Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Ion-exchange polymer or process of preparing
Reexamination Certificate
2000-09-19
2001-10-09
Zitomer, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Ion-exchange polymer or process of preparing
C521S028000, C525S390000, C525S418000, C525S471000, C525S480000
Reexamination Certificate
active
06300381
ABSTRACT:
This invention is directed to polymer blends and polymer blend membranes which consist of a polymeric sulfonic acid and of a polymer which contains primary, secondary or tertiary amino groups, which are prepared via mixing of a polymeric sulfonic acid or a polymeric sulfonic acid salt with a polymer which contains primary, secondary or tertiary amino groups.
A further object of this invention is the application of these polymer blend membranes in membrane fuel cells, i.e., direct methanol fuel cells (DMFC) or H
2
-polymer electrolyte fuel cells (PEFC), in membrane electrolysis, in aqueous or non-aqueous electrodialysis, in diffusion dialysis, in the perstractive separation of alkenes from alkenelalkane mixtures (here the membranes are in the SO
3
Ag form, where the Ag
+
forms a reversible complex with the alkene double bond (>facilitated transport)), in the pervaporative separation of water from water/organics mixtures, or in gas separation.
A key-component of the PEFC is the proton-conducting membrane. The commercially available ionomer NAFION® (Grot, W. G.: Perfluorinated Ion-Exchange Polymers and Their Use in Research and Industry, Macromolecular Symposia, 82, 161-172 (1994)) fulfils the requirements of chemical stability for the application in PEFC (Ledjeff, K.; Heinzel, A.; Mahlendorf, F.; Peinecke, V.: Die reversible Membran-Brennstoffzelle, Dechema-Monographien Band 128, VCH Verlagsgesellschaft, 103-118 (1993)). However, it shows some disadvantages requiring the search for alternative materials. It is very expensive (U.S.$ 800/m
2
). The very complex production process involves highly toxic intermediates (see Grot, W. G.). Its environment-compatibility is poor: as a perfluorinated polymer, it is difficultly degradable, and the recyclability of NAFION® is questionable. When applying NAFION® in DMFC, it was discovered that it shows (especially when applying pure methanol) a very high methanol-permeability (Surampudi, S., Narayanan, S. R.; Vamos, E.; Frank, H.; Halpert, G.; LaConti, A.; Kosek, J.; Surya Prakash, G. K.; Olah, G. A.: Advances in direct oxidation methanol fuel cells J. Power Sources, 47, 377-385 (1994)) which reduces the energy-efficiency of the DMFC via mix-potential formation.
Partially fluorinated membranes are under investigation at present. At this point, the scientific work of G. G. Scherer et al can be mentioned (Scherer, G. G.: Polymer Membranes for Fuel Cells, Ber. Bunsenges. Phys. Chem. 94, 1008-1014 (1990)); (Scherer, G. G.; Büchi, F. N.; Gupta, B.; Rouilly, M.; Hauser, P. C; Chapiro, A.: Radiation Grafted and Sulfonated (FEP-g-Polystyrene)—An Altemative to Perfluorinated Membranes for PEM Fuel Cells? Proceedings of the 27th Intersociety Energy Conversion Engineering Conference IECEC-92, San Diego, USA, August 3-7, 3.419-3.424 (1992)); (Gupta, B.; Büchi, F. N; Scherer, G. G: Materials Research Aspects of Organic Solid Proton Conductors, Solid State Ionics 61, 213-218 (1993)). Scherer et al. has formed radicals in perfluorinated polymer foils (FEP) by gamma-irradiation. In a second step, styrene was grafted onto the formed radicals. In a third step, polystyrene chains of the interpenetrating network (IPN) formed were sulfonated. These polymer membranes showed a good performance in the PEFC application. However, the applied synthesis process seems to be unsuitable for mass production. The Canadian company Ballard has developed a partially fluorinated proton-conducting membrane from alpha,beta,beta-trifluorostyrene (Wei, J.; Stone, C.; Steck, A. E.: Trifluorostyrene and substituted trifluorostyrene copolymeric compositions and ion-exchange membranes formed therefrom, WO 95/08581, Ballard Power Systems). A disadvantage of this membrane is its high price because of the complex synthesis process for the monomer alpha,beta,beta-trifluorostyrene (Livingston, D. I.; Kamath, P. M.; Corley, R. S.: Poly-alpha,beta,beta-trifluorostyrene, Journal of Polymer Science, 20, 485-490 (1956)) and because of the bad sulfonation-ability of poly(alpha,beta,beta-trifluorostyrene).
