Raman longitudinal acoustic mode (LAM) spectra have been obtained during isothermal crystallization from the melt at various temperatures of a poly(ethylene oxide) (PEO) fraction of molecular weight about 3000. At all temperatures, we find an initial single well-defined LAM band corresponding to a helical chain length that represents a non-integral-fold (NIF) structure. With time, and more rapidly at higher crystallization temperatures, the NIF chains transform into integer-fold (IF) structures. The final morphology consists of IF mixed crystals composed mainly of extended (E) chains but with once-folded (F2) chains embedded in them. This solid-state transformation from the NIF state may proceed through the F2 state.