one or more of potassium carbonate, cesium carbonate, and sodium hydride.

6. The intrinsically high thermal conductivity remodelable liquid crystal epoxy resin according to claim 2 or 5, characterized in that, The substitution reaction is carried out at a temperature of 70-130°C for a time of 40-60 hours.

7. The intrinsically high thermal conductivity remodelable liquid crystal epoxy resin according to claim 2, characterized in that, The phase transfer catalyst includes one or more of tetrabutylammonium bromide, dodecyltrimethylammonium chloride, benzyltriethylammonium chloride, cyclodextrin, and pyridine.

8. The intrinsically high thermal conductivity remodelable liquid crystal epoxy resin according to claim 2 or 7, characterized in that, The ring-opening-ring-closing reaction includes a ring-opening reaction and a ring-closing reaction; the temperature of the ring-opening reaction is 100~130℃; the time of the ring-opening reaction is 1~5h; the temperature of the ring-closing reaction is 30~60℃; and the time of the ring-closing reaction is 0.5~4h.

9. The method for preparing the intrinsically high thermal conductivity remodelable liquid crystal epoxy resin according to any one of claims 1 to 8, characterized in that, Includes the following steps: A carboxylic acid curing agent containing disulfide bonds and an ester exchange catalyst are added to a heated and molten liquid crystal epoxy monomer. The resulting molten mixture is then hot-pressed and cured to obtain an intrinsically high thermal conductivity remodelable liquid crystal epoxy resin.

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