EP2268684A1

EP2268684A1 - Oxymethylene copolymers, uses thereof, and methods for producing oxymethylene copolymers

Info

Publication number: EP2268684A1
Application number: EP09731583A
Authority: EP
Inventors: Michael Haubs; Michael Hoffmockel; Jürgen LINGNAU; Michael G. Yearwood; Robert Gronner
Original assignee: Ticona GmbH
Current assignee: Ticona GmbH
Priority date: 2008-04-16
Filing date: 2009-04-14
Publication date: 2011-01-05
Also published as: JP2011516702A; WO2009127385A1; CN102007155B; US8133966B2; DE102008018965A1; CN102007155A; US20090270572A1; JP5664868B2; JP2015028185A

Abstract

The invention relates to oxymethylene copolymers having a large part of alkyl ether terminal groups, and hydroxy alkylene terminal groups. Said polymers are characterised by high thermal stability and high hot water resistence. The invention also relates to a method for producing oxymethylene copolymers, according to which the polymerisation of at least one monomer forming a -CH2-O- unit is carried out in the presence of at least one acetal of formaldehyde and at least one initiator of cationic polymerisation, the quantity of initiators of the cationic polymerisation being less than 10-4 mol %, in relation to the quantity of monomers forming -CH2-O- units at the beginning of the polymerisation; starting materials of the polymerisation are selected such that the water and formic acid contents at the beginning of the polymerisation are less than 40 ppm; and the initiator and/or the active polymer chains are deactivated by treating the produced polymer with a protic solvent containing a base.

Description

description

Oxymethylene copolymers and their use, as well as processes for the preparation of oxymethylene copolymers

The present invention relates to novel oxymethylene copolymers having high thermal stability and hot water resistance and their use. Furthermore, the invention relates to a process for the preparation of oxymethylene copolymers.

The preparation of polyoxymethylenes ("POM") is known per se For example, cyclic oligomers of formaldehyde such as 1,3,5-trioxane ("trioxane") or tetraoxocane are polymerized with the aid of cationic initiators. The polymerization can be carried out both in bulk as a precipitation polymerization and in the melt under pressure. After polymerization, the active chain ends are deactivated by addition of basic compounds.

Different methods for deactivating reaction mixtures are already known. These can be classified into processes in which the polymer melt is treated with a basic deactivator, or in processes in which the reaction mixture is dissolved in a solvent containing a basic deactivator. Suitable solvents are e.g. protic compounds, such as methanol, or methanol / water mixtures.

Furthermore, it is known that in the deactivation of the reaction mixture with protic compounds chain scission occurs. This lowers both the molecular weight of the polymers produced and produces unstable hemiacetal chain ends. This leads to oxymethylene homopolymers to complete degradation of such chains, since no oxyalkylene units are present with at least two carbon atoms in the polymer chain. Among oxyalkylene units having at least two carbon atoms in this Description preferably units of the formula - (CH ₂ ) mO- understood, where m is an integer from 2 to 6.

Impurities in the monomers also reduce the molecular weight during the polymerization. Therefore, purified monomers are used. The sum of the protic impurities such as water and formic acid is typically below 40 ppm.

Examples of the deactivation methods described above are described in DE-A-44 36 107, US-A-3,269,988, EP-A-80,656 and GB-A-1, 524,410.

J P-A-04 / 114,003 and JP-A-04 / 145,114 describe the deactivation of the polymerization catalyst in oxymethylene polymer mixtures by adding mixtures of selected oxides and melting the mixture.

It has long been known to increase the stability of oxymethylene polymers by capping the end groups, for example by introducing ether or ester end groups. Examples of these can be found in DE-AS-1, 158,709, US-A-3,998,791, US-A-3,393,179, DE-A-1, 445,255, DE-AS-1, 158,709, US-A-4,097,453 and US Pat. A-3,161,616.

