EP2542611A1

EP2542611A1 - Method for producing polyalkylene carbonates

Info

Publication number: EP2542611A1
Application number: EP11705904A
Authority: EP
Inventors: Tobias Heinz Steinke; Anna Katharina Ott; Hans-Helmut Görtz
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2010-03-05
Filing date: 2011-03-02
Publication date: 2013-01-09
Also published as: CN102884103A; WO2011107499A1; KR20130044223A

Abstract

Polyalkylene carbonates are produced by polymerizing carbon dioxide with at least one epoxide of the general formula (I), in which the radicals R, independently of one another, can be H, halogen, NO₂, CN, COOR' or C_1-20 hydrocarbon radical, which can be substituted, wherein one of the radicals R can also mean OH, and wherein two radicals R together can form a C_3-5 alkylene radical, 1 R' can be H or C_1‑20 hydrocarbon radical which can be substituted, in the presence of a zinc salt of C_4‑8 alkanedicarboxylic acids as catalyst, wherein the reaction mixture obtained after the reaction is admixed with a water-immiscible organic solvent which dissolves the polyalkylene carbonate, and with a carboxylic acid or an acidic ion exchanger, the organic phase is washed with water, and the polyalkylene carbonate is optionally obtained from the organic phase.

Description

The invention relates to a process for the preparation of polyalkylene carbonates with improved purification of the polyalkylene carbonates and to a purification process and the use of monomeric or polymeric carboxylic acids or acidic ion exchangers in the purification of polyalkylene carbonates. Polyalkylene carbonates such as polypropylene carbonate are obtained by alternating copolymerization of carbon dioxide and alkylene oxide such as propylene oxide. For this purpose, a wide variety of homogeneous as well as heterogeneous catalysts are used. Zinc glutarates are used in particular as heterogeneous catalysts. WO 03/029325 describes processes for preparing aliphatic polycarbonates. In addition to multimetal cyanide compounds, it is also possible to use zinc carboxylates, in particular zinc glutarate or zinc adipate. After preparation of the aliphatic polycarbonates, the resulting reaction mixture is poured into methanol, which is acidified with concentrated hydrochloric acid. It precipitates a polymer which is filtered off and dried overnight.

Commercially available zinc-catalyzed polypropylene carbonates (PPCs) are not purified. The materials are milky cloudy and still contain high levels of zinc from the catalyst, for example 0.3 to 1.2 g Zn / 100 g polymer.

The use of hydrochloric acid in the work-up of the reaction product can lead to acid-catalyzed depolymerization, which can be undesirable. In addition, traces of chlorine are introduced into the resulting polyalkylene carbonate by the use of hydrochloric acid.

The object of the present invention is to provide an improved process for the preparation of polypropylene carbonates in the presence of zinc salts of C ₄ - ₈ alkanedicarboxylic acids as catalysts, wherein the resulting reaction mixture can be worked up in a simple manner and freed of catalyst residues. Preferably, no depolymerization should occur, and the polyalkylene should be accessible in high purity.

The object is achieved according to the invention by a process for the preparation of polyalkylene carbonates by polymerization of carbon dioxide with at least one epoxide of the general formula (I) with the meaning

R independently of one another H, halogen, NO ₂ , CN, COOR 'or Ci _-20 - hydrocarbon radical which may be substituted, wherein one of the radicals R may also be OH, and wherein two radicals R together form a C _3-5 alkylene radical can,

R 'H or Ci- ₂ o-hydrocarbon radical which may be substituted on a zinc salt of C ₄ - ₈ alkanedicarboxylic acids as catalyst, wherein the reaction mixture obtained after the reaction with a non-water-miscible organic see solvent which dissolves the polyalkylene carbonate , And with a carboxylic acid or an acidic ion exchanger is added, the organic phase is washed with water and optionally the polyalkylene carbonate is recovered from the organic phase. An R in formula (I) may e.g. Example, a radical -CH ₂ -OH or -CH ₂ -O-C (= 0) R 'represent. The C _3-5 -alkylene radical is preferably a linear, terminal alkylene radical.

In addition, the object is achieved by a process for the purification of one or more zinc salts of polyalkylene carbonates containing C _4-8 -alkanedicarboxylic acids, in which the preceding purification step (s) is carried out.

It has been found according to the invention that by using monomeric or polymeric carboxylic acids or acidic ion exchangers instead of hydrochloric acid, the workup of the polyalkylene carbonates is significantly simplified and depolymerization can be largely prevented.

Any suitable carboxylic acids or acidic ion exchangers can be used according to the invention. The carboxylic acids may be mono- or polycarboxylic acids. It may be low molecular weight or polymeric carboxylic acids. The (poly) carboxylic acids or acidic ion exchangers can be used in (partially) neutralized form. Neutralized polyacrylates are obtainable, for example, from BASF SE under the name Sokalan ^®. The carboxylic acids or acidic ion exchangers are used in the purification of the polyalkylene carbonates, in particular for the separation of the polymerization catalysts. The polymerization catalysts used are zinc salts of C _4-8 -alkanedicarboxylic acids, preferably zinc glutarate or zinc adipate, in particular zinc glutarate. The preparation and the use of these catalysts are described, for example, in WO 03/029325.

