WO2012140181A1

WO2012140181A1 - Method for producing aqueous dispersions of aliphatic polycarbonates

Info

Publication number: WO2012140181A1
Application number: PCT/EP2012/056743
Authority: WO
Inventors: Julien Courtois; Martin Schneele; Willi Riegel; Hubertus KRÖNER
Original assignee: Basf Se
Priority date: 2011-04-15
Filing date: 2012-04-13
Publication date: 2012-10-18

Abstract

The invention relates to a method for producing aqueous dispersions of aliphatic polycarbonates, in particular polypropylene carbonate, comprising: i. providing a solution of the aliphatic polycarbonate in at least one aprotic, organic solvent, which comprises 50 volume percent, in particular at least 80 volume percent, and especially at least 90 volume percent of ethyl acetate relative to the total amount of organic solvent and which preferably contains less than 10 volume percent, in particular less than 5 volume percent or less than 2 volume percent of solvent components having a boiling point above 100°C at normal pressure relative to the total solvent amount; ii. emulsifying the solution of the aliphatic polycarbonate provided in step i. in an aqueous emulsifying medium in the presence of at least one surface-active substance, wherein an aqueous emulsion of the solution of the aliphatic polycarbonate is obtained; and iii. removing the aprotic, organic solvent from the emulsion by evaporation.

Description

Process for the preparation of aqueous dispersions of aliphatic polycarbonates

Description: The present invention relates to a process for preparing aqueous dispersions of aliphatic polycarbonates. The invention also relates to the aqueous polycarbonate dispersions obtainable by this process and their use.

Aliphatic polycarbonates, such as, for example, polypropylene carbonate, are of interest as biodegradable polymers for numerous applications. For many applications, aqueous dispersions of polyalkylene carbonates would be of interest. Unlike aqueous polymer dispersions whose polymer chains have a backbone built up from carbon atoms, aqueous dispersions of polyalkylene carbonates can not be prepared by an emulsion polymerization process. Rather, such polymers are usually prepared by polycondensation of aliphatic diols with phosgene or by polyaddition of aliphatic oxiranes to CO2 in the presence of suitable catalysts in a non-aqueous polymerization medium and usually fall after removal of the solvent as solids. In order to obtain aqueous dispersions, they would have to be dispersed in water. However, it must be taken into account that there is a risk of hydrolysis-induced molecular weight degradation in the case of polycarbonates owing to the hydrolysis-labile carbonate groups present in the polymer backbone.

In principle, several processes for the dispersion of thermoplastic polymers, which include aliphatic polycarbonates and, in particular, polypropylene carbonate, are known in water.

On the one hand, using high shear forces, it is possible to emulsify a melt of the thermoplastic polymer in the aqueous dispersing medium containing surface-active substances and then to cool it. Such methods are known, for example, from US 4320041, DE 41 15531, EP 1302502, EP 1514891 and WO 97/49762. This procedure can usually be applied only to polymers with a sufficiently low melt viscosity. Alternatively, one can reduce the melt viscosity by additives, but this has problems for many applications. With polycarbonates, however, there is a great risk that due to the drastic processing conditions, a reduction in molecular weight as a result of hydrolysis of the carbonate groups in the polymer backbone occurs.

On the other hand, it is possible to mix a solution of the polymer in an organic, preferably water-miscible solvent with the aqueous dispersing medium and then to remove the organic solvent again. Such methods are described, for example, in US Pat. Nos. 3,238,173, 3,726,824 and US Pat WO 2007/074042 described. However, this procedure does not necessarily lead to stable polymer dispersions or it leads to dispersions having a very broad particle size distribution. WO 2006/136555 discloses a process for the preparation of aqueous polymer dispersions in which the polymer, for example a polyalkylene carbonate, is slightly dissolved in water dissolves soluble organic solvent, this solution in an aqueous medium, which contains surface-active substances, to obtain a crude emulsion with droplet sizes> 2 μιτι obtained, the crude emulsion obtained by a microporous membrane to form an oil-in-water emulsion having an average droplet diameter <1000 nm and then the solvent is removed. However, due to the use of the microporous membrane, the process is comparatively complicated and the resulting solids contents of the dispersions are low.

The earlier international patent application PCT / EP 201 1/054471 describes a process for preparing aqueous dispersions of thermoplastic polymers which have a plurality of ester groups and / or carbonate groups in the polymer backbone which have an acid number of less than 5 mg KOH / g, in particular not more than 3 mg KOH / g and at 180 ° C have a zero shear viscosity η ₀ (180 ° C) of at least 60 Pa s, in which introducing the thermoplastic polymer by means of a mixing device in the aqueous dispersion medium having at least one rotor-stator mixer. In the case of the polyalkylene carbonates, however, only dispersions having a low solids content and a comparatively large particle size of the dispersed polyalkylene carbonate particles can be produced by this process.

So far, no method has been described which reliably allows the preparation of aqueous dispersions of polyalkylene carbonates, in particular aqueous dispersions of polyalkylene carbonates whose particle size is below 1 μmol (weight average) and / or whose polymer content is at least 25% by weight and in particular at least 30 Wt .-% is.

The object of the present invention is thus to provide a reliable process for the preparation of aqueous dispersions of aliphatic polyalkylenecarbonates. In particular, the method should allow to solve at least one of the following tasks:

Polyalkylencarbonate and in particular polypropylene carbonates without significant molecular weight degradation in an aqueous dispersion to transfer;

preparing aqueous dispersions of polyalkylene carbonates having a solids content of at least 30% by weight; and to produce aqueous dispersions of polyalkylene, wherein the polymer particles have a weight-average particle diameter below 1000 nm, in particular below 800 nm. These and other objects are achieved by the method described here and below.

