Multiblock poly(arylene ether nitrile) disulfonated poly(arylene ether sulfone) copolymers for proton exchange membranes: Part 1 synthesis and characterization Jarrett R. Rowlett a , Yu Chen a , Andy T. Shaver a , Ozma Lane a , Cortney Mittelsteadt b , Hui Xu b , Mingqiang Zhang a , Robert B. Moore a , Sue Mecham a , James E. McGrath a, * a Department of Chemistry, Macromolecules and Interfaces Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA b Giner Inc. Newton, MA 02466, USA article info Article history: Received 4 July 2013 Received in revised form 16 September 2013 Accepted 17 September 2013 Available online 24 September 2013 Keywords: Partially fluorinated polymer Multiblock copolymer Proton exchange membrane abstract A series of multiblock copolymers based upon alternating segments of a hydrophilic disulfonated pol- y(arylene ether sulfone) and a hydrophobic fluorine-terminated poly(arylene ether benzonitrile) (6FPAEB) were synthesized and characterized for use as proton exchange membranes (PEM). The ion- exchange capacity of the block copolymers were varied by utilizing 4,4 0 -biphenol or hydroquinone in combination with 3,3 0 -disulfonated-4,4 0 -dichlorodiphenyl sulfone (SDCDPS) to form the hydrophilic segments. The alternating block copolymer morphology was achieved by using mild temperatures to link the oligomers together and minimize ethereether interchange reactions. Both the 4,4 0 -biphenol and hydroquinone based membranes showed high proton conductivity with moderate water uptake and good mechanical properties. The block copolymers displayed nanophase separated morphologies, confirmed by transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS). The strong membrane performance was attributed to the multi-phase morphology. Published by Elsevier Ltd. 1. Introduction Over the past few decades fuel cells have been extensively studied as an environmentally favorable alternative method for generating energy. These electrochemical devices work by con- verting chemical energy into electrical energy, and only water is produced as a by-product when hydrogen (H 2 ) gas is used as the fuel source. Among the various types of fuel cells, polymer elec- trolyte membrane fuel cells (PEMFC)s are considered promising candidates due to their high efficiency, high energy density, quiet operation, and elimination of carbon dioxide emission [1]. In these fuel cells the electrolyte is a solid polymer membrane known as the proton exchange membrane (PEM), the PEM is responsible for the transport of protons, forming a gas/fuel barrier for the electrodes, and electronic insulation [2]. Currently, the state-of-the-art material used in PEMFCs is the poly(perfluorosulfonic acid) membrane Nafion Ò , produced by DuPont. The highly fluorinated Nafion Ò membrane has strong mechanical properties and chemical resistance along with high proton conductivity. However, the high cost and reduced conduc- tivity at low relative humidities of these membranes are prob- lematic [3,4]. Ideally a PEM material should exhibit high proton conductivity, good mechanical strength, high oxidative and hy- drolytic stability, low fuel and oxidant permeability, ease of fabri- cation, and low cost [2]. Sulfonated poly(arylene ether) statistical copolymers have been comprehensively investigated as potential alternatives to Nafion Ò for use in PEMFCs do to their strong membrane properties, and well-established oxidative, hydrolytic and chemical stability [5e 14]. Although these copolymers showed high conductivity under well hydrated conditions, like Nafion Ò the conductivity signifi- cantly decreases at lower relative humidity (RH). The randomly distributed sulfonic acid groups on these membranes resulted in isolated morphological domains, which limited the conductivity at low RH. One solution to this issue is to use hydrophilicehydro- phobic multiblock copolymers based on sulfonated poly(arylene ether sulfone) hydrophilic regions and fluorinated poly(arylene ether) hydrophobic regions [15e24]. These polymers showed well- defined phase separated morphology, with a network of hydro- philic and hydrophobic domains [10,18]. The well-connected hy- drophilic channels of the block copolymers allowed for significantly enhanced proton conductivity even under partially hydrated * Corresponding author. E-mail address: jmcgrath@vt.edu (J.E. McGrath). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.polymer.2013.09.032 Polymer 54 (2013) 6305e6313