Method for producing polyoxymethylenes

Detailed Description of the Invention The present invention relates to an improved method for producing polyoxymethylene and the POM polymer obtained by the method.

Melt polymerization of POM in tubular reactors is known. For example, tube reactors of various configurations have been described: "fliessendem Uebergang", ie, on the one hand geometrically indistinguishable mixed regions (EP-A638599, EP-A638357), on the other hand the reaction. Spatial separation between region and stop region (EP-A80656). Both methods are the starting point to ensure a good mixing of liquids of different material fluxes or viscosities.

A particular problem is the addition of terminators during melt polymerization. In this case, very small amounts of low molecular weight components (inorganic salts or organic bases) and (high) viscosity polymer melts must be efficiently mixed.

The prior art primarily sets the reactor configuration to solve this problem: --optimization of stop zone dwell time (EP-A638599, EP-A638357) --incorporation of bottleneck and flow velocity in the reactor. Change (EP-A80656).

The terminator is, according to the prior art, always introduced into the reaction mixture with an auxiliary agent (water, alcohol, or other solvent), see, eg, DE-A3703790.

If it is an organic terminator, in each case it is a foreign substance in the polymer melt, i.e. the terminator introduces new structural units into the final product. Additional structural units may be introduced if the organic terminator is further present in the solvent. In this case, chain stability and color characteristics are disadvantageous.

For inorganic stop reagents, the amount introduced is ideally matched exactly to the amount of initiator. This is because excess base (without vapor pressure) cannot be removed. You can work with an excess amount.

In both cases, it is desirable to minimize the amount of terminator to improve the quality of the product.

Furthermore, it is desirable to minimize the amount of foreign matter (solvents, low molecular weight liquids).

Therefore, an object of the present invention is to provide an improved method for producing polyoxymethylene having the following advantages over the prior art: --addition of terminator in polymer melt and optimization of more uniform distribution. , --Improved final product quality, --Reduction of foreign matter in the compound, --Optimization of residence time in the stop region of the reactor, --Better reproducibility of polymer properties, --By aliphatic solvents Improved polymer color, -more stable polymer end groups reached by aprotonic solvents.

A further object of the present invention is to produce a polyoxymethylene homo- or-copolymer containing as little small molecule POM as possible.

Correspondingly, the monomer a) is polymerized in the presence of the cationic initiator b) and optionally in the presence of the regulator c), then the polymer is deactivated and separated to polyoxy. In the method of producing methylene, polymerization is carried out in a tubular reactor having a static mixing element, wherein the tubular reactor has a mixing region, a polymerization region and a deactivated region, and the tubular type. We have found a method for producing polyoxymethylene, characterized in that the diameter of the mixing region of the reactor is <90% of the diameter of the polymerization region.

Preferred embodiments are described in the cited form claims.

Furthermore, we have found a POM polymer with an asymmetric molar mass distribution.

The method is based on each reactor with a high degree of mixing action, such as trays, prober mixers, tubular reactors, List reactors, kneaders, agitator reactors, extruders and belt reactors. Can be carried out.

Suitable reactors are, for example: Kenics (Chemineer Inc.); interfacial surface generator ISG and low pressure drop mixer (ROSS Engineering Inc.); SMV, SMX, SMXL. , SMR (Sulzer Koch-Glitsch); Inliner system 45 (Lightnin Inc.); CSE mixer (Fluitec Georg AG).

The resulting POM polymer is known to those of skill in the art and is described in the literature.

Particularly in general, this polymer has at least 50 mol% of repeating units in the polymer backbone-CH.₂Has O-.

Homopolymers are generally produced by polymerization of monomer a), for example formaldehyde or trioxane, preferably in the presence of a suitable catalyst.

