Monodisperse polymer / metal composite microsphere and preparation method thereof

Abstract

The invention provides a preparation method of a monodisperse polymer / metal composite microsphere, which comprises the following steps: A) under an ice bath condition, reacting a multi-sulfydryl monomer with other monomers in a liquid-phase medium to obtain a microsphere with sulfydryl on the surface; and B) placing the microspheres containing sulfydryl on the surfaces in a chemical plating solution, and reacting to obtain the polymer / metal composite microspheres. The polymer / metal composite microsphere provided by the invention is simple in preparation process and low in energy consumption. According to the preparation method, the low-temperature condition is adopted, the nucleation time is delayed, the monodispersity of the microspheres is improved, the compactness of the metal conducting layer is improved in a click chemistry mode, and then the conductivity of the monodisperse polymer / metal composite microspheres is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of composite materials, and particularly relates to a monodisperse polymer / metal composite microsphere and a preparation method thereof. BACKGROUND

[0002] The monodisperse polymer / metal composite microsphere is a new type of composite material, and is mainly applied to the fields of conductive rubber, conductive adhesive, antistatic shielding coating, antistatic rubber and the like. Compared with pure metal microspheres, the polymer / metal composite microsphere has relatively low manufacturing cost, and thus has strong competitive advantage in market competition.

[0003] The polymer / metal composite microsphere is generally prepared by using a polymer microsphere as a template and adopting a chemical plating or electroplating method to construct a metal layer on the surface of the polymer microsphere. Generally, the common polymer / metal composite microspheres are polystyrene / nickel composite microspheres, polystyrene / copper composite microspheres, polystyrene / silver composite microspheres and polystyrene / gold composite microspheres and the like.

[0004] At present, there are disadvantages such as high energy consumption and long preparation period in the synthesis of the polymer / metal composite microsphere. Therefore, it is a problem to be solved to provide a polymer / metal composite microsphere with a simplified preparation method and low energy consumption. SUMMARY

[0005] In view of this, the technical problem to be solved by the present application is to provide a monodisperse polymer / metal composite microsphere and a preparation method thereof. The preparation process of the polymer / metal composite microsphere provided by the present application is simple, and the energy consumption is low.

[0006] The present application provides a preparation method of a monodisperse polymer / metal composite microsphere, which comprises the following steps:

[0007] A) under ice bath conditions, a multi-thiol monomer is reacted with other monomers in a liquid medium to obtain microspheres containing thiol groups on the surface;

[0008] B) the microspheres containing thiol groups on the surface are placed in a chemical plating solution to obtain polymer / metal composite microspheres.

[0009] Preferably, in step A), a stirring paddle is used for stirring during the reaction, and the stirring paddle is selected from a turbine type or a propeller type stirring paddle.

[0010] The rotation speed of the stirring is 200-1000 r / min.

[0011] Preferably, the other monomer contains at least two functional groups capable of reacting, and the functional groups are one or more of isocyanate groups, epoxy groups, allyl groups and propargyl groups.

[0012] The polythiol monomer is selected from one or more of 1,6-hexanedithiol, trimethylolpropane tris(3-mercaptopropionate), pentaerythritol tetra-3-mercaptopropionate, and hexakis(3-mercaptopropionate)dipentaerythritol ester.

[0013] Preferably, the molar ratio of the polythiol monomer to other monomers is 1: (1.1-2).

[0014] Preferably, the liquid medium is selected from ethanol.

[0015] The liquid medium contains polyvinylpyrrolidone; the content of the polyvinylpyrrolidone in each 100 mL of the liquid medium is 1-5 g.

[0016] In step A), the reaction is carried out in the presence of a catalyst; the catalyst is one or more of triethylamine, tributylamine, 1,8-diazabicycloundec-7-ene, 1,5,7-triazabicyclodec-5-ene, and N,N'-dimethylformamide.

[0017] Preferably, the reaction time is 10 min-2 h.

[0018] Preferably, the metal elements in the electroless plating solution include one or more of gold, silver, platinum, palladium, copper, iron, nickel, titanium, zinc, tin, aluminum, lead, cobalt, indium, cadmium, chromium, germanium, antimony, and bismuth.

