Macroporous hydrogel beads of high toughness and superfast responsivity

Macroporous hydrogel beads based on the monomers acrylamide and 2-acrylamido-2-methylpropane sulfonic acid sodium salt were prepared by dropwise addition of the monomer solution into the paraffin oil as the continuous phase at subzero temperatures. The beads prepared between −15 and −20 °C have irregular large pores of 1-10 μm in diameter, typical for macroporous networks created by the cryogelation technique, while nonporous hydrogels were obtained at room temperature. Swelling measurements show that the low temperature beads swell within seconds to attain their equilibrium states in water. The beads formed at subzero temperatures were very tough and can be compressed up to 94% strain without any crack development while those formed at room temperature were fragile and broke at a strain of about 40%. The results indicate that the tough hydrogel beads formed at subzero temperatures can be used in separation processes in which the separated compounds can easily be recovered by compression of the beads under a piston.