In the carboxylic acids used in the invention, the number of carboxyl and hydroxyl groups together is preferably at least 2, more preferably at least 3, in particular at least 4. The number may, for. B. 2 to 7, preferably 3 to 6, in particular 3 to 4.

Preferably, at least one hydroxyl group or at least one nitrogen atom is included in the structure of the carboxylic acid.

The carboxylic acid preferably has at least four carbon atoms.

The carboxylic acids used according to the invention can thus have, for example, 2 to 10 C atoms, preferably 4 to 10 C atoms.

According to one embodiment of the invention, the carboxylic acids have at least two carboxyl groups and at least one hydroxyl group or, instead of the hydroxyl group, at least one nitrogen atom. Preference is given to di- or tricarboxylic acids which are additionally hydroxy-functionalized.

In addition to acetic acid and gluconic acid as monocarboxylic acids are in particular citric acid, tartaric acid, malic acid, ascorbic acid and complexing agents such as ethylenediaminetetraacetic acid (EDTA) and Methylglycindiessigsäure, z. B. as trisodium salt (eg., Trilon ^® M from BASF SE) into consideration.

In particular, the use of the di- and tricarboxylic acids, which are additionally hydroxy-functionalized, again leads to the following advantages over the use of acetic acid:

Less acid can be used to remove a certain amount of catalyst compared to acetic acid (5 to 30 wt% instead of about 40 wt%, based on the amount of catalyst). The separation effect is better when using equivalent amounts of polyfunctional carboxylic acids.

It is possible to use acids which are harmless to food technology and in some cases are even used as food additives, such as citric acid, ascorbic acid, tartaric acid.

The number of washing steps until the product is clear can be reduced, e.g. B. except for a washing step.

The use of hydroxycarboxylic acids leads to a lower risk potential, since they are only irritating and not corrosive like acetic acid.

Less molecular weight degradation by the hydroxy-functionalized di- and tricarboxylic acids is observed as compared with acetic acid and hydrochloric acid.

Also suitable polycarboxylic acids, such as polyacrylic into account how they are marketed for example under the name Sokalan ^® from BASF SE. In addition, according to the invention, acidic ion exchangers can also be used. These may be ion exchangers with carboxyl or sulfonyl or sulfoxyl groups. Frequently, ion exchangers have been derivatized acid-starting from polystyrene substrates by reaction with concentrated sulfuric acid. Suitable ion exchangers, for example, under the name Dowex ^®, for example Dowex50WX8-200-strongly acidic Dow available. Similar ion exchangers can also be used according to the invention.

Today's most common ion exchangers are polystyrene resins which are crosslinked with divinylbenzene (DVB) and thus show a high high molecular weight, three-dimensional structure and are usually present in spherical form.

Sulfonation of the crosslinked polystyrene resin, for example with oleum, produces a strongly acidic cation exchanger. An alternative to the reaction with sulfuric acid is the reaction with perfluorosulfonic acid, cf. Applied Catalysis A: General 221 (2001), pages 45 to 62. For the preparation of weakly acidic cation exchangers, instead of styrene, acrylic acid derivatives are cross-linked with divinylbenzene. The free carboxyl groups of the polyacrylates can be obtained by basic hydrolysis of the ester groups. Furthermore, phenol-formaldehyde gels can also be used. The amount of carboxylic acid is preferably 5 to 80 wt .-%, particularly preferably 7.5 to 40 wt .-%, in particular 10 to 25 wt .-%, based on the polyalkylene carbonate.

The carboxylic acid can be used as a liquid, solid or in dissolved form.

The reaction mixture obtained after the reaction is treated with a non-water-miscible organic solvent which dissolves the polyalkylene carbonate. Examples of suitable solvents are esters, preferably C-12-alkyl esters of C-12-alkanecarboxylic acids. Particularly preferably, ethyl acetate is used as the solvent. The amount of solvent added is preferably 10 to 1000%, particularly preferably 50 to 500%, in particular 70 to 140%, based on the amount of reaction mixture (polymer solution) after the polymerization. The amount can be adjusted depending on the solids content of the polymer solution or the reaction mixture. Typically, the same amount (by volume) of ethyl acetate is added to the polymer solution. If the solids content of the polymer solution is below 18% by weight, the amount of ethyl acetate may be somewhat reduced.

The reaction with the carboxylic acid or the acidic ion exchanger is preferably carried out with agitation of the mixture of reaction mixture and organic solvent. For this purpose, suitable mixing equipment such as conventional agitators can be used.

The reaction with the carboxylic acid or the acidic ion exchanger is preferably carried out for a period in the range from 5 minutes to 5 days, more preferably 15 minutes to 5 hours.

The reaction with the carboxylic acid takes place at a temperature of preferably 10 to 60 ° C. In particular, it is reacted at room temperature (22 ° C.).