[0019] Preferably, step B) comprises:

[0020] The surface thiol-containing microspheres are placed in an electroless plating solution, stirred to react, and a metal layer is deposited on the surface of the surface thiol-containing microspheres to obtain polymer / metal composite microspheres.

[0021] The electroless plating solution contains 0.1-1 mol / L of a metal salt, 0.01-1 mol / L of a complexing agent, and 0.1-2 mol / L of a reducing agent.

[0022] The metal salt can be any one or a combination of metal sulfate, metal nitrate, and metal chloride salt.

[0023] The complexing agent is any one or a combination of EDTA, citric acid, citrate, sodium acetate, ammonium chloride, succinic acid, succinate, triethanolamine, ethylenediamine, and lactic acid.

[0024] The reducing agent is one or a combination of hypophosphite, borohydride, dimethylamine borate, and hydrazine.

[0025] The metal layer is deposited using a chemical deposition method, the chemical deposition temperature is room temperature (20℃~30℃), and the chemical deposition time is 0.5-5h; the thickness of the metal layer is 50nm~150nm.

[0026] Preferably, before performing chemical plating, the method further includes sensitizing and activating the microspheres containing thiol groups on the surface in sequence. The sensitization includes dispersing the microspheres containing thiol groups on the surface in water and then adding an aqueous solution of stannous chloride for sensitization.

[0027] The activation process includes: adding sensitized microspheres containing thiol groups to a dilute palladium chloride hydrochloric acid solution for activation, thereby obtaining activated microspheres.

[0028] The present invention also provides a polymer / metal composite microsphere prepared by the above preparation method, wherein the CV value of the polymer / metal composite microsphere is ≤2%.

[0029] Compared with existing technologies, this invention provides a method for preparing monodisperse polymer / metal composite microspheres, comprising the following steps: A) reacting a polythiol monomer with other monomers in a liquid medium under ice bath conditions to obtain microspheres with thiol-containing surfaces; B) placing the thiol-containing microspheres in a chemical plating solution to react and obtain polymer / metal composite microspheres. The preparation process of the polymer / metal composite microspheres provided by this invention is simple and energy-efficient. This invention improves the monodispersity performance of the microspheres by using low-temperature conditions to delay nucleation time. Furthermore, this invention improves the density of the metal conductive layer through click chemistry, thereby increasing the conductivity of the monodisperse polymer / metal composite microspheres. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of a turbine-type impeller.

[0031] Figure 2 Schematic diagram of a propulsion impeller

[0032] Figure 3 SEM image of the polymer / nickel composite microspheres prepared in Example 1;

[0033] Figure 4 SEM image of the surface-containing thiol microspheres prepared in Example 2;

[0034] Figure 5 SEM image of the polymer / nickel composite microspheres prepared in Example 2;

[0035] Figure 6 SEM image of the polymer / silver / gold composite microspheres prepared in Example 3;

[0036] Figure 7SEM image of the sulfonated polystyrene / nickel composite microspheres prepared in Comparative Example 1;

[0037] Figure 8 SEM image of the thiol microspheres prepared in Comparative Example 2;

[0038] Figure 9 SEM image of the thiol microspheres prepared in Comparative Example 3. Detailed Implementation

[0039] This invention provides a method for preparing monodisperse polymer / metal composite microspheres, comprising the following steps:

[0040] A) Under ice bath conditions, a polythiol monomer is reacted with other monomers in a liquid medium to obtain microspheres with thiol groups on the surface;

[0041] B) The microspheres containing thiol groups on their surface are placed in a chemical plating solution and reacted to obtain polymer / metal composite microspheres.

[0042] This invention employs an ice bath condition in the preparation of microspheres containing thiol groups on their surface. Under this condition, multi-thiol monomers react with other monomers in a liquid medium. The ice bath condition used in this invention pertains to dispersion polymerization, which, in principle, follows the principles of free radical polymerization. In most cases, moderately lowering the temperature helps improve the monodispersity of the resulting microspheres. At low temperatures, free radical generation is slow, and polymer chain growth is also slow. This increases the time required for the system to reach the critical chain length. Due to the slow reaction, the monomer concentration in the system decreases slowly, maintaining a high supersaturation level for a longer period. This allows more oligomer chains nearing the critical chain length sufficient time to form and reach the precipitation conditions, resulting in more uniform particle size after precipitation. At high temperatures, the reaction is extremely fast, and the first batch of oligomers reaching the critical chain length rapidly precipitates and forms nuclei. Simultaneously, a large amount of monomer is rapidly consumed, and the system's supersaturation drops sharply. This results in a smaller number of effective nuclei, and the nuclei are generated at dispersed times, which is detrimental to monodispersity. Click chemistry is a rapid reaction process that can be completed in just a few minutes (more than 80% of the time). Therefore, lowering the temperature can slow down the nucleation process to some extent and improve the uniformity of the particles.

[0043] Specifically, the number of thiol groups in the polythiol monomer is preferably 2 to 4; the polythiol monomer may be selected from one or more of 1,6-hexanedithiol, trimethylolpropane tris(3-mercaptopropionic acid) ester, pentaerythritol tetra-3-mercaptopropionic acid ester, and hexa(3-mercaptopropionic acid) dipentaerythritol ester.

[0044] The other monomers contain at least two reactive functional groups, which are one or more selected from isocyanate group, epoxy group, allyl group, and propargyl group. In this invention, the other monomers are preferably isocyanate group monomers containing 2 to 4 isocyanate groups, epoxy group monomers containing 2 to 4 epoxy groups, allyl group monomers containing 2 to 6 allyl groups, or monomers containing at least one allyl group and at least one propargyl group.

[0045] The isocyanate monomer is preferably isophorone diisocyanate and / or hexamethylene diisocyanate.

[0046] The epoxy monomer is preferably one or more of the following: compound (i), compound (ii), trimethylolpropane triglycidyl ether, and pentaerythritol glycidyl ether;

[0047]

[0048] In equation (i), R is a residue of an alkane or cycloalkane after removing two hydrogens; in equation (ii), n is an integer greater than zero.

[0049] The compound of formula (i) may specifically be selected from 1,6-hexanediol diglycidyl ether, 1,4-butanediol diglycidyl ether or 1,2-cyclohexanediol diglycidyl ether.

[0050] The allyl monomer preferably has the structure of formula (iii):

[0051]

[0052] In formula (iii), R1 and R3 are independently selected from -H or -CH3, and R2 is one of the following structural substituents:

[0053]

[0054] Where m is an integer greater than zero.

[0055] The allyl monomer may specifically be selected from trimethylolpropane triacrylate and / or polyethylene glycol diacrylate, wherein the number average molecular weight of the polyethylene glycol diacrylate is preferably 500-1000, more preferably 575-700.

[0056] The monomer containing at least one allyl group and at least one propyne group is preferably propyne acrylate.

[0057] The molar ratio of the polythiol monomer to other monomers is 1:(1.1 to 2), and can be any value between 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2, or 1:(1.1 to 2).

[0058] The liquid medium includes, but is not limited to, ethanol; the liquid medium preferably also contains a certain amount of polyvinylpyrrolidone (PVP); the grade of the polyvinylpyrrolidone is preferably K30; the content of the polyvinylpyrrolidone in each 100mL of liquid medium is preferably 1 to 5g, specifically 1g, 1.5g, 2g, 2.5g, 3g, 3.5g, 4g, 4.5g or 5g.

[0059] In step A), the reaction is preferably carried out in the presence of a catalyst; the catalyst is preferably one or more selected from triethylamine, tributylamine, 1,8-diazabicycloundec-7-ene, 1,5,7-trizabicyclodec-5-ene, and N,N'-dimethylformamide; the content of the catalyst in each 100 mL of liquid medium is preferably 0 to 0.5 mL, specifically 0 mL, 0.1 mL, 0.15 mL, 0.2 mL, 0.25 mL, 0.3 mL, 0.35 mL, 0.4 mL, 0.45 mL, or 0.5 mL.

