Preparation of macroporous acrylamide-based hydrogels: Cryogelation under isothermal conditions

Macroporous hydrogels based on acrylamide, as well as on 2-acrylamido-2-methylpropane sulfonic acid monomers, were prepared using N,N'-methylenebis(acrylamide) crosslinker in frozen aqueous solutions. The cryogelation reactions at temperatures as low as -25 degrees C were carried out isothermally by use of two techniques. First, after addition of the polymerization initiator into the reaction solution, the system was immediately cooled down to - 196 degrees C using liquid nitrogen and then, the system was immersed into a thermostate at the desired subzero temperature T-prep, It was found that the precooling of the reaction system before the onset of the reactions provides formation of superfast responsive hydrogels at temperatures close to the freezing point of water. The precooling step however destroyed the regularity of the pores in the hydrogel networks. As a second technique to achieve isothermal cryogelation, hydroquinone as the polymerization inhibitor was included into the reaction solution. It was shown that, the addition of hydroquinone produces more monodisperse and smaller pores. The hydrogels obtained by both techniques exhibit size-independent superfast swelling behavior in response to the external stimuli.