Ion-exchange polymers

Details Ion-exchange polymers Ion-exchange polymers

2001-03-12

2004-12-07

Teskin, Fred (Department: 1713)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Ion-exchange polymer or process of preparing

C521S030000, C429S006000, C429S209000, C429S314000, C429S317000, C525S328500, C525S328600, C525S344000, C525S471000, C525S534000, C525S535000, C528S125000, C528S128000, C528S171000, C528S174000, C528S212000

Reexamination Certificate

active

06828353

ABSTRACT:

This invention relates to ion-exchange polymers and particularly, although not exclusively, relates to sulphonaced polymers, for example sulphonated polyaryletherketones, polyarylethersulphones and/or copolymers of the aforesaid. Preferred embodiments of the invention relate to ion-conductive membranes, for example of polymer electrolyte membrane fuel cells, made using such polymers. The invention also relates to novel, non-sulphonated polyaryletherketones and/or polyarylethersulphones used for preparing said sulphonated polymers and processes for the preparation of polymers described herein.
BACKGROUND OF THE INVENTION
A polymer electrolyte membrane fuel cell (PEMFC), shown schematically in
FIG. 1
of the accompanying diagrammatic drawings, may comprise a thin sheet 2 of a hydrogen-ion conducting Polymer Electrolyte Membrane (PEM) sandwiched on both sides by a layer 4 of platinum catalyst and an electrode 6. The layers 2, 4, 6 make up a Membrane Electrode Assembly (MEA) of less than 1 mm thickness.
In a PEMFC, hydrogen is introduced at the anode (fuel electrode) which results in the following electrochemical reaction:
Pt-Anode (Fuel Electrode) 2H
2
→4H
+
+4e
The hydrogen ions migrate through the conducting PEM to the cathode. Simultaneously, an oxidant is introduced at the cathode (oxidant electrode) where the following electrochemical reaction takes place:
 Pt-Cathode (Oxidant Electrode) O
2
+4H
+
+4e→2H
2
O
Thus, electrons and protons are consumed to produce water and heat. Connecting the two electrodes through an external circuit causes an electrical current to flow in the circuit and withdraw electrical power from the cell.
U.S. Pat. No. 5,561,202 (Hoechst) discloses the production of PEMs from sulphonated aromatic polyether ketones. At least 5% of the sulphonic groups in the sulphonic acid moieties are converted into sulphonyl chloride groups and then reacted with an amine containing at least one cross-linkable substituent or a further functional group. An aromatic sulphonamide is, then isolated, dissolved in an organic solvent, converted into a film and then the cross-linkable substituents in the film are cross-linked. The invention is said to provide ion-conductive membranes suitable for use as polymeric solid electrolytes which have adequate chemical stability and can be produced from polymers which are soluble in suitable solvents.
One problem associated with known PEMFCs is that of providing PEMs which have desirable properties at elevated temperatures and which are cheap to manufacture.
SUMMARY OF THE INVENTION
It is an object of the present invention to address problems associated with PEMs.
According to a first aspect of the invention, there is provided a polymer electrolyte membrane which includes a polymer having a moiety of formula
and/or a moiety of formula
and/or a moiety of formula
wherein at least some of the units I, II and/or III are sulphonated; wherein the phenyl moieties in units I, II, and III are independently optionally substituted and optionally cross-linked; and wherein m,r,s,t,v,w and z independently represent zero or a positive integer, E and E′ independently represent an oxygen or a sulphur atom or a direct link, G represents an oxygen or sulphur atom, a direct link or a —O—Ph—O— moiety where Ph represents a phenyl group and Ar is selected from one of the following moieties (i) to (x) which is bonded via one or more of its phenyl moieties to adjacent moieties
The invention extends to a polymer electrolyte membrane which includes a polymer having a moiety of formula I and/or a moiety of formula II and/or a moiety of formula III as described according to said first aspect, wherein at least some of units I, II and/or III are functionalised to provide ion exchange sites. Suitably, to provide said ion exchange sites, said polymer is sulphonated, phosphorylated, carboxylated, quaternary-aminoalkylated or chloromethylated, and optionally further modified to yield —CH
