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 zw itterionic monomer (SPV) in the absence and presence, respectively, of N,N' -methylene-bisacrylamide (MBA). The crosslinked xerogel was swollen to equi librium at ambient temperature in water and in aqueous solutions of KSCN, K Br and KCI 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]. Th e content of water within hydrogel increased with salt concentration in swe lling medium for low values of [salt] but thereafter fell with further incr ease in [salt]. In contrast, the salt content within swollen hydrogel displ ayed a continuous increase with increasing [salt]. The partition coefficien t expressing concentration of salt in hydrogel relative to that in swelling medium increased sharply with [salt] at low values, but levelled out to va lues of 0.8-1.2 at higher values of [salt]. The difference in behaviour amo ng the three salts was not dramatic, but indicated that the affinity of sal t for the polymer lay generally in the order KSCN > KBr > KCl. This affinit y was confirmed by conductometric determinations of the coefficient of sele ctive adsorption of salt to polymer in solutions of linear PSPV. (C) 1999 S ociety of Chemical Industry.