|Title of Invention||
A COVALENTLY CROSS-LINKED COMPOSITE POLYMER MEMBRANE AND A PROCESS THEREOF
|Abstract||The invention relates to a covalently cross-linked polymer or polymer membrane consisting of one or more polymers, which can bear the following functional groups (M-Hal (F, CI, Br, I), OR, NR2; R=alkyl, hydroxyalkyl, aryl; (Me=H, Li, Na, K, Cs, or other metal cations or ammonium ions); a) precursors of cation exchange groups; S02M and/or PM02 and/or COM b) sulphinate groups SO2Me and which can be covalenely cross-linked using the following organic compounds: a) di, tri or oligofunctionai haloalkanes or haloaromatics which have been reacted with sulphinate groups S02Me, whereby the following cross-linking bridges are present in the polymer/in the polymer blend/in the polymer membrane (Y-cross-linking bridges, X=Hal (F, CI, Br, I), OR, Y=(CH2)X-; arylene; -(CH2)x-arylene-; CH2arylene-CH2-, x=3-12); polymer-SO2Y-S02-polymer and/or b) compounds containing the following groups: Hal-(CH2)X-NHR, one side of which (Hal-) has been reacted with sulphinate groups SO2ME and the other side (-NHR) with SO2M groups, whereby the following cross-linking bridges are present in the polymer/in the polymer blend/in the polymer membrane; polymer-S02-(CH2)x.NR-S02-polymer and/or c) compounds containing the following groups; NHR-(CH2)X)-NHR, which have been reacted with sulphinate groups SO2Me, whereby the following cross-linking bridges are present in the polymer/in the polymer blend/in the polymer membrane: polymer-SO2-NR-(CH2)x-NR-SO2-polymer.|
|Full Text||Prior art
The present invention relates to a method for preparing covalently cross-linked ionomer membranes, which is based on an alkylation reaction of sulfinate groups-containing polymers, polymer blends and polymer (blend) membranes (J. Kerres, W. Cui, W. Schnurnberger: "Vernetzung von modifizierten Engineering Thermoplasten", German Patent 196 22 337.7 (Application dated June 4, 1996), German Patent Office (1997), "Reticulation de Materizuxf hermoplastiques Industriels Modifies", French Patent F 97 06706 dated May 30, 1997). An advantage of the covalent network is its resistance to hydrolysis even at higher temperatures. A disadvantage of the ion conductive, covalently cross-linked polymers and polymer blends described in the above invention is the formation of a hydrophobic network when alkylating the sulfinate groups during forming the membrane, this hydrophobic network being partially incompatible with the ion conductive polymer (blend) component such as a sulfonated polymer polymer-SOaMe, so that an inhomogeneous polymer (blend) morphology is generated, which reduces the mechanical stability (embrittlement on drying up!) and also prevents a complete cross-linking due to the partial separation of sulfinate phase and sulfonate phase.
The products and processes, respectively of application No. DE 100245.7 to which priority has been claimed has following disadvantages:
For membranes which are prepared by the described processes, moistered gases are still needed for operation in the hydrogen fuel cell. If the gases are not moistened, the membrane dries up and the proton conductivity is decreased to a large extent.
To solve this problem, of the application No. DE 10054233.6 priority of whose is also claimed suggests incorporating tectosilicates and phyllosilicates which are optionally functionalized according to the parent application, particularly into a covalent network.
The invention as per first priority application application only describes the incorporation of polymers into the covalent network. When using functionalized phyllosilica'tes and/or tectosilicates it was surprisingly found, that the compounds which have low molecular functional groups and are bound to the phyllosilicates and/or tectosilicate are not discharged or only moderately discharged during employment of the membrane, especially in the case of employment in a hydrogen fuel cell. This allows an increase in the concentration of ion conductive groups within the covalent network without having the usual effect of extremely deteriorating the mechanical characteristics of the membrane (brittlement or strong swelling). In an extreme case it is therefore possible to completely eliminate the use of enclosed ion conductive polymers in the covalent network. Ion conduction then exclusively occurs via silicates having functional groups.
Thus, the invention disclosed in the second priority application solves the problem of drying up the membrane and of a limitation in the number of ion conductive groups within the membranes to a not marginal extent.
