Proton exchange material and method therefor

Abstract

A proton exchange material includes a linear perfluorinated carbon backbone chain and a side chain extending off of the linear perfluorinated carbon backbone chain. The side chain includes at least one sulfonimide group, SO2-NHSO2-, and a carbon chain link between the at least one sulfonimide group and the linear perfluorinated carbon backbone chain. The carbon chain link has less than three carbon atoms.

Claims

1. A proton exchange material comprising: a linear perfluorinated carbon backbone chain; and a side chain extending off of the linear perfluorinated carbon backbone chain, the side chain being OCF.sub.2CF.sub.2SIRfSICF.sub.3, wherein SI is sulfonamide and Rf is (CF.sub.2).sub.nO(CF.sub.2).sub.n, where n is 1-4.

2. The proton exchange material as recited in claim 1, having an equivalent weight of 800 or less.

3. The proton exchange material as recited in claim 1, wherein the linear perfluorinated carbon backbone chain is (CF.sub.2CF.sub.2).sub.x(CF.sub.2CF), where x is 2-7.

4. The proton exchange material as recited in claim 3, wherein x is 4-5.

5. A method for producing a proton exchange material, the method comprising: forming a polymer having a linear perfluorinated carbon backbone chain and a side chain extending off of the linear perfluorinated carbon backbone chain, the side chain being OCF.sub.2CF.sub.2SIRfSICF.sub.3, wherein SI is sulfonimide and Rf is (CF.sub.2).sub.nO(CF.sub.2).sub.n, where n is 1-4.

6. The method as recited in claim 5, wherein the forming includes: (a) copolymerizing tetrafluoroethylene and a perfluorinated vinyl ether monomer to produce the linear perfluorinated carbon backbone chain and a precursor side chain extending off of the linear perfluorinated carbon backbone chain, the precursor side chain terminating in a sulfonyl fluoride group, SO.sub.2F, (b) exposing a product of said step (a) to ammonia to convert sulfonyl fluoride group to a sulfonamide group, SO.sub.2NH.sub.2, and (c) contacting a product of said step (b) with an end-capping agent to convert the sulfonamide group to the side chain including a sulfonimide group.

7. The method as recited in claim 6, wherein the end-capping agent is FSO.sub.2RfSICF.sub.3, wherein SI is sulfonimide and Rf is (CF.sub.2).sub.nO(CF.sub.2).sub.n, where n is 1-4.

8. The method as recited in claim 5, wherein the forming includes synthesizing a perfluorinated sulfonic acid precursor and converting sulfonyl fluoride groups, SO.sub.2F, in the perfluorinated sulfonic acid precursor to amide groups, SO.sub.2NH.sub.2.

9. The method as recited in claim 8, wherein the forming includes converting the amide groups, SO.sub.2NH.sub.2, to a sulfonimide group.

Description

DETAILED DESCRIPTION

(1) Electrochemical devices, such as fuel cells for automobiles or other similar applications, can operate at relatively high temperatures and low relative humidity conditions to reduce radiator size, simplify system construction and improve overall system efficiency. It is therefore desirable to utilize proton exchange materials that maintain high proton conductivity at the relatively high temperatures and low relative humidity conditions. In this regard, disclosed is a proton exchange material that has a relatively low equivalent weight and good chemical stability in harsh environments that may include free radical chemical intermediaries.

(2) The proton exchange material includes a linear perfluorinated carbon backbone chain and a side chain extending off the linear perfluorinated carbon backbone chain. As can be appreciated, the proton exchange material can include many of the linear perfluorinated carbon backbone chains and each of these chains can include many of the side chains. In this disclosure, the term linear refers to the architecture of the polymer with respect to the perfluorinated carbon backbone chain (i.e., main chain) being free of crosslink connections to any other linear perfluorinated carbon backbone chains.

(3) The side chain that extends off the linear perfluorinated carbon backbone chain includes one or more sulfonimide groups, SO.sub.2NHSO.sub.2, and a carbon chain link between the one or more sulfonimide groups and the linear perfluorinated carbon backbone chain. The carbon chain link has less than three carbon atoms. In a further example, the carbon chain link has two carbon atoms or one carbon atom.

(4) In a further example, the one or more sulfonimide groups includes a foremost sulfonimide group, with respect to the linear perfluorinated carbon backbone chain. In other words, the foremost sulfonimide group is the closest sulfonimide group along the side chain to the linear perfluorinated carbon backbone chain. In one example, the carbon chain link is located between the foremost sulfonimide group and the linear perfluorinated carbon backbone chain. The carbon chain link can be a foremost, or closest, carbon chain link along the side chain with respect to the linear perfluorinated carbon backbone chain.

(5) In a further example, the side chain terminates at a free end with a CF.sub.3 group. Additionally, the one or more sulfonimide groups can include at least two sulfonimide groups and in other examples may include more than two sulfonimide groups. In a further example, the equivalent weight of the proton exchange material is 800 or less.

(6) In a further example, the proton exchange material has a repeat unit, Structure I shown below. In this example, the side chain OCF.sub.2CF.sub.2SIRfSICF.sub.3 has an ether linkage connecting the side chain to the linear perfluorinated carbon backbone chain. SI is sulfonimide and Rf is (CF.sub.2), where n is 1-6, or Rf is (CF.sub.2).sub.nO(CF.sub.2).sub.n, where n is 1-4. The linear perfluorinated carbon backbone chain is (CF.sub.2CF.sub.2).sub.x(CF.sub.2CF), where x is 2-7. In a further example, x is 4-5.

(7) ##STR00001##

(8) The disclosed proton exchange material thus has a relatively short side chain which permits a low EW without water-solubility. Each of the side chains can also include multiple sulfonimide groups to further lower EW, while not sacrificing water-stability. Further, the side chains of the disclosed proton exchange material are free terminal carbon-sulfur bonded groups, such as the group CF.sub.2SO.sub.3H, which may be susceptible to chemical attack from hydroxyl (OH) and hydroperoxyl (OOH) radicals. The proton exchange material thus also has good chemical stability.

(9) A method for producing a proton exchange material includes forming a polymer having any or all of the above chemical structural features. In one example, the forming includes synthesizing a perfluorinated sulfonic acid precursor and converting sulfonic acid groups, SO.sub.2F, in the perfluorinated sulfonic acid precursor to amide groups, SO.sub.2NH.sub.2. The amide groups are then converted to the one or more sulfonimide groups.

(10) In one example, the forming includes free radical copolymerizing tetrafluoroethylene and a perfluorinated vinyl ether monomer to produce the linear perfluorinated carbon backbone chain and a precursor side chain extending off of the linear perfluorinated carbon backbone chain. The precursor side chain terminates in a sulfonyl fluoride group, SO.sub.2F. This product is then exposed to ammonia to convert the sulfonyl fluoride group to a sulfonamide group, SO.sub.2NH.sub.2. This product is then contacted with an end-capping agent to convert the sulfonamide group to the side chain including the one or more sulfonimide group. In a further example, the end-capping agent is FSO.sub.2RfSICF.sub.3, where SI is sulfonimide and Rf is either (CF.sub.2).sub.n, where n is 1-6, or (CF.sub.2).sub.nO(CF.sub.2).sub.n, where n is 1-4. Further useful techniques can be found in PCT Application No. PCT/US2012/017358, entitled METHOD OF FABRICATING AN ELECTROLYTE MATERIAL, incorporated herein by reference in its entirety.

(11) Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.

(12) The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.