Preparation of organic/inorganic composite membranes using two types of polymer matrix via a sol–gel process

Organic/inorganic composite membranes were prepared using two different polymers. BPO4 particles were introduced into polymers via an in situ sol–gel process. Pre-/post-sulfonated polymers were used to prepare composite membranes as matrix. Pre-sulfonated poly(aryl ether ketone) (SPAEK-6F) copolymer was synthesized via nucleophilic aromatic substitution. Degree of sulfonation was adjusted by the percentage of sulfonated monomer. Post-sulfonated poly(ether ether ketone) (SPEEK) was prepared using concentrated sulfuric acid as sulfonation agent. The membranes were characterized in terms of the ion-exchange capacity (IEC), proton conductivity, water uptake, AFM, SEM and their thermal properties. The SPAEK-6F plain membranes showed higher proton conductivity than that of the SPEEK plain membranes at similar water uptake or IEC due to their structural difference. SEM images of the composite membranes showed that the BPO4 particles were homogenously dispersed in the polymer matrices and BPO4 particle size was greatly influenced by polymer matrix. The SPAEK-6F/BPO4 composite membranes had much smaller BPO4 particle size than the SPEEK/BPO4 composite membranes due to well dispersion of BPO4 sol-like particulates in SPAEK-6F polymer solutions forming more hydrophobic/hydrophilic nanophase than SPEEK polymer solutions. The latter containing a few micrometer-scale BPO4 particles showed higher proton conductivity than the former containing hundreds nanometer-scale BPO4 particles at similar water uptake due to the increase in freezable water and effect of particle size.