Ring-transmutation polymerization: Synthesis and characterization of aromatic poly(pyridinium salts)

The objective of this work was the synthesis of a new series of aromatic poly(pyridinium salts) via the reaction of 4,4{dollar}spprime{dollar}-p-phenylene-bis(2,6-diphenylpyrylium)bis(tetrafluoroborate) with aromatic diamines. In these reactions, the oxygen-containing pyrylium ring essentially undergoes a transmutation to the nitrogen-containing pyridinium ring. To describe such polymerizations, the term "ring-transmutation" has been coined. Although there have been attempts to obtain polymers from similar reactions, this dissertation now reports the first successful ring-transmutation polymerizations. Thus, the bis(pyrylium salt) was polymerized with various aromatic diamines in dimethyl sulfoxide (DMSO) under reflux to afford the corresponding fibrous poly(pyridinium salts) in quantitative yields. The structure of the diamine was varied so that the flexibility of the polymeric backbones varied from extremely-rigid to semi-flexible. The inherent viscosities of the polymers in N,N-dimethylformamide (DMF) at 30{dollar}spcirc{dollar}C ranged from 0.8 to 2.9 dL/g. The intrinsic viscosity determinations were complicated by the polyelectrolyte effect. The wide-angle X-ray diffraction patterns of the rigid and semi-rigid polymers were similar to those of smectic liquid crystalline glasses. The long range order in the rigid-rod polymers was considerably higher than that in polymers containing oxygen or methylene linkages. Poly(pyridinium salts) containing flexible oxyethylene linkages, on the other hand, displayed X-ray diffraction patterns typical of semi-crystalline polymers. Cyclic voltammetry showed that the poly(pyridinium salt) prepared from benzidine undergoes four consecutive reversible reduction reactions in dry DMSO. A series of charge transfer complexes prepared from the poly(pyridinium salts) and the radical anion of 7,7,8,8-tetracyanoquinodimethane (TCNQ) displayed conductivities that ranged from 10{dollar}sp{lcub}-7{rcub}{dollar} to 10{dollar}sp{lcub}-8{rcub}{dollar} ohm{dollar}sp{lcub}-1{rcub}{dollar}cm{dollar}sp{lcub}-1{rcub}{dollar}. An ionene elastomer was also prepared by treating bis(pyrylium salt) with a diamine-terminated poly(tetrahydrofuran). The tensile strength of the elastomer, which underwent phase separation, was in the range of 25 to 40 MPa and the elongation was approximately 300%.