Aromatic poly(pyridinium salt)s: synthesis and structure of organo-soluble, rigid-rod poly(pyridinium tetrafluoroborate)s

A series of phenylated, aromatic poly(pyridinium tetrafluoroborate)s has been prepared by the polymerization of 4,4′-(1,4-phenylene)bis(2,6-diphenylpyrylium tetrafluoroborate) with aromatic diamines in a dimethylsulfoxide/toluene mixture at 145–150°C. The water generated by the transformation of the pyrylium rings to pyridinium rings was distilled from the reaction mixture as a water/toluene azeotrope. All-para-catenated, rigid-rod polymers with inherent viscosities as high as 4.9 dl g−1 were obtained that were soluble in polar aprotic solvents. The polymers could be solution cast into tough, flexible films. Although the glass transition temperatures of the poly(pyridinium salt)s were difficult to detect with differential scanning calorimetry, they displayed distinctive melting endotherms with minima above 380°C. Thermogravimetric analysis showed that the polymers began to decompose near 360°C prior to melting. Wide-angle X-ray diffraction analysis revealed that the chains were packed in a structure similar to that of a smectic liquid crystalline glass.