Method for producing polyphenylene oxide

Abstract

The present invention provides a method for producing polyphenylene oxide with excellent processability in good yield under mild oxidative coupling reaction conditions, without the need for a separate separation and purification process for ortho-cresol produced after the alkylation reaction of phenol, thereby reducing energy costs.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0087374 dated July 2, 2021, and Korean Patent Application No. 10-2021-0087375 dated the same date, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a method for producing polyphenylene oxide. [Background technology]

[0003] Polyphenylene oxide (PPO) is a type of engineering plastic that exhibits excellent chemical and heat resistance, as well as excellent mechanical and electrical properties. Commercially available PPO products typically have a number-average molecular weight of 20,000 to 60,000 g / mol and are synthesized by oxidative coupling using phenolic monomers. Commercially available PPO products consist of oligomers with a number-average molecular weight of 1,300 to 2,700 g / mol and polymers with a number-average molecular weight of 17,000 to 29,000 g / mol.

[0004] Meanwhile, 2,6-xylenol, one of the phenolic monomers used in PPO production, is obtained by alkylating phenol. This process produces by-products, o-cresol and 2,4,6-trimethylphenol, in addition to 2,6-xylenol. Therefore, a separation and purification process for these by-products is necessary. However, because the boiling point difference between these by-products and 2,6-xylenol is approximately 10°C, this separation and purification process is difficult and expensive. In particular, to separate the main by-product, o-cresol, a 140-plate column or azeotropic distillation with decane is used. This is a major factor in increasing the costs of producing 2,6-xylenol and PPO using it.

[0005] Therefore, there is a need to develop a method for producing PPO that can reduce energy costs. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention provides a method for producing polyphenylene oxide, which does not require a separate separation and purification process for ortho-cresol produced after the alkylation reaction of phenol, thereby reducing energy costs, and which can produce polyphenylene oxide in excellent yield under mild oxidative coupling reaction conditions. [Means for solving the problem]

[0007] The present disclosure provides a method for producing polyphenylene oxide, comprising: a first step of alkylating phenol with methanol to produce a mixture containing 2,6-xylenol and ortho-cresol; a second step of subjecting the mixture to an oxidative coupling reaction in the presence of a copper-based catalyst and an amine-based additive; and a third step of separating ortho-cresol from the reaction product obtained in the second step to obtain polyphenylene oxide having repeating units represented by the following chemical formula 1, wherein the mixture contains 0.2 to 0.8 moles of ortho-cresol per mole of 2,6-xylenol, and the amine-based additive includes a secondary amine, a pyridine-based compound, or a mixture thereof:

[0008] [ka]

[0009] In the above Chemical Formula 1, n is an integer of 1 or more.

[0010] In the present invention, terms such as first and second are used to describe various components, and the terms are used only to distinguish one component from another.

[0011] Furthermore, the terms used in this specification are merely used to describe exemplary embodiments and are not intended to limit the present invention.

[0012] The singular expression includes the plural expression unless the context clearly indicates otherwise.

[0013] In this specification, the terms "comprises," "comprises," or "having" are intended to describe embodied features, numbers, steps, components, or combinations thereof, and do not exclude the possibility of one or more other features, numbers, steps, components, combinations, or additions thereof.

[0014] Although the present invention can be embodied in various forms and with various modifications, specific embodiments are described in detail below by way of example, but it should be understood that the present invention is not limited to the specific disclosed embodiments, and that the present invention encompasses all modifications, equivalents, and alternatives falling within the spirit and technical scope of the present invention.

[0015] The present invention will be described in detail below.

[0016] The method for producing polyphenylene oxide according to the present invention comprises the steps of: The first step involves alkylating phenol with methanol to produce a mixture containing 2,6-xylenol and ortho-cresol; a second step of subjecting the mixture to an oxidative coupling reaction in the presence of a copper catalyst and an amine additive; and a third step of separating ortho-cresol from the reaction product obtained as a result of the second step to obtain polyphenylene oxide having repeating units represented by the following chemical formula 1; The mixture contains 1 mole of 2,6-xylenol and 0.2 to 0.8 moles of ortho-cresol; The amine-based additive includes a secondary amine, a pyridine-based compound, or a mixture thereof:

[0017] [ka]

[0018] In the above Chemical Formula 1, n is an integer of 1 or more.

[0019] The present inventors have confirmed that, in producing polyphenylene oxide by the oxidative coupling reaction of 2,6-xylenol, 2,6-xylenol produced by the alkylation reaction of phenol is used in a state where it is mixed with ortho-cresol produced by a side reaction, and the content ratio of ortho-cresol to 2,6-xylenol is controlled by adjusting the alkylation reaction conditions. Furthermore, by using an amine-based additive capable of acting as a ligand for an oxidative coupling reaction catalyst together with the catalyst, polyphenylene oxide with excellent processability can be produced in an excellent yield.

[0020] In addition, ortho-cresol generally has a small difference in boiling point from 2,6-xylenol, which makes separation and purification difficult and expensive. In contrast, the present invention can omit the separation and purification process of ortho-cresol from 2,6-xylenol, and after producing polyphenylene oxide through the oxidative coupling reaction, the ortho-cresol remaining in the reaction system can be separated and removed by utilizing the difference in boiling point, thereby significantly reducing energy costs.

[0021] Furthermore, in the present invention, the oxidative coupling reaction is carried out under milder conditions than in the past, thereby improving process stability.

[0022] On the other hand, in the present invention, the above steps, that is, steps 1 to 3, can proceed as a series of continuous reactions.

[0023] Each stage will be explained in detail below.

[0024] Phase 1 In the method for producing polyphenylene oxide according to the present invention, the first step is to produce a mixture containing 2,6-xylenol and ortho-cresol by alkylation reaction with phenol.

[0025] In the production method according to the present invention, the mixture contains ortho-cresol in a molar ratio of 0.2 to 0.8 per mole of 2,6-xylenol.

[0026] Typically, the reaction product obtained as a result of the alkylation reaction contains 2,6-xylenol and ortho-cresol in an amount of 95 wt% or more, based on the total weight of the reaction product, and 2,4,6-trimethylphenol in an amount of 5 wt% or less. Furthermore, in the 95 wt% or more mixture of 2,6-xylenol and ortho-cresol, 2,6-xylenol is present in an amount of 60 wt% or more and ortho-cresol is present in an amount of 40 wt% or less. More specifically, 2,6-xylenol is present in an amount of 75-80 wt% and ortho-cresol is present in an amount of 20-25 wt%. Therefore, in conventional polyphenylene oxide manufacturing methods, in order to prevent or minimize the effects of ortho-cresol, a process of separating and removing ortho-cresol from the reaction product obtained after the alkylation reaction is essential, and 2,6-xylenol from which ortho-cresol has been separated and removed is used.

