CN104927404B - A kind of method that in-situ copolymerization technology prepares hud typed CNT dielectric filler - Google Patents

Abstract

The invention discloses a method for preparing a core-shell type carbon nanotube dielectric filler by an in-situ copolymerization technique. Utilizing the characteristics of small molecules containing benzene rings (divinylbenzene) that are easy to generate physical adsorption with the surface of carbon nanotubes through π-π conjugation, the small molecule monomer is used as a bridge to add the second monomer maleic anhydride, and BPO Activating the surface of carbon nanotubes generates active radical centers and initiates the polymerization of divinylbenzene, which further initiates the copolymerization of maleic anhydride and divinylbenzene, thereby forming a copolymer coating on the surface of pristine carbon nanotubes. Ultrasonically disperse carbon nanotubes in a solvent, then add an initiator, heat up the reaction, and adjust the ratio between the initiator and the two monomers to obtain a series of core-shell carbon nanotube dielectric fillers with different coating thicknesses. The method does not need to carry out pretreatment processes such as acidification and oxidation on the surface of the carbon nanotube, has a simple process, can prepare a large amount of dielectric fillers with a controllable coating layer, and has a non-toxic solvent, and has good industrialization prospects.

Description

A method for preparing core-shell carbon nanotube dielectric filler by in-situ copolymerization technology

technical field

The invention relates to a method for preparing a core-shell composite dielectric filler by controllable polymerization of multifunctional divinylbenzene and maleic anhydride to coat original carbon nanotubes, and belongs to the technical field of composite material preparation.

Background technique

Carbon nanotubes have excellent and unique mechanical, electrical, and thermal conductivity properties, and have received extensive attention in recent decades. The seamless tubular structure of carbon nanotubes and the good degree of graphitization of the tube endow carbon nanotubes with excellent mechanical properties. Conventional graphite fiber is an order of magnitude higher, so it is called "super strong fiber". And because the carbon nanotubes evolved from graphene have a large number of p electrons in their carbon atoms, the existence of p electrons leads to the formation of a wide range of delocalized π bonds, and unpaired electrons can move freely along the tube wall, resulting in carbon Nanotubes have metal conductivity and semiconductor properties, so they have good application prospects in functional composite materials.

However, due to the large specific surface area of carbon nanotubes, there is a strong van der Waals force between the tubes, so carbon nanotubes usually exist in the form of agglomerates and are difficult to disperse, and are difficult to dissolve in water and various organic solvents. , it is more difficult to disperse in the polymer matrix, so it is necessary to modify the surface of carbon nanotubes to make them easy to disperse in various matrices and solvents. In recent years, the method of preparing core-shell composite fillers by using coating technology to modify the surface of carbon nanotubes has attracted widespread attention. The coated carbon nanotubes can be used alone as hybrid materials, such as electrochemical sensors, etc., and can also be used as fillers to prepare polymer-based composite materials, such as conductive and dielectric composite materials. Controllable cladding has very broad application prospects.

Divinylbenzene is a monomer with two vinyl groups, similar in structure to styrene. It can form insoluble polymers with three-dimensional structures during copolymerization, so it is a very useful crosslinking agent, widely used in ion exchange resins, ion exchange membranes, ABS resins, polystyrene resins, unsaturated polyester resins, synthetic rubber, Wood processing, carbon processing and other fields. Moreover, due to the π-π conjugation between divinylbenzene and carbon nanotubes, it is easy to physically adsorb on the surface of carbon nanotubes, so it can effectively reduce the probability of homopolymerization between monomers during polymerization, so that it is easy to A coating layer is formed on the surface of carbon nanotubes. In addition, because it is a by-product of the alkylation of ethylene and benzene to produce ethylbenzene, it is plentiful and inexpensive.

