阅读说明：本技术 一种高导热可重塑液晶弹性体复合材料及制备方法与应用 (High-thermal-conductivity remoldable liquid crystal elastomer composite material and preparation method and application thereof ) 是由 吕满庚 张倩 吴昆� 于 2020-05-27 设计创作，主要内容包括：本发明属于聚合物复合材料技术领域,公开了一种高导热可重塑液晶弹性体复合材料及制备方法与应用。本发明的高导热可重塑液晶弹性体复合材料,由包括巯基封端的液晶预聚物与填料混合后,在巯基交联剂作用下交联反应A得到。本发明还提供一种上述复合材料的制备方法。本发明先通过光致巯基烯点击化学制备了巯基封端的液晶预聚物,然后通过预聚物和巯基交联剂之间的氧化反应得到含二硫键的自修复液晶弹性体,同时,通过原位聚合的方式将导热填料等引入上述弹性体体系中,从而获得具有良好导热性能、可回收重塑功能的复合材料,可应用于航天航空、微电子等领域。(The invention belongs to the technical field of polymer composite materials, and discloses a high-thermal-conductivity remoldable liquid crystal elastomer composite material, and a preparation method and application thereof. The high-thermal-conductivity remoldable liquid crystal elastomer composite material is obtained by mixing a liquid crystal prepolymer containing a mercapto end capping and a filler, and then performing crosslinking reaction A under the action of a mercapto crosslinking agent. The invention also provides a preparation method of the composite material. The invention firstly prepares sulfhydryl terminated liquid crystal prepolymer by photoinduced sulfhydryl alkene click chemistry, then obtains self-repairing liquid crystal elastomer containing disulfide bond by oxidation reaction between the prepolymer and sulfhydryl crosslinking agent, and simultaneously introduces heat-conducting filler and the like into the elastomer system by in-situ polymerization, thereby obtaining composite material with good heat-conducting property and recoverable and remolding functions, which can be applied to the fields of space flight and aviation, microelectronics and the like.)

1. A high-thermal-conductivity remoldable liquid crystal elastomer composite material is characterized in that the composite material is obtained by a crosslinking reaction A under the action of a mercapto crosslinking agent after a mercapto-terminated liquid crystal prepolymer and a filler are mixed.

2. A highly thermally conductive, remodelable liquid crystal elastomer composite as claimed in claim 1, wherein: the mercapto-terminated liquid crystal prepolymer is obtained by a photoinduced mercapto-alkene click chemistry reaction B of a liquid crystal monomer containing ethyleneoxy and a dimercapto compound.

3. A highly thermally conductive, remodelable liquid crystal elastomer composite as claimed in claim 2, wherein: the liquid crystal monomer containing the ethyleneoxy group comprises at least one of 4,4 ' -diethenyloxy biphenyl, 2, 5-bis [4- (allyloxy) benzoyloxy ] benzoate and 4,4 ' -bis (allyloxy) -3,3 ', 5,5 ' -tetramethyl-1, 1 ' -biphenyl; the dimercapto compound comprises at least one of 3, 6-dioxa-1, 8-octane dithiol, 1, 2-ethanedithiol, 1, 4-butanedithiol and 1, 6-hexanedithiol.

4. A highly thermally conductive, remodelable liquid crystal elastomer composite as claimed in claim 2, wherein: the molar ratio of the liquid crystal monomer containing the ethyleneoxy group to the dimercapto compound is 1:1.1-1: 1.7.

5. A highly thermally conductive, remodelable liquid crystal elastomer composite as claimed in claim 2, wherein: the reaction B is carried out under the action of a photoinitiator; the photoinitiator comprises at least one of benzoin dimethyl ether, benzophenone, 2-hydroxy-2-methyl-1-phenyl-1-propyl ketone, 1-hydroxycyclohexyl phenyl ketone and phenyl bis (2,4, 6-trimethyl benzoyl) phosphine oxide.

6. A highly thermally conductive, remodelable liquid crystal elastomer composite as claimed in claim 1, wherein: the mercapto crosslinking agent is a compound containing three or more mercapto structures, and comprises at least one of trimethylolpropane tri (3-mercaptopropionate), pentaerythritol tetramercaptoacetate, pentaerythritol tetrakis (3-mercaptopropionate) and pentaerythritol tetrakis (3-mercaptobutyrate).

7. A highly thermally conductive, remodelable liquid crystal elastomer composite as claimed in claim 1, wherein: the filler comprises at least one of heat-conducting filler, electric-conducting filler and flame-retardant filler; the content of the filler is 0-50 wt% of the total mass of the composite material.

