Proton conducting behavior in non-crosslinked and crosslinked polyethylenimine with excess phosphoric acid

Linear polyethylenimine (PEI) was treated with calculated amounts of H3PO4 to prepare PEI-xH(3)PO(4) composites. Their proton conductivity at a fixed temperature depended strongly on x. When the range of,x was extended to as high as 2.5-3.0, conductivity at 50 degrees C reached ca. 10(-4) S cm(-1). But the systems became very hygroscopic, deliquescent, and difficult to handle. To obviate this problem, composites were made from crosslinked PEI (c-PEI) and H3PO4. They were dry to touch and much less hygroscopic. The patterns of dependence of conductivity on x were quite similar regardless of whether the matrix was PEI or c-PEI, although the magnitude of conductivity was somewhat smaller in the crosslinked systems. (C) 2000 Elsevier Science Ltd. All rights reserved.