| Abstract: | The swelling of five types of Sephadex that are either nonionic (G) or possess one of four different ionic groups sodium carboxymethyl (CM), sodium sulfopropyl (SP), diethyl-aminoethyl chloride (DEAE), diethyl - (2-hydroxypropyl) aminoethyl chloride (QAE)] in the same skeleton of the molecule has been studied by picture analysis and by calorimetry. Inducing dissociation of the ionic group in the polymer skeleton increased the water swelling. By the addition of sodium chloride, the maximum swelling volume of nonionic Sephadex was only slightly decreased. However, that of ionic polymers was considerably decreased. The variation of the apparent first-order rate constant of the swelling and that of the maximum swelling volume show the same tendency. The maximum heats of swelling were 93.2 ± 7.1 J g?1 for G, 128.8 ± 9.1 J g?1 for CM, 92.3 ± 8.0 J g?1 for SP, 68.8 ± 10.5 J g?1 for DEAE, and 67.0 ± 7.2 J g?1 for QAE and did not depend on the concentration of sodium chloride. From the results obtained, we conclude that the nonionic Sephadex swells only by hydration but that ionic Sephadexes swell mainly by the osmotic pressure due to the counterions of the ionic groups and that the swelling ratio is not dependent on the kinds of ions but on the ionic concentration. Most of the water in the gels of ionic Sephadexes is free water that does not interact with the Sephadexes. © 1993 John Wiley & Sons, Inc. |
