Soluble Ladder Aromatic Polymers: Synthesis and Characterization of Non-Ladder Intermediates and Final Polymers; Electronic Properties.

2,6-Diaminotoluene was reacted with 3-pyridinecarboxaldehyde in acidic medium and the intermediate polymer was further condensed in polyphosphoric acid at high temperature (335 C) to obtain a soluble heterocyclic ladder polymer, poly 4-(3-pyridyl), 8-methyl,2,3-6,7-quinolino) (PPMO). NMR spectra of the intermediate polymer indicated that a linear polymer was formed. Electronic paramagnetic resonance (EPR) and conductivity of pristine and iodine doped PPMO were studied. Unpaired spin density measurements indicated that the spin concentrations of the undoped polymer lay in the range of one spin per 150-190 repeat units at room temperature. Doping with iodine affected the spectrum. Conductivity is increased 5 orders of magnitude by iodine doping; at room temperature, the highest value found was 0.017 S/cm. The activation energy for conductance after doping is about half that of pristine polymer. 2,6-Diaminotoluene reacts with formaldehyde in aqueous solution with acid catalysis to produce a crystallizable prepolymer, poly(3,5'-methylene,2,6-diaminotoluene). The reaction temperature and time substantially affect its molecular weight. Further condensation in polyphosphoric acid at high temperature (345 C), produced a soluble linear ladder aromatic polymer, poly(8-methyl,2,3-6,7-quinolino). The polymer, PMO, condensed at four different temperatures was studied. At low temperatures, unpaired spin concentration of PMO4 increases as temperature decreases. PMO was doped with nitrosyl hexafluorophosphate (NFP) and iodine. X -ray diffraction indicates that iodine may intercalate. EPR studies suggests that NO mainly oxidized the polymer to produce charged non-magnetic species, e.g. bipolarons. Narrow line width plus the strong temperature dependence of unpaired spin concentration for PMO4 suggests motional narrowing, which is consistent with its high intrinsic electronic conductivity, 2.1 x 10('-5) S/cm at 25 C. The intrinsic conductivity at 25 C is of the order of 10(' -11) S/cm for PMO1 and 10('-9) S/cm for PMO2 and PMO3. The conductivity of PMO3 increases by 6 and 7 orders of magnitude upon doping with NFP and iodine, respectively. The best value found at room temperature is 2.4 x 10('-2) S/cm. Electronic conductivity in NFP doped PMO2 may occur through either a three dimensional variance range hopping near Fermi energy or tunneling in metallic grains. Temperature dependence of electronic conductivity of iodine doped PMO3 shows that the high metallic domain concentration might be induced by doping. (Abstract shortened with permission of author.).