Raman and ir spectroscopic investigation of aromatic 1,3,4-oxadiazole polymers and oligomers

The molecular structure of poly(p-phenylene 1,3,4-oxadiazole) (POD) is investigated using i.r. and Raman spectroscopy. Both methods reveal characteristic differences for the alpha- and beta-POD forms that are most obvious in the spectral region between 1500 and 1650 cm(-1). The spectra for dimer and tetramer compounds already show the same features as found for longer chains. Based on molecular modelling calculations these differences are assigned to cia and trans conformations of the main chain segments. High pressure measurements show a linear shift of the Raman lines and support the result of the thermodynamic stability of the trans conformation. (C) 1997 Elsevier Science Ltd.