CN111647113B - Pyrenyl terpolymer and intermediate, preparation and application thereof - Google Patents
Pyrenyl terpolymer and intermediate, preparation and application thereof Download PDFInfo
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Abstract
The invention discloses a pyrenyl terpolymer and an intermediate, preparation and application thereof. The pyrenyl terpolymer is prepared by the following method: catalyzing ethylene, a pyrene-containing monomer shown in a formula (I) and a bromine-containing monomer BIEA by using a Pd-diimine catalyst to perform one-step chain removal copolymerization to prepare a hyperbranched terpolymer HBPE @ Py @ Br simultaneously containing pyrene end groups and acyl bromide end groups; then, the hyperbranched terpolymer HBPE @ Py @ Br is used as a macroinitiator, and the acyl bromide end groups are used for initiating acrylic ester monomers to graft copolymerization based on an ATRP mechanism to obtain the pyrenyl terpolymer. The invention provides application of the pyrenyl terpolymer in preparation of a graphene dispersion liquid, and the prepared graphene dispersion liquid is used for preparing an EVA dielectric composite material. The pyrenyl terpolymer can effectively improve the dispersibility of graphene in an EVA substrate and improve the dielectric constant of EVA.
Description
Technical Field
The invention relates to a pyrenyl terpolymer and an intermediate thereof, a preparation method and application thereof in preparation of graphene dispersion liquid and an EVA dielectric composite material.
Background
Ethylene Vinyl Acetate (EVA) copolymers have been of interest for the past few decades. The great interest in these copolymers has mainly been attributed to their wide industrial application from cables to gas films. Although EVA copolymers have unique properties, their low dielectric constant and somewhat weak storage modulus substantially limit their applications.
One of the most straightforward ways to overcome the above challenges is to incorporate nanofillers such as barium titanate, titanium dioxide, alumina, graphite and their derivatives into the polymer matrix. As for EVA copolymers, the addition of various types of clay minerals has been intensively studied. However, the use of the graphene filler has not attracted much attention, and the graphene filler is well known for its excellent electrical properties, thermal properties, electromagnetic shielding properties, and mechanical properties. They are similarly composed of thin 2D sheets of sp2 carbon atoms arranged in a honeycomb structure. The graphene filler can greatly improve mechanical properties, enhance thermal stability, and more importantly, provide a composite material with high electrical conductivity. Due to its high aspect ratio, the properties of the polymer substrate can be improved at very low GNP contents. Due to its many excellent properties, it has attracted much attention to promote the development of biology, energy storage, electronics, etc. The emergence of the material provides a new element for the progress of each subject, and has extremely high value and wide application prospect. However, efficient preparation of graphene is difficult to achieve so far, and a simple process must be first devised to achieve efficient and macro-quantitative preparation of low-defect graphene to obtain the finally required graphene. At present, methods for preparing graphene include a mechanical exfoliation method, a redox method, a liquid phase exfoliation method, a chemical vapor deposition method, an epitaxial growth method, and the like, wherein the liquid phase exfoliation method maintains the structural integrity of graphene, and has great advantages in practical application. The most common liquid phase stripping process is to oxidize natural graphite by a chemical method to obtain graphite oxide, and further disperse the graphite oxide in an aqueous solution under the action of ultrasonic waves to obtain Graphene Oxide (GO) nanosheets. Since GO is not conductive, GO is often further reduced by a chemical or thermal method, however, the prepared Redox Graphene (RGO) has more defects, and the difference of electrical properties is larger than that of the original graphene.
In order to make the graphene well dispersed in the polymer, a favorable interaction between the polymer and the graphene should be established. The presence of strong interactions also ensures strong interfacial adhesion and thus enhanced dielectric and mechanical properties. One of the most efficient methods of preparation in preparation is solution compounding, where the graphene is well dispersed in the polymer matrix solution, and the mixture is then cast/molded.
In our earlier studies, it has been found that in a suitable organic solvent such as Tetrahydrofuran (THF) or chloroform, by utilizing the non-covalent CH-pi interaction between HBPE and graphene surface, natural graphite can be effectively exfoliated by means of ultrasound to obtain a graphene organic dispersion solution (fig. 1) with a higher concentration, and the HBPE can be obtained by catalyzing ethylene polymerization by a catalyst alpha-diimine palladium (Pd-diimine) and by a one-step chain "walking" mechanism (fig. 2), which has the advantages of rich raw material sources and simple synthesis process, and the obtained graphene has few structural defects and stable dispersion, and through the functional modification of the graphene surface polymer, a strong interaction can be established between the polymer on the graphene surface and the polymer substrate. However, the interaction between the HBPE and the graphene is limited to a weak hydrogen bonding (CH-pi), which results in low preparation efficiency of the graphene and still exists a certain distance from large-scale application.
In a word, how to realize the efficient and macro-quantitative preparation of the low-defect graphene by a simple process, and applying the prepared graphene to various fields still remains an important and key technical problem to be solved.
Disclosure of Invention
The first purpose of the invention is to provide a pyrenyl terpolymer which can be used for efficiently preparing low-defect graphene.
The second purpose of the invention is to provide a preparation method of the pyrenyl terpolymer.
The third purpose of the invention is to provide the application of the pyrenyl terpolymer in the preparation of the graphene dispersion liquid, the application condition is mild, the process is simple, and the low-defect graphene can be efficiently prepared.
The fourth purpose of the invention is to provide the application of the pyrenyl terpolymer in the preparation of the EVA dielectric composite material, the application process is simple, and the EVA/graphene composite membrane with higher dielectric constant can be prepared.
The fifth purpose of the invention is to provide a hyperbranched terpolymer HBPE @ Py @ Br which can be used as an intermediate for preparing pyrenyl terpolymers.
The technical solution adopted by the present invention is specifically explained below.
In a first aspect, the present invention provides a pyrenyl terpolymer prepared by the method comprising: catalyzing ethylene, a pyrene-containing monomer shown in a formula (I) and a bromine-containing monomer BIEA by using a Pd-diimine catalyst to perform one-step chain removal copolymerization to obtain a hyperbranched terpolymer HBPE @ Py @ Br containing pyrene end groups and acyl bromide end groups; then, taking the hyperbranched terpolymer HBPE @ Py @ Br as a macroinitiator, and initiating an acrylate monomer to graft copolymerization by virtue of an acyl bromide end group based on an ATRP mechanism to obtain a pyrenyl terpolymer;
preferably, the number average molecular weight of the pyrenyl terpolymer is between 5000-50000 (preferably between 10000-50000); in the pyrenyl ternary copolymer, the grafting proportion of the pyrenyl and the acrylic ester monomer is 0.5-20mol% (preferably 0.5-10 mol%) and 0.5-100mol% (preferably 10-100 mol%). The grafting ratio is defined as the number of corresponding groups per 100 ethylene structural units.
Preferably, the feeding molar ratio of the pyrene-containing monomer to the bromine-containing monomer BIEA is 0.1-1.0: 0.1 to 1.0, preferably 1 to 3: 1.
Preferably, the specific reaction conditions of the one-step "chain-removal" copolymerization are as follows: the reaction is carried out under stirring at 10-40 ℃ and ethylene pressure of 0.01-5 atm for 12-72 hours, preferably at 25 ℃ and ethylene pressure of 1atm for 24 hours.
Preferably, the ratio of Br in the acrylate monomer and the hyperbranched terpolymer HBPE @ Py @ Br is controlled to be 10-1000:1
Preferably, the acrylic ester monomer is methyl acrylate, methyl methacrylate or butyl acrylate.
Preferably, the conditions for graft copolymerization based on the ATRP mechanism are: polymerizing for 5min-24h at 25-150 ℃ by using cyclohexanone, bipyridyl or PMDETA (N, N, N' -pentamethyl diethylene triamine) as an ATRP reaction ligand and CuBr as a catalyst.