Depending on the carboxylic acid used, it may be useful to react the polyalkylene carbonate with a carboxylic acid anhydride before adding to the carboxylic acid or the acidic ion exchanger. As the carboxylic anhydride, any suitable carboxylic acid anhydrides can be used, the anhydrides of monocarboxylic acids and anhydrides of dicarboxylic acids. Examples are maleic anhydride and acetic anhydride. Particular preference is given to using acetic anhydride. The amount of carboxylic anhydride is preferably 0.5 to 25 wt .-%, more preferably 1 to 15 wt .-%, in particular 2 to 10 wt .-%, based on the polyalkylene carbonate.

The reaction with the carboxylic anhydride is preferably carried out at a temperature in the range of 10 to 60 ° C. In particular, it is reacted at room temperature (22 ° C.). The addition preferably takes place before the acid addition. By reacting with carboxylic anhydride, especially acetic anhydride, the chain ends of the polyalkylene carbonate are protected. Thus, possible molecular weight degradation is prevented by anionic attack, for example by the acetate of acetic acid. When using the preferred polybasic carboxylic acids, in particular di- and tricarboxylic acids, which are additionally hydroxy-functionalized, there is generally no significant or substantial reduction in the molecular weight of the polyalkylene carbonates. Therefore, when used on the protection of the chain ends by carboxylic anhydride, especially acetic anhydride, are dispensed with. For example, when citric acid is used as the carboxylic acid, chain end protection by carboxylic acid anhydride such as acetic anhydride is not required. This simplifies the purification process by one component and can eliminate a dosing step (for the anhydride). After reaction of the reaction mixture with the carboxylic acid or the acidic ion exchanger, the reaction mixture is washed with water. For this purpose, the reaction mixture is mixed intensively with water, and after a subsequent phase separation, the aqueous phase is separated off. The amount of water added per wash is preferably 0.01 to 5 times, more preferably 0.5 to 2 times the amount (weight) of the reaction mixture with non-water-miscible organic solvent. The water may also already be contained in the acid solution.

It is possible according to the invention to carry out one or more washing steps one after the other. Preferably, so many washing steps are carried out until the final pH of the organic phase is about 4 or more.

Depending on the carboxylic acid used, the time for the phase separation in organic phase and aqueous phase may vary. The number of washing steps required may also depend on the type of carboxylic acid used, as described below in the examples. After washing the organic phase with water and separating the water phase, the polyalkylene carbonate can be recovered from the organic phase. This can be done for example by evaporation of the organic solvent.

If the polyalkylene carbonate is to be further processed in solution, this may also remain in the organic phase.

The process for the preparation of polyalkylene carbonates by polymerization of carbon dioxide with at least one epoxide of the general formula (I) is described in general form in WO 03/029325. The preparation of the zinc glutarate catalyst described therein by reacting zinc oxide with glutaric acid can also be carried out according to the invention. The zinc glutarate catalysts described in WO 03/029325 can also be used according to the invention.

In the preparation of the catalysts, the zinc oxide particles are preferably reacted with terminal C ₄ - ₈ alkanedicarboxylic acids. Preferably, the reaction is carried out with glutaric acid, adipic acid or mixtures thereof. Thus, the zinc salts are preferably zinc glutarates or zinc adipates.

In the polymerization, the catalyst is preferably used in anhydrous form. Anhydrous in the context of the invention means that the water content in the catalyst is preferably less than 1 wt .-%, more preferably at most 10 ppm, based on the total catalyst. Anhydrous means particularly preferred that the catalyst - apart from chemically bound water (for example, water of crystallization) contains no water or only insignificant traces of water, in particular no superficially adhering or physically trapped in cavities water. The epoxide used is preferably ethylene oxide, propylene oxide, butene oxide, cyclopentene oxide, cyclohexene oxide, i-butene oxide, acryloxides or mixtures thereof. Particular preference is given to using propylene oxide, cyclohexene oxide, ethylene oxide or a mixture thereof. In particular, propylene oxide is used. For further possible epoxides, reference may be made to WO 03/029325, pages 6 and 7. When C0 ₂ and two or more epoxides are used, polycarbonate terpolymers are formed. Suitable mixtures of two epoxides are, for example, ethylene oxide and propylene oxide, ethylene oxide and cyclohexene oxide, propylene oxide and cyclohexene oxide, i-butene oxide and ethylene oxide or propylene oxide, butylene oxide and ethylene oxide or propylene oxide. The ratio of carbon dioxide to epoxide can be varied within wide limits. Carbon dioxide is usually used in excess, ie more than 1 mol of carbon dioxide per 1 mol of epoxide. The process according to the invention preferably comprises essentially the following process steps:

1 . Drying of the catalyst,

2. Submitting the anhydrous catalyst in a polymerization reactor,

3. optionally adding an inert reaction medium,

4. adding carbon dioxide,

5. adding the epoxide,

6. heating the reactor to the reaction temperature,

7. optionally adding more carbon dioxide and

8. After the polymerization reaction has ended, the reactor contents are worked up onto the polycarbonate, wherein steps 5 and 6 can be reversed.

The reaction can be carried out in an inert reaction medium in which the catalyst can be dissolved or dispersed.

