Polyoxymethylene manufacturing method

Abstract

To provide a method for simply at high yield, producing polyoxymethylene low in content of low molecular weight component.SOLUTION: Disclosed is a method for producing polyoxymethylene by polymerizing at least one monomer selected from the group consisting of trioxane, cyclic ether and cyclic formal. The method includes a polymerization process of obtaining polyoxymethylene by mixing a monomer with a catalyst solution to polymerize. The catalyst solution includes tin tetrachloride and aliphatic hydrocarbon solvent. The catalyst solution is added so that in the polymerization process, the molar number of tin tetrachloride is in a range of 5.0×10-6 to 1.0×10-4 based on total molar number of the monomer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing polyoxymethylene. [Background technology]

[0002] Polyoxymethylene has an excellent balance of mechanical properties, chemical resistance, sliding properties, etc., and is easy to process, so it is widely used as a representative engineering plastic, mainly in electrical parts, electronic parts, automotive parts, and various other mechanical parts. In recent years, as the range of its use expands, there has been a trend toward increasingly high mechanical properties being required.

[0003] Polyoxymethylene can be obtained by cationic polymerization of formaldehyde or cyclic ethers such as 1,3,5-trioxane, or by anionic polymerization of formaldehyde.

[0004] Thermally stable polyoxymethylene can be synthesized by cationic polymerization of a monomer that forms formaldehyde units (preferably 1,3,5-trioxane) with a small amount of comonomer, thereby incorporating a small amount of oxyalkylene units substantially randomly into the chain. Brønsted or Lewis acids are used as initiators.

[0005] Polymers obtained by such methods solidify in the early stages of polymerization, resulting in a wide molecular weight distribution. Typically, a maximum in the molecular weight distribution curve exists in a relatively low molecular weight region (e.g., 2,000 to 5,000 daltons), and another maximum in the molecular weight distribution curve exists in a relatively high molecular weight region (e.g., 50,000 to 200,000 daltons). The content of these low molecular weight components affects the mechanical properties of the polymer (Patent Document 1). It is known that cationic polymerization of a monomer that forms a [—CH—O—] unit in the presence of an initiator can produce polyoxymethylene with a low content of low molecular weight components and excellent mechanical strength (Patent Document 1). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2020 / 054730 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the production method described in Patent Document 1 is complicated, as it requires a cooling step during polymerization because the monomer is used in a solid state, and a heating step to remove residual monomer.

[0008] The present invention has been made in view of the above circumstances, and discloses a method for simply producing polyoxymethylene with a high yield and a low content of low-molecular-weight components by using tin tetrachloride as a polymerization catalyst and a mixture of tin tetrachloride and a specific solvent for polymerization. [Means for solving the problem]

[0009] The present inventors have conducted extensive studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by using tin tetrachloride as a polymerization catalyst in the polymerization of at least one monomer selected from the group consisting of 1,3,5-trioxane (hereinafter sometimes simply referred to as trioxane), a cyclic ether, and a cyclic formal, and by using a catalyst solution that is a mixed liquid containing a specific aliphatic hydrocarbon solvent in the polymerization, and by using the catalyst solution at a concentration within a specific range, thereby completing the present invention.

[0010] That is, the present invention is as follows. [1] A method for producing polyoxymethylene by polymerizing at least one monomer selected from the group consisting of trioxane, a cyclic ether, and a cyclic formal, a polymerization step of mixing the monomer with a catalyst solution and polymerizing the monomer to obtain polyoxymethylene, the catalyst solution contains tin tetrachloride and an aliphatic hydrocarbon solvent; During the polymerization step, the number of moles of tin tetrachloride relative to the total number of moles of the monomers was 5.0 × 10 -6 ~1.0×10 -4 The catalyst solution is added so that A method for producing polyoxymethylene. [2] The method for producing polyoxymethylene according to [1], wherein the concentration of tin tetrachloride in the catalyst solution is 10 mmol / L to 500 mmol / L. [3] The method for producing polyoxymethylene according to [1] or [2], wherein the aliphatic hydrocarbon solvent has 4 to 8 carbon atoms. [4] The method for producing polyoxymethylene according to any one of [1] to [3], wherein the aliphatic hydrocarbon solvent contains cyclohexane. [Effects of the Invention]

[0011] According to the present invention, polyoxymethylene can be produced with a high yield and a small proportion of low molecular weight regions. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail.

