WO2004029131A1 - Method for producing polyether alcohols - Google Patents

Abstract

The invention relates to a method for producing polyether alcohols by means of catalytic polymerisation of alkylene oxides. Said method is characterised in that the alkylene oxide contains propylene oxide, at least one multimetal cyanide compound is used as a catalyst, and the free alkylene oxide content in the reactor is lower than or equal to 8 wt. %, in relation to the total amount of educts and reaction products in the reactor.

Description

Process for the preparation of polyether alcohols

description

The invention relates to a process for the preparation of polyether alcohols using multimetal cyanide compounds as catalysts.

Polyether alcohols are important feedstocks in the production of polyurethanes. They are usually produced by catalytic addition of lower alkylene oxides, in particular ethylene oxide and / or propylene oxide, to H-functional starters.

Soluble basic metal hydroxides or salts are mostly used as catalysts, with potassium hydroxide being of the greatest practical importance. A disadvantage of the use of potassium hydroxide as a catalyst is above all that the production of high molecular weight polyether alcohols leads to the formation of unsaturated by-products which reduce the functionality of the polyether alcohols and are very disadvantageously noticeable in the production of polyurethanes.

To reduce the content of unsaturated fractions in the polyether alcohols and to increase the reaction rate in the addition of propylene oxide, it is proposed to use multi-, preferably double-metal cyanide compounds, in particular zinc hexacyanometalates, as catalysts. These catalysts are often referred to as DMC catalysts. There are a large number of publications in which such compounds have been described.

The polyether alcohols produced using multimetal cyanide compounds are distinguished by a very low content of unsaturated constituents. Another advantage of using multimetal cyanide compounds as catalysts is the significantly increased space-time yield during the addition of the alkylene oxides.

However, there are also disadvantages. When alkylene oxides are added using multimetal cyanide compounds, very high molecular weight fractions often form in the polyether alcohol, which have a very disadvantageous effect in the subsequent conversion to polyurethanes. To remedy this deficiency, special structures of the polyether chain are usually proposed. WO 99/51661 describes a polyether alcohol catalyzed with multimetal cyanide compounds, in which at least 95% by weight of the propylene oxide is added in the presence of another alkylene oxide, preferably ethylene oxide. In US-A-5, 958, 994 it is proposed to add a propylene oxide block to the chain end. Although these measures reduce the disadvantages which result from the presence of the very high molecular weight fractions in the polyether alcohols, the formation of these constituents is not prevented. In addition, polyether alcohols with such a chain structure are not suitable for all applications. In US Pat. No. 6,083,420, in which polyether alcohols containing ethylene oxide in the polyether chain and a propylene oxide end block are described, the formation of the high molecular weight fractions is also associated with the structure of the DMC catalysts.

Another disadvantage of these polyether alcohols is that they differ in their reactivity from otherwise identical polyether alcohols that were produced with other catalysts. This is very troublesome when processing into foams, since every change of the polyether alcohols involves changes in the process of foam production. To influence the reactivity of such polyether alcohols, WO 00/63270 proposes adding small amounts of salts to the polyether alcohol before the reaction with the isocyanates. WO 01/16209 proposes to control the reactivity of the polyether alcohol by adding a propylene oxide end block. However, these measures also restrict the use of the polyether alcohols.

Furthermore, it has been found that, when propylene oxide is added using multimetal cyanide compounds under the reaction conditions customary in industry, in contrast to the use of basic catalysts, primary hydroxyl groups can form at the chain end. In the lecture by Dr. G. Behrendt "Propylene Oxide Polymers by Metallic-Coordinative Polymerization", held on III. International polyurethane symposium on the occasion of the Leipzig Autumn Fair 1981, describes the polymerization of propylene oxide under non-pressurized conditions and found that no primary hydroxyl groups were found. However, such reaction conditions are unusual in the art. Primary hydroxyl groups formed from propylene oxide are not always desired for certain areas of use, for example the production of flexible flexible foams.

Another problem in the production of polyether alcohols using multimetal cyanide compounds as catalysts can be observed in the addition of ethylene oxide at the chain end. Here- in ethylene oxide is often attached to certain chains of the polyether alcohol, while no other ethylene oxide attaches to other chains. This leads to a broad molecular weight distribution of the polyether alcohols, which is very disadvantageous for their use.

The object of the invention was to provide polyether alcohols catalyzed with multimetal cyanide compounds which have a low content of very high molecular weight fractions. Furthermore, when dosing propylene oxide at the chain end of the polyether alcohols, only a small proportion of primary hydroxyl groups derived from propylene oxide units should form. Furthermore, products with a narrow molecular weight distribution should also be formed when ethylene oxide is added to the chain end.

