DE102011079778A1 - Membrane useful for nano-filtration and for separating higher molecular weight compounds of an organic solvent, comprises a photochemically crosslinked polyimide prepared by e.g. reacting imide group of the polyimide with a primary amine - Google Patents

Abstract

Membrane formed by phase inversion, comprises at least one photochemically crosslinked polyimide, which is prepared by (1) reacting at least one imide group contained in the polyimide with at least one primary amine of (I) forming polyimide containing at least one primary amino group, and (2) reacting the product of the step (1) with at least one compound of (II) to intercept all the free primary amino groups in the polyimide, which are generated in the step (1). Membrane formed by phase inversion, comprises at least one photochemically crosslinked polyimide, which is prepared by (1) reacting at least one imide group contained in the polyimide with at least one primary amine of formula (NH 2-R-A) (I) forming polyimide containing at least one primary amino group, and (2) reacting the product of the step (1) with at least one compound of formula (B 1>-R11-D 1>) (II) to intercept all the free primary amino groups in the polyimide, which are generated in the step (1). R, R11 : 1-12C alkylene, 1-12C oxyalkylene, 1-12C carboxy-alkylene (all optionally substituted); and A : A 1>or A 2>, which is not primary amino group; A 1>group, which stabilizes a group of the compound (I); A 2>group, which produces radicals under UV irradiation and/or heat; B 1>group, which reacts with a primary amine forming a covalent bond; and D 1>group, which does not react with an amine by forming a covalent bond. An independent claim is also included for producing a membrane by phase inversion, comprising (a) providing a polyimide prepared by the above mentioned method, (b) providing a casting solution comprising (b1) polyimide synthesized in the step (1), (b2) optionally at least one additional polyimide, where the polyimide is same or different from the polyimide, which is used as starting material for producing polyimide synthesized in the step (1), (b3) a solvent system for dissolving the polyimide (b1) and optionally at least one additional polyimide (b2), (b4) optionally an additive for increasing the viscosity of the casting solution, (b5) optionally an additive for suppressing the formation of macropores, and (b6) optionally a surfactant, (c) knife coating a film from the casting solution on a substrate, which is optionally a carrier material, (d) subjecting the film to UV irradiation prior to and/or after precipitating the membrane in a coagulating bath, (e) treating the film in a coagulating bath, where the film before and/or after entering into the coagulation bath is exposed to UV radiation, and (f) optionally washing the membrane.

Description

Membrane processes are known especially in the field of separation. They thus have a wide range of applications, such as the selective separation of substances of almost all molecular weights from liquid or gaseous mixtures ( RW Baker, Membrane Technology and Applications; 2nd Edition, John Wiley, ISBN 0-470-85445-6 ).

The membrane process of nanofiltration is often defined in a very general way: this definition encompasses the use of membranes that have pores smaller than 2 nm and thus have a "molecular weight cut-off" (MWCO) of 200 to 2000 g / mol. The MWCO refers to the molecular weight of a substance, which is retained by 90% through the membrane. Such membranes have a layer which is also referred to as free of pores.

Nanofiltration is widely used in filtration and separation in aqueous media. However, a very high potential also lies in the application in organic media. Processes such as solvent purification or separation, catalyst recovery, and the concentration of dissolved substances or the implementation of a solvent exchange for such substances can be implemented by continuous membrane processes considerably more efficient and usually more cost-effective. Precisely in the area of the production of active pharmaceutical ingredients, these processes could be effectively utilized for obtaining the intermediate and end product. There is therefore a great deal of interest in applying Organic Solvent Nanofiltration (OSN) on a large scale.

However, especially in the production of pharmaceutical agents, there are often extreme conditions to which a membrane is exposed. Above all, the presence of organic solvents in the individual stages of a drug synthesis limits the scope of organic membranes. Organic membranes - that is, polymer-based membranes - inherently have a tendency to dissolve or at least to swell in organic solvents. Through this process, the membranes lose their separation properties and mechanical stability.

Therefore, the main focus of OSN research is to provide more efficient membranes, that is, membranes whose swelling in organic solvents is minimized and thereby provide high selectivity and high flux even under such conditions. Here, especially the class of polyimides for the production of the membranes of particular interest, since these have a high mechanical, thermal and chemical stability, polyimides are known especially for gas separation processes, but are finding more and more application in the OSN.

The US 5,264,166 and US 6,180,008 describe, for example, processes for preparing non-porous asymmetric polyimide membranes which are solvent stable in toluene, benzene, xylene, methyl ethyl ketone and methyl isobutyl ketone. The use of polyimide membranes for solvent recovery from lubricating oil is also known ( US 5,360,530 ; US 5,494,566 ; and US 5,651,877 ).

Recent strategies aim to chemically stronger cross-link membranes based on polyimide in order to minimize the swelling tendency of the membrane JP 09324049 A the crosslinking of polyimides in hot air. In the WO 2004/087739 A the crosslinking is described by crosslinkable polyamide. Some strategies are also based on the approach of incorporating monomeric crosslinker groups into the resulting polyimide already in the synthesis of the polyimide, which then later enable crosslinking of the polymer ( WO 2003/053548 A ; JP 2001-323067 A ; European Polymer Journal 43 (2007) 1541-1548 ; Journal of Membrane Science 285 (2006) 432-443) ,

A very quick and easy way to crosslink polyimides is, for example, in the patents US 4,981,497 . WO 201 0/111 755 A . WO 2007/125367 A . US 201 0/01 81 253 A . US 7,169,885 and US 2004/01 77753 A describe. In this case, the crosslinking is realized by reacting the structure-immanent imide groups of the starting polymer with primary or secondary mono-, di-, tri- or polyamines. For this purpose, the already formed membranes are dipped after their preparation in a bath with the described amines, in which then the crosslinking takes place. First, this type of crosslinking was used for gas separation membranes, but later adapted for OSN applications ( WO 2007/125367 A ). These concepts have in common that this is always a so-called "post-synthesis cross-linking" method (POST method). Thus, the crosslinking always includes an additional step during membrane production. In the WO 2011/111755 A The corresponding amines are added directly into the casting solution or directly into the precipitation bath of the membrane. This can indeed However, this method still involves the disadvantage that the added amines must be carefully rinsed out of the membrane afterwards. Bleeding of such additives during use (for example, during purification of a pharmaceutical product) could lead to serious negative consequences. It is also disadvantageous that most of the membranes resulting from these strategies have a finger structure.

In another concept, the polyimides are crosslinked by UV irradiation. For example, this describes US 4,717,393 the photochemical crosslinking of a specific polyimide, which is based on the abstraction of a hydrogen by means of a structure-intrinsic benzophenone group. However, a membrane formed on this basis does not meet the above requirements. The photoreaction has a too low selectivity and efficiency, so that the membrane properties are changed relatively small compared to the uncrosslinked membrane. In the reference European Polymer Journal 35 (1999) 1739-1741 Photocrosslinking of polyimides is also described, but with an exposure time of 2 to 4 hours is very time-consuming and cost-intensive and results, above all, in non-solvent-resistant membranes. Some references also report the photocrosslinking of polyimides, but the casting solutions prepared are not chemically stable and the resulting membranes do not have the desired properties. (US Pat. S. Behnke, M. Ulbricht, Membranes for Organophilic Nanofiltration based on photo-crosslinkable polyimides, Abstract to the European Membrane Society Summer School 2010 ; S. Behnke, M. Ulbricht, Tailored membranes for organophilic nanofiltration based on photocrosslinkable polyimides, Abstract to the 3rd International Conference on Organic Nanofiltration 2010 ; S: Behnke, M. Ulbricht, Preparation of membranes for organophilic nanofiltration based on photo-crosslinkable polyimides, Abstract to the International Congress on Membranes 2011 ).

Starting from this prior art, the object of the present invention is to provide a membrane which preferably eliminates at least one of the above-discussed disadvantages of the membranes known from the prior art.

In this case, the present invention should preferably provide a membrane which is substantially stable in the solvents in which the polymer forming the membrane is soluble.

Likewise, the present invention is preferably intended to provide a membrane whose microstructure and macrostructure can be selectively controlled.

This object is initially achieved by providing a membrane formed by phase inversion.