Thus, the object of the invention is to provide new covalently cross-linked polymers/membranes in which the covalently cross-linked polymer (blend) component is well compatible with the ion conductive polymer (blend) component.
This object is achieved by providing membranes reproduced in claim 1. Further the process according to the invention adds to this purpose. Thereto a polymer solution comprising polymers containing the following functional groups:
* sulfinate groups -SO2Me
sulfochloride groups and/or other precursors of cation exchange
groups, is prepared.
Additionally, a bifunctional or oligofunctional alkylation cross-linking agent (typically an α,ω-dihaloalkane) and optionally a secondary diamine cross-linking agent NHR-(CH2)X-NHR is added to the polymer solution. The formation of the covalent cross-linking bridges takes place during formation of the membrane when evaporating the solvent by alkylating the sulfinate groups and optionally by the formation of sulfonamide via reaction of the sulfohalogenide groups present in the polymer with the secondary amino groups of the diamine cross-linking agent. During the acidic and/or basic and/or neutral aqueous after-treatment of the membranes following the membrane formation, the precursors of the cation exchange groupings are hydrolyzed to form cation exchange groups.
Thus the object of the invention is to provide new covaiently cross-linked polymers/membranes displaying proton coductivity even when used with gases which are not moistened or only slightly moistened. Moreover, a further object is to incorporate low molecular functionalized compounds which are coupled to a silicate into the covalent network such that they remain in the membrane for an industrially useful period of time.
Further the process according to the invention helps to solve this object. The following text expressively refers to the parent patent application DE 100 24 575.7:
A mixture in a suitable solvent, preferably an aprotic one, is prepared, which contains polymers and functionalized tectosilicates and/or phyllosilicates and optionally low molecular compounds.
The mixture contains polymers and the following functional groups:
sulfinate groups S02Me (Me is a monovalent or polyvalent metal
sulfochloride groups and/or other precursors of cation exchange
Additionally, a bifunctional or oligofunctional alkylation cross-linking agent (typically an α,ω-dihaloalkane) and optionally a secondary diamine cross-linking agent NHR-(CH2)X-NHR is added to the mixture, preferably a polymer solution. The formation of the covalent cross-linking bridges takes place during the formation of the membrane when evaporating the solvent by alkylating the sulfinate groups and optionally by formation of sulfonamide via reaction of the sulfohalide groups present in the polymer with the secondary amino groups of the diamine cross-linking agent. During the acidic and/or basic and/or neutral aqueous after-treatment of the membranes following the formation of the membrane the precursors of the ion exchange groupings are hydrolyzed and oxidized to form ion exchange groups, respectively.
Figure 1 schematically shows the formation of the covalent cross-linking
bridges in blends of sulfochlorinated polymer and sulfinated polymer, Figure
2, shows the formation of the covalent cross-linking bridges in a polymer
containing both sulfinate groups and sulfochloride groups.
The composites according to the invention consist of polymers having the
following functional groups:
After membrane preparation, before hydrolysis:
* -S02M and/or -POM2 and/or -COM (M = Hal (F, CI, Br, I), OR, NR2; R = alkyl, hydroxyalkyl, aryl)
* cross-linking bridges:
a) polymer -S02-Y-S02-polymer optionally:
* -SO2M-, -PO3M2-, -COOM-groups
* above-mentioned cross-linking bridges
The covalently cross-linking of the sulfinate polymers in a mixture with precursors of cation exchange polymers results in a better mixing of blend phases and thus a higher degree of cross-linking, so as to achieve a better mechanical stability of the resultant polymer film compared to covalently
cross-linked polymer (blend) films made from cation exchange polymers and polymeric sulfinates. A further improvement of the mechanical characteristics is achieved by a controlled incorporation of a cross-linking component containing amino groups, which reacts with the precursors of the cation exchange groups, into the polymer network.
The invention will be illustrated in more detail by two examples as follows. The weights/volumes of the components used are listed in table 1. 1. Instruction for membrane preparation
Sulfochlorinated PSU Udel® (IEC=1.8 meq S02CL/g) and PSUS02Li (IEC=1.95 meq SO2Li/g) (for polymer structures see figure 2) are dissolved in N-methylpyrrolidinone (NMP). Then α,ω-diiodobatane is added to the solution of the cross-linking agents. After stirring for 15 minutes the solution is filtered and degassed. A thin film of the polymer solution is knife-coated onto a glass plate. The glass plate is placed into a vacuum drying oven and the solvent is removed at temperatures of from 80 to 130°C at a low pressure of from 700 up to finally 15 mbar. The film is taken out of the drying oven and cooled. The polymer film is peeled off the glass plate underwater and is hydro lyzed/after-treated at first in 10% hydrochloric acid and then in completely desalted water at temperatures of from 60 to 90°C for 24 h respectively.
