Polymer and Materials Science
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
Details are given of a further modification to the Ray ebulliometer which permits easy interchange of the Cottrell pump tube. The stability of the apparatus with different pump tubes and pumping conditions was also examined. Molecular weights obtained with the use of two ebulliometers and three solvent systems are compared. The validity of the recently developed ultracentrifuge methods for determining physical properties of molecules with molecular weights in the range 300 to 10,000 was checked by using a pure compound of known molecular weight. Agreement was obtained also between the data obtained by the Klainer and Kegeles method and separate sedimentation and diffusion data. The molecular weight of an ethyl acetate extract of black wattle tannin was determined by the ebulliometric and these ultracentrifuge methods. The ultracentrifuge value for the whole extract decreased with time due to sedimentation of high molecular weight impurities. The final ultracentrifuge weight-average molecular weight (1175) is in good agreement with the number-average value for the tannin polyphenols (922) obtained by ebulliometry. The difference between the values confirms the known heterogeneity of the polyphenols.
Type of Medium: