A low molecular weight polyphenylene ether and preparation method thereof

Abstract

The invention discloses a low molecular weight polyphenylene ether and a preparation method thereof, and the preparation method of the low molecular weight polyphenylene ether comprises: 1) preparing materials: respectively configuring an oxidant, a catalyst, and a substrate solution; 2) premixing of materials: adding the substrate solution dropwise to a mixed solution of an oxidant and a catalyst; 3) isothermal reaction: isothermal stirring polymerization reaction; 4) washing and purification: washing the product after centrifugation in a graded manner. Compared with the prior art, the preparation method of the low molecular weight polyphenylene ether provided by the invention can obtain a low molecular weight polyphenylene ether with less copper content or no copper, so as to improve the processing performance and dielectric properties of the polyphenylene ether; at the same time, the content of the byproduct diphenylquinone generated during the reaction is very small, which improves the selectivity of the reaction, simplifies the separation and purification steps compared with the purification steps of repeated dissolution-reprecipitation in the traditional synthesis method, saves resources, and protects the environment.

Description

Technical Field

[0001] The invention relates to the technical field of polymer synthesis, in particular to a low molecular weight polyphenylene ether and a preparation method thereof. Background Art

[0002] Polyphenylene ether is one of the important engineering plastics. Due to its good thermal stability, flame retardancy, dimensional stability and low hygroscopicity, it is widely used in electrical or electronic equipment, automotive parts, commercial machines and high-frequency printed circuit boards. Generally, the number average molecular weight of synthesized polyphenylene ether is greater than 20,000, its glass transition temperature is about 210°C, the melt viscosity is high, and the mobile phase is poor. When this high molecular weight polyphenylene ether material is used in high-frequency printed circuit boards and composite materials, it has the characteristics of poor processing performance, high melt viscosity and low reactivity. Therefore, it is necessary to improve the above properties of polyphenylene ether.

[0003] Low molecular weight polyphenylene ether is a good choice to solve the above problems while maintaining excellent performance. At present, the methods for producing low molecular weight polyphenylene ether include redistribution method and direct polymerization method. For example, Chinese patent CN101389691 adopts the redistribution method, and free radical initiator, phenolic substance and polyphenylene ether with a number average molecular weight of more than 10,000 are added to the solvent for reaction to obtain low molecular weight polyphenylene ether with a number average molecular weight of less than 4,000. However, the redistribution method also has some defects, such as the molecular weight of the obtained product shows double dispersion, it is easy to introduce free radical initiator into the polymer chain, and toluene, an organic solvent with high toxicity, is mostly used, which is harmful to the environment. In addition, the direct polymerization method can effectively solve some problems. For example, Chinese patent CN1334836A adopts solution polymerization in aromatic solvents such as benzene and toluene to prepare low molecular weight polyphenylene ether resin, but this method has the defects of high content of diphenylquinone by-product, and needs to use a large amount of anti-solvent for repeated precipitation and washing and pressure explosion-proof device. Therefore, it is necessary to develop a more efficient and economical method for preparing low molecular weight polyphenylene ether by direct polymerization.

[0004] Persulfate is a strong oxidant with a high redox potential and has been used to prepare polyaniline, polybenzole and polypyrrole. Generally, persulfate can be homogeneously activated by alkali, heat, divalent copper and other metal ions to produce active oxidizing substances and carry out subsequent oxidation reactions. Studies have shown that persulfate can be activated by copper and cobalt metal oxides such as copper oxide and cobalt tetraoxide in alkaline solutions, and then various phenolic substances are polymerized into low molecular weight polyphenol substances through a dehydrogenation mechanism. This makes it possible to prepare polyphenylene ether using persulfate as an oxidant under the catalysis of copper ions.

[0005] Generally, copper catalysts are indispensable in the preparation process of polyphenylene ether. However, when used as an insulating material, the high residual copper content in polyphenylene ether often has an adverse effect on its dielectric properties. And in the production process, the use of heavy metal catalysts means that strong acids need to be added for treatment in the subsequent washing steps, which has a bad impact on the equipment and the environment. Therefore, in the preparation process of polyphenylene ether, the use of solvents that are conducive to the dissolution of copper ions to reduce the amount of copper residue in polyphenylene ether, or the use of heavy metal-free catalysts in the preparation of polyphenylene ether is very beneficial to the improvement of the performance of polyphenylene ether and the environment. Persulfate can be activated by metal-free carbon materials, such as nanocarbon, reduced graphene oxide and carbon nitride, which means that the activation of persulfate with a non-metallic catalyst to synthesize polyphenylene ether is a suitable alternative method.

[0006] In view of this, it is necessary to develop an efficient and convenient method for preparing high-purity low molecular weight polyphenylene ether using persulfate as an oxidant under metal or non-metal catalytic conditions. Summary of the invention

[0007] The purpose of the present invention is to provide a method for obtaining low molecular weight polyphenylene ether by oxidizing and polymerizing monomer 2,6-dimethylphenol with persulfate as an oxidant in view of the deficiencies in the prior art, wherein the low molecular weight polyphenylene ether with less copper content or no copper is obtained under the catalysis of metal or non-metal, so as to improve the processing performance and dielectric properties of the polyphenylene ether; at the same time, the content of the by-product diphenoquinone generated during the reaction is very small, so that the washing and purification steps are simplified compared with the purification steps of repeated dissolution-reprecipitation in the traditional synthesis method, thereby saving resources and protecting the environment.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] According to a first aspect of the present invention, the present invention provides a method for preparing a low molecular weight polyphenylene ether, comprising the following steps:

[0010] S1. Preparation: placing a metal catalyst or a non-metal catalyst in water and adjusting the pH value to a preset value to obtain a homogeneous catalyst solution; preparing a persulfate aqueous solution with the same pH value to obtain a homogeneous oxidant solution; dissolving 2,6-dimethylphenol in an organic solvent and stirring to dissolve to obtain a uniform substrate solution;

[0011] S2, premixing: pouring the catalyst solution into the reactor containing the oxidant solution to obtain a mixed solution, then adding the substrate solution dropwise into the mixed solution, and adjusting the reactor to a predetermined first stirring speed for stirring, and slowly heating up to premix the reaction materials;

[0012] S3, constant temperature reaction: adjusting the reactor to a predetermined second stirring speed, and performing a constant temperature stirring reaction;

[0013] S4, washing and purification: After the reaction is completed, the precipitate is obtained by centrifugation, and the precipitate is graded and washed to obtain the low molecular weight polyphenylene ether.

[0014] Preferably, in step S1, the pH values ​​of the oxidant solution and the catalyst solution are both 10-13, in order to make the substrate in a deprotonated state within this range and promote the reaction. More preferably, the pH value is 11-12.

[0015] Preferably, in step S1, the metal catalyst is a complex of a divalent copper salt and an amine, and the molar ratio of the divalent copper salt to the amine is 1:1 to 1:50; more preferably, the molar ratio of the divalent copper salt to the amine is 1:10; wherein the divalent copper salt is at least one of copper chloride, copper sulfate, copper carbonate, and copper nitrate, and more preferably, the divalent copper salt is copper chloride; the amine is at least one of a primary amine, a secondary amine, a tertiary amine, a monoamine, and a diamine; the amine includes but is not limited to methylamine, ethylamine, diethylamine, triethylamine, propylamine, butylamine, dibutylamine, dimethyl-n-butylamine, pyridine, 2,2'-bipyridine, imidazole, and N-methylimidazole. More preferably, the amine is ethylenediamine.

[0016] Preferably, in step S1, the molar ratio of the metal salt to 2,6-dimethylphenol is 1:100 to 1:10. More preferably, the molar ratio of the metal salt to 2,6-dimethylphenol is 1:50 to 1:20.

[0017] Preferably, in step S1, the non-metal catalyst is a nitrogen-containing heterocyclic compound and / or an amine substance, the nitrogen-containing heterocyclic compound includes at least one of porphyrin and phthalocyanine, and the amine substance includes at least one of aromatic amine and aliphatic amine. More preferably, the non-metal catalyst includes but is not limited to porphyrin hydrochloride, phthalocyanine, imidazole, N-methylimidazole, pyridine, 2,2'-bipyridine, 4-aminopyridine, methylamine, ethylamine, diethylamine, triethylamine, propylamine, butylamine, and dibutylamine.