• (a) Umsetzung der mindestens einen im Polyimid enthaltenen Imidgruppe mit mindestens einem primären Amin der allgemeinen Formel (I) NH₂-R-A (I) unter Ausbildung eines mindestens eine primäre Aminogruppe aufweisenden Polyimids; wobei in dem primären Amin R für ein gegebenenfalls substituiertes C₁-C₁₂-Alkylen, C₁-C₁₂-Oxyalkylen, C₁-C₁₂-Carboxyalkylen steht, und A für einen Rest A1 oder A2 steht, der keine primäre Aminogruppe umfasst, wobei A1 einen Rest darstellt, der dazu geeignet ist, ein Radikal in dem Rest R der Verbindung der allgemeinen Formel (I) zu stabilisieren und A2 einen Rest darstellt, der dazu geeignet ist, unter UV-Bestrahlung und/oder Wärme Radikale zu erzeugen;
• (b) Umsetzung des Produktes aus Schritt (a) mit mindestens einer Verbindung der allgemeinen Formel (II) B-R'-D (II) um im Wesentlichen alle freien, im Schritt (a) erzeugten primären Aminogruppen im Polyimid abzufangen; wobei B eine funktionelle Gruppe ist, die dazu geeignet ist, mit einem primären Amin unter Ausbildung einer kovalenten Bindung zu reagieren, R' für ein gegebenenfalls substituiertes C₁-C₁₂-Alkylen, C₁-C₁₂-Oxyalkylen, C₁-C₁₂-Carboxyalkylen steht und D für einen Rest steht, der nicht mit einem Amin unter Ausbildung einer kovalenten Bindung reagiert.

The membrane of the invention is characterized by comprising at least one polyimide prepared by a process comprising the steps

• (a) Reaction of the at least one imide group contained in the polyimide with at least one primary amine of the general formula (I) NH ₂ -RA (I) forming a polyimide having at least one primary amino group; wherein in the primary amine R is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C ₁₂ carboxyalkylene, and A is an A1 or A2 radical which does not comprise a primary amino group wherein A1 represents a radical capable of stabilizing a radical in the radical R of the compound of the general formula (I) and A2 represents a radical capable of generating radicals under UV irradiation and / or heat ;
• (b) reaction of the product from step (a) with at least one compound of the general formula (II) B-R'-D (II) to scavenge substantially all of the free primary amino groups generated in step (a) in the polyimide; in which B is a functional group capable of reacting with a primary amine to form a covalent bond, R 'is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C ₁₂ -Carboxyalkylene and D is a radical that does not react with an amine to form a covalent bond.

In a preferred embodiment, the amine of general formula (I) NH ₂ -RA (I) characterized in that R and A are selected as follows:
R is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C ₁₂ carboxyalkylene. These groups may have at least one substituent selected from the group consisting of hydrogen, linear or branched C ₁ -C ₆ -alkyl, C ₃ -C ₇ -cycloalkyl, C ₁ -C ₄ -alkoxy, C ₁ -C _4- alkoxycarbonyl and optionally substituted phenyl. In this case, the phenyl is preferably substituted by a group A1.

R is preferably selected from the group consisting of methylene, ethylene, n-propylene, i-propylene, n-butylene, tert-butylene, n-pentylene, n-hexylene, n-heptylene, n-octylene, n-nonylene, n-decylene, n-undecylene, n-dodecylene, oxymethylene, oxyethylene, oxypropylene, oxybutylene, oxypentylene, oxyhexylene, oxyheptylene, oxyoctylene, oxynonylene, oxydecylene, oxyundecylene, oxydodecylene, carboxymethylene, carboxyethylene, carboxypropylene, carboxybutylene, carboxypentylene, carboxyhexylene, carboxyheptylene, Carboxyoctylen, carboxynonylene, carboxydecylen, carboxyundecylene and carboxydodecylene, wherein R may optionally be substituted with the abovementioned radicals. R is particularly preferably ethylene.

In one embodiment, the radical A represents a radical A1 which is suitable for stabilizing a radical in the radical R of the compound of the general formula (I). This radical is particularly preferably formed under UV irradiation by hydrogen abstraction at the radical R of the general formula (I). In this case, more preferably, A1 can also form a radical by UV irradiation.

A1 is preferably a radical which is suitable for hyperconjugation.

Likewise, substitution by radicals having a + I effect (inductive effect) as listed below is particularly preferred. Further preferably, A1 is a radical which has a + M effect (mesomeric effect).

It is preferable that at A1 to residues which are selected from the group consisting of optionally substituted benzyl, optionally substituted allyl, -OH, -O ^-, -NR ₁ R _2, -OR _1, -NHC = OR _1, - OC = OR ₁ , -aryl, -Br, -Cl, -I, -F, tert-butyl, iso-propyl, -alkyl, particularly preferably C ₁ -C ₄ -alkyl, methyl, ethyl, n-propyl and n butyl.

Particularly preferred for A1 is the radical -NR ₁ R ₂ , wherein R ₁ and R _{2 are} each independently methyl, ethyl, n-propyl, i-propyl, tert-butyl, phenyl, C ₁ -C ₄ alkoxycarbonyl, C ₁ -C ₄ alkoxy, C ₁ -C ₄ carbonyl or together with the nitrogen atom to which they are attached, can form a 5 to 7-membered optionally substituted carbon ring in which optionally 1 to 3 carbons independently by hetero atoms such as nitrogen, oxygen and / or sulfur may be replaced and which may preferably be substituted by one of the above-mentioned radicals with + I effect (inductive effect).

The radicals R ₁ and R ₂ are particularly preferably identical substituents.

The radicals R ₁ and R ₂ are particularly preferably methyl.

Further preferably, the radicals R ₁ and R ₂ are ethyl.

Further preferably, the radicals R ₁ and R ₂ are isopropyl.

Further preferably, R ₁ and R ₂ , together with the nitrogen atom to which they are attached, form a six-membered ring. Particularly preferably, in this hexyl ring, a CH ₂ group is replaced by an NH group.

In another embodiment, the radical A is a radical A2 which is suitable for generating radicals under UV irradiation and / or heat.

Heat is particularly preferably generated by UV irradiation.

In a further embodiment, during the UV irradiation, the doctored film from which the membrane according to the invention is produced is additionally heated.

The radical A2 preferably comprises a functional group selected from the group consisting of optionally substituted carbon double bonds, optionally substituted peroxides, optionally substituted azo compounds, wherein the optional substituents of these groups are selected so that they can stabilize a radical. The radicals A2 are preferably substituted by at least one radical A1. In this case, the general formula (I) is preferably a compound of the formula NH ₂ -R-A2-Al.

Most preferably, the radical A2 is a C-C double bond.

In a particularly preferred embodiment, the compound of the general formula (II) B-R'-D (II) characterized in that B, R 'and D can be selected from the following groups:
B is a functional group capable of reacting with a primary amine to form a covalent bond. The radical B is preferably selected from the group consisting of carboxylic acid groups, activated carboxylic acid groups such as halocarboxylic acids, carbonyl groups, aldehyde groups and alcohol groups. B is preferably an optionally substituted, activated carboxylic acid group.

R 'is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C ₁₂ carboxyalkylene.

When these radicals are substituted, the substituent is preferably selected from the group consisting of hydrogen, linear or branched C ₁ -C ₆ -alkyl, C ₃ -C ₇ -cycloalkyl, C ₁ -C ₄ -alkoxy, C ₁ C ₄ alkoxycarbonyl, optionally substituted phenyl. In this case, the phenyl is preferably substituted by a group A1.

R 'is preferably selected from the group consisting of methylene, ethylene, n-propylene, i-propylene, n-butylene, tert-butylene, n-pentylene, n-hexylene, n-heptylene, n-octylene, n-nonylene, n-decylene, n-undecylene, n-dodecylene, oxymethylene, oxyethylene, oxypropylene, oxybutylene, oxypentylene, oxyhexylene, oxyheptylene, oxyoctylene, oxynonylene, oxydecylene, oxyundecylene, oxydodecylene, carboxymethylene, carboxyethylene, carboxypropylene, carboxybutylene, carboxypentylene, carboxyhexylene, carboxyheptylene, Carboxyoctylen, carboxynonylene, carboxydeclyene, carboxyundecylene and carboxydodecylene, wherein R 'may optionally be substituted with the abovementioned radicals. R 'is particularly preferably n-propylene.

