Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2001-10-22
2003-10-14
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C521S033000, C521S037000, C528S125000, C528S220000, C429S010000, C429S006000, C429S047000
Reexamination Certificate
active
06632847
ABSTRACT:
Polymer composition, membrane comprising the same, process for production thereof and use thereof.
The present invention relates to a polymer composition which is suitable in particular for producing membranes, and also to the use of these membranes in fuel cells, in high-performance capacitors, in dialysis equipment and in ultrafiltration.
Fuel cells are electrochemical energy converters which feature in particular a high level of efficiency. Among the various types of fuel cells, polymer electrolyte fuel cells (PEM hereinafter) feature high power density and a low weight to power ratio.
Conventional fuel cells generally operate using membranes based on fluorine-containing polymers, for example using the material Nafion®.
For the commercialization of fuel cell technology, in particular for relatively large-scale applications, it is necessary to reduce the production costs of the materials used without thereby having to accept sacrifice of performance compared with the materials conventionally used.
Proton-conducting membranes based on sulfonated polyether ketones are known, for example from a report article by A. Steck in Proc. 1
st
Inter. Symp. on New Materials for Fuel Cell Systems, Montreal 1995, pp. 74 or from an article by C. A. Linkous et al. in Int. J. Hydrogen Energy, Vol. 23, No. 7, pp. 525-9 (1998). WO-A-96/29359 and WO-A-96/29360 describe polymer electrolytes made from sulfonated aromatic polyether ketones, and the production of membranes from these materials.
EP-A-0152161 describes polyether ketones (PEK hereinafter) composed predominantly of the repeat unit —O—Ar—CO—Ar—Ar—, and molded structures produced therefrom.
Sulfonated, strictly alternating polyether ketones with the repeat unit —O—Ar—CO—Ar— are described in J. Polym. Sci.: Vol. 23, 2205-2222, 1985. The structure of the polyether ketones here is a result of electrophilic attack, and not nucleophilic attack as described in EP-A-0152161. The polymers were sulfonated by sulfur trioxide using triethyl phosphate in dichloroethane. Another sulfonation method used in this literature reference is chlorosulfonation using chlorosulfonic acid. However, in this method, depending on the degree of sulfonation, molecular-weight degradation is also observed. The amidation of the acid chloride follows on. A possible application sector given for polymers of this type is use as ion exchanger or as salt remover. Use in fuel cells is not described. Property profiles which suggest use in fuel cells are also absent.
EP-A-0688824 mentions membranes also for use in electrochemical cells and made from homogeneous polymer alloys based on sulfonated aromatic polyether ketones and polyether sulfones and a third, hydrophilic polymer.
WO-A-98/07164 has disclosed mixtures made from high-molecular-weight acids (sulfonated polyether ketones, for example) and high-molecular-weight bases (polybenzimidazoles, for example). However, there is no indication here of the combinations of properties. required to permit operation in fuel cells. The invention described in this document is also directed toward a water-free conductivity mechanism brought about by acid/base interaction, and therefore permitting use of these materials at temperatures above 100° C. and at atmospheric pressure.
The application of polybenzimidazoles in the fuel cell has previously been described by Savinell et al. in J. Electrochemical Soc., 141, 1994, pp. L46-L48. Mixtures of different polymers with polybenzimidazoles are also known, e.g. from U.S. Pat. No. 5,290,884.
The suitability of nonfluorinated aromatic polymers, a class which includes aromatic polyether ketones, for use in fuel cells is questioned in the literature (A. Steck, Proc. 1
st
Inter. Symp. on New Materials for Fuel Cell Systems, Montreal 1995, pp 74).
Modifying the properties of polymeric materials by admixing other components is a well known process. However, the property profile of polymer mixtures is difficult to predict. It is doubtful that there is any theory which reflects the complex nature of polymer-polymer interactions (Macromolecules, Vol. 16, 1983, pp. 753-7).
The invention provides compositions from which high-performance membranes can be produced using cost-effective materials. The novel compositions moreover provide a material whose performance exceeds that of the standard fluorinated materials conventionally used. The novel compositions also provide a material from which membranes with good mechanical properties, and also excellent proton conductivity, can be produced.
This combination of properties was not to be expected and does not arise with other polymer mixtures. For example, with compositions made from sulfonated polyether ketone and polyether sulfone it is found that addition of even small amounts of polyether sulfone leads to a marked fall-off of proton conductivity of the membranes made from this material.
The present invention provides compositions comprising from 30 to 99.5% by weight of a sulfonated aromatic polyether ketone which has an ion-exchange capacity of from 1.3 to 4.0 meq (—SO
3
H)/g of polymer and from 0.5 to 70% by weight of a polybenzimidazole.
The ion-exchange capacity (hereinafter also “IEC”) is determined by elemental analysis of the washed and dried polymer via determination of the ratio of carbon to sulfur (C/S quotient).
For the purposes of this invention, aromatic polyether ketones are any polymer which has structural units —Ar—O— and —Ar—CO—, where Ar is an aromatic radical. These structural units may have been linked to one another in a variety of ways, particularly in the para position. Following widely used terminology the first unit is termed “E” (ether) and the second unit “K” (ketone). Depending on the sequence of the ether units and ketone units, a distinction can be made between, for example, PEK, PEEK, PEKK and PEEKK types. All of these types of polymer are included in the term polyether ketones for the purposes of this invention. The sulfonated aromatic polyether ketones used according to the invention may be any desired polymers, for example PEEK, PEKK, PEEKK or in particular PEK, as long as they have the ion-exchange capacity defined above.
Particular preference is given to compositions in which the sulfonated polyether ketone has the repeat unit of formula I
—[Ar
1
—O—Ar
2
—CO]— (I),
where Ar
1
and Ar
2
, independently of one another, are bivalent aromatic radicals, unsubstituted or substituted by one or more monovalent organic groups inert under usage conditions, and where at least a portion of the radicals Ar
1
and Ar
2
have substitution by radicals of the formula —(SO
3
)
w
M, where M is a metal cation of valency w, an ammonium cation or in particular hydrogen, and w is an integer, in particular 1 or 2. M is preferably a cation of an alkali metal or of an alkaline earth metal.
If any radicals are bivalent aromatic radicals, these are mono- or polynuclear aromatic hydrocarbon radicals or heterocyclic-aromatic radicals which may be mononuclear or polynuclear. In the case of heterocyclic-aromatic radicals, these have in particular one or two oxygen, nitrogen or sulfur atoms in the aromatic radical.
Polynuclear aromatic radicals may have been fused with one another or bonded via C—C bonds or via bridging groups, such as —O—, —S—, —CO—, —SO
2
— or —C
n
H
2n
—, where n is an integer from 1 to 10.
In the case of the bivalent aromatic radicals, the location of the valence bonds may be in the para position or in a comparable coaxial or parallel position or in the meta position or in a comparable angled position relative to one another.
The valence bonds which are in a coaxial or parallel position relative to one another point in opposite directions. An example of coaxial bonds which point in opposite directions is given by the bonds in 4,4′-biphenylene. An example of parallel bonds which point in opposite directions is given by the bonds in 1,5- or 2,6-naphthalene, while the 1,8-naphthalene bonds are parallel and point in the same direction.
Examples of preferred bivalent aromatic radicals Ar
1
and Ar
2
, the locatio
Baurmeister Jochen
Frank Georg
Knauf Rüdiger
Pawlik Jürgen
Soczka-Guth Thomas
Celanese Ventures GmbH
Zitomer Fred
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