It was surprisingly found that when using multimetal cyanide compounds as catalysts, the amount of primary hydroxyl groups present in the reactor during the reaction of free alkylene oxide, in particular propylene oxide, which can be controlled by various parameters, in particular catalyst activity, amount of catalyst and metering rate and the content of very high molecular weight components in the polyether alcohol can be influenced. Furthermore, it was found that in the course of the metering, in particular at the end of the reaction and in the course of the so-called post-reaction phase, the content of high molecular weight components and the content of primary hydroxyl groups increased sharply. The term "very high molecular weight" is understood below to mean a molecular weight (M ") of more than 3 times the average molecular weight (M _w ) of the polyether alcohol.

The post-reaction phase describes the period of time which is necessary after the end of the metering in of the alkylene oxides in order to allow free alkylene oxide still present in the reaction mixture to react. The post-reaction phase is ended when the pressure in the reactor is constant.

We have now surprisingly found that, in order to achieve the object of the invention, the amount of free alkylene oxide in the reactor during the reaction, at least when metering in the last 10% by weight of the alkylene oxide, based on the total amount of the alkylene oxide, is preferably less than or equal to 8 6 particularly preferably 5% by weight, in particular 2% by weight, and particularly preferably 0.5% by weight, in each case based on the total amount of the starting materials and reaction products present in the reactor. In the context of the invention, starting materials are understood to mean the starting substance and the alkylene oxides. Reaction products mean the reaction products of the starting materials located in the reactor.

The invention accordingly relates to a process for the preparation of polyether alcohols by polymerizing alkylene oxides with multimetal cyanide compounds as catalysts, characterized in that, at least when the last 10% by weight of alkylene oxide is metered in, based on the total amount of alkylene oxide, the amount of in the reactor free alkylene oxide present is less than or equal to 8, preferably 6 and in particular 5% by weight, in each case based on the total amount of the starting materials and reaction products in the reactor.

The invention further relates to polyether alcohols which can be prepared by the process according to the invention and have a functionality of 2 to 8, in particular those with a functionality of 2 to 3 and a hydroxyl number in the range between 20 and 150 mgKOH / g and contain high molecular weight compounds of less than 2% by weight .-%, preferably less than 1 wt .-%, each based on the weight of the polyether alcohol.

The invention furthermore relates to polyether alcohols which can be prepared by the process according to the invention, in particular those having an end block of propylene oxide units and containing primary hydroxyl groups derived from propylene oxide units of a maximum of 10%, preferably a maximum of 8% and in particular a maximum of 6%, preferably 5 %, particularly preferably 4%, particularly preferably 3%, and preferably 2%, in each case based on the total number of hydroxyl groups of the polyether alcohol. The polyether alcohols produced by the process according to the invention preferably have a content of very high molecular weight of at most 5% by weight, particularly preferably 4% by weight, particularly preferably 3% by weight, particularly preferably 2% by weight, and particularly preferably 1 wt .-%, each based on the polyether alcohol.

The invention further relates to a process for the preparation of polyurethanes by reacting polyisocyanates with compounds having at least two hydrogen atoms reactive with isocyanate groups, characterized in that polyether alcohols which can be prepared by the process according to the invention are used as compounds having at least two hydrogen atoms reactive with isocyanate groups. The amount of free alkylene oxide present in the reactor can be influenced by various parameters, but especially, as stated, by catalyst activity, amount of catalyst and metering rate.

The higher the amount of catalyst and the activity of the catalyst and the lower the metering rate of the propylene oxide, the lower the amount of free propylene oxide in the reactor. Ideally, the metering is carried out in such a way that the propylene oxide reacts immediately after the metering and thus there is practically no free alkylene oxide in the reactor. If necessary, the pressure in the reactor can be maintained with inert gases, preferably nitrogen.

The amount of free alkylene oxide in the reactor can be measured by different methods.

The most common are calorimetric determinations, for example heat balancing or heat flow calorimetry.

In heat balancing, the heat of reaction actually released is compared with the theoretical heat of reaction, as would otherwise have been released under the same reaction conditions and recipes for the implementation of the total amount of alkylene oxide, and the amount of the unreacted, that is to say present in the reactor, determined therefrom.

