Abstract: We have investigated the properties of electron paramagnetic resonance (EPR) spectra from undoped-, FeCl₃-and iodine-doped poly (paraphenylene) (PPP) prepared by the method of Kovacic. EPR measurements were used to characterize electronic states relevant for polaron transformation in doped PPP. it was found that a novel phenomenon of ihe dependence of room temperature linewidth(△H_pp) and spin concentration (N_spin) on the dopant concentrations for iodine-doped PPP, namely, △H_pp first decreased and increased; and then decreased and increased again with increasing of iodine concentrations in the iodine-doped PPP, Correspondingly, N_spin first increased and decreased; and then increased and decreased again with increasing of iodine concentration in PPP. However, the changes of △H_pp and N_spin in FeCl₃-doped PPP are not similar to those in the iodine-doped PPP system. We explained this difference、Due to the interaction between spins on the polymer chains and dopant molecule, the observed g-factor values are close to the free electron value and do not substantially vary with the kind of dopant and temperature.

Key words: EPR, Spin concentration, Polaron