[0013] <Method of producing polyoxymethylene> The method for producing polyoxymethylene of the present embodiment is a method for producing polyoxymethylene by polymerizing at least one monomer selected from the group consisting of trioxane, cyclic ethers, and cyclic formals, and includes a polymerization step of mixing the monomer with a catalyst solution and polymerizing the mixture to obtain polyoxymethylene.

[0014] In the method for producing polyoxymethylene according to the present embodiment, the catalyst solution contains tin tetrachloride and an aliphatic hydrocarbon solvent.

[0015] In the method for producing polyoxymethylene according to the present embodiment, the number of moles of tin tetrachloride relative to the total number of moles of the monomers during the polymerization step is 5.0 × 10 -6 ~1.0×10 -4 The catalyst solution is added so that the

[0016] <Polyoxymethylene> The polyoxymethylene according to this embodiment includes polyoxymethylene homopolymers and polyoxymethylene copolymers.

[0017] <Monomer> In the method for producing polyoxymethylene in this embodiment, at least one monomer selected from the group consisting of trioxane, cyclic ethers, and cyclic formals is used.

[0018] <Trioxane> The trioxane used in this embodiment can be produced, for example, by reacting formaldehyde in the presence of an acidic catalyst. The trioxane thus obtained typically contains chain-transferable components (impurities), such as water and formic acid. The presence of these chain-transferable components renders the polymer end groups of the polyoxymethylene obtained by polymerization thermally unstable, making it difficult to obtain polyoxymethylene with high thermal stability. Therefore, it is preferable to purify and remove these chain-transferable components (impurities) to a certain concentration before the start of polymerization. The total content of these chain-transferable components (impurities) in trioxane is preferably 100 ppm by mass or less, more preferably 50 ppm by mass or less, and even more preferably 30 ppm by mass or less, based on the trioxane. Using trioxane with a content of these chain-transferable components (impurities) within the above range tends to enable the production of polyoxymethylene with excellent thermal stability.

[0019] <Cyclic ether> The cyclic ether used in this embodiment is not particularly limited as long as it can be polymerized using tin tetrachloride. Specific examples include ethylene oxide, propylene oxide, butylene oxide, epichlorohydrin, epibromohydrin, styrene oxide, oxetane, etc. These may be used alone or in combination of two or more.

[0020] <Cyclic formal> The cyclic formal used in this embodiment is not particularly limited as long as it can be polymerized using tin tetrachloride. Specific examples include 1,3-dioxolane, 1,3-dioxane, 1,3-dioxepane, 1,3-dioxocane, 1,3-dioxonane, and 1,3,6-trioxocane. These may be used alone or in combination of two or more.

[0021] <Catalyst liquid> The catalyst solution in this embodiment contains tin tetrachloride as a polymerization catalyst and an aliphatic hydrocarbon solvent as a solvent.

[0022] The polymerization catalyst and the solvent will be described in detail below.

[0023] <Polymerization catalyst> The catalyst solution used in this embodiment contains tin tetrachloride as a polymerization catalyst. By using tin tetrachloride as a polymerization catalyst, polyoxymethylene with a low oligomer content can be obtained. In this embodiment, the oligomer refers to a component having a molecular weight of 10,000 or less as determined by gel permeation chromatography (GPC).

[0024] <Aliphatic hydrocarbon solvent> The catalyst liquid in this embodiment contains an aliphatic hydrocarbon solvent as a solvent. It is preferable to use a mixture of tin tetrachloride and an inert aliphatic hydrocarbon solvent, and specifically, it is preferable to use an aliphatic hydrocarbon solvent having 4 to 8 carbon atoms.

[0025] Tin tetrachloride has high catalytic activity, and if used without a solvent, polymerization often begins only where the tin tetrachloride comes into contact with trioxane, resulting in the precipitation of polymer. By mixing tin tetrachloride with an aliphatic hydrocarbon solvent, the tin tetrachloride can be dispersed in the trioxane before polymerization begins, allowing the polymerization reaction to proceed uniformly, preventing the polymer from precipitating suddenly in one area, and resulting in a high polymerization yield.

[0026] The aliphatic hydrocarbon solvent is not particularly limited as long as it does not adversely affect the polymerization, but examples thereof include pentane, isopentane, hexane, cyclohexane, heptane, octane, etc., and from the viewpoint of boiling point, cyclohexane and heptane are particularly preferred. These hydrocarbon solvents may be used alone or in combination of two or more.

