Freezing characteristics of acrylamide-based aqueous solution used for the preparation of supermacroporous cryogels via cryo-copolymerization

Solvent freezing crystallization is a crucial step to the satisfactory formation of homogenous and interconnected supermacropores within cryogels during the preparation of supermacroporous cryogel beds via cryo-copolymerization. In this work, the freezing characteristics of an aqueous solution system containing acrylamide (AAm), N', N'-methylene-bis-acrylamide (MBAAm) and allyl glycidyl ether (AGE) for the production of polyacrylamide-based cryogels were investigated experimentally under various cooling conditions. Freezing curves of solution of AAm + AGE + MBAAm under various concentrations were measured to determine the corresponding values of freezing point temperature T-mc and the actual initial solvent crystallization temperature T-c. The effects of freezing rate and monomer concentration on T-c and T-mc were addressed. The results showed that the freezing rate had a limited effect on Tmc when the freezing rate was very low under the present work. At the same time, T-c changed randomly in a certain range with monomer concentration and freezing rate, while T-mc decreased with the increase of monomer concentration under freezing condition at a constant freezing rate. Based on these results, the in-column freezing behaviors of 7% (w/w) aqueous solution of AAm + AGE + MBAAm reactive system initiated by ammonium persulfate (APS) and NN,N',N'-tetramethylethylenediamine (TEMED) under different freezing-temperature variation conditions were measured to reveal the actual solvent crystallization processes occurring within the column during the cryo-copolymerization. The properties of these cryogels were also measured and discussed. (c) 2006 Elsevier Ltd. All rights reserved.