DE10335959A1 - Alcohols as cocatalysts in POM production - Google Patents

Abstract

Process for the preparation of polyoxymethylene by precipitation polymerization of the monomers a) in the presence of cationic initiators b) and cocatalysts c) and optionally in the presence of regulators d), the polymer optionally deactivated and then separated, characterized in that is used as cocatalyst c) alcohols ,

Description

The The invention relates to an improved process for the production of Polyoxymethylenes.

It It is known that oxymethylene polymers by continuous bulk polymerization the monomers prepared in the presence of cationic initiators can be. This polymerization is common in Kneading or extruding performed. In this case, the temperature control be done so that the resulting oxymethylene polymer either in solid form (DE-A 1 161 421, DE-A 1 495 228, DE-A 1 720 358, DE-A 3 018 898) or as a melt (DE-A 3 147 309) is obtained. The Work-up of the polymer obtained in solid form is known see: DE-A 3147309, DE-A 3628561, EP-A 678535, EP-A 699965 and DE-A 4423617.

at the bulk polymerization are different process variants Prior art, including batch polymerization in trays, the continuous polymerization in kneader reactors at temperatures below the melting point or the polymerization at temperatures above the melting point of trioxane in the extruder (see WO 01/58974).

The Preparation by suspension or precipitation polymerization with cationic Iniators are generally known. In the solvent used here in particular, the resulting polymer should not be soluble, so that this is easier to separate.

Either in bulk and precipitation polymerization the catalysts used are not in these reaction media soluble and must In larger quantities and over a longer one Period are used. This adversely affects the stability of the resulting polymer, which degraded by such acids becomes. It is therefore essential that as little catalyst as possible is used but at the same time the reaction time is not significantly extended.

• – Die Neutralisation der Produkte ist leichter durchführbar,
• – Der Molekulargewichtsabbau bei Erhitzen wird reduziert,
• – Die Katalysator(Initiator)-Mengen sollen vermindert werden,
• – Ausbeute und Reproduzierbarkeit sollten möglichst hoch sein,
• – Restmonomergehalt soll sehr gering sein,
• – Die Reaktionsgeschwindigkeit soll erhöht werden.

The object of the present invention was therefore to provide an improved process for the preparation of polyoxymethylenes which has the following advantages over the prior art:

• - The neutralization of the products is easier to carry out,
• The molecular weight reduction on heating is reduced,
• - The catalyst (initiator) amounts should be reduced,
• Yield and reproducibility should be as high as possible
• - residual monomer content should be very low,
• - The reaction rate should be increased.

Accordingly, became a process for the preparation of polyoxymethylenes by polymerization of the monomers a) in the presence of cationic initiators b) and cocatalysts c) and optionally in the presence of regulators d) optionally deactivating the polymer and then separating it off, found, which is characterized in that as a cocatalyst c) using alcohols.

preferred embodiments are the dependent claims refer to.

The Procedure can basically be carried out on any reactors with a high mixing effect, such as trays, ploughshare mixers, tubular reactors, cunning reactors, Kneaders, stirred reactors.

The resulting POM polymers are known in the art per se and described in the literature.

Generally, these polymers have at least 50 mole percent of repeating units - CH ₂ O - in the polymer backbone.

The Homopolymers are generally obtained by the polymerization of Monomers a) such as formaldehyde or trioxane produces, preferably in the presence of suitable catalysts.

wobei R¹ bis R⁴ unabhängig voneinander ein Wasserstoffatom, eine C₁-bis C₄-Alkylgruppe oder eine halogensubstituierte Alkylgruppe mit 1 bis 4 C-Atomen und R⁵ eine -CH₂-, -CH₂O-, eine C₁- bis C₄-Alkyl- oder C₁- bis C₄-Haloalkyl substituierte Methylengruppe oder eine entsprechende Oxymethylengruppe darstellen und n einen Wert im Bereich von 0 bis 3 hat. Vorteilhafterweise können diese Gruppen Ringöffnung von cyclischen Ethern in die Copolymere eingeführt werden. Bevorzugte cyclische Ether sind solche der Formel

wobei R¹ bis R⁵ und n die oben genannte Bedeutung haben. Nur beispielsweise seien Ethylenoxid, 1,2-Propylenoxid, 1,2-Butylenoxid, 1,3-Butylenoxid, 1,3-Dioxan, 1,3-Dioxolan und 1,3-Dioxepan als cyclische Ether genannt sowie lineare Oligo- oder Polyformale wie Polydioxolan oder Polydioxepan als Comonomere genannt.In the context of the invention, preference is given to polyoxymethylene copolymers, in particular those which, in addition to the repeating units -CH ₂ O-, also contain up to 50, preferably 0.1 to 20, in particular 0.3 to 10 mol% and very particularly preferably 2 to 6 mol -% of recurring units.