[0027] <Catalyst liquid> In this embodiment, the lower limit of the tin tetrachloride concentration in the catalyst solution is preferably 1 mmol / L or more, more preferably 5 mmol / L or more, and even more preferably 10 mmol / L or more, and the upper limit is preferably 500 mmol / L or less, more preferably 100 mmol / L or less, and even more preferably 50 mmol / L or less. If the concentration of the polymerization catalyst in the catalyst solution when added to the monomer is within the above range, the polymerization reaction can be carried out uniformly, rapid partial precipitation of the polymer can be suppressed, and the reaction proceeds with a high polymerization yield.

[0028] <Amount of polymerization catalyst> The amount of the polymerization catalyst added to the monomer is preferably 5.0×10 based on the total amount of trioxane, cyclic ether, and cyclic formal expressed in moles. -6 ~1.0×10 -4 mol, more preferably in the range of 1.0 × 10 -6 ~1.0×10 -4 mol, more preferably 2.0 × 10 -5 ~1.0×10 -5When monomers are continuously supplied to the polymerization reaction, it is advisable to adjust the amount of monomer supplied per unit time and the amount of polymerization catalyst supplied per unit time to be within the above ranges.

[0029] <Chain transfer agent> In the polymerization of polyoxymethylene according to the present embodiment, a chain transfer agent may be used in some cases for the purpose of controlling the molecular weight.

[0030] For example, when polymerization is carried out using a cationic catalyst containing tin tetrachloride or the like, a low molecular weight acetal represented by the following general formula can also be used. R 1 O-(CH2-O) n -R 2 (In the formula, R 1 and R 2 represents any one selected from the group consisting of hydrogen and branched or linear alkyl groups, and n represents an integer of 1 or more and 20 or less. In particular, by using an acetal having a molecular weight of 200 or less, preferably 60 to 170, the molecular weight of the polyoxymethylene finally obtained can be well adjusted. Examples of the low molecular weight acetal represented by the above general formula include, but are not limited to, methylal, methoxymethylal, dimethoxymethylal, trimethoxymethylal, etc. These may be used alone or in combination of two or more.

[0031] The amount of the low-molecular-weight acetal represented by the general formula to be added is 0.1 × 10 relative to the total amount of trioxane, cyclic ether, and cyclic formal expressed in moles, from the viewpoint of controlling the molecular weight of the target polyoxymethylene within a suitable range. -5 ~0.2×10 -2 The preferred range is 0.1 × 10 -5 ~0.2×10 -3 The mol range is more preferred, with 0.1 x 10 -5 ~0.1×10 -3 The molar range is more preferred.

[0032] The method for producing polyoxymethylene is cationic polymerization using tin tetrachloride as a polymerization catalyst. Furthermore, in the production of polyoxymethylene according to this embodiment, it is possible to remove the remaining monomers after polymerization and deactivate the catalyst. In addition, in the production of polyoxymethylene according to this embodiment, a terminal stabilization step can be carried out after polymerization.

[0033] <Polymerization process> The polymerization step in this embodiment is a step of polymerizing the above-mentioned monomers using tin tetrachloride as a polymerization catalyst. When tin tetrachloride is used as a catalyst, polymerization proceeds by what is generally called cationic polymerization. In cationic polymerization, for example, polymerization can be carried out by a bulk method using trioxane as a monomer. The shape (structure) of the polymerization reactor to be used is not particularly limited, but in general, a two-screw paddle-type or screw-type stirring and mixing polymerization reactor capable of passing a heat medium through a jacket can be suitably used. Examples of the polymerization method include a method in which a monomer containing trioxane, a cyclic ether, a cyclic formal, etc., a catalyst solution containing tin tetrachloride, an aliphatic hydrocarbon solvent, etc., and an optional chain transfer agent are supplied to a polymerization reactor and polymerized. The polymerization reaction temperature may be any temperature higher than the melting point and lower than the boiling point of the monomer used. For example, when trioxane is used, the temperature is preferably kept in the range of 63 to 135°C, more preferably in the range of 70 to 120°C, and even more preferably in the range of 70 to 100°C. The residence (reaction) time in the polymerization reactor is preferably 0.1 to 30 minutes, more preferably 0.1 to 25 minutes, and even more preferably 0.1 to 20 minutes. It is also preferable to appropriately sample the polymer and set the residence (reaction) time to achieve the desired yield. By adjusting the polymerization reaction temperature and the residence time in the polymerization reactor to be within the above ranges, the thermal decomposition of polyoxymethylene can be more effectively suppressed, and polyoxymethylene that is more thermally stable can be produced.