As a commonly used copolymerization raw material, maleic anhydride is widely used in industry. For example, styrene-maleic anhydride copolymer is a new type of polymer material commonly used in the market, with excellent performance and low price. It is widely used in water treatment agents, adhesive modifiers, latex coatings, and floor polishing emulsifiers. , Pesticide emulsifier, pigment dispersant, epoxy resin curing agent and other fields. The introduction of acid anhydride groups to the surface of carbon nanotubes can effectively improve the compatibility of carbon nanotubes with various resin matrices (PVC, nylon), thereby improving the dispersion of carbon nanotubes in the resin matrix and improving the composite material. performance, so it has a good application prospect.

The traditional method of modifying carbon nanotubes is to acidify carbon nanotubes under concentrated acid conditions, and use the acidified carboxyl or other functional groups to further react or initiate polymerization, thereby improving the dispersion and compatibility of carbon nanotubes in materials sex. However, acidification treatment severely damages the structure of carbon nanotubes, which greatly affects their performance. For this reason, many workers have tried to modify carbon nanotubes by using conjugated double bonds or physical adsorption on the surface of carbon nanotubes in recent years. However, the force between the physical coating and the carbon tube is not strong, and the coating layer will fall off under some changes in external conditions, thereby affecting the performance of the composite material. Therefore, this method has many advantages such as tight and controllable coating, simple operation of the experimental process, and good material adjustability.

Contents of the invention

The purpose of the present invention is to provide a simple method for preparing core-shell carbon nanotube composite fillers by divinylbenzene-maleic anhydride copolymerized coated carbon nanotubes. In the preparation process, the carbon nanotubes are first dispersed in a certain amount of solvent at a certain ultrasonic frequency and power, and then the free radical active centers are formed on the surface of the carbon nanotubes by adding an initiator in an _N2 atmosphere, thereby initiating two Copolymerization of vinylbenzene monomer and maleic anhydride to finally obtain core-shell carbon nanotube composite filler.

The specific steps for preparing carbon nanotube core-shell dielectric fillers from the divinylbenzene-maleic anhydride copolymer provided by the invention are:

a) Mix carbon nanotubes and butyl acetate, and prepare a suspension with a concentration of 1-1.5 mg/mL by ultrasonication for more than 1 hour;

b) adding dibenzoyl peroxide whose mass is 0.2-0.8 times that of the carbon nanotubes in a) to the above suspension, and continuing to sonicate for 10 minutes under the protection of _N2 to fully activate the carbon nanotubes, and obtain a uniform system after dissolution;

c) Raise the temperature of the system to 80°C, add divinylbenzene monomer (purity 80%) with 2-10 times the mass of carbon nanotubes dropwise, and after 2 hours of reaction, add divinylbenzene mass fraction of 10%-80 % maleic anhydride (purity 95%) and reacted 12h under this condition;

d) After the reaction is stopped, the product is obtained by centrifugation and suction filtration, washed with toluene and ethyl acetate in sequence, and dried in vacuum to obtain the final product.

Further, the ultrasonic power in step a) is between 300-600W.

Further, changing the amount of divinylbenzene and maleic anhydride in step c) controls the thickness of the cladding layer; the increase of the ratio of maleic anhydride feed will reduce the thickness of the cladding layer, so that the thickness of the cladding layer is controlled between 5-20nm between.

The characteristics of the method for preparing core-shell type dielectric fillers by copolymerizing polyfunctional vinyl monomers and acid anhydrides to coat carbon nanotubes provided by the present invention are:

1. Utilize the activation of the free radical initiator dibenzoyl peroxide on the wall of carbon nanotubes to directly initiate the polymerization of polyvinyl monomers in a homogeneous system, and then initiate the crossover of maleic anhydride and polyene monomers. Joint copolymerization to achieve the coating of carbon nanotubes. This method does not need acidification, oxidation and other treatments on the carbon nanotubes, and has a low degree of damage to the structure of the carbon nanotubes, thus retaining the original properties of the carbon nanotubes to the greatest extent.