Within the scope of the present invention, polyoxymethylene copolymers are preferred, especially the repeating unit -CH.₂In addition to O-, a repeating unit of up to 50, preferably 0.01 to 20, particularly 0.1 to 10 mol%, particularly preferably 0.5 to 3 mol%.<chemistry num="1"><img file="JP2008521950A_D0001.tif" /></chemistry>[In the formula, R¹~ R⁴Are independent of each other, the hydrogen atom, C₁~ C₄-Alkyl group or halogen-substituted alkyl group having 1 to 4 C atoms and R⁵Is -CH₂-, -CH₂O-, C₁~ C₄-Alkyl- or C₁~ C₄-A polyoxymethylene copolymer having a methylene group substituted with haloalkyl or a corresponding oxymethylene group, and n is a value in the range of 0 to 3. Advantageously, these groups may be introduced into the copolymer by ring opening of the cyclic ether. The preferred cyclic ether is the formula:<chemistry num="2"><img file="JP2008521950A_D0002.tif" /></chemistry>[In the formula, R¹~ R⁵And n represent the above meanings] cyclic ethers. For example, ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxolane and 1,3-dioxepane are mentioned as cyclic ethers, and Linear oligoformal or polyformal, such as polydioxolane or polydioxepan, can be mentioned as comonomer.

Similarly, for example, trioxane, the cyclic ether described above, and a third monomer, preferably of formula.<chemistry num="3"><img file="JP2008521950A_D0003.tif" /></chemistry>And / or<chemistry num="4"><img file="JP2008521950A_D0004.tif" /></chemistry>[In the formula, Z is a chemical bond, -O-, -ORO- (R = C)₁~ C₈-Alkylene or C₃~ C₈-Cycloalkylene)] oxymethylene terpolymer produced by reaction with a bifunctional compound is suitable.

Preferred monomers of this type are ethylene diglycid, diglycidyl ether and diether in a 2: 1 molar ratio of glycidylene to formaldehyde, dioxane or trioxane, and 2 mol and 2 to 8 glycidyl compounds, to name a few. Diethers consisting of 1 mol of an aliphatic diol having a C atom, such as ethylene glycol, 1,4-butanediol, 1,3-butanediol, cyclobutane-1,3-diol, 1,2-propanediol and cyclohexane-1, It is a 4-diol diglycidyl ether.

CC bond or -O-CH at the end of the chain₃Polyoxymethylene polymers with bonds and stabilized end groups are particularly advantageous.

Preferred polyoxymethylene copolymers have a melting point of at least 150 ° C and a molecular weight (weight average) M in the range of 5000 to 300,000, preferably 7,000 to 250,000._wHave.

Non-uniformity (M_w/ M_n) POM copolymers having 2 to 15, preferably 3 to 12, particularly preferably 3.5 to 9, are particularly preferred. This measurement is generally performed by (GPC) SEC (Size Exclusion Chromatography) and M_nThe value (number average molecular weight) is generally measured by (GPC) SEC (Size Exclusion Chromatography).

The POM polymer obtained by this method preferably has a monomodal molecular weight distribution, in which the proportion of small molecules is small.

Polyoxymethylene homo-or-copolymers are particularly d of 2.25 to 5.5, preferably 2.75 to 5, especially 3.2 to 4.5.₅₀/ d₁₀Value (M_wHas a quotient (based on). d₉₀/ d₅₀Value (M_wThe quotient (based on) is preferably 1.25 to 3.25, preferably 1.75 to 2.75, especially 2 to 2.5.

The POM polymer has a very small proportion of small molecules, preferably has an asymmetric monomodal distribution curve, in which the quotient d described above.₅₀/ d₁₀And d₉₀/ d₅₀The difference from is at least 0.25, preferably 1-3, especially 1.0-2.3.

Molar mass measurement by GPC (gel permeation chromatography): Eluent: Hexafluoroisopropanol + 0.05% Potassium trifluoroacetate Column temperature: 40 ° C Flow rate: 0.5 mL / min Detector: Differential refraktometer Agilent G1362A

Equilibration was performed using a narrowly distributed PMMA standard of Fa.PSS with a molecular weight of M = 505 to M = 2740000. Elution ranges outside this interval were evaluated by extrapolation.

d₅₀Values are generally 50% smaller than M for those skilled in the art._wHas, and correspondingly 50% is greater than M_wIt is understood that the value has.