[0034] After polymerization, residual monomers can be removed from the resulting polyoxymethylene and the catalyst can be deactivated. Conventional methods can be used for this purpose. For example, the polyoxymethylene discharged from the polymerization reactor can be added to an aqueous solution containing only water or, for the purpose of efficiently deactivating the catalyst, at least one deactivator, such as ammonia, amines (e.g., triethylamine, tri-n-butylamine), hydroxides of alkali metals or alkaline earth metals, inorganic salts, or organic acid salts. The solution is then continuously stirred for several minutes to several hours at room temperature to 100°C or lower to remove and deactivate the residual monomers and catalyst remaining in the polyoxymethylene. To increase the efficiency of catalyst removal by washing, if the polyoxymethylene is in the form of large blocks, it is also preferable to pulverize the polyoxymethylene to make it finer.

[0035] Polyoxymethylene obtained by the above-mentioned polymerization method often has terminal hydroxyl groups that are prone to become the starting point for thermal decomposition. In such cases, the terminal hydroxyl groups can be stabilized by, for example, reacting an organic acid anhydride with the terminal hydroxyl groups, or the polyoxymethylene can be heated before use to decompose the easily decomposed components and sites.

[0036] <Terminal stabilization> The polyoxymethylene homopolymers and copolymers obtained by polymerization often have thermally unstable terminal groups. Therefore, after catalyst deactivation, it is preferable to block and stabilize these unstable terminal groups by reacting them with an esterifying agent, etherifying agent, or the like in the liquid or gas phase, or, in the case of crude polyoxymethylene copolymers, to decompose and remove the unstable terminals as described below, in order to prevent decomposition of the polyoxymethylene during melt processing.

[0037] For example, the case where stabilization is achieved by reacting an organic acid anhydride with a hydroxyl terminal is shown below. In this embodiment, the organic acid anhydride is not particularly limited as long as it reacts with the unstable hydroxyl group terminal of the crude polyoxymethylene. Specific examples include propionic anhydride, benzoic anhydride, acetic anhydride, succinic anhydride, maleic anhydride, glutaric anhydride, and phthalic anhydride. Among these, acetic anhydride and propionic anhydride, which become gaseous at or below the melting point of polyoxymethylene, are preferred from the viewpoint of being easily removed by high-temperature drying of the polyoxymethylene after the reaction. The reaction between the organic acid anhydride and the hydroxyl terminal may be in a liquid phase or a gas phase. For example, the polyoxymethylene obtained by polymerization may be dispersed or dissolved in an organic solvent inert to the hydroxyl terminals of the polyoxymethylene and the organic acid anhydride, and then reacted with the organic acid anhydride. Alternatively, the polyoxymethylene may be brought into contact with a gasified organic acid anhydride and reacted. The reaction temperature, reaction time (which may be contact time), and amount of organic acid anhydride used can be determined arbitrarily. The reaction apparatus is not particularly limited, and known reactors and dryers can be used. Examples include a stirred tank, an autoclave, a conical ribbon dryer, a rotary dryer, and a paddle dryer. Any device necessary for carrying out the reaction may be provided.

[0038] For example, stabilization by decomposition and removal of unstable terminal portions is shown below. The resulting polyoxymethylene copolymer contains thermally unstable terminal groups [-(OCH2) n (Hereinafter, such a polyoxymethylene copolymer may be referred to as a "polyoxymethylene copolymer before terminal stabilization.") Therefore, it is preferable to carry out a decomposition treatment to remove these unstable terminals (terminal stabilization) using a decomposition treatment agent. The decomposition treatment agent is not particularly limited, and examples thereof include basic substances such as aliphatic amine compounds such as ammonia, triethylamine, and tributylamine; inorganic weak acid salts of alkali metals or alkaline earth metals such as hydroxides, carbonates, phosphates, silicates, and borates of alkali metals or alkaline earth metals such as sodium, potassium, magnesium, calcium, and barium; and organic acid salts of alkali metals or alkaline earth metals such as formates, acetates, stearates, palmitates, propionates, and oxalates. Among these, aliphatic amine compounds are preferred, and triethylamine is more preferred.

