Chemical oxidation stability and anhydrous proton conductivity of polyimides/phosphoric acid/imidazole blends

Abstract

Polyimides (PIs) based on 3,3′,4,4′-tetracarboxylicdiphenyl ether dianhydride, 3,3′,4,4′-benzophenonetetracarboxylic dianhydride, 4,4′-diaminodiphenylsulfone and 4,4′-methylenedianiline were synthesized. They are easily dissolved in many strong and polar solvents like dimethylformamide, N,N-dimethylacetamide, 1-methyl-2-pyrrolidinone, and dimethylsulfoxide. A new kind of anhydrous proton conducting system based on PI/H3PO4 and PI/H3PO4/ imidazole (Imi) blends was prepared. The chemical oxidation stability of the composite membranes was studied. The flexible PIs have better chemical oxidation stability. The addition of phosphoric acid can accelerate the degradation process of PIs, while the addition of Imi in PI/H3PO4 blends can greatly improve their chemical oxidation stability, which becomes much better than that of pure PIs. The proton conductivity of PI/H3PO4 blends is still lower compared with that of polybenzimidazole/H3PO4 blends. After the addition of Imi, the anhydrous proton conductivity of PI/H3PO4 blends increases significantly with increasing Imi content. © 2006 Society of Chemical Industry.