Preferably, the crude polyoxymethylene obtained by the method according to the invention has a residual formaldehyde content of pellets up to 3%, preferably up to 1% and preferably up to 0.05% according to VDA275.

The method according to the present invention preferably applies to homo- and copolymerization of trioxane. However, as the monomer a), in principle, the above-mentioned monomers such as Tetroxan or (para) formaldehyde can also be used, respectively.

Monomers, such as trioxane, are preferably metered and supplied in a molten state, typically at a temperature of 60-180 ° C.

Preferably, the temperature of the reaction mixture during metered feed is 62-170 ° C, especially 120-160 ° C.

The molecular weight of the polymer can optionally be adjusted to the desired value by the usual modifier c) during (trioxane) polymerization. Modulators include the monohydric alcohol acetal or formal, the alcohol itself, and a small amount of water acting as a chain transfer agent (this presence is generally not completely avoided). The adjusting agent is used in an amount of 10 to 10000 ppm, preferably 50 to 5000 ppm.

As the initiator b) (also referred to as a catalyst), a usual cationic initiator is used during the (trioxane) polymerization. Protonic acids such as fluorinated or chlorinated alkyl- and aryl sulfonic acids such as perchloric acid, trifluoromethane sulfonic acid or Lewis acid such as tin tetrachloride, arsenic pentafluoride, phosphorus pentafluoride and trifluoride Boron and complex and salty compounds thereof such as boron trifluoride-etherate and triphenylmethylene hexafluorophosphate are suitable. This catalyst (initiator) is used in an amount of about 0.001 to 1000 ppm, preferably 0.01 to 500 ppm, particularly 0.05 to 10 ppm. In general, it is recommended that the initiator be added in diluted form, preferably at a concentration of 0.005-5% by weight. As the solvent for this, an inert compound such as an aliphatic or cyclic aliphatic hydrocarbon such as cyclohexane, a halogenated aliphatic hydrocarbon, a glycol ether or the like can be used. Particularly preferred are trigrim (triethylene glycol dimethyl ether) as a solvent and 1,4-dioxane.

The monomers and comonomer a), initiator b) and optionally modifier c) can optionally be premixed or added to the polymerization reactor separately from each other. Further, as described in EP-A129369 or EP-A128739, components a), b) and / or c) may contain sterically hindered phenol for stabilization.

It has been found advantageous to dissolve the initiator b) in the modifier c) prior to addition to the monomer a) and optionally the comonomer a) in order to minimize the proportion of unstable end groups. are doing.

It has proven advantageous to meter the initiator at various points in the tubular reactor. In this case, the preferred minimum spacing is 1D (D = reactor diameter at the location described above).

Polymerization is carried out in a tubular reactor having a mixed region, a polymerization region and an inactivated region.

According to the present invention, the diameter of the mixed region of the tubular reactor is &lt;90%, preferably 10 to 90%, preferably 10 to 90% of the diameter of the polymerization region, specifically the maximum diameter of the polymerization region. It is 10 to 70%, especially 10 to 60%.

In particular, the number of webs of the static mixing element in the mixing region is 0 to 500%, preferably 0 to 300%, particularly 0 to 100% larger than that in the polymerization region.

In another embodiment of the method according to the invention, the mixed region may be divided into sections of various diameters. Preferably, the diameter of the entire mixing region in the reactor is the same.

The residence time in this mixed region is preferably 1 to 300 seconds, particularly 5 to 60 seconds.

Shearing in the mixed region in the reactor is preferably 5 to 1000, preferably 10 to 750, particularly 20 to 500 1 / s.