[0060] In this invention, the reaction in step A) is carried out under stirred conditions, and the reaction is stirred using a stirring paddle, which is selected from turbine-type or propeller-type stirring paddles. See also Figure 1 and Figure 2 , Figure 1 This is a schematic diagram of a turbine-type agitator. Figure 2 This is a schematic diagram of a propulsion-type stirring impeller. The present invention utilizes a specific type of stirring impeller to increase the uniformity of the system's mixing and further improve the monodispersity of the microspheres.

[0061] The stirring speed is 200 to 1000 r / min, specifically 200 r / min, 300 r / min, 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min, 1000 r / min, or any value between 200 and 1000 r / min.

[0062] The reaction time is 10 min to 2 h, specifically 10 min, 30 min, 1 h, 1.5 h, 2 h, or any value between 10 min and 2 h.

[0063] After preparation, the obtained microspheres were washed to obtain microspheres with thiol groups on the surface.

[0064] This invention uses click chemistry to ensure that the surface of the thiol-containing microspheres has a sufficient and uniform thiol content, thus guaranteeing the formation of a dense metal layer on the surface of the thiol-containing microspheres.

[0065] Specifically, the microspheres containing thiol groups on their surface are placed in a chemical plating solution and reacted to obtain polymer / metal composite microspheres.

[0066] The metallic element in the electroless plating solution includes one or more of the following: gold, silver, platinum, palladium, copper, iron, nickel, titanium, zinc, tin, aluminum, lead, cobalt, indium, cadmium, chromium, germanium, antimony, and bismuth. The metallic element can be a single metallic element or an alloy, such as a silver-tin alloy, a copper-tin alloy, a lead-tin alloy, or a silver, lead, and tin alloy. In some preferred embodiments of the invention, the metallic element is preferably at least one of gold, silver, platinum, copper, and nickel.

[0067] In some specific embodiments of the present invention, before chemical plating, the microspheres containing thiol groups on the surface are sequentially sensitized and activated. The sensitization includes: dispersing the microspheres containing thiol groups on the surface in water, and then adding an aqueous solution of stannous chloride for sensitization; the concentration of the aqueous solution of stannous chloride is 10~100 mg / ml, and can be any value between 10, 30, 50, 70, 100, or 10~100 mg / ml.

[0068] The activation process includes: adding sensitized microspheres containing thiol groups to a dilute palladium chloride hydrochloric acid solution for activation, thereby obtaining activated microspheres.

[0069] When thiol microspheres are dispersed in their solution and stirred, Sn 2+ Ions can be physically adsorbed or attached to the surface of the microspheres through coordination, forming a reducing surface layer. Sn adsorbed on the surface of the microspheres... 2+ Ions have strong reducing properties. This transforms the surface of the microspheres from an inert surface into a reducing-active surface.

[0070] Upon addition of palladium chloride (PdCl2) solution, Pd will dissociate. 2+ Ions. When Pd is present. 2+ When the solution comes into contact with the sensitized microspheres, Sn adsorbed on the surface of the microspheres... 2+ It will immediately target the nearby Pd 2+ Reduced to metallic palladium (Pd) 0 Formation of palladium "cores" or "activation centers": These reduced palladium atoms are firmly attached to the surface of the microspheres in the form of nanoparticles, forming dispersed catalytic active centers.

[0071] After activation, a catalytic active center can be introduced. The thiol group has a strong coordinating ability and can interact with palladium ions (Pd) through sulfur atoms. 2+Stable coordination bonds are formed, allowing palladium species to be firmly adsorbed onto the microsphere surface. Serving as catalytic active centers, these centers can initiate electroless plating reactions. Furthermore, selective deposition activation processes are achieved, confining the catalytic sites solely to the microsphere surface, preventing spontaneous nucleation in solution, and ensuring a uniform metal layer coating the microspheres rather than a disordered deposition.

[0072] The activated microspheres are then subjected to chemical plating. The microspheres containing thiol groups on their surface are placed in a chemical plating solution to react and obtain polymer / metal composite microspheres.