[0027] However, the present inventors have confirmed that, within an optimal content range, ortho-cresol improves the dielectric constant of the solvent and the solubility of the catalyst during the oxidative coupling reaction for producing polyphenylene oxide, and have therefore controlled the content of ortho-cresol in the mixture used in producing polyphenylene oxide.

[0028] Therefore, in the method for producing polyphenylene oxide according to the present invention, a separate process for separating and removing ortho-cresol produced together with 2,6-xylenol after the alkylation reaction is not performed. As a result, the content of ortho-cresol in the mixture used in the subsequent oxidative coupling reaction step is higher in the present invention than in the case where it is contained as a by-product of 2,6-xylenol in the conventional method, as described above.

[0029] Specifically, the mixture contains 0.2 to 0.8 moles of ortho-cresol per mole of 2,6-xylenol. The ortho-cresol improves the dielectric constant of the solvent used in the oxidative coupling reaction and the solubility of the catalyst, thereby improving the PPO yield. If the ortho-cresol content is less than 0.2 moles, the effect of improving the dielectric constant of the solvent and the solubility of the catalyst is minimal, resulting in a reduced PPO yield and a deterioration in the physical properties of the PPO produced, particularly the molecular weight distribution characteristics. Furthermore, if the amount of ortho-cresol used exceeds a molar ratio of 0.8, the excessively high content may cause ortho-cresol to coordinate with the catalyst, reducing catalytic activity. Furthermore, ortho-cresol may copolymerize with the PPO produced, reducing the physical properties of the PPO. When taking into consideration the effect of improving processability by controlling the glass transition temperature (Tg), number average molecular weight (Mn), and molecular weight distribution (PDI) of the final PPO, the mixture may more specifically contain 0.2 mol or more, or 0.3 mol or more, or 0.35 mol or more, or 0.4 mol or more, or 0.45 mol or more, or 0.48 mol or more and 0.8 mol or less, or 0.75 mol or less, or 0.6 mol or less, or 0.55 mol or less, or 0.5 mol or less of ortho-cresol per 1 mol of 2,6-xylenol.

[0030] Therefore, in the process of the present invention, the alkylation reaction in the first step can be performed by appropriately adjusting the reaction conditions, such as the reactants and their amounts, catalyst, reaction temperature, etc., so as to satisfy the content ratio of ortho-cresol in the final mixture obtained.

[0031] Specifically, in the alkylation reaction, methanol can be used in a ratio of 2 to 8 moles per mole of phenol. If the ratio of methanol to phenol is too low, the amount of ortho-cresol produced will increase significantly. Conversely, if the ratio of methanol to phenol is too high, the 2,6-xylenol content will increase, but there is a risk of side reactions due to unreacted methanol. Therefore, it is preferable to appropriately adjust the amount of methanol added within the above range, taking into account the content ratio of 2,6-xylenol to ortho-cresol in the mixture containing 2,6-xylenol and ortho-cresol obtained as a result of the alkylation reaction. More specifically, to achieve the above molar ratio conditions, the methanol can be used in a ratio of 2 moles or more, or 3 moles or more and 8 moles or less, or 5 moles or less, per mole of phenol.

[0032] The alkylation reaction is carried out in the presence of an alkylation catalyst such as a zirconium-tungsten catalyst, a magnesium oxide catalyst, an iron-vanadium oxide catalyst, a manganese oxide catalyst, a cobalt-ferrite catalyst, an alumina catalyst, or a Y-zeolite catalyst.

[0033] The alkylation catalyst can be used in the form of a supported catalyst supported on a carrier such as silica.

[0034] More specifically, in the present invention, a zirconium-tungsten catalyst that exhibits excellent catalytic activity during the alkylation reaction can be used, and the catalyst may be a supported catalyst supported on silica.

[0035] During the alkylation reaction, water is optionally added, and in this case, it is added in a ratio of 3 moles or less, more specifically 1 to 3 moles, per mole of phenol.

[0036] The alkylation reaction is carried out at a temperature of 250°C to 500°C, more specifically, 250°C or higher, or 300°C or higher and 500°C or lower, or 450°C or lower.

[0037] Furthermore, the alkylation reaction is carried out under a pressure condition of 1 atm to 3 atm, more specifically 1 atm or more, or 1.2 atm or more and 3 atm or less, or 1.5 atm or less.

[0038] The alkylation reaction is carried out in an inert gas atmosphere such as nitrogen or argon, and may be carried out in a reducing atmosphere such as hydrogen depending on the catalyst used.

[0039] As a result of this alkylation reaction, ortho-cresol is produced as a by-product along with 2,6-xylenol, and the produced ortho-cresol satisfies the content ratio requirement described above. If necessary, 2,6-xylenol or ortho-cresol may be added to further adjust the content ratio of ortho-cresol to 2,6-xylenol within the above content ratio range. In this case, the production method according to the present invention may optionally further include a step of adding 2,6-xylenol or ortho-cresol to the mixture obtained after the alkylation reaction so that the ortho-cresol content requirement is satisfied.

[0040] Furthermore, as a result of the alkylation reaction, isomers such as 2,4,6-trimethylphenol may be further produced as by-products. Therefore, the mixture of the present invention may contain 2,6-xylenol and ortho-cresol so as to satisfy the above content ratio range conditions, and may additionally contain 2,4,6-trimethylphenol. When 2,4,6-trimethylphenol is further contained, the mixture may contain 2,4,6-trimethylphenol in an amount greater than 0 wt %, or 0.0001 wt % or more and less than 2 wt %, or 1 wt % or less, or 0.1 wt % or less, or 0.01 wt % or less, based on the total weight of the mixture.

[0041] Phase 2 The second step is a step of subjecting the mixture prepared in the first step to an oxidative coupling reaction.

[0042] Specifically, the oxidative coupling reaction is carried out in the presence of a copper-based catalyst and an amine-based additive.

[0043] Examples of the copper-based catalyst include copper (I) compounds such as cuprous oxide, copper (I) halide, copper (I) sulfate, and copper (I) nitrate; copper (II) compounds such as cupric oxide, copper (II) halide, copper (II) sulfate, and copper (II) nitrate; and salts thereof, and a mixture of any one or more of these can be used.

[0044] The copper catalyst can be used in a ratio of 0.001 to 0.1 moles per mole of 2,6-xylenol. When used within this range, sufficient catalytic activity is achieved, improving the yield of polyphenylene oxide and preventing color formation due to the catalyst. If the amount of copper catalyst used is less than 0.001 moles, the yield of polyphenylene oxide is low. If the amount exceeds 0.1 moles, a large amount of acid treatment is required for subsequent catalyst removal, and if the catalyst remains, color formation may occur. To enhance the above effects, the copper catalyst can be used in an amount of 0.001 moles or more, or 0.003 moles or more, or 0.005 moles or more, or 0.0075 moles or more, or 0.008 moles or more, or 0.01 moles or more and 0.1 moles or less, or 0.05 moles or less, or 0.03 moles or less, per mole of 2,6-xylenol.