2. Used amounts of reactants and characterisation results
Table 1 : Used amounts of reactants and characterisation results
* 2 SO2CI groups per PSU repititive unit
By covalently cross-linking the sulfinate polymers mixed with precursors of ion exchange polymers, especially cation exchange polymers, in the presence of funcationalized phyllosilicates and/or tectosilicates a better mixing of the blend phases and thus also a higher degree of cross-linking is achieved, giving raise to a better mechanical stability of the resultant polymer film compared to covalently cross-linked polymer (blend) films made of cation exchange polymers and polymeric sulfinates. By a controlled inclusion of a cross-linking component having amino groups, which reacts with the precursors of the cation exchange groups, into the polymer network a further improvement of the mechanical characteristics is achieved.
By incorporating functionalized tectosilicates and/or phyllosilicates into the covalent network during the formation of the membrane, the water retention capability of formation of the membrane, the water retention capability of the membrane is increased. The functional groups protruding from the surface of the functionalized tectosilicates or phyllosilicate, additionally change the membrane characteristics in accordance with their functionality.
Description of the inorganic filler
The inorganic active filler is a phyllosilicate based on montmorillonite, smectite, illite, sepiolite, palygorskite, muscovite, allevardite, amesite, hectorite, talc, fluorhestorite, saponite, beidelite, nontronite, stevensite, bentonite, mica, vermiculite, fluorvermiculite, halloysite, fluor containing synthetical talc types or blends of two or more of the above-mentioned phyllosilicates. The phyllosilicate can be delaminated or pillard. Particularly preferred is montmorillonite.
The weight ratio of the phyllosilicate is preferably from 1 to 80%, more preferably from 2 to 30% by weight, more preferably from 5 to 20%.
If the functionalized filler, especially zeolites and members of the beidelite series and bentonites, is the only ion-conducting component, its weight ratio is susually in a range of from 5 to 80 wt%, preferably of from 20 to 70 wt% and especially in a range of from 30 to 60 wt%.
Description of the functionalized phyllosilicate :
The term "aphyllosilicate" in general means a silicate, in which the Si04 tetraeders are connected in two-dimensional infinite networks. (The empirical formula for the anion is (Si2O52~) n )■ The single layers are linked to one another by the cations positioned between them, which are usually Na, K, Mg, Al or/and Ca in the naturally occurring phyllosilicates.
By the term "a delaminated functionalized phyllosilicate" we understand phyllosilicates in which the layer distances are at first increased by reaction with so-called functionalisation agents. The layer thickness of such silicates before delamination is preferably 5 to 100 angstrom, more preferably 5 to 50 and most preferably 8 to 20 angstrom. To increase the layer distances (hydrophobisation) the phyllosilicates are reacted (before production of the
composites according to the invention) with so-called functionalizing hydrophobisation agents which are often also called oniom ions or onium salts.
The cations of the phyllosilicates are replaced by organic functionalizing hydrophobisation agents whereby the desired layer distances which depend on the kind of the respective functionalizing molecule or polymer which is to be incorporated into the phyllosilicate can be adjusted by the kind of the organic residue.
The exchange of the metal ions or protons can be complete or partial. Preferred is the complete exchange of metal ions or protons. The quantity of exchangeable metal ions or protons is usually expressed as milli equivalent (meq) per 1 g of phyllosilicate or tectosilicate and is referred to as ion exchange capacity.
Preferred are phyllosilicates or tectosilicates having a cation exchange capacity of at least 0, 5, preferably 0, 8 to 1, 3 meq/g.
Suitable organic functionalizing hydrophobisation agents are derived from oxonium, ammonium, phosphonium and sulfonium ions, which may carry one or more organic residues.