The present invention relates to a process for preparing aqueous dispersions of aliphatic polycarbonates, in particular of polypropylene carbonate, comprising:

i. Providing a solution of the aliphatic polycarbonate in at least one aprotic organic solvent which comprises at least 50% by volume, in particular at least 80% by volume and especially at least 90% by volume, based on the total amount of organic solvent, of ethyl acetate and which preferably contains less than 10% by volume, in particular less than 5% by volume or less than 2% by volume, based on the total amount of solvent, of solvent constituents having a boiling point above 100 ° C. under atmospheric pressure;

ii. Emulsify the in step i. solution of the aliphatic polycarbonate provided in an aqueous emulsifying medium in the presence of at least one surface-active substance, to obtain an aqueous emulsion of the solution of the aliphatic polycarbonate;

iii. Removing the aprotic organic solvent from the emulsion by evaporation.

The process according to the invention has a number of advantages. On the one hand, it allows the preparation of aqueous dispersions of aliphatic polycarbonates in a simple and reliable manner, without the need for complicated processes, such as the passage of polymer / solvent / water emulsions through microporous membranes. The ethyl acetate used here for dissolving the aliphatic polycarbonate is also toxicologically comparatively harmless and thus constitutes a further advantage of the method according to the invention. In addition, the inventive method does not or not significantly to a molecular weight reduction, as he see due to the in the polymer backbone aliphatic Polycarbonate contained carbonate functions would have been expected in principle. In addition, the process according to the invention can be used to prepare low-viscosity dispersions having viscosity values of 2 Pa.s (Brookfield, 20 ° C., determined in accordance with DIN EN ISO 2555) or below, such viscosity values also being achievable at solids contents of 40% by weight or more.

Furthermore, the process according to the invention allows for the first time the preparation of aqueous dispersions of aliphatic polycarbonates, in particular of polypropylene carbopolymers. which have a polymer content of at least 25 wt .-%, in particular at least 30 wt .-%, z. B. 25 to 60 wt .-% and in particular 30 to 55 wt .-%, in which the polymer particles have a weight-average particle diameter below 1000 nm, in particular below 800 nm. Such aqueous polycarbonate dispersions are new.

Accordingly, the present invention also relates to aqueous dispersions of at least one aliphatic polycarbonate having a polymer content of at least 25 wt .-%, in particular at least 30 wt .-%, for. B. 25 to 60 wt .-% and in particular 30 to 50 wt .-%, has, wherein the polycarbonate particles have a weight-average particle diameter, determined by light scattering, of at most 1000 nm, in particular at most 800 nm.

The particle diameters or particle radii or particle sizes given here, as well as the particle size distributions of the polycarbonate particles, are particle diameters which can be determined with the aid of photon correlation spectroscopy (PCS), also known as quasi-elastic light scattering (QELS) or dynamic light scattering. The mean particle diameters are the average of the cumulant analysis (mean of fits). The "mean of fits" is a mean intensity-weighted particle diameter in nm, which corresponds to the weight-average particle diameter. The measuring method is described in the IS013321 standard. Methods for this purpose are also familiar to the skilled worker from the relevant specialist literature, for example from H. Wiese in D. Distler, Aqueous Polymer Dispersions, Wiley-VCH 1999, Chapter 4.2.1, p. 40ff and references cited therein, and H. Auweter, D Horn, J. Colloid Interf. Be. 105 (1985) 399, D. Lie, D. Horn, Colloid Polym. Be. 269 (1991) 704 or H. Wiese, D. Horn, J. Chem. Phys. 94 (1991) 6429. The particle diameters specified here refer to the values determined at 0.degree. 1 to 0.25% by weight at 0.degree. The determination of the average particle diameter can also be carried out by means of hydrodynamic chromatography (HDC) using a particle size distribution analyzer (PSDA, Varian Deutschland GmbH) with a cartridge of type No. 2 (standard) at a wavelength of 254 nm (measurement temperature 23 ° C and measuring time eg 480 seconds). The polycarbonate dispersions according to the invention or obtainable by the process according to the invention typically have a weight-average particle diameter in the range from 100 to 1000 nm, frequently in the range from 120 to 800 nm and especially in the range from 150 to 600 nm. According to the invention, the polymers to be dispersed are aliphatic polycarbonates, which are also referred to as polyalkylene carbonates, in particular polypropylene carbonates. Aliphatic polycarbonates are polymers which are predominantly composed of repeating units of formula I defined below. In addition, the polyalkylene carbonates may also have repeating units of the formula II:

(I) (Ii) where A is an alkane-1,2-diyl radical having 2 to 10 carbon atoms or a cycloalkane-1, 2-diyl radical having 5 to 10 carbon atoms, where A is within a polymer may also have different meanings. The symbols + and * each represent the junctions to adjacent repeating units, where * is linked to + of the adjacent repeating unit. Preferably, A is selected from alkane-1, 2-diyl radicals, especially those having 2 to 4 carbon atoms, such as. B. 1, 2-ethanediyl, 1, 2-propanediyl, 1, 2-butanediyl, 1-methyl-1, 2-propanediyl and 2-methyl-1, 2-propanediyl. In a specific embodiment of the invention, A is predominantly, i. at least 70 mol%, in particular at least 80 mol% or at least 90 mol%, based on all repeating units, for 1, 2-propanediyl. In this case, the aliphatic polycarbonate is polypropylene carbonate. The proportion of carbonate repeat units of the formula I in the polycarbonate depends on the reaction conditions, in particular the catalyst used. In the preferred polycarbonates, more than 80 mole% and preferably more than 90% of all repeating units are those of formula I. Aliphatic polycarbonates are generally prepared by reacting aliphatic oxiranes, i. H. Alkylene oxides having usually 2 to 10 carbon atoms or cycloalkylene with generally 5 to 10 carbon atoms with CO2 in the presence of one or more suitable catalysts prepared, see, for. Inoue, macromol. Chem., Rapid Municipal. 1, 775 (1980), Soga et al., Polymer Journal, 1981, 13, 407-10, US 4,789,727 and US 7,304,172. Particularly suitable are zinc and cobalt catalysts, as described, for example, in the abovementioned literature and in particular in US Pat. Nos. 4,789,727 and 7,304,172.