D is a radical that does not react with an amine to form a covalent bond. Particularly preferred is hydrogen. Further preferably, D represents a radical A1 which is suitable for stabilizing a radical in the radical R 'of the compound of the general formula (II) or a radical A2 which is suitable for generating radicals under UV irradiation and / or heat to create. With regard to special embodiments of the radicals A1 and A2, reference is made to the above statements.

oder mindestens zwei Wiederholungseinheiten der allgemeinen Formel (III), welche verschieden sind, aufweist,
wobei
Ar₁ eine tetravalente organische Gruppe darstellt, die ausgewählt wird aus der Gruppe, bestehend aus

wobei
Z ausgewählt wird aus der Gruppe, bestehend aus

Ar₂ eine aromatische Gruppe darstellt, die ausgewählt wird aus der Gruppe, bestehend aus

wobei Z die gleiche Bedeutung wie oben hat;
X, X₁, X₂, und X₃ unabhängig voneinander ausgewählt werden aus der Gruppe, bestehend aus Wasserstoff, Alkylgruppen mit 1 bis 5 Kohlenstoffatomen, Alkoxygruppen mit 1 bis 5 Kohlenstoffatomen, Phenylgruppen, substituierte Phenylgruppen, Phenoxygruppen und substituierte Phenoxygruppen; und
wobei das Polyimid mindestens eine photoaktive Gruppe aufweist.In a further aspect of the present invention, the membrane according to the invention is characterized in that the polyimide used in step (a) comprises at least one repeat unit of the general formula (III)

or at least two repeat units of the general formula (III) which are different,
in which
Ar _{1 represents} a tetravalent organic group selected from the group consisting of

in which
Z is selected from the group consisting of

Ar _{2 represents} an aromatic group selected from the group consisting of

where Z has the same meaning as above;
X, X ₁ , X ₂ , and X _{3 are} independently selected from the group consisting of hydrogen, alkyl groups of 1 to 5 carbon atoms, alkoxy groups of 1 to 5 carbon atoms, phenyl groups, substituted phenyl groups, phenoxy groups, and substituted phenoxy groups; and
wherein the polyimide has at least one photoactive group.

In the context of this invention, the term starting polyimide is used below for the polyimide which is used in step (a).

oder mindestens zwei Wiederholungseinheiten der allgemeinen Formel (III), welche verschieden sind, aufweist,
wobei
Ar₁ die Gruppe

mit Z als
darstellt
und Ar₂ eine aromatische Gruppe darstellt, die ausgewählt wird aus der Gruppe, bestehend aus

mit Z als -CH₂-.In a preferred embodiment, the membrane according to the invention is characterized in that the starting polyimide has at least one repeat unit of the general formula (III)

or at least two repeat units of the general formula (III) which are different,
in which
Ar _{1 is} the group

with Z as
represents
and Ar _{2 represents} an aromatic group selected from the group consisting of

with Z as -CH ₂ -.

In another preferred embodiment, the membrane according to the invention is characterized in that the starting polyimide has at least one of the following repeat units:

die über Imidverknüpfungen mit 90–10% der folgenden Wiederholungseinheiten in einem Copolymer verknüpft sind

Particularly preferred as starting polyimide is the commercially available polymer Lenzing P84 from HP Polymers GmbH, Austria. This polyimide is a copolymer of a cocondensation of benzophenone with 3,3 ', 4,4'-tetracarboxylic dianhydride (BTDA) and a mixture of di- (4-aminophenyl) methane and toluenediamine or corresponding diioscyanates, 4,4'-methylenebis ( phenylisocyanate) and toluene diisocyanate. The resulting copolyimide has 10-90% of the repeating units having the following structural formula

which are linked via imide linkages with 90-10% of the following repeating units in a copolymer

Particularly preferred is a copolymer having the following structure and a ratio of repeating units of 20% and 80%.

The commercially available Matrimid ^® (CAS 62929-02-6, available from Huntsman) is also preferred as Ausgangspolyimid used which 1 (or 3) - (4-Aminopheyl) -2,3-dihydro-1,3,3 (or 1,1,3) -trimethyl-1H-inden-5-amine and 5,5'-carbonyl-bis-1,3-isobenzofuranedione.

Further preferred as starting polyimide is a commercially available polyetherimide from Sigma Aldrich used (700193, CAS 61128-46-9). This polyetherimide is also referred to as poly (bisphenol A anhydride-co-1,3-phenylenediamine) or poly [2,2'-bis (4- (3,4-dicarboxyphenoxy) phenylpropane) -1,3-phenylenebisimide].

The commercially available Torlon, is also preferred as Ausgangspolyimid ^® such as Torlon ^® 4000F used (available from Solvay, Belgium). This is a polyamide-imide which comprises amide linkages alternating with imide linkages. It is the product of the reaction of trimellitic anhydride with aromatic diamines.

Inventive polyimide

In a further aspect, the present invention relates to a novel polyimide suitable for undergoing a controlled crosslinking reaction under UV irradiation.

This polyimide should preferably be chemically stable in solution, so that casting solutions can be prepared to provide membranes of this polyimide which can be stored for a long time.

• (a) Umsetzung der mindestens einen im Polyimid enthaltenen Imidgruppe mit mindestens einem primären Amin der allgemeinen Formel (I) NH₂-R-A (I) unter Ausbildung eines mindestens eine primäre Aminogruppe aufweisenden Polyimids; wobei in dem primären Amin R für ein gegebenenfalls substituiertes C₁-C₁₂-Alkylen, C₁-C_{1 2}-Oxyalkylen, C₁-C₁₂-Carboxyalkylen steht, und A für einen Rest A1 oder A2 steht, der keine primäre Aminogruppe umfasst, wobei A1 einen Rest darstellt, der dazu geeignet ist, ein Radikal in dem Rest R der Verbindung der allgemeinen Formel (I) zu stabilisieren und A2 einen Rest darstellt, der dazu geeignet ist, unter UV-Bestrahlung und/oder Wärme Radikale zu erzeugen;
• (b) Umsetzung des Produktes aus Schritt (a) mit mindestens einer Verbindung der allgemeinen Formel (II) B-R'-D (II) um im Wesentlichen alle freien, im Schritt (a) erzeugten primären Aminogruppen im Polyimid abzufangen; wobei B eine funktionelle Gruppe ist, die dazu geeignet ist, mit einem primären Amin unter Ausbildung einer kovalenten Bindung zu reagieren, R' für ein gegebenenfalls substituiertes C₁-C₁₂-Alkylen, C₁-C₁₂-Oxyalkylen, C₁-C₁₂-Carboxyalkylen steht und D für einen Rest steht, der nicht mit einem Amin unter Ausbildung einer kovalenten Bindung reagiert.

The polyimide of the invention is characterized in that it is produced by a process comprising the following steps:

• (a) Reaction of the at least one imide group contained in the polyimide with at least one primary amine of the general formula (I) NH ₂ -RA (I) forming a polyimide having at least one primary amino group; wherein in the primary amine R represents an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C _{1 2} oxyalkylene C ₁ -C ₁₂ -Carboxyalkylen, and A is a radical A1 or A2 is that no primary amino group wherein A1 represents a radical capable of stabilizing a radical in the radical R of the compound of the general formula (I) and A2 represents a radical capable of generating radicals under UV irradiation and / or heat produce;
• (b) reaction of the product from step (a) with at least one compound of the general formula (II) B-R'-D (II) to scavenge substantially all of the free primary amino groups generated in step (a) in the polyimide; wherein B is a functional group capable of reacting with a primary amine to form a covalent bond, R 'is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C _{12 is} carboxyalkylene and D is a radical which does not react with an amine to form a covalent bond.

In carrying out reaction step (a) to prepare the polyimide of the present invention, it has been observed that reaction of the starting polyimide with at least one of the compounds of general formula (I) results in chain degradation of the starting polyimide. This degradation can be adjusted in a targeted manner by the concentration of the compound of the general formula (I) and / or the reaction time of step (a) (see, by way of example, Tables 1 and 2). The degradation is always associated with a degree of modification of the starting polyimide. It is assumed that always two compounds of the general formula (I) lead to a degradation in the polyimide chain. The degree of modification is the degree of introduced groups A of the compound of the general formula (I) in relation to the number of polyimide repeating units in the polymer. It is assumed that a 1 to 1 reaction, this means that per repeat unit of the 2 immanent imide imide groups only 1 has reacted with a compound of general formula (I). By the degree of modification, the photoactivity of the polyimide according to the invention can be estimated. A high degree of modification here means that many groups A of the general formula (I) have been introduced into the polyimide, but that a strong chain degradation has occurred. It has been observed that when, for example, the polymer Lenzing P84 is used as the starting polyimide, at a degree of modification of 100%, a molecular weight of the degraded chains of 2000 to 3000 g / mol, as measured by gel permeation chromatography with universal calibration, results.

It has likewise been possible to observe that the radicals R and / or A of the general formula (I) have an influence on the resulting molar mass of the polyimide. More sterically demanding radicals R and / or A degrade the starting polyimide less. This could be attributed to the fact that the degradation is always associated with an attack of two compounds of general formula (I) on a polyimide group. If a compound of the general formula (I) has already reacted with a polyimide group, the probability of a further attack by an optionally identical compound of the general formula (I) with, if appropriate, the same steric requirement is considerably lower. Likewise, the use of the radical A2 of the general formula (I) surprisingly leads to an even more suppressed degradation effect.

