Liquid–liquid extraction using thermoresponsive polymers as solvents in aqueous two phase systems followed by induced phase separation to recover the polymers is a potential technology for water–salt separations. Here we report for seven polymers on their ternary systems containing water, sodium sulfate and the (block co)poly ether. Equilibrium data were measured at 298.15 K and 313.15 K and atmospheric pressure. Empirical equations have been used to correlate the experimental equilibria for both temperatures separately and the semi-empirical NRTL model has been applied with a temperature dependent parameter to describe the complete dataset for both temperatures together. Model predictions were in good agreement with the experimental data.