In a second aspect, the invention provides a preparation method of a pyrenyl terpolymer, which comprises the following steps:
(1) under the protection of ethylene, mixing a pyrene-containing monomer shown in the formula (I), bromine-containing monomer BIEA, a Pd-diimine catalyst and an anhydrous solvent in a reaction vessel, stirring and polymerizing under a certain ethylene pressure condition, and after full reaction, separating and purifying to obtain a hyperbranched terpolymer HBPE @ Py @ Br simultaneously containing pyrene end groups and acyl bromide end groups;
(2) under the protection of nitrogen, mixing an ATRP reaction ligand, hyperbranched terpolymer HBPE @ Py @ Br, CuBr, an acrylate monomer and an anhydrous solvent in a reaction container, introducing nitrogen to remove oxygen, sealing the reactor, fully polymerizing, and separating and purifying to obtain the pyrenyl terpolymer.
The anhydrous grade solvents described in steps (1) and (2) of the present invention are each independently preferably one of the following: anhydrous dichloromethane, trichloromethane, toluene, THF, ethanol, methanol or chlorobenzene.
In the present invention, the Pd-diimine catalyst is preferably one of the following: the acetonitrile group Pd-diimine catalyst 1 and the six-membered ring Pd-diimine catalyst 2 containing a carbomethoxy group have the following structural formulas:
the two Pd-diimine catalysts, the pyrene monomer and the BIEA can be synthesized in a laboratory by referring to the following documents:
[1]Johnson L.K.Killian C.M.Brookhart M.J.Am.Chem.Soc.1995,117,6414；[2]Johnson L.K. Mecking S.BrookhartM.J.Am.Chem.Soc.1996,118,267.
[2]X.Lou,R.Daussin,S.Cuenot,A.-S.Duwez,C.Pagnoulle,C.Etrembleur,C.Bailly,R.
Chem. Mater.2004,16,4005.
[3]K.Matyjaszewski,S.G.Gaynor,A.Kulfan,M.Podwika,Macromolecules 1997,30,5192.
in the polymerization system in the step (1), the amount of the Pd-diimine catalyst is preferably 0.5-10.0 g/L based on the total volume of the anhydrous solvent, the feeding concentration of the pyrene-containing monomer is 0.1-1.0 mol/L, and the feeding concentration of BIEA is 0.1-1.0 mol/L.
In step (1) of the present invention, the polymerization conditions are preferably: stirring and reacting for 12-72 hours at the temperature of 10-40 ℃ and the ethylene pressure of 0.01-5 atm, and preferably: the reaction was stirred at 25 ℃ and 1atm ethylene pressure for 24 hours.
In step (1) of the present invention, the separation and purification methods can all adopt the corresponding conventional procedures of "chain-removal" copolymerization reported in the literature, such as: the separation and purification of the polymerization mixture can be carried out as follows:
(i) removing the solvent from the polymerization reaction mixture;
(ii) dissolving the obtained product in THF, adding acetone to precipitate the product, removing supernatant to obtain the polymerization product again; repeating the process for 1-10 times to fully remove unreacted pyrene-containing monomers contained in the product;
(iii) dissolving the obtained product in THF again, adding a small amount of hydrochloric acid and hydrogen peroxide (for example, 3-20 drops of each), stirring for 1-10 hours to dissolve a small amount of Pd particles contained in the product, and then adding methanol or acetone to precipitate the product;
(iv) and carrying out vacuum drying on the obtained product at the temperature of 20-100 ℃ for 24-72h to obtain the product.
In step (2) of the present invention, the ATRP ligand is preferably one of the following: cyclohexanone, bipyridine, or PMDETA.
In step (2) of the present invention, the acrylic ester monomer is preferably methyl acrylate, methyl methacrylate or butyl acrylate.
In step (2) of the invention, the acrylic ester monomer is preferably fed according to the molar ratio of HBPE @ Py @ Br: and (3) CuBr: ATRP reaction ligands are from 10 to 1000:1:1 to 500, more preferably 100-.
In the polymerization system in the step (2), the concentration of the macromolecular initiator HBPE @ Py @ Br is 0.01-10mol/L based on the total volume of the organic solvent.
In step (2) of the present invention, the polymerization conditions are preferably: polymerizing for 5min-24h at 25-150 ℃.
In step (2) of the present invention, the separation and purification of the polymerization reaction mixture can be carried out by the corresponding conventional procedures of ATRP copolymerization, such as the following steps:
(i) exposing the reaction flask to air, and removing the solvent;
(ii) adding a certain amount of THF to dissolve the product, slowly adding acetone to precipitate the polymer, removing the upper solution, and repeating for multiple times;
(iii) and collecting the product, and performing vacuum drying at the temperature of between 20 and 100 ℃ for 24 to 72 hours to obtain the pyrenyl terpolymer.
In a third aspect, the invention provides an application of the pyrenyl terpolymer in preparation of a graphene dispersion liquid, and an application method comprises the following steps:
(a) mixing graphite powder, pyrenyl terpolymer and organic solvent A, sealing, performing ultrasonic treatment on the obtained mixture to obtain graphene initial dispersion, and further performing low-speed centrifugation and standing treatment to obtain graphene dispersion containing excessive pyrenyl terpolymer; wherein the feeding concentration of graphite powder is 0.01-15000 mg/mL, the mass ratio of the pyrenyl terpolymer to the graphite powder is 0.0005-10: 1, and the organic solvent A is selected from one of the following chemically pure or analytically pure reagents: THF, chloroform, chlorobenzene, dichloromethane, toluene, n-heptane, DMF, NMP.
The graphite powder can adopt one of the following sources: natural phosphorus flake graphite or expanded graphite, preferably natural phosphorus flake graphite; the particle size of the graphite powder is controlled to be 50-1500 meshes, and 500 meshes are preferred.
The organic solvent A in the step (a) can adopt one of the following analytically pure or chemically pure solvents: chloroform, THF, chlorobenzene, n-heptane, dichloromethane, DMF, NMP, preferably chloroform or THF.
In the step (a), the concentration of graphite powder in the graphene initial dispersion liquid is preferably 0.5-500 mg/mL, and the feeding mass ratio of the pyrenyl terpolymer to the graphite powder is 0.1-10: 1.
In the step (a), the ultrasound is recommended to be carried out under the conditions that the ultrasound power is 20-300W and the constant temperature is 10-80 ℃, and the ultrasound duration is preferably 4-1500 h, so as to obtain the graphene initial dispersion liquid. The low-speed centrifugation is recommended to be carried out at room temperature and 1000-8000 rpm, and the centrifugation time is preferably 10-120 min. The standing treatment time is preferably 8-24 h.
Preferably, in the step (a), continuously performing ultrasonic treatment on the obtained mixture for 4-150 hours under the conditions that the ultrasonic power is 10-800W and the constant temperature is 10-50 ℃ to obtain an initial graphene dispersion liquid; centrifuging the graphene initial dispersion liquid for 10-120 min at room temperature under the condition of 1000-8000 rpm, standing for 1-24 h, and collecting a centrifugal upper layer liquid to obtain the graphene dispersion liquid containing the excess pyrenyl terpolymer.
In the present invention, from the viewpoint of recovering the pyrenyl terpolymer for use to reduce the production cost thereof, it is preferable that the application method further comprises the steps of:
(b) and (2) carrying out high-speed centrifugation or vacuum filtration on the graphene dispersion liquid containing the excess pyrenyl terpolymer obtained in the step (1) to remove the excess pyrenyl terpolymer, and carrying out ultrasonic treatment again to disperse the graphene dispersion liquid into an organic solvent A to obtain the graphene organic dispersion liquid.
In the step (b), the high-speed centrifugation condition is recommended to be carried out at 15-35 ℃ and 30000-50000 rpm, and the centrifugation time is preferably 25-60 min. In order to sufficiently remove the excess pyrenyl terpolymer contained in the graphene dispersion liquid, the bottom sediment obtained by high-speed centrifugation can be subjected to ultrasonic washing again by using an organic solvent A, and then high-speed centrifugation is performed again; the "ultrasonic washing-high speed centrifugation" step may be repeated as many times as necessary.