where R ¹ to R ⁴ independently of one another are a hydrogen atom, a C _{1 to} C ₄ alkyl group or a halogen-substituted alkyl group having 1 to 4 C atoms and R ^{5 is} a -CH ₂ -, -CH ₂ O-, a C ₁ - to C ₄ alkyl or C ₁ - to C ₄ haloalkyl substituted methylene group or a corresponding oxymethylene group and n has a value in the range of 0 to 3. Advantageously, these ring opening groups of cyclic ethers can be introduced into the copolymers. Preferred cyclic ethers are those of the formula

wherein R ¹ to R ⁵ and n have the abovementioned meaning. 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 oligo- or polyformals such as polydioxolane or polydioxepan called comonomers.

wobei Z eine chemische Bindung, -O-, -ORO- (R=C₁- bis C₈-Alkylen oder C₃- bis C₈-Cycloalkylen) ist, hergestellt werden.Also suitable are Oxymethylenterpolymerisate, for example, by reacting trioxane, one of the cyclic ethers described above with a third monomer, preferably bifunctional compounds of the formula

wherein Z is a chemical bond, -O-, -ORO- (R = C ₁ - to C ₈ -alkylene or C ₃ - to C ₈ -cycloalkylene) can be prepared.

preferred Monomers of this type are ethylene diglycidyl, diglycidyl ether and diether from glycidylene and formaldehyde, dioxane or trioxane in the molar ratio 2: 1 and diether from 2 mol glycidyl compound and 1 mol of an aliphatic Diols with 2 to 8 carbon atoms such as the diglycidyl ethers of ethylene glycol, 1,4-butanediol, 1,3-butanediol, cyclobutane-1,3-diol, 1,2-propanediol and cyclohexane-1,4-diol, to name just a few examples to call.

End-group stabilized polyoxymethylene polymers which have C-C or -O-CH ₃ bonds at the chain ends are particularly preferred.

The preferred polyoxymethylene copolymers have melting points of at least 150 ° C and weight average molecular weights M _w in the range of 5,000 to 300,000, preferably 7,000 to 250,000.

Particular preference is given to POM copolymers having a non-uniformity (M _w / M _n ) of from 2 to 15, preferably from 3 to 12, particularly preferably from 4 to 9. The measurements are generally carried out by (GPC) SEC (size exclusion chromatography). The M _n value (number average molecular weight) is generally determined by (GPC) SEC (size exclusion chromatography).

Especially preferred POM copolymers have a bimodal molecular weight distribution on, wherein the low molecular weight fraction has a molecular weight of 500 to 20,000, preferably from 1,000 to 15,000 and in area proportions from 1 to 15, preferably 8 to 10% in the distribution graph w (log M) is present against log M.

Prefers have the according to the inventive method available Raw polyoxymethylene one Residual formaldehyde content in accordance with VDA 275 in the granules of a maximum of 3%, preferably at most 1%, preferably maximum 0.05%.

The average particle size (d ₅₀ value) (particle size) of the POM polymers is preferably from 0.5 to 20 mm, preferably from 0.75 to 15 mm and in particular from 1 to 7 mm.

A d ₅₀ value is understood by those skilled in the art usually the particle size value at which 50% of the particles have a smaller particle size and 50% have a larger particle size. This is to be understood accordingly for the stated d ₁₀ and d ₉₀ values.

The d ₁₀ value is preferably less than 1 mm, in particular 0.75 mm and very particularly preferably less than 0.5 mm.

Preferred d ₉₀ values are less than 30 mm and in particular less than 20 mm and very particularly preferably less than 10 mm.

Determination of the particle size distribution:

The particle size distribution was divided into different sieve fractions using a standard sieve set (analytical sieves according to DIN 4188) and these were weighed out. For example, d ₅₀ = 1 mm means that 50% by weight of the sample has a particle size less than or equal to 1 mm.

