Raman longitudinal acoustic mode (LAM) studies of folded‐chain morphology in poly(ethylene oxide) (PEO). I. Normal mode analysis of LAM of a helical‐chain oligomer of PEO

Normal mode analyses were done for the exact structures of model oligomers of PEO to investigate the longitudinal acoustic mode (LAM) in this helical polymer. It quickly became apparent that it is impossible to reproduce observed LAM frequencies without incorporating explicit interchain interactions. We have developed a force field that includes interchain interactions through an atom‐atom potential and have shown that this force field reproduces very well the observed LAM frequencies of helical‐chain oligomers of PEO. This result indicates that the LAM of helical chains is much more sensitive to intermolecular interactions than that of planar zigzag chains.