[0018] Preferably, the reaction is carried out in water / organic solvent. Under the catalytic conditions of the metal, a suitable organic solvent is selected and water is added to dissolve most of the metal ions. The organic solvents used include but are not limited to acetonitrile, methanol, dioxane, acetone, and tetrahydrofuran. These organic solvents are less toxic than the organic solvents used in traditional methods such as toluene, benzene, and nitrobenzene, and have better solubility for divalent copper salts and persulfates. More preferably, the organic solvent is acetonitrile or methanol. Wherein, the volume ratio of water to organic solvent in the reaction is 1:20 to 2:3.

[0019] Preferably, the persulfate used in the reaction includes but is not limited to sodium persulfate, potassium persulfate, and ammonium persulfate. More preferably, the persulfate is ammonium persulfate. Wherein, the molar ratio of the persulfate to 2,6-dimethylphenol is 1:2 to 2:1. More preferably, the molar ratio of the persulfate to 2,6-dimethylphenol is 1:1.

[0020] Preferably, in step S2, the first stirring speed is 300 r / min to 500 r / min, and the temperature is set to 25° C. to 40° C.; the mixing between the materials is accelerated, and the temperature and concentration at each position in the reactor are uniform.

[0021] Preferably, in step S2, a peristaltic pump is used to add the substrate solution dropwise, and the dropping speed is set to 10 mL / min to 20 mL / min; the purpose is to make the catalyst and the oxidant in excess relative to 2,6-dimethylphenol, so as to avoid excessive 2,6-dimethylphenol, which will directly react to form diphenoquinone after being oxidized. More preferably, the dropping speed is set to 10 mL / min to 15 mL / min.

[0022] Preferably, in step S3, the second stirring speed is 500r / min to 1000r / min, the temperature is set to 40°C to 75°C, and the reaction time is 30min to 4h. The reaction involved in the present invention is precipitation polymerization. As the reaction proceeds, precipitation continues to precipitate. High-speed stirring promotes the mixing of solid and liquid phases and the uniformity of temperature and concentration, which can eliminate mass transfer and heat transfer resistance to a certain extent; and high temperature can increase the solubility of each substance in the solvent, so that the reaction can proceed fully. More preferably, the reaction time is 30min to 2h.

[0023] Preferably, in step S4, the washing and purification process includes a primary water wash, a secondary water wash and a tertiary solvent wash;

[0024] The first-stage water washing uses an acidic solution with a pH value of 3 to 6 to wash away a small amount of metal ions encapsulated in the polyphenylene ether obtained under the catalysis of the metal;

[0025] The secondary water washing uses an alkaline aqueous solution with a pH value of 10 to 12 to wash away unreacted persulfate and small molecular weight benzoquinone; a small amount of the crude product after the secondary water washing is taken and dried in a vacuum oven at 80°C overnight to obtain off-white particles, and the content of the by-product diphenoquinone is measured by ultraviolet spectrophotometry.

[0026] The organic solvents used in the third-stage solvent washing include, but are not limited to, acetonitrile, methanol, ethanol, and propanol to wash away the byproduct diphenoquinone in the crude product. The washed product is dried in a vacuum oven at 80° C. overnight to obtain white polyphenylene ether for subsequent performance testing.

[0027] According to the second aspect of the present invention, the present invention further provides a low molecular weight polyphenylene ether, which is prepared by the above-mentioned preparation method of the low molecular weight polyphenylene ether.

[0028] Compared with the prior art, the method for preparing low molecular weight polyphenylene ether provided by the present invention has at least the following beneficial effects:

[0029] (1) The method provided by the present invention uses persulfate as an oxidant, which is cheaper, easier to store and transport, and has lower requirements on equipment than oxygen or hydrogen peroxide used in traditional polymerization to prepare polyphenylene ether; and the persulfate oxidation efficiency is high, and a high yield can be achieved in a very short reaction time, and a low molecular weight polyphenylene ether with a number average molecular weight in the range of 4000 to 6000 is obtained. The polyphenylene ether obtained by the reaction lowers the glass transition temperature (159°C to 167°C) (wherein the high molecular weight polyphenylene ether: 215°C) while maintaining the good thermal stability (427°C to 439°C) of the high molecular weight polyphenylene ether, so that the processing performance is improved.