[0045] Meanwhile, the amine additive acts as a ligand for the copper catalyst.

[0046] The amine-based additive specifically includes a secondary amine, a pyridine-based compound, or a mixture thereof.

[0047] Specifically, the secondary amine has C 1-20 It has two aliphatic alkyl groups. More specifically, C 1-20The amine has two linear or branched alkyl groups. This structure facilitates coordination with copper-based catalysts, resulting in increased catalytic reactivity. This significantly increases the yield of polyphenylene oxide compared to the use of primary amines, tertiary amines, diamines containing two amino groups in the molecule, or secondary amines containing a cycloalkyl group or an aromatic ring structure. Specific examples of the secondary amine include dimethylamine, diethylamine, di-n-propylamine, di-i-propylamine, di-n-butylamine (or dibutylamine), di-i-butylamine, di-t-butylamine, dipentylamine, dihexylamine, dioctylamine, didecylamine, methylethylamine, methylpropylamine, and methylbutylamine. Mixtures of any one or more of these can be used.

[0048] Specific examples of the pyridine compound include aminopyridine compounds such as 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 4-dimethylaminopyridine, 2,3-diaminopyridine, 2,5-diaminopyridine, 2,6-diaminopyridine, 2-amino-6-methylpyridine, 3-amino-6-isopropylpyridine, and 4-pyrrolidinopyridine; monoalkylpyridine compounds such as 2-methylpyridine, 3-methylpyridine, and 4-methylpyridine; and dialkylpyridine compounds such as 2,3-dimethylpyridine (or 2,3-lutidine), 2,4-dimethylpyridine, 2,5-dimethylpyridine, 2,6-dimethylpyridine, 3,4-dimethylpyridine, and 3,5-dimethylpyridine. One or a mixture of two or more of these compounds can be used. Furthermore, the alkyl group can be C 1-20 Alkyl, or C 1-10 Alkyl, or C 1-4 It may also be alkyl.

[0049] The amine-based additive can be appropriately selected and used depending on the type of copper-based catalyst. When the copper-based catalyst and the amine-based additive are used in an optimal combination, the yield of polyphenylene oxide can be further increased, and the physical properties of the produced polyphenylene oxide can also be further improved.

[0050] Specifically, when a copper (I) compound, specifically, copper (I) oxide, copper (I) halide, copper (I) sulfate, copper (I) nitrate, or a salt thereof, is used as the copper-based catalyst and a pyridine-based compound is used as the amine-based additive, the yield of polyphenylene oxide is increased and the processability of the produced polyphenylene oxide is improved. More specifically, the copper (I) compound may be a copper (I) halide compound, such as copper (I) chloride or copper (I) bromide, and even more specifically, copper (I) chloride. Furthermore, the pyridine-based compound may be an aminopyridine-based compound, such as 2-aminopyridine, 3-aminopyridine, or 4-aminopyridine. Due to their structural characteristics that facilitate coordination with the catalyst, the aminopyridine-based compounds can exhibit superior effects of improving the yield and processability of polyphenylene oxide.

[0051] When a copper-based catalyst is a copper (II) compound, specifically, copper (II) oxide, copper (II) halide, copper (II) sulfate, copper (II) nitrate, or a salt thereof, and a secondary amine is used as the amine additive, the yield of polyphenylene oxide increases and the processability of the produced polyphenylene oxide improves. More specifically, the copper (II) compound may be a copper (II) halide compound such as copper (II) chloride or copper (II) bromide, and even more specifically, copper (II) chloride. In addition, the secondary amine may be C 1-8 , or C 2-6The secondary amine may be one having two chain alkyl groups, more specifically, di-n-butylamine, diethylamine, di-n-hexylamine, or di-n-propylamine. The secondary amine not only easily coordinates with the catalyst, but also allows the coordinated complex to exhibit high reactivity, thereby further improving the yield of polyphenylene oxide and achieving the effects of increasing the molecular weight and improving the thermal properties of the produced polyphenylene oxide.

[0052] The amine additive can be used in a ratio of 0.1 to 1 mole per mole of 2,6-xylenol. When used in a manner that satisfies this content ratio requirement, polyphenylene oxide can be produced in excellent yield without the risk of side reactions caused by excessive amine additive. More specifically, the amine additive can be used in an amount of 0.1 moles or more, or 0.2 moles or more, or 0.3 moles or more, or 0.34 moles or more, or 0.4 moles or more, and 1 mole or less, or 0.8 moles or less, or 0.7 moles or less, or 0.68 moles or less, or 0.5 moles or less, per mole of 2,6-xylenol.

[0053] In addition, in the production method according to the present invention, the oxidative coupling reaction is carried out under oxygen or air conditions. In particular, since the oxidative coupling reaction can be carried out under air conditions, the production process can be carried out under milder reaction conditions than the conventional oxidative coupling reaction carried out under oxygen input conditions. More specifically, the oxidative coupling reaction is carried out by inputting air at a rate of 80 to 350 cc / min by air bubbling.

[0054] The oxygen content in the air is specifically 30% or less, more specifically 21% or less, and may be 10% or more. Oxygen in air acts to promote the oxidative coupling reaction. However, when the oxidative coupling reaction is carried out under oxygen-injection conditions as in the past, problems such as reduced yield and explosion have been encountered. In contrast, the present invention improves process safety and yield by carrying out the oxidative coupling reaction under air conditions with a low oxygen content as described above.

[0055] Additionally, the air is introduced at a rate of 80 to 350 cc / min, as described above. If the introduction rate is too slow, the air in the reaction system is not uniformly mixed, resulting in a decrease in the yield of polyphenylene oxide and limited chain extension, which can degrade the physical properties. Furthermore, if the introduction rate is too fast, the oxygen concentration in the solvent increases, which can lead to copolymerization of ortho-cresol or a coupling reaction of 2,6-xylenol, resulting in the generation of by-products. In the present invention, introducing air within this rate range can further enhance the effect of improving the yield and physical properties of polyphenylene oxide. More specifically, the air is introduced by air bubbling at a rate of 80 cc / min or more, or 90 cc / min or more, or 100 cc / min or more, and 350 cc / min or less, or 330 cc / min or less, or 300 cc / min or less.

[0056] The air is introduced by air bubbling under conditions that satisfy the above-mentioned introduction rate so that the air can be uniformly mixed in the reaction system.

[0057] The oxidative coupling reaction is carried out in an aromatic solvent such as benzene, toluene, or xylene, which exhibits high solubility for the catalyst and polyphenylene oxide and is therefore advantageous for the production of polyphenylene oxide.

[0058] Phase 3 The third step is to separate ortho-cresol from the reaction product obtained in the second step to obtain polyphenylene oxide.