Examples of suitable polyalkylene carbonates are the polyethylene carbonates known from EP-A 1264860, which are obtained by copolymerization of ethylene oxide and carbon dioxide in the presence of suitable catalysts, and in particular polypropylene carbonate (see, for example, WO 2007/125039), obtainable by copolymerization of propylene oxide and carbon dioxide in the presence of suitable catalysts. The polymer is also commercially available and is marketed, for example, by Empower Materials Inc. or Aldrich.

The number average molecular weight M _{n of} the polyalkylene carbonates, in particular of the polypropylene carbonates, is generally from 5000 to 500,000 daltons, in particular from 10,000 to 250,000 daltons. The weight-average molecular weight M _w is then usually in the range from 7000 to 5,000,000 daltons, in particular in the range from 15,000 to 2,000,000 daltons. In a specific embodiment of the invention, the number average molecular weight M _{n of} the polypropylene carbonates is in the range from 50,000 to 100,000 daltons and especially in the range from 70,000 to 90,000 daltons. The weight-average molecular weight M _w is then usually in the range of 100,000 to 500,000 daltons, in particular in the range of 150,000 to 400,000 daltons. The proportion of the carbonate repeat units in the total amount of the carbonate and ether repeat units in the polymer is generally at least 80 mol%, in particular 90 mol%. The polydispersity (ratio of weight average (Mw) to number average (MN)) is usually between 1 and 80 and preferably between 2 and 10. The polypropylene carbonates used may contain up to 1% of carbamate and urea groups.

Suitable aliphatic polycarbonates are also chain-extended polyalkylene carbonates. Particularly suitable chain extenders for the polyalkylene carbonates are maleic anhydride, acetic anhydride, di- or polyisocyanates, di- or polyoxazolines or -oxazines or di- or polyepoxides. Examples of isocyanates are aromatic diisocyanates such as toluylene-2,4-diisocyanate, toluylene-2,6-diisocyanate, 2,2'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, naphthylene-1, 5-diisocyanate or xylylene diisocyanate and aliphatic diisocyanates such as in particular 1, 6-hexamethylene diisocyanate, isophorone diisocyanate or methylene bis (4-isocyanatocyclohexane). Particular preference is given to aliphatic diisocyanates and, among these, especially isophorone diisocyanate and in particular 1,6-hexamethylene diisocyanate. As bisoxazolines are 2,2'-bis (2-oxazoline),

Bis (2-oxazolinyl) methane, 1, 2-bis (2-oxazolinyl) ethane, 1, 3-bis (2-oxazolinyl) propane or 1, 4-bis (2-oxazolinyl) butane, especially 1,4-bis (2-oxazolinyl) benzene,

1, 2-bis (2-oxazolinyl) benzene or 1, 3-bis (2-oxazolinyl) benzene called. The chain extenders are preferably used in amounts of from 0.01 to 5, preferably from 0.05 to 2, particularly preferably from 0.08 to 1% by weight, based on the amount of polycarbonate. Chain-extended polyalkylene carbonates typically have a number average molecular weight M _n of 30,000 to 500,000 daltons, preferably 35,000 to 250,000 daltons, and more preferably from 40,000 to 150,000 daltons. In addition to the at least one aliphatic polycarbonate, the polymers to be dispersed may also comprise small amounts of other polymers selected in particular from aliphatic or partially aromatic polyesters, aliphatic or partially aromatic polyesteramides, aliphatic or partially aromatic polyetheresters, and aliphatic or partially aromatic polyestercarbonates. These include, in particular, polylactides, polycaprolactones, aliphatic and partially aromatic copolyesters, in particular aliphatic polyesters based on aliphatic dicarboxylic acids, such as succinic acid, adipic acid, sebacic acid, azelaic acid, brassylic acid, or mixtures thereof, with aliphatic diols, such as ethanediol, 1, 2 and 1 , 3-propanediol, 1, 4-butanediol, neopentyl glycol, 1, 6-hexanediol, diethylene glycol or mixtures thereof, and partially aromatic copolyesters based on aliphatic dicarboxylic acids, in particular those mentioned above, and aromatic dicarboxylic acids such as phthalic acid and / or terephthalic acid and aliphatic diols , in particular the aforementioned. The proportion of the polymers other than the aliphatic polycarbonates is usually not more than 20% by weight, especially not more than

10 wt .-%, based on the total amount of the polymers to be dispersed.

In step i. In the process according to the invention, a solution of the aliphatic polycarbonate in at least one aprotic organic solvent which is at least 50% by volume, in particular at least 80% by volume and especially at least 90% by volume, based on the total amount of organic solvent , Acetic acid ethyl ester, provided. In other words, the content of ethyl acetate, based on the total volume of the organic solvent used for dissolving the aliphatic polycarbonate, is at least 50% by volume, in particular at least 80% by volume, and especially at least 90% by volume. In addition to ethyl acetate, which is also referred to as ethyl acetate, the solvent may also contain ethyl acetate various aproptic solvents. These further solvents are preferably selected so that they contain less than 20% by volume, in particular less than 10% by volume or less than 2% by volume, based on the total amount of solvent, of solvents which are above a boiling point 100 ° C at atmospheric pressure. Examples of suitable further aprotic organic solvents are methyl acetate, i-propyl acetate, methyl formate, ethyl formate, n-propyl formate, i-propyl formate, tetrahydrofuran, methyl ethyl ketone, dichloromethane and trichloromethane. Preferably, the other organic solvents do not include halogenated organic solvents and are especially selected from the aforementioned esters of formic acid and acetic acid. The solution is generally prepared by dissolving the polyalkylene carbonate in the aprotic organic solvent. The dissolution is typically carried out at temperatures in the range of 5 to 80 ° C, preferably in the range of 10 to 40 ° C. At the step i. The solution provided may also be the product discharge of a preparation of the polyalkylene carbonate, from which preferably catalysts and other impurities, eg. As the monomers used for the preparation were removed.

The concentration of the aliphatic polycarbonate in the step i. provided and in step ii. The solution used is typically in the range of 5 to

50 wt .-% and in particular in the range of 5 to 40 wt .-% and especially in the range of 5 to 30 wt .-%, based on the total weight of the solution.