2. The coating layer is a cross-linked structure, so it is firmly coated on the surface of the carbon nanotubes and is not easy to fall off.

3. The carbon nanotubes are fully coated, and the coating is relatively uniform, and the thickness of the coating layer is controllable, which greatly improves the dispersibility of the carbon nanotubes in the organic solution.

4. The operation is relatively simple, the cost is low, and the solvent used is non-toxic and harmless.

Description of drawings

Figure 1: The process flow chart for preparing core-shell composite fillers by coating multi-walled carbon nanotubes with divinylbenzene-maleic anhydride copolymer provided by the present invention.

Figure 2: Infrared spectrum of multi-walled carbon nanotube core-shell composite filler coated with divinylbenzene-maleic anhydride copolymer.

a) The mass ratio of carbon nanotubes, divinylbenzene, and maleic anhydride is 1:10:1

b) The mass ratio of carbon nanotubes, divinylbenzene, and maleic anhydride is 1:8:2

c) The mass ratio of carbon nanotubes, divinylbenzene, and maleic anhydride is 1:5:2.5

d) The mass ratio of carbon nanotubes, divinylbenzene, and maleic anhydride is 1:2:1.6

Figure 3: Transmission electron micrograph of multi-walled carbon nanotube core-shell composite filler coated with divinylbenzene-maleic anhydride copolymer

a) The mass ratio of carbon nanotubes, divinylbenzene, and maleic anhydride is 1:10:1

b) The mass ratio of carbon nanotubes, divinylbenzene, and maleic anhydride is 1:8:2

c) The mass ratio of carbon nanotubes, divinylbenzene, and maleic anhydride is 1:5:2.5

d) The mass ratio of carbon nanotubes, divinylbenzene, and maleic anhydride is 1:2:1.6

detailed description

The surface of carbon nanotubes can capture the free radicals generated in the polymerization reaction to initiate further polymerization of monomers with double bonds, so that high molecular weight polymers are grafted or coated on the surface of carbon nanotubes. However, there are certain problems in this way. Due to the existence of a variety of small molecule free radical components in the solution system, such as carbon tube free radicals, initiator free radicals, and monomer free radicals, the tendency of self-aggregation between monomers during the reaction is extremely serious, resulting in carbon nanotube The covering effect becomes worse. The use of multifunctional divinylbenzene monomers with conjugated structures can solve this problem well. The benzene rings with conjugated structures tend to physically adsorb on the surface of carbon nanotubes, so that carbon nanotubes free radicals It preferentially reacts with the monomer, initiates polymerization on the surface of carbon nanotubes, and forms a cross-linked network structure. At the same time, in order to further improve the thickness and controllability of the coating, we reduce the occurrence of self-polymerization as much as possible by reducing the monomer concentration of the system and gradually adding reactive monomers. At the same time, considering the low polymerization rate caused by too low monomer concentration and the low coating thickness, we adopted the following dosage and operation method.

Example 1

Weigh 500 mg of carbon nanotubes, place them in a three-necked flask, add 500 ml of butyl acetate as a solvent, ultrasonically disperse for 1 h, add 400 mg of initiator dibenzoyl peroxide and continue ultrasonication for 10 min. Measure 5g of divinylbenzene (DVB) monomer and add it into the dripping device after dilution. The three-neck flask was moved into an oil bath, and stirred at room temperature for 10 min under nitrogen protection. Raise the temperature to 80°C, gradually add divinylbenzene (DVB) monomer dropwise in the dripping device to carry out the polymerization reaction, add 0.5g maleic anhydride at one time after 2 hours, and stop heating after 12 hours to complete the reaction. The product was obtained by suction filtration, washed twice with toluene and butyl acetate respectively, and finally centrifuged, suction filtered, and vacuum-dried to obtain the target product. Figure 2(a) is the infrared spectrogram of the core-shell composite of divinylbenzene-coated carbon nanotubes prepared in this example (the specific flow chart is shown in Figure 1), and the analysis of characteristic peaks can preliminarily prove that divinylbenzene Benzene-maleic anhydride cross-linked copolymer is coated on carbon nanotubes. Fig. 3 (a) is the transmission electron micrograph of the core-shell composite of divinylbenzene-coated carbon nanotubes prepared in this example. It can be seen from the figure that there is a thicker layer of uniform The thickness of the cladding is about 20nm, indicating that a thicker cladding layer can be obtained under this formula. Combining these two points of data can prove that divinylbenzene-maleic anhydride cross-linked copolymer was successfully coated on the surface of carbon nanotubes. When the dielectric filler of this thickness is mixed with the polystyrene system, when the addition amount is 12wt%, the dielectric constant of the prepared composite material can reach 30 at the test frequency of 10 ⁴ Hz, which is pure polystyrene system 7 times of that, while the dielectric loss does not exceed 0.02. This material has great potential application value in the preparation of microelectronic devices.