[0059] Here, the order of the ortho-cresol separation and polyphenylene oxide preparation processes is not particularly limited. Specifically, the ortho-cresol separation process may be performed after polyphenylene oxide is obtained, or the ortho-cresol separation process may be performed after polyphenylene oxide is obtained. Alternatively, polyphenylene oxide may be obtained through the ortho-cresol separation process.

[0060] For example, when an ortho-cresol separation process is performed after the polyphenylene oxide is obtained, alcohol is added to the reaction product obtained as a result of the oxidative coupling reaction to precipitate polyphenylene oxide, which is then filtered and dried. The filtrate obtained as a result of the filtration is then fractionally distilled at a temperature in the range of 180 to 220°C or 190 to 200°C to separate ortho-cresol.

[0061] The alcohol to be added for the precipitation of polyphenylene oxide may be, for example, a lower alcohol having 1 to 3 carbon atoms, such as methanol, ethanol, isopropyl alcohol, etc. Among these, the addition of methanol allows the precipitation of polyphenylene oxide in a superior yield and is also advantageous in terms of subsequent removal by fractional distillation.

[0062] The amount of alcohol to be added is not particularly limited, and is added so that the precipitation reaction with polyphenylene oxide occurs sufficiently.

[0063] In addition, when adding the alcohol, an acid such as hydrochloric acid may be optionally added to promote the precipitation reaction of polyphenylene oxide and thereby improve the yield. In this case, the acid is added in an amount of 0.01 to 0.5 parts by weight, more specifically 0.1 to 0.3 parts by weight, per 100 parts by weight of the alcohol.

[0064] If polyphenylene oxide precipitates upon addition of the alcohol, it can be separated by filtration and dried to obtain the polyphenylene oxide.

[0065] The filtration and drying processes can be carried out by a conventional method. For example, the filtration is carried out using a filter, and the drying is carried out by a heat drying method using an oven or the like. Preferably, the drying is carried out under vacuum or an inert gas atmosphere.

[0066] The precipitation, filtration and drying steps for obtaining the polyphenylene oxide are repeated two or more times.

[0067] After obtaining polyphenylene oxide through the precipitation, filtration and drying, the filtrate obtained from the filtration process can be subjected to a fractional distillation process at a temperature range of 180 to 220°C or 190 to 210°C to separate ortho-cresol.

[0068] The fractional distillation step for separating ortho-cresol is carried out by a conventional method, except that it is carried out under the above temperature conditions.

[0069] In addition to ortho-cresol, the filtrate also contains isomers such as 2,4,6-trimethylphenol formed as a side reaction during the oxidative coupling reaction, aromatic hydrocarbon solvents such as toluene used in the oxidative coupling reaction, and alcohols added during the precipitation reaction of polyphenylene oxide. These compounds can also be separated and removed by fractional distillation. For example, when heated within the above temperature range, the alcohols, which have low boiling points, are first removed by evaporation at a temperature range of 50 to 80°C or 60 to 80°C. Next, aromatic hydrocarbon solvents such as toluene are removed by evaporation at a temperature range of 100 to 150°C or 110 to 130°C. Subsequently, ortho-cresol is removed by evaporation at a temperature range of 180 to 220°C or 190 to 210°C.

[0070] As another example, when a process for obtaining polyphenylene oxide is carried out after separating ortho-cresol from the reaction product obtained as a result of the second step, the reaction product obtained as a result of the second step is fractionally distilled at a temperature range of 180 to 220°C or 190 to 210°C to separate ortho-cresol, and then alcohol is added to the resulting reaction product to precipitate polyphenylene oxide, which can be obtained by filtering and drying.

[0071] Polyphenylene oxide is produced as a result of the oxidative coupling reaction in the second stage, but ortho-cresol is present in the reaction system as a mixture introduced during the oxidative coupling reaction. Because the boiling point of ortho-cresol is significantly different from the boiling point (or decomposition temperature) of polyphenylene oxide, the present invention allows ortho-cresol to be separated and removed by fractional distillation. Specifically, since the boiling point of ortho-cresol is 191°C and the decomposition temperature of polyphenylene oxide is above 400°C, ortho-cresol can be separated by fractional distillation in the temperature range of 180 to 220°C or 190 to 200°C.

[0072] The fractional distillation step for separating ortho-cresol is carried out by a conventional method, except that it is carried out under the above temperature conditions.

[0073] In addition to ortho-cresol, the reaction product obtained in the second step may contain other isomers such as 2,4,6-trimethylphenol. These isomers also have a large difference in boiling point from polyphenylene oxide, so they can be simultaneously separated in the fractional distillation step, resulting in polyphenylene oxide with even higher purity.

[0074] After separating the ortho-cresol, the resulting reaction mixture is charged with alcohol to precipitate polyphenylene oxide, which is then filtered and separated.

[0075] In this case, the precipitation, filtration, and separation processes of polyphenylene oxide can be performed in the same manner as described above, except that if the resulting reaction product is obtained in a solid state, the reaction product can be dissolved in a solvent and then an alcohol can be added to carry out the precipitation reaction of polyphenylene oxide.

[0076] Meanwhile, the ortho-cresol separated by the fractional distillation can be reused as an intermediate in the alkylation reaction for producing 2,6-xylenol. Therefore, the method of the present invention may further include a step of introducing the separated ortho-cresol into the alkylation reaction after separating the ortho-cresol.

[0077] The above-described production method enables the production of PPO under mild oxidative coupling reaction conditions in an excellent yield, specifically, a high yield of 70% by weight or more, 80% by weight or more, 90% by weight or more, 95% by weight or more, or 99% by weight or more.

[0078] Here, the yield can be calculated from the amount of 2,6-xylenol added during the production of PPO and the amount of PPO finally produced using the following Equation 1:

[0079] [Formula 1] Yield (wt%) = [weight of PPO produced / weight of 2,6-xylenol added] × 100

[0080] The PPO produced by the above production method is a linear homopolymer consisting only of repeating units represented by the following chemical formula 1:

[0081] [ka]

[0082] In the above Chemical Formula 1, n is an integer of 1 or more, and more specifically, may be 10-100.

[0083] When polyphenylene oxide is produced by conventional production methods, an ortho-cresol-derived structure, which is contained as a by-product in 2,6-xylenol, is contained as a repeating unit of the polymer. However, the production method of the present invention can produce the homopolymer with high selectivity to 2,6-xylenol, even though it contains a high content of ortho-cresol as a reactant.

[0084] As a result, the PPO produced by the above-mentioned production method has the following properties: 1 During H NMR analysis, the ortho-cresol peak in the range of 6.8 to 7.4 ppm does not appear.

[0085] Regarding the PPO 1 1 H NMR analysis is carried out by the method and conditions described in the following experimental examples.