In step ii. of the method according to the invention is in step i. provided solution of the aliphatic polycarbonate emulsified in an aqueous medium, which is also referred to below as an aqueous emulsifying medium. The emulsification is carried out according to the invention in the presence of at least one surface-active substance.

An aqueous emulsifying medium is understood as meaning water or a mixture of water with small amounts of an organic solvent or solvent mixture which preferably has a boiling point below 100 ° C. under normal pressure or which forms an azeotrope with water which has a boiling point below atmospheric pressure 100 ° C and which is preferably miscible with water at atmospheric pressure and 20 ° C or at least has a miscibility of at least 50 g / l, in particular at least 100 g / l (at pH 6-8). The proportion of organic solvents in such mixtures will generally not exceed 20% by volume, in particular 10% by volume and especially 5% by volume. Examples of suitable organic solvents are C 1 -C 4 alkanols, the aforementioned methyl and ethyl esters of formic acid and acetic acid, tetrahydrofuran, acetone and methyl ethyl ketone.

According to the invention, the emulsification of the polyalkylene carbonate solution is carried out in the aqueous emulsifying medium in the presence of at least one surface-active substance. In general, the surface-active substance is used in an amount of from 0.1 to 10% by weight, in particular in an amount of from 0.2 to 5% by weight, based on the amount of polyalkylene carbonate to be dispersed.

The at least one surfactant serves to stabilize the in step ii. prepared emulsion as well as for stabilizing the particles of the aliphatic polycarbonate in the in step iii. obtained aqueous dispersion of the aliphatic polycarbonate.

Since these surface-active substances, unlike those in step i. used organic solvents are non-volatile, they remain in the polymer dispersion and are therefore in the aqueous dispersion of the aliphatic polycarbonate in an amount of usually 0.1 to 10 wt .-%, in particular in an amount of 0.2 to 5 wt .-%, based on the aliphatic polycarbonate.

The surface-active substances can basically be all surface-active substances which are basically suitable for emulsifying organic solvents in water. These include in principle all emulsifiers and protective colloids suitable for this purpose, including mixtures thereof. Emulsifiers are generally low molecular weight or oligomeric substances which, unlike the polymeric protective colloids, have a (number average) molecular weight of not more than 2000 daltons, in particular not more than 1500 daltons. In contrast, protective colloids generally have a molecular weight above 2000 daltons (number average), z. B. in the range of 2200 to 10 ⁶ daltons on.

The surface-active substances may in principle be nonionic, anionic, cationic or zwitterionic. Preferably, the at least one surfactant is selected from anionic surfactants and nonionic surfactants and mixtures thereof.

Examples of protective colloids are water-soluble polymers such as:

neutral protective colloids: for example polyvinyl alcohols, including partially saponified polyvinyl acetate having a saponification degree of preferably at least 40%, in particular at least 60%, polyacrylamide, polyvinylpyrrolidone, poly-C 2 -C 3 -alkylene glycols, in particular polyethylene glycols, which are also referred to as poly (ethylene oxide) , and poly (ethylene-co-propylene) glycols, which are also referred to as poly (ethylene oxide-co-propylene oxide), among them specifically

Poly (ethylene oxide-co-propylene oxide) -Triblockcopolymere, further graft polymers of vinyl acetate and / or vinyl propionate on poly-C2-C3-alkylene glycols, one or both sides with alkyl, carboxyl or amino groups endgruppenverschlos- sene poly-C2-C3-alkylene glycols ; and

anionic water-soluble polymers (anionic protective colloids) whose polymer backbone has a multiplicity of carboxyl groups, sulfonic acid groups or sulfonate groups and / or phosphonic acid groups or phosphonate groups, for example carboxymethylcellulose, homopolymers and copolymers of ethylenically unsaturated monomers which contain at least 20% by weight , based on the total amount of the monomers, of at least one ethylenically unsaturated monomer which contains at least one carboxyl group, sulfonic acid group and / or phosphonic acid group in copolymerized form, and their salts, in particular the alkali metal and ammonium salts. In the abovementioned anionic water-soluble polymers, the sulfonic acid groups bound to the polymer backbone in the salt form, ie as sulfonate groups, and the phosphonic acid groups are accordingly present in the aqueous phase as phosphonate groups. The counterions are then typically AI alkali metal and alkaline earth metal ions such as sodium ions, calcium ions and ammonium ions (NHV).

Common nonionic emulsifiers are z. B .:

C 2 -C 3 -alkoxylated, in particular ethoxylated mono-, di- and tri-alkylphenols which generally have a degree of alkoxylation, in particular a degree of ethoxylation in the range from 3 to 50, in particular 5 to 30, and whose alkyl groups generally have a total of 4 to Have 26 carbon atoms, and C2-C3 alkoxylated, in particular ethoxylated aliphatic alkanols having 8 to 36, in particular 10 to 22 carbon atoms, which usually have a degree of alkoxylation, in particular a degree of ethoxylation in the range of 3 to 50, especially 5 bis 30 have. Examples include the Lutensol® A grades (C12 to C fatty alcohol ethoxylates, degree of ethoxylation from 3 to 50), Lutensol® AO grades (C13 to Cis oxo alcohol ethoxylates, degree of ethoxylation from 3 to 50), Lutensol® AT grades (C16 to Cis-fatty alcohol ethoxylates, degree of ethoxylation from 1 1 to 80), Lutensol® ON grades (Cio-oxo alcohol ethoxylates, degree of ethoxylation from 3 to

1 1) and the Lutensol® TO grades (Ci3-oxoalcohol ethoxylates, degree of ethoxylation from 3 to 20) from BASF SE.