Suitable inert reaction medium are all substances which do not adversely affect the catalyst activity, in particular aromatic hydrocarbons such as toluene, xylenes, benzene, and also aliphatic hydrocarbons such as hexane, cyclohexane, and halogenated hydrocarbons such as dichloromethane, chloroform, isobutyl chloride. Likewise suitable are ethers, such as diethyl ether, furthermore tetrahydrofuran, diethylene glycol dimethyl ether (diglyme), dioxane, and nitro compounds, such as nitromethane. Preferably, toluene is used.

The inert medium can be pressed into the polymerization reactor, for example, as such or preferably with a gas stream, it being possible to use an inert gas, such as nitrogen, or else the reactant C0 ₂ as the gas.

The catalyst is preferably initially introduced into the reactor, rendered anhydrous by heating in an inert gas stream, allowed to cool if necessary, and the agitated inert gas is pressed into the reactor while stirring.

Based on the catalyst solution or dispersion (sum of catalyst and reaction medium), the catalyst concentration is preferably 0.01 to 20, in particular 0.1 to 10 wt .-%. Based on the sum of epoxide and inert reaction medium, the catalyst concentration is preferably 0.01 to 10, particularly preferably 0.1 to 1,% by weight.

In another, likewise preferred embodiment, the reaction is carried out without an inert reaction medium.

According to the invention, the catalyst is first brought into contact with at least a portion of the C0 ₂ , before adding the epoxide. In this context, "with at least one subset" means that, before the epoxide is added, either a subset of the total amount of C0 _{2 used is} added, or already the total amount of C0 ₂ .

Preference is given to adding only a subset of the C0 ₂ and more preferably this subset is 20 to 80, in particular 55 to 65 wt .-% of C0 ₂ - total.

Typically, one adds the C0 ₂ as a gas added, and the C0 ₂ amount is set by the C0 ₂ gas pressure as a function of temperature. At room temperature (23 ° C) in the reactor, the C0 ₂ pressure prior to the addition of the epoxide (hereinafter called C0 ₂ -Vordruck), which corresponds to the preferred C0 ₂ subset, when using the zinc carboxylate catalysts from 5 to 70, especially 10 to 30 bar, and when using the multimetal cyanide catalysts 5 to 70, in particular 10 to 50 bar. Typical values for the C0 ₂ blank are 15 bar for zinc carboxylate catalysts and 50 bar for multimetal cyanide catalysts, each at 23 ° C.

All pressures are absolute pressures. The C0 ₂ -Vordruck can be set discontinuously at once or divided into several steps, or even continuously over a certain period of time linearly or following a linear exponential or stepwise gradient.

When choosing the C0 ₂ -Vordrucks the pressure increase in the reactor due to the subsequent heating of the reactor to the reactor temperature is observed. The C0 ₂ pre-pressure (eg at 23 ° C) must be selected so that the desired final C0 ₂ pressure at the reaction temperature (eg 80 ° C) is not exceeded.

The contacting of the catalyst with C0 ₂ is usually at temperatures of 20 to 80 ° C, preferably 20 to 40 ° C instead. Particularly preferably, the reaction is carried out at room temperature (23 ° C.). The duration of the contacting of catalyst and C0 ₂ is dependent on the reactor volume and is usually 30 sec to 120 min. In general, the catalyst or the solution or dispersion of the catalyst in the inert reaction medium, during the contacting with the C0 _{2 is} stirred.

Only after the catalyst has been contacted with C0 ₂ is the epoxide added to the reactor. The epoxide is usually pressed as such or preferably with a small amount of inert gas or C0 ₂ in the reactor.

The addition of the epoxide is usually carried out with stirring and can take place all at once (especially in the case of a small reactor volume) or continuously over a period of generally 1 to 100 minutes, preferably 10 to 40 minutes, the addition may be constant in time, or a gradient can follow, the z. B. ascending or descending, linear, exponential or may be stepwise.

The temperature during the addition of the epoxide is generally from 20 to 100, preferably from 20 to 70 ° C. In particular, it is possible to a) either add the epoxide at low temperature (eg room temperature 23 ° C.) and then adjust the reactor to the reaction temperature T _R (eg 80 ° C.) or b) conversely, first to the reactor to the reaction temperature T _R adjust and then add the epoxy. Variant a) is preferred.

Accordingly, the reactor is brought to the reaction temperature T _R before or, preferably, after the addition of the epoxide. The reaction temperature is usually adjusted to 30 to 180, in particular 50 to 130 ° C. This is usually done by heating the reactor with stirring. The reaction temperature is usually 40 to 120, preferably 60 to 90 ° C.

After reaching the reaction temperature are added, preferably with stirring, the remaining amount of C0 ₂ in the reactor, unless the C0 ₂ total amount was already supplied when contacting the catalyst with C0 ₂ (see above). Usually prepared the C0 ₂ amount again over the C0 ₂ gas pressure one.