[0030] (2) The persulfate-metal / non-metal catalytic oxidation system used in the present invention has high selectivity for the oxidative polymerization of 2,6-dimethylphenol, and the yield of the by-product diphenoquinone obtained in the reaction is very low. The yield of the crude product diphenoquinone after secondary water washing can be as low as 0.015%.

[0031] (3) The present invention uses a non-metallic catalyst in the preparation process of polyphenylene ether, so that the product polyphenylene ether does not contain metal copper ions, thereby improving the dielectric properties of the product and avoiding the harm of heavy metal emissions to the environment. The metal catalyst divalent copper salt used in the reaction can be well dissolved in the water / organic solvent in the reaction and can be removed by simple water washing. Compared with the monovalent copper salt used in the traditional polymerization method, which requires additional acid washing, it avoids corrosion to the equipment and also reduces the copper content in the product, thereby improving the dielectric properties of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the thermogravimetric analysis diagram obtained in Example 1 of the present invention.

[0033] Figure 2 This is the differential scanning calorimetry analysis diagram obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0034] In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] A method for preparing low molecular weight polyphenylene ether using persulfate as an oxidant under metal catalysis conditions comprises the following steps:

[0037] (1) Preparation: Weigh 13.6 mg of anhydrous cupric chloride and dissolve it in a mixture of 5 mL of water and 10 mL of ethylenediamine, stir to completely dissolve the copper salt, and adjust the pH to 10 with a 1 M sodium hydroxide solution to obtain a catalyst solution; weigh 1.14 g of ammonium persulfate and dissolve it in 5 mL of water, shake to dissolve, and adjust the pH to 10 with a 1 M sodium hydroxide solution to obtain an oxidant solution; weigh 0.611 g of 2,6-dimethylphenol and dissolve it in 80 mL of methanol.

[0038] (2) Premixing: Add the catalyst solution and oxidant solution into a constant temperature water bath reactor, and use a peristaltic pump to add the substrate solution into the reactor at a rate of 10 mL / min, while stirring at 30°C, and set the stirring rate to 300 r / min.

[0039] (3) Constant temperature reaction: After the dropwise addition is completed, the stirring rate is set to 500 r / min and the reaction temperature is set to 50° C. to carry out the polymerization reaction.

[0040] (4) Washing and purification: After the reaction is completed, the reactant is centrifuged to obtain a precipitate, which is washed with a hydrochloric acid solution having a pH value of 4 and washed with a sodium hydroxide aqueous solution having a pH value of 10. A small amount of the product after the secondary washing is placed in a vacuum oven at 80° C. and dried overnight to obtain an off-white crude polyphenylene ether product for determination of the diphenoquinone content. The remaining product is washed with methanol for a third solvent, and the obtained product is placed in a vacuum oven at 80° C. and dried overnight to obtain white polyphenylene ether particles, which are subjected to thermogravimetric and differential thermal analysis. The results are as follows: Figure 1 , 2 shown.

[0041] The diphenoquinone content was measured by ultraviolet spectrophotometry. 1.2 mg of the crude product was weighed and dissolved in 10 mL of toluene, and the absorbance of the solution at 421 nm was measured. The diphenoquinone concentration in the solution was calculated by Lambert-Beer law, and the diphenoquinone content in the crude product was calculated accordingly.

[0042] Example 2

[0043] A method for preparing low molecular weight polyphenylene ether using persulfate as an oxidant under non-metallic catalytic conditions comprises the following steps:

[0044] (1) Preparation: Weigh 0.94 g of imidazole and dissolve it in 5 mL of water, adjust the pH to 11 with a 1 M sodium hydroxide solution to obtain a catalyst solution; weigh 1.14 g of ammonium persulfate and dissolve it in 5 mL of water, shake to dissolve, and adjust the pH to 11 with a 1 M sodium hydroxide solution to obtain an oxidant solution; weigh 0.611 g of 2,6-dimethylphenol and dissolve it in 80 mL of acetonitrile.

[0045] (2) Premixing: Add the catalyst solution and oxidant solution into a constant temperature water bath reactor, and use a peristaltic pump to add the substrate solution into the reactor at a rate of 20 mL / min, while stirring at 30°C, and set the stirring rate to 500 r / min.

[0046] (3) Constant temperature reaction: After the dropwise addition is completed, the stirring rate is set to 1000 r / min and the reaction temperature is set to 70° C. to carry out the polymerization reaction.