While ester-terminated, capped oxymethylene polymers degrade at elevated temperatures or in basic environments, ether-capped oxymethylene polymers are characterized by very high stability. However, the processes proposed so far for the preparation of these polymers comprise a separate step for capping the polymers (cf., for example, US Pat. No. 3,161,616). However, these oxymethylene polymers do not contain oxyalkylene units having at least two carbon atoms which suffer from thermal and hydrolytic stability. In addition, oxymethylene polymers are known from EP-A-504,405, which in addition to oxymethylene units contain small amounts of oxyalkylene units having at least two carbon atoms, in particular on oxyethylene units, and which have a low content of formyl end groups. The proportion of oxyalkylene units, based on the proportion of oxymethylene units, is 0.07 to 0.5 mol%. Falling below the stated content of oxyethylene units produce polymers with insufficient heat resistance and hot water resistance. These polymers are prepared in the presence of a selected amount of a perfluoroalkyl sulfonic acid (derivative) as a catalyst, and low-water and low-acid monomers are used. The deactivation of the polymerization mixture is carried out by addition of selected crystalline basic adsorbents, for example of oxides or hydroxides of alkali or alkaline earth metals.

The object of the present invention is to provide selected oxymethylene copolymers which are characterized by a very high thermal stability and stability against bases.

Another object of the present invention is to provide a simple process for producing oxymethylene copolymers.

It has now surprisingly been found that stable high molecular weight oxymethylene copolymers by reaction of monomers in the presence of at least one acetal of formaldehyde followed by the

Deactivation with basic compounds in a protic solvent can be prepared if proton acids are used in very small amounts as initiators and if starting products of low water content and low content of formic acid are used. Surprisingly, this produces polymers with high thermal

Stability and with high hot water resistance. Preferably are doing Polymers obtained whose proportion of oxyalkylene groups moves well below the limit specified in EP-A-504,405.

The present invention relates to oxymethylene copolymers containing oxymethylene units and oxyalkylene units having at least two carbon atoms and a proportion of Alkyletherendgruppen and Hydroxyalkylenendgruppen having at least two carbon atoms, wherein the proportion of Alkyletherendgruppen, based on all end groups, at least 80% and the proportion of Hydroxyalkylenendgruppen with at least two carbon atoms, based on all end groups, up to 20%.

Preferred oxymethylene copolymers contain a proportion of oxyalkylene units having at least two carbon atoms, based on the proportion of oxymethylene units, between 0.001 mol% and 0.05 mol%, very particularly preferably between 0.01 mol% and 0.05 mol%.

The oxymethylene copolymers of the invention are further distinguished by no or a very low content of formyl end groups. This is typically between 0.01 to 2% of all end groups. Preference is given to oxymethylene copolymers having a content of formyl end groups of less than 1% of all end groups. Other customary end groups, for example hemiacetal end groups, may optionally still be present in very small amounts, for example in amounts of less than 1%.

Typical oxymethylene copolymers of the present invention are polymers of general formula I.

- (O-CH ₂ ) χ- (OC _m H _2m ) _y - (I), the alkyl ether end groups of the formula -OR ¹ and hydroxyalkylene end groups of the formula -OC _m H ₂ m-OH, and optionally end groups of the formula -OR ² , wherein x is a positive integer, preferably from 10 to 10,000, especially preferably between 300 and 10,000, m is an integer from 2 to 6, preferably 2, y is an integer from 0 to 10, the ratio of y _ar / x _{ar is} between 0.001 and 0.05, where y _{ar is} the arithmetic mean of all Values y in the polymer mixture and x _{ar are} the arithmetic mean of all values x in the polymer mixture,

R ^{1 is} a linear or branched alkyl group, and R ^{2 is} a formyl group -CHO, with the proviso that the proportion of the alkyl ether end groups of the formula -OR ¹ , based on all end groups, is at least 80%, and that Proportion of the hydroxyalkylene end groups of the formula -OC _m H ₂ m -OH, based on all

End groups, up to 20%.

y _ar mean the arithmetic mean of all values y in the polymer mixture and x _ar the arithmetic mean of all values x in the polymer mixture

The mean value x _ar is preferably between 50 and 5000.

R ¹ and R ² are preferably C 1 -C ₆ -alkyl radicals, which are preferably straight-chain.

More preferably, R ¹ and R ^{2 are} independently methyl or ethyl, especially methyl.