The pressure drop after the end of the alkylene oxide metering can also be used as an indirect measure of the amount of free alkylene oxide in the reactor. The higher this is, the greater the amount of free alkylene oxide. The pressure drop is measured using the normal pressure measurement of the reactor. However, since the amount of free alkylene oxide also depends on other boundary conditions, for example the level of the reactor and the solubility of the alkylene oxide in the liquid phase, only a relatively rough estimate is possible here.

Another indirect measure of the amount of free alkylene oxide is the duration of the after-reaction to constant pressure or a low value of free alkylene oxide, preferably. 0.2% by weight, based on the total amount of the reactants and reaction products in the reactor.

To achieve the object of the present invention, it is advantageous for the amount of free alkylene oxide to be less than or equal to 8, preferably less than or equal to 5% by weight, particularly preferably less than or equal to 3% by weight, in particular less than or equal to 2 wt .-%, based in each case on the total amount of the reactants and reaction products in the reactor. The pressure drop between the completion of the metering and the completion of the after-reaction phase should be less than or equal to 10, preferably 5, particularly preferably 2 bar, 1 bar and in particular 0.5 bar, and particularly preferably 0.2 bar. The post-reaction time should be less than 60, 40 minutes, preferably less than 20, preferably less than 10, preferably less than 5, and in particular less than 2 minutes.

In principle, the amount of free alkylene oxide can be in the range according to the invention during the entire metering time. In this case, there is a particularly marked reduction in the high molecular weight content.

For many applications, especially if it is primarily a matter of reducing the proportion of primary hydroxyl groups in the metering of propylene oxide at the chain end or the uniform distribution of the ethylene oxide units at the chain end, it is sufficient if the metering is only towards the end of the supply of the alkylene oxides, especially during the metering of the last 10% by weight of the alkylene oxide is such that the amount of free propylene oxide is less than or equal to 8% by weight, based on the total amount of the starting materials and reaction products in the reactor.

The concentration of the alkylene oxides in the reactor is usually not uniform over the entire volume. In general, the concentration of the alkylene oxides in the area of the metering point is higher than in areas of the reactor which are further away from the metering point. As long as the total concentration of the alkylene oxides, averaged over the entire reactor, is in the range according to the invention, these concentration differences are irrelevant.

Propylene oxide and ethylene oxide, individually or in any mixtures with one another, are preferably used as alkylene oxides. As mentioned, the production process according to the invention, regardless of the type of alkylene oxides used, leads to a significant reduction in the high molecular weight proportions in the polyether alcohol.

In addition, the process according to the invention makes it possible to adjust the content of primary hydroxyl groups in the polyether alcohol and thus the reactivity of the polyether alcohols. Since the formation of primary hydroxyl groups from propylene oxide is suppressed, the amount of ten ethylene oxide, which forms only primary hydroxyl groups, the

Amount of primary hydroxyl groups can be set specifically.

The process according to the invention can be used to produce polyether alcohols, the chain of which only contains propylene oxide or the end of which is pure propylene oxide. Such polyether alcohols can be used in particular for the production of flexible block foams.

In a preferred embodiment of the process according to the invention when using ethylene oxide and propylene oxide as alkylene oxides, a mixture of ethylene oxide and propylene oxide is added at the beginning of the chain or after addition of a pure ethylene oxide or propylene oxide block. A pure propylene oxide block then preferably follows at the chain end. This preferably has a length of 2 to 50% by weight, preferably 5 to 20% by weight and in particular 5 to 15% by weight, in each case based on the total weight of the polyether alcohol. With these structures of the polyether chain, the advantages of the method according to the invention are particularly noticeable.

The content of primary hydroxyl groups from ethylene oxide and propylene oxide and secondary hydroxyl groups was determined in the context of the invention by derivatization of the

Hydroxyl groups of the polyether alcohol with trichloroacetyl isocyanate and subsequent measurement with an NMR spectrometer BRUCKER DPX 250 with z-shielded inverse probe 5 mm. The primary hydroxyl groups from ethylene oxide, the primary hydroxyl groups from propylene oxide and the secondary hydroxyl groups have different peaks.

In a further preferred embodiment of the invention, propylene oxide, ethylene oxide or mixtures of ethylene oxide and propylene oxide is formed at the beginning of the chain and a block is formed at the end of the chain

Ethylene oxide deposited. The end block made of ethylene oxide preferably has a content of 5 to 50% by weight, in particular 5 to 20% by weight, in each case based on the weight of the polyether alcohol. Surprisingly, such polyether alcohols have a very narrow molecular weight distribution. Such polyether alcohols are used in particular for the production of flexible molded foams.

