EP1819745A1

EP1819745A1 - Method for producing polyoxymethylenes

Info

Publication number: EP1819745A1
Application number: EP05815897A
Authority: EP
Inventors: Jens Assmann; Knut ZÖLLNER; Johannes Heinemann; Elmar STÖCKELMANN; Achim Stammer
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2004-11-30
Filing date: 2005-11-28
Publication date: 2007-08-22
Also published as: KR20070086796A; JP2008521950A; WO2006058679A1; JP5502280B2; DE102004057867A1; CN101068840A; KR101246508B1; US7863393B2; US20080167439A1; CN101068840B

Abstract

The invention relates to a method for producing polyoxymethylenes by the polymerisation of monomers in the presence of cationically active initiators and optionally in the presence of chain transfer agents and by the subsequent deactivation and isolation of the polymers. Said method is characterised in that the polymerisation takes place in a tubular reactor comprising static mixing elements, said reactor having a mixing zone, a polymerisation zone and a deactivation zone and that the diameter of the tubular reactor in the mixing zone is < 90 % of the diameter in the polymerisation zone.

Description

Process for the preparation of polyoxymethylenes

description

The invention relates to an improved process for the preparation of polyoxymethylenes and the POM polymers obtainable in this process.

The melt polymerization of POM in a tubular reactor is known. For example, Tubular reactors of different design: on the one hand with "flowing transition", ie geometrically not excellent mixing zones (EP-

A 638 599, EP-A 638 357), on the other hand with spatial separation between reaction and termination zone (EP-A 80 656). Both methods are approaches to ensure adequate mixing of different flow rates or different viscous fluids.

A particular problem in the melt polymerization is the addition of the terminator. Here, a low molecular weight component in very small amounts (inorganic salts or organic bases) must be mixed effectively with the (highly) viscous polymer melt.

The prior art is mainly used to solve the problem of the design of the reactor:

Optimization of the residence time in the demolition zone (EP-A 638 599, EP-A 638 357) - The installation of bottlenecks and the variation of the flow rate in the reactor (EP-A 80 656).

The terminating agents are always introduced according to the prior art with an auxiliary (water, alcohols but also other solvents) in the reaction mixture, see, e.g. DE-A 37 03 790.

In the case of organic termination reagents, it is in any case an impurity in the polymer melt, i.e. the demolition agent introduces new structural units into the final product. Additional structural units may be introduced if the organic terminator is also present in a solvent. The stability of the chains and color properties are disadvantageous.

In the case of inorganic quenching reagents, the amount introduced is ideally matched to the amount of initiator, since excess base (no vapor pressure) can not be removed. You can also work in excess. In either case, it is desirable to minimize the amount of terminator in order to improve product quality.

In addition, it is desirable to minimize the amount of foreign substances (solvents, low molecular weight liquids).

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:

Optimization of the addition and more homogeneous distribution of the demolition agent in the

Polymer melt, improved quality of the final product,

Reduction of impurities in the synthesis, - Optimization of the residence time in the demolition zone of the reactor, better reproducibility of the polymer properties, aliphatic solvents improve the color of the polymer, aprotic solvents achieve more stable end groups of the polymer.

Another object was to produce polyoxymethylene homopolymers or copolymers which contain the lowest possible levels of low molecular weight POM.

Accordingly, a process for the preparation of polyoxymethylenes by polymerization of the monomers a) in the presence of cationic initiators b) and optionally in the presence of regulators c) and subsequent deactivation and separation of the polymer was found, characterized in that the polymerization in a tubular reactor with static Performs mixing elements, which has a mixing zone, a polymerization zone and a deactivation zone and the diameter of the tubular reactor in the mixing zone is <90% of the diameter in the polymerization zone.

Preferred embodiments are given in the dependent claims.

Furthermore, POM polymers were found which have an asymmetric molar mass distribution.

The process may in principle be performed on any high mixing efficiency reactor, such as, for example, trays, ploughshare mixers, tubular reactors, lump reactors, kneaders, stirred reactors, extruders and belt reactors.

Suitable reactors include: Kenics (Chemineer Inc.); interfacial surface generator lSG and low pressure drop mixer (Ross Engineering Ine); SMV, SMX, SMXL, SMR (Sulzer Koch-Glitsch); Inliner series 45 (Lightnin Inc.); CSE mixer (Fluentec Georg AG).

The resulting POM polymers are known in the art 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 prepared by the polymerization of monomers a) such as formaldehyde or trioxane, preferably in the presence of suitable catalysts.

