| Abstract: | Ion-selective membranes similar to those described by Graydon and Stewart [J. Phys. Chem. 59 , 86 (1955)] were prepared by improved methods involving copolymerization of styrene, n-propyl-p-vinylbenzenesulfonate, and divinylbenzene (DVB) with subsequent hydrolysis of the ester. Both the highly reactive ester and DVB were purified by column chromatography and were well characterized by their infrared and proton magnetic resonance spectra. For preparation of membranes about 25% by weight of N,N-dimethylformamide (DMF) was included with the vinyl monomers in the polymerization mixture. Thermal polymerization was initiated by benzoyl peroxide, and membranes were formed in special molds of two types. In one type a free surface of the mixture was exposed, while in the other the mixture filled the mold. The DMF in the fresh membranes was replaced with aqueous KOH by diffusion, and hydrolysis was then carried out. By this method hydrolysis times were decreased from several days to a few hours. Capacity, water content, and thickness were determined for all membranes, and density, swelling in salt solutions, and Young's modulus were measured for selected membranes. The Vermaas-Hermans-Flory theory of polyelectrolyte gels was found to account satisfactorily for the swelling properties and water content of these membranes, the solvent interaction parameter χ1 increasing with increasing volume fraction of polymer from 0.7 to 1.0 at zero external salt concentration and up to 1.8 for membranes deswollen in 1M KCl. No differences in average water contents for given densities of fixed charge and crosslinking were observed with (1) different molds, (2) commercial or pure DVB, and (3) a swelling agent (DMF) or no swelling agent. The results in general indicate that the state of the membrane at a given temperature and pressure can be specified by any two of the parameters: degree of ionization per unit volume of an average structural unit, concentration of crosslinking agent, and degree of swelling. Young's modulus decreased markedly with increasing water content, but data were not sufficiently extensive or precise to permit a quantitative treatment. |
