Hydration of a short chain poly(oxyethylene) (C1E2C1) studied by analysis of the O—H Raman band

Abstract

The hydration of the short chain poly(oxyethylene) CH ₃ (OCH ₂ CH ₂ ) ₂ O CH ₃ (C ₁ E ₂ C ₁ ) has been studied in the range of concentrations up to 0.3 mole fraction (m.f.) by analysing the parameters of the main components of the water O–H stretching band at ca. 3200 and 3400 cm ^-1 . Two interesting regions of enhancement of the hydrogen bond network in the solution characterize different hydration structures. In the first at ca. 0.03 m.f., the coordination of the water network around the C ₁ E ₂ C ₁ molecules has a local maximum owing to hydrogen bonding at the sites of the ether oxygens from one side, and the hydrophobic hydration around the methylene groups and the CH ₃ end groups, from the other. The increased local order in the hydration structure is a consequence of the favourable incorporation of the oxyethylene groups of C ₁ E ₂ C ₁ molecules with gauche conformation in the water network because of their similar O···O distances. In contrast, the second type of hydration structure at ca. 0.11 m.f. can be explained by the build up of the most compact homogeneous hydrogen bond network in which C ₁ E ₂ C ₁ molecules are interconnected with direct hydrogen bonds to the most water molecules possible and the effect of hydrophobic hydration is diminished. Above 0.11 m.f. the hydrogen bond network in the system is gradually destroyed.