DIVALENT-CATION DOPANTS FOR POLYPARAPHENYLENE

Free-standing films of polyparaphenylene (PPP) were synthesized from the electrochemical oxidation of benzene. A potential of about 4.7 V was applied across the counter and working electrodes in a nitrobenzene solution containing lithium hexafluoroarsenate and copper (II) chloride as electrolytes. The PPP chain length was estimated by infrared analysis to be at least 14 monomer units. Alkaline earth metals and the lanthanides Eu and Yb dissolve in liquid ammonia to make very strong reducing solutions by forming solvated electrons. PPP is partially reduced in these solutions with the divalent cations (Ca, Sr, Ba, Eu, or Yb) diffusing into the polymer to balance the charge. At room temperature, the conductivities of films and pressed pellets of divalent doped PPP increase up to about 0.1 Scm-1. These can be compared to values of about 10 Scm-1 for potassium doped PPP prepared in liquid ammonia. Luminescence spectra confirm that the europium incorporated into the PPP is in a +2 oxidation state.