2
PO
3
H
2
, —CH
2
NR
3
20+
where R
20
is an alkyl, or —CH
2
NAr
3
x+
where Ar
x
is an aromatic (arene), to provide a cation or: anion exchange membrane. Further still, the aromatic moiety may contain a hydroxyl group which can be readily elaborated by existing methods to generate —OSO
3
H and —OPO
3
H
2
cationic exchange sites on the polymer. Ion exchange sites of the type stated may be provided as described in WO95/08581.
References to sulphonation include a reference to substitution with a group —SO
3
M wherein M stands for one or more elements selected with due consideration to ionic valencies from the following group: H, NR
4
y+
, in which R
y
stands for H, C
1
-C4 alkyl, or an alkali or alkaline earth metal or a metal of sub-group 8, preferably H, NR
4
y+
, Na, K, Ca, Mg, Fe, and Pt. Preferably M represents H. Sulphonation of the type stated may be provided as described in WO96/29360.
Unless otherwise stated in this specification, a phenyl moiety may have 1,4- or 1,3-, especially 1,4-, linkages to moieties to which it is bonded.
Said polymer may include more than one different type of repeat unit of formula I; more than one different type of repeat unit of formula II; and more than one different type of repeat unit of formula III.
Said moieties I, II and III are suitably repeat units. In the polymer, units I, II and/or III are suitably bonded to one another—that is, with no other atoms or groups being bonded between units I, II, and III.
Where the phenyl moieties in units I, II or III are optionally substituted, they may be optionally substituted by one or more halogen, especially fluorine and chlorine, atoms or alkyl, cycloalkyl or phenyl groups. Preferred alkyl groups are C
1-10
, especially C
1-4
, alkyl groups. Preferred cycloalkyl groups include cyclohexyl and multicyclic groups, for example adamantyl. In some cases, the optional substituents may be used in the cross-linking of the polymer. For example, hydrocarbon optional substituents may be functionalised, for example sulphonated, to allow a cross-linking reaction to take place. Preferably, said phenyl moieties are unsubstituted.
Another group of optional substituents of the phenyl moieties in units I, II or III include alkyls, halogens, C
y
F
2y+1
, where y is an integer greater than zero, O—R
q
(where R
q
is selected from the group consisting of alkyls, perfluoralkyls and aryls), CF═CF
2
, CN, NO
2
and OH. Trifluormethylated phenyl moieties may be preferred in some circumstances.
Where said polymer is cross-linked, it is suitably cross-linked so as to improve its properties as a polymer electrolyte membrane, for example to reduce its swellability in water. Any suitable means may be used to effect cross-linking. For example, where E represents a sulphur atom, cross-linking between polymer chains may be effected via sulphur atoms on respective chains. Alternatively said polymer may be cross-linked via sulphonamide bridges as described in U.S. Pat. No. 5,561,202. A further alternative is to effect cross-linking as described in EP-A-0008895.
However, for polymers according to the first aspect or second aspect which are crystalline (which some are) there may be no need to effect cross-linking to produce a material which can be used as a polymer electrolyte membrane. Such polymers may be easier to prepare: than cross-linked polymers. Thus, said polymer of the first and/or second aspects may be crystalline. Preferably, said polymer is not optionally cross-linked as described.
Where w and/or z is/are greater than zero, the respective phenylene moieties may independently have; 1,4- or 1,3-linkages to the other moieties in the repeat units of formulae II and/or III. Preferably, said phenylene moieties have 1,4- linkages.
Preferably, the polymeric chain of the polymer does not include a —S— moiety. Preferably, G represents a direct link.
Suitably, “a” represents the mole % of units of formula I in said polymer, suitably wherein each unit I is the same; “b” represents the mole % of units of formula II in said polymer, suitably wherein each un

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