8. A highly thermally conductive, remodelable liquid crystal elastomer composite as claimed in claim 1, wherein: and adding at least one of an anti-aging auxiliary agent, an antistatic agent, a light stabilizer and a flame retardant, mixing with the mercapto-terminated liquid crystal prepolymer and the filler, and then carrying out crosslinking reaction under the action of a mercapto crosslinking agent.

9. A preparation method of the high-thermal-conductivity remoldable liquid crystal elastomer composite material as set forth in any one of claims 1-8, is characterized by comprising the following specific steps:

(1) adding a liquid crystal monomer containing ethyleneoxy, a dimercapto compound and a photoinitiator into an organic solvent, and reacting for 1.5-3h under UV light to obtain a mercapto-terminated liquid crystal prepolymer;

(2) and (2) adding the mercapto-terminated liquid crystal prepolymer obtained in the step (1), a mercapto cross-linking agent and a filler into an organic solvent, dispersing, adding hydrogen peroxide and sodium iodide, and stirring to react until gel is formed, thereby obtaining the high-thermal-conductivity remoldable liquid crystal elastomer composite material.

10. Use of a highly thermally conductive remodelable liquid crystal elastomer composite as claimed in any one of claims 1 to 8 in the aerospace and microelectronics fields.

Technical Field

The invention belongs to the technical field of polymer composite materials, and particularly relates to a high-thermal-conductivity remoldable liquid crystal elastomer composite material, and a preparation method and application thereof.

Background

In recent years, in the field of polymer composite materials, polymer composite materials having high mechanical properties and high thermal conductivity have become a focus and an important point of research, and have received high attention from a large number of researchers. This is because, since the information age, the microelectronics industry, which is known to be highly integrated, miniaturized, and multifunctional, has rapidly developed, and at the same time, the voltage requirements of electronic devices or apparatuses have been continuously increased, and the operating frequency thereof has rapidly increased, which causes the electronic apparatuses to generate huge heat in a very small space, and to maintain the components in a high-temperature environment for a long time. Studies have shown that the stability of the electronic device decreases by almost 10% for every 2 ℃ increase in temperature during operation. The large amount of heat accumulation not only accelerates the aging of internal materials and hinders signal transmission, but also seriously affects the reliability, safety, service life and user experience of equipment, and simultaneously, can cause major safety accidents such as explosion, fire and the like. The traditional high-mechanical and high-heat-conducting material has different defects which are difficult to overcome, and the requirements of modern industry on the functional diversity of the heat-conducting material are difficult to meet. Therefore, the development of novel high-mechanical and high-thermal-conductivity composite materials aiming at different application fields has become an important direction and urgent need for the research of high-mechanical and high-thermal-conductivity materials.

On the other hand, the electronic products are rapidly updated, so that the total amount of the electronic products discarded in the whole world is up to the million ton level. The three-dimensional network structure of the solidified resin for packaging causes extremely high difficulty and cost of degradation and recycling, and precious metals and monocrystalline silicon packaged in the electronic product are difficult to be reused. Therefore, realizing the low-energy consumption rapid recycling of the electronic product packaging material is a problem to be solved urgently at present, and has important significance for relieving the increasingly severe problems of energy shortage, resource waste and the like.

In addition, the prior art thermally conductive composite materials have inherent disadvantages, i.e., they do not have a self-healing function. Conventional thermally conductive composites are susceptible to microcracking when subjected to external stresses during use. Once the surface or the interior of the composite material generates micro-cracks, the micro-cracks can slowly expand under the action of stress, so that the three-dimensional network of the heat-conducting composite material is damaged, and the performance of the material is rapidly reduced.

Therefore, it is urgently needed to develop a heat-conducting composite material with good heat-conducting property, self-repairing function and recyclable and remolding function.

Disclosure of Invention

In order to overcome the shortcomings and drawbacks of the prior art, a primary object of the present invention is to provide a high thermal conductivity remodelable liquid crystal elastomer composite material.

The liquid crystal elements are self-oriented in the liquid crystal elastomer, so that the phonon scattering phenomenon of the material is inhibited, and the heat conduction performance of the material is enhanced. The material is a composite material which takes a liquid crystal elastomer as a polymer substrate and is compounded with a high-thermal-conductivity filler and contains reversible covalent bonds (disulfide bonds), and has high thermal conductivity coefficient, good self-repairing performance and recoverable and remolding performance.

The invention also aims to provide a preparation method of the high-thermal-conductivity remoldable liquid crystal elastomer composite material.

The invention further aims to provide application of the high-thermal-conductivity remoldable liquid crystal elastomer composite material in the fields of aerospace, microelectronics and the like.