[0086] The PPO produced by the above production method is an oligomeric PPO having a number-average molecular weight of 1,600 to 3,500 g / mol. In addition, the PPO has a molecular weight distribution (PDI, Mw / Mn) of 1.7 to 3 and a glass transition temperature (Tg) of 140 to 180°C, which allows it to exhibit excellent processability.

[0087] Specifically, the PPO has a number-average molecular weight of 1,600 g / mol or more and 3,500 g / mol or less, or 3,000 g / mol or less, and a higher Mn than oligomeric PPOs produced by conventional production methods, which allows compounds using the PPO to exhibit excellent processability during production. More specifically, the number average molecular weight of the PPO is 1,600 g / mol or more, 1,750 g / mol or more, or 1,900 g / mol or more, or 2,000 g / mol or more, or 2,100 g / mol or more, or 2,200 g / mol or more, or 2,300 g / mol or more, or 2,400 g / mol or more, and 3,500 g / mol or less, or 3,300 g / mol or less, or 3,200 g / mol or less, or 3,000 g / mol or less, or 2,800 g / mol or less, or 2,700 g / mol or less.

[0088] The PPO also has a molecular weight distribution (PDI, Mw / Mn) of 1.7 to 3, which is broader than that of oligomeric PPOs produced by conventional production methods, resulting in excellent processability. More specifically, the molecular weight distribution of the PPO is 1.7 or more, or 1.8 or more, or 1.9 or more, or 2.0 or more, or 2.1 or more, 2.2 or more, or 2.3 or more, or 2.45 or more, and 3 or less, or 2.8 or less, or 2.7 or less, or 2.5 or less.

[0089] The PPO has a glass transition temperature of 140 to 180°C. A high glass transition temperature increases the processing temperature and reduces processability, while a low glass transition temperature reduces thermal stability. The PPO of the present invention has a glass transition temperature within the above range, allowing it to exhibit excellent processability without reducing thermal stability. More specifically, the PPO has a glass transition temperature of 140°C or higher, or 145°C or higher, or 148°C or higher, or 150°C or higher, or 152°C or higher, or 155°C or higher, or 156°C or higher, and 180°C or lower, or 175°C or lower, or 170°C or lower, or 169°C or lower, or 165°C or lower, or 162°C or lower, or 160°C or lower, or 159°C or lower.

[0090] The number-average molecular weight and molecular weight distribution (PDI, Mw / Mn) of the PPO can be measured by gel permeation chromatography, and the glass transition temperature can be measured by a differential scanning calorimeter. Specific measurement methods and conditions are described in detail in the following experimental examples.

[0091] Furthermore, the oligomeric PPO produced by the above-described method can be further subjected to an oxidative coupling reaction in the presence of a copper catalyst and an amine-based additive to produce a high molecular weight PPO (or polymeric PPO), specifically a high molecular weight PPO having a number average molecular weight of 4,000 g / mol or more. Therefore, the method according to the present invention may further include a step of subjecting the polyphenylene oxide obtained after separating the ortho-cresol, specifically the oligomeric PPO, to a secondary oxidative coupling reaction in the presence of a copper catalyst and an amine-based additive.

[0092] The copper catalyst, amine additive, and oxidative coupling reaction conditions that can be used in producing the high molecular weight PPO are as described above.

[0093] However, the copper-based catalyst can be used in a ratio of 0.001 to 0.1 moles per mole of oligomeric PPO; more specifically, the copper-based catalyst can be used in an amount of 0.001 moles or more, or 0.003 moles or more, or 0.005 moles or more and 0.1 moles or less, or 0.05 moles or less, or 0.01 moles or less, per mole of oligomeric PPO.

[0094] The amine additive can be used in a ratio of 0.1 to 1 mole per mole of the oligomeric PPO. More specifically, the amine additive can be used in an amount of 0.1 mole or more, or 0.3 moles or more, or 0.5 moles or more and 1 mole or less, or 0.8 moles or less, or 0.7 moles or less, or 0.68 moles or less, per mole of the oligomeric PPO.

[0095] Specifically, the high-molecular-weight PPO produced in the production process has a number-average molecular weight of 4,000 g / mol or more, or 5,000 g / mol or more, or 8,000 g / mol or more, or 10,000 g / mol or more, or 12,000 g / mol or more, and 20,000 g / mol or less, or 18,000 g / mol or less, or 16,500 g / mol or less, or 16,200 g / mol or less, or 15,000 g / mol or less.

[0096] Furthermore, the high-molecular-weight PPO has a number-average molecular weight and a molecular weight distribution (PDI, Mw / Mn) of 2 to 3, more specifically 2 or more, or 2.1 or more, or 2.2 or more and 3 or less, or 2.8 or less, or 2.6 or less, or 2.5 or less, and thus has a broader molecular weight distribution than conventional PPOs, thereby exhibiting excellent processability.

[0097] Meanwhile, the number average molecular weight and molecular weight distribution of the polymeric PPO can be measured by gel permeation chromatography, and the specific measurement method and conditions will be described in detail in the following experimental examples. [Effects of the Invention]

[0098] According to the production method of the present invention, a separate separation and purification process for ortho-cresol produced after the alkylation of phenol is not required, thereby reducing energy costs, and PPO can be produced in excellent yields under mild oxidative coupling reaction conditions. Furthermore, the produced PPO exhibits excellent processability. [Brief explanation of the drawings]

[0099] [Figure 1] 1 is a graph showing 1H NMR analysis of polyphenylene oxide prepared in Example 1-1. DETAILED DESCRIPTION OF THE INVENTION

[0100] The functions and effects of the present invention will be described in more detail below through specific examples of the present invention, but these examples are presented only as examples of the present invention and do not define the scope of the invention.

[0101] Example 1-1 10 g of fumed silica was added to 50 ml of methanol, followed by the addition of 1 g of ZrO2. Aqueous ammonia was added to the resulting mixture to adjust the pH to 9 or higher. The mixture was then stirred at room temperature (25 ± 3°C) for 3 hours, filtered to remove all solvent, and then dried in an oven at 110°C. The resulting dried product was mixed with a solution prepared by dissolving 1.4 g of WO3 in 20 mL of water, and reacted at room temperature (25 ± 3°C) for 2 hours. The resulting reactant was filtered to remove all solvent, and then calcined at 750°C to produce a zirconium-tungsten alkylation catalyst in which zirconium and tungsten were supported on a silica support.

[0102] 10 g of the alkylation catalyst was loaded into a cylindrical reactor, and the temperature inside the reactor was raised to 400°C while a mixed gas (containing 97% argon by volume and 3% hydrogen by volume) was introduced to activate the alkylation catalyst. After activation was complete, a mixture of phenol, methanol, and water (phenol:methanol:water molar ratio = 1:5:1) was introduced together with the mixed gas at a rate of 10 mL / h, and the reaction was continued until the phenol conversion rate reached 98%. As a result, a mixture containing 2,6-xylenol and ortho-cresol was obtained.