[0039] The method for decomposing and removing the unstable terminals is not particularly limited, and examples thereof include a method of heat-treating the polyoxymethylene copolymer in a molten state in the presence of a decomposition agent such as triethylamine at a temperature above the melting point of the polyoxymethylene copolymer (e.g., 170° C. or higher) and below 260° C. Examples of the heat-treating method include a single-screw or twin-screw extruder equipped with a vent pressure reduction device, and a twin-screw extruder is preferred.

[0040] The weight average molecular weight of the polyoxymethylene obtained in this embodiment is preferably 10,000 or more, more preferably 100,000 or more, from the viewpoints of mechanical properties and moldability, and is preferably 2,000,000 or less, more preferably 1,000,000 or less. The weight average molecular weight can be measured using a GPC device, specifically by the method described in the examples.

[0041] The polydispersity index (PDI) of the polyoxymethylene obtained in this embodiment is preferably 7 or less, more preferably 4 or less, from the viewpoint of mechanical properties. The polydispersity index (PDI) can be measured using a GPC device, specifically by the method described in the Examples.

[0042] From the viewpoint of mechanical properties, the polyoxymethylene obtained in this embodiment preferably has a content of low molecular weight components of 20% or less, more preferably 15% or less, and even more preferably 10% or less.

[0043] The stabilized polyoxymethylene produced by the manufacturing method of this embodiment can be blended with commonly used known additives such as antioxidants, formic acid scavengers, weather (light) stabilizers, release (lubricants), reinforcing agents, conductive agents, thermoplastic resins, thermoplastic elastomers, pigments, plasticizers, peroxide decomposers, basic aids, antistatic agents, flame retardants, dyes, and fillers, as desired. Furthermore, the polyoxymethylene of this embodiment can also be blended with other polymers to the extent that its physical properties are not impaired. The blending ratios of these additives are within appropriate ranges.

[0044] The polyoxymethylene with reduced oligomer content produced by the manufacturing method of this embodiment, and optionally compositions incorporating the above-mentioned compounding agents, can be used in a variety of applications as molded articles or parts after various molding processes. It can be used for, but is not limited to, known applications of polyoxymethylene, such as electrical and electronic components and industrial parts, including gears, cams, sliders, levers, arms, clutches, pulleys, rollers, key stems, key tops, shafts, bearings, and guides. It can also be used as automotive parts, such as fuel-related parts such as gasoline tanks, fuel pump modules, valves, and gasoline tank flanges; door-related parts such as door locks, door handles, window regulators, and speaker grills; seatbelt-related parts such as seatbelt slip rings and press buttons; combination switch parts; and switches.

[0045] Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to the above-described embodiments. The present invention can be modified in various ways without departing from the spirit of the invention. [Example]

[0046] The following examples illustrate the invention without limiting it.

[0047] (Examples 1 to 2 and Comparative Examples 1 to 4) The analytical and evaluation methods used in Examples 1 and 2 and Comparative Examples 1 to 4 are as follows.

[0048] <Measurement of weight average molecular weight, polydispersity index (PDI), and content of low molecular weight components> The polyoxymethylenes obtained in the examples and comparative examples were measured for weight average molecular weight, polydispersity index (PDI), and content of components in the low molecular weight range using a GPC apparatus (HPLC8320) manufactured by Tosoh Corporation. The eluent used was 1,1,1,3,3,3-hexafluoropropanol (HFIP) in which 0.4 wt % sodium trifluoroacetate was dissolved. Polyoxymethylene was dissolved in the above eluent to prepare a sample solution with a concentration of 0.5 mg / mL. The columns consisted of one Shodex K-G4A column and one Shodex KF-606M column connected in series, and the solvent was replaced with HFIP. An RI (differential refractive index) detector was used as the detector, the flow rate of the eluent was 0.3 mL / min, the column temperature was 40°C, and the injection amount of the sample solution was 60 μL. The elution times obtained by GPC measurement were converted to molecular weights using a calibration curve prepared in advance using standard polymethyl methacrylates, all of which were manufactured by Agilent and had the following product numbers: Part numbers: PL2022-3001, PL2022-6001, PL2023-1001, PL2023-4001, PL2023-8001, PL2024-1001. Each compound was dissolved in the eluent to a concentration of 0.5 mg / mL, and 60 μL of the solution was injected to create a calibration curve, which was a cubic equation obtained by approximating the curve using the least squares method. The baseline was a straight line connecting the points at 10 and 18 minutes of elution time. However, if the difference between the two points was 3% or more of the height of the main peak in the GPC curve, the measurement was repeated until it was less than 3%. The content (%) of components in the low molecular weight region was calculated by determining the ratio of the area of the region where the molecular weight was 500 or more and 10,000 or less, as determined by the calibration curve, to the area above the baseline.