As suitable functionalizing hydrophobisation agents those of general formula I and/or II are mentioned:
where the substituents have the following meaning :
R1, R2, R3, R4 are independently from each other hydrogen, a straight chain,
branched, saturated or unsaturated hydrocarbon radical with 1 to 40,
preferably 1 to 20 C atoms, optionally carrying at least one functional group or
2 of the radicals are linked with each other, preferably to a heterocyclic
residue having 5 to 10 C atoms, more preferably having one or more N
X represents phosphorous, nitrogen or carbon, Y represents oxygen or sulfur, n is an integer from 1 to 5, preferably 1 to 3 and Z is an anion.
Suitable functional groups are hydroxyl, nitro or sulfo groups, whereas carboxyl or sulfonic acid groups are especially preferred. In the same way sulfochloride and carboxylic acid chloride groups are especially preferred.
Suitable anions Z are derived from proton delivering acids, in particular mineral acids, wherein halogens such as chlorine, bromine, fluorine, iodine, sulfate, sulfonate, phosphate, phosphonate, phosphite and carboxylate, especially acetate are preferred. The phyllosilicates used as starting materials are generally reacted as a suspension. The preferred suspending agent is water, optionally mixed with alcohols, especially lower alcohols having 1 to 3 carbon atoms. If the functionalizing hydrophobisation agent is not water-soluble, then a solvent is preferred in which said agent is soluble. In such cases, this is especially an aprotic solvent. Further examples for suspending agents are ketones and hydrocarbons. Usually a suspending agent miscible with water is preferred. On addition of the hydrophobizing agent to the phyllosilicate, ion exchange occurs whereby the phyllosilicate usually precipitates from the solution. The metal salt resulting as a by-product of the ion exchange is preferably water-soluble, so that the hydrophobized phyllosilicate can be separated as a crystalline solid, for example, by filtration.
The ion exchange is mostly independent from the reaction temperature. The temperature is preferably above the crystallization point of the medium and below the boiling point thereof. For aqueous systems the temperature is between 0 and 1009C, preferably between 40 and 80eC.
For a cation and anion exchange polymer alkylammonium ions are preferred, in particular if as a functional group additionally a carboxylic acid chloride or sulfonic acid chloride is present in the same molecule. The alkylammonium ions can be obtained via usual methylation reagents such as methyl iodide. Suitable amonium ions are omega-aminocarboxylic acids, especially preferred are omega-aminoarylsulfonic acids and omega-alkylaminosulfonic acids. Omega-aminoarylsulfonic acids and omega-alkylaminosulfonic acids can be obtained with usual mineral acids, for example hydrochloric acid, sulfuric acid or phosphoric acid or by methylation reagents such as methyl iodide.
Additional preferred ammonium ions are pyridine and laurylammonium ions. After hydrophobizing the layer distance of the phyllosilicates is in general between 10 and 50 angstrom, preferably 13 and 40 angstrom.
The hydrophobized and functionalized phyllosilicate is freed of water by drying. In general a thus treated phyllosilicate still contains a residual water content of 0-5 weight % of water. Subsequently the hydrophobized phyllosilicate can be mixed in form of a suspension in a suspending agent which is free as much as possible from water with the mentioned polymers and be further processed to obtain a membrane.
An especially preferred functionalization of the tectosilicates and/or phyllosilicates is, in general, achieved with modified dyes or their precursors,
especially with triphenylmethane dyes. They are represented by the general formula:
R1 = alkyl (especially CH3; C2H5)
In the present invention dyes derived from the following basic skeleton are
R contains C-i - C2o, and 0-4 N-atoms, and 0-3 S-atoms, R can be charged positively.
In order to functionalize the phyllosilicate the dye or its reduced precursor is sufficiently stirred in an aprotic solvent (e.g. tetrahydrofuran, DMAc, NMP) together with the silicate in a vessel. After 24 hours the dye and the precursor, respectively, is intercalated into the cavities of the phyllosilicate.
The intercalation must be such that the ion conductive group is located on the
surface of the silicate particle.
The following figure schematically shows the process:
Thus the functionalized phyllosilicate is added as an additive to the polymer solution as described in the priority application DE 100 24 575.7. It was found to be especially preferable to use the precursor of the dyes. Only in the acidic after-treatment the dyes themselves are formed by splitting off water.
