NMR study of temperature-induced phase separation and polymer-solvent interactions in poly(vinyl methyl ether)/D2O/ethanol solutions

The changes in the dynamic structure during temperature-induced phase transition in D₂O/ethanol solutions of poly(vinyl methyl ether) (PVME) were studied using NMR methods. The effect of polymer concentration and ethanol (EtOH) content in D₂O/EtOH mixtures on the appearance and extent of the phase separation was determined. Measurements of ¹H and ¹³C spin-spin and spin-lattice relaxations showed the presence of two kinds of EtOH molecules: besides the free EtOH expelled from the PVME mesoglobules there are also EtOH molecules bound in PVME mesoglobules. The existence of two different types of EtOH molecules at temperatures above the phase transition was in solutions with polymer concentration 20 wt% manifested by two well-resolved NMR signals (corresponding to free and bound EtOH) in ¹³C and ¹H NMR spectra. With time the originally bound EtOH is slowly released from globular-like structures. From the point of view of polymer-solvent interactions in the phase-separated PVME solutions both EtOH and water (HDO) molecules show a similar behaviour so indicating that the decisive factor in this behaviour is a polar character of these molecules and hydrogen bonding.