Poly[2-(hydroxyethylmethacrylate)-co-(sulfobetaine)]s hydrogels: 1. Synthesis and swelling behaviors of the 2-(hydroxyethylmethacrylate)-co-2-(vinyl-1-pyridiniumpropanesulfonate) hydrogels

A series of the 2-hydroxyethyl methacrylate/2-vinyl-1-pyridinium propane sulfonate (HEMA/VPPS) copolymeric gels have been prepared from HEMA and zwitterionic monomer VPPS of various molar ratios. The influence of the amount of VPPS in copolymeric gels on their swelling behavior in water and various saline solutions at different temperatures was investigated. Results indicate that the PHEMA hydrogels exhibit an overshooting phenomenon in their dynamic swelling behavior. The maximum overshooting value decreases with increasing temperature. The same results are also shown for the lower VPPS content HEMA/VPPS copolymeric gels. In the equilibrium swelling ratio, the PHEMA hydrogel. exhibits a minimum swelling ratio at 55 degrees C. Then, the minimum swelling ratio disappears gradually with increasing VPPS content in HEMA/VPPS copolymeric gels. In the saline solution, the swelling ratios of HEMA/VPPS copolymeric gels increase rapidly with increasing salt concentration, for salts with a smaller ratio of charge/radius.