[0047] (4) Washing and purification: After the reaction is completed, the reactant is centrifuged to obtain a precipitate, which is washed with a hydrochloric acid solution with a pH value of 6 and washed with a sodium hydroxide aqueous solution with a pH value of 12. A small amount of the product after the secondary washing is placed in a vacuum oven at 80°C and dried overnight to obtain an off-white crude polyphenylene ether product for determination of the diphenoquinone content. The remaining product is washed with a tertiary solvent of methanol, and the obtained product is placed in a vacuum oven at 80°C and dried overnight to obtain white polyphenylene ether particles.

[0048] The diphenoquinone content was measured by ultraviolet spectrophotometry. 1.2 mg of the crude product was weighed and dissolved in 10 mL of toluene, and the absorbance of the solution at 421 nm was measured. The diphenoquinone concentration in the solution was calculated by Lambert-Beer law, and the diphenoquinone content in the crude product was calculated accordingly.

[0049] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also change and modify the above embodiment. Therefore, the present invention is not limited to the above specific embodiment, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention belongs to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing a low molecular weight polyphenylene ether, characterized in that: The following steps are involved: S1. Preparation of materials: placing a metal catalyst or a non-metal catalyst in water and adjusting the pH value to a preset value to obtain a homogeneous catalyst solution; preparing a persulfate aqueous solution with the same pH value to obtain a homogeneous oxidant solution; dissolving 2,6-dimethylphenol in an organic solvent and stirring to dissolve to obtain a uniform substrate solution; wherein the pH values ​​of the oxidant solution and the catalyst solution are both 10 to 13; the metal catalyst is a complex of a divalent copper salt and an amine, and the molar ratio of the divalent copper salt to the amine is The ratio of water to organic solvent used in the reaction is 1:1 to 1:50; the divalent copper salt is at least one of copper chloride, copper sulfate, copper carbonate and copper nitrate; the amine is selected from methylamine, ethylamine, diethylamine, triethylamine, propylamine, butylamine, dibutylamine, dimethyl-n-butylamine, pyridine, 2,2'-bipyridine, imidazole and N-methylimidazole; the non-metallic catalyst is imidazole; the volume ratio of water to organic solvent used in the reaction is 1:20 to 2:3; the molar ratio of persulfate to 2,6-dimethylphenol is 1:2 to 2:1; S2, premixing: pouring the catalyst solution into the reactor containing the oxidant solution to obtain a mixed solution, then adding the substrate solution dropwise into the mixed solution, and adjusting the reactor to a predetermined first stirring speed for stirring, and slowly heating up to premix the reaction materials; S3, constant temperature reaction: adjusting the reactor to a predetermined second stirring speed, and performing a constant temperature stirring reaction; S4, washing and purification: after the reaction is completed, centrifuge to obtain a precipitate, which is graded and washed to obtain the low molecular weight polyphenylene ether; the washing and purification process includes primary water washing, secondary water washing and tertiary solvent washing; the primary water washing uses an acidic solution with a pH value of 3 to 6 to wash away a small amount of metal ions coated in the polyphenylene ether obtained under the catalysis of the metal; the secondary water washing uses an alkaline aqueous solution with a pH value of 10 to 12 to wash away unreacted persulfate and small molecular benzoquinone; the tertiary solvent washing uses an organic solvent including at least one of acetonitrile, methanol, ethanol and propanol to wash away the by-product diphenylquinone in the crude product.

2. The method for preparing a low molecular weight polyphenylene ether according to claim 1, characterized in that: In step S2, the first stirring speed is 300 r / min to 500 r / min, and the temperature is set to 25°C to 40°C.

3. The method for preparing a low molecular weight polyphenylene ether according to claim 1, characterized in that: In step S2, the substrate solution is added dropwise using a peristaltic pump, and the dropping speed is set to 10 mL / min to 20 mL / min.

4. The method for preparing a low molecular weight polyphenylene ether according to claim 1, characterized in that: In step S3, the second stirring speed is 500 r / min to 1000 r / min, the temperature is set to 40° C. to 75° C., and the reaction time is 30 min to 4 h.

5. A low molecular weight polyphenylene ether, characterized in that: The low molecular weight polyphenylene ether is prepared by the preparation method of any one of claims 1 to 4.

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