With respect to the degradation reaction, a continuous effect could be observed. This means that the more sterically demanding the radicals R and / or A are of the general formula (I), the lower the degradation of the starting polyimide. If, for example, the polymer Lenzing P84 with a molar mass of 34000 g / mol is used as starting polyimide and reacted with dimethylaminoethyldiamine (exemplary compound of general formula (I) with radical A1) to a degree of modification of 100%, the product has a molecular weight of 2000 g / mol. Using aminoethyl methacrylate (exemplary compound of general formula (I) with radical A2) under otherwise identical conditions, results in a molecular weight of 23,000 g / mol.

In a preferred embodiment, only one kind of the compound of general formula (I) is used for step (a).

In another embodiment, two different compounds of formula (I) are used for step (a). In this case, different radicals A1 are preferably used. Further preferably, different radicals A2 are used. Particular preference is given to using a combination of the radicals A1 and A2.

The reaction of the starting polyimide with compound of the general formula (I) can be carried out heterogeneously or homogeneously.

The heterogeneous reaction uses a solvent in which the starting polyimide is insoluble. Preferably, the solvent may be an alcohol, more preferably ethanol, methanol and / or mixtures thereof. In this embodiment, the compound of the general formula (I) in this Dissolved solvent and give the starting polyimide to this. The heterogeneous mixture should preferably be stirred during the reaction.

It has been found that the chain degradation of the starting polyimide can be minimized by a heterogeneous reaction. It follows that the ratio between the desired degree of modification increases to undesirable continued fractions. Furthermore, in the case of the heterogeneous reaction, the size of the compound of the general formula (I), ie its steric demand, plays a much greater role than in the comparable homogeneous reaction. Again, the chain degradation by the choice of a sterically more demanding substituent A of the compound of general formula (I) can be further minimized.

In a further embodiment, the reaction of the starting polyimide with a compound of general formula (I) is carried out homogeneously. For this purpose, the polyimide is dissolved in a suitable solvent. The compound of the general formula (I) is added to this solution.

Preferably, the synthesis step (a) is carried out with exclusion of light.

The implementation of the reaction step (b) for the preparation of the polyimide according to the invention is preferably carried out with only one kind of the compound of the general formula (II). Particularly preferably, two different compounds of the formula (II) are used.

The processing of steps (a) and (b) is particularly efficient, inexpensive and resource-saving.

In a further aspect of the present invention, a process is to be provided by which a membrane can be obtained, which is preferably solvent-stable.

This process should preferably not comprise any additional process step to the usual membrane production process.

Likewise, the method should preferably make it possible by the use of special Polyimidblends targeted to adjust the properties of the resulting membrane can.

Furthermore, the method should preferably comprise a simple, that is efficient, cost-effective and resource-saving purification of a polyimide.

• (1) Bereitstellung eines Polyimids durch ein Verfahren, umfassend die Schritte: (a) Umsetzung der mindestens einen im Polyimid enthaltenen Imidgruppe mit mindestens einem primären Amin der allgemeinen Formel (I) NH₂-R-A (I) unter Ausbildung eines mindestens eine primäre Aminogruppe aufweisenden Polyimids; wobei in dem primären Amin R für ein gegebenenfalls substituiertes C₁-C₁₂-Alkylen, C₁-C₁₂-Oxyalkylen, C₁-C₁₂-Carboxyalkylen steht, und A für einen Rest A1 oder A2 steht, der keine primäre Aminogruppe umfasst, wobei A1 einen Rest darstellt, der dazu geeignet ist, ein Radikal in dem Rest R der Verbindung der allgemeinen Formel (I) zu stabilisieren und A2 einen Rest darstellt, der dazu geeignet ist, unter UV-Bestrahlung und/oder Wärme Radikale zu erzeugen;
• (b) Umsetzung des Produktes aus Schritt (a) mit mindestens einer Verbindung der allgemeinen Formel (II) B-R'-D (II) um im Wesentlichen alle freien, im Schritt (a) erzeugten primären Aminogruppen im Polyimid abzufangen; wobei B eine funktionelle Gruppe ist, die dazu geeignet ist, mit einem primären Amin unter Ausbildung einer kovalenten Bindung zu reagieren, R' für ein gegebenenfalls substituiertes C₁-C₁₂-Alkylen, C₁-C₁₂-Oxyalkylen, C₁-C₁₂-Carboxyalkylen steht und D für einen Rest steht, der nicht mit einem Amin unter Ausbildung einer kovalenten Bindung reagiert.
• (2) Bereitstellung einer Gießlösung, welche im Wesentlichen umfasst: (i) das unter Schritt (1) synthetisierte Polyimid; (ii) gegebenenfalls mindestens ein weiteres Polyimid, wobei das Polyimid gleich oder verschieden sein kann zu dem Polyimid, welches als Edukt für die Herstellung des unter Schritt (1) synthetisierten Polyimids verwendet wurde; (iii) ein Lösungsmittelsystem, welches geeignet ist, das Polyimid (i) und gegebenenfalls auch das mindestens eine weitere Polyimid (ii) zu lösen; (iv) gegebenenfalls ein Additiv, welches dazu geeignet ist, die Viskosität der Gießlösung zu erhöhen; (v) gegebenenfalls ein Additiv, welches dazu geeignet ist, die Bildung von Makroporen zu unterdrücken; (vi) gegebenenfalls ein Tensid;
• (3) Rakeln eines Films aus der Gießlösung auf ein Substrat, welches gegebenenfalls ein Trägermaterial ist;
• (4) UV-Bestrahlen des Films vor und/oder nach dem Ausfällen der Membran in einem Koagulationsbad
• (5) Eintragen des Films in ein Koagulationsbad, wobei der Film vor und/oder nach dem Eintragen in das Koagulationsbad UV-bestrahlt wird;
• (5) gegebenenfalls Waschen der Membran.

The present invention therefore also relates to a process for producing a membrane, the process comprising the following steps:

• (1) providing a polyimide by a process comprising the steps: (a) reacting the at least one imide group contained in the polyimide with at least one primary amine of the general formula (I) NH ₂ -RA (I) forming a polyimide having at least one primary amino group; wherein in the primary amine R is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C ₁₂ carboxyalkylene, and A is an A1 or A2 radical which does not comprise a primary amino group wherein A1 represents a radical capable of stabilizing a radical in the radical R of the compound of the general formula (I) and A2 represents a radical capable of generating radicals under UV irradiation and / or heat ;
• (b) reaction of the product from step (a) with at least one compound of the general formula (II) B-R'-D (II) to scavenge substantially all of the free primary amino groups generated in step (a) in the polyimide; wherein B is a functional group capable of reacting with a primary amine to form a covalent bond, R 'is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C ₁₂ carboxyalkylene and D is a radical which does not react with an amine to form a covalent bond.
• (2) providing a casting solution which essentially comprises: (i) the polyimide synthesized in step (1); (ii) optionally at least one further polyimide, which polyimide may be the same or different from the polyimide used as starting material for the preparation of the polyimide synthesized under step (1); (iii) a solvent system suitable for dissolving the polyimide (i) and optionally also the at least one further polyimide (ii); (iv) optionally, an additive which is capable of increasing the viscosity of the casting solution; (v) optionally, an additive which is capable of suppressing the formation of macropores; (vi) optionally a surfactant;
• (3) knife coating a film of the casting solution onto a substrate which is optionally a carrier material;
• (4) UV irradiation of the film before and / or after precipitation of the membrane in a coagulation bath
• (5) introducing the film into a coagulation bath, wherein the film is UV irradiated before and / or after being introduced into the coagulation bath;
• (5) optionally washing the membrane.

casting solution

In one embodiment, the casting solution is prepared by dissolving the polyimide of the invention in a suitable solvent. It is particularly preferred that the polyimide according to the invention has a low proportion of degradation but high photoactivity, ie a high degree of modification. Particularly preferred here is a degree of modification of 100%.

In a preferred embodiment, the casting solution is prepared by adding 1 to 15 wt .-%, preferably 1 to 9 wt .-%, particularly preferably 1 to 3 wt .-% of the polyimide according to the invention, which by the process steps (a) and (b ) having corresponding weight percent of starting polyimide, which need not necessarily be chemically identical to the starting polyimide of step (1), dissolved in a suitable solvent (the weight percentages are based on the total weight of the casting solution). The total concentration of the polyimides in the total solution is 15 to 35 wt .-%, preferably 20 to 30 wt .-%, particularly preferably 24 to 26 wt .-% and it is added as much starting polyimide until this total concentration is reached.

