Abstract
An alternating copolymer of maleic anhydride and 2-methyl-2-propen-1-ol [Poly(MAn-altMAA)] was prepared and the alternative arrangement of carboxyl and 1, 5-lactone units were mainly found in the copolymer. In order to evaluate a function of vicinal carboxyl and lactone moieties in the active transport of alkali metal cations, Poly (MAn-alt-MAA)poly(acrylonitrile) (3: 7 by weight) blended membranes were prepared by casting from N, Ndimethylformamide solution.
By using a diaphram cell, two pairs of alkali cations, K+-Na+ and Na+-Li, were actively trasnported through the membrane from alkaline to acidic solution (Fig.3 and 4). Transport behaviors, such as maximum transport ratio, transport rate and transport selectivity, were evaluated by varying the membrane thickness (20-60μm) and the initial concentration of cell solution (0.08-0.8 mol·dm3). The maximum transport value was high, e. g.88% for K+, at the low initial concentration, and it decreased with the initial concentration. The transport rate was approximately proportional to the initial concentration and inversely proportional to the membrane thickness. It is interesting that the transport rate of Na + was changed in the presence of the other alkali metal ion. The transport selectivity was slightly affected by the membrane thickness and it decreased somewhat with the initial concentration. The average transport selectivities of K+/Na+ and Na+/Li+ were 1.8 and 1.9, respectively (Table 2, Figs.5and 6). The transport mechanism was discussed and the apparent diffusion coefficient was calculated. Scanning electron micrographs (SEM) showed that the membrane was consisted of three layers, i. e. dense layer, central layer and porous layer (air side in preparation). The remarkable change in morphology of the used membrane at the high initial concentration was observed (Fig.7).