In the step (b), the graphene dispersion liquid containing the excess pyrenyl terpolymer can be subjected to vacuum suction filtration by using a microfiltration membrane to remove the excess pyrenyl terpolymer, and a filtration product obtained after the filtrate is removed is leached by using an organic solvent A. The preferable average aperture of the micro-porous filtering membrane is 0.01-0.05 mu m, and the material is one of polytetrafluoroethylene, polyvinylidene fluoride or alumina.
In the step (b), after removing the excessive pyrenyl terpolymer from the graphene dispersion liquid C containing the excessive pyrenyl terpolymer through high-speed centrifugation or vacuum filtration, dispersing the graphene dispersion liquid C in an organic solvent A with a certain volume through an ultrasonic process (15-35 ℃, 0.5-24 h and 40-100W of power), and thus obtaining the graphene dispersion liquid without the excessive pyrenyl terpolymer.
In a fourth aspect, the invention provides an application of the pyrenyl terpolymer in preparation of an EVA dielectric composite material, and the application method comprises the following steps:
(A) mixing graphite powder, pyrenyl terpolymer and organic solvent A, sealing, performing ultrasonic treatment on the obtained mixture to obtain graphene initial dispersion, and further performing low-speed centrifugation and standing treatment to obtain graphene dispersion containing excessive pyrenyl terpolymer; wherein the feeding concentration of graphite powder is 0.01-15000 mg/mL, the mass ratio of the pyrenyl terpolymer to the graphite powder is 0.0005-10: 1, and the organic solvent A is selected from one of the following chemically pure or analytically pure reagents: THF, chloroform, chlorobenzene, dichloromethane, toluene, n-heptane, DMF, NMP;
(B) and (B) dispersing the graphene obtained in the step (A) into EVA through solution mixing or melt mixing to obtain the EVA dielectric composite material.
Preferably, the content of graphene in the EVA dielectric composite material is controlled to be 0.1-10 wt%.
The operation of step (A) is the same as that of step (a), and details of preparation and preferred conditions thereof are not repeated herein. Similarly, from the viewpoint of recycling the pyrenyl terpolymer for use to reduce the production cost thereof, it is preferable that the use further comprises the steps of:
(A-1) carrying out high-speed centrifugation or vacuum filtration on the graphene dispersion liquid containing the excessive pyrenyl terpolymer obtained in the step (A) to remove the contained excessive pyrenyl terpolymer, and carrying out ultrasonic treatment again to disperse the excessive pyrenyl terpolymer into the organic solvent A to obtain a graphene dispersion liquid; the graphene dispersion was used again in step (B).
The operation of the step (A-1) is the same as that of the step (b), and details and preferred conditions thereof are not repeated herein.
Preferably, the solution mixing of step (B) is carried out as follows:
(B-1) preparing an organic solvent solution of EVA, wherein the concentration of the EVA is 1-1500 mg/mL, and the solvent is selected from one of the following chemically pure or analytically pure reagents: THF, chloroform, chlorobenzene, dichloromethane, toluene, n-heptane, DMF, NMP;
and (B-2) uniformly mixing the EVA organic solvent solution prepared in the step (B-1) with the graphene dispersion liquid prepared in the step (A), then casting the mixture on a mold, and drying to obtain the EVA dielectric composite material.
In the step (B-1), the preparation of the organic solvent solution of EVA may be carried out by conventional means such as heating and stirring to promote the dissolution of EVA in the solvent.
In the above step (B-1), the solvent is preferably chloroform or THF.
In the step (B-2), after the organic solvent solution of EVA and the graphene dispersion are mixed, it is preferable to sufficiently stir at 25 to 70 ℃ to mix them uniformly.
In the step (B-2), the mold may be one of the following: glass sheet, PTFE mold, iron sheet, silicon sheet, preferably silicon sheet or glass sheet.
In the step (B-2), the drying temperature is 10-500 ℃, and the drying time is 1-48 h; preferably, the drying temperature is 50-100 ℃, and the drying time is 5-10 hours; most preferably 80 ℃ for 8 h.
In a fifth aspect, the present invention provides a hyperbranched terpolymer HBPE @ Py @ Br, prepared by the following method: the hyperbranched terpolymer HBPE @ Py @ Br containing pyrene end groups and acyl bromide end groups is prepared by catalyzing ethylene, pyrene-containing monomers shown in a formula (I) and bromine-containing monomers BIEA through one-step chain-removal copolymerization;
preferably, the number average molecular weight of the hyperbranched terpolymer HBPE @ Py @ Br is between 5000 and 50000; in the pyrenyl ternary copolymer, the grafting proportion of pyrenyl and Br is 0.5-20mol% (preferably 0.5-10 mol%) and 0.5-10 mol% (preferably 1-10 mol%). The grafting ratio is defined as the number of corresponding groups per 100 ethylene structural units.
Preferably, the feeding molar ratio of the pyrene-containing monomer to the bromine-containing monomer BIEA is 0.1-1.0: 0.1 to 1.0, most preferably 1-3: 1.
Preferably, the specific reaction conditions for the one-step "chain-removal" copolymerization are: the reaction is carried out under stirring at 10-40 ℃ and ethylene pressure of 0.01-5 atm for 12-72 hours, preferably at 25 ℃ and ethylene pressure of 1atm for 24 hours.
The preparation method of the hyperbranched terpolymer HBPE @ Py @ Br is shown in the step (1) and is not described again.
Compared with the prior art, the invention has the following outstanding advantages and beneficial effects:
firstly, catalyzing ethylene and a pyrene-containing monomer chain to perform 'walking' copolymerization through a Pd-diimine catalyst, introducing multiple pyrenyl into HBPE, grafting an ester monomer on the HBPE by utilizing ATRP, and finally obtaining a pyrenyl terpolymer. Compared with pure HBPE (only single CH-pi effect can be formed on the surface of graphene), the preparation efficiency of graphene can be further improved by utilizing the pyrenyl terpolymer.
Secondly, the pyrenyl terpolymer and the surface of the graphene simultaneously form multiple CH-pi and pi-pi stacking functions, based on the synergistic effect of the pyrenyl terpolymer and the graphene, the non-covalent interaction strength between the graphene and the polymer can be effectively improved, the pyrenyl terpolymer is stably adsorbed on the surface of the graphene, and by virtue of the stable protection function of the pyrenyl terpolymer, the dispersion stability of the obtained graphene in an organic solvent can be remarkably improved, and meanwhile, the structure of the graphene is kept stable in various application processes.
And meanwhile, the preparation process of the graphene mainly depends on two non-covalent actions, does not relate to harsh chemical reaction, and is beneficial to obtaining high-quality graphene with few structural defects, so that the structural integrity and the original performance advantages of the graphene can be better maintained.
And fourthly, the pyrenyl terpolymer is stripped to obtain the graphene solution, so that the graphene solution is functionally modified, the surface of the graphene solution has a hyper-branched structure and an ester group, and the hyper-branched structure and the ester group have good compatibility with EVA, so that the dispersibility of the graphene in the EVA substrate can be effectively improved, and the dielectric constant of the EVA is improved.
Drawings
FIG. 1 is a schematic diagram of a preparation process of an EVA and graphene composite material;
FIG. 2 is a schematic diagram of characters prepared from the EVA and graphene composite material;
fig. 3 (a) SEM image of comparative example 1; (b) SEM image of example 1; (c) and (d) dielectric constant versus dielectric loss plots for example 1 and comparative example 1, respectively;
fig. 4 (a) SEM image of comparative example 1; (b) SEM image of example 2; (c) and (d) dielectric constant vs. dielectric loss plots for example 2 and comparative example 1, respectively;
fig. 5(a) SEM image of example 3; (b) SEM image of comparative example 2; (c) and (d) are graphs of dielectric constant and dielectric loss for example 3 and comparative example 2, comparative example 1, respectively;
fig. 6(a) SEM image of example 4; (b) SEM image of comparative example 3; (c) and (d) are graphs of dielectric constant and dielectric loss for example 4 and comparative example 3, comparative example 1, respectively;
fig. 7, (a) and (b) are HRTEM results for preparation of graphene from pyrenylated ester-containing hyperbranched polyethylene copolymer in example 5; (c) and (d) are both HRTEM results for graphene preparation with HBPE @ Py @ Br as in comparative example 4;
FIG. 8 is an optical diagram of example 6 and comparative examples 5 and 6;
FIG. 9 is a graph showing the charge ratios of different polymers in example 7 and comparative examples 7 and 8;
FIG. 10 is a graph showing different graphite charge ratios of example 8 and comparative examples 9 and 10;
FIG. 11 different ultrasound time profiles for example 9 and comparative examples 11, 12.