The invention further relates to a process for the preparation of the oxymethylene polymers described above, which is characterized by: a) polymerization of at least one -CH ₂ -O- units-forming monomer and at least one oxyalkylene units having at least two carbon atoms forming monomer in the presence of at least one acetal of formaldehyde with at least one protic acid or one of its derivatives as an initiator, wherein the concentration of the initiator is less than 10 ^{" 4} mol%, based on the amount of forming at the beginning of the polymerization -CH ₂ -O units forming monomers, b) use of starting materials of the polymerization, so that the content of water and formic acid at the beginning of the polymerization is less than or equal to 40 ppm , and c) deactivating the initiator and / or the active polymer chains by treating the prepared polymer with basic compounds in a protic solvent.

The invention further relates to the obtainable by this process oxymethylene copolymers.

In step a) of the process according to the invention is a known polymerization of -CH ₂ -O units-forming monomers having at least one oxyalkylene units having at least two carbon atoms forming monomer and optionally further comonomers and / or branching agents. The polymerization can be homogeneous or preferably heterogeneous.

For this purpose, a -CH ₂ -O- units forming monomer and a oxyalkylene units having at least two carbon atoms forming monomer or a mixture of different monomers with protonic acids as initiator of the cationic polymerization and with acetals of formaldehyde as a regulator in a conventional manner. The polymerization can be carried out without pressure or at moderate pressures up to 25 bar, for example at pressures between 1 and 10 bar. The polymerization temperature is preferably below the melting temperature of the resulting polymer.

Typical polymerization temperatures range from 60 to 160 ^° C., preferably from 70 to 140 ^° C.

The molecular weights, characterized as volume melt index MVR, of these polymers can be adjusted within wide ranges. Typical MVR values are from 0.1 to 100 g / 10 min, preferably 1 to 80 g / 10min measured according to EN ISO 1133 at 190 ⁰ C under a load of 2.16 kg.

If desired, small amounts of branching agents can be used. Usually, the amount of branching agent is not more than 1% by weight based on the total amount of the monomer used for producing the oxymethylene polymers, preferably not more than 0.3% by weight. Preferred branching agents are polyfunctional epoxides, glycidyl ethers or cyclic formals.

Preferred chain transfer agents (regulators) are compounds of the formula II

R ³ - (O-CH ₂ ) _q -OR ⁴ (II),

wherein R ³ and R ⁴ independently of one another are linear or branched alkyl radicals, in particular C 1 -C ₆ -alkyl radicals, which are preferably straight-chain.

R ³ and R ⁴ are particularly preferably independently of one another methyl, ethyl, propyl or butyl, in particular methyl.

Particularly preferred chain transfer agents are compounds of formula II wherein q = 1, most preferably methylal. The chain transfer agents are usually used in amounts of up to 20,000 ppm, preferably from 100 to 5,000 ppm, more preferably from 200 to 2,000 ppm, based on the monomer mixture.

Particularly suitable initiators are strong protic acids, such as fluorinated or chlorinated alkyl and arylsulfonic acids, e.g. Trifluoromethanesulfonic acid or derivatives thereof, such as esters or anhydrides of protic acids, in particular trifluoromethanesulfonic anhydride or Trifluormethansulfon- acid esters, such as the alkyl esters, in question. Also suitable are perchloric acid and its esters and protic acids in the presence of their salts.

According to the invention, initiators are those compounds which start at concentrations of <10 ^"4 mol% polymerization.

The initiators are used in very small quantities. In the process according to the invention are initiators in an amount of less than or equal to 10 ^"4 mol%, preferably from 10 ^{" 6} mol% to 10 ^{~ 4} mol%, based on the amount of present at the beginning of the polymerization -CH ₂ -O units forming monomers , for use.

In the process according to the invention, purified starting materials are used in the polymerization, so that the content of water and formic acid during the polymerization is less than 100 ppm, preferably less than 40 ppm, based on the amount of -CH ₂ -O units present at the start of the polymerization monomers. The measures for the purification of the starting materials are known to the person skilled in the art. The determination of the water and formic acid content in the monomers is carried out by the customary methods, ie water according to Karl Fischer and formic acid by acid-base titration. After the polymerization, the solid or liquid polymerization mixture according to point c) is dissolved with a protic solvent containing at least one base. This deactivates the initiator and active polymer chains. This involves a thermal, controlled degradation of the unstable end groups.

The solution is typically carried out at temperatures of 130 to 200 ° C, preferably from 140 to 190 ⁰ C.

