Polyurethane pervaporation membranes

Polyurethane membranes were prepared by the reaction of toluene-2,4-diisocy anate with hydroxy-terminated oligomers. Oligomers were either liquid polyb utadiene (MW 3000) or propylene oxide-based polyethers (MW 420 and 4800). T he prepared membranes were used in pervaporation of binary mixtures of wate r/ethanol, water/dioxane and ethanol/toluene, respectively. Polyurethanes w ith linking segments formed predominantly by high-molecular-weight oligomer s (MW 3000 or 4800) were rubbery materials, while hard glassy membranes wer e obtained if the linking segments comprised high amounts of a polyether wi th MW 420. In pervaporation, all glassy membranes preferably transported sm all molecules of the feed mixture. In case a rubbery membrane was used in p ervaporation in the presence of one feed component with a high affinity to the linking segments, the membrane preferentially transported this componen t.