Detailed Description
The present invention will be described in further detail with reference to the following examples and drawings, but the embodiments of the present invention are not limited thereto.
Example 1 and comparative example 1
1. Preparation of samples
(1) Example 1 the preparation of the sample was carried out as follows:
step 1: adding the pyrene-containing monomer (2.8g/9.8mmol) obtained in the step 1 and anhydrous dichloromethane (15mL) into a Schlenk reaction bottle with the protection of ethylene, then injecting BIEA (1.2g/4.5mmol), controlling the temperature at 25 ℃, then adding acetonitrile Pd-diimine catalyst 1(0.1g/0.12mmol) dissolved in 5mL anhydrous dichloromethane, stirring and reacting for 24 hours under the conditions of 25 ℃ and 1atm of ethylene pressure, pouring the obtained product into a 100mL beaker after the polymerization is finished, removing the solvent in the obtained reaction mixture by air purge, dissolving the product in THF (15mL), slowly adding acetone (20mL) under stirring to precipitate the polymerization product, removing the upper solution to obtain the polymerization product, and repeating the purification process for 3 times. And dissolving the obtained product in THF (15mL) again, adding a small amount of hydrochloric acid and hydrogen peroxide (3-5 drops each), stirring for 2 hours to dissolve a small amount of Pd particles contained in the product, adding methanol (40mL) to precipitate the product, and vacuum-drying at 50 and 80 ℃ for 24 hours to obtain a macromolecular initiator HBPE @ Py @ Br, wherein the polymer results are characterized as shown in Table 1 (note: the initial concentrations of a pyrene-containing monomer and a catalyst 1 are respectively 0.50mol/L and 5.0g/L in terms of the total volume of dichloromethane).
Step 2: injecting 7.48mL of anhydrous toluene into a reactor under the protection of nitrogen, then dissolving the macroinitiator HBPE @ Py @ Br (0.56 g/wherein the mole number of Br is 0.285mmol) synthesized in the step 2 in the anhydrous toluene (10mL), further injecting 20.45mL of methyl acrylate into the reactor, then injecting PMDETA (0.0544g/0.314mmol), further removing oxygen and water, further pouring a transition metal complex CuBr (0.0409g/0.285mmol), reacting for 4h at the temperature of 90 ℃, pouring the obtained product into a 100mL beaker after the polymerization is finished, removing the solvent in the obtained reaction mixture by air purging, dissolving the product in THF (15mL), slowly adding acetone (20mL) under stirring to precipitate the polymerization product, removing the upper solution to obtain the polymerization product, repeating the purification process 3, drying under vacuum at 50 ℃ and 80 ℃ for 24h respectively to obtain the pyrenylated hyperbranched polyethylene copolymer, the polymer results are characterized in table 1.
And 3, step 3: natural flaky graphite (640mg) and CHCl were sequentially added to a 100mL cylindrical glass bottle 3 (80mL) and from aboveAnd (3) sealing the pyrenyl ester-containing hyperbranched polyethylene copolymer (80mg) obtained in the step (3), placing the sealed pyrenyl ester-containing hyperbranched polyethylene copolymer in a 250W ultrasonic water pool, performing constant temperature ultrasonic treatment for 48h at 25 ℃ to obtain an initial graphene dispersion liquid, further performing low speed centrifugation for 45min at 4000rpm, and then standing for 8h to obtain a graphene dispersion liquid containing the excess pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 8mg/mL, and the mass ratio of the pyrenyl ester-containing hyperbranched polyethylene copolymer to the graphite powder is 0.125).
And 4, step 4: and (3) carrying out vacuum filtration on the graphene dispersion liquid (about 7mL) obtained in the step (4) by using an alumina filter membrane (anodis 47, the average pore diameter is 0.02 mu m), further leaching the filtered product by using 14mL of chloroform (which is 2 times of the volume of the original dispersion liquid), then placing the obtained filter membrane (containing the graphene product) in 10mL of chloroform, and carrying out continuous ultrasonic treatment for 8h at 25 ℃ in a 250W ultrasonic pool to obtain the graphene dispersion liquid without the excessive pyrenylation ester-containing hyperbranched polyethylene copolymer.
And 5, step 5: dissolving EVA in organic solvent CHCl at 50 deg.C 3 And stirring for 10min to dissolve EVA in organic solvent CHCl completely 3 In (1). Wherein the feeding concentration of the EVA is 100 mg/mL.
And 6, step 6: and (3) naturally cooling the EVA solution obtained in the step (6) to room temperature, adding the solution containing 3mg of graphene prepared in the step (5), continuously stirring at 50 ℃ for 5min, casting on a silicon wafer, drying at 80 ℃ for 8h, and finally removing the film from the mold.
(2) Comparative example 1 the preparation of the sample was carried out as follows:
step 1: see step 5 in example 1 for the preparation of the EVA solution.
Step 2: and (2) casting the EVA solution obtained in the step (1) on a silicon wafer, drying at 80 ℃ for 8 hours, and finally removing the film from the die.
2. Characterization and testing
Testing is carried out by adopting a 4294A type impedance analyzer produced by Keysight company in America, silver electrodes are uniformly coated on the front surface and the back surface of a sample before testing, and the testing frequency is as follows: 100Hz-106 Hz, bias voltage of 0.5V, test temperature of room temperature, and test sample size: 1cm × 1 cm.
3. Comparison and analysis of test results
FIG. 3 compares two samples made in example 1 and comparative example 1. The preparation processes and steps of the two samples were identical except whether graphene was added. As shown in the figure, the SEM images of the cross-sections of example 1 and comparative example 1 are (b) and (a) of fig. 3, respectively, and it can be seen from the comparison of the SEM images that in example 1, graphene is uniformly dispersed in the EVA substrate, while comparative example 1 is pure EVA, and the cross-section is free of other fillers. The dielectric constant of the two samples obtained is significantly different from the dielectric loss, and it can be seen from the figure that at 100HZ, the dielectric constant of the pure EVA film is 4.6, while the dielectric constant increases to 6.1 after 0.3 wt% graphene is added, for the following reasons: the pure EVA film has a certain dielectric constant, and the dielectric constant of the composite film is increased mainly due to the influence of Maxwell-Wagnare-Sillars interface polarization effect between the pure EVA film and the graphene after the graphene is added to a polymer matrix. After the graphene is introduced into the EVA matrix, due to good dispersion of the graphene in the polymer, a large number of interfaces can be generated between the graphene and the EVA, and after an electric field is applied, a large number of carriers can be accumulated at the interfaces, so that interface polarization is generated, and finally the dielectric constant of the composite film is increased. The dielectric loss of the two samples is shown in fig. 3(d), and the dielectric loss of the samples is firstly reduced and then increased along with the increase of the frequency, and the dielectric loss is mainly dominated by the conductance loss in the extremely narrow ultra-low frequency range of 100Hz-130 Hz. In the range of 130 Hz-106Hz, the dielectric loss increases again and again, mainly due to the loss of oriented polarization of the C ═ O bonds in the EVA polymer. It is noted that the dielectric loss of the composite film is not particularly significantly changed by adding the graphene to the polymer matrix, and is still kept low, and the dielectric loss at 100Hz is shown as the dielectric loss is kept below 0.1. The reason is that the pyrenyl ester-containing hyperbranched polyethylene copolymer polymer adsorbed on the surface of the graphene by the non-covalent CH-pi and pi-pi functions prevents the graphene from directly contacting with a polymer base, reduces the generation of leakage current of the composite membrane, and maintains the dielectric loss at a lower level. The above results thus confirm: after the graphene without the excessive pyrenyl ester-containing hyperbranched polyethylene copolymer is added, the dielectric constant of the EVA film can be obviously improved, and the lower dielectric loss can be maintained.