The starting polyimide may preferably have the same chemical structure as the starting polyimide which was used for the synthesis steps (a) and (b).

In another embodiment, the starting polyimide has a different chemical structure than the polyimide used as the starting polyimide for the synthesis steps (a) and (b).

In a further embodiment, a mixture of different starting polyimides is used.

It has been found that the use of a blend of the polyimide of the present invention and the starting polyimide has beneficial effects on the resulting membrane. At the same time, it is possible to profit from the mechanical stability of the starting polyimide and the increased photoactivity of the polyimide according to the invention. This results in a membrane with properties that are superadditive than those of membranes from the individual polyimides.

Preferred solvents for the preparation of the casting solution can be selected from the group consisting of N-methylpyrrolidone (NMP), tetrahydrofuran (THF), N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), N, N-dimethylacetamide (DMAc), 1,4-dioxane, γ-butyrolactone and mixtures thereof. Particularly suitable is NMP as a solvent.

The total amount of the polyimides or, if only the polyimide of the invention is used, of the polyimide according to the invention alone in the entire casting solution is 15 to 35 wt .-%, preferably 20 to 30 wt .-%, particularly preferably 24 to 26 wt .-%.

The resulting casting solution preferably has a viscosity of 13 to 25 Pa · s, preferably 14 to 24 Pa · s, more preferably 16 to 22 Pa · s.

The casting solution may optionally contain other ingredients which may affect the macro- and / or microstructure of the resulting membrane.

The casting solution preferably contains a further additive which increases the viscosity of the casting solution. Preferably, the casting solution comprises these additives in a concentration of 0 to 10 wt .-%, particularly preferably 5 to 10 wt .-%. The additives are preferably selected from the group consisting of polyvinylpyrrolidones, polyethylene glycols and / or polyurethanes.

Further preferably, the casting solution contains an additive which is suitable for suppressing the formation of macropores. Preferably, the casting solution comprises these additives in a concentration of 0 to 10 wt .-%, particularly preferably 5 to 10 wt .-%. The additive is preferably maleic acid.

Further preferably, the casting solution contains a surfactant which can influence the pore structure of the membrane. Preferably, the casting solution comprises the surfactant in a concentration of less than 7% by weight, more preferably less than 5% by weight. The surfactant is preferably Triton X-100 (available from Sigma-Aldrich UK Ltd).

The casting solution may optionally be heated. The temperature of the solution should preferably not exceed 100 ° C. Particularly preferred is a temperature of 60 C. The resulting solution is preferably filtered through a depth filter. Preferably, the solution may be degassed in vacuo to remove air bubbles from the high viscosity solution.

• (i) 1–3 Gew.-% des unter Schritt (1) synthetisierten Polyimids;
• (ii) 23–25 Gew.-% mindestens eines weiteren Polyimids, wobei dieses Polyimid gleich oder verschieden sein kann zu dem Polyimid, welches als Edukt für die Herstellung des unter Schritt (1) synthetisierten Polyimids verwendet wurde,
• (iii) NMP; wobei die Polyimidgesamtkonzentration im NMP 24 bis 26 Gew.-%, bezogen auf die gesamte Gießlösung, beträgt.

In one embodiment, the casting solution essentially comprises:

• (i) 1-3% by weight of the polyimide synthesized under step (1);
• (ii) 23-25% by weight of at least one further polyimide, which polyimide may be identical or different from the polyimide used as starting material for the preparation of the polyimide synthesized under step (1),
• (iii) NMP; wherein the total polyimide concentration in the NMP is 24 to 26% by weight, based on the total casting solution.

It has surprisingly been found that a polyimide which has been modified only by the reaction (a) with at least one compound of the general formula (I) and which has been dissolved in a suitable solvent to prepare a casting solution is further degraded. Without wishing to be bound by theory, it is believed that the free primary amino groups introduced by step (a) on the starting polyimide can further cleave the polyimide chains. They split on the one hand, the product of step (a) on, so that the molecular weight of these polyimides is lower. If, optionally, a starting polyimide is added to this casting solution, this starting polyimide can also be split. This time-dependent chain degradation can be detected by gel permeation chromatography or viscosity measurements. Therefore, a casting solution which comprises the product of step (a) and optionally also a starting polyimide must be processed as quickly as possible, since too pronounced chain degradation also brings about a deterioration in the properties of the resulting membrane. Above all, such membranes are mechanically unstable and have defects or cracks.

However, a timely use of the casting solution is not suitable especially for industrial applications. Surprisingly, it has been found that a casting solution comprising the polyimide according to the invention is chemically stable. Without wishing to be bound by theory, it is believed that carrying out the second step (b) to obtain the polyimide of the present invention captures all the primary amino groups resulting from step (a). This means that the primary amino groups are converted by the covalent bond with at least one compound of general formula (II) into a form which is not suitable to degrade polyimide chains. Particularly preferred is the radical D of the general formula (II) as a radical which does not react with an amine to form a covalent bond.

As a result, the casting solution comprising the polyimide of the present invention is stable in the sense that no chain degradation of the polyimide of the invention and also the optional added starting polyimide does not occur. Such a casting solution is preferably stable for at least 3 months, more preferably at least 1 month, most preferably at least 1 week.

Particularly preferably, in addition to the interception of the primary amino groups by the compound of general formula (II), further groups D can also be introduced into the polyimide of the invention, which are either suitable for generating a radical in the radical R 'of the compound of the general formula (H) or are capable of generating radicals under UV irradiation and / or heat. The radicals D are particularly preferably one of the radicals A1 and / or A2. This additional possibility of increasing the photoactivity of the polyimide according to the invention allows the resulting membrane properties to be controlled and, preferably, also improved. Preferably, especially the crosslinking properties of the resulting membrane can be improved.

phase inversion

The membrane according to the invention is produced by phase inversion. This represents a process already known from the literature, which is described, for example, in US Pat US 3,556,305 . US 3,567,810 . US 3,615,024 . US 4,029,582 . US 4,188,354 . GB 2,000,720 A . Office of Saline Water R & D Report no. 357, October 196 ; Reverse Osmosis and Synthetic Membranes, Ed. Sourirajan or Murari et al., J. Membr. Sci. 16: 121-135 and 181-193, 1983 is described.

In one embodiment of the present invention, the phase inversion process is selected from the group consisting of non-solvent induced phase separation (NIPS), temperature induced phase separation (TIPS), evaporation induced phase separation (EIPS), vapor induced phase separation "(VIPS) and hybrids from these processes. Particularly preferred in the present invention, the NIPS method is used.

The casting solution is preferably heated to a temperature of from 25 to 100 ° C., preferably from 30 to 90 ° C., particularly preferably from 50 to 70 ° C., before it is used for doctoring. Subsequently, the casting solution is cooled to room temperature.

In one embodiment, the casting solution as described above is preferably doctored onto a suitable substrate. In this case, the materials which substantially comprise the suitable substrates are preferably selected from the group consisting of glass, metal, paper and plastic. The resulting membrane should preferably be able to be detached from this substrate afterwards.

In another embodiment, the casting solution as described above is preferably doctored onto a suitable carrier. Preferably, this suitable carrier is a carrier membrane. In another embodiment, the resulting membrane is preferably a composite membrane.

In one embodiment, a scintered polyimide film comprising the polyimide of the invention may also be applied to a support material. It was observed that when using the solvent DMF for the casting solution and subsequent UV irradiation, this film precipitated even before contact with a coagulation bath. In this case, the polyimide is so strongly crosslinked that it already precipitates out of the evaporating DMF. The degree of crosslinking can be adjusted both via the UV irradiation time and via the type of polyimide according to the invention.

The suitable carrier is preferably porous. Particularly preferably, the support is designed such that it essentially comprises an inert porous material and does not affect the flow through the membrane. Preferably, the carrier material does not react with the solvent used for filtration through the membrane.

In one embodiment, the carrier material reacts with the scrape-on polyimide of the invention so that a covalent bond is formed between the scrape-coated layer and the carrier material. This covalent bond is particularly preferably formed under UV irradiation. For this purpose, the support material may preferably itself have groups which are suitable for reacting with the polyimide under UV irradiation. The support material preferably comprises groups having the radicals A1 and / or A2.

In another embodiment, the support material is inert to the reactions which the polyimide of the invention undergoes under UV irradiation.

The support material preferably does not degrade under UV irradiation. Furthermore, preferably, the carrier material does not react with the other substances of the casting solution except, if appropriate, the polyimide according to the invention. Particularly preferably, the carrier material does not react with the solvent of the coagulation bath.

