Acid functional fluoropolymer membranes and method of manufacture

• US 6,423,784 B1
• Filed: 12/15/1999
• Issued: 07/23/2002
• Est. Priority Date: 12/15/1999
• Status: Expired due to Fees

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Hamrock, Steven J., Jing, Naiyong, Hardy, L. Charles, Mao, Shane S.
• Primary Examiner(s): Wilson, D. R.
• Application Number:
  US09/464,337
• Time in Patent Office: 951 Days
• Field of Search: 525/326.2, 525/326.3, 525/344, 525/366, 525/374
• US Class Current: 525/326.2
• CPC Class Codes: C08F 14/18 Monomers containing fluorine
• CPC Class Codes: C08F 8/26 Removing halogen atoms or halogen-containing groups from the molecule
• CPC Class Codes: C08J 5/225 containing fluorine
• CPC Class Codes: C08L 2205/02 containing two or more polymers of the same C08L -group
• CPC Class Codes: C08L 2666/04 Macromolecular compounds according to groups C08L7/00 - C08L49/00, or C08L55/00 - C08L57/00; Derivatives thereof
• CPC Class Codes: C08L 27/16 Homopolymers or copolymers or vinylidene fluoride
• CPC Class Codes: C08L 27/22 modified by chemical after-treatment
• CPC Class Codes: H01M 8/1023 having only carbon, e.g. polyarylenes, polystyrenes or polybutadiene-styrenes
• CPC Class Codes: H01M 8/1039 halogenated, e.g. sulfonated polyvinylidene fluorides
• CPC Class Codes: H01M 8/1072 by chemical reactions, e.g. insitu polymerisation or insitu crosslinking
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

Methods are provided to make acid functional fluoropolymers by: a) dehydrofluorinating a starting fluoropolymer with a dehydrofluorinating agent to form an unsaturated fluoropolymer; b) adding an acidifiable nucleophilic functionalizing agent to a double bond of the unsaturated fluoropolymer; and c) acidifying the added acidifiable function. Acid functional fluoropolymers and ion conducting membranes thereof are also provided, including acid functional fluoropolymer having pendent groups according to the formula: —X—Ar—A_n, wherein X is selected from O, S or NR, where R is selected from H and C1-C30 alkyl or aryl, which are optionally substituted, wherein Ar is a C6-C30 aromatic group, which is optionally substituted, wherein A is an acidic function or salt thereof, wherein a can be independently chosen to be 1, 2 or 3.

Claims

1. A method of making an acid functional fluoropolymer comprising the steps of:

a) dehydrofluorinating a starting fluoropolymer with a dehydrofluorinating agent to form an unsaturated fluoropolymer;

b) adding an acidifiable nucleophilic functionalizing agent to a double bond of the unsaturated fluoropolymer to form a fluoropolymer bearing an acidifiable function, wherein said acidifiable nucleophilic functionalizing agent is aryloxide (ArO⁻

); and

c) acidifying said acidifiable function;

wherein said acid functional fluoropolymer is sufficiently acidified as to meet a condition selected from the group consisting of;

a) the equivalent weight of the polymer is 5000 or less; and

b) the proton conductivity of the polymer at 25°

C. is 0.01 Siemens per centimeter (S/cm) or higher.

2. The method of claim 1 wherein the starting fluoropolymer is a polymer or copolymer of vinylidene fluoride (1,1-difluoroethene).

3. The method of claim 1 wherein the starting fluoropolymer and the acid functional fluoropolymer are membranes.

4. The method of claim 1 wherein said acidifiable nucleophilic functionalizing agent is phenoxide (PhO⁻

).

5. The method of claim 1 wherein said acid functional fluoropolymer has an equivalent weight of 3000 g/mol or less.

6. The method of claim 1 wherein said acid functional fluoropolymer has an equivalent weight of 1600 g/mol or less.

7. The method of claim 1 additionally comprising the step of:

d) cation exchange.

8. The method of claim 7, wherein said cation exchange yields a acid functional fluoropolymer which is a Li⁺ salt.

9. A method of making an acid functional fluoropolymer comprising the steps of:

a) adding an acidifiable function to a fluoropolymer to form;

fluoropolymer bearing an acidifiable function; and

b) acidifying said acidifiable function;

wherein said acid functional fluoropolymer is sufficiently acidified as to meet a condition selected from the group consisting of;

a) the equivalent weight of the polymer is 5000 or less; and

b) the proton conductivity of the polymer at 25°

C. is 0.01 Siemens per centimeter (S/cm) or higher;

wherein said acidifiable function is a group according to the formula;

—

X—

Ar, wherein X is O, S or NR, where R is H or C1-C30 alkyl or aryl, which are optionally substituted, wherein Ar is a C6-C30 aromatic group, which is optionally substituted.

10. The method of claim 9, wherein X is O.

11. The method of claim 10, wherein Ar is phenyl.