WO2005012380A1

WO2005012380A1 - Alcohols used as cocatalysts during the production of pom

Info

Publication number: WO2005012380A1
Application number: PCT/EP2004/007865
Authority: WO
Inventors: Burkhardt Dames; Johannes Heinemann
Original assignee: Basf Aktiengesellschaft
Priority date: 2003-08-04
Filing date: 2004-07-15
Publication date: 2005-02-10
Also published as: DE10335959A1

Abstract

Disclosed is a method for producing polyoxymethylene by performing precipitation polymerization of monomers (a) in the presence of cationically active initiators (b) and cocatalysts (c) and, optionally, in the presence of modifiers (d), optionally deactivating and then separating the polymer. The inventive method is characterized in that alcohols are used as a cocatalyst (c).

Description

Alcohols as cocatalysts in POM production

description

The invention relates to an improved process for the preparation of polyoxymethylene.

It is known that oxymethylene polymers can be prepared by continuous bulk polymerization of the monomers in the presence of cationically active initiators. This polymerization is often carried out in kneaders or extruders. The temperature can be controlled so that the resulting oxymethylene polymer is either in solid form (DE-A 1 161 421, DE-A 1 495228, DE-A 1 720358, DE-A 3 018898) or as a melt (DE-A 3 147309) occurs. The processing 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.

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

The production by means of suspension or precipitation polymerization with cationic initiators is generally known. In particular, the resulting polymer should not be soluble in the solvent used here, so that it can be separated more easily.

In both bulk and precipitation polymerization, the catalysts used are not soluble in these reaction media and must be used in larger amounts and over a longer period of time. This has a disadvantageous effect on the stability of the resulting polymer, which is degraded by such acids. It is therefore essential that as little catalyst as possible is used, but at the same time the reaction time is not significantly extended.

The object of the present invention was therefore to provide an improved method for

To provide production of polyoxymethylenes, which has the following advantages over the prior art:

The neutralization of the products is easier to carry out, the reduction in molecular weight when heated is reduced, the amounts of catalyst (initiator) 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, a process for the preparation of polyoxymethylenes by polymerizing the monomers a) in the presence of cationically active initiators b) and cocatalysts c) and, if appropriate, in the presence of regulators d), the polymer optionally deactivated and subsequently separated, was found, which is characterized in that alcohols used as cocatalyst c).

Preferred embodiments can be found in the subclaims.

In principle, the process can be carried out on any reactor with a high mixing action, such as, for example, trays, ploughshare mixers, tubular reactors, list reactors, kneaders, stirred reactors.

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

In general, these polymers have at least 50 mol% of recurring units - CH ₂ O - in the main polymer chain.

The homopolymers are generally prepared by polymerizing monomers a), such as formaldehyde or trioxane, preferably in the presence of suitable catalysts.

In the context of the invention, polyoxymethylene copolymers are preferred, in particular those which, in addition to the repeating units —CH ₂ O—, 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 to C 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 to C ₄ -Alkyl- or C to C ₄ -haloalkyl substituted methylene group or a corresponding oxymethylene group and n has a value in the range from 0 to 3. Advantageously, these groups can ring opening from cyclic ethers are introduced into the copolymers. Preferred cyclic ethers are those of the formula

where R ¹ to R ⁵ and n have the meaning given above. For example, ethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1,3-dioxane, 1,3-dioxoxane and 1,3-dioxepane may be mentioned as cyclic ethers and linear oligo- or polyformals such as polydioxolane or polydioxepane as comonomers.

Also suitable are oxymethylene terpolymers, for example by reacting trioxane, one of the cyclic ethers described above, with a third monomer, preferably bifunctional compounds of the formula

CΗ— CH - CH ₂ - Z— CH ₂ - CH— CH ₃

and or

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

Preferred monomers of this type are ethylene diglycide, diglycidyl ether and diether from glycidylene and formaldehyde, dioxane or trioxane in a molar ratio of 2: 1 and diether from 2 mol of glycidyl compound and 1 mol of an aliphatic diol with 2 to 8 carbon atoms, such as, for example, the diglycidyl ether 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 CC 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 molecular weights (weight average) M _w in the range from 5,000 to 300,000, preferably from 7,000 to 250,000. POM copolymers with a non-uniformity (M _w / M _n ) from 2 to 15, preferably from 3 to 12, particularly preferably from 4 to 9 are particularly preferred. The measurements are generally carried out using (GPC) SEC (size exclusion chromatography) , The M _n value (number average molecular weight) is generally determined using (GPC) SEC (size exclusion chromatography).

Particularly preferred POM copolymers have a bimodal molecular weight distribution, the low molecular weight fraction having a molecular weight of 500 to 20,000, preferably 1,000 to 15,000 and in area proportions of 1 to 15, preferably 8 to 10% in the case of the distribution graph w (log M) versus log M is present.

The crude polyoxymethylenes obtainable by the process according to the invention preferably have a residual formaldehyde content according to VDA 275 in the granulate of a maximum of 3%, preferably a maximum of 1%, preferably a maximum of 0.05%.

