Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/20—Manufacture of shaped structures of ion-exchange resins
  • C08J5/22—Films, membranes or diaphragms
  • C08J5/2206—Films, membranes or diaphragms based on organic and/or inorganic macromolecular compounds
  • C08J5/2218—Synthetic macromolecular compounds
  • C08J5/2231—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds
  • C08J5/2243—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds obtained by introduction of active groups capable of ion-exchange into compounds of the type C08J5/2231
  • C08J5/225—Synthetic macromolecular compounds based on macromolecular compounds obtained by reactions involving unsaturated carbon-to-carbon bonds obtained by introduction of active groups capable of ion-exchange into compounds of the type C08J5/2231 containing fluorine
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/24—Crosslinking, e.g. vulcanising, of macromolecules
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/20—Manufacture of shaped structures of ion-exchange resins
  • C08J5/22—Films, membranes or diaphragms
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2327/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers
  • C08J2327/02—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment
  • C08J2327/12—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms

Definitions

• This invention relates to a method of obtaining crosslinked polymers, particularly fluorinated polymers having pendent sulfonic acid groups, by crosslinking through pendent groups which include a sulfonyl chloride group (-SO2CI).
• pendent groups which include a sulfonyl chloride group (-SO2CI).
• TFE tetrafluoroethylene
• a polymer electrolyte membrane having a thickness of 90 microns or less and comprising a polymer, said polymer comprising a highly fluorinated backbone and recurring pendant groups according to the formula: YOSO2-CF2-CF2-CF2-CF2-O-[polymer backbone] where Y is H + or a monovalent cation such as an alkali metal cation.
• the membrane is a cast membrane.
• the polymer has a hydration product of greater than 22,000.
• the polymer has an equivalent weight of 800-1200.
• the present invention provides methods of making crosslinked polymers comprising the steps of: a) providing a polymer comprising first pendent groups which include a group according to the formula -SO2CI; and b) crosslinking said polymer.
• the crosslinking step typically comprises exposure to electromagnetic radiation, typically in the ultraviolet band, or exposure to a radical initiator.
• the first pendent group is typically according to the formula: -R.I-SO2CI, wherein Rl may be straight- chain, branched, cyclic, heteroatomic, polymeric, halogenated, fluorinated or substituted.
• Rl is typically an aliphatic linking group containing 1-20 carbon or oxygen atoms, more typically R.1 is -O-R ⁇ - 5 where R 2 is a branched or unbranched perfluoroalkyl or perfluoroether group comprising 1-15 carbon atoms and 0-4 oxygen atoms, typically -O-CF2-CF(CF3)-O-CF2-CF2- or more typically -O-(CF2)4-.
• the polymer typically comprises second pendent groups which include a group according to the formula -SO2X', wherein each X' is independently selected from the group consisting of F and -OH, which second pendent groups are typically according to the formula: -RI-SO2F, where R! is as described above.
• the polymer is typically fluorinated, more typically highly fluorinated, and most typically perfluorinated.
• the polymer may be formed into a membrane prior to crosslinking, typically having a thickness of 90 microns or less.
• this step of membrane formation may include imbibing said mixture into a porous supporting matrix, typically a porous polytetrafluoroethylene web.
• the polymer may be brought into contact with a crosslinking agent prior to crosslinking, such as a polyaromatic species or a polyvinyl species.
• the crosslinking step is followed by a step of converting any remaining groups according to the formula -SO2 ' to sulfonic acid groups.
• the resulting polymer typically has an equivalent weight of less than 1200.
• the polymer may be made by providing a polymer comprising pendent groups which include a group according to the formula -SO2X and converting at least a portion of the -SO2X groups to -SO2CI.
• the present invention provides crosslinked polymers or membranes made according to the methods of the present invention.
• EW equivalent weight
• HP hydrolysis product
• highly fluorinated means containing fluorine in an amount of 40 wt% or more, typically 50 wt% or more and more typically 60 wt% or more.
• substituted means, for a chemical species, substituted by conventional substituents which do not interfere with the desired product or process, e.g., substituents can be alkyl, alkoxy, aryl, phenyl, halo (F, CI, Br, I), cyano, nitro, etc.
• the present invention provides a method of obtaining crosslinked polymers, particularly fluorinated polymers having pendent sulfonic acid groups, by crosslinking through pendent groups which include a sulfonyl chloride group (-SO2CI).
• pendent groups which include a sulfonyl chloride group (-SO2CI).