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 0.01 to 20, in particular 0.1 to 10 mol% and very particularly preferably 0, 5 to 3 mol% of recurring units.

where R ¹ to R ^{4 are} independently a hydrogen atom, a C ₁ -Ws 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-dioxane and 1, 3-dioxepane as cyclic ethers and linear oligo- or polyformals such as polydioxolane or polydioxepan called comonomers. 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

and or

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

Preferred monomers of this type are ethylene diglycide, 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 diol having 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.

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.sub.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 nonuniformity (M _w / M _n ) of from 2 to 15, preferably from 3 to 12, particularly preferably from 3.5 to 9. The measurements are generally carried out by (GPC) SEC (size exclusion The M _n value (number average molecular weight) is generally determined by (GPC) SEC (size exclusion chromatography).

The POM polymers obtainable by the process preferably have a unimodal molecular weight distribution, the low molecular weight fraction being low.

The polyoxymethylene homopolymers or copolymers have in particular quotients of the d ₅₀ / d ₁₀ values (based on M _w ) of 2.25 to 5.5, preferably of 2.75 to 5 and in particular 3.2 to 4.5. The quotient of the dgo / dsr values (based on M _w ) is preferably from 1.25 to 3.25, preferably from 1.75 to 2.75 and in particular from 2 to 2.5. The POM polymers have very low proportions of low molecular weight fractions and preferably an asymmetric, unimodal distribution curve, the difference of the abovementioned quotients d ₅₀ / d ₁₀ to d ₁₀ / d ₅ o being at least 0.25, preferably 1 to 3 and in particular 1 , 0 to 2.3.

Molecular Mass Determination by GPC (Gel Permeation Chromatography):

Eluent: hexafluoroisopropanol + 0.05% trifluoroacetic acid-Kalliumsalz Column temperature: 40 ⁰ C Flow rate: 0.5 mumin

Detector: Differential Refractometer Agilent G1362A.

The calibration was carried out with narrowly distributed PMMA standards of the company PSS with molecular weights of M = 505 to M = 2,740,000. Elution regions outside this interval were estimated by extrapolation.

As a rule, a d ₅₀ value is understood by the skilled person to mean the value at which 50% of the polymer has a smaller M _w and correspondingly 50% has a larger M _w .

The crude polyoxymethylenes obtainable by the process according to the invention preferably have a residual formaldehyde content in accordance with VDA 275 in the granules of not more than 3%, preferably not more than 1%, preferably not more than 0.05%.

The process of the invention is preferably used for the homo- and the copolymerization of trioxane. As monomer a), however, it is possible in principle to use any of the monomers described above, for example tetroxane or (para) formaldehyde.

The monomers, for example trioxane, are preferably metered in the molten state, generally at temperatures of 60 to 180 ^° C.

Preferably, the temperature of the reaction mixture at the dosage 62 to 170 ⁰ C, in particular 120 to 160 ⁰ C.

The molecular weights of the polymer can optionally be adjusted to the desired values by the regulators c) customary in the (trioxane) polymerization. Suitable regulators are acetals or formals of monohydric alcohols, the alcohols themselves and the small amounts of water acting as chain transfer agents whose presence generally can never be completely avoided. The regulators are used in amounts of from 10 to 10,000 ppm, preferably from 50 to 5,000 ppm. Initiators b) (also referred to as catalysts) are the cationic initiators customary in (trioxane) polymerization. Proton acids are suitable, such as fluorinated or chlorinated alkyl- and arylsulfonic acids, eg perchloric acid, trifluoromethanesulfonic acid or Lewis acids, for example tin tetrachloride, arsenic pentafluoride, phosphoric pentafluoride and boron trifluoride and their complex compounds and salt-like compounds, for example boron trifluoride etherates and triphenylmethylene hexafluorophosphate. The catalysts (initiators) are used in amounts of about 0.001 to 1000 ppm, preferably 0.01 to 500 ppm and in particular from 0.05 to 10 ppm. In general, it is advisable to add the catalyst in dilute form, preferably in concentrations of 0.005 to 5 wt .-%. Suitable solvents for this purpose are inert compounds such as aliphatic, cycloaliphatic hydrocarbons such as cyclohexane, halogenated aliphatic hydrocarbons, glycol ethers, etc. can be used. Particular preference is given to triglyme as solvent (triethylene glycol dimethyl ether) and 1,4-dioxane.

Monomers and comonomers a), initiators b) and, if appropriate, regulator c) can be premixed in any desired manner or else added separately to the polymerization reactor. In addition, the components a), b) and / or c) may contain sterically hindered phenols for stabilization as described in EP-A 129369 or EP-A 128 739.

