Raman analysis of a conformational distribution of poly(ethylene oxide) and its model compound in the liquid state

Isotropic Raman spectra of poly(ethylene oxide) in aqueous solution and in the melt show differences in the skeletal stretching vibration bands near 800 cm(-1) and in the disordered longitudinal acoustic mode feature in the 200-400 cm(-1) region. These spectra may be simulated by superposing calculated spectra resulting from a series of normal coordinate calculations performed for an Ensemble of conformers. The conformational distribution for poly(ethylene oxide) in the molten state appears to favor the tgg' conformer, which dominates the spectrum calculated to match closely the observed isotropic Raman spectrum. It appears that the experimental data suggest that the tgg' conformation is present by a greater amount than is predicted by previous simulation methods. On the same basis, it appears that the aqueous solution of poly(ethylene oxide) contains mostly tgt conformers. The results for poly(ethylene oxide) were supported by measurements and computations made using 1,2-dimethoxyethane as a model.