Spectroscopic and Morphological Studies of Highly Conducting Ion-Implanted Rigid-Rod and Ladder Polymers

We report on the spectroscopic (UV-visible, IR, XPS, and Raman) characterization and morphological studies of ⁸⁴Kr⁺-implanted conducting rigid-rod and ladder polymers at a dose of 4 × 10¹⁶ ions/cm² and an energy of 200 keV. The rigid-rod polymers poly(p-phenylenebenzobis(thiazole)) (PBZT) and poly(p-phenylenebenzobis(oxazole)) (PBO), pseudo-ladder polymer poly((p-2,5-dihydroxyphenylene)- benzobis(thiazole)) (DPBT), and ladder polymer poly(benzimidazobenzophenanthroline) (BBL), all showed similar optical properties after implantation, namely, broad metallic absorption. XPS data of films revealed significant reduction in the heteroatoms and increased carbon content after implantation, which corroborates the observed insolubility of the implanted polymers even in the presence of Lewis acid-base coordination agents. The implanted samples were IR inactive, presumably due to symmetry and the small values or the absence of bond-dipole moments. However, the Raman spectrum of the implanted PBZT showed two principal bands with a drastic reduction in intensity and loss of the bands in the 1160-1300-cm^-1 region compared to the Raman spectrum of the pristine polymer. PBO and BBL showed “brush-heap” morphologies after implantation, while the surface features of PBZT revealed a blistering effect of implantation. The morphology and electrical conductivity of the implanted materials were found to depend on the processing history of the pristine polymers. The room-temperature conductivity of these implanted rigid-rod and ladder polymers, typically ~80-200 S/cm, is significantly higher than that obtained to date by conventional doping techniques and was found to be remarkably stable even after annealing at temperatures up to 400 °C.