Such porous support materials are preferably selected from the group consisting of nonwovens or woven supports. These essentially comprise a material which is preferably selected from the group consisting of cellulose, polyethylene, polypropylene, nylon, homopolymer and / or copolymer comprising vinyl chloride, polystyrene, polyesters such as polyethylene terephthalate, polyvinylidene fluoride, polytetrafluoroethylene, polysulfones, polyether sulfones, polyether ketones (PEEK), polyphenylene oxide, Polyphenylinsulphid, ethylene (R) -chlorotrifluorethylen (Halar ^® ECTFE), glass wool, metal mesh, sintered metal, porous ceramics, sintered glass, porous carbon or carbon fiber material, graphite, inorganic membranes based on aluminum and / or silica optionally coated with zirconia and / or other oxides and / or combinations of the materials.

The carrier materials defined above may also be selected preferably as carrier for producing a composite membrane comprising the membrane according to the invention.

The casting solution may be applied to the appropriate substrate or carrier such that the resulting membrane preferably has a shape selected from the group consisting of flat membrane, hollow fiber membrane, capillary membrane, and / or tubular membrane. In another embodiment, the suitable support preferably already has the shape to form a composite membrane having one of the abovementioned forms.

During the doctoring process, if appropriate, part of the solvent or solvent mixture used for the casting solution may evaporate.

The doctoring process can be carried out by conventional methods. Preferably, a doctor blade is used with a slot of 50 microns to 1000 microns, preferably 75 microns to 500 microns, more preferably 100 microns to 300 microns. The thickness of the resulting film may also be affected by the feed rate at which the doctor blade is moved. Preferably, a preferred speed of 5 to 50 mm / s, more preferably 10 to 40 mm / s, most preferably 15 to 25 mm / s is used. In a preferred embodiment, the casting solution at room temperature.

The UV irradiation for crosslinking of the photoactive groups can be carried out before and / or after precipitation of the membrane in the coagulation bath.

In one embodiment, the UV irradiation takes place directly after doctoring, that is, before precipitation in the coagulation bath. In this case, the gerakelte film of radiation that is substantially in the UV range exposed. In this case, wavelengths in the range of 100 to 800 nm, more preferably 200 in the range of up to 400 nm are preferably used. Preferably, a mercury vapor lamp is used. If necessary, the wavelength range can be adjusted in a targeted manner by means of suitable filters. Particularly preferred is a filter is used, which filters out the IR radiation. Preferably, a UV irradiation with an energy density of 5 to 50 mW / cm ² , more preferably from 10 to 45 mW / cm ² , most preferably from 20 to 40 mW / cm ^{2 is} used.

The irradiation time may preferably be between 10 s and 30 h, more preferably between 1 min and 1 h, most preferably between 1.5 min and 30 min. It has surprisingly been found that just short irradiation times of 2 minutes are sufficient to achieve a membrane with the desired properties. This short irradiation period is especially suitable for the large-scale production of the membrane of the invention.

In one embodiment, the doctored film is also additionally heated externally for UV irradiation. This can preferably be carried out by overflow and / or underflow of the film / the forming membrane with heated air. The temperature is preferably in a range which is suitable for activating the remainder A2, so that additional crosslinking takes place.

In a further embodiment, the UV irradiation takes place after precipitation of the membrane in the coagulation bath. The irradiation is preferably carried out in the same way as described for the irradiation before precipitation of the membrane in the coagulation bath.

In a further embodiment, the UV irradiation takes place before and after precipitation of the membrane in the coagulation bath.

The coagulation bath used, regardless of when the UV irradiation occurs, comprises a non-solvent for the starting polyimide. It serves to completely precipitate the forming membrane. By the immersion rate of the forming membrane, the structure of the membrane can preferably be further influenced. Furthermore, the composition of the coagulation bath preferably further influences the structure of the membrane. The coagulation bath comprises solvents which are preferably selected from the group consisting of water, water-miscible organic solvents such as glycerol, NMP, THF, DMF, DMAc, DMS; 1,4-dioxane, γ-butyrolactone, alcohols, ketones or formamides and mixtures thereof. In one embodiment, the coagulation bath comprises further additives such as surfactants.

The person skilled in the art knows the methods of modifying the NIPS process described here in such a way as to obtain one of the other phase inversion processes and / or hybrids from several of these processes.

In one embodiment, the membrane is washed after coagulation. For this purpose, the membrane is preferably exposed to a water bath. As a result, residues of the solvent used in the casting solution can be removed from the membrane. Preferably, however, other additives which have been added to the casting solution can also be washed out. Further preferably, additives which have been added to the coagulation bath can also be washed out.

A particular advantage of the method according to the invention for producing the membrane according to the invention is that no further additives have to be washed out of the membrane. In one embodiment, only the solvent or solvent mixture used for the casting solution needs to be washed out of the membrane. This is especially important for the later use of the membrane. Due to the fact that no further additives were used, they can not bleed out during the separation process when using the membrane. Thus, neither the retentate nor the permeate are contaminated with bleeding additives. The membrane according to the invention thus has an increased potential for use. Furthermore, the use of water is sufficient for the washing process of the membrane. In common processes, organic solvents must be added to the wash bath so that the additives to be washed out dissolve in the bath. The inventive method is therefore more economical and saves resources.

In one embodiment, after exposure to the coagulation bath and / or after being washed, the membrane is additionally dried.

In a further embodiment, the method according to the invention comprises a further step in which the membrane according to the invention obtained as flat membrane or hollow fiber membrane, optionally as composite membrane, in a tube module, capillary module, plate membrane module, wound module, optionally pleated in filter cartridges or in to them built-in related modules.

The particular advantage of the method according to the invention is that a membrane can be produced without further additives in the squeegee solution and / or in the precipitation bath and / or in a subsequent process step of the precipitation. This will result in more efficient membrane production, producing less waste.

Invention membrane

Furthermore, the present invention is intended to provide a membrane which has substantially a sponge structure.

Likewise, the present invention is intended to provide a membrane which is preferably suitable for ONS application.

To achieve this object, the present invention provides a membrane which is obtainable by the method according to the invention described above.

In one aspect of the present invention, a membrane is provided which preferably has substantially an asymmetric structure. Asymmetric membranes are from the literature known and characterized in that they have at least one layer which has a smaller pore size than the rest of the membrane. This layer has a microstructure and acts as a barrier layer. Such membranes are available in the literature mainly through different phase inversion processes.

In a preferred embodiment of this invention, barrier layer is non-porous. The term pore-free means that it has pores which are preferably less than 2 nm, more preferably less than 1 nm. This layer is preferably above a thicker substructure having larger pores than the dense layer. The substructure has a macrostructure. In one embodiment, the substantially dense layer may also be coated onto a suitable substrate to obtain a composite membrane. In this case, carrier materials are used, as described above.

In another aspect of the present invention, a membrane is provided which has a dense symmetric structure. Symmetrically means that the pore size over the entire thickness of the membrane is substantially constant. Such membranes are also available in the literature essentially by phase inversion processes.

In another aspect of the present invention, a membrane is provided which is porous. Porous in this context means that the membrane has pores having a pore diameter greater than 2 nm. Preferably, this membrane is symmetrical. Further preferred, this membrane is asymmetric.

In a preferred embodiment, the membrane according to the invention essentially has a sponge structure. A sponge structure is characterized by an interconnecting pore volume. This sponge structure causes the membrane of the invention is mechanically very stable. A compaction effect can thereby be minimized. Furthermore, a preferably asymmetric sponge structure means that at the same time a high flow through the membrane can be ensured.

In one aspect of the present invention, the membrane according to the invention is characterized in that the membrane is resistant in the solvents in which the starting polyimide is soluble. These solvents are preferably selected from the group consisting of NMP, THF, DMAc, DMF, DMSO, 1 , 4-dioxane, toluene, benzene, xylene, methyl ethyl ketone, methyl isobutyl ketone, γ-butyrolactone, iso-propanol, n-hexane, chlorinated solvents and mixtures thereof. The term solvent-resistant in the context of the present invention means that the membrane, which has been inserted for at least 2 months in one of the abovementioned solvents, has only a small mass loss. The mass loss determined by differential weighing is at most 20%, preferably at most 10%, particularly preferably at most 5% and very particularly preferably at most 1%.

In one aspect of the invention, the membrane according to the invention comprises at least one photocrosslinked polyimide according to the invention. Without wishing to be bound by theory, it is believed that the solvent resistance of the membrane according to the invention is produced by the high photoactivity of the polyimide according to the invention, which leads to a high degree of crosslinking.