The average particle size (d ₅ o value) (grain size) of the POM polymers is preferably from 0.5 mm to 20, preferably from 0.75 mm to 15 mm and in particular 1 to 7

A d ₅₀ value is generally understood by the person skilled in the art to mean the particle size value, in 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 dio and dgo values.

The d-io 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 grain size distribution:

The particle size distribution was divided into different sieve fractions using a standard sieve set (test 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 of less than or equal to 1 mm. The process according to the invention is preferably used for the homo- and copolymerization of trioxane. Basically, however, any monomer described above, for example also tetroxane or (para) formaldehyde, can be used as monomer a).

The monomers, for example trioxane, are preferably metered in in the molten state, generally at temperatures from 60 to 120 ° C.

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

The molecular weights of the polymer can, if appropriate, be adjusted to the desired values by the regulators d) customary in (trioxane) polymerization. Possible regulators are acetals or formals of monohydric alcohols, the alcohols themselves and the small amounts of water which act as chain transfer agents, the presence of which can generally never be completely avoided. The regulators are used in amounts of 10 to 10,000 ppm, preferably 100 to 1,000 ppm.

Initiators b) (also referred to as catalysts) are the cationic initiators customary in (trioxane) polymerization. Protonic acids such as fluorinated or chlorinated alkyl and arylsulfonic acids, e.g. Perchloric acid, trifluoromethanesulfonic acid or Lewis acids, e.g. Tin tetrachloride, arsenic pentafluoride, phosphoric acid pentafluoride and boron trifluoride as well as 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 from 0.01 to 200 ppm. In general, it is advisable to add the catalyst in dilute form, preferably in concentrations of 0.005 to 5% by weight. Inert compounds such as aliphatic, cycloaliphatic hydrocarbons, e.g. Cyclohexane, halogenated aliphatic hydrocarbons, glycol ethers, etc. can be used. Triglyme is particularly preferred as the solvent (triethylene glycol dimethyl ether).

Monomers a), initiators b), cocatalyst c) and optionally regulator d) can be premixed in any manner or can be added to the polymerization reactor separately. Components a), b) and / or c) can furthermore contain sterically hindered phenols for stabilization, as described in EP-A 129369 or EP-A 128739. In order to minimize the proportion of unstable end groups, it has proven to be advantageous to dissolve the initiator b) in the regulator d) before it is added to the monomer a) and, if appropriate, comonomer a).

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

In a particularly preferred embodiment, the polymerization is carried out as precipitation polymerization (depending on the degree of solubility of the individual components, also known as suspension polymerization) in a solvent in which the resulting polyoxyethylene homo- or copolymer is largely insoluble. The term “largely insoluble” should be understood to mean that the polymer precipitates from a degree of polymerization of at least 4.

Inert compounds are used in particular as solvents, for example aliphatic hydrocarbons such as propane, butane, pentane, iso-octane, n-hexanes, n-heptane, n-octane, iso-octane and cycloaliphatic hydrocarbons such as cyclohexane or cycloheptane and cyclopentane, which may optionally be heteroatoms can wear as substituents.

Suitable aromatic hydrocarbons are those which have at least 6 to 30 carbon atoms, with nitrobenzene, toluene and benzene being preferred.

Dichloromethane, chloroform, dichloroethane and trichloroethane may be mentioned as further suitable halogenated hydrocarbons.

Furthermore, ethers such as dioxane or THF and triglyme (triethylene glycol dimethyl ether) are suitable as inert solvents.

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

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

Alcohols of any kind are used as cocatalysts according to the invention. Here are some preferred types: 1. aliphatic alcohols with 1 to 20 carbon atoms, t-amyl alcohol, methanol, ethanol, propanol, butanol, pentanol, hexanol etc. being preferred,

2. aromatic alcohols with 6 to 30 C atoms, with hydroquinone being preferred, 3. halogenated alcohols with 6 to 20 C atoms, with hexafluoroisopropanol being preferred,

4. very particularly preferred alcohols c) are glycols of all kinds, diethylene glycol and triethylene glycol being particularly preferred,

5. Of the aliphatic dihydroxy compounds are diols with 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 are preferred.

The residence time for the polymerization in the solvent (precipitation polymerization) is preferably 0.1 to 240 min, in particular 5 to 120 min. The polymerization is preferably carried out up to a conversion of at least 30%, in particular more than 60%. Under favorable conditions, sales of 90% and above can also be achieved, quantitative sales of up to 100% are easily reproducible.

In general, a procedure has proven successful in which a pressure in the starting phase of the polymerization of 4 bar abs to 10 bar abs, preferably 5 bar abs to 7 bar abs, is set.

The polymerization mixture is preferably deactivated immediately after the polymerization, preferably without a phase change taking place.

The deactivation e) of the catalyst residues is generally carried out by adding 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 added to the polymers in amounts of preferably up to 1% by weight.

