Raman spectra of polyethylene glycols: Comparative experimental and DFT study

Abstract Experimental Raman spectra of liquid and solid polyethylene glycols (PEGs) with various molecular weights were compared with the results of the density functional theory (DFT) calculations. The structure, energies and Raman spectra of molecules in the trans and 72 helical conformations with various orientations of the terminal groups were calculated for PEG molecule with 9 monomer units. Recorded spectrum of PEG with the average molecular weight of 400 Da (8–9 monomer units) matches very well the calculated spectrum of the most thermodynamically stable g’G(TTG)8g’ conformation. DFT-calculated Raman spectra for the g’G(TTG)ng’ conformation depend on the amount of the monomer units in PEG molecule. The peak position of the PEG Raman line at about 1100 cm−1 can be used to estimate the molecular weight distribution of short molecules.