[0073] The specific steps are as follows:

[0074] The microspheres containing thiol groups on their surface are placed in a chemical plating solution and stirred to react, thereby depositing a metal layer on the surface of the microspheres containing thiol groups to obtain polymer / metal composite microspheres.

[0075] The electroless plating solution comprises: a metal salt of 0.1~1 mol / L, which can be 0.1, 0.3, 0.5, 0.7, 1, or any value between 0.1~1 mol / L; a complexing agent of 0.01~1 mol / L, which can be 0.01, 0.05, 0.1, 0.3, 0.5, 0.7, 1, or any value between 0.1~1 mol / L; and a reducing agent of 0.1~2 mol / L, which can be 0.1, 0.5, 1, 1.5, 2, or any value between 0.1~2 mol / L.

[0076] The metal salt can be any one or a combination of several metal sulfates, metal nitrates, and metal chlorides;

[0077] The complexing agent is any one or a combination of several of the following: EDTA, citric acid, citrate, sodium acetate, ammonium chloride, succinic acid, succinate, triethanolamine, ethylenediamine, and lactic acid.

[0078] The reducing agent is one or a combination of several of hypophosphite, borohydride, dimethylamine borate and hydrazine;

[0079] The metal layer is deposited using a chemical deposition method. The chemical deposition temperature is room temperature, which is 20°C to 30°C, and can be any value between 20°C, 25°C, 30°C, or 20°C to 30°C. The chemical deposition time is 0.5-5 hours, and can be any value between 0.5, 1, 2, 3, 4, 5 hours, or 0.5-5 hours. The thickness of the metal layer is 50 nm to 150 nm.

[0080] The present invention also provides a polymer / metal composite microsphere prepared by the above-described preparation method, wherein the polymer / metal composite microsphere comprises microspheres containing thiol groups on the surface and a metal layer composited on the surface of the microspheres. The particle size of the thiol-containing microspheres is 1~10 μm, and can be any value between 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 1~10 μm; the thickness of the metal layer is 50 nm~150 nm, and can be any value between 50, 100, 150, or 50 nm~150 nm.

[0081] The CV value of the polymer / metal composite microspheres is ≤2%.

[0082] The polymer / metal composite microspheres provided by this invention have a simple preparation process and low energy consumption. This invention improves the monodispersity of the microspheres by using low-temperature conditions to delay nucleation time. Furthermore, this invention improves the density of the metal conductive layer through click chemistry, thereby increasing the conductivity of the monodisperse polymer / metal composite microspheres.

[0083] The improved conductivity is achieved through two aspects: the good monodispersity of the microspheres and the direct synthesis of thiol-functionalized microspheres. The surface of the microspheres contains a large number of thiol groups, and the distribution of thiol groups formed by click chemistry is uniform. The complexation effect between thiol groups and metal ions is also the strongest, thus ultimately forming a dense metal layer.

[0084] To further understand the present invention, the following examples illustrate the monodisperse polymer / metal composite microspheres and their preparation method provided by the present invention. The scope of protection of the present invention is not limited by the following examples.

[0085] Example 1

[0086] (1) Add 3g PVP(k30) to 100mL ethanol, stir evenly in an ice bath, add 0.005mol pentaerythritol tetra-3-mercaptopropionate and 0.006mol trimethylolpropane triglycidyl ether, stir at 500r / min for 10min, add 0.2mL 1,8-diazabicycloundec-7-ene, continue stirring at 500r / min for 30min, then wash the product three times with ethanol to obtain D. 90 Thiol-containing microspheres with a particle size of 1.0 μm have a CV of 1.5%.

[0087] (2) Add 1g of thiol microspheres to 20mL of aqueous solution and disperse evenly by ultrasonication. Add 20mL of 20mg / ml stannous chloride aqueous solution to the dispersion, heat to 40℃, and mechanically stir at 200r / min for 20 minutes. Centrifuge to remove the supernatant, wash twice with 0.01M hydrochloric acid aqueous solution, and then disperse. Add 20mL of 2mg / ml palladium chloride, heat to 60℃, and mechanically stir at 200r / min for 20 minutes to activate the microsphere surface by capturing palladium ions. Centrifuge to remove the supernatant, wash the microspheres twice with deionized water, and then disperse. While stirring, add 10mL of 10mg / ml sodium hypophosphite and maintain for 10min to complete the reduction of the remaining palladium ions.