Preferably C0 _{2 is} added until the C0 ₂ pressure (hereinafter C0 ₂ - called final pressure) when using zinc carboxylate catalysts 1 to 200, preferably 10 to 100 bar and when using multimetal cyanide catalysts 20 to 200, preferably 80 to 100 bar, is. Typical values for the CO ₂ final pressure are 20 to 100 bar for zinc carboxylate and 100 bar for multimetal cyanide catalysts.

All pressures are absolute pressures. The added in this process step C0 ₂ amount (C0 ₂ -Enddruck) naturally depends also on the C0 ₂ -Teilmenge that had been previously added. From the mentioned CO ₂ pressures and reaction temperatures, it follows that the CO ₂ in the reactor can be in the supercritical state (ie liquid). Especially at C0 ₂ final pressures above 74 bar and reaction temperatures T _R above 31 ° C, the C0 _{2 is} in the supercritical state. In contrast to conventional chemical reactions in critical C0 ₂ , the C0 ₂ in the present process, however, not only reaction medium, but at the same time feed (reactants) and reaction medium.

The C0 ₂ final pressure can be adjusted discontinuously at once or continuously as described for the C0 ₂ -Vordruck.

After reaching the final C0 ₂ pressure can be maintained by replenishment of the spent C0 ₂ , if necessary. If no C0 _{2 is} metered in, the C0 ₂ pressure during the reaction usually falls by the consumption of C0 ₂ . This procedure is also possible.

Usually, the time to complete the polymerization reaction is 60 to 500 minutes, preferably 120 to 300 minutes. A typical value for this post-reaction time is 3 to 4 hours.

Usually keeping the reaction temperature constant; however, you can also raise or lower it depending on the progress of the reaction.

The proportions C0 ₂ : epoxide used in the process depend in a known manner on the desired properties of the polymer. Usually, the quantitative ratio (weight ratio) total amount C0 ₂ : total amount of epoxy 1: 1 to 2: 1.

In a preferred embodiment, all of the abovementioned process steps are carried out with the exclusion of water: not only the catalyst, but also the inert reaction medium, the CO ₂ and the epoxide are anhydrous or are rendered anhydrous in a customary manner.

After the polymerization reaction has subsided, the reactor contents are worked up onto the polycarbonate. In general, the reactor is allowed to cool with stirring, the pressure equalization with the environment ago (venting of the reactor) and extends the polycarbonate polymer-containing reaction mixture. The reactor contents can be added to a suitable precipitation medium, if desired. Usually used as precipitation medium alcohols such as methanol, ethanol, propanol, or ketones such as acetone. Methanol is preferred. It is advantageous to acidify the precipitation medium to pH 0 to 5.5.

The precipitated polymer can be separated as usual, for. B. by filtration, and dried in vacuo.

In some cases, part of the reaction product polycarbonate is also dissolved or dispersed in the precipitation medium, for example in the acidified methanol. This polycarbonate can be isolated in the usual way by removing the precipitant. For example, the methanol can be distilled off under reduced pressure, for example on a rotary evaporator. Preferably, however, the reaction mixture is added directly to the non-water-miscible organic solvent and the carboxylic acid or the ion exchanger without prior precipitation. A previously precipitated polymer may also subsequently be redissolved in the non-water-miscible organic solvent. The polyalkylene carbonates obtained in accordance with the invention can be further processed in many ways into moldings, films, films, coatings and fabrics, see for example WO 03/029325, pages 21 and 22.

The invention is further illustrated by the following examples.

Examples

The polypropylene carbonate was prepared analogously to WO 2003/029325.

1 . catalyst Preparation

In a 1 l four-necked flask equipped with stirring bones, heating bath and a water separator, 35 g of crushed zinc oxide in 250 ml of absolute toluene were introduced. After addition of 53 g glutaric acid was heated to 55 ° C with stirring for 2 hours. The mixture was then heated to boiling, the reaction water was distilled off azeotropically under reflux until no more water passed. The toluene was distilled off and the residue was dried at 80 ° C under high vacuum. 2. Polymerization

12 g of zinc glutarate were placed in the reactor. A 3.5 l autoclave with mechanical stirrer was used. After closing the reactor was rinsed several times with N ₂ gas. Then 620 g of toluene were added, and at room temperature (23 ° C) 6 bar C0 _{2 were} forced into the reactor. Subsequently, 310 g of propylene oxide were pressed into the reactor and heated to 80 ° C. Thereafter, at 80 ° C as long C0 _{2 was} pressed into the reactor until a C0 ₂ pressure of 40 bar was reached. The reactor was kept for 4 h at 80 ° C, with no C0 _{2 was} dosed. Then allowed to cool to room temperature.

3.1 Workup with HCl (Comparison) Workup with HCl: The work-up was carried out according to WO 03/029325 A1. The reactor was vented and the reactor contents were poured into 1 L of methanol acidified with 5 mL of concentrated hydrochloric acid (37% by weight). It precipitated a polymer, which was filtered off and dried overnight at 60 ° C in vacuo. 3.2 Work up with acetic acid (HAc)

The polymer solution from 2. was mixed with the equivalent amount of ethyl acetate. If the solids content of the polymer solution should be below 18%, the amount of ethyl acetate was corrected slightly downwards. After subsequent stirring, 4% acetic anhydride (amount based on the amount of acetic acid) was added and stirred again. After the addition of 40% acetic acid, based on the solids content, and stirring was diluted with water (amount of water corresponds to the amount of organic phase) and washed out. The phase separation could take 1 h up to 48 h, depending on the approach. This washing step was carried out four to five times. The initial pH, d. H. after addition of the acid, it was about 1. After four to five washings, the pH was 4.

