EP2542341A2

EP2542341A2 - Modified zinc salts of c4-8-alkane dicarboxylic acids and use thereof as polymerization catalysts

Info

Publication number: EP2542341A2
Application number: EP11709662A
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: 2011-03-04
Publication date: 2013-01-09
Also published as: WO2011107577A2; CN102869444A; WO2011107577A3

Abstract

The invention relates to zinc salts of C_4-8-alkane dicarboxylic acids, which can be obtained by reacting C_4-8-alkane dicarboxylic acids with surface-modified zinc oxide particles, wherein the surface-modified zinc oxide particles can be obtained by treating zinc oxide particles with organosilanes, silazanes and/or polysiloxanes and subsequently heat treating and/or UV irradiating the treated zinc oxide particles, and to the use thereof as polymerization catalysts for producing polyalkylene carbonates.

Description

Modified zinc salts of C ₄ - ₈ alkanedicarboxylic acids and their use as polymerization catalysts

description

The invention relates to modified zinc salts of C _4-8 alkanedicarboxylic acids, to processes for their preparation, to their use as catalysts, in particular as polymerization catalysts for the preparation of polyalkylene carbonates, to processes for the preparation of polyalkylene carbonates and to polyalkylene carbonates obtainable by the process.

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. The zinc glutarate catalyst is prepared by reaction of crushed zinc oxide with glutaric acid in toluene. After the reaction, the reaction water is distilled off azeotropically. Then the solvent toluene is distilled off, and the residue is dried under high vacuum. For the zinc glutarate catalyst, the catalyst activity depends on the moisture content of the catalyst. Zinc glutarate shows no or only a very low polymerization activity when completely dried. Only by addition of water or absorption of air humidity, the maximum activity is reached. In addition, the zinc glutarate catalyst powder tends to clump and can thus be difficult to dose especially after prolonged storage.

The object of the present invention is to provide improved polymerization catalysts for the preparation of polyalkylene carbonates, which avoid the abovementioned disadvantages of the normal zinc glutarate catalysts and preferably additionally show an improved activity. In addition, the catalyst should preferably lead to an increase in the glass transition temperature in the resulting polyalkylene carbonate.

The objects are achieved by zinc salts of C _4-8 - alkanedicarboxylic acids, obtainable by reaction of C _4-8 alkanedicarboxylic with surface-modified zinc oxide particles, wherein the surface-modified zinc oxide particles are obtainable by treatment of zinc oxide particles with organosilanes, silazanes and / or polysiloxanes and subsequent heat treatment and / or UV irradiation of the treated zinc oxide particles.

It has been found according to the invention that the surface modification of the zinc oxide particles which are used to prepare the zinc salts of C ₄ - ₈ alkanedicarboxylic acids leads to more active catalysts which have improved storage stability and dispersibility, provide more stable polymerization results independently of the moisture range and do not need additional activation after drying. In addition, the use of the catalyst according to the invention increases the glass transition temperature for the polyalkylene carbonates obtained. The catalyst is much finer in particle size than the unmodified zinc glutarate catalyst and does not tend to cake or clump. The bulk density of the silane-modified catalyst according to the invention is significantly lower than the bulk density of the unmodified catalyst.

The catalysts according to the invention are prepared analogously to processes known from the prior art. For example, reference may be made to the procedure according to WO 03/029325, there in particular example 1 on page 22. Here, instead of unmodified zinc oxide, surface-modified zinc oxide in particle form is used. The surface modification of the zinc oxide is carried out by treatment or coating with organosilanes, silazanes and / or polysiloxanes and subsequent heat treatment and / or UV irradiation of the treated or coated zinc oxide particles.

Such surface-modified zinc oxide particles are known from the prior art and described for example in EP-A-1 508 599 and WO 2006/092442. Surface-modified zinc oxide particles which are obtained according to EP-A-1 508 599 or WO 2006/092442 can preferably be used according to the invention. For the preparation of zinc oxide particles and their properties can be made to these two documents.

The modified zinc oxide described in WO 2006/092442 is used in heterogeneous catalysis, in particular for the decomposition of chlorinated hydrocarbons, and in photovoltaics and for the coating of photoelectrodes. The modified ZnO prepared according to EP-A-1 508 599 is used in cosmetics.

In EP-A-1 508 599, paragraph [0061] also describes suitable surface-modifying agents according to the invention. These are organosilanes, halo- organosilanes, silazanes or polysiloxanes, although cyclic polysiloxanes may also be considered.

According to the invention, the treatment or coating of the zinc oxide particles with organosilanes, especially with alkoxyalkylsilanes, is particularly preferably carried out.

