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

Abstract

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 F s within the range of 0 < F s < 0.45. (b) In aq. KSCN, the degree of total swelling ( W) 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 F s (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.