EFFECT OF DOPING SYSTEMS, HEAT, AND TIME ON THE ELECTRICAL-CONDUCTIVITY OF POLY-P-PHENYLENES

Poly-p-phenylenes (PPPs) were synthesized by the Kovacic procedure usi ng CuCl2 as the oxidant and AlCl3 as the catalyst. The alternating ele ctrical conductivity of PPPs was investigated considering the doping s ystem (dopant-solvent), heat treatment, and time. Doped poly-p-phenyle nes remained semiconductors even 1 year after doping with a lower cond uctivity compared to the initial one. The most effective doping system s for PPPs were FeCl3-ACN (ACN: acetonitrile) and FeCl3-N (N: nitroben zene), while SnCl4-ACN yielded material with a lower but comparable co nductivity. FTIR spectra and X-ray diffractograms of doped materials h aving a lower conductivity (i.e. PPP doped with SnCl4-ACN) approached that of the undoped PPP. The conductivity depends on the stability of the polymer-dopant complex, which is affected by the electron donor-ac ceptor (EDA) interactions between the dopant and the solvent. Annealin g after doping resulted in a decrease in conductivity, due to the ther mal deactivation of the polymer-dopant complex. The ratio of sigma'(ta u)/sigma'(0) (where sigma'(tau) and sigma'(0) are the real part of the electrical conductivity at log f = 7 and log f = 1, respectively) ran ges from 10(1) for the doped polymers at a time of t = 0 to 10(1)-10(2 ) at t = 12 months, and to 10(4) for the heat-treated doped polymers. The conductivity measurements suggested an indirect method to characte rize the stability of the complexes formed.