The inventive method is preferred for the homo- and copolymerization of trioxane applied. As a monomer a) but in principle any monomer described above, for example Tetroxane or (para) formaldehyde can be used.

The Monomers, for example trioxane, are preferably in the molten state Condition added, generally at temperatures of 60 to 120 ° C.

Preferably is the temperature of the reaction mixture at the dosage 62 to 114 ° C, in particular 70 to 90 ° C.

The If appropriate, molecular weights of the polymer can be determined by in the (trioxane) polymerization conventional regulator d) to the desired Values are set. The regulators are acetals or formals monohydric alcohols, the alcohols themselves and acting as chain transfer agents small amounts of water whose presence usually never Completely avoid, in question. The regulators are used in quantities of 10 to 10,000 ppm, preferably from 100 to 1,000 ppm.

When Initiators b) (also called catalysts) are the in the (trioxane) polymerization usual cationic starter used. Proton acids are suitable, such as fluorinated or chlorinated alkyl and arylsulfonic acids, e.g. perchloric acid, trifluoromethanesulfonic or Lewis acids, such as. Tin tetrachloride, arsenic pentafluoride, phosphoric pentafluoride and boron trifluoride and their complex compounds and salt-like Compounds, e.g. Boron trifluoride etherates and triphenylmethylene hexafluorophosphate. The catalysts (initiators) are used in amounts of about 0.01 to 1,000 ppm, preferably 0.01 to 500 ppm and in particular 0.01 used up to 200 ppm. In general, it is recommended that the catalyst in dilute Add form, preferably in concentrations of 0.005 to 5 Wt .-%. As a solvent therefor can inert compounds such as aliphatic, cycloaliphatic hydrocarbons e.g. Cyclohexane, halogenated aliphatic hydrocarbons, glycol ethers etc. are used. Particularly preferred is triglyme as a solvent (Triethylene glycol dimethyl ether).

monomers a), initiators b), cocatalyst c) and optionally regulator d) can in any way premixed or separated from each other Polymerization reactor are added. Furthermore, the Components a), b) and / or c) for stabilizing sterically hindered Phenols contain as described in EP-A 129369 or EP-A 128739.

Around To minimize the proportion of unstable end groups, it has proven to be proved advantageous the initiator b) in the controller d) before its addition to the monomer a) and optionally comonomer a) to solve.

For greater flexibility in the desired M _{w of} the POM polymer, it has proved to be advantageous proved the controller d) to dissolve small amounts of solvent and then mix with the monomers or comonomers and metered.

In a particularly preferred embodiment the polymerization is carried out as precipitation polymerization (depending by degree of solubility the individual components also as suspension polymerization markable) in a solvent carried out, in which the resulting polyoxymethylene homo- or copolymer largely insoluble is. Under "largely" insoluble be understood that from a degree of polymerization of at least 4, the polymer precipitates.

When solvent in particular inert compounds are used, for example aliphatic hydrocarbons such as propane, butane, pentane, iso-octane, n-hexanes, n-heptane, n-octane, isooctane and cycloaliphatic hydrocarbons such as cyclohexane or cycloheptane, as well as cyclopentane, which optionally Can carry heteroatoms as substituents.

When aromatic hydrocarbons are those which are suitable at least 6 to 30 carbon atoms, with nitrobenzene, toluene, benzene preferred are.

When further suitable halogenated hydrocarbons are dichloromethane, Chloroform, dichloroethane and trichloroethane.

Further are ethers such as dioxane or THF and triglyme (triethylene glycol dimethyl ether) as inert solvent suitable.

The solvent preferably has temperatures at the beginning of the reaction (metered addition) from 50 to 250 ° C preferably 55 to 130 and in particular 60 to 120 ° C on. The Addition of the cocatalyst c) is preferably carried out after addition the monomers a), or before the addition of the catalyst b).

Preferably, at the beginning of the reaction under inert gas conditions, preferably under N ₂ , worked at pressures up to 5, preferably up to 2 bar abs.

