MONTE-CARLO SIMULATION STUDY OF SHORT POLY(ETHYLENE OXIDE) CHAINS AT DIFFERENT CONCENTRATIONS

A model for describing the anomalous conformational behavior of short poly(ethylene oxide) chains in dilute water solutions is proposed. Exp erimental investigations have shown that the percentage of gauche conf ormers around the C-C bond reaches a maximum as the water concentratio n is increased. The behavior is in disagreement with predictions from simple theory, suggesting that the conformation mainly depends on the dielectric permittivity of the solution. The higher dielectric constan t favors a gauche conformation around the C-C bond. The essence of the new suggested model is that apart from the dielectric effect also the hydrophobic interactions between the methyl and methylene groups must be considered. At dilute solutions the poly(ethylene oxide) chains on ly have intramolecular hydrophobic interactions, which are more favora ble if the C-C bonds adapt the anti conformation. This will lead to a maximum in the gauche population around the C-C bond as the amount of poly(ethylene oxide) is lowered.