• water electrolysis
• block copolymer
• anion exchange membrane

The present work aimed at preparing anion exchange membranes (AEMs) for water electrolysis using a commercial styrene-butadiene block copolymer (SBC) as starting material. Side chains of vinylbenzyl chloride (VBC) were grafted from the copolymer by free radical polymerization, providing functional groups that were easily converted into quaternary ammonium groups. The molar content of VBC (functionalization degree, FD or x) in the g-VBC-x copolymers was varied in the range 13–60 mol%, simply by varying the concentration of VBC monomer in the feed. Novel VBC/poly(ethylene glycol) methacrylate (PEGMA) grafted SBC copolymers (g-VBC-x-PEGMA-y) were successfully synthesized by free radical polymerization, obtaining copolymers with a molar content of VBC and PEGMA ranging from 9 to 40 mol% and from 4 to 6 mol%, respectively. g-VBC-x copolymers were used for the preparation of films by solution casting from chloroform followed by a quaternization step in which different amines (trimethylamine, N-methylpiperdine, tetramethyl-1,3-propanediamine and N, N’, N’, N’’, N’’-pentamethyldiethylenetriamine) were used in order to highlight their effects on the membrane properties. On the other hand, membranes deriving from g-VBC-x-PEGMA-y and the blends g-VBC-x/poly(p-phenylene oxide) (PPO) were quaternized with trimethylamine, as in this cases the effect of PEGMA and PPO had to be pointed out, respectively.
Thermal, mechanical, water uptake, water transport and electrochemical (ionic conductivity, ion exchange capacity and hydrogen crossover) properties of the membranes were evaluated and especially correlated with the FD of the respective copolymer. The effect of PEGMA, PPO and type of amine were also highlighted in the case g-VBC-x-PEGMA-y, g-VBC-x/PPO and g-VBC-x quaternized with different amines, respectively.
Thanks to its excellent electrochemical performance, g-VBC-27 membrane was tested into a single electrolysis cell in which the operative conditions of an AEM electrolyzer were simulated, in particular, the temperature was in the range 50–55 °C and a KOH 1 wt% solution was used as supporting electrolyte. The test lasted about 40 days and the cell maintained a low voltage of about 1.78 V (current density of 800 mA·cm–2) similar to that of the benchmark (1.75 V), during the entire period.