Structural characterization of monomeric and oligomeric arylamides by solution and solid-state NMR spectroscopy

An extensive study of both liquid- and solid-state NMR spectroscopy was undertaken in order to elucidate the structural features of a phenyleneterephthalamide oligomer (OPTA) and of some related diarylamides. 1D- and 2D-COSY measurements allowed us to assign completely the proton signals of the title compounds in solution, while 1D-, 2D-HETCOR and 2D-COLOC measurements were used to assign C-13 resonances. Solid-state C-13 NMR experiments, by conventional cross-polarization (CP) at different contact times and with the dipolar dephased CP technique, were used to characterize these molecules in the solid state. Such techniques allowed us to differentiate among different carbon atoms; in the resulting spectra it was then possible to observe the selective appearance of signals from protonated and quaternary carbon atoms. It was also ascertained that the limited structural mobility of the insoluble OPTA, existing as a single monophasic species, can be explained in terms of hydrogen-type bonds present in the solid state. Copyright of (C) 2002 John Wiley Sons, Ltd.