Poly(arylene ether)s bounded with disulfonaphthoxyl pendants by post functionalization for polymer electrolyte membrane application in fuel cells

A novel series of side-chain type of sulfonated poly(aryl ether) copolymers containing disulfonaphthanoxyl pendants (sSPFAE) were synthesized from 9,9′-dihydroxyfluorene, 4,4′-biphenol, decafluorobiphenyl and disodium 4-hydroxy-2,7-naphthalene disulfonate (or dipotassium 7-hydroxy-1,3-naphthalene disulfonate) through two-step aromatic nucleophilic substitution. The structure was characterized by 1H NMR and FTIR. Structure-property relationships of the solution cast sSPFAE membranes, including ion exchange capacity (IECw, weight-based; IECv, volume-based), density, mechanical properties, water swelling, morphology, proton and methanol transport properties, thermal and hydrolytic stability were investigated and compared with those of perfluorinated ionomer (Nafion 112). The inclusion of high content perfluorobiphenyl segments in the sSPFAE back bone and disulfonated naphthalene in the side chain led to moderate water uptake, low swelling, excellent thermal, oxidative and hydrolytic stability. The sSPFAE membranes also exhibited good proton conductivity and low methanol permeability, enabling them good candidates for future polymer electrolyte membrane fuel cell applications.