MXPA99008253A - Procedure for preparing polyace copolymers - Google Patents

Abstract

The present invention relates to: A continuous process for the preparation of polyacetal copolymers of 1,3,5-trioxane and the comonomers known for this purpose using strong protonic acids as an initiator, in which the initiator is added in an amount of 0.01. at 0.6 ppm, based on the total amount of monomers, in finely divided form to the monomer mixture, after the polymerization step the raw polymer is transferred from the polymerization reactor to a mixing unit without additional intermediate steps, the excess monomer is removes from the raw polymer in the mixing unit or between the polymerization reactor and the mixing unit by applying reduced pressure and, if desired, incorporated stabilizers, auxiliaries, fillers, reinforcing materials and / or colorants generally used within of the polymer in the mixing unit

Description

PROCEDURE FOR PREPARING POLYACETAL COPOLYMERS DESCRIPTIVE MEMORY The present invention relates to a process for the continuous preparation of polyacetal copolymers from trioxane with known comonomers for this purpose, in which the initiators which are used are strong protonic acids which are added in a finely divided form to the mixture of monomer, and in which, immediately after the polymerization step, the raw polymer is transferred directly, ie without the use of deactivators, to a mixing unit in which additional additives are incorporated into the polymer. The material that is prepared in this way has excellent stability. Polyacetal copolymers have been known for several years and have proven to be useful as materials in a wide variety of applications. Since its launch approximately 30 years ago, polyacetal copolymers based particularly on polyoxymethylene (POM) have established themselves as extremely useful industrial materials in many applications. The POM copolymer is widely used, especially as building material in automotive construction and in the electrical industry. Examples of this can be found in the application brochures of polyacetal producers.

After the polymerization step, the polyoxymethylene copolymers in the form of crude polymers have insufficient stability and are therefore generally subjected to particular treatment steps before they are mixed with stabilizers and auxiliaries in an additional step, generally with the use of a granulation extruder, and in this way are introduced into the commercial state. It is known that the steps of the process to treat crude polymers include: a) the deactivation of initiators b) the elimination of unstable chain ends c) the removal of unconverted monomers d) the incorporation of stabilizers and auxiliaries. There are many known industrial processes that combine these steps for the preparation of polyacetal copolymers (Sebel et al. In Becker / Braun (Editors), Kunststoffhandbuch [Manual of Plastics] volume 3/1, 1992). Common to all known methods is the fact that cationic initiators are used for the preparation of 1, 3,5-trioxane copolymers. It is also generally known that cationic polymerization does not involve any true termination reaction in which the active center is irreversibly destroyed (see Elias HG., Makromoleküle [Macromolecules], Hüthig and Wepf Verlag, 4th Edition, page 513). and Penzek et al., Cationic Ring Opening Polymerization: Advances in Polymer Science No. 68/69, page 122).