Typical anionic emulsifiers are the salts of amphiphilic substances which have at least one anionic functional group, eg. B. at least one sulfonate, phosphonate, sulfate or phosphate group. These include, for example, the salts, in particular the alkali metal and ammonium salts of sulfuric monoesters of aliphatic alcohols, in particular alkanols, generally having 8 to 22 carbon atoms, the salts, in particular the alkali metal and ammonium salts of amphiphilic compounds which sulfated a or phosphated oligo-C 2 -C 3 -alkylene oxide group, in particular a sulfated or phosphated oligoethylene oxide group, such as, for example, the salts, in particular the alkali metal and ammonium salts of sulfuric monoesters of ethoxylated aliphatic alcohols, in particular alkanols, generally having from 10 to 30, in particular 12 to 18 C atoms, which generally have a degree of ethoxylation in the range from 2 to 50, in particular 4 to 30, the salts, in particular the alkali metal and ammonium salts of sulfuric monoesters of ethoxylated alkylphenols whose alkyl radicals are generally 4 to 12 C Atoms, and which usually have an ethoxylation gradient d in the range of 2 to 50, the salts, in particular the alkali metal and ammonium salts of Phosphorsäurehalbestern ethoxylated aliphatic alcohols, in particular alkanols, with usually 10 to 30, in particular 12 to 18 carbon atoms, which usually has a degree of ethoxylation in Range of 2 to 50, especially 4 to 30, the salts, in particular the alkali metal and ammonium salts of Phosphorsäurehalbestern ethoxylated alkylphenols whose alkyl radicals usually have 4 to 12 carbon atoms, and which usually has a degree of ethoxylation in the range of 2 to 50, the salts, in particular the alkali metal and ammonium salts of alkylsulfonic acids, preferably having 12 to 18 C atoms, the salts, in particular the alkali metal and ammonium salts of alkyl Arylsulfonsäuren (alkyl radical: C ₄ to Cis) and the salts, in particular the alkali metal and ammonium salts of Alkylbiphenylethersulfonsäuren (alkyl radical: C ₄ to Cis) such. B. the product sold under the name Dowfax® 2A1 product. Preferably, the surfactant is selected from the alkali metal salts, especially the sodium salts, the aforementioned sulfuric monoesters of aliphatic alcohols, the alkali metal salts, especially the sodium salts, the aforementioned sulfuric monoesters of ethoxylated aliphatic alcohols, P0IV-C2-C3-alkylene oxides, preferably those of number average molecular weight in the range of 2000 to 20,000 daltons, e.g. For example, polyethylene oxide and poly (ethylene oxide-co-propylene oxide), in particular poly (ethylene oxide-co-propylene oxide) di- and -Triblock- copolymers and mixtures thereof, preferably those having a number average molecular weight in the range of 2000 to 20,000 daltons. The surfactant may be added during emulsification, and is preferably contained in the aqueous dispersing medium or the polymer solution or both.

Furthermore, it has proven to be advantageous if the aqueous emulsifying medium contains one or more thickeners. Thickeners are substances which increase the viscosity of the aqueous emulsifying medium. Preferred are thickeners that are soluble in the aqueous emulsifying medium. In particular, thickeners which impart structural viscosity to the aqueous dispersing medium, ie a high viscosity at low shear rates of, for example, <10 sec. ¹ , with a low viscosity in the sheared state, eg. B. at shear rates> 100 sec ¹ .

In a preferred embodiment of the invention, the thickener is selected from polysaccharide thickeners. These include modified celluloses and modified starches, in particular cellulose ethers such as methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, methylhydroxypropylcellulose, methylhydroxyethylcellulose, natural polysaccharides such as xanthan, carrageenan, in particular κ-carrageenan, λ-carrageenan or ι-carrageenan, alginates, guaran and agar and modified xanthan such as succinylglycan or modified carrageenan. Preferred are polysaccharide thickeners, with anionic groups such as carboxymethylcellulose, xanthan, modified xanthan, carrageenan, modified carrageenan and alginates and especially xanthan and modified xanthan, z. B. under the trade names Kelzan ^® the Fa. Kelco and Rhodopol ^® , z. As the Rhodopol ^® types 23, 50MC, G, T and TG of the company. Rhodia distributed xanthan products. The amount of thickener can be varied over a wide range and depends in a conventional manner on the desired viscosity and the type of thickener. The amount of thickener needed to achieve the desired viscosity can be Determine man in routine experiments. The concentration of thickener in the aqueous emulsifying medium is typically in the range of 0.01 to 1% by weight, based on the total weight of the aqueous emulsifying medium. Preferably, the amount of thickener is chosen so that the aqueous emulsifying or dispersing at 20 ° C and a shear rate <10 sec ^{1 has} a viscosity in the range of 100 to

10000 mPa.s, in particular in the range of 150 to 5000 mPa.s, determined according to ISO 6721.

The emulsification of the solution of the polycarbonate in the aqueous emulsifying medium can be carried out in a manner known per se in analogy to the customary processes of the prior art for emulsifying organic, water-immiscible or only limited miscible liquids.

Suitable measures are, for example, methods in which energy is introduced by shear into the mixture of aqueous emulsifying medium and the solution of the polycarbonate in the organic solvent. These include, for example, mixing using conventional dynamic mixing devices such as stirrers, in particular stirrers, which bring about effective shear, dispersants, in particular sprocket dispersers or rotor-stator mixers, and static mixers such as nozzles and mixing chambers into which the liquids to be mixed be introduced at high speed. Preferably, for emulsification, shear rates of> 1000 sec ¹ , z. B. in the range of 1000 to 100,000 sec ¹ , especially in the range of 5000 to 50,000 sec ¹ , at. For example, you can process step iL, ie the emulsification, perform discontinuously, for. B. by shearing in a vessel, in particular a mixing vessel, the solution of the polycarbonate and the aqueous emulsifying medium, for. By stirring or by a suitable means of dispersion until a stable emulsion is obtained. Alternatively, you can submit a subset or the total amount of the polymer solution or the aqueous emulsifying in a vessel and this under shear to add the missing component.

Likewise, emulsification can also be carried out continuously by simultaneously introducing the polymer solution and the aqueous emulsifying agent in the desired quantitative ratio into a mixing zone and removing the emulsion from the mixing zone. In this case, the mixing zone as a rule has dynamic and / or static mixing devices, which cause a shear of the mixture when the polymer solution is mixed with the aqueous emulsifying medium. Such a method is described, for example, in WO 00/33820.

