PROTON NMR-STUDIES OF A POLYBENZIMIDAZOLE IN SOLUTION

In the reported experiments, molecular aggregation of poly(4,4 prime -diphenyl ether-5,5 prime -bibenzimidazole) (PBI) in solution has been studied by high resolution proton NMR. PBI and model compounds have been synthesized, purified, and characterized. Proton resonances in the NMR spectrum of PBI are assigned by comparison with the proton resonances of the model compounds. Spectra are studied by total line-shape analysis, assuming each absorption curve to be Lorentzian. The dependence of the chemical shifts of protons in PBI on the dielectric constant of the solvent is demonstrated by using polar solvents of varying dielectric constant, such as N-methylpyrrolidone, dimethylsulfoxide, and formic acid. The viscosity of the PBI-DMAc solutions is reported at various temperatures and concentrations of LiCl. The results from viscometry are explicable in terms of the NMR observations.