New anion conducting membranes based on functionalized styrene–butadiene–styrene triblock copolymer for fuel cells applications

In this work, the functionalization of polystyrene‐b‐poly(butadiene)‐b‐polystyrene triblock copolymer (SBS) with vinylbenzyl chloride and benzoyl peroxide (BPO) or α,α′‐azo‐bis‐isobutyronitrile (AIBN) as free radical initiators was reported. The functionalization degree (FD), calculated by ¹H NMR spectroscopy and confirmed by elemental analysis, was highly tunable (from 4 to 10 mol %) and positively correlated to the starting percentage of radical initiator. More specifically, at the same initiator molar percentage grafting efficiency is higher using BPO rather than AIBN. Quaternization reaction of the grafted benzyl chloride groups with the bifunctional tertiary amine 1,4‐diazabicyclo[2.2.2]octane (Dabco) led to a chemically and thermally stable homogeneous anion‐exchange membrane. Electrochemical parameters were evaluated for Dabco‐quaternized grafted copolymers having different FDs, and compared with a commercial Tokuyama benchmark membrane. Experimental data showed a positive correlation between FD and both water swelling and ionic conductivity. Best trade‐off between ionic conductivity and water swelling was found for membrane having FD 9.1 mol %, which conductivity is comparable with the Tokuyama benchmark one and water uptake is only slightly higher. The results are discussed based on the molecular parameters with particular reference to ionic content and distribution. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011