In the case of the triphenylmethane dyes it was hereby surprisingly found that these dyes support the proton conductivity in the membranes prepared thereby. Whether this is even a water-free proton conductivity cannot be stated with sufficient certainty. If the dyes are not bound to the silicate, thus if they are present in the membrane in a free form, they are discharged from the fuel cell with the reaction water already after a short period of time.
According to the invention the polymer blends containing sulfinate groups of the above-mentioned parent application, most preferably the thermoplastic functionalized polymers (ionomers) are added to the suspension of the hydrophobized phyllosilicates. This can be done by using an already dissolved form or the polymers are solubilized in the suspension it self. Preferably the amount of the phyllosilicates is of from 1 to 70 weight %, more preferably of from 2 to 40 weight % and most preferably of from 5 to 15 weight %.
A further improvement with respect to the present patent application can be the additional blending of zirconyl chloride (ZrOCk) into the membrane polymer solution and into the cavities of the phyllosilicates and/or tectosilicates. If the after-treatment of the membrane is performed in phosphoric acid, hardly soluble zirconium phosphate precipitates in the direct proximity of the silicate grain in the membrane. Zirconium phosphate shows self-proton conductivity when operating the fuel cell. The proton conductivity acts through the formation of hydrogen phosphates as intermediate steps and is part of the state of the art. A controlled inclusion in the direct proximity of a water storing agent (silicates) is novel.
1. Embodiment for membrane preparation
Sulfochlorinated PSU Udel® (IEC=1.8 meq S02CI/g) and PSU S02 Li (IEC=1.95 meq S02Li/g) (for polymer structures see figure 2) and montmorillonite functionalized with triphenylmethane dye are dissolved in N-methylpyrrolidinone (NMP). The a, co-diiodobutane as a cross-linking agent is added to the solution. After stirring for 15 minutes the solution is filtered and degassed. A thin film of the polymer solution is knife-coated onto a glass plate. The glass plate is placed into a vacuum drying oven and the solvent is removed at temperatures of from 80 to 130ºC at a low pressure of from 700 up to finally 15 mbar. The film is taken out of the drying oven and cooled. The polymer film is peeled off the glass plate underwater and is hydrolyzed/after-
treated at first in 10% hydrochloric acid and then in completely desaltec water at temperatures of from 60 to 90-C for 24 h, respectively.
Sulfochlorinated PSU Udel® (IEC=1.2 meq SO2CI/g) and PSU S02 Li (IEC=1.95 meq SO2Li/g) and montmorillonite treated with a, w -aminoalkylsulfochloride (with sulfochloride groups facing to the outside) are dissolved in N-methylpyrrolidinone (NMP). Then the cross-linking agent -diiodobutane is added to the solution. After stirring for 15 minutes the solution is filtered and degassed and processed to a membrane as described in example 1.
This membrane has a higher IEC value after curing than a control without the functionalized phyllosilicate.
Sulfochlorinated PSU Udef (IEC=1.8 meq SO2CI/g) and PSU S02 Li (IEC=1.95 meq SO2Li/g)) (for polymer structures see figure 2) and montmorillonite treated with zirconyl chloride are dissolved in dimethylsulfoxide (DMSO).
The dissolution takes place in the following order: First montmorillonite K10 is suspended in DMSO and 10 weight % zircynyl chloride, based on the total membrane amount, is added. Then the other polymer components are added. Then the cross-linking agent - diiodobutane is added to the solution. After stirring for 15 minutes the solution is filtered and degassed. A thin film of the polymer solution is knife-coated onto a glass plate. The glass plate is placed into a vacuum drying oven and the solvent is removed at temperatures of
from 80 to 130ºC at a low pressure of from 700 up to finally 15 mbar. The film is taken out of the drying oven and cooled. The polymer film is peeled off the glass plate under phosphoric acid and stored in phosphoric acid at a temperature of between 30 and 90ºC for about 10 hours and then optionally further hydrolyzed/after-treated in 10% hydrochloric acid and then in completely desalted water at temperatures of from 60 to 90ºC for 24 h respectively.
