Facile Synthesis and Polymerization of 2,6- Difluoro-2(-sulfobenzophenone for Aromatic Proton Conducting Ionomers with Pendant Sulfobenzoyl Groups Elin Persson Jutemar, Shogo Takamuku, Patric Jannasch* Introduction Proton-exchange membrane fuel cells (PEMFCs) are cur- rently developed into efficient and environmentally benign power sources for a variety of different applications. [1,2] The overall goals of most of the efforts are to reduce cost, increase durability and performance, and to expand the operating window of the fuel cell system. The proton- exchange membrane is central for the overall PEMFC performance and there is currently an extensive worldwide research ongoing to replace the current perfluorinated proton-exchange membranes with alternative ones. [3–6] Aromatic polymers such as poly(arylene ether sulfone)s, poly(arylene ether ketone)s, and poly(phenylene)s nor- mally have a sufficiently high thermal and chemical stability, combined with good mechanical properties, to be considered as the basis for candidate membrane materials. Consequently, over the last few years a large number of different aromatic polymers have first been functionalized with the sulfonic acid groups necessary for proton conduction and then evaluated as fuel cell membranes. [5,6] The sulfonic acid groups are generally introduced by post-modification of commercial polymers by using, for example, fuming sulfonic acid or chlorosulfonic acid. [7] These electrophilic substitutions lead to sulfonations of the most activated positions in the aromatic polymer structure, typically on positions close to ether substituents. Unfortu- nately, electrophilic sulfonations are often troubled by side reactions leading to polymer degradation or crosslinking, as well as loss of sulfonic acid groups from the unstable activated positions during PEMFC operation. [7] For certain aromatic polymers these problems may however be circumvented by the use of an organolithium approach, which allows the introduction of sulfonic groups and other Communication P. Jannasch, E. P. Jutemar, S. Takamuku Polymer and Materials Chemistry, Department of Chemistry, Lund University, P.O. Box 124, SE-221 00 Lund, Sweden Fax: (þ46) 46 222 4012.; E-mail: patric.jannasch@polymat.lth.se The lithium salt of 2,6-difluoro-2 0 -sulfobenzophenone was conveniently synthesized in one- pot by reacting 2,6-difluorophenyllithium with 2-sulfobenzoic acid cyclic anhydride in THF at 70 8C whereafter the product crystallized out of solution. A poly(arylene ether) and a poly(arylene sulfide) were prepared by polycon- densation reactions to demonstrate the reactivity and efficacy of this new monomer to produce sulfonated high-molecular weight aromatic poly- mers for fuel cell proton-exchange membranes. This work demonstrated that organolithium chemistry may offer versatile and straightfor- ward pathways to new functional monomers with fluorine atoms activated for nucleophilic aromatic substitution reactions. 1348 Macromol. Rapid Commun. 2010, 31, 1348–1353 ß 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/marc.201000081