Example 2 and comparative example 1
1. Preparation of samples
(1) Example 2 the preparation of the sample was carried out as follows:
step 1: see steps 1 to 4 in example 1 for graphene dispersions without excess pyrenylated ester-containing hyperbranched polyethylene copolymer.
Step 2: the EVA solution was prepared according to step 5 in example 1.
And 3, step 3: and (3) naturally cooling the EVA solution obtained in the step (2) to room temperature, adding the solution containing 10mg of graphene prepared in the step (1), continuously stirring at 50 ℃ for 5min, then casting on a silicon wafer, drying at 80 ℃ for 8h, and finally removing the film from the mold.
(2) Comparative example 1 was used for comparison.
2. Characterization and testing
Testing is carried out by adopting a 4294A type impedance analyzer produced by Keysight company in America, silver electrodes are uniformly coated on the front surface and the back surface of a sample before testing, and the testing frequency is as follows: 100Hz-106 Hz, bias voltage of 0.5V, test temperature of room temperature, and test sample size: 1cm × 1 cm.
3. Comparison and analysis of test results
FIG. 4 compares two samples made in example 1 and comparative example 1. The preparation processes and steps of the two samples were identical except whether graphene was added. As shown in the figure, the SEM images of the cross-sections of example 2 and comparative example 1 are fig. 4(b) and (a), respectively, and it can be seen from the comparison of the SEM images that, in example 2, graphene is uniformly dispersed in the EVA substrate, while comparative example 1 is pure EVA, and the cross-section has no other fillers. The dielectric constant of the two samples obtained is significantly different from the dielectric loss, and it can be seen from the figure that at 100HZ, the dielectric constant of the pure EVA film is 4.6, while the dielectric constant increases to 9.1 after 1 wt% graphene is added, for the following reasons: the pure EVA film has a certain dielectric constant, and after the graphene is added to a polymer matrix, the dielectric constant of the composite film is increased mainly due to the effect of Maxwelle-Wagnare-Sillars interface polarization effect between the pure EVA film and the graphene. After the graphene is introduced into the EVA matrix, due to good dispersion of the graphene in the polymer, a large number of interfaces can be generated between the graphene and the EVA, and after an electric field is applied, a large number of current carriers can be accumulated at the interfaces, so that interface polarization is generated, and finally the dielectric constant of the composite film is increased. The dielectric losses of the two samples are shown in fig. 4(d), and the dielectric losses of the samples decrease and then increase with increasing frequency, and the dielectric losses are mainly the conductance losses in the extremely narrow ultra-low frequency range of 100Hz to 130 Hz. In the range of 130 Hz-106Hz, the dielectric loss increases again and again, mainly due to the loss of oriented polarization of the C ═ O bonds in the EVA polymer. It is noted that the dielectric loss of the composite film is not particularly significantly changed by adding the graphene to the polymer matrix, and is still kept low, and the dielectric loss at 100Hz is shown as the dielectric loss is kept below 0.1. The reason is that the pyrenyl ester-containing hyperbranched polyethylene copolymer polymer adsorbed on the surface of the graphene by the non-covalent CH-pi and pi-pi functions prevents the graphene from directly contacting with a polymer base, reduces the generation of leakage current of the composite membrane, and maintains the dielectric loss at a lower level. The above results thus confirm: after the graphene without the excessive pyrenyl ester-containing hyperbranched polyethylene copolymer is added, the dielectric constant of the EVA film can be obviously improved, and the lower dielectric loss can be maintained.
Example 3, comparative examples 1 and 2
1. Preparation of samples
(1) Example 3 the preparation of the sample was carried out as follows:
step 1: see steps 1 to 4 in example 1 for graphene dispersions without excess pyrenylated ester-containing hyperbranched polyethylene copolymer.
Step 2: the EVA solution was prepared according to step 5 in example 1.
And 3, step 3: naturally cooling the EVA solution obtained in the step 2 to room temperature, adding a solution containing 1mg of graphene, continuously stirring at 50 ℃ for 5min, casting on a silicon wafer, drying at 80 ℃ for 8h, and finally removing the film from the mold.
(2) Comparative example 2 the preparation of the sample was carried out as follows:
step 1: under the protection of ethylene, 100mL of anhydrous grade dichloromethane is injected into a Schlenk bottle with the size of 250mL, and stirred for 30min to ensure that the temperature is constant at 35 ℃; pd-diimine catalyst 1(0.2g, previously dissolved in 10mL of anhydrous dichloromethane at a concentration of 1.82g/L based on the total volume of the reaction) was then added under ethylene protection. After the above solution was stirred at a constant polymerization temperature (35 ℃ C.) and an ethylene pressure (1atm) to continue the polymerization for 24 hours, the resultant was added to 200mL of acidified methanol (1% by mass) to terminate the polymerization. The resulting polymer product was purified as follows: first, the solvent was removed by air purge at room temperature, the resulting product was dissolved in 50mL of THF, a small amount of hydrochloric acid and an aqueous hydrogen peroxide solution (5 drops each) were added and the resulting solution was stirred for 2 hours to dissolve a small amount of Pd particles contained in the product; methanol (100mL) was then added to precipitate the polymer. In order to further remove a small amount of catalyst ligand contained in the product, the product is dissolved in 20mL of THF again and precipitated out by methanol; this "dissolve-precipitate" step was repeated 2 times. The product is dried in vacuum at 50 ℃ for 48h to obtain HBPE.
Step 2: adding natural flaky graphite (20mg), analytically pure chloroform (10mL) and the HBPE (40mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic pool, performing constant-temperature ultrasonic treatment at 25 ℃ for 48h to obtain an initial graphene dispersion solution, further performing low-speed centrifugation at 4000rpm for 45min, and standing for 8h to obtain a graphene dispersion solution containing excessive HBPE (note: the feeding concentration of graphite powder is 2mg/mL, and the mass ratio of HBPE to graphite powder is 2).
And 3, step 3: and (3) carrying out vacuum filtration on the graphene dispersion liquid (10mL) obtained in the step (2) by using an alumina filter membrane (anodis 47, the average pore diameter is 0.02 mu m), further carrying out leaching on a filtered product by using 20mL of chloroform (which is 2 times of the volume of the original dispersion liquid), then placing the obtained filter membrane (containing the graphene product) into 10mL of chloroform, and carrying out continuous ultrasonic treatment for 8h at 25 ℃ in a 250W ultrasonic pool to obtain the graphene dispersion liquid without excessive HBPE.
And 4, step 4: dissolving EVA in organic solvent CHCl at 50 deg.C 3 And stirring for 10min to dissolve EVA in organic solvent CHCl completely 3 In (1). Wherein the feeding concentration of the EVA is 100 mg/mL.
And 5, step 5: and (3) naturally cooling the EVA solution obtained in the step (4) to room temperature, adding the solution containing 1mg of graphene prepared in the step (3), continuously stirring at 50 ℃ for 5min, casting on a silicon wafer, drying at 80 ℃ for 8h, and finally removing the film from the die.
2. Characterization and testing
Testing is carried out by adopting a 4294A type impedance analyzer produced by Keysight company in America, silver electrodes are uniformly coated on the front surface and the back surface of a sample before testing, and the testing frequency is as follows: 100Hz-106 Hz, bias voltage of 0.5V, test temperature of room temperature, and test sample size: 1cm × 1 cm.