In order to minimize the proportion of unstable end groups, it has proved to be advantageous to dissolve the initiator b) in the regulator c) before it is added to the monomer a) and optionally comonomer a).

It has proven to be advantageous to meter the initiator at different points in the tubular reactor. The preferred minimum distance is 1 D (D = diameter of the reactor at the given point).

The polymerization is carried out in a tubular reactor which has a mixing zone, a polymerization zone and a deactivation zone.

The diameter of the tube reactor in the mixing zone is according to the invention <90%, preferably 10 to 90%, preferably 10 to 70%, in particular 10 to 60% of the diameter of the polymerization zone, u.z. each related to the largest diameter in the polymerization zone.

In particular, the number of webs of the static mixing elements in the mixing zone is 0 to 500%, preferably 0 to 300% and in particular 0 to 100% higher than in the polymerization zone. In a further embodiment of the method according to the invention, the mixing zone can be divided into sections of different diameters. Preferably, the diameter of the entire mixing zone in the reactor is the same.

The residence time in the mixing zone is preferably from 1 to 300 seconds, in particular 5 to 60 seconds.

The shear in the reactor in the mixing zone is preferably 5 to 1000, preferably 10 to 750 and in particular 20 to 500 1 / s.

The shear in the static mixer is calculated according to:

^{T ~} D

y: shear [1 / s] k: manufacturer constant for the static mixer

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

The viscosity is calculated according to: ApD ² η =

NeReLv

η: viscosity

Δp: Pressure drop across the mixing element D: Diameter of the static mixer

NeRe: static mixer index - Newton Reynolds number

L: length of the static mixer

V: flow velocity in the mixer

The residence time for the polymerization is preferably 0.1 to 40 minutes, in particular 1 to 20 minutes. The polymerization is preferably carried out to a conversion of at least 30%, in particular more than 60%.

In general, a procedure has proven in which one sets a pressure in the polymerization of 5 to 200 bar abs, preferably 10 to 100 bar abs.

In a further embodiment of the method according to the invention, the polymerization zone can be divided into sections of different diameters, in particular 2 to 10 sections, preferably 2 to 5 sections. The smallest diameter is to the largest diameter preferably 20 to 100%, in particular 30 to 90% and particularly preferably 45 to 75%.

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

According to the invention, the polymerization mixture is deactivated directly after the polymerization, preferably without a phase change taking place.

The deactivation of the catalyst residues is usually carried out by adding at least one deactivator d).

Suitable deactivators are e.g. Ammonia, aliphatic and aromatic amines, basic salts such as soda and borax. These are usually added to the polymers in amounts of preferably up to 1% by weight.

The organic compounds of the (alkaline) alkali metals, preferably of the sodium, include the corresponding salts of (cyclo) aliphatic, araliphatic or aromatic carboxylic acids having preferably up to 30 carbon atoms and preferably 1 to 4 carboxyl groups. Examples thereof are: alkali metal salts of formic acid, acetic acid, propionic acid, butyric acid, isobutyric acid, caprylic acid, stearic acid, cyclohexanecarboxylic acid, succinic acid, adipic acid, suberic acid, 1,10-decanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, 1,2,3- Propanetricarboxylic acid, 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). Also salts with other acidic residues, such. Alkali-paraffin, alkali-olefin and alkali arylsulfonates or else phenolates and also alcoholates, such as e.g. Methanolates, ethanolates, glycolates can be used according to the invention.

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

Furthermore, alkaline earth metal alkyls are preferred as deactivators d) which have 2 to 30 C atoms in the alkyl radical. As particularly preferred metals called its Li, Mg and Na, with n-butyllithium being particularly preferred.

Preferred deactivators d) are those of the formula I.

R '

/

2 ^R

wherein R ¹ , R ³ , R ⁴ and R 5 are independently hydrogen or a Ci-C ₁₀ alkyl group and

R ^{2 is} hydrogen or a dC ₁₀ alkyl group or OR ⁵ .

Preferred radicals R ¹ to R ⁵ are, independently of one another, hydrogen or a C ₁ -C ₄ -alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, s-butyl, t-butyl.

Particularly preferred deactivators d) are substituted N-containing heterocycles, in particular derivatives of piperidine, with triacetonediamine (4-amino-2,2,6,6-tetramethylpiperidine) being particularly preferred.

The deactivator is, based on the throughput of trioxane in amounts of 0.001 to 25 ppm, preferably 0.01 to 5 ppm, in particular 0.05 to 2 ppm added. The deactivator is preferably present diluted in one of the following carrier / solvent. The concentration of the deactivator in the carrier / solvent is 0.001 to 10%, preferably 0.01 to 5%, in particular 0.05 to 2%, very particularly preferably 0.1 to 1%.

