Behaviour of crosslinked and linear poly[1-(3-sulphopropyl)-2-vinyl-pyridinium-betaine] in aqueous salt solutions

Linear and crosslinked poly[1-(3-sulphopropyl)-2-vinyl-pyridinium-betaine] (PSPV) samples have been prepared by free radical polymerization of the zwitterionic monomer (SPV) in the absence and presence, respectively, of N,N′-methylene-bisacrylamide (MBA). The crosslinked xerogel was swollen to equilibrium at ambient temperature in water and in aqueous solutions of KSCN, KBr and KCl having concentrations ([salt]) extending up to 2 mol dm−3. In aqueous salt the degree of swelling exceeded the value in pure water (0.70), the enhancement in swelling being most marked at low values of [salt]. The content of water within hydrogel increased with salt concentration in swelling medium for low values of [salt] but thereafter fell with further increase in [salt]. In contrast, the salt content within swollen hydrogel displayed a continuous increase with increasing [salt]. The partition coefficient expressing concentration of salt in hydrogel relative to that in swelling medium increased sharply with [salt] at low values, but levelled out to values of 0.8–1.2 at higher values of [salt]. The difference in behaviour among the three salts was not dramatic, but indicated that the affinity of salt for the polymer lay generally in the order KSCN>KBr>KCl. This affinity was confirmed by conductometric determinations of the coefficient of selective adsorption of salt to polymer in solutions of linear PSPV.