Usually, step ii will be carried out at temperatures in the range above the freezing point of the aqueous emulsifying medium. To premature evaporation to avoid the organic solvent, you will step ii. usually below the boiling point of the lower boiling component of the mixture, usually ethyl acetate or ethyl acetate / water azeotrope, under the emulsification conditions. Typically, you will step ii. at temperatures> 0 ° C to 80 ° C, in particular in the range of 10 to 50 ° C. The pressure at which emulsification is carried out is generally of lesser importance. As a rule, step ii will be carried out at a pressure in the range from 900 mbar to 1500 mbar, but it is also possible to use higher or lower pressures. As a rule, in step ii. the solution of the aliphatic polycarbonate and the aqueous dispersing medium in a weight ratio in the range of 20: 1 to 1:10, in particular in a weight ratio in the range of 10: 1 to 1:10 and especially in a weight ratio in the range of 10: 1 to 1 : Emulsify. In this way a stable emulsion of the solution of the aliphatic polycarbonate in the aqueous dispersing medium is obtained, wherein as a rule the aqueous emulsifying medium forms the continuous phase and the polymer solution forms the discontinuous phase. Optionally, however, there may also be a reverse phase arrangement.

From the aqueous emulsion thus prepared, the organic solvent is then removed by evaporation. In this case, a subset of the water is usually removed together with the organic solvent. In this way you can adjust the desired solids content. If necessary, you can also during step iii. Replace evaporated water with fresh water or in the vaporized mixture of water and solvent, carry out a separation into water and organic solvent and return the water partially or completely. The solvent thus obtained can be recycled to prepare further solutions of the aliphatic polycarbonate.

Optionally, one or more defoamers may be added to the aqueous emulsion prior to or during removal of the solvent to reduce foaming. It is also possible to add the defoamer already to the aqueous emulsifying medium. Suitable defoamers are especially those based on polysiloxanes and fatty alcohol mixtures.

Typically, you will step iii. at temperatures 5 ° C to 80 ° C, in particular in the range of 20 to 50 ° C. Preferably, the removal of the organic solvent is carried out at reduced pressure. Naturally, the pressure depends on step iii. is carried out after the vapor pressure of the solvent-water mixture of the emulsion. Typically, the pressure will be in the range of 0.5 to 800 mbar, in particular in the range of 2 to 300 mbar. The pressure during the Removal of the organic solvent and optionally a portion of water can be kept constant. In general, however, one will lower the pressure during the removal of the organic solvent. The lowering of the pressure can be done continuously or in one or more stages.

As a rule, the organic solvent will be removed to such an extent that the residual organic solvent content, ie. H. organic substances having a boiling point below 200 ° C at atmospheric pressure not more than 1000 ppm, often not more than 500 ppm, in particular not more than 100 ppm. Further reductions in the amount of solvent can be achieved by further concentration or by dialysis or by a combination of these measures.

Following this, the aqueous dispersion of the aliphatic polycarbonate can be prepared in the usual way, for example by adding microbicides.

Stable aqueous dispersions of aliphatic polycarbonates, in particular polypropylene carbonates, can be produced by the process according to the invention. The polymer contents are typically in the range of 10 to 60 wt .-%. However, the process is particularly suitable for the preparation of stable concentrated dispersions of aliphatic polycarbonates, in particular of polypropylene carbonates, which have a polycarbonate content of at least 20% by weight, frequently at least 25% by weight and in particular at least 30% by weight. -%, z. B. 10 to 65 wt .-%, often 20 to 60 wt .-%, preferably 25 to 60 wt .-% and in particular 30 to 50 wt .-% have.

The aqueous dispersions of aliphatic polycarbonates according to the invention have a low viscosity, even at high solids contents, at least under shear, which generally at 20 ° C. and a shear rate of> 100 sec ¹ not more than 2000 mPa s and in particular not more than 1000 mPa-s is. Depending on whether they contain a thickener, in particular a polysaccharide thickener, the aqueous dispersions of aliphatic polycarbonates according to the invention can be structurally viscous, in particular thixotropic. The aqueous dispersions of aliphatic polycarbonates according to the invention are sedimentation-stable even under freeze-thaw conditions.

Unlike the dispersions of the prior art, low-viscosity dispersions can be prepared by the process according to the invention, even at high polymer contents. Preferably, the viscosity of the dispersions obtainable according to the invention, determined according to Brookfield at 20 ° C. at a value of not more than 2 Pa.s, is frequently at a maximum of 1 Pa.s, eg. B. in the range of 1 to 2000 mPa-s, in particular in the range of 10 to 1000 mPa-s. The polymer dispersions obtainable by the process according to the invention and the polymer dispersions according to the invention are suitable for a large number of applications which are usually suitable for aqueous polymer dispersions. The polymer dispersions obtainable by the process according to the invention and the aqueous dispersions of aliphatic polycarbonates according to the invention, in particular those in which the polycarbonate is a polypropylene carbonate, are particularly suitable for those applications in which a biodegradability of the polymer constituent is desirable. In particular, the aqueous dispersions are suitable as a binder component in aqueous binder compositions, in particular for binder compositions for papermaking, for. Example, as a sizing agent for paper, as engine size or as a means for Oberflächenlei- mung, as a means for solidification of paper, as a binder for Papierstreicherei, and as a binder in non-pigmented coating compositions, for the production of barrier coatings on paper, cardboard or cardboard Binder for pigment-containing coating compositions such as paints for interior and exterior applications, and also in binder compositions for fiber bonding and for the production of nonwovens. In addition, the aqueous dispersions are suitable in adhesives, for example as laminating adhesives, especially as laminating adhesives for laminating plastic films on flat supports, such as paper, cardboard, or plastic films, or for formulating active ingredients in the agrochemical sector or in pharmacy. The polymer dispersions according to the invention can also be used for the production of film materials.

