Synthesis of superporous hydrogels by a postpolymerization foaming protocol and their water absorbent behavior

<p> The rate of swelling is one of the most important parameters of hydrogel polymeric networks; therefore, the objective of this study was to develop a new method to synthesize superporous poly(acrylic acid-co-acrylamide) hydrogels to improve swelling rate. The hydrogel was prepared in the presence of a foaming agent (comprising azodicarbonamide and zinc oxide), using 2,2&#39;-Azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride as the initiator. The N2 released during the polymerization led to the formation of a slightly foamed gel; we refer to the process as a prefoaming process. The obtained gel underwent a further foaming process to form a superporous hydrogel. Unlike in existing methods, the consistent time control of the foaming agent addition and the onset of gelling were not necessary in this simplified gel preparation procedure. The water absorbent behavior of the superporous hydrogels suggested that the polymers obtained from the prefoaming process reached the swelling equilibrium more rapidly than those with little prefoaming, and their absorbent capacity was greater. Scanning electron microscope images show that interconnected pores inside these superporous gels formed capillary channels, which are critical for the fast swelling rate. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012