• 1. aliphatische Alkohole mit 2 bis 20 C-Atomen, wobei t-Amylalkohol, Methanol, Ethanol, Propanol, Butanol, Pentanol, Hexanol usw. bevorzugt sind,
• 2. aromatische Alkohole mit 2 bis 30 C-Atomen, wobei Hydrochinon bevorzugt ist,
• 3. halogenierte Alkohole mit 2 bis 20 C-Atomen, wobei Hexafluorisopropanol bevorzugt ist,
• 4. ganz besonders bevorzugte Alkohole c) sind Glykole jeder Art, wobei Diethylenglykol und Triethylenglykol besonders bevorzugt sind,
• 5. Von den aliphatischen Dihydroxyverbindungen werden Diole mit 2 bis 6 Kohlenstoffatomen, insbesondere 1,2-Ethandiol, 1,3-Propandiol, 1,4-Butandiol, 1,6-Hexandiol. 1,4-Hexandiol, 1,4-Cyclohexandiol, 1,4-Cyclohexandimethanol und Neopentylglykol oder deren Mischungen bevorzugt.

Alcohols of any type are used as cocatalysts according to the invention. Here are some preferred species:

• 1. aliphatic alcohols having 2 to 20 C atoms, with t-amyl alcohol, methanol, ethanol, propanol, butanol, pentanol, hexanol, etc. being preferred,
• 2. aromatic alcohols having 2 to 30 carbon atoms, with hydroquinone being preferred,
• 3. halogenated alcohols having 2 to 20 carbon atoms, hexafluoroisopropanol being preferred,
• 4. very particularly preferred alcohols c) are glycols of any type, with diethylene glycol and triethylene glycol being particularly preferred,
• 5. Of the aliphatic dihydroxy compounds are diols having 2 to 6 carbon atoms, in particular 1,2-ethanediol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol. 1,4-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol and neopentyl glycol or mixtures thereof.

The Residence time for the polymerization in the solvent (Precipitation) is preferably 0.1 to 240 minutes, in particular 5 to 120 minutes. The polymerization is preferably up to a conversion of at least 30%, in particular more than 60% led. Under cheap Conditions can also be sales from 90% and above achieve quantitative sales up to 100% are well reproducible.

in the Generally, a driving has proven to be a pressure at the starting phase of the polymerization from 4 bar abs to 10 bar abs, preferably 5 bar abs to 7 bar abs sets.

Preferably will be followed directly the polymerization mixture deactivates the polymerization mixture, preferably without a phase change takes place.

The Deactivation e) of the catalyst residues usually takes place Addition of deactivators e) to the polymerization melt. suitable Deactivators are e.g. Ammonia, aliphatic and aromatic amines, basic salts, such as soda and borax. These are usually the polymers are added in amounts of preferably up to 1 wt .-%.

The organic compounds of the (alkaline) alkali metals, preferably of sodium, include the corresponding salts of (cyclo) aliphatic, araliphatic or aromatic carboxylic acids preferably up to 30 carbon atoms and preferably 1 to 4 carboxyl groups. Examples are: alkali metal salts of formic, acetic, propionic, butyric, isobutyric, caprylic, stearic, cyclohexanecarboxylic, succinic, adipic, suberic, 1,10-decanedicarboxylic, 1,4-cyclohexanedicarboxylic, terephthalic, 1,2,3-propanetricarboxylic, 1,3,5-cyclohexane tricarboxylic acid, trimellitic acid, 1,2,3,4-cyclopentanetetracarboxylic acid, pyromellitic acid, benzoic acid, substituted benzoic acids, dimer acid and trimer acid, and neutral and partially neutral montan wax salts or montan wax ester salts (montanates). Salts with different acid residues, such as alkali-paraffin, alkali-olefin and alkali arylsulfonates or phenolates and alcoholates such as methanolates, ethanolates, glycolates, can be used according to the invention.

Prefers are sodium salts of mono and polycarboxylic acids, especially the aliphatic mono- and polycarboxylic acids, preferably those having 2 to 18 C atoms, in particular having 2 to 6 C atoms and up to four, preferably up to two carboxyl groups, as well as Sodium alcoholates with preferably 2 to 15, in particular 2 to 8 C atoms used. Examples of particularly preferred representatives are sodium acetate, sodium propionate, sodium butyrate, sodium oxalate, Sodium malonate, sodium succinate, sodium methoxide, sodium ethanolate, Natirumglykonat. Very particular preference is given to sodium methoxide, which is particularly advantageous in an amount of 1-5 times equimolar used for the component b) is used. It can too Mixtures of various (alkaline) alkali metal compounds used become.

