Degradation of radiation grafted anion exchange membranes tethered with different amine functional groups via removal of vinylbenzyl trimethylammonium hydroxide

Low-density polyethylene (LDPE)-based anion exchange membranes (AEMs) with 65% degree of grafting of vinylbenzyl chloride (VBC) were tethered with different amine functionalities namely, trimethyl amine (TMA), 1,4-diazabicyclo[2.2.2]octane (DABCO), 1-azabicyclo[2.2.2]octane (ABCO) and N-methylpiperidine (NMP), and were subjected to degradation test by immersing the OH- exchanged AEMs in deionised water at 60 C, a condition analogous to fuel cell and electrolyser environment. All the quaternised membranes, regardless of the tethered amine functional group, exhibited similar degradation loss of ca. 5% IEC per month. Benzylic peroxide was detected in the degradation solution in all the tested AEMs. The observed degradation of the OH- exchanged AEMs was mainly attributed to peroxide and hydroxide radical attacks on the ternary (benzylic) carbon resulting in the release of vinylbenzyl trimethylammonium hydroxide (VBTMA) as a whole which was also detected. The degradation test performed on TMAfunctionalised membrane under nitrogen, oxygen and 3 wt% H2O2 showed similar degradation products namely benzylic peroxide and VBTMA suggesting that the degradation mechanisms under these three conditions are similar. The over three-fold increase in the degradation rate under oxygen saturated solution compared to nitrogen is due to the higher peroxide concentration produced from oxygen reduction to superoxide via ylide. (C) 2017 The Authors. Published by Elsevier B.V.