1. A covalently cross linked composite polymer membrane comprising one or more polymers of the kind herein described and silicates selected from the group of tectosilicates and phyllosilicates, wherein the silicates can be functionalized and form 1 to 80 % of the composite polymer, wherein the polymers are characterized by the functional groups:
(a) precursors of cation exchange groups selected from the following groups: SO2M, POM2, COM; and
(b) sulfinate groups SO2Me,
wherein M is independently Hal, OR, NR or mixture thereof;
Hal is selected from the group F, CI, Br and I;
R is selected from the group alkyl, hydroxyalkyl and aryl;
Me is selected from the group H, Li, Na, K, Cs, a metal cation and ammonium ion;
and wherein the polymers are covalently cross linked by crosslinking agents selected from the group consisting of:
(a) difunctional, trifunctional, oligofunctional haloalkanes;
(b) difunctional, trifunctional, oligofunctional haloaromatics;
(c) compounds containing the group Hal-(CH2)2-NHR;
(d) compounds containing the group NHR-(CH2)2-NHR; and a combination thereof.
2. A covalently cross linked composite polymer membrane as claimed in claim 1, wherein the said
(a) one polymer comprising at least SO2M groups; and
(b) one polymer comprising at least SO2Me groups.
3. A covalently cross linked composite polymer membrane as claimed in claim 1, wherein said polymer comprises SO2M groups and SO2Me groups.
4. A covalently cross linked composite polymer membrane as claimed in claim 1, wherein one or more polymers having the functional groups are selected from the group consisting of polyether sulfones, polysulfones, polyphenylsulfones, polyether ether-sulfones, polyether ketones,
polyether ether-ketones, polyphenylene ether, polydiphenylphenylene ether, polyphenylene sulfide or copolymers containing at least one of these components.
5. A covalently cross linked composite polymer membrane as claimed in claim 1, wherein preferred polymers are: polysulfones, polyphenylene ether or other polymers which can be lithiated.
6. A covalently cross linked composite polymer membrane as claimed in claim 1, wherein the cross-linking agents are having following formula:
Hal-(CH2)X-Hal or Hal-CH2-phenylene-CH2-Hal (x= 3-12; Hal = F, CI, Br, I).
7. A process for preparing covalently cross-linked composite polymer membrane as claimed in
claim 1, comprising dissolving the polymers and the silicates simultaneously or successively in
a dipolar aprotic solvent selected from the group consisting on N,N-dimethylformamide
(DMF), N,N- dimethylacetamide (DMAc), N-methylpyrrolidinone (NMP), dimethylsulfoxide
(DMSO) or sulfonate, adding the cross-linking agent as claimed in claim 1 ,stirring the cross-
linking agent to homogeneously dispers it in the polymer solution, thereafter the filtering the
polymer solution followed by degassing, spreading the polymer solution as a thin film on
a base like glass plate, metal plate, woven fabric, non-woven fabric or others, removing the
solvent by heating to 80°C -130°C and/or by applying low pressure or in a circulating air dryer,
peeling off the polymer film and the curing the polymer film by treating with:
(a) 1-50 weight % aqueous alkali at a temperature ranging from ambient to 95°C;
(b) completely desalted water at a temperature ranging from ambient to 95°C;
(c) 1-50 weight % aqueous mineral acid at a temperature ranging from ambient to 95°C;
(d) completely desalted water at a temperature ranging from ambient to 95°C; wherein one or more of such curing steps may optionally be omitted.
8. A covalently cross linked composite polymer membrane as claimed in claim 1 to 8 as and
when used in membrane separation processes such as gas separation, prevaporation
perstraction, reverse osmosis, electrodialysis, diffusion dialysis, electrochemical cells,
secondary batteries, electrolytic cells, fuel cells and for producing energy on an electrochemical
9. A covalently cross linked composite polymer membrane as hereinbefore described with reference to the foregoing examples and accompanying drawings.
10. A process for preparing a covalently cross linked composite polymer membrane as hereinbefore described with reference to the foregoing examples and accompanying drawings.
|Indian Patent Application Number||IN/PCT/2002/00148/DEL|
|PG Journal Number||33/2010|
|Date of Filing||04-Feb-2002|
|Name of Patentee||UNIVERSITAT STUTTGART INSTITUT FUR CHEMISCHE VERFAHRENSTECHNIK|
|Applicant Address||BOBLINGER STR. 72, 70199 STUTTGART, GERMANY|
|PCT International Classification Number||C08G 75/00|
|PCT International Application Number||PCT/EP2001/05826|
|PCT International Filing date||2001-05-21|