4. Work up with polyfunctional carboxylic acids / hydroxycarboxylic acids 4.1 Citric acid C ₆ H ₈ 0 ₇

The polymer solution was added with the equivalent amount of ethyl acetate. If the solids content of the polymer solution should be below 18%, the amount of ethyl acetate was corrected slightly downwards. After subsequent stirring, 4% acetic anhydride (amount based on the amount of citric acid) was added and stirred again. Only 20% of citric acid, based on the solids content, had to be content, in the form of a saturated solution (500 g of citric acid per 1 L of water). The polymer solution was already clear at the first leaching.

For this reason, less leaching is needed than in the case of acidic leaching. Furthermore, the use of citric acid provides a further advantage: the starting pH is already 2.5-3 and therefore fewer washing steps are required to reach the final pH of 4. Here are 2-3 washing steps in contrast to the 4-5 washes in the acetic acid variant. Separation of the organic and aqueous phases was much faster when using citric acid (max 5 min) than when using HAc (15-30 min). Furthermore, the organic phase was clear after the first wash, when citric acid was used. This was the case with HAc only after several washes.

Another advantage of citric acid over acetic acid is its chemical properties: acetic acid is classified as corrosive (C) (R10-35, S (1/2) -23- 26-45), whereas citric acid is only irritating (R36 , S26). This also results in a much more comfortable handling of the acid. The acids are used in excess, based on the amount of catalyst to be destroyed. As a result, optionally deprotonated acid which has not reacted with a catalyst particle attack the chain ends of the polymers. In the case of hydrochloric acid and (attenuated) acetic acid this could be observed. In the case of the di- and tricarboxylic acids, which are additionally hydroxy-functionalized, the effect did not occur. Due to the geometry of the acids, it is possible that the negative charge of the carboxylates is shielded by the proton of the adjacent hydroxy unit through hydrogen bonds. This attenuates the attack of the carboxylates on the polymer chain ends and thus reduces the molecular weight degradation. The optional addition of about 4% acetic anhydride (ESA) is carried out for the following reason: The chain ends of the PPC should be protected with acetic anhydride, and so should a molecular weight reduction by anionic attack z. B. be prevented by the acetate of acetic acid. Comparing experiments in which 20% citric acid and 4% acetic anhydride were added at 40 ° C and washed three times with analogous experiments without acetic anhydride, the absence of acetic anhydride in the use of citric acid instead of acetic acid causes no disadvantages. Thus, when citric acid is used, one does not require protection of the chain ends by acetic anhydride and thus simplifies the purification process by one component and one dosing step. The washout quality is still maintained, the zinc values are at about 20 ppm. The molecular weights are Mn of 100,000 g / mol and Mw of 800,000 g / mol.

Also in the reduction of the amount of citric acid to 10%, based on the solids content of polymer, without the addition of acetic anhydride washing performance (40 ppm zinc) at 40 ° C and molecular weight (Mn = 99,700, Mw = 773000 g / mol) remain very good , With only 5% citric acid, the molecular weight remains unaffected, but the content of residual zinc does not drop below 200 ppm for three washes. If the reactions are carried out with 5% and 10% at room temperature, the separation of the organic and the aqueous phase from each other takes much longer (10 min-30 min) than at 40 ° C otherwise the polymer properties (M _n = 124,000 g / mol) and the zinc content (150 ppm) but unchanged.

4.2 tartaric acid C ₄ H ₆ O ₆ (2,3-dihydroxy succinic acid or 2,3-dihydroxybutanedioic acid)

The tests with tartaric acid were carried out analogously to those with acetic acid and citric acid. Tartaric acid behaved slightly worse than citric acid in the quality of the leaching, but also better than the conventional acetic acid. At room temperature, as in the case of acetic acid, 40%, based on the solids content, had to be added, but only 3 washing steps were required instead of 4-5. It was also possible to minimize the number of washing steps to 1 -2 for tartaric acid when the temperature of the polymer solution and the washing solution were raised to 40 ° C. At a working temperature of 40 ° C, the quantity could be reduced from 40 to 20%. However, the residual zinc concentration increased from 0.023 g / 100g polymer at room temperature and 40% acid to 0.06 g / 100g polymer at 40 ° C and 20% acid.