In a further embodiment of the process according to the invention, at least some of the alkylene oxides can be added

Use of more than two different alkylene oxides' in any mixing ratio as mixing blocks. O

The mixing ratio of the alkylene oxides can be kept constant during the entire metering time or can be varied both batchwise and continuously during metering, as described in WO 01/44347.

Apart from the adjustment of the amount of free propylene oxide in the reaction mixture, the polyether alcohols are prepared by a known method of adding alkylene oxides to H-functional starter substances using multimetal cyanide compounds as catalysts.

Alcohols with functionalities in the range between 2 and 8, preferably 2 to 3, are usually used as H-functional starter substances. Examples of these are glycols, such as ethylene glycol or propylene glycol, 1,4-butanediol, glycerol or trimethylolpropane. Since low molecular weight alcohols often show a delayed reaction start when reacting with alkylene oxides using multimetal cyanide compounds as catalysts, it is customary to use propoxylates of the alcohols mentioned with a molecular weight in the range between 400 and 1000 as starting substances as starting substances. These polymers can be prepared, for example, by conventional addition of the propylene oxide with basic catalysts, the basic catalyst having to be removed thoroughly after the end of the addition, since it deactivates the multimetal cyanide compounds. It is also possible to prepare these polymers using heterogeneous catalysts, as described, for example, in WO 99/44739. Another possibility is to prepare a prepolymer by simultaneously metering in a low molecular weight alcohol and an alkylene oxide, as described in DD-A-203 734.

At the start of the reaction, the starting substance is introduced and, if necessary, water and other volatile compounds are removed. This is usually done by distillation, preferably under vacuum. The catalyst may already be present in the starting substance, but it is also possible to add the catalyst only after the starting substance has been treated. In the latter variant, the catalyst is subjected to less thermal stress. As described in WO 98/52689, the stripping can also be carried out in the presence of inert gas.

An advantageous embodiment of the method according to the invention consists, at least during part of the

Implementation of metering the starter and the alkylene oxides together, as described, for example, in WO 97/29146 or in WO 98/03571 is described. In this embodiment of the process according to the invention, for example, part of the starter substance can be initially charged with the catalyst and, after the reaction has started, further starters and alkylene oxide can be fed in continuously up to the desired chain length of the polyether alcohol 5. It is also possible to meter in starters continuously only at the beginning of the addition of the alkylene oxides and then, as usual, to meter in only alkylene oxides up to the desired chain length of the polyether alcohol.

10

Furthermore, it is also possible to carry out the process in such a way that starter, alkylene oxides and optionally catalyst are metered in continuously in a continuous reactor and the finished polyether alcohol is removed continuously.

15

The advantage of the procedure described is, on the one hand, that the problems at the start of the reaction, in particular the delayed start of the reaction, are avoided. On the other hand, the molecular weight distribution of such polyether alcohols

20 mostly narrower than those of other polyether alcohols produced using DMC catalysts.

Before metering in the alkylene oxides, it is customary to inertize the reactor in order to avoid undesirable reactions of the alkylene oxides

25 to avoid with oxygen. The alkylene oxides are then metered in, the addition being carried out in the manner described above. The alkylene oxides are usually added at pressures in the range from 0.01 bar and 20 bar and temperatures in the range from 50 to 200 ° C., preferably 90 to

30 150 ° C. If the amount of free alkylene oxide present in the reactor is not sufficient to set the necessary pressures, inert gas, for example nitrogen, can also be used as described above. After the alkylene oxides have been metered in, an after-reaction follows in order to obtain a

35 ensure complete implementation of the alkylene oxides contained in the reaction mixture. The complete conversion of the alkylene oxides, as stated above, ends when the pressure in the reactor is constant. In the process according to the invention, the post-reaction phase is usually shorter than in the case of

40 conventional processes, which can increase the space-time yield of the process.

As described above, it is advantageous for the process according to the invention to meter the alkylene oxides, in particular the propylene oxide, as slowly as possible in order not to exceed the amount of free propylene oxide in the reactor according to the invention: the amount metered in in each case depends on the amount of the free one Alkylene oxide in the reactor, which, as stated above, can be monitored continuously.