[0103] Approximately 1.43 g of the obtained mixture (containing 2,6-xylenol (1 g, 8.2 mmol) and ortho-cresol (0.43 g, 4 mmol, corresponding to a molar ratio of 0.49 based on 1 mole of 2,6-xylenol)) was placed in a glass bottle equipped with a magnetic bar, and 10 ml of toluene was added thereto and dissolved with stirring.

[0104] The resulting solution was added with catalyst CuCl at a molar ratio of 0.0075 based on 1 mole of 2,6-xylenol and stirred at 25°C for 5 minutes, and then 2.8 mmol of di-n-butylamine (corresponding to a molar ratio of 0.34 based on 1 mole of 2,6-xylenol) was added and the polymerization reaction was carried out by air bubbling, which was carried out at a rate of 100 cc / min using a flow controller.

[0105] After the reaction was completed, the resulting reactant was slowly poured into a flask containing 100 ml of HCl / MeOH solution (HCl content: 0.1 wt%) to precipitate the synthesized polymer, i.e., polyphenylene oxide. The precipitated polymer was separated by filtration and dried in a vacuum oven. The dried polymer was dissolved in dichloromethane and then precipitated using methanol, a process repeated twice to obtain polyphenylene oxide.

[0106] The solution remaining after the separation of the polyphenylene oxide contained methanol, toluene, and ortho-cresol. The solution was heated to 190-220°C, and the methanol, toluene, and ortho-cresol were separated by fractional distillation in this order at temperatures around 65°C, 110°C, and 190°C. The ortho-cresol separated by fractional distillation was subsequently reused as an intermediate in the alkylation reaction of 2,6-xylenol.

[0107] Examples 1-2 to 1-10 Polyphenylene oxide was prepared in the same manner as in Example 1-1, except that the amounts of reactants and polymerization conditions were changed as shown in Table 1 below.

[0108] Examples 1-11 10 g of fumed silica was added to 50 ml of methanol, followed by the addition of 1 g of ZrO2. Aqueous ammonia was added to the resulting mixture to adjust the pH to 9 or higher. The mixture was then stirred at room temperature (25 ± 3°C) for 3 hours, filtered to remove all solvent, and then dried in an oven at 110°C. The resulting dried product was mixed with a solution prepared by dissolving 1.4 g of WO3 in 20 mL of water, and reacted at room temperature (25 ± 3°C) for 2 hours. The resulting reactant was filtered to remove all solvent, and then calcined at 750°C to produce a zirconium-tungsten alkylation catalyst in which zirconium and tungsten were supported on a silica support.

[0109] 10 g of the alkylation catalyst was loaded into a cylindrical reactor, and the temperature inside the reactor was raised to 400°C while a mixed gas (containing 97% argon by volume and 3% hydrogen by volume) was introduced to activate the alkylation catalyst. After activation was complete, a mixture of phenol, methanol, and water (phenol:methanol:water molar ratio = 1:5:1) was introduced together with the mixed gas at a rate of 10 mL / h, and the reaction was continued until the phenol conversion rate reached 98%. As a result, a mixture containing 2,6-xylenol and ortho-cresol was obtained.

[0110] Approximately 1.43 g of the obtained mixture (containing 2,6-xylenol (1 g, 8.2 mmol) and ortho-cresol (0.43 g, 4 mmol, corresponding to a molar ratio of 0.49 based on 1 mole of 2,6-xylenol)) was placed in a glass bottle equipped with a magnetic bar, and 10 ml of toluene was added thereto and dissolved with stirring.

[0111] The resulting solution was added with catalyst CuCl at a molar ratio of 0.01 based on 1 mole of the 2,6-xylenol and stirred at 25°C for 5 minutes, and then 2.8 mmol of 3-aminopyridine (corresponding to a molar ratio of 0.34 based on 1 mole of the 2,6-xylenol) was added and the polymerization reaction was carried out by air bubbling, which was carried out at a rate of 100 cc / min using a flow controller.

[0112] After the reaction was completed, the resulting reactant was slowly poured into a flask containing 100 ml of HCl / MeOH solution (HCl content: 0.1 wt%) to precipitate the synthesized polymer, i.e., polyphenylene oxide. The precipitated polymer was separated by filtration and dried in a vacuum oven. The dried polymer was dissolved in dichloromethane and then precipitated using methanol, a process repeated twice to obtain polyphenylene oxide.

[0113] The solution remaining after the separation of the polyphenylene oxide contained methanol, toluene, and ortho-cresol. The solution was heated to 190-220°C, and the methanol, toluene, and ortho-cresol were separated by fractional distillation in this order at temperatures around 65°C, 110°C, and 190°C. The ortho-cresol separated by fractional distillation was subsequently reused as an intermediate in the alkylation reaction of 2,6-xylenol.

[0114] Examples 1-12 to 1-19 Polyphenylene oxide was prepared in the same manner as in Examples 1-11, except that the amounts of reactants and polymerization conditions were changed as shown in Table 2 below.

[0115] On the other hand, in Examples 1-17 and 1-18, the contents of ortho-cresol in the mixtures correspond to molar ratios of 0.61 and 0.73, respectively, based on 1 mole of 2,6-xylenol.

[0116] Comparative Example 1-1 Polyphenylene oxide was prepared in the same manner as in Example 1-1, except that the alkylation reaction step was omitted and 2,6-xylene (1 g, 8.2 mmol) was used instead of the mixture containing 2,6-xylenol and ortho-cresol.

[0117] Comparative Example 1-2 Polyphenylene oxide was prepared in the same manner as in Example 1-1, except that the amounts of reactants and polymerization conditions were changed as shown in Table 1 below.

[0118] Comparative Examples 1-3 The same procedure as in Example 1-1 was carried out, except that the alkylation reaction step was omitted and ortho-cresol (9.2 mmol) was used instead of the mixture containing 2,6-xylenol and ortho-cresol. However, polyphenylene oxide could not be produced due to lack of reactivity.

[0119] Comparative Examples 1-4 and 1-5 Polyphenylene oxide was prepared in the same manner as in Example 1-1, except that the amounts of reactants and polymerization conditions were changed as shown in Table 1 below.

[0120] Comparative Examples 1-6 Polyphenylene oxide was prepared in the same manner as in Examples 1-11, except that the amounts of reactants and polymerization conditions were changed as shown in Table 2 below.

[0121] Comparative Examples 1-7 Polyphenylene oxide was prepared in the same manner as in Examples 1-11, except that the alkylation reaction step was omitted and 2,6-xylene (1 g, 8.2 mmol) was used instead of the mixture containing 2,6-xylenol and ortho-cresol.