4.3 Gluconic acid C ₆ H ₁₂ 0 ₇ In the case of gluconic acid, similar amounts had to be used as are known from acetic acid (about 40%). The separation performance was similar. After three washes zinc contents were 2-40 mg zinc per 100 g polymer. The polymer was also crystal clear after only three separations. Although it required as much acid as acetic acid, only 3 instead of 4-5 were necessary. The clear advantage of the use of gluconic acid is to be found in the molecular weight of the polypropylene carbonate. This is always between 40,000 and 50,000 g / mol (M _n ) and thus significantly higher than those typically obtained in the work-up with acetic acid (M _n = 25,000-40,000 g / mol). 4.4 Ethylenediaminetetraacetic acid (EDTA) CioH ₁₆ N ₂ 0 ₈

Upon addition of 40 mol% Na-EDTA to the polymer solution to be washed (based on the solids content) at room temperature, a moderate separation of the zinc glutarate was achieved by washing three times. The zinc residues were about 1 g per 100 g of polymer. The polymer solution was also not clear. However, the highest molecular weights were observed for PPC with an M _n of more than 50,000 g / mol. The pH value was already about 7 with only three washes and thus in the optimum range. This could not be achieved with the conventional methods and also the acids mentioned above.

4.5 Malic Acid C ₄ H ₆ 0 ₅

If a PPC solution containing 40% by weight of malic acid, based on the solids content, was used (as an aqueous solution: 500 g / L) and washed three times with water, a clear polymer solution was obtained. The separation behavior was comparable to that of citric and tartaric acid. At 40 ° C, as expected, leaching was slightly improved over the room temperature procedure.

Acid ion exchanger (Dowex50WX8-200-strong acid)

A column with glass frit (pore size 1) was filled with the ion exchanger and moistened with ethyl acetate. Then, a highly diluted PPC solution (5% solids content) was filtered through the ion exchanger.

Although the polymer solution had to be greatly diluted, the polymer solution was clear after filtration through the ion exchanger. The ion exchanger was suitable for the destruction and separation of zinc glutarate from PPC solutions. Furthermore, here is the option to implement a continuous process.

The results are summarized in the following tables. Where:

EE ethyl acetate

FG solids content

ESA acetic anhydride

GPC gel permeation chromatography used PPC addition solution with acid for degradation ESA TempeDisplay of dispersion analysis of the dispersion after acid dispersion temperature on

GPC-GPC-bez. Quantity Poly-Lsg Type Quantity bez. on acid treatment zinc GPC- GPC- Mn Mw acid Mn Mw

28,000 440,000 50 wt% EA acetic acid 20 wt% 40 ° C After drying opaque

FG

75 wt% EE 40 wt% resp. 40 ° C clear 5 mg / 100 g 31,000 660.00

FG

75 wt% EE 40 wt% resp. 20% 40 ° C clear 73 mg / 100 g 46,000 750.00

FG

35,000 510,000 75 wt% EE 40 wt% rel. 2% 40 ° C clear 0, l g / 100 g

FG

used PPC addition solution with acid for degradation ESA TempeDisplay of dispersion analysis of the dispersion after acid dispersion temperature on

75 wt% EE 40 wt% resp. 2% 40 ° C clear 3 mg / 100 g

FG

34,000 420,000 100 wt% EE 33 wt% resp. 2% 40 ° C clear 3 mg / 100 g 91,000 680.00

FG

100 wt% EE 50 wt% 2% 40 ° C clear 12 mg / 100 g 68,000 660.00

FG

100 wt% EE without 110 crystal clear 0, l g / 100 g 62,000 739.00 mol%

bez. FG

49,000 560,000 100 wt% EE acetic acid 40 wt% rel. 4% 40 ° C clear 0.01 g / 100 g 77.500 839.00

FG

62,000 739,000 100 wt% EE acetic acid 40 wt% rel. 4% 40 ° C clear 41.400 527.00

FG not measured 20 wt% EE 40 wt% rel. 4% RT very well flowing, clear 0.062 g / 100 g 105.000 789.00

80 wt% butyl acetate FG

20 wt% EE 40 wt% resp. 4% RT good flowing, crystal clear 0.003 g / 100 g 100,000 789.00 80 wt% butyl acetate FG

20 wt% EE 40 wt% resp. 4% RT Poor separation, hazy 0.081 g / 100 g 132.000 621.00 80 wt% Isopentylace- FG to white

did

100 wt% EE 40 wt% resp. 4% RT organic phase to 0.009 g / 100 g 90,000 891.00

FG water 1: 3;

very good separation; org.

Phase clear

100% by weight of oleic acid 40% by weight 4% RT Relatively good separation, 1720 609,000

FG streaks

org. Phase opaque

100 wt% EE citric acid 40 wt% 4% RT Very fast clarification, 101.000 1.020.00 re FG good separation

Org. Phase very clear

77,000 778,000 100 wt% EE citric acid 40 wt% rel. 4% RT Very good separation <0.001 g / 100 64.200 594.000 re FG Org. Phase very clear g

100% by weight of citric acid 80% by weight, based on Without RT Very good separation <0.001 g / 100 65.300 587.000 re FG Org. Phase very clear g

100 wt% EE citric acid 40 wt% 4% RT Fast very clear, good <0,001 g / 100 63,700 598,000 re FG separation g

200 wt% EE citric acid 40 wt% rel. 4% RT Fast very clear, good <0.001 g / 100 81,000 782,000 re FG separation g