In a further aspect of the invention, the membrane according to the invention is produced from at least one polyimide which has a lower molecular weight than the starting polyimide. In this case, the membrane is preferably made of at least one polyimide, which has a lower molecular weight than the starting polyimide, and additionally a starting polyimide.

Surprisingly, it was found that the UV irradiation before the precipitation of the membrane in the coagulation allows control of both the microstructure and the macrostructure of the membrane. By choosing the degree of modification of the polyimide according to the invention and the length and / or intensity of the UV exposure, it is possible to control the microstructure without further additives. The control over the thickness and density of the microstructure leads to a specific control over the separation properties of the membrane. By choosing the degree of modification of the polyimide according to the invention and the length and / or intensity of the UV exposure, it is additionally possible to control the macrostructure without further additives. Control over the macrostructure produces improved mechanical stability of the membrane. This may result in higher selectivity at high flux through the cross-linked, nonporous barrier layer with controlled solvent swelling. By the UV exposure of the gerakelten film, so before the precipitation of the membrane in the coagulation bath, a membrane which has a substantially sponge structure can be provided. The resulting membranes according to the invention are in Essentially solvent resistant. This can mainly be attributed to the fact that the macrostructure also has a certain amount of cross-linking. The strength of this effect can be influenced by suitable selection of the compounds of the general formula (I) and the degree of modification of the polyimide according to the invention. The higher the photoactivity of the effect according to the invention, the more crosslinked is the barrier layer.

Surprisingly, it has been found that by UV irradiation of the membrane according to the invention after precipitation in the coagulation bath, the microstructure can be controlled so that the retention is increased and the flow is lowered. The macrostructure in this embodiment remains the same as that of a membrane of the starting polyimide. Although the resulting membrane according to the invention is not completely solvent-resistant, the barrier layer is so crosslinked that at least this layer is solvent-resistant. As a result, essentially no swelling of the barrier layer occurs, resulting in a high retention. The strength of the effects can be influenced by suitable selection of the compounds of the general formula (I) and the degree of modification of the polyimide according to the invention. The higher the photoactivity of the effect according to the invention, the more crosslinked is the barrier layer.

In one aspect of the present invention, there is provided a membrane wherein said membranes are selected from the group consisting of gas separation membrane, nanofiltration membrane, nanofiltration membrane for separation into organic solvents, ultrafiltration membrane, microfiltration membrane, reverse osmosis membrane and pervaporation membrane. The membrane according to the invention is preferably a nanofiltration membrane. Furthermore, the membrane according to the invention is preferably a nanofiltration membrane for separation in organic solvents.

In one aspect of the present invention, the membrane is used for nanofiltration. The membrane of the invention is preferably used for a separation process for the separation of compounds having molecular weights between 200 and 2000 g / mol from a solution comprising this compound. Most preferably, this solution comprises an organic solvent. Further preferably, this organic solvent is an aprotic organic solvent. This organic solvent is particularly preferably selected from the group consisting of NMP, THF, DMAc, DMF, DMSO, 1,4-dioxane, toluene, benzene, xylene, methyl ethyl ketone, methyl isobutyl ketone, γ-butyrolactone, chlorinated solvents, isopropanol, n-hexane and mixtures thereof. The membrane according to the invention preferably has a permeability of 0.5 to 12 L / hm ² bar, preferably 0.5 to 5 L / hm ² bar, more preferably from 0.5 to 2.5 L / hm ² bar.

Description of the figures

1 : Filtration plant for the characterization of the membrane

LIST OF REFERENCE NUMBERS

1

Input for cooling circuit

2

Input for filtration solution

3

Pressure sensor; Pressure is kept constant during the entire filtration process, the pressure is regulated via the pump flow, pumps are controlled by pressure sensors

4

Temperature sensor; Temperature is kept constant during the entire filtration, the temperature is controlled by the cooling circuit (1 and 6), the cryostat is controlled by temperature sensors

5

Output for filtration solution; closed during dead-end filtration; opened during cross-flow filtration (withdrawal of retentate here)

6

Output for cooling circuit

7

stirrer

8th

membrane

9

Stainless steel mesh with perforated stainless steel base plate

10

Output for filtration solution; here removal permeate

2 : Stirrer of the filtration plant for characterizing the membrane stirrer is designed so that laminar boundary film and thus concentration polarization is minimized.

3 : SEM image - image of the entire cross-section of the membrane according to the invention, 1768 × magnification (sputtered with gold)

4 : SEM image - recording of the barrier layer of the membrane according to the invention, 100,000 times magnification (sputtered with gold)

Examples

I. Preparation of a Polyimide According to the Invention

I.1 step (a) - homogeneous reaction

30 g of Lenzing P84 (0.0705 mol) were dissolved in 150 ml of DMF. For a degree of modification of 100%, 7.047 mL (0.0705 mol) of N, N'-diisopropylethylenediamine (DIPEDA) was added and stirred at room temperature for 14 h. The reaction solution was concentrated in an oil pump vacuum to increase the viscosity. Subsequently, the product was precipitated in 1 L of distilled water. After 30 minutes in the precipitation bath, the water was changed and after a further 30 minutes filtered through a pleated filter. The modified polymer was dried in a drying oven at 40 ° C and 180 mbar for 70 h.

I.2 step (a) - homogeneous reaction

30 g Lenzing P84 were dissolved in 500 mL DMF. For a resulting 10% degree of modification, 1.29364 g of 2-aminoethyl methacrylate hydrochloride (AEMA) was dissolved in another 15 mL of DMF and added to the polymer solution along with 1.077 g of K ₂ CO ₃ . For a degree of modification of 5%, 0.645 g AEMA were dissolved in another 15 mL DMF and added to the polymer solution together with 0.5385 g K ₂ CO ₃ . For a degree of modification of 1%, 0.129 g AEMA was dissolved in another 15 mL DMF and added to the polymer solution together with 0.1077 g K ₂ CO ₃ . The respective reaction mixture was stirred for 18 h overnight with the exclusion of light and then concentrated by about 200 ml in vacuo. The viscous polymer solution was added to 11 distilled water. For complete precipitation, the water was exchanged for fresh water for two to three hours several times. Subsequently, the precipitated polymer was dried at 60 ° C for several days to constant weight. The polymer is stored under the exclusion of light.

I.3 step (a) - heterogeneous reaction

For a theoretical degree of modification of 40%, 2 g of Lenzing P84 were added to a solution of 0.338 g of AEMA in 15 ml of ethanol or methanol and stirred. To terminate the reaction, the polymer was filtered off at different times (5 min to 7 days) and washed with 300 ml of ethanol or methanol. The drying of the polymer was carried out at 60 ° C for 18 h. The dry polymer was stored under exclusion of light.

I.4 step (a) - degree of modification

Table 1: Modification levels using the example of a Lenzing P84 with N, N-dimethylethylenediamine Theoretical degree of modification (%) Experimentally determined degree of modification of the product from step (a) by ¹ H-NMR (%) Molecular weight of the product of step (a) by gel permeation chromatography * (g / mol) Molecular weight of the product from step (a) calculated by ¹ H-NMR (g / mol) 100 115 2900 n / A 80 79 2100 860 70 64 2600 1300 50 39 3,100 2000 30 - * 4000 2300 20 15 9500 7000 10 6 18700 17000 0 0 30000 - * Universal Calibration Table 2: Modification Levels - Group A steric effect Reaction time (min) Molar mass by gel permeation chromatography * (g / mol) N, N-dimethylethylenediamine N, N'-diisopropyl Aminoethyl-piperidine 5 10800 19500 13400 10 9400 14400 12200 15 8300 13700 11200 30 7500 12000 9100 Reaction time (min) Degree of modification by ¹ H-NMR (%) N, N-dimethylethylenediamine Of N, N'-diisopropyl aminoethylpiperidine 5 26 22 26 15 29 40 30 30 32 45 34 * Universal Calibration

I.5 step (b) - heterogeneous reaction

To trap the free amino groups, a reaction with an acid chloride was carried out by one-pot method. To this was added 1.2 mL (14 mmol) of oxalyl chloride to 3.2 mL of DMF in 50 mL of acetonitrile under argon in the cold (-18 ° C) and stirred for 15 min. Subsequently, 2.2 g (12.1 mmol) of dimethylamino-propionic acid were added and the mixture was stirred for a further 15 minutes. Next, 10 grams of the DIPEDA-modified polyimide was added to trap the primary amino groups in a heterogeneous reaction. After a reaction time of 60 minutes, part of the solvent was removed in an oil pump vacuum, and then 100 ml of water were added to stop the reaction. The reaction product did not precipitate, but went completely into solution. The low sediment was removed by centrifuging and the supernatant was dried in an oil pump vacuum. The dried product could not be redissolved in water and was washed twice with 150 mL of water. Subsequently, the product was dried in a drying oven at 40 ° C and 180 mbar.

