A Method for improving the Solute Selectivity of Osmotic Membranes

Abstract

AN examination of the results obtained with a pair of ‘Ultracella’filters (fein)—manufactured by the Membranfiltergesellschaft, Göttingen—which had been used for several months in benzene at 30° C. to determine the number-average molecular weights (M̄ _n) of polymer samples, showed that during this time the membranes had become markedly less permeable to solvent. A similar observation has been made by Philipp and Bjork¹ with a gel ‘Cellophane’ membrane, and they attributed the phenomenon to gradual ageing of the membranes. However, with the ‘Ultracella’ filters (fein) closer examination of the results indicated that the change in permeability had occurred in two distinct stages both of which could be associated with attempts to measure the M̄ _n of a sample of poly(diallyl phthalate). Experiments were therefore carried out with three other pairs of ‘Ultracella’ filters (fein) in order to investigate this phenomenon further.