100% by weight of citric acid 20% by weight, based on 4% RT Initially slightly opaque, 0.017 g / 100 g 83.500 843.000 re FG later clear

Good separation

Not measured 100 wt% EE citric acid 20 wt% resp. 4% 40 ° C Very clear, good separation 0.025 g / 100 g 98.100 747.000 re FG Inclusion of water bubbles

100% by weight of citric acid 20% by weight, based on without 40 ° C very fast very clear 0.002 g / 100 g 108.000 806.000 re FG

100% by weight of citric acid 10% by weight, based on without 40 ° C within a few minutes 0.004 g / 100 g 99.700 773.000 re FG clear

100 wt% EE citric acid 5 wt% rel. without 40 ° C org. phase clear 0.024 g / 100 g 106.000 812.000 re FG

100% by weight of citric acid 10% by weight, based on 4% RT approx. 30 min. up to 0,015 g / 100 g 124,000 857,000 re FG clearing

Then clearly

56,000 349,000 100 wt% EE tartaric acid 40 wt% resp. 4% RT Aqueous phase turbid 0.023 g / 100 g 61.400 339.000

FG Org. Phase clear

100% by weight of tartaric acid 40% by weight. 4% 40 ° C Aqueous phase turbid 0.028 g / 100 g 64.300 376.000

FG Org. Phase clear

100% by weight of tartaric acid 20% by weight, based on 4% 40 ° C Aqueous phase turbid 0.06 g / 100 g 76.700 382.000

FG Org. Phase clear

40,200 236,000 80 wt% EE gluconic acid 40 wt% rel. 4% RT White foam at 0.002 g / 100 g 49,600 382,000

(FG <18%) e FG dividing line

Org. Phase clear

80 wt% EE gluconic acid 40 wt% rel. 4% 40 ° C White foam at 0.037 g / 100 g 41.800 246.000 e FG parting line

Org. Phase clear

80 wt% EA Na-EDTA 20 mol% without RT Org. Phase cloudy, pH> 1.2 g / 100 g 55.400 586.000

7.5

80 wt% EA Na-EDTA 20 mol% without 40 ° C Org. Phase turbid, pH> 0.89 g / 100 g 47,800 552,000

7.6

100 wt.% EE malic acid 40 wt. 4% 40 ° C is getting clear, good

FG separation

100 wt.% EE malic acid 40 wt. 4% RT is getting clear, good

FG separation

300 wt% EE Strong acid Without RT solution

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Claims

claims

1 . Process for the preparation of polyalkylene carbonates by polymerization of carbon dioxide with at least one epoxide of the general formula (I) with the meaning

R independently of one another H, halogen, NO ₂ , CN, COOR 'or C ₁ - ₂ 0-

Hydrocarbon radical which may be substituted, where one of the radicals R may also denote OH, and wherein two radicals R may together form a C _3-5 alkylene radical, R 'is H or Ci _-2 o hydrocarbon radical which may be substituted on a zinc salt of C ₄ - ₈ alkanedicarboxylic acids as catalyst, characterized in that the reaction mixture obtained after the reaction is treated with a non-water-miscible organic solvent which dissolves the polyalkylene carbonate and with a carboxylic acid or an acidic ion exchanger, the organic Is washed phase with water and optionally the polyalkylene carbonate is recovered from the organic phase.

2. The method according to claim 1, characterized in that the zinc salt of C _4-8 alkanedicarboxylic acids zinc glutarate or zinc adipate.

3. The method according to claim 1 or 2, characterized in that in the carboxylic acid, the number of carboxyl and hydroxyl groups together is at least 2.

4. The method according to any one of claims 1 to 3, characterized in that the carboxylic acid contains in its structure at least one hydroxyl group or at least one nitrogen atom.

5. The method according to any one of claims 1 to 4, characterized in that the carboxylic acid contains at least four carbon atoms.

6. The method according to any one of claims 1 to 5, characterized in that the carboxylic acid is selected from acetic acid, citric acid, tartaric acid, gluconic acid, malic acid, ethylenediaminetetraacetic acid (EDTA),

Methylglycinediacetic acid (MGDA), ascorbic acid, polycarboxylic acids or mixtures thereof.

7. The method according to any one of claims 1 to 6, characterized in that the amount of carboxylic acid 5 to 80 wt .-%, based on the polyalkylene carbonate is.

8. The method according to any one of claims 1 to 7, characterized in that the organic solvent is an ester.

9. The method according to any one of claims 1 to 8, characterized in that the polyalkylene carbonate is reacted before the addition of the carboxylic acid or the acidic ion exchanger with a carboxylic acid anhydride.

10. The method according to claim 9, characterized in that the amount of carboxylic anhydride 0.5 to 25 wt .-%, based on the polyalkylene carbonate is.

1 1. Use of carboxylic acids or acid ion exchangers in the purification of polyalkylene carbonates.

12. A process for the purification of zinc salts of C ₄ - ₈ alkanedicarboxylic polyalkylene containing polycarbonates, characterized in that one carries out the purification steps defined in any one of claims 1 to 10.