The multimetal cyanide compounds used as catalysts for the process according to the invention mostly have the general formula (I)

M ^l _a [M ² (CN) _b (A) _c ] _d • fM ⁱ gX _n ^• h (H20) ^■ eL (I)

is where

M ^{1 is} a metal ion selected from the group containing Zn2 +,

Fe2 +, Co3 +, Ni2 +, Mn2 +, Co2 +, Sn2 +, Pb2 +, Mo4 +, Mo6 +, A13 +,

V4 +, V5 +, Sr2 +, W4 +, W6 +, Cr2 +, Cr3 +, Cd2 +,

M ^{2 is} a metal ion selected from the group containing Fe2 +,

Fe3 +, Co2 +, Co3 +, Mn2 +, Mn3 +, V4 +, V5 +, Cr2 +, Cr3 +, Rh3 +,

Ru2 +, Ir3 +

mean and M ¹ and M ^{2 are the} same or different,

A is an anion selected from the group containing halide,

Hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate,

Cyanate, carboxylate, oxalate or nitrate,

X is an anion selected from the group containing halide,

Hydroxide, sulfate, carbonate, cyanide, thiocyanate, isocyanate,

Cyanate, carboxylate, oxalate or nitrate,

L is a water-miscible ligand, selected from the group consisting of alcohols, aldehydes, ketones, ethers, polyether esters, ureas, amides, nitriles, and sulfides,

mean as well

a, b, c, d, g and n are selected so that the electro-neutrality of the connection is ensured, where c can be zero, and

e zero or the coordination number of the ligand,

f a fractional or whole number greater than or equal to 0

h is a fractional or whole number greater than or equal to 0. These compounds are prepared by generally known processes by combining the aqueous solution of a water-soluble metal salt with the aqueous solution of a hexacyanometalate compound, in particular a salt or an acid, and optionally adding a water-soluble ligand to it during or after the combination.

It has been shown that multimetal cyanide compounds which have been prepared using an acid as the hexacyanometalate compound are mostly particularly active and are therefore very suitable for the process according to the invention.

The catalyst is usually obtained in an amount of less than 1% by weight, preferably in an amount of less than 0.5% by weight, particularly preferably in an amount of less than 1000 ppm and in particular in an amount of less than 500 ppm on the weight of the polyether alcohol used. For particularly active catalysts it is also possible to use 100 ppm, 50 ppm or less.

The reaction can be carried out continuously or preferably batchwise. After the reaction has ended, the unreacted monomers and volatile compounds can be removed from the reaction mixture, usually by means of distillation. Usually, the polyether alcohols are added with customary antioxidants and / or stabilizers after their production.

In principle, the catalyst can remain in the polyether alcohol since it does not interfere with the further processing of the polyether alcohols to give polyurethanes.

However, it is also possible to remove all or part of the catalyst from the polyether alcohol. This can be done in a customary and known manner, for example by sedimentation, filtration, filter aids mostly being used here, or by centrifugation.

The polyether alcohols produced by the process according to the invention are mostly used for the production of polyurethanes. Preferred areas of application are the production of elastomers, for example thermoplastic elastomers, and the production of polyurethane foams, in particular rigid polyurethane foams and flexible polyurethane foams. The flexible polyurethane foams can be molded foams and preferably block foams, also referred to as slabstock foams. With these foam Substances are particularly dependent on well-coordinated reactivity. While a reactivity that is too low can usually be compensated for in the formulation, this is difficult with a reactivity that is too high, such as is caused by an excessively high content of primary hydroxyl groups. If the reactivity is too high, the foams will shrink undesirably.

A low reactivity of the polyether alcohols is also desirable in the production of rigid polyurethane foams. This is intended to ensure that when cavities are foamed, for example in the case of cooling devices or ro-jackets, the liquid reaction mixture reaches the entire area to be foamed, as long as the reaction mixture is still flowable.

The polyether alcohols suitable for the production of flexible polyurethane foams preferably have a functionality of 2 to 3, a hydroxyl number in the range between 20 and 150, preferably 30 to 70 mgKOH / g and are preferably composed of propylene oxide, optionally mixtures of propylene oxide and ethylene oxide. For the production of Slabstock foams, as stated, in particular those polyether alcohols are used which contain ethylene oxide in the interior of the polyether chain, as a pure block or preferably in a mixture with propylene oxide, and at the chain end a pure block of propylene oxide. Furthermore, such polyether alcohols can also be used as starting substances for the production of high molecular weight polyether alcohols.

The polyether alcohols suitable for the production of rigid polyurethane foams mostly have a functionality in the range between 3 and 8 and a hydroxyl number in the range between 150 and 800 mgKOH / g.