3. Comparison and analysis of test results
FIGS. 5(c) and (d) compare three samples made in example 3 and comparative examples 1 and 2. As shown in the figure, the SEM images of the cross sections of example 3 and comparative example 2 are shown in fig. 5(a) and (b), respectively, and it can be seen from the comparison of the SEM images that the graphene is uniformly dispersed in the EVA substrate in example 3, and the graphene has a significant stacking phenomenon in the EVA substrate in comparative example 2. The dielectric constants of the three obtained samples are significantly different from the dielectric loss, and it can be seen from the figure that at 100HZ, the dielectric constant of a pure EVA film is 4.6, the dielectric constant of the graphene prepared by peeling the pyrenyl ester-containing hyperbranched polyethylene copolymer is increased to 5.2 after 0.1 wt% of the graphene is added, and the dielectric constant of the graphene prepared by peeling the HBPE is increased to 4.7 after 0.1 wt% of the graphene is added. This is due to the following reasons: the graphene prepared by peeling the pyrenyl ester-containing hyperbranched polyethylene copolymer has high dielectric property, and the pyrenyl ester-containing hyperbranched polyethylene copolymer is attached to the surface of the graphene, so that the graphene can be uniformly dispersed in the EVA substrate, and the measured dielectric property is high.
Example 4, comparative examples 1 and 3
1. Preparation of samples
(1) Example 4 the preparation of the sample was carried out as follows:
step 1: see steps 1 to 4 in example 1 for graphene dispersions without excess pyrenylated ester-containing hyperbranched polyethylene copolymer.
Step 2: the EVA solution was prepared according to step 5 in example 1.
And 3, step 3: naturally cooling the EVA solution obtained in the step 2 to room temperature, adding the solution containing 5mg of graphene prepared in the step 1, continuously stirring at 50 ℃ for 5min, casting on a silicon wafer, drying at 80 ℃ for 8h, and finally removing the film from the mold.
(2) Comparative example 3 the preparation of the sample was carried out as follows:
step 1: see steps 1 to 3 in comparative example 2 for graphene dispersions without excess HBPE.
Step 2: dissolving EVA in organic solvent CHCl at 50 deg.C 3 And stirring for 10min to dissolve EVA in organic solvent CHCl completely 3 In (1). Wherein the feeding concentration of the EVA is 100 mg/mL.
And 3, step 3: naturally cooling the EVA solution obtained in the step 2 to room temperature, adding the solution containing 5mg of graphene prepared in the step 1, continuously stirring at 50 ℃ for 5min, casting on a silicon wafer, drying at 80 ℃ for 8h, and finally removing the film from the mold.
2. Characterization and testing
Testing is carried out by adopting a 4294A type impedance analyzer produced by Keysight company in America, silver electrodes are uniformly coated on the front surface and the back surface of a sample before testing, and the testing frequency is as follows: 100Hz-106 Hz, bias voltage of 0.5V, test temperature of room temperature, and test sample size: 1cm × 1 cm.
3. Comparison and analysis of test results
FIGS. 6(c) and (d) compare three samples made in example 4 and comparative examples 1 and 3. As shown in the figure, the SEM images of the cross sections of example 4 and comparative example 3 are shown in fig. 6(a) and (b), respectively, and it can be seen from the comparison of the SEM images that the graphene is uniformly dispersed in the EVA substrate in example 4, and the graphene has a significant stacking phenomenon in the EVA substrate in comparative example 3. The dielectric constants of the three obtained samples are significantly different from the dielectric loss, and it can be seen from the figure that at 100HZ, the dielectric constant of a pure EVA film is 4.6, the graphene prepared by pyrenyl ester-containing hyperbranched polyethylene copolymer stripping is added with 0.5 wt% of graphene, and the dielectric constant is increased to 7.3, while the graphene prepared by HBPE stripping is added with 0.1 wt% of graphene, and the dielectric constant is increased to 5.0. This is due to the following reasons: the graphene prepared by peeling the pyrenyl ester-containing hyperbranched polyethylene copolymer has high dielectric property, and the pyrenyl ester-containing hyperbranched polyethylene copolymer is attached to the surface of the graphene, so that the graphene can be uniformly dispersed in the EVA substrate, and the measured dielectric property is high.
Example 5 and comparative example 4
1. Preparation of samples
(1) Example 5 the preparation of the sample was carried out as follows:
see steps 1 to 4 in example 1 for graphene dispersion without excess pyrenylated ester-containing hyperbranched polyethylene copolymer-4 h.
(2) Comparative example 4 the preparation of the sample was carried out as follows:
the graphene dispersion without excess pyrenylated ester-containing hyperbranched polyethylene copolymer-0.5 h (characterization parameters see table 1) is seen in steps 1 to 4 in example 1, except that the ATRP reaction time is 0.5h, the conditions are identical.
2. Characterization and testing
Microscopic morphology analysis of graphene
The observation was carried out by High Resolution Transmission Electron Microscopy (HRTEM) and the tests were carried out on a transmission electron microscope model 300kVJEM-100 CXII. And (3) dropwise adding a small amount of graphene dispersion liquid on the surface of a TEM copper mesh (a carbon-containing support film, a product of a medium-scope instrument), and naturally drying at room temperature for testing.
3. Comparison and analysis of test results
In example 5 and comparative example 4, both chloroform was used as a solvent, and under the same initial composition and ultrasonic process, the graphene dispersion liquid without the excess pyrenyl ester-containing hyperbranched polyethylene copolymer and the graphene dispersion liquid without the excess pyrenyl ester-containing hyperbranched polyethylene copolymer were used for-0.5 h, respectively. Two corresponding graphene dispersions were recovered after another ultrasonic dispersion, and their HRTEM results were compared in fig. 7(a) - (d). Wherein fig. 7(a) and (b) correspond to example 5 (no excess pyrenyl ester-containing hyperbranched polyethylene copolymer-4 h), and fig. 7(c) and (d) correspond to comparative example 4 (no excess pyrenyl ester-containing hyperbranched polyethylene copolymer-0.5 h); the figures show that the graphene obtained from the two systems has a relatively close physical size of about 0.5 μm and is generally electronically transparent, indicating that the samples obtained are relatively thin in thickness. The above results thus confirm: the polymer pyrenyl ester-containing hyperbranched polyethylene copolymer-4 h and the pyrenyl ester-containing hyperbranched polyethylene copolymer-0.5 h can be attached to the surface of graphene through the CH-pi/pi-pi synergistic effect, so that the polymer pyrenyl ester-containing hyperbranched polyethylene copolymer can be firmly attached to the surface of graphene.
Example 6 and comparative examples 5 and 6
1. Preparation of samples
(1) Example 6 the preparation of the sample was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 and 2 in example 1.
Step 2: 10mg of pyrenylated ester-containing hyperbranched polyethylene copolymer was added to 10mL of CHCl 3 In the solution, shake for 10 min.
And 3, step 3: adding the solution obtained in the second step into a cylindrical glass bottle with the size of 100mL, adding natural flaky graphite (20mg), sealing, placing in a 250W ultrasonic pool, performing constant-temperature ultrasonic treatment at 25 ℃ for 48h to obtain an initial graphene dispersion solution, further performing low-speed centrifugation at 4000rpm for 45min, and standing for 8h to obtain the graphene dispersion solution.
(2) Comparative example 5 the preparation of the sample was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 and 2 in example 1.
Step 2: 10mg of pyrenyl ester-containing hyperbranched polyethylene copolymer was added to 10mL of a THF solution, and shaken for 10 min.
And 3, step 3: adding the solution obtained in the second step into a cylindrical glass bottle with the size of 100mL, adding natural flaky graphite (20mg), sealing, placing in a 250W ultrasonic pool, performing constant-temperature ultrasonic treatment at 25 ℃ for 48h to obtain an initial graphene dispersion solution, further performing low-speed centrifugation at 4000rpm for 45min, and standing for 8h to obtain the graphene dispersion solution.
(3) Comparative example 6 the preparation of the sample was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 and 2 in example 1.
Step 2: 10mg of pyrenyl ester-containing hyperbranched polyethylene copolymer was added to 10mL of a toluene solution, and shaken for 10 min.
And 3, step 3: adding the solution obtained in the second step into a cylindrical glass bottle with the size of 100mL, adding natural flaky graphite (20mg), sealing, placing in a 250W ultrasonic pool, performing constant-temperature ultrasonic treatment at 25 ℃ for 48h to obtain an initial graphene dispersion solution, further performing low-speed centrifugation at 4000rpm for 45min, and then standing for 8h to obtain the graphene dispersion solution.