[0122] Comparative Examples 1-8 and 1-9 Polyphenylene oxide was prepared in the same manner as in Examples 1-11, except that the amounts of reactants and polymerization conditions were changed as shown in Table 2 below.

[0123] [Table 1]

[0124] [Table 2]

[0125] Experimental Example 1 The polyphenylene oxide (PPO) obtained in Example 1-1 was subjected to NMR analysis.

[0126] Specifically, the PPO produced in Example 1-1 was dissolved in CDCl3, and then analyzed using a 500 MHz NMR spectrometer manufactured by Varian. 1 H NMR analysis was performed, and the results are shown in Figure 1.

[0127] According to reported literature, when ortho-cresol is copolymerized into a polymer, 1 In the H NMR spectrum, an ortho-cresol peak is observed in the range of 6.8 to 7.4 ppm, but as shown in Figure 1, no ortho-cresol peak was observed in the PPO of Example 1-1 produced by the production method of the present invention.

[0128] This shows that the PPO produced by the production method of the present invention is a homopolymer consisting only of repeating units derived from 2,6-xylenol.

[0129] Experimental Example 2 The yield, glass transition temperature, number average molecular weight, and molecular weight distribution of the PPO obtained in the above examples and comparative examples were measured by the following methods, and the results are shown in Tables 3 and 4 below.

[0130] (1) Yield (%) The yield was calculated from the amount of 2,6-xylenol added during the production of PPO in the Examples and Comparative Examples and the amount of PPO finally produced, using the following Equation 1.

[0131] [Formula 1] Yield (wt%) = [weight of PPO produced / weight of 2,6-xylenol added] × 100

[0132] (2) Glass transition temperature (Tg) The glass transition temperature was measured using a differential scanning calorimeter (DSC) under the following conditions: Measurement equipment: DSC250 (TA Instruments) Measurement temperature: 0~300℃ Heating rate: 10℃ / min Measurement environment: N2

[0133] (3) Number average molecular weight (Mn) and molecular weight distribution (PDI) The polymers produced in the examples and comparative examples were dissolved in chloroform and then analyzed by gel permeation chromatography (GPC) under the following conditions. The number average molecular weight (Mn) and molecular weight distribution (PDI) of PPO were calculated from the results.

[0134] The GPC system used was a Waters PL-GPC220 instrument, with a Polymer Laboratories PLgel MIX-B 300 mm column. The measurement temperature was 40°C, chloroform was used as the solvent, and the flow rate was 1.0 mL / min. Polymer samples from the examples and comparative examples were pretreated using a GPC analyzer (PL-GP220) by dissolving them in chloroform containing 0.0125% BHT at 160°C for 10 hours to a concentration of 1 mg / mL, and then added in 100 μL. The weight-average molecular weight (Mw) and number-average molecular weight (Mn) values ​​were derived using a calibration curve generated using polystyrene standard specimens, and the molecular weight distribution (PDI, Mw / Mn) was calculated by dividing the weight-average molecular weight by the number-average molecular weight. At this time, nine types of weight average molecular weights (Mw) of polystyrene standard test pieces were used: 2000 g / mol, 10000 g / mol, 30000 g / mol, 70000 g / mol, 200000 g / mol, 700000 g / mol, 2000000 g / mol, 4000000 g / mol, and 10000000 g / mol.

[0135] <Measurement conditions> Column: PLgel Mixed-B x 2 Solvent: Chloroform (stabilized with BHT) Flow rate: 1.0ml / min Sample concentration: 1 mg / ml Injection volume: 100μl Column temperature: 40℃ Detector: Waters RI detector Data processing: Empower

[0136] [Table 3]

[0137] [Table 4]

[0138] Experimental results confirmed that the combined use of a copper catalyst and the amine additive of the present invention significantly increased the PPO yield compared to conventional methods, and that the PPO produced had optimal Tg, Mn, and PDI, demonstrating excellent processability. Furthermore, it was confirmed that the production method of the present invention enables the polymerization of oligomeric PPO even under mild conditions with air injection.

[0139] Specifically, from the experimental results of Examples 1-1 to 1-4, it was confirmed that when PPO is produced by the production method according to the present invention, the yield increases as the amount of catalyst increases within a certain range, and the Tg and molecular weight or PDI of PPO increase as the amount of amine-based additive increases.

[0140] In addition, it was confirmed that the use of an aminopyridine compound as an amine additive enabled the production of PPO with a higher molecular weight, a broad molecular weight distribution, and an optimal Tg range, resulting in excellent processability, in a significantly increased yield. However, in the case of Example 1-15, in which an alkylpyridine compound was used, the yield was slightly lower than that of Example 1-11, in which an aminopyridine compound was used, due to the bulky properties of the alkylpyridine compound.

[0141] Furthermore, from the results of Examples 1-11 and 1-16, it was confirmed that when cuprous bromide was used instead of cuprous chloride as the copper-based catalyst, there was no significant difference in reactivity, but the molecular weight distribution of the produced PPO increased.

[0142] Furthermore, from the results of Examples 1-1, 1-7, and 1-8, it was confirmed that due to the excellent solubility characteristics of the catalyst, the Tg, molecular weight, and molecular weight distribution of the PPO produced increase as the ortho-cresol content increases up to a certain level under the same conditions. However, once the ortho-cresol content exceeds a certain level, specifically a molar ratio of 0.6 per mole of 2,6-xylene, the Tg, molecular weight, and molecular weight distribution of the PPO produced decrease relatively.

[0143] On the other hand, in Comparative Example 1-1, in which only 2,6-xylene was used without ortho-cresol, despite an increased catalyst input, the PPO yield was lower than in Examples 1-2, 1-5, and 1-6, in which 2,6-xylene and ortho-cresol were mixed at the optimal ratio under the same conditions. Furthermore, the Tg and Mn of the PPO produced increased excessively, and the PDI decreased, resulting in poor processability. Furthermore, in Comparative Example 1-7, PPO polymerization did not proceed as smoothly as in Example 1-14. These results are due to the fact that ortho-cresol improves the dielectric constant of the solvent and catalyst solubility during the oxidative coupling reaction, but the omission of ortho-cresol in Comparative Examples 1-1 and 1-7 reduced catalyst solubility.

[0144] In addition, in Comparative Example 1-2, in which a mixture containing 2,6-xylene and an equal amount of ortho-cresol was used, the PPO yield was significantly reduced, and in Comparative Example 1-3, in which only ortho-cresol was used without 2,6-xylene, PPO could not be produced due to lack of reactivity.

[0145] Furthermore, it was confirmed that in Comparative Example 1-4, in which triethylamine was used as the amine additive, and Comparative Example 1-6, in which n-butylamine was used, the PPO yield was significantly reduced compared to Examples 1-2, 1-8, and 1-14, and the PPO produced had a lower Tg and reduced Mn and PDI.