The calculation of shear in a static mixer is performed as follows:<maths num="1"><img file="JP2008521950A_D0005.tif" /></maths>γ: Shear [1 / s]

k: Constant of the manufacturer of the static mixer

The viscosity is preferably 0.1 mPas to 100 Pas, preferably 0.1 mPas to 10 Pas.

The viscosity calculation is performed as follows:<maths num="2"><img file="JP2008521950A_D0006.tif" /></maths>η: Viscosity Δp: Pressure loss across the mixing element D: Static mixer diameter NeRe: Static mixer characteristic value (Newton-Reynolds (Newton-Reynolds)<u style="single">Ne</u>ston-<u style="single">Re</u>ynolds) Number) L: Length of static mixer V: Flow velocity in mixer

The residence time for polymerization is preferably 0.1 to 40 minutes, particularly 1 to 20 minutes. This polymerization is preferably carried out until a conversion of at least 30%, particularly greater than 60%.

In general, it has been found that a method of adjusting the pressure at the time of polymerization of 5 to 200 bar (absolute pressure), preferably 10 to 100 bar (absolute pressure) is effective.

In another embodiment of the invention, the polymerization region may be divided into sections of various diameters, particularly 2-10 sections, preferably 2-5 sections. The minimum diameter is preferably 20 to 100%, particularly 30 to 90%, particularly preferably 45 to 75% of the maximum diameter.

The shear in the polymerization region is preferably 1 to 300, preferably 2 to 100, particularly 3 to 50 1 / s. The viscosity is preferably 1 to 1000, preferably 10 to 500, and particularly 100 to 400 Pas.

According to the present invention, following this polymerization, the polymerization mixture is preferably directly deactivated without phase change.

The deactivation of this catalyst residue is generally carried out by the addition of at least one deactivating agent d).

Suitable deactivators are, for example, ammonia, aliphatic and aromatic amines, salts that exhibit a basic reaction, such as soda and borax. These are usually added to the polymer in an amount preferably up to 1% by weight.

Organic compounds of alkaline (earth) metals, preferably sodium, preferably have up to 30 C atoms and preferably 1 to 4 carboxyl groups (cyclic) aliphatic, alicyclic, or aromatic carboxylic acid. Contains the appropriate salt of acid. Examples of this are: formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, capric acid, stearic acid, cyclohexanecarboxylic acid, succinic acid, adipic acid, corkic acid, 1,10-decandicarboxylic acid, 1,4-cyclohexanedicarboxylic acid. , Telephthalic acid, 1,2,3-propanetricarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid, trimellitic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, pyromellitic acid, benzoic acid, substitution Alkali metal salts of benzoic acid, dimeric acid and trimeric acid, and neutral and partially neutral montan wax salts or montan wax ester salts (montanato). According to the present invention, salts having acid groups of other properties, such as alkaline paraffin-, alkaline olefin- and alkaline aryl sulfonate or phenolate, and alcoholates such as methanolate, etanolate, glycolate may be used.

Preferably, mono- and polycarboxylic acids having 2 to 18 C atoms, particularly 2 to 6 C atoms and up to 4 and preferably up to 2 carboxyl groups, especially aliphatics. It is preferred to use sodium salts of mono- and polycarboxylic acids and preferably sodium alcoholates having 2 to 15, especially 2 to 8 C atoms. Particularly preferred representative examples are sodium acetate, sodium propionate, sodium butyrate, sodium oxalate, sodium malonate, sodium succinate, sodium metanolate, sodium ethanolate, and sodium glycolate. Particularly advantageously, it is particularly preferred to use sodium methanolate in an equimolar amount that is 1 to 5 times that of the component b) used. Mixtures of various alkaline (earth) metal compounds can also be used, in which hydroxides can also be used.

Further, an alkaline earth metal alkyl having 2 to 30 C atoms in the alkyl group is preferable as the deactivator d). Particularly advantageous metals include Li, Mg and Na, with n-butyllithium being particularly preferred.