[0088] (3) Add the microspheres to 100 mL of 0.1 M sodium citrate aqueous solution, sonicate for 30 minutes, adjust the pH to 9 with 0.1 M sodium hydroxide, heat to 40 °C while stirring, and stir at 200 rpm. Finally, add a solution containing nickel ions (0.57 M nickel sulfate + 0.1 M sodium citrate) and reducing agent (1.40 M sodium hypophosphite, 2 M sodium hydroxide) to the dispersion at a rate of 1 mL / min until no more bubbles are generated, to obtain polymer / nickel composite microspheres.

[0089] See Figure 3 , Figure 3 The image shows a SEM image of the polymer / nickel composite microspheres prepared in Example 1.

[0090] Example 2

[0091] (1) Add 3g PVP(k30) to 100mL ethanol, stir evenly in an ice bath, add 0.005mol trimethylolpropane tris(3-mercaptopropionic acid) ester and 0.003mol pentaerythritol glycidyl ether, stir at 450r / min for 2h, then wash three times with ethanol to obtain microspheres with thiol-containing surfaces and a D90 particle size of 3.5μm, CV 1.5%, and their microstructure is as follows. Figure 4 As shown. Figure 4 The microspheres with thiol-containing surfaces were prepared in Example 2.

[0092] (2) Add 1g of thiol-containing microspheres to 20mL of aqueous solution and disperse evenly by ultrasonication. Add 20mL of 20mg / ml stannous chloride aqueous solution to the dispersion, heat to 40℃, and mechanically stir at 200r / min for 20 minutes. Centrifuge to remove the supernatant, wash twice with 0.01M hydrochloric acid aqueous solution, and then disperse. Add 20mL of 2mg / ml palladium chloride, heat to 60℃, and mechanically stir at 200r / min for 20 minutes to activate the microsphere surface by capturing palladium ions. Centrifuge to remove the supernatant, wash the microspheres twice with deionized water, and then disperse. While stirring, add 10mL of 10mg / ml sodium hypophosphite and maintain for 10min to complete the reduction of the remaining palladium ions.

[0093] (3) Add the microspheres to 100 mL of a 0.1 M sodium citrate aqueous solution, sonicate for 30 minutes, then adjust the pH to 9 with 0.1 M sodium hydroxide. Heat to 40 °C while stirring at 200 rpm. Finally, simultaneously add a solution containing nickel ions (0.57 M nickel sulfate + 0.1 M sodium citrate) and a reducing agent (1.40 M sodium hypophosphite, 2 M sodium hydroxide) to the dispersion at a rate of 1 mL / min until no more bubbles are generated. See [link to relevant documentation] Figure 5 , Figure 5 The image shows a SEM image of the polymer / nickel composite microspheres prepared in Example 2. Figure 5 The images, from top to bottom, show SEM images of polymer / nickel composite microspheres under different magnification conditions. Figure 5 It can be seen that the surface of the polymer / nickel composite microspheres prepared in Example 2 is uniform and dense.

[0094] Example 3

[0095] (1) Add 3g PVP(k30) to 100mL ethanol, stir evenly in an ice bath, add 0.01mol trimethylolpropane tris(3-mercaptopropionic acid) ester and 0.006mol pentaerythritol glycidyl ether, stir at 500r / min for 2h, and then wash three times with ethanol to obtain microspheres with thiol-containing surface and D90 particle size of 3μm, CV2%.

[0096] (2) Add 1g of thiol-containing microspheres to 20mL of aqueous solution and disperse evenly by ultrasonication. Add 20mL of 20mg / ml stannous chloride aqueous solution to the dispersion, heat to 40℃, and mechanically stir at 200r / min for 20 minutes. Centrifuge to remove the supernatant.

