A hydroxylated poly(aryl ether sulfone) (PES-OH) was synthesized by a demethylation reaction of a methoxy-functionalized PES (PES-OCH3) using the HCl/pyridine system. Derived from this hydroxylated PES precursor,bulky (2-trifluoromethyl-4-nitro) phenyl (TFN) and benzophenone (BZP) were introduced to the PES backbones as side groups via aromatic nucleophilic substitution reactions. A direct property comparison of PES-OH,PES-OCH3, PES-TFN and PES-BZP has been made, and these analogues exhibited different solubility, thermal properties and gas permeability. PES grafted with the trifluoromethyl side group (PES-TFN) demonstrated more attractive permeabilities and permselectivities for O2/N2 separation compared to the others, and it exhibited the best P(O2)/P(N2) value of 8.44.