The preferred inactivating agent d) is Formula I<chemistry num="5"><img file="JP2008521950A_D0007.tif" /></chemistry>[In the formula, R¹, R³, R⁴And R⁵Are independent of each other, hydrogen or C₁~ C₁₀-Alkyl group and R²Is hydrogen or C₁~ C₁₀-Alkyl group or OR⁵Is a deactivating agent.

Preferred group R¹~ R⁵Are independent of each other, hydrogen or C₁~ C₄-Alkyl groups such as methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butyl, t-butyl.

A particularly preferred deactivator d) is a substituted N-containing heterocyclic compound, particularly a derivative of piperidine, with triacetone diamine (4-amino-2,2,6,6-tetramethylpiperidine) being particularly preferred.

This inactivating agent is measured and supplied in an amount of 0.001 to 25 ppm, preferably 0.01 to 5 ppm, particularly 0.05 to 2 ppm, based on the treated amount of trioxan. The deactivator is preferably present diluted in one of the carriers / solvents described below. The concentration of this deactivator in the carrier / solvent is 0.001 to 10%, preferably 0.01 to 5%, particularly 0.05 to 2%, particularly preferably 0.1 to 1%.

According to the present invention, the diameter of the deactivated region of the tubular reactor is &lt;95%, preferably 20-95%, particularly 30-90%, particularly preferably 50-85% of the diameter of the polymerization region. is there.

In particular, the number of webs of the static mixing element in the deactivated region is 0 to 500%, preferably 50 to 300%, particularly 50 to 200% larger than that in the polymerization region.

In another embodiment of the invention, the deactivated region may be divided into sections of various diameters, particularly 1-5 sections, preferably 2 sections. In this case, the diameter of the minimum section is 20 to 100%, preferably 30 to 90%, particularly 50 to 90% of the diameter of the maximum section.

In a particularly preferred embodiment of the two sections of the deactivated region, the first section contains a number of webs 20-500, preferably 50-300, particularly 50-200% larger than the polymerization region, and the first. Section 2 contains a number of webs that are -100 to 500%, -100 to 300%, preferably -100 to 200% larger than the polymerization region.

Shear in the deactivated region is preferably 0.1 to 500, preferably 1 to 100, especially 3 to 75 1 / s. In the preferred embodiment of the plurality of sections (1-5, preferably 2), the shearing of the section having the smallest diameter, preferably the first section following the polymerization region, is 10-200, preferably 15-100, Particularly preferably, it is 20 to 75 1 / s. In the subsequent sections, the above values apply.

The viscosity is preferably 1 to 1000, preferably 100 to 800, and particularly 150 to 600 Pas.

The residence time in the deactivated region is preferably 0.5 to 20 minutes, particularly 1 to 10 minutes.

Preferably, the deactivator d) is added in an aprotonic, non-aromatic solvent such as the above-mentioned monomers and comonomeres such as dioxolane, trioxane, butanediol formal, ethylene oxide or oligomers or polymer polyacetals.

In a particularly preferred embodiment of the method according to the invention, the deactivator d) is added to the polymerization mixture in a carrier material having ether structural units.

Preferably, carrier materials having the same structural units as those present in the POM polymers to be produced are preferred. These are particularly understood as the above-mentioned monomer a) and oligomers or polymers polyoxymethylene or polyacetal.

Addition in a preferred liquid is carried out at a temperature of 140-220 ° C.

If an oligomer or polymer POM polymer is used as the carrier material, it is similarly preferred to add in liquid form at a temperature of 160-220 ° C. Such polymers may optionally contain conventional additives. Equipment such as an attached extruder, plug screw (Stopfschnecke), melting pump (Schmelzepumpe), etc. is preferably used for the metered supply of such melts of carrier material containing the deactivator d).

The resulting polymer is then generally fed into the deaerator.

The resulting polyoxymethylene polymer may then be routinely post-treated with conventional additives such as stabilizers, rubbers, fillers and the like.

According to the method according to the present invention, the terminator (inactivating agent) can be better weighed and mixed.