Preferred organosilanes correspond to the type (RO) ₃ Si (CnH ₂ n + i) and (RO) ₃ Si (CnH ₂ ni) meaning

R is alkyl such as methyl, ethyl, n-propyl, i-propyl, butyl and

n is from 1 to 20, preferably from 1 to 10.

More preferred organosilanes are of the type R _'x (RO) y Si (C n H ₂ n + i) and R' _x (RO) _y Si (CnH ₂ ni) with the meaning

R and R 'independently of one another are alkyl such as methyl, ethyl, n-propyl, i-propyl, butyl, where R' can also be cycloalkyl,

n number from 1 to 20,

x + y = 3,

x 1 or 2,

y 1 or 2.

Such suitable organosilanes are described in EP-A-1 508 599 in paragraph [0061] in paragraphs a) and b). The alkoxyalkylsilanes described in WO 2006/092442 can also preferably be used according to the invention, see in particular page 3, last paragraph, page 4, first paragraph. Preferred alkoxyalkylsilanes are trimethoxyalkylsilanes. Preference is given to methyltrimethoxysilane, isooctyltrimethoxysilane, trimethoxyvinylsilane, triethoxyoctylsilane, 3-methacryloxypropyltrimethoxysilane, isooctyltriethoxysilane, methyltriethoxysilane, vinyltriethoxysilane,

Isobutylisopropyldimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, [3- (2,3-epoxypropoxy) propyl] trimethoxysilane, N- (2-aminoethyl) -3-aminopropaltrimethoxysilane, (3-methacryloxypropyl) methyldimethoxysilane, dicyclopentyldimethoxysilane, dimethoxymethyloctadecylsilane.

The organosilanes, silazanes and / or polysiloxanes can be used in any suitable amounts for modifying the ZnO particles. They are preferably used in a concentration of 0.1 to 15 mol%, in particular of 2 to 10 mol%.

The treatment or coating of the zinc oxide particles with the organosilanes, silazanes and / or polysiloxanes can be carried out in any suitable manner. For example, the surface modifying agent may be sprayed on the zinc oxide become. Optionally, the zinc oxide can be previously sprayed with water. The spraying can take place at any suitable temperature, for example room temperature (22 ° C.). It is also possible to suspend or disperse the ZnO particles in a polar protic solvent and then to treat them with the surface modifying agents, especially with alkoxyalkylsilanes. The polar protic solvents are preferably selected from the group consisting of aliphatic, aromatic or cyclic monohydric or polyhydric alcohols or thioalcohols and aldehydes. Preferably, the polar protic solvent is methanol.

When working in solvent, the treatment of the suspended and / or dispersed ZnO particles with the surface-modifying agents, in particular alkoxyalkylsilanes, preferably at a temperature of 40 to 70 ° C, in particular at about 60 ° C.

The treatment or coating of the zinc oxide particles with the surface-modifying agents is followed by heat treatment and / or UV irradiation of the treated zinc oxide particles. The UV irradiation can be carried out as described in WO 2006/092442. The treated zinc oxide particles are preferably exposed to UV irradiation in an aqueous medium. The duration of the UV irradiation can be chosen freely. The treated zinc oxide particles are preferably exposed to UV irradiation for 45 to 90 minutes, in particular about 60 minutes. When heat treatment is applied to the treatment or coating of the zinc oxide particles with the surface modifying agents, it is preferably carried out at a temperature in the range of 50 to 400 ° C for a period of 1 to 6 hours. For corresponding procedures, reference may be made to EP-A-1 508 599.

Alternatively, the surface modifying agent may also be applied in vapor form to the zinc oxide, followed by a temperature treatment in the range of 50 to 800 ° C for 0.5 to 6 hours. The zinc oxides used for modification according to the invention can be derived from any suitable sources. For example, zinc oxide can be used as described in WO 92/13517 or DE-A-102 12 680. Nanoscale ZnO with a particle diameter of less than 100 nm can be prepared via precipitation reactions in the sol-gel process, compare the references cited in WO 2006/092442 on pages 1 and 2. The silane molecules, in particular alkoxyalkylsilane molecules, are preferably covalently bound to the ZnO particles, whereby an inorganic network of -O-Si-O-Si-O units is formed in the aqueous medium under UV irradiation, which partially increases put together polycyclic silsesquioxane units.

Without being bound by theory, it is possible that the subsequent thermal or UV irradiation oxidizes the organic radicals of the silanes. Between the individual ZnO particles, an inorganic oxide network of -O-Si-O-Si-O units can be formed, which bridges the particles and keeps them at defined intervals. A material obtained in this way has a high surface area of up to 130 m ² / g.

In the UV treatment, which can also take place with the addition of H ₂ 0 ₂ and / or under air during UV irradiation, UV light with a wavelength of less than 390 nm is preferably used.