• the sulfonyl chloride group may be removed by application of electromagnetic radiation, typically in the ultraviolet band, or a radical initiator, leaving behind a radical which readily binds covalently to other polymer strands or to crosslinking agents to form crosslinks.
• electromagnetic radiation typically in the ultraviolet band
• a radical initiator typically, the polymer is made by providing a polymer comprising pendent groups which include a group according to the formula -SO2F and converting at least a portion of the -SO2F groups to -SO2CI. After crosslinking, the remaining
• -SO2F groups may be converted to sulfonic acid groups, yielding a crosslinked polymer electrolyte.
• Polymer electrolytes are typically fluorinated but may also be non- fluorinated.
• Such crosslinked polymer electrolytes may be used to make polymer electrolyte membranes (PEM's) that may be used in electrolytic cells such as fuel cells.
• PEM's manufactured from the crosslinked polymer according to the present invention may be used in the fabrication of membrane electrode assemblies (MEA's) for use in fuel cells.
• An ME A is the central element of a proton exchange membrane fuel cell, such as a hydrogen fuel cell.
• Fuel cells are electrochemical cells which produce usable electricity by the catalyzed combination of a fuel such as hydrogen and an oxidant such as oxygen.
• Typical MEA's comprise a polymer electrolyte membrane (PEM) (also known as an ion conductive membrane (ICM)), which functions as a solid electrolyte.
• PEM polymer electrolyte membrane
• ICM ion conductive membrane
• Each electrode layer includes electrochemical catalysts, typically including platinum metal.
• GDL's Gas diffusion layers facilitate gas transport to and from the anode and cathode electrode materials and conduct electrical current.
• the GDL may also be called a fluid transport layer (FTL) or a diffuser/current collector (DCC).
• the anode and cathode electrode layers may be applied to GDL's in the form of a catalyst ink, and the resulting coated GDL's sandwiched with a PEM to form a five-layer MEA.
• the anode and cathode electrode layers may be applied to opposite sides of the PEM in the form of a catalyst ink, and the resulting catalyst-coated membrane (CCM) sandwiched with two GDL's to form a five-layer MEA.
• the five layers of a five-layer MEA are, in order: anode GDL, anode electrode layer, PEM, cathode electrode layer, and cathode GDL.
• the polymer to be crosslinked is typically fluorinated, more typically highly fluorinated, and most typically perfluorinated, but may also be non-fluorinated.
• the polymer to be crosslinked comprises a backbone, which may be branched or unbranched but is typically unbranched. The backbone is optionally fluorinated, typically highly fluorinated, and more typically perfluorinated.
• the polymer comprises first pendent groups that include sulfonyl chloride groups, typically according to the formula: -RI-SO2CI, wherein R ⁇ maybe straight-chain, branched, cyclic, heteroatomic, polymeric, halogenated, fluorinated or substituted.
• Rl is typically an aliphatic linking group containing 1-20 carbon or oxygen atoms.
• the polymer may also comprise second pendent groups that include sulfonyl fluoride or sulfonic acid groups, typically according to the formula: -RI-SO2X', where X' is F or OH and Rl is as above.
• Each R! may be selected independently, but more typically, substantially all R! groups are identical.
• the backbone may comprise units derived from tetrafluoroethylene (TFE), i.e., typically -CF2-CF2- units, and units derived from co-monomers, typically including at least one according to the formula where Y is typically F but may also be CF3, and where RlO is a pendant group which includes a group according to the formula -SO2X wherein X is selected from F, CI, Br, I, or -OH. X is most typically F.
• pendant groups may be added to the backbone by grafting. Typically, pendant groups lO are highly fluorinated and more typically perfluorinated. R u may be aromatic or non-aromatic.
• R 0 is -R1 I-SO2X, where R 1 1 is a branched or unbranched perfluoroalkyl or perfluoroether group comprising 1-15 carbon atoms and 0-4 oxygen atoms, R! 1 is typically -O-R12- wherein Rl2 is a branched or unbranched perfluoroalkyl or perfluoroether group comprising 1-15 carbon atoms and 0-4 oxygen atoms.
• RU is more typically -O-R ⁇ - wherein Rl3 is a perfluoroalkyl group comprising 1-15 carbon atoms.
