Ultrafein filters as osmotic membranes

Abstract

The use of ultrafein filters as osmotic membranes has been investigated in various solvents. It has been found that, at 30°C., measurements can be made in benzene, toluene, ethanol, water, and, with difficulty, methyl ethyl ketone, but not in chloroform or dimethylformamide. In benzene it has been found that all grades of the membranes are more selective than the corresponding ultracella filters and that, with the allerfeinst grade, molecular weights of the order of 2000 can be determined. With solutions of pentaerythritol tetrastearate (M.W. 1200), tristearin (M.W. 891), and sucrose octaacetate (M.W. 679), the osmotic pressures developed were less than the theoretical values. The ratios of observed to theoretical osmotic pressure decreased with molecular weight, and these ratios appear to be examples of the reflection coefficients predicted by Staverman.

Dynamic osmotic pressure measurements on low molecular weight polymers

“…The lower limit of number average molecular weight (Gn) obtained from osmotic pressure measurements is determined by the semipermeability of the membrane (1,2). Many membranes have been described (3)(4)(5)(6)(7) for low molecular weight polymers, but in most cases the low rate of attainment of the theoretical osmotic pressure is inconvenient, especially when static osmometers are used. Because of these limitations, relatively few membranes provide a satisfactory overlap between osmometry and other techniques for measuring an.…”

“…With the aid of a dynamic osmometer* (8) and the ultrafein membranes described by Vaughan (6,7), it has been possible to accurately measure the un of several well-characterized, narrow molecular weight distribution polystyrene samples a s well a s pure pentaerythritol tetrastearate (molecular weight = 1200). Vaughan found that the ultrafein membranes originally produced for use only in aqueous systems were suitable in certain organic solvents and had a high selectivity.…”