The POM obtained by the method according to the present invention has quality advantages such as improved thermal stability, color, reduced chain decomposition, good flow and mechanical properties.

According to the method according to the present invention, it is also possible to produce a polyacetal having a multimodal, preferably bimodal molar mass distribution. To this end, for example, a trioxane stream is polymerized in parallel tubular reactors (at least two) to produce fractions of various molar masses, which are then mixed. In a separate route, one or a combination of parameters produce the desired polymer, then upstream or downstream of the mixing region, with a terminator, downstream of the deactivation region, or in a deaerator or extruder. Can be mixed again on. It is also possible to mix the partial flows at the above locations.

Examples according to the invention A tube reaction with a mixture of 96.495% by weight liquid trioxane, 3.5% by weight dioxolane and 0.005% by weight methylal heated to 160 ° C and with a static mixer (4 webs and 8 webs). Pumped into the vessel.

This tubular reactor consisted of a reaction region and a stop region. On the other hand, this reaction region consisted of three compartments with various diameters (first reactor section 12 mm, second reactor section 15 mm, third reactor section 27 mm). The stop region consisted of two compartments of various diameters (first reactor section 8 web bodies 17 mm, second reactor section 4 web bodies 27 mm).

The conduit between the reactor and the degassing stage also served as a stop region.

Polymerization was initiated by the addition of Xppm perchloric acid (as a 0.01 mass% solution in 1,4-dioxane) and the pressure at the reactor outlet was adjusted by a control valve to 20 bar. The temperature in the reaction region (165 ° C) and the temperature in the stop region (195 ° C) were adjusted via a double jacket.

Triacetone diamine (1,3-dioxolane) as a terminator in the terminator region of the reactor so that after a residence time of 2 minutes, the terminator is present in the amount of substance 10 times excess of perchloric acid. (As a 0.1% by weight solution in) was metered and mixed via a static mixer.

After an additional 3 minute residence time, the product (crude POM) was reduced to a pressure of 3 bar in a deaerator via a control valve, thereby separating the volatile components of the polymer melt. Residues of trioxane and formaldehyde remained in this polymer melt.

This product was discharged and subjected to GPC.

Comparative Example 2, Comparative Example 3 A mixture from 96.495 mass% liquid trioxane, 3.5 mass% dioxolane and 0.005 mass% methylal was heated to 160 ° C and pumped into a tubular reactor with a static mixer. ..

The tubular reactor consisted of a flat tube with a metering feeder for the initiator and terminator. This weighing and feeding device was provided at an angle of 60 ° with respect to the direction of flow. The diameter of this tube was 12 mm. A static mixing element was provided for mixing the initiator and terminator. The temperature in the reaction region (165 ° C) and the temperature in the stop region (195 ° C) were adjusted via a double jacket.

Polymerization was initiated by the addition of Xppmw of perchloric acid (as a 0.01 mass% solution in 1,4-dioxane) and the pressure in the reactor was Pbar.

Triacetone diamine (1,3-dioxolane) as a terminator in the terminator region of the reactor so that after a residence time of 2 minutes, the terminator is present in the amount of substance 10 times excess of perchloric acid. Weigh in (as a 0.1% by weight solution) and mix via a static mixer.

After an additional 3 minute residence time, the product (crude POM) was reduced to a pressure of 3 bar in a deaerator via a control valve, thereby separating the volatile components of the polymer melt. Residues of trioxane and formaldehyde remained in this polymer melt.

This product was discharged and subjected to GPC.<tables num="1"><img file="JP2008521950A_D0008.tif" /></tables>

At an initiator amount of 0.05 ppmw, the polymerization was carried out only in the reactor according to the present invention, and in Comparative Example 1, turbidity of trioxane was only observed. In the comparative example in which the initiator concentration was increased 20 times, polymerization was carried out, but only a low molecular weight product was obtained. On the other hand, according to the tubular reactor according to the present invention, a high molar mass of polyacetal can be produced with an extremely small amount of initiator.