Journal of Membrane Science 278 (2006) 26–34 Sulfonated copoly(phthalazinone ether ketone nitrile)s as proton exchange membrane materials  Yan Gao a,b , Gilles P. Robertson a , Michael D. Guiver a,∗ , Guoqing Wang b , Xigao Jian b , Serguei D. Mikhailenko c , Xiang Li c , Serge Kaliaguine c a Institute for Chemical Process and Environmental Technology, National Research Council, Ottawa, Ont. K1A 0R6, Canada b Department of Polymer Science and Materials, Dalian University of Technology, Zhongshan Road 158-42#, Dalian 116012, PR China c Chemical Engineering Department, Laval University, Que. G1K 7P4, Canada Received 19 July 2005; received in revised form 26 October 2005; accepted 29 October 2005 Available online 1 December 2005 Abstract Sulfonated poly(phthalazinone ether ketone nitrile) copolymers (SPPEKN) were prepared by copolymerization of disodium 3,3 ′ -disulfonate- 4,4 ′ -difluorobenzophenone (SDFB-Na), 2,6-difluorobenzonitrile (2,6-DFBN), and 4-(4-hydroxyphenyl)-1(2H)-phthalazinone (DHPZ) at 160 ◦ C in N-methyl-2-pyrrolidione containing anhydrous potassium carbonate. The polymerization reactions proceeded smoothly and in high yield giving high molecular weight SPPEKN copolymers with different sulfonic acid content (SC) values. The polymer structures were defined by 1 H NMR and FT-IR. Membrane films of SPPEKN copolymers in both salt and acid forms, prepared at SDFB-Na to 2,6-DFBN feed ratios up to 60/40 mol/mol, were cast from the N,N-dimethylacetamide (DMAc) polymer solutions. The presence of highly polar nitrile groups are expected to increase inter- chain molecular forces, contributing to the observed reduction in water swelling over previously prepared sulfonated poly(phthalazinone ether ketone) (SPPEK) copolymers. Membranes containing nitrile groups are expected to show improved adhesion between polymer and catalyst when utilized in a fuel cell. All SPPEKN copolymers exhibited tensile strength higher than that of Nafion ® 117. The proton conductivities of acid form SPPEKN copolymers (SPPEKNH)s, prepared at the sulfonated/unsulfonated monomer feed ratio above 0.35 mol/mol, were around 10 -1 S/cm at 80 ◦ C, which is close to or higher than that of Nafion ® 117 under same measurement conditions. © 2005 Elsevier B.V. All rights reserved. Keywords: Sulfonated poly(phthalazinone ether ketone nitrile); Copolymerization; Proton exchange membrane; Fuel cell; Ionomer; Poly(ether ketone); Poly(ether nitrile) 1. Introduction Proton exchange membrane fuel cells (PEMFCs) are promis- ing clean power sources for vehicular transportation, residential and institutional, and also for computers, mobile communica- tion equipment, etc. [1]. Numerous investigations have been performed to improve the PEMFCs cost efficiency and perfor- mance [2,3]. One of the challenges of the current researches is to develop alternatives to perfluorinated sulfonic acid polymer materials, which are the state-of-the-art polymer electrolyte for PEMFCs. Although perfluorinated sulfonic acid polymers, such as Nafion ® developed by DuPont, exhibit good mechanical  NRCC No. 47863. ∗ Corresponding author. Tel.: +1 613 993 9753; fax: +1 613 991 2384. E-mail address: michael.guiver@nrc-cnrc.gc.ca (M.D. Guiver). properties, extremely high oxidative stability, high proton conductivity and long-term durability under PEMFC operating conditions. However, they suffer from some drawbacks, such as extremely high cost, dehydration at operating temperatures >80 ◦ C causing the conductivity decline, high permeability for liquid fuels and poor environmental safety. To achieve a practical applicability in fuel cells, many new polymer elec- trolytes have been prepared recently aiming to satisfy several rigorous requirements: high proton conductivity ≥10 -2 S/cm, an increased barrier to fuel cross-over compared with Nafion, reasonable hydrophilicity and hydrothermal stability, mechanical strength and low cost. The well-known excellent thermal, mechanical, and dielec- tric properties, oxidative resistance and other favorable prop- erties of high performance thermoplastic polymers, such as poly(aryl ether sulfone)s, and poly(aryl ether ketone)s are a good basis for their development as proton conducting mate- 0376-7388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2005.10.041