Some references are found in the literature to the application of arylene mainhain polymers to PEFC. The most important articles will be mentioned in the following:
Polybenzimidazole—Phosphoric Acid
Membranes of the engineering-thermoplast polybenzimidazole are soaked with phosphoric acid (Wainright, J. S.; Wang, J.-T.; Savinell, R. F.; Litt, M.; Moaddel, H.; Rogers, C.: Acid Doped Polybenzimidazoles, A New Polymer Electrolyte The Electrochemical Society, Spring Meeting, San Francisco, May 22-27, Extended Abstracts, Vol. 94-1, 982-983 (1994)), and the phosphoric acid works as a proton conductor. The H
3
PO
4
-molecules are held in the membrane via hydrogen bridges and via protonation of the basic imidazole-N by formation of the salt H
2
PO
4
−+
HNPolymer. However, these membranes can lose a part of the H
3
PO
4
-molecules when water is formed during the fuel cell reaction, because the relation of H
3
PO
4
-molecules to imidazole-N's is roughly 3:1—the H
3
PO
4
is dragged out of the membrane by the reaction water.
Sulfonated Polyethersulfone
Ledjeff et al. (Nolte, R.; Ledjeff, K.; Bauer, M.; Mülhaupt, R.: Partially Sulfonated poly(arylene ether sulfone)—A Versatile Proton Conducting Membrane Material for Modem Energy Conversion Technologies, Journal of Membrane Science 83, 211-220 (1993)) suggest the application of crosslinked sulfonated polyethersulfone ionomers, prepared via electrophilic sulfonation of polyethersulfone, in PEFC. However, in this paper no U/i curve of the presented membrane is provided, precluding an evaluation of the suitability of this ionomer for the PEFC application.
Sulfonated Polyetheretherketone (PEEK)
The application of sulfonated polyetherketones in PEFC is presented by Helmer-Metzmann, F.; Ledjeff, K.; Nolte, R., et al.: Polymerelektrolyt-Membran und Verfahren zu ihrer Herstellung, EP 0 574 791 A2. Good performance of these polymers in PEFC is claimed. However, these membranes show high swelling values at the high proton conductivities required for a good performance in PEFC, which results in poor mechanical stability and thus limited lifetime in fuel cells. In addition, especially when PEEK is sulfonated heterogeneously, there is the risk that the polymer partially recrystallizes which leads to brittleness.
Sulfonated Polyphenylene
Membranes prepared from organics-soluble, chemically and thermally stable poly(phenylene)s are suggested as alternative proton-conductors for the application in PEFC (Matejcek, L.; Nolte, R.; Heinzel, A.; Ledjeff, K.; Zerfass, T.; Mülhaupt, R.; Frey, H.: Die Membranbrennstoffzelle: Untersuchungen an Membran/Elektrodeneinheiten, Jahrestagung 1995 der Fachgruppe Angewandte Elektrochemie der GDCh, Duisburg, Sep. 27-29, 1995, Abstract Poster Nr. 20 (1995)). However, no investigations of these membranes in PEFC have been published.
Sulfonated Polyphenylenesulfide
The development of a chemically and thermally stable polyphenylenesulfide via polysulfoniumcation-intermediate is reported in Miyatake, K.; Iyotani, H.; Yamamoto, K.; Tsuchida, E.: Synthesis of Poly(phenylene sulfide sulfonic acid) via Poly(sulfonium cation) as a Thermostable Proton-Conducting Polymer Macromolecules 1996, 29, 6969-6971 (1996). The disadvantage of this preparation process is, however, that it is relatively complicated and thus expensive.
Acid-base polymer blends based on vinyl polymers are often mentioned in the respective literature (Bazuin, C. G.: Ionomers (Compatibilization of Blends), in: Polymeric Materials Encyclopedia (Ed.-in-Chief J. C. Salomone), Vol. 5 (H-L), CRC Press (Boca Raton, New York, London, Tokyo) 3454-3460 (1996)) including, for example, such acid-base blends containing polymethacrylates as acidic component and polyvinylpyridinium salts as basic component (Zhang, X.; Eisenberg, A.: NMR and Dynamic Mechanical Studies of Miscibility Enhancement via Ionic Interactions in Polystyrene/poly(ethyl Acrylate) Blends, J. Polym. Sci.: Part B: Polymer Physics, 28, 1841-1857 (1990)). These blends have been investigated in terms of
Cui Wei
Kerres Jochen
BakerBotts L.L.P.
Universitat Stuttgart
Zitomer Fred
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