The invention will be explained in more detail below with reference to examples.

analytics

The viscosity of the emulsifying medium was determined on the basis of DIN EN ISO 6721 using a Physika MCR rotational viscometer / double-gap geometry DG 26.7, at shear rates of 0.1 to 10 sec ¹ and a measuring temperature of 20 ° C.

The particle size distribution was determined on an approximately 0.02% strength by weight dilution of the dispersion by light scattering at 23 ° C. using a Mastersizer from Malvern. The average particle diameter can also be determined by means of hydrodynamic chromatography (HDC) using a particle size distribution analyzer (PSDA, Varian Deutschland GmbH) with a cartridge of type No. 2 (standard) at a wavelength of 254 nm (measurement temperature 23 ° C and measuring time 480 seconds). The viscosity of the dispersions was determined at 20 ° C. in accordance with DIN EN ISO 6721 using a rotational viscometer (Physika MCR / double-gap geometry DG 26.7) at a shear rate of 10 sec ¹ . The solids content is determined by means of a Halogen Moisture Analyzer from Mettler-Toledo. The determination of the residual concentration of solvent is carried out by gas chromatography.

Feedstocks: For the following experiments, a polypropylene carbonate (hereinafter PPC) having a number average molecular weight of 80,000 daltons and a weight average molecular weight of 250,000 daltons was used.

The following surfactants were used:

Emulsifier Solution 1: Aqueous 27% by weight solution of ethoxylated lauryl sulfate,

Na salt (Hansanol® NS 242 from HANSA Group AG)

Emulsifier solution 2: Aqueous 57% strength by weight solution of amine salt of laurylbenzylsulfonate (Lutensit® A-LBA from BASF SE)

Protective Colloid 1: Poly (ethylene oxide-co-propylene oxide) triblock copolymer (Pluronic PE

6800 from BASF SE)

Thickener: xanthan gum (Xanthan gum from Sigma Aldrich Chemie GmbH) defoamer: 10% strength by weight aqueous emulsion of a silicone-based defoamer (Tego® Foamex from Evonik Tego GmbH)

Preparation of the aqueous polycarbonate dispersions Example 1

To 100 g of a 10% by weight solution of PPC in ethyl acetate was added 0.56 g of emulsifier solution 1 (corresponds to 1.3% by weight of emulsifier, based on PPC). To this was added at 20 ° C 66 g of a 0.25 wt .-% solution of xantan in water (viscosity 127 mPas at 20 ° C and a shear rate of 10 sec ¹ ) and dispersed by means of an Ultraturrax at 24000 Umirr ¹ , until a stable emulsion was obtained (about 55 sec). To this was added 0.2 wt .-% of the defoamer and removed the organic solvent and a subset of the water at 35 ° C by means of a rotary evaporator in vacuo (300 to 70 mbar). In this way, an aqueous dispersion of PPC having a polymer content of 34.2 wt .-% was obtained. The mean particle diameter, determined by means of HDC, was 450 nm. Example 2:

To 100 g of a 10% by weight solution of PPC in ethyl acetate was added 0.53 g of emulsifier solution 2 (corresponding to 3% by weight of emulsifier, based on PPC). To this was added at 20 ° C 66 g of a 0.2 wt .-% solution of xantan in water and dispersed with the aid of an Ultraturrax at 24000 Umirr ¹ until a stable emulsion was obtained (about 55 sec). To this was added 0.2 wt .-% of the defoamer and removed the organic solvent and a subset of the water at 35 ° C by means of a rotary evaporator in vacuo (300 to 70 mbar). In this way, an aqueous dispersion of PPC having a polymer content of 21, 2 wt .-% was obtained. The mean particle diameter, determined by means of HDC, was 400 nm.

Example 3: To 100 g of a 10% by weight solution of PPC in ethyl acetate was added 2.48 g of protective colloid 1 (corresponding to 24.8% by weight of protective colloid, based on PPC). To this was added at 20 ° C 72 g of a 0.15 wt .-% solution of xanthan in water and dispersed by means of an Ultraturrax at 24000 Umirr ¹ until a stable emulsion was obtained (about 55 sec). To this was added 0.14% by weight of the defoamer and the organic solvent and a subset of the water were removed at 35 ° C. by means of a rotary evaporator under reduced pressure (300 to 70 mbar). In this way, an aqueous dispersion of PPC having a polymer content of 34.8 wt .-% was obtained. The average particle diameter, determined by means of HDC, was 192 nm. In analogy to Examples 1 to 3, the dispersions of Examples 4, 4a, 5, 5a, 6, 6a and 6b were prepared. The preparation instructions, solids content, the viscosity and the particle size are summarized in the following Table 1.

Table 1

1) Dso value determined by HDC

2) Dso value, determined by means of dynamic light scattering Examples 7, 7a and 7b (general rule):

To 250 g of a 10% by weight solution of PPC in ethyl acetate were added 1.84 g of emulsifier solution 1 (corresponding to 2.0% by weight of emulsifier, based on PPC) and homogenized with an Ultraturrax. To this was added at 20 ° C 140 g of a 0.25 wt .-% solution of xanthan in water containing 0.6 wt .-% defoamer and dispersed at 20 ° C using an Ultraturrax for about 1 min at 24000 Umirr ¹ until a stable emulsion was obtained. Subsequently, the organic solvent was removed at 33 ° C by means of a rotary evaporator in vacuo at 150 mbar and then lowered the pressure to 30 mbar to remove more water. In this way, an aqueous dispersion of PPC was obtained. The properties are given in the following Table 2.

Table 2

Example 8:

To 125 g of a 10% strength by weight solution of PPC in ethyl acetate, 0.92 g of emulsifier solution 1 (corresponding to 2% by weight of emulsifier, based on PPC) were homogenized with an Ultraturrax and heated to 60 ° C. , For this purpose at 60 ° C was added 70 g of a 0.25 wt% solution of xanthan in water containing 0.4 g of defoamer and dispersed using an Ultraturrax about 55 sec. At 24,000 rpm for ¹ until a stable emulsion was obtained. Subsequently, the organic solvent was removed at 33 ° C. by means of a rotary evaporator under reduced pressure at 240 mbar and then the pressure was lowered to 12 mbar in order to remove further water. In this way, an aqueous dispersion of PPC was obtained. The properties are given in Table 3.

