Vibrational spectroscopic studies of cation effects in low molecular weight poly(propylene oxide) complexed with lithium, sodium and potassium thiocyanate

This paper presents the results of room temperature Raman scattering and infrared transmission investigations of an approximately 450 average molecular weight poly(propylene oxide), PPO, complexed with varying concentrations of lithium, sodium and potassium thiocyanate. The strength of interaction between the metal cation and the polymer is observed to increase in the order Li>Na>K. Spectral changes in the O---H stretching region show that the cations interact with the alcoholic oxygen atoms as well as the ether oxygen atoms. Frequency shifts in the C---H stretching region combined with the growth of splittings and structure in lower frequency bands suggest that increasing complexation is accompanied by changes in the polymer backbone dynamics and structure. The metal-oxygen stretching band is easily identified in the infrared transmission spectra. Finally, cation-dependent frequency shifts of the thiocyanate ion bands indicate the formation of contact ion pairs coordinated at the nitrogen end of the anion.