Crystallinity of uniform oligo(oxyethylene) mono-alkyl ethers studied by Raman spectroscopy

Abstract

Low-frequency Raman spectra have been recorded for two series of uniform oligo(oxyethylene) mono-n-alkyl ethers: α-alkyl,ω-hydroxyoligo(oxyethylene)s, H(CH₂)_n(OCH₂CH₂)_mOH, and α-alkyl,ω-methoxyoligo(oxyethylene)s, H(CH₂)_n(OCH₂CH₂)_mOCH₃. LAM-1 frequencies were identified and compared with those determined previously for n-alkanes, oligo(oxyethylene) di-n-alkyl ethers and oligo(oxyethylene) dimethyl ethers. On the basis of the linear crystal model of Minoni and Zerbi (J. Phys. Chem., 1982, 86, 4791), non-linear relationships between whole-chain LAM-1 frequency and reciprocal chain length have been explained as effects of end masses and end forces. Prominent bands in the spectra of the α-alkyl,ω-hydroxyoligo(oxyethylene)s were assigned to LAM-1 and LAM-3 of the H-bonded dimer crystallised in a bilayer structure.