II. Production of the Membrane of the Invention

II.1 Preparation of a casting solution - according to the invention

4.5 g of the product prepared in I.5 were mixed with 29 g Lenzing P84 with 115 mL NMP and stirred at 60 ° C for 6 h. The mixture was then stirred at room temperature for a further 72 h. The solution was filtered with argon overpressure (6 bar) through a depth filter. It was then degassed for 6 minutes in an oil pump vacuum. The solution was airtight for later use and sealed with the exclusion of light,

II.2 Preparation of a casting solution

4.5 g of the product prepared in I.1 were combined with 29 g of Lenzing P84 with 115 ml of NMP and stirred at 60 ° C. for 6 hours. The mixture was then stirred at room temperature for a further 72 h. The solution was filtered with argon overpressure (6 bar) through a depth filter. It was then degassed for 6 minutes in an oil pump vacuum. The solution was airtight for later use and sealed with the exclusion of light.

II.3 Preparation of a casting solution

23.5 g of Lenzing P84 were dissolved in 115 ml of NMP and stirred at 60 ° C. for 6 hours. The mixture was then stirred at room temperature for a further 72 h. The solution was filtered with argon overpressure (6 bar) through a depth filter. It was then degassed for 6 minutes in an oil pump vacuum. The solution was airtight for later use and sealed with the exclusion of light.

II.4 Making a membrane

First, the casting solutions from step II.1 to II.3 were heated to 60 C for 2 h to obtain a homogeneous solution and cooled again to room temperature. Then the respective solution was applied in a doctor blade with a 300 micron slot on a cleaned glass plate at a feed rate of 20 m / s. After application to the glass plate, this was optionally immediately placed in a UV box (Hönle, UV Cube) and irradiated. The UV irradiation was carried out for 2 min with a Hg lamp at an energy density of 29 ± 2 mW / cm ² . Immediately after the irradiation, the respective film with the glass plate was put in a 4 L water bath to finally obtain the membrane structure by NIPS. After detachment from the gas plate, the membrane was placed in a further water bath for curing. Here the membrane remained at least 24 h. For comparison, identical membranes were prepared without irradiation.

III. membrane characterization

The prepared membrane was first punched out to an appropriate size and equilibrated for 1 h in isopropanol. The membranes now had a flow of less than 7 L / hm ² bar. Subsequently, the membranes were placed in iso-propanol for a further 24 h. Membrane samples were collected in a continuous dead-end filtration unit (see 1 ) are equilibrated in isopropanol, hexane and toluene over a period of 12 h to 24 bar and then the permeabilities are determined. The same equipment was used to measure the retention (see 1 ) used in cross-flow mode. The temperature was carried out constantly at 25 ° C. Table 3 summarizes the results.

The retention was carried out with the dyes Unisol Blue (molecular weight: 322 g / mol) and Rose Bengal (molecular weight: 1100 g / mol) in a concentration of 0.01 g / l.

wobei c_p für die Konzentration der Verbindung i im Permeat steht, wobei das Permeat die Lösung ist, die durch die Membran gegangen ist und c_R für die Konzentration der Verbindung i im Retentat steht, wobei das Retentat die Lösung ist, die nicht durch die Membran geflossen ist.In this case, the retention R was calculated by the following formula

where c _{p is} the concentration of compound i in the permeate, the permeate being the solution that has passed through the membrane and c _{R is} the concentration of compound i in the retentate, the retentate being the solution that is not affected by the Membrane has flowed.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

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Cited non-patent literature

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• S. Behnke, M. Ulbricht, Tailored membranes for organophilic nanofiltration based on photocrosslinkable polyimides, Abstract to the 3rd International Conference on Organic Nanofiltration 2010 [0009]
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Claims (10)

A membrane formed by phase inversion comprising at least one photochemically crosslinked polyimide, characterized in that the polyimide is prepared by a process comprising the steps of (a) reacting the at least one imide group contained in the polyimide with at least one primary amine of the general formula (I) NH ₂ -RA (I) forming a polyimide having at least one primary amino group; wherein R is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C ₁₂ carboxyalkylene, and A is an A1 or A2 radical which is not a primary amino group, wherein A1 is a Radical which is capable of stabilizing a radical in the radical R of the compound of the general formula (I) and A2 represents a radical capable of generating radicals under UV irradiation and / or heat; (b) reaction of the product from step (a) with at least one compound of the general formula (II) B-R'-D (II) to scavenge substantially all of the free primary amino groups generated in step (a) in the polyimide; wherein B is a functional group capable of reacting with a primary amine to form a covalent surf, R 'is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C _{12 is} carboxyalkylene and D is a radical which does not react with an amine to form a covalent bond. Phase inversion-formed membrane according to claim 1, characterized in that the membrane is resistant to the solvents in which the polyimide used in step (a) of claim 1 is soluble. Phase inversion-formed membrane according to one of claims 1 or 2, characterized in that the polyimide used in step (a) of claim 1 comprises at least one repeat unit of the general formula (III)

or at least two repeat units of the general formula (III), which are different, wherein Ar _{1 represents} a tetravalent organic group selected from the group consisting of

wherein Z is selected from the group consisting of

Ar _{2 represents} an aromatic group selected from the group consisting of

where Z has the same meaning as above; X, X ₁ , X ₂ , and X _{3 are} independently selected from the group consisting of hydrogen, alkyl groups of 1 to 5 carbon atoms, alkoxy groups of 1 to 5 carbon atoms, phenyl groups, substituted phenyl groups, phenoxy groups, and substituted phenoxy groups; and wherein the polyimide has at least one photoactive group. A phase inversion-formed membrane according to any one of claims 1 to 3, characterized in that it is prepared from at least one polyimide having a lower molecular weight than the polyimide used in step (a) of claim 1. Phase inversion formed membrane according to one of claims 1 to 4, characterized in that the membrane has a substantially sponge structure. Process for the preparation of a membrane by means of phase inversion, comprising the following steps: (1) providing a polyimide by a process comprising the steps of (a) reacting the at least one imide group contained in the polyimide with at least one primary amine of the general formula (I) NH ₂ -RA (I) forming a polyimide having at least one primary amino group; wherein R is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C ₁₂ carboxyalkylene, and A is an A1 or A2 radical which is not a primary amino group, wherein A1 is a Radical which is capable of stabilizing a radical in the radical R of the compound of the general formula (I) and A2 represents a radical capable of generating radicals under UV irradiation and / or heat; (b) reaction of the product from step (a) with at least one compound of the general formula (II) B-R'-D (II) to scavenge substantially all of the free primary amino groups generated in step (a) in the polyimide; wherein B is a functional group capable of reacting with a primary amine to form a covalent bond, R 'is an optionally substituted C ₁ -C ₁₂ alkylene, C ₁ -C ₁₂ oxyalkylene, C ₁ -C _{12 is} carboxyalkylene and D is a radical which does not react with an amine to form a covalent bond; (2) providing a casting solution which essentially comprises: (i) the polyimide synthesized in step (1); (ii) optionally at least one further polyimide, which polyimide may be the same or different from the polyimide used as starting material for the preparation of the polyimide synthesized under step (1); (iii) a solvent system suitable for dissolving the polyimide (i) and optionally also the at least one further polyimide (ii); (iv) optionally, an additive which is capable of increasing the viscosity of the casting solution; (v) optionally, an additive which is capable of suppressing the formation of macropores; (vi) optionally a surfactant; (3) knife coating a film of the casting solution onto a substrate which is optionally a carrier material; (4) UV-irradiating the film before and / or after precipitating the membrane in a coagulation bath; (5) introducing the film into a coagulation bath, wherein the film is UV irradiated before and / or after being introduced into the coagulation bath; (5) optionally washing the membrane. A method according to claim 6, characterized in that the membrane obtained is a flat membrane or hollow fiber membrane, each optionally as a composite membrane, which is installed in a tube module, capillary module, plate-membrane module, winding module, optionally pleated in filter cartridges or related to these modules is. Use of the membrane according to one of claims 1 to 5 for nanofiltration. Use of the membrane according to claim 8 for a separation process for the separation of compounds having molecular weights between 200 and 2000 g / mol from a solution comprising this compound. Use of the membrane according to any one of claims 8 or 9, wherein the solution comprises an organic solvent.

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