[0097] (3) Add 10 ml of 5 wt% ammonia water to 40 ml of 1 wt% silver nitrate. A brown-black precipitate will immediately form in the silver nitrate solution. Continue to add 3 ml of 5 wt% ammonia water until the solution becomes clear. Finally, add 0.2 g of sodium citrate to obtain a silver ammonia solution.

[0098] (4) Add 30 ml of the silver ammonia solution obtained in step (3) to 70 ml of 2 wt% polymer microspheres from step (2), stir at 40°C and 200 r / min for 3 h, centrifuge and wash to obtain polymer / silver composite microspheres. Take 2 g of polymer-silver composite microspheres and add them to 15 ml of 1 wt% chloroauric acid for a displacement reaction to obtain polymer / silver / gold composite microspheres. See Figure 6 , Figure 6 SEM image of the polymer / silver / gold composite microspheres prepared in Example 3. Figure 6 In the middle, from top to bottom, are SEM images of polymer / silver / gold composite microspheres under different magnification conditions. Figure 6 It can be seen that the polymer / silver / gold composite microspheres prepared in Example 3 have a dense surface.

[0099] Comparative Example 1

[0100] (1) Add 0.5g PVP(k30) to 26.8mL of ethanol, stir evenly, then add 5g of styrene and 0.15g of azobisisobutyronitrile, heat to 75℃, stir at 200r / min for 8h, and then wash three times with ethanol to obtain polystyrene microspheres with a D90 particle size of 2.7μm.

[0101] (2) Add 10g of the above microspheres to 100ml of concentrated sulfuric acid, stir overnight at 60℃, then wash with ice water and centrifuge, repeating several times to obtain surface sulfonated microspheres.

[0102] (3) Following steps (2) and (3) in Example 1, sulfonated polystyrene / nickel composite microspheres are obtained. See [link to relevant documentation] Figure 7 , Figure 7 SEM image of the sulfonated polystyrene / nickel composite microspheres prepared in Comparative Example 1. Figure 7 In the middle, from top to bottom, are SEM images of sulfonated polystyrene / nickel composite microspheres under different magnification conditions. Figure 7 It can be seen that the sulfonated polystyrene / nickel composite microspheres prepared in Comparative Example 1 have a loose and rough surface.

[0103] Comparative Example 2

[0104] Based on Example 1, only step 1) was changed, replacing the ice bath condition with a room temperature condition of 30°C. All other conditions remained unchanged, resulting in polymer / nickel composite microspheres. (See also...) Figure 8 , Figure 8 The image shows a SEM image of the thiol microspheres prepared in Comparative Example 2. The prepared thiol microspheres have an average particle size of 1 micrometer and exhibit poor monodispersity.

[0105] Comparative Example 3

[0106] Based on Example 1, only step 1) was changed, replacing the stirring paddle with a paddle mixer. All other conditions remained the same, resulting in polymer / nickel composite microspheres. See [link to example]. Figure 9 , Figure 9 The image shows a SEM image of the thiol microspheres prepared in Comparative Example 3. The prepared thiol microspheres have an average particle size of 1 μm and exhibit poor monodispersity.

[0107] Test case

[0108] The CV values ​​and resistivity of the polymer / metal composite microspheres prepared in the above examples and comparative examples were tested, and the results are shown in Table 1.

[0109] Table 1

[0110]

[0111] As shown in Table 1, the polymer / metal composite microspheres prepared by this invention have a CV value ≤2% and good density, thus exhibiting excellent conductivity. The high conductivity ultimately requires both conditions to be met: uniform and abundant thiol groups on the surface and monodispersity of the microspheres.

[0112] Comparative Example 1 shows that although the monodispersity is good, the functional modification method cannot obtain a surface with uniform and abundant functional groups. Therefore, the conductive layer is loose and has very low conductivity.

[0113] In Comparative Example 2, microspheres are prepared under normal temperature conditions, resulting in poor monodispersity and low conductivity.

[0114] Comparative Example 3 uses a paddle stirrer. The paddle stirrer affects the uniformity of the reaction system because the reaction is relatively fast. Even at low temperatures, it is actually faster than general free radical polymerization. Therefore, if the stirring system is not uniform, it will lead to poor monodispersity of the microspheres and low electrical conductivity.

