Effect of Cross-Linking on Polyimide Ionomer Membranes

In order to improve the stability and the proton conductivity of sulfonated polyimide ionomer membranes, effect of cross-linking has been investigated. The cross-linking moieties have been introduced into the ionomer structure by applying 2 mol% of trifunctional monomer in the polymerization reaction. Tough, flexible, and processable membranes were obtained by solution casting. Among the three cross-linking agents investigated, tris(aminoethyl)amine (TE) was the most effective to improve the membrane properties. Having high ion exchange capacity (2.33 meq/g), the cross-linked SPI-5TE showed good stability to the oxidative and hydrolytic degradation, superior mechanical strength, and high proton conductivity at low humidity conditions. Low methanol permeation of the cross-linked SPI-5TE membrane than the uncross-linked SPI-5 and Nafion 112 membranes has been confirmed.