ANISOTROPIC IONIC-CONDUCTIVITY OF LITHIUM-DOPED SULFONATED PBI

The conductivity study results of lithium-doped sulfonated PBI, a conj ugated rigid rod polymer, poly[(1,7-dihydrobenzo[1,2-d:4,5-d'] dimidaz ole-2,6-diyl)-2-(2-sulfo)-p-phenylene], derivatized with pendants of p ropane sulfonate Li+ ionomer are reported. The room-temperature DC fou r-probe conductivity parallel to the surface of cast films was as larg e as 8.3 x 10(-3) S/cm. Similar measurements with an eight-probe confi guration showed no difference between bulk and surface conductivity. T he ionic nature of the conductivity was indicated by constant voltage depletion experiments and by secondary ion mass spectroscopy measureme nts of the residues near the electrodes. The DC two-probe conductivity measured transverse to the sample surface was three to four orders of magnitude smaller than longitudinal conductivity, while the AC two-pr obe conductivity was even less. Electron microscopy indicated that the films had a layered structure parallel to the surfaces. This structur al anisotropy was confirmed by refractive index values obtained from w ave-guide experiments and by wide angle X-ray scattering. (C) 1997 Joh n Wiley & Sons, Inc.