Nonionic polyacrylamide (PAAm) hydrogels were synthesized using three methods: room temperature polymerization, cryo-polymerization, and modified cryo-polymerization. Anionic PAAm hydrogels were obtained after hydrolyzing the nonionic hydrogels under alkaline conditions. The composition of anionic hydrogels was characterized by Fourier transform infrared (FT-IR) spectroscopy and element analysis. Morphological studies showed that the hydrogels exhibited various pore structures when they were synthesized using different methods. An additional mechanism for the formation of cryogels was proposed. Investigation of the swelling properties of the hydrogels and analysis of the swelling kinetics showed that the hydrolyzed PAAm hydrogels had rapid pH-sensitive rates. (C) 2010 Elsevier Ltd. All rights reserved.