The purpose of the invention is realized by the following scheme:

a high-thermal-conductivity remoldable liquid crystal elastomer composite material is obtained by a crosslinking reaction A under the action of a mercapto crosslinking agent after mixing a mercapto-terminated liquid crystal prepolymer and a filler.

In the present invention, the mercapto crosslinking agent is a compound having three or more mercapto groups, and may include at least one of trimethylolpropane tris (3-mercaptopropionate), pentaerythritol tetramercaptoacetate, pentaerythritol tetrakis (3-mercaptopropionate), pentaerythritol tetrakis (3-mercaptobutyrate), and the like.

In the present invention, the molar ratio of the mercapto group content of the mercapto group crosslinking agent to the mercapto group content of the mercapto group-terminated liquid crystal prepolymer is preferably 0.9:1 to 1.1:1, and more preferably, the molar equivalents are the same.

In the present invention, the filler may include a thermally conductive filler, an electrically conductive filler, a flame retardant filler, and the like. The filler content is preferably 0 to 50 wt% of the total mass of the composite material.

Further, the thermally conductive filler may include at least one of graphene, graphene oxide, hexagonal boron nitride, carbon nanotubes, graphite, MXene, and the like.

Further, the conductive filler may include at least one of gold, silver, copper, graphene oxide, liquid metal (gallium indium alloy), and the like.

Further, the flame retardant filler may include at least one of red phosphorus, black phosphorus, phosphorus alkene, molybdenum disulfide, melamine, and the like.

Furthermore, the crosslinking reaction A can be carried out after adding conventional aids in the field, for example, at least one of the aids such as an anti-aging aid, an antistatic agent, a light stabilizer, a flame retardant and the like is mixed with the sulfhydryl-terminated liquid crystal prepolymer and the filler, and then the crosslinking reaction is carried out under the action of a sulfhydryl crosslinking agent.

In the present invention, the crosslinking reaction a is preferably carried out under the action of hydrogen peroxide and sodium iodide.

Further, the amount of the hydrogen peroxide is preferably 3 to 7 wt%, more preferably 5 wt% of the total amount of the mercapto group-terminated liquid crystal prepolymer and the mercapto group crosslinking agent.

Further, the amount of sodium iodide is preferably 0.2 to 0.6 wt%, more preferably 0.5 wt% of the total amount of the mercapto group-terminated liquid crystal prepolymer and the mercapto group-crosslinking agent.

In the present invention, the crosslinking reaction a is preferably carried out in an organic solvent.

Further, the organic solvent may include at least one of dichloromethane, chloroform, tetrahydrofuran, toluene, and the like.

In the invention, the sulfhydryl-terminated liquid crystal prepolymer is obtained by a photoinduced thiol alkene click chemistry reaction B of a liquid crystal monomer containing ethyleneoxy and a dimercapto compound.

Further, the liquid crystal monomer having an ethyleneoxy group may include at least one of 4,4 ' -diethenyloxybiphenyl, 2, 5-bis [4- (allyloxy) benzoyloxy ] benzoate, 4 ' -bis (allyloxy) -3,3 ', 5,5 ' -tetramethyl-1, 1 ' -biphenyl, and the like.

Further, the dimercapto compound may include at least one of 3, 6-dioxa-1, 8-octane dithiol, 1, 2-ethanedithiol, 1, 4-butanedithiol, 1, 6-hexanedithiol, and the like.

Further, the molar ratio of the vinyloxy group-containing liquid crystal monomer to the dimercapto compound is preferably 1:1.1-1:1.7, more preferably 1: 1.5.

further, the reaction B is carried out under the action of a photoinitiator. The photoinitiator may include at least one of benzoin bis methyl ether (DMPA), Benzophenone (BP), 2-hydroxy-2-methyl-1-phenyl-1-propyl ketone (1173), 1-hydroxycyclohexyl phenyl ketone (184), phenyl bis (2,4, 6-trimethylbenzoyl) phosphine oxide (819). The photoinitiator is preferably used in an amount of 1 to 5 wt%, more preferably 2 wt%, based on the total amount of the vinyloxy-containing liquid crystal monomer and the dimercapto compound.

Further, the reaction B is preferably carried out at a light intensity of 45-75mW/cm²Reacting for 1.5-3h under the UV light with the maximum emission wavelength of 365 nm; more preferably 60mW/cm in light intensity²And reacting for 2 hours under UV light with the maximum emission wavelength of 365 nm.

Further, the reaction B is preferably carried out in an organic solvent system. The organic solvent may include at least one of dichloromethane, chloroform, tetrahydrofuran, toluene, and the like.

Further, the system after the reaction can separate the product by a precipitation method and dry the product. The precipitation can be specifically precipitated by adding the post-reaction system into methanol. The drying is preferably carried out at 60 ℃ for 12 h.