Farther alkaline earth metal alkyls are preferred as deactivators e), which 2 bis Have 30 C atoms in the alkyl radical. As particularly preferred metals Li, Mg and Na may be mentioned, wherein n-Butyllithium is particularly preferred.

Then you can the resulting polymer with inert solvent, for example Acetone or cyclohexane are washed and with suitable devices of solvent separated, optionally cooled become.

By the driving style according to the invention receives a compact, powdery one Granules, whereby the emergence of coarse parts according to the state the technique is avoided.

The according to the inventive method available Polyoxymethylene has a low residual content of cyclic ethers (Trioxane) and high uniformity in terms of granule particle size distribution and molecular weight the discharged polyoxymethylene on.

Then you can the corresponding Polyoxymethylenpolymerisat with conventional Additives such as stabilizers, rubbers, fillers, etc. in usual Be further processed.

Examples

Experimental setup I:

• 4I HWS vessel, oil bath, anchor stirrer, ball cooler, measurement the internal temperature with PT 100,
• stirring speed: 200 rpm
• Procedure: Cyclohexane was initially charged and stirred up Heated to 68 ° C. Trioxane and butanediol formal were then added and the polytemperature to 60 ° C set. Subsequently became the catalyst solution closed in 1 h.
• 1 h after the end of the catalyst feed was stabilized with BuLi, Stirred for 30 min and mixed with 800 g of acetone, cooled and filtered.

The Results are summarized in Table 1.

Experimental setup II:

Trioxane polymerization in the 2I pressure vessel

In an inerted 2 l (3 l) steel kettle was added cyclohexane (CH 2) over the Line (control over flow meter) submitted. Thereafter, the boiler was heated (T = 70 ° C) and the stirrer activated (stirrer speed 200 rpm). From the heated pot was the desired amount Trioxane pumped. The amount was weighed using a balance on the the jug stands, measured. Ratio CH: trioxane = 1: 1 (each 435 g).

It was then the comonomer (BuFo) added (3.6 wt .-% relative on trioxane). If desired, was a regulator (MTBE) or co-catalysts / accelerators and a fixed time (1 min to 30 min), the catalyst is metered.

The Starting temperature was 80 ° C up to 110 ° C, a nitrogen pressure of 2 bar was set before the polymerization. After the metered addition, most polymerizations became active Temperature rise from 5 to 20 ° C observed. The pressure in the boiler rose up to 7 bar.

To a total reaction time (including cat dosage) of 2 h (BF3: 3 h) the reaction was stopped by heating to room temperature chilled was and a pressure equalization was made. The kettle was expanded. The suspension was filtered off by means of a suction filter, the POM washed with cyclohexane, then dried and weighed.

The results are summarized in Table 2.

Claims (9)

A process for the preparation of polyoxymethylenes by polymerization of the monomers a) in the presence of cationic initiators b) and cocatalysts c) and optionally in the presence of regulators d), the polymer is optionally deactivated and then separated, characterized in that it is used as cocatalyst c) alcohols. Method according to claim 1, characterized in that that the polymerization is carried out at temperatures of 50 to 250 ° C. Process according to claims 1 or 2, characterized that as cocatalyst c) aliphatic or aromatic alcohols or glycols or mixtures thereof, which heteroatoms as substituents. Process according to claims 1 to 3, characterized that as cocatalyst c), hexafluoroisopropanol, t-amyl alcohol, Diethylene glycol, triethylene glycol, 1,2-ethylene glycol, 1,3-propanediol, 1,4-butanediol or mixtures thereof. Process according to claims 1 to 4, characterized that as deactivator e), ammonia, aliphatic amines, aromatic Amines, basic salts, organic (alkaline) alkaline compounds, (alkaline) alkaline alkyls or mixtures thereof. Process according to claims 1 to 5, characterized that you are in a solvent works in which the resulting polyoxymethylene homo- or copolymerizate largely insoluble is. Process according to claims 1 to 6, characterized that inert solvent used in the polymerization. Process according to claims 1 to 7, characterized that as a solvent Hydrocarbons are used which carry halogen substituents can. Process according to claims 1 to 8, characterized that the cocatalyst c) is used in quantities of 10 to 5000 ppm.