This is important precisely for the copolymerization of trioxane since the chain ends that live, ie are not deactivated, and the unconverted radicals of the initiators can decompose the polymer during further processing. Therefore, all known preparation methods include a step in which the remaining amount of the initiator is deactivated after the polymerization. The considerable complication of this procedure increases the preparation costs too much. Therefore, it is known that deactivation of the initiator is carried out in an aqueous phase or in an organic solvent, subsequently the filtration, washing and drying steps are required. The deactivation of the initiators with the addition of different deactivators can also be affected in the fusion (DE 3703790). The deactivation step is often carried out together with the demonomerization and the elimination of non-stable chain ends (DE 37 38 632 and EP 0 137 305). EP 0673 955 describes a process in which the crude polymer is treated with a vapor stream which also contains small amounts of volatile base. In this way, the unconverted residual monomer is removed and the initiator is deactivated. JP 05059255 states that the initiator is deactivated by adding alkali metal or alkaline earth metal oxides to the polymer melt. The elimination of unstable end groups, which generally remain in the crude polymer after polymerization and in particular lead to chain degradation when the polymer is heated, it is also a usual step of the process in the preparation of POM copolymers. Hydrolysis, in which the crude polymer is dissolved in a solvent under elevated pressure at elevated temperature is frequently used for this purpose. After hydrolysis, the polymer must be precipitated again, washed and dried. This shows that all the procedures known to date cause considerable ss which serve only to remove non-stable terminal groups and residual monomers, to deactivate initiators or their reaction products and to prepare the undesirable secondary reaction results. The object is therefore to develop a process that makes it possible economically to prepare stable 1,3,5-trioxane copolymers in a continuous process while avoiding deficiencies of known methods. The object is achieved if the ng protonic acids are used as initiator and are added in a finely divided form to the monomer mixture and if, after the polymerization step, the polymer is transferred without intermediate steps from the polymerization reactor to a unit of mixture in which the material is fused, the conventional and auxiliary additives are added and thus the material is transformed into a suitable form for sale. The invention thus relates to a continuous process for the preparation of 1, 3,5-trioxane polyacetal copolymers and the comonomers known for this purpose that use a ng protonic acid as an initiator, in which the initiator is added in an amount of 0.01 to 0.6 ppm, based on the total amount of monomers, in finely divided form to the liquid monomer mixture , the crude polymer is transferred from the polymerization reactor directly to a mixing unit immediately after the polymerization step without additional intermediate steps, the excess of monomer is removed from the crude polymer in the mixing unit or between the polymerization reactor and the polymer. mixing unit by applying reduced pressure and, if desired, stabilizers, auxiliaries, fillers, reinforcing materials and / or colorants generally customary in the mixing unit are incorporated into the polymer. The procedural advantages according to the invention are that neither the step of the process for the deactivation of the initiators nor the passage of the separation process for the removal of non-stable end groups throughout the process sequence is required. Therefore, two usual steps of the procedure to date are saved by the procedure, with the result that the preparation of POM is more economical. These POM copolymers no longer have to be treated with deactivators after the polymerization step before they can be granulated with the addition of customary stabilizers and auxiliaries to date, it was surprising and surpassed a prejudice that has existed to date. In particular it is surprising, however, that the copolymers of POM that were obtained without the addition of deactivators and without additional hydrolysis have a very high stability. In accordance with the invention, ng protonic acids are used as initiators, this being possible in principle to utilize all ng protonic acids. Polyheterogeneous acids, perchloric acids or perfluoroalkenesulfonic acids are particularly suitable, and trifluoromethanesulfonic acid is preferred. The concentration of the initiators is generally in the range of 0.01 to 0.6 ppm, preferably in the range of 0.3 to 0.4 ppm, and preferably in particular in the range of 0.05 to 0.19 ppm, based on each case in the monomer mixture. It is essential for the process according to the invention that the initiator be added in a finely divided form to the mixture of the monomer comprising trioxane and the comonomers. This is advantageously done by dissolving the initiator in a solvent that is selected from a group consisting of aliphatic ethers, such as ethylene glycol dimethyl ether or diethylene glycol dimethyl ether, aliphatic acetals such as formaldehyde dialkylacetals, cyclic acetals such as 1,3-dioxolane, or cycloaliphatic ethers, such as 1,6-dioxane. Surprisingly, cyclic acetals and dialkyl acetals of formaldehyde having 3 to 9, preferably 3 to 5 carbon atoms are particularly suitable, for example formaldehyde dimethylacetal, formaldehyde diethylacetal, formaldehyde dipropylacetal and formaldehyde dibutylacetal. The weight ratio of the initiator to the solvent is generally from 1: 100 to 1: 1000,000, preferably 1: 500 to 1: 10,000. When formaldehyde dialkyl acetals are used as a solvent for the initiator, the amount of solvent is preferably 3.4 to 34 mmoles per kilogram of monomer mixture. Comonomers suitable for the preparation of POM copolymers are compounds that are copolymerizable with 1, 3, 5 trioxane. Preferred are cyclic acetals, preferably formaldehydes, having 5 to 11, preferably 5 to 8, ring members. Suitable cyclic acetals are in particular cyclic formaldehydes of a ,? aliphatic or cycloaliphatic diols having 2 to 8, preferably 2, 3 or 4, carbon atoms, the carbon chain of which may be interrupted by an oxygen atom in intervals of 2 carbon atoms. In addition, cyclic ethers having 3 to 5, preferably 3, ring members can also be used. The cyclic ethers may be substituted by aliphatic or aromatic radicals. The comonomers can be used, either individually or in combination, in an amount of 0.01 to 20% by weight, preferably 0.1 to 10% by weight, in particular 1 to 7% by weight, based in each case on the monomer mixture, fraction of mass indicated in% by weight corresponding to the sum of quantities of all comonomers that were used. Substances that are known to act as molar mass regulators can also be added to the monomer mixture. In particular, dialkyl acetals of formaldehyde having 3 to 9, preferably 3 to 5, carbon atoms, for example formaldehyde dimethylacetal, formaldehyde diethylacetal, formaldehyde dipropylacetal and formaldehyde dibutylacetal, are especially suitable for this purpose. The regulator is generally used in an amount greater than 2% by weight (= 20,000 ppm), preferably 0.1 to 1.5% by weight, particularly preferably 0.3 to 1.2% by weight, based on the monomer mixture. All continuous transport and mixing units can be used as polymerization reactors. The use of double-screw extruders is very advantageous. In a preferred embodiment, which was shown in Figure 1, the polymerization is carried out in a polymerization reactor (1) at melting temperatures above 65 ° C, the initial liquid reaction mixture containing the molten monomers , the initiator and optionally the regulator solidifies during the polymerization to give a resistant material leaving the polymerization reactor (1) in the form of small particles by means of a drip arrow (5) in which the reduced pressure prevails. As a result of the reduced pressure, the unconverted monomers are removed from the polymer and subsequently fed to separate the treatment or completely condensed and recycled upstream of the polymerization reactor. The polymer that leaves the polymerization reactor falls, without additional intermediate steps, directly into another transport and continuous mixing unit (6), which is preferably as in a double-screw extruder, In this unit, the polymer is fused, it is mixed with conventional and auxiliary stabilizers and leads to its commercial form. The designations in Figure 1 have the following meanings: 1: polymerization reactor 2: feed of trioxane and comonomers 3: feed of the initiator dissolved in a solvent and optionally of regulator 4: removal of unconverted monomers 5: drip arrow for the raw polymer 6: continuous transport and mixing unit 7: stabilizer and auxiliary supply 8: product in commercial form It is also possible to carry out all the steps of the process in a single unit or to use a combination of more than two interconnected units. In each case, however, the residual monomer is removed from the crude polymer between the polymerization zone and the addition of stabilizers and auxiliaries by applying reduced pressure. Antioxidants, acid acceptors, lubricants, waxes, UV stabilizers, nitrogen-containing co-stabilizers and other products known as stabilizers for POM can be used as stabilizers and auxiliaries, either individually or in combination.