[0115] The composite microspheres synthesized using this method can solve the problem of poor density in existing technologies (which can be clearly seen from the SEM images). Poor density leads to poor conductivity; the resistivity of Examples 1-3 is as low as 10. -5 Ω•cm, comparative resistivity is 10 -3 ~10 -4 Ω•cm.

[0116] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing monodisperse polymer / metal composite microspheres, characterized in that, Includes the following steps: A) Under ice bath conditions, a polythiol monomer is reacted with other monomers in a liquid medium to obtain microspheres with thiol groups on the surface; B) The microspheres containing thiol groups on their surface are placed in a chemical plating solution and reacted to obtain polymer / metal composite microspheres.

2. The preparation method according to claim 1, characterized in that, In step A), the reaction process is carried out by stirring with a stirring paddle, which is selected from turbine-type or propeller-type stirring paddles; The stirring speed is 200-1000 r / min.

3. The preparation method according to claim 1, characterized in that, The other monomers contain at least two reactive functional groups, which are one or more of isocyanate group, epoxy group, allyl group and propargyl group; The polythiol monomer is selected from one or more of 1,6-hexanedithiol, trimethylolpropane tris(3-mercaptopropionic acid) ester, pentaerythritol tetra-3-mercaptopropionic acid ester, and hexa(3-mercaptopropionic acid) dipentaerythritol ester.

4. The preparation method according to claim 1, characterized in that, The molar ratio of the polythiol monomer to other monomers is 1:(1.1-2).

5. The preparation method according to claim 1, characterized in that, The liquid medium is selected from ethanol; The liquid medium contains polyvinylpyrrolidone; the content of polyvinylpyrrolidone in each 100 mL of liquid medium is 1-5 g; In step A), the reaction is carried out in the presence of a catalyst; the catalyst is one or more of triethylamine, tributylamine, 1,8-diazabicycloundec-7-ene, 1,5,7-trizabicyclodec-5-ene, and N,N'-dimethylformamide.

6. The preparation method according to claim 1, characterized in that, The reaction time is 10 min to 2 h.

7. The preparation method according to claim 1, characterized in that, The metallic elements in the electroless plating solution include one or more of the following: gold, silver, platinum, palladium, copper, iron, nickel, titanium, zinc, tin, aluminum, lead, cobalt, indium, cadmium, chromium, germanium, antimony, and bismuth.

8. The preparation method according to claim 1, characterized in that, Step B) includes: The microspheres containing thiol groups on their surface are placed in a chemical plating solution and stirred to react, thereby depositing a metal layer on the surface of the microspheres containing thiol groups to obtain polymer / metal composite microspheres. The electroless plating solution comprises 0.1~1 mol / L of metal salt, 0.01~1 mol / L of complexing agent, and 0.1~2 mol / L of reducing agent; The metal salt can be any one or a combination of several metal sulfates, metal nitrates, and metal chlorides; The complexing agent is any one or a combination of several of the following: EDTA, citric acid, citrate, sodium acetate, ammonium chloride, succinic acid, succinate, triethanolamine, ethylenediamine, and lactic acid. The reducing agent is one or a combination of several of hypophosphite, borohydride, dimethylamine borate and hydrazine; The metal layer is deposited using a chemical deposition method, the chemical deposition temperature is room temperature, and the chemical deposition time is 0.5-5 hours; the thickness of the metal layer is 50 nm to 150 nm.

9. The preparation method according to claim 1, characterized in that, Before performing electroless plating, the process further includes sensitizing and activating the surface-containing thiol microspheres sequentially. The sensitization process includes dispersing the surface-containing thiol microspheres in water and then adding an aqueous solution of stannous chloride for sensitization. The activation process includes: adding sensitized microspheres containing thiol groups to a dilute palladium chloride hydrochloric acid solution for activation, thereby obtaining activated microspheres.

10. A polymer / metal composite microsphere prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The CV value of the polymer / metal composite microspheres is ≤2%.

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