Polymer Electrolytes: Ionic Liquid Modified Phenolphthalein Based Hybrid Multiblock Poly(Arylene Ether) Copolymers

A new class of phenolphthalein based poly (arylene ether) multiblock copolymers treated with ionic liquid were synthesized to cast proton conductive membranes. A nucleophilic condensation reaction of 4, 4'- bis (4-hydroxyphenyl) valeric acid based hydrophilic oligomer (M.Wt = 8 kDa) with a series of phenolphthalein based hydrophobic oligomers (M.Wt = 5, 8 and 10 kDa) was carried out to synthesize nano-phase separated multiblock copolymers. Characterization of the synthesized copolymers was carried out using FT-IR, 1HNMR and gel permeation chromatographic techniques. The fabricated hybrid membranes obtained by the impregnation of ionic liquid (1-butyl-3-methyl-imidazolium tetrafluoroborate (I.L)) in the synthesized multiblock copolymers showed better thermal and oxidative stability. Highly interconnected ionic channels in the hybrid membrane led to improved water uptake and proton conductivity while maintaining the mechanical stability. The Atomic Force Microscopy (AFM) images and Scanning Electron Microscopy (SEM) images showed the hydrophobic-hydrophilic nano-phase separation in the pristine and hybrid multiblock membranes.