All fillers and reinforcing materials customary and known as plastics, in particular polyacetal copolymers, can be used as fillers and reinforcing materials.

EXAMPLES EXAMPLE 1 A molten monomer mixture comprising 97% by weight of trioxane and 3% by weight of dioxolane was fed at a rate of 3kg / h to a double-screw extruder used as a polymerization reactor. 0.15 ppm, based on the monomer mixture, of trifluoromethanesulfonic acid dissolved in 1,6-dioxane and 1050 ppm, based on the monomer mixture, of formaldehyde dimethylacetal were added continuously to the monomer mixture. The crude polymer obtained was transported to the exit of the polymerization reactor by means of a drip arrow in a second double-screw extruder. The unconverted monomers were removed by means of reduced pressure and absorbed in a water circulation. The amount of monomers separated per hour was 600g. In the second double-screw extruder, the crude polymer was fused and mixed with a mixture of 46% by weight of Irganox 245 (produced by Ciba Spezialchemie), 31% by weight of an amide wax, Hostalub FA, 15% by weight of tricalcium citrate and 8% by weight of dicyandiamide. This mixture was fed to the Second extruder at a speed of 15.6 g / h. After passing through to the discharge zone, the polymer was removed as a molten extrudate, cooled in a water bath and subsequently cut into granules. The granules thus obtained were completely dried and kept under inert gas at a temperature of 240 ° C for several hours to determine the heat stability. The material obtained is suitable for further use in injection molding or extrusion process and has good heat stability.

