The thermosensitive phase-separation of poly-(vinyl methyl ether) in water has been investigated by micro-Raman spectroscopy in the presence of tetraalkylammonium bromides. The equilibrium distribution of both polymer and salts to the polymer-rich and solvent-rich phases was determined as a function of temperature. Tetraalkylammonium ions with longer alkyl chains associate more strongly with PVME and raise the phase-transition temperature due to an increase in hydrophilicity.