2. Characterization and testing
And (4) carrying out optical photo shooting on the finally obtained graphene dispersion liquid of each sample.
3. Comparison and analysis of test results
FIG. 8 compares four samples made in example 6 and comparative examples 5, 6. The preparation processes and procedures were identical for all three samples except for the different solvents. As shown in the figure, example 6 and comparative example 5 both sonicated graphene well, whereas comparative example 6 did not. This is due to the following reasons: solvent CHCl from example 6 3 To ratio ofThe surface energy of the solvent THF in the comparative example 5 is similar to that of graphite, so that the graphite sheet can be ultrasonically processed into a sheet of graphene, the polymer can be further attached to the graphene to form a stable graphene solution, and the difference between the surface energy of the solvent toluene and the surface energy of the graphite in the comparative example 6 is large, so that the graphite cannot be effectively stripped. The above results thus confirm: according to the principle of similar surface energy, in example 6, the graphene solution can be obtained by stripping well in comparative example 5, while the graphene solution cannot be obtained by stripping in comparative example 6.
Example 7 and comparative examples 7 and 8
1. Preparation of samples
Example 8 the preparation of the sample was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 to 2 in example 1.
Step 2: adding natural flaky graphite (40mg), analytically pure chloroform (10mL) and the pyrenyl ester-containing hyperbranched polyethylene copolymer (20mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic water pool, performing constant-temperature ultrasonic treatment at 25 ℃ for 48h to obtain a graphene initial dispersion liquid, further performing low-speed centrifugation at 4000rpm for 45min, and standing for 8h to obtain a graphene dispersion liquid containing an excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 4mg/mL, and the mass ratio of the pyrenyl ester-containing hyperbranched polyethylene copolymer to the graphite powder is 0.5).
The preparation of the sample of comparative example 7 was carried out as follows:
step 1: the synthesis steps and process of pyrenylated ester-containing hyperbranched polyethylene copolymer are as in steps 1 to 2 in example 1.
Step 2: adding natural flaky graphite (40mg) and analytical pure chloroform (10mL) into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic water tank, performing constant-temperature ultrasonic treatment at 25 ℃ for 48h to obtain an initial graphene dispersion liquid, further performing low-speed centrifugation at 4000rpm for 45min, and then standing for 8h to obtain a graphene dispersion liquid containing excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 4mg/mL, and the mass ratio of the pyrenyl ester-containing hyperbranched polyethylene copolymer to the graphite powder is 0).
The preparation of the sample of comparative example 8 was carried out as follows:
step 1: the synthesis steps and process of pyrenylated ester-containing hyperbranched polyethylene copolymer are as in steps 1 to 2 in example 1.
Step 2: adding natural flaky graphite (40mg), analytical pure chloroform (10mL) and the pyrenyl ester-containing hyperbranched polyethylene copolymer (40mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic water pool, performing constant-temperature ultrasonic treatment for 48h at 25 ℃ to obtain an initial graphene dispersion liquid, further performing low-speed centrifugation for 45min at 4000rpm, and then standing for 8h to obtain a graphene dispersion liquid containing an excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 4mg/mL, and the mass ratio of the pyrenyl ester-containing hyperbranched polyethylene copolymer to the graphite powder is 1).
2. Characterization and testing
The graphene concentration was characterized using a UV-Vis spectrophotometer model Lambda 750S from Perkin Elmer, USA. The scanning wavelength range is 350-800 nm, the scanning step length is 1nm, and a standard quartz cuvette (the optical path is 10nm) is adopted. The samples to be tested are tested after appropriate dilution.
3. Comparison and analysis of test results
As can be seen from FIG. 9, the concentration of the graphene solution in example 7 is the highest and is 0.09mg/mL, and the concentration in comparative examples 7 and 8 is lower and is 0.02mg/mL and 0.07mg/mL respectively. From the trend, as the charge ratio of the polymer to the graphite is increased and other conditions are unchanged, the concentration of the graphene solution obtained by stripping is increased and then decreased, which is caused by the following reasons: the method is characterized in that graphite is opened excessively by utilizing ultrasound with the increase of the concentration of a polymer, the polymer is attached to the surface of graphene, the concentration of a graphene solution is increased, once the concentration of the polymer is too high, the polymer can wrap the graphite, the graphite is not beneficial to the opening exceeding of the graphite, and the concentration of the graphene solution is reduced.
Example 8 and comparative examples 9 and 10
1. Preparation of samples
Example 8 sample preparation was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 to 2 in example 1.
Step 2: and (2) sequentially adding natural flaky graphite (40mg), analytically pure chloroform (10mL) and the pyrenyl ester-containing hyperbranched polyethylene copolymer (10mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL, sealing, placing in a 250W ultrasonic water pool, performing constant-temperature ultrasonic treatment for 48h at 25 ℃ to obtain an initial graphene dispersion solution, further performing low-speed centrifugation for 45min at 4000rpm, and standing for 8h to obtain a graphene dispersion solution containing an excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the charging concentration of graphite powder is 4mg/mL, and the charging concentration of the pyrenyl ester-containing hyperbranched polyethylene copolymer is 1 mg/mL).
Comparative example 9 the preparation of the sample was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 to 2 in example 1.
Step 2: adding natural flaky graphite (10mg), analytical pure chloroform (10mL) and the pyrenyl ester-containing hyperbranched polyethylene copolymer (10mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic water pool, performing constant-temperature ultrasonic treatment for 48h at 25 ℃ to obtain an initial graphene dispersion liquid, further performing low-speed centrifugation for 45min at 4000rpm, and then standing for 8h to obtain a graphene dispersion liquid containing an excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 1mg/mL, and the feeding concentration of the pyrenyl ester-containing hyperbranched polyethylene copolymer is 1 mg/mL).
The preparation of the sample of comparative example 10 was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 to 2 in example 1.
Step 2: adding natural flaky graphite (80mg), analytically pure chloroform (10mL) and the pyrenyl ester-containing hyperbranched polyethylene copolymer (10mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic water pool, performing constant-temperature ultrasonic treatment for 48h at 25 ℃ to obtain an initial graphene dispersion liquid, further performing low-speed centrifugation for 45min at 4000rpm, and standing for 8h to obtain a graphene dispersion liquid containing an excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 8mg/mL, and the feeding concentration of the pyrenyl ester-containing hyperbranched polyethylene copolymer is 1 mg/mL).
2. Characterization and testing
The graphene concentration was characterized using a UV-Vis spectrophotometer model Lambda 750S from Perkin Elmer, USA. The scanning wavelength range is 350-800 nm, the scanning step length is 1nm, and a standard quartz cuvette (the optical path is 10nm) is adopted. The sample to be tested is suitably diluted and tested.
3. Comparison and analysis of test results
As can be seen from FIG. 10, the concentration of the graphene solution in comparative example 10 is the highest and is 0.52mg/mL, and in example 8 and comparative example 9 are lower and are respectively 0.27mg/mL and 0.04 mg/mL. From the trend, as the graphite concentration increases and other conditions do not change, the concentration of the graphene solution obtained by stripping always increases due to the following reasons: the more the graphite is overflown into graphene due to the increase of the graphite concentration, the more easily the polymer is attached to the graphene, and the existence of the graphene solution is stabilized.
Example 9 and comparative examples 11 and 12
1. Preparation of samples
Example 9 the preparation of the sample was carried out as follows:
step 1: the synthesis steps and process of pyrenylated ester-containing hyperbranched polyethylene copolymer are as in steps 1 to 2 in example 1.
Step 2: adding natural flaky graphite (80mg), analytically pure chloroform (10mL) and the pyrenyl ester-containing hyperbranched polyethylene copolymer (10mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic water pool, performing constant-temperature ultrasonic treatment for 48h at 25 ℃ to obtain an initial graphene dispersion liquid, further performing low-speed centrifugation for 45min at 4000rpm, and standing for 8h to obtain a graphene dispersion liquid containing an excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 8mg/mL, and the feeding concentration of the pyrenyl ester-containing hyperbranched polyethylene copolymer is 1 mg/mL).