EXAMPLES 2-4 The procedure was as in Example 1, the amount of trifluoromethanesulfonic acid going off (for information, CF. Table 1).

EXAMPLE 5 A molten monomer mixture comprising 97% by weight of trioxane and 3% by weight of dioxolane was fed at a rate of 3 kg / h to a double-screw extruder used as a polymerization reactor. 0.1 ppm, based on the monomer mixture, of trifluoromethanesulfonic acid dissolved in 300 ppm, based on the monomer mixture, of formaldehyde dimethylacetal and furthermore 850 ppm, based on the monomer mixture, of formaldehyde dimethylacetal were continuously added to the monomer mixture. The obtained raw polymer was transported at the exit of the polymerization reactor by means of a drip arrow in a second double-screw extruder and was further processed as in Examples 2-4.

COMPARATIVE EXPERIMENT A commercial POM copolymer (Hostaform) was also tested as in Example 1 in relation to its heat stability. The result is shown in Table 1.

TABLE 1 * Heat stability was measured as the rate of weight loss in% / hr at a temperature of 240 ° C under inert gas.

Claims (9)

NOVELTY OF THE INVENTION CLAIMS

1. A continuous process for the preparation of 1, 3,5-trioxane polyacetal copolymers and the comonomers known for this purpose using strong protonic acids as an initiator, in which the initiator is added in an amount of 0.01 to 0.6 ppm, based on the total amount of monomers, in finely divided form to the monomer mixture, after the polymerization step the crude polymer is transferred from the polymerization reactor to a mixing unit without additional intermediate steps, the excess monomer is removed from the polymer in the mixing unit or between the polymerization reactor and the mixing unit by applying reduced pressure and, if desired, stabilizers, auxiliaries, fillers, reinforcing materials and / or dyes generally used within the polymer are incorporated in the the mixing unit.

2. The process according to claim 1, further characterized in that at least one polyheteregeneous acid, perchloric acid or perfluoroalkannesulfonic acid, preferably trifluoromethanesulfonic acid or a combination thereof is used as the initiator.

3. - The method according to claim 1 or 2, further characterized in that the amount of the initiator is in the range of 0.03 to 0.4 ppm, preferably in the range of 0.05 to 0.19 ppm, based on each case in the monomer mixture.

4. The process according to any of claims 1 to 3, further characterized in that the initiator is added in the form of a solution in a solvent to the monomer mixture.

5. The process according to claim 4, further characterized in that at least one aliphatic or cycloaliphatic ether or an aliphatic or cycloaliphatic acetal is used as the solvent for the initiator.

6. The process according to claim 4 or 5, further characterized in that 1,3-dioxolane, 1,6-dioxane or a formaldehyde dialkylacetal, preferably formaldehyde dimethylacetal, formaldehyde dipropylacetal or formaldehyde dibutylacetal, is used as the solvent for the initiator.

7. The process according to any of claims 4 to 6, further characterized in that the weight ratio of the initiator to the solvent is 1: 100 to 1: 100.00, preferably 1: 500 to 1: 10,000.

8. The process according to any of claims 4 to 6, further characterized in that formaldehyde dialkylacetals are used in an amount of 3.4 to 34 mmoles per kg of the monomer mixture as solvents for the initiator.

9. - The process according to any of claims 1 to 8, further characterized in that the double-screw extruder is used as the polymerization reactor and / or mixing unit.