IONIC-CONDUCTIVITY OF CONJUGATED WATER-SOLUBLE RIGID-ROD POLYMERS

Poly[( 1,7-dihydrobenzo [1,2-d:4,5-d'] diimidazole-2,6-diyl) -2-(2-sul fo)-p-phenylene], a conjugated rigid-rod polymer, was derivatized with pendants of propane-sulfonated ionomers. The derivatized rigid-rod po lymer was soluble in aprotic solvents as well as in water for isotropi c solutions that were processed into isotropic films. Direct-current e lectrical conductivity sigma of the films was measured using the four- probe technique. Room-temperature sigma as high as 2.9 X 10(-4) S/cm w as achieved on pristine isotropic films without using dopants. When th e rigid-rod polymer concentration exceeded 25 wt %, the isotropic solu tion could be transformed into a liquid-crystalline solution that allo wed deformations to be applied to produce anisotropic films. Significa nt increase in sigma was obtained in a sheared film along both the par allel direction (parallel to) and the transverse direction (perpendicu lar to) with a sigma(parallel to)/sigma(perpendicular to) = 5. Additio nally, enhanced sigma was realized in films heat-treated at about 100 degrees C, in the derivatized polymer with higher molecular weight fro m dialysis, and in substituting the sulfonated ion Na+ by H+ in the pe ndants of the polymers. Constant-voltage measurements were applied to the polymers to monitor the sigma stability for ascertaining the natur e of the conductivity. No electronic contribution in sigma was detecte d. Instead, a monotonically decreasing sigma was consistently observed indicative of ionic conductivity. (C) 1993 John Wiley & Sons, Inc.