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

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 are preferred 2 to 15, in particular 2 to 8 carbon atoms used. Examples of particularly preferred representatives are sodium acetate, sodium propionate, sodium butyrate, sodium oxalate, sodium immalonate, sodium succinate, sodium methoxide, sodium ethanolate, sodium glyconate. Sodium methoxide is very particularly preferred, which is used particularly advantageously in an amount of 1-5 times equimolar to component b) used. Mixtures of different (earth) alkali metal compounds can also be used.

In addition, alkaline earth alkyls are preferred as deactivators e) which have 2 to 30 carbon atoms in the alkyl radical. Li, Mg and Na may be mentioned as particularly preferred metals, n-butyllithium being particularly preferred.

The resulting polymer can then be washed with inert solvents, for example acetone or cyclohexane, and separated from the solvent using suitable devices, and optionally cooled.

The procedure according to the invention gives compact, powdery granules, the formation of coarse fractions according to the prior art being avoided.

The polyoxymethylene obtainable by the process according to the invention has a low residual cyclic ether content (trioxane) and a high degree of uniformity with regard to the granule particle size distribution and the molecular weight across the discharged polyoxymethylene.

The corresponding polyoxymethylene polymer can then be processed further in the usual manner with conventional additives such as stabilizers, rubbers, fillers, etc. Examples

Experimental setup I:

41 HWS vessel, oil bath, anchor stirrer, ball cooler, measurement of the internal temperature with PT 100,

Stirring speed: 200 U / min

Procedure: Cyclohexane was introduced and heated to 68 ° C. with stirring. Trioxane and butanediol formal were then added and the poly temperature set to 60 ° C. The catalyst solution was then run in in 1 h.

1 h after the end of the catalyst feed, the mixture 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 a 2I pressure vessel

Cyclohexane (CH) was introduced via the line (control via flow meter) into an inertized 2 I (3 I) steel kettle. The boiler was then heated up (T ^: 70 ° C.) and the stirrer activated (stirrer speed 200 rpm). The desired amount of trioxane was pumped in from the heated jug. The amount was measured using a scale on which the jug is standing. CH: trioxane ratio = 1: 1 (435 g each).

The comonomer (BuFo) was then metered in (3.6% by weight, based on trioxane). If desired, a regulator (MTBE) or co-catalyst / accelerator and the catalyst were metered in over a fixed time (1 min to 30 min).

The starting temperature was 80 ° C to 110 ° C, a nitrogen pressure of 2 bar was set before the polymerization. After cat. Dosing, a temperature increase of 5 to 20 ° C was observed in most polymerizations. The pressure in the boiler rose up to 7 bar.

After a total reaction time (including cat. Metering) of 2 h (BF ₃ : 3 h), the reaction was stopped by cooling to room temperature and pressure compensation. The boiler was removed. The suspension was filtered off using a suction filter, the POM was washed with cyclohexane, then dried and weighed.

The results are summarized in Table 2. Table 1

TFMS = trifluoromethanesulfonic acid

Table 2

all experiments started at an initial pressure (nitrogen) of 2 bar TFMS = trifluoromethanesulfonic acid (dissolved in triglyme) (CF ₃ S0 ₂ ) ₂ θ = trifluoromethanesulfonic anhydride (dissolved in cyclohexane) perchloric acid (dissolved in triglyme) HFIP = hexafluoroisopropanol MTBE = methyl tert-Butyl ether temperature means start temperature

Claims

claims

1. Process for the preparation of polyoxymethylenes by polymerizing the monomers a) in the presence of cationically active initiators b) and cocatalysts c) and, if appropriate, in the presence of regulators d), the polymer optionally deactivated and then separated off, characterized in that c) as the cocatalyst Alcohols used.

2. The method according to claim 1, characterized in that one carries out the polymerization at temperatures of 50 to 250 ° C.

3. Process according to claims 1 or 2, characterized in that aliphatic or aromatic alcohols or glycols or mixtures thereof are used as cocatalyst c), which may have heteroatoms as substituents.

4. Process according to claims 1 to 3, characterized in that the cocatalyst c), hexafluoroisopropanol, t-amyl alcohol, diethylene glycol, triethylene glycol, 1, 2-ethylene glycol, 1,3-propanediol, 1, 4-butanediol or uses their mixtures.

5. Process according to claims 1 to 4, characterized in that the deactivator e), ammonia, aliphatic amines, aromatic amines, basic salts, organic (earth) alkali compounds, (earth) alkali alkyls or mixtures thereof are used.

6. Process according to claims 1 to 5, characterized in that one works in a solvent in which the resulting polyoxymethylene homo- or copolymer is largely insoluble.

7. Process according to claims 1 to 6, characterized in that inert solvents are used in the polymerization.

8. The method according to claims 1 to 7, characterized in that the solvent used is hydrocarbons which can carry halogen substituents.

9. The method according to claims 1 to 8, characterized in that the cocatalyst c) is used in amounts of 10 to 5000 ppm.