[0146] Example 2-1 The oligomeric polyphenylene oxide (PPO) prepared in Example 1-1 was placed in a glass bottle equipped with a magnetic bar, and 10 ml of toluene was added thereto and dissolved under stirring.

[0147] The resulting solution was added with catalyst CuCl in a molar ratio of 0.005 based on 1 molar of the oligomeric PPO and stirred at 25°C for 5 minutes. Next, di-n-butylamine as an amine additive was added in a molar ratio of 0.68 based on 1 molar of the oligomeric PPO, and the polymerization reaction was carried out by air bubbling. Air bubbling was carried out at a rate of 300 cc / min using a flow controller.

[0148] After the reaction was complete, the resulting reactant was slowly poured into a flask containing 100 ml of HCl / MeOH solution (HCl content: 0.1 wt%) to precipitate the synthesized polymer. The precipitated polymer was separated by filtration and dried in a vacuum oven. The dried polymer was dissolved in dichloromethane and then precipitated using methanol. This process was repeated twice to obtain high molecular weight polyphenylene oxide.

[0149] Examples 2-2 and 2-3 Polyphenylene oxide was prepared in the same manner as in Example 2-1, except that the amounts of reactants and polymerization conditions were changed as shown in Table 5 below.

[0150] Examples 2-4 The oligomeric PPO prepared in Example 1-11 was placed in a glass bottle equipped with a magnetic bar, and 10 ml of toluene was added thereto and dissolved under stirring.

[0151] The resulting solution was added with catalyst CuCl in a molar ratio of 0.005 based on 1 mole of the oligomeric PPO and stirred at 25°C for 5 minutes. Next, di-n-butylamine as an amine additive was added in a molar ratio of 0.28 based on 1 mole of the oligomeric PPO, and the polymerization reaction was carried out by air bubbling. Air bubbling was carried out at a rate of 300 cc / min using a flow controller.

[0152] After the reaction was complete, the resulting reactant was slowly poured into a flask containing 100 ml of HCl / MeOH solution (HCl content: 0.1 wt%) to precipitate the synthesized polymer. The precipitated polymer was separated by filtration and dried in a vacuum oven. The dried polymer was dissolved in dichloromethane and then precipitated using methanol. This process was repeated twice to obtain high molecular weight polyphenylene oxide.

[0153] Examples 2-5 Polyphenylene oxide was prepared in the same manner as in Example 2-4, except that the amounts of reactants and polymerization conditions were changed as shown in Table 5 below.

[0154] Experimental Example 3 The high molecular weight polyphenylene oxides prepared in Examples 2-1 to 2-5 were subjected to GPC analysis to measure the number average molecular weight (Mn) and molecular weight distribution (PDI, Mw / Mn) in the same manner as in Experimental Example 2. The results are shown in Table 5 below.

[0155] [Table 5]

[0156] As a result of experiments, it was confirmed that high molecular weight PPO can be produced by subjecting the oligomeric PPO produced by the production method of the present invention to an oxidative coupling reaction again using a catalyst.

Claims

1. A first step in which phenol is alkylated with methanol to produce a mixture containing 2,6-xylenol and ortho-cresol; a second step of subjecting the mixture to an oxidative coupling reaction in the presence of a copper catalyst and an amine additive; and A third step of separating ortho-cresol from the reaction product obtained as a result of the second step to obtain polyphenylene oxide having a repeating unit represented by the following chemical formula 1: In the alkylation reaction, methanol is used in a ratio of 2 to 8 moles per mole of phenol, and water is introduced in a ratio of 1 to 3 moles per mole of phenol. the mixture comprises a molar ratio of 0.3 to 0.75 ortho-cresol per mole of 2,6-xylenol; The amine additive comprises a secondary amine, a pyridine compound, or a mixture thereof; The number average molecular weight is 1,600 to 3,500 g / mol, the molecular weight distribution is 1.7 to 3, the glass transition temperature is 140 to 180° C., and it is an oligomer type. Method for producing polyphenylene oxide: 【Chemistry 1】 In the above formula 1, n is an integer of 1 or more.

2. The process of claim 1 , wherein the steps are carried out in a series of consecutive reactions.

3. 2. The method according to claim 1, wherein the copper-based catalyst is at least one selected from the group consisting of cuprous oxide, cuprous halide, cuprous sulfate, cuprous nitrate, cupric oxide, cupric halide, cupric sulfate, cupric nitrate, and salts thereof.

4. The method according to claim 1, wherein the copper-based catalyst is used in a ratio of 0.001 to 0.1 moles per mole of 2,6-xylenol.

5. The secondary amine has a C １－２０ The method according to claim 1, wherein the aliphatic alkyl group has two groups.

6. 2. The method according to claim 1, wherein the secondary amine is dimethylamine, diethylamine, di-n-propylamine, di-i-propylamine, di-n-butylamine, di-i-butylamine, di-t-butylamine, dipentylamine, dihexylamine, dioctylamine, didecylamine, methylethylamine, methylpropylamine, or methylbutylamine.

7. The method according to claim 1 , wherein the pyridine compound is an aminopyridine compound, a monoalkylpyridine compound, or a dialkylpyridine compound.

8. The method according to claim 1, wherein the pyridine-based compound is 2-aminopyridine, 3-aminopyridine, 4-aminopyridine, 4-dimethylaminopyridine, 2,3-diaminopyridine, 2,5-diaminopyridine, 2,6-diaminopyridine, 2-amino-6-methylpyridine, 3-amino-6-isopropylpyridine, 4-pyrrolidinopyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 2,3-dimethylpyridine, 2,4-dimethylpyridine, 2,5-dimethylpyridine, 2,6-dimethylpyridine, 3,4-dimethylpyridine, or 3,5-dimethylpyridine.

9. The method according to claim 1, wherein the amine additive is used in a ratio of 0.1 to 1 mole based on 1 mole of 2,6-xylenol.

10. The copper catalyst is at least one selected from the group consisting of cuprous oxide, cuprous halide, cuprous sulfate, cuprous nitrate, and salts thereof, and the amine additive is a pyridine compound; or 3. The production method according to claim 1, wherein the copper-based catalyst is one or more selected from the group consisting of cupric oxide, cupric halide, cupric sulfate, cupric nitrate, and salts thereof, and the amine-based additive is a secondary amine.

11. 3. The method according to claim 1, wherein the oxidative coupling reaction is carried out by introducing air at a rate of 80 to 350 cc / min by air bubbling.

12. The process of claim 1 or 2, wherein the ortho-cresol is separated by fractional distillation.

13. 2. The method of claim 1, further comprising the step of subjecting the polyphenylene oxide obtained in the third step to a secondary oxidative coupling reaction in the presence of a copper-based catalyst and an amine-based additive.

14. 2. The method of claim 1, further comprising, after separation of ortho-cresol in the third step, subjecting the separated ortho-cresol to the alkylation reaction in the first step.

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