[0049] <Measurement of polymerization yield> The amount of polyoxymethylene discharged from the polymerization reactor per unit time was measured, and this measured value was divided by the total amount of trioxane, cyclic ether, and cyclic formal fed to the polymerization reactor per unit time to determine the polymerization yield (%).

[0050] [Example 1] The polymerization reaction apparatus used was a co-rotating, twin-screw paddle-type continuous polymerization reactor (manufactured by Kurimoto Iron Works Co., Ltd., diameter 2B, L / D=14.8) set at 80°C. To prevent oxygen contamination, 60 L of nitrogen was flowed per hour from near the feed port of the polymerization reactor. Trioxane was then fed into the polymerization reactor at 3500 g / hr. Tin tetrachloride, the polymerization catalyst, was mixed in advance with a mixed solution of cyclohexane and heptane as an aliphatic hydrocarbon solvent to a concentration of 26 mmol / L, and the polymerization amount was 0.2 × 10 per 1 mol of trioxane. -4 The mixture was fed to the polymerization reactor so that the total amount of the copolymer was 100 mol. The trioxane and the polymerization catalyst solution were supplied through separate lines so as not to come into contact with each other until they reached the paddle section installed in the polymerization reactor. Thirty minutes after the start of the polymerization reaction, the polymerization yield was measured by the method described above. The results are shown in Table 1. The polyoxymethylene discharged from the polymerization reactor was then placed in water and stirred at room temperature for 1 hour to wash away the polymerization catalyst. The polyoxymethylene from which the polymerization catalyst had been removed was filtered using a centrifuge and then dried at 120°C for 3 hours. The weight-average molecular weight and polydispersity of the resulting polyoxymethylene were measured using the methods described above. The results are shown in Table 1. In Table 1, SnCl4 is tin tetrachloride, BF3OEt2 is boron trifluoride dibutyl ether complex, the amount of catalyst at the start of polymerization is the molar ratio of the amount of catalyst to the total amount of trioxane, cyclic ether, and cyclic formal expressed in moles at the start of polymerization (number of moles of catalyst / number of moles of cyclic ether and cyclic formal), and M w x10 -4 is the weight average molecular weight divided by 10,000, and PDI is the polydispersity index.

[0051] [Example 2] As shown in Table 1, in Example 1, the amount of catalyst at the start of polymerization was 0.1 × 10 -4 Except for the above, polymerization evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0052] [Comparative Example 1] As shown in Table 1, in Example 1, the amount of catalyst at the start of polymerization was 0.04 × 10 -4 Except for the above, polymerization evaluation was carried out in the same manner as in Example 1. The results are shown in Table 1.

[0053] Comparative Example 2 As shown in Table 1, polymerization evaluation was carried out in the same manner as in Example 1, except that tin tetrachloride as the polymerization catalyst was changed to boron trifluoride dibutyl ether complex and the amount of the polymerization catalyst was changed to 30 mmol / L. The results are shown in Table 1.

[0054] [Table 1] [Industrial Applicability]

[0055] According to the method for producing polyoxymethylene of the present invention, it is possible to obtain polyoxymethylene with a low content of low-molecular-weight components in good yield.

Claims

1. A method for producing polyoxymethylene by polymerizing a monomer containing trioxane, a polymerization step of mixing the monomer with a catalyst solution and polymerizing the monomer to obtain polyoxymethylene, the catalyst solution contains tin tetrachloride and an aliphatic hydrocarbon solvent; During the polymerization step, the number of moles of tin tetrachloride relative to the total number of moles of the monomers was 5.0 × 10 －６ ~1.0 x 10 －４ The catalyst solution is added so that A method for producing polyoxymethylene.

2. 2. The method for producing polyoxymethylene according to claim 1, wherein the concentration of tin tetrachloride in the catalyst solution is 10 mmol / L to 500 mmol / L.

3. 3. The method for producing polyoxymethylene according to claim 1, wherein the aliphatic hydrocarbon solvent has 4 to 8 carbon atoms.

4. The method for producing polyoxymethylene according to any one of claims 1 to 3, wherein the aliphatic hydrocarbon solvent comprises cyclohexane.

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