SynopsisPreparative gel permeation chromatography was used to produce a number of polypropylene reference samples, within the molecular weight range of 10,000-600,OoO, from commercial materials. Some of these materials were degraded in a controlled manner to give base materials having suitable molecular weight characteristics. A procedure has been developed using a single preparative column packed with equal quantities of Styragel with nominal exclusion limits of lo2, lo3, lo4, and lo5 nm.The volume of solvent for recovery was minimized by use of higher loading factors than in analytical GPC (some 2-20 times more polymer was thus fractionated in each experiment). Under these conditions the fractions first eluted were sharpest having polydispersities of about 1.5. First fractions, from different base materials, were characterized by analytical GPC, and those of similar molecular weight and polydispersity were combined to give the reference samples. Refractionation was necessary with the highest molecular weight base material because the first stage fractions were not sharp enough. Some of these fractions were recovered at elution volumes where much lower molecular weight material was expected. Comparison with results from the other base materials indicates that the primary cause of the spreading is not overloading. This spreading is explained in terms of slower partitioning of the larger molecules between the interstitial fluid and the gel particles.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.