The diameter of the tube reactor in the deactivation zone is according to the invention <95%, preferably from 20 to 95%, in particular from 30 to 90% and particularly preferably from 50 to 85% of the diameter in the polymerization zone.

In particular, the number of webs of the static mixing elements in the deactivation zone is 0 to 500%, preferably 50 to 300% and in particular 50 to 200% higher than in the polymerization zone. In a further embodiment of the method according to the invention, the deactivation zone can be divided into sections of different diameters, in particular from 1 to 5 sections, preferably 2 sections. The diameter of the smallest portion is in this case 20 to 100%, preferably 30 to 90% of the diameter of the largest portion, and in particular 50 to 90%.

In the particularly preferred embodiment of the deactivation zone in two sections, the first section contains a 20 to 500, preferably 50 to 300 and in particular 50 to 200% higher number of bars than in the polymerization zone and the second section a -100 to 500 , -100 to 300 and preferably -100 to 200% higher number of bars than in the polymerization zone.

The shear in the deactivation zone is preferably 0.1 to 500, preferably 1 to 100 and in particular 3 to 75 1 / s. In the preferred embodiment in several sections (1 to 5, preferably 2), the shear in the smallest diameter section, preferably the 1st section following the polymerization zone, is 10 to 200, preferably 15 to 100 and more preferably 20 to 75 1 / s. In the following sections according to the above values.

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

The residence time in the deactivation zone is preferably from 0.5 to 20 minutes, in particular from 1 to 10 minutes.

The deactivator d) is preferably added in an aprotic, non-aromatic solvent, for example the abovementioned monomers and comonomers, such as dioxolane, trioxane, butanediol formal, ethylene oxide or oligomeric to polymeric polyacetals.

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

Carrier substances which have the same structural units which are present in the particular POM polymer to be produced are preferably suitable. These are in particular the monomers a) listed above and oligomeric to polymeric polyoxymethylene or polyacetals.

The preferably liquid addition takes place at temperatures of 140 to 220 ⁰ C. If oligomeric or polymeric POM polymers are used as carrier substances, addition in liquid form at temperatures of 160 to 220 ^° C. is likewise preferred. Such polymers may optionally contain conventional additives. For metering such melts of the carrier substances which contain the deactivators d), devices such as side extruder, plug screw, melt pump, etc. are preferably used.

Subsequently, as a rule, the resulting polymer is transferred to a degassing device.

Subsequently, the corresponding Polyoxymethylenpolymerisat with conventional additives such as stabilizers, rubbers, fillers, etc. in usually weitervera.r- beitet.

By the driving according to the invention, the stopping agent (deactivator) can be better dosed and mixed.

The POM obtainable by the process according to the invention has quality advantages such as improved thermal stability, color, lower chain degradation, good flowability and mechanics.

According to the procedure of the invention, it is also possible to produce polyacetals with multimodal, preferably bimodal molecular weight distributions. Of the. e.g. Trioxane stream is polymerized in parallel tubular reactors (at least 2) and fractions of different molar mass are formed, which are then mixed. In the separate strands, the desired polymer can be prepared by one or a combination of parameters, which is then mixed again before or after the mixing zone with the terminating agent, after the deactivating zone or in the degassing step or on the extruder. It is also possible to mix substreams at said locations.

Inventive example

A mixture of 96.495 wt .-% liquid trioxane, 3.5 wt .-% dioxolane and 0.005 wt .-% methylal was heated to 160 ⁰ C and pumped into a tubular reactor with static mixers (4-Stegler and 8 Stirler).

The tubular reactor consisted of a reaction zone and a termination zone. The reaction zone again consisted of 3 sections with different diameters (1st reactor shot 12 mm, 2nd reactor shot 15 mm, 3rd reactor shot 27 mm). The demolition zone consisted of 2 sections with different diameters (1st reactor shot 8-flight 17 mm, 2nd reactor shot 4-flight 27 mm). The pipeline between reactor and degassing also functioned as a demolition zone.

By adding X ppm perchloric acid (as 0.01 wt .-% solution in 1, 4-dioxane) started the polymerization, the pressure at the outlet of the reactor via a control valve set and is 20 bar. The temperature in the reaction zone (165 ° C) and the termination zone (195 ⁰ C) is controlled by a double jacket.