The preparation of the sample of comparative example 11 was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 to 2 in example 1.
Step 2: adding natural flaky graphite (80mg), analytically pure chloroform (10mL) and the pyrenyl ester-containing hyperbranched polyethylene copolymer (10mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic water pool, performing constant-temperature ultrasonic treatment for 0h at 25 ℃ to obtain an initial graphene dispersion liquid, further performing low-speed centrifugation for 45min at 4000rpm, and standing for 8h to obtain a graphene dispersion liquid containing an excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 8mg/mL, and the feeding concentration of the pyrenyl ester-containing hyperbranched polyethylene copolymer is 1 mg/mL).
Comparative example 12 the preparation of the sample was carried out as follows:
step 1: the synthesis steps and process of the pyrenyl ester-containing hyperbranched polyethylene copolymer are shown in steps 1 to 2 in example 1.
Step 2: adding natural flaky graphite (80mg), analytically pure chloroform (10mL) and the pyrenyl ester-containing hyperbranched polyethylene copolymer (10mg) obtained in the step 1 into a cylindrical glass bottle with the size of 100mL in sequence, sealing, placing in a 250W ultrasonic water pool, performing constant temperature ultrasonic treatment for 96h at 25 ℃ to obtain an initial graphene dispersion liquid, further performing low speed centrifugation for 45min at 4000rpm, and standing for 8h to obtain a graphene dispersion liquid containing an excessive pyrenyl ester-containing hyperbranched polyethylene copolymer (note: the feeding concentration of graphite powder is 8mg/mL, and the feeding concentration of the pyrenyl ester-containing hyperbranched polyethylene copolymer is 1 mg/mL).
2. Characterization and testing
The graphene concentration was characterized using a UV-Vis spectrophotometer model Lambda 750S from Perkin Elmer, USA. The scanning wavelength range is 350-800 nm, the scanning step length is 1nm, and a standard quartz cuvette (the optical path is 10nm) is adopted. The sample to be tested is suitably diluted and tested.
3. Comparison and analysis of test results
As can be seen from FIG. 11, the graphene concentration gradually increased with increasing sonication time, with the highest concentration of 0.86mg/mL in comparative example 12, and the second highest concentration of 0.70mg/mL in example 9, and the concentration of 0mg/mL in comparative example 11 without sonication. This is due to the following reasons: with the increase of the ultrasonic time, the graphite is gradually opened, more and more graphene is generated, and the polymer is further stably attached to the surface of the graphene, so that the final graphene concentration is gradually increased.
Example 10
Under the protection of ethylene, a pyrene-containing monomer (1.33g/0.23M), BIEA (1.22g/0.23M) obtained in the step 2 and anhydrous dichloromethane (15mL) were added into a Schlenk reaction flask with a size of 50mL, the temperature was controlled at 25 ℃, then an acetonitrile group Pd-diimine catalyst (0.5g/0.6mmol) dissolved in 5mL of anhydrous dichloromethane was added, and the mixture was stirred and reacted for 24 hours under the conditions of 25 ℃ and 1atm of ethylene pressure, and after the polymerization was completed, the resultant was poured into 100mL of acidified methanol (the mass concentration of HCl therein was 1%) to terminate the polymerization. The solvent in the resulting reaction mixture was removed by air purge, the product was dissolved in THF (15mL), the polymerization product was precipitated by slowly adding acetone (20mL) with stirring, and the purification was repeated 3 times after removing the upper solution to obtain the polymerization product. The obtained product is dissolved in THF (15mL) again, a small amount of hydrochloric acid and hydrogen peroxide (3-5 drops each) are added, stirring is carried out for 2 hours to dissolve a small amount of Pd particles contained in the product, then methanol (40mL) is added to precipitate the product, and vacuum drying is carried out at 60 ℃ for 24 hours to obtain 9.26 g of HBPE @ Py @ Br. The characterization data are shown in Table 1.
TABLE 1
Claims (5)
1. An application of pyrenyl terpolymer in preparing EVA dielectric composite material is characterized in that: the pyrenyl terpolymer is prepared by the following method: catalyzing ethylene, a pyrene-containing monomer shown in a formula (I) and a bromine-containing monomer BIEA by using a Pd-diimine catalyst to perform one-step chain removal copolymerization to prepare a hyperbranched terpolymer HBPE @ Py @ Br simultaneously containing pyrene end groups and acyl bromide end groups; then, taking the hyperbranched terpolymer HBPE @ Py @ Br as a macroinitiator, and initiating an acrylate monomer to graft copolymerization by virtue of an acyl bromide end group based on an ATRP mechanism to obtain a pyrenyl terpolymer;
the application method comprises the following steps:
(A) mixing graphite powder, pyrenyl terpolymer and organic solvent A, sealing, carrying out ultrasonic treatment on the obtained mixture to obtain graphene initial dispersion liquid, and further carrying out low-speed centrifugation and standing treatment to obtain graphene dispersion liquid containing excessive pyrenyl terpolymer; wherein the feeding concentration of graphite powder is 0.01-15000 mg/mL, the mass ratio of the pyrenyl terpolymer to the graphite powder is 0.0005-10: 1, and the organic solvent A is selected from one of the following chemically pure or analytically pure reagents: THF, chloroform, chlorobenzene, dichloromethane, toluene, n-heptane, DMF, NMP;
(B) and (B) dispersing the graphene dispersion liquid obtained in the step (A) into EVA through solution mixing or melt mixing to obtain the EVA dielectric composite material.
2. The use of claim 1, wherein: the number average molecular weight of the pyrenyl terpolymer is 5000-50000; in the pyrenyl ternary copolymer, the grafting proportion of pyrenyl and acrylate monomers is 0.5-20mol% and 0.5-100 mol%.
3. The use of claim 1, wherein: the preparation method of the pyrenyl terpolymer comprises the following steps:
(1) under the protection of ethylene, mixing a pyrene-containing monomer shown in a formula (I), a bromine-containing monomer BIEA, a Pd-diimine catalyst and an anhydrous solvent in a reaction vessel, stirring and polymerizing under a certain ethylene pressure condition, and after full reaction, separating and purifying to obtain a hyperbranched terpolymer HBPE @ Py @ Br containing pyrene end groups and acyl bromide end groups;
(2) under the protection of nitrogen, mixing an ATRP reaction ligand, a hyperbranched terpolymer HBPE @ Py @ Br, a transition metal complex, an acrylate monomer and an anhydrous solvent in a reaction container, introducing nitrogen to remove oxygen, sealing the reactor, fully polymerizing, and separating and purifying to obtain the pyrenyl terpolymer.
4. The use of claim 1, wherein: the application further comprises the steps of:
(A-1) carrying out high-speed centrifugation or vacuum filtration on the graphene dispersion liquid containing the excessive pyrenyl terpolymer obtained in the step (A) to remove the excessive pyrenyl terpolymer, and carrying out ultrasonic treatment again to disperse the excessive pyrenyl terpolymer into an organic solvent A to obtain a graphene dispersion liquid; the graphene dispersion was reused in step (B).
5. The use of claim 1, wherein: in the step (B), the content of graphene in the EVA dielectric composite material is controlled to be 0.1-10 wt%.
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| CN103923234A (en) * | 2014-04-08 | 2014-07-16 | 青岛科技大学 | Pyrenyl-containing radical initiator, and synthesis method and use thereof |
| CN104292376A (en) * | 2014-10-11 | 2015-01-21 | 浙江工业大学 | Pyrenyl hyperbranched polyethylene and application thereof in preparing graphene |
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| CN103923234A (en) * | 2014-04-08 | 2014-07-16 | 青岛科技大学 | Pyrenyl-containing radical initiator, and synthesis method and use thereof |
| CN104292376A (en) * | 2014-10-11 | 2015-01-21 | 浙江工业大学 | Pyrenyl hyperbranched polyethylene and application thereof in preparing graphene |
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