Example 2

Weigh 500 mg of carbon nanotubes, place them in a three-necked flask, add 450 ml of butyl acetate as a solvent, ultrasonically disperse for 1 h, add 300 mg of initiator dibenzoyl peroxide and continue ultrasonication for 10 min. Measure 4g of divinylbenzene (DVB) monomer and add it to the dropping device after dilution. The three-neck flask was moved into an oil bath, and stirred at room temperature for 10 min under nitrogen protection. Raise the temperature to 80°C, gradually add the divinylbenzene (DVB) monomer in the dripping device dropwise to carry out the polymerization reaction, add 1 g of maleic anhydride at one time after 2 hours, and stop heating after 12 hours to complete the reaction. The product was obtained by suction filtration, washed twice with butyl acetate and toluene respectively, and finally centrifuged, suction filtered, and vacuum-dried to obtain the target product. Figure 2(b) is the infrared spectrogram of the core-shell composite of divinylbenzene-coated carbon nanotubes prepared in this example (the specific flow chart is shown in Figure 1), and the analysis of characteristic peaks can preliminarily prove that divinylbenzene Benzene-maleic anhydride cross-linked copolymer is coated on carbon nanotubes. Fig. 3 (b) is the transmission electron micrograph of the core-shell composite of the divinylbenzene-coated carbon nanotubes prepared by the present embodiment. Thin uniform coating, about 10nm in thickness. Combining these two points of data can prove that divinylbenzene-maleic anhydride cross-linked copolymer was successfully coated on the surface of carbon nanotubes. When this thickness of dielectric filler is mixed with epoxy resin, polystyrene and other systems, when the addition amount is 10wt% and ^30wt %, the dielectric constants of the prepared composites can be Up to 180 and 112, 60 times that of pure epoxy resin system, 30 times that of pure polystyrene system, and the dielectric loss is not more than 0.02. This composite material has great potential application value in the preparation of microelectronic devices.

Example 3

Weigh 500 mg of carbon nanotubes, place them in a three-necked flask, add 400 ml of butyl acetate as a solvent, ultrasonically disperse for 1 h, add 187.5 mg of initiator dibenzoyl peroxide and continue ultrasonication for 10 min. Measure 2.5g of divinylbenzene (DVB) monomer and add it into the dropping device after dilution. The three-neck flask was moved into an oil bath, and stirred at room temperature for 10 min under nitrogen protection. Raise the temperature to 80°C, gradually add divinylbenzene (DVB) monomer dropwise in the dripping device to carry out polymerization reaction, add 1.25g maleic anhydride at one time after 2 hours, stop heating after 12 hours to complete the reaction, and obtain the product by suction filtration. Wash twice with butyl acetate and toluene respectively, and finally centrifuge, filter with suction, and dry in vacuum to obtain the target product. Figure 2(c) is the infrared spectrogram of the core-shell composite of divinylbenzene-coated carbon nanotubes prepared in this example (the specific flow chart is shown in Figure 1), and the analysis of characteristic peaks can preliminarily prove that divinylbenzene Benzene-maleic anhydride cross-linked copolymer is coated on carbon nanotubes. Fig. 3 (c) is the transmission electron micrograph of the core-shell composite of divinylbenzene-coated carbon nanotubes prepared in this example. It can be seen from the figure that the thickness of the cladding on the outer wall of the multi-walled carbon nanotubes is thinner , and the uniformity has decreased, and the thickness is about 8nm. Combining these two points of data can prove that divinylbenzene-maleic anhydride cross-linked copolymer was successfully coated on the surface of carbon nanotubes.