As the base, it is possible to use all those compounds capable of terminating cationic polymerization, for example compounds which react basicly with water. Preference is given to bases which do not react with formaldehyde. Examples are tertiary amines, such as triethylamine, or secondary alkali metal phosphates, such as disodium hydrogen phosphate, or amides, such as dimethylformamide or dimethylacetamide, or aromatic amines, such as melamine.

Typical deactivation pressures range from 1 to 50 bar, preferably from 2 to 30 bar, in particular from 3 to 20 bar.

The duration of the thermal treatment is 10 seconds to 2 hours, preferably 1 minute to 60 minutes, depending on the temperature. The treatment is preferably carried out with substantial exclusion of oxygen.

As a protic solvent, a mixture containing water and methanol is preferably used. The water concentration is between 2% by weight and 50% by weight, preferably between 5% by weight and 30% by weight. The methanol concentration is between 50 and 90% by weight, preferably between 70% by weight and 90% by weight. Following deactivation and degradation of the unstable moieties in the basic protic solvent described above, the polymer precipitates. The precipitation can be carried out, for example, by cooling the solution. The precipitation is followed by drying of the polymer. For drying, mechanical and / or thermal processes can be used. These methods are known to the person skilled in the art.

The polymer thus obtained can be stabilized and modified by the known additives and then granulated.

As components of the mixture of additives, the compounds commonly used to stabilize and / or modify oxymethylene polymers can be used.

These are, for example, antioxidants, acid scavengers, formaldehyde scavengers, UV stabilizers or heat stabilizers. In addition, the mixture of additives may contain processing aids, for example adhesion promoters, lubricants, nucleating agents, mold release agents, fillers, reinforcing materials or antistatic agents and additives which impart a desired property to the molding composition, such as dyes and / or pigments and / or impact modifiers and / or electrical conductivity imparting agents Additions; and mixtures of these additives, but without limiting the scope of the examples mentioned.

The oxymethylene copolymers obtained in this way are distinguished by good thermal stability, hot water resistance and low-temperature impact strength.

Examples Min was a POM polymer having 86% -OCH ₃ end groups, 13% hydroxyethylene end groups, 0.025 mol% of oxyethylene groups, based on the content of oxymethylene, and a melt index MVR of 2.5 ml / 10 for 8 weeks in 95 ⁰ C stored hot water. The weight loss of the specimens was less than 1 wt.%. and the breaking strength remained unchanged at 70 MPa.

In contrast, the weight loss of a POM homopolymer having the same MVR but containing 60-70% of -OCH ₃ end groups, no hydroxyethylene end groups and no oxyethylene groups was 10% by weight, and the breaking strength dropped below 40 MPa after 8 weeks.

Claims

claims

1. Oxymethylene copolymers containing oxymethylene units and oxyalkylene units having at least two carbon atoms and a proportion of Alkyletherendgruppen and to Hydroxyalkylenendgruppen having at least two carbon atoms, wherein the proportion of Alkyletherendgruppen, based on all end groups, at least 80% and the proportion of Hydroxyalkylenendgruppen with at least two carbon atoms, based on all end groups, up to 20%.

2. oxymethylene copolymers according to claim 1, characterized in that at least 90% of all end groups are alkyl ether end groups, preferably ethyl ether or in particular methyl ether end groups, and that up to 10% of all end groups are Hydroxyalkylenendgruppen having at least two Kohienstoffatomen, preferably hydroxyethylene end groups.

3. Oxymethylene copolymers according to one of claims 1 or 2, characterized in that the proportion of oxyalkylene units, based on the

Proportion of oxymethylene units, between 0.001 mol% and 0.05 mol%.

4. oxymethylene copolymers according to claim 3, characterized in that the proportion of oxyalkylene units, based on the proportion of

Oxymethylene units, from 0.01 mol% to 0.05 mol%.

5. oxymethylene copolymers according to one of claims 1 to 4, characterized in that they have the general formula I.