The average particle size is preferably in the range from 50 to 300 nm. According to one embodiment of the invention, the ZnO particles are nanoscale. This means that they have a mean diameter of at most 100 nm.

Generally, the zinc oxide may have a BET surface area of 10 to 200 m ² / g. The surface-modified ZnO particles preferably have a surface area of at least 100 m ² / g, determined by the BET method, as described, for example, in WO 2006/092442 on page 5.

The surface-modified ZnO particles according to the invention preferably have a zinc content of at least 60% by weight, in particular from 65 to 75% by weight, determined in accordance with DIN 55908.

By reacting with C _4-8 alkanedicarboxylic acids, the surface-modified zinc oxide particles lead to preferred polymerization catalysts for the preparation of polyalkylene carbonates. The surface-modified 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.

The production of the zinc salts is carried out by carrying out the specified process steps. The zinc salts can generally be used as catalysts and are especially suitable as polymerization catalysts for the preparation of polyalkylene carbonates, in particular of polypropylene carbonate. The catalysts of the invention show the following advantages:

Increasing the surface area and thus improving the catalytic activity - hydrophobization of the catalyst surface and thus reduction of water absorption

Polymerization at lower CO ₂ pressures is possible, yielding more polymer with better properties

Reducing the formation of by-products such as cyclic polycarbonates (cPC) better handling of the catalyst due to the improved flowability and the possible handling of atmospheric oxygen no clumping due to improved flowability and thus improved shelf life. The catalysts according to the invention are preferably used in 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 is independently H, halogen, N0 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, wherein the polymerization is carried out on a catalyst according to the invention. An R in formula (I) may e.g. For example, a radical may be -CH ₂ -OH or -CH ₂ -O-C (= C) R '. The C _3-5 alkylene radical is preferably a linear, terminal alkylene radical.

In this case, 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. Usually, carbon dioxide is used in excess, i. H. more than 1 mole of carbon dioxide per 1 mole of epoxide. The process according to the invention preferably comprises essentially the following process steps:

1 . Drying of the catalyst,

2. presentation of the anhydrous catalyst in a polymerization reactor, 3. optional addition of 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 reaction medium is forced into the reactor with gas 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 amount.

Usually, the C0 ₂ is added as a gas and the C0 ₂ amount is - depending on the temperature - adjusted via the C0 ₂ gas pressure. 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.

C0 ₂ is preferably added until the CO ₂ pressure (hereinafter referred to as CO ₂ - 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 up to 100 bar. 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 CO 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} added, it falls into usually the C0 ₂ pressure during the reaction by consumption of C0 ₂ from. 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 the above-mentioned process steps are carried out in the absence 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 the usual way.

After the polymerization reaction has subsided, the reactor contents are worked up onto the polycarbonate. This is done in a known manner. As a rule, the reactor is allowed to cool while stirring, the pressure is equalized with the environment (venting of the reactor) and the polycarbonate polymer is precipitated by adding the reactor content into a suitable precipitation medium.

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 with hydrochloric acid or another suitable acid.

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. The invention also relates to polyalkylene carbonates which are obtainable by the process described above.

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

1. Catalyst Preparation Silane-modified ZnO (modified) was prepared according to WO 2006/092442, in particular Example 2 and 3 on pages 6 and 7.

In a 1 l four-necked flask equipped with stirring bones, heating bath and a water separator, 35 g of triturated zinc oxide in 250 ml of absolute toluene were introduced. After addition of 53 g of 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.

For comparison, an unmodified zinc glutarate (standard) was prepared according to WO 03/029325, Example 1 on page 22.

2. Polymerization

The polypropylene carbonate was prepared analogously to WO 2003/029325, in particular Example 2b on page 23.

12 g of zinc glutarate from Example 1 were initially introduced into 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 pressed at room temperature (23 ° C) 6 bar C0 ₂ in the reactor. Subsequently, 310 g of propylene oxide were pressed into the reactor and heated to 80 ° C. Thereafter, at 80 ° C while 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. Work-up Work-up was carried out according to WO 03/029325 A1, in particular Example 2c on page 24. The reactor was aerated and the reactor contents were poured into 1 l of methanol, concentrated with 5 ml. Hydrochloric acid (37 wt .-%) was acidified, poured. It precipitated a polymer which was filtered off and dried overnight at 60 ° C vacuum. analytics

The results of the catalytic copolymerization and the obtained polypropylene carbonate are shown in Table 1 below.

The PO turnover is determined by the pressure drop. The number average molecular weight and polydispersity index (PDI) are determined from gel permeation chromatography (GPC) measurements. The contents of polypropylene carbonate and cyclic carbonate are derived from NMR measurements.

