Swelling behaviour of crosslinked hydrogels based on (2-hydroxyethyl methacrylate) with a zwitterionic comonomer (1-3-sulfopropyl-2-vinyl-pyridinium-betaine)

Copolymeric hydrogels were prepared by the chemically initiated free radical copolymerization in aqueous solution of mixtures of [1-(3-sulfopropyl)-2-vinyl-pyridinium-betaine] (SPV) and (2-hydroxyethyl methacrylate) (HEMA) in the presence of a crosslinking agent N,N'-methylene-bis-acrylamide (MBA). The hydrogels were swollen to equilibrium in water and aqueous KSCN at 298 K and their swelling behaviour has been investigated using gravimetric measurements. The effects of the concentration of KSCN and the mole fraction of SPV in the feed (F-s) have been noted and discussed. The main findings are: (a) In water, the water content (W-1) of copolymeric hydrogels is insensitive to SPV content at F-s >= 0.45. In contrast, W-1 decreases sharply with decreasing Fs within the range of 0 < F-s < 0.45. (b) In aq. KSCN, the degree of total swelling (M exceeds the value in pure water, the enhancement in swelling being most marked at low values of [KSCN]. The content of water within the hydrogel increases with KSCN concentration in the swelling medium for low values of [KSCN], but thereafter falls with further increase in salt concentration. In contrast, the salt content within the swollen hydrogel displays a continuous increase with increasing [KSCN]. All these results of item (b) are for copolymeric hydrogels within the full range of Fs (0 < F-s < 1). (c) at a fixed aq. KSCN concentration, both W and W-1 increase sharply with increasing F-s over the entire range of copolymer composition. (c) 2006 Elsevier Ltd. All rights reserved.