Crystallinity of uniform oligo(oxyethylene) mono-n-alkyl ethers studied by X-ray diffraction and differential scanning calorimetry

Abstract

The crystallinity of two series of uniform oligo(oxyethylene) mono-n-alkyl ethers has been investigated: α-alkyl,ω-hydroxyoligo(oxyethylene)s, H(CH₂)_n(OCH₂CH₂)_mOH, and α-alkyl,ω-methoxyoligo(oxyethylene)s, H(CH₂)_n(OCH₂CH₂)_mOCH₃. The hydroxy-ended oligomers formed bilayer crystals, and the methoxy-ended oligomers formed monolayer crystals. The helical oxyethylene blocks were oriented normal to the layer-crystal end-group plane, whilst the trans-planar alkyl blocks were generally tilted at an angle δ= 60°. The melting temperature and enthalpy of fusion were higher for hydroxy-ended oligomers than for corresponding methoxyended oligomers.