Spectroscopic Analysis of Chain Conformation of Poly(propylene oxide)-Based Polymer Electrolytes

Abstract

Fourier transform Raman spectroscopy has been utilized, in combination with normal coordinate analysis, to characterize chain conformational changes of amorphous poly(propylene oxide) (PPO) when used as a matrix for polymer electrolytes. Our data indicate that in the presence of salt, poly(propylene oxide) displays a characteristic Raman band at 810 cm -1 increasing in intensity with an increase in LiClO 4 concentration. 1,2-Dimethoxypropane (DMP) was found to be an excellent model for data interpretation. Both the intensity and frequency ofRaman active 1,2-dimethoxypropane vibrations were calculated. The C-C or C-O bands in the 700-900 cm -1 region were found to be particularly sensitive to chain conformational changes. The bands at 810 and 836 cm -1 were assigned to TG α T and TTT conformations of the -O-C-C-O- sequence along the backbone, respectively. Therefore an increase in intensity at 810 cm -1 directly correlates to an increase in the TG α T conformation with an increase in salt concentration. The effects of end groups on chain conformational changes were also studied since Li + can interact with both -OH end groups and ether oxygens. Poly(propylene oxide)s having hydroxy and methoxy end groups were compared. Our analyses indicate the interaction between hydroxy end groups and the lithium cation does not contribute as significantly to formation of the TG α T conformation as does the interaction between the ether oxygen and lithium cation.