Example 4

Weigh 500 mg of carbon nanotubes, place them in a three-necked flask, add 350 ml of butyl acetate as a solvent, ultrasonically disperse for 1 h, add 100 mg of initiator dibenzoyl peroxide and continue ultrasonication for 10 min. Measure 1 g of divinylbenzene (DVB) monomer and add it to the dropping device after dilution. The three-neck flask was moved into an oil bath, and stirred at room temperature for 10 min under nitrogen protection. Raise the temperature to 80°C, gradually add divinylbenzene (DVB) monomer dropwise in the dripping device to carry out polymerization reaction, add 0.8g maleic anhydride at one time after 2 hours, and stop heating after 12 hours to complete the reaction. The product was obtained by suction filtration, washed twice with butyl acetate and toluene respectively, and finally centrifuged, suction filtered, and vacuum-dried to obtain the target product. Fig. 2 (d) is the infrared spectrogram of the core-shell composite of divinylbenzene-coated carbon nanotubes prepared in this embodiment (the specific flow chart is shown in Figure 1), as can be seen from the figure: divinylbenzene The characteristic peak intensity of phenyl-maleic anhydride copolymer is obviously weaker than that of the above examples. Fig. 3 (d) is the transmission electron micrograph of the core-shell compound of the divinylbenzene-coated carbon nanotubes prepared in this example. It can be seen from the figure that the outer wall of the multi-walled carbon nanotube has a very thin coating layer with a thickness of approximately 5 nm. Combining these two points of data can prove that divinylbenzene-maleic anhydride cross-linked copolymer is coated on the surface of carbon nanotubes in a small amount, and can form a very thin coating layer, which proves again that the amount of maleic anhydride can be adjusted by controlling the amount of maleic anhydride added. cladding thickness. When the dielectric filler of this thickness is compounded with the thermoplastic polyurethane (TPU) system, when the addition amount is 15wt%, the dielectric constant of the prepared composite material can reach 32 at the test frequency of 10 ⁴ Hz, which is a pure TPU resin system. 4 times of that, the dielectric loss does not exceed 0.1. The prepared composite material has great potential application value in the preparation of high dielectric elastomer.

Claims (1)

1. a kind of method that in-situ copolymerization technology prepares hud typed CNT dielectric filler, it is characterised in that step is：

A) CNT and butyl acetate are mixed, ultrasonic more than 1h is configured to concentration 1-1.5mg/mL suspension；

B) by 0.2-0.8 times of quality a) in the dibenzoyl peroxide of CNT add in above-mentioned suspension, in N₂Under protection Continue ultrasound 10min with abundant activated carbon nano-tube, homogeneous system is obtained after dissolving；

C) system is warming up to 80 DEG C, be added dropwise after the divinylbenzene monomers of 2-10 times of carbon nanotube mass, reaction 2h, one Secondary property adds divinylbenzene mass fraction 10%-80% maleic anhydride and with this conditioned response 12h；

D) centrifugation, suction filtration obtain product after reaction stops, and are washed successively with toluene, ethyl acetate, and vacuum drying obtains final production Thing；

Ultrasonic power is between 300-600W in step a)；

Change the thickness of the consumption control clad of divinylbenzene and maleic anhydride in step c)；Maleic anhydride ingredient proportion Increase can reduce coating thickness, so that coating thickness control is between 5-20nm.