Example 9:

An aqueous emulsifying medium was prepared by adding 70 g of a 0.25% strength by weight solution of xanthan in water, 0.4 g of defoamer and 0.92 g of emulsifier solution 1 (corresponding to 2% by weight of emulsifier, on PPC). Was heated 125 g of a 10 wt .-% solution of PPC in ethyl acetate to 60 ° C and gave this while running Ultraturrax (24000 Umin ¹ ) within 30 min. the emulsifying medium heated to 60 ° C and dispersed for a further 55 sec. with the aid of an Ultraturrax at 24000 rpm ¹ to a stable emulsion was obtained. Subsequently, the organic solvent was removed at 33 ° C by means of a rotary evaporator under vacuum at 240 mbar and then lowered the pressure to 12 mbar to remove more water. In this way, an aqueous dispersion of PPC was obtained. The properties are given in Table 3.

Table 3

Examples 10, 10a and Comparative Examples 11, 11a (general procedure):

To 150 g of a 10 wt .-% solution of PPC in the respective solvent (ethyl acetate in Example 10, 10a, dichloromethane in Comparative Example 1 1, 1 1 a) was added 4.6 g of emulsifier 1 (5.0 equivalent. -% emulsifier, based on PPC) and homogenized with an Ultraturrax. For this purpose at 20 ° C was added 140 g of a 0.25 wt% solution of xanthan in water containing 0.8 g of defoamer and dispersed at 20 ° C by means of an Ultraturrax about 55 sec. At 24,000 Umirr ^1, until a stable emulsion was obtained. Subsequently, the organic solvent was removed at 33 ° C by means of a rotary evaporator under vacuum at 240 mbar and then lowered the pressure to 12 mbar to remove more water. In this way, an aqueous dispersion of PPC was obtained. The properties are given in the following Table 4.

Table 4

Ex. Solids content Residual solvent content Particle size distribution

(Light scattering)

[% By weight] [ppm] D10 [nm] D50 [nm] _D90 [nm]

10 30.9 <10 190 290 440

10a 31, 4 15 240 370 660

V1 1 26.3 <10 940 2230 7600

V1 1 a 32.1 10 870 1600 3220

Claims

claims:

Process for preparing aqueous dispersions of aliphatic polycarbonates comprising

i. Providing a solution of the aliphatic polycarbonate in at least one aprotic organic solvent comprising at least 50% by volume, in particular at least 80% by volume, based on the total amount of organic solvent, of ethyl acetate;

ii. Emulsify the in step i. provided solution of the aliphatic polycarbonate in an aqueous emulsifying medium in the presence of at least one surface-active substance, to obtain an aqueous emulsion of the solution of the aliphatic polycarbonate;

iii. Removing the aprotic organic solvent from the emulsion by evaporation.

The method of claim 1, wherein the concentration of the aliphatic polycarbonate in the in step ii. used solution in the range of 5 to 50 wt .-% is.

Method according to one of the preceding claims, wherein the surface-active substance is selected from anionic surface-active substances and non-ionic surface-active substances.

A process according to claim 3, wherein the surfactant is selected from the alkali metal salts of sulfuric monoesters of aliphatic alcohols, the alkali metal salts of sulfuric monoesters of ethoxylated aliphatic alcohols, poly (ethylene oxide-co-propylene oxide) and mixtures thereof.

Method according to one of the preceding claims, wherein the surface-active substance in an amount of 0.1 to 10 wt .-%, based on the aliphatic polycarbonate, is used.

Method according to one of the preceding claims, wherein the aqueous dispersion medium contains at least one thickener.

The method of claim 6, wherein the thickener comprises at least one polysaccharide.

A process according to any one of the preceding claims, wherein the aqueous

Dispersing medium at 20 ° C has a viscosity in the range of 100 to

10000 mPa-s, determined according to ISO 6721 at a shear rate <10 sec ¹ .

9. The method according to any one of the preceding claims, wherein the emulsification in step ii. shearing the solution of the aliphatic polycarbonate with the aqueous emulsifying medium. 10. The method of claim 9, wherein one applies shear rates of> 1000 sec ¹ .

1 1. Method according to one of the preceding claims, wherein step ii. at a temperature in the range of> 0 to 80 ° C is performed. 12. The method according to any one of the preceding claims, wherein in step ii. the solution of the aliphatic polycarbonate and the aqueous dispersing medium are emulsified in a weight ratio ranging from 20: 1 to 1:10.

13. The method according to any one of the preceding claims, wherein the aliphatic polycarbonate is a polypropylene carbonate.

14. The method according to any one of the preceding claims, wherein the aliphatic polycarbonate has a number average molecular weight in the range of 5000 to 500,000 daltons.

15. The method according to any one of the preceding claims, wherein step iii. at a temperature in the range of 5 to 80 ° C is performed.

16. Aqueous dispersions of at least one aliphatic polycarbonate which have a polymer content of at least 25% by weight, in which the polycarbonate

Particles have a weight-average particle diameter, determined by light scattering, of at most 1000 nm.

17. Aqueous dispersion according to claim 16, wherein the aliphatic polycarbonate is a polypropylene carbonate.

18. Aqueous dispersion according to claim 16 or 17, wherein the aliphatic polycarbonate has a number average molecular weight in the range of 5000 to 500,000 daltons.

19. An aqueous dispersion according to any one of claims 16 to 18 having a viscosity of not more than 2000 mPa · s at 20 ° C and a shear rate of> 100 sec ¹ .

20. Use of an aqueous polymer dispersion according to one of the preceding claims as a binder in coating compositions, as a sizing agent for paper, as a paper strengthening agent, as a binder composition for nonwovens, in adhesives, for the production of barrier coating tions or for the formulation of active substances.