- (O-CH ₂ ) χ- (OC _m H ₂ m) y- (I), and alkyl ether end groups of the formula -OR ¹ and hydroxyalkylene end groups of the formula -OC _m H _2m -OH, and optionally end groups of the formula -OR ² , x is a positive integer, preferably from 10 to 10,000, m is an integer from 2 to 6, y is an integer of 0 to 10, the ratio of y _ar / x _{ar is} between 0.001 and 0.05, where y _{ar is} the arithmetic mean of all values y in the polymer mixture and x _{ar is} the arithmetic mean of all values x in the polymer mixture,

R ^{1 is} a linear or branched alkyl group, and R ^{2 is} a formyl group -CHO, with the proviso that the proportion of the alkyl ether end groups of the formula -OR ¹ , based on all end groups, is at least 80%, and that the proportion of Hydroxyalkylenendgruppen of the formula -O-CmH ₂ m-OH, based on all

End groups, up to 20%.

6. oxymethylene copolymers according to claim 5, characterized in that the index x is an integer of 300 to 10,000.

7. A process for the preparation of oxymethylene copolymers according to claim 1 with the measures: a) polymerization of at least one -CH ₂ -O units-forming monomer and at least one oxyalkylene units having at least two carbon atoms forming monomer in

The presence of at least one acetal of formaldehyde with at least one protic acid or one of its derivatives as initiator, wherein the concentration of the initiator is less than or equal to 10 ^"4 mol%, based on the amount of forming at the beginning of the polymerization -CH ₂ -O units forming monomers . b) use of starting materials of the polymerization, so that the content of water and formic acid is less than or equal to 40 ppm at the beginning of the polymerization, and c) deactivation of the initiator and / or the active polymer chains by treating the polymer produced with at least one basic compound in one protic solvent.

8. A process for the preparation of oxymethylene copolymers according to claim 7, characterized in that the polymerization of the -CH ₂ -O- units forming monomers and the or at least oxyalkylene units having at least two carbon atoms forming monomers is carried out as a heterogeneous polymerization and that the deactivation of the initiator and / or the active polymer chains takes place by dissolving the polymer produced in a protic solvent containing at least one basic compound.

9. The method according to any one of claims 7 or 8, characterized in that as -CH ₂ -O- units forming monomer formaldehyde or preferably trioxane is used.

10. The method according to any one of claims 7 to 9, characterized in that a compound of formula II is used as the acetal of formaldehyde

R ³ - (O-CH ₂ ) _q -OR ⁴ (II),

wherein R ³ and R ^{4 are} independently alkyl radicals, preferably methyl, and q is an integer from 1 to 100.

11. The method according to claim 10, characterized in that the acetal of formaldehyde is a compound of formula II is used, in which q = 1, preferably methylal.

12. The method according to any one of claims 7 to 11, characterized in that are used as initiator of the cationic polymerization strong protic acids, preferably fluorinated or chlorinated alkyl and arylsulfonic acids, in particular trifluoromethanesulfonic acid, and / or esters and / or anhydrides of strong protic acids.

13. The method according to claim 12, characterized in that is used as the initiator of the cationic polymerization perchloric acid, fluoroalkanesulfonic acid, in particular trifluoromethanesulfonic acid.

14. The method according to any one of claims 7 to 13, characterized in that the initiator of the cationic polymerization in an amount of 10 ^'6 mol% to 10 ^{~ 4} mol%, based on the amount of present at the beginning of the polymerization -CH ₂ - O-units forming monomer, is present in the polymerization mixture.

15. The method according to any one of claims 7 to 14, characterized in that the produced oxymethylene polymer is cooled after the polymerization, ground to powder and that the powder is dissolved in the base-containing protic solvent.

16. The method according to any one of claims 7 to 15, characterized in that the produced oxymethylene polymer is dissolved directly after the polymerization as a hot precipitation polymer in the base-containing protic solvent.

17. The method according to any one of claims 7 to 16, characterized in that a mixture of water and alcohol is used as the protic solvent, preferably a mixture of water and methanol.

18. The method according to claim 17, characterized in that a mixture of 50 to 98 wt.% Methanol and 2 to 50 wt.% Water is used as protic solvent, which preferably contains a tertiary amine, most preferably triethylamine.

19. The method according to any one of claims 7 to 18, characterized in that the deactivation takes place at a pressure of 1 to 50 bar, preferably from 2 to 30 bar and in particular from 3 to 20 bar.

20. Use of the oxymethylene copolymers according to one or more of claims 1 to 6 for the production of moldings.