The high-thermal-conductivity remodelable liquid crystal elastomer composite material is a gel-like material after a crosslinking reaction. The gel material can be pulverized, washed with ethanol, and dried to obtain granule. The drying is preferably carried out at 60 ℃ for 12 h.

Further, the pellets may be subjected to hot press molding to obtain a composite material having a desired shape. The hot pressing temperature is preferably 100-150 ℃, the pressure is preferably more than or equal to 0.3MPa, and the hot pressing time is preferably 1.5-3 h.

The invention also provides a preparation method of the high-thermal-conductivity remoldable liquid crystal elastomer composite material, which comprises the following specific steps:

(1) adding a liquid crystal monomer containing ethyleneoxy, a dimercapto compound and a photoinitiator into an organic solvent, and reacting for 1.5-3h under UV light to obtain a mercapto-terminated liquid crystal prepolymer;

(2) and (2) adding the mercapto-terminated liquid crystal prepolymer obtained in the step (1), a mercapto cross-linking agent and a filler into an organic solvent, dispersing, adding hydrogen peroxide and sodium iodide, and stirring to react until gel is formed, thereby obtaining the high-thermal-conductivity remoldable liquid crystal elastomer composite material.

The light intensity of the UV light in the step (1) is preferably 45-75mW/cm²The maximum emission wavelength is preferably 365 nm.

The dispersion in step (2) is preferably ultrasonic dispersion, more preferably ultrasonic dispersion for 2 hours.

In the step (2), conventional additives in the field can be added, such as an anti-aging additive, an antistatic agent, a light stabilizer, a flame retardant and the like, and then dispersing and reacting are carried out.

The invention firstly prepares sulfhydryl terminated liquid crystal prepolymer by photoinduced sulfhydryl alkene click chemistry, then obtains self-repairing liquid crystal elastomer containing disulfide bond by oxidation reaction between the prepolymer and sulfhydryl crosslinking agent, and simultaneously introduces heat-conducting filler and the like into the elastomer system by in-situ polymerization, thereby obtaining composite material with good heat-conducting property and recoverable and remolding functions, which can be applied to the fields of space flight and aviation, microelectronics and the like.

Compared with the prior art, the invention has the following advantages and beneficial effects:

(1) the composite material prepared by adopting the liquid crystal elastomer as the polymer substrate and introducing the heat-conducting filler has good heat-conducting property, and the heat-conducting filler is wrapped by the high polymer as a dispersion phase and is mutually connected with the liquid crystal elastomer along with the increase of the addition amount to mutually penetrate to form an integral heat-conducting network structure, so that the heat-conducting coefficient of the obtained composite material is obviously improved.

(2) The liquid crystal elastomer composite material prepared by the invention introduces dynamic covalent disulfide bonds, so that the composite material has good self-repairing performance, the disulfide bonds can be subjected to reduction reaction and fracture to form sulfydryl, oxidation reaction is carried out, and disulfide bonds are formed again, so that multiple fracture and recombination can be realized in a system, and conditions are provided for self-repairing of the material, therefore, the composite material can be subjected to self-repairing when local damage and microcracks are generated, the fracture caused by macroscopic cracks is avoided, the service life of the product is prolonged, the use reliability of the product is improved, and the production cost is saved. Meanwhile, the dynamic covalent disulfide bond can also be broken and recombined at high temperature, so that the composite material has thermoplasticity, is easier to process and recycle compared with a thermosetting high polymer material with a stable and unchangeable cross-linked network structure, reduces energy consumption and is more environment-friendly.

Drawings

FIG. 1 is a schematic reaction scheme of a liquid crystal elastomer of example 1.

Fig. 2 is a schematic diagram of a recycling remodeling efficiency test operation of a material.

Detailed Description

The present invention will be described in further detail with reference to examples, but the embodiments of the present invention are not limited thereto.

The materials referred to in the following examples are commercially available without specific reference. The method is a conventional method unless otherwise specified. The using amount of each component is g and mL in parts by mass.

The thermal conductivity of the material is measured by a TC3000 series thermal conductivity meter.

The method for testing the recovery and remodeling efficiency of the material comprises the following steps: the material was tested for tensile strength before recovery (T1), then crushed, re-hot pressed and tested again for tensile strength (T2), with T2/T1 × 100% being the recovery remodeling efficiency. The operation is schematically shown in fig. 2.

Thermogravimetric analysis (TGA) of the material the thermal stability of the sample was determined, the test conditions: the temperature was raised from room temperature to 800 ℃ at a ramp rate of 10 ℃/min under a continuous stream of nitrogen (20 mL/min).