After a residence time of 2 minutes, triacetonediamine was metered in as a terminating agent (as a 0.1% strength by weight solution in 1,3-dioxolane) in the demolition zone of the reactor and mixed in via a static mixer so that the terminating agent was in 10 times the weight - surplus to perchloric acid was present.

After a further residence time of 3 min, the product (crude POM) was released via a control valve into a degassing pot to a pressure of 3 bar, whereby the volatile components were separated from the polymer melt. Residues of trioxane and formaldehyde remained in the polymer melt.

The product was discharged and subjected to GPC.

Comparative Example 2.3

A mixture of 96.495 wt .-% liquid trioxane, 3.5 wt .-% dioxolane and 0.005 wt .-% Methyia! was heated to 160 ⁰ C and pumped into a tube reactor with static see blenders.

The tube reactor consisted of a smooth tube equipped with metering devices for the initiator and the stopper. The metering devices were mounted at an angle of 60 ° to the flow direction. The diameter of the tube is 12 mm. Static mixing elements were added to mix in the initiator and the terminator. The temperature in the reactor is controlled by a double jacket in the reaction zone (165 ° C) and the termination zone (195 ° C).

By adding X ppmw perchloric acid (as 0.01 wt .-% solution in 1, 4-dioxane) started the polymerization, the pressure in the reactor was P bar.

After a residence time of 2 minutes, triacetonediamine was metered in as a terminating agent (as a 0.1% strength by weight solution in 1,3-dioxolane) in the demolition zone of the reactor and mixed in via a static mixer, so that the terminator in 10 times the substance - surplus to perchloric acid was present. After a further residence time of 3 min, the product (crude POM) was released via a control valve into a degassing pot to a pressure of 3 bar, whereby the volatile components were separated from the polymer melt. Residues of trioxane and formaldehyde remained in the polymer melt.

The product was discharged and subjected to GPC.

With 0.05 ppmw amount of starter polymerization was carried out only in the reactor according to the invention, in Comparative Example 1, only a turbidity of the trioxane was observed. A 20-fold increase in the starter concentration in the comparative example led to the polymerization, but only low molecular weight product is obtained. By contrast, the tube reactor according to the invention makes it possible to produce polyacetals of high molecular weight with extremely low starter quantities.

Claims

claims

1. A process for the preparation of polyoxymethylenes by polymerization of the monomers a) in the presence of cationic initiators b) and optionally in the presence of regulators c) and subsequent deactivation and separation of the polymer, characterized in that the polymerization in a tubular reactor with static Performs mixing elements, which has a mixing zone, a polymerization zone and a deactivation zone and the diameter of the tubular reactor in the mixing zone is <90% of the diameter in the polymerization zone.

2. The method according to claim 1, characterized in that the diameter of the deactivation zone of the reactor is <95% of the diameter of the polymerization zone.

3. Process according to claims 1 or 2, characterized in that the deactivation zone is made up of 1 to 5 sections.

4. Process according to claims 1 to 3, characterized in that the diameter of the smallest section in the deactivation zone is 30 to 95% of the diameter of the largest section.

5. Process according to claims 1 to 4, characterized in that the number of lands in the static mixing elements in the mixing zone is 0 to 500% higher than in the polymerization zone.

6. Process according to claims 1 to 5, characterized in that the number of lands in the static mixing elements in the deactivation zone is 20 to 500% higher than in the polymerization zone.

7. Process according to claims 1 to 6, characterized in that the deactivator is added in an aprotic, non-aromatic solvent.

8. Process according to claims 1 to 7, characterized in that the deactivator d) is added in a carrier substance with Etherstruktureinheiten in the polymerization mixture.

9. Process according to claims 1 to 8, characterized in that the carrier has the same structural units which are contained in the polyoxymethylene polymer produced.

10. The method according to claims 1 to 9, characterized in that the carrier substance used is an oligomeric or polymeric polyoxymethylene.

11. The method according to claims 1 to 10, characterized in that the deactivator, based on the throughput of trioxane, in amounts of 0.001 to

25 ppm is added.

12. Polyoxymethylene homopolymers or copolymers obtainable in accordance with the process conditions of claims 1 to 11, wherein the quotient of d ₅ o / d ₁₀ values (based on M _w ) is from 2.25 to 5.5.

13. polyoxymethylene homo- or copolymers according to claim 12, wherein the quotient of the dgo / d _5O values (based on M _w ) of 1, 25 to 3.25.

14. Polyoxymethylenhomo- or copolymers, according to claims 12 or 13, wherein the difference of the quotients of d ₅₀ / d ₁₀ to d ₉ o / d ₅ o is at least 0.25.