The zinc glutarate catalysts are not sensitive to atmospheric oxygen. However, the humidity affects both the handling and the activity of the catalyst. The unmodified standard catalyst forms agglomerates (lumps) a few centimeters in diameter when stored under normal atmospheric conditions. Under the same storage conditions, this is not the case for the silane-modified analog. The catalyst according to the invention is distinguished by improved storage stability and meterability over a period of at least 6 to 12 months.

The activity of the unmodified standard zinc glutarate catalyst is sensitive to the degree of drying or to the water content of the catalyst together. The silane-modified zinc glutarate system provides far more stable polymerization results over the range of moisture examined.

Both catalysts are active in the range of 0% water to 2 μί H ₂ 0 to 1 g of catalyst. The activity of the modified zinc glutarate catalyst is up to an addition from 1 μΙ_ water to 1 g catalyst constant and reproducible. This catalyst does not require additional activation after drying, as is the case with the unmodified zinc glutarate. This shows in the completely dried state no to very little activity. Only by the addition of water or absorption of air humidity, the maximum activity is reached here.

The modified catalyst gives twice as much polymer at 20 bar C0 ₂ pressure in the completely dried state as the unmodified zinc glutarate. As the polymerization pressure is lowered, the performance of the modified system becomes better and better compared to the unmodified standard. At 10 bar, 6 bar and 5 bar it delivers three times as much polymer in the same time. At lower pressures, when using the unmodified standard catalyst, in addition to the low activity, there is increasing softening of the polymer due to increased polyether content in the product. On the other hand, an influence on the glass transition temperature T _{g is} visible. This drops to below 10 ° C for polymers made at low pressures, while it does not fall below 20 ° C when using the modified catalyst.

The two catalysts also differ in bulk density. This was determined according to DIN ISO 697. For the unmodified zinc glutarate, 0.485 g of catalyst occupy a volume of 1 ml. The silane-modified catalyst is characterized by a much lower bulk density of 0.299 g / mL.

Claims

Patent claims

1 . Zinc salts of _C4-8 -alkanedicarboxylic acids, obtainable by reacting _C4-8 -alkanedicarboxylic acids with surface-modified zinc oxide particles, the surface-modified zinc oxide particles being obtainable by _treating

Zinc oxide particles with organosilanes, silazanes and/or polysiloxanes and subsequent heat treatment and/or UV irradiation of the treated zinc oxide particles.

2. Zinc salts according to claim 1, characterized in that the C _4-8 alkanedicarboxylic acids are selected from glutaric acid and adipic acid.

3. Zinc salts according to claim 1 or 2, characterized in that the zinc oxide particles are treated with alkoxyalkylsilanes.

4. Zinc salts according to one of claims 1 to 3, characterized in that the zinc oxide particles are obtainable by suspending and / or dispersing ZnO particles in polar-protic solvents, subsequent treatment with alkoxyalkylsilanes and treatment of the ZnO particles thus produced treated with alkoxyalkylsilanes in aqueous medium with UV irradiation.

5. Process for the production of zinc salts according to one of claims 1 to 4, characterized in that the specified process steps are carried out.

6. Use of the zinc salts according to one of claims 1 to 4 as catalysts.

7. Use according to claim 5 as a polymerization catalyst for the production of polyalkylene carbonates.

8. Process for producing polyalkylene carbonates by polymerizing carbon dioxide with at least one epoxide of the general formula (I) with the meaning R independently H, halogen, N0 ₂ , CN, COOR' or C1-2 ₀ - hydrocarbon radical, which can be substituted, where one of the radicals R can also mean OH, and where two radicals R together represent a C _3-5 alkylene radical can form,

R' H or Ci _-2 o-hydrocarbon radical, which can be substituted, characterized in that the polymerization is carried out on a catalyst according to one of claims 1 to 4.

9. The method according to claim 8, characterized in that the catalyst is used in anhydrous form.

10. The method according to claim 8 or 9, characterized in that the epoxide is selected from ethylene oxide, propylene oxide, butene oxide, cyclopentene oxide,

Cyclohexene oxide, i-butene oxide, acrylic oxides or mixtures thereof.

1 1 . Method according to one of claims 8 to 10, characterized in that it essentially comprises the following method steps:

1 . Drying or making the catalyst water-free,

2. placing the anhydrous catalyst in a polymerization reactor,

3. optionally adding an inert reaction medium,

4. adding carbon dioxide,

5. Adding the epoxy,

6. Heating the reactor to the reaction temperature,

7. optionally adding further carbon dioxide and

8. after the polymerization reaction has subsided, working up the reactor contents to produce the polycarbonate, whereby steps 5 and 6 can be swapped.

12. Polyalkylene carbonates, obtainable by a process according to one of claims 8 to 11.