In a particular embodiment of the process according to the invention, polyether alcohols with low molecular weights, in particular those with a functionality in the range between 2 and 8, preferably 2 and 4, particularly preferably 2 and 3 and a hydroxyl number in the range between 150 and 500 mgKOH / g, manufactured. In a particularly advantageous embodiment of this method, the addition is carried out in such a way that, in addition to the continuous metering of the alkylene oxides, there is also a continuous metering of at least part of the starting substance. The products produced according to this embodiment of the method according to the invention are distinguished by a particularly narrow molecular weight distribution. So is in particular the proportion of very high molecular weight proportions in the polyether alcohol is very low, in particular less than 5% by weight, based on the polyether alcohol. In this embodiment, the term “very high molecular weight” also means a molecular weight (M _w ) of more than 3 times the average molecular weight (M- of the polyether alcohol).

Such low molecular weight products can be used, for example, for the production of rigid polyurethane foams or as starting substances for the production of high molecular weight polyether alcohols by further addition of alkylene oxides, in particular using DMC catalysts.

The process according to the invention has the advantage that it can be carried out in any plant for the production of polyether alcohols without additional effort. The resulting polyether alcohols are characterized by a low content of primary hydroxyl groups, which are derived from propylene oxide, and a low content of fractions with a very high molecular weight.

Surprisingly, the polyether alcohols produced by the process according to the invention also contain less volatile components than polyether alcohols produced by conventional processes. The volatile constituents are very undesirable as odor carriers in polyether alcohols, since a strong smell of the polyurethanes produced from the polyether alcohols is perceived as a poor quality.

The polyether alcohols produced by the process according to the invention are mostly used for the production of polyurethanes by reaction with polyisocyanates, usually in the presence of catalysts and, in the case of the production of polyurethane foams, in the presence of blowing agents. Further possible uses of the polyether alcohols produced by the process according to the invention are surfactants and carrier oils.

The following should be said in detail about the starting materials used to produce the polyurethanes.

All isocyanates with two or more isocyanate groups in the molecule can be used as polyisocyanates. Both aliphatic isocyanates, such as hexamethylene diisocyanate (HDI) or isophorone diisocyanate (IPDI), or preferably aromatic isocyanates, such as tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI) or mixtures of diphenylmethane diisocyanate and Polymethylene polyphenylene polyisocyanates (raw MDI) can be used. It is also possible to use isocyanates which, through the incorporation of uretane, uretdione, isocyanurate, allophanate,

Uretonimine and other groups have been modified, so-called modified isocyanates.

TDI is used in particular for the production of flexible flexible foams, while MDI and its higher homologues are preferably used in the production of molded foams. Raw MDI is mostly used in the production of rigid foams.

In a mixture with the polyether alcohols produced by the process according to the invention, further compounds having at least two hydrogen atoms reactive with isocyanate groups, preferably polyols, can be used. Among the polyols, the polyether polyols and the polyester polyols have the greatest technical importance. The polyether polyols used for the production of polyurethanes are mostly produced by base-catalyzed addition of alkylene oxides, in particular ethylene oxide and / or propylene oxide, onto H-functional starter substances. Polyester polyols are mostly produced by esterification of polyfunctional carboxylic acids with polyfunctional alcohols.

The compounds with at least two groups reactive with isocyanate groups also include the chain extenders and / or crosslinking agents, which can optionally also be used. These are at least two-functional amines and / or alcohols with molecular weights in the range from 60 to 400.

The blowing agent used is mostly water and, at the reaction temperature of the urethane reaction, gaseous compounds which are inert to the starting materials of the polyurethanes, so-called physically acting blowing agents, and mixtures thereof. Hydrocarbons with 2 to 6 carbon atoms, halogenated hydrocarbons with 2 to 6 carbon atoms, ketones, acetals, ethers, inert gases such as carbon dioxide or noble gases are used as physical blowing agents.

Amine compounds and / or metal compounds, in particular heavy metal salts and / or organometallic compounds, are preferably used as catalysts. In particular, known tertiary amines and / or with organic metal compounds are used as catalysts. The catalysts can be used individually or in the form of mixtures. Auxiliaries and / or additives are, for example

Release agents, flame retardants, dyes, fillers and / or

Reinforcing agents used.

In industry, it is customary to mix all of the starting materials with the exception of the polyisocyanates to form a so-called polyol component and to convert this with the polyisocyanates to give the polyurethane.

The polyurethanes can be produced by the so-called one-shot process or by the prepolymer process. The flexible polyurethane foams can be block foams as well as molded foams.

An overview of the starting materials for the production of polyurethanes and the processes used for this can be found, for example, in the Plastics Handbook, Volume 7 "Polyurethanes", Carl-Hanser-Verlag Munich Vienna, 1st Edition 1966, 2nd Edition 1983 and 3rd Edition 1993.

The invention is illustrated by the following examples.

Examples

Examples 1 to 4

The synthesis was carried out in a cleaned and dried 25-1 stirred autoclave. The amounts of prepolymer given in Table 1 were added to the stirred tank and 50 ppm of a multimetal cyanide compound, prepared from zinc acetate and hexacyanocobaltoic acid in the presence of a surface-active agent, were added. The contents of the kettle were rendered inert with nitrogen and treated in vacuo for a total of 1 hour at 120 ° C. The indicated amounts of alkylene oxides were metered in at 120 ° C. using the metering rates given in the table. After the metering had ended, stirring was continued until the pressure was constant and then the reaction mixture was degassed at 105 ° C. and 10 mbar. Samples were taken from the reactor using gas-tight locks.

The respective free propylene oxide content was determined by heat balancing.

The characteristic values of the resulting polyether alcohols can also be found in the table. The characteristic values were determined using the following methods:

The viscosity given in the examples was measured analogously to DIN 53 015. The OH number was determined in accordance with DIN 51 562.

The content of primary hydroxyl groups from ethylene oxide and propylene oxide was determined by derivatizing the hydroxyl groups of the polyether alcohol with trichloroacetyl isocyanate and subsequent measurement using a BRUKER DPX 250 NMR spectrometer with a 5 mm z-shielded inverted probe head. The primary hydroxyl groups from ethylene oxide, the primary hydroxyl groups from propylene oxide and the secondary hydroxyl groups have different peaks.

The percentage of volatile constituents was determined by means of gas chromatography.

The proportion of high molecular weight components was determined by GPC.

A device system consisting of a liquid chromatograph HP 1090 with an RI detector HP 1047A, an autosampler HP 79847 A and an evaluation unit is used for this. The separation is carried out on 3 PL-gel columns (2 x 3 μm Mixed E, 1 x 5 μ 50 Ä).

Tetrahydrofuran is used as the eluent. To determine the molar mass distribution, calibration was carried out using PEG and PPG standards in the corresponding molar mass range. The high molecular weight fraction is defined as greater than 3 x M (w). The elution volume is determined from the molar mass calibration, which corresponds to 3 x M (w). To determine the content of high molecular weight components, a PEG standard with a molecular weight of 6000 g / mol was measured in various concentrations. The function concentration = f (area) was used to evaluate the high molecular weight fraction.

Explanations to the table

EO ethylene oxide PO propylene oxide

Prepolymer produced by propoxylation of a mixture of glycerol and monoethylene glycol in the molar ratio of glycerol to monoethylene glycol of 3: 1, with a hydroxyl number of 168 mg KOH / g free propylene oxide during the metering in of the propylene oxide

Pressure difference between the end of metering and the end of the post-reaction phase

Content of primary hydroxyl groups from propylene oxide, based on the total content of hydroxyl groups

***** Proportion of compounds with a molecular weight greater than 80,000 g / mol

Explanations to the table

V Comparative example PO propylene oxide

Polypropylene glycol with a molecular weight of 400 g / mol free propylene oxide during the metering of the propylene oxide. Pressure difference between the end of the metering and the end of the post-reaction phase

Primary hydroxyl group content, based on the total hydroxyl group content

The examples clearly show that with a decrease in the free propylene oxide in the reactor, the proportions of the primary hydroxyl groups in the polyether alcohol decrease significantly.

Manufacture of flexible polyurethane foams

Example 9 (comparison)

100 parts by weight of polyether alcohol from Example 1, 3.5 parts by weight of water, 0.8 parts by weight of foam stabilizer Tegostab® B 4900 from Goldschmidt AG, 0.15 parts by weight of catalyst Lupragen® N201 from BASF Aktiengesellschaft and 0.18 part by weight of Kosmos® 29 catalyst from Goldschmidt AG were mixed to form a polyol component and with TDI 80/20 (Lupranat® T 80 from BASF Aktiengesellschaft) at an index of 110 in an open form to give a polyurethane - Soft foam implemented. The resulting block of soft foam was badly torn and had to be discarded.

Example 10 5

The procedure was as in Example 9, but instead of the polyether alcohol from Example 1, 100 parts by weight of the polyether alcohol from Example 3 were used.

10 The resulting soft foam block was crack-free and open-celled and had a good foam structure.

Example 11 (comparison)

15 18 parts by weight of polyether alcohol from Example 5, 40 parts by weight of a glycerol-started ethylene oxide / propylene oxide polyether alcohol with an ethylene oxide content of 21% by weight, based on the total amount of alkylene oxide and a hydroxyl number of 25 mgKOH / g, 38 Parts by weight of one started with glycerol

20 ethylene oxide / propylene oxide polyether alcohols with an ethylene oxide content of 72% by weight, based on the total amount of alkylene oxide and a hydroxyl number of 44 mgKOH / g, 0.7 parts by weight of foam stabilizer Tegostab® B 4690 from Goldschmidt AG, 0.5 part by weight of Lupragen® N201 catalyst from BASF Aktien-

25 companies, 0.4 parts by weight of Lupragen® N206 catalyst

BASF Aktiengesellschaft, 0.4 parts by weight of diet anolamine and 2 parts by weight of water were combined to form a polyol component. This polyol component was made with a prepolymer containing NCO groups and based on MDI with an NCO content of 27% by weight.

30 at an index of 85 in an open form to a sound-absorbing flexible polyurethane foam of 3 cm thickness.

The polyol component tended to phase separate and had to be stirred intensively before the reaction. The resulting foam showed inhomogeneities and hardening. The loss factor according to ISO 7626 was strong and was below 0.2.

Example 12

The procedure was as in Example 11, but instead of the polyether alcohol from Example 1, 100 parts by weight of the polyether alcohol from Example 8 were used.

The polyol component was phase stable. The resulting foam had a uniform foam structure and a density of 55 kg / m ³ . The loss factor according to ISO 7626 was 0.52.

Claims

claims 1. A process for the preparation of polyether alcohols by catalytic polymerization of alkylene oxides, characterized in that the alkylene oxide contains propylene oxide, at least one multimetal cyanide compound is used as catalyst and the content of the free alkylene oxide in the reactor is less than or equal to 8% by weight, based on the Total amount of starting materials and reaction products in the reactor is. 2. The method according to claim 1, characterized in that the content of the free alkylene oxide in the reactor is less than or equal to 5 wt .-%, based on the total amount of the reactants and reaction products in the reactor. 3. The method according to claim 1, characterized in that the content of the free alkylene oxide in the reactor during the entire metering of the alkylene oxides is less than or equal to 8% by weight, based on the total amount of the reactants and reaction products in the reactor. 4. The method according to claim 1, characterized in that the content of the free alkylene oxide present in the reactor during the metering of the last 10% by weight of the alkylene oxides, based on the total amount of the alkylene oxides, is less than or equal to 8% by weight, based on is the total amount of reactants and reaction products in the reactor. 5. The method according to any one of claims 1 and 2, characterized in that the pressure drop between the completion of the metering and the completion of the post-reaction phase is less than or equal to 2 bar. 6. The method according to claim 1, characterized in that only propylene oxide is used as alkylene oxide. 7. The method according to claim 1, characterized in that mixtures of propylene oxide and ethylene oxide are used as alkylene oxide. 8. The method according to claim 1, characterized in that mixtures of propylene oxide and ethylene oxide are used as alkylene oxide, a mixture of ethylene oxide and propylene oxide and pure propylene oxide being metered in at the beginning of the chain and / or after the addition of a pure alkylene oxide. 9. The method according to claim 1, characterized in that the amount of pure propylene oxide metered at the chain end is 2 to 50 wt .-%, based on the weight of the polyether alcohol. 10. The method according to claim 1, characterized in that the amount of pure propylene oxide metered at the chain end is 2 to 20 wt .-%, based on the weight of the polyether alcohol. 11. The method according to claim 1, characterized in that the amount of pure propylene oxide metered at the chain end is 5 to 15 wt .-%, based on the weight of the polyether alcohol. 12. Polyether alcohols, producible according to one of claims 1 to 11. 13. Polyether alcohols, producible according to one of claims 1 to 11, with a content of components with a molecular weight (M *,) of more than 3 times the average molecular weight (U ^) of the polyether alcohol of at most 5, wt .-% %, based on the weight of the polyether alcohol. 14. Polyether alcohols, producible according to one of claims 6 to 11, characterized in that they have a content of primary hydroxyl groups derived from propylene oxide units of at most 10%, based on the total number of hydroxyl groups. 15. Use of polyether alcohols according to one of claims 12 to 14 for the production of polyurethanes, in particular flexible polyurethane foams. 16. Use of polyether alcohols according to claim 12 to 14 as a starting substance for the production of polyether alcohols by catalytic addition of alkylene oxides. 7. A process for the preparation of polyurethanes by reacting polyisocyanates with compounds having at least two hydrogen atoms reactive with isocyanate groups, characterized in that at least one polyether alcohol which can be prepared according to one of claims 12 to 16 is used as compounds having at least two hydrogen atoms reactive with isocyanate groups.