• Rl 1 examples include: -(CF 2 ) n - where n is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 (-CF 2 CF(CF 3 )-) n where n is 1, 2, 3, 4, or 5 (-CF(CF 3 )CF2-) n where n is 1, 2, 3, 4, or 5(-CF 2 CF(CF 3 )-) n -CF2- where n is 1, 2, 3 or 4 (-O-CF2CF2-) n where n is 1, 2, 3, 4, 5, 6 or 7 (-O-CF2CF2CF2-) n where n is 1, 2, 3, 4, or 5 (-O-CF2CF 2 CF CF2-) n where n is 1, 2 or 3 (-O-CF 2 CF(CF 3 )-) n where n is 1, 2, 3, 4, or 5 (-O-CF2CF(CF 2 CF3)-) n where n is 1, 2 or 3 (-O-CF(CF )CF2-) n where n is 1
• the -SO2X group is most typically -SO2F during polymerization, i.e., X is F.
• the -SO2X group is typically converted to -SO3H at some point prior to use of the fluoropolymer as an polymer electrolyte.
• the fluoromonomer providing first side group RlO may be synthesized by any suitable means, including methods disclosed in U.S. Pat. No. 6,624,328.
• the polymer may be made by any suitable method, including emulsion polymerization, extrusion polymerization, polymerization in supercritical carbon dioxide, solution or suspension polymerization, and the like, including methods disclosed in U.S. Pat. App. No. 10/697,768, filed October 30, 2003 [Arty Docket No. 58585US002] and references cited therein.
• most or all of the of the -SO2X groups included on pendent groups are in -SO2F form during polymerization and a portion of the -SO2F groups are then converted to -SO2CI prior to crosslinking.
• -SO2F groups are converted to -SO2CI.
• the degree of conversion may be selected so that the resulting crosslinked polymer will meet the hydration product and equivalent weight parameters described below when uncrosslinked sulfonyl groups are converted to sulfonic acid.
• -SO2F groups may be converted to -SO2CI groups by any suitable method.
• -SO2F groups are reduced to -SO2H by use of a suitable reducing agent, such as a hydrazine or mercaptan such as mercaptoethanol, and subsequently converted to -SO2CI with a hypochloride or chlorine,
• a suitable reducing agent such as a hydrazine or mercaptan such as mercaptoethanol
• -SO2F groups may be converted to -SO2CI groups by hydrolyzing the -SO2F groups to sulfonic acid and subsequently reacting with oxalyl chloride in dry toluene with pyridine catalyst.
• the polymer provided may include -SO3H groups and a portion of the -SO3H groups are then converted to -SO2CI prior to crosslinking.
• -SO3H groups typically, between 1 and 50% of -SO3H groups are converted to -SO2CI.
• the degree of conversion may be selected so that the resulting crosslinked polymer will meet the hydration product and equivalent weight parameters described below when uncrosslinked groups are converted to sulfonic acid.
• -SO3H groups may be converted to -SO2CI groups by any suitable method. In one such method, -SO3H groups may be converted to -SO2CI groups by reaction with oxalyl chloride in dry toluene with pyridine catalyst.
• the -SO2X groups included on pendent groups are in -SO2F form or -SO2H form (sulfinic acid) during polymerization; that is, the monomer mixture contains both sulfonyl fluoride functional monomers and sulfinic acid functional monomers.
• the proportions of monomers are selected so that the resulting crosslinked polymer will meet the hydration product and equivalent weight parameters described below when sulfonyl fluoride groups are converted to sulfonic acid, and so that the desired degree of crosslinking will be achieved when sulfinic acid groups are crosslinked.
• the -SO2H groups Prior to crosslinking, are converted to -SO2CI by any suitable method.
• -SO2H groups are converted to -SO2CI with a hypochloride or chlorine.
• the -SO2X groups included on pendent groups are in -SO2F form or -SO2CI form during polymerization; that is, the monomer mixture contains both sulfonyl fluoride functional monomers and sulfonyl chloride functional monomers.
• the proportions of monomers are selected so that the resulting crosslinked polymer will meet the hydration product and equivalent weight parameters described below when sulfonyl fluoride groups are converted to sulfonic acid, and so that the desired degree of crosslinking will be achieved when sulfonyl chloride groups are crosslinked.
• the polymer is brought into contact with a crosslinking agent prior to crosslinking.
• a crosslinking agent Any suitable crosslinking agent may be used, such that it will react with at least two radicals generated by removal of -SO2CI from a pendent group.
• Crosslinking agents which may be useful in the practice of the present invention may include polyaromatic species or polyvinyl species. Examples of crosslinking agents useful in the practice of the present invention include: diphenyl ethers, diphenoxy alkanes, diphenoxy ethers, diphenoxy polyethers, di-, tri- and tetraallyl species, and the like.
• the crosslinking agent and polymer may be mixed by any suitable method, including mixing in solution or suspension, kneading, milling, or the like.
• the crosslinking agent may be added in any suitable amount relative to the number of first pendent groups. If an excess of crosslinking agent is added, the excess may be removed after crosslinking. Alternately, if the crosslinking agent is added in a less than an equimolar amount, it is expected that only a portion of the crosslinks formed will be through molecules of the crosslinking agent.
• the polymer or polymer/crosslinking agent blend is formed into a membrane prior to crosslinking. Any suitable method of forming the membrane may be used.
• the polymer is typically cast from a suspension or solution.
• the membrane may be formed from neat polymer in a melt process such as extrusion. After forming, the membrane may be annealed. Typically the membrane has a thickness of 90 microns or less, more typically 60 microns or less, and most typically 30 microns or less. A thinner membrane may provide less resistance to the passage of ions. In fuel cell use, this results in cooler operation and greater output of usable energy. Thinner membranes must be made of materials that maintain their structural integrity in use.
• the polymer may be imbibed into a porous supporting matrix prior to crosslinking, typically in the form of a thin membrane having a thickness of 90 microns or less, more typically 60 microns or less, and most typically 30 microns or less.
• a porous supporting matrix typically in the form of a thin membrane having a thickness of 90 microns or less, more typically 60 microns or less, and most typically 30 microns or less.
• Any suitable method of imbibing the polymer into the pores of the supporting matrix may be used, including overpressure, vacuum, wicking, immersion, and the like.
• the polymer becomes embedded in the matrix upon reaction of the amidine groups.
• Any suitable supporting matrix may be used.
• the supporting matrix is electrically non-conductive.
• the supporting matrix is composed of a fluoropolymer, which is more typically perfluorinated.
• Typical matrices include porous polytetrafluoroethylene (PTFE), such as biaxially stretched PTFE webs. Additional embodiments may be found in U.S. Pats. Nos. RE37,307, RE37,656, RE37.701, and 6,254,978.
• the crosslinking reaction may be carried out by any suitable method. Typically, the reaction is accomplished by exposure to electromagnetic radiation, typically in the ultraviolet band, sufficient to produce the desired degree of crosslinking. Alternately, the polymer may be exposed to a radical initiator. Any suitable initiator may be used, such that it is adequate to produce the desired degree of crosslinking in the amount used.
• the radical initiator may be a thermal initiator or a photochemical initiator.
• Suitable initators may include dithionates such as sodium dithionate, peroxides, azo compounds, benzophenones, acetophenones, and the like.
• the crosslinking agent and polymer may be mixed by any suitable method, including mixing in solution or suspension, kneading, milling, or the like. Activation of the initiator may occur in whole or part during annealing of the membrane or may be carried out separately from any annealing step, by application of heat, light or both.
• the sulfonyl chloride group is removed by application of electromagnetic radiation or a radical initiator leaving behind a radical which readily binds covalently to other polymer strands or to crosslinking agents to form crosslinks.
• the step of crosslinking the polymer may occur in whole or part during annealing of the membrane or may be carried out separately from any annealing step.
• the remaining sulfur-containing functions of the pendant groups may be converted to sulfonic acid form by any suitable process.
• Sulfonyl halide groups may be converted by hydrolysis. In one typical process, the polymer is immersed in an aqueous solution of a strong base and subsequently acidified.
• a polymer membrane is immersed in 15% KOH in water at 80 °C for 1 hour, then washed twice in 20% nitric acid at 80 °C, then boiled in deionized water twice.
• the acid-functional pendant groups typically are present in an amount sufficient to result in an hydration product (HP) of greater than 15,000, more typically greater than 18,000, more typically greater than 22,000, and most typically greater than 25,000. In general, higher HP correlates with higher ionic conductance.
• HP hydration product
• the acid-functional pendant groups typically are present in an amount sufficient to result in an equivalent weight (EW) of less than 1200, more typically less than 1100, and more typically less than 1000, and more typically less than 900.
• membranes made according to the method of the present invention may differ in chemical structure from those made by other methods, in the structure of crosslinks, the placement of crosslinks, the placement of acid- functional groups, and the like.
• This invention is useful in the manufacture of polymer electrolyte membranes for use in electrolytic cells such as fuel cells.
• electrolytic cells such as fuel cells.

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• 2003
  • 2003-12-08 US US10/730,238 patent/US7112614B2/en not_active Expired - Fee Related
• 2004
  • 2004-11-16 CA CA002548293A patent/CA2548293A1/en not_active Abandoned
